Palmitate induced mitochondrial deoxyribonucleic acid damage and apoptosis in l6 rat skeletal muscle cells

Bridging lipid metabolism and mitochondrial genome maintenance

Mitochondria are the nexus of cellular energy metabolism and major signaling hubs that integrate information from within and without the cell to implement cell function. Mitochondria harbor a distinct polyploid genome, mitochondrial DNA (mtDNA), that encodes respiratory chain components required for energy production. MtDNA mutation and depletion have been linked to obesity and metabolic syndrome in humans. At the cellular and subcellular levels, mtDNA synthesis is coordinated by membrane contact sites implicated in lipid transfer from the endoplasmic reticulum, tying genome maintenance to lipid storage and homeostasis. Here, we examine the relationship between mtDNA and lipid trafficking, the influence of lipotoxicity on mtDNA integrity, and how lipid metabolism may be disrupted in primary mtDNA disease.

Treatment of manganese and lead poisoning with sodium para-aminosalicylic acid: A contemporary update

Sodium para-aminosalicylic acid (PAS-Na) treatment for manganese (Mn) intoxication has shown efficacy in experimental and clinical studies, giving rise to additional studies on its efficacy for lead (Pb) neurotoxicity and its associated mechanisms of neuroprotection. The difference between PAS-Na and other metal complexing agents, such as edetate calcium sodium (CaNa2-EDTA), is firstly that PAS-Na can readily pass through the blood-brain barrier (BBB), and complex and facilitate the excretion of manganese and lead. Secondly, PAS-Na has anti-inflammatory effects. Recent studies have broadened the understanding on the mechanisms associated with efficacy of PAS-Na. The latter has been shown to modulate multifarious manganese- and lead- induced neurotoxicity, via its anti-apoptotic and anti-inflammatory effects, as well as its ability to inhibit pyroptosis, and regulate abnormal autophagic processes. These observations provide novel scientific bases and new concepts for the treatment of lead, mercury, copper, thallium, as well as other toxic encephalopathies, and implicate PAS-Na as a compound with greater prospects for clinical medical application.

Trodusquemine (MSI-1436) Restores Metabolic Flexibility and Mitochondrial Dynamics in Insulin-Resistant Equine Hepatic Progenitor Cells (HPCs)

Equine metabolic syndrome (EMS) is a significant global health concern in veterinary medicine. There is increasing interest in utilizing molecular agents to modulate hepatocyte function for potential clinical applications. Recent studies have shown promising results in inhibiting protein tyrosine phosphatase (PTP1B) to maintain cell function in various models. In this study, we investigated the effects of the inhibitor Trodusquemine (MSI-1436) on equine hepatic progenitor cells (HPCs) under lipotoxic conditions. We examined proliferative activity, glucose uptake, and mitochondrial morphogenesis. Our study found that MSI-1436 promotes HPC entry into the cell cycle and protects them from palmitate-induced apoptosis by regulating mitochondrial dynamics and biogenesis. MSI-1436 also increases glucose uptake and protects HPCs from palmitate-induced stress by reorganizing the cells' morphological architecture. Furthermore, our findings suggest that MSI-1436 enhances 2-NBDG uptake by increasing the expression of SIRT1, which is associated with liver insulin sensitivity. It also promotes mitochondrial dynamics by modulating mitochondria quantity and morphotype as well as increasing the expression of PINK1, MFN1, and MFN2. Our study provides evidence that MSI-1436 has a positive impact on equine hepatic progenitor cells, indicating its potential therapeutic value in treating EMS and insulin dysregulation.

Prognostic impact of obesity in newly-diagnosed glioblastoma: a secondary analysis of CeTeG/NOA-09 and GLARIUS

Purpose

The role of obesity in glioblastoma remains unclear, as previous analyses have reported contradicting results. Here, we evaluate the prognostic impact of obesity in two trial populations; CeTeG/NOA-09 (n = 129) for MGMT methylated glioblastoma patients comparing temozolomide (TMZ) to lomustine/TMZ, and GLARIUS (n = 170) for MGMT unmethylated glioblastoma patients comparing TMZ to bevacizumab/irinotecan, both in addition to surgery and radiotherapy.

Methods

The impact of obesity (BMI ≥ 30 kg/m²) on overall survival (OS) and progression-free survival (PFS) was investigated with Kaplan–Meier analysis and log-rank tests. A multivariable Cox regression analysis was performed including known prognostic factors as covariables.

Results

Overall, 22.6% of patients (67 of 297) were obese. Obesity was associated with shorter survival in patients with MGMT methylated glioblastoma (median OS 22.9 (95% CI 17.7–30.8) vs. 43.2 (32.5–54.4) months for obese and non-obese patients respectively, p = 0.001), but not in MGMT unmethylated glioblastoma (median OS 17.1 (15.8–18.9) vs 17.6 (14.7–20.8) months, p = 0.26). The prognostic impact of obesity in MGMT methylated glioblastoma was confirmed in a multivariable Cox regression (adjusted odds ratio: 2.57 (95% CI 1.53–4.31), p < 0.001) adjusted for age, sex, extent of resection, baseline steroids, Karnofsky performance score, and treatment arm.

Conclusion

Obesity was associated with shorter survival in MGMT methylated, but not in MGMT unmethylated glioblastoma patients.

Lipid pathway dysfunction is prevalent in patients with Parkinson's disease

Many genetic risk factors for Parkinson's disease have lipid-related functions and lipid-modulating drugs such as statins may be protective against Parkinson's disease. Moreover, the hallmark Parkinson's disease pathological protein, α-synuclein, has lipid membrane function and pathways dysregulated in Parkinson's disease such as the endosome-lysosome system and synaptic signaling rely heavily on lipid dynamics. Despite the potential role for lipids in Parkinson's disease, most research to date has been protein-centric, with large-scale, untargeted serum and CSF lipidomic comparisons between genetic and idiopathic Parkinson's disease and neurotypical controls limited. In particular, the extent to which lipid dysregulation occurs in mutation carriers of one of the most common Parkinson's disease risk genes, LRRK2, is unclear. Further, the functional lipid pathways potentially dysregulated in idiopathic and LRRK2 mutation Parkinson's disease is underexplored. To better determine the extent of lipid dysregulation in Parkinson's disease, untargeted high performance liquid chromatography-tandem mass spectrometry was performed on serum (N = 221) and CSF (N = 88) obtained from a multiethnic population from the Michael J Fox Foundation LRRK2 Clinical Cohort Consortium. The cohort consisted of controls, asymptomatic LRRK2 G2019S carriers, LRRK2 G2019S carriers with Parkinson's disease and Parkinson's disease patients without a LRRK2 mutation. Age and sex were adjusted for in analyses where appropriate. Approximately one thousand serum lipid species per participant were analyzed. The main serum lipids that distinguished both Parkinson's disease patients and LRRK2 mutation carriers from controls included species of ceramide, triacylglycerol, sphingomyelin, acylcarnitine, phosphatidylcholine and lysophosphatidylethanolamine. Significant alterations in sphingolipids and glycerolipids were also reflected in Parkinson's disease and LRRK2 mutation carrier CSF, although no correlations were observed between lipids identified in both serum and CSF. Pathway analysis of altered lipid species indicated that sphingolipid metabolism, insulin signaling and mitochondrial function were the major metabolic pathways dysregulated in Parkinson's disease. Importantly, these pathways were also found to be dysregulated in serum samples from a second Parkinson's disease cohort (N = 315). Results from this study demonstrate that dysregulated lipids in Parkinson's disease generally, and in LRRK2 mutation carriers, are from functionally and metabolically related pathways. These findings provide new insight into the extent of lipid dysfunction in Parkinson's disease and therapeutics manipulating these pathways may potentially be beneficial for Parkinson's disease patients. Moreover, serum lipid profiles may be novel biomarkers for both genetic and idiopathic Parkinson's disease.

Molecular Mechanism of Lipotoxicity as an Interesting Aspect in the Development of Pathological States-Current View of Knowledge

Free fatty acids (FFAs) play numerous vital roles in the organism, such as contribution to energy generation and reserve, serving as an essential component of the cell membrane, or as ligands for nuclear receptors. However, the disturbance in fatty acid homeostasis, such as inefficient metabolism or intensified release from the site of storage, may result in increased serum FFA levels and eventually result in ectopic fat deposition, which is unfavorable for the organism. The cells are adjusted for the accumulation of FFA to a limited extent and so prolonged exposure to elevated FFA levels results in deleterious effects referred to as lipotoxicity. Lipotoxicity contributes to the development of diseases such as insulin resistance, diabetes, cardiovascular diseases, metabolic syndrome, and inflammation. The nonobvious organs recognized as the main lipotoxic goal of action are the pancreas, liver, skeletal muscles, cardiac muscle, and kidneys. However, lipotoxic effects to a significant extent are not organ-specific but affect fundamental cellular processes occurring in most cells. Therefore, the wider perception of cellular lipotoxic mechanisms and their interrelation may be beneficial for a better understanding of various diseases’ pathogenesis and seeking new pharmacological treatment approaches.

