Alpha-lipoic acid attenuates adipocyte differentiation and lipid accumulation in 3T3-L1 cells via AMPK-dependent autophagy

α-lipoic acid ameliorates consequences of copper overload by up-regulating selenoproteins and decreasing redox misbalance

α-lipoic acid (LA) is an essential cofactor for mitochondrial dehydrogenases and is required for cell growth, metabolic fuel production, and antioxidant defense. In vitro, LA binds copper (Cu) with high affinity and as an endogenous membrane permeable metabolite could be advantageous in mitigating the consequences of Cu overload in human diseases. We tested this hypothesis in 3T3-L1 preadipocytes with inactivated Cu transporter Atp7a; these cells accumulate Cu and show morphologic changes and mitochondria impairment. Treatment with LA corrected the morphology of Atp7a-/- cells similar to the Cu chelator bathocuproinedisulfonate (BCS) and improved mitochondria function; however, the mechanisms of LA and BCS action were different. Unlike BCS, LA did not decrease intracellular Cu but instead increased selenium levels that were low in Atp7a-/- cells. Proteome analysis confirmed distinct cell responses to these compounds and identified upregulation of selenoproteins as the major effect of LA on preadipocytes. Upregulation of selenoproteins was associated with an improved GSH:GSSG ratio in cellular compartments, which was lowered by elevated Cu, and reversal of protein oxidation. Thus, LA diminishes toxic effects of elevated Cu by improving cellular redox environment. We also show that selenium levels are decreased in tissues of a Wilson disease animal model, especially in the liver, making LA an attractive candidate for supplemental treatment of this disease.

Alpha-lipoic acid inhibits sodium arsenite-mediated autophagic death of rat insulinoma cells

AIM

To investigate the protective effect of α-lipoic acid on sodium arsenite (NaAsO₂) induced INS-1 cells injury and its mechanism.

METHODS

The cell viability was measured by CCK-8 assay. The autophagosomes was observed under transmission electron microscopy. The autophagosomes in cells transfected with green fluorescent protein microtubule-associated protein light chain 3 (GFP-LC3) plasmids were observed under a laser scanning con-focal microscope. The expression of LC3-II, P62, PI3K, and mTOR proteins in INS-1 cells treated with a combination of chloroquine (CQ, autophagy inhibitor) and NaAsO₂ were detected by Western blot assay. The expression of LC3-II, P62, PI3K, and mTOR proteins were detected in INS-1 cells treated with a combination of rapamycin (autophagy inducer, mTOR inhibitor) and α-LA.

RESULTS

The cytotoxicity induced by NaAsO₂ was reversed by α-LA, and the viability of NaAsO₂-treated INS-1 cells increased. α-LA pretreatment decreased the autophagosome accumulation induced by NaAsO_2. α-LA also reduced the fluorescence spot aggregation of GFP-LC3 in INS-1 cells exposed to NaAsO₂ as observed under a laser scanning con-focal microscope. α-LA inhibited NaAsO₂ induced autophagy by up-regulating PI3K and mTOR and down-regulating LC3-II and P62. CQ inhibited NaAsO₂ induced autophagy by up-regulating PI3K, mTOR, P62 and down-regulating LC3-II. α-LA inhibited rapamycin-induced autophagy by up-regulating PI3K, mTOR and P62 and down-regulating LC3-II. The results showed that NaAsO₂ could induce autophagy activation in INS-1 cells. The α-LA may inhibit autophagy activation by regulating the PI3K/mTOR pathway.

CONCLUSION

The data indicated that α-LA might inhibit the NaAsO₂-induced autophagic death of INS-1 cells by regulating the PI3K/mTOR pathway.

