A novel AMPK activator improves hepatic lipid metabolism and leukocyte trafficking in experimental hepatic steatosis

MP Allosterically Activates AMPK to Enhance ABCA1 Stability by Retarding the Calpain-Mediated Degradation Pathway

It is widely recognized that macrophage cholesterol efflux mediated by the ATP-binding cassette transporter A1 (ABCA1) constitutes the initial and rate-limiting step of reverse cholesterol transport (RCT), displaying a negative correlation with the development of atherosclerosis. Although the transcriptional regulation of ABCA1 has been extensively studied in previous research, the impact of post-translational regulation on its expression remains to be elucidated. In this study, we report an AMP-activated protein kinase (AMPK) agonist called ((2R,3S,4R,5R)-3,4-dihydroxy-5-(6-((3-hydroxyphenyl) amino)-9H-purin-9-yl) tetrahydrofuran-2-yl) methyl dihydrogen phosphate (MP), which enhances ABCA1 expression through post-translational regulation rather than transcriptional regulation. By integrating the findings of multiple experiments, it is confirmed that MP directly binds to AMPK with a moderate binding affinity, subsequently triggering its allosteric activation. Further investigations conducted on macrophages unveil a novel mechanism through which MP modulates ABCA1 expression. Specifically, MP downregulates the Cav1.2 channel to obstruct the influx of extracellular Ca2+, thereby diminishing intracellular Ca2+ levels, suppressing calcium-activated calpain activity, and reducing the interaction strength between calpain and ABCA1. This cascade of events culminates in the deceleration of calpain-mediated degradation of ABCA1. In conclusion, MP emerges as a potentially promising candidate compound for developing agents aimed at enhancing ABCA1 stability and boosting cellular cholesterol efflux and RCT.

Protective effects of caffeine against palmitate-induced lipid toxicity in primary rat hepatocytes is associated with modulation of adenosine receptor A1 signaling

BACKGROUND

Epidemiological evidence has shown an association between coffee consumption and reduced risk for chronic liver diseases, including metabolic-dysfunction-associated liver disease (MALFD). Lipotoxicity is a key cause of hepatocyte injury during MAFLD. The coffee component caffeine is known to modulate adenosine receptor signaling via the antagonism of adenosine receptors. The involvement of these receptors in the prevention of hepatic lipotoxicity has not yet been explored. The aim of this study was to explore whether caffeine protects against palmitate-induced lipotoxicity by modulating adenosine receptor signaling.

METHODS

Primary hepatocytes were isolated from male rats. Hepatocytes were treated with palmitate with or without caffeine or 1,7DMX. Lipotoxicity was verified using Sytox viability staining and mitochondrial JC-10 staining. PKA activation was verified by Western blotting. Selective (ant)agonists of A1AR (DPCPX and CPA, respectively) and A2AR (istradefyline and regadenoson, respectively), the AMPK inhibitor compound C, and the Protein Kinase A (PKA) inhibitor Rp8CTP were used. Lipid accumulation was verified by ORO and BODIPY 453/50 staining.

RESULTS

Caffeine and its metabolite 1,7DMX prevented palmitate-induced toxicity in hepatocytes. The A1AR antagonist DPCPX also prevented lipotoxicity, whereas both the inhibition of PKA and the A1AR agonist CPA (partially) abolished the protective effect. Caffeine and DPCPX increased lipid droplet formation only in palmitate-treated hepatocytes and decreased mitochondrial ROS production.

CONCLUSIONS

The protective effect of caffeine against palmitate lipotoxicity was shown to be dependent on A1AR receptor and PKA activation. Antagonism of A1AR also protects against lipotoxicity. Targeting A1AR receptor may be a potential therapeutic intervention with which to treat MAFLD.

Rice Bran Extract Suppresses High-Fat Diet-Induced Hyperlipidemia and Hepatosteatosis through Targeting AMPK and STAT3 Signaling

Rice bran, a by-product of rice milling, is abundant in bioactive molecules and is highly recognized for its health-promoting properties, particularly in improving metabolic conditions. Building on this knowledge, we aimed to optimize the extraction conditions to maximize the functional efficacy of rice bran extract (RBE) and further validate its impact on lipid metabolism. We found that the optimized RBE (ORBE) significantly suppressed high-fat diet-induced weight gain, hyperlipidemia, and hepatosteatosis in mouse models. ORBE treatment not only suppressed lipid uptake in vivo, but also reduced lipid accumulation in HepG2 cells. Importantly, we discovered that ORBE administration resulted in activation of AMPK and inhibition of STAT3, which are both crucial players in lipid metabolism in the liver. Collectively, ORBE potentially offers promise as a dietary intervention strategy against hyperlipidemia and hepatosteatosis. This study underlines the value of optimized extraction conditions in enhancing the functional efficacy of rice bran.

