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

Regulatory Roles of Quercetin in Alleviating Fructose-Induced Hepatic Steatosis: Targeting Gut Microbiota and Inflammatory Metabolites

While fructose is a key dietary component, concerns have been raised about its potential risks to the liver. This study aimed to assess quercetin's protective effects against fructose-induced mouse hepatic steatosis. Thirty-two male C57BL/6J mice were randomly allocated into four groups: control, high fructose diet (HFrD), HFrD supplemented with low-dose quercetin (HFrD+LQ), and HFrD supplemented with high-dose quercetin (HFrD+HQ). Biochemical, pathological, immune, and metabolic parameters were assessed. Quercetin treatment significantly reduced liver fat percentages in mice on a high fructose diet, with the most notable reduction observed in the HFrD+HQ group. Histological examination confirmed this reduction, revealing diminished lipid droplets and decreased inflammation and steatosis in hepatocytes. Compared to the high fructose group, interleukin-1 β and tumor necrosis factor alpha were significantly decreased, serum aspartate aminotransferase concentrations were markedly reduced, and blood high-density lipoprotein concentrations were substantially elevated after quercetin intervention (p < 0.05). Total bilirubin and triglyceride levels, which were significantly altered following high fructose intervention and reversed after quercetin intervention. Following the administration of 100 mg/kg quercetin, the Firmicutes/Bacteroidetes ratio was significantly reduced compared to the high fructose group. At the genus level, Erysipelotrichaceae_uncultured, Faecalibaculum, Odoribacter, and Allobaculum were significantly decreased (p < 0.05), Lacnospiraceae NK4A136 group, Parabacteroides, and Alloprevotella significantly increased (p < 0.05). However, the 50 mg/kg quercetin treatment only decreased the abundance of Erysipelotrichaceae_uncultured (p < 0.05). In addition, quercetin significantly enhanced the content of propionic acid and total acid (p < 0.05). Moreover, the intestinal flora showed a significant correlation with the hepatic health-related phenotype in mice. Both 50 and 100 mg/kg quercetin treatments significantly mitigated liver fat deposition in mice with fructose-induced hepatic steatosis. However, the higher dose of quercetin (100 mg/kg) demonstrated a more pronounced effect in reducing liver inflammation, likely due to its impact on gut microbiota regulation. This suggests quercetin's potential as a therapeutic agent for fructose-related hepatic steatosis, emphasizing the importance of dose considerations.

Integrated Ultrasound Characterization of the Diet-Induced Obesity (DIO) Model in Young Adult c57bl/6j Mice: Assessment of Cardiovascular, Renal and Hepatic Changes

Consuming an unbalanced diet and being overweight represent a global health problem in young people and adults of both sexes, and may lead to metabolic syndrome. The diet-induced obesity (DIO) model in the C57BL/6J mouse substrain that mimics the gradual weight gain in humans consuming a "Western-type" (WD) diet is of great interest. This study aims to characterize this animal model, using high-frequency ultrasound imaging (HFUS) as a complementary tool to longitudinally monitor changes in the liver, heart and kidney. Long-term WD feeding increased mice body weight (BW), liver/BW ratio and body condition score (BCS), transaminases, glucose and insulin, and caused dyslipidemia and insulin resistance. Echocardiography revealed subtle cardiac remodeling in WD-fed mice, highlighting a significant age-diet interaction for some left ventricular morphofunctional parameters. Qualitative and parametric HFUS analyses of the liver in WD-fed mice showed a progressive increase in echogenicity and echotexture heterogeneity, and equal or higher brightness of the renal cortex. Furthermore, renal circulation was impaired in WD-fed female mice. The ultrasound and histopathological findings were concordant. Overall, HFUS can improve the translational value of preclinical DIO models through an integrated approach with conventional methods, enabling a comprehensive identification of early stages of diseases in vivo and non-invasively, according to the 3Rs.

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.