Alpha-lipoic acid induces adipose triglyceride lipase expression and decreases intracellular lipid accumulation in HepG2 cells

FOXO1 induced fatty acid oxidation in hepatic cells by targeting ALDH1L2

BACKGROUND AND AIM

Lipid metabolism disorder is the primary feature of numerous refractory chronic diseases. Fatty acid oxidation, an essential aerobic biological process, is closely related to the progression of NAFLD. The forkhead transcription factor FOXO1 has been reported to play an important role in lipid metabolism. However, the molecular mechanism through which FOXO1 regulates fatty acid oxidation remains unclear.

METHODS

Transcriptomic analysis was performed to examine the cellular expression profile to determine the functional role of FOXO1 in HepG2 cells with palmitic acid (PA)-induced lipid accumulation. FOXO1-binding motifs at the promoter region of aldehyde dehydrogenase 1 family member L2 (ALDH1L2) were predicted via bioinformatic analysis and confirmed via luciferase reporter assay. Overexpression of ALDH1L2 was induced to recover the impaired fatty acid oxidation in FOXO1-knockout cells.

RESULTS

Knockout of FOXO1 aggravated lipid deposition in hepatic cells. Transcriptomic profiling revealed that knockout of FOXO1 increased the expression of genes associated with fatty acid synthesis but decreased the expression of carnitine palmitoyltransferase1a (CPT1α) and adipose triglyceride lipase (ATGL), which contribute to fatty acid oxidation. Mechanistically, FOXO1 was identified as a transcription factor of ALDH1L2. Knockout of FOXO1 significantly decreased the protein expression of ALDH1L2 and CPT1α in vitro and in vivo. Furthermore, overexpression of ALDH1L2 restored fatty acid oxidation in FOXO1-knockout cells.

CONCLUSION

The findings of this study indicate that FOXO1 modulates fatty acid oxidation by targeting ALDH1L2.

Forkhead box O1 in metabolic dysfunction-associated fatty liver disease: molecular mechanisms and drug research

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a chronic liver disease that progresses from hepatic steatosis to non-alcoholic steatohepatitis, cirrhosis, and liver cancer, posing a huge burden on human health. Existing research has confirmed that forkhead box O1 (FOXO1), as a member of the FOXO transcription factor family, is upregulated in MAFLD. Its activity is closely related to nuclear-cytoplasmic shuttling and various post-translational modifications including phosphorylation, acetylation, and methylation. FOXO1 mediates the progression of MAFLD by regulating glucose metabolism, lipid metabolism, insulin resistance, oxidative stress, hepatic fibrosis, hepatocyte autophagy, apoptosis, and immune inflammation. This article elaborates on the regulatory role of FOXO1 in MAFLD, providing a summary and new insights for the current status of drug research and targeted therapies for MAFLD.

Diet-inducing hypercholesterolemia show decreased O-GlcNAcylation of liver proteins through modulation of AMPK

O-GlcNAcylation, a nutritionally driven, post-translational modification of proteins, is gaining importance because of its health implications. Changes in O-GlcNAcylation are observed in various disease conditions. Changes in O-GlcNAcylation by diet that causes hypercholesterolemia are not critically looked into in the liver. To address it, both in vitro and in vivo approaches were employed. Hypercholesterolemia was induced individually by feeding cholesterol (H)/high-fat (HF) diet. Global O-GlcNAcylation levels and modulation of AMPK activation in both preventive and curative approaches were looked into. Diet-induced hypercholesterolemia resulted in decreased O-GlcNAcylation of liver proteins which was associated with decreased O-linked N-acetylglucosaminyltransferase (OGT) and Glutamine fructose-6-phosphate amidotransferase-1 (GFAT1). Activation of AMPK by metformin in preventive mode restored the O-GlcNAcylation levels; however, metformin treatment of HepG2 cells in curative mode restored O-GlcNAcylation levels in HF but failed to in H condition (at 24 h). Further, maternal faulty diet resulted in decreased O-GlcNAcylation in pup liver despite feeding normal diet till adulthood. A faulty diet modulates global O-GlcNAcylation of liver proteins which is accompanied by decreased AMPK activation which could exacerbate metabolic syndromes through fat accumulation in the liver.

The immunosuppressive, growth-hindering, hepatotoxic, and oxidative stress and immune related-gene expressions-altering effects of gibberellic acid in Oreochromis niloticus: A mitigation trial using alpha-lipoic acid

This study aimed to examine the effects of gibberellic acid (GBA) on growth, hemato-biochemical parameters related to liver functions, digestive enzymes, and immunological response in Oreochromis niloticus. Besides, the probable underlying mechanisms were explored by assessing antioxidant, apoptotic, and immune-related gene expression. Furthermore, the likelihood of restoration following alpha-lipoic acid (LIP) dietary supplementation was explored. The fish (average initial weight 30.75 ± 0.46) were equally classified into four groups: the control group, the LIP group (fed on a basal diet plus 600 mg/kg of LIP), the GBA group (exposed to 150 mg GBA/L), and the GBA + LIP group (exposed to 150 mg GBA/L and fed a diet containing LIP and GBA) for 60 days. The study findings showed that LIP supplementation significantly reduced GBA's harmful effects on survival rate, growth, feed intake, digestive enzymes, and antioxidant balance. Moreover, the GBA exposure significantly increased liver enzymes, stress markers, cholesterol, and triglyceride levels, all of which were effectively mitigated by the supplementation of LIP. Additionally, LIP addition to fish diets significantly minimized the histopathological alterations in the livers of GBA-treated fish, including fatty change, sharply clear cytoplasm with nuclear displacement to the cell periphery, single-cell necrosis, vascular congestion, and intralobular hemorrhages. The GBA-induced reduction in lysozyme activity, complement C3, and nitric oxide levels, together with the downregulation of antioxidant genes (cat and sod), was significantly restored by dietary LIP. Meanwhile, adding LIP to the GBA-exposed fish diets significantly corrected the aberrant expression of hsp70, caspase- 3, P53, pcna, tnf-a, and il-1β in O. niloticus liver. Conclusively, dietary LIP supplementation could mitigate the harmful effects of GBA exposure on fish growth and performance, physiological conditions, innate immunity, antioxidant capability, inflammatory response, and cell apoptosis.

