Evolving therapies for non-alcoholic steatohepatitis

Environmental microcystin targets the microbiome and increases the risk of intestinal inflammatory pathology via NOX2 in underlying murine model of Nonalcoholic Fatty Liver Disease

With increased climate change pressures likely to influence harmful algal blooms, exposure to microcystin, a known hepatotoxin and a byproduct of cyanobacterial blooms can be a risk factor for NAFLD associated comorbidities. Using both in vivo and in vitro experiments we show that microcystin exposure in NAFLD mice cause rapid alteration of gut microbiome, rise in bacterial genus known for mediating gut inflammation and lactate production. Changes in the microbiome were strongly associated with inflammatory pathology in the intestine, gut leaching, tight junction protein alterations and increased oxidative tyrosyl radicals. Increased lactate producing bacteria from the altered microbiome was associated with increased NOX-2, an NADPH oxidase isoform. Activationof NOX2 caused inflammasome activation as shown by NLRP3/ASCII and NLRP3/Casp-1 colocalizations in these cells while use of mice lacking a crucial NOX2 component attenuated inflammatory pathology and redox changes. Mechanistically, NOX2 mediated peroxynitrite species were primary to inflammasome activation and release of inflammatory mediators. Thus, in conclusion, microcystin exposure in NAFLD could significantly alter intestinal pathology especially by the effects on microbiome and resultant redox status thus advancing our understanding of the co-existence of NAFLD-linked inflammatory bowel disease phenotypes in the clinic.

A Cell-Based Assay to Investigate Hypolipidemic Effects of Nonalcoholic Fatty Liver Disease Therapeutics

In the recent past, there has been a growing interest in developing nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) therapeutics. As a result, a need for in vitro cell models of human hepatic steatosis and high-throughput assays to measure intracellular lipid levels has arisen. To address this growing need, we optimized the conditions based on the current literature to fatten HepG2 hepatocytes by adding a mixture of saturated and unsaturated fatty acids (oleate/palmitate, 2:1 molar ratio) without inducing any overt cytotoxicity. Our results indicate that hepatocytes fatten in a concentration- (0.75-1.5 mM of fatty acids) and time-dependent manner, with a substantial increase in intracellular lipid levels seen within 6 h. Additionally, a method to quantify lipid levels in cells using a fluorescent reagent that is more sensitive than that in conventional assays and adaptable for high-throughput screening is presented. Lastly, the utility of the in vitro cell model and an assay based on AdipoRed to measure hypolipidemic effects of therapeutic drugs is demonstrated using fenofibrate, a molecule that was previously shown to lower lipid levels in the liver.

A cellular model to study drug-induced liver injury in nonalcoholic fatty liver disease: Application to acetaminophen

Obesity and nonalcoholic fatty liver disease (NAFLD) can increase susceptibility to hepatotoxicity induced by some xenobiotics including drugs, but the involved mechanisms are poorly understood. For acetaminophen (APAP), a role of hepatic cytochrome P450 2E1 (CYP2E1) is suspected since the activity of this enzyme is consistently enhanced during NAFLD. The first aim of our study was to set up a cellular model of NAFLD characterized not only by triglyceride accumulation but also by higher CYP2E1 activity. To this end, human HepaRG cells were incubated for one week with stearic acid or oleic acid, in the presence of different concentrations of insulin. Although cellular triglycerides and the expression of lipid-responsive genes were similar with both fatty acids, CYP2E1 activity was significantly increased only by stearic acid. CYP2E1 activity was reduced by insulin and this effect was reproduced in cultured primary human hepatocytes. Next, APAP cytotoxicity was assessed in HepaRG cells with or without lipid accretion and CYP2E1 induction. Experiments with a large range of APAP concentrations showed that the loss of ATP and glutathione was almost always greater in the presence of stearic acid. In cells pretreated with the CYP2E1 inhibitor chlormethiazole, recovery of ATP was significantly higher in the presence of stearate with low (2.5mM) or high (20mM) concentrations of APAP. Levels of APAP-glucuronide were significantly enhanced by insulin. Hence, HepaRG cells can be used as a valuable model of NAFLD to unveil important metabolic and hormonal factors which can increase susceptibility to drug-induced hepatotoxicity.

Nonalcoholic fatty liver disease - current status and future directions

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide with a reported prevalence ranging 6-33%, depending on the studied populations. It encompasses a spectrum of liver manifestations ranging from simple steatosis (also known as nonalcoholic fatty liver, NAFL) to nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis, which may ultimately progress to hepatocellular carcinoma. NAFLD is strongly associated with the components of metabolic syndrome, mainly obesity and type 2 diabetes mellitus. NAFLD patients are at increased risk of liver-related as well as cardiovascular mortality. Current paradigm suggests a benign course for NAFL whereas NASH is considered to be the progressive phenotype. Although previously under-recognized accumulating evidence suggests that NAFL may also progress, suggesting a higher number of patients at risk than previously appreciated. Liver biopsy remains the gold standard for definitive diagnosis, but the majority of patients can be diagnosed accurately by noninvasive methods. Approved therapies for NAFLD are still lacking and lifestyle modifications aiming at weight loss remain the mainstay of NAFLD treatment. Intensive research could identify insulin resistance, lipotoxicity and dysbiosis of the gut microbiota as major pathophysiological mechanisms, leading to the development of promising targeted therapies which are currently investigated in clinical trials. In this review we summarized the current knowledge of NAFLD epidemiology, natural history, diagnosis, pathogenesis and treatment and considered future directions.

