UNIVERSITÀ DI PISA
Dipartimento di Farmacia
Corso di Laurea Magistrale in Farmacia
Tesi di laurea
Proton Pump Inhibitors (PPIs): from widely prescribed safe drugs to
the emerging side effects due to an excess of confidence.
Relatore
Dott.ssa Alma Martelli
Candidato
Waleed Rizek
2
Index
1.
Introduction ……… 4
2.
Gastric H
+/K
+-ATPase ………. 5
2.1 Gastric H+ /K+ -ATPase location ………... 5
2.2 Gastric H+ /K+ -ATPase structure ………..…… 8
2.3 Gastric H+ /K+ -ATPase function ……….... 10
3.
Proton pump inhibitors ……….... 12
3.1 Chemical structure ………... 12
3.2 Mechanism of action ………..…….. 18
3.3 Pharmacokinetic and Pharmacodynamic ……….. 22
3.4 Therapeutic implications ………..……… 27
3.4.1 Peptic ulcer disease ………. 28
3.4.2 Zollinger Ellison-induced peptic ulcer disease ………..… 32
3.4.3 Gastroesophageal reflux disease ……….. 33
3.5 Side effects ………...………… 35
3.5.1 Vitamin deficiency ………..………. 35
3.5.2 Iron deficiency ……….. 39
3.5.3 Hypergastrinemia and gastric cell hyperplasia …………. 40
3.5.4 Cardiac Adverse Reactions ………...………. 41
3
3.5.6 Clostridium difficile infection (CDI) ………...…. 45
3.5.7 Community-acquired pneumonia (CAP) ………. 48
3.5.8 Osteoporosis, bone fractures and falls ……… 50
3.5.9 Kidney disease ……….. 53
3.6 Inappropriate prescription of PPIs ………..………. 56
4
Discussion and conclusion ………...………. 60
4.1 Discussion ………. 60
4.2 Conclusions ………..…… 62
5
Bibliography ………..……… 63
4
Chapter 1
Introduction
Proton-pump inhibitors (PPIs) are a largely prescribed class of medications used to decrease gastric acidity via the inhibition of the parietal cell H+/K+ -ATPase pump and their use has significantly increased over the last few decades. The United States Food and Drug Administration (FDA) has approved this drug class for the treatment of a variety of gastric acid-related conditions, including gastric and duodenal ulcers, erosive esophagitis, gastroesophageal reflux disorder (GERD), Helicobacter pylori eradication and pathological hypersecretory conditions such as Zollinger–Ellison syndrome [Rotman and Bishoop ., 2013]. However, PPIs are often improperly prescribed, such as administered for inappropriate indications or at higher dosages than guidelines recommendations [Orlaith et al., 2015].
Since they have been on the market, numerous post-marketing studies have been published demonstrating that prolonged PPI therapy is linked to the emergence of adverse effects with variable severity, particularly in older adults [Marina et al., 2017]. Based on these studies, most of them were case-control, cohort studies, and meta-analyses, PPIs have been associated with an increased risk of presenting a number of adverse effects including osteoporotic-related fractures, Clostridium difficile infection, community-acquired pneumonia, vitamin B12 deficiency, kidney disease and dementia [Marina et al., 2017].
5
Chapter 2
Gastric H
+/K
+-ATPase: location, structure and
function
The gastric H+/K+-adenosine triphosphatase (ATPase) is an integral membrane protein that belongs to the P2-type ATPase family, a group of protein that alters the membrane helix interactions to enable active transport- i.e. against concentration gradient- of alkali cations and small cations like Mg++ and Ca++. The H+/K+-ATPase acts as a transporter of H+ and K+, thus regulating the secretion of gastric acid.
2.1 Gastric H
+/K
+-ATPase: location
The gastric H+/K+-ATPase is predominantly located in the parietal cells of
the stomach but it can be also found in the renal medulla [Yu et al., 2017]. The location of the gastric H+/K+-ATPase is not stable as it varies depending on the
activation state of the parietal cells, showing two possible expression sites (Figure
6
Figure 2.1.1. Resting and activated (“stimulated”) states of parietal cells. Upon activation (by
gastrin, acetylcholine:Ach, or histamine), H+/K+-ATPases migrate from the cytoplasmic
tubulovesicles to the apical membrane of the parietal cell and the canaliculi elongates.
Specifically, the H+/K+-ATPase appears in the cytoplasmic tubular membranes when the cells are resting, as observed in fixed parietal cells [Ogata and Yamasaki ., 2000]. Differently, it appears in the microvilli of the expanded secretory canaliculus during the activated state, when the parietal cells are functional, as observed in a model of isolated gastric mucosa [Sawaguki A. et al., 2005]. In vivo, the parietal cells are activated by histamine, gastrin or acetylcholine [Soll and Walsh ., 1979].
It has been hypothesized that the transition from one conformation to the other is a consequence of the fusion of cytoplasmic vesicles and microvilli, creating elongated microvilli of the expanded secretory canaliculus [Forte J.G. et al., 1983; Sawaguchi A. et al., 2005]. At the apical membrane of the parietal cell, the enzyme is functional and able to secret acid into the stomach through the exchange of cytoplasmic hydronium (H3O+) with extracellular potassium ion (K+).
Recent studies evidenced that the presence of K+ near the luminal surface of the
pump is guaranteed by the presence of K+ efflux channels associated with the
7
efflux channels are the voltage gated KCNQ1-KCNE2 ones. They are heteromeric potassium channels located in the gastric epithelium that co-localize with H+/K+ -ATPase in the secretory canaliculus of the parietal cell [Heitzmann et al., 2004].
8
2.2 Gastric H
+/K
+-ATPase: structure
The gastric H+/K+-ATPase is an heterodimeric enzyme that exchanges
cytoplasmic H3O+ with extracellular K+ [Shin et al., 2009]. It is composed of two
subunits, alpha (α, 114 KDa) and beta (β, 35 KDa), as shown in Figure 2.2.1.
Figure 2.2.1. Structure of the gastric H+/K+-ATPase. In grey is the α subunit, in black is the β
subunit. [Lixin ., 2008]
The first description of the α subunit dates back to the 1986, when Shull and colleagues investigated its structure in rats [Shull G.E. et al., 1986]. In the following years, the structure of the α subunit has been confirmed in several other species (Meada et al.,1990). The primary structure of this subunit is made of 1,033 or 1,034 amino acids and is very conserved among species, presenting a high percentage of homology [Sweadner et al., 2001].
The α subunit consists of ten transmembrane segments (Figure 2.2.2) [Munson k. et al., 2000] containing the binding site for ATP, the catalytic site of phosphorylation/dephosphorylation, the binding ion domain and the transporter [Toyoshima et al., 2000; Toyoshima et al., 2003]. Specifically, The TM8 contains
9
the catalytic site (aspartyl at position 386) and TM6 contains the ion-binding domain. Moreover, in position 791 of TM5 there is an amino acid lysine that seems to be responsible for the outward transport of H3O+.