Effect of Tea Polyphenols, α-Lipoic Acid and Their Joint Use on the Antioxidant and Lipid Metabolism Performance of Hybrid Grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) Fed with High-Lipid Diets

This study investigated tea polyphenols (TP), α-lipoic acid (ALA) and their joint use on the antioxidant and lipid metabolic performance of hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) took food with high-fat diets. Six high-lipid diets with isonitrogen (50% of dry matter) and isolipid (17% of dry value) were designed, in which a total content of 1,000 mg/kg additives were added to each group except for the control group (FL). The additives addition ratios in each group were ALA (AL), TP (PL), ALA : TP = 1 : 1 (EL), ALA : TP = 1 : 2 (OL), ALA : TP = 2 : 1 (TL). Each diet was divided into three repeat groups with 30 tails (6.84 ± 0.01 g) in each group and fed for 8 weeks. The consequences were as follows: (1) the highest weight gain rate, specific growth rate, as well as the lowest feed conversion ratio and ingestion rate were discovered in the OL team, which were opposite to the TL group. (2) The body fat content and muscle fat content in the fish oil group were the lowest (P < 0.05), while those of the TL group were the highest. (3) Serum catalase, glutathione peroxidase, total antioxidant capacity, and superoxide dismutase activities were the highest, and the content of reactive oxygen species was the lowest in the OL group. (4) The OL group has the highest hepatic lipase activity and the lowest very low-density lipoprotein content of the liver. In contrast, the TL group had the highest fatty acid synthetase (FAS) activity (P < 0.05). (5) The oil-red aspects of liver tissue displayed lipid particles in other groups were reduced to different degrees compared with FL group, and the OL group showed the best lipid-lowering effect. (6) Compared with the FL group, the relative expressions of FAS, acetyl-CoA carboxylase (acc), and apolipoprotein b-100 (apoB100) genes in the liver were decreased. The relative expressions of lipoprotein lipase (lpl) and peroxisome proliferators-activated receptors-α (pparα) genes related to lipid catabolism were increased, among which the OL group had the most significant change (P < 0.05). (7) According to the 7-day challenge test of Vibrio alginolyticus, the OL group had the highest survival rate. To sum up, both ALA and TP have positive effects on relieving the lipid metabolism disorder of hybrid grouper. If they are jointly used, adding ALA : TP in a ratio of 1 : 2 (OL) may have the best effect, and an addition ratio of 2 : 1 (TL) may inhibit the hybrid grouper growth and increase the feeding cost.

Sesamin ameliorates lipotoxicity and lipid accumulation through the activation of the estrogen receptor alpha signaling pathway

Nonalcoholic fatty liver disease (NAFLD) has been linked to fat accumulation in the liver and lipid metabolism imbalance. Sesamin, a lignan commonly found in sesame seed oil, possesses antioxidant, anti-inflammatory, and anticancer properties. However, the precise mechanisms by which sesamin prevents hepatic steatosis are not well understood. This study aimed to explore the molecular mechanisms by which sesamin may improve lipid metabolism dysregulation. A in vitro hepatic steatosis model was established by exposing HepG2 cells to palmitate sodium. The results showed that sesamin effectively mitigated lipotoxicity and reduced reactive oxygen species production. Additionally, sesamin suppressed lipid accumulation by regulating key factors involved in lipogenesis and lipolysis, such as fatty acid synthase (FASN), sterol regulatory element-binding protein 1c (SREBP-1c), forkhead box protein O-1, and adipose triglyceride lipase. Molecular docking results indicated that sesamin could bind to estrogen receptor α (ERα) and reduce FASN and SREBP-1c expression via the Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ)/AMP-activated protein kinase (AMPK) signaling pathway. Sesamin attenuated palmitate-induced lipotoxicity and regulated hepatic lipid metabolism in HepG2 cells by activating the ERα/CaMKKβ/AMPK signaling pathway. These findings suggest that sesamin can improve lipid metabolism disorders and is a promising candidate for treating hepatic steatosis.