Association of measures of body fat with serum alpha-tocopherol and its metabolites in middle-aged individuals

BACKGROUND AND AIMS

The accumulation of fat increases the formation of lipid peroxides, which are partly scavenged by alpha-tocopherol (α-TOH). Here, we aimed to investigate the associations between different measures of (abdominal) fat and levels of urinary α-TOH metabolites in middle-aged individuals.

METHODS AND RESULTS

In this cross-sectional analysis in the Netherlands Epidemiology of Obesity study (N = 511, 53% women; mean [SD] age of 55 [6.1] years), serum α-TOH and α-TOH metabolites from 24-h urine were measured as alpha-tocopheronolactone hydroquinone (α-TLHQ, oxidized) and alpha-carboxymethyl-hydroxychroman (α-CEHC, enzymatically converted) using liquid-chromatography-tandem mass spectrometry. Body mass index and total body fat were measured, and abdominal subcutaneous and visceral adipose tissue (aSAT and VAT) were assessed using magnetic resonance imaging. Using multivariable-adjusted linear regression analyses, we analysed the associations of BMI, TBF, aSAT and VAT with levels of urinary α-TOH metabolites, adjusted for confounders. We observed no evidence for associations between body fat measures and serum α-TOH. Higher BMI and TBF were associated with lower urinary levels of TLHQ (0.95 [95%CI: 0.90, 1.00] and 0.94 [0.88, 1.01] times per SD, respectively) and with lower TLHQ relative to CEHC (0.93 [0.90, 0.98] and 0.93 [0.87, 0.98] times per SD, respectively). We observed similar associations for VAT (TLHQ: 0.94 [0.89, 0.99] times per SD), but not for aSAT.

CONCLUSIONS

Opposite to our research hypothesis, higher abdominal adiposity was moderately associated with lower levels of oxidized α-TOH metabolites, which might reflect lower vitamin E antioxidative activity in individuals with higher abdominal fat instead.

Lactobacillus crispatus BC1 Biosurfactant Counteracts the Infectivity of Chlamydia trachomatis Elementary Bodies

Lactobacilli-derived biosurfactants (BS) have shown promising effects as antimicrobial molecules. Since Lactobacillus crispatus plays a crucial role in maintaining vaginal eubiosis, BS from this species could represent novel therapeutic agents to counteract sexually transmitted pathogens, such as Chlamydia trachomatis (CT). The aim of the present study was to assess the inhibitory effects of a BS produced by the vaginal strain L. crispatus BC1 on the infectivity of CT elementary bodies (EBs). For concentrations ranging between 1 and 0.5 mg/mL at 60-min contact time, L. crispatus BC1 BS displayed a highly significant anti-CT activity, with about 50% reduction of EB infectivity towards HeLa cells. To identify the components responsible for chlamydial inhibition, a panel of selected fatty acids, including those present in BS lipopeptidic structure, was tested against CT EBs. Pentadecanoic acid, myristic acid, β-hydroxy-myristic acid, and β-hydroxy-palmitic acid were able to significantly reduce EBs infectivity up to 5–0.5 µg/mL, concentrations that resulted to be non-toxic for HeLa cells. These data can contribute to the understanding of the biological role of lactobacilli in the vaginal niche, as well as to promote the application of their produced BS as an innovative and antibiotic-sparing anti-chlamydial strategy.

Cladophora glomerata enriched by biosorption with Mn(II) ions alleviates lipopolysaccharide-induced osteomyelitis-like model in MC3T3-E1, and 4B12 osteoclastogenesis

Chronic osteomyelitis, a bone infectious disease, is characterized by dysregulation of bone homeostasis, which results in excessive bone resorption. Lipopolysaccharide (LPS) which is a gram‐negative endotoxin was shown to inhibit osteoblast differentiation and to induce apoptosis and osteoclasts formation in vitro. While effective therapy against bacteria‐induced bone destruction is quite limited, the investigation of potential drugs that restore down‐regulated osteoblast function remains a major goal in the prevention of bone destruction in infective bone diseases. This investigation aimed to rescue LPS‐induced MC3T3‐E1 pre‐osteoblastic cell line using the methanolic extract of Cladophora glomerata enriched with Mn(II) ions by biosorption. LPS‐induced MC3T3‐E1 cultures supplemented with C. glomerata methanolic extract were tested for expression of the main genes and microRNAs involved in the osteogenesis pathway using RT‐PCR. Moreover, osteoclastogenesis of 4B12 cells was also investigated by tartrate‐resistant acid phosphatase (TRAP) assay. Treatment with algal extract significantly restored LPS‐suppressed bone mineralization and the mRNA expression levels of osteoblast‐specific genes such as runt‐related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and osteocalcin (OCN), osteopontin (OPN), miR‐27a and miR‐29b. The extract also inhibited osteoblast apoptosis, significantly restored the down‐regulated expression of Bcl‐2, and decreased the loss of MMP and reactive oxygen spices (ROS) production in MC3T3‐E1 cells induced by LPS. Furthermore, pre‐treatment with algal extract strongly decreased the activation of osteoclast in MC3T3‐E1‐4B12 coculture system stimulated by LPS. Our findings suggest that C. glomerata enriched with Mn(II) ions may be a potential raw material for the development of drug for preventing abnormal bone loss induced by LPS in bacteria‐induced bone osteomyelitis.

Omega-3 Polyunsaturated Fatty Acids Mitigate Palmitate-Induced Impairments in Skeletal Muscle Cell Viability and Differentiation

Accumulation of excess saturated free fatty acids such as palmitate (PAL) in skeletal muscle leads to reductions in mitochondrial integrity, cell viability and differentiation. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) counteract PAL-induced lipid accumulation. EPA and DHA, as well as the n-3 PUFA docosapentaenoic acid (DPA), may therefore mitigate PAL-induced lipotoxicity to promote skeletal muscle cell survival and differentiation. C2C12 myoblasts were treated with 50 μM EPA, DPA, or DHA in the absence or presence of 500 μM PAL for 16 h either prior to myoblast analysis or induction of differentiation. Myoblast viability and markers of apoptosis, endoplasmic reticulum (ER) stress and myotube differentiation capacity were investigated using fluorescence microscopy and immunoblotting. High-resolution respirometry was used to assess mitochondrial function and membrane integrity. PAL induced cell death via apoptosis and increased protein content of ER stress markers BiP and CHOP. EPA, DPA, and DHA co-treatment maintained cell viability, prevented PAL-induced apoptosis and attenuated PAL-induced increases in BiP, whereas only DPA prevented increases in CHOP. PAL subsequently reduced protein content of the differentiation marker myogenin and inhibited myotube formation, and all n-3 PUFAs promoted myotube formation in the presence of PAL. Furthermore, DPA prevented PAL-induced release of cytochrome c and maintained mitochondrial integrity. These findings demonstrate the n-3 PUFAs EPA, DPA and DHA elicit similar protective effects against PAL-induced impairments in muscle cell viability and differentiation. Mechanistically, the protective effects of DPA against PAL lipotoxicity are attributable in part to its ability to maintain mitochondrial respiratory capacity via mitigating PAL-induced loss of mitochondrial membrane integrity.

Inhibition of Protein-tyrosine Phosphatase PTP1B and LMPTP Promotes Palmitate/Oleate-challenged HepG2 Cell Survival by Reducing Lipoapoptosis, Improving Mitochondrial Dynamics and Mitigating Oxidative and Endoplasmic Reticulum Stress

Objectives: Non-alcoholic fatty liver disease (NAFLD) is considered a well-known pathology that is determined without using alcohol and has emerged as a growing public health problem. Lipotoxicity is known to promote hepatocyte death, which, in the context of NAFLD, is termed lipoapoptosis. The severity of NAFLD correlates with the degree of hepatocyte lipoapoptosis. Protein–tyrosine phosphatases (PTP) including PTP1B and Low molecular weight PTP (LMPTP), are negative regulators of the insulin signaling pathway and are considered a promising therapeutic target in the treatment of diabetes. In this study, we hypothesized that the inhibition of PTP1B and LMPTP may potentially prevent hepatocyte apoptosis, mitochondrial dysfunction and endoplasmic reticulum (ER) stress onset, following lipotoxicity induced using a free fatty acid (FFA) mixture. Methods: HepG2 cells were cultured in the presence or absence of two PTP inhibitors, namely MSI-1436 and Compound 23, prior to palmitate/oleate overloading. Apoptosis, ER stress, oxidative stress, and mitochondrial dynamics were then evaluated by either MUSE or RT-qPCR analysis. Results: The obtained data demonstrate that the inhibition of PTP1B and LMPTP prevents apoptosis induced by palmitate and oleate in the HepG2 cell line. Moreover, mitochondrial dynamics were positively improved following inhibition of the enzyme, with concomitant oxidative stress reduction and ER stress abrogation. Conclusion: In conclusion, PTP’s inhibitory properties may be a promising therapeutic strategy for the treatment of FFA-induced lipotoxicity in the liver and ultimately in the management of the NAFLD condition.