Figure 2.2.2. Schematic representation of the H+/K+-ATPase. [Munson et al., 1999]
The β subunit is composed by 291 aminoacids that form single trans membrane segment. It presents six or seven N-linked glycosylation sites [Reuben et al., 1990; Shull ., et al 1990; Toh et al., 1990]. Data have shown that the N-linked glycosylation sites are responsible for the ion trafficking [Vagin O. et al., 2002; Vagin O. et al., 2004; Vagin O. et al., 2005]. It has been hypothesized that the β subunit has the role of preserving the structure, and thus the function, of the α subunit. Particularly, it seems to be responsible for the peculiar characteristic of interacting with the structure of the counter-cation K+. This hypothesis is corroborated by the fact that the β subunit unit is always expressed in association with a K+ countertransport ATPase. Moreover, the β subunit establishes
hydrophobic interactions with the α subunit, especially with the TM7 and the TM8 that is thought to be responsible for the formation of the high affinity K+
10
2.3 Gastric H
+/K
+-ATPase: function
As reported in a review published by Post R.L. and colleagues in 1972, numerous studies established that the structure and function of the gastric H+/K+
-ATPase resembles the one of the Na+/K+-ATPase [Post et al.,1972]. As far as the
function concerns, both of them show phosphorylation/dephosphorylation cycles that lead to the secretion of H3O+.
ATP and H3O+ bind the high affinity inward-facing (facing the cytoplasm)
binding site of H+/K+-ATPase. The pump undergoes phosphorylation on the amino acid aspartyl at position 386, within the sequence DKTGTLT [Walderhaug et al., 1985]. This phosphorylation alters the conformation of the pump into an outward-facing ion-binding site with lower affinity. This conformational transition is referred to as the E1 (inward binding state) to E2 (outward ion-binding state) transition that allows the shift of H3O+ from the cytoplasm
compartment to the extracytoplasmic (or luminal) space (Figure 2.3.1) [Wallmark et al., 1980; Stewart et al., 1981; Rabon et al., 1991].
It has been observed that actually, between the E1 and the E2 conformations, a third one exists. This intermediate conformation is referred to as the “occluded state” as both sides of the membrane are “occluded” as the ion cannot move out of the membrane domain in either directions.
In summary, for the transport of one H3O+, the following steps take place:
1. On the cytoplasmic side, H3O+ binds to the inward ion-binding site; then,
the catalytic subunit of the pump is phosphorylated by Mg-ATP to form Mg.E1-P H3O+
2. Transition into the “occluded state”: Mg.E1-P [H3O+]
3. Transition into the outward ion-binding state: Mg.E2-P H3O+
4. The H3O+ is released in the luminal space.
Then, the subsequent steps serve for the transport of K+ from the cytoplasm to the stomach lumen through the following steps:
1. One extracytoplasmic K+ replaces one H3O+ at the outward ion-binding
11
2. The pump is dephosphorylated (one inorganic phosphate is released in the cytoplasm) and changes its conformation into the “occluded state”: E2-P [K+] 3. Transition into the inward ion-binding state: E1- K+
4. The K+ is released in the cytoplasm.
Figure 2.3.1. Catalytic cycle of H+/K+-ATPase. Release of one H
3O+ in the extracytoplasmic site
(gastric lumen) and entry of one K+ in the cytoplasmic compartment of the gastric parietal cell
12
3. Proton Pump Inibitors
3.1 Chemical structure of PPIs
PPIs are solid, odourless, weak bases poorly soluble in water. PPIs are chiral compounds characterized by an asymmetric chemical structure; they exist into two identical mirror images (optical isomers known as enantiomers R – “right hand” - and S – “left hand”). Most of the PPIs on the market are prepared as racemic mixtures (same quantity of R and S enantiomers), like Omeprazole, Lansoprazole, Pantoprazole and Rabeprazole, while Esomeprazole is formulated as S-enantiomer of Omeprazole.
PPIs share a common core structure that consists in a 2-pyridylmethyl-sulfinyl– benzimidazole (Figure 3.1.1). This structure is made of three major parts: two heterocylcic structures (a methylpyridine and a benzimidazole) linked through a sulfinyl (-SO-) group [Lindberg et al., 1986].
k
13
The imidazole PPIs currently on the market (Omeprazole, Esomeprazole, Lansoprazole, Pantoprazole, and Rabeprazole) share the same basic structure and differ only for the substituents on the pyridine and benzimidazole rings. Omeprazole (Figure 3.1.2) is a derivate of Timoprazole, formulated as sodium or magnesium salt. It exists as a racemic mixture of (R)- and (S)-isomers. Esomeprazole has the same chemical structure of Omeprazole, as it consists in S enantiomer of Omeprazole.
-
Omeprazole and Esomeprazole-IUPAC Name: 6-methoxy-2-[(4-methoxy-3,5-dimethylpyridin-2- yl)methylsulfinyl]-1H-benzimidazole
-Molecular Formula: C17H19N3O3S - Molecular Weight: 345.417 g/mol
Figure 3.1.2. Omeprazole and Esomeprazole structure.
pKa1= 4.06, pKa2= 0.79
14
Lansoprazole (Figure 3.1.3) is a derivate of Timoprazole formulated as a racemic mixture of (R)- and (S)-isomers.
-
Lansoprazole. IUPAC Name: 2-[[3-methyl-4-(2,2,2-trifluoroethoxy)pyridin-2-yl]methylsulfinyl]-1H-benzimidazole
. Molecular Formula: C16H14F3N3O2S . Molecular Weight: 369.362 g/mol
Figure 3.1.3. Lansoprazole structure.
pKa1= 3.83, pKa2= 0.62
15
Pantoprazole (Figure 3.1.4) is a lipophilic compound, formulated as sodium salt racemic mixture of (R)- and (S)-isomers.
-
Pantoprazole. IUPAC Name: 6-(difluoromethoxy)-2-[(3,4-dimethoxypyridin-2-yl)methylsulfinyl]-1H-benzimidazole
. Molecular Formula: C16H15F2N3O4S . Molecular Weight: 383.37 g/mol
Figure 3.1.4. Pantoprazole structure.
pKa1= 3.83, pKa2= 0.11
16
Rabeprazole (Figure 3.1.5) is a derivate of Timoprazole formulated as sodium salt racemic mixture of (R)- and (S)-isomers.
-
Rabeprazole. IUPAC Name: 2-[[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl]-1H-benzimidazole
. Molecular Formula: C18H21N3O3S . Molecular Weight: 359.444 g/mol
Figure 3.1.5. Rabeprazole structure.
pKa1= 4.53, pKa2= 0.62
17
Tenatoprazole, instead, has an imidazopyridine moiety in the place of the benzimidazole (Figure 3.1.6) formulated as sodium salt racemic mixture of (R)- and (S)-isomers.
-
Tenatoprazole:-IUPAC Name: 5-methoxy-2-[(4-methoxy-3,5-dimethylpyridin-2-yl)methylsulfinyl]-1H-imidazo[4,5-b]pyridine
-Molecular Formula: C16H18N4O3S - Molecular Weight: 346.405 g/mol
Figure 3.1.6. Tenatoprazole structure.
pKa1= 4.04, pKa2= -0.12
18
3.2 Mechanism of action of PPIs
PPIs are selective inhibitors of the H+/K+-ATPase, which is the enzyme that catalyses the last step of gastric acid secretion process. Briefly, this process consists in the activation of the basolateral membrane of gastric parietal cells by acetylcholine, histamine or gastrin, resulting in the release of intracellular second messengers that activate protein kinases [Welage., 2003], which ultimately activate the pump [Cornelius and Mahmmoud ., 2003].
PPIs are “prodrugs”- even though their activation does not require an enzymatic reaction- that are converted into pharmacologically active molecules in acidic conditions like pH 3 or below, which is typical in the activated parietal cell canalicules.
PPIs are weak bases characterized by two half equivalent points (pKa1 and pKa2) of about 4.0 (3.83-4.53, depending on the drug) and 0.5 (0.11-0.79), respectively (see Figure 3.2.1 for drug-specific pKa1 values) [Shin et al., 2004]. pKa1 values were experimentally measured while pKa2 values have been estimated in silico as the second protonation takes places in a very short time.