Bioactive compounds in childhood obesity and associated metabolic complications: Current evidence, controversies and perspectives

Obesity represents the most frequent chronic disease among children worldwide, with a significant global burden on society. Metabolically unhealthy obesity (MUO) can affect children since their first years of life, and novel therapeutic strategies to tackle metabolic complications are under investigation. This review focuses on bioactive compounds and their possible beneficial effects on obesity, particularly omega-3, docosahexaenoic acid, vitamin D, biotics, polysaccharide macromolecules, polyphenols, inositols, alpha lipoic acid, and bromelaine. Our aim is to summarize current evidence about bioactive compounds in the treatment of obesity, highlighting recent findings on their use in children and adolescents. Most studied molecules are omega-3 and vitamin D, despite the heterogeneity between the studies. Moreover, given the emerging interest in the gut-brain axis in the link between metabolic health and microbiota, various studies on prebiotics, probiotics, synbiotics, postbiotics and polysaccharide macromolecules have been considered. Some preclinical studies seem to highlight a possible role of the polyphenols, even if their clinical evidence is still discussed. Lastly, we describe possible effects of inositols and alpha-lipoic acid. Despite some dietary supplements seem to be promising in overweight subjects, only in a few of them a dose/response efficacy has been found in the pediatric age. Innovative, well-designed and targeted clinical trials are then needed to prove the beneficial effects of these compounds that could support the standard behavioral therapy for obesity.

Emerging Roles of Lipophagy in Cancer Metastasis

Simple Summary

Metastasis is the main cause of death in patients with malignant tumors worldwide. Mounting evidence suggests lipid droplet metabolism is involved in the process of metastasis. As a mechanism to selectively degrade lipid droplets, the current research on lipophagy and tumor metastasis is quite limited. This review summarizes the crosstalk among lipophagy, tumor lipid metabolism and cancer metastasis, which will provide a new reference for the development of effective targeted drugs.

Abstract

Obesity is a prominent risk factor for certain types of tumor progression. Adipocytes within tumor stroma contribute to reshaping tumor microenvironment (TME) and the metabolism and metastasis of tumors through the production of cytokines and adipokines. However, the crosstalk between adipocytes and tumor cells remains a major gap in this field. Known as a subtype of selective autophagy, lipophagy is thought to contribute to lipid metabolism by breaking down intracellular lipid droplets (LDs) and generating free fatty acids (FAs). The metastatic potential of cancer cells closely correlates with the lipid degradation mechanisms, which are required for energy generation, signal transduction, and biosynthesis of membranes. Here, we discuss the recent advance in the understanding of lipophagy with tumor lipid metabolism and review current studies on the roles of lipoghagy in the metastasis of certain human malignancies. Additionally, the novel candidate drugs targeting lipophagy are integrated for effective treatment strategies.

GPR43 activation-mediated lipotoxicity contributes to podocyte injury in diabetic nephropathy by modulating the ERK/EGR1 pathway

Background: G-protein-coupled receptor 43 (GPR43) is a posttranscriptional regulator involved in cholesterol metabolism. This study aimed to investigate the possible roles of GPR43 activation in podocyte lipotoxicity in diabetic nephropathy (DN) and explore the potential mechanisms.

Methods: The experiments were conducted by using diabetic GPR43-knockout mice and a podocyte cell culture model. Lipid deposition and free cholesterol levels in kidney tissues were measured by BODIPY staining and quantitative cholesterol assays, respectively. The protein expression of GPR43, LC3II, p62, beclin1, low-density lipoprotein receptor (LDLR) and early growth response protein 1 (EGR1) in kidney tissues and podocytes was measured by real-time PCR, immunofluorescent staining and Western blotting.

Results: There were increased LDL cholesterol levels in plasma and cholesterol accumulation in the kidneys of diabetic mice. However, GPR43 gene knockout inhibited these changes. An in vitro study further demonstrated that acetate treatment induced cholesterol accumulation in high glucose-stimulated podocytes, which was correlated with increased cholesterol uptake mediated by LDLR and reduced cholesterol autophagic degradation, as characterized by the inhibition of LC3 maturation, p62 degradation and autophagosome formation. Gene knockdown or pharmacological inhibition of GPR43 prevented these effects on podocytes. Furthermore, GPR43 activation increased extracellular regulated protein kinases 1/2 (ERK1/2) activity and EGR1 expression in podocytes, which resulted in an increase in cholesterol influx and autophagy inhibition. In contrast, after GPR43 deletion, these changes in podocytes were improved, as shown by the in vivo and in vitro results.

Conclusion: GPR43 activation-mediated lipotoxicity contributes to podocyte injury in DN by modulating the ERK/EGR1 pathway.

