Synergy in Free Radical Generation is Blunted by High-Fat Diet Induced Alterations in Skeletal Muscle Mitochondrial Metabolism

Due to their role in cellular energetics and metabolism, skeletal muscle mitochondria appear to play a key role in the development of insulin resistance and type II diabetes. High-fat diet can induce higher levels of reactive oxygen species (ROS), evidenced by hydrogen peroxide (H₂O₂) emission from mitochondria, which may be causal for insulin resistance in skeletal muscle. The underlying mechanisms are unclear. Recent published data on single substrate (pyruvate, succinate, fat) metabolism in both normal diet (CON) and high-fat diet (HFD) states of skeletal muscle allowed us to develop an integrated mathematical model of skeletal muscle mitochondrial metabolism. Model simulations suggested that long-term HFD may affect specific metabolic reaction/pathways by altering enzyme activities. Our model allows us to predict oxygen consumption and ROS generation for any combination of substrates. In particular, we predict a synergy between (iso-membrane potential) combinations of pyruvate and fat in ROS production compared to the sum of ROS production with each substrate singly in both CON and HFD states. This synergy is blunted in the HFD state.     

Sex hormones regulate metainflammation in diet-induced obesity in mice

Men have a statistically higher risk of metabolic and cardiovascular disease than premenopausal women, but the mechanisms mediating these differences are elusive. Chronic inflammation during obesity contributes to disease risk and is significantly more robust in males. Prior work demonstrated that compared with obese males, obese females have reduced proinflammatory adipose tissue macrophages (ATMs). Given the paucity of data on how sex hormones contribute to macrophage responses in obesity, we sought to understand the role of sex hormones in promoting obesity-induced myeloid inflammation. We used gonadectomy, estrogen receptor–deficient alpha chimeras, and androgen-insensitive mice to model sex hormone deficiency. These models were evaluated in diet-induced obesity conditions (high-fat diet [HFD]) and in vitro myeloid assays. We found that ovariectomy increased weight gain and adiposity. Ovariectomized females had increased ATMs and bone marrow myeloid colonies compared with sham-gonadectomized females. In addition, castrated males exposed to HFD had improved glucose tolerance, insulin sensitivity, and adiposity with fewer Ly6c^hi monocytes and bone marrow myeloid colonies compared with sham-gonadectomized males, although local adipose inflammation was enhanced. Similar findings were observed in androgen-insensitive mice; however, these mice had fewer CD11c⁺ ATMs, implying a developmental role for androgens in myelopoiesis and adipose inflammation. We concluded that gonadectomy results in convergence of metabolic and inflammatory responses to HFD between the sexes, and that myeloid estrogen receptor alpha contributes minimally to diet-induced inflammatory responses, whereas loss of androgen-receptor signaling improves metabolic and inflammatory outcomes. These studies demonstrate that sex hormones play a critical role in sex differences in obesity, metabolic dysfunction, and myeloid inflammation.     

Spatial and temporal control of mitochondrial H2O2 release in intact human cells

Hydrogen peroxide (H₂O₂) has key signaling roles at physiological levels, while causing molecular damage at elevated concentrations. H₂O₂ production by mitochondria is implicated in regulating processes inside and outside these organelles. However, it remains unclear whether and how mitochondria in intact cells release H₂O₂. Here, we employed a genetically encoded high‐affinity H₂O₂ sensor, HyPer7, in mammalian tissue culture cells to investigate different modes of mitochondrial H₂O₂ release. We found substantial heterogeneity of HyPer7 dynamics between individual cells. We further observed mitochondria‐released H₂O₂ directly at the surface of the organelle and in the bulk cytosol, but not in the nucleus or at the plasma membrane, pointing to steep gradients emanating from mitochondria. Gradient formation is controlled by cytosolic peroxiredoxins, which act redundantly and with a substantial reserve capacity. Dynamic adaptation of cytosolic thioredoxin reductase levels during metabolic changes results in improved H₂O₂ handling and explains previously observed differences between cell types. Our data suggest that H₂O₂‐mediated signaling is initiated only in close proximity to mitochondria and under specific metabolic conditions.     

