Fatty acid-induced mitochondrial uncoupling in adipocytes as a key protective factor against insulin resistance and beta cell dysfunction: a new concept in the pathogenesis of obesity-associated type 2 diabetes mellitus

Patient-derived colon epithelial organoids reveal lipid-related metabolic dysfunction in pediatric ulcerative colitis

Ulcerative colitis (UC) is associated with epithelial metabolic derangements which exacerbate gut inflammation. Patient-derived organoids recapitulate complexities of the parent tissue in health and disease; however, whether colon organoids (colonoids) model the metabolic impairments in the pediatric UC epithelium is unclear. Here, we developed colonoid lines from pediatric patients with endoscopically active UC, inactive UC, and those without endoscopic or histologic evidence of colon inflammation (non-IBD controls) to interrogate functional metabolic differences in the colon epithelia. We demonstrate that colonoids from active UC patients exhibit hypermetabolic features and cellular stress, specifically during differentiation. Hypermetabolism in differentiating active UC colonoids was driven, in part, by increased proton leak, and supported by enhanced glycolytic capacity and dysregulated neutral lipid accumulation. Transcriptomic and pathway analyses indicated a role for PPAR-α in lipid-induced hypermetabolism in aUC colonoids, which was validated by PPAR-α activation in non-IBD colonoids. Accordingly, limiting neutral lipid accumulation in active UC colonoids through pharmacological inhibition of PPAR-α induced a metabolic shift towards glucose utilization, suppressed hypermetabolism and chemokine secretion, and improved markers of cellular stress and epithelial differentiation. Taken together, we reveal a role for lipid-related metabolic dysfunction in the pediatric UC epithelium and support the advancement of colonoids as a preclinical human model for testing epithelial-directed therapies against such metabolic dysfunction.

Increased Perfluorooctanesulfonate (PFOS) Toxicity and Accumulation Is Associated with Perturbed Prostaglandin Metabolism and Increased Organic Anion Transport Protein (OATP) Expression

Perfluorooctanesulfonate (PFOS) is a widespread environmental pollutant with a long half-life and clearly negative outcomes on metabolic diseases such as fatty liver disease and diabetes. Male and female Cyp2b-null and humanized CYP2B6-transgenic (hCYP2B6-Tg) mice were treated with 0, 1, or 10 mg/kg/day PFOS for 21 days, and surprisingly it was found that PFOS was retained at greater concentrations in the serum and liver of hCYP2B6-Tg mice than those of Cyp2b-null mice, with greater differences in the females. Thus, Cyp2b-null and hCYP2B6-Tg mice provide new models for investigating individual mechanisms for PFOS bioaccumulation and toxicity. Overt toxicity was greater in hCYP2B6-Tg mice (especially females) as measured by mortality; however, steatosis occurred more readily in Cyp2b-null mice despite the lower PFOS liver concentrations. Targeted lipidomics and transcriptomics from PFOS-treated Cyp2b-null and hCYP2B6-Tg mouse livers were performed and compared to PFOS retention and serum markers of toxicity using PCA. Several oxylipins, including prostaglandins, thromboxanes, and docosahexaenoic acid metabolites, are associated or inversely associated with PFOS toxicity. Both lipidomics and transcriptomics indicate PFOS toxicity is associated with PPAR activity in all models. GO terms associated with reduced steatosis were sexually dimorphic with lipid metabolism and transport increased in females and circadian rhythm associated genes increased in males. However, we cannot rule out that steatosis was initially protective from PFOS toxicity. Moreover, several transporters are associated with increased retention, probably due to increased uptake. The strongest associations are the organic anion transport proteins (Oatp1a4-6) genes and a long-chain fatty acid transport protein (fatp1), enriched in female hCYP2B6-Tg mice. PFOS uptake was also reduced in cultured murine hepatocytes by OATP inhibitors. The role of OATP1A6 and FATP1 in PFOS transport has not been tested. In summary, Cyp2b-null and hCYP2B6-Tg mice provided unique models for estimating the importance of novel mechanisms in PFOS retention and toxicity.

Mitochondria as a target for exercise-mitigated type 2 diabetes

Type 2 diabetes mellitus (T2DM) is one of most common metabolic diseases and continues to be a leading cause of death worldwide. Although great efforts have been made to elucidate the pathogenesis of diabetes, the underlying mechanism still remains unclear. Notably, overwhelming evidence has demonstrated that mitochondria are tightly correlated with the development of T2DM, and the defects of mitochondrial function in peripheral insulin-responsive tissues, such as skeletal muscle, liver and adipose tissue, are crucial drivers of T2DM. Furthermore, exercise training is considered as an effective stimulus for improving insulin sensitivity and hence is regarded as the best strategy to prevent and treat T2DM. Although the precise mechanisms by which exercise alleviates T2DM are not fully understood, mitochondria may be critical for the beneficial effects of exercise.

High glucose-induced inhibition of osteoblast like MC3T3-E1 differentiation promotes mitochondrial perturbations

Diabetes mellitus is a metabolic disorder that causes health concerns worldwide. Patients with diabetes exhibit multisystemic symptoms, including loss of bone quality over time. The progressive deterioration of bone promotes failure to withstand damage and increases the risk of fractures. Much of the molecular and metabolic mechanism(s) in diabetic bone remains unclear. In vitro studies suggest that hyperglycemia inhibits mineralization, affecting bone formation and function. In this study, inhibition of osteoblast differentiation was induced using hyperglycemia to assess whether high glucose promotes mitochondrial impairment along with altered bone matrix formation. It was hypothesized that bone energy metabolism would be altered in these cells as calcium deposition, a key phase for bone function, is suppressed. Early passages of osteoblast like MC3T3-E1 cells were differentiated under normal and high glucose conditions. To investigate osteoblast differentiation, we quantified calcium accumulation by alizarin red staining and analyzed immunoblots of key proteins. To assess mitochondrial function, we quantified mitochondrial DNA (mtDNA), detected expression and function of key proteins from the Tricarboxylic (TCA) cycle, measured mitochondrial respiration, and fuel oxidation of alternative nutrients. Results confirmed previous work showing that mineralization was inhibited and AKT expression was reduced in high glucose-treated bone cells. Unexpectedly, high glucose-treated osteoblast cells utilize both mitochondrial respiration and glycolysis to maintain energy demands with partial help of fatty acid for reliance of baseline bioenergetics. These metabolic shifts suggest that hyperglycemia maintain bone metabolic needs in an early differentiated state concurrent to the inhibition in bone matrix formation.

Palmitate induces DNA damage and senescence in human adipocytes in vitro that can be alleviated by oleic acid but not inorganic nitrate

Hypertrophy in white adipose tissue (WAT) can result in sustained systemic inflammation, hyperlipidaemia, insulin resistance, and onset of senescence in adipocytes. Inflammation and hypertrophy can be induced in vitro using palmitic acid (PA). WAT adipocytes have innately low β-oxidation capacity, while inorganic nitrate can promote a beiging phenotype, with promotion of β-oxidation when cells are exposed to nitrate during differentiation. We hypothesized that treatment of human adipocytes with PA in vitro can induce senescence, which might be attenuated by nitrate treatment through stimulation of β-oxidation to remove accumulated lipids. Differentiated subcutaneous and omental adipocytes were treated with PA and nitrate and senescence markers were analyzed. PA induced DNA damage and increased p16INK4a levels in both human subcutaneous and omental adipocytes in vitro. However, lipid accumulation and lipid droplet size increased after PA treatment only in subcutaneous adipocytes. Thus, hypertrophy and senescence seem not to be causally associated. Contrary to our expectations, subsequent treatment of PA-induced adipocytes with nitrate did not attenuate PA-induced lipid accumulation or senescence. Instead, we found a significantly beneficial effect of oleic acid (OA) on human subcutaneous adipocytes when applied together with PA, which reduced the DNA damage caused by PA treatment.

