Lithuanian University of Health Sciences
Faculty of Medicine
Department of Infectious Diseases
Clara Rodríguez de Castro Zaloña
Title of Final Master’s Thesis:
THE CHRONIC INFLAMMATORY STATUS IN PATIENTS WITH HIV IN FECTION
Thesis supervisor: Dr. Daiva Vėlyvytė
TABLE OF CONTENTS
1. SUMMARY ……… 3 2. ACKNOWLEDGEMENTS ……… 4 3. CONFLICT OF INTEREST ………... 4 4. ABBREVIATION LIST ………. 5 5. INTRODUCTION ………... 76. AIMS AND OBJECTIVES ……… 8
6.1 Aims ………... 8
6.2 Objectives ………. 8
7. PATHOGENESIS AND DESCRIPTION OF THE INVOLVEMENT OF THE DIFFERENT ORGANS ……….………. 9
7.1 Mechanisms and markers associated with the chronic inflammatory state and the premature ageing ………. 9
7.2 Metabolic disorders associated to HIV infection ………. 16
7.3 Cardiovascular diseases associated to HIV infection ………... 19
7.4 Neurological disorders associated to HIV infection ………. 23
7.5 Renal diseases associated to HIV infection ……….. 27
7.6 Hepatic disorders associated to HIV infection ………. 31
7.7 Bone disorders associated to HIV infection ………. 35
8. METHODOLOGY ………. 40
9. DISCUSSION OF THE RESULTS ……… 41
10. CONCLUSIONS ………. 47
11. REFERENCES ……….... 48
12. ANNEXES ……….. 64
12.1 Table 10. The most relevant studies ……… 64
1. SUMMARY
Author: Clara Rodríguez de Castro Zaloña
Research title: The Chronic Inflammatory Status in Patients with HIV Infection
Aim: To evaluate the mechanisms that cause multi-organ damage in patients infected with HIV, despite the
effective treatment.
Objectives:
1. To create a literature review to update the knowledge of the mechanisms that maintain a situation of sustained immunological activation with a continued inflammatory activity in HIV patients, which may explain the early onset of different pathologies in HIV-infected individuals that typically affect the elderly.
2. To characterize markers that can help in the early diagnosis of damage in different affected organs. 3. To describe different pathologies triggered by the persistent inflammation and immune activation at the metabolic, cardiovascular, neurological, renal, hepatic and osseous levels.
Methodology: this was a Literature review where searches were conducted using several databases PubMed, Cochrane, UpToDate and Ovid. The period has covered the last 10 years and all the articles that could be obtained as full text have been assessed. The terms used were: "HIV and inflammation", "HIV and immune and activation", "HIV and inflammatory and markers", "HIV and cardiovascular and disease", "HIV and neurocognitive and disorder", "HIV and premature and ageing", "HIV and kidney (or renal) and disease", "HIV and hepatic (or liver) disease", "HIV and metabolic and disease", "HIV and bone and disease". Keywords were matched to database indexing terms.
Results and conclusions: HIV triggers a persistent immune activation with inflammatory effects that are not corrected by the combined antiretroviral therapy (cART) and that occur from the beginning of the infection. It generates multiorgan affectation with the appearance of comorbidities that are
2. ACKNOWLEDGEMENTS
I dedicate this thesis to my family for their constant support in me. I owe a special debt of gratitude to my father, Dr. Eduardo Rodríguez de Castro, for his enormous encouragement and
guidance during this years.
Lastly, I would like to extend my thanks to my supervisor Dr. Daiva Vėlyvytė for her advice thought this literature review project.
3. CONFLICT OF INTERESTS
4. ABBREVIATION LIST
AICD Activation induced cell death HAD HIV-associated dementia AIDS Acquired immune deficiency
syndrome
HAND HIV-associated neurocognitive disorders
AKI Acute kidney injury HBV Hepatitis B virus
ANI Asymptomatic neurocognitive impairment
HCC Hepatocellular carcinoma
ART Antiretroviral therapy HCV Hepatitis C Virus
BAFF B-cell activating factor HDL-c High-density lipoprotein cholesterol
BBB Blood brain barrier HF Heart failure
BMD Bone mineral density HIV Human immunodeficiency virus
CAC Coronary artery calcium HIV+ HIV-positive patients
CAD Coronary artery disease HIV- HIV-negative patients
cART Combined antiretroviral therapy HIVAN HIV-associated nephropathy CHD Coronary heart disease HIVICK HIV immune complex disease of
the kidney
CHF Chronic heart failure HSCs Hepatic stellate cells
cIMT Carotid intima-media thickness IFN Interferon
CKD Chronic kidney disease IL Interleukin
CMV Cytomegalovirus IP Inducible protein
CNS Central nervous system IRIS Immune reconstitution
inflammatory syndrome
CRP C-reactive protein LA Lipoatrophy
CSF Cerebrospinal fluid LD Lipodystrophy
CTL Cytotoxic T lymphocyte LDL-c Low-density lipoprotein cholesterol
CVD Cardiovascular disease LH Lipohypertrophy
DILI Drug-induced liver injury LPS Lipopolysaccharides
DM Diabetes Mellitus MCP Monocyte chemotactic protein
DNA Deoxyribonucleic acid MCSF Macrophage colony-stimulating
factor
eGFR Estimated glomerular filtration rate MI Myocardial infarction
ER Endoplasmic reticulum MND Mild neurocognitive disorder
ESRD End-stage kidney disease NAFLD Non-alcoholic fatty liver disease FCR Fibroblastic reticular cells NASH Non-alcoholic steatohepatitis
FFA Free fatty acid NCI Neurocognitive impairment
FSGS Focal segmental glomerulosclerosis NFκB Nuclear factor kappa-light-chain-enhancer of activated B-cells GALT Gut-associated lymphoid tissue NRTI Nucleoside reverse transcriptase
inhibitors
RANKL Receptor activator of nuclear factor kappa-B ligand
RNA Ribonucleic acid
ROS Reactive oxygen species SDC Sudden cardiac death
SIV Simian immunodeficiency virus TC Total cholesterol
TDF Tenofovir disoproxil fumarate TG Triglycerides
TGF Transforming growth factor TLR Toll-like receptor
TNF Tumor necrosis factor Tregs Regulatory T-cells
5. INTRODUCTION
Since its discovery in 1983, HIV has become one of the most extensively studied and notorious pathogen in history. HIV is an encapsulated retrovirus, belonging to the family of human retroviruses (Retroviridae) and the subfamily of lentiviruses. HIV infection is present worldwide. Majority of the HIV transmissions mainly occur through mucosal surface, for instance the anorectal or vaginal mucosa, sexual transmission and transmission from mother to child, or by parenteral way such as the exchange of infected needles amid intravenous drug users. There are two types of HIV: HIV-1 and HIV-2, of which HIV-1 is more widely distributed and more pathogenic [1]. Therefore, the infection with HIV-1 and its end stage are the major public health challenges of modern times. Nevertheless, since the introduction of a prosperous cART, the life expectancy of HIV positive patients (HIV+) has increased to such magnitude that nowadays HIV is thought-out as a chronic, controllable disease within the countries that guarantee patient’s access to the treatment, pointing the rise in the percentage of HIV+ population entering adulthood and old age with a relatively normal expected lifespan. As HIV-infected individuals live longer, this has led to an unforeseen growth in chronic non-AIDS comorbidities that are commonly related with older age, comprising cardiovascular disease (CVD), bone disorders, liver and kidney diseases, non-AIDS-associated cancers, dementia and premature ageing and frailty [2, 3]. Despite the fact that some of these diseases may be the outcome of
characteristic mechanisms of HIV infection, associated to cART or to other opportunistic and/or viral co-infections, most of these disorders are presumed to derive from a dysregulated systemic
inflammation, which is present in both the elderly and HIV-infected individuals exhibiting a raise in the inflammatory markers [4]. These disorders develop rashly in HIV+ patients; despite that the treatment ensures the virological suppression, still exists an increase in the non-AIDS comorbidities [5]. As it is still unclear why HIV+ individuals experience these disorders earlier in life, researches have begun to explain the intricacies of the immune function that continues being modified regardless of the suppressive treatment. These researches propose that HIV-associated chronic immune activation and inflammation may speed the immune ageing and senescence, resulting in an early deterioration of the immune system and age-related diseases [4].