19
The pKa1 concerns a pyridine whereas the pKa2 is relative to a benzimidazole structure, in the case of benzimidazole derivates (Omeprazole, Lansoprazole, Pantoprazole and Rabeprazole), or to an imidazopyridine ring, in the case of Tenatoprazole (Figure 3.2.2).
These two structures are implicated in a two-step protonation process that leads firstly to the migration and accumulation of the molecules into the activity site and then to their conversion into biologically active drugs.
Figure 3.2.2. Benzimidazole-derivate PPIs structural units and relative pKa1 and pKa2.
[Shin et al., 2004]
The first protonation concerns the pyridine nitrogen that allows selective accumulation of the drug in the secretory canalicules of the activated parietal cells, where it binds to the pump (Figure 3.2.2). As the canalicules are characterized by a lower pH (about 1), the second protonation takes place. This latter represents the activation step; it consists in the protonation of the nitrogen vicinal to the C-2 position of the benzimidazole, leading to the conversion of the PPIs into thiophilic sulfenic acids and then in sulfonamides by a dehydration reaction (Figure 3.2.3).
20
21
Both thiophilic sulfenic acids and sulfonamides can react with one or several of the cysteine sulfhydryl exposed on the luminal side of the H+/K+-ATPase pump, forming covalent bonds (i.e. disulfite bonds) (see table Figure 3.2.1 for drug-specific binding sites). As shown in the table all PPIs bind the Cys813 that is located in the loop between TM5 and TM6. The reaction, between PPIs and Cys813, is extremely fast and very efficient. The binding to Cys813 allows the pump to fix into the E2 conformation. Subsequently, PPIs may bind to a second cysteine residue. This reaction takes places when the activation process is less efficient, thus providing enough time to bind a second cysteine: Omeprazole binds Cys892, Lansoprazole binds Cys321 and both Pantoprazole and Tenatoprazole bind Cys822.
Cys321 and Cys822 are located in the proton-transport domain of the pump; specifically, Cys321 is on the luminal surface, thus easily accessible, while Cys822 is located deeper within the TM6. As far as Cys892 concerns, it is situated in TM7/8 on the luminal surface, outside the transport domain, thus without any inhibitor activity on the pump [Shin et al., 2004]. Furthermore, it has been shown that anionic amino-acid residues glutamine at position 820 and glutamine or aspartate at position 824 have a crucial role in bolstering the stability of the PPI-pump complex [Roche ., 2006].
Table 3.2.1. Cysteine binding sites on the H+/K+ ATP pump in several PPIs
PPIs Cysteine sites of H+/K+ ATP pump
Omeprazole 813 and 892
Lansoprazole 813 and 321
Pantoprazole 813 and 822
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3.3 Pharmacokinetic and Pharmacodynamic
The oral administration represents the preferred route of administration for PPIs; nevertheless, the parenteral route is also frequently used in clinics [Baker ., 2006]. In the case of the oral administration, as PPIs are labile to acid environments, like the stomach, they must be protected to prevent premature protonation/activation in the gastric lumen. For this reason, PPIs are typically protected by acid-resistant enteric coating for the production of enteric-coated tablets (e.g. Pantoprazole and Rabeprazole) or capsules containing enteric-coated granules/pellets (e.g. Omeprazole, Lansoprazole and Esomeprazole). Although PPIs are subjected to a first-pass metabolism, the bioavailability is high. After oral administration, the bioavailability of Lansoprazole, Pantoprazole and Rabeprazole is higher than 75% and is stable over time. Differently, Omeprazole is the most labile of the PPIs and its bioavailability is lower, about 64%; if the therapy with Omeprazole is protracted for few consecutive days, the bioavailability increases over time during the first five days of administration as the gastric pH gradually rises and, thus, the degradation gradually decreases.
As soon as the pharmaceutical formulation reaches the duodenum, at a pH of about 5.5-5.6, the enteric coat dissolves and the unprotonated PPI is released and rapidly absorbed across the intestinal epithelium, transported to the liver and then transferred into the systemic circulation where it strongly binds to serum proteins by 95-98%.
To be activated, PPIs must penetrate into the parietal cell membrane and then migrate to the secretory canaliculus. As PPIs are weak bases with a pKa1 of about 4, the protonation on pyridine nitrogen allows selective and fast accumulation of the drug in the secretory canalicules where the pH is particularly low (1.7 +/- 0.2) [Schreiber et al., 2007]. Once the protonation takes place, the membrane permeability to PPIs drastically decreases and the PPIs remain trapped into the parietal cell. As a consequence, the concentration of PPIs at this active site is very high, about a 1000 time higher than that in the blood. This peculiar property determines a substantial increase of the therapeutic index. PPIs with higher values
23
of pKa1 show a more nucleophilic pyridine moiety; this results in a faster accumulation process [Shin et al., 2004] Rabeprazole, for example, has the highest pKa1 among PPIs (see Table 3.3.1) and, in fact, is the most rapidly accumulated in the secretory canalicules and activated.
Once at the active sites, PPIs are activated (by the protonation of the benzimidazole or the imidazopyridine ring) and converted into therapeutically functional molecules: the activation takes place if the parietal cells are actively secreting acids into the gastric lumen, for two reasons. First, the pKa2 of the benzimidazole and imidazopyridine ring is below 1; second, specific cysteine residues need to be faced toward the luminal side. Thus, as the acid secretion is fundamental for the activation of PPIs, these drugs should be administered about half an hour before meals. Moreover, it has been shown that food intake interferes with the intestinal absorption of Esomeprazole and Lansoprazole. Differently, Omeprazole, Pantoprazole and Rabeprazole bioavailability is not affected by food intake [Welage ., 2003].
PPIs with higher values of pKa2, show a faster reaction of protonation; for example Omeprazole, whose pKa2 is 0.89, undergoes protonation faster that Pantoprazole, whose pKa2 is 0.11 (see Figure 3.2.1). Importantly, the pKa2 represents the activation-limiting factor.
After being activated, PPIs bind the pump via a disulfide bond with Cys813 of the H+/K+-ATPase that is exposed on the luminal surface, thus easily accessible. Subsequently, PPIs might bind other cysteine residues. The number of covalent bonds with other cysteines modifies the overall binding kinetics and the half-life of the drug. Specifically, PPIs may react with cysteine residues exposed on the luminal surface or located deeper in the phospholipidic membrane of the parietal cell; this latter situation would translate into a longer activation time. At the same time, this binding setting (bonds with a cysteine deep in the membrane) is more stable as compared to the binding to a single cysteine or to a second cysteine located on the luminal surface; furthermore, deeper bonds are hardly accessible and not easily deactivated by reducing (deactivating) agents such as glutathione, resulting in a longer half-life. Pantoprazole and even more Tenatoprazole are the two PPIs with the longest activation time and half-life as they bind an
intra-24
membrane cysteine; specifically, after binding Cys813, they bind a cysteine of the TM6 domain – i.e. Cys822 – deep in the phospholipidic layer. Thus, the binding with Cys822 is irreversible [Shin and Sachs ., 2004].
Omeprazole, instead, binds the Cys813 in the TM5/6 domain and Cys892 in TM7/8 domain (outside the transport domain), which are both located on the luminal surface of the pump; bond with Cys892 is thus reversible [Shin and Sachs ., 2004].
It has been argued that as disulfide bonds have a covalent nature, their inhibitory effect is long lasting and irreversible. If this was the case, the half-life of PPIs would coincide with the half-life of the pump. In rats, it has been shown that the half-life of the α subunit is about 54 hours [Gedda et al., 1995]. Indeed, in order to restore acid secretion, it is necessary to synthetize new pumps, a process that takes about 15 hours [Im et al., 1985].
