Respiration in adipocytes is inhibited by reactive oxygen species

Effects of mitochondrial dysfunction on cellular function: Role in atherosclerosis

Atherosclerosis, an immunoinflammatory disease of medium and large arteries, is associated with life-threatening clinical events, such as acute coronary syndromes and stroke. Chronic inflammation and impaired lipoprotein metabolism are considered to be among the leading causes of atherosclerosis, while numerous risk factors, including arterial hypertension, diabetes mellitus, obesity, and aging, can contribute to the development of the disease. In recent years, emerging evidence has underlined the key role of mitochondrial dysfunction in the pathogenesis of atherosclerosis. Mitochondrial dysfunction is believed to result in an increase in reactive oxygen species, leading to oxidative stress, chronic inflammation, and intracellular lipid deposition, all of which can contribute to the pathogenesis of atherosclerosis. Critical cells, including endothelial cells, vascular smooth muscle cells, and macrophages, play an important role in atherosclerosis. Mitochondrial function is also involved in maintaining the normal function of these cells. To better understand the relationship between mitochondrial dysfunction and atherosclerosis, this review summarizes the findings of recent studies and discusses the role of mitochondrial dysfunction in the risk factors and critical cells of atherosclerosis. FACTS: OPEN QUESTIONS.

Role of flavonoids in controlling obesity: molecular targets and mechanisms

Obesity presents a major health challenge that increases the risk of several non-communicable illnesses, such as but not limited to diabetes, hypertension, cardiovascular diseases, musculoskeletal and neurological disorders, sleep disorders, and cancers. Accounting for nearly 8% of global deaths (4.7 million) in 2017, obesity leads to diminishing quality of life and a higher premature mortality rate among affected individuals. Although essentially dubbed as a modifiable and preventable health concern, prevention, and treatment strategies against obesity, such as calorie intake restriction and increasing calorie burning, have gained little long-term success. In this manuscript, we detail the pathophysiology of obesity as a multifactorial, oxidative stress-dependent inflammatory disease. Current anti-obesity treatment strategies, and the effect of flavonoid-based therapeutic interventions on digestion and absorption, macronutrient metabolism, inflammation and oxidative stress and gut microbiota has been evaluated. The use of several naturally occurring flavonoids to prevent and treat obesity with a long-term efficacy, is also described.

The neutral amino acid transporter SLC7A10 in adipose tissue, obesity and insulin resistance

Obesity, insulin resistance and type 2 diabetes represent major global health challenges, and a better mechanistic understanding of the altered metabolism in these conditions may give improved treatment strategies. SLC7A10, a member of the SLC7 subfamily of solute carriers, also named ASC-1 (alanine, serine, cysteine transporter-1), has recently been implicated as an important modulator of core processes in energy- and lipid metabolism, through its particularly high expression in adipocytes. In human cohorts, adipose SLC7A10 mRNA shows strong inverse correlations with insulin resistance, adipocyte size and components of the metabolic syndrome, strong heritability, and an association with type 2 diabetes risk alleles. SLC7A10 has been proposed as a marker of white as opposed to thermogenic beige and brown adipocytes, supported by increased formation of thermogenic beige adipocytes upon loss of Slc7a10 in mouse white preadipocytes. Overexpression of SLC7A10 in mature white adipocytes was found to lower the generation of reactive oxygen species (ROS) and stimulate mitochondrial respiratory capacity, while SLC7A10 inhibition had the opposite effect, indicating that SLC7A10 supports a beneficial increase in mitochondrial activity in white adipocytes. Consistent with these beneficial effects, inhibition of SLC7A10 was in mouse and human white adipocyte cultures found to increase lipid accumulation, likely explained by lowered serine uptake and glutathione production. Additionally, zebrafish with partial global Slc7a10b loss-of-function were found to have greater diet-induced body weight and larger visceral adipocytes compared to controls. However, challenging that SLC7A10 exerts metabolic benefits only in white adipocytes, suppression of SLC7A10 has been reported to decrease mitochondrial respiration and expression of thermogenic genes also in some beige and brown adipocyte cultures. Taken together, the data point to an important but complex role of SLC7A10 in metabolic regulation across different adipose tissue depots and adipocyte subtypes. Further research into SLC7A10 functions in specific adipocyte subtypes may lead to new precision therapeutics for mitigating the risk of insulin resistance and type 2 diabetes.

Nicotinamide-riboside shifts the differentiation of human primary white adipocytes to beige adipocytes impacting substrate preference and uncoupling respiration through SIRT1 activation and mitochondria-derived reactive species production

Beige adipocytes play key roles in organismal energy and metabolic balance. In this study, we assessed whether the supplementation of human white adipocytes, differentiated from human adipose tissue-derived stem cells, with nicotinamide riboside (NR), a potent NAD + precursor, can shift differentiation to beige adipocytes (beiging). NR induced mitochondrial biogenesis and the expression of beige markers (TBX1 and UCP1) in white adipocytes demonstrating that NR can declutch beiging. NR did not induce PARP activity but supported SIRT1 induction, which plays a key role in beiging. NR induced etomoxir-resistant respiration, suggesting increases in the oxidation of carbohydrates, carbohydrate breakdown products, or amino acids. Furthermore, NR boosted oligomycin-resistant respiration corresponding to uncoupled respiration. Enhanced etomoxir and oligomycin-resistant respiration were dependent on mitochondrial reactive-species production. Taken together, NR supplementation can induce beiging and uncoupled respiration, which are beneficial for combatting metabolic diseases.

Exercise training remodels subcutaneous adipose tissue in adults with obesity even without weight loss

Excessive adipose tissue mass underlies much of the metabolic health complications in obesity. Although exercise training is known to improve metabolic health in individuals with obesity, the effects of exercise training without weight loss on adipose tissue structure and metabolic function remain unclear. Thirty-six adults with obesity (body mass index = 33 ± 3 kg · m^-2 ) were assigned to 12 weeks (4 days week^-1 ) of either moderate-intensity continuous training (MICT; 70% maximal heart rate, 45 min; n = 17) or high-intensity interval training (HIIT; 90% maximal heart rate, 10 × 1 min; n = 19), maintaining their body weight throughout. Abdominal subcutaneous adipose tissue (aSAT) biopsy samples were collected once before and twice after training (1 day after last exercise and again 4 days later). Exercise training modified aSAT morphology (i.e. reduced fat cell size, increased collagen type 5a3, both P ≤ 0.05, increased capillary density, P = 0.05) and altered protein abundance of factors that regulate aSAT remodelling (i.e. reduced matrix metallopeptidase 9; P = 0.02; increased angiopoietin-2; P < 0.01). Exercise training also increased protein abundance of factors that regulate lipid metabolism (e.g. hormone sensitive lipase and fatty acid translocase; P ≤ 0.03) and key proteins involved in the mitogen-activated protein kinase pathway when measured the day after the last exercise session. However, most of these exercise-mediated changes were no longer significant 4 days after exercise. Importantly, MICT and HIIT induced remarkably similar adaptations in aSAT. Collectively, even in the absence of weight loss, 12 weeks of exercise training induced changes in aSAT structure, as well as factors that regulate metabolism and the inflammatory signal pathway in adults with obesity. KEY POINTS: Exercise training is well-known to improve metabolic health in obesity, although how exercise modifies the structure and metabolic function of adipose tissue, in the absence of weight loss, remains unclear. We report that both 12 weeks of moderate-intensity continuous training (MICT) and 12 weeks of high-intensity interval training (HIIT) induced modifications in adipose tissue structure and factors that regulate adipose tissue remodelling, metabolism and the inflammatory signal pathway in adults with obesity, even without weight loss (with no meaningful differences between MICT and HIIT). The modest modifications in adipose tissue structure in response to 12 weeks of MICT or HIIT did not lead to changes in the rate of fatty acid release from adipose tissue. These results expand our understanding about the effects of two commonly used exercise training prescriptions (MICT and HIIT) on adipose tissue remodelling that may lead to advanced strategies for improving metabolic health outcomes in adults with obesity.