Non-esterified Fatty Acid Induce Dairy Cow Hepatocytes Apoptosis via the Mitochondria-Mediated ROS-JNK/ERK Signaling Pathway

Elevated plasma non-esterified fatty acid (NEFA) levels and hepatocytes damage are characteristics of ketosis in dairy cows. Oxidative stress is associated with the pathogenesis of NEFA-induced liver damage. However, the exact mechanism by which oxidative stress mediates NEFA-induced hepatocytes apoptosis and liver injury remains poorly understood. The results of the present study demonstrated that NEFA contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c (cyt c) into the cytosol, leading to hepatocytes apoptosis. Besides, NEFA triggered apoptosis in dairy cow hepatocytes via the regulation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), caspase 9 and poly (ADP-ribose) polymerase (PARP). Pretreatment with the inhibitor SP600125 or PD98059 or the antioxidant N-acetylcysteine (NAC) revealed that NEFA-ROS-JNK/ERK-mediated mitochondrial signaling pathway plays a crucial role in NEFA-induced hepatocytes apoptosis. Moreover, the results suggested that the transcription factors p53 and Nrf2 function downstream of this NEFA-ROS-JNK/ERK pathway and are involved in NEFA-induced hepatocytes apoptosis. In conclusion, these findings indicate that the NEFA-ROS-JNK/ERK-mediated mitochondrial pathway plays an important role in NEFA-induced dairy cow hepatocytes apoptosis and strongly suggests that the inhibitors SP600125 and PD98059 and the antioxidant NAC may be developed as therapeutics to prevent hyperlipidemia-induced apoptotic damage in ketotic dairy cows.

The Influence of Dietary Fatty Acids on Immune Responses

Diet-derived fatty acids (FAs) are essential sources of energy and fundamental structural components of cells. They also play important roles in the modulation of immune responses in health and disease. Saturated and unsaturated FAs influence the effector and regulatory functions of innate and adaptive immune cells by changing membrane composition and fluidity and by acting through specific receptors. Impaired balance of saturated/unsaturated FAs, as well as n-6/n-3 polyunsaturated FAs has significant consequences on immune system homeostasis, contributing to the development of many allergic, autoimmune, and metabolic diseases. In this paper, we discuss up-to-date knowledge and the clinical relevance of the influence of dietary FAs on the biology, homeostasis, and functions of epithelial cells, macrophages, dendritic cells, neutrophils, innate lymphoid cells, T cells and B cells. Additionally, we review the effects of dietary FAs on the pathogenesis of many diseases, including asthma, allergic rhinitis, food allergy, atopic dermatitis, rheumatoid arthritis, multiple sclerosis as well as type 1 and 2 diabetes.

Osteosarcopenia: A case of geroscience

Many older persons lose their mobility and independence due to multiple diseases occurring simultaneously. Geroscience is aimed at developing innovative approaches to better identify relationships among the biological processes of aging. Osteoporosis and sarcopenia are two of the most prevalent chronic diseases in older people, with both conditions sharing overlapping risk factors and pathogenesis. When occurring together, these diseases form a geriatric syndrome termed "osteosarcopenia," which increases the risk of frailty, hospitalizations, and death. Findings from basic and clinical sciences aiming to understand osteosarcopenia have provided evidence of this syndrome as a case of geroscience. Genetic, endocrine, and mechanical stimuli, in addition to fat infiltration, sedentarism, and nutritional deficiencies, affect muscle and bone homeostasis to characterize this syndrome. However, research is in its infancy regarding accurate diagnostic markers and effective treatments with dual effects on muscle and bone. To date, resistance exercise remains the most promising strategy to increase muscle and bone mass, while sufficient quantities of protein, vitamin D, calcium, and creatine may preserve these tissues with aging. More recent findings, from rodent models, suggest treating ectopic fat in muscle and bone marrow as a possible avenue to curb osteosarcopenia, although this needs testing in human clinical trials.

Heteroxenia Ghardaqensis Extract Protects Against DNA Damage in Streptozotocin-Induced Experimental Diabetes

DNA damage is correlated to type-2 diabetes mellitus (T2DM) and its complications via oxidative stress. This study aimed to evaluate the anti-diabetic effect of Heteroxenia ghardaqensis extract on streptozotocin (STZ) induced-diabetes and how far can this extract attenuate DNA damage in this model. Forty male albino rats (160-180 g) were used in this study and divided into four groups: control, diabetic, diabetic rats received H. ghardaqensis extract (30 mg/kg body weight/day) orally for four weeks and diabetic rats received H. ghardaqensis extract (60 mg/kg body weight/day) orally for four weeks. After the experimental period, fasting blood sugar and serum cholesterol were determined. Urinary 8-hydroxyguanosine (8-OHdG) as a marker of DNA damage was estimated by reversed phase (HPLC). Liver and kidney nitic oxide (NO) and malondialdehyde (MDA) were estimated. Pancreatic tissues were histopathologicaly examined. Our results suggested that diabetes mellitus is accompanied by elevation of DNA damage that enhances the tendency to mutagens and reduce the efficacy of DNA repair. H. ghardaqensis extract appeared to be effective against the oxidative stress induced by STZ which may be due to sesquiterpenoids and diterpenes compounds that scavenge free radicals and increase the antioxidant enzymes as appeared in attenuation of DNA damage.

Role of reactive oxygen species-total antioxidant capacity status in Telfairia occidentalis leaves-associated spermatoprotective effect: a pointer to fatty acids benefit

Background The present study used reactive oxygen species (ROS)-total antioxidant capacity (TAC) score to understand the role of redox status on the effect of Telfairia occidentalis (TO) on testicular parameters. The fatty acids (FAs) components of methanol extract of TO (METO) and its fractions were also identified with gas chromatography-mass spectrometry. Methods A total of 66 male Wistar rats were randomly divided in a blinded fashion into six oral treatment groups as follows: group I (control, n=6) received 10% ethanol (vehicle for TO administration). Groups II to VI (n=12 rats each) were subdivided into two treatment subgroups (n=6 each) that received 200 mg/kg and 600 mg/kg of METO and its chloroform, petroleum ether, acetone, and ethanol fractions, respectively. All treatments lasted for 30 days. Results The major FAs detected in TO were myristic, palmitic, oleic, linoleic, linolenic, and stearic acids including their esters. Both doses of METO and its fractions increased the semen parameters, TAC and ROS-TAC scores but decreased the ROS when compared with control. Conclusions Using the ROS-TAC score, this study suggests that TO-associated improvement in semen parameters might be partly mediated by a reduction in free radical generation, and that the FAs present in TO might be involved in its spermatoprotective effect.

The DNA Repair Protein OGG1 Protects Against Obesity by Altering Mitochondrial Energetics in White Adipose Tissue

Obesity and related metabolic pathologies represent a significant public health concern. Obesity is associated with increased oxidative stress that damages genomic and mitochondrial DNA. Oxidatively-induced lesions in both DNA pools are repaired via the base-excision repair pathway, initiated by DNA glycosylases such as 8-oxoguanine DNA glycosylase (OGG1). Global deletion of OGG1 and common OGG1 polymorphisms render mice and humans susceptible to metabolic disease. However, the relative contribution of mitochondrial OGG1 to this metabolic phenotype is unknown. Here, we demonstrate that transgenic targeting of OGG1 to mitochondria confers significant protection from diet-induced obesity, insulin resistance, and adipose tissue inflammation. These favorable metabolic phenotypes are mediated by an increase in whole body energy expenditure driven by specific metabolic adaptations, including increased mitochondrial respiration in white adipose tissue of OGG1 transgenic (Ogg1^Tg) animals. These data demonstrate a critical role for a DNA repair protein in modulating mitochondrial energetics and whole-body energy balance.

