Sitagliptin can inhibit the development of hepatic steatosis in high-fructose diet-fed ob/ob mice

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

Protective Effects of Evogliptin on Steatohepatitis in High-Fat-Fed Mice

There are few studies on the effects of dipeptidyl peptidase-4 inhibitors on steatohepatitis. We explored whether evogliptin (Evo), a dipeptidyl peptidase-4 inhibitor, protects against steatohepatitis in a high-fat diet (HFD)-fed mice and whether these effects involve modulation of mitophagy. Adult male C57BL/J mice were divided into the normal diet (ND), HFD (45% of energy from fat) with Evo (250 mg/kg) (HFD + Evo), and HFD groups at 4 weeks of age and were sacrificed at 20 weeks of age. The HFD group showed hepatic lipid accumulation; this was decreased in the Evo + HFD group. There was an increased 8-hydroxydeoxyguanosine (8-OHDG) expression in the HFD group compared to ND mice. However, 8-OHDG expression levels were significantly decreased in the HFD + Evo group. Expressions of the mitophagy markers PTEN-induced kinase 1 (PINK1), Parkin, and BNIP-3 (BCL2 Interacting Protein 3) were significantly increased in the HFD group. However, the expressions of these markers were lower in the HFD + Evo group than that in the HFD group. Phospho-Akt was upregulated and p53 was downregulated in the HFD + Evo group compared to the HFD group. Evogliptin may alleviate steatohepatitis in HFD-fed mice by ameliorating steatosis and oxidative stress and by modulating mitophagy in the liver.

High levels of dietary methionine improves sitagliptin-induced hepatotoxicity by attenuating oxidative stress in hypercholesterolemic rats

Background

Both cholesterol (Cho) and methionine (Met, a precursor for homocysteine) are risk factors for fatty liver disease. Since Western diets are rich in Cho and Met, we investigated the hepatic effects of feeding a diet enriched in Met and Cho. Further, based on the reported anti-oxidative and lipid lowering properties of sitagliptin (an antidiabetic drug), we tested whether it could counteract the negative effects of high Cho and Met. We therefore hypothesized that sitagliptin would ameliorate the development of liver pathology that is produced by feeding diets rich in either Cho, Met, or both.

Methods

Male Sprague Dawley rats were fed ad libitum a) control diet, or b) high Met or c) high Cho, or d) high Met + high Cho diets for 35 days. From day 10 to 35, 50% of rats in each dietary group were gavaged with either vehicle or an aqueous suspension of sitagliptin (100 mg/kg/day). Liver samples were harvested for histological, molecular, and biochemical analyses.

Results

The high Cho diet produced significant hepatic steatosis which was unaffected by sitagliptin. Contrary to expectation, sitagliptin exacerbated expression of hepatic markers of oxidative stress and fibrosis in rats fed high Cho. Corresponding increases in 4-hydroxynonenal adducts and collagen deposition were demonstrated by immunohistochemistry and sirius red staining. These hepatic changes were absent in rats on the high Met diet and they were comparable to controls. The inclusion of Met in the high Cho diet resulted in significant reduction of the hepatic steatosis, oxidative stress, and fibrosis produced by high Cho alone.

Conclusion

Sitagliptin exacerbated the effects of high Cho on both oxidative stress and fibrosis, resulting in NASH like symptoms that were significantly reversed by the inclusion of Met.

Assessing the impact of wastewater treatment plant effluent on downstream drinking water-source quality using a zebrafish (Danio Rerio) liver cell-based metabolomics approach

Cell-based metabolomics was used in a proof-of-concept fashion to investigate the biological effects of contaminants as they traveled from a wastewater treatment plant (WWTP) discharge to a drinking water treatment plant (DWTP) intake in a surface-water usage cycle. Zebrafish liver (ZFL) cells were exposed to water samples collected along a surface-water flowpath, where a WWTP was located ∼14.5 km upstream of a DWTP. The sampling sites included: 1) upstream of the WWTP, 2) the WWTP effluent discharging point, 3) a proximal location downstream of the WWTP outfall, 4) a distal location downstream of the WWTP outfall, 5) the drinking water intake, and 6) the treated drinking water collected prior to discharge to the distribution system. After a 48-h laboratory exposure, the hydrophilic and lipophilic metabolites in ZFL cell extracts were analyzed by proton nuclear magnetic resonance (¹H NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS), respectively. Multivariate statistical analysis revealed distinct changes in metabolite profiles in response to WWTP effluent exposure. These effects on the hydrophilic metabolome gradually diminished downstream of the WWTP, becoming non-significant at the drinking water intake (comparable to upstream of the WWTP, p = 0.98). However, effects on the lipophilic metabolome increased significantly as the river flowed from the distal location downstream of the WWTP to the drinking water intake (p < 0.001), suggesting a source of bioactive compounds in this watershed other than the WWTP. ZFL cells exposed to treated drinking water did not exhibit significant changes in either the hydrophilic (p = 0.15) or lipophilic metabolome (p = 0.83) compared to the upstream site, suggesting that constituents in the WWTP effluent were efficiently removed by the drinking water treatment process. Impacts on ZFL cells from the WWTP effluent included disrupted energy metabolism, a global decrease in amino acids, and altered lipid metabolism pathways. Overall, this study demonstrated the utility of cell-based metabolomics as an effective tool for assessing the biological effects of complex pollutant mixtures, particularly when used as a complement to conventional chemical monitoring.