ATP-consuming futile cycles as energy dissipating mechanisms to counteract obesity

Obesity results from an imbalance in energy homeostasis, whereby excessive energy intake exceeds caloric expenditure. Energy can be dissipated out of an organism by producing heat (thermogenesis), explaining the long-standing interest in exploiting thermogenic processes to counteract obesity. Mitochondrial uncoupling is a process that expends energy by oxidizing nutrients to produce heat, instead of ATP synthesis. Energy can also be dissipated through mechanisms that do not involve mitochondrial uncoupling. Such mechanisms include futile cycles described as metabolic reactions that consume ATP to produce a product from a substrate but then converting the product back into the original substrate, releasing the energy as heat. Energy dissipation driven by cellular ATP demand can be regulated by adjusting the speed and number of futile cycles. Energy consuming futile cycles that are reviewed here are lipolysis/fatty acid re-esterification cycle, creatine/phosphocreatine cycle, and the SERCA-mediated calcium import and export cycle. Their reliance on ATP emphasizes that mitochondrial oxidative function coupled to ATP synthesis, and not just uncoupling, can play a role in thermogenic energy dissipation. Here, we review ATP consuming futile cycles, the evidence for their function in humans, and their potential employment as a strategy to dissipate energy and counteract obesity.

Protective Effects of Curcumin in Cardiovascular Diseases—Impact on Oxidative Stress and Mitochondria

Cardiovascular diseases (CVDs) contribute to a large part of worldwide mortality. Similarly, two of the major risk factors for these diseases, aging and obesity, are also global problems. Aging, the gradual decline of body functions, is non-modifiable. Obesity, a modifiable risk factor for CVDs, also predisposes to type 2 diabetes mellitus (T2DM). Moreover, it affects not only the vasculature and the heart but also specific fat depots, which themselves have a major impact on the development and progression of CVDs. Common denominators of aging, obesity, and T2DM include oxidative stress, mitochondrial dysfunction, metabolic abnormalities such as altered lipid profiles and glucose metabolism, and inflammation. Several plant substances such as curcumin, the major active compound in turmeric root, have been used for a long time in traditional medicine and for the treatment of CVDs. Newer mechanistic, animal, and human studies provide evidence that curcumin has pleiotropic effects and attenuates numerous parameters which contribute to an increased risk for CVDs in aging as well as in obesity. Thus, curcumin as a nutraceutical could hold promise in the prevention of CVDs, but more standardized clinical trials are required to fully unravel its potential.

Metabolic and Epigenetic Regulation by Estrogen in Adipocytes

Sex hormones contribute to differences between males and females in body fat distribution and associated disease risk. Higher concentrations of estrogens are associated with a more gynoid body shape and with more fat storage on hips and thighs rather than in visceral depots. Estrogen-mediated protection against visceral adiposity is shown in post-menopausal women with lower levels of estrogens and the reduction in central body fat observed after treatment with hormone-replacement therapy. Estrogen exerts its physiological effects via the estrogen receptors (ERα, ERβ and GPR30) in target cells, including adipocytes. Studies in mice indicate that estrogen protects against adipose inflammation and fibrosis also before the onset of obesity. The mechanisms involved in estrogen-dependent body fat distribution are incompletely understood, but involve, e.g., increased mTOR signaling and suppression of autophagy and adipogenesis/lipid storage. Estrogen plays a key role in epigenetic regulation of adipogenic genes by interacting with enzymes that remodel DNA methylation and histone tail post-translational modifications. However, more studies are needed to map the differential epigenetic effects of ER in different adipocyte subtypes, including those in subcutaneous and visceral adipose tissues. We here review recent discoveries of ER-mediated transcriptional and epigenetic regulation in adipocytes, which may explain sexual dimorphisms in body fat distribution and obesity-related disease risk.

Sex-specific genetic regulation of adipose mitochondria and metabolic syndrome by Ndufv2

We have previously suggested a central role for mitochondria in the observed sex differences in metabolic traits. However, the mechanisms by which sex differences affect adipose mitochondrial function and metabolic syndrome are unclear. Here we show that in both mice and humans, adipose mitochondrial functions are elevated in females and are strongly associated with adiposity, insulin resistance and plasma lipids. Using a panel of diverse inbred strains of mice, we identify a genetic locus on mouse chromosome 17 that controls mitochondrial mass and function in adipose tissue in a sex- and tissue-specific manner. This locus contains Ndufv2 and regulates the expression of at least 89 mitochondrial genes in females, including oxidative phosphorylation genes and those related to mitochondrial DNA content. Overexpression studies indicate that Ndufv2 mediates these effects by regulating supercomplex assembly and elevating mitochondrial reactive oxygen species production, which generates a signal that increases mitochondrial biogenesis.

Beneficial effects of Se/Zn co-supplementation on body weight and adipose tissue inflammation in high-fat diet-induced obese rats

This research investigated the effect of co-supplementation of selenium with zinc on weight control and the inflammatory and oxidative status in relation to obesity. Male Wistar rats (N = 32) were randomly divided into four groups after induction of obesity model: 1) "Zn" was supplemented with zinc sulfate (15 mg/kg BW), 2) "Se" supplemented with selenium as sodium selenate (0.5 mg/kg BW), 3) "Zn + Se" which received Zn (15 mg/kg BW) + Se (0.5 mg/kg BW), and 4) "HFD" as the control group. The intervention was done for eight weeks. At the end of treatment, serum and tissue level of Zn, Se, SOD, GSH-Px, MDA, leptin, TNF-α, and IL-6 was evaluated. Weight and food intake were significantly reduced in the Se group(p < .001), while in the Zn group, weight gain due to obesity was prevented compared to the control group (p = .48). There was a significant and stronger increase in SOD, GSH-Px levels and a remarkable decrease in MDA, leptin, TNF-α, and IL-6 in the group receiving the combination of two supplements than either alone(p < .001). Leptin had a positive correlation with inflammatory factors and lipid peroxidation marker and showed an inverse relationship with Zn and Se levels and anti-oxidative enzymes(p < .05). The analysis showed the mediating role of leptin in the effects of zinc. Co-supplementation of selenium and zinc may have a synergistic effect in reduction of oxidative and inflammatory markers. Regarding the effect of zinc on inflammatory factors and lipid peroxidation, leptin can play a mediating role.

Dermal white adipose tissue: Much more than a metabolic, lipid-storage organ?

The role of dermal white adipose tissue (dWAT) has emerged in the biomedical science as an ancillary fat district in the derma without a defined and distinct function respect to the subcutaneous adipose tissue (sWAT). Despite some evidence describing dWAT as an immune-competent compartment, particularly engaged in wound repair, very few reports dealing with dWAT has elucidated its major modulatory role within the skin biology. Whereas an increasing bulk of evidence allows researcher to describe the main activity of sWAT, in humans dWAT is not properly a separated fat compartment and therefore scarcely considered in the scientific debate. Due to its strategic position between epidermis and sWAT, dermal fat might play a much more intriguing role than expected. This review tries to shed light on this issue, by expanding the debate about a possible role of dWAT in skin physiology.

Anti-obesity properties and mechanism of action of flavonoids: A review

Obesity is a major public health problem, and there is increasing scientific interest in its mechanisms, as well as a search for new compounds with antioxidant and anti-inflammatory properties that can minimize the metabolic complications associated with its pathology. One potential source of these compounds is natural products; Among these, flavonoids are a promising group of natural substances. Flavonoids are active constituents with diverse biological activities and are widely found in plants kingdom. Numerous studies have shown that flavonoids can effectively inhibit obesity and related metabolic disorders. The review synthesizes recent evidence in respect of progress in the understanding of the anti-obesity effects of flavonoids. Such effects which occurs through the modulation of proteins, genes and transcriptional factors involved in decreasing lipogenesis, increasing lipolysis, expenditure energy, stimulating fatty acids B-oxidation, digestion and metabolism of carbohydrates. In addition to mitigating inflammatory responses and suppress oxidative stress. A better understanding of the modulating effects and mechanisms of flavonoids in relation to obesity will allow us to better use these compounds to treat or even prevent obesity and its associated comorbidities.

Role of the Neutral Amino Acid Transporter SLC7A10 in Adipocyte Lipid Storage, Obesity, and Insulin Resistance

Elucidation of mechanisms that govern lipid storage, oxidative stress, and insulin resistance may lead to improved therapeutic options for type 2 diabetes and other obesity-related diseases. Here, we find that adipose expression of the small neutral amino acid transporter SLC7A10, also known as alanine-serine-cysteine transporter-1 (ASC-1), shows strong inverse correlates with visceral adiposity, insulin resistance, and adipocyte hypertrophy across multiple cohorts. Concordantly, loss of Slc7a10 function in zebrafish in vivo accelerates diet-induced body weight gain and adipocyte enlargement. Mechanistically, SLC7A10 inhibition in human and murine adipocytes decreases adipocyte serine uptake and total glutathione levels and promotes reactive oxygen species (ROS) generation. Conversely, SLC7A10 overexpression decreases ROS generation and increases mitochondrial respiratory capacity. RNA sequencing revealed consistent changes in gene expression between human adipocytes and zebrafish visceral adipose tissue following loss of SLC7A10, e.g., upregulation of SCD (lipid storage) and downregulation of CPT1A (lipid oxidation). Interestingly, ROS scavenger reduced lipid accumulation and attenuated the lipid-storing effect of SLC7A10 inhibition. These data uncover adipocyte SLC7A10 as a novel important regulator of adipocyte resilience to nutrient and oxidative stress, in part by enhancing glutathione levels and mitochondrial respiration, conducive to decreased ROS generation, lipid accumulation, adipocyte hypertrophy, insulin resistance, and type 2 diabetes.