Oroxylin-A alleviates hepatic lipid accumulation and apoptosis under hyperlipidemic conditions via AMPK/FGF21 signaling

Oroxylin-A (OA) is an O-methylated flavone that has been demonstrated to have anti-inflammatory properties in various disease models. However, the roles of OA in hepatic lipid metabolism and the specific molecular mechanisms by which it exerts these effects are not yet fully understood. In the current study, we aimed to investigate the effects of OA on hepatic lipid deposition and apoptosis, which play a pivotal role in the development of nonalcoholic fatty liver disease (NAFLD) in obesity in vitro models. We found that treatment with OA attenuated lipid accumulation, the expression of lipogenesis-associated proteins and apoptosis in palmitate-treated primary mouse hepatocytes. OA treatment suppressed phosphorylated NFκB and IκB expression in as well as TNFα and MCP-1 release from hepatocytes treated with palmitate. Treatment of hepatocytes with OA augmented AMPK phosphorylation and FGF21 expression. siRNA of AMPK or FGF21 abolished the effects of OA on inflammation as well as lipid accumulation and apoptosis in hepatocytes under palmitate treatment conditions. In conclusion, OA improves inflammation through the AMPK/FGF21 pathway, thereby attenuating lipid accumulation and apoptosis in hepatocytes. This study may help identify new targets for developing treatments for NAFLD.

Dietary sinapic acid attenuated high-fat diet-induced lipid metabolism and oxidative stress in male Syrian hamsters

The current study investigated the effects of sinapic acid on high-fat diet (HFD)-induced lipid metabolism and oxidative stress in male Syrian hamsters. Sinapic acid treatment significantly reduced body weight, epididymal fat, and perirenal fat mass in HFD hamsters. Sinapic acid also improved dyslipidemia levels (reducing the serum levels of total cholesterol, triglycerides, and low-density lipoprotein cholesterol, and increasing the high-density lipoprotein cholesterol) and increased T-AOC levels to mitigate oxidative stress injury. Moreover, sinapic acid intervention increased the activations of PPAR-γ, CPT-1, and CYP7A1 and decreased the activations of FAS, ACC1, SREBP1, SREBP2, and HMGCR in the livers of HFD hamsters. In addition, sinapic acid intervention also significantly inhibited the intestinal mRNA levels of Srebp2 and Npc1l1 in HFD hamsters. In conclusion, sinapic acid can significantly attenuate abnormal lipid metabolism in the development of HFD-induced obesity and reduce the level of oxidative stress to exert its anti-obesity effect. PRACTICAL APPLICATIONS: Obesity is the main cause of some chronic metabolic syndromes, such as dyslipidemia, nonalcoholic fatty liver disease, diabetes, and hyperuricemia. Searching for new, safe, and effective natural products in weight loss and fat reduction has become one of the hot research topics. As a natural source of simple phenolic acids, sinapic acid is present in fruits, vegetables, and grains and has been indicated to have anti-inflammatory, antioxidant, antihyperuricemic, lipid homeostasis regulation, and anticancer activities. However, the lipid metabolism- and oxidative stress-regulating activities of sinapic acid are not clear. Here, the current study investigated the lipid metabolism and oxidative stress regulating activities of sinapic acid in male Syrian hamsters fed a high-fat diet.

Soyasapogenol C from Fermented Soybean (Glycine Max) Acting as a Novel AMPK/PPARα Dual Activator Ameliorates Hepatic Steatosis: A Novel SANDA Methodology

(1) Background: Soyasapogenol C (SSC), a derivative of soyasapogenol B (SSB), is specifically found high in many fermented soybean (Glycine max) products, including Cheonggukjang (in Korean). However, the biological activities for preventing and treating hepatic steatosis, and the precise underlying mechanisms of SSC, remain to be explored. (2) Methods: A novel SANDA (structural screening, ADMET prediction, network pharmacology, docking validation, and activity evaluation) methodology was used to examine whether SSC exerts hepatoprotective effects in silico and in vitro. (3) Results: SSC had better ADMET characteristics and a higher binding affinity with predicted targets chosen from network pathway analysis than SSB. SSC induced the phosphorylation of AMP-activated protein kinase (AMPK) and stimulated the nuclear translocation of peroxisome proliferator-activated receptor alpha (PPARα), further enhancing PPAR response element (PPRE) binding activity in HepG2 cells. Concurrently, SSC significantly inhibited triglyceride accumulation, which was associated with the suppression of lipogenesis genes and the enhancement of fatty acid oxidation gene expression in HepG2 cells. (4) Conclusions: Soyasapogenol C, discovered using a novel SANDA methodology from fermented soybean, is a novel AMPK/PPARα dual activator that is effective against hepatic steatosis. Dietary supplementation with soyasapogenol C may prevent the development of hepatic steatosis and other diseases associated with fat accumulation in the liver.