Heat-Killed Enterococcus faecalis Inhibit FL83B Hepatic Lipid Accumulation and High Fat Diet-Induced Fatty Liver Damage in Rats by Activating Lipolysis through the Regulation the AMPK Signaling Pathway

Continuous consumption of high-calorie meals causes lipid accumulation in the liver and liver damage, leading to non-alcoholic fatty liver disease (NAFLD). A case study of the hepatic lipid accumulation model is needed to identify the mechanisms underlying lipid metabolism in the liver. In this study, the prevention mechanism of lipid accumulation in the liver of Enterococcus faecalis 2001 (EF-2001) was extended using FL83B cells (FL83Bs) and high-fat diet (HFD)-induced hepatic steatosis. EF-2001 treatment inhibited the oleic acid (OA) lipid accumulation in FL83B liver cells. Furthermore, we performed lipid reduction analysis to confirm the underlying mechanism of lipolysis. The results showed that EF-2001 downregulated proteins and upregulated AMP-activated protein kinase (AMPK) phosphorylation in the sterol regulatory element-binding protein 1c (SREBP-1c) and AMPK signaling pathways, respectively. The effect of EF-2001 on OA-induced hepatic lipid accumulation in FL83Bs enhanced the phosphorylation of acetyl-CoA carboxylase and reduced the levels of lipid accumulation proteins SREBP-1c and fatty acid synthase. EF-2001 treatment increased the levels of adipose triglyceride lipase and monoacylglycerol during lipase enzyme activation, which, when increased, contributed to increased liver lipolysis. In conclusion, EF-2001 inhibits OA-induced FL83B hepatic lipid accumulation and HFD-induced hepatic steatosis in rats through the AMPK signaling pathway.

Chlorella unsaturated fatty acids suppress high-fat diet-induced obesity in C57/BL6J mice

Chlorella has been identified as a rich source of unsaturated fatty acids. Since the antiobesity effects of unsaturated fatty acids have been well documented; therefore, we explored the antiobesity actions of chlorella unsaturated fatty acids (C.UFAs) in the current study. The obtained results demonstrated C.UFAs, which contain abundant linoleic acid, could retard body weight gain (reducing body weigh by 13.93% after 16 weeks of treatment), improve blood glucose (19.29% lower) and lipid profile (23.45% lower in TG, 8.76% lower in TC) compared to high-fat diet-fed C57BL/6J mice. The possible underlying mechanisms might involve reducing hepatic lipid accumulation via down-regulation of lipogenic genes (PPARγ, C/EBPα, LPL, aP2, FAS, and SREBP-1c) and up-regulation of lipolytic gene (adiponectin). We also demonstrate C.UFAs could reduce HFD-induced adipocyte hypertrophy via activation of AMPK signaling pathway in adipose tissue and liver. In summary, our study highlights the potential of C.UFAs as a functional food for obesity management. PRACTICAL APPLICATION: Chlorella has already been commercialized as a functional food antiobesity function. In the current study, the unsaturated fatty acids isolated from chlorella were found to exert beneficial effects on hyperglycemia, hyperlipidemia, hepatic steatosis, and adipocyte hypertrophy in high-fat diet-fed mice. This may provide theoretical foundation for developing novel chlorella-based functional foods.

Phytochemicals targeting NAFLD through modulating the dual function of forkhead box O1 (FOXO1) transcription factor signaling pathways

Literature evidence reveals that natural compounds are potential candidates for ameliorating obesity-associated non-alcoholic fatty liver disease (NAFLD) by targeting forkhead box O1 (FOXO1) transcription factor. FOXO1 has a dual and complex role in regulating both increase and decrease in lipid accumulation in hepatocytes and adipose tissues (AT) at different stages of NAFLD. In insulin resistance (IR), it is constitutively expressed, resulting in increased hepatic glucose output and lipid metabolism irregularity. The studies on different phytochemicals indicate that dysregulation of FOXO1 causes disturbance in cellular nutrients homeostasis, and the natural entities have an enduring impact on the mitigation of these abnormalities. The current review communicates and evaluates certain phytochemicals through different search engines, targeting FOXO1 and its downstream cellular pathways to find lead compounds as potential therapeutic agents for treating NAFLD and related metabolic disorders. The findings of this review confirm that polyphenols, flavonoids, alkaloids, terpenoids, and anthocyanins are capable of modulating FOXO1 and associated signaling pathways, and they are potential therapeutic agents for NAFLD and related complications. HIGHLIGHTS: • FOXO1 has the potential to be targeted by novel drugs from natural sources for the treatment of NAFLD and obesity. • FOXO1 regulates cellular autophagy, inflammation, oxidative stress, and lipogenesis through alternative mechanisms. • Phytochemicals treat NAFLD by acting on FOXO1 or SREBP1c and PPARγ transcription factor signaling pathways.

Sucralose, a Non-nutritive Artificial Sweetener Exacerbates High Fat Diet-Induced Hepatic Steatosis Through Taste Receptor Type 1 Member 3

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally, and it is strongly associated with obesity. To combat obesity, artificial sweeteners are often used to replace natural sugars, and sucralose is one of the most extensively used sweeteners. It was known that sucralose exerted effects on lipid metabolism dysregulation, and hepatic inflammation; however, the effects of sucralose on hepatic steatosis were still obscure. In this study, we found that supplements of sucralose enhanced high-fat-diet (HFD)-induced hepatic steatosis. In addition, treatment of sucralose increased reactive oxygen species (ROS) generation and induced endoplasmic reticulum (ER) stress in HepG2 cells. Pretreatment of ROS or ER stress inhibitors reversed the effects of sucralose on lipogenesis. Furthermore, pretreatment of taste receptor type 1 membrane 3 (T1R3) inhibitor or T1R3 knockdown reversed sucralose-induced lipogenesis in HepG2 cells. Taken together, sucralose might activate T1R3 to generate ROS and promote ER stress and lipogenesis, and further accelerate to the development of hepatic steatosis.