Growth performance, physiological parameters, and transcript levels of lipid metabolism-related genes in hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) fed diets containing Siberian ginseng

In high-density aquaculture, fish health can suffer because of excessive feeding, which causes fatty liver disease. Siberian ginseng (Acanthopanax senticosus) has been used as a feed additive to promote animal growth, immunity, and lipid metabolism. In this study, we explored the effects of A. senticosus on the physiology of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂). A control group and five groups fed diets containing A. senticosus (0.5, 1, 2, 4, and 8 g A. senticosus/kg feed) were established and maintained for 8 weeks. Dietary supplementation with A. senticosus at 4 g/kg promoted growth of the hybrid yellow catfish. Serum total cholesterol (TC) and triacylglycerol (TG) levels at 2 g/kg A. senticosus (TC: 1.31 mmol/L; TG: 1.08 mmol/L) were significantly lower than in the control group (TC: 1.51 mmol/L; TG: 1.41 mmol/L), and 4 g/kg A. senticosus (17.20 μmol/g tissue) reduced the liver TG level compared with the control group (21.36 μmol/g tissue) (P <0.05). Comparative transcriptomic analysis of liver tissue between the control group and the group showing optimum growth (4 g/kg A. senticosus) revealed 820 differentially expressed genes and 44 significantly enriched pathways, especially lipid metabolism pathways such as unsaturated fatty acid and fatty acid metabolism. The transcript levels of five lipid metabolism-related genes were determined by quantitative real-time PCR. The results showed that 2–4 g/kg A. senticosus supplementation reduced the FADS2, ELOVL2, CYP24a, and PLPP3 transcript levels and 4 g/kg A. senticosus increased the DIO2 transcript level (P <0.05), leading to altered synthesis of TG and thyroxine and reduced fat deposition in the liver. Our results show that dietary A. senticosus affects the regulation of fat metabolism and promotes the growth of hybrid yellow catfish. A. senticosus is a healthy feed additive, and the appropriate dietary supplementation rate is 2–4 g/kg.

Differential effects of pre-exercise on cancer cachexia-induced muscle atrophy in fast- and slow-twitch muscles

We hypothesized that pre-exercise may effectively prevent cancer cachexia-induced muscle atrophy in both fast- and slow-twitch muscle types. Additionally, the fast-twitch muscle may be more affected by cancer cachexia than slow-twitch muscle. This study aimed to evaluate the effects of pre-exercise on cancer cachexia-induced atrophy and on atrophy in fast- and slow-twitch muscles. Twelve male Wistar rats were randomly divided into sedentary and exercise groups, and another 24 rats were randomly divided into control, pre-exercise, cancer cachexia induced by intraperitoneal injections of ascites hepatoma AH130 cells, and pre-exercise plus cancer cachexia groups. We analyzed changes in muscle mass and in gene and protein expression levels of major regulators and indicators of muscle protein degradation and synthesis pathways, angiogenic factors, and mitochondrial function in both the plantaris and soleus muscles. Pre-exercise inhibited muscle mass loss, rescued protein synthesis, prevented capillary regression, and suppressed hypoxia in the plantaris and soleus muscles. Pre-exercise inhibited mitochondrial dysfunction differently in fast- and slow-twitch muscles. These results suggested that pre-exercise has the potential to inhibit cancer-cachexia-induced muscle atrophy in both fast- and slow-twitch muscles. Furthermore, the different progressions of cancer-cachexia-induced muscle atrophy in fast- and slow-twitch muscles are related to differences in mitochondrial function.

3-Hydroxyisobutyrate, A Strong Marker of Insulin Resistance in Type 2 Diabetes and Obesity That Modulates White and Brown Adipocyte Metabolism

Circulating branched-chain amino acids (BCAAs) associate with insulin resistance and type 2 diabetes. 3-Hydroxyisobutyrate (3-HIB) is a catabolic intermediate of the BCAA valine. In this study, we show that in a cohort of 4,942 men and women, circulating 3-HIB is elevated according to levels of hyperglycemia and established type 2 diabetes. In complementary cohorts with measures of insulin resistance, we found positive correlates for circulating 3-HIB concentrations with HOMA2 of insulin resistance, as well as a transient increase in 3-HIB followed by a marked decrease after bariatric surgery and weight loss. During differentiation, both white and brown adipocytes upregulate BCAA utilization and release increasing amounts of 3-HIB. Knockdown of the 3-HIB-forming enzyme 3-hydroxyisobutyryl-CoA hydrolase decreases release of 3-HIB and lipid accumulation in both cell types. Conversely, addition of 3-HIB to white and brown adipocyte cultures increases fatty acid uptake and modulated insulin-stimulated glucose uptake in a time-dependent manner. Finally, 3-HIB treatment decreases mitochondrial oxygen consumption and generation of reactive oxygen species in white adipocytes, while increasing these measures in brown adipocytes. Our data establish 3-HIB as a novel adipocyte-derived regulator of adipocyte subtype-specific functions strongly linked to obesity, insulin resistance, and type 2 diabetes.

The biology of lipid droplet-bound mitochondria

Proper regulation of cellular lipid storage and oxidation is indispensable for the maintenance of cellular energy homeostasis and health. Mitochondrial function has been shown to be a main determinant of functional lipid storage and oxidation, which is of particular interest for the adipose tissue, as it is the main site of triacylglyceride storage in lipid droplets (LDs). Recent studies have identified a subpopulation of mitochondria attached to LDs, peridroplet mitochondria (PDM) that can be separated from cytoplasmic mitochondria (CM) by centrifugation. PDM have distinct bioenergetics, proteome, cristae organization and dynamics that support LD build-up, however their role in adipose tissue biology remains largely unexplored. Therefore, understanding the molecular basis of LD homeostasis and their relationship to mitochondrial function and attachment in adipocytes is of major importance.

Withania somnifera Extract Enhances Energy Expenditure via Improving Mitochondrial Function in Adipose Tissue and Skeletal Muscle

Withania somnifera (WS), commonly known as ashwagandha, possesses diverse biological functions. WS root has mainly been used as an herbal medicine to treat anxiety and was recently reported to have an anti-obesity effect, however, the mechanisms underlying its action remain to be explored. We hypothesized that WS exerts its anti-obesity effect by enhancing energy expenditure through improving the mitochondrial function of brown/beige adipocytes and skeletal muscle. Male C57BL/6J mice were fed a high-fat diet (HFD) containing 0.25% or 0.5% WS 70% ethanol extract (WSE) for 10 weeks. WSE (0.5%) supplementation significantly suppressed the increases in body weight and serum lipids, and lipid accumulation in the liver and adipose tissue induced by HFD. WSE supplementation increased oxygen consumption and enhanced mitochondrial activity in brown fat and skeletal muscle in the HFD-fed mice. In addition, it promoted browning of subcutaneous fat by increasing mitochondrial uncoupling protein 1 (UCP1) expression. Withaferin A (WFA), a major compound of WS, enhanced the differentiation of pre-adipocytes into beige adipocytes and oxygen consumption in C2C12 murine myoblasts. These results suggest that WSE ameliorates diet-induced obesity by enhancing energy expenditure via promoting mitochondrial function in adipose tissue and skeletal muscle, and WFA is a key regulator in this function.

Tissue-specific responses of antioxidant pathways to poor hygiene conditions in growing pigs divergently selected for feed efficiency

BACKGROUND

Poor hygiene of housing induces a systemic inflammatory response. Because inflammation and oxidative stress are processes that can sustain each other, the ways pigs are able to activate their antioxidant defenses are critical for production performance and health during periods when the immune system is solicited. Selection for production performance can also influence reactive oxygen species (ROS) production and expression levels of genes involved in cellular response to oxidative stress in different tissues. To establish the extent by which poor hygiene and selection for feed efficiency affected redox status, pigs divergently selected for residual feed intake (RFI) were housed in poor or good hygiene during 6 weeks. At the end, blood was collected in all pigs, and half of them were killed for tissue sampling. The remaining pigs were reared in good hygiene conditions during a recovery period of 7-8 weeks.