It is commonly accepted that ageing is related to a gradual decline in the immune function, nevertheless, in the aged, the deficient immune system coexists with the results of chronic
6. AIMS AND OBJECTIVES
6.1 AIMS
To evaluate the mechanisms that cause multi-organ damage in patients infected with HIV, despite the effective treatment.
6.2 OBJECTIVES
1. To create a literature review to update the knowledge of the mechanisms that maintain a situation of sustained immunological activation with a continued inflammatory activity in HIV patients, which may explain the early onset of different pathologies in HIV-infected individuals that typically affect the elderly.
2. To characterize markers that can help in the early diagnosis of damage in different affected organs.
7. PATHOGENESIS AND DESCRIPTION OF THE
INVOLVEMENT OF THE DIFFERENT ORGANS
7.1 MECHANISMS AND MARKERS ASSOCIATED WITH THE
CHRONIC INFLAMMATORY STATE AND THE PREMATURE
AGEING
The course of HIV-1 infection
HIV solely targets and infects cells expressing the CD4 molecule, i.e., T -helper lymphocytes, monocytes, macrophages, and dendritic cells. The infection takes place through the coupling of the viral envelope gp120 to the CD4 molecule and to the chemokine receptors CCR5 or CXCR4 that are present on the cell surface. Once the virus is within the cell, the enzyme reverse transcriptase
transcribes viral ribonucleic acid (RNA) to deoxyribonucleic acid (DNA), thus occurring the
assimilation into the host cell genome, and ultimately the viral progeny is produced through the host cellular mechanisms [1, 6].
Natural course of HIV infection:
1. Acute infection, is defined by widespread viral dissemination, which is paused within 1 -4 weeks with the induction of host cellular immune response, prompting resolution of the clinical symptoms related with the primary infection. Despite the fact that the immune system is adept in controlling viral replication, it is unsuccessful in eliminating HIV-1, which remains in the organism and keeps replicating. Hence, this response is characterized by a marked increase in the number of circulating CD4+ and by a high production of the virus, whose presence is identified by its
considerable number of viral copies in the patient’s plasma. This acute viremia is related to a substantial activation of CD8+ T-cells, some of which are HIV-1 specific and start expressing the senescence marker CD57 on the time of primary infection [4]. During this syndrome, the massive activation of the immune system is accompanied by a high tendency to apoptosis of the activated cells [7].
2. Chronic infection, the patient enters a period of clinical latency with minimal or no symptoms, whose duration is subjected to many factors, being the age the most influencing factor [4].
The pathogenesis of HIV infection can be simplified in three main features: the substantial depletion of CD4+ T-cells, the paradoxical immune activation, and the exhaustion of the immune system (Fig. 1).
Figure 1. A model of HIV pathogenesis. Causes and consequences of immune activation are in yellow or red, respectively. Hypothetical consequences of immune activation that make a parallel
with human ageing are in italic [7] (Appay V., Sauce D.)
Mechanisms prompting the establishment of a persistent inflammation and immune activation in HIV infection
HIV infection is unrivalled amongst human viral infections. Owing to that as soon as the infection has been set, the virus harbours a number of mechanisms to escape successfully a complete immune-mediated clearance, incongruently increasing the immune activation, and establishing a thriving persistence in the host. Consequently, developing a chronic infection with constant varying degrees of endless virus replication, and establishing a persistent immune activation and inflammation [7, 9]. Pointing out that the chronicity of the infection is the peculiarity of HIV disease.
In acute HIV-1 infection there is a rise in plasma viremia, which can be related with the increase in plasma of various cytokines and chemokines, including: fast and brief elevations in interferon-α (IFN-α) and interleukin-15 (IL-15) levels; a substantial raise in inducible protein-10 (IP-10) levels; rapid and constant increase in tumor necrosis factor-α (TNF-α) and monocyte chemotactic protein-1 (MCP-1) levels; a prolonged increment in levels of further proinflammatory factors
replication, it never reaches a complete viral suppression. Thus, resulting in persistent high levels of proinflammatory cytokines.
One of the fundamental mechanisms of viral escape is the amount of errors occurring during viral replication, originating mutations that cause continuous variations of the antigenic epitopes, leading to a sustained antigenic cascade keeping the immune system activated, consuming itself causing its exhaustion [7].
A diverse number of defects emerge in HIV+ individuals with chronically increased viral loads. One of the hallmarks in the pathogenesis of HIV is the chronic immune-cell activation, which leads to both direct and indirect effects on B cells. Various cytokines and growth factors have been suggested to directly or indirectly trigger the activation of B cells in HIV-viraemic individuals, including IFNα, TNF, IL-6, IL-10, CD40 ligand and B-cell activating factor (BAFF) [12]. Many of these factors are thought to be associated with B-cell hyperactivation in HIV-viraemic individuals because of their increased serum levels during the infection. In addition, increased B-cell levels reveal a sustained HIV replication involving elevated numbers of activated and exhausted B-cells, increased levels in the circulation of immature transitional B-cells associated with CD4+ T-cell lymphopenia and a decreased frequency of memory B-cells that is not reversed by antiretroviral therapy (ART) [13, 14].
virological control acquired by cART do not return to their CD4+ T lymphocytes before the infection [21, 22, 23]). The rate of microbial translocation is related to the severity of HIV progression [24]. Some studies have implied that microbial translocation is linked to the massive immune activation, and that the development of sCD14 and pro-inflammatory cytokines are important in the pathogenesis of the disease, being somehow capable for the CD4+ T-cell depletion and HIV-related comorbidities [25]. In addition, the increased levels of LPS have been suggested as another indirect mechanism in the activation of B-cells [13, 16], as well as, a marker of immune activation in HIV+ individuals [25].
Regulatory T-cells (Tregs) expressing CD4+ molecule become infected and depleted across time, being able to associate this event with the persistent immune activation [26]. Since the onset of the infection, HIV infects and greatly depletes memory CD4+ T-cells; therefore, the chronic phase is distinguished by an immune activation with a massive production of proinflammatory cytokines, and a gradual loss of peripheral CD4+ T-cells over time. HIV-induced immune activation alters CD4+ and CD8+ T-cells; however, both suggest an increase in proliferation and loss of the naïve subset, CD4+ cells are depleted and CD8+ cells expanded [27]. The proliferation of both CD4+ and CD8+ T-cells are driven by different pathways. On the one hand, the proliferation of CD4+ T-T-cells managed by an association of antigen stimulation and homeostatic response; on the other hand, CD8+ T -cell proliferation is driven mostly by the virus per se [28]. As the infection modifies the homeostatic response, this results in the defective regulation of the production of T -cell precursors, resulting in the loss of naïve memory T-cells; thus, naïve CD4+ and CD8+ T-cells (usually CD45RA-, CCR7+) are depleted in HIV+ individuals, as well as in the elderly HIV negative patients (HIV-). When comparing HIV infection to ageing can be noted the similarity present in both populations, high-levels of antigen-experienced T-cells that are CD28-, but CD57+; showing immune inability and weakened proliferative capacity (related with telomere length shortening in HIV+ patients [29]) [4, 8].