High Fat With High Sucrose Diet Leads to Obesity and Induces Myodegeneration

Skeletal muscle utilizes both free fatty acids (FFAs) and glucose that circulate in the blood stream. When blood glucose levels acutely increase, insulin stimulates muscle glucose uptake, oxidation, and glycogen synthesis. Under these conditions, skeletal muscle preferentially oxidizes glucose while the oxidation of fatty acids (FAs) oxidation is reciprocally decreased. In metabolic disorders associated with insulin resistance, such as diabetes and obesity, both glucose uptake, and utilization muscle are significantly reduced causing FA oxidation to provide the majority of ATP for metabolic processes and contraction. Although the causes of this metabolic inflexibility or disrupted "glucose-fatty acid cycle" are largely unknown, a diet high in fat and sugar (HFS) may be a contributing factor. This metabolic inflexibility observed in models of obesity or with HFS feeding is detrimental because high rates of FA oxidation in skeletal muscle can lead to the buildup of toxic metabolites of fat metabolism and the accumulation of pro-inflammatory cytokines, which further exacerbate the insulin resistance. Further, HFS leads to skeletal muscle atrophy with a decrease in myofibrillar proteins and phenotypically characterized by loss of muscle mass and strength. Overactivation of ubiquitin proteasome pathway, oxidative stress, myonuclear apoptosis, and mitochondrial dysfunction are some of the mechanisms involved in muscle atrophy induced by obesity or in mice fed with HFS. In this review, we will discuss how HFS diet negatively impacts the various physiological and metabolic mechanisms in skeletal muscle.

Human Mesenchymal Stem Cell Derived Exosomes Alleviate Type 2 Diabetes Mellitus by Reversing Peripheral Insulin Resistance and Relieving β-Cell Destruction

Exosomes are nanosized extracellular vesicles (EVs) that show great promise in tissue regeneration and injury repair as mesenchymal stem cell (MSC). MSC has been shown to alleviate diabetes mellitus (DM) in both animal models and clinical trials. In this study, we aimed to investigate whether exosomes from human umbilical cord MSC (hucMSC-ex) have a therapeutic effect on type 2 DM (T2DM). We established a rat model of T2DM using a high-fat diet and streptozotocin (STZ). We found that the intravenous injection of hucMSC-ex reduced blood glucose levels as a main paracrine approach of MSC. HucMSC-ex partially reversed insulin resistance in T2DM indirectly to accelerate glucose metabolism. HucMSC-ex restored the phosphorylation (tyrosine site) of the insulin receptor substrate 1 and protein kinase B in T2DM, promoted expression and membrane translocation of glucose transporter 4 in muscle, and increased storage of glycogen in the liver to maintain glucose homeostasis. HucMSC-ex inhibited STZ-induced β-cell apoptosis to restore the insulin-secreting function of T2DM. Taken together, exosomes from hucMSC can alleviate T2DM by reversing peripheral insulin resistance and relieving β-cell destruction, providing an alternative approach for T2DM treatment.

Cellular Stresses and Stress Responses in the Pathogenesis of Insulin Resistance

Insulin resistance (IR), a key component of the metabolic syndrome, precedes the development of diabetes, cardiovascular disease, and Alzheimer's disease. Its etiological pathways are not well defined, although many contributory mechanisms have been established. This article summarizes such mechanisms into the hypothesis that factors like nutrient overload, physical inactivity, hypoxia, psychological stress, and environmental pollutants induce a network of cellular stresses, stress responses, and stress response dysregulations that jointly inhibit insulin signaling in insulin target cells including endothelial cells, hepatocytes, myocytes, hypothalamic neurons, and adipocytes. The insulin resistance-inducing cellular stresses include oxidative, nitrosative, carbonyl/electrophilic, genotoxic, and endoplasmic reticulum stresses; the stress responses include the ubiquitin-proteasome pathway, the DNA damage response, the unfolded protein response, apoptosis, inflammasome activation, and pyroptosis, while the dysregulated responses include the heat shock response, autophagy, and nuclear factor erythroid-2-related factor 2 signaling. Insulin target cells also produce metabolites that exacerbate cellular stress generation both locally and systemically, partly through recruitment and activation of myeloid cells which sustain a state of chronic inflammation. Thus, insulin resistance may be prevented or attenuated by multiple approaches targeting the different cellular stresses and stress responses.

The Essential Element Manganese, Oxidative Stress, and Metabolic Diseases: Links and Interactions

Manganese (Mn) is an essential element that is involved in the synthesis and activation of many enzymes and in the regulation of the metabolism of glucose and lipids in humans. In addition, Mn is one of the required components for Mn superoxide dismutase (MnSOD) that is mainly responsible for scavenging reactive oxygen species (ROS) in mitochondrial oxidative stress. Both Mn deficiency and intoxication are associated with adverse metabolic and neuropsychiatric effects. Over the past few decades, the prevalence of metabolic diseases, including type 2 diabetes mellitus (T2MD), obesity, insulin resistance, atherosclerosis, hyperlipidemia, nonalcoholic fatty liver disease (NAFLD), and hepatic steatosis, has increased dramatically. Previous studies have found that ROS generation, oxidative stress, and inflammation are critical for the pathogenesis of metabolic diseases. In addition, deficiency in dietary Mn as well as excessive Mn exposure could increase ROS generation and result in further oxidative stress. However, the relationship between Mn and metabolic diseases is not clear. In this review, we provide insights into the role Mn plays in the prevention and development of metabolic diseases.

Insulin resistance in obesity: an overview of fundamental alterations

Obesity is a major health risk factor, and obesity-induced morbidity and complications account for huge costs for affected individuals, families, healthcare systems, and society at large. In particular, obesity is strongly associated with the development of insulin resistance, which in turn plays a key role in the pathogenesis of obesity-associated cardiometabolic complications, including metabolic syndrome components, type 2 diabetes, and cardiovascular diseases. Insulin sensitive tissues, including adipose tissue, skeletal muscle, and liver, are profoundly affected by obesity both at biomolecular and functional levels. Altered adipose organ function may play a fundamental pathogenetic role once fat accumulation has ensued. Modulation of insulin sensitivity appears to be, at least in part, related to changes in redox balance and oxidative stress as well as inflammation, with a relevant underlying role for mitochondrial dysfunction that may exacerbate these alterations. Nutrients and substrates as well as systems involved in host-nutrient interactions, including gut microbiota, have been also identified as modulators of metabolic pathways controlling insulin action. This review aims at providing an overview of these concepts and their potential inter-relationships in the development of insulin resistance, with particular regard to changes in adipose organ and skeletal muscle.

Chemokine (C-X-C motif) ligand 1 is a myokine induced by palmitate and is required for myogenesis in mouse satellite cells

AIM

The functional significance of the myokines, cytokines and peptides produced and released by muscle cells has not been fully elucidated. The purpose of this study was to identify a myokine with increased secretion levels in muscle cells due to saturated fatty acids and to examine the role of the identified myokine in the regulation of myogenesis.

METHODS

Human primary myotubes and mouse C2C12 myotubes were used to identify the myokine; its secretion was stimulated by palmitate loading. The role of the identified myokine in the regulation of the activation, proliferation, differentiation and self-renewal was examined in mouse satellite cells (skeletal muscle stem cells).

RESULTS

Palmitate loading promoted the secretion of chemokine (C-X-C motif) ligand 1 (CXCL1) in human primary myotubes, and it also increased CXCL1 gene expression level in C2C12 myotubes in a dose- and time-dependent manner. Palmitate loading increased the production of reactive oxygen species along with the activation of nuclear factor-kappa B (NF-κB) signalling. Pharmacological inhibition of NF-κB signalling attenuated the increase in CXCL1 gene expression induced by palmitate and hydrogen peroxide. Palmitate loading significantly increased CXC receptor 2 gene expression in undifferentiated cells. CXCL1 knockdown attenuated proliferation and myotube formation by satellite cells, with reduced self-renewal. CXCL1 knockdown also significantly decreased the Notch intracellular domain protein level.

CONCLUSION

These results suggest that secretion of the myokine CXCL1 is stimulated by saturated fatty acids and that CXCL1 promotes myogenesis from satellite cells to maintain skeletal muscle homeostasis.

Adipocyte Fatty Acid-Binding Protein Promotes Palmitate-Induced Mitochondrial Dysfunction and Apoptosis in Macrophages

A high level of circulating free fatty acids (FFAs) is known to be an important trigger for macrophage apoptosis during the development of atherosclerosis. However, the underlying mechanism by which FFAs result in macrophage apoptosis is not well understood. In cultured human macrophage Thp-1 cells, we showed that palmitate (PA), the most abundant FFA in circulation, induced excessive reactive oxidative substance production, increased malondialdehyde concentration, and decreased adenosine triphosphate levels. Furthermore, PA treatment also led to mitochondrial dysfunction, including the decrease of mitochondrial number, the impairment of respiratory complex IV and succinate dehydrogenase activity, and the reduction of mitochondrial membrane potential. Mitochondrial apoptosis was also detected after PA treatment, indicated by a decrease in cytochrome c release, downregulation of Bcl-2, upregulation of Bax, and increased caspase-3 activity. PA treatment upregulated the expression of adipocyte fatty acid-binding protein (A-FABP), a critical regulator of fatty acid trafficking and lipid metabolism. Inhibition of A-FABP with BMS309403, a small-molecule A-FABP inhibitor, almost reversed all of these indexes. Thus, this study suggested that PA-mediated macrophage apoptosis through A-FABP upregulation, which subsequently resulted in mitochondrial dysfunction and reactive oxidative stress. Inhibition of A-FABP may be a potential therapeutic target for macrophage apoptosis and to delay the progress of atherosclerosis.