RESULTS

At week 6, poor hygiene was associated with a lower total antioxidant capacity assessed by plasma ferric reducing ability in all pigs, and with greater plasma levels of hydrogen peroxides in the high RFI pigs (less efficient). Adipose tissue of high RFI pigs exhibited higher activities of catalase and glutathione reductase, and greater thiobarbituric acid reactive substances (TBARS) concentrations when compared with the low RFI pigs (more efficient). Poor hygiene conditions activated the antioxidant enzymes activities (glutathione reductase, superoxide dismutase and catalase) in adipose tissue of both lines, but led to higher ROS production by mature adipocytes isolated from the high RFI pigs only. In liver and muscle, there were only minor changes in antioxidant molecules due to genetics and hygiene conditions. After the resilience period, adipose tissue of pigs previously challenged by poor hygiene maintained higher antioxidant enzyme activities, and for the high RFI line, displayed higher TBARS concentrations.

CONCLUSIONS

Pigs selected for improved feed efficiency showed a lower susceptibility to oxidative stress induced by poor hygiene conditions. This could led to a lower inflammatory response and less impaired growth when these pigs are facing sanitary challenges during the production period.

Adipose Mitochondrial Respiratory Capacity in Obesity is Impaired Independently of Glycemic Status of Tissue Donors

OBJECTIVE

The study aimed to investigate how obesity and glycemic state affect mitochondrial respiration and ATP-generating pathways in mature human adipocytes.

METHODS

Subcutaneous (sc) and visceral (vc) adipocytes were isolated from patients undergoing abdominal surgery. Respiratory chain function was analyzed by high-resolution respirometry. Adipocyte ATP levels and lactate release were measured separately in the presence of either glycolysis (2-deoxy-D-glucose) or ATP synthase (oligomycin) inhibitors.

RESULTS

A significant negative correlation between oxidative phosphorylation capacity and the BMI of tissue donors found in sc adipocytes (P < 0.05). Furthermore, respirometry revealed an inverse relationship between BMI and the electron transfer system capacity of sc (P < 0.05) but not vc adipocytes. In both depots, the respiratory capacity was not affected by the glycemic state. A positive correlation between BMI and adipocyte lactate release was measured independently of the tissue origin (sc: P = 0.01; vc: P < 0.05). Direct ATP measurements indicated that energy demands of adipocytes were predominantly fulfilled by glycolytic activity.

CONCLUSIONS

The study's data suggest that obesity is the primary driver of impaired adipocyte mitochondrial respiration because the glycemic state did not further deteriorate this situation. The adipocytes' energy needs are covered primarily by the glycolytic pathway.

Redox control of non-shivering thermogenesis

Background

Thermogenic adipocytes reorganize their metabolism during cold exposure. Metabolic reprogramming requires readily available bioenergetics substrates, such as glucose and fatty acids, to increase mitochondrial respiration and produce heat via the uncoupling protein 1 (UCP1). This condition generates a finely-tuned production of mitochondrial reactive oxygen species (ROS) that support non-shivering thermogenesis.

Scope of review

Herein, the findings underlining the mechanisms that regulate ROS production and control of the adaptive responses tuning thermogenesis in adipocytes are described. Furthermore, this review describes the metabolic responses to substrate availability and the consequence of mitochondrial failure to switch fuel oxidation in response to changes in nutrient availability. A framework to control mitochondrial ROS threshold to maximize non-shivering thermogenesis in adipocytes is provided.

Major conclusions

Thermogenesis synchronizes fuel oxidation with an acute and transient increase of mitochondrial ROS that promotes the activation of redox-sensitive thermogenic signaling cascade and UCP1. However, an overload of substrate flux to mitochondria causes a massive and damaging mitochondrial ROS production that affects mitochondrial flexibility. Finding novel thermogenic redox targets and manipulating ROS concentration in adipocytes appears to be a promising avenue of research for improving thermogenesis and counteracting metabolic diseases.

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Mitochondrial ROS support non-shivering thermogenesis.

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Thermogenic ROS are tightly related to mitochondrial metabolic reorganization.

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Uncontrolled mitochondrial ROS production is causative of metabolic inflexibility.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Antioxidant treatment induces reductive stress associated with mitochondrial dysfunction in adipocytes

β-Adrenergic stimulation of adipose tissue increases mitochondrial density and activity (browning) that are associated with improved whole-body metabolism. Whereas chronically elevated levels of reactive oxygen species (ROS) in adipose tissue contribute to insulin resistance, transient ROS elevation stimulates physiological processes such as adipogenesis. Here, using a combination of biochemical and cell and molecular biology-based approaches, we studied whether ROS or antioxidant treatment affects β3-adrenergic receptor (β3-AR) stimulation-induced adipose tissue browning. We found that β3-AR stimulation increases ROS levels in cultured adipocytes, but, unexpectedly, pretreatment with different antioxidants (N-acetylcysteine, vitamin E, or GSH ethyl ester) did not prevent this ROS increase. Using fluorescent probes, we discovered that the antioxidant treatments instead enhanced β3-AR stimulation-induced mitochondrial ROS production. This pro-oxidant effect of antioxidants was, even in the absence of β3-AR stimulation, associated with decreased oxygen consumption and increased lactate production in adipocytes. We observed similar antioxidant effects in WT mice: N-acetylcysteine blunted β3-AR stimulation-induced browning of white adipose tissue and reduced mitochondrial activity in brown adipose tissue even in the absence of β3-AR stimulation. Furthermore, N-acetylcysteine increased the levels of peroxiredoxin 3 and superoxide dismutase 2 in adipose tissue, indicating increased mitochondrial oxidative stress. We interpret this negative impact of antioxidants on oxygen consumption in vitro and adipose tissue browning in vivo as essential adaptations that prevent a further increase in mitochondrial ROS production. In summary, these results suggest that chronic antioxidant supplementation can produce a paradoxical increase in oxidative stress associated with mitochondrial dysfunction in adipocytes.

Age-Related Changes in Glucose Metabolism, Hyperglycemia, and Cardiovascular Risk

Aging and diabetes mellitus are 2 well-known risk factors for cardiovascular disease (CVD). During the past 50 years, there has been an dramatic increase in life expectancy with a simultaneous increase in the prevalence of diabetes mellitus in the older population. This large number of older individuals with diabetes mellitus is problematic given that CVD risk associated with aging and diabetes mellitus. In this review, we summarize epidemiological data relating to diabetes mellitus and CVD, with an emphasis on the aging population. We then present data on hyperglycemia as a risk factor for CVD and review the current knowledge of age-related changes in glucose metabolism. Next, we review the role of obesity in the pathogenesis of age-related glucose dysregulation, followed by a summary of the results from major randomized controlled trials that focus on cardiovascular risk reduction through glycemic control, with a special emphasis on older adults. We then conclude with our proposed model of aging that body composition changes and insulin resistance link possible dysregulation of physiological pathways leading to obesity and diabetes mellitus-both forms of accelerated aging-and risks for CVD.

Adipocyte DIO2 Expression Increases in Human Obesity but Is Not Related to Systemic Insulin Sensitivity

Deiodinase type II (D2), encoded by DIO2, catalyzes the conversion of T4 to bioactive T3. T3 not only stimulates adaptive thermogenesis but also affects adipose tissue (AT) lipid accumulation, mitochondrial function, inflammation, and potentially systemic metabolism. Although better defined in brown AT, the precise role of DIO2 expression in white AT remains largely unknown, with data derived only from whole fat. Therefore, the purpose of this study was to determine whether subcutaneous (SAT) and visceral (VAT) adipocyte-specific gene expression of DIO2 differs between obese and lean patients and whether these differences relate to alterations in mitochondrial function, fatty acid flux, inflammatory cytokines/adipokines, and ultimately insulin sensitivity. Accordingly, adipocytes of 73 obese and 21 lean subjects were isolated and subjected to gene expression analyses. Our results demonstrate that obese compared to lean human individuals have increased adipocyte-specific DIO2 expression in both SAT and VAT. Although higher DIO2 was strongly related to reduced fatty acid synthesis/oxidation and mitochondrial function, we found no relationship to proinflammatory cytokines or insulin resistance and no difference based on diabetic status. Our results suggest that adipocyte-derived DIO2 may play a role in weight maintenance but is likely not a major contributor to obesity-related insulin resistance.

