Atorvastatin impaired glucose metabolism in C2C12 cells partly via inhibiting cholesterol-dependent glucose transporter 4 translocation

Dietary Betaine Improves Glucose Metabolism in Obese Mice

BACKGROUND

Obesity caused by the overconsumption of energy-dense foods high in fat and sugar has contributed to the growing prevalence of type 2 diabetes. Betaine, found in food or supplements, has been found to lower blood glucose concentrations, but its exact mechanism of action is not well understood.

OBJECTIVES

A comprehensive evaluation of the potential mechanisms by which betaine supplementation improves glucose metabolism.

METHODS

Hyperglycemic mice were fed betaine to measure the indexes of glucose metabolism in the liver and muscle. To explore the mechanism behind the regulation of betaine on glucose metabolism, Ribonucleic Acid-Seq was used to analyze the livers of the mice. In vitro, HepG2 and C2C12 cells were treated with betaine to more comprehensively evaluate the effect of betaine on glucose metabolism.

RESULTS

Betaine was added to the drinking water of high-fat diet-induced mice, and it was found to reduce blood glucose concentrations and liver triglyceride concentrations without affecting body weight, confirming its hypoglycemic effect. To investigate the specific mechanism underlying its hypoglycemic effect, protein-protein interaction enrichment analysis of the liver revealed key nodes associated with glucose metabolism, including cytochrome P450 family activity, insulin sensitivity, glucose homeostasis, and triglyceride concentrations. The Kyoto Encyclopedia of Genes and Genomes and gene ontogeny enrichment analyses showed significant enrichment of the Notch signaling pathway. These results provided bioinformatic evidence for specific pathways through which betaine regulates glucose metabolism. Key enzyme activities involved in glucose uptake, glycogen synthesis, and glycogenolysis pathways of the liver and muscle were measured, and improvements were observed in these pathways.

CONCLUSIONS

This study provides new insight into the mechanisms by which betaine improves glucose metabolism in the liver and muscle and supports its potential as a drug for the treatment of metabolic disorders related to glucose.

Effects of statin therapy on glycemic control and insulin resistance: A systematic review and meta-analysis

AIMS

To update the evidence about the diabetogenic effect of statins.

METHODS

We searched for randomized-controlled trials reporting the effects of statin therapy on glycosylated hemoglobin (HbA1c) and/or homeostatic model insulin resistance (i.e., HOMA-IR) as indexes of diabetes. Studies were classified between the ones testing normal vs individuals with already altered glycemic control (HbA1c ≥ 6.5%; and HOMA-IR ≥ 2.15). Furthermore, studies were separated by statin type and dosage prescribed. Data are presented as mean difference (MD) and 95% confidence intervals.

RESULTS

A total of 67 studies were included in the analysis (>25,000 individuals). In individuals with altered glycemic control, statins increased HbA1c levels (MD 0.21%, 95% CI 0.16-to-0.25) and HOMA-IR index (MD 0.31, 95% CI 0.24-to-0.38). In individuals with normal glycemic control, statin increased HbA1c (MD 1.33%, 95% CI 1.31-to-1.35) and HOMA-IR (MD 0.49, 95% CI 0.41-to-0.58) in comparison to the placebo groups. The dose or type of statins did not modulate the diabetogenic effect.

CONCLUSIONS

Statins, slightly but significantly raise indexes of diabetes in individuals with adequate or altered glycemic control. The diabetogenic effect does not seem to be influenced by the type or dosage of statin prescribed.

Geranylgeranyl pyrophosphate depletion by statins compromises skeletal muscle insulin sensitivity

BACKGROUND

Statins are widely prescribed cholesterol-lowering drugs but have been shown to increase the risk of type 2 diabetes mellitus. However, the molecular mechanisms underlying the diabetogenic effect of statins are still not fully understood.