Melatonin Enhances the Mitochondrial Functionality of Brown Adipose Tissue in Obese-Diabetic Rats

Developing novel drugs/targets remains a major effort toward controlling obesity-related type 2 diabetes (diabesity). Melatonin controls obesity and improves glucose homeostasis in rodents, mainly via the thermogenic effects of increasing the amount of brown adipose tissue (BAT) and increases in mitochondrial mass, amount of UCP1 protein, and thermogenic capacity. Importantly, mitochondria are widely known as a therapeutic target of melatonin; however, direct evidence of melatonin on the function of mitochondria from BAT and the mechanistic pathways underlying these effects remains lacking. This study investigated the effects of melatonin on mitochondrial functions in BAT of Zücker diabetic fatty (ZDF) rats, which are considered a model of obesity-related type 2 diabetes mellitus (T2DM). At five weeks of age, Zücker lean (ZL) and ZDF rats were subdivided into two groups, consisting of control and treated with oral melatonin for six weeks. Mitochondria were isolated from BAT of animals from both groups, using subcellular fractionation techniques, followed by measurement of several mitochondrial parameters, including respiratory control ratio (RCR), phosphorylation coefficient (ADP/O ratio), ATP production, level of mitochondrial nitrites, superoxide dismutase activity, and alteration in the mitochondrial permeability transition pore (mPTP). Interestingly, melatonin increased RCR in mitochondria from brown fat of both ZL and ZDF rats through the reduction of the proton leak component of respiration (state 4). In addition, melatonin improved the ADP/O ratio in obese rats and augmented ATP production in lean rats. Further, melatonin reduced mitochondrial nitrosative and oxidative status by decreasing nitrite levels and increasing superoxide dismutase activity in both groups, as well as inhibited mPTP in mitochondria isolated from brown fat. Taken together, the present data revealed that chronic oral administration of melatonin improved mitochondrial respiration in brown adipocytes, while decreasing oxidative and nitrosative stress and susceptibility of adipocytes to apoptosis in ZDF rats, suggesting a beneficial use in the treatment of diabesity. Further research regarding the molecular mechanisms underlying the effects of melatonin on diabesity is warranted.

High metabolic substrate load induces mitochondrial dysfunction in rat skeletal muscle microvascular endothelial cells

The influence of glucose and palmitic acid (PA) on mitochondrial respiration and emission of hydrogen peroxide (H2 O2 ) was determined in skeletal muscle-derived microvascular endothelial cells. Measurements were assessed in intact and permeabilized (cells treated with 0.025% saponin) low passage endothelial cells with acute-or prolonged (3 days) incubation with regular (1.7 mM) or elevated (2.2 mM) PA concentrations and regular (5 mM) or elevated (11 mM) glucose concentrations. In intact cells, acute incubation with 1.7 mM PA alone or with 1.7 mM PA + 5 mM glucose (p < .001) led to a lower mitochondrial respiration (p < 0.01) and markedly higher H2 O2 /O2 emission (p < 0.05) than with 5 mM glucose alone. Prolonged incubation of intact cells with 1.7 mM PA +5 mM glucose led to 34% (p < 0.05) lower respiration and 2.5-fold higher H2 O2 /O2 emission (p < 0.01) than incubation with 5 mM glucose alone. Prolonged incubation of intact cells with elevated glucose led to 60% lower (p < 0.05) mitochondrial respiration and 4.6-fold higher H2 O2 /O2 production than incubation with 5 mM glucose in intact cells (p < 0.001). All effects observed in intact cells were present also in permeabilized cells (State 2). In conclusion, our results show that acute and prolonged lipid availability, as well as prolonged hyperglycemia, induces mitochondrial dysfunction as evidenced by lower mitochondrial respiration and enhanced H2 O2/ O2 emission. Elevated plasma substrate availability may lead to microvascular dysfunction in skeletal muscle by impairing endothelial mitochondrial function.

Seipin: harvesting fat and keeping adipocytes healthy

Seipin is a key protein in the assembly of cytoplasmic lipid droplets (cLDs) and their maintenance at endoplasmic reticulum (ER)-LD junctions; the absence of seipin results in generalized lipodystrophy. How seipin mediates LD dynamics and prevents lipodystrophy are not well understood. New evidence suggests that seipin attracts triglyceride monomers from the ER to sites of droplet formation. By contrast, seipin may not be directly involved in the assembly of nuclear LDs and may actually suppress their formation at a distance. Seipin promotes adipogenesis, but lipodystrophy may also involve postadipogenic effects. We hypothesize that among these are a cycle of runaway lipolysis and lipotoxicity caused by aberrant LDs, resulting in a depletion of fat stores and a failure of adipose and other cells to thrive.

Network Pharmacology-Based Strategy Reveals the Effects of Hedysarum multijugum Maxim.-Radix Salviae Compound on Oxidative Capacity and Cardiomyocyte Apoptosis in Rats with Diabetic Cardiomyopathy

Objective

To explore the effects of the Hedysarum multijugum Maxim.-Radix Salviae compound (Huangqi-Danshen Compound (HDC)) on oxidative capacity and cardiomyocyte apoptosis in rats with diabetic cardiomyopathy by a network pharmacology-based strategy.

Methods

Traditional Chinese Medicine (TCM)@Taiwan, TCM Systems Pharmacology Database and Analysis Platform (TCMSP), TCM Integrated Database (TCMID), and High-Performance Liquid Chromatography (HPLC) technology were used to obtain and screen HDC's active components, and the PharmMapper database was used to predict HDC human target protein targets. The DCM genes were collected from the GeneCards and OMIM databases, and the network was constructed and analyzed by Cytoscape 3.7.1 and the Database for Annotation, Visualization, and Integrated Discovery (DAVID). Finally, HDC was used to intervene in diabetic cardiomyopathy (DCM) model rats, and important biological processes and signaling pathways were verified using techniques such as immunohistochemistry.

Results

A total of 176 of HDC's active components and 442 potential targets were obtained. The results of network analysis show that HDC can regulate DCM-related biological processes (such as negative regulation of the apoptotic process, response to hypoxia, the steroid hormone-mediated signaling pathway, cellular iron ion homeostasis, and positive regulation of phosphatidylinositol 3-kinase signaling) and signaling pathways (such as the HIF-1 signaling pathway, the estrogen signaling pathway, insulin resistance, the PPAR signaling pathway, the VEGF signaling pathway, and the PI3K-Akt signaling pathway). Animal experiments show that HDC can reduce fasting plasma glucose (FPG), HbA1c, and malondialdehyde (MDA) and increase superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) (P < 0.05). The results of immunohistochemistry showed that HDC can regulate the protein expression of apoptosis-related signaling pathways in DCM rats (P < 0.05).

Conclusion

It was initially revealed that HDC improves DCM through its antiapoptotic and anti-inflammatory effects. HDC may play a therapeutic role by improving cardiomyocyte apoptosis in DCM rats.

Increased mitochondrial respiration of adipocytes from metabolically unhealthy obese compared to healthy obese individuals

Among obese subjects, metabolically healthy (MHO) and unhealthy obese (MUHO) subjects exist, the latter being characterized by whole-body insulin resistance, hepatic steatosis, and subclinical inflammation. Insulin resistance and obesity are known to associate with alterations in mitochondrial density, morphology, and function. Therefore, we assessed mitochondrial function in human subcutaneous preadipocytes as well as in differentiated adipocytes derived from well-matched donors. Primary subcutaneous preadipocytes from 4 insulin-resistant (MUHO) versus 4 insulin-sensitive (MHO), non-diabetic, morbidly obese Caucasians (BMI > 40 kg/m²), matched for sex, age, BMI, and percentage of body fat, were differentiated in vitro to adipocytes. Real-time cellular respiration was measured using an XF24 Extracellular Flux Analyzer (Seahorse). Lipolysis was stimulated by forskolin (FSK) treatment. Mitochondrial respiration was fourfold higher in adipocytes versus preadipocytes (p = 1.6*10^–9). In adipocytes, a negative correlation of mitochondrial respiration with donors’ insulin sensitivity was shown (p = 0.0008). Correspondingly, in adipocytes of MUHO subjects, an increased basal respiration (p = 0.002), higher proton leak (p = 0.04), elevated ATP production (p = 0.01), increased maximal respiration (p = 0.02), and higher spare respiratory capacity (p = 0.03) were found, compared to MHO. After stimulation with FSK, the differences in ATP production, maximal respiration and spare respiratory capacity were blunted. The differences in mitochondrial respiration between MUHO/MHO were not due to altered mitochondrial content, fuel switch, or lipid metabolism. Thus, despite the insulin resistance of MUHO, we could clearly show an elevated mitochondrial respiration of MUHO adipocytes. We suggest that the higher mitochondrial respiration reflects a compensatory mechanism to cope with insulin resistance and its consequences. Preserving this state of compensation might be an attractive goal for preventing or delaying the transition from insulin resistance to overt diabetes.

