Different Types of Dietary Fat and Fructose Interactions Result in Distinct Metabolic Phenotypes in Male Mice

Hepatocyte-Specific Fads1 Overexpression Attenuates Western Diet-Induced Metabolic Phenotypes in a Rat Model

Fatty acid desaturase 1 (FADS1) is a rate-limiting enzyme in long-chain polyunsaturated fatty acid (LCPUFA) synthesis. Reduced activity of FADS1 was observed in metabolic dysfunction-associated steatotic liver disease (MASLD). The aim of this study was to determine whether adeno-associated virus serotype 8 (AAV8) mediated hepatocyte-specific overexpression of Fads1 (AAV8-Fads1) attenuates western diet-induced metabolic phenotypes in a rat model. Male weanling Sprague-Dawley rats were fed with a chow diet, or low-fat high-fructose (LFHFr) or high-fat high-fructose diet (HFHFr) ad libitum for 8 weeks. Metabolic phenotypes were evaluated at the endpoint. AAV8-Fads1 injection restored hepatic FADS1 protein levels in both LFHFr and HFHFr-fed rats. While AAV8-Fads1 injection led to improved glucose tolerance and insulin signaling in LFHFr-fed rats, it significantly reduced plasma triglyceride (by ~50%) and hepatic cholesterol levels (by ~25%) in HFHFr-fed rats. Hepatic lipidomics analysis showed that FADS1 activity was rescued by AAV8-FADS1 in HFHFr-fed rats, as shown by the restored arachidonic acid (AA)/dihomo-γ-linolenic acid (DGLA) ratio, and that was associated with reduced monounsaturated fatty acid (MUFA). Our data suggest that the beneficial role of AAV8-Fads1 is likely mediated by the inhibition of fatty acid re-esterification. FADS1 is a promising therapeutic target for MASLD in a diet-dependent manner.

Effects of riboflavin deficiency and high dietary fat on hepatic lipid accumulation: a synergetic action in the development of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive lipid accumulation in the liver. Riboflavin, one of water soluble vitamins, plays a role in lipid metabolism and antioxidant function. However, the effects of riboflavin deficiency on NAFLD development have not yet to be fully explored.

METHODS

In the present study, an animal model of NAFLD was induced by high fat diet feeding in mice and a cellular model of NAFLD was developed in HepG2 cells by palmitic acid (PA) exposure. The effects of riboflavin deficiency on lipid metabolism and antioxidant function were investigated both in vivo and in vitro. In addition, the possible role of peroxisome proliferator-activated receptor gamma (PPARγ) was studied in HepG2 cells using gene silencing technique.

RESULTS

The results showed that riboflavin deficiency led to hepatic lipid accumulation in mice fed high fat diet. The expressions of fatty acid synthase (FAS) and carnitine palmitoyltransferase 1 (CPT1) were up-regulated, whereas that of adipose triglyceride lipase (ATGL) down-regulated. Similar changes in response to riboflavin deficiency were demonstrated in HepG2 cells treated with PA. Factorial analysis revealed a significant interaction between riboflavin deficiency and high dietary fat or PA load in the development of NAFLD. Hepatic PPARγ expression was significantly upregulated in mice fed riboflavin deficient and high fat diet or in HepG2 cells treated with riboflavin deficiency and PA load. Knockdown of PPARγ gene resulted in a significant reduction of lipid accumulation in HepG2 cells exposed to riboflavin deficiency and PA load.

CONCLUSIONS

There is a synergetic action between riboflavin deficiency and high dietary fat on the development of NAFLD, in which PPARγ may play an important role.