Nutritional support contributes to recuperation in a rat model of aplastic anemia by enhancing mitochondrial function

OBJECTIVES

Acquired aplastic anemia (AA) is a hematopoietic stem cell disease that leads to hematopoietic disorder and peripheral blood pancytopenia. We investigated whether nutritional support is helpful to AA recovery.

METHODS

We established a rat model with AA. A nutrient mixture was administered to rats with AA through different dose gavage once per day for 55 d. Animals in this study were assigned to one of five groups: normal control (NC; group includes normal rats); AA (rats with AA); high dose (AA + nutritional mixture, 2266.95 mg/kg/d); medium dose (1511.3 mg/kg/d); and low dose (1057.91 mg/kg/d). The effects of nutrition administration on general status and mitochondrial function of rats with AA were evaluated.

RESULTS

The nutrient mixture with which the rats were supplemented significantly improved weight, peripheral blood parameters, and histologic parameters of rats with AA in a dose-dependent manner. Furthermore, we observed that the number of mitochondria in the liver, spleen, kidney, and brain was increased after supplementation by transmission electron microscopy analysis. Nutrient administration also improved mitochondrial DNA content, adenosine triphosphate content, and membrane potential but inhibited oxidative stress, thus, repairing the mitochondrial dysfunction of the rats with AA.

CONCLUSIONS

Taken together, nutrition supplements may contribute to the improvement of mitochondrial function and play an important role in the recuperation of rats with AA.

The Contribution of Singlet Oxygen to Insulin Resistance

Insulin resistance contributes to the development of diabetes and cardiovascular dysfunctions. Recent studies showed that elevated singlet oxygen-mediated lipid peroxidation precedes and predicts diet-induced insulin resistance (IR), and neutrophils were suggested to be responsible for such singlet oxygen production. This review highlights literature suggesting that insulin-responsive cells such as endothelial cells, hepatocytes, adipocytes, and myocytes also produce singlet oxygen, which contributes to insulin resistance, for example, by generating bioactive aldehydes, inducing endoplasmic reticulum (ER) stress, and modifying mitochondrial DNA. In these cells, nutrient overload leads to the activation of Toll-like receptor 4 and other receptors, leading to the production of both peroxynitrite and hydrogen peroxide, which react to produce singlet oxygen. Cytochrome P450 2E1 and cytochrome c also contribute to singlet oxygen formation in the ER and mitochondria, respectively. Endothelial cell-derived singlet oxygen is suggested to mediate the formation of oxidized low-density lipoprotein which perpetuates IR, partly through neutrophil recruitment to adipose tissue. New singlet oxygen-involving pathways for the formation of IR-inducing bioactive aldehydes such as 4-hydroperoxy-(or hydroxy or oxo)-2-nonenal, malondialdehyde, and cholesterol secosterol A are proposed. Strategies against IR should target the singlet oxygen-producing pathways, singlet oxygen quenching, and singlet oxygen-induced cellular responses.

NOD2 activation induces oxidative stress contributing to mitochondrial dysfunction and insulin resistance in skeletal muscle cells

Nucleotide-binding oligomerization domain protein-2 (NOD2) activation in skeletal muscle cells has been associated with insulin resistance, but the underlying mechanisms are not yet clear. Here we demonstrate the implication of oxidative stress in the development of mitochondrial dysfunction and insulin resistance in response to NOD2 activation in skeletal muscle cells. Treatment with the selective NOD2 ligand muramyl dipeptide (MDP) increased mitochondrial reactive oxygen species (ROS) generation in L6 myotubes. MDP-induced ROS production was associated with increased levels of protein carbonyls and reduction in citrate synthase activity, cellular ATP level, and mitochondrial membrane potential, as well as altered expression of genes involved in mitochondrial function and metabolism. Antioxidant treatment attenuated MDP-induced ROS production and restored mitochondrial functions. In addition, the presence of antioxidant prevented NOD2-mediated activation of MAPK kinases and the inflammatory response. This was associated with reduced serine phosphorylation of insulin receptor substrate-1 (IRS-1) and improved insulin-stimulated tyrosine phosphorylation of IRS-1 and downstream activation of Akt phosphorylation. These data indicate that oxidative stress plays a role in NOD2 activation-induced inflammatory response and that MDP-induced oxidative stress correlates with impairment of mitochondrial functions and induction of insulin resistance in skeletal muscle cells.

C1q tumor necrosis factor α-related protein isoform 5 attenuates palmitate-induced DNA fragmentation in myocytes through an AMPK-dependent mechanism

This article reports the data for the effects of C1q tumor necrosis factor α-related protein isoform 5 (CTRP5) on the palmitate-induced apoptosis in myocytes. The data obtained from in vitro cultured myocytes shows that the cellular treatment with the globular domain of CTRP5 (gCTRP5) significantly inhibits the palmitate-induced MTT reduction, caspase-3 activation, and DNA fragmentation in a time-dependent manner. The data presented in this article also shows that AraA, an inhibitor of AMPK, almost completely abolished the protective effect of gCTRP5 on the DNA fragmentation induced by palmitate in myocytes. Interpretation of our data and further extensive insights into the protective role of CTRP5 in palmitate-induced apoptosis in myocytes can be found in Yang and Lee (2014) [1].

A comparison of melatonin and α-lipoic acid in the induction of antioxidant defences in L6 rat skeletal muscle cells

Aging is characterized by a progressive deterioration in physiological functions and metabolic processes. The loss of cells during aging in vital tissues and organs is related to several factors including oxidative stress and inflammation. Skeletal muscle degeneration is common in elderly people; in fact, this tissue is particularly vulnerable to oxidative stress since it requires large amounts of oxygen, and thus, oxidative damage is abundant and accumulates with increasing age. Melatonin (N-acetyl-5-methoxytryptamine) is a highly efficient scavenger of reactive oxygen species and it also exhibits beneficial anti-inflammatory and anti-aging effects. This study investigated the susceptibility of rat L6 skeletal muscle cells to an induced oxidative stress following their exposure to hydrogen peroxide (50 μM) and evaluating the potential protective effects of pre-treatment with melatonin (10 nM) compared to the known beneficial effect of alpha-lipoic acid (300 μM). Hydrogen peroxide-induced obvious oxidative stress; it increased the expression of tumour necrosis factor-alpha and in turn promoted nuclear factor kappa-B and overrode the endogenous defence mechanisms. Conversely, pre-treatment of the hydrogen peroxide-exposed cells to melatonin or alpha-lipoic acid increased endogenous antioxidant enzymes, including superoxide dismutase-2 and heme oxygenase-1; moreover, they ameliorated significantly oxidative stress damage and partially reduced alterations in the muscle cells, which are typical of aging. In conclusion, melatonin was equally effective as alpha-lipoic acid; it exhibited marked antioxidant and anti-aging effects at the level of skeletal muscle in vitro even when it was given in a much lower dose than alpha-lipoic acid.

Low alpha-synuclein levels in the blood are associated with insulin resistance

Mutations in the protein alpha-synuclein (SNCA) have been linked to Parkinson's disease. We recently reported that non-mutated SNCA enhanced glucose uptake through the Gab1-PI3 kinase-Akt pathway and elucidated its effects on glucose regulation. Here, we examined the association of SNCA with insulin resistance (IR), a condition that is characterized by decreased tissue glucose uptake. Our observations include those from a population study as well as a SNCA-deficient mouse model, which had not previously been characterized in an IR scenario. In 1,152 patients, we found that serum SNCA levels were inversely correlated with IR indicators--body mass index, homeostatic model assessment for IR (HOMA-IR) and immunoreactive insulin (IRI)--and, to a lesser extent, with blood pressure and age. Additionally, SNCA-deficient mice displayed alterations in glucose and insulin responses during diet-induced IR. Moreover, during euglycemic clamp assessments, SNCA knock-out mice fed a high-fat diet (HFD) showed severe IR in adipose tissues and skeletal muscle. These findings provide new insights into IR and diabetes and point to SNCA as a potential candidate for further research.