Oxidative Stress in Mouse Sperm Impairs Embryo Development,Fetal Growth and Alters Adiposity and Glucose Regulation in Female Offspring

Paternal health cues are able to program the health of the next generation however the mechanism for this transmission is unknown. Reactive oxygen species (ROS) are increased in many paternal pathologies, some of which program offspring health, and are known to induce DNA damage and alter the methylation pattern of chromatin. We therefore investigated whether a chemically induced increase of ROS in sperm impairs embryo, pregnancy and offspring health. Mouse sperm was exposed to 1500 µM of hydrogen peroxide (H₂O₂), which induced oxidative damage, however did not affect sperm motility or the ability to bind and fertilize an oocyte. Sperm treated with H₂O₂ delayed on-time development of subsequent embryos, decreased the ratio of inner cell mass cells (ICM) in the resulting blastocyst and reduced implantation rates. Crown-rump length at day 18 of gestation was also reduced in offspring produced by H₂O₂ treated sperm. Female offspring from H₂O₂ treated sperm were smaller, became glucose intolerant and accumulated increased levels of adipose tissue compared to control female offspring. Interestingly male offspring phenotype was less severe with increases in fat depots only seen at 4 weeks of age, which was restored to that of control offspring later in life, demonstrating sex-specific impacts on offspring. This study implicates elevated sperm ROS concentrations, which are common to many paternal health pathologies, as a mediator of programming offspring for metabolic syndrome and obesity.     

The influence of sex and strain on trace element dysregulation in the brain due to diet-induced obesity

BackgroundThe objective of this study was to identify interaction effects between diet, sex, and strain on trace element dysregulation and gene expression alterations due to diet-induced obesity (DIO) in the hippocampus, striatum, and midbrain.MethodsMale and female C57BL/6 J (B6 J) and DBA/2 J (D2 J) mice were fed either a low fat (10 % kcal) diet (LFD) or high fat (60 % kcal) diet (HFD) for 16 weeks, then assessed for trace element concentrations and gene expression patterns in the brain.ResultsIn the hippocampus, zinc was significantly increased by 48 % in D2 J males but decreased by 44 % in D2 J females, and divalent metal transporter 1 was substantially upregulated in B6 J males due to DIO. In the striatum, iron was significantly elevated in B6 J female mice, and ceruloplasmin was significantly upregulated in D2 J female mice due to DIO. In the midbrain, D2 J males fed a HFD had a 48 % reduction in Cu compared to the LFD group, and D2 J females had a 37 % reduction in Cu compared to the control group.ConclusionsThe alteration of trace element homeostasis and gene expression due to DIO was brain-region dependent and was highly influenced by sex and strain. A significant three-way interaction between diet, sex, and strain was discovered for zinc in the hippocampus (for mice fed a HFD, zinc increased in male D2 Js, decreased in female D2 Js, and had no effect in B6 J mice). A significant diet by sex interaction was observed for iron in the striatum (iron increased only in female mice fed a HFD). A main effect of decreased copper in the midbrain was found for the D2 J strain fed a HFD. These results emphasize the importance of considering sex and genetics as biological factors when investigating potential associations between DIO and neurodegenerative disease.     

Taurine protection of PC12 cells against endoplasmic reticulum stress induced by oxidative stress

Background

Taurine is a free amino acid present in high concentrations in a variety of organs of mammalians. As an antioxidant, taurine has been found to protect cells against oxidative stress, but the underlying mechanism is still unclear.

Methods

In this report, we present evidence to support the conclusion that taurine exerts a protective function against endoplasmic reticulum (ER) stress induced by H₂O₂ in PC 12 cells. Oxidative stress was introduced by exposure of PC 12 cells to 250 uM H₂O₂ for 4 hours.