Nutraceuticals as Modulators of Autophagy: Relevance in Parkinson’s Disease

Dietary supplements and nutraceuticals have entered the mainstream. Especially in the media, they are strongly advertised as safe and even recommended for certain diseases. Although they may support conventional therapy, sometimes these substances can have unexpected side effects. This review is particularly focused on the modulation of autophagy by selected vitamins and nutraceuticals, and their relevance in the treatment of neurodegenerative diseases, especially Parkinson’s disease (PD). Autophagy is crucial in PD; thus, the induction of autophagy may alleviate the course of the disease by reducing the so-called Lewy bodies. Hence, we believe that those substances could be used in prevention and support of conventional therapy of neurodegenerative diseases. This review will shed some light on their ability to modulate the autophagy.

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.

Adipose and non-adipose perspectives of plant derived natural compounds for mitigation of obesity

ETHNOPHARMACOLOGICAL RELEVANCE

Phyto-preparations and phyto-compounds, by their natural origin, easy availability, cost-effectiveness, and fruitful traditional uses based on accumulated experiences, have been extensively explored to mitigate the global burden of obesity.

AIM OF THIS REVIEW

The review aimed to analyse and critically summarize the prospect of future anti-obesity drug leads from the extant array of phytochemicals for mitigation of obesity, using adipose related targets (adipocyte formation, lipid metabolism, and thermogenesis) and non-adipose targets (hepatic lipid metabolism, appetite, satiety, and pancreatic lipase activity). Phytochemicals as inhibitors of adipocyte differentiation, modulators of lipid metabolism, and thermogenic activators of adipocytes are specifically discussed with their non-adipose anti-obesogenic targets.

MATERIALS AND METHODS

PubMed, Google Scholar, Scopus, and SciFinder were accessed to collect data on traditional medicinal plants, compounds derived from plants, their reported anti-obesity mechanisms, and therapeutic targets. The taxonomically accepted name of each plant in this review has been vetted from "The Plant List" (www.theplantlist.org) or MPNS (http://mpns.kew.org).

RESULTS

Available knowledge of a large number of phytochemicals, across a range of adipose and non-adipose targets, has been critically analysed and delineated by graphical and tabular depictions, towards mitigation of obesity. Neuro-endocrinal modulation in non-adipose targets brought into sharp dual focus, both non-adipose and adipose targets as the future of anti-obesity research. Numerous phytochemicals (Berberine, Xanthohumol, Ursolic acid, Guggulsterone, Tannic acid, etc.) have been found to be effectively reducing weight through lowered adipocyte formation, increased lipolysis, decreased lipogenesis, and enhanced thermogenesis. They have been affirmed as potential anti-obesity drugs of future because of their effectiveness yet having no threat to adipose or systemic insulin sensitivity.

CONCLUSION

Due to high molecular diversity and a greater ratio of benefit to risk, plant derived compounds hold high therapeutic potential to tackle obesity and associated risks. This review has been able to generate fresh perspectives on the anti-diabetic/anti-hyperglycemic/anti-obesity effect of phytochemicals. It has also brought into the focus that many phytochemicals demonstrating in vitro anti-obesogenic effects are yet to undergo in vivo investigation which could lead to potential phyto-molecules for dedicated anti-obesity action.

R-α-Lipoic Acid and 4-Phenylbutyric Acid Have Distinct Hypolipidemic Mechanisms in Hepatic Cells

The constitutive activation of the mechanistic target of rapamycin complex 1 (mTORC1) leads to the overproduction of apoB-containing triacylglycerol-rich lipoproteins in HepG2 cells. R-α-lipoic acid (LA) and 4-phenylbutyric acid (PBA) have hypolipidemic function but their mechanisms of action are not well understood. Here, we reported that LA and PBA regulate hepatocellular lipid metabolism via distinct mechanisms. The use of SQ22536, an inhibitor of adenylyl cyclase, revealed cAMP’s involvement in the upregulation of CPT1A expression by LA but not by PBA. LA decreased the secretion of proprotein convertase subtilisin/kexin type 9 (PCSK9) in the culture media of hepatic cells and increased the abundance of LDL receptor (LDLR) in cellular extracts in part through transcriptional upregulation. Although PBA induced LDLR gene expression, it did not translate into more LDLR proteins. PBA regulated cellular lipid homeostasis through the induction of CPT1A and INSIG2 expression via an epigenetic mechanism involving the acetylation of histone H3, histone H4, and CBP-p300 at the CPT1A and INSIG2 promoters.