Clerodendrum trichotomum extract improves metabolic derangements in high fructose diet-fed rats

Clerodendrum trichotomum has been reported to possess beneficial properties for human health, but its effects on metabolic syndrome have not been reported. In this study, we investigated the effect of C. trichotomum leaf extract (CT) on the metabolic derangements induced by a high-fructose (HF) diet. Sprague–Dawley rats were fed with a 46% carbohydrate diet (HC group), 60% high-fructose diet (HF group), or HF diet supplemented with CT (500 mg/kg of body weight/day, CT group) via drinking water for 16 weeks. Results showed that CT alleviated HF diet-induced insulin resistance, dyslipidemia, and hepatic steatosis In liver tissues, CT affected the signaling pathways of AMP-activated protein kinase, peroxisome proliferator-activated receptor α (PPARα), and sterol regulatory element binding protein 1. CT enriched the genes that were mainly involved in cytokine-cytokine receptor interaction, PPAR, PI3K-Akt signaling pathways, and fatty acid metabolism pathway. These results suggest that CT is a promising therapeutic against metabolic disorders.

Maternal Exercise Mediates Hepatic Metabolic Programming via Activation of AMPK-PGC1α Axis in the Offspring of Obese Mothers

Maternal obesity is associated with an increased risk of hepatic metabolic dysfunction for both mother and offspring and targeted interventions to address this growing metabolic disease burden are urgently needed. This study investigates whether maternal exercise (ME) could reverse the detrimental effects of hepatic metabolic dysfunction in obese dams and their offspring while focusing on the AMP-activated protein kinase (AMPK), representing a key regulator of hepatic metabolism. In a mouse model of maternal western-style-diet (WSD)-induced obesity, we established an exercise intervention of voluntary wheel-running before and during pregnancy and analyzed its effects on hepatic energy metabolism during developmental organ programming. ME prevented WSD-induced hepatic steatosis in obese dams by alterations of key hepatic metabolic processes, including activation of hepatic ß-oxidation and inhibition of lipogenesis following increased AMPK and peroxisome-proliferator-activated-receptor-γ-coactivator-1α (PGC-1α)-signaling. Offspring of exercised dams exhibited a comparable hepatic metabolic signature to their mothers with increased AMPK-PGC1α-activity and beneficial changes in hepatic lipid metabolism and were protected from WSD-induced adipose tissue accumulation and hepatic steatosis in later life. In conclusion, this study demonstrates that ME provides a promising strategy to improve the metabolic health of both obese mothers and their offspring and highlights AMPK as a potential metabolic target for therapeutic interventions.

Tanshinone IIA Downregulates Lipogenic Gene Expression and Attenuates Lipid Accumulation through the Modulation of LXRα/SREBP1 Pathway in HepG2 Cells

Abnormal and excessive accumulation of lipid droplets within hepatic cells is the main feature of steatosis and nonalcoholic fatty liver disease (NAFLD) or metabolic-associated fatty liver disease (MAFLD). Dysregulation of lipogenesis contributes to hepatic steatosis and plays an essential role in the pathological progress of MAFLD. Tanshinone IIA is a bioactive phytochemical isolated from Salvia miltiorrhiza Bunge and exhibits anti-inflammatory, antiatherosclerotic and antihyperlipidemic effects. In this study, we aimed to investigate the lipid-lowering effects of tanshinone IIA on the regulation of lipogenesis, lipid accumulation, and the underlying mechanisms in hepatic cells. We demonstrated that tanshinone IIA can significantly inhibit the gene expression involved in de novo lipogenesis including FASN, ACC1, and SCD1, in HepG2 and Huh 7 cells. Tanshinone IIA could increase phosphorylation of ACC1 protein in HepG2 cells. We further demonstrated that tanshinone IIA also could suppress the fatty-acid-induced lipogenesis and TG accumulation in HepG2 cells. Furthermore, tanshinone IIA markedly downregulated the mRNA and protein expression of SREBP1, an essential transcription factor regulating lipogenesis in hepatic cells. Moreover, we found that tanshinone IIA attenuated liver X receptor α (LXRα)-mediated lipogenic gene expression and lipid droplet accumulation, but did not change the levels of LXRα mRNA or protein in HepG2 cells. The molecular docking data predicted tanshinone IIA binding to the ligand-binding domain of LXRα, which may result in the attenuation of LXRα-induced transcriptional activation. Our findings support the supposition that tanshinone IIA possesses a lipid-modulating effect that suppresses lipogenesis and attenuates lipid accumulation by modulating the LXRα/SREBP1 pathway in hepatic cells. Tanshinone IIA can be potentially used as a supplement or drug for the prevention or treatment of MAFLD.

