Oral Recombinant Methioninase Prevents Nonalcoholic Fatty Liver Disease in Mice on a High Fat Diet

Pathophysiological Features of Rat Models of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) is caused by various factors, including genetic and/or environmental factors, and has complicated pathophysiological features during the development of the disease. NAFLD/NASH is recognized as an unmet medical need, and NAFLD/NASH animal models are essential tools for developing new therapies, including potential drugs and biomarkers. In this review, we describe the pathological features of the NAFLD/NASH rat models, focusing on the histopathology of hepatic fibrosis. NAFLD/NASH rat models are divided into three categories: diet-induced, genetic, and combined models based on diet, chemicals, and genetics. Rat models of NASH with hepatic fibrosis are especially expected to contribute to the development of new therapies, such as drugs and biomarkers.

Methionine gamma lyase: Structure-activity relationships and therapeutic applications

Methionine gamma lyase (MGL) is a bacterial and plant enzyme that catalyzes the conversion of methionine in methanthiol, 2-oxobutanoate and ammonia. The enzyme belongs to fold type I of the pyridoxal 5'-dependent family. The catalytic mechanism and the structure of wild type MGL and variants were determined in the presence of the natural substrate as well as of many sulfur-containing derivatives. Structure-function relationship studies were pivotal for MGL exploitation in the treatment of cancer, bacterial infections, and other diseases. MGL administration to cancer cells leads to methionine starvation, thus decreasing cells viability and increasing their vulnerability towards other drugs. In antibiotic therapy, MGL acts by transforming prodrugs in powerful drugs. Numerous strategies have been pursued for the delivering of MGL in vivo to prolong its bioavailability and decrease its immunogenicity. These include conjugation with polyethylene glycol and encapsulation in synthetic or natural vesicles, eventually decorated with tumor targeting molecules, such as the natural phytoestrogens daidzein and genistein. The scientific achievements in studying MGL structure, function and perspective therapeutic applications came from the efforts of many talented scientists, among which late Tatyana Demidkina to whom we dedicate this review.

Methionine-Restricted Diet: A Feasible Strategy Against Chronic or Aging-Related Diseases

Dietary methionine restriction (MR) has been associated with multifaceted health-promoting effects. MR is conducive to prevention of several chronic diseases and cancer, and extension of lifespan. A growing number of studies on new phenotypes and mechanisms of MR have become available in the past five years, especially in angiogenesis, neurodegenerative diseases, intestinal microbiota, and intestinal barrier function. In this review, we summarize the characteristics and advantages of MR, and current knowledge on the physiological responses and effects of MR on chronic diseases and aging-associated pathologies. Potential mechanisms, in which hydrogen sulfide, fibroblast growth factor 21, gut microbiota, short-chain fatty acids, and so on are involved, are discussed. Moreover, directions for epigenetics and gut microbiota in an MR diet are presented in future perspectives. This review comprehensively summarizes the novel roles and interpretations of the mechanisms underlying MR in the prevention of chronic diseases and aging.

Novel Biomarker Establishment for Evaluation of Excessive Fructose Consumption Using a Rat Model

BACKGROUND/AIM

The habitual consumption of excessive fructose is associated with the onset and progression of lifestyle-related diseases, such as nonalcoholic fatty liver disease (NAFLD). In this study, we investigated the physiological changes observed when consuming a diet containing excessive fructose on the viewpoints of hepatotoxicity biological markers using a rat model and explored the biomarker candidates that could detect the effects of excessive fructose intake at an early stage.

MATERIALS AND METHODS

Male rats were fed 63% high fructose diet (HFrD) ad libitum and their blood samples were collected before and at 1, 2, 3, and 4 weeks after allocation. The plasma biochemical parameters, hepatotoxic enzyme activities including alkaline phosphatase (ALP) isozymes were analyzed.

RESULTS

HFrD consumption for 4-weeks created NAFLD-like symptoms, including elevated plasma lipid parameters and hepatotoxicity markers, as well as fat accumulation in the liver compared with rats consuming a control diet. Alanine aminotransferase (ALT) and glutamate dehydrogenase (GLDH) were increased from the 3^rd and 2^nd weeks, respectively, but no changes were observed on ALP activity. However, the daily consumption of the HFrD increased the plasma activities of liver-type ALP isozyme, and decreased plasma small intestinal-type ALP isozyme soon after the start of feeding.

CONCLUSION

ALP isozyme analysis in combination with GLDH and ALT activities in the plasma samples could be a useful tool to detect the physiological changes induced by excessive fructose intake at an early stage of the development of NAFLD.

Herp knockout protects against nonalcoholic fatty liver disease in mice on a high fat diet

This study aims to discover the role of Homocysteine-induced ER protein (Herp) deficiency in high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD). After 8 weeks of feeding with normal-fat diet (NFD) or HFD, WT (wild type) and Herp^-/- mice were measured for the body weight, liver weight and serum biochemical parameters. HE, Oil Red O, and Sirius red stainings were used to evaluate the histopathological changes of liver tissues. QRT-PCR, Western blotting and Immunohistochemistry were employed to detect the mRNA and protein expression. TUNEL staining was used to observe the hepatocyte apoptosis. Herp knockout reduced the liver/body weight ratio of mice fed with HFD with the decreased serum levels of TG, TC, HDL, LDL, GGT, Hcy, ALT, and AST. Besides, WT mice fed with HFD presented obvious steatosis, inflammation and hepatocytes ballooning, which was relieved in Herp^-/- mice. HFD-induce NFALD mice demonstrated increased Oil Red, Sirius red, and α-SMA staining than NFD-induced mice, but mice in the Herp^-/-  + HFD group was lower than the WT + HFD group. HFD-induce NFALD mice showed up-regulated expression of Grp78, Chop, and Atf4 in liver tissues when compared with NFD fed mice. However, regarding to the mice fed with HFD, Herp deficiency decrease in the expression of Grp78, Chop, and Atf4 in liver tissues with the reduced hepatocyte apoptosis. Herp was highly expressed in HFD-induced NAFLD mice. Herp knockout improved liver function and histopathological conditions with the decreased hepatocyte apoptosis and endoplasmic reticulum stress (ERS) of HFD-induce NFALD mice.