A role for long-chain acyl-CoA synthetase-4 (ACSL4) in diet-induced phospholipid remodeling and obesity-associated adipocyte dysfunction

Objective

Regulation of fatty acid (FA) metabolism is central to adipocyte dysfunction during diet-induced obesity (DIO). Long-chain acyl-CoA synthetase-4 (ACSL4) has been hypothesized to modulate the metabolic fates of polyunsaturated FA (PUFA), including arachidonic acid (AA), but the in vivo actions of ACSL4 are unknown. The purpose of our studies was to determine the in vivo role of adipocyte ACSL4 in regulating obesity-associated adipocyte dysfunction.

Methods

We developed a novel mouse model with adipocyte-specific ablation of ACSL4 (Ad-KO) using loxP Cre recombinase technology. Metabolic phenotyping of Ad-KO mice relative to their floxed littermates (ACSL4^floxed) was performed, including body weight and body composition over time; insulin and glucose tolerance tests; and energy expenditure, activity, and food intake in metabolic cages. Adipocytes were isolated for ex vivo adipocyte oxygen consumption by Clark electrode and lipidomics analysis. In vitro adipocyte analysis including oxygen consumption by Seahorse and real-time PCR analysis were performed to confirm our in vivo findings.

Results

Ad-KO mice were protected against DIO, adipocyte death, and metabolic dysfunction. Adipocytes from Ad-KO mice fed high-fat diet (HFD) had reduced incorporation of AA into phospholipids (PL), free AA, and levels of the AA lipid peroxidation product 4-hydroxynonenal (4-HNE). Additionally, adipocytes from Ad-KO mice fed HFD had reduced p53 activation and increased adipocyte oxygen consumption (OCR), which we demonstrated are direct effects of 4-HNE on adipocytes in vitro.

Conclusion

These studies are the first to elucidate ACSL4's in vivo actions to regulate the incorporation of AA into PL and downstream effects on DIO-associated adipocyte dysfunction. By reducing the incorporation of AA into PL and free fatty acid pools in adipocytes, Ad-KO mice were significantly protected against HFD-induced increases in adipose and liver fat accumulation, adipocyte death, gonadal white adipose tissue (gWAT) inflammation, and insulin resistance (IR). Additionally, deficiency of adipocyte ACSL4 expression in mice fed a HFD resulted in increased gWAT adipocyte OCR and whole body energy expenditure (EE).

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ACSL4 expression is upregulated in murine white adipocytes during diet-induced obesity.

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Mice with adipocyte-specific ablation of ACSL4 (Ad-KO) are protected against diet-induced obesity, adipocyte death and metabolic dysfunction.

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Lipidomics profiling of isolated adipocytes from Ad-KO mice fed a high-fat diet (HFD) had reduced arachidonic acid (AA) in phospholipids.

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Adipocytes from Ad-KO mice fed HFD had reduced free AA and levels of the AA lipid peroxidation product 4-hydroxynonenal (4-HNE).

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Adipocytes from Ad-KO mice fed HFD had reduced p53 activation and increased adipocyte oxygen consumption (OCR).

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P53 activation and inhibited adipocyte OCR are direct effects of 4-HNE on adipocytes in vitro.

Fat-specific Dicer deficiency accelerates aging and mitigates several effects of dietary restriction in mice

Aging increases the risk of type 2 diabetes, and this can be prevented by dietary restriction (DR). We have previously shown that DR inhibits the downregulation of miRNAs and their processing enzymes - mainly Dicer - that occurs with aging in mouse white adipose tissue (WAT). Here we used fat-specific Dicer knockout mice (AdicerKO) to understand the contributions of adipose tissue Dicer to the metabolic effects of aging and DR. Metabolomic data uncovered a clear distinction between the serum metabolite profiles of Lox control and AdicerKO mice, with a notable elevation of branched-chain amino acids (BCAA) in AdicerKO. These profiles were associated with reduced oxidative metabolism and increased lactate in WAT of AdicerKO mice and were accompanied by structural and functional changes in mitochondria, particularly under DR. AdicerKO mice displayed increased mTORC1 activation in WAT and skeletal muscle, where Dicer expression is not affected. This was accompanied by accelerated age-associated insulin resistance and premature mortality. Moreover, DR-induced insulin sensitivity was abrogated in AdicerKO mice. This was reverted by rapamycin injection, demonstrating that insulin resistance in AdicerKO mice is caused by mTORC1 hyperactivation. Our study evidences a DR-modulated role for WAT Dicer in controlling metabolism and insulin resistance.

The Beneficial Effects of Quercetin, Curcumin, and Resveratrol in Obesity

Over the past two decades, obesity has been one of the major public health concerns in most countries. In the search for new molecules that could be used for the treatment of obesity, good perspectives have been opened up for polyphenols, a class of natural bioactive phytochemicals. Experimental and limited clinical trial evidence supports that some polyphenols such as quercetin, curcumin, and resveratrol have potential benefit functions on obesity treatment. This brief review focuses on the main functions of the above-named polyphenols on adipose tissue. These polyphenols may play beneficial effects on adipose tissue under obese condition by alleviating intracellular oxidative stress, reducing chronic low-grade inflammation, inhibiting adipogenesis and lipogenesis, and suppressing the differentiation of preadipocytes to mature adipocytes.

Glycated human albumin alters mitochondrial respiration in preadipocyte 3T3-L1 cells

Diabetes and obesity are strongly associated with increased levels of circulating advanced glycation end products (AGEs) and reactive oxygen species (ROS). These two molecular phenomena affect the physiology of adipose tissue, a biological driver of the metabolic syndrome, leading to an inflammatory profile and insulin resistance, which could contribute to obesity/diabetes-associated complications, such as cardiovascular diseases. Herein, we investigated the impact of AGEs on mitochondrial bioenergetics in murine preadipocyte cells (3T3-L1) and cellular redox homeostasis. We show that incubation of preadipocytes with AGEs stimulates mitochondrial activity and respiration while inducing oxidative stress. This AGE-induced intracellular ROS production was blocked by diphenylene iodonium, an NAD(P)H oxidase inhibitor. In parallel, antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) were found to be activated upon AGE treatment. Our results suggest that AGE-induced oxidative stress is generated by NAD(P)H oxidase and leads to a cellular proliferation arrest associated with enhanced mitochondrial metabolism and biogenesis, and with increased levels of ROS-detoxifying enzymes, as well. These new data show how AGEs may be involved in hyperglycemia-induced oxidative damage in preadipocytes and their potential links to diabetes progression. © 2017 BioFactors, 43(4):577-592, 2017.

Impact of gut hormone FGF-19 on type-2 diabetes and mitochondrial recovery in a prospective study of obese diabetic women undergoing bariatric surgery

BACKGROUND

The ileal-derived hormone, fibroblast growth factor 19 (FGF-19), may promote weight loss and facilitate type-2 diabetes mellitus remission in bariatric surgical patients. We investigated the effect of different bariatric procedures on circulating FGF-19 levels and the resulting impact on mitochondrial health in white adipose tissue (AT).

METHODS

Obese and type-2 diabetic women (n = 39, BMI > 35 kg/m²) undergoing either biliopancreatic diversion (BPD), laparoscopic greater curvature plication (LGCP), or laparoscopic adjustable gastric banding (LAGB) participated in this ethics approved study. Anthropometry, biochemical, clinical data, serum, and AT biopsies were collected before and 6 months after surgery. Mitochondrial gene expression in adipose biopsies and serum FGF-19 levels were then assessed.

RESULTS

All surgeries led to metabolic improvements with BPD producing the greatest benefits on weight loss (↓30%), HbA1c (↓28%), and cholesterol (↓25%) reduction, whilst LGCP resulted in similar HbA1c improvements (adjusted for BMI). Circulating FGF-19 increased in both BPD and LGCP (χ²(2) = 8.088; P = 0.018), whilst, in LAGB, FGF-19 serum levels decreased (P = 0.028). Interestingly, circulating FGF-19 was inversely correlated with mitochondrial number in AT across all surgeries (n = 39). In contrast to LGCP and LAGB, mitochondrial number in BPD patients corresponded directly with changes in 12 of 14 mitochondrial genes assayed (P < 0.01).

CONCLUSIONS

Elevated serum FGF-19 levels post-surgery were associated with improved mitochondrial health in AT and overall diabetic remission. Changes in circulating FGF-19 levels were surgery-specific, with BPD producing the best metabolic outcomes among the study procedures (BPD > LGCP > LAGB), and highlighting mitochondria in AT as a potential target of FGF-19 during diabetes remission.

