Association Between Gut Permeability and Insulin Resistance: Any Role for Zonulin in Patients with Non-Alcoholic Fatty Liver Disease?
Chiara Rosso1,*, Gian Paolo Caviglia1, Angelo Armandi1, Davide Giuseppe Ribaldone1, Elisabetta Bugianesi1
1 Department of Medical Sciences, University of Turin, Turin, Italy
Correspondence: Chiara Rosso, Department of Medical Sciences, University of Turin, 10126, Turin, Italy.
Tel/Fax +39-11-6333532 Email chiara.rosso@unito.it
Keywords: HOMA-IR, non-alcoholic fatty liver disease, NAFLD, type 2 diabetes mellitus, T2DM
Funding: The study was supported by local research grant of the University of Turin n. ROSC_RILO_18_01
The impairment of intestinal barrier, due to alterations in gut microbiota, has been
implicated in the onset and progression of non-alcoholic fatty liver disease (NAFLD).1 Recently, several studies have focusing on the role of zonulin as non-invasive biomarker of intestinal permeability. Zonulin is a 47 kDa protein responsible for the regulation of intestinal barrier function.2 Zonulin acts as a fine modulator of tight junction integrity, controlling the passage of molecules trough the paracellular pathway. Altered intestinal permeability may play a key role in the development and progression of several chronic disease; possibly, in genetically predisposed individuals, the uncontrolled influx of luminal antigen to the lamina propria triggers the imposing inflammatory response observed in chronic inflammatory diseases.2 In addition, recent evidences suggested that the interplay between gut microbiota and intestinal barrier could represent an additional piece of the intricate puzzle that characterizes the pathogenesis of metabolic diseases such as type 2 diabetes mellitus (T2DM) and NAFLD.3,4
Insulin resistance (IR) is a common feature in patients with NAFLD and is one of the main determinant of progression to non-alcoholic steatohepatitis (NASH).1 However, the association between intestinal permeability by zonulin and IR in the setting of NAFLD has not fully elucidated. Recently, Mkumbuzi et al. investigated the association between circulating zonulin and IR by the homeostasis model of assessment (HOMA)-IR index in young healthy adults.5 Overall, the authors showed that circulating zonulin was associated with glucose homeostasis markers (HOMA-IR, r = 0.24, P = 0.038; insulin, r = 0.27, P = 0.019) only in female; moreover, at multivariable analysis, insulin remained the only factor significantly associated with zonulin ( = 0.268, P = 0.021).
The HOMA is a rather crude index for the assessment of IR; it is widely used in clinical practice and it is based on fasting glucose and insulin levels;moreover, high HOMA-IR values have been observed in NAFLD patients with severe hepatic fibrosis.6
We previously investigated the association between intestinal permeability and the severity of liver disease in patients with NAFLD;7 we observed that higher zonulin levels were associated with waist circumference suggesting that visceral fat can exert its effect on the impairment of intestinal permeability. Moreover, we found that patients with a more severe necroinflammation showed higher levels of zonulin compared to those with a mild/moderate disease.8 Here, in the same cohort of 108 NAFLD subjects, we investigated the association between circulating zonulin and HOMA-IR. Spearman’s correlation was used for correlations between zonulin and continuous variables. The Mann-Whitney test was used to assess differences between groups. Univariate and multivariable logistic regression analysis were performed to find variables associated with high zonulin concentration; to this purpose, we used the median value of 42.7 ng/ml as a cut-off for zonulin.
Zonulin concentration showed a significant correlation with waist circumference (rS = 0.22,
P = 0.038), HOMA-IR values (rS = 0.24, P = 0.024) and with total cholesterol levels (rS = 0.20, P =
0.046). Accordingly, HOMA-IR was significantly higher in subjects with high circulating zonulin compared to the counterpart (Figure 1A). After univariate logistic regression analysis, visceral fat by waist circumference, ALT levels, glucose concentration, total cholesterol levels and HOMA-IR values, were significantly associated with higher levels of zonulin (Table 1). No association between circulating insulin and zonulin was found but the prevalence of T2DM was higher in subjects with high zonulin levels compared to those with zonulin < 42.7 ng/ml, even if the statistical significance was not reached (25% vs 13%, P =0.07; Figure 1B). After multivariable logistic regression analysis adjusted for age, waist circumference, sex and the presence of T2DM, only HOMA-IR was significantly associated with higher circulating zonulin (OR = 1.4, 95% CI 1.1 - 1.9, P = 0.009) (Table 1).
Zonulin is a protein involved in the regulation of intestinal barrier and alterations in its expression have been described in different clinical conditions. NAFLD is the most common chronic hepatitis in Western countries and IR is considered one of the hallmarks of the disease. Our data showed that in subjects with NAFLD, IR was significantly associated with gut permeability by circulating zonulin. Furthermore, the increased prevalence of T2DM in patients with higher zonulin levels suggests that zonulin could be investigated as a potential risk factor for the development of both T2DM as well as other clinical conditions such as cardiovascular disease. Further studies are necessary to deepen the potential role of zonulin in the onset and progression of metabolic
References
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Tables
Table 1. Univariate and multivariable logistic regression analysis for the association with zonulin concentration.
Univariate analysis Multivariable analysis
Variables OR (95% CI) P value OR (95% CI) P value
Age (years) 0.99 (0.97-1.03) 0.900 0.99 (0.94-1.04) 0.585 Waist (cm) 1.04 (0.99-1.08) 0.050 0.97 (0.91-1.04) 0.419 Gender 1.67 (0.74-3.79) 0.218 0.60 (0.15-2.36) 0.461 T2DM 2.34 (0.86-6.35) 0.095 3.43 (0.50-23.38) 0.208 HOMA-IR 1.18 (1.01-1.37) 0.032 1.43 (1.09-1.88) 0.009 ALT (U/l) 1.01 (1.0-1.02) 0.034 1.0 (0.99-1.02) 0.337 Total-Cholesterol (mg/dl) 1 (1-1.01) 0.047 1.0 (0.99-1.03) 0.241
Abbreviations: ALT, alanine aminotransferase; CI, confidence interval; HOMA-IR, homeostasis model of assessment of insulin resistance; OR, odds ratio; T2DM, type 2 diabetes mellitus.
Figures
Figure 1. Relation between HOMA-IR (A) and type 2 diabetes (B) with circulating zonulin. Abbreviations: HOMA-IR, homeostasis model of assessment of insulin resistance; T2DM, type 2 diabetes mellitus.