No matter how, the persistent stimulation of the immune system, at the end, induces anergy or apoptosis of activated CD4+ T-cells [7], the mechanism inducing apoptosis is the activation induced cell death (AICD), which works via both death receptor (Fas) dependent and independent [30]. Apart from CD4+ T-cell depletion, the continuous antigenic stimulation and inflammatory status leads to immune exhaustion, in which the effector T-cells function decreases along with its proliferative
capability and progressively becoming less responsive [31]. Multiple markers of exhaustion have been observed such as the upregulation of PD-1 [32] and Tim-3 on CD4+ and CD8+ T-cells, whose high levels are positively associated with markers of disease progression, as well as, viral load and CD4+ T -cell count [16, 33].
which induces collagen deposition and tissue fibrosis leading to the loss of fibroblastic reticular cells (FCR), impairing the antigen presentation and lymphocyte stimulation [16].
A relatively young HIV+ adult is able to show some of the specific immune features and non-AIDS related comorbidities displayed by a HIV-, healthy individual three times older; as both processes, HIV infection and ageing, experience a shared pathway that may develop into early immunosenescence [4] (Fig. 2).
Factors Conditions End Organ Disease
Fig. 2. Factors Related to Non-AIDS Comorbidities in HIV-Infected Patients [34]
Premature ageing
From a biologic point of view, ageing is commonly described as the progressive decline in physiologic function that appears as the result of the acquired molecular, cellular, and organ harm and/or impairment; these alterations culminate in an increased sensitivity to disease, reduced response to stress, and eventually death. The typical signs comprise loss in end organ function, e.g., liver, kidney, and heart; bone loss (osteoporosis); muscle wasting; neurocognitive decline, and loss in immunologic function (immunosenescence: age-associated changes in the immune system that are associated with morbidity and mortality). The characteristic alterations of the immune system as people get old are [35]: a) reduced number and function of hematopoietic stem cells, b) thymic involution, c) reduced circulating naïve T-cells, d) increased frequencies of well-differentiated memory CD28- T-cells with limited proliferative potential, e) increased levels of many
proinflammatory cytokines, including IL-6 and TNF-α, and f) decreased CD4/CD8 ratios.
The introduction of highly active cART has resulted in drastically raised life span among HIV+ individuals, who are now ageing. Owing to the prolonged life expectancy, the results of ageing on HIV-1 individuals have emerged to be obvious [36]. The resemblance between ageing and the course of HIV, imply that HIV infection may compress the ageing process, accelerating comorbidities. Therefore, that could explain that diverse number of disorders that usually occur in the elderly now arise in fairly young HIV patients who experience various pathologies, su ch as CVD, metabolic and neurocognitive disorders, bone abnormalities, etc. The majority of these age-associated diseases are the result of the persistent inflammation and activation of the immune system [37], which is described
Ageing Genetics Obesity, exercise, diet,
smoking Stress Depression
as “inflammageing” [38, 39], or in the event of AIDS, could be defined as “inflammaids”, considering the alterations that appear during HIV infection (which have a distinctive similarity to those which occur during immunosenescence (Fig. 3)) [16].
Figure 3. Relationships between immunological changes present during aging and HIV infection that cause inflammation or “inflammaids” [39] (De Biasi S.)
Given the increased survival rate of HIV patients, their age proportion is increasing (Fig. 4) (amount of HIV+ patients ≥ 50 years of age to increase from 28% in 2010 to 73% in 2030 - with average age of 43.9 years to 56.6 years) [40], therefore being at increased risk for multiple comorbidities [41] (Fig. 5).
HIV and immunosenescene
Some of the peculiarities that occur to T-cells with ageing resemble to those noticed in untreated HIV patients [4, 8]. Both elderly and untreated HIV+ individuals generally present low CD4/CD8 ratios; reduced naïve/memory ratios; T-cell depletion; decreased sensitivity to vaccines, despite the fact that effective cART improves CD4+ T-cell levels, in the terms of efficiency regarding
Figure 4. Projected age distribution of HIV-infected patients [40] (Smit M.)
Figure 5. Distribution of the number of age-associated
a normalization of the immunity, the responsiveness to cART is not so robust; oppositely the response is waned in HIV+ individuals, appearing to be at the levels from an aged immune system [42], and an increase of CD28- effector T-cells [4] (Table 1).
Table 1. Possible similarities between HIV-associated and age-associated immunologic changes [37] (Deeks S)
a A number of studies have suggested persistent immunologic impairment during HAART, but the
subjects of these studies have generally received therapy for only a short period of time (<3 years). Also, most subjects at the time of the study had lower than normal peripheral CD4 + T cell counts.
The HIV+ individuals receiving cART that unsuccessfully present marked CD4+ T-cell gain compared to those who reach a normal CD4+ T-cell count, exhibit more commonly T-cell
characteristic occurring in immunosenescence, such as a decreased T-cell activation and regenerative potential, and thymic dysfunction [43]. Thus, a low CD4+ T-cell count on therapy is considered as a predictor of non-AIDS-comorbidities [44], implying that HIV-associated immunosenescence
participates in the immunodeficiency chronicity and causing an early onset of age-associated diseases in HIV+ individuals.
The causes for this persistent inflammation are multifactorial and contribute to the
development of premature ageing (Fig. 6). Particularly, those viruses that are reactivated by the HIV infection are one of the major causes for the persistent inflammation; since their reactivation results harmful to other organs (that can be seen also in other chronic disorders, such as Lupus). Taking as example the cytomegalovirus (CMV), this virus causes chronic antigenic stimulation which leads to senescent T-cells with restricted proliferative potential; resulting in an exhausted immune system with restricted ability to recognize new antigens, and thus, preventing the disease. Since these co-infections occur more frequently in HIV infected individuals and possess a damaging impact on the immune system [45], it has been proposed that these co-pathogens may participate in the “premature ageing” syndrome noticed in HIV+ population [46].
directly affect hematopoietic stem cells, and regarding ageing, it is well known that in ageing occurs a progressive loss of hematopoietic cells [47].
Figure 6. Accelerated aging model in HIV infection [4] (Desai S., Landay A.)
7.2 METABOLIC DISORDERS ASSOCIATED TO HIV
INFECTION
As aforementioned, since the introduction in the mid 1990’s of highly active antiretroviral therapy (HAART), HIV+ individuals have experienced a significant decline in immunodeficiency-associated episodes [48]; as a result, HIV-infected individuals live longer [40], which uncover the effects of ageing itself, hence, contributing to the appearance of obesity, diabetes mellitus (DM), and CVD [36, 49]. Besides ageing, in HIV-infected individuals, may be specific factors associated such as chronic immune activation and inflammation, persistent immune deficiency, and specific antiretroviral drug’s effects on insulin resistance, and plasma lipids.
The microbial translocation happening during HIV-infection may contribute to insulin resistance, elevated triglycerides (TG), and risk for myocardial infarction (MI). Furthermore, lower levels of high-density lipoprotein cholesterol (HDL-c) and increased levels of TG, low-density lipoprotein cholesterol (LDL-c), and insulin resistance were associated with greater microbial translocation in HIV+ patients during prolonged ART [50, 51, 52].
Alterations of body fat distribution
Following ART introduction, it was soon revealed the appearance of alterations in the body fat distribution, such as the abnormal accumulation of central fat (lipohypertrophy - LH) and the abnormal fat loss observed from the arms and legs, as well as the buttocks and face (lipoatrophy - LA), coining the term lipodystrophy (LD) [53].
and is related with insulin resistance; both being common in HIV-infected individuals and being an important feature of ageing [54, 55].
In HIV-infected individuals, instead of adipocytes, macrophages are the ones responsible for the chronic low-grade inflammation in the subcutaneous adipose tissue. HIV infection changes these macrophages into a more proinflammatory phenotype, and these modifications are not completely diminished by ART. Moreover, circulating HIV-infected and activated proinflammatory CD14+ and CD16+ monocytes predispose the pathogenesis of LA [56]. Guaraldi et al. [57] propose that CD8+ T-cell activation was related with clinical LD and neutrally measured visceral fat accumulation in virologically supressed HIV-infected individuals.