Effects of alpha lipoic acid on metabolic syndrome: A comprehensive review

Metabolic syndrome (MetS) is a multifactorial disease with medical conditions such as hypertension, diabetes, obesity, dyslipidemia, and insulin resistance. Alpha-lipoic acid (α-LA) possesses various pharmacological effects, including antidiabetic, antiobesity, hypotensive, and hypolipidemia actions. It exhibits reactive oxygen species scavenger properties against oxidation and age-related inflammation and refines MetS components. Also, α-LA activates the 5' adenosine monophosphate-activated protein kinase and inhibits the NFκb. It can decrease cholesterol biosynthesis, fatty acid β-oxidation, and vascular stiffness. α-LA decreases lipogenesis, cholesterol biosynthesis, low-density lipoprotein and very low-density lipoprotein levels, and atherosclerosis. Moreover, α-LA increases insulin secretion, glucose transport, and insulin sensitivity. These changes occur via PI3K/Akt activation. On the other hand, α-LA treats central obesity by increasing adiponectin levels and mitochondrial biogenesis and can reduce food intake mainly by SIRT1 stimulation. In this review, the most relevant articles have been discussed to determine the effects of α-LA on different components of MetS with a special focus on different molecular mechanisms behind these effects. This review exhibits the potential properties of α-LA in managing MetS; however, high-quality studies are needed to confirm the clinical efficacy of α-LA.

Sesamol ameliorates hepatic lipid accumulation and oxidative stress in steatosis HepG2 cells via the PPAR signaling pathway

Non-alcoholic fatty liver disease (NAFLD) is a chronic hepatopathy caused by disordered lipid metabolism in the liver. Sesamol, a phenolic compound derived from sesame oil, has been shown to inhibit obesity, hyperlipidemia, and atherosclerosis in previous investigations. However, the preventive effect of sesamol against hepatic steatosis and oxidative stress in NAFLD has not been well-studied. In this work, sesamol was observed to alleviate lipid accumulation and oxidative stress in high oleic acid (300 μM)/cholesterol (25 μM) induced HepG2 cells, thus indicating that sesamol was involved in regulating hepatic lipid metabolism and oxidative injury. Mechanism studies found that the activated peroxisome proliferator-activated receptors (PPAR) signaling pathway by sesamol intervention up-regulated gene and protein expressions related to fatty acid oxidation and cholesterol efflux and catabolism, thus accelerating lipid consumption and reducing intracellular lipid accumulation in the process of NAFLD. These data suggested that sesamol can effectively ameliorate hepatic steatosis and sesamol riched sesamol oil may be a potential agent for finding therapeutic strategies to treat the NAFLD. PRACTICAL APPLICATIONS: Sesamol and sesamol-rich sesame oil have received much attention due to their performance on hepatic lipid regulation. The results of this study indicate that sesamol treatment could ameliorate hepatic steatosis by inhibiting lipid accumulation and oxidative stress, thus demonstrating that sesamol and sesame oil can be used for functional foods and nutraceutical applications in the future. In addition, the present work provides knowledge of the effects of sesamol on NAFLD and involved mechanisms, and further supplies nutritional guidelines for sesame oil consumption.

Shikonin Attenuates Hepatic Steatosis by Enhancing Beta Oxidation and Energy Expenditure via AMPK Activation

Shikonin, a natural plant pigment, is known to have anti-obesity activity and to improve insulin sensitivity. This study aimed to examine the effect of shikonin on hepatic steatosis, focusing on the AMP-activated protein kinase (AMPK) and energy expenditure in Hepa 1-6 cells and in high-fat fed mice. Shikonin increased AMPK phosphorylation in a dose- and time-dependent manner, and inhibition of AMPK with compound C inhibited this activation. In an oleic acid-induced steatosis model in hepatocytes, shikonin suppressed oleic acid-induced lipid accumulation, increased AMPK phosphorylation, suppressed the expression of lipogenic genes, and stimulated fatty acid oxidation-related genes. Shikonin administration for four weeks decreased body weight gain and the accumulation of lipid droplets in the liver of high-fat fed mice. Furthermore, shikonin promoted energy expenditure by activating fatty acid oxidation. In addition, shikonin increased the expression of PPARγ coactivator-1α (PGC-1α), carnitine palmitoyltransferase-1 (CPT1) and other mitochondrial function-related genes. These results suggest that shikonin attenuated a high fat diet-induced nonalcoholic fatty liver disease by stimulating fatty acid oxidation and energy expenditure via AMPK activation.

Chronic Microcystin-LR Exposure Induces Abnormal Lipid Metabolism via Endoplasmic Reticulum Stress in Male Zebrafish

In order to explore effects of low levels of continuous microcystin-LR (MC-LR) (a cyanotoxin) exposure on hepatic lipid metabolism on the basis of the endoplasmic reticulum stress (ERS) pathway, we exposed adult male zebrafish to MC-LR (0, 1, 5, and 25 μg/L) for 60 days, and hepatic histopathology as well as lipid metabolic parameters were determined with mRNA levels of ERS signal molecules and downstream factors, along with genes associated with lipid metabolism in zebrafish liver. The results revealed that prolonged exposure to MC-LR remarkably altered the levels of hepatic total cholesterol and triglyceride and led to hepatic steatosis, which was also confirmed by hepatic cytoplasmic vacuolization in Hematoxylin/eosin (H&E) stain and lipid droplet accumulation in Oil Red O stain. The severity of hepatic damage and lipidation was increased in a dose-related manner. MC-LR exposure significantly upregulated transcriptional levels of ERS markers including hspa5, mapk8, and chop, indicating the occurrence of ERS in the liver of zebrafish. Concurrently, MC-LR significantly improved mRNA expression of unfolded protein response (UPR) pathway-related genes including atf6, eif2ak3, ern1, and xbp1s, suggesting that all of the three UPR branches were activated by MC-LR. MC-LR also induced significant upregulation of downstream lipid metabolism-related factors and genes including srebf1, srebf2, fatty acid synthase (fasn), acetyl-CoA carboxylase (acaca), stearoyl-CoA desaturase (scd), HMG CoA reductase (hmgcra), and HMG CoA synthase (hmgcs1), and downregulation of genes associated with lipolysis such as triglyceride hydrolase gene (atgl), hormone-sensitive enzyme gene (hsla), and carnitine palmitoyltransferase gene (cpt1aa). Our present results indicated that the cause of hepatic lipid accumulation by MC-LR was mainly by upregulating lipogenic and cholesterol genes but downregulating the expression of lipolytic genes through the induction of srebf1 and srebf2, which were involved in the activation of ERS signal pathways.