Metformin attenuates palmitic acid-induced insulin resistance in L6 cells through the AMP-activated protein kinase/sterol regulatory element-binding protein-1c pathway

AMP-activated protein kinase (AMPK) is an important effector of metformin action on glucose uptake in skeletal muscle cells. We recently reported that metformin improved insulin receptor substrate-1 (IRS-1)-associated insulin signaling by downregulating sterol regulatory element-binding protein-1c (SREBP-1c) expression. In this study, we investigated whether AMPK activation and SREBP-1c inhibition contribute to the beneficial effects of metformin on IRS-1-associated insulin signaling in L6 myotubes. L6 muscle cells were incubated with palmitic acid (PA) to induce insulin resistance and then treated with metformin and/or the AMPK inhibitor, compound C. AMPK, SREBP-1c, IRS-1 and Akt protein expression levels were determined by western blot analysis. The effects of metformin on SREBP-1c gene transcription were determined by a luciferase reporter assay. Glucose uptake was evaluated using the 2-NBDG method. In the PA-treated L6 cells, metformin treatment enhanced AMPK phosphorylation, reduced SREBP-1c expression and increased IRS-1 and Akt protein expression, whereas treatment with compound C blocked the effects of metformin on SREBP-1c expression and the IRS-1 and Akt levels. Moreover, metformin suppressed SREBP-1c promoter activity and promoted glucose uptake through AMPK. The results from this study demonstrate that metformin ameliorates PA-induced insulin resistance through the activation of AMPK and the suppression of SREBP-1c in skeletal muscle cells.

Phosphorylation of caveolin-1 on tyrosine-14 induced by ROS enhances palmitate-induced death of beta-pancreatic cells

A considerable body of evidence exists implicating high levels of free saturated fatty acids in beta pancreatic cell death, although the molecular mechanisms and the signaling pathways involved have not been clearly defined. The membrane protein caveolin-1 has long been implicated in cell death, either by sensitizing to or directly inducing apoptosis and it is normally expressed in beta cells. Here, we tested whether the presence of caveolin-1 modulates free fatty acid-induced beta cell death by reexpressing this protein in MIN6 murine beta cells lacking caveolin-1. Incubation of MIN6 with palmitate, but not oleate, induced apoptotic cell death that was enhanced by the presence of caveolin-1. Moreover, palmitate induced de novo ceramide synthesis, loss of mitochondrial transmembrane potential and reactive oxygen species (ROS) formation in MIN6 cells. ROS generation promoted caveolin-1 phosphorylation on tyrosine-14 that was abrogated by the anti-oxidant N-acetylcysteine or the incubation with the Src-family kinase inhibitor, PP2 (4-amino-5-(4-chlorophenyl)-7(dimethylethyl)pyrazolo[3,4-d]pyrimidine). The expression of a non-phosphorylatable caveolin-1 tyrosine-14 to phenylalanine mutant failed to enhance palmitate-induced apoptosis while for MIN6 cells expressing the phospho-mimetic tyrosine-14 to glutamic acid mutant caveolin-1 palmitate sensitivity was comparable to that observed for MIN6 cells expressing wild type caveolin-1. Thus, caveolin-1 expression promotes palmitate-induced ROS-dependent apoptosis in MIN6 cells in a manner requiring Src family kinase mediated tyrosine-14 phosphorylation.

High-fat feeding does not induce an autophagic or apoptotic phenotype in female rat skeletal muscle

Apoptosis and autophagy are critical in normal skeletal muscle homeostasis; however, dysregulation can lead to muscle atrophy and dysfunction. Lipotoxicity and/or lipid accumulation may promote apoptosis, as well as directly or indirectly influence autophagic signaling. Therefore, the purpose of this study was to examine the effect of a 16-week high-fat diet on morphological, apoptotic, and autophagic indices in oxidative and glycolytic skeletal muscle of female rats. High-fat feeding resulted in increased fat pad mass, altered glucose tolerance, and lower muscle pAKT levels, as well as lipid accumulation and reactive oxygen species generation in soleus muscle; however, muscle weights, fiber type-specific cross-sectional area, and fiber type distribution were not affected. Moreover, DNA fragmentation and LC3 lipidation as well as several apoptotic (ARC, Bax, Bid, tBid, Hsp70, pBcl-2) and autophagic (ATG7, ATG4B, Beclin 1, BNIP3, p70 s6k, cathepsin activity) indices were not altered in soleus or plantaris following high-fat diet. Interestingly, soleus muscle displayed small increases in caspase-3, caspase-8, and caspase-9 activity, as well as higher ATG12-5 and p62 protein, while both soleus and plantaris muscle showed dramatically reduced Bcl-2 and X-linked inhibitor of apoptosis protein (XIAP) levels. In conclusion, this work demonstrates that 16 weeks of high-fat feeding does not affect tissue morphology or induce a global autophagic or apoptotic phenotype in skeletal muscle of female rats. However, high-fat feeding selectively influenced a number of apoptotic and autophagic indices which could have implications during periods of enhanced muscle stress.

CTRP5 ameliorates palmitate-induced apoptosis and insulin resistance through activation of AMPK and fatty acid oxidation

Lipotoxicity resulting from a high concentration of saturated fatty acids is closely linked to development of insulin resistance, as well as apoptosis in skeletal muscle. CTRP5, an adiponectin paralog, is known to activate AMPK and fatty acid oxidation; however, the effects of CTRP5 on palmitate-induced lipotoxicity in myocytes have not been investigated. We found that globular domain of CTRP5 (gCTRP5) prevented palmitate-induced apoptosis and insulin resistance in myocytes by inhibiting the activation of caspase-3, reactive oxygen species accumulation, and IRS-1 reduction. These beneficial effects of gCTRP5 are mainly attributed to an increase in fatty acid oxidation through phosphorylation of AMPK. These results provide a novel function of CTRP5, which may have preventive and therapeutic potential in management of obesity, insulin resistance, and type 2 diabetes mellitus.

Integrated analysis of chronic lipotoxicity on muscle metabolism and stress and its reversal by antioxidants

Apart from elevated glucose, triglyceride and cholesterol, elevated levels of serum free-fatty acid (FFA) are observed in diabetic patients. Increased FFA load can cause multiple dysregulation which are collectively known as lipotoxicity. Impacts of FFA induced lipotoxicity were evaluated on various cellular responses of metabolism and stress in skeletal muscle myotubes. Under lipotoxicity, oxidative capacity of C2C12 myotubes was reduced and decreased levels ATP and NAD were observed. Lipotoxicity augmented non-oxidative disposal of metabolites in terms of lactate release, IMTG and ceramide synthesis. Concomitantly, insulin resistance was also observed. These impacts were in conjunction with increased cellular stress, inflammation, proteolysis and apoptosis. Quenching of lipotoxicity mediated oxidative stress by antioxidant reverted its deleterious impacts and restored insulin stimulated glucose uptake. In conclusion, the in vitro lipotoxicity makes a system which resembles in vivo pathology of muscle as seen in diabetic patients and represents an integrated perspective of lipotoxicity on various parameters of metabolism and stress.

Oleate prevents palmitate-induced mitochondrial dysfunction, insulin resistance and inflammatory signaling in neuronal cells

Elevated circulating levels of saturated free fatty acids (sFFAs; e.g. palmitate) are known to provoke inflammatory responses and cause insulin resistance in peripheral tissue. By contrast, mono- or poly-unsaturated FFAs are protective against sFFAs. An excess of sFFAs in the brain circulation may also trigger neuroinflammation and insulin resistance, however the underlying signaling changes have not been clarified in neuronal cells. In the present study, we examined the effects of palmitate on mitochondrial function and viability as well as on intracellular insulin and nuclear factor-κB (NF-κB) signaling pathways in Neuro-2a and primary rat cortical neurons. We next tested whether oleate preconditioning has a protective effect against palmitate-induced toxicity. Palmitate induced both mitochondrial dysfunction and insulin resistance while promoting the phosphorylation of mitogen-activated protein kinases and nuclear translocation of NF-κB p65. Oleate pre-exposure and then removal was sufficient to completely block subsequent palmitate-induced intracellular signaling and metabolic derangements. Oleate also prevented ceramide-induced insulin resistance. Moreover, oleate stimulated ATP while decreasing mitochondrial superoxide productions. The latter were associated with increased levels of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). Inhibition of protein kinase A (PKA) attenuated the protective effect of oleate against palmitate, implicating PKA in the mechanism of oleate action. Oleate increased triglyceride and blocked palmitate-induced diacylglycerol accumulations. Oleate preconditioning was superior to docosahexaenoic acid (DHA) or linoleate in the protection of neuronal cells against palmitate- or ceramide-induced cytotoxicity. We conclude that oleate has beneficial properties against sFFA and ceramide models of insulin resistance-associated damage to neuronal cells.

