Liver-Specific Bmal1 Depletion Reverses the Beneficial Effects of Nobiletin on Liver Cholesterol Homeostasis in Mice Fed with High-Fat Diet

Fisetin Ameliorates Hepatocyte Lipid Droplet Accumulation via Targeting the Rhythmic Protein BMAL1 to Regulate Cell Death-Inducing DNA Fragmentation Factor-α-like Effector C-Mediated Lipid Droplet Fusion

High fat diet (HFD) induces the enlargement and accumulation of lipid droplets (LDs) in hepatocytes, thereby influencing the homeostasis of lipid metabolism. Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC), a surface protein of LDs, facilitates their fusion and growth, transforming small LDs into larger ones. Lipophagy, a selective form of autophagy, primarily targets small LDs for degradation. Fisetin (FIS), a natural dietary flavonoid present in various fruits and vegetables, has an unclear mechanism for reducing LD accumulation. In this study, we observed that FIS significantly ameliorated HFD-induced lipid accumulation in the hepatocytes of C57BL/6 mice. In further mechanistic studies, we revealed that FFA enhanced the expression of CIDEC, which promoted the fusion of LDs and caused them to become larger. The enlarged LDs could not be degraded by autophagy, which ultimately led to accumulation of LDs. Conversely, FIS alleviated LD accumulation by inhibiting CIDEC-mediated fusion, resulting in smaller LDs that facilitated lipophagy. Additionally, studies indicated that the dysfunction of circadian rhythms is closely related to lipid metabolism. In our study, we showed that HFD and FFA disrupted circadian rhythm in C57BL/6 mouse hepatocytes and AML12 cells, while FIS modified the rhythm disturbances and increased protein expression of the core clocks BMAL1 and CLOCK. We silenced the BMAL1 protein and revealed that si-BMAL1 upregulated CIDEC proteins. These data suggested that FIS might inhibit CIDEC-mediated LD fusion and enhance hepatocyte lipophagy by promoting the expression of rhythm protein BMAL1, thereby alleviating LD accumulation in C57BL/6 and AML12 cells caused by the HFD and FFA. The present study provided novel insights and potential targets for utilizing functional food factors to mitigate the accumulation of LD in hepatocytes.

Nobiletin promotes lipolysis of white adipose tissue in a circadian clock-dependent manner

Nobiletin has been reported to protect against obesity-related metabolic disorders by enhancing the circadian rhythm; however its effects on lipid metabolism in adipose tissue are unclear. In this study, mice were fed with high-fat diet (HFD) for four weeks firstly and gavaged with 50 or 200 mg/kg bodyweight/day nobiletin at Zeitgeber time (ZT) 4 for another four weeks while still receiving HFD. At the end of the 8-week experimental period, the mice were sacrificed at ZT4 or ZT8 on the same day. Mature 3T3-L1 adipocytes were treated with nobiletin in the presence or absence of siBmal1, siRora, siRorc, SR8278 or SR9009. Nobiletin reduced the weight of white adipose tissue (WAT) and the size of adipocytes in WAT. At ZT4, nobiletin decreased the TG, TC and LDL-c levels and increased serum FFA level and glucose tolerance. Nobiletin triggered the lipolysis of mesenteric and epididymal WAT at both ZT4 and ZT16. Nobiletin increased the level of RORγ at ZT16, that of BMAL1 and PPARγ at ZT4, and that of ATGL at both ZT4 and ZT16. Nobiletin increased lipolysis and ATGL levels in 3T3-L1 adipocytes in Bmal1- or Rora/c- dependent manner. Dual luciferase assay indicated that nobiletin enhanced the transcriptional activation of RORα/γ on Atgl promoter and decreased the repression of RORα/γ on PPARγ-binding PPRE. Promoter deletion analysis indicated that nobiletin inhibited the suppression of PPARγ-mediated Atgl transcription by RORα/γ. Taken together, nobiletin elevated lipolysis in WAT by increasing ATGL levels through activating the transcriptional activity of RORα/γ and decreasing the repression of RORα/γ on PPARγ-binding PPRE.

Nobiletin Protects Against Alcoholic Liver Disease in Mice via the BMAL1-AKT-Lipogenesis Pathway

SCOPE

Alcoholic liver disease (ALD) is a global public health concern. Nobiletin, a polymethoxyflavone abundant in citrus fruits, enhances circadian rhythms and ameliorates diet-induced hepatic steatosis, but its influences on ALD are unknown. This study investigates the role of brain and muscle Arnt-like protein-1 (Bmal1), a key regulator of the circadian clock, in nobiletin-alleviated ALD.