Plasma half-life is quite short, ranging from 0.6 to 1.9 hours for most of the PPIs (Figure 3.3.1), while for Tenatoplazole is much higher, of about 9 hours.
Figure 3.3.1. Comparison of the pharmacokinetics of the PPIs.
AUC is the area under the curve plasma concentration/time. Cmax= pick of plasma concentration. [Roche ., 2006]
25
Comparing plasma concentration of Tenatoprazole with that one of Esomeprazole over 24 hours, the pharmacokinetic difference clearly emerges (Figure 3.3.2). The peculiar properties of Tenatoprazole are due to its unique chemical structure: instead of having the typical benzimidazole moiety it presents an imidazopyridine ring (Figure 3.1.6).
Figure 3.3.1. Blood concentration (umol/L) of Tenatoprazole as compared to Esomeprazole. [Sachs et al., 2006]
Tolerance to PPI has not been observed. In fact, once acid suppression has been achieved, it is not required any adjustment of the dosage; to maintain the effect over time, PPI can be administered for several months at the same dosage achieving the same therapeutic effect. However, after cessation of PPI therapy, rebound of acid hypersecretion may occur. It has been hypothesized that this may be due to the increase of gastrin secretion during acid suppression, which in turn stimulates Enterochromaffin-like (ECL) cells growth deputed to histamine release. In rats, for example, acid hypersecretion persisted for more than 70 days. In two human studies on asymptomatic volunteers, it has been found that 44% of them experienced acid-related symptoms up to 4 weeks after treatment withdrawal
26
[Lødrup et al., 2013]. However, some scientific evidences do not support these data: at least five studies did not find any evidence for rebound acid hypersecretion after proton pump inhibitor therapy [Hunfeld et al., 2007].
PPIs are metabolized predominantly by the enzymatic activity of the cytochrome family CYP450 in the liver. Among the enzymes of this family, the polymorphic CYP2C19 isoform plays a major role. The genotype of CYPC19 can lead to three different phenotypes of metabolic efficiency: extensive metabolizers, poor metabolizers and heterozygous extensive metabolizers. Poor metabolizers have high AUC (area under the curve of plasma level time over time) and high gastric pH values over the 24 hours following administration, as compared to extensive metabolizers.
Omeprazole and Esomeprazole are predominantly metabolized by CYP2C19 up to saturation and, at a lower extent, by CYP2C8; Pantoprazole and Rabeprazole are metabolized by both CYPC19 and CYP3A. Additionally, Pantoprazole is metabolized by the sulfotransferase (enzyme not belonging to the cytochrome family) that catalyses a sulfate conjugation. Rabeprazole, instead, undergoes non-enzymatic reduction.
Following hepatic metabolism, about 100% of the PPI is completely deactivated and the inactive compound undergoes renal excretion, though Lansoprazole is also excreted via the biliary tree [Shi and Klotz ., 2008]. For example, the clearance of Omeprazole is 60 l/h, 11-17 for Lansoprazole and 9 for Pantoprazole [Petersen ., 1999].
27
3.4 Therapeutic implications
PPIs are a class of medications used to treat disorders related to gastric acidity, showing great efficacy and safety [Farley et al., 2000; Huang et al., 1996]. The first PPI was synthetized by a modification of an antiviral compound - pyridine-2-thioacetamide – named Timoprazole. In 1979, Omeprazole, a molecule with higher affinity for the H+/K+-ATPase and less side effects was synthetized.
Starting by the Timoprazole structure, several other PPIs (Esomeprazole, Pantoprazole, Lansoprazole and Rabeprazole) with different characteristics from Omeprazole were synthetized.
Several studies showed the advantages of PPIs as compared to histamine-2 receptor blockers, and their utility in many diseases [Gisbert et al., 2001]. Recently, the high efficacy of PPIs has been ascribed to their mechanism of action as they irreversibly block the final common step of acid secretion ensuring a long-lasting reduction of stomach acid production.
According to FDA, PPIs are indicated for the treatment of a variety of acid-related disorders such as: peptic ulcer disease, peptic ulcer-related gastrointestinal bleeding, eradication of Helicobacter (H.) pylori infection, prevention of non-steroidal anti-inflammatory drugs (NSAIDs)-induced gastroduodenal ulcers, Zollinger-Ellison syndrome, erosive esophagitis, non-erosive reflux disease and functional dyspepsia [Lynda et al., 1999]. At the beginning of the twentieth century, the treatment of these disorders consisted in the prescription of alkaline diet, like milk [Sippy ., 1962]. Actually, the benefits of milk were confuted later on because of its buffering effect and stimulation of gastric acid secretion [Ippoliti et al, 1976]. The use of sodium bicarbonate was then introduced to improve symptoms, however, without preventing complications. Muscarinic antagonists, like atropine, were also introduced, but their effect on gastric secretion was only partial and accompanied by numerous adverse effects due to the inhibition of muscarinic receptors throughout the body. Then, histamine 2 receptor antagonists (H2 blockers) like Ranitidine and Famotidine were introduced with great clinical efficacy. However, these drugs were unable to completely inhibit the gastric acid
28
secretion [Vela ., 2014] and were almost completely supplanted by PPIs soon after.
3.4.1 Peptic ulcer disease
Peptic ulcer disease is a very frequent disorder that affects almost 4 million people in the world every year, with high morbidity and mortality rates. It is a disorder of the gastrointestinal tract characterized by extensive alteration of the mucosal barrier function and integrity with appearance of open sores. Peptic ulcer disease can manifest in both gastric and duodenal traits. In the first case, the ulcer usually occurs in the lesser curvature of the stomach, while in the second case the ulcer typically affects the bulb of the duodenum, where gastric content enters in the small intestine [Longstreth ., 1995].
The most typical symptom of peptic ulcer disease is represented by epigastric pain that appears during the fasting state or during the night and is usually relieved by food intake or acid-neutralising agents. Moreover, this can be accompanied by other symptoms like nausea, bloating, fullness, and early satiety. Furthermore, indigestion, vomiting, loss of appetite, weight loss, intolerance of fatty foods, and heartburn are less common symptoms [Spiegelhalter et al ., 1987]. Peptic ulcer maybe induced by several different factors, such as H. pylori infection and NSAID therapy, chemotherapeutic agents, bisphosphonate and others drugs [Kurata et al., 1997]. Nevertheless, H. pylori and NSAIDs play a major role:
a) H. pylori infection is very common all over the world, affecting more than 50% of the general population. However, only a minority of subjects (about 10 -15%) develop duodenal or gastric ulcers. H. pylori is a gram negative spiral bacterium which inhibits the release of somatostatin by the antral cells, thus attenuating somatostatin-dependent inhibition of gastrin release, resulting in an overall increase of acid secretion (Figure 3.4.1.1) [Sipponen P. et al., 1992; Malfertheiner P. et al., 2005] [Graham et al., 1993; El-Omar et al., 1995; Oble et al., 1995]. This increase may lead to
29
the development of metaplasia in the duodenal bulb. Importantly, metaplasia bolsters H. pylori colonisation in the gastric epithelium, increasing the duodenal mucosa susceptibility to acid attack and ulceration.[ Harris et al .,1996]
Figure 3.4.1.1 Mechanism of altered acid secretion in peptic ulcer. [McColl et al.,
30
H. pylori leads to the recall, in the gastric mucosa, of inflammatory mediators like cytokines, leukotrienes and phagocytes such as neutrophils and macrophages. Moreover, lysosomal enzymes and reactive oxygen species are released, which altogether concur in damaging the gastric mucosa [Harris et al., 1996].
b) NSAIDs are common cause of peptic ulcer. It has been reported that the annual risk of duodenal and gastric ulcer complications, like haemorrhage and perforation, is about 0.4% in patients who were chronically treated with NSAIDs [Drini M., 2017]; however, the percentage raises up to 9% in patients carrying multiple risk factors [Bhala et al., 2013]. Risk factors may include gastric cancer, lymphomas, lung cancers, Crohn disease, tuberculosis, hepatic cirrhosis as well as smoking and excessive alcohol consumption [Kurata et al., 1997]. Moreover, the risk of developing NSAIDs-induced ulcers is 2-fold higher for gastric ulcers as compared to duodenal ulcers.
