Low-frequency electroacupuncture improves disordered hepatic energy metabolism in insulin-resistant Zucker diabetic fatty rats via the AMPK/mTORC1/p70S6K signaling pathway

Background and aim: Disordered hepatic energy metabolism is found in obese rats with insulin resistance (IR). There are insufficient experimental studies of electroacupuncture (EA) for IR and type 2 diabetes mellitus (T2DM). The aim of this study was to probe the effect of EA on disordered hepatic energy metabolism and the adenosine monophosphate (AMP)-activated protein kinase (AMPK)/mammalian target of rapamycin complex 1 (mTORC1)/ribosomal protein S6 kinase, 70-kDa (p70S6K) signaling pathway. Methods: Zucker Diabetic Fatty (ZDF) rats were randomly divided into three groups: EA group receiving EA treatment; Pi group receiving pioglitazone gavage; and ZF group remaining untreated (n = 8 per group). Inbred non-insulin-resistant Zucker lean rats formed an (untreated) healthy control group (ZL, n = 8). Fasting plasma glucose (FPG), fasting insulin (FINS), C-peptide, C-reactive protein (CRP) and homeostatic model assessment of insulin resistance (HOMA-IR) indices were measured. Hematoxylin–eosin (H&E) staining was used to investigate the liver morphologically. The mitochondrial structure of hepatocytes was observed by transmission electron microscopy (TEM). Western blotting was adopted to determine protein expression of insulin receptor substrate 1 (IRS-1), mTOR, mTORC1, AMPK, tuberous sclerosis 2 (TSC2) and p70S6K, and their phosphorylation. RT-PCR was used to quantify IRS-1, mTOR, mTORC1, AMPK and p70S6K mRNA levels. Results: Compared with the ZF group, FPG, FINS, C-peptide, CRP and HOMA-IR levels were significantly reduced in the EA group ( p < 0.05, p < 0.01). Evaluation of histopathology showed improvement in liver appearances following EA. Phosphorylation levels of AMPK, mTOR and TSC2 decreased, and IRS-1 and p70S6K increased, in hepatocytes of the ZF group, while these negative effects appeared to be alleviated by EA. Conclusions: EA can effectively ameliorate IR and regulate energy metabolism in the ZDF rat model. AMPK/mTORC1/p70S6K and related molecules may represent a potential mechanism of action underlying these effects.

Changes in PGC-1α-Dependent Mitochondrial Biogenesis Are Associated with Inflexible Hepatic Energy Metabolism in the Offspring Born to Dexamethasone-Treated Mothers

In the present study we investigated the participation of hepatic peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) in the metabolic programming of newborn rats exposed in utero to dexamethasone (DEX). On the 21st day of life, fasted offspring born to DEX-treated mothers displayed increased conversion of pyruvate into glucose with simultaneous upregulation of PEPCK (phosphoenolpyruvate carboxykinase) and G6Pase (glucose-6-phosphatase). Increased oxidative phosphorylation, higher ATP/ADP ratio and mitochondrial biogenesis and lower pyruvate levels were also found in the progeny of DEX-treated mothers. On the other hand, the 21-day-old progeny of DEX-treated mothers had increased hepatic triglycerides (TAG) and lower CPT-1 activity when subjected to short-term fasting. At the mechanistic level, rats exposed in utero to DEX exhibited increased hepatic PGC-1α protein content with lower miR-29a-c expression. Increased PGC-1α content was concurrent with increased association to HNF-4α and NRF1 and reduced PPARα expression. The data presented herein reveal that changes in the transcription machinery in neonatal liver of rats born to DEX-treated mothers leads to an inflexible metabolic response to fasting. Such programming is hallmarked by increased oxidative phosphorylation of pyruvate with impaired FFA oxidation and hepatic TAG accumulation.