METHODS

The effects of geranylgeranyl transferase I and II (GGTase I and II) inhibition on insulin-stimulated glucose uptake and GLUT4 translocation, and the dependence of these effects on insulin signalling were investigated in skeletal muscle cells. The protective effects of geranylgeranyl pyrophosphate (GGPP) and its precursor geranylgeraniol (GGOH) on simvastatin-induced insulin resistance were evaluated in vitro and in vivo. The effect of GGTase II inhibition in skeletal muscle on insulin sensitivity in vivo was confirmed by adeno-associated virus serotype 9 (AAV9)-mediated knockdown of the specific subunit of GGTase II, RABGGTA. The regulatory mechanisms of GGTase I on insulin signalling and GGTase II on insulin-stimulated GLUT4 translocation were investigated by knockdown of RhoA, TAZ, IRS1, geranylgeranylation site mutation of RhoA, RAB8A, and RAB13.

RESULTS

Both inhibition of GGTase I and II mimicked simvastatin-induced insulin resistance in skeletal muscle cells. GGPP and GGOH were able to prevent simvastatin-induced skeletal muscle insulin resistance in vitro and in vivo. GGTase I inhibition suppressed the phosphorylation of AKT (Ser473) (-51.3%, P < 0.01), while GGTase II inhibition had no effect on it. AAV9-mediated knockdown of RABGGTA in skeletal muscle impaired glucose disposal without disrupting insulin signalling in vivo (-46.2% for gastrocnemius glucose uptake, P < 0.001; -52.5% for tibialis anterior glucose uptake, P < 0.001; -17.8% for soleus glucose uptake, P < 0.05; -31.4% for extensor digitorum longus glucose uptake, P < 0.01). Inhibition of RhoA, TAZ, IRS1, or geranylgeranylation deficiency of RhoA attenuated the beneficial effect of GGPP on insulin signalling in skeletal muscle cells. Geranylgeranylation deficiency of RAB8A inhibited insulin-stimulated GLUT4 translocation and concomitant glucose uptake in skeletal muscle cells (-42.8% for GLUT4 translocation, P < 0.01; -50.6% for glucose uptake, P < 0.001).

CONCLUSIONS

Geranylgeranyl pyrophosphate regulates glucose uptake via GGTase I-mediated insulin signalling-dependent way and GGTase II-mediated insulin signalling-independent way in skeletal muscle. Supplementation of GGPP/GGOH could be a potential therapeutic strategy for statin-induced insulin resistance.

Implication of Lipids in Calcified Aortic Valve Pathogenesis: Why Did Statins Fail?

Calcific Aortic Valve Disease (CAVD) is a fibrocalcific disease. Lipoproteins and oxidized phospholipids play a substantial role in CAVD; the level of Lp(a) has been shown to accelerate the progression of valve calcification. Indeed, oxidized phospholipids carried by Lp(a) into the aortic valve stimulate endothelial dysfunction and promote inflammation. Inflammation and growth factors actively promote the synthesis of the extracellular matrix (ECM) and trigger an osteogenic program. The accumulation of ECM proteins promotes lipid adhesion to valve tissue, which could initiate the osteogenic program in interstitial valve cells. Statin treatment has been shown to have the ability to diminish the death rate in subjects with atherosclerotic impediments by decreasing the serum LDL cholesterol levels. However, the use of HMG-CoA inhibitors (statins) as cholesterol-lowering therapy did not significantly reduce the progression or the severity of aortic valve calcification. However, new clinical trials targeting Lp(a) or PCSK9 are showing promising results in reducing the severity of aortic stenosis. In this review, we discuss the implication of lipids in aortic valve calcification and the current findings on the effect of lipid-lowering therapy in aortic stenosis.