Mechanisms of marrow adiposity and its implications for skeletal health

The bone marrow niche is composed of cells from hematopoietic and mesenchymal origin. Both require energy to power differentiation and these processes are intimately connected to systemic metabolic homeostasis. Glycolysis is the preferred substrate for mesenchymal stromal cells in the niche, although fatty acid oxidation and glutaminolysis are important during stage specific differentiation. Autophagy and lipophagy, in part triggered by adenosine monophosphate-activated protein kinase (AMPK), may also play an important but temporal specific role in osteoblast differentiation. Enhanced marrow adiposity is caused by clinical factors that are genetically, environmentally, and hormonally mediated. These determinants mediate a switch from the osteogenic to the adipogenic lineage. Preliminary evidence supports an important role for fuel utilization in those cell fate decisions. Although both the origin and function of the marrow adipocyte remain to be determined, and in some genetic mouse models high marrow adiposity may co-exist with greater bone mass, in humans changes in marrow adiposity are closely linked to adverse changes in skeletal metabolism. This supports an intimate relationship between bone and fat in the marrow. Future studies will likely shed more light on the relationship of cellular as well as whole body metabolism on the ultimate fate of bone marrow stromal cells.

Extracellular Redox Regulation of Intracellular Reactive Oxygen Generation, Mitochondrial Function and Lipid Turnover in Cultured Human Adipocytes

Background

Many tissues play an important role in metabolic homeostasis and the development of diabetes and obesity. We hypothesized that the circulating redox metabolome is a master metabolic regulatory system that impacts all organs and modulates reactive oxygen species (ROS) production, lipid peroxidation, energy production and changes in lipid turnover in many cells including adipocytes.

Methods

Differentiated human preadipocytes were exposed to the redox couples, lactate (L) and pyruvate (P), β–hydroxybutyrate (βOHB) and acetoacetate (Acoc), and the thiol-disulfides cysteine/ cystine (Cys/CySS) and GSH/GSSG for 1.5–4 hours. ROS measurements were done with CM-H₂DCFDA. Lipid peroxidation (LPO) was assessed by a modification of the thiobarbituric acid method. Lipolysis was measured as glycerol release. Lipid synthesis was measured as ¹⁴C-glucose incorporated into lipid. Respiration was assessed using the SeaHorse XF24 analyzer and the proton leak was determined from the difference in respiration with oligomycin and antimycin A.

Results

Metabolites with increasing oxidation potentials (GSSG, CySS, Acoc) increased adipocyte ROS. In contrast, P caused a decrease in ROS compared with L. Acoc also induced a significant increase in both LPO and lipid synthesis. L and Acoc increased lipolysis. βOHB increased respiration, mainly due to an increased proton leak. GSSG, when present throughout 14 days of differentiation significantly increased fat accumulation, but not when added later.

Conclusions

We demonstrated that in human adipocytes changes in the external redox state impacted ROS production, LPO, energy efficiency, lipid handling, and differentiation. A more oxidized state generally led to increased ROS, LPO and lipid turnover and more reduction led to increased respiration and a proton leak. However, not all of the redox couples were the same suggesting compartmentalization. These data are consistent with the concept of the circulating redox metabolome as a master metabolic regulatory system.

Role of oxidative stress and antioxidants in daily nutrition and human health

Diet may be defined as a complex process that should involve a deeper comprehension of metabolism, energy balance, and the molecular pathways involved in cellular stress response and survival, gut microflora genetics, enzymatic polymorphism within the human population, and the role of plant-derived polyphenols in this context. Metabolic syndrome, encompassing pathologies with a relatively high morbidity, such as type 2 diabetes, obesity, and cardiovascular disease, is a bullet point of the big concern about how daily dietary habits should promote health and prevent metabolic impairments to prevent hospitalization and the need for health care. From a clinical point of view, very few papers deal with this concern, whereas most of the evidence reported focuses on in vitro and animal models, which study the activity of phytochemicals contained in the daily diet. A fundamental issue addressed by dietitians deals with the role exerted by redox-derived reactive species. Most plant polyphenols act as antioxidants, but recent evidence supports the idea that these compounds primarily activate a mild oxidative stress to elicit a positive, beneficial response from cells. How these compounds may act upon the detoxifying system exerting a scavenging role from reactive oxygen or nitrogen species is still a matter of debate; however, it can be argued that their role is even more complex than expected, acting as signaling molecules in the cross-talk mitochondria-endoplasmic reticulum and in enzymatic pathways involved in the energetic balance. In this relationship, a fundamental role is played by the brain-adipose tissue-gut axis. The aim of this review was to elucidate this topic and the state of art about the role of reactive species in cell signaling and the function of metabolism and survival to reappraise the role of plant-derived chemicals.

The two faces of reactive oxygen species (ROS) in adipocyte function and dysfunction

White adipose tissue (WAT) is actively involved in the regulation of whole-body energy homeostasis via storage/release of lipids and adipokine secretion. Current research links WAT dysfunction to the development of metabolic syndrome (MetS) and type 2 diabetes (T2D). The expansion of WAT during oversupply of nutrients prevents ectopic fat accumulation and requires proper preadipocyte-to-adipocyte differentiation. An assumed link between excess levels of reactive oxygen species (ROS), WAT dysfunction and T2D has been discussed controversially. While oxidative stress conditions have conclusively been detected in WAT of T2D patients and related animal models, clinical trials with antioxidants failed to prevent T2D or to improve glucose homeostasis. Furthermore, animal studies yielded inconsistent results regarding the role of oxidative stress in the development of diabetes. Here, we discuss the contribution of ROS to the (patho)physiology of adipocyte function and differentiation, with particular emphasis on sources and nutritional modulators of adipocyte ROS and their functions in signaling mechanisms controlling adipogenesis and functions of mature fat cells. We propose a concept of ROS balance that is required for normal functioning of WAT. We explain how both excessive and diminished levels of ROS, e.g. resulting from over supplementation with antioxidants, contribute to WAT dysfunction and subsequently insulin resistance.

N-acetylcysteine inhibits lipid accumulation in mouse embryonic adipocytes

Oxidative stress plays critical roles in the pathogenesis of diabetes, hypertension, and atherosclerosis; some authors reported that fat accumulation correlates to systemic oxidative stress in human and mice, but cellular redox environment effect on lipid accumulation is still unclear. In our laboratory we used mouse embryonic fibroblasts (undifferentiated cells: CC), which are capable of differentiating into mature adipocytes (differentiated cells: DC) and accumulate lipids, as obesity model. Here we analyzed the role of the well-known antioxidant and glutathione precursor N-acetylcysteine (NAC) in cellular MAPK modulation and lipid accumulation. We evaluated the effect of NAC on the adipogenic differentiation pathway using different doses: 0.01, 0.1, 1 and 5 mM; no toxic doses in these cells. A dose of 5 mM NAC [DCN-5] provoked a significant decrease in triglyceride accumulation (72±10 [DCN-5] vs 169±15 [DC], p<0.01), as well in Oil Red O stained neutral lipid content (120±2 [DCN-5] vs 139±12 [DC], p<0.01). Molecular mechanisms responsible for adipogenic differentiation involve increase of the expression of phosphoERK½ and phosphoJNK, 5 mM NAC treatment inhibited both pERK½ and pJNK protein levels. We also evaluated the mitotic clonal expansion (MCE) which takes place during adipogenesis and observed an increase in DC at a rate of 1.5 cells number compared to CC at day 2, whereas the highest doses of NAC significantly inhibited MCE. Our results suggest that NAC inhibits lipid accumulation and the MAPK phosphorylation in mouse embryonic fibroblasts during adipogenic differentiation and further contribute to probe the importance of cellular redox environment in adipogenesis.

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NAC, up to 5 mM, is not toxic in adipocytes obtained from mouse embryonic fibroblasts.

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NAC inhibited phosphorylation of ERK½ and JNK in adipogenic differentiation.

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NAC inhibited mitotic clonal expansion in adipogenic differentiation.

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NAC inhibited triglyceride and lipid accumulation in mouse embryonic adipocytes.

Skeletal integration of energy homeostasis: Translational implications

New evidence has recently emerged defining a close relationship between fat and bone metabolism. Adipose tissue is one of the largest organs in the body but its functions vary by location and origin. Adipocytes can act in an autocrine manner to regulate energy balance by sequestering triglycerides and then, depending on demand, releasing fatty acids through lipolysis for energy utilization, and in some cases through uncoupling protein 1 for generating heat. Adipose tissue can also act in an endocrine or paracrine manner by releasing adipokines that modulate the function of other organs. Bone is one of those target tissues, although recent evidence has emerged that the skeleton reciprocates by releasing its own factors that modulate adipose tissue and beta cells in the pancreas. Therefore, it is not surprising that these energy-modulating tissues are controlled by a central regulatory mechanism, primarily the sympathetic nervous system. Disruption in this complex regulatory circuit and its downstream tissues is manifested in a wide range of metabolic disorders, for which the most prevalent is type 2 diabetes mellitus. The aim of this review is to summarize our knowledge of common determinants in the bone and adipose function and the translational implications of recent work in this emerging field.