Results

It was found that the cell viability of PC 12 cells decreased with an increase of H₂O₂ concentration ranging from approximately 76% cell viability at 100 uM H₂O₂ down to 18% at 500 uM H₂O₂. At 250 uM H₂O₂, cell viability was restored to 80% by taurine at 25 mM. Furthermore, H₂O₂ treatment also caused a marked reduction in the expression of Bcl-2 while no significant change of Bax was observed. Treatment with taurine restored the reduced expression of Bcl-2 close to the control level without any obvious effect on Bax. Furthermore, taurine was also found to suppress up-regulation of GRP78, GADD153/CHOP and Bim induced by H₂O₂, suggesting that taurine may also exert a protective function against oxidative stress by reducing the ER stress.

Conclusion

In summary, taurine was shown to protect PC12 cells against oxidative stress induced by H₂O₂. ER stress was induced by oxidative stress and can be suppressed by taurine.

     

Myocardial glutathione metabolic status in fat-fed rabbits

Short-term fat feeding could exert adverse cardiac effects by altering myocardial glutathione-related antioxidant defenses. We have here assessed total glutathione (TG), the activities of glutathione reductase (GSSG-Red), γ-glutamylcysteine synthetase (γ-GCS), γ-glutamyl transpeptidase (γ-GT) and glutathione peroxidase (GSH-Px), fluorescent damage products of lipid peroxidation (FDPL), thiobarbituric acid-reactive substances (TBARS), H₂O₂, and ATP in the aerobically perfused hearts of control rabbits and of rabbits fed a fat-enriched diet for 18 days. Such biochemical parameters, myocardial hemodynamics and infarct size were assessed in the perfused hearts of other control and fat-fed rabbits subjected to 60 min global ischemia plus 30 min reperfusion. Compared to controls, a reduced activity of GSSG-Red and γ-GT associated with decreased TG content was detected in the aerobically perfused hearts of fat-fed rabbits, which also showed insignificant γ-GCS activation, GSH-Px depressed activity, FDPL, TBARS and H₂O₂ burden, and unaltered ATP content. Ischemia–reperfusion decreased the myocardial levels of TG, ATP, and γ-GCS activity and augmented those of FDPL, TBARS, and H₂O₂ especially in the fat-fed rabbits, without significant changes in myocardial GSSG-Red, γ-GT, and GSH-Px activities. Ischemia–reperfusion induced greater hemodynamic dysfunction and infarct size in the hearts of fat-fed rabbits than in those of controls. Thus, short-term fat feeding and hyperlipidemia alter glutathione metabolic status of the rabbit myocardium, inducing a GSSG-Red- and γ-GT-related decrement of myocardial glutathione content, which, together with GSH-Px dysfunction, may favor tissue oxidative stress and render the myocardium more susceptible to ischemia–reperfusion injury.     

Hypothalamic Neuroendocrine Circuitry is Programmed by Maternal Obesity: Interaction with Postnatal Nutritional Environment

Objective

Early life nutrition is critical for the development of hypothalamic neurons involved in energy homeostasis. We previously showed that intrauterine and early postnatal overnutrition programmed hypothalamic neurons expressing the appetite stimulator neuropeptide Y (NPY) and suppressor proopiomelanocortin (POMC) in offspring at weaning. However, the long-term effects of such programming and its interactions with post-weaning high-fat-diet (HFD) consumption are unclear.

Research Design and Methods

Female Sprague Dawley rats were exposed to chow or HFD for 5 weeks before mating, throughout gestation and lactation. On postnatal day 1, litters were adjusted to 3/litter to induce postnatal overnutrition (vs. 12 in control). At postnatal day 20, half of the rats from each maternal group were weaned onto chow or HFD for 15 weeks. Hypothalamic appetite regulators, and fuel (glucose and lipid) metabolic markers were measured.