PXR activation impairs hepatic glucose metabolism partly via inhibiting the HNF4α-GLUT2 pathway

Drug-induced hyperglycemia/diabetes is a global issue. Some drugs induce hyperglycemia by activating the pregnane X receptor (PXR), but the mechanism is unclear. Here, we report that PXR activation induces hyperglycemia by impairing hepatic glucose metabolism due to inhibition of the hepatocyte nuclear factor 4-alpha (HNF4α)‒glucose transporter 2 (GLUT2) pathway. The PXR agonists atorvastatin and rifampicin significantly downregulated GLUT2 and HNF4α expression, and impaired glucose uptake and utilization in HepG2 cells. Overexpression of PXR downregulated GLUT2 and HNF4α expression, while silencing PXR upregulated HNF4α and GLUT2 expression. Silencing HNF4α decreased GLUT2 expression, while overexpressing HNF4α increased GLUT2 expression and glucose uptake. Silencing PXR or overexpressing HNF4α reversed the atorvastatin-induced decrease in GLUT2 expression and glucose uptake. In human primary hepatocytes, atorvastatin downregulated GLUT2 and HNF4α mRNA expression, which could be attenuated by silencing PXR. Silencing HNF4α downregulated GLUT2 mRNA expression. These findings were reproduced with mouse primary hepatocytes. Hnf4α plasmid increased Slc2a2 promoter activity. Hnf4α silencing or pregnenolone-16α-carbonitrile (PCN) suppressed the Slc2a2 promoter activity by decreasing HNF4α recruitment to the Slc2a2 promoter. Liver-specific Hnf4α deletion and PCN impaired glucose tolerance and hepatic glucose uptake, and decreased the expression of hepatic HNF4α and GLUT2. In conclusion, PXR activation impaired hepatic glucose metabolism partly by inhibiting the HNF4α‒GLUT2 pathway. These results highlight the molecular mechanisms by which PXR activators induce hyperglycemia/diabetes.

Updated Understanding of the Crosstalk Between Glucose/Insulin and Cholesterol Metabolism

Glucose and cholesterol engage in almost all human physiological activities. As the primary energy substance, glucose can be assimilated and converted into diverse essential substances, including cholesterol. Cholesterol is mainly derived from de novo biosynthesis and the intestinal absorption of diets. It is evidenced that glucose/insulin promotes cholesterol biosynthesis and uptake, which have been targeted by several drugs for lipid-lowering, e.g., bempedoic acid, statins, ezetimibe, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. Inversely, these lipid-lowering drugs may also interfere with glucose metabolism. This review would briefly summarize the mechanisms of glucose/insulin-stimulated cholesterol biosynthesis and uptake, and discuss the effect and mechanisms of lipid-lowering drugs and genetic mutations on glucose homeostasis, aiming to help better understand the intricate relationship between glucose and cholesterol metabolism.

Drugs Interfering with Insulin Resistance and Their Influence on the Associated Hypermetabolic State in Severe Burns: A Narrative Review

It has become widely accepted that insulin resistance and glucose hypermetabolism can be linked to acute pathologies, such as burn injury, severe trauma, or sepsis. Severe burns can determine a significant increase in catabolism, having an important effect on glucose metabolism and on muscle protein metabolism. It is imperative to acknowledge that these alterations can lead to increased mortality through organ failure, even when the patients survive the initial trauma caused by the burn. By limiting the peripheral use of glucose with consequent hyperglycemia, insulin resistance determines compensatory increased levels of insulin in plasma. However, the significant alterations in cellular metabolism lead to a lack of response to insulin's anabolic functions, as well as to a decrease in its cytoprotective role. In the end, via pathological insulin signaling associated with increased liver gluconeogenesis, elevated levels of glucose are detected in the blood. Several cellular mechanisms have been incriminated in the development of insulin resistance in burns. In this context, the main aim of this review article is to summarize some of the drugs that might interfere with insulin resistance in burns, taking into consideration that such an approach can significantly improve the prognosis of the burned patient.

