Alpha-lipoic acid supplementation reduces mTORC1 signaling in skeletal muscle from high fat fed, obese Zucker rats

An mTOR inhibitor discovery system using drug-sensitized yeast

Inhibition of the target of rapamycin (TOR/mTOR) protein kinase by the drug rapamycin extends lifespan and health span across diverse species. However, rapamycin has potential off-target and side effects that warrant the discovery of additional TOR inhibitors. TOR was initially discovered in Saccharomyces cerevisiae (yeast) which contains two TOR paralogs, TOR1 and TOR2. Yeast lacking functional Tor1 are viable but are hypersensitive to growth inhibition by TORC1 inhibitors, which is a property of yeast that can be exploited to identify TOR inhibitors. Additionally, yeast lacking FK506-sensitive proline rotamase (FPR1) or containing a tor1-1 allele (a mutation in the Fpr1-rapamycin binding domain of Tor1) are robustly and selectively resistant to rapamycin and analogs that allosterically inhibit TOR activity via an FPR1-dependent mechanism. To facilitate the identification of TOR inhibitors, we generated a panel of yeast strains with mutations in TOR pathway genes combined with the removal of 12 additional genes involved in drug efflux. This creates a drug-sensitive strain background that can sensitively and effectively identify TOR inhibitors. In a wild-type yeast strain background, 25 µM of Torin1 and 100 µM of GSK2126458 (omipalisib) are necessary to observe TOR1-dependent growth inhibition by these known TOR inhibitors. In contrast, 100 nM Torin1 and 500 nM GSK2126458 (omipalisib) are sufficient to identify TOR1-dependent growth inhibition in the drug-sensitized background. This represents a 200-fold and 250-fold increase in detection sensitivity for Torin1 and GSK2126458, respectively. Additionally, for the TOR inhibitor AZD8055, the drug-sensitive system resolves that the compound results in TOR1-dependent growth sensitivity at 100 µM, whereas no growth inhibition is observed in a wild-type yeast strain background. Our platform also identifies the caffeine analog aminophylline as a TOR1-dependent growth inhibitor via selective tor1 growth sensitivity. We also tested nebivolol, isoliquiritigenin, canagliflozin, withaferin A, ganoderic acid A, and taurine and found no evidence for TOR inhibition using our yeast growth-based model. Our results demonstrate that this system is highly effective at identifying compounds that inhibit the TOR pathway. It offers a rapid, cost-efficient, and sensitive tool for drug discovery, with the potential to expedite the identification of new TOR inhibitors that could serve as geroprotective and/or anti-cancer agents.

Influence of maternal α-lipoic acid supplementation in Sprague Dawley rats on maternal and fetal metabolic health in pregnancies complicated by obesity

The objective of this study was to investigate the influence of α-lipoic acid (LA; R enantiomer) supplementation on maternal and fetal metabolic health in pregnancies complicated by maternal obesity. Forty female Sprague-Dawley rats were randomized to one of 4 treatment groups (n=10/group) throughout prepregnancy (3 weeks) and gestation (20 days): (1) a low calorie control (CON); (2) a high calorie obesity-inducing diet (HC); (3) the HC diet with 0.25% LA (HC+LA) or; (4) the HC diet pair-fed to match the caloric intake of the HC+LA group (HC+PF). On gestation day 20, pregnant rats were placed under anesthesia for collection of maternal/fetal blood and tissues. Compared with the HC group, LA-supplemented mothers demonstrated lower maternal prepregnancy and gestational weight gain (GWG), improved glycemic control (lower homeostatic model assessment for insulin resistance), and higher cholesterol concentrations in serum [high-density lipoprotein cholesterol (HDL-C) and low-and very-low density lipoprotein cholesterol (LDL/VLDL) fractions] and liver. Male and female fetuses from LA-supplemented mothers exhibited lower body weight, improved insulin sensitivity, and evidence of altered lipid metabolism including lower serum HDL-C, lower serum triglyceride (TG), and increased hepatic TG accumulation. Although maternal LA supplementation showed some benefit for both mothers and fetuses with respect to obesity and glycemic control, concern about the potential longer-term implications of liver cholesterol (mothers) and TG accumulation (fetuses) needs further investigation.

Metformin-induced TTP mediates communication between Kupffer cells and hepatocytes to alleviate hepatic steatosis by regulating lipophagy and necroptosis

OBJECTIVE

Emerging evidence suggests that crosstalk between Kupffer cells (KCs) and hepatocytes protects against non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms that lead to the reduction of steatosis in NAFLD remain obscure.

METHODS

Ttp^+/+ and Ttp^-/- mice were fed with a high-fat diet. Hepatic steatosis was analyzed by Nile Red staining and measurement of inflammatory cytokines. Lipid accumulation and cell death were evaluated in co-culture systems with primary hepatocytes and KCs derived from either Ttp^+/+ or Ttp^-/- mice.