Proteomic and Metabolite Profiling Reveals Profound Structural and Metabolic Reorganization of Adipocyte Mitochondria in Obesity

OBJECTIVE

Previous studies have revealed decreased mitochondrial respiration in adipocytes of obese mice. This study aimed to identify the molecular underpinnings of altered mitochondrial metabolism in adipocytes.

METHODS

Untargeted proteomics of mitochondria isolated from adipocytes and metabolite profiling of adipose tissues were conducted in diet-induced obese (DIO) and lean mice. Subcutaneous and intra-abdominal adipose tissues were studied to depict depot-specific alterations.

RESULTS

In subcutaneous adipocytes of DIO mice, changes in proteins related to mitochondrial structure and function were observed. Mitochondrial proteins of the inner and outer membrane were strongly reduced, whereas proteins of key matrix metabolic pathways were increased in the obese versus lean state, as further substantiated by metabolite profiling. A pronounced decrease in the oxidative phosphorylation (OXPHOS) enzymatic equipment and cristae density of the inner membrane was identified. In intra-abdominal adipocytes, similar systematic downregulation of the OXPHOS machinery in obesity occurred, but there was no regulation of outer membrane or matrix proteins.

CONCLUSIONS

Protein components of the OXPHOS machinery are systematically downregulated in adipose tissues of DIO mice compared with lean mice. Loss of the mitochondrial OXPHOS capacity in adipocytes may aggravate the development of metabolic disease.

On the role of macrophages in the control of adipocyte energy metabolism

The crosstalk between macrophages (MΦ) and adipocytes within white adipose tissue (WAT) influences obesity-associated insulin resistance and other associated metabolic disorders, such as atherosclerosis, hypertension and type 2 diabetes. MΦ infiltration is increased in WAT during obesity, which is linked to decreased mitochondrial content and activity. The mechanistic interplay between MΦ and mitochondrial function of adipocytes is under intense investigation, as MΦ and inflammatory pathways exhibit a pivotal role in the reprogramming of WAT metabolism in physiological responses during cold, fasting and exercise. Thus, the underlying immunometabolic pathways may offer therapeutic targets to correct obesity and metabolic disease. Here, I review the current knowledge on the quantity and the quality of human adipose tissue macrophages (ATMΦ) and their impact on the bioenergetics of human adipocytes. The effects of ATMΦ and their secreted factors on mitochondrial function of white adipocytes are discussed, including recent research on MΦ as part of an immune signaling cascade involved in the 'browning' of WAT, which is defined as the conversion from white, energy-storing adipocytes into brown, energy-dissipating adipocytes.

Palmitoleic acid (16:1n7) increases oxygen consumption, fatty acid oxidation and ATP content in white adipocytes

Background

We have recently demonstrated that palmitoleic acid (16:1n7) increases lipolysis, glucose uptake and glucose utilization for energy production in white adipose cells. In the present study, we tested the hypothesis that palmitoleic acid modulates bioenergetic activity in white adipocytes.

Methods

For this, 3 T3-L1 pre-adipocytes were differentiated into mature adipocytes in the presence (or absence) of palmitic (16:0) or palmitoleic (16:1n7) acid at 100 or 200 μM. The following parameters were evaluated: lipolysis, lipogenesis, fatty acid (FA) oxidation, ATP content, oxygen consumption, mitochondrial mass, citrate synthase activity and protein content of mitochondrial oxidative phosphorylation (OXPHOS) complexes.

Results

Treatment with 16:1n7 during 9 days raised basal and isoproterenol-stimulated lipolysis, FA incorporation into triacylglycerol (TAG), FA oxidation, oxygen consumption, protein expression of subunits representing OXPHOS complex II, III, and V and intracellular ATP content. These effects were not observed in adipocytes treated with 16:0.

Conclusions

Palmitoleic acid, by concerted action on lipolysis, FA esterification, mitochondrial FA oxidation, oxygen consumption and ATP content, does enhance white adipocyte energy expenditure and may act as local hormone.

Mapping metabolic changes by noninvasive, multiparametric, high-resolution imaging using endogenous contrast

Monitoring subcellular functional and structural changes associated with metabolism is essential for understanding healthy tissue development and the progression of numerous diseases, including cancer, diabetes, and cardiovascular and neurodegenerative disorders. Unfortunately, established methods for this purpose either are destructive or require the use of exogenous agents. Recent work has highlighted the potential of endogenous two-photon excited fluorescence (TPEF) as a method to monitor subtle metabolic changes; however, mechanistic understanding of the connections between the detected optical signal and the underlying metabolic pathways has been lacking. We present a quantitative approach to detecting both functional and structural metabolic biomarkers noninvasively, relying on endogenous TPEF from two coenzymes, NADH (reduced form of nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide). We perform multiparametric analysis of three optical biomarkers within intact, living cells and three-dimensional tissues: cellular redox state, NADH fluorescence lifetime, and mitochondrial clustering. We monitor the biomarkers in cells and tissues subjected to metabolic perturbations that trigger changes in distinct metabolic processes, including glycolysis and glutaminolysis, extrinsic and intrinsic mitochondrial uncoupling, and fatty acid oxidation and synthesis. We demonstrate that these optical biomarkers provide complementary insights into the underlying biological mechanisms. Thus, when used in combination, these biomarkers can serve as a valuable tool for sensitive, label-free identification of changes in specific metabolic pathways and characterization of the heterogeneity of the elicited responses with single-cell resolution.

Selection and Characterization of Palmitic Acid Responsive Patients with an OXPHOS Complex I Defect

Mitochondrial disorders are genetically and clinically heterogeneous, mainly affecting high energy-demanding organs due to impaired oxidative phosphorylation (OXPHOS). Currently, effective treatments for OXPHOS defects, with complex I deficiency being the most prevalent, are not available. Yet, clinical practice has shown that some complex I deficient patients benefit from a high-fat or ketogenic diet, but it is unclear how these therapeutic diets influence mitochondrial function and more importantly, which complex I patients could benefit from such treatment. Dietary studies in a complex I deficient patient with exercise intolerance showed increased muscle endurance on a high-fat diet compared to a high-carbohydrate diet. We performed whole-exome sequencing to characterize the genetic defect. A pathogenic homozygous p.G212V missense mutation was identified in the TMEM126B gene, encoding an early assembly factor of complex I. A complementation study in fibroblasts confirmed that the p.G212V mutation caused the complex I deficiency. The mechanism turned out to be an incomplete assembly of the peripheral arm of complex I, leading to a decrease in the amount of mature complex I. The patient clinically improved on a high-fat diet, which was supported by the 25% increase in maximal OXPHOS capacity in TMEM126B defective fibroblast by the saturated fatty acid palmitic acid, whereas oleic acid did not have any effect in those fibroblasts. Fibroblasts of other patients with a characterized complex I gene defect were tested in the same way. Patient fibroblasts with complex I defects in NDUFS7 and NDUFAF5 responded to palmitic acid, whereas ACAD9, NDUFA12, and NDUFV2 defects were non-responding. Although the data are too limited to draw a definite conclusion on the mechanism, there is a tendency that protein defects involved in early assembly complexes, improve with palmitic acid, whereas proteins defects involved in late assembly, do not. Our data show at a clinical and biochemical level that a high fat diet can be beneficial for complex I patients and that our cell line assay will be an easy tool for the selection of patients, who might potentially benefit from this therapeutic diet.

Cumulus cell mitochondrial activity in relation to body mass index in women undergoing assisted reproductive therapy

Most studies have considered the negative influence of obesity on fertility in both genders. In the present study, we assessed mitochondrial activity expressed as the mitochondrial potential index (MPI) in cumulus cells from obese women and women with a normal body mass index (BMI) during assisted reproductive therapy. The results revealed a significant reduction of MPI with increased body mass. The lower MPI levels in cumulus cells from obese women may reflect mitochondrial dysfunction caused by oxidative stress, which can affect the cumulus-oocyte complex and have an impact on oocyte development.