LD syndrome can be presented separately or in combination in the same individual (mixed forms), and is usually associated with metabolic disorders such as dyslipidaemia, hypertension, insulin resistance and diabetes. With the introduction of new antiretroviral drugs, the incidence of LD has decreased [53, 58].
LA: - Risk factors: the main risk factor for the development of LA is the use of nucleoside reverse transcriptase inhibitors (NRTIs), especially with zidovudine, didanosine and stavudine; with these drugs, LA can manifest itself before the first two years of treatment. Some studies have suggested that protease inhibitors (PIs) would enhance the capacity of NRTIs to produce LA, although PIs by
themselves do not seem to condition the development of LA [58, 59]. In addition, among the non-pharmacological factors associated with LA are older age, lower amount of body fat before the start of ART, and a lower CD4 nadir [58].
- Clinical picture: LA is characterized by a loss of subcutaneous fat on the face, arms, legs,
abdomen and buttocks, but not in muscle mass.
LH: - Risk factors: unlike what it is observed in LA, no particular antiretroviral drug is clearly implicated, so it can be developed with any regimen [58]. Women, older patients, with
hypertriglyceridemia, and with a higher percentage of fat appear to have an increased risk of LH during ART.
- Clinical picture: the accumulation of abdominal fat occurs mainly at the expense of visceral
Figure 7. Link between visceral fat distribution abnormalities, adipokines, macrophages and inflammation in HIV-infected patients [61] (De Lorenzo F.)
Carbohydrate metabolism disorders
The prevalence of alterations in carbohydrate metabolism is higher in HIV+ patients (5-25%), with an incidence of 5-10% of new diagnoses of DM [62]. However, some authors associate this increase only in the case with previous treatment with first generation PIs [63]. The etiopathogenesis of DM adds the classic factors of the non-HIV population to those of the infection itself, its treatment or comorbidities [64] (table 2). Recently, a relationship between weight gain during the first year of ART and a higher incidence of DM has been described [65].
Table 2. General and specific factors related with the development of DM [64] General population HIV-infected population - ≥ 45 years old
- BMI ≥25kg/m2
- First degree family history of DM - Lack of physical activity
- Ethnic groups with increased risk for DM (Hispanic, Afro-American) - Gestational diabetes - HTA ≥140/90 mmHg - Dyslipidaemia HDL-c ≤ 35mg/dl TG ≥250mg/dl
- High doses of statins in predisposed population (glucose intolerance)
Due to HIV-infection per se: - Inflammation (TNFα) - Low CD4+ nadir Due to comorbidities: - Hepatitis C (HCV) co-infection - Hepatic steatosis - Hypogonadism Due to treatment: - Direct:
· PIs (GLU-4 inhibition, dyslipidaemia) · NRTIs (zidovudine, didanosine): mitochondrial damage
- Indirect: · Opiates · LD
old, with only 5 years of DM evolution and, therefore, little risk for vascular damage) suggested that DM wasn’t consider to have the same importance in developing a coronary event compared to those HIV- individuals with DM [66], whom are at greater risk of developing coronary events according the Framingham score [67].
The association of DM and HIV also increases the risk of chronic kidney disease (CKD) [68]. A higher incidence of neuropathy and neurological damage has also been reported in seropositive patients with DM [62].
Besides, HCV co-infection has a bidirectional relationship with DM; DM favours hepatic fibrosis and HCV infection produces insulin resistance, progression to DM and worse metabolic control, in addition to conditioning the use of potentially hepatotoxic drugs [62].
Lipid metabolism disorders
Dyslipidaemia in patients with HIV infection is very common and is associated with an increased cardiovascular risk. This is due, in part, to ART and an increase and persistence of the inflammation and immune activation due to the chronicity of HIV infection.
The disturbances of lipid metabolism in HIV-infected patients have different characteristics than those of the general population. On the one hand, HIV increases insulin resistance, and on the other hand, ART can induce the appearance of dyslipidaemia, but it can also cause interactions with lipid-lowering drugs. The pattern observed most frequently in patients on ART is usually that of atherogenic dyslipidaemia, characterized by low HDL-c and high TG, coexisting with variable elevations of total cholesterol (TC) and LDL-c [69].
Lipoproteins from HIV+ individuals on ART are larger and more neutral lipid-rich, their HDL is less receptor competent and unstable compared with normolipemic individuals, implying the
disturbances in plasma lipolytic activity or hepatic cholesteryl ester uptake, supporting the metabolic model for HIV dyslipidaemia that starts with peripheral tissue hyperlipolytic activity, leading to the release of large quantities of free fatty acids producing a hypertriglyceridemic state [70].
7.3 CARDIOVASCULAR DISEASE ASSOCIATED TO HIV
INFECTION
diastolic dysfunction, fibrosis and myocardial steatosis, pulmonary arterial hypertension, stroke, fibrillation atrial and sudden cardiac death (SDC) [71]. In developed countries, CVD has become the second cause of mortality due to non-AIDS events in HIV-infected individuals [72].
Despite the high efficacy of ART, HIV+ patients are exposed to a higher risk of MI and death from cardiovascular causes than general population. This has been reported by HIV-infected patients showing an increased risk of coronary artery disease (CAD) by 1.5- to 2-fold, 1.8 times higher risk of HF, and 6-fold increase risk of myocardial fibrosis. Being infected with HIV provides as much cardiovascular risk as being diabetic, which was recognised by both FRAM study [73], reporting an increased risk of atherosclerosis in HIV+ patients, and Veterans [74], describing an increased risk of MI.
Initial studies proposed that this excess of cardiovascular risk was due to a great frequency of traditional risk factors between the HIV population as regards to the non-infected population:
dyslipidaemia, insulin resistance, alterations in the fat redistribution of fat, low HDL-c, elevated LDL-c, elevated triglycerides, hypertension, smoking and cocaine use [75]. ART has also been implicated in several studies, especially PI, in the D : A : D study [76], an increased risk for CVD was reported due to the cumulative effect of 2 PIs (Indinavir and Lopinavir/Ritonavir), but not for Saquinavir and Nelfinavir. Although ART is initially a possible mechanism of increased cardiovascular risk, the results of the SMART study changed this paradigm. This study randomized more than 5000 HIV+ patients with stable ART and CD4 counts >350 cells/µl continuing with the ART vs
interrupting/delaying ART until the CD4 dropped to 250 cells/µl and then restarting ART. The study concluded that those who interrupted or delayed ART had a 70% increase in the probability of suffering CVD vs the continuous ART group [77].
Given that HIV patients are generally young and that their cardiovascular risk in a short space of time is low, few events appear. Therefore, many studies are using surrogate markers that indirectly assess the tendency to suffer from CVD. These studies have shown an increase in the prevalence of subclinical atherosclerosis in HIV patients vs. non-infected patients, an increase in the thickness of the carotid intima-media thickness (cIMT) and of the intraluminal arterial plaque evaluated by ultrasound and CT has been found [78].
Figure 8. Hypotheses for the Pathophysiology of Atherosclerotic Coronary Artery Disease in HIV-Infected Patients Taking cART [77] (Boccara F, Lang S)
Pathogenesis of CVD in HIV-infected individuals
The development of atherosclerosis that underlies CVD and its events is a multifactorial process that affects inflammation and immune dysregulation, leading to endothelial dysfunction and rupture of the plaque, associated with traditional risk factors such as hypertension, diabetes,
dyslipidaemia and smoking. 1. Inflammation
1.1. C-reactive protein (CRP): elevated levels are found more frequently in HIV-infected
patients (59% vs 39%). The risk of MI was 4 times higher among HIV patients and increased CRP. There was no relationship between CRP level with HIV viral load or CD4 count, but the use of PI was related to elevated CRP [79].