Results

Offspring from obese dams gained more weight than those from lean dams independent of post-weaning diet. Maternal obesity interacted with post-weaning HFD consumption to cause greater levels of hyperphagia, adiposity, hyperlipidemia, and glucose intolerance in offspring. This was linked to increased hypothalamic NPY signaling and leptin resistance in adult offspring. Litter size reduction had a detrimental impact on insulin and adiponectin, while hypothalamic NPY and POMC mRNA expression were suppressed in the face of normal energy intake and weight gain.

Conclusions

Maternal obesity, postnatal litter size reduction and post-weaning HFD consumption caused obesity via different neuroendocrine mechanims. There were strong additive effects of maternal obesity and post-weaning HFD consumption to increase the metabolic disorders in offspring.     

Catalase is required for peroxisome maintenance during adipogenesis

Although obesity contributes to the onset and pathogenesis of metabolic diseases, it has been repeatedly demonstrated that being overweight or mildly obese carries a survival advantage compared with being thin or normal-weight. This relationship is called the obesity paradox. Hence, it is necessary to clarify the underlying mechanism of obesity onset for the prevention and treatment of these diseases. Catalase is distributed in peroxisomes under normal redox conditions and catalase activity is increased during the differentiation of 3T3-L1 preadipocytes to adipocytes. Although peroxisomes are responsible for lipid metabolism, the role of peroxisomal catalase in the process of lipid accumulation remains unclear. The present study aimed to investigate the relationships among catalase activity, peroxisome content, and lipid accumulation during the differentiation of 3T3-L1 preadipocytes to adipocytes. Increased catalase activity and lipid accumulation were observed during the differentiation of preadipocytes. Silencing of catalase by small interfering RNA or treatment with 3-amino-1,2,4-triazole (3-AT), a catalase inhibitor, resulted in reduced lipid accumulation. Inhibition of catalase activity in peroxisomes increases hydrogen peroxide (H₂O₂) levels, which results in a reduction of peroxisome content. Extracellular H₂O₂ had no influence on lipid accumulation during differentiation. The occurrence of autophagy was clearly enhanced in cells treated with 3-AT. Spautin-1, an inhibitor of autophagy flux, protected against a reduction in lipid accumulation by treatment with 3-AT. Our data provide evidence that catalase protects against the degradation of peroxisomes via the occurrence of autophagy triggered by the generation of H₂O₂ in peroxisomes. These results suggest that catalase in peroxisomes is crucial to adipogenesis.     

Nicotinamide Nucleotide Transhydrogenase (Nnt) Links the Substrate Requirement in Brain Mitochondria for Hydrogen Peroxide Removal to the Thioredoxin/Peroxiredoxin (Trx/Prx) System

Mitochondrial reactive oxygen species are implicated in the etiology of multiple neurodegenerative diseases, including Parkinson disease. Mitochondria are known to be net producers of ROS, but recently we have shown that brain mitochondria can consume mitochondrial hydrogen peroxide (H₂O₂) in a respiration-dependent manner predominantly by the thioredoxin/peroxiredoxin system. Here, we sought to determine the mechanism linking mitochondrial respiration with H₂O₂ catabolism in brain mitochondria and dopaminergic cells. We hypothesized that nicotinamide nucleotide transhydrogenase (Nnt), which utilizes the proton gradient to generate NADPH from NADH and NADP⁺, provides the link between mitochondrial respiration and H₂O₂ detoxification through the thioredoxin/peroxiredoxin system. Pharmacological inhibition of Nnt in isolated brain mitochondria significantly decreased their ability to consume H₂O₂ in the presence, but not absence, of respiration substrates. Nnt inhibition in liver mitochondria, which do not require substrates to detoxify H₂O₂, had no effect. Pharmacological inhibition or lentiviral knockdown of Nnt in N27 dopaminergic cells (a) decreased H₂O₂ catabolism, (b) decreased NADPH and increased NADP⁺ levels, and (c) decreased basal, spare, and maximal mitochondrial oxygen consumption rates. Nnt-deficient cells possessed higher levels of oxidized mitochondrial Prx, which rendered them more susceptible to steady-state increases in H₂O₂ and cell death following exposure to subtoxic levels of paraquat. These data implicate Nnt as the critical link between the metabolic and H₂O₂ antioxidant function in brain mitochondria and suggests Nnt as a potential therapeutic target to improve the redox balance in conditions of oxidative stress associated with neurodegenerative diseases.     

