ARHGAP21 deficiency impairs hepatic lipid metabolism and improves insulin signaling in lean and obese mice

ARHGAP21 is a Rho-GAP that controls GTPases activity in several tissues, but its role on liver lipid metabolism is unknown. Thus, to achieve the Rho-GAP role in the liver, control and ARHGAP21-haplodeficient mice were fed chow (Ctl and Het) or high-fat diet (Ctl-HFD and Het-HFD) for 12 weeks, and pyruvate and insulin tolerance tests, insulin signaling, liver glycogen and triglycerides content, gene and protein expression, and very-low-density lipoprotein secretion were measured. Het mice displayed reduced body weight and plasma triglycerides levels, and increased liver insulin signaling. Reduced gluconeogenesis and increased glycogen content were observed in Het-HFD mice. Gene and protein expression of microsomal triglyceride transfer protein were reduced in both Het mice, while the lipogenic genes SREBP-1c and ACC were increased. ARHGAP21 knockdown resulted in hepatic steatosis through increased hepatic lipogenesis activity coupled with decreases in CPT1a expression and very-low-density lipoprotein export. In conclusion, liver of ARHGAP21-haplodeficient mice are more insulin sensitive, associated with higher lipid synthesis and lower lipid export.

Liver Enzymes, Fatty Liver and Type 2 Diabetes Mellitus in a Jinchang Cohort: A Prospective Study in Adults

OBJECTIVES

It is unclear whether liver enzymes or the interactions of various liver enzymes is a predictor of type 2 diabetes mellitus (T2DM), which is independent of fatty liver.

METHODS

A total of 48,001 subjects participated in baseline examinations. Among the subjects, 33,355 were followed for an average of 2.2 years. Cox proportional hazard models were used to examine the adjusted associations of AST, GGT and ALT with T2DM.

RESULTS

The cumulative incidence of T2DM was 8.05% to 9.02% for fatty liver and 2.25% to 4.10% for non-fatty liver, both showing statistically significant differences. Compared with the normal liver enzyme levels in the group with fatty liver, the adjusted incident hazard ratios in T2DM were: ALT 1.23 (95% CI 1.10 to 1.50); AST 1.30 (95% CI 1.07-1.59); and GGT 1.34 (95% CI 1.08 to 1.65). In addition, compared with the normal liver enzyme levels in the group with non-fatty liver, the adjusted incident hazard ratios in type 2 diabetes were: ALT 1.27 (95% CI 1.02 to 1.59); AST 1.33 (95% CI 1.02 to 1.59); and GGT 1.53 (95% CI 1.19 to 1.98). There are significant interactions of T2DM hazard ratios between GGT and ALT and between GGT and AST in addition to ALT and AST.

CONCLUSIONS

Our results suggest that the incidence of T2DM in the group with fatty liver is significantly higher than that in the normal population, and the rise of serum AST, GGT and ALT levels are risk factors independent of fatty liver for the development of T2DM after adjusting for confounding factors.

Weight loss enhances hepatic antioxidant status in a NAFLD model induced by high-fat diet

Nonalcoholic fatty liver disease (NAFLD) is a benign condition that can progress to more severe liver damage in a process mediated, in part, by disturbances in redox balance. Additionally, some argue that it is set to become the main cause of end-stage liver disease in the near future. Here, we investigated whether diet-induced weight loss is able to reverse hepatic lipid accumulation and reduce oxidative stress in liver from C57BL/6 mice fed a high-fat (HF) diet. Male C57BL/6 mice were divided into 4 groups: standard chow (SC; 10% energy from fat, 16 weeks); HF (50% energy from fat, 16 weeks); SC-HF (SC for 8 weeks followed by HF for 8 weeks); and HF-SC (HF for 8 weeks followed by SC for 8 weeks). The HF diet during 8 (SC-HF) and 16 weeks (HF) downregulated messenger RNA levels and protein expression of Nrf2 and endogenous antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) in the liver; caused liver steatosis; affected liver function markers; increased intra-abdominal and subcutaneous adipose tissue; and induced glucose intolerance and hypercholesterolemia compared with controls (SC). Diet-induced weight loss significantly reduced the intrahepatic lipid accumulation, improved glucose tolerance, and restored both gene and protein expression of the antioxidant enzymes. Our findings suggest that a dietary intervention aimed to induce weight loss may exert protective effects in NAFLD as it can reduce hepatic oxidative stress and intrahepatic lipid accumulation, which can hinder the progression of this condition to more severe states.

Molecular factors involved in the hypolipidemic- and insulin-sensitizing effects of a ginger (Zingiber officinale Roscoe) extract in rats fed a high-fat diet

Hypolipidemic and hypoglycemic properties of ginger in animal models have been reported. However, information related to the mechanisms and factors involved in the metabolic effects of ginger at a hepatic level are limited. The aim of the present study was to investigate molecular factors involved in the hypoglycemic and hypolipidemic effects of a hydroethanolic ginger extract (GE) in the liver of rats fed a high-fat diet (HFD). The study was conducted in male Wistar rats divided into the following 3 groups: (i) Rats fed a standard diet (3.5% fat), the control group; (ii) rats fed an HFD (33.5% fat); and (iii) rats fed an HFD treated with GE (250 mg·kg-1·day-1) for 5 weeks (HFD+GE). Plasma levels of glucose, insulin, lipid profile, leptin, and adiponectin were measured. Liver expression of glycerol phosphate acyltransferase (GPAT), cholesterol 7 alpha-hydroxylase, peroxisome proliferator-activated receptors (PPAR), PPARα and PPARγ, glucose transporter 2 (GLUT-2), liver X receptor, sterol regulatory element-binding protein (SREBP1c), connective tissue growth factor (CTGF), and collagen I was measured. Data were analyzed using a 1-way ANOVA, followed by a Newman-Keuls test if differences were noted. The study showed that GE improved lipid profile and attenuated the increase of plasma levels of glucose, insulin, and leptin in HFD rats. This effect was associated with a higher liver expression of PPARα, PPARγ, and GLUT-2 and an enhancement of plasma adiponectin levels. Furthermore, GE reduced liver expression of GPAT, SREBP1c, CTGF, and collagen I. The results suggest that GE might be considered as an alternative therapeutic strategy in the management of overweight and hepatic and metabolic-related alterations.