Bezafibrate induces autophagy and improves hepatic lipid metabolism in glycogen storage disease type Ia

Glucose-6-phosphatase α (G6Pase) deficiency, also known as von Gierke's Disease or Glycogen storage disease type Ia (GSD Ia), is characterized by decreased ability of the liver to convert glucose-6-phosphate to glucose leading to glycogen accumulation and hepatosteatosis. Long-term complications of GSD Ia include hepatic adenomas and carcinomas, in association with the suppression of autophagy in the liver. The G6pc-/- mouse and canine models for GSD Ia were treated with the pan-peroxisomal proliferator-activated receptor agonist, bezafibrate, to determine the drug's effect on liver metabolism and function. Hepatic glycogen and triglyceride concentrations were measured and western blotting was performed to investigate pathways affected by the treatment. Bezafibrate decreased liver triglyceride and glycogen concentrations and partially reversed the autophagy defect previously demonstrated in GSD Ia models. Changes in medium-chain acyl-CoA dehydrogenase expression and acylcarnintine flux suggested that fatty acid oxidation was increased and fatty acid synthase expression associated with lipogenesis was decreased in G6pc-/- mice treated with bezafibrate. In summary, bezafibrate induced autophagy in the liver while increasing fatty acid oxidation and decreasing lipogenesis in G6pc-/- mice. It represents a potential therapy for glycogen overload and hepatosteatosis associated with GSD Ia, with beneficial effects that have implications for non-alcoholic fatty liver disease.

Alpha-lipoic acid suppresses Nε-(carboxymethyl) lysine-induced epithelial mesenchymal transition in HK-2 human renal proximal tubule cells

N^ε-(carboxymethyl) lysine (CML) plays causal roles in diabetic complications. In the present study, we investigated whether CML-induced HIF-1α accumulation and epithelial-mesenchymal transition (EMT) in HK-2 renal proximal tubular epithelial cells. Treatment with CML-BSA increased reactive oxygen species (ROS) production reduced the mitochondrial membrane potential and induced mitochondrial fragmentation. Pre-treatment of cells with antioxidant, α-lipoic acid, normalised the ROS production and restored the mitochondrial membrane potential. These changes were accompanied with morphological changes of epithelial mesenchymal transition. CML-BSA increased the protein level of hypoxia-inducible factor-1α (HIF-1α), and the EMT-associated transcription factor, TWIST. These effects were reversed by α-lipoic acid. CML-BSA increased the protein levels of mesenchymal-specific markers, including vimentin, α-smooth muscle actin, which were alleviated by pre-treatment with α-lipoic acid. Our data suggest that CML-BSA induces EMT through a ROS/HIF-1α/TWIST-dependent mechanism, and that α-lipoic acid may alleviate the CML-induced EMT in renal tubular cells.

Flavone glycosides from Sicyos angulatus and their inhibitory effects on hepatic lipid accumulation

A library of extracted natural materials (Korea Bioactive Natural Material Bank) have been screened to discover candidates for the treatment of non-alcoholic liver disease (NAFLD), and the 70% ethanol extract of Sicyos angulatus was found to inhibit hepatic lipid accumulation. Bioassay-guided fractionation of this bioactive extract yielded five previously undescribed flavonoid glycosides and one previously undescribed flavonolignan glycoside along with seven known flavonoid glycosides. The chemical structures of these compounds were elucidated by a combination of extensive spectroscopic analysis, including MS, NMR and UV techniques. Eight compounds of all isolated compounds showed inhibitory effects on the lipid accumulation induced by high concentrations of palmitic acid and glucose in HepG2 cells. Four selected compounds were tested for lipid content in a dose-dependent manner (10, 20 and 40 μM), and among those compounds, kaempferol 3-O-β-d-glucopyranosyl-7-O-α-l-rhamnopyranoside showed the strongest inhibition of hepatic lipid production in HepG2 cells. In an oil-red O staining assay, five compounds were shown to reduce hepatic lipid accumulation better than what was observed in the vehicle control group. The present study suggests a new class of chemical entities for developing bioactive agents for the treatment of diseases caused by fat accumulation in the liver.