Evaluation of a cell model expressing βKlotho for screening FGF21 analogues

βKlotho as the major role is a necessary auxiliary protein when fibroblast growth factor 21 (FGF21) binds FGF21 receptors (FGFR) for activating intracellular signaling pathways that ultimately generate biological effects. To achieve the aim of high throughput screening of FGF21 analogues, we established 3T3-L1-βKlotho cells that could stably express βklotho protein. The glucose uptake, expression of GLUT1 mRNA and activation of FGF signaling molecules ERK1/2 phosphorylation were detected by GOD-POD assay, real-time PCR analysis and western blotting assay in 3T3-L1-βKlotho cells and 3T3-L1 adipocytes, respectively. The results showed that FGF21 increased glucose uptake significantly in a dose-dependent and time-dependent manner in 3T3-L1-βKlotho cells. 3T3-L1-βKlotho cells stimulated with FGF21 up-regulated the transcriptional levels of GLUT1 mRNA obviously. FGF21 activated the FGF signaling molecules ERK1/2 in 3T3-L1-βKlotho cells. In addition, the same results were obtained in 3T3-L1 adipocytes. Furthermore, FGF21-stimulated elevation of glucose uptake, GLUT1 mRNA transcription and the phosphorylation of ERK1/2 were dramatically attenuated by pretreatment of cells with FGFR specific inhibitor SU5402 in 3T3-L1-βKlotho cells. This study demonstrated that the cell model could be applied to high throughput screen FGF21 analogues.

[Role of lipophagy in the regulation of lipid metabolism and the molecular mechanism]

Recent studies have discovered a selective autophagy-lipophagy, which can selectively identify and degrade lipids and plays an important role in regulating cellular lipid metabolism and maintaining intracellular lipid homeostasis. The process of lipophagy can be directly or indirectly regulated by genes, enzymes, transcriptional regulators and other factors. This review examines the role of lipophagy in reducing liver lipid content, regulating pancreatic lipid metabolism, and regulating adipose tissue differentiation, and summarizes the findings of the molecules (Rab GTPase, enzymes, ion channels, transcription factors, small molecular substances) involved in the regulation of lipophagy, which points to new directions for the treatment of diseases caused by lipid accumulation.

α‑lipoic acid protects against carbon tetrachloride‑induced liver cirrhosis through the suppression of the TGF‑β/Smad3 pathway and autophagy

α-lipoic acid (ALA) is a naturally occurring antioxidant with protective effects against various hepatic injuries. The aim of the present study was to investigate the mechanisms by which ALA protects the liver from carbon tetrachloride (CCl₄)-induced liver cirrhosis. The widely used liver cirrhosis rat model was established via an intraperitoneal injection of 2 mg/kg 50% CCl_4, three times/week for 8 weeks. Simultaneously, 50 or 100 mg/kg ALA was orally administrated to the rats every day for 8 weeks. The activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was detected in the serum. The pathological liver injuries were analyzed using hematoxylin and eosin and Masson's trichrome staining. The principal factors involved in the transforming growth factor-β (TGF-β)/mothers against decapentaplegic homolog 9 (Smad3) and protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathways and in autophagy were examined using reverse transcription-quantitative polymerase chain reaction or western blot analysis. The results demonstrated that the administration of ALA alleviated CCl₄-induced liver injury, as demonstrated by decreased ALT and AST activity, improved pathological injuries and reduced collagen deposition. The CCl4-induced increase in TGF-β and phosphorylated-Smad3 expression levels was additionally inhibited by treatment with ALA. Furthermore, the administration of ALA reversed the CCl₄-induced upregulation of light chain 3II and Beclin-1, and downregulation of p62. The CCl₄-induced suppression of the AKT/mTOR pathway was additionally restored following treatment with ALA. In combination, the results of the present study demonstrated that ALA was able to protect CCl₄-induced liver cirrhosis, an effect that may be associated with inactivation of the TGF-β/Smad3 pathway and suppression of autophagy.

