Protective Effects of Curcumin on Hepatic Steatosis in High Fat-Fed Obese Mice

Introduction and hypothesis: Metabolic dysfunction-associated fatty liver disease (MAFLD) is a chronic disorder marked by liver inflammation, lipid accumulation, and oxidative stress. MAFLD is often linked to adiposity and metabolic syndrome. Our previous research suggests the curcumin, a naturally occurring polyphenol found in turmeric, has protective metabolic effects in dietary obesity. The objective of this study was to explore the effects and mediating mechanisms of curcumin in improving inflammation and lipid metabolism in the liver of high-fat (HF)-induced obese mice and in cultured hepatoma cells. We hypothesized that curcumin would reduce high-fat diet-induced hepatic lipid synthesis and inflammation in obese mice and HF-induced inflammation in cultured hepatoma cells. Methods and approaches: Five-week-old male B6 mice were randomly assigned into either a HF diet (45% kcal fat) or HF diet with curcumin (HFC, 0.4% w/w curcumin) for 13 weeks. At the end of the intervention, livers were harvested and used for histological analyses and subsequent gene expression analysis using qPCR and RNA sequencing. Moreover, hepatoma Hep-G2 cells were treated with palmitic acid to induce inflammation and then with curcumin or its metabolites (tetrahydro curcumin and curcumin-o-glucuronide); media were collected for cytokine analyses by immunoassays and cells were harvested for gene expression analyses by qPCR. All data were analyzed using GraphPad Prism Software (v10.0.3). Results: Curcumin significantly reduced the expression of inflammatory genes in liver, such as the toll-like receptor-4 (TLR-4, p<0.05). Transcriptome analyses by RNA Seq revealed 631 differentially expressed genes (FDR-adjusted p value ≤ 0.05, fold change ≥ 2), with 263 downregulated and 368 upregulated genes. Curcumin increased gene expression of several pathways including fatty acid-beta oxidation (z = 1.342), lipid metabolism regulation by peroxisome proliferator-activated receptor (Ppar) alpha (z = 2.236), and downregulated lipopolysaccharide /Interleukin-1 mediated inhibition of retinoid x receptor (Rxr) pathways (z = -1.633). In the in vitro HepG2 cell study with palmitic acid induction, curcumin, and its metabolites did not affect fatty acid synthesis such as the acetyl CoA carboxylase alpha (Acaca), or inflammatory mRNA levels including interleukin-8 (Il-8). Conclusion: Our results indicate protective metabolic effects of curcumin in reducing specific markers of lipid accumulation and inflammation in the liver. These findings suggest potential therapeutic benefits of curcumin in MAFLD and warrant further mechanistic studies in animals and cells as well as future clinical studies in people with obesity.