The gastrointestinal side effects of NSAIDs are mostly caused by the inhibition of the enzyme cyclooxygenase-1 (COX-1). The further discovery of the COX-2 isoform led to the development of selective inhibitors of COX-2, known as “coxibs”, with a dramatic reduction of the risk of gastroduodenal ulcers [Lanas et al., 2007]. As a matter of fact, COX-1 and 2 are highly homologue enzymes, both metabolizing arachidonic acid into prostaglandins, leukotrienes and lipoxins. However, COX-1 is constitutively expressed in most of the tissues and exerts some protective activity on the gastric mucosa, while COX-2 expression is induced by inflammatory stimuli.
Although H. pylori and NSAIDs can act as independent risks factors for peptic ulcer disease, several studies indicated that they act synergistically in the inflammatory process underpinning peptic ulcer (Figure 3.4.1.2) [Huang et al., 2002].
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Figure 3.4.1.2. H. pylori and NSAIDs pathways in the inflammatory process: a synergistic effect inducing the peptic ulcer. [Huang et al., 2002]
The treatment for H. pylori-associated peptic ulcer is effective in both duodenal and gastric ulcers. It consists in the eradication of H. pylori with antibiotics and in the administration of PPIs to reduce acid secretion:
a) First line treatment: triple therapy (PPI standard dose twice a day plus Clarithromycin 500 mg or Metronidazole 400 mg twice a day, and Amoxicillin 1 g twice a day) for 7-14 days; antibiotic resistance (especially to clarithromycin), poor compliance and rapid metabolism of PPI are very common and require switching to the second line treatment. b) Second line treatment: quadruple therapy (Bismuth 120 mg four times a
day plus PPI standard dose twice a day plus Tertracycline 500 mg twice a day and Metronidazole 250 mg three times a day [Malfertheiner et al., 2007].
In the event that both first line and second line therapies are not effective, the European guideline recommends susceptibility testing to select other antibiotics according to the individual microbial sensitivity. For instance, Levofloxacin and Rifabutin (an antitubercolous agent) are two antibiotics that can be administered after first and second line failure in combination with PPIs and amoxicilin. The combination with Levofloxacin has a rate of eradication ranging from 63% to
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94% and is now becoming the second line therapy in several European countries [Gisbert et al., 2007; Saad et al., 2007].
For the treatment for NSAIDs–induced ulcer, the following therapies may be prescribed:
a) Prostaglandin-analogue Misoprostol;
b) Histamine H2 receptor antagonists, e.g. Ranitidine, Cimetidine and Famotidine, useful in the prevention of NSAID-induced duodenal ulcers, but not gastric ulcers;
c) PPIs, e.g Omeprazole and Pantoprazole seems to be the most effective therapeutic agents;
d) Barrier agents, e.g. sucralfate.
3.4.2 Zollinger Ellison- induced peptic ulcer disease
Zollinger Ellison (ZES) is a rare syndrome caused by ectopic secretion of gastrin by gastrinoma, which is a neuroendocrine tumor of duodenum (60% - 80%) and, to a lower extent, of pancreas (10% - 40%). Untreated ZES may lead to refractive peptic ulcer disease, gastroesophageal reflux, severe esophagitis, intestinal malabsorption of fatty acids, steatorrhoea (due to the inactivation of lipases by the acid), weight loss, and, eventually, death. In the treatment of ZES, it is important to control the gastric acid secretion with H2 receptor antagonists and PPIs to counteract symptoms, improve the survival and prevent surgery. H2 blockers have shown efficacy to the control the acid hypersecretion with an improvement of the symptoms over 80% in patients with ZES. The use of H2 blockers has shown the disadvantage of tolerance development in long-term treatments, which requires gradual increases of doses and more frequent administrations. H2 blockers have been replaced by PPIs for ZES treatment as
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they are more effective in managing acid hypersecretion, resolution of symptoms, and in improving survival and prevention of surgery.
Use of PPIs for ZES treatment:
a) Omeprazole: used in delayed-release capsules, with doses ranging from
20 mg in alternate days to 360 mg per day. It is effective in the inhibition of gastric acid secretion and resolves symptoms such as diarrhoea, anorexia and pain.
b) Pantoprazole: given intravenously in patients with ZES is very
effective.
c) Lansoprazole: 60-180 mg every day inhibits acid secretion and resolves
associated symptoms such as diarrhoea and pain and is well tolerated at these high doses for prolonged periods (> 4 years in some patients).
d) Esomeprazole: 80 mg per day is effective and sufficient to control ZES
symptoms in the majority of patients.
3.4.3 Gastroesophageal reflux disease
Gastroesophageal reflux disease (GERD) is a common disease, with very high prevalence of 10-20% in the western countries. GERD consists in mucosal damage caused by excess reflux of gastric juice into the oesophagus.
The symptoms include typical symptoms, like acid regurgitation and heartburn, atypical symptoms, like epigastric fullness, epigastric pressure, epigastric pain, dyspepsia, nausea, bloating, belching, and extra-esophageal symptoms, like chronic cough, bronchospasm, wheezing, hoarseness, sore throat, asthma, laryngitis and dental erosions.
The treatment of GERD takes a long time, firstly it requires changes in lifestyles; for patients failing lifestyle interventions pharmacological agents are administered such as H2 blockers and PPIs.
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a) Lifestyle modifications: sleep with the head of the bed elevated, avoid late meals and avoid recumbent position 3 hours after meals, avoid coffee and chocolate, weight loss. However, for many patients it is very difficult to follow and change the long-term lifestyle.
b) Medical options for GERD: healing of GERD requires to reach a pH 4 and above, and to maintain this pH for at least 16 hours a day [Aguillera et al., 2002]. H2 receptor blockers are used with a dose three times higher than that used in the treatment of peptic ulcer, with healing symptoms of about 50%. PPIs are preferred to H2 blockers: Omeprazole 20 mg/day, Lansoprazole 30 mg/day, Pantoprazole 40 mg/day and Rabeprazole 20 mg/day decrease the symptoms of gastroesophageal reflux disease within a few days and reach complete healing within 4-8 weeks from the beginning of the therapy. It has been shown that PPIs guarantee a pH above 4 for 10.1 to 14 hours as reported in Figure 3.4.3.1.
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3.5 Side effects
PPIs are considered first choice drugs for a variety of acid-related disorders, however, emerging evidence indicates that PPI therapy, particularly with long-term and/or high-dose administration, is associated with many potential adverse effects of variable severity. Less than 5% of treated subjects develop side effects such as constipation, diarrhea, nausea, headache and rash independently by the duration of the treatment [Chubineh and Birk ., 2012]. However, in long-term treatment an increase of other side effects has been observed, including vitamin and mineral deficiency, hypergastrinemia and related pathologies, cardiovascular pathologies, dementia, Clostridium difficile infection, community-acquired pneumonia, and osteoporotic-related fractures, as shown by a number of case-control and cohort studies, and meta-analyses.