α, β-Amyrin, a pentacyclic triterpenoid from Protium heptaphyllum suppresses adipocyte differentiation accompanied by down regulation of PPARγ and C/EBPα in 3T3-L1 cells

Previous studies have reported the anti-obesity effects of α, β-Amyrin in high fat-fed mice. This study aimed to evaluate whether α, β-Amyrin has an anti-adipogenic effect in 3T3-L1 murine adipocytes and to explore the possible underlying mechanisms. 3T3-L1 pre-adipocytes were differentiated in a medium containing insulin, dexamethasone, and 1-methyl-3-isobutylxanthine. Cytotoxicity of α, β-Amyrin was assessed by MTT assay. Lipid content in adipocytes was determined by Oil-Red O staining. In addition, the protein expression levels of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer binding proteins alpha (C/EBPα), beta (C/EBPβ), and delta (C/EBPδ) and glucose transporter 4 (GLUT4) were determined by qRT-PCR and western blot analysis. Oil-Red O staining revealed markedly reduced fat accumulation by α, β-Amyrin (6.25-50 μg/mL) without affecting cell viability. Furthermore, our results indicate that α, β-Amyrin can significantly suppress the adipocyte differentiation by downregulating the expression levels of adipogenesis-related key transcription factors such as PPARγ and C/EBPα, but not C/EBPβ or C/EPBδ. In addition, the protein expression of membrane GLUT4 in 3T3- L1 adipocytes treated with α, β-Amyrin was significantly higher than in control cells, indicating that α, β-Amyrin augments glucose uptake. These findings suggest that α, β-Amyrin exerts an anti-adipogenic effect principally via modulation of lipid and carbohydrate metabolism in 3T3-L1cells. The present in vitro findings, taken together with our earlier observation of the anti-obesity effect in vivo, suggest that α, β-Amyrin can be developed as a new therapeutic agent for treatment and prevention of obesity.

p62 is linked to mitophagy in oleic acid-induced adipogenesis in human adipose-derived stromal cells

BACKGROUND

Obesity is closely related to the abnormal differentiation of adipocytes, which are subjected to high plasma levels of free fatty acids (FFAs). As the most abundant FFA in the bloodstream, oleic acid (OA) has the ability to induce adipogenic differentiation in human adipose-derived stromal cells (hADSCs). Recently, p62, an autophagy mediator, has been shown to play a role in obesity and adipose tissue metabolism. Therefore, the aim of this study was to investigate the roles of autophagy and mitochondrial function at different stages of OA (in combination with insulin and dexamethasone)-induced adipogenesis in hADSCs.

METHODS

The hADSCs were incubated with OA, insulin, and dexamethasone after pretreatment with autophagy inhibitors or knockdown of p62 with shRNA. The adiposeness level was then analyzed by oil red O staining in the cells. The related proteins or mRNA levels were detected by western blot analysis or quantitative real-time polymerase chain reaction (PCR).

RESULTS

Treatment with 80 μM OA (substituted for isobutylmethylxantine; IBMX) for 10 days successfully induced hADSCs to adipocytes. During OA-induced adipogenesis, autophagy was induced, with an increased LC3II/I ratio on day 3 and a decreased protein level of p62 on and after day 3. Inhibition of autophagy with 3-methyladenine (3MA) at the early stage (day 0 to day 3) of differentiation, but not at the middle or late stage, significantly decreased OA-induced adipogenesis; while knockdown of p62 with shRNA significantly promoted adipogenesis in hADSCs. Moreover, the copy number of mtDNA (the ND1 gene) and the protein level of TOM20, a mitochondrial membrane protein, were increased following OA treatment, which was related to the stability of mitochondria. Interestingly, knockdown of p62 increased the mito-LC3II/I and cyto-LC3II/I ratios by 110.1% and 73.3%, respectively. The increase in the ratio of mito-LC3II/I was higher than that of cyto-LC3II/I. Furthermore, p62 knockdown-enhanced adipogenesis in hADSCs was abolished by inhibiting mitophagy with cyclosporine A.

CONCLUSIONS

These results suggested that p62 plays a protective role in adipogenesis of hADSCs through regulating mitophagy.

