Dipeptedyl peptidase-4 (DPP-4) inhibitor downregulates HMGB1/TLR4/NF-κB signaling pathway in a diabetic rat model of non-alcoholic fatty liver disease

Regulatory Networks, Management Approaches, and Emerging Treatments of Nonalcoholic Fatty Liver Disease

The pathogenesis of NAFLD is complex and diverse, involving multiple signaling pathways and cytokines from various organs. Hepatokines, stellakines, adipokines, and myokines secreted by hepatocytes, hepatic stellate cells, adipose tissue, and myocytes play an important role in the occurrence and development of nonalcoholic fatty liver disease (NAFLD). The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) contributes to the progression of NAFLD by mediating liver inflammation, immune response, hepatocyte death, and later compensatory proliferation. In this review, we first discuss the crosstalk and interaction between hepatokines, stellakines, adipokines, and myokines and NF-κB in NAFLD. The characterization of the crosstalk of NF-κB with these factors will provide a better understanding of the molecular mechanisms involved in the progression of NAFLD. In addition, we examine new expert management opinions for NAFLD and explore the therapeutic potential of silymarin in NAFLD/NASH.

Role of Dipeptidyl Peptidase 4 Inhibitors in Antidiabetic Treatment

In recent years, important changes have occurred in the field of diabetes treatment. The focus of the treatment of diabetic patients has shifted from the control of blood glucose itself to the overall management of risk factors, while adjusting blood glucose goals according to individualization. In addition, regulators need to approve new antidiabetic drugs which have been tested for cardiovascular safety. Thus, the newest class of drugs has been shown to reduce major adverse cardiovascular events, including sodium-glucose transporter 2 (SGLT2) and some glucagon like peptide 1 receptor (GLP1) analog. As such, they have a prominent place in the hyperglycemia treatment algorithms. In recent years, the role of DPP4 inhibitors (DPP4i) has been modified. DPP4i have a favorable safety profile and anti-inflammatory profile, do not cause hypoglycemia or weight gain, and do not require dose escalation. In addition, it can also be applied to some types of chronic kidney disease patients and elderly patients with diabetes. Overall, DPP4i, as a class of safe oral hypoglycemic agents, have a role in the management of diabetic patients, and there is extensive experience in their use.

Peroxisome proliferator-activated receptor-alpha activation and dipeptidyl peptidase-4 inhibition target dysbiosis to treat fatty liver in obese mice

BACKGROUND

Obesity and comorbidities onset encompass gut dysbiosis, altered intestinal permeability, and endotoxemia. Treatments that target gut dysbiosis can cope with obesity and nonalcoholic fatty liver disease (NAFLD) management. Peroxisome proliferator-activated receptor (PPAR)-alpha activation and dipeptidyl-peptidase-4 (DPP-4) inhibition alleviate NAFLD, but the mechanism may involve gut microbiota modulation and merits further investigation.

AIM

To address the effects of PPAR-alpha activation and DPP-4 inhibition (isolated or combined) upon the gut-liver axis, emphasizing inflammatory pathways in NAFLD management in high-fat-fed C57BL/6J mice.

METHODS

Male C57BL/6J mice were fed a control diet (C, 10% of energy as lipids) or a high-fat diet (HFD, 50% of energy as lipids) for 12 wk, when treatments started, forming the groups: C, HF, HFA (HFD + PPAR-alpha agonist WY14643, 2.5 mg/kg body mass), HFL (HFD + DPP-4 inhibitor linagliptin, 15 mg/kg body mass), and HFC (HFD + the combination of WY14643 and linagliptin).

RESULTS

The HFD was obesogenic compared to the C diet. All treatments elicited significant body mass loss, and the HFC group showed similar body mass to the C group. All treatments tackled oral glucose intolerance and raised plasma glucagon-like peptide-1 concentrations. These metabolic benefits restored Bacteroidetes/Firmicutes ratio, resulting in increased goblet cells per area of the large intestine and reduced lipopolysaccharides concentrations in treated groups. At the gene level, treated groups showed higher intestinal Mucin 2, Occludin, and Zo-1 expression than the HFD group. The reduced endotoxemia suppressed inflammasome and macrophage gene expression in the liver of treated animals. These observations complied with the mitigation of liver steatosis and reduced hepatic triacylglycerol, reassuring the role of the proposed treatments on NAFLD mitigation.

