Oral

Background and objectives:
Studies have pointed out that there is a significant correlation between nonalcoholic fatty liver diseases (NAFLD) and increased gut permeability. Up to date the relationship between zonulin level and tight junction (TJ) proteins in liver is still unclear. The aim of this study is to explore the role of zonulin on liver barrier dysfunction.

Methods:
Male C57BL/6 mice (44–46 weeks of age) were randomly divided into two groups: (1) standard diet control group (n=7, CHOW); (2) high-fat-diet induced NAFLD model group (n=10, HFD). Mice in the CHOW group were fed standard chow diet (13.1% of calories from fat). The remaining mice were fed HFD (45% of calories from fat) for 12 weeks to induce NAFLD. Body weight was monitored before and after the experiments. Serum ZO-1 and zonulin levels were measured by ELISA. TJ protein-1 (TJP-1), EGFR, PKC-α, PAR2, MyD88 and CXCR3 of liver tissue were analyzed by Weste blot.

Results:
Serum level of ZO-1 was higher in the CHOW group (6.13±0.34 ng/ml) when compared to the HFD group (4.87±0.45 ng/ml) but without significant difference (p=0.058). However, serum level of zonulin was significantly lower in the CHOW group (0.37±0.08 ng/ml) when compared to the HFD group (1.68 ± 0.30 ng/ml) (p=0.003). The Spearman's coefficient revealed a moderate negative correlation between serum zonulin and ZO-1 values. Levels of EGFR, PKC-α and PAR2 were significantly increased in the HFD group. Level of TJP-1 was significantly decreased in the HFD group when compared to the CHOW group.

Conclusions:
We demonstrate that HFD could lead to increased serum zonulin levels and decreased serum levels of TJ proteins in NAFLD mice model. Our results evidenced the activation of the zonulin pathway in liver. We conclude that zonulin might be associated with leaky gut phenomenon and hepatic TJ dysfunction.