In Vitro Effects of Emerging Bisphenols on Myocyte Differentiation and Insulin Responsiveness

Bisphenols are endocrine disrupting chemicals to which humans are ubiquitously exposed to. Prenatal bisphenol A exposure can lead to insulin resistance. However, the metabolic effects of other emerging bisphenols, such as bisphenol S (BPS) and bisphenol F (BPF), are less understood. Because the skeletal muscle is the largest of the insulin target tissues, the goal of this study was to evaluate the effects of 2 emerging bisphenols (BPS and BPF) on cytotoxicity, proliferation, myogenic differentiation, and insulin responsiveness in skeletal muscle cells. We tested this using a dose-response approach in C2C12 mouse and L6 rat myoblast cell lines. The results showed that C2C12 mouse myoblasts were more susceptible to bisphenols compared with L6 rat myoblasts. In both cell lines, bisphenol A was more cytotoxic, followed by BPF and BPS. C2C12 myoblast proliferation was higher upon BPF exposure at the 10-4 M dose and the fusion index was increased after exposure to either BPF or BPS at doses over 10-10 M. Exposure to BPS and BPF also reduced baseline expression of p-AKT (Thr) and p-GSK-3β, but not downstream effectors such as mTOR and glucose transporter-4. In conclusion, at noncytotoxic doses, BPS and BPF can alter myoblast cell proliferation, differentiation, and partially modulate early effectors of the insulin receptor signaling pathway. However, BPS or BPF short-term exposure evaluated here does not result in impaired insulin responsiveness.

Zebrafish as a Model for the Study of Lipid-Lowering Drug-Induced Myopathies

Drug-induced myopathies are classified as acquired myopathies caused by exogenous factors. These pathological conditions develop in patients without muscle disease and are triggered by a variety of medicaments, including lipid-lowering drugs (LLDs) such as statins, fibrates, and ezetimibe. Here we summarise the current knowledge gained via studies conducted using various models, such as cell lines and mammalian models, and compare them with the results obtained in zebrafish (Danio rerio) studies. Zebrafish have proven to be an excellent research tool for studying dyslipidaemias as a model of these pathological conditions. This system enables in-vivo characterization of drug and gene candidates to further the understanding of disease aetiology and develop new therapeutic strategies. Our review also considers important environmental issues arising from the indiscriminate use of LLDs worldwide. The widespread use and importance of drugs such as statins and fibrates justify the need for the meticulous study of their mechanism of action and the side effects they cause.

Rationale for the use of metformin and exercise to counteract statin-associated side effects

INTRODUCTION

Statins are the most widely prescribed drugs for lowering low-density lipoprotein cholesterol (LDL-C) and reducing cardiovascular morbidity and mortality. They are usually well-tolerated, but have two main safety concerns: statin-associated muscle symptoms (SAMS) and new-onset type 2 diabetes (NOD).

METHODS

A PubMed search was carried out using the following key words were used: statins, statin-associated muscle symptoms, statin myalgia, statin-associated diabetes, metformin and statins, exercise and statins.

RESULTS

Mitochondrial damage and muscle atrophy are likely the central mechanisms producing SAMS, whereas decreased glucose transport, fatty acid oxidation and insulin secretion are likely involved in the development of NOD. Metformin and exercise training share many pathways that could potentially contrast SAMS and NOD. Clinical evidence also supports the combination of statins with metformin and exercise.

CONCLUSION

This combination appears attractive both from a clinical and an economical viewpoint, since all three therapies are highly cost-effective and their combination could result in diabetes and cardiovascular disease prevention.

C2C12 cell model: its role in understanding of insulin resistance at the molecular level and pharmaceutical development at the preclinical stage

OBJECTIVES

The myoblast cell line, C2C12, has been utilised extensively in vitro as an examination model in understanding metabolic disease progression. Although it is indispensable in both preclinical and pharmaceutical research, a comprehensive review of its use in the investigation of insulin resistance progression and pharmaceutical development is not available.