3.5.1 Vitamin deficiency
PPI treatment has been associated with vitamin B12 and C deficiencies. The risk of developing these deficiencies seems to be limited, however in malnourished patients and in the elderly the risk notably increases, especially for vitamin B12. Nevertheless, at date, no specific clinical indication has been recommended about vitamin supplementation in association with PPI treatment. As far as vitamin C concerns, there are few evidences linking its deficiency to PPI intake. In a study by Mowat and colleagues showed that omeprazole 40 mg for 4 weeks decreased vitamin C concentrations reflecting a decrease in the biologically active form of ascorbic acid [Mowat et al., 1999].
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Vitamin B12, also called cyanocobalamin, is an essential vitamin necessary for DNA synthesis, the formation of red blood cells and holds important neurological functions [Marina et al., 1996]. As the human organism is not able to synthetize vitamin B12, it is taken from the diet; for instance, meat and eggs are rich in vitamin B12 where it exists in close association with proteins. Vitamin B12 is released from the protein complex in the first stage of food processing by enzymatic cut by pepsin, which is produced from pepsinogen in acidic environment. As a matter of fact, acid secretion is necessary for the absorption of food vitamins B12. Vitamin B12 binds to the R protein secreted by salivary parietal cells. Afterward, the pancreatic enzymes degrade the protein complex of R-cyanocobalamin, releasing cyanocobalamin and allowing the formation of a binding with the intrinsic factor secreted by the gastric parietal cells. Therefore the complex intrinsic factor-cyanocobalamin is absorbed through the intestine.
A decrease in gastric acid is thought to inhibit the separation of vitamin B12 from the food proteins, consequently, reducing the absorption of vitamin B12, thus ultimately leading to vitamin B12 deficiency. Additionally, it has been shown that also an increase of the intestinal pH affects vitamin B12 absorption as it favours bacterial growth.
Even though increasing evidences support a causative role of PPI therapy on vitamin B12, there are several inconsistent literature data, showing no link between PPI use and vitamin B12 deficiency [Koop ., 1992; Schenk et al., 1996; den Elzen et al., 2008]. Moreover, as suggested by two studies, one of which is very recent, even though PPIs can decrease vitamin B12 absorption, the change in plasma concentration does not have any clinically relevant deficiency [Hirschowitz et al., 2008; Hasime et al., 2018].
Here is a summary of the studies supporting a role for PPIs in vitamin B12 deficiency:
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1) Cohort study [Marcuard et al., 1994]: this study from Marcuard and colleagues represent the first study on the effect of PPIs on vitamin B12. The short-term effect of Omeprazole on vitamin B12 absorption was evaluated in a small group of ten healthy male volunteers. Half of the subjects received 20 mg of Omeprazole, while the others received 40 mg daily for two weeks. At the end of the therapy, in patients receiving Omeprazole 20 mg, cyanocobalamin absorption decreased by 2,3%; and in patients receiving 40 mg, cyanocobalamin absorption decreased by 3%.
2) Prospective trial in patients with Zollinger Ellison Syndrome (ZES) [Termanini B. et al., 1998]: this study from Termanini and colleagues successfully replicated the effect of Omeprazole on serum vitamin B12. The trial included 131 patients treated with Omeprazole (n= 111) or histamine H2 receptor antagonist (n= 20). Serum vitamin B12 was significantly lower in patients treated with Omeprazole. Moreover, the duration of Omeprazole treatment was inversely correlated with serum vitamin B12 levels.
3) Case-control study [Lam et al., 2013]: in a very large sample of 25,696 cases and 184,199 controls, an increased risk for vitamin B12 deficiency was associated with receiving two or more years treatment with PPIs . Similarly, prolonged treatment with H2 receptor antagonist also significantly increased the risk of vitamin B12 deficiency but to a lesser extent than PPIs.
4) Case-control study [Valuck and Ruscin ., 2004]: in this study plasma concentration of vitamin B12 was measured in 53 patients treated with PPIs and H2 receptor antagonists and in 212 non-treated controls. In the chronic use, both PPIs and H2 receptor antagonists significantly increased the risk of vitamin B12 deficiency. Instead, the short-term use showed no significant effect. (Figure
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5) Retrospective case-control study [Force et al., 2003]: the concentration of plasma vitamin B12 has been measured in 125 patients under chronic PPIs or histamine H2 receptor inhibitors and 500 controls. The results show that the 18% of patients showed a vitamin B12 deficiency.
6) Prospective case-control study [Rozgony et al., 2010]: the effect of PPI long-term treatment on vitamin B12 serum levels was investigated; also, nasal vitamin B12 spray (500 μg, once week) was administered for 8 weeks to 36 patients, 17 of whom were under chronic PPI therapy, and the other 19 were not taking PPI. At the beginning, those who were taking chronic PPI therapy showed lower serum vitamin B12 levels (75% of the PPI users and 11% of non-PPI users). As expected, after vitamin B12 nasal treatment, vitamin B12 levels were significantly increased in comparison to pre-treatment in the chronic PPI users. (Figure 3.5.1)
7) Cross sectional sample [Dharmarajan et al., 2008]: the effect on vitamin B12 of PPIs and histamine H2 receptor inhibitors was investigated in 141 and 150 subjects, respectively, as compared to 247 untreated subjects. Additionally, the effect on vitamin B12 deficiency of oral vitamin B12 supplementation was evaluated. The results showed that PPI treatment significantly decreased vitamin B12 plasma levels, while histamine H2 receptor inhibitor showed no effect. Moreover, oral vitamin B12 supplementation slowed PPI-induced vitamin B12 deficiency without preventing it. (Figure 3.5.1)
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Figure 3.5.1. Schematic representation of clinical studies that have investigated the effect on vitamin B12 of PPI and histamine H2 inhibitor treatment. [Tetsuhide et al., 2010].
3.5.2 Iron deficiency
An increasing number of studies suggest that PPI treatment could be associated with mineral deficiencies, particularly concerning iron and ferritin plasma concentration. For example, three independent dtudies have shown that
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Omeprazole treatment under long-term regimen, but not in short-term treatments [Tempel et al., 2013], induced iron deficiency [Hashimoto et al., 2014; Khatib et al., 2002; Sharma V.R. et al., 2004] and reduced the accumulation of iron in tissue stores [Hutchinson C. et al., 2007]. Another study showed, instead, that malabsorption is generally not developed in the first three of four years of Omeprazole intake [Koop and Bachem ., 1992]. Longer therapy with Omeprazole might causes a prominent iron deficiency that could lead to severe anemia as observed in the case of a 58 years old man that after ten years of PPI therapy developed gastrointestinal iron malabsorption [David et al., 2017].
3.5.3 Hypergastrinemia and related pathologies
A direct consequence of PPI treatment, due to H+/K+-ATPases inhibition and the consequent increase of gastric pH, is the augmentation of the release of the hormone gastrin, a phenomenon known as hypergastrinemia. Gastrin induces the migration of H+/K+-ATPases to the membrane of secretory canaliculi and
stimulates pump activity in order to counterbalance the PPI effect. Thus, upon PPI withdrawal, rebound acid hypersecretion is observed in 40% of cases [Lamberts R. et al., 2001; Waldum et al., 2010]. Hypergastrinemia may lead to gastric cell hyperplasia, formation of polyps of the fundus and the body of the stomach in up to 10% of the cases treated with PPIs for more than one year [Choudhry et al., 1998], and more rarely to gastric carcinoids [Hodgson J.Q. et al., 2005]. Moreover, hypergastrinemia, by acting as a trophic factor, increases enterochromatin-like cells which may develop gastric carcinoid tumors as observed in rats treated with Omeprazole for two years [Havu ., 1986]. Actually, in humans this mechanism was not sufficient to generate gastric tumors and Omeprazole was commercialized.