Glucocorticoid-activated IRE1α/XBP-1s signaling: an autophagy-associated protective pathway against endotheliocyte damage

Glucocorticoid-induced endothelial injury has been reported in several diseases. Although there are several theories, the exact mechanism underlying the role of glucocorticoids in this process remains unclear. Autophagy has been reported to occur as a response to different stimuli and can affect cell survival and function. In this study, we found that glucocorticoids induced apoptosis and endoplasmic reticulum (ER) stress in endotheliocytes. Furthermore, we discovered that glucocorticoids induced autophagy in these cells and the inositol requiring protein 1 (IRE1α)/X-box binding protein 1s (XBP-1s) axis, one of the downstream signaling pathways of ER stress, was associated with the glucocorticoid-induced autophagy. The autophagy partly protected endotheliocytes from glucocorticoid-induced apoptosis and inhibition of proliferation. In conclusion, glucocorticoid-induced endoplasmic reticulum stress activated the IRE1α/XBP-1s signaling and induced autophagy, which, in turn, played a protective role in endotheliocyte survival and proliferation, avoiding further cellular damage caused by glucocorticoids.

Natural products as modulator of autophagy with potential clinical prospects

Natural compounds derived from living organisms are well defined for their remarkable biological and pharmacological properties likely to be translated into clinical use. Therefore, delving into the mechanisms by which natural compounds protect against diverse diseases may be of great therapeutic benefits for medical practice. Autophagy, an intricate lysosome-dependent digestion process, with implications in a wide variety of pathophysiological settings, has attracted extensive attention over the past few decades. Hitherto, accumulating evidence has revealed that a large number of natural products are involved in autophagy modulation, either inducing or inhibiting autophagy, through multiple signaling pathways and transcriptional regulators. In this review, we summarize natural compounds regulating autophagy in multifarious diseases including cancer, neurodegenerative diseases, cardiovascular diseases, metabolic diseases, and immune diseases, hoping to inspire further investigation of the underlying mechanisms of natural compounds and to facilitate their clinical use for multiple human diseases.

Raspberry Ketone Reduced Lipid Accumulation in 3T3-L1 Cells and Ovariectomy-Induced Obesity in Wistar Rats by Regulating Autophagy Mechanisms

This study aimed to determine the antiobesity effects of raspberry ketone (RK), one of the major aromatic compounds contained in raspberry, and its underlying mechanisms. During adipogenesis of 3T3-L1 cells, RK (300 μM) significantly reduced lipid accumulation and downregulated the expression of CCAAT/enhancer-binding protein α (C/EBPα), peroxisome proliferation-activated receptor γ (PPARγ), fatty acid-binding protein 4 (FABP4), and fatty acid synthase (FAS). RK also reduced the expression of light chain 3B (LC3B), autophagy-related protein 12 (Atg12), sirtuin 1 (SIRT1), and phosphorylated-tuberous sclerosis complex 2 (TSC2), whereas it increased the level of p62 and phosphorylated-mammalian target of rapamycin (mTOR). Daily administration of RK decreased the body weight (ovariectomy [Ovx] + RK, 352.6 ± 5 vs Ovx, 386 ± 5.8 g; P < 0.05), fat mass (Ovx + RK, 3.2 ± 0.05 vs Ovx, 5.0 ± 0.4 g; P < 0.05), and fat cell size (Ovx + RK, 6.4 ± 0.6 vs Ovx, 11.1 ± 0.7 × 10³ μm²; P < 0.05) in Ovx-induced obesity in rats. The expression of PPARγ, C/EBPα, FAS, and FABP4 was significantly reduced in the Ovx + RK group compared with that in the Ovx group. Similar patterns were observed in autophagy-related proteins and endoplasmic reticulum stress proteins. These results suggest that RK inhibited lipid accumulation by regulating autophagy in 3T3-L1 cells and Ovx-induced obese rats.