Microarray analysis of differentially expressed genes and their functions in omental visceral adipose tissues of pregnant women with vs. without gestational diabetes mellitus

Increasing evidence has shown that insulin resistance in omental visceral adipose tissue (OVAT) is a characteristic of gestational diabetes mellitus (GDM). The present study aimed to identify differentially expressed genes (DEGs) and their associated functions and pathways involved in the pathogenesis of GDM by comparing the expression profiles of OVATs obtained from pregnant Chinese women with and without GDM during caesarian section. A total of 935 DEGs were identified, including 450 downregulated and 485 upregulated genes. In the gene ontology category cellular components, the DEGs were predominantly associated with functions of the extracellular region, while receptor binding was predominant in the molecular function category and biological process terms included antigen processing and presentation, extracellular matrix organization, positive regulation of cell-substrate adhesion, response to nutrients and response to dietary excess. Functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were performed and a functional interaction network was constructed. Functions of downregulated genes included antigen processing and presentation as well as cell adhesion molecules, while those of upregulated genes included transforming growth factor (TGF)-β-signaling, focal adhesion, phosphoinositide-3 kinase-Akt-signaling, P53 signaling, extracellular matrix-receptor interaction and regulation of actin cytoskeleton pathway. The five main pathways associated with GDM were antigen processing and presentation, cell adhesion molecules, Type 1 diabetes mellitus, natural killer cell-mediated cytotoxicity and TGF-β signaling. These pathways were included in the KEGG pathway categories of ‘signaling molecules and interaction’, ‘immune system’ and ‘inflammatory response’, suggesting that these processes are involved in GDM. The results of the present study enhanced the present understanding of the mechanisms associated with insulin resistance in OVATs of GDM.

Alterations of Mitochondrial Function and Insulin Sensitivity in Human Obesity and Diabetes Mellitus

Mitochondrial function refers to a broad spectrum of features such as resting mitochondrial activity, (sub)maximal oxidative phosphorylation capacity (OXPHOS), and mitochondrial dynamics, turnover, and plasticity. The interaction between mitochondria and insulin sensitivity is bidirectional and varies depending on tissue, experimental model, methodological approach, and features of mitochondrial function tested. In human skeletal muscle, mitochondrial abnormalities may be inherited (e.g., lower mitochondrial content) or acquired (e.g., impaired OXPHOS capacity and plasticity). Abnormalities ultimately lead to lower mitochondrial functionality due to or resulting in insulin resistance and type 2 diabetes mellitus. Similar mechanisms can also operate in adipose tissue and heart muscle. In contrast, mitochondrial oxidative capacity is transiently upregulated in the liver of obese insulin-resistant humans with or without fatty liver, giving rise to oxidative stress and declines in advanced fatty liver disease. These data suggest a highly tissue-specific interaction between insulin sensitivity and oxidative metabolism during the course of metabolic diseases in humans.

Metabolically healthy obesity--does it exist?

The prevalence of obesity has been increasing worldwide over the past 30 years and is a major public health concern. Obesity is known to be associated with metabolic disturbances including insulin resistance and inflammation; however, there is a subset of obese subjects who have normal metabolic profiles, and they have been identified as the metabolically healthy obese (MHO). Several studies have described MHO as obese individuals who have high levels of insulin sensitivity and the absence of diabetes, dyslipidemia, or hypertension. The prevalence of MHO varies from 20 to 30% among obese individuals. This review will discuss the MHO phenotype; the differences between MHO and metabolically unhealthy obese (MUO) individuals; and the possible underlying mechanisms including adipocyte differentiation, immune regulation, and cellular energy metabolism.

The beta-3 adrenergic agonist (CL-316,243) restores the expression of down-regulated fatty acid oxidation genes in type 2 diabetic mice

Background

The hallmark of Type 2 diabetes (T2D) is hyperglycemia, although there are multiple other metabolic abnormalities that occur with T2D, including insulin resistance and dyslipidemia. To advance T2D prevention and develop targeted therapies for its treatment, a greater understanding of the alterations in metabolic tissues associated with T2D is necessary. The aim of this study was to use microarray analysis of gene expression in metabolic tissues from a mouse model of pre-diabetes and T2D to further understand the metabolic abnormalities that may contribute to T2D. We also aimed to uncover the novel genes and pathways regulated by the insulin sensitizing agent (CL-316,243) to identify key pathways and target genes in metabolic tissues that can reverse the diabetic phenotype.

Methods

Male MKR mice on an FVB/n background and age matched wild-type (WT) FVB/n mice were used in all experiments. Skeletal muscle, liver and fat were isolated from prediabetic (3 week old) and diabetic (8 week old) MKR mice. Male MKR mice were treated with CL-316,243. Skeletal muscle, liver and fat were isolated after the treatment period. RNA was isolated from the metabolic tissues and subjected to microarray and KEGG database analysis.

Results

Significant decreases in the expression of mitochondrial and peroxisomal fatty acid oxidation genes were found in the skeletal muscle and adipose tissue of adult MKR mice, and the liver of pre-diabetic MKR mice, compared to WT controls. After treatment with CL-316,243, the circulating glucose and insulin concentrations in the MKR mice improved, an increase in the expression of peroxisomal fatty acid oxidation genes was observed in addition to a decrease in the expression of retinaldehyde dehydrogenases. These genes were not previously known to be regulated by CL-316,243 treatment.

Conclusions

This study uncovers novel genes that may contribute to pharmacological reversal of insulin resistance and T2D and may be targets for treatment. In addition, it explains the lower free fatty acid levels in MKR mice after treatment with CL-316,243 and furthermore, it provides biomarker genes such as ACAA1 and HSD17b4 which could be further probed in a future study.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-015-0003-8) contains supplementary material, which is available to authorized users.

Melatonin improves mitochondrial function in inguinal white adipose tissue of Zücker diabetic fatty rats

Mitochondrial dysfunction in adipose tissue may contribute to obesity-related metabolic derangements such as type 2 diabetes mellitus (T2DM). Because mitochondria are a target for melatonin action, the goal of this study was to investigate the effects of melatonin on mitochondrial function in white (WAT) and beige inguinal adipose tissue of Zücker diabetic fatty (ZDF) rats, a model of obesity-related T2DM. In this experimental model, melatonin reduces obesity and improves the metabolic profile. At 6 wk of age, ZDF rats and lean littermates (ZL) were subdivided into two groups, each composed of four rats: control (C-ZDF and C-ZL) and treated with oral melatonin in the drinking water (10 mg/kg/day) for 6 wk (M-ZDF and M-ZL). After the treatment period, animals were sacrificed, tissues dissected, and mitochondrial function assessed in isolated organelles. Melatonin increased the respiratory control ratio (RCR) in mitochondria from white fat of both lean (by 26.5%, P < 0.01) and obese (by 34.5%, P < 0.01) rats mainly through a reduction of proton leaking component of respiration (state 4) (28% decrease in ZL, P < 0.01 and 35% in ZDF, P < 0.01). However, melatonin treatment lowered the RCR in beige mitochondria of both lean (by 7%, P < 0.05) and obese (by 13%, P < 0.05) rats by maintaining high rates of uncoupled respiration. Melatonin also lowered mitochondrial oxidative status by reducing nitrite levels and by increasing superoxide dismutase activity. Moreover, melatonin treatment also caused a profound inhibition of Ca-induced opening of mPTP in isolated mitochondria from both types of fat, white and beige, in both lean and obese rats. These results demonstrate that chronic oral melatonin improves mitochondrial respiration and reduces the oxidative status and susceptibility to apoptosis in white and beige adipocytes. These melatonin effects help to prevent mitochondrial dysfunction and thereby to improve obesity-related metabolic disorders such as diabetes and dyslipidemia of ZDF rats.

Increased β-oxidation with improved glucose uptake capacity in adipose tissue from obese after weight loss and maintenance

OBJECTIVE

We investigated protein markers for pathways of the fatty acids (FAs) and glucose metabolism in human adipose tissue after a weight loss program by calorie restriction.

METHODS

Overweight/obese subjects underwent an intervention of 5 weeks of a very low-calorie diet followed by a 3-week weight maintenance diet. Abdominal subcutaneous adipose tissue biopsies were sampled before and after the intervention. Seventeen target proteins as markers of metabolic pathways for the uptake and handling of FAs and glucose were quantified by Western blotting and 11 were retrieved from previous proteomics work. Correlation coefficients were calculated among changes of these proteins.

RESULTS

Short-chain 3-hydroxyacyl-CoA dehydrogenase, catalase, fatty acid translocase, fatty acid transporter protein 3, adipose triglyceride lipase, fatty acid-binding protein 4, aldolase-C, tubulin-β-5, and annexin A2 changed significantly, and lipoprotein lipase, perilipin 1, and hormone-sensitive lipase tended to change. On an average, increased glucose transporter type 4 translocation was observed, supported by a consistent increase of tyr-24 phosphorylated annexin A2.

CONCLUSIONS

Our findings suggest that after weight loss by calorie restriction and a short period of maintenance, adipose tissue has an increased capacity for glucose uptake, and lipid mobilization and oxidation. Such metabolic profile may relate to the health benefit of weight loss.