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3.5.4 Cardiac Adverse Reactions
Nowadays, accumulating evidences suggest that prolonged PPI intake may increases cardiovascular risk [Sukhovershin and Cooke ., 2016]. The exact mechanism underpinning PPI-induced increase of cardiovascular risk is not completely understood; nevertheless several hypotheses have been proposed (Figure 3.5.4.1).
Figure 3.5.4.1 Possible mechanisms underpinning PPI-induced cardiovascular risk.
[Sukhovershin and Cooke., 2016]
A possible mechanism could be the reduction of the activity of nitric oxide synthase (NOS) and, thus, a consequent reduction of endothelium-derived nitric oxide (NO) leading to vascular endothelium dysfunction such as vascular resistance that leads to inflammation and thrombosis [Shah et al., 2015]. NO released by endothelium is known to induce vasodilation of the smooth muscle, to inhibit platelet adhesion and aggregation and to promote endothelial-leukocyte interactions. As a matter of fact, subject with an altered activity of NOS are at higher risk of developing major adverse cardiac events [Kielstein et al., 2006; Wilson et al., 2010]. In these patients the concentration of an endogenous inhibitor of NOS known as asymmetric dimethylarginine is elevated with consequent increase of NOS-derived oxygen reactive species [Böger et al., 2005].
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It has been shown that PPIs directly inhibit the activity of the enzyme that metabolizes the asymmetric dimethylarginine [Ghebremariam et al., 2012; Ghebremariam et al., 2013]. In addition to this indirect mechanism of NOS inhibition, PPIs seem also to directly inhibit the expression of NOS, as observed in patients treated with Omeprazole [Ghebremariam et al., 2013]. Moreover, PPI-induced increase of gastric pH inhibits the release of NO from dietary inorganic nitrite; in acidic environment, inorganic nitrite is converted in nitrous acid, which in turns releases NO. Low NO concentration may be linked also to vitamin C and B12 levels that, as discussed before, are affected by PPIs. These vitamins act as antioxidants that prevent the degradation of NO. Moreover, vitamin B12 is essential for the conversion of homocysteine to methionine, and homocysteine are known to increase asymmetric dimethylarginine levels and to induce oxidative stress and endothelial NOS uncoupling [Stühlinger et al., 2003; Dayal and Lentz., 2005].
Another possible mechanism by which PPI increase the cardiovascular risk could be represented by electrolyte abnormalities. Calcium and magnesium concentration were shown to be decreased by PPI treatment [Perazella 2013; Toh et al., 2015]. Hypomagnesaemia and hypocalcaemia may cause cardiac arrhythmias and, in the most serious cases, even heart failure [Leto et al., 2014]. A very recent study has found that about 40% of PPI-treated patients develop hypomagnesaemia and this subjects were at higher risk of experiencing changes in cardiac rhythm [Lazzerini et al., 2018].
Last, increased risk of serious cardiovascular events occurs when PPI is administered concomitantly with Clopidogrel, a pro-drug converted to an active metabolite by the same cytochrome that metabolizes PPIs, i.e. the cytochrome P450 CYP2C19 [Melloni et al., 2015]. The active metabolite of Clopidogrel irreversibly binds to the platelet adenosine diphosphate P2Y receptor and inhibits platelet aggregation. Thus, the concomitant intake of PPIs and Clopidogrel reduces Clopidogrel activation and efficacy. For this reason, FDA recommends to monitor this interaction, especially for Omeprazole.
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To reduce the competitive metabolism with Clopidogrel it is possible to use other PPIs that have reduced interaction with the enzyme CYP2C19, like Esomeprazole or Pantoprazole [Angiolillo et al., 2011]. Alternatively, it is possible to use the H2 receptor antagonists which can suppress acid production without involving CYP2C19 activity. Another possibility is to use a new generation of antiplatelet agents that do not depend on the enzyme CYP2C19, like Ticagrelore and Prasugrel.
3.5.5 Dementia
Dementia is a syndrome characterized by progressive cognitive decline that influences the ability to live independently, thinking, and behaviour. It is one of the major causes of disability among older populations around the world [Wimo et al., 2013]. About 80% of dementia cases occur in Alzheimer’s disease (AD) patients. AD is characterized by the accumulation of neurofibrillary tangles and amyloid plaques in the brain, which lead to neuronal loss and neurodegeneration. Today, 46.8 million people worldwide have dementia, and it is expected to increase by three times by 2050 [Prince et al., 2015].
It has been hypothesizes that PPIs cross the blood–brain barrier, enter in the central nervous system where they can inhibit the vacuolar proton pumps that are expressed on microglia membrane. The inhibition of these pumps could result in increased lysosomal pH leading to decreased lysosomal protease function. Lysosomal proteases are responsible for digesting beta amyloid (Aß) fragments; lack of appropriate digestion may lead to Aß accumulation, which may conduce AD [Fallahzadeh et al., 2010].
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In vitro and in vivo studies have investigated the effect of Lansoprazole on amyloid cells showing that Lansoprazole increases the production of Aß37, Aß40, and Aß42 and reduces the production of Aß38 [Badiola et al., 2013]. It has been hypothesized that Lansoprazole influences Aß synthesis by interfering with the enzymes y-secretase and BACE1, which are responsible for the cleavage of the beta amyloid precursor.
However, data linking PPI intake with dementia are not unanimous. Two studies have shown that that patients taking PPI therapy had an increased risk for any dementia [Haenisch et al., 2015; Gomm et al., 2016]. A more recent study confirmed this association. Specifically, Tai and colleagues analysed 15726 subjects of which 7863 under PPI treatment; PPI users had a significantly increased risk of dementia as compared to non-PPI users [Tai et al., 2017]. Conversely, a study by Goldstein and colleagues did not find such association: the study included 884 subjects taking continuously PPIs, 1,925 taking PPIs intermittently, and 7,677 subjects that never reported taking PPIs [Goldstein et al., 2017]. All subjects had baseline normal cognitive abilities or mild cognitive impairment. Surprisingly, PPI use (either continuous and intermittent) was associated with lower risk of decline in cognitive function and lower risk of conversion to mild cognitive impairment or AD. Another study conducted on 11,956 subjects supports the hypothesis that PPI may actually decrease the risk of dementia [Booker et al., 2016].
In conclusion, there are not definitive evidences clearly indicating that PPI use increases the risk of developing dementia. Perspective studies are needed to gain a better understanding of the potential risks or benefits of PPI treatment over dementia susceptibility.
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3.5.6 Clostridium difficile infection (CDI)
Clostridium difficile (CD) is a gram-positive anaerobic bacterium, which manifests with diarrhoea. Studies have indicated the possible association between PPI treatment and increased risk of Clostridium difficile infection (CDI). Since 2011, when Yip and colleagues published an association data between PPIs and CDI, a great number of studies have been published on this topic [Yip et al., 2001].
A meta-analysis published in 2017 has reviewed literature on this topic from 1999 to 2017, including 56 studies (40 case-control and 16 cohort) involving 35,6683 patients (Figure 3.5.6.1) [Trifan et al., 2017]. Despite the heterogeneity of the studies, overall, PPI therapy and CDI were significantly associated.