The protein-sparing effect of α-lipoic acid in juvenile grass carp, Ctenopharyngodon idellus: effects on lipolysis, fatty acid β-oxidation and protein synthesis

To investigate the protein-sparing effect of α-lipoic acid (LA), experimental fish (initial body weight: 18·99 (sd 1·82) g) were fed on a 0, 600 or 1200 mg/kg α-LA diet for 56 d, and hepatocytes were treated with 20 μm compound C, the inhibitor of AMP kinase α (AMPKα), treated for 30 min before α-LA treatment for 24 h. LA significantly decreased lipid content of the whole body and other tissues (P<0·05), and it also promoted protein deposition in vivo (P<0·05). Further, dietary LA significantly decreased the TAG content of serum and increased the NEFA content of serum (P<0·05); however, there were no significant differences among all groups in the hepatopancreas and muscle (P>0·05). Consistent with results from the experiment in vitro, LA activated phosphorylation of AMPKα and notably increased the protein content of adipose TAG lipase in intraperitoneal fat, hepatopancreas and muscle in vivo (P<0·05). Meanwhile, LA significantly up-regulated the mRNA expression of genes involved in fatty acid β-oxidation in the same three areas, and LA also obviously down-regulated the mRNA expression of genes involved in amino acid catabolism in muscle (P<0·05). Besides, it was observed that LA significantly activated the mammalian target of rapamycin (mTOR) pathway in muscle of experimental fish (P<0·05). LA could promote lipolysis and fatty acid β-oxidation via increasing energy supply from lipid catabolism, and then, it could economise on the protein from energy production to increase protein deposition in grass carp. Besides, LA might directly promote protein synthesis through activating the mTOR pathway.

A global perspective on FOXO1 in lipid metabolism and lipid-related diseases

Lipid metabolism is a complex physiological process that is involved in nutrient adjustment, hormone regulation, and homeostasis. An unhealthy lifestyle and chronic nutrient overload can cause lipid metabolism disorders, which may lead to serious lipid-related diseases, including obesity, non-alcoholic fatty liver disease (NAFLD), and type 2 diabetes mellitus (T2DM). Therefore, tools for preventing dysfunctional lipid metabolism are urgently needed. The transcription factor forkhead box protein O1 (FOXO1) is involved in lipid metabolism and plays a critical role in the development of lipid-related diseases. In this review, we provide a global perspective on the role of FOXO1 in lipid metabolism and lipid-related diseases. The information included here may be useful for the design of future studies and advancing investigations of FOXO1 as a therapeutic target.

The effect of chitooligosaccharides on oleic acid-induced lipid accumulation in HepG2 cells

This experiment aimed to evaluate the capacities of two types of chitooligosaccharides (COS) with different molecular weights for the ability to eliminate lipid accumulation in hepatocytes. We have established a lipid accumulation model in HepG₂ cells for these studies in vitro, which was established by induction with oleic acid. The capacity of COS to eliminate lipid accumulation was evaluated using three metrics: the thiazolyl blue dye absorbance (MTT value), the morphology of intracellular lipid droplets and the triglyceride level (TG). Two types of COS with different molecular weights (1000 Da and 3000 Da) can significantly reduce intracellular lipid accumulation and decrease TG content in HepG₂ cells, in a dose-dependent fashion. We found that low molecular weight COS is more efficacious than high molecular weight COS. Two types of COS can eliminate lipid accumulation induced by oleic acid in HepG₂ cells, leading to an obvious hypolipidemic effect in vitro. These results suggest that COS may be effective preventive agents in fatty liver disease.

Isomeric effects of anti-diabetic α-lipoic acid with γ-cyclodextrin

AIMS

Previous studies reported the anti-diabetic effects of α-lipoic acid (αLA) isomers: racemic-αLA, R-αLA, or S-αLA. Previously, we examined the anti-diabetic effects of αLA administered as a food additive, but were unable to demonstrate the differences among different isomers. In this study, αLAs were complexed with γ-cyclodextrin (γCD) for the stability.We then investigated the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs in KKAy mice.

MAIN METHODS

Male type 2 diabetic KKAy mice were divided into 5 groups, and fed either a high-fat-diet (HFD),HFD supplemented with γCD, or HFD supplemented with racemic-αLA/γCD, R-αLA/γCD, or S-αLA/γCD for 4 weeks. At the end of the feeding period, HbA1c and adiponectin levels were measured, PPARγ2mRNA expression levels were assessed in adipose tissues using real-time PCR, and AMP-activated protein kinase (AMPK) phosphorylation levels were evaluated in the liver by Western blotting.

KEY FINDINGS

The anti-diabetic effects of αLA; the isomeric compounds racemic-, R-, and S-αLA/γCD were investigated using amale type 2 diabetic KKAy mousemodel. Significant differences were observed in HbA1c and plasma adiponectin levels between R-αLA/γCD-treated mice and control mice. PPARγ2 mRNA expression levels were slightly higher in racemic- and R-αLA/γCD-treated mice. Moreover, AMPK phosphorylation levels were elevated in racemic-αLA/γCD- and R-αLA/γCD-treated mice, but remained unchanged in S-αLA/γCD-treated mice.

SIGNIFICANCE

These results suggested that the stereoisomerism mediates a difference in the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs. Furthermore, the anti-diabetic mechanism of αLA/γCD action may be attributed to the activation of AMPK in the liver.