Dietary Beta-Hydroxy Beta-Methyl Butyrate Supplementation Alleviates Liver Injury in Lipopolysaccharide-Challenged Piglets

The current study was performed to investigate whether dietary β-hydroxy-β-methylbutyrate (HMB) could regulate liver injury in a lipopolysaccharide- (LPS-) challenged piglet model and to determine the mechanisms involved. Thirty piglets ( 21 ± 2 days old , 5.86 ± 0.18 kg body weight) were randomly divided into the control (a basal diet, saline injection), LPS (a basal diet), or LPS+HMB (a basal diet + 0.60% HMB-Ca) group. After 15 d of treatment with LPS and/or HMB, blood and liver samples were obtained. The results showed that in LPS-injected piglets, HMB supplementation ameliorated liver histomorphological abnormalities induced by LPS challenge. Compared to the control group, the activities of serum aspartate aminotransferase and alkaline phosphatase were increased in the LPS-injected piglets ( P < 0.05 ). The LPS challenge also downregulated the mRNA expression of L-PFK, ACO, L-CPT-1, ICDH β, and AMPKα1/2 and upregulated the mRNA expression of PCNA, caspase 3, TNF-α, TLR4, MyD88, NOD1, and NF-κB p65 ( P < 0.05 ). However, these adverse effects of the LPS challenge were reversed by HMB supplementation ( P < 0.05 ). These results indicate that HMB may exert protective effects against LPS-induced liver injury, and the underlying mechanisms might involve the improvement of hepatic energy metabolism via regulating AMPK signaling pathway and the reduction of liver inflammation via modulating TLR4 and NOD signaling pathways.

Palmitate and pyruvate carbon flux in response to choline and methionine in bovine neonatal hepatocytes

Choline and methionine may serve unique functions to alter hepatic energy metabolism. Our objective was to trace carbon flux through pathways of oxidation and glucose metabolism in bovine hepatocytes exposed to increasing concentrations of choline chloride (CC) and d,l-methionine (DLM). Primary hepatocytes were isolated from 4 Holstein calves and maintained for 24 h before treatment with CC (0, 10, 100, 1000 μmol/L) and DLM (0, 100, 300 μmol/L) in a factorial design. After 21 h, [1-14C]C16:0 or [2-14C]pyruvate was added to measure complete and incomplete oxidation, and cellular glycogen. Reactive oxygen species (ROS), cellular triglyceride (TG), and glucose and ß-hydroxybutyrate (BHB) export were quantified. Exported very-low density lipoprotein particles were isolated for untargeted lipidomics and to quantify TG. Interactions between CC and DLM, and contrasts for CC (0 vs. [10, 100, 1000 μmol/L] and linear and quadratic contrast 10, 100, 1000 μmol/L) and DLM (0 vs. [100, 300 μmol/L] and 100 vs. 300 μmol/L) were evaluated. Presence of CC increased complete oxidation of [1-14C]C16:0 and decreased BHB export. Glucose export was decreased, but cellular glycogen was increased by the presence of CC and increasing CC. Presence of CC decreased ROS and marginally decreased cellular TG. No interactions between CC and DLM were detected for these outcomes. These data suggest a hepato-protective role for CC to limit ROS and cellular TG accumulation, and to alter hepatic energy metabolism to support complete oxidation of FA and glycogen storage regardless of Met supply.

Gut-liver axis modulation in fructose-fed mice: a role for PPAR-alpha and linagliptin

Fructose dietary intake affects the composition of the intestinal microbiota and influences the development of hepatic steatosis. Endotoxins produced by gram-negative bacteria alter intestinal permeability and cause bacterial translocation. This study evaluated the effects of gut microbiota modulation by a purified PPAR-alpha agonist (WY14643), a DPP-4 inhibitor (linagliptin), or their association on intestinal barrier integrity, endotoxemia, and hepatic energy metabolism in high-fructose-fed C57BL/6 mice. Fifty mice were divided to receive the control diet (C group) or the high-fructose diet (HFRU) for 12 weeks. Subsequently, the HFRU group was divided to initiate the treatment with PPAR-alpha agonist (3.5 mg/kg/BM) and DPP-4 inhibitor (15 mg/kg/BM). The HFRU group had glucose intolerance, endotoxemia, and dysbiosis (with increased Proteobacteria) without changes in body mass in comparison with the C group. HFRU group showed damaged intestinal ultrastructure, which led to liver inflammation and marked hepatic steatosis in the HFRU group when compared to the C group. PPAR-alpha activation and DPP-4 inhibition countered glucose intolerance, endotoxemia, and dysbiosis, ameliorating the ultrastructure of the intestinal barrier and reducing Tlr4 expression in the liver of treated animals. These beneficial effects suppressed lipogenesis and mitigated hepatic steatosis. In conclusion, the results herein propose a role for PPAR-alpha activation, DPP-4 inhibition, and their association in attenuating hepatic steatosis by gut-liver axis modulation in high-fructose mice model. These observations suggest these treatments as potential targets to treat hepatic steatosis and avoid its progression.