KEY FINDINGS

C2C12 is a well-documented model, which can facilitate our understanding in glucose metabolism, insulin signalling mechanism, insulin resistance, oxidative stress, reactive oxygen species and glucose transporters at cellular and molecular levels. With the aid of the C2C12 model, recent studies revealed that insulin resistance has close relationship with various metabolic diseases in terms of disease progression, pathogenesis and therapeutic management. A holistic, safe and effective disease management is highly of interest. Therefore, significant efforts have been paid to explore novel drug compounds and natural herbs that can elicit therapeutic effects in the targeted sites at both cellular (e.g. mitochondria, glucose transporter) and molecular level (e.g. genes, signalling pathway).

SUMMARY

The use of C2C12 myoblast cell line is meaningful in pharmaceutical and biomedical research due to their expression of GLUT-4 and other features that are representative to human skeletal muscle cells. With the use of the C2C12 cell model, the impact of drug delivery systems (nanoparticles and quantum dots) on skeletal muscle, as well as the relationship between exercise, pancreatic β-cells and endothelial cells, was discovered.

Statin Treatment-Induced Development of Type 2 Diabetes: From Clinical Evidence to Mechanistic Insights

Statins are the gold-standard treatment for the prevention of primary and secondary cardiovascular disease, which is the leading cause of mortality worldwide. Despite the safety and relative tolerability of statins, observational studies, clinical trials and meta-analyses indicate an increased risk of developing new-onset type 2 diabetes mellitus (T2DM) after long-term statin treatment. It has been shown that statins can impair insulin sensitivity and secretion by pancreatic β-cells and increase insulin resistance in peripheral tissues. The mechanisms involved in these processes include, among others, impaired Ca²⁺ signaling in pancreatic β-cells, down-regulation of GLUT-4 in adipocytes and compromised insulin signaling. In addition, it has also been described that statins’ impact on epigenetics may also contribute to statin-induced T2DM via differential expression of microRNAs. This review focuses on the evidence and mechanisms by which statin therapy is associated with the development of T2DM. This review describes the multifactorial combination of effects that most likely contributes to the diabetogenic effects of statins. Clinically, these findings should encourage clinicians to consider diabetes monitoring in patients receiving statin therapy in order to ensure early diagnosis and appropriate management.

Effects of Astaxanthin on Inflammation and Insulin Resistance in a Mouse Model of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is a condition in which a hormone made by the placenta prevents the body from using insulin effectively. It is important to find an effective treatment. A mouse model of GDM was used to testify the effects of astaxanthin on glucose tolerance and insulin sensitivity. Production of inflammatory cytokines, reactive oxygen species (ROS), and glucose transporter type 4 (GLUT4) translocation and insulin-related signaling were measured in the presence of astaxanthin both in vivo and in vitro. It was found that astaxanthin improved insulin sensitivity, glucose tolerance, and litter size of offspring and reduced birth weight of offspring and inflammation in GDM mouse. Moreover, astaxanthin increased GLUT4 translocating to membrane without altering its secretion/expression and glucose uptake and consumption in C2C12 skeletal muscle cells. Furthermore, ROS generation and insulin-related signaling inhibited by tumor necrosis factor α was restored by astaxanthin. It is concluded that astaxanthin has the potential to attenuate GDM symptoms by regulating inflammation and insulin resistance in skeletal muscle of pregnant mice. Our findings suggest that astaxanthin could be a promising and effective molecule to treat GDM.

Diabetogenic effect of pravastatin is associated with insulin resistance and myotoxicity in hypercholesterolemic mice

Background

HMG-CoA reductase inhibitors (statins) are cholesterol-lowering drugs widely used to treat hypercholesterolemia and prevent cardiovascular disease. Statins are generally well tolerated, but adverse reactions may occur, particularly myopathy and new onset of diabetes. The exact mechanism of statin-induced myopathy and diabetes has not been fully elucidated. We have previously shown that treatment of hypercholesterolemic (LDLr^−/−) mice with pravastatin for 2 months decreased pancreatic islet insulin secretion and increased oxidative stress and cell death, but no glucose intolerance was observed. The purpose of the current work was to study long-term pravastatin effects on glucose homeostasis, insulin sensitivity, muscle protein turnover and cell viability.