Energy Excess, Glucose Utilization, and Skeletal Remodeling: New Insights

Skeletal complications have recently been recognized as another of the several comorbidities associated with diabetes. Clinical studies suggest that disordered glucose and lipid metabolism have a profound effect on bone. Diabetes-related changes in skeletal homeostasis result in a significant increased risk of fractures, although the pathophysiology may differ from postmenopausal osteoporosis. Efforts to understand the underlying mechanisms of diabetic bone disease have focused on the direct interaction of adipose tissue with skeletal remodeling and the potential influence of glucose utilization and energy uptake on these processes. One aspect that has emerged recently is the major role of the central nervous system in whole-body metabolism, bone turnover, adipose tissue remodeling, and beta cell secretion of insulin. Importantly, the skeleton contributes to the metabolic balance inherent in physiologic states. New animal models have provided the insights necessary to begin to dissect the effects of obesity and insulin resistance on the acquisition and maintenance of bone mass. In this Perspective, we focus on potential mechanisms that underlie the complex interactions between adipose tissue and skeletal turnover by focusing on the clinical evidence and on preclinical studies indicating that glucose intolerance may have a significant impact on the skeleton. In addition, we raise fundamental questions that need to be addressed in future studies to resolve the conundrum associated with glucose intolerance, obesity, and osteoporosis.

Altered metabolic and stemness capacity of adipose tissue-derived stem cells from obese mouse and human

Adipose stem cells (ASCs) are an appealing source of cells for therapeutic intervention; however, the environment from which ASCs are isolated may impact their usefulness. Using a range of functional assays, we have evaluated whether ASCs isolated from an obese environment are comparable to cells from non-obese adipose tissue. Results showed that ASCs isolated from obese tissue have a reduced proliferative ability and a loss of viability together with changes in telomerase activity and DNA telomere length, suggesting a decreased self-renewal capacity. Metabolic analysis demonstrated that mitochondrial content and function was impaired in obese-derived ASCs resulting in changes in favored oxidative substrates. These findings highlight the impact of obesity on adult stem properties. Hence, caution should be exercised when considering the source of ASCs for cellular therapies since their therapeutic potential may be impaired.

N-Acetylcysteine affects obesity-related protein expression in 3T3-L1 adipocytes

OBJECTIVES

Oxidative stress plays critical roles in the pathogeneses of diabetes, hypertension, and atherosclerosis, but its effect on fat accumulation is still unclear. In this study, we analyzed the role of the well-known antioxidant and a glutathione (GSH) precursor N-acetylcysteine (NAC) in fat accumulation and the expression of obesity-associated proteins.

METHODS

We studied the effects of 10 µM NAC on obesity-related protein expression in cultured 3T3-L1 preadipocytes, which are able to differentiate into mature adipocytes and accumulate lipids.

RESULTS

NAC treatment inhibited fat accumulation and reduced the expression of obesity-related proteins, including monoamine oxidase A, heat shock protein 70 (HSP70), aminoacylase -1 (ACY-1), and transketolase.

DISCUSSION

Our results suggest that the effects of NAC on triglycerides (Tgs) and protein expression are correlated. In support of this, we showed that NAC treatment affected both the Tg synthesis pathway and the expression levels of proteins implicated in human obesity.

A method for assessing mitochondrial bioenergetics in whole white adipose tissues

Obesity is a primary risk factor for numerous metabolic diseases including metabolic syndrome, type II diabetes (T2DM), cardiovascular disease and cancer. Although classically viewed as a storage organ, the field of white adipose tissue biology is expanding to include the consideration of the tissue as an endocrine organ and major contributor to overall metabolism. Given its role in energy production, the mitochondrion has long been a focus of study in metabolic dysfunction and a link between the organelle and white adipose tissue function is likely. Herein, we present a novel method for assessing mitochondrial bioenergetics from whole white adipose tissue. This method requires minimal manipulation of tissue, and eliminates the need for cell isolation and culture. Additionally, this method overcomes some of the limitations to working with transformed and/or isolated primary cells and allows for results to be obtained more expediently. In addition to the novel method, we present a comprehensive statistical analysis of bioenergetic data as well as guidelines for outlier analysis.

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Obesity and metabolic disease affect 1/3 of the US population; incidence is rising.

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WAT is emerging as an endocrine organ and major contributor to metabolism.

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The relationship between mitochondria and white adipose tissue needs to be explored.

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Current bioenergetics methods are limited to transformed or cultured primary cells.

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A novel method for tissue preparation, data acquisition and analysis is presented.

A transient increase in lipid peroxidation primes preadipocytes for delayed mitochondrial inner membrane permeabilization and ATP depletion during prolonged exposure to fatty acids

Preadipocytes are periodically subjected to fatty acid (FA) concentrations that are potentially cytotoxic. We tested the hypothesis that prolonged exposure of preadipocytes of human origin to a physiologically relevant mix of FAs leads to mitochondrial inner membrane (MIM) permeabilization and ultimately to mitochondrial crisis. We found that exposure of preadipocytes to FAs led to progressive cyclosporin A-sensitive MIM permeabilization, which in turn caused a reduction in MIM potential, oxygen consumption, and ATP synthetic capacity and, ultimately, death. Additionally, we showed that FAs induce a transient increase in intramitochondrial reactive oxygen species (ROS) and lipid peroxide production, lasting roughly 30 and 120min for the ROS and lipid peroxides, respectively. MIM permeabilization and its deleterious consequences including mitochondrial crisis and cell death were prevented by treating the cells with the mitochondrial FA uptake inhibitor etomoxir, the mitochondrion-selective superoxide and lipid peroxide antioxidants MitoTempo and MitoQ, or the lipid peroxide and reactive carbonyl scavenger l-carnosine. FAs also promoted a delayed oxidative stress phase. However, the beneficial effects of etomoxir, MitoTempo, and l-carnosine were lost by delaying the treatment by 2h, suggesting that the initial phase was sufficient to prime the cells for the delayed MIM permeabilization and mitochondrial crisis. It also suggested that the second ROS production phase is a consequence of this loss in mitochondrial health. Altogether, our data suggest that approaches designed to diminish intramitochondrial ROS or lipid peroxide accumulation, as well as MIM permeabilization, are valid mechanism-based therapeutic avenues to prevent the loss in preadipocyte metabolic fitness associated with prolonged exposure to elevated FA levels.

Curative diet supplementation with a melon superoxide dismutase reduces adipose tissue in obese hamsters by improving insulin sensitivity

SCOPE

Obesity-related metabolic syndrome is often associated with a decrease of insulin sensitivity, inducing several modifications. However, dietary antioxidants could prevent insulin resistance. We have previously shown the preventive effects of a melon superoxide dismutase (SOD) in obese hamsters. However, its antioxidant effects have never been studied on adipose tissue.

METHODS AND RESULTS

We evaluated the effects of a 1-month curative supplementation with SODB on the adipose tissue of obese hamsters. Animals received either a standard diet or a cafeteria diet for 15 wk. Cafeteria diet induced obesity and related disorders, including insulin resistance and oxidative stress, in the abdominal adipose tissue. After SODB supplementation, the adipose tissue weight was decreased, probably by activating adipocytes lipolysis and thus reducing their size. SODB treatment also resulted in abdominal adipose tissue fibrosis reduction. Finally, SODB administration increased the expression of endogenous antioxidant enzymes and thus reduced oxidative stress and insulin resistance. The improvement of insulin sensitivity observed after SODB treatment could explain adipocyte lipolysis activation and fibrosis reduction.

CONCLUSION

These findings demonstrate that a dietary SOD supplementation could be a useful strategy against obesity-related modifications in adipose tissue.