Ciliary neurotrophic factor analogue aggravates CCl4-induced acute hepatic injury in rats

Ciliary neurotrophic factor (CNTF) and CNTF analogs were reported to have hepatoprotective effect and ameliorate hepatic steatosis in db/db or high-fat-diet-fed mice. Because hepatic steatosis and injury are also commonly induced by hepatotoxin, the aim of the present study is to clarify whether CNTF could alleviate hepatic steatosis and injury induced by carbon tetrachloride (CCl₄). Unexpectedly, when combined with CCl₄, CNTF aggravated hepatic steatosis and liver injury. The mechanism is associated with effects of CNTF that inhibited lipoprotein secretion and drastically impaired the ability of lipoproteins to act as transport vehicles for lipids from the liver to the circulation. While injected after CCl₄ cessation, CNTF could improve liver function. These data suggest that CNTF could be a potential hepatoprotective agent against CCl₄-induced hepatic injury after the cessation of CCl₄ exposure. However, it is forbidden to combine recombinant mutant of human CNTF treatment with CCl₄.

The ergogenic supplement β-hydroxy-β-methylbutyrate (HMB) attenuates insulin resistance through suppressing GLUT-2 in rat liver

This study investigates the effect of the ergogenic supplement β-hydroxy-β-methylbutyrate (HMB) on insulin resistance induced by high-fructose diet (HFD) in rats. Male Sprague Dawley rats were fed 60% HFD for 12 weeks and HMB (320 mg·kg(-1)·day(-1), orally) for 4 weeks. HFD significantly increased fasting insulin, fasting glucose, glycosylated hemoglobin (HBA1C), liver glycogen content, and homeostasis model assessment of insulin resistance (HOMA-IR) index, while it decreased glucose and insulin tolerance. Furthermore, HFD significantly increased serum triglycerides (TG), low density lipoprotein cholesterol (LDL-C), and very low density lipoprotein cholesterol (VLDL-C) levels, while it significantly decreased high density lipoprotein cholesterol (HDL-C). Moreover, HFD significantly increased mRNA expression of glucose transporter type-2 (GLUT-2), the mammalian target of rapamycin (mTOR), and sterol regulatory element-binding protein-1c (SREBP-1c) but decreased peroxisome proliferator-activated receptor-alpha (PPAR-α) in liver. Aortic relaxation to acetylcholine (ACh) was impaired and histopathology showed severe hepatic steatosis. HMB significantly increased insulin tolerance and decreased fasting insulin, HOMA-IR, HBA1C, hepatic glycogen content, serum TG, LDL-C, and VLDL-C. Additionally, HMB enhanced ACh-induced relaxation, ameliorated hepatic steatosis, and decreased mRNA expression of GLUT-2. In conclusion, HMB may attenuate insulin resistance and hepatic steatosis through inhibiting GLUT-2 in liver.

Combining metformin therapy with caloric restriction for the management of type 2 diabetes and nonalcoholic fatty liver disease in obese rats

Weight loss is recommended for patients with nonalcoholic fatty liver disease (NAFLD), while metformin may lower liver enzymes in type 2 diabetics. Yet, the efficacy of the combination of weight loss and metformin in the treatment of NAFLD is unclear. We assessed the effects of metformin, caloric restriction, and their combination on NAFLD in diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Male OLETF rats (age 20 weeks; n = 6-8 per group) were fed ad libitum (AL), given metformin (300 mg·kg(-1)·day(-1); Met), calorically restricted (70% of AL; CR), or calorically restricted and given metformin (CR+Met) for 12 weeks. Met lowered adiposity compared with AL but not to the same magnitude as CR or CR+Met (p < 0.05). Although only CR improved fasting insulin and glucose, the combination of CR+Met was needed to improve post-challenge glucose tolerance. All treatments lowered hepatic triglycerides, but further improvements were observed in the CR groups (p < 0.05, Met vs. CR or CR+Met) and a further reduction in serum alanine aminotransferases was observed in CR+Met rats. CR lowered markers of hepatic de novo lipogenesis (fatty acid synthase, acetyl-CoA carboxylase (ACC), and stearoyl-CoA desaturase-1 (SCD-1)) and increased hepatic mitochondrial activity (palmitate oxidation and β-hydroxyacyl CoA dehydrogenase (β-HAD) activity). Changes were enhanced in the CR+Met group for ACC, SCD-1, β-HAD, and the mitophagy marker BNIP3. Met decreased total hepatic mTOR content and inhibited mTOR complex 1, which may have contributed to Met-induced reductions in de novo lipogenesis. These findings in the OLETF rat suggest that the combination of caloric restriction and metformin may provide a more optimal approach than either treatment alone in the management of type 2 diabetes and NAFLD.