Mechanism of the effect of glycosyltransferase GLT8D2 on fatty liver

Background

Recent studies have shown that some glycosyltransferases are involved in the development of nonalcoholic fatty liver disease (NAFLD). The objective of this study was to explore the effect and mechanism of glycosyltransferase GLT8D2 on fatty liver.

Methods

Rat model of NAFLD was established by induction with high-fat-diet. The GLT8D2 expression in rat liver was examined using immunohistochemistry. Oil Red O staining and triglyceride assay were used to measure the effect of abnormal GLT8D2 expression on lipid accumulation in HepG2 cells. The expression levels of lipid metabolism-related key molecules, namely sterol regulatory element-binding protein-1c (SREBP-1c), stearoyl-coA desaturase (SCD), carnitine palmitoyltransferase-1 (CPT1) and microsomal triglyceride transfer protein (MTP), in HepG2 cells with abnormal GLT8D2 expression were determined by western blot analyses.

Results

The expression of GLT8D2 was higher in the liver of rats with NAFLD than in the control rats, and GLT8D2 was mainly located around lipid droplets in hepatocytes. GLT8D2 expression increased in steatosis HepG2 cells compared with that in normal HepG2 cells. GLT8D2 positively regulated lipid droplet accumulation and triglyceride content in HepG2 cells. Upregulation or knockdown of GLT8D2 had no effect on the expressions of SREBP-1c, SCD or CPT-1 proteins in HepG2 cells. However, GLT8D2 expression negatively regulated the expression of MTP protein in HepG2 cells.

Conclusion

GLT8D2 participated in NAFLD pathogenesis possibly by negatively regulating MTP expression. Specific inhibition of GLT8D2 via an antagonistic strategy could provide a potential candidate approach for treatment of NAFLD.

Early investigational drugs targeting PPAR-α for the treatment of metabolic disease

INTRODUCTION

The fibrates have been used for many years to treat dyslipidemias and have also recently been shown to have anti-inflammatory effects. They are relatively weak PPAR-α agonists and do have some adverse effects. Novel compounds are in development, which are selective PPAR modulators (SPPARMs) and have more potent PPAR-α agonist activity. These may prove to have advantages in the treatment of dyslipidemia, insulin resistance and non-alcoholic fatty liver disease (NAFLD).

AREAS COVERED

This review focuses on PPAR-α agonists or SPPARMs in development describing the preclinical and early clinical studies. The information was obtained by searching the published literature and abstracts from recent meetings. Ongoing clinical trials were identified using the Clinicaltrial.gov database.

EXPERT OPINION

There is still a need for new drugs to treat atherogenic dyslipidemia. The highly potent and selective PPAR-α agonist K-877 has shown beneficial effects on atherogenic dyslipidemia and absence of some adverse effects seen with fibrates. The dual PPAR-α/PPAR-δ agonist GFT-505 has shown favorable results in improving atherogenic dyslipidemia and insulin resistance and appears to be a potential candidate for the treatment of NAFLD. Long-term trials are needed to assess the safety and efficacy of these new agents for cardiovascular and liver outcomes.

Osteocalcin protects against nonalcoholic steatohepatitis in a mouse model of metabolic syndrome

Nonalcoholic fatty liver disease, particularly its more aggressive form, nonalcoholic steatohepatitis (NASH), is associated with hepatic insulin resistance. Osteocalcin, a protein secreted by osteoblast cells in bone, has recently emerged as an important metabolic regulator with insulin-sensitizing properties. In humans, osteocalcin levels are inversely associated with liver disease. We thus hypothesized that osteocalcin may attenuate NASH and examined the effects of osteocalcin treatment in middle-aged (12-mo-old) male Ldlr(-/-) mice, which were fed a Western-style high-fat, high-cholesterol diet for 12 weeks to induce metabolic syndrome and NASH. Mice were treated with osteocalcin (4.5 ng/h) or vehicle for the diet duration. Osteocalcin treatment not only protected against Western-style high-fat, high-cholesterol diet-induced insulin resistance but substantially reduced multiple NASH components, including steatosis, ballooning degeneration, and fibrosis, with an overall reduction in nonalcoholic fatty liver disease activity scores. Further, osteocalcin robustly reduced expression of proinflammatory and profibrotic genes (Cd68, Mcp1, Spp1, and Col1a2) in liver and suppressed inflammatory gene expression in white adipose tissue. In conclusion, these results suggest osteocalcin inhibits NASH development by targeting inflammatory and fibrotic processes.