Inhibitory effects of high stability fucoxanthin on palmitic acid-induced lipid accumulation in human adipose-derived stem cells through modulation of long non-coding RNA

Obesity is a serious worldwide disease, which is growing in epidemic proportions. Adipose-derived stem cells (ADSCs) are characterized as a source of mesenchymal stem cells that have acted as a potential application for regeneration. Recently, seaweeds rich in flavonoids and polysaccharides have been supposed to show the ability to modulate risk factors for obesity and related diseases. In the present study, we investigated the anti-obesity properties of high stability fucoxanthin (HS-Fx) derived from brown seaweeds on the adipogenesis of ADSCs upon treatment with palmitic acid (PA). First, we showed the differentiation capability of ADSCs from morbid obesity patients to transform into different cell types. Second, we found that the co-treatment of ADSCs with HS-Fx and PA showed no significant cytotoxicity against ADSCs, but PA induced the elevation of reactive oxygen species (ROS) and lipid droplet accumulation was abolished. Thirdly, the PA-mediated down-regulation of lipid metabolism genes was reversed by the treatment of HS-Fx. By long non-coding RNAs (lncRNAs) screening, we found that PA-induced increases in the targeted lncRNAs were also decreased upon treatment with HS-Fx. On Silencing, these lncRNAs corresponded to the decrease in the lipid droplet accumulation of ADSCs induced by PA. ADSCs from obese patients would be direct and meaningful model cells to investigate the development of obesity-related diseases and their treatments, rather than cell lines from other species. HS-Fx showed anti-obesity capability through modulating the elevation of ROS, down-regulation of lipid metabolism genes induced by PA, and upstream signaling, which might be critically resulted from the expression of lncRNAs.

Essential role of Nrf2 in the protective effect of lipoic acid against lipoapoptosis in hepatocytes

Excess of saturated free fatty acids, such as palmitic acid (PA), in hepatocytes has been implicated in nonalcoholic fatty liver disease. α-Lipoic acid (LA) is an antioxidant that protects against oxidative stress conditions. We have investigated the effects of LA in the early activation of oxidative and endoplasmic reticulum stress, lipid accumulation, and Nrf2-mediated antioxidant defenses in hepatocytes treated with PA or in rats fed a high-fat diet. In primary human hepatocytes, a lipotoxic concentration of PA triggered endoplasmic reticulum stress, induced the apoptotic transcription factor CHOP, and increased the percentage of apoptotic cells. Cotreatment with LA prevented these effects. Similar results were found in mouse hepatocytes in which LA attenuated PA-mediated activation of caspase 3 and reduced lipid accumulation by decreasing PA uptake and increasing fatty acid oxidation and lipophagy, thereby preventing lipoapoptosis. Moreover, LA augmented the proliferation capacity of hepatocytes after PA challenge. Antioxidant effects of LA ameliorated reactive oxygen species production and endoplasmic reticulum stress and protected against mitochondrial apoptosis in hepatocytes treated with PA. Cotreatment with PA and LA induced an early nuclear translocation of Nrf2 and activated antioxidant enzymes, whereas reduction of Nrf2 by siRNA abolished the benefit of LA on PA-induced lipoapoptosis. Importantly, posttreatment with LA reversed the established damage induced by PA in hepatocytes, as well as preventing obesity-induced oxidative stress and lipoapoptosis in rat liver. In conclusion, our work has revealed that in hepatocytes, Nrf2 is an essential early player in the rescue of oxidative stress by LA leading to protection against PA-mediated lipoapoptosis.

Microcystin-LR altered mRNA and protein expression of endoplasmic reticulum stress signaling molecules related to hepatic lipid metabolism abnormalities in mice

To explore the effects of microcystin-LR (MC-LR), a hepatotoxin, on the incidence of liver lipid metabolism abnormality, and the potential molecular mechanisms of action, healthy male Balb/c mice were intraperitoneally injected with MC-LR at doses of 0, 5, 10, and 20 μg/kg/d for 14 days. Hepatic histopathology and serum lipid parameters of mice were determined, and the changes of mRNA and protein expression of endoplasmic reticulum (ER) stress signaling molecules related to the lipid metabolism abnormalities in the livers of mice were investigated by quantitative real-time polymerase chain reaction (qPCR) and Western blotting, respectively. The results indicated that 5-20 μg/kg/d MC-LR altered serum lipid parameters and caused hepatic steatosis. MC-LR treatment at 10 or 20 μg/kg/d changed mRNA and protein expression of ER stress signaling molecules, including upregulation of mRNA and protein expression of activating transcription factor 6 (ATF6), pancreatic ER eukaryotic translation initiation factor 2α (eIF-2α) kinase (PERK), and eIF-2α. MC-LR exposure at 10 or 20 μg/kg/d also altered mRNA and protein expression of downstream factors and genes of ER stress signaling pathways, including the downregulation of sterol regulatory element binding protein 1c (SREBP-1c) and fatty acid synthase (FASn), and upregulation of acetyl-coenzyme A carboxylase α (ACACA) and glycogen synthase kinase 3β (Gsk-3β). Our results reveal that ER stress plays a significant role in hepatic lipid metabolism abnormalities in mice exposed to MC-LR.

Neural innervation of white adipose tissue and the control of lipolysis

White adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS) and its activation is necessary for lipolysis. WAT parasympathetic innervation is not supported. Fully-executed SNS-norepinephrine (NE)-mediated WAT lipolysis is dependent on β-adrenoceptor stimulation ultimately hinging on hormone sensitive lipase and perilipin A phosphorylation. WAT sympathetic drive is appropriately measured electrophysiologically and neurochemically (NE turnover) in non-human animals and this drive is fat pad-specific preventing generalizations among WAT depots and non-WAT organs. Leptin-triggered SNS-mediated lipolysis is weakly supported, whereas insulin or adenosine inhibition of SNS/NE-mediated lipolysis is strongly supported. In addition to lipolysis control, increases or decreases in WAT SNS drive/NE inhibit and stimulate white adipocyte proliferation, respectively. WAT sensory nerves are of spinal-origin and sensitive to local leptin and increases in sympathetic drive, the latter implicating lipolysis. Transsynaptic viral tract tracers revealed WAT central sympathetic and sensory circuits including SNS-sensory feedback loops that may control lipolysis.

