Alpha-lipoic acid inhibits endoplasmic reticulum stress-induced cell death through PI3K/Akt signaling pathway in FRTL5 thyroid cells

The effect of alpha-lipoic acid supplementation on anthropometric, glycemic, lipid, oxidative stress, and hormonal parameters in individuals with polycystic ovary syndrome: a systematic review and meta-analysis of randomized clinical trials

This systematic review and meta-analysis aimed to examine the effect of the antioxidant alpha-lipoic acid (ALA) on various cardiometabolic risk factors and hormonal parameters in patients with polycystic ovary syndrome (PCOS). We searched PubMed, EMBASE, SCOPUS, Cochrane Library, and Web of Science databases without language restrictions until May 2023 to find randomized controlled trials (RCTs) that assessed the impact of ALA supplementation on anthropometric, glycemic, lipid, oxidative stress, and hormonal parameters in women with PCOS. Outcomes were summarized using the standardized mean difference (SMD) and 95% confidence interval (CI) in a random-effects model. An I2 statistic of >60% established significant between-study heterogeneity. The overall certainty of the evidence for each outcome was determined using the grading of recommendations, assessment, development, and evaluations system. Seven RCTs met the inclusion criteria. The ALA group had significant reductions in fasting blood sugar (fasting blood sugar (FBS), n=7 RCTs, SMD, -0.60; 95% CI, -1.10 to -0.10; I2=63.54%, moderate certainty of evidence) and homeostatic model assessment for insulin resistance (homeostatic model assessment of insulin resistance (HOMA-IR), n=4 RCTs, SMD, -2.03; 95% CI, -3.85 to -0.20; I2=96.32%, low certainty of evidence) compared with the control group. However, significant differences were observed between the groups in body mass index, insulin, estrogen, follicle-stimulating hormone, luteinizing hormone, testosterone, low-density lipoprotein, highdensity lipoprotein, triglyceride, total cholesterol, malondialdehyde, or total antioxidant capacity profiles. ALA supplementation improves FBS and HOMA-IR levels in women with PCOS. ALA consumption is an effective complementary therapy for the management of women with PCOS.

Hyperglycaemia augments lipopolysaccharide-induced reduction in rat and human macrophage phagocytosis via the endoplasmic stress-C/EBP homologous protein pathway

BACKGROUND

Macrophage phagocytosis constitutes an essential part of the host defence against microbes and the resolution of inflammation. Hyperglycaemia during sepsis is reported to reduce macrophage function, and thus, potentiate inflammatory deterioration. We investigated whether high-glucose concentrations augment lipopolysaccharide-induced reduction in macrophage phagocytosis via the endoplasmic stress-C/EBP homologous protein (CHOP) pathway using animal and laboratory investigations.

METHODS

Peritoneal macrophages of artificially ventilated male Wistar rats, divided into four groups based on target blood glucose concentrations achieved by glucose administration with or without lipopolysaccharide, were obtained after 24 h. Human macrophages were also cultured in normal or high glucose with or without lipopolysaccharide exposure for 72 h. Changes in the phagocytic activity, intranuclear CHOP expression, and intracellular Akt phosphorylation status of macrophages were evaluated. These changes were also evaluated in human macrophages after genetic knock-down of CHOP by specific siRNA transfection or resolvin D2 treatment.

RESULTS

Lipopolysaccharide impaired phagocytosis, increased intranuclear expression of CHOP, and inhibited Akt phosphorylation in both rat peritoneal and human macrophages. Hyperglycaemic glucose concentrations augmented these changes. Genetic knock-down of CHOP restored phagocytic ability and Akt phosphorylation in human macrophages. Furthermore, resolvin D2 co-incubation restored the inhibited phagocytosis and Akt phosphorylation along with the inhibition of intranuclear CHOP expression in human macrophages.

CONCLUSIONS

These findings imply that controlling endoplasmic reticulum stress might provide new strategies for restoring reduced macrophage phagocytosis in sepsis-induced hyperglycaemia.

Protective Effects of Alpha-Lipoic Acid on Glutamate-Induced Cytotoxicity in C6 Glioma Cells

Glutamate-mediated cytotoxicity has been implicated in the pathogenesis of neurological diseases, including Parkinson's disease, Alzheimer's disease, and stroke. In this study, we investigated the protective effects of alpha-lipoic acid (ALA), a naturally occurring thiol antioxidant, on glutamate-induced cytotoxicity in cultured C6 astroglial cells. Exposure to high-dose glutamate (10 mM) caused oxidative stress and mitochondrial dysfunction through the elevation of reactive oxygen species, depletion of glutathione, and loss of the mitochondrial membrane potential (ΔΨ_m). Pretreatment with ALA (200 µM), however, significantly inhibited the glutamate-induced oxidative stress and mitochondrial dysfunction. ALA pretreatment dose-dependently suppressed glutamate-induced apoptotic events including altered nuclear morphology and activation of caspase-3. In addition, ALA significantly attenuated glutamate-induced endoplasmic reticulum (ER) stress markers; namely, glucose-regulated protein 78 (GRP78), activating transcription factor 6 (ATF6), protein kinase regulated by RNA (PKR)-like ER-associated kinase (PERK), eukaryotic translation initiation factor 2 alpha (eIF2α), inositol-requiring enzyme 1 (IRE1), CCAAT/enhancer binding protein homologous protein (CHOP), and caspase-12. We confirmed that CHOP and caspase-12 are key mediators of glutamate-induced ER stress. Furthermore, exposure of the cells to a caspase-12-specific inhibitor and CHOP small interfering RNAs (siRNAs) led to restoration of the ΔΨ_m that was damaged by glutamate treatment. These results suggest that ALA can effectively suppress oxidative stress, mitochondrial dysfunction, and ER stress in astroglial cells.