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Figure 3.5.6.1 Studies included in the meta-analysis by Trifan and colleagues in 2017. [Trifan
et al., 2017]
During the past two decades, seven major meta-analysis have been performed:
1) Leonardo and colleagues [Leonard et al., 2007]: included 11 studies involving 126,999 patients reporting a significant association between PPI therapy and CDI.
2) Janarthanan and colleagues [Janarthanan et al., 2012]: including 23 observational studies involving about 300,000 patients reporting a 65% increase in the incidence of CDI among PPIs users.
3) Desphande and colleagues [Desphande et al., 2012]: including 30 studies involving 202,965 patients reporting that PPI therapy was associated with a 2-fold increase of CDI risk. Confirmed by the same authors in a subsequent study [Desphande et al., 2015].
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4) Kwok and colleagues [Kwok et al., 2012]: including 42 studies involving 313,000 participants reporting a statistically significant association between PPIs use and CDI risk.
5) Tleyjeh and colleagues [Tleyjeh et al., 2012]: including 51 observational studies (37 case-control and 14 cohort) reporting evidence of publication bias and significant statistical heterogeneity among the studies.
6) Arriola and colleagues [Arriola et al., 2016]: including 23 observational studies involving 186,033 participants, all inpatients, reporting that PPIs use significantly increases the risk of hospital-acquired CDI.
7) Bavishi and colleagues [Bavishi et al., 2011]: including 27 studies evaluating an association between PPI therapy and the risk of CDI, 17 of which reported a significant association.
It has been hypothesized that the increased risk of CDI in relation to PPI exposure is due to the increase in gastric pH that allows CD to survive. Perhaps, the real mechanism of proliferation of CD is still not so clear, further studies are needed to confirm this association and better explain the true mechanism of proliferation of CD.
3.5.7 Community-acquired pneumonia (CAP)
Long-term PPI treatment could lead to respiratory infections. The risk may be due to changes in pulmonary physiology, through the reduction of mucus elimination, which leads to greater colonization in the upper airway.
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Community-acquired pneumonia (CAP), one of the most common pulmonary infectious disease by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, was higher among patients who used PPIs than non-users and the risk was greater with increasing PPI doses. Several studies evaluated the association between CAP risk and PPIs [Laheij et al., 2004; Gulmez et al., 2007; Johnstone et al., 2010; Hermos et al., 2012].
For instance, as shown by Jagen and colleagues in a cohort comprising 463 patients, PPI therapy was associated with an approximately 2-fold increased risk to develop CAP, possibly as a result of Streptococcus pneumoniae infection [de Jager et al., 2012].
Indeed, based on a study published in 2018, PPI treatment in the elderly significantly increases CAP risk [Zirk-Sadowski et al., 2018]: a large sample of 75,050 individuals aged 60 and older and receiving PPIs for 1 year or longer in primary care were recruited, as well as 75,050 age- and sex-matched controls; PPI prescription was associated with increased risk of pneumonia in the second year of treatment. PPI treatment in early life, instead, doesn’t seem to increase CAP risk: a cohort consisting of 21,991 patients without a history of CAP who were born between 1 January 2005 and 31 December 2012 and that were given Omeprazole, Lansoprazole, or Pantoprazole on at least one occasion during the first year of life, was recruited; PPIs did not appear to increase the risk of CAP. Overall, the different studies that were carried out to evaluate the association between the use of PPIs and the risk of developing CAP did not lead to a clear and precise result. It seems that the risk is increased of approximately 30%. Further, studies are needed to define the CAP risk and the mechanism associated with prolonged use of PPI.
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3.5.8 Osteoporosis,bone fractures and falls
Osteoporosis is a very frequent disease that predisposes to fractures and falls in most of the elderly person. Among fractures, hip fracture is one of the most disabling as it leads to loss of independence, a condition associated with high mortality rate in older adults [O’Mahony et al., 2015]. Because of the burden of bone fractures, FDA published a safety alert in 2010 to aware of a possible increased risk of fractures among PPI users.
Use of PPIs may decrease bone density and increases fracture risk by reducing intestinal calcium absorption. It has been hypothesized that low stomach acid might modify calcium absorption in the gut.
A review from 2016 has revised the most recent literature on this topic, reporting that PPIs represent a risk factor for the development of osteoporosis and osteoporotic fractures and suggesting that short-term use of PPIs is not safer than long-term use in terms of osteoporosis risk. Also, the review highlighted the lack of conclusive studies on the direct pathogenesis through direct effects on calcium absorption or on osteoblast or osteoclast action [Andersen et al, 2016].
A number of case-control studies, cohort studies and meta-analysis support the linkage between PPIs and bone fractures as reported below:
Case-control studies:
1) Chiu and colleagues [Chiu et al., 2010] found an increased risk of hip fracture in patients prescribed PPI as compared with no PPI users independently by the use of anticoagulants, antipsychotics, sedatives, and diuretics.
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2) Pouwels and colleagues [Pouwels et al., 2011], is a sample of 6,763 cases with a first hip/femur fracture and 26,341 matched controls, found that the use of PPI therapy was associated with an increased risk in hip/femur fracture, however, the risk was diminished with increasing duration of use.
3) Adams and colleagues [Adams et al., 2014], in a sample of men aged 45 years, showed opposite results than earlier evidences as they found that there was an increased risk of fractures in long-term PPI treatment.
4) Lee and colleagues [Lee et al., 2013], in a Korean sample of 24,710 cases and 98,642 matched controls, found an increased risk of hip fracture in PPI users compared with nonusers.
5) Abrahamsen and Vestergaard [Abrahamsenand and Vestergaard ., 2013] evaluated the interaction between PPI and histamine-1-receptor blockers on fracture risk. From their results, they hypothesized that histamine blockers may reduce the negative effect of PPIs on the bone.
Cohort studies:
1) Fraser and colleagues [Fraser et al., 2013], in a cohort of 9,423 patients observed for 10 years, found that PPI use was associated with a 40% increased risk of non-traumatic fractures, after adjusting for several potential confounders including age, sex, body mass index, prior non traumatic fracture, femoral neck T-score, corticosteroid use, alcohol intake, and activity levels.
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2) Khalili and colleagues [Khalili et al., 2012], found that women who took PPIs for two years had an increased risk of hip fractures. Furthermore, prolonged use has been associated with an increased risk of hip fractures. Also, the risk of hip fractures was greater among current and former smokers who used PPIs.
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Meta-analyses:1) Eom and colleagues [Eom et al., 2011] evaluated the influence of PPI and histamine H2 receptor inhibitor use on hip fracture risk in 11 observational studies They found that fractures were associated with PPI use but not with histamine receptor inhibitors. Moreover, they found that long-term use of PPIs was associated with increased risk of hip fractures.
2) Ngamruengphong and colleagues [Ngamruengphong et al., 2011] included 10 observational studies in their study. They found an increased risk of hip fractures and increased risk of vertebral fractures associated with PPI use. Furthermore, long use of PPI did not lead to a significant risk of hip fractures perhaps due to the heterogeneity of these studies.
3.5.9 Kidney disease
Chronic kidney disease, also called chronic kidney failure, is a serious medical condition that manifests, persists 3 months, as alteration of renal structure and function. PPI use is associated with an increased risk of acute kidney injury (AKI), incident chronic kidney disease (CKD), and progression to end-stage renal disease (ESRD). CKD is characterized by a reduced glomerular filtration rate or by at least one renal damage marker such as an albumin-creatinine ratio persisting for at least 3 months [KDIGO, 2012]. In patients aged over 60 years, CDK prevalence increased from 18.8% to 24.5%, may leading to the development of kidney failure and mortality.