RESULTS

Tristetraprolin (TTP), an mRNA binding protein, was essential for the protective effects of metformin in NAFLD. Metformin activated TTP via the AMPK-Sirt1 pathway in hepatocytes and KCs. TTP inhibited TNF-α production in KCs, which in turn decreased hepatocyte necroptosis. Downregulation of Rheb expression by TTP promoted hepatocyte lipophagy via mTORC1 inhibition and increased nuclear translocation of transcription factor-EB (TFEB). Consistently, TTP-deficient NAFLD mice failed to respond to metformin with respect to alleviation of hepatic steatosis, protection of hepatocyte necroptosis, or induction of lipophagy.

CONCLUSIONS

TTP, which is essential for the protective effects of metformin, may represent a novel primary therapeutic target in NAFLD.

Protective role of mitoquinone against impaired mitochondrial homeostasis in metabolic syndrome

Mitochondria control various processes in cellular metabolic homeostasis, such as adenosine triphosphate production, generation and clearance of reactive oxygen species, control of intracellular Ca²⁺ and apoptosis, and are thus a critical therapeutic target for metabolic syndrome (MetS). The mitochondrial targeted antioxidant mitoquinone (MitoQ) reduces mitochondrial oxidative stress, prevents impaired mitochondrial dynamics, and increases mitochondrial turnover by promoting autophagy (mitophagy) and mitochondrial biogenesis, which ultimately contribute to the attenuation of MetS conditions, including obesity, insulin resistance, hypertension and cardiovascular disease. The regulatory effect of MitoQ on mitochondrial homeostasis is mediated through AMPK and its downstream signaling pathways, including MTOR, SIRT1, Nrf2 and NF-κB. However, there are few reviews focusing on the critical role of MitoQ as a therapeutic agent in the treatment of MetS. The purpose of this review is to summarize the mitochondrial role in the pathogenesis of MetS, especially in obesity and type 2 diabetes, and discuss the effect and underlying mechanism of MitoQ on mitochondrial homeostasis in MetS.

Alpha-lipoic acid effect on leptin and adiponectin concentrations: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

New evidence suggests that dysregulation of adipocytokines caused by excess adiposity plays an important role in the pathogenesis of various obesity comorbidities. Our aim in this meta-analysis was to determine the effect of alpha-lipoic acid (ALA) supplementation on serum levels of leptin and adiponectin.

METHODS

We searched Scopus, PubMed, Google Scholar, and ISI Web of Science from inception up to July 2019. Mean difference for leptin and adiponectin were calculated by subtracting the change from baseline in each study group. Summary estimates for the overall effect of ALA on serum leptin and adiponectin concentrations were calculated using random effects model. Results were presented as weighted mean difference (WMD) and their 95% confidence intervals (CI). Between-study heterogeneity was examined using the I² statistics.

RESULT

Eight studies were included in systematic review and seven studies in meta-analysis. The overall effect suggested a significant decrement in serum leptin concentrations (WMD = - 3.63; 95% CI, - 5.63, - 1.64 μg/ml; I² = 80.7%) and a significant increase in serum levels of adiponectin (WMD = 1.98 μg/ml; 95% CI, 0.92, 3.04; I² = 95.7%). Subgroup analyses based on age showed a significant reduction in leptin levels only in younger adults, and subgroup analysis based on duration indicated in studies with a duration of more than 8 weeks adiponectin levels increased significantly and leptin levels decreased significantly.

CONCLUSION

Our results revealed ALA decreased leptin and increased adiponectin especially in studies lasted more than 8 weeks. We still need more studies with different ALA dose, intervention duration, and separately on male and female.

Alpha-lipoic acid preserves skeletal muscle mass in type 2 diabetic OLETF rats

Background

Increased oxidative stress and impaired antioxidant defense are important mechanisms in the pathogenesis of diabetic myopathy. Alpha-lipoic acid (ALA) has been indicated as a weight-loss treatment in rodents and humans, but studies are limited. In the present study, we aimed to determine the influence of ALA, a potent biological antioxidant, on metabolic and growth processes in diabetic rat skeletal muscle.

Methods

Male 25-week-old type 2 diabetic rats (OLETF) were randomly divided into two groups, a control group (OLETF-C) and an ALA-treated group (OLETF-ALA) supplemented with 100 mg/kg ALA for 8 weeks. Age-matched, healthy, nondiabetic LETO (LETO-C) rats were used as controls.

Results

At 32 weeks of age, body weight was decreased by 6.8%, and the areas under the curve of IP-GTT, fasting glucose, and insulin were less in OLETF-ALA rats compared with OLETF-C rats. ALA significantly preserved muscle mass and enhanced muscle fiber cross-sectional area and fiber frequency percentage in the skeletal muscle of OLETF rats. Although the activation of myoD, myogenin, and myostatin in gastrocnemius muscle was significantly inhibited in OLETF-ALA rats relative to OLETF-C rats, there were no differences in the expression levels of muscle atrogin-1 and MuRF1 between the two groups. ALA treatment significantly increased the levels of phosphorylated 5'-AMPK, SIRT1, and PGC-1α, as well as the levels of phosphorylated AKT, mTOR, and p70S6 kinase in OLETF-ALA rats compared with OLETF-C rats. In contrast, the levels of phosphorylated p38 MAPK, IRS-1, and FOXO1 were decreased in OLETF-ALA rats compared with OLETF-C rats.