LXRα fuels fatty acid-stimulated oxygen consumption in white adipocytes

Liver X receptors (LXRs) are transcription factors known for their role in hepatic cholesterol and lipid metabolism. Though highly expressed in fat, the role of LXR in this tissue is not well characterized. We generated adipose tissue LXRα knockout (ATaKO) mice and showed that these mice gain more weight and fat mass on a high-fat diet compared with wild-type controls. White adipose tissue (WAT) accretion in ATaKO mice results from both a decrease in WAT lipolytic and oxidative capacities. This was demonstrated by decreased expression of the β2- and β3-adrenergic receptors, reduced level of phosphorylated hormone-sensitive lipase, and lower oxygen consumption rates (OCRs) in WAT of ATaKO mice. Furthermore, LXR activation in vivo and in vitro led to decreased adipocyte size in WAT and increased glycerol release from primary adipocytes, respectively, with a concomitant increase in OCR in both models. Our findings show that absence of LXRα in adipose tissue results in elevated adiposity through a decrease in WAT oxidation, secondary to attenuated FA availability.

Plasma and urine metabolic profiles are reflective of altered beta-oxidation in non-diabetic obese subjects and patients with type 2 diabetes mellitus

OBJECTIVES

The two primary pathophysiological characteristics of patients with type 2 diabetes mellitus (T2DM) are insulin resistance (IR) and beta cell dysfunction. It has been proposed that the development of IR is secondary to the accumulation of triacylglycerols and fatty acids in the muscle and liver, which is in turn thought to be secondary to an enzymatic defect in mitochondrial beta-oxidation. The purpose of the present study was to analyze the molecules of intermediary metabolism to determine if an alteration in mitochondrial function exists in T2DM patients and, if so, to determine whether this alteration is caused by excess nutrients or an enzymatic defect.

DESIGN AND METHODS

Seventy-seven subjects were recruited and divided into four groups (21 T2DM patients, 17 non-diabetic overweight/obese subjects, 20 offspring of T2DM patients, and 19 healthy subjects). Anthropometric parameters were determined by air plethysmography, and biochemical and metabolic parameters were measured, including 31 acylcarnitines (ACs) and 13 amino acids quantified by MS/MS and 67 organic acids measured by GC/MS.

RESULTS

Patients with T2DM showed elevation of short-chain ACs (C2, C4), a glycogenic amino acid (valine), a glycogenic and ketogenic amino acid (tyrosine), and a ketogenic amino acid (leucine) as well as altered excretion of dicarboxylic acids. T2DM offspring with abnormal glucose tolerance test GTT showed increased levels of C16. Subjects in the obese group who were dysglycemic also showed altered urinary excretion of dicarboxylic acids and lower levels of a long-chain AC (C14:2).

CONCLUSIONS

These results suggest that mitochondrial beta-oxidation is altered in T2DM patients and that the alteration is most likely caused by nutrient overload through a different pathway from that observed in obese subjects.

Insulin resistance in non-diabetic patients of chronic Hepatitis C

Objective: To determine insulin resistance in non-diabetic chronic hepatitis C patients using Homeostatic Model Assessment of Insulin Resistance (HOMA-IR).

Methodology: Patients having anti-HCV positive were included in this study. Patients with diabetes mellitus, thyroid disease, hyperlipidemias, hypercortisolism and infective diseases other than hepatitis C were excluded. Age, weight, height and absence of diabetes were documented. Fasting blood glucose and fasting insulin levels were done. Body mass index and insulin resistance was calculated using the formulas. Patients having insulin resistance using formula HOMA-IR>2.5 were labeled as insulin resistant. Data was analyzed using SPSS-18.

Results: One hundred and fifty five patients according to sample size estimation were enrolled, in whom HOMA-IR was calculated, the mean value was found to be 2.47 ±1.30. A total of 79 (51%) of patients had HOMA-IR more than 2.5 showing insulin resistance.

Conclusion: In a third world country like Pakistan, where there is a high prevalence of hepatitis C infection, the consequences of the disease are also very common. Insulin resistance was found in 51% of patients with chronic hepatitis C.

Discovery of metabolite biomarkers: flux analysis and reaction-reaction network approach

Background

Metabolism is a vital cellular process, and its malfunction can be a major contributor to many human diseases. Metabolites can serve as a metabolic disease biomarker. An detection of such biomarkers plays a significant role in the study of biochemical reaction and signaling networks. Early research mainly focused on the analysis of the metabolic networks. The issue of integrating metabolite networks with other available biological data to reveal the mechanics of disease-metabolite associations is an important and interesting challenge.

Results

In this article, we propose two new approaches for the identification of metabolic biomarkers with the incorporation of disease specific gene expression data and the genome-scale human metabolic network. The first approach is to compare the flux interval between the normal and disease sample so as to identify reaction biomarkers. The second one is based on the Reaction-Reaction Network (RRN) to reveal the significant reactions. These two approaches utilize reaction flux obtained by a Linear Programming (LP) based method that can contribute to the discovery of potential novel biomarkers.

Conclusions

Biomarker identification is an important issue in studying biochemical reactions and signaling networks. Two efficient and effective computational methods are proposed for the identification of biomarkers in this article. Furthermore, the biomarkers found by our proposed methods are shown to be significant determinants for diabetes.

The effect of LXRα, ChREBP and Elovl6 in liver and white adipose tissue on medium- and long-chain fatty acid diet-induced insulin resistance

AIMS

We aimed to investigate the effects of LXRα, ChREBP and Elovl6 in the development of insulin resistance-induced by medium- and long-chain fatty acids.

METHODS

Sprague Dawley rats were fed a standard chow diet (Control group) or a high-fat, high sucrose diet with different fat sources (coconut oil, lard, sunflower and fish oil) for 8 weeks. These oils were rich in medium-chain saturated fatty acids (MCFA group), long-chain saturated fatty acids (LCFA group), n-6 and n-3 long-chain polyunsaturated fatty acids (n-6 PUFA and n-3 PUFA groups), respectively, which had different chain lengths and degrees of unsaturation. Hyperinsulinemic-euglycemic clamp with [6-(3)H] glucose infusion was performed in conscious rats to assess hepatic insulin sensitivity.

RESULTS

LCFA and n-6 PUFA groups induced hepatic insulin resistance and increased liver X receptor α (LXRα), carbohydrate response element binding protein (ChREBP) and long-chain fatty acid elongase 6 (Elovl6) expression in liver and white adipose tissue (WAT). Furthermore, LCFA and n-6 PUFA groups suppressed Akt serine 473 phosphorylation in liver and WAT. By contrast, in liver and WAT, MCFA and n-3 PUFA groups decreased LXRα, ChREBP and Elovl6 expression and improved insulin signaling and insulin resistance, but Akt serine 473 phosphorylation was not restored by MCFA group in WAT.

CONCLUSIONS

This study demonstrated that the mechanism of the different effects of medium- and long-chain fatty acids on hepatic insulin resistance involves LXRα, ChREBP and Elovl6 alternations in liver and WAT. It points to a new strategy for ameliorating insulin resistance and diabetes through intervention on Elovl6 or its control genes.

Differential proinflammatory and oxidative stress response and vulnerability to metabolic syndrome in habitual high-fat young male consumers putatively predisposed by their genetic background

The current nutritional habits and lifestyles of modern societies favor energy overloads and a diminished physical activity, which may produce serious clinical disturbances and excessive weight gain. In order to investigate the mechanisms by which the environmental factors interact with molecular mechanisms in obesity, a pathway analysis was performed to identify genes differentially expressed in subcutaneous abdominal adipose tissue (SCAAT) from obese compared to lean male (21–35 year-old) subjects living in similar obesogenic conditions: habitual high fat dietary intake and moderate physical activity. Genes involved in inflammation (ALCAM, CTSB, C1S, YKL-40, MIF, SAA2), extracellular matrix remodeling (MMP9, PALLD), angiogenesis (EGFL6, leptin) and oxidative stress (AKR1C3, UCHL1, HSPB7 and NQO1) were upregulated; whereas apoptosis, signal transcription (CITED 2 and NR3C1), cell control and cell cycle-related genes were downregulated. Interestingly, the expression of some of these genes (C1S, SAA2, ALCAM, CTSB, YKL-40 and tenomodulin) was found to be associated with some relevant metabolic syndrome features. The obese group showed a general upregulation in the expression of inflammatory, oxidative stress, extracellular remodeling and angiogenic genes compared to lean subjects, suggesting that a given genetic background in an obesogenic environment could underlie the resistance to gaining weight and obesity-associated manifestations.