Antidiabetic effect of the α-lipoic acid γ-cyclodextrin complex

In recent years, the number of patients suffering from diabetes mellitus has been increasing worldwide. In particular, type 2 diabetes mellitus, a lifestyle-related disease, is recognized as a serious disease with various complications. Many types of pharmaceutics or specific health foods have been used for the management of diabetes mellitus. At the same time, the relationship between diabetes mellitus and α-lipoic acid has been recognized for many years. In this study, we found that the α-lipoic acid γ-cyclodextrin complex exhibited an HbA_1c lowering effect for treating type 2 diabetes mellitus in animal models. Moreover, in this study, we investigated the activation of phosphorylation of AMP-activated protein kinase, which plays a role in cellular energy homeostasis, in the liver of KKA^y mice by using α-lipoic acid and the α-lipoic acid γ-cyclodextrin complex. Our results show that the α-lipoic acid γ-cyclodextrin complex strongly induced the phosphorylation of AMP-activated protein kinase. Thus, we concluded that intake of the α-lipoic acid γ-cyclodextrin complex exerted an antidiabetic effect by suppressing the elevation of postprandial hyperglycemia as well as doing exercise.

Alpha-lipoic acid improves high-fat diet-induced hepatic steatosis by modulating the transcription factors SREBP-1, FoxO1 and Nrf2 via the SIRT1/LKB1/AMPK pathway

Understanding the mechanism by which alpha-lipoic acid supplementation has a protective effect upon nonalcoholic fatty liver disease in vivo and in vitro may lead to targets for preventing hepatic steatosis. Male C57BL/6J mice were fed a normal diet, high-fat diet or high-fat diet supplemented with alpha-lipoic acid for 24 weeks. HepG2 cells were incubated with normal medium, palmitate or alpha-lipoic acid. The lipid-lowering effects were measured. The protein expression and distribution were analyzed by Western blot, immunoprecipitation and immunofluorescence, respectively. We found that alpha-lipoic acid enhanced sirtuin 1 deacetylase activity through liver kinase B1 and stimulated AMP-activated protein kinase. By activating the sirtuin 1/liver kinase B1/AMP-activated protein kinase pathway, the translocation of sterol regulatory element-binding protein-1 into the nucleus and forkhead box O1 into the cytoplasm was prevented. Alpha-lipoic acid increased adipose triacylglycerol lipase expression and decreased fatty acid synthase abundance. In in vivo and in vitro studies, alpha-lipoic acid also increased nuclear NF-E2-related factor 2 levels and downstream target amounts via the sirtuin 1 pathway. Alpha-lipoic acid eventually reduced intrahepatic and serum triglyceride content. The protective effects of alpha-lipoic acid on hepatic steatosis appear to be associated with the transcription factors sterol regulatory element-binding protein-1, forkhead box O1 and NF-E2-related factor 2.

Cellular mechanisms regulating fuel metabolism in mammals: role of adipose tissue and lipids during prolonged food deprivation

Food deprivation in mammals results in profound changes in fuel metabolism and substrate regulation. Among these changes are decreased reliance on the counter-regulatory dynamics by insulin-glucagon due to reduced glucose utilization, and increased concentrations of lipid substrates in plasma to meet the energetic demands of peripheral tissues. As the primary storage site of lipid substrates, adipose tissue must then be a primary contributor to the regulation of metabolism in food deprived states. Through its regulation of lipolysis, adipose tissue influences the availability of carbohydrate, lipid, and protein substrates. Additionally, lipid substrates can act as ligands to various nuclear receptors (retinoid x receptor (RXR), liver x receptor (LXR), and peroxisome proliferator-activated receptor (PPAR)) and exhibit prominent regulatory capabilities over the expression of genes involved in substrate metabolism within various tissues. Therefore, through its control of lipolysis, adipose tissue also indirectly regulates the utilization of metabolic substrates within peripheral tissues. In this review, these processes are described in greater detail and the extent to which adipose tissue and lipid substrates regulate metabolism in food deprived mammals is explored with comments on future directions to better assess the contribution of adipose tissue to metabolism.

Inhibition of LXRα/SREBP-1c-Mediated Hepatic Steatosis by Jiang-Zhi Granule

Nonalcoholic fatty liver (NAFL) is increasingly recognized as one of the most common causes of chronic liver disease worldwide. Traditional Chinese medicine (TCM), as the alternative and complementary medicine, may provide some profound health benefit. “Jiang-Zhi” Granule (JZG) was composed based on TCM pathogenesis of NAFL: the retention of inner dampness, heat and blood stasis. This study investigated effects of JZG on liver X receptor-α (LXRα)/sterol regulatory element binding protein-1c (SREBP-1c) pathway in high-fat-diet-(HFD-)induced hepatic steatosis, as well as in free-fatty-acid-(FFA-)and T0901317-treated HepG2 cells. The results showed that JZG had an antisteatotic effect on HFD-fed rats. JZG decreased the activation of SREBP-1c through inhibiting LXRα-mediated SREBP-1c transcription, as well as through inhibiting the maturation of SREBP-1c independent of LXRα. These findings may provide molecular evidence for the use of JZG as a promising therapeutic option for NAFL and support us to continue JZG treatment in NAFL. For JZG treatment to be widely accepted, a randomized, double-blind, multicenter, placebo-controlled, phase III trial is ongoing.