Conclusions

ALA treatment preserved mass in the gastrocnemius muscles of OLETF rats. ALA significantly upregulated the AMPK/SIRT1/PGC-1α and AKT/mTOR/p70S6K signaling pathways in OLETF rat skeletal muscle. Therefore, ALA may be a potential therapeutic intervention for skeletal muscle loss in animal models of insulin resistance.

A system to identify inhibitors of mTOR signaling using high-resolution growth analysis in Saccharomyces cerevisiae

The mechanistic target of rapamycin (mTOR) is a central regulator of growth and proliferation and mTOR inhibition is a promising therapy for a variety of diseases and disorders. Inhibition of mTOR complex I (mTORC1) with rapamycin delays aging and increases healthy longevity in laboratory animals and is used clinically at high doses to prevent organ transplant rejection and to treat some forms of cancer. Clinical use of rapamycin is associated with several unwanted side effects, however, and several strategies are being taken to identify mTORC1 inhibitors with fewer side effects. We describe here a yeast-based growth assay that can be used to screen for novel inhibitors of mTORC1. By testing compounds using a wild-type strain and isogenic cells lacking either TOR1 or FPR1, we can resolve not only whether a compound is an inhibitor of mTORC1 but also whether the inhibitor acts through a mechanism similar to rapamycin by binding Fpr1. Using this assay, we show that rapamycin derivatives behave similarly to rapamycin, while caffeine and the ATP competitive inhibitors Torin 1 and GSK2126458 are mTORC1 inhibitors in yeast that act independently of Fpr1. Some mTOR inhibitors in mammalian cells do not inhibit mTORC1 in yeast, and several nutraceutical compounds were not found to specifically inhibit mTOR but resulted in a general inhibition of yeast growth. Our screening method holds promise as a means of effectively assaying drug libraries for mTOR-inhibitory molecules in vivo that may be adapted as novel treatments to fight diseases and extend healthy longevity.

Effects of oral α-lipoic acid administration on body weight in overweight or obese subjects: a crossover randomized, double-blind, placebo-controlled trial

OBJECTIVE

Alpha-lipoic acid (ALA) has shown beneficial properties on diabetes and obesity. The aim of this study was to examine the effects of oral ALA on body weight in subjects with overweight or obese.

DESIGN

Single-centre, randomized, double-blind, crossover controlled study.

PARTICIPANTS

A total of 166 subjects of Chinese Han ethnicity with a BMI ≥25 kg/m² were screened and 103 subjects fulfilled the study requirements, in terms of informed consent and participation to the study.

MEASUREMENTS

The subjects were randomized (1:1) to receive either ALA (1200 mg/day) or placebo treatment in a crossover design for 8 weeks. The primary end-point was the change in body weight. The secondary end-points were the changes in waist circumference, BMI, lipid profile, plasma leptin levels and the adverse events that occurred following ALA treatment.

RESULTS

The changes in the body weight and waist circumference noted in the ALA group were significantly different compared to the placebo group as demonstrated by mixed model statistical analysis (both P < 0·05). No real weight reduction was seen in the ALA group, and no significant differences were noted as regards cholesterol levels, triglyceride levels, high-density lipoprotein cholesterol levels and adverse events between the two groups. The administration of ALA was well tolerated, and no serious adverse events were noted.

CONCLUSIONS

Oral administration of ALA (1200 mg/day) for 8 weeks induced mild weight loss accompanied by a reduction in waist circumference.

Effects of treadmill exercise on skeletal muscle mTOR signaling pathway in high-fat diet-induced obese mice

[Purpose] The aim of this study was to investigate the effects of regular treadmill exercise on skeletal muscle Rictor-Akt and mTOR-Raptor-S6K1 signaling pathway in high-fat diet-induced obese mice. [Subjects and Methods] Four- week-old C57BL/6 mice were adopted and classified into normal diet group (ND, n = 10), normal diet and training group (NDT, n = 10), high-fat diet group (HF, n = 10), and high-fat diet and training group (HFT, n = 10). The exercise program consisted of a treadmill exercise provided at low intensity for 1–4 weeks, and moderate intensity for 5–8 weeks. [Results] The Western blot method was used to measure the expression of mTOR, Raptor, S6K1, Rictor, and Akt proteins in the soleus muscle. mTOR levels were significantly higher in the HF group than in the ND and NDT groups. Raptor/mTORC1 and S6K1 levels were significantly higher in the HF group than in all the other groups. Akt levels were significantly lower in the HF group than in the NDT group. The risk of obesity may be associated with the overactivation of the mTOR-Raptor-S6K1 signaling pathway and a decrease in Akt levels. [Conclusion] This study also indicates that performing aerobic exercise may be associated with the downregulation of the mTOR-Raptor-S6K1 pathway.

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.