1.2. IL-6: in the SMART study, which evaluated continuation of ART vs. treatment
interruption based on CD4 count, increased levels of IL-6 were associated with HIV viral load, cardiovascular events and any cause of mortality [80]. HIV-infected individuals on ART, baseline levels of sTNFαR-I and sTNFαR-II, IL-6, sCD14, and D-Dimer were associated with increased risk of MI and stroke and mortality [81]. These findings are demonstrated in Vos et al. [82], who examined the relationship between proinflammatory markers and CVD (CHD, MI, stroke and markers of CVD such as arterial stiffness and cIMT) in the HIV-infected population. This systematic review concluded that IL-6, D-Dimer and CRP were associated with an increased CVD risk, which is congruous with the data from general population-based studies.
of the aorta in HIV+ patients is higher compared to non-infected patients (adjusted for the absence of known CVD, age, sex, and Framingham score), but very similar to uninfected population with known CVD (mean age of 69 years) [83].
2. Immune activation
CVD risk is intensified in HIV infection by increased monocyte/macrophage-mediated
inflammation and damage within atherosclerotic lesions; it is especially distinguished by the increased activation of both intermediate/proinflammatory CD14+/CD16+ and non-classical CD14dim/CD16+ monocytes in HIV-infected patients after modifying the traditional risk factors [84]. HIV-infected population show higher proportions of CD16+ monocytes compared to HIV- individuals with stable CAD [85]; this increase of CD16+ monocytes, both intermediate and non-classic, was related with coronary artery calcium (CAC) progression [86]. On the other hand, activated CD4+ and CD8+ T-cells phenotype were not associated with CAC progression [87]. Furthermore, there is evidence suggesting that activated T-cells, CD38+ HLADR+, and senescent T-cells, CD28- CD57+, are associated with subclinical carotid atherosclerosis and carotid artery stiffness [88].
Microbial translocation leads to increase LPS levels inducing thromboplastin expression in circulating monocytes, which has been associated with increased CD8+ T-cell activation, D-Dimer levels and elevated risk of thrombosis [89].
3. Endothelial dysfunction
Persistent inflammatory processed in endothelial cells that support atherosclerosis constitute a complex interaction between inflammatory cells with lymphocyte and macrophage activation, injury to the mucosal barrier, metabolic changes, and other factors directly or indirectly associated to HIV replication. For instance, chemokines and vascular cell adhesion protein-1 (VCAM-1), are capable to attract monocytes and promote inflammatory cell entry, are present on endothelial cells that are modified by inflammation or injury by HIV infection [90].
4. Activation of coagulation
Numerous studies have shown that in HIV infection there is a pro-coagulative effect with increased levels of D-Dimer, Factor VII, von Willebrand and thromboplastin [80, 81, 89, 90]. 5. Co-infections
5.1. CMV: the presence of continued inflammation may also promote the development of
atherosclerosis and CVD in HIV patients [91].
5.2. HCV: HIV-HCV co-infection has been related to endothelial dysfunction, but it is not clear
whether the presence of HCV increases the risk of MI [92]. 6. Adipose tissue dysfunction
ectopic fat deposition and promotion of atherosclerosis which lead to both direct inflammatory effects on the myocardium and coronary arteries, and indirectly through immune and endocrine mechanisms, promoting the development of diseases. In addition, the interplay between the use of ART, direct viral effects, microbial translocation and persistent inflammation has predisposed HIV-infected population to the development of sick fat [93].
Pericardial fat volume is associated with higher rates of CVD events, stroke and chronic heart failure (CHF). Brener et al. [94] observed that HIV-infected patients have increased pericardial fat volumes compared with uninfected individuals, which was associated with increased levels of systemic inflammatory biomarkers such as TNF-α, IL-6 and sCD163 [95].
Moreover, HIV+ patients exhibit fat depots within the myocardium, myocardial inflammation and fibrosis, and abnormal cardia strain [96].
7.4 NEUROLOGICAL DISEASES ASSOCIATED TO HIV
INFECTION
The CNS is one of the target organs where the HIV can be detected within a few weeks of the infection, causing damage through direct and indirect mechanisms. HIV-1 penetrates the central nervous system (CNS) early, initiating a cascade of persistent neuroinflammation and activation, and ultimately CNS injury [97]. Since the first descriptions of HIV infection in the 80s were reported inflammatory changes in the CSF (particularly suggesting encephalitis), mostly pleocytosis and mild increase in the protein concentration [98]. Besides, prior to cART introduction, the onset of HIV-associated dementia (HAD) coincided with high plasma viral loads and CD4+ cell count <200μL. However, despite the occurrence of HAD is reduced in patients on HAART, the increased life
expectancy has increased HIV-associated neurocognitive disorders (HAND) prevalence. Neurological disease, that is secondary to opportunistic pathologies or caused by the virus itself, is the first
manifestation of HIV infection in 10-20% of cases, and between 30-40% if the disease is advanced [99]. Despite the fact that early infection is usually asymptomatic, MRS imaging and cerebrospinal fluid (CSF) examination can recognise CNS irregularities during this period [97]. Chronic HIV-1 infection culminates in neurodegenerative disease, labelled NeuroAIDS [97, 100].
Neurocognitive impairment (NCI) have been described to be more frequent in HIV+
categorized as HAND (Table 3), whose prevalence is around 50% even in patients treated and/or with undetectable viral load [103].
Table 3. Classification of HAND [104] Asymptomatic neurocognitive impairment (ANI) Mild neurocognitive disorder (MND) HAD Evidence of pre-existent* cause NO NO NO
Delirium or dementia NO NO NO DELIRIUM
Impairment of the daily living^
NO MILD SEVERE
Deviation of ≥2 cognitive” domains
YES YES SEVERE
* Previous neurological disease, psychiatric disorder or abuse of toxic substances
^ At least mild interference in one of the following: work, housework and social activities, evaluated through: a) the subject itself or b) standardized objective measures
Score >1 standard deviation below the average of the normative data corrected for age and education and other recommended norms in the standardized neuropsychological evaluation. “ Obligatory cognitive domains evaluated: Work memory/attention, abstraction
memory/execution (learning, short-term memory), verbal fluency, speed of information processing, motor skills.
Furthermore, Ances et al. [105] reported that the notable decrease in brain volumetrics due to HIV is predominantly observed within subcortical regions, such as caudate, corpus callosum and amygdala; these changes in brain volume were observed in HIV-infected participants regardless the presence or absence of HAART. In addition, the report concluded that the caudate volume atrophies after approximately 13 years of HIV infection, HIV leads to approximately 17 years of ageing of the brain, and that the changes in brain volume caused by the HIV infection were independently of ageing.
Pathophysiology
The HIV spreads in the bloodstream, facilitating its entry into the CNS through the blood brain barrier (BBB); this entry is primarily mediated by lymphocytes and monocytes that enter the
perivascular spaces [106]. The access of HIV into the brain causes a chain of events leading to CNS disease and neurologic impairment.
Mechanisms of HIV for entry and infection of the CNS [106] (Fig. 9):
a. Infected, activated monocytes transport HIV across the BBB through a “Trojan H orse” mechanism.
c. The appearance of multinucleated giant cells is produced as a result of cell-to-cell fusion. They are a characteristic feature of HIV-associated brain pathology.
d. Infected CD4+ T-cells also transport the HIV across the BBB, providing HIV pools within the CNS. This process is aggravated by systemic infection and immune system activation, resulting in the release of chemotactic mediators (for example: CCL2, CCL19, CCL20 and IP-10) into
circulation, attracting more activated cells and promoting the harbouring of HIV in the brain. This process may explain the mechanism of viral entry and the later neuroinflammation [107].
e. Astrocytes are known to harbour HIV; however, they do not result in a productive infection.