Methods

LDLr^−/− mice were treated with pravastatin for 3, 6 and 10 months. Glucose tolerance, insulin resistance and glucose-stimulated insulin secretion were evaluated. The rates of protein synthesis and degradation were determined in gastrocnemius muscle after 10 months of treatment. Insulin signalling, oxidative stress and cell death were analysed in vitro using C2C12 myotubes.

Results

After 6 and 10 months of treatment, these mice became glucose intolerant, and after 10 months, they exhibited marked insulin resistance. Reduced islet glucose-stimulated insulin secretion was observed after the 3rd month of treatment. Mice treated for 10 months showed significantly decreased body weight and increased muscle protein degradation. In addition, muscle chymotrypsin-like proteasomal activity and lysosomal cathepsin were markedly elevated. C2C12 myotubes exposed to increasing concentrations of pravastatin presented dose-dependent impairment of insulin-induced Akt phosphorylation, increased apoptotic markers (Bax protein and cleaved caspase-3) and augmented superoxide anion production.

Conclusions

In addition to reduced insulin secretion, long-term pravastatin treatment induces insulin resistance and muscle wasting. These results suggest that the diabetogenic effect of statins is linked to the appearance of myotoxicity induced by oxidative stress, impaired insulin signalling, proteolysis and apoptosis.

MiR-4500 Regulates PLXNC1 and Inhibits Papillary Thyroid Cancer Progression

Although most patients with papillary thyroid cancer (PTC) are curable, there are still a few patients showing poor outcomes and increased risk of secondary cancers after therapies. In this study, we aimed to investigate the correlation between miR-4500 and PTC and to explore its molecular functions. A total of 50 patients were included, and sonography and histological examinations were used for diagnosis. Quantitative real-time polymerase chain reaction (qRT-PCR) was applied for detection of mRNA levels while Western blotting was used for measuring protein expression. Cell proliferation was tested using CCK-8 and colony formation assays. Caspase-3 activity and nucleosomal fragmentation assays were employed to test cell apoptosis. Cell invasive ability was measured using transwell assay. MiR-4500 target was identified using luciferase assay and RNA pull-down assay. MiR-4500 expression was significantly decreased in five PTC cell lines compared with Nthy-ori 3-1 cells and in PTC tissues compared with adjacent normal thyroid tissues, respectively. Decreased expression of miR-4500 showed lower survival rate, higher cancer stage, and lymphatic metastasis. Therefore, our results implied that miR-4500 could serve as a potential biomarker for PTC prognosis. Overexpression of miR-4500 repressed colony formation, proliferation, and invasiveness of PTC cells whereas increased cell apoptosis. We identified that PLXNC1 was a direct target of miR-4500. PLXNC1 knockdown showed similar effects on cell viability, colony formation, and cell apoptosis as overexpression of miR-4500 in PTC cells. In conclusion, miR-4500 inhibits the malignant transformation of PTC cells by directly targeting and repressing PLXNC1.

Insulin prevents and reverts simvastatin-induced toxicity in C2C12 skeletal muscle cells

Simvastatin is an inhibitor of the 3-hydroxy-3-methylglutaryl-CoA reductase used for decreasing low density lipoprotein (LDL)-cholesterol in patients. It is well-tolerated but can cause myopathy. Our aims were to enlarge our knowledge regarding mechanisms and effects of insulin on simvastatin-associated myotoxicity in C2C12 myotubes. Simvastatin (10 µM) reduced membrane integrity and ATP content in myotubes treated for 24 hours, which could be prevented and partially reversed concentration- and time-dependently by insulin. Furthermore, simvastatin impaired the phosphorylation of Akt (Protein Kinase B) mainly at Ser473 and less at Thr308, indicating impaired activity of the mammalian Target of Rapamycin Complex 2 (mTORC2). Impaired activation of Akt increased mRNA expression of the muscle atrophy F-Box (MAFbx), decreased activation of the mammalian Target of Rapamycin Complex 1 (mTORC1) and stimulated apoptosis by impairing the Ser9 phosphorylation of glycogen synthase kinase 3β. Decreased phosphorylation of Akt at both phosphorylation sites and of downstream substrates as well as apoptosis were prevented concentration-dependently by insulin. In addition, simvastatin caused accumulation of the insulin receptor β-chain in the endoplasmic reticulum (ER) and increased cleavage of procaspase-12, indicating ER stress. Insulin reduced the expression of the insulin receptor β-chain but increased procaspase-12 activation in the presence of simvastatin. In conclusion, simvastatin impaired activation of Akt Ser473 most likely as a consequence of reduced activity of mTORC2. Insulin could prevent the effects of simvastatin on the insulin signaling pathway and on apoptosis, but not on the endoplasmic reticulum (ER) stress induction.