The production of nitric oxide, IL-6, and TNF-alpha in palmitate-stimulated PBMNCs is enhanced through hyperglycemia in diabetes

We examined nitric oxide (NO), IL-6, and TNF-α secretion from cultured palmitate-stimulated PBMNCs or in the plasma from type 2 diabetes mellitus (T2MD) patients or nondiabetic (ND) controls. Free fatty acids (FFA) have been suggested to induce chronic low-grade inflammation, activate the innate immune system, and cause deleterious effects on vascular cells and other tissues through inflammatory processes. The levels of NO, IL-6, TNF-α, and MDA were higher in supernatant of palmitate stimulated blood cells (PBMNC) or from plasma from patients. The results obtained in the present study demonstrated that hyperglycemia in diabetes exacerbates in vitro inflammatory responses in PBMNCs stimulated with high levels of SFA (palmitate). These results suggest that hyperglycemia primes PBMNCs for NO, IL-6, and TNF-alpha secretion under in vitro FFA stimulation are associated with the secretion of inflammatory biomarkers in diabetes. A combined therapy targeting signaling pathways activated by hyperglycemia in conjunction with simultaneous control of hyperglycemia and hypertriglyceridemia would be suggested for controlling the progress of diabetic complications.

Ceramide inhibits insulin-stimulated Akt phosphorylation through activation of Rheb/mTORC1/S6K signaling in skeletal muscle

Ceramide is a negative regulator of insulin activity. At the molecular level, it causes a decrease in insulin-stimulated Akt Ser473 phosphorylation in C2C12 myotubes. Interestingly, we found that the phosphorylation of S6K at Thr389 was increased under the same conditions. Utilizing both rapamycin to inhibit mTORC1 activity and shRNA to knock down Rheb, we demonstrated that the decrease in Akt Ser473 phosphorylation stimulated by insulin after C2-ceramide incubation can be prevented. The mechanism by which C2-ceramide impairs signaling would seem to involve a negative feedback of activated S6K via phosphorylation of insulin receptor substrate-1 at Ser636/639, since S6K inhibitor can block this phenomenon. Finally, rapamycin treatment was found not to affect C2-ceramide-induced PKCζ activation, suggesting that the pathway revealed in this study is parallel to the one involving PKCζ activation. We proposed a novel pathway/mechanism involving Rheb/mTORC1/S6K signaling to explain how C2-ceramide impairs insulin signaling via Akt phosphorylation. The existence of multiple pathways involved in insulin signaling impairment by C2-ceramide treatment implies that different strategies might be needed to ameliorate insulin resistance caused by C2-ceramide.

Role for sterol regulatory element binding protein-1c activation in mediating skeletal muscle insulin resistance via repression of rat insulin receptor substrate-1 transcription

AIMS/HYPOTHESIS

Sterol regulatory element binding protein-1c (SREBP-1c) is a master regulator of fatty acid synthase and controls lipogenesis. IRS-1 is the key insulin signalling mediator in skeletal muscle. In the present study, we investigated the role of SREBP-1c in the regulation of IRS-1 in skeletal muscle cells.

METHODS

L6 muscle cells were treated with palmitic acid (PA) or metformin. Adenovirus vectors expressing Srebp-1c (also known as Srebf1) and small interfering RNA (siRNA) against Srebp-1c were transfected into the L6 cells. Protein-DNA interactions were assessed by luciferase reporter analysis, electrophoretic mobility shift assay and chromatin immunoprecipitation assay.

RESULTS

We found that both gene and protein expression of SREBP-1c was increased in contrast to IRS-1 expression in PA-treated L6 cells. SREBP-1c overproduction decreased Irs-1 mRNA and IRS-1 protein expression in a dose-dependent manner, and suppressed the resultant insulin signalling, whereas SERBP-1c knockdown by Serbp-1c siRNA blocked the downregulation of IRS-1 induced by PA. Protein-DNA interaction studies demonstrated that SREBP-1c was able to bind to the rat Irs-1 promoter region, thereby repressing its gene transcription. Of particular importance, we found that metformin treatment downregulated Srebp-1c promoter activity, decreased the specific binding of SREBP-1c to Irs-1 promoter and upregulated Irs-1 promoter activity in PA-cultured L6 cells.

CONCLUSIONS/INTERPRETATION

Our data indicate for the first time that SREBP-1c activation participates in skeletal muscle insulin resistance through a direct effect of suppressing Irs-1 transcription. These findings imply that SREBP-1c could serve as an attractive therapeutic target for insulin resistance.

The effects of obesity on skeletal muscle regeneration

Obesity and metabolic disorders such as type 2 diabetes mellitus are accompanied by increased lipid deposition in adipose and non-adipose tissues including liver, pancreas, heart and skeletal muscle. Recent publications report impaired regenerative capacity of skeletal muscle following injury in obese mice. Although muscle regeneration has not been thoroughly studied in obese and type 2 diabetic humans and mechanisms leading to decreased muscle regeneration in obesity remain elusive, the initial findings point to the possibility that muscle satellite cell function is compromised under conditions of lipid overload. Elevated toxic lipid metabolites and increased pro-inflammatory cytokines as well as insulin and leptin resistance that occur in obese animals may contribute to decreased regenerative capacity of skeletal muscle. In addition, obesity-associated alterations in the metabolic state of skeletal muscle fibers and satellite cells may directly impair the potential for satellite cell-mediated repair. Here we discuss recent studies that expand our understanding of how obesity negatively impacts skeletal muscle maintenance and regeneration.

Clinical biomarkers in metabolic syndrome

A biomarker can be defined as a measurable variable that may be used as an indicator of a given biological state or condition. Biomarkers have been used in health and disease for diagnostic purposes, as tools to assess effectiveness of nutritional or drug intervention, or as risk markers to predict the development of certain diseases. In nutrition studies, selecting appropriate biomarkers is important to assess compliance, or incidence of a particular dietary component in the biochemistry of the organism, and in the diagnosis and prognosis of nutrition-related diseases. Metabolic syndrome is a cluster of cardiovascular risk factors that occur simultaneously in the same individual, and it is associated with systemic alterations that may involve several organs and tissues. Given its close association with obesity and the increasing prevalence of obesity worldwide, identifying obese individuals at risk for metabolic syndrome is a major clinical priority. Biomarkers for metabolic syndrome are therefore potential important tools to maximize the effectiveness of treatment in subjects who would likely benefit the most. Choice of biomarkers may be challenging due to the complexity of the syndrome, and this article will mainly focus on nutrition biomarkers related to the diagnosis and prognosis of the metabolic syndrome.

Mitochondrial DNA damage via augmented oxidative stress regulates endoplasmic reticulum stress and autophagy: crosstalk, links and signaling

Saturated free fatty acids (FFAs) have been implicated in the increase of oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, autophagy, and insulin resistance (IR) observed in skeletal muscle. Previously, we have shown that palmitate-induced mitochondrial DNA (mtDNA) damage triggers mitochondrial dysfunction, mitochondrial reactive oxygen species (mtROS) production, apoptosis and IR in L6 myotubes. The present study showed that mitochondrial overexpression of human 8-oxoguanine DNA glycosylase/AP lyase (hOGG1) decreased palmitate-induced carbonylation of proteins in mitochondria. Additionally, we found that protection of mtDNA from palmitate-induced damage significantly diminished markers of both ER stress and autophagy in L6 myotubes. Moreover, we observed that the addition of ROS scavenger, N-acetylcystein (NAC), to palmitate diminished both ER stress and autophagy markers mimicking the effect of mitochondrial overexpression of hOGG1. This is the first study to show that mtDNA damage is upstream of palmitate-induced ER stress and autophagy in skeletal muscle cells.