Control of mitochondrial metabolism and systemic energy homeostasis by microRNAs 378 and 378*

Obesity and metabolic syndrome are associated with mitochondrial dysfunction and deranged regulation of metabolic genes. Peroxisome proliferator-activated receptor γ coactivator 1β (PGC-1β) is a transcriptional coactivator that regulates metabolism and mitochondrial biogenesis through stimulation of nuclear hormone receptors and other transcription factors. We report that the PGC-1β gene encodes two microRNAs (miRNAs), miR-378 and miR-378*, which counterbalance the metabolic actions of PGC-1β. Mice genetically lacking miR-378 and miR-378* are resistant to high-fat diet-induced obesity and exhibit enhanced mitochondrial fatty acid metabolism and elevated oxidative capacity of insulin-target tissues. Among the many targets of these miRNAs, carnitine O-acetyltransferase, a mitochondrial enzyme involved in fatty acid metabolism, and MED13, a component of the Mediator complex that controls nuclear hormone receptor activity, are repressed by miR-378 and miR-378*, respectively, and are elevated in the livers of miR-378/378* KO mice. Consistent with these targets as contributors to the metabolic actions of miR-378 and miR-378*, previous studies have implicated carnitine O-acetyltransferase and MED13 in metabolic syndrome and obesity. Our findings identify miR-378 and miR-378* as integral components of a regulatory circuit that functions under conditions of metabolic stress to control systemic energy homeostasis and the overall oxidative capacity of insulin target tissues. Thus, these miRNAs provide potential targets for pharmacologic intervention in obesity and metabolic syndrome.

Induction of mitochondrial uncoupling enhances VEGF₁₂₀ but reduces MCP-1 release in mature 3T3-L1 adipocytes: possible regulatory mechanism through endogenous ER stress and AMPK-related pathways

Although white adipocytes contain a larger number of mitochondria per cytoplasmic volume, adipocyte mitochondrial uncoupling to reduce the efficiency of ATP production on cellular function including secretory regulation of bioactive molecules such as VEGF and MCP-1 remains to be elucidated. Here we induce mitochondrial uncoupling under hypoxia-independent conditions in mature 3T3-L1 adipocytes using a metabolic uncoupler, dinitrophenol (DNP). MCP-1 release was significantly decreased by 26% (p<0.01) in 24h DNP (30 μmol/L)-treated adipocytes compared to control cells. In contrast, secreted VEGF(120) lacking a heparin-binding domain was markedly increased 2.0-fold (p<0.01). CHOP content in these cells also were augmented (p<0.01), but no significant increase of endogenous oxidative stress was observed. Treatment with thapsigargin, which can induce exogenous endoplasmic reticulum (ER) stress, clearly attenuated MCP-1 release (p<0.01), but exhibited no effects on VEGF(120) secretion. On the other hand, exogenous H(2)O(2) amplified both MCP-1 and VEGF(120) secretion (p<0.05). In addition, under chronic activation of AMPK by AICAR, MCP-1 release was significantly diminished (p<0.05) but VEGF(120) secretion was increased (p<0.01). JNK phosphorylation in mature adipocytes was decreased by treatment with either DNP or AICAR (p<0.01). Enhanced VEGF(120) secretion with either DNP or AICAR was markedly suppressed by PI3K inhibitor LY294002 (p<0.01). Thus, induced mitochondrial uncoupling in adipocytes can reduce MCP-1 release through induction of endogenous ER stress and by reduced JNK activities via chronic activation of AMPK. Under this condition, VEGF(120) secretion was increased through PI3K-dependent pathways, which were chronically activated by AMPK, and not through ER stress. Because the decrease of MCP-1 secretion under mitochondrial uncoupling might attenuate chronic low-grade inflammation by suppressing macrophages recruitment to adipose tissue, clarification of the mechanism might reveal novel therapeutic targets for ameliorating obesity-associated insulin resistance in metabolic syndrome and type 2 diabetes.

Augmenting energy expenditure by mitochondrial uncoupling: a role of AMP-activated protein kinase

Strategies to prevent and treat obesity aim to decrease energy intake and/or increase energy expenditure. Regarding the increase of energy expenditure, two key intracellular targets may be considered (1) mitochondrial oxidative phosphorylation, the major site of ATP production, and (2) AMP-activated protein kinase (AMPK), the master regulator of cellular energy homeostasis. Experiments performed mainly in transgenic mice revealed a possibility to ameliorate obesity and associated disorders by mitochondrial uncoupling in metabolically relevant tissues, especially in white adipose tissue (WAT), skeletal muscle (SM), and liver. Thus, ectopic expression of brown fat-specific mitochondrial uncoupling protein 1 (UCP1) elicited major metabolic effects both at the cellular/tissue level and at the whole-body level. In addition to expected increases in energy expenditure, surprisingly complex phenotypic effects were detected. The consequences of mitochondrial uncoupling in WAT and SM are not identical, showing robust and stable obesity resistance accompanied by improvement of lipid metabolism in the case of ectopic UCP1 in WAT, while preservation of insulin sensitivity in the context of high-fat feeding represents the major outcome of muscle UCP1 expression. These complex responses could be largely explained by tissue-specific activation of AMPK, triggered by a depression of cellular energy charge. Experimental data support the idea that (1) while being always activated in response to mitochondrial uncoupling and compromised intracellular energy status in general, AMPK could augment energy expenditure and mediate local as well as whole-body effects; and (2) activation of AMPK alone does not lead to induction of energy expenditure and weight reduction.

Carnitine palmitoyltransferase 1A prevents fatty acid-induced adipocyte dysfunction through suppression of c-Jun N-terminal kinase

The adipocyte is the principal cell type for fat storage. CPT1 (carnitine palmitoyltransferase-1) is the rate-limiting enzyme for fatty acid β-oxidation, but the physiological role of CPT1 in adipocytes remains unclear. In the present study, we focused on the specific role of CPT1A in the normal functioning of adipocytes. Three 3T3-L1 adipocyte cell lines stably expressing hCPT1A (human CPT1A) cDNA, mouse CPT1A shRNA (short-hairpin RNA) or GFP (green fluorescent protein) were generated and the biological functions of these cell lines were characterized. Alteration in CPT1 activity, either by ectopic overexpression or pharmacological inhibition using etomoxir, did not affect adipocyte differentiation. However, overexpression of hCPT1A significantly reduced the content of intracellular NEFAs (non-esterified fatty acids) compared with the control cells when adipocytes were challenged with fatty acids. The changes were accompanied by an increase in fatty acid uptake and a decrease in fatty acid release. Interestingly, CPT1A protected against fatty acid-induced insulin resistance and expression of pro-inflammatory adipokines such as TNF-α (tumour necrosis factor-α) and IL-6 (interleukin-6) in adipocytes. Further studies demonstrated that JNK (c-Jun N terminal kinase) activity was substantially suppressed upon CPT1A overexpression, whereas knockdown or pharmacological inhibition of CPT1 caused a significant enhancement of JNK activity. The specific inhibitor of JNK SP600125 largely abolished the changes caused by the shRNA- and etomoxir-mediated decrease in CPT1 activity. Moreover, C2C12 myocytes co-cultured with adipocytes pre-treated with fatty acids displayed altered insulin sensitivity. Taken together, our findings have identified a favourable role for CPT1A in adipocytes to attenuate fatty acid-evoked insulin resistance and inflammation via suppression of JNK.

Insulin resistance: pathophysiology and rationale for treatment

After binding to its receptor and activating the β-subunit, insulin is faced with two divergent pathways: one is phosphatidylinositol 3-kinase (PI 3-K) dependent, while another is dependent upon activation of mitogen-activated protein kinase (MAP-K). The former is absolutely necessary for mediating most metabolic and antiapoptotic effects; the latter is linked to nonmetabolic, proliferative and mitogenic effects. In obese patients, especially with type 2 diabetes mellitus (DM2), only the PI 3-K, but not the MAP-K, is resistant to insulin stimulation: hence insulin resistance is better defined as metabolic insulin resistance. The resulting 'compensatory hyperinsulinemia' is an unsuccessful attempt to overcome the inhibition of the metabolic pathway at the price of unopposed stimulation of the MAP-K pathway, and the administration of exogenous insulin might worsen the metabolic dysfunction. As the preferential activation of the MAP-K pathway in insulin-resistant patients has atherogenic and mitogenic properties, this leads to atherosclerosis and cancer. Metformin may carry out direct protective action on human β cells, inasmuch as it improves both primary and secondary endpoints through selective inhibition of fatty acyl oxidation.