Mechanisms of statin-associated skeletal muscle-associated symptoms

Statins lower the serum low-density lipoprotein cholesterol and prevent cardiovascular events by inhibiting 3-hydroxy-3-methyl-glutaryl-CoA reductase. Although the safety of statins is documented, many patients ingesting statins may suffer from skeletal muscle-associated symptoms (SAMS). Importantly, SAMS are a common reason for stopping the treatment with statins. Statin-associated muscular symptoms include fatigue, weakness and pain, possibly accompanied by elevated serum creatine kinase activity. The most severe muscular adverse reaction is the potentially fatal rhabdomyolysis. The frequency of SAMS is variable but in up to 30% of the patients ingesting statins, depending on the population treated and the statin used. The mechanisms leading to SAMS are currently not completely clarified. Over the last 15 years, several research articles focused on statin-induced mitochondrial dysfunction as a reason for SAMS. Statins can impair the function of the mitochondrial respiratory chain, thereby reducing ATP and increasing ROS production. This can induce mitochondrial membrane permeability transition, release of cytochrome c into the cytosol and induce apoptosis. In parallel, statins inhibit activation of Akt, mainly due to reduced function of mTORC2, which may be related to mitochondrial dysfunction. Mitochondrial dysfunction by statins is also responsible for activation of AMPK, which is associated with impaired activation of mTORC1. Reduced activation of mTORC1 leads to increased skeletal muscle protein degradation, impaired protein synthesis and stimulation of apoptosis. In this paper, we discuss some of the different hypotheses how statins affect skeletal muscle in more detail, focusing particularly on those related to mitochondrial dysfunction and the impairment of the Akt/mTOR pathway.

Mechanisms of insulin resistance by simvastatin in C2C12 myotubes and in mouse skeletal muscle

Statins inhibit cholesterol biosynthesis and lower serum LDL-cholesterol levels. They are generally well tolerated, but can cause insulin resistance in patients. Therefore, we investigated the mechanisms underlying the statin-induced insulin resistance. We used mice and C2C12 myotubes (murine cell line): mice (n = 10) were treated with oral simvastatin (5 mg/kg/day) or water (control) for 21 days and C2C12 cells were exposed to 10 μM simvastatin for 24 h. After intraperitoneal glucose application (2 g/kg), simvastatin-treated mice had higher glucose but equal insulin plasma concentrations than controls and lower glucose transport into skeletal muscle. Similarly, glucose uptake by C2C12 myotubes exposed to 10 μM simvastatin for 24 h was impaired compared to control cells. In simvastatin-treated C2C12 myotubes, mRNA and protein expression of the insulin receptor (IR) β-chain was increased, but the phosphorylation (Tyr1361) was impaired. Simvastatin decreased numerically Akt/PKB Thr308 phosphorylation (via insulin signaling pathway) and significantly Akt/PKB Ser473 phosphorylation (via mTORC2), which was explained by impaired phosphorylation of mTOR Ser2448. Reduced phosphorylation of Akt/PKB impaired downstream phosphorylation of GSK3β, leading to impaired translocation of GLUT4 into plasma membranes of C2C12 myotubes. In contrast, reduced phosphorylation of AS160 could be excluded as a reason for impaired GLUT4 translocation. In conclusion, simvastatin caused insulin resistance in mice and impaired glucose uptake in C2C12 myotubes. The findings in myotubes can be explained by diminished activation of Akt/PKB by mTORC2 and downstream effects on GSK3β, impairing the translocation of GLUT4 and the uptake of glucose.