RKIP phosphorylation-dependent ERK1 activation stimulates adipogenic lipid accumulation in 3T3-L1 preadipocytes overexpressing LC3

3T3-L1 preadipocytes undergo adipogenesis in response to treatment with dexamethaxone, 1-methyl-3-isobutylxanthine, and insulin (DMI) through activation of several adipogenic transcription factors. Many autophagy-related proteins are also highly activated in the earlier stages of adipogenesis, and the LC3 conjugation system is required for formation of lipid droplets. Here, we investigated the effect of overexpression of green fluorescent protein (GFP)-LC3 fusion protein on adipogenesis. Overexpression of GFP-LC3 in 3T3-L1 preadipocytes using poly-l-lysine-assisted adenoviral GFP-LC3 transduction was sufficient to produce intracellular lipid droplets. Indeed, GFP-LC3 overexpression stimulated expression of some adipogenic transcription factors (e.g., C/EBPα or β, PPARγ, SREBP2). In particular, SREBP2 was highly activated in preadipocytes transfected with adenoviral GFP-LC3. Also, phosphorylation of Raf kinase inhibitory protein (RKIP) at serine 153, consequently stimulating extracellular-signal regulated kinase (ERK)1 activity, was significantly increased during adipogenesis induced by either poly-l-lysine-assisted adenoviral GFP-LC3 transduction or culture in the presence of dexamethasone, 1-methyl-3-isobutylxanthine, and insulin. Furthermore, RKIP knockdown promoted ERK1 and PPARγ activation, and significantly increased the intracellular accumulation of triacylglycerides in DMI-induced adipogenesis. In conclusion, GFP-LC3 overexpression in 3T3-L1 preadipocytes stimulates adipocyte differentiation via direct modulation of RKIP-dependent ERK1 activity.

α-Lipoic Acids Promote the Protein Synthesis of C2C12 Myotubes by the TLR2/PI3K Signaling Pathway

Skeletal muscle protein turnover is regulated by endocrine hormones, nutrients, and inflammation. α-Lipoic acid (ALA) plays an important role in energy homeostasis. Therefore, the aim of this study was to investigate the effects of ALA on protein synthesis in skeletal muscles and reveal the underlying mechanism. ALA (25 μM) significantly increased the protein synthesis and phosphorylation of Akt, mTOR, and S6 in C2C12 myotubes with attenuated phosphorylation of AMPK, Ikkα/β, and eIF2α. Intraperitoneal injection of 50 mg/kg ALA also produced the same results in mouse gastrocnemius. Both the PI3K (LY294002) and mTOR (rapamycin) inhibitors abolished the effects of ALA on protein synthesis in the C2C12 myotubes. However, AICAR (AMPK agonist) failed to block the activation of mTOR and S6 by ALA. ALA increased TLR2 and MyD88 mRNA expression in the C2C12 myotubes. TLR2 knockdown by siRNA almost eliminated the effects of ALA on protein synthesis and the Akt/mTOR pathway in the C2C12 myotubes. Immunoprecipitation data showed that ALA enhanced the p85 subunit of PI3K binding to MyD88. These findings indicate that ALA induces protein synthesis and the PI3K/Akt signaling pathway by TLR2.

Inhibitory Effects of α-Lipoic Acid on Oxidative Stress-Induced Adipogenesis in Orbital Fibroblasts From Patients With Graves Ophthalmopathy

A choice of the optimal treatment for Graves ophthalmopathy (GO) is a challenge due to the complexity of the pathogenesis. Alpha-lipoic acid (ALA) is well known as a multifunctional antioxidant, helping to protect cells against oxidative stress and inflammatory damage.The aim of this study was to investigate the effects of ALA on intracellular production of reactive oxygen species (ROS), inflammation, and adipogenesis using primary cultured orbital fibroblasts from patients with GO.Intracellular ROS levels and mRNA expressions of proinflammatory cytokines and chemokines including intercellular adhesion molecule-1 (ICAM-1), interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, and regulated upon activation normal T cell expressed and presumably secreted (RANTES) were measured. After adipogenesis, the expressions of peroxisome proliferator-activated receptor (PPAR)γ, CCAAT-enhancer-binding proteins (C/EBP)α and β, and heme oxygenase-1 (HO-1) were investigated.H2O2 dose-dependently stimulated ROS production and HO-1 expression. Addition of ALA strongly attenuated ROS production and further increased HO-1 expression. However, by pretreatment of zinc protoporphyrin (ZnPP), HO-1 inhibitor, ALA inhibition of ROS generation by H2O2 was abolished. Tumor necrosis factor (TNF)α-induced mRNA expressions of ICAM-1, IL-6, MCP-1, and RANTES were inhibited by ALA treatment. In this context, TNFα-induced phosphorylation of P65 was also inhibited. In addition, ALA dose-dependently inhibited H2O2-induced intracellular accumulation of lipid droplets. The expression of adipogenic transcription factors, including PPARγ, C/EBPα, and β, was also inhibited.ALA is a potential therapeutic agent for GO because of the inhibitory effects on ROS production and gene expression of proinflammatory cytokines and chemokines, resulting in prevention of adipose-tissue expansion.