The Immunomodulatory Effect of Alpha-Lipoic Acid in Autoimmune Diseases

Αlpha-lipoic acid is a naturally occurring antioxidant in human body and has been widely used as an antioxidant clinically. Accumulating evidences suggested that α-lipoic acid might have immunomodulatory effects on both adaptive and innate immune systems. This review focuses on the evidences and potential targets involved in the immunomodulatory effects of α-lipoic acid. It highlights the fact that α-lipoic acid may have beneficial effects in autoimmune diseases once the immunomodulatory effects can be confirmed by further investigation.

Impaired endocrine-metabolic homeostasis: underlying mechanism of its induction by unbalanced diet

To characterize the intrinsic mechanism by which sucrose induces β-cell dysfunction. Normal rats received for 3 weeks a standard diet supplemented with 10% sucrose in the drinking water (high sucrose (HS)) with/out an antioxidant agent (R/S α-lipoic acid). We measured plasma glucose, insulin, triglyceride, leptin, and lipid peroxidation levels; homeostasis model assessment (HOMA)-insulin resistance (HOMA-IR) and HOMA for β-cell function (HOMA-β) indexes were also determined. Insulin secretion, β-cell apoptosis, intracellular insulin and leptin mediators, and oxidative stress (OS) markers were also measured in islets isolated from each experimental group. HS rats had increased plasma triglyceride, insulin, leptin, and lipid peroxidation (OS marker) levels associated with an insulin-resistant state. Their islets developed an initial compensatory increase in glucose-induced insulin secretion and mRNA and protein levels of β-cell apoptotic markers. They also showed a significant decrease in mRNA and protein levels of insulin and leptin signaling pathway mediators. Uncoupling protein 2 (UCP2), peroxisome proliferator-activated receptor (PPAR)-α and -δ mRNA and protein levels were increased whereas mRNA levels of Sirtuin-1 (Sirt-1), glutathione peroxidase, and catalase were significantly lower in these animals. Development of all these endocrine-metabolic abnormalities was prevented by co-administration of R/S α-lipoic acid together with sucrose. OS may be actively involved in the mechanism by which unbalanced/unhealthy diet induces β-cell dysfunction. Since metabolic-endocrine dysfunctions recorded in HS rats resembled those measured in human pre-diabetes, knowledge of its molecular mechanism could help to develop appropriate strategies to prevent the progression of this metabolic state toward type 2 diabetes (T2D).

Selenium supplementation modulates apoptotic processes in thyroid follicular cells

Selenium (Se) is an essential micronutrient modulating several physiopathological processes in the human body. The aim of the study is to characterize the molecular effects determined by Se-supplementation in thyroid follicular cells, using as model the well-differentiated rat thyroid follicular cell line FRTL5. Experiments have been performed to evaluate the effects of Se on cell growth, mortality and proliferation and on modulation of pro- and antiapoptotic pathways. The results indicate that Se-supplementation improves FRTL5 growth rate. Furthermore, Se reduces the proportion of cell death and modulates both proapoptotic (p53 and Bim) and antiapoptotic (NF-kB and Bcl2) mRNA levels. In addition, incubation with high doses of Na-Se might prevent the ER-stress apoptosis induced by tunicamycin, as assessed by membrane integrity maintenance, reduction in caspase 3/7 activities, and reduction in Casp-3 and PARP cleavage. Taken together, these results provide molecular evidences indicating the role of Se supplementation on cell death and apoptosis modulation in thyroid follicular cells. These observations may be useful to understand the effects of this micronutrient on the physiopathology of the thyroid gland. © 2016 BioFactors, 43(3):415-423, 2017.

Alpha Lipoic Acid Modulated High Glucose-Induced Rat Mesangial Cell Dysfunction via mTOR/p70S6K/4E-BP1 Pathway

The aim of this study was to investigate whether alpha lipoic acid (LA) regulates high glucose-induced mesangial cell proliferation and extracellular matrix production via mTOR/p70S6K/4E-BP1 signaling. The effect of LA on high glucose-induced cell proliferation, fibronectin (FN), and collagen type I (collagen-I) expression and its mechanisms were examined in cultured rat mesangial cells by methylthiazol tetrazolium (MTT) assay, flow cytometry, ELISA assay, and western blot, respectively. LA at a relatively low concentration (0.25 mmol/L) acted as a growth factor in rat mesangial cells, promoted entry of cell cycle into S phase, extracellular matrix formation, and phosphorylated AKT, mTOR, p70S6K, and 4E-BP1. These effects disappeared when AKT expression was downregulated with PI3K/AKT inhibitor LY294002. Conversely, LA at a higher concentration (1.0 mmol/L) inhibited high glucose-induced rat mesangial cell proliferation, entry of cell cycle into S phase, and extracellular matrix exertion, as well as phosphorylation of mTOR, p70S6K, and 4E-BP1 but enhanced the activity of AMPK. However, these effects disappeared when AMPK activity was inhibited with CaMKK inhibitor STO-609. These results suggest that LA dose-dependently regulates mesangial cell proliferation and matrix protein secretion by mTOR/p70S6K/4E-BP1 signaling pathway under high glucose conditions.