Coenzyme Q10 does not improve peripheral insulin sensitivity in statin-treated men and women: the LIFESTAT study

Simvastatin is a cholesterol-lowering drug that is prescribed to lower the risk of cardiovascular disease following high levels of blood cholesterol. There is a possible risk of new-onset diabetes mellitus with statin treatment but the mechanisms behind are unknown. Coenzyme Q10 (CoQ10) supplementation has been found to improve glucose homeostasis in various patient populations and may increase muscle glucose transporter type 4 content. Our aim was to investigate if 8 weeks of CoQ10 supplementation can improve glucose homeostasis in simvastatin-treated subjects. Thirty-five men and women in treatment with a minimum of 40 mg of simvastatin daily were randomized to receive either 2 × 200 mg/day of CoQ10 supplementation or placebo for 8 weeks. Glucose homeostasis was investigated with fasting blood samples, oral glucose tolerance test (OGTT) and intravenous glucose tolerance test. Insulin sensitivity was assessed with the hyperinsulinemic-euglycemic clamp. Different indices were calculated from fasting samples and OGTT as secondary measures of insulin sensitivity. A muscle biopsy was obtained from the vastus lateralis muscle for muscle protein analyzes. There were no changes in body composition, fasting plasma insulin, fasting plasma glucose, or 3-h glucose with intervention, but glycated hemoglobin decreased with time. Glucose homeostasis measured as the area under the curve for glucose, insulin, and C-peptide during OGTT was unchanged after intervention. Insulin secretory capacity was also unaltered after CoQ10 supplementation. Insulin sensitivity was unchanged but hepatic insulin sensitivity increased. No changes in muscle GLUT4 content was observed after intervention. CoQ10 supplementation does not change muscle GLUT4 content, insulin sensitivity, or secretory capacity, but hepatic insulin sensitivity may improve.

The IL-10-1082 (rs1800896) G allele is associated with a decreased risk of developing premature coronary artery disease and some IL-10 polymorphisms were associated with clinical and metabolic parameters. The GEA study

Interleukin 10 (IL-10) is an anti-inflammatory cytokine with a protective role in the formation and the development of the atherosclerotic plaque. The aim of the present study was to establish if IL-10 gene polymorphisms are associated with the development of premature coronary artery disease (pCAD) and cardiovascular risk factors in Mexican individuals. Three IL-10 gene polymorphisms [-592C/A (rs1800872), -819C/T (rs1800871), and -1082 A/G (rs1800896)] and IL-10 plasma levels were analyzed in 2266 individuals (1160 pCAD patients and 1106 healthy controls). Under recessive and co-dominant2 models, the -1082 A/G (rs1800896) G allele was associated with decreased risk of developing pCAD (OR = 0.572, P_rec = 0.022 and OR = 0.567, P_cod2 = 0.023). In pCAD patients, the polymorphisms were associated with hyperinsulinemia, small and dense LDLs, hypertension, and diabetes mellitus. In the control group, the polymorphisms were associated with hypertension, hyperuricemia, and small and dense LDLs. pCAD patients have significantly higher IL-10 plasma levels than healthy controls [0.91 (0.55-1.67) pg/mL vs 0.45 (0.24-0.98) pg/mL, respectively, P < 0.0001]. Nevertheless, these levels were not associated with the genotypes analyzed in the present study. The results suggest that the IL-10-1082 A/G (rs1800896) G allele is associated with a decreased risk of developing pCAD. In patients and controls, the polymorphisms analyzed were associated with some cardiovascular risk factors. Although, in pCAD patients the IL-10 plasma levels were higher, they were not associated with the genotypes of the polymorphisms examined.