Figure 9. Potential models for HIV neuroinvasion and infection of the CNS [106] (Spudich S., Gonzalez-Scarano F.)
Mechanisms of injury
Amongst the various macrophages subtypes, perivascular macrophages are highly infected in the brains of HIV-infected individuals, being able to be identified by CD163 [106], this marker is also present in the macaques with simian immunodeficiency virus (SIV) [108]. Soulas et al. [109]
compared monocytes and macrophages presence in both HIV and SIV encephalitic lesions, and concluded that the development of encephalitis comprises the recruitment and gathering of three types of monocytes /macrophages: MAC387+ monocytes/macrophages that are not productively infected and do not express CCR2 (unlike perivascular macrophages), CD163+ perivascular macrophages, and CD68+ or HAM56+ resident macrophages. Originally, it was believed that perivascular macrophages didn’t contribute to the persistent presence of HIV in the brain, because of their fast turnover;
increased susceptibility of T-cells to HIV [110]. In the CSF appear other indicators of macrophage activation and chemotaxis [111] such as β2-microglobulin, neopterin, quinolinic acid and MCP-1 (Table 4). Neopterin and MCP-1 in CSF are indicators of macrophage activation and chemotaxis. Interpreted together with the detection of the virus, the elevation of these markers suggests that, in addition to the infection of the CNS, there is a state of macrophage activation, which is necessary for the development of HAND. It has also been reported the association between the systemic
immunological activation and HAND. This has been observed in the variable concentrations of proteins involved in chemotaxis such as sICAM (related to the extravasation of circulating leukocytes in areas of inflammation), which have been found elevated in the serum of HIV patients with
encephalopathy [112] (Table 4).
Table 4. Surrogate biomarkers of HIV-associated neurocognitive disorders [112] (Ciborowski P.)
Moreover, Ancuta et al. [18] reports that the microbial translocation in the gut
and the resulting persistent immune activation leads to neurological complications in HIV-infected patients. This mechanism favours the appearance of HAND despite the fact that the replication of HIV is controlled by the cART. The systemic activation of monocytes, resulting partially from the
microbial translocation in the gut, makes it easier for macrophages to penetrate into the perivascular spaces, leading to HIV infection of the CNS [106]. Moreover, as some of these cells are infected, they carry the virus into the CNS from the systemic circulation, being able to replicate independently from the systemic circulation. This is supported by data of increased levels of HIV specific
immunoglobulins within the CSF, intrathecally produced anti-HIV antibodies, and increased levels of CD8+ cytotoxic T lymphocyte (CTLs) [99]. The perivascular invasion and resultant inflammation leads to the release of chemokines (MCP1 and IP-10, some of the most commonly associated with HIV infection) and cytokines, which boost the immune reaction by attracting other circulating monocytes and infected CD4+ T-cells [113].
with ART, who exhibit new-onset neurological deficits and clear CNS HIV replication in the CSF, known as “CNS viral escape”. Regardless low viral suppression in the plasma or low viral levels [114, 115], a dominant pleocytosis is observed in those individuals, being CD8 pleocytosis the most
common. Moreover, in most of these patients is reported drug resistance of the CSF virus.
Epidemiology
Despite the fact that the incidence of HAD has decreased, the overall prevalence of HAND has increased in the HAART era, primarily because the incidence of subtle forms of HIV-1-associated cognitive impairment has increased, even among patients with viral suppression [99, 101]. Heaton et
al. [101] compared HIV+ individuals from the periods before and after cART, they reported that NCI
of any type was more commonly in the post-ART rather than in pre-ART cohorts. ART has not only been related to the frequency of NCI, but also to the pattern of neuropsychological impairment, as there is new evidence revealing the possible neurotoxicity caused by cART [116].
In addition, different risk factors have been described in the development of HAND: those that depend on the patient and those that depend on HIV per se or the consequences of HIV infection.
Table 5. Risk factors associated with the development of HAND [98, 111, 112, 117-132]
Factors that depend on the patient
Factors that depend on the HIV or from the consequences of the HIV
HIV-specific factors Factors related with the consequences of the HIV
1. Genetic predisposition 2. Ageing
3. Use of toxic substances 4. Co-infection with HCV 5. Metabolic disturbances
6. CVD
7. Family history of dementia 8. History of brain trauma
1. HIV subtype 2. Tat protein 3. Viral envelop 4. Neuroadaptation 5. Compartmentalisation and resistance 1. CD4+ nadir 2. AIDS 3. Microbial translocation and immune activation
4. ART effect
7.5 RENAL DISEASES ASSOCIATED TO HIV INFECTION
As a result of the prolonged use of effective cART and the resulting increase in life expectancy, HIV-infected individuals are at increased risk for kidney diseases related to diabetes and hypertension treatment, or associated with HCV or hepatitis B virus (HBV) co-infection; moreover, this has led to the appearance of new patterns of HIV-associated CKD 134. A state of chronic inflammation and disturbed metabolism persists and it is related to renal diseases such as arterionephrosclerosis, focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy. Furthermore, as previously
mentioned, resemblances between HIV infection and ageing have been observed, suggesting that the HIV involves the ageing process, precipitating comorbidity and frailty 135. This can be observed in HIV+ and elder patients with low estimated glomerular filtration rate (eGFR) who are at increased risk of CVD and drug toxicity.
Table 6. Differential diagnosis of kidney disease in HIV-infected patients 136 (Campos P., Ortiz A., and Soto K.)
AKI
CKD
Both HIV infection and the adverse effects of cART have been associated with CKD, which has become as a cause of morbidity and mortality in HIV population 139. Risk factors for CKD include both traditional and HIV-related:
- Traditional risk factors for CKD are ageing, hypertension, CVD, diabetes mellitus, and previous AKI, which are becoming more prevalent in HIV-infected populations.
- HIV-related factors include low CD4+ counts, high viral load, IV drug use, HCV co-infection and cART.
The most common forms of renal injury in HIV infection
HIV infection and associated treatments are related to various renal pathologies, such as tubular injury, mainly because of tenofovir therapy; glomerular diseases, including HIV-associated nephropathy (HIVAN) and HIV immune complex disease of the kidney (HIVICK), and becoming more frequently, diseases related with chronic inflammation, obesity, diabetes, metabolic syndrome and premature ageing, such as arterionephrosclerosis, FSGS and diabetic nephropathy.
HIVAN
HIVAN was firstly known as FSGS, which generally presents with high-grade proteinuria and rapid progression to end-stage kidney disease (ESRD) without the use of cART.
Since the initial description of HIVAN it has been identified that African population are generally predisposed to this complication of HIV infection. This predilection is due to high frequencies of the APOL1 genetic variants G1 and G2 in this population 140.
HIVAN kidney injury results from different mechanisms comprising direct viral cell injury and host susceptibility factors. It is still unclear how HIV enters renal parenchymal cells. One of the proposed mechanism reported that the typical receptors mediating the entry of HIV into T-cells and macrophages are absent from renal cells; although, both CD209 antigen, which may contribute to infection of dendritic cells and podocytes, and lymphocytic antigen 75, which contributes to infection of tubular epithelial cells, have been suggested to be part of HIV infection of T -cells and macrophages
141. Other mechanisms proposed: a) Singh et al. 142 has suggested that HIV may enter the tubular cells by phagocytosing apoptotic CD4+ T-cells, and b) Khatua et al. 143 reported that HIV may access podocytes via dynamin-mediated endocytosis, although unable to establish a productive infection.
Classic HIVAN is defined by the pathognomic characteristic changes that are present along the full length of the nephron including glomerulus and tubular interstitium, these are: visceral glomerular epitheliosis, podocyte hypertrophy and proliferation, mesangial protrusion and hypercellularity,
All these pathologic changes affect glomerular filtration, proliferation, apoptosis, dedifferentiation and immunomodulation. Development of HIVAN results from the alteration in nephron morphogenesis and dedifferentiation. Podocytes and renal tubular epithelia cells express Tat and Nef leading to dedifferentiation and/or epithelial mesenchymal transdifferentiation, which results in proliferation and tubular microcyst formation 145.