Combined gene and protein expression of hormone-sensitive lipase and adipose triglyceride lipase, mitochondrial content, and adipocyte size in subcutaneous and visceral adipose tissue of morbidly obese men

AIMS

Lipotoxicity in obesity might be a failure of adipocytes to respond sufficiently adequate to persistent energy surplus. To evaluate the role of lipolytic enzymes or mitochondria in lipotoxicity, we studied expression levels of genes and proteins involved in lipolysis and mitochondrial DNA (mtDNA) content.

METHODS

As differences in lipid metabolism between men and women are extremely complex, we recruited only men (lean and morbidly obese) and collected subcutaneous and visceral adipose tissue during abdominal surgery for real-time PCR gene expression, protein expression, and microscopic study.

RESULTS

Although mRNA levels of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) were increased in visceral adipose tissue of morbidly obese men, this was not paralleled by alterations in protein expression and phosphorylation of HSL and ATGL. mtDNA content of visceral adipose tissue was increased in morbidly obese men as compared to lean controls (p < 0.013). Positive correlations were observed between visceral adipocyte size and serum triacylglycerol (r = 0.6, p < 0.007) as well as between visceral adipocyte size and CRP (r = 0.6, p < 0.009) in analyses performed separately in obese men.

CONCLUSION

Lipotoxicity of morbidly obese men might be related to the quantitative impact of the visceral fat depot rather than to important dysregulation of involved lipolytic enzymes or adipocyte mitochondria.

Taurine prevents free fatty acid-induced hepatic insulin resistance in association with inhibiting JNK1 activation and improving insulin signaling in vivo

We infused the 48 h intralipid plus heparin (IH) to normal rats to elevate plasma free fatty acids (FFAs). Co-infusion of taurine was designed for the purpose of studying the effects of taurine on insulin sensitivity, oxidative stress, c-Jun NH-terminal kinase (JNK)1 activity and insulin signaling in livers of prolonged IH-infused rats. Cannulated rats were infused for 48 h intravenously with either saline or IH, with or without taurine. Hyperinsulinemic-euglycemic clamps with [6-3H] glucose infusion were performed to assess hepatic insulin sensitivity. IH infusion increased plasma 8-isoprostaglandin and hepatic malondialdehyde (MDA). IH also increased JNK1 activity and insulin receptor substrate 1/2 (IRS-1/2) serine phosphorylation, reduced insulin-stimulated IRS-1/2 tyrosine phosphorylation and Akt serine 473 phosphorylation, and induced hepatic insulin resistance. Taurine co-infusion with IH prevented the rise in 8-isoprostaglandin and MDA, inhibited the activation of JNK1, and improved insulin signaling and insulin resistance in liver. The present study has demonstrated that taurine, as an antioxidant, prevented hepatic oxidative stress and ameliorated hepatic insulin resistance. And this effect may be associated with the inhibition of JNK1 activation and the improvement of insulin signaling. This study suggests the therapeutic value of taurine in protecting from hepatic insulin resistance caused by elevated FFAs.

Acute stimulation of white adipocyte respiration by PKA-induced lipolysis

OBJECTIVE

We examined the effect of β-adrenergic receptor (βAR) activation and cAMP-elevating agents on respiration and mitochondrial uncoupling in human adipocytes and probed the underlying molecular mechanisms.

RESEARCH DESIGN AND METHODS

Oxygen consumption rate (OCR, aerobic respiration) and extracellular acidification rate (ECAR, anaerobic respiration) were examined in response to isoproterenol (ISO), forskolin (FSK), and dibutyryl-cAMP (DB), coupled with measurements of mitochondrial depolarization, lipolysis, kinase activities, and gene targeting or knock-down approaches.

RESULTS

ISO, FSK, or DB rapidly increased oxidative and glycolytic respiration together with mitochondrial depolarization in human and mouse white adipocytes. The increase in OCR was oligomycin-insensitive and contingent on cAMP-dependent protein kinase A (PKA)-induced lipolysis. This increased respiration and the uncoupling were blocked by inhibiting the mitochondrial permeability transition pore (PTP) and its regulator, BAX. Interestingly, compared with lean individuals, adipocytes from obese subjects exhibited reduced OCR and uncoupling capacity in response to ISO.

CONCLUSIONS

Lipolysis stimulated by βAR activation or other maneuvers that increase cAMP levels in white adipocytes acutely induces mitochondrial uncoupling and cellular energetics, which are amplified in the absence of scavenging BSA. The increase in OCR is dependent on PKA-induced lipolysis and is mediated by the PTP and BAX. Because this effect is reduced with obesity, further exploration of this uncoupling mechanism will be needed to determine its cause and consequences.

Platelets of type 2 diabetic patients are characterized by high ATP content and low mitochondrial membrane potential

Platelet dysfunction plays a critical role in vascular complications of type 2 diabetes mellitus (T2DM). But the relationship between platelet hyperactivity and its energy metabolic process remains unclear. This study was designed to explore alterations of platelet mitochondrial ATP production and the possible mechanism. A total of 39 T2DM patients without macrovascular and microvascular complications and 32 normal controls were fasting sampled. Platelet ATP content was measured by a high performance liquid chromatograph (HPLC). The flow cytometry technique was adopted to evaluate mitochondrial membrane potential (DeltaPsim), the stored force for platelet ATP production. Consequently, T2DM patients exhibited obvious hyperglycemia, hyperlipidemia and hypertension, but normal platelet morphology. Platelet ATP content was significantly higher in T2DM (0.032 +/- 0.010 micromol/10(9) platelets versus 0.017 +/- 0.006 micromol/10(9) platelets, p < 0.001) than in the control group. Interestingly, DeltaPsim was markedly decreased in T2DM patients (0.79 +/- 0.18 versus 2.70 +/- 1.03, p < 0.001) compared with normal controls. For whole subjects, a stepwise regression showed that plasma glycated hemoglobin A1c (HbA1c) level positively correlated to platelet ATP content (beta = 0.552, 95% CI = 0.072-1.451), and fasting plasma glucose (FPG) level was negatively correlated to DeltaPsim (beta = -0.372, 95% CI = -0.471 to -0.089). These data support that hyperglycemia of T2DM promotes platelet mitochondria to generate more ATP, but decreases platelet mitochondrial potential. The discordance between them requires further researches to elucidate.

Short-term endurance training does not alter the oxidative capacity of human subcutaneous adipose tissue

Endurance training results in adaptations that enhance regulation of energy storage and expenditure at rest and during exercise. While processes involved in skeletal muscle oxidative remodelling are well described, it is unknown whether oxidative capacity of human subcutaneous white adipose tissue (WAT) is modified by endurance training. Since human WAT retains rudimentary characteristics required for upregulation of oxidative function, we hypothesised that 10 days of intense endurance training would promote changes in WAT that favour an increase in oxidative capacity. Eleven untrained males (age 22 +/- 1 years, body mass 81 +/- 5 kg, peak oxygen uptake (VO(2peak)) 3.7 +/- 0.2 l/min) undertook a 10-day endurance training protocol. Subcutaneous adipose tissue biopsies were taken from the abdomen prior to and 1 day after completion of training and analysed for fatty acid oxidative capacity, citrate synthase activity, and mitochondrial content via electron microscopy and gene expression analyses. There was a reduction in whole-body rates of carbohydrate oxidation, and concomitant increases in fat oxidation rate measured during 20-min of submaximal cycling (70% of pre-training VO(2peak)) and an increase in basal GLUT4 protein in skeletal muscle. Despite these training-induced adaptations, there were no changes in WAT of ex-vivo fat oxidation rate, maximal citrate synthase activity, mitochondrial volume or in selected genes involved in adipose tissue oxidative capacity. We conclude that 10 days training in previously untrained subjects results in adaptations in skeletal muscle but does not increase the oxidative capacity of WAT.

Genetic association analysis of LARS2 with type 2 diabetes

AIMS/HYPOTHESIS

LARS2 has been previously identified as a potential type 2 diabetes susceptibility gene through the low-frequency H324Q (rs71645922) variant (minor allele frequency [MAF] 3.0%). However, this association did not achieve genome-wide levels of significance. The aim of this study was to establish the true contribution of this variant and common variants in LARS2 (MAF > 5%) to type 2 diabetes risk.