CONCLUSION

PPAR alpha activation and DPP-4 inhibition (isolated or combined) tackled NAFLD in diet-induced obese mice by restoration of gut-liver axis. The reestablishment of the intestinal barrier and the rescued phylogenetic gut bacteria distribution mitigated liver steatosis through anti-inflammatory signals. These results can cope with NAFLD management by providing pre-clinical evidence that drugs used to treat obesity comorbidities can help to alleviate this silent and harmful liver disease.

Efficacy of Sitagliptin on Nonalcoholic Fatty Liver Disease in High-fat-diet-fed Diabetic Mice

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a common cause of clinical liver dysfunction and an important prepathological change of liver cirrhosis. Central obesity, type 2 diabetes mellitus, dyslipidemia, and metabolic syndrome are the major risk factors for NAFLD. Sitagliptin (Sig) is a novel hypoglycemic agent that improves blood glucose levels by increasing the level of active incretin. Sig has been shown to prevent the development of fatty livers in mice on a fructose-rich diet. The purpose of this study was to observe the efficacy of Sig on NAFLD in type 2 diabetic mice.

METHODS

The diet-induced obesity mouse model was established, and the diabetic mice were screened by an intraperitoneal glucose tolerance trial. The mice were randomly divided into four groups for 8 weeks of intervention: high-fat diet (HFD) group, Sig group, metformin (Met) group, and Sig+Met group. After the intervention, the liver function indexes as well as the blood glucose and blood lipid levels of the mice were measured. In addition, the wet weight of the liver was measured; the pathological sections of the liver tissues were stained to observe the hepatocyte fatty degeneration, inflammation, necrosis, and fibrosis; and the hepatic histological injury was recorded as the NAFLD activity score (NAS).

RESULTS

Compared with the normal control group, the body weight, liver weight, blood glucose level, insulin resistance (IR), blood lipid level, and transaminase level of the mice in the HFD group were significantly increased, showing typical metabolic syndrome. After treatment with Sig and/or Met, the mice gained less weight, had lower levels of blood glucose, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and transaminase, and had improved IR compared with the HFD group. The liver pathological NASs in the Sig group (P=0.01), Met group (P=0.028), and Sig+Met group (P<0.001) were lower than those in the HFD group (P<0.05), suggesting that the use of the two drugs alone or in combination can improve the state of liver inflammation. In terms of fibrosis, there was no fibrosis in the control group but there was significant fibrosis in the HFD group (P<0.001). There was no significant difference between the drug intervention groups and the HFD group, indicating that the drug therapy (Sig and/or Met) did not significantly improve the pre-existing fibrosis.

CONCLUSION

Our experiment proved that Sig can improve NAFLD, including improvement of the serum transaminase level, hepatic pathological inflammation level, and hepatocyte adiposis, suggesting that Sig may play a role by improving glucose and lipid metabolism, reducing the body weight and liver weight, improving insulin sensitivity, and inhibiting fatty liver inflammation. Sig may be a new direction for the treatment of patients with a nonalcoholic fatty liver and diabetes, delaying the progression of NAFLD.

Sitagliptin Is More Effective Than Gliclazide in Preventing &nbsp;Pro-Fibrotic and Pro-Inflammatory Changes in a Rodent Model of Diet-Induced Non-Alcoholic Fatty Liver Disease

A diet-induced non-alcoholic fatty liver disease (NAFLD) model causing obesity in rodents was used to examine whether sitagliptin and gliclazide therapies have similar protective effects on pathological liver change. Methods: Male mice were fed a high-fat diet (HFD) or standard chow (Chow) ad libitum for 25 weeks and randomly allocated to oral sitagliptin or gliclazide treatment for the final 10 weeks. Fasting blood glucose and circulating insulin were measured. Inflammatory and fibrotic liver markers were assessed by qPCR. The second messenger ERK and autophagy markers were examined by Western immunoblot. F4/80, collagens and CCN2 were assessed by immunohistochemistry (IHC). Results: At termination, HFD mice were obese, hyperinsulinemic and insulin-resistant but non-diabetic. The DPP4 inhibitor sitagliptin prevented intrahepatic induction of pro-fibrotic markers collagen-IV, collagen-VI, CCN2 and TGF-β1 and pro-inflammatory markers TNF-α and IL-1β more effectively than sulfonylurea gliclazide. By IHC, liver collagen-VI and CCN2 induction by HFD were inhibited only by sitagliptin. Sitagliptin had a greater ability than gliclazide to normalise ERK-protein liver dysregulation. Conclusion: These data indicate that sitagliptin, compared with gliclazide, exhibits greater inhibition of pro-fibrotic and pro-inflammatory changes in an HFD-induced NAFLD model. Sitagliptin therapy, even in the absence of diabetes, may have specific benefits in diet-induced NAFLD.