Lipoic acid inhibits the DNA repair protein O 6-methylguanine-DNA methyltransferase (MGMT) and triggers its depletion in colorectal cancer cells with concomitant autophagy induction

Alkylating agents are present in food and tobacco smoke, but are also used in cancer chemotherapy, inducing the DNA lesion O (6)-methylguanine. This critical adduct is repaired by O (6)-methylguanine-DNA methyltransferase (MGMT), resulting in MGMT inactivation and degradation. In the present study, we analyzed the effects of the natural disulfide compound lipoic acid (LA) on MGMT in vitro and in colorectal cancer cells. We show that LA, but not its reduced form dihydrolipoic acid, potently inhibits the activity of recombinant MGMT by interfering with its catalytic Cys-145 residue, which was partially reversible by N-acetyl cysteine. Incubation of HCT116 colorectal cancer cells with LA altered their glutathione pool and caused a decline in MGMT activity. This was mirrored by LA-induced depletion of MGMT protein, which was not attributable to changes in MGMT messenger RNA levels. Loss of MGMT protein coincided with LA-induced autophagy, a process resulting in lysosomal degradation of proteins, including presumably MGMT. LA-stimulated autophagy in a p53-independent manner as revealed by the response of isogenic HCT116 cell lines. Knockdown of the crucial autophagy component beclin-1 and chemical inhibitors blocked LA-induced autophagy, but did not abrogate LA-triggered MGMT degradation. Concomitant with MGMT depletion, LA pretreatment resulted in enhanced O (6)-methylguanine levels in DNA. It also increased the cytotoxicity of the alkylating anticancer drug temozolomide in temozolomide-resistant colorectal cancer cells. Taken together, our study showed that the natural compound LA inhibits MGMT and induces autophagy. Furthermore, LA enhanced the cytotoxic effects of temozolomide, which makes it a candidate for a supplement in cancer therapy.

Apoptotic events induced by high glucose in human hepatoma HepG2 cells involve endoplasmic reticulum stress and MAPK's activation

To investigate whether endoplasmic reticulum (ER) stress participates in the induction of apoptosis in HepG2 cells exposed to high glucose and explore its probable mechanism. A series of experiments were performed following HepG2 cells treated with different concentrations of glucose for 48 h. The apoptosis was detected by means of Hoechst staining and flow cytometry. Caspase-3 activity assay was performed by measuring the pNA (p-nitroaniline) to indirectly reveal the catalytic activity of caspase-3. The expression levels of apoptosis-, ER stress-associated proteins and MAPKs were analyzed by western blot. To further characterize the molecular mechanisms, the effects of antioxidant alpha-lipoic acid (ALA) and specific inhibitors for JNK and p38 (SP600125 and SB203580, respectively) were examined by Hoechst staining, immunofluorescence, and western blot. After HepG2 cells were incubated with high glucose for 48 h, both Hoechst staining and flow cytometry analyses unveiled the apoptosis of HepG2 cells. Caspase-3 activity assay revealed that the activity of caspase-3 was enhanced. Western blot showed an enhancement of pro-caspase-9 degradation, a reduction of Bcl-2/Bax ratio, a decrease in GRP78 expression, and increases in CHOP and p47/phox levels. In addition, western blot analysis presented that phosphorylation of p38 and JNK was triggered and that the expression of ASK1 was elevated. In the case of the contributions of oxidative stress and the MAPK signaling pathways, all ALA, SP600125 and SB203580 were able to largely rescue high glucose-induced apoptosis. High glucose induced the apoptosis in HepG2 cells through the activation of ASK1-p38/JNK pathway mediated by ER stress and oxidative stress.