METHODS AND RESULTS

This study uses chronic ethanol feeding plus an ethanol binge to establish ALD models in Bmal1flox/flox and Bmal1 liver-specific knockout (Bmal1LKO) mice. Nobiletin mitigates ethanol-induced liver injury (alanine aminotransferase [ALT]), glucose intolerance, hepatic apoptosis, and lipid deposition (triglyceride [TG], total cholesterol [TC]) in Bmal1flox/flox mice. Nobiletin fails to modulated liver injury (ALT, aspartate aminotransferase [AST]), apoptosis, and TG accumulation in Bmal1LKO mice. The expression of lipogenic genes (acetyl-CoA carboxylase alpha [Acaca], fatty acid synthase [Fasn]) and fatty acid oxidative genes (carnitine pamitoyltransferase [Cpt1a], cytochrome P450, family 4, subfamily a, polypeptide 10 [Cyp4a10], and cytochrome P450, family4, subfamily a, polypeptide 14 [Cyp4a14]) is inhibited, and the expression of proapoptotic genes (Bcl2 inteacting mediator of cell death [Bim]) is enhanced by ethanol in Bmal1flox/flox mice. Nobiletin antagonizes the expression of these genes in Bmal1flox/flox mice and not in Bmal1LKO mice. Nobiletin activates protein kinase B (PKB, also known as AKT) phosphorylation, increases the levels of the carbohydrate response element binding protein (ChREBP), ACC1, and FASN, and reduces the level of sterol-regulatory element binding protein 1 (SREBP1) and phosphorylation of ACC1 in a Bmal1-dependent manner.

CONCLUSION

Nobiletin alleviates ALD by increasing the expression of genes involved in fatty acid oxidation by increasing AKT phosphorylation and lipogenesis in a Bmal1-dependent manner.

Metabolic Profile and Lipid Metabolism Phenotype in Mice with Conditional Deletion of Hepatic BMAL1

The disruption of circadian rhythms (CRs) has been linked to metabolic disorders, yet the role of hepatic BMAL1, a key circadian regulator, in the whole-body metabolism and the associated lipid metabolic phenotype in the liver remains unclear. Bmal1 floxed (Bmal1f/f) and hepatocyte-specific Bmal1 knockout (Bmal1hep-/-) C57BL/6J mice underwent a regular feeding regimen. Hepatic CR, lipid content, mitochondrial function, and systemic metabolism were assessed at zeitgeber time (ZT) 0 and ZT12. Relevant molecules were examined to elucidate the metabolic phenotype. Hepatocyte-specific knockout of Bmal1 disrupted the expression of rhythmic genes in the liver. Bmal1hep-/- mice exhibited decreased hepatic TG content at ZT0, primarily due to enhanced lipolysis, reduced lipogenesis, and diminished lipid uptake. The β-oxidation function of liver mitochondria decreased at both ZT0 and ZT12. Our findings on the metabolic profile and associated hepatic lipid metabolism in the absence of Bmal1 in hepatocytes provides new insights into metabolic syndromes from the perspective of liver CR disturbances.

Mechanism insights into the pleiotropic effects of nobiletin as a potential therapeutic agent on non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases and is emerging as one of the fastest-growing causes of liver-related deaths worldwide. It is necessary to find strategies to effectively prevent and treat NAFLD, as no definitive drug has been approved. Nobiletin (NOB) is the critical active ingredient of Chinese herbal medicines such as Citrus aurantium and Citri Reticulatae Pericarpium, which have anti-inflammatory, antioxidant, lipid regulating, and insulin resistance regulating effects. Numerous studies have demonstrated that NOB can prevent and treat the onset and progression of NAFLD. In this review, the mechanisms of NOB for treating NAFLD have been summarized, hoping to provide a basis for subsequent studies of NOB and to provide a research ground for the development of therapeutic drugs for NAFLD.

Nobiletin from citrus peel: a promising therapeutic agent for liver disease-pharmacological characteristics, mechanisms, and potential applications

Nobiletin (NOB) is a flavonoid derived from citrus peel that has potential as an alternative treatment for liver disease. Liver disease is a primary health concern globally, and there is an urgent need for effective drugs. This review summarizes the pharmacological characteristics of NOB and current in vitro and in vivo studies investigating the preventive and therapeutic effects of NOB on liver diseases and its potential mechanisms. The findings suggest that NOB has promising therapeutic potential in liver diseases. It improves liver function, reduces inflammation and oxidative stress, remodels gut microflora, ameliorates hepatocellular necrosis, steatosis, and insulin resistance, and modulates biorhythms. Nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear transcription factor kappa (NF-κB), AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor α(PPAR-α), extracellular signal-regulated kinase (ERK), protein kinase B (AKT), toll-like receptor 4 (TLR4) and transcription factor EB (TFEB) signaling pathways are important molecular targets for NOB to ameliorate liver diseases. In conclusion, NOB may be a promising drug candidate for treating liver disease and can accelerate its application from the laboratory to the clinic. However, more high-quality clinical trials are required to validate its efficacy and identify its molecular mechanisms and targets.