Via direct viral cell injury and host susceptibility factors HIVAN is capable to damage the kidney. Infiltrating leukocytes express two HIV co-receptors infecting lymphocytes and macrophages which leads to the release of inflammatory mediators promoting further kidney injury. In addition, it has been suggested that cell death caused by HIV infection occurs in tubular cells via apoptosis, maybe driven by Vpr, and in podocytes through mitotic catastrophe, in which impaired chromosomes
replication or other DNA damage results in cell death 146. HIVICK
HIVICK has become more common renal injury than HIVAN in HAART -naïve HIV-infected individuals 147, and less likely to progress to ESRD. HIVICK results from repeated infections and polyclonal immunoglobulin expansion. Moreover, viral replication and the immune responses to viral proteins and other infection-associated antigens are believed to contribute to immune-mediated glomerulonephritis that comprises HIVICK 148.
The nephrotoxicity of antiretroviral therapy
Various studies have reported that cART may result in nephrotoxic effects, including both AKI and CKD 149. cART-induced nephrotoxicity can appear even in individuals with normal baseline renal function. The most common forms of renal injury are crystalluria, obstruction due to PIs use, and proximal tubular damage due to tenofovir therapy (table 7).
Table 7. Manifestations of antiretroviral toxicity 136 (Campos P., Ortiz A., and Soto K.)
Others
environmental or genetics factors in the pathogenesis of the disease. It has been reported that various disorders such as diabetes, metabolic syndrome, hypertension and atherosclerosis may interact with HIV infection and/or cART to accelerate the impairment of renal function, resulting in CKD
presenting as increased urinary protein excretion, or other abnormal urinary findings, and decreased eGFR 150.
7.6 HEPATIC DISORDERS ASSOCIATED TO HIV INFECTION
Non-AIDS diseases have become significant causes of morbidity and mortality in the HIV-infected population; within this group, liver disease has arisen as the most common related cause of death among HIV+ individuals, constituting for 14-18% of all deaths [151].Liver dysfunction in HIV can be due to HIV itself or by different pathologies, for instance, HCV, HBV, hepatotoxicity related to cART, opportunistic infections (CMV especially), alcohol and non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH) [152, 153, 154] (Fig. 10).
The mechanisms of liver disease in HIV-infected individuals are, to some extent, dependant on the function of the immune system, as it has been suggested that the progression to advanced hepatic fibrosis is related to poorly controlled HIV infection [155].
Figure 10. Causes of liver disease in patients with HIV infection [154] (Joshi D.) Causes and their pathogenetic mechanisms
HIV damage to the liver
apoptosis and increases production of TGF-β1) effects [153]. Activated HSCs express CCR5 and CXCR4, the two major co-receptors essential for HIV entry into cells [153, 156].
The development of liver fibrosis represents the final common pathway of hepatic injury. Fibrogenesis may be the result of two mechanisms: downregulation of IL-10, and/or by the increase ratio of CD8+ to CD4+, as CD8+ cells have a fibrogenic effect [153].
Systemic inflammation and immune dysfunction
Systemic inflammation may produce fibrosis via various mechanisms such as accelerated senescence, oxidative stress and endoplasmic reticulum (ER) stress resulting in mitochondrial dysfunction. The main causes of systemic inflammation in HIV-infected individuals are chronic infections (HIV and co-infection with HCV and/or HBV) and NAFLD.
- NAFLD increases levels of free fatty acids (FFAs) in the liver and decreases insulin sensitivity resulting in an increase of lipid peroxidation, reactive oxygen species (ROS), ER stress and systemic inflammation, releasing IL-6 and TNF-α; the overall produces a profibrotic state in the liver.
- Chronic viral infections (HCV, HBV and HIV) causes a systemic inflammatory response. The inflammatory responses of HCV and HBV are featured by: diminished NF-kB activity, resulting in decreased expression of hepatoprotective genes; the upregulation of TGF-β which activates HSC, and the increased fibrotic phenotype and consequently impaired HSCs fibrosis, caused by the overexpression of IL-1, IL-6 and TNF-α. Moreover, the CD4/CD8 inequality seen in both HIV and viral hepatitis results in the decrease of HSCs apoptosis, due to the under-expression of IFN-γ, boosting a profibrotic state in the liver [157, 158].
Gut microbial translocation
HIV promotes gut microbial translocation increasing hepatic levels of bacterial LPS, which leads to hepatic inflammation and subsequent liver damage by one of the following mechanisms [18, 152]:
a. Recruitment and activation Kupffer cells and HSCs
b. Indirectly inducing immune response leading to hepatocyte cell death
c. Inducing the release of proinflammatory cytokines and acute phase reactants, for example TGF-β1, IL-6 and IL-10.
LPS modulates HSCs activity and phenotype via toll-like receptor-4 (TLR4)-mediated signalling pathway, activating nuclear factor kappa-light-chain-enhancer of activated B-cells (NFκB), IFN regulatory factors and AP-1. This results in the upregulation of inflammatory/fibrotic HSC phenotype and increases the lifespan of HSC cell lines, leading to the release of proinflammatory and
profibrogenic cytokines such as TNF-α, IL-1, IL-6, IL-12, macrophage chemoattractants and
nitric oxygen synthase [159, 160]. Moreover, TLR4 increases the activity and migration of Kupffer cells, intensifying the interaction between HSCs and Kupffer cells by activating the production of fibrogenic factors [160].
Furthermore, it is demonstrated that gut microbial translocation participates in both alcoholic and non-alcoholic liver diseases, along with HIV+ patients co-infected with HCV that develop more rapid fibrosis [159] that those infected only with HCV.
Antiretroviral drug-induced hepatotoxicity
In HIV-infected individuals is common drug-induced liver injury (DILI) and is generally attributed to HAART, of which PIs are the most common source. The severity of liver impairment is classified according by the concentration of aminotransferases [154]. HAART-induced hepatotoxicity occurs through various mechanisms: direct liver injury, immune reconstitution inflammatory syndrome (IRIS), idiosyncratic hepatotoxicity, hypersensitivity, mitochondrial toxicity, and hepatic steatosis [152, 153, 154] (Table 8).
Table 8. Presentations of highly effective anti-retroviral therapy-related liver injury (Puri P. and Kumar S.) [153]
HBV infection
HBV infection in HIV-infected individuals is associated with an increased risk of chronic carrier state, if the infection by HIV precedes that of HBV, resulting in reduced ability to clear HBV infection, which is correlated with low CD4+ cell count [153, 154].
HIV infection alters the course of HBV infection as intensifies HBV replication, which is displayed by increased HBV viraemia with higher levels of HBV DNA and increased HBeAg titre [153].
Other implications of HIV-infection with HBV are that infected individuals present increased HBV DNA viral load, which is associated with increased risk of hepatocellular carcinoma (HCC) [153, 154].
HCV infection
Prior to cART era, no distinction between HIV-infected individuals with or without HCV co-infection were reported regarding CD4+ T-cell counts or progression to AIDS and death. Nevertheless, since the introduction of cART, new data published has demonstrated that HCV co-infection does affect HIV course through different mechanisms that lead to a decreased rate of spontaneous HCV RNA clearance [153, 154]. This results in accelerated progression of HCV-related liver disease (particularly by increasing the rate of fibrosis) and final cirrhosis, which is observed 12-16 years earlier in HIV co-infection with HCV than in HCV infection alone [153].