Spare mitochondrial respiratory capacity permits human adipocytes to maintain ATP homeostasis under hypoglycemic conditions

Mitochondrial dysfunction in white adipose tissue plays a key role in the pathogenesis of type 2 diabetes. Emerging evidence specifically suggests that altered oxidative phosphorylation in adipocytes may have a relevant effect on systemic glucose homeostasis, requiring understanding of adipocyte bioenergetics. We analyzed energetic flux of an intact human adipocyte cell model by plate-based respirometry and extracellular acidification. During differentiation, we discovered that glycolytic ATP production was increasingly replaced by mitochondrial oxidative metabolism (from 20 to 60%). This observation was corroborated by simultaneous up-regulation of canonical mitochondrial gene programs, such as peroxisome proliferator-activated receptor γ coactivator α (PGC1α; 150-fold) and cytochrome c-1 (CytC; 3-fold). Mimicking diabetic phenotypes by exposure to various glucose levels (0, 5, and 25 mM) resulted in immediate adjustments of glycolytic and mitochondrial activity that aimed to maintain intracellular ATP. We conclude that ATP deficits by mitochondrial failure are compensated by glycolytic ATP production, resulting in inefficient conversion of glucose to cellular ATP. Metabolic inefficiency may enhance glucose uptake, therefore improving systemic glucose homeostasis. Notably, mature adipocytes developed a high spare respiratory capacity (increased by 6-fold) permitting rapid adaptation to metabolic changes. Spare respiratory capacity may also allow additional metabolic scope for energy dissipation, potentially offering new therapeutic targets for the treatment of metabolic disease.

10E,12Z-conjugated linoleic acid impairs adipocyte triglyceride storage by enhancing fatty acid oxidation, lipolysis, and mitochondrial reactive oxygen species

Conjugated linoleic acid (CLA) is a naturally occurring dietary trans fatty acid found in food from ruminant sources. One specific CLA isomer, 10E,12Z-CLA, has been associated with health benefits, such as reduced adiposity, while simultaneously promoting deleterious effects, such as systemic inflammation, insulin resistance, and dyslipidemia. The precise mechanisms by which 10E,12Z-CLA exerts these effects remain unknown. Despite potential health consequences, CLA continues to be advertised as a natural weight loss supplement, warranting further studies on its effects on lipid metabolism. We hypothesized that 10E,12Z-CLA impairs lipid storage in adipose tissue by altering the lipid metabolism of white adipocytes. We demonstrate that 10E,12Z-CLA reduced triglyceride storage due to enhanced fatty acid oxidation and lipolysis, coupled with diminished glucose uptake and utilization in cultured adipocytes. This switch to lipid utilization was accompanied by a potent proinflammatory response, including the generation of cytokines, monocyte chemotactic factors, and mitochondrial superoxide. Disrupting fatty acid oxidation restored glucose utilization and attenuated the inflammatory response to 10E,12Z-CLA, suggesting that fatty acid oxidation is critical in promoting this phenotype. With further investigation into the biochemical pathways involved in adipocyte responses to 10E,12Z-CLA, we can discern more information about its safety and efficacy in promoting weight loss.

Adipose tissue remodeling in rats exhibiting fructose-induced obesity

PURPOSE

To explore the effect of a fructose-rich diet on morphological and functional changes in white adipose tissue (WAT) that could contribute to the development of insulin resistance.

METHODS

Adult sedentary rats were fed a fructose-rich diet for 8 weeks. Glucose tolerance test was carried out together with measurement of plasma triglycerides, non-esterified fatty acids and lipid peroxidation. In subcutaneous abdominal and intra-abdominal WAT, number and size of adipocytes together with cellular insulin sensitivity and lipolytic activity were assessed.

RESULTS

Rats fed a fructose-rich diet exhibited a significant increase in plasma insulin, triglycerides, non-esterified fatty acids and lipid peroxidation, together with significantly increased body lipids and epididymal and mesenteric WAT, compared to controls. Mean adipocyte volume in subcutaneous abdominal WAT was significantly lower, while mean adipocyte volume in intra-abdominal WAT was significantly higher, in rats fed a fructose-rich diet compared to controls. A significant increase in larger adipocytes and a significant decrease in smaller adipocytes were found in intra-abdominal WAT in rats fed a fructose-rich diet compared to controls. Insulin's ability to inhibit lipolysis was blunted in subcutaneous abdominal and intra-abdominal adipocytes from fructose-fed rats. Accordingly, lower p-Akt/Akt ratio was found in WAT in rats fed a fructose-rich diet compared to controls.

CONCLUSIONS

Long-term consumption of high levels of fructose elicits remarkable morphological and functional modifications, particularly in intra-abdominal WAT, that are highly predictive of obesity and insulin resistance and that contribute to the worsening of metabolic alterations peculiar in a fructose-rich, hypolipidic diet.

Increased oxidative stress impairs adipose tissue function in sphingomyelin synthase 1 null mice

Sphingomyelin synthase 1 (SMS1) catalyzes the conversion of ceramide to sphingomyelin. Here, we found that SMS1 null mice showed lipodystrophic phenotype. Mutant mice showed up-regulation of plasma triglyceride concentrations accompanied by reduction of white adipose tissue (WAT) as they aged. Lipoprotein lipase (LPL) activity was severely reduced in mutant mice. In vivo analysis indicated that fatty acid uptake in WAT but not in liver decreased in SMS1 null compared to wild-type mice. In vitro analysis using cultured cell revealed that SMS1 depletion reduced fatty acid uptake. Proteins extracted from WAT of mutant mice were severely modified by oxidative stress, and up-regulation of mRNAs related to apoptosis, redox adjustment, mitochondrial stress response and mitochondrial biogenesis was observed. ATP content of WAT was reduced in SMS1 null mice. Blue native gel analysis indicated that accumulation of mitochondrial respiratory chain complexes was reduced. These results suggest that WAT of SMS1 null mice is severely damaged by oxidative stress and barely functional. Indeed, mutant mice treated with the anti-oxidant N-acetyl cysteine (NAC) showed partial recovery of lipodystrophic phenotypes together with normalized plasma triglyceride concentrations. Altogether, our data suggest that SMS1 is crucial to control oxidative stress in order to maintain WAT function.

Effect of taurine and N-acetylcysteine on methionine restriction-mediated adiposity resistance

OBJECTIVES

Methionine-restricted (MR) rats, which are lean and insulin sensitive, have low serum total cysteine (tCys) and taurine and decreased hepatic expression and activity indices of stearoyl-coenzyme A desaturase-1 (SCD1). These effects are partly or completely reversed by cysteine supplementation. We investigated whether reversal of MR phenotypes can be achieved by other sulfur compounds, namely taurine or N-acetylcysteine (NAC).

METHODS

MR and control-fed (CF) rats were supplemented with taurine (0.5%) or NAC (0.5%) for 12weeks. Adiposity, serum sulfur amino acids (SAA), Scd1 gene expression in liver and white adipose tissue, and SCD1 activity indices (calculated from serum fatty acid profile) were monitored.

RESULTS

Taurine supplementation of MR rats did not restore weight gain or hepatic Scd1 expression or indices to CF levels, but further decreased adiposity. Taurine supplementation of CF rats did not affect adiposity, but lowered triglyceridemia. NAC supplementation in MR rats raised tCys and partly or completely reversed MR effects on weight, fat %, Scd1 expression in liver and white adipose tissue, and estimated SCD1 activity. In CF rats, NAC decreased body fat % and lowered SCD1-18 activity index (P<0.001). Serum triglycerides and leptin were over 40% lower in CF+NAC relative to CF rats (P≤0.003 for both). In all groups, change in tCys correlated with change in SCD1-16 index (partial r=0.60, P<0.001) independent of other SAA.

CONCLUSION

The results rule out taurine as a mediator of increased adiposity produced by cysteine in MR, and show that NAC, similar to L-cysteine, blocks anti-obesity effects of MR. Our data show that dietary SAA can influence adiposity in part through mechanisms that converge on SCD1 function. This may have implications for understanding and preventing human obesity.

B cell activating factor in obesity is regulated by oxidative stress in adipocytes

Adipose tissue functions as a key endocrine organ by releasing multiple bioactive substances, and plays a key role in the integration of systemic metabolism. We have previously shown that B cell activating factor is produced mainly in visceral adipose tissue and affects insulin sensitivity in obese individuals. In this study, we identified the signals that lead to production of B cell activating factor in adipocytes. 3T3-L1 and C3H/10T 1/2-clone 8 cells showed increased B cell activating factor expression upon exposure to hydrogen peroxide, and these changes were inhibited by treatment with the antioxidant N-acetyl-cysteine. B cell activating factor levels in both serum and visceral adipose tissue were increased in high fat diet-fed mice, and these increases were correlated with oxidative stress. In addition, serum BAFF levels in high fat diet-fed mice were reduced by N-acetyl-cysteine treatment. We also found that oxidative stress-induced B cell activating factor expression in adipocytes was regulated by NF-κB activation. These data indicate that control of the redox state in visceral adipose tissue is a potentially useful target for treating metabolic syndromes through regulation of adipokine production.