Protein tyrosine phosphatase 1B inhibition ameliorates palmitate-induced mitochondrial dysfunction and apoptosis in skeletal muscle cells

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of the insulin signaling pathway and is considered a promising therapeutic target in the treatment of diabetes. However, the role of PTP1B in palmitate-induced mitochondrial dysfunction and apoptosis in skeletal muscle cells has not been studied. Here we investigate the effects of PTP1B modulation on mitochondrial function and apoptosis and elucidate the underlying mechanisms in skeletal muscle cells. PTP1B inhibition significantly reduced palmitate-induced mitochondrial dysfunction and apoptosis in C2C12 cells, as these cells had increased expression levels of PGC-1α, Tfam, and NRF-1; enhanced ATP level and cellular viability; decreased TUNEL-positive cells; and decreased caspase-3 and -9 activity. Alternatively, overexpression of PTP1B resulted in mitochondrial dysfunction and apoptosis in these cells. PTP1B silencing improved mitochondrial dysfunction by an increase in the expression of SIRT1 and a reduction in the phosphorylation of p65 NF-κB. The protection from palmitate-induced apoptosis by PTP1B inhibition was also accompanied by a decrease in protein level of serine palmitoyl transferase, thus resulting in lower ceramide content in muscle cells. Exogenous addition of C2-ceramide to PTP1B-knockdown cells led to a reduced generation of reactive oxygen species (ROS), whereas PTP1B overexpression demonstrated an elevated ROS production in myotubes. In addition, PTP1B inhibition was accompanied by decreased JNK phosphorylation and increased insulin-stimulated Akt (Ser473) phosphorylation, whereas overexpression of PTP1B had the opposite effect. The overexpression of PTP1B also induced the nuclear localization of FOXO-1, but in contrast, suppression of PTP1B reduced palmitate-induced nuclear localization of FOXO-1. In summary, our results indicate that PTP1B modulation results in (1) alterations in mitochondrial function by changes in the activity of SIRT1/NF-κB/PGC-1α pathways and (2) changes in apoptosis that result from either a direct effect of PTP1B on the insulin signaling pathway or an indirect influence on ceramide content, ROS generation, JNK activation, and FOXO-1 nuclear translocation.

Saturated fatty acid palmitate aggravates neointima formation by promoting smooth muscle phenotypic modulation

OBJECTIVE

Obesity is a major risk factor of atherosclerotic cardiovascular disease. Circulating free fatty acid levels are known to be elevated in obese individuals and, along with dietary saturated fatty acids, are known to associate with cardiovascular events. However, little is known about the molecular mechanisms by which free fatty acids are linked to cardiovascular disease.

APPROACH AND RESULTS

We found that administration of palmitate, a major saturated free fatty acid, to mice markedly aggravated neointima formation induced by carotid artery ligation and that the neointima primarily consisted of phenotypically modulated smooth muscle cells (SMCs). In cultured SMCs, palmitate-induced phenotypic modulation was characterized by downregulation of SMC differentiation markers, such as SM α-actin and SM-myosin heavy chain, and upregulation of mediators involved in inflammation and remodeling of the vessel wall, such as platelet-derived growth factor B and matrix metalloproteinases. We also found that palmitate induced the expression of proinflammatory genes via a novel toll-like receptor 4/myeloid differentiation primary response 88/nuclear factor-κB/NADPH oxidase 1/reactive oxygen species signaling pathway: nuclear factor-κB was activated by palmitate via toll-like receptor 4 and its adapter, MyD88, and once active, it transactivated Nox1, encoding NADPH oxidase 1, a major reactive oxygen species generator in SMCs. Pharmacological inhibition and small interfering RNA-mediated knockdown of the components of this signaling pathway mitigated the palmitate-induced upregulation of proinflammatory genes. More importantly, Myd88 knockout mice were resistant to palmitate-induced exacerbation of neointima formation.

CONCLUSIONS

Palmitate seems to promote neointima formation by inducing inflammatory phenotypes in SMCs.

Alteration of mitochondrial function and insulin sensitivity in primary mouse skeletal muscle cells isolated from transgenic and knockout mice: role of ogg1

Recent evidence has linked mitochondrial dysfunction and DNA damage, increased oxidative stress in skeletal muscle, and insulin resistance (IR). The purpose of this study was to determine the role of the DNA repair enzyme, human 8-oxoguanine DNA glycosylase/apurinic/apyrimidinic lyase (hOGG1), on palmitate-induced mitochondrial dysfunction and IR in primary cultures of skeletal muscle derived from hind limb of ogg1(-/-) knockout mice and transgenic mice, which overexpress human (hOGG1) in mitochondria (transgenic [Tg]/MTS-hOGG1). Following exposure to palmitate, we evaluated mitochondrial DNA (mtDNA) damage, mitochondrial function, production of mitochondrial reactive oxygen species (mtROS), mitochondrial mass, JNK activation, insulin signaling pathways, and glucose uptake. Palmitate-induced mtDNA damage, mtROS, mitochondrial dysfunction, and activation of JNK were all diminished, whereas ATP levels, mitochondrial mass, insulin-stimulated phosphorylation of Akt (Ser 473), and insulin sensitivity were increased in primary myotubes isolated from Tg/MTS-hOGG1 mice compared to myotubes isolated from either knockout or wild-type mice. In addition, both basal and maximal respiratory rates during mitochondrial oxidation on pyruvate showed a variable response, with some animals displaying an increased respiration in muscle fibers isolated from the transgenic mice. Our results support the model that DNA repair enzyme OGG1 plays a pivotal role in repairing mtDNA damage, and consequently, in mtROS production and regulating downstream events leading to IR in skeletal muscle.

Protection from antimycin A-induced mitochondrial dysfunction by Nelumbo nucifera seed extracts

Antimycin A (AMA) damages the mitochondria through inhibition of mitochondrial electron transport. In this study, exposure of L6 rat skeletal muscle cells to AMA induced a decrease in ATP content, followed by a decrease in mitochondrial membrane potential, leading to apoptosis. We evaluated the protective effects of water and ethanol extracts of Nelumbo nucifera seeds on L6 cells with AMA-induced oxidative stress. We found that the extracts reduced cellular apoptosis; preserved the mitochondrial membrane potential; protected mitochondrial ATP production; inhibited p53, Bax, and caspase 3 activities; and induced Bcl-2 production. Our results suggested that AMA induced apoptosis in L6 cells via impairment of mitochondrial function. N. nucifera extracts protected the cells from this mitochondria-mediated cell death.

Mitochondrial dysfunction and activation of iNOS are responsible for the palmitate-induced decrease in adiponectin synthesis in 3T3L1 adipocytes

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are considered the key determinants of insulin resistance. Impaired mitochondrial function in obese animals was shown to induce the ER stress response, resulting in reduced adiponectin synthesis in adipocytes. The expression of inducible nitric oxide synthase (iNOS) is increased in adipose tissues in genetic and dietary models of obesity. In this study, we examined whether activation of iNOS is responsible for palmitate-induced mitochondrial dysfunction, ER stress, and decreased adiponectin synthesis in 3T3L1 adipocytes. As expected, palmitate increased the expression levels of iNOS and ER stress response markers, and decreased mitochondrial contents. Treatment with iNOS inhibitor increased adiponectin synthesis and reversed the palmitate-induced ER stress response. However, the iNOS inhibitor did not affect the palmitate-induced decrease in mitochondrial contents. Chemicals that inhibit mitochondrial function increased iNOS expression and the ER stress response, whereas measures that increase mitochondrial biogenesis (rosiglitazone and adenoviral overexpression of nuclear respiratory factor-1) reversed them. Inhibition of mitochondrial biogenesis prevented the rosiglitazone-induced decrease in iNOS expression and increase in adiponectin synthesis. These results suggest that palmitate-induced mitochondrial dysfunction is the primary event that leads to iNOS induction, ER stress, and decreased adiponectin synthesis in cultured adipocytes.

Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat

Mitochondrial dysfunction has a significant role in the development of diabetic cardiomyopathy. Mitochondrial oxidant stress has been accepted as the singular cause of mitochondrial DNA (mtDNA) damage as an underlying cause of mitochondrial dysfunction. However, separate from a direct effect on mtDNA integrity, diabetic-induced increases in oxidant stress alter mitochondrial topoisomerase function to propagate mtDNA mutations as a contributor to mitochondrial dysfunction. Both glucose-challenged neonatal cardiomyocytes and the diabetic Goto-Kakizaki (GK) rat were studied. In both the GK left ventricle (LV) and in cardiomyocytes, chronically elevated glucose presentation induced a significant increase in mtDNA damage that was accompanied by decreased mitochondrial function. TTGE analysis revealed a number of base pair substitutions in the 3' end of COX3 from GK LV mtDNA that significantly altered the protein sequence. Mitochondrial topoisomerase DNA cleavage activity in isolated mitochondria was significantly increased in the GK LV compared with Wistar controls. Both hydroxycamptothecin, a topoisomerase type 1 inhibitor, and doxorubicin, a topoisomerase type 2 inhibitor, significantly exacerbated the DNA cleavage activity of isolated mitochondrial extracts indicating the presence of multiple functional topoisomerases in the mitochondria. Mitochondrial topoisomerase function was significantly altered in the presence of H2O2 suggesting that separate from a direct effect on mtDNA, oxidant stress mediated type II diabetes-induced alterations of mitochondrial topoisomerase function. These findings are significant in that the activation/inhibition state of the mitochondrial topoisomerases will have important consequences for mtDNA integrity and the well being of the diabetic myocardium.