Mechanisms resulting in persistence of HCV infection and rapid fibrosis progression [154]:
a. Exhausted adaptive immune system and reduced IFN-γ response of CD8+. b. Constant liver injury activates HSCs, which in turn produce type I collagen. c. Reduced ratio CD4+ to CD8+ cells.
d. Decreased IL-10 expression
e. Insulin resistance is commonly related with HCV infection, despite of HIV co-infection. f. Gut microbial translocation
Since HCV infection affects directly the liver, unlike the immune hepatic damage caused by HBV infection, is believed that deteriorated cell immunity in HIV-infected individuals enables greater HCV replication, thus resulting in exalted infection and injury to hepatocytes [153].
Opportunistic infections
Multiple opportunistic infections have been related with hepatic involvement in HIV-infected patients, which are related with asymptomatic elevation of liver enzymes. The most common
infections are Mycobacterium avium complex, Mycobacterium tuberculosis, CMV, Cryptococcus
neoformans, and extrapulmonary Pneumocystis jiroveci.
NAFLD
NAFDL is defined as fat deposition in the liver not caused by chronic alcohol abuse. Its prevalence is higher in HIV-infected population (30-40%) compared to general population (14-31%) [154]; moreover, it is present in about 30% of HIV+ individuals without any other co-infections, such as HBV or HCV infection [161].
NAFLD may evolve into NASH, which is associated with macrovesicular steatosis,
with HBV or HCV, and metabolic abnormalities, such as hypertriglyceridemia, low HDL and low TC [153, 161, 163].
7.7 BONE DISORDERS ASSOCIATED TO HIV INFECTION
The life expectancy of people with HIV infection has increased significantly, and this has made osteoporosis an emerging comorbidity. The ageing of patients will undoubtedly contribute to making this clinical problem even more frequent in the near future than it is today. Within the bone
involvement found in HIV, the most common problems are osteopenia, osteoporosis, osteomalacia and osteonecrosis. A higher prevalence of osteopenia and osteoporosis has been found in patients who do not receive ART in comparison with healthy subjects, although in the majority of the studies, due to its insufficient sample size, it could not be adjusted to the traditional risk factors [164]. In a sub-study on bone mineral density (BMD) of the START trial, which included 424 naïve patients with a higher CD4+ T-lymphocytes counts and a mean age of 34 years, a high prevalence of osteopenia and osteoporosis was detected (35.1% and 1.9%, respectively), which was associated not only with
traditional risk factors, but also with the duration of HIV infection [165]. In a longitudinal study of the HIV-UPBEAT cohort adjusted for traditional risk factors, which included 474 subjects infected and HIV- individuals, HIV infection and its duration were associated with a decrease in BMD [166].
Osteoporosis in HIV-infected patients is the final product of two etiological factors: in addition to the traditional risk factors that may affect the general population, there are others directly or
indirectly related to HIV infection that may contribute to this risk, including ART. Epidemiological studies have shown that HIV-infected patients are at increased risk of osteoporosis or lower BMD, about 3.7 times higher than in control subjects [167, 168] (Fig. 11).
Figure 11. Flow chart indicating bone mass loss after HIV infection [168] (Borderi M.) Disturbances in bone and calcium metabolism [169, 171]
Alterations in bone metabolism generally result from systemic inflammation and circulating cytokines, along with HIV-associated opportunistic infections, neoplasms, and/or medications affect bone via indirect mechanisms, rather than affecting directly the bone or parathyroid gland.
Pathogenic bases of osteoporosis in HIV infection
Under normal circumstances bone remodelling is maintained in a state of equilibrium, but it can be altered by a decrease in formation or by an increase in resorption. The most frequent causes of both events are discussed in the following section. In any case, the predominance of resorption leads to a negative balance of remodelling, decreased BMD, deterioration of the micro-architecture of the bone and weakening of the resistance of the bone (fragility), which leads to an increased risk of fractures.
In patients with HIV infection, the etiopathogenesis of osteoporosis is multifactorial because, in addition to factors dependent on the host, other factors related to HIV infection and ART are involved [172].
Traditional risk factors for osteoporosis
Traditional risk factors such as vitamin D deficiency [169] and HCV co-infection [173] have been observed more frequently in HIV-infected individuals rather than in the general population. Effects of HIV and associated inflammation
There are specific factors linked to HIV infection that have a negative effect on bone
metabolism, since they induce a predominance of bone resorption and, therefore, alter the balance of remodelling. Numerous experimental evidences suggest that HIV infection per se and/or the
Table 9. Possible effects of HIV infection in the bone compartment [164]
Osteoclast Osteoblast
HIV proteins
Gp 120 - Stimulates the activity of osteoclasts through RANKL
- Stimulates the apoptosis of osteoblasts
Vpr - Stimulates the activity of osteoclasts through RANKL
P55-gag - Stimulates the apoptosis of
osteoblasts
- Inhibits the differentiation of mesenchymal cells into osteoblasts
Inflammatory markers
TNF-α - Stimulates the differentiation and activity of osteoclasts
- Induces the apoptosis of osteoblasts
RANKL - Stimulates the differentiation and activity of osteoclasts IL-6 - Stimulates the activity of
osteoclasts through RANKL M-CSF - Stimulates the differentiation
of osteoclasts
Osteoprotegerin - Induces the apoptosis of osteoclasts
Several in vitro studies have shown the influence of HIV proteins on the activity of osteoblasts and osteoclasts (Fig. 12). Gp120 and Vpr stimulate osteoclastic activity through the activation of receptor activator of nuclear factor kappa-B ligand (RANKL) expression at the surface level of peripheral mononuclear cells [168, 174]. RANKL, is also found in osteoblasts and T lymphocytes, promoting the activation of osteoclasts. The gp120 and p55-gag stimulate the apoptosis of the osteoblasts [175, 176], and there is evidence that p55-gag is also capable of inhibiting the transformation of mesenchymal cells in functioning osteoblasts [175].
Figure 12. Interaction between HIV and osteoblast lineage [168] (Borderi M.) The association of osteopenia with inflammatory and immune activation biomarkers has also been observed in cross-sectional studies. In one of them, with 78 patients mostly virologically
suppressed, low BMD was associated with immune activation measured by HLA-DR + CD4 +/CD8 + in an analysis adjusted for demographic and HIV-related factors [174]. Other report studied 331 patients in whom various biomarkers of bone remodelling were examined before the start of ART, the analysis was adjusted for traditional factors, and revealed that low BMD is associated with low levels of osteoprotegerin and high levels of adiponectin, a cytokine that has been linked to increase in bone remodelling [177]. However, other studies have not been able to demonstrate the association of low BMD with inflammatory biomarkers and immune activation after adjusting for traditional factors linked to the bone [178].
Effects of ART
The effect of ART can be non-specific, caused by any regimen, or related to certain
Despite the fact that all antiretrovirals can induce BMD loss, the magnitude of this varies considerably from one to another, suggesting that some of them exert a specific effect on bone metabolism. Tenofovir disoproxil fumarate (TDF) is the antiretroviral whose association with bone demineralization has been demonstrated more consistently. In several randomized clinical trials, in which TDF was compared with abacavir or stavudine, as part of the initial treatment regimen, it was observed that regimens that included TDF were associated with significantly higher BMD drops than those compared to [182].
8. METHODOLOGY
The updating of knowledge about the chronic inflammatory state secondary to HIV and its consequences are of a great amplitude. For selecting the medical literature, the following databases were used: PubMed, Cochrane Library Plus, OVID and UpToDate. The period has covered the last 10 years and all the articles that could be obtained as full text have been assessed. The terms used were: "HIV and inflammation", "HIV and immune and activation", "HIV and inflammatory and markers", "HIV and cardiovascular and disease", "HIV and neurocognitive and disorder", "HIV and premature and ageing", "HIV and kidney (or renal) and disease", "HIV and hepatic (or liver) disease", "HIV and metabolic and disease ", "HIV and bone and disease". Keywords were matched to database indexing terms.