Effect of sitagliptin on hepatic histological activity and fibrosis of nonalcoholic steatohepatitis patients: a 1-year randomized control trial

Background/purpose

Dipeptidyl peptidase 4 (DPP-4) expression is directly associated with hepatic lipogenesis and liver injury in nonalcoholic steatohepatitis (NASH). This study has been designed to elucidate the histological improvement of NASH with the DPP-4 inhibitor sitagliptin.

Materials and methods

In this open-label randomized control trial, paired liver biopsy was taken from 40 NASH patients. Sitagliptin 100 mg was given once daily to the SL group and no sitagliptin was given to the L group for 1 year. Patients from both groups were encouraged to exercise moderately and advised to avoid saturated fat, excessive sugar, soft drinks, fast food, and refined carbohydrates to reduce weight.

Results

Steatosis improved in the SL group (from 2.3±0.6 to 1.2±0.8; P=0.000) and the L group (from 2.1±0.6 to 1.6±0.9; P=0.008), ballooning decreased from 1.8±0.6 to 1.3±06 (P=0.002) in the SL group, but not in the L group. Nonalcoholic fatty liver disease activity score (NAS) attenuated in both groups: the SL group (from 5.8±0.9 to 3.9±1.4; P=0.000) and the L group (from 5.3±0.6 to 4.6±1.2; P=0.009). NAS improvement was much higher in the SL group (1.9±1.4) than in the L group (0.7±1.1) (P=0.006), with NAS improving by ≥2 in 13 patients from the SL group and five patients from the L group (P=0.01). Improvement was irrespective of diabetes. Regression analysis explored that sitagliptin had odds of 6.38 and weight reduction had odds of 4.51 for NAS reduction.

Conclusion

Sitagliptin 100 mg once daily for 1 year ameliorates NAS by improving steatosis and ballooning, irrespective of diabetes. Sitagliptin has stronger efficacy than that of weight reduction.

Dipeptidyl peptidase-4 inhibitors have adverse effects for the proliferation of human T cells

Dipeptidyl peptidase-4 (DPP-4) is a critical molecule for the metabolism of incretins. In addition, DPP-4 is known as CD26, the receptor of T cells, and plays important role in activation of T cells. Recently, DPP-4 inhibitors (DPP4i) are reported to have several immunologic effects beyond glycemic control. DPP4i seem to have anti-inflammatory effects in patients with type 2 diabetes. This might be direct effects on T cells. However, the close mechanism is not clear. To evaluate the possibility, we performed ex vivo assays by using primarily human CD4⁺ T cells (CD4) and CD8⁺ T cells (CD8). We purified primary naïve CD4 and CD8 from human peripheral blood. Then, we evaluated the effect of DPP4i on the proliferation of naïve T cells and the cytokine production in ex vivo experiments. The proliferation of CD4 and CD8 were suppressed by adding DPP4i in a dose dependent manner. However, DPP4i did not inhibit cytokine production from CD4. It was revealed by phospho-flow that the T cell receptor (TCR) signaling was attenuated in the presence of DPP4i. Taken together, DPP4i modulated TCR signaling, which contributed to attenuate the proliferation of CD4 and CD8. DPP4i have adverse effects for the proliferation of human T cells.

Pathogenesis and novel treatment options for non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease affects 20-40% of the population. Its active form, non-alcoholic steatohepatitis (NASH), is characterised by hepatocyte injury, liver inflammation, and progression of fibrosis, and has emerged as one of the most important causes of liver failure and hepatocellular carcinoma. Weight reduction of 10% by dietary restriction and regular exercise is sufficient to reverse NASH in most patients, but in practice this reduction is often not achieved. Available drugs such as vitamin E, pioglitazone, and pentoxifylline have borderline efficacy, but are limited by potential side-effects and toxicities, and do not improve liver fibrosis. However, basic and translational research has improved our understanding of the pathophysiology of NASH, thereby identifying several promising new treatment targets. Several drugs are in phase 2 and 3 development and could enter clinical practice in the near future. In this Review, we discuss the pathogenesis, treatment evaluation, existing therapies, and potential new treatments for NASH.