Hypolipidemic properties of Chlorella pyrenoidosa organic acids via AMPK/HMGCR/SREBP-1c pathway in vivo

The aim of this study was to explore the effects and mechanisms of 95% ethanol extract of Chlorella pyrenoidosa (CPE95) on lipid metabolism in hyperlipidemic rats. For the sake of chemical composition analysis of CPE95, liquid chromatography-mass spectrometry (LC-MS) was used for determination. After treatment with CPE95, serum high-density lipoprotein cholesterol content of the hyperlipidemic rats was increased, while the contents of cholesterol, triglyceride, and low-density lipoprotein cholesterol were decreased strikingly. Moreover, the result of histopathology analysis showed that the accumulation and fatty deformation of the livers were relieved. Real-time quantitative PCR and Western blotting were used to determine the expression levels of lipid metabolism-related genes. The gene expression level of adenosine 5'-monophosphate-activated protein kinase was descended, and expressions of sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase, and 3-hydroxy-3-methylglutaryl coenzyme A reductase were all downregulated in the CPE95-treated rats. It suggested that CPE95 may effectively improve the hyperlipidemia in rats and would be potential for functional food component to reduce blood lipid.

Sestrin2 protects against bavachin induced ER stress through AMPK/mTORC1 signaling pathway in HepG2 cells

Bavachin (BV), a natural flavonoid compound derived from Psoralea corylifolia L, has been reported to be a potential hepatotoxin. Our previous studies have found that BV can induce endoplasmic reticulum (ER) stress-related cell apoptosis, but the molecular mechanism underlying BV-induced ER stress remains obscure. Sestrin2, a highly conserved stress-inducible protein, is involved in the cellular responses of various stress conditions and homeostatic regulation. However, whether Sestrin2 participated in the ER stress related hepatotoxicity against BV is still elusive. In the present study, we aim to investigate the role of BV on liver injury of mice and the impact of Sestrin2 on BV-induced ER stress in HepG2 cells. The results in mice showed that BV induced ER stress related liver injury with increased Sestrin2 expression involvement. Knockdown of Sestrin2 with siRNA aggravated BV-induced ER stress significantly in HepG2 cells. Further mechanistic study uncovered that inhibition of mTORC1 with rapamycin blocked BV-induced ER stress, and treatment with Sestrin2 siRNA blocked the inhibition effect of AMPK to mTORC1. Therefore, constant mTORC1 would lead to accumulation of misfolded or unfolded proteins and aggravated ER stress. Collectively, our study indicates that Sestrin2 confers protection against BV-induced ER stress via activating of the AMPK/mTORC1 pathway.

From overnutrition to liver injury: AMP-activated protein kinase in nonalcoholic fatty liver diseases

Nonalcoholic fatty liver diseases (NAFLDs), especially nonalcoholic steatohepatitis (NASH), have become a major cause of liver transplant and liver-associated death. However, the pathogenesis of NASH is still unclear. Currently, there is no FDA-approved medication to treat this devastating disease. AMP-activated protein kinase (AMPK) senses energy status and regulates metabolic processes to maintain homeostasis. The activity of AMPK is regulated by the availability of nutrients, such as carbohydrates, lipids, and amino acids. AMPK activity is increased by nutrient deprivation and inhibited by overnutrition, inflammation, and hypersecretion of certain anabolic hormones, such as insulin, during obesity. The repression of hepatic AMPK activity permits the transition from simple steatosis to hepatocellular death; thus, activation might ameliorate multiple aspects of NASH. Here we review the pathogenesis of NAFLD and the impact of AMPK activity state on hepatic steatosis, inflammation, liver injury, and fibrosis during the transition of NAFL to NASH and liver failure.