METHODS

We combined genome-wide association data (n = 10,128) from the DIAGRAM consortium with independent data derived from a tagging single nucleotide polymorphism (SNP) approach in Dutch individuals (n = 999) and took forward two SNPs of interest to replication in up to 11,163 Dutch participants (rs17637703 and rs952621). In addition, because inspection of genome-wide association study data identified a cluster of low-frequency variants with evidence of type 2 diabetes association, we attempted replication of rs9825041 (a proxy for this group) and the previously identified H324Q variant in up to 35,715 participants of European descent.

RESULTS

No association between the common SNPs in LARS2 and type 2 diabetes was found. Our replication studies for the two low-frequency variants, rs9825041 and H324Q, failed to confirm an association with type 2 diabetes in Dutch, Scandinavian and UK samples (OR 1.03 [95% CI 0.95-1.12], p = 0.45, n = 31,962 and OR 0.99 [0.90-1.08], p = 0.78, n = 35,715 respectively).

CONCLUSIONS/INTERPRETATION

In this study, the largest study examining the role of sequence variants in LARS2 in type 2 diabetes susceptibility, we found no evidence to support previous data indicating a role in type 2 diabetes susceptibility.

Baseline serum 25-hydroxy vitamin D in predicting glycemic status and insulin levels

Vitamin D may have a protective role in insulin secretion and an effect on insulin resistance. Low levels of vitamin D are indicated as a risk factor for both type 1 and type 2 diabetes, however, clinical evidence that increased vitamin D levels benefit diabetic patients has not yet been established.

n-3 PUFA: bioavailability and modulation of adipose tissue function

Adipose tissue has a key role in the development of metabolic syndrome (MS), which includes obesity, type 2 diabetes, dyslipidaemia, hypertension and other disorders. Systemic insulin resistance represents a major factor contributing to the development of MS in obesity. The resistance is precipitated by impaired adipose tissue glucose and lipid metabolism, linked to a low-grade inflammation of adipose tissue and secretion of pro-inflammatory adipokines. Development of MS could be delayed by lifestyle modifications, while both dietary and pharmacological interventions are required for the successful therapy of MS. The n-3 long-chain (LC) PUFA, EPA and DHA, which are abundant in marine fish, act as hypolipidaemic factors, reduce cardiac events and decrease the progression of atherosclerosis. Thus, n-3 LC PUFA represent healthy constituents of diets for patients with MS. In rodents n-3 LC PUFA prevent the development of obesity and impaired glucose tolerance. The effects of n-3 LC PUFA are mediated transcriptionally by AMP-activated protein kinase and by other mechanisms. n-3 LC PUFA activate a metabolic switch toward lipid catabolism and suppression of lipogenesis, i.e. in the liver, adipose tissue and small intestine. This metabolic switch improves dyslipidaemia and reduces ectopic deposition of lipids, resulting in improved insulin signalling. Despite a relatively low accumulation of n-3 LC PUFA in adipose tissue lipids, adipose tissue is specifically linked to the beneficial effects of n-3 LC PUFA, as indicated by (1) the prevention of adipose tissue hyperplasia and hypertrophy, (2) the induction of mitochondrial biogenesis in adipocytes, (3) the induction of adiponectin and (4) the amelioration of adipose tissue inflammation by n-3 LC PUFA.

Low fasting triglycerides: hallmark of the healthy large hip?

Body fat distribution modulates risk for type 2 diabetes mellitus. We evaluated potentially involved metabolic risk factors. In a population of 282 male and 157 female healthy subjects (data from the San Antonio and the European Group of Insulin Resistance (EGIR) study cohorts), we evaluated associations between body fat distribution (assessed by waist and hip circumference) and parameters of lipid- and glucose metabolism, including clamp measurements of insulin sensitivity. After stratification for BMI, fasting triglycerides were lower in the presence of a large hip, and higher in a large waist. Persons with the largest BMI (3rd tertile) showed a difference in triglyceride levels of 1.5 vs. 2.4 mmol/l in large vs. small hip circumference groups (P < 0.038), and a difference of 1.5 vs. 1.2 mmol/l in large vs. small waist circumference groups (P < 0.025). A similar analysis did not reveal a difference in insulin sensitivity. Linear regression analyses confirmed the findings; they revealed negative associations between triglycerides and hip, and (for women borderline statistically significant) positive associations between triglycerides and waist, after adjustment for BMI, mutual confounding, and age (beta +/- s.e.; men: -0.48 +/- 0.005, P < 0.001, and 0.21 +/- 0.005, P < 0.05; women: -0.78 +/- 0.007, P < 0.001, and 0.24 +/- 0.005, P < 0.065), respectively. Linear regression analyses revealed similar opposite associations with high-density lipoprotein (HDL)-cholesterol, though not with glucose, insulin, or insulin sensitivity as measured with the clamp method. In our study population of healthy persons, body fat distribution is associated with fasting triglycerides and HDL-cholesterol, and not with insulin sensitivity. Metabolic risk of unfavorable body fat distribution may be modulated by lower triglyceride storage capacity.

Lifestyle-induced metabolic inflexibility and accelerated ageing syndrome: insulin resistance, friend or foe?

The metabolic syndrome may have its origins in thriftiness, insulin resistance and one of the most ancient of all signalling systems, redox. Thriftiness results from an evolutionarily-driven propensity to minimise energy expenditure. This has to be balanced with the need to resist the oxidative stress from cellular signalling and pathogen resistance, giving rise to something we call 'redox-thriftiness'. This is based on the notion that mitochondria may be able to both amplify membrane-derived redox growth signals as well as negatively regulate them, resulting in an increased ATP/ROS ratio. We suggest that 'redox-thriftiness' leads to insulin resistance, which has the effect of both protecting the individual cell from excessive growth/inflammatory stress, while ensuring energy is channelled to the brain, the immune system, and for storage. We also suggest that fine tuning of redox-thriftiness is achieved by hormetic (mild stress) signals that stimulate mitochondrial biogenesis and resistance to oxidative stress, which improves metabolic flexibility. However, in a non-hormetic environment with excessive calories, the protective nature of this system may lead to escalating insulin resistance and rising oxidative stress due to metabolic inflexibility and mitochondrial overload. Thus, the mitochondrially-associated resistance to oxidative stress (and metabolic flexibility) may determine insulin resistance. Genetically and environmentally determined mitochondrial function may define a 'tipping point' where protective insulin resistance tips over to inflammatory insulin resistance. Many hormetic factors may induce mild mitochondrial stress and biogenesis, including exercise, fasting, temperature extremes, unsaturated fats, polyphenols, alcohol, and even metformin and statins. Without hormesis, a proposed redox-thriftiness tipping point might lead to a feed forward insulin resistance cycle in the presence of excess calories. We therefore suggest that as oxidative stress determines functional longevity, a rather more descriptive term for the metabolic syndrome is the 'lifestyle-induced metabolic inflexibility and accelerated ageing syndrome'. Ultimately, thriftiness is good for us as long as we have hormetic stimuli; unfortunately, mankind is attempting to remove all hormetic (stressful) stimuli from his environment.

Involvement of the vitamin D receptor in energy metabolism: regulation of uncoupling proteins

Recent studies have established that vitamin D plays multiple biological roles beyond calcium metabolism; however, whether vitamin D is involved in energy metabolism is unknown. To address this question, we characterized the metabolic phenotypes of vitamin D receptor (VDR)-null mutant mice. Under a normocalcemic condition, VDR-null mice displayed less body fat mass and lower plasma triglyceride and cholesterol levels compared with wild-type (WT) mice; when placed on a high-fat diet, VDR-null mice showed a slower growth rate and accumulated less fat mass globally than WT mice, even though their food intake and intestinal lipid transport capacity were the same as WT mice. Consistent with the lower adipose mass, plasma leptin levels were lower and white adipocytes were histologically smaller in VDR-null mice than WT mice. The rate of fatty acid beta-oxidation in the white adipose tissue was higher, and the expression of uncoupling protein (UCP) 1, UCP2 and UCP3 was markedly upregulated in VDR-null mice, suggesting a higher energy expenditure in the mutant mice. Experiments using primary brown fat culture confirmed that 1,25-dihydroxyvitamin D3 directly suppressed the expression of the UCPs. Consistently, the energy expenditure, oxygen consumption, and CO2 production in VDR-null mice were markedly higher than in WT mice. These data indicate that vitamin D is involved in energy metabolism and adipocyte biology in vivo in part through regulation of beta-oxidation and UCP expression.