Glutamate receptor-mediated taurine release from the hippocampus during oxidative stress

Background

Hippocampal slices swell and release taurine during oxidative stress. The influence of cellular signalling pathways on this process is unclear. Glutamate signalling can facilitate volume regulation in other CNS preparations. Therefore, we hypothesize activation of taurine release by oxidative stress results from tissue swelling and is coupled to activation of glutamate receptors.

Methods

Rat hippocampi were incubated at room temperature for 2 hr in artificial cerebrospinal fluid (aCSF) equilibrated with 95% O₂ plus 5% CO₂. For some slices, 1 mM taurine was added to the aCSF to maintain normal tissue taurine content. Slices then were perfused with aCSF at 35° C and baseline data recorded before 2 mM H₂O₂ was added. For some studies, mannitol or inhibitors of glutamate receptors or the volume-regulated anion channel (VRAC) were added before and during H₂O₂ treatment. The intensity of light transmitted through the slice (the intrinsic optical signal, IOS) was determined at 1-min intervals. Samples of perfusate were collected at 2-min intervals and amino acid contents determined by HPLC. Data were analyzed by repeated measures ANOVA and post hoc Dunnett’s test with significance indicated for p<0.05.

Results

IOS of slices prepared without taurine treatment increased significantly by 3.3±1.3% (mean±SEM) during oxidative stress. Little taurine was detected in the perfusate of these slices and the rate of taurine efflux did not change during H₂O₂ exposure. The α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate antagonist, 25 µM CNQX, but not the N-methyl-D-aspartate (NMDA) receptor antagonist, 10 µM MK-801, inhibited the increase in IOS during H₂O₂ treatment. Taurine-treated slices exposed to H₂O₂ showed no change in IOS; however, taurine efflux increased by 335±178%. When these slices were perfused with hypertonic aCSF (350 mOsm) or exposed to the VRAC inhibitor, 20 µM DCPIB, no increase in the taurine efflux rate was observed during H₂O₂ exposure. Taurine-treated slices perfused with 10 µM MK-801 during H₂O₂ exposure showed a 4.6±1.9% increase in IOS but no increase in the taurine efflux rate.

Conclusions

Taurine efflux via VRAC is critical for volume regulation of hippocampal slices exposed to oxidative stress. This increased taurine efflux does not result from direct activation of the taurine release pathway by H₂O₂. NMDA receptor activation plays an important role in taurine release during oxidative stress.

     

Carbon monoxide improves cardiac function and mitochondrial population quality in a mouse model of metabolic syndrome

Aims

Metabolic syndrome induces cardiac dysfunction associated with mitochondria abnormalities. As low levels of carbon monoxide (CO) may improve myocardial and mitochondrial activities, we tested whether a CO-releasing molecule (CORM-3) reverses metabolic syndrome-induced cardiac alteration through changes in mitochondrial biogenesis, dynamics and autophagy.

Methods and Results

Mice were fed with normal diet (ND) or high-fat diet (HFD) for twelve weeks. Then, mice received two intraperitoneal injections of CORM-3 (10 mg.kg⁻¹), with the second one given 16 hours after the first. Contractile function in isolated hearts and mitochondrial parameters were evaluated 24 hours after the last injection. Mitochondrial population was explored by electron microscopy. Changes in mitochondrial dynamics, biogenesis and autophagy were assessed by western-blot and RT-qPCR. Left ventricular developed pressure was reduced in HFD hearts. Mitochondria from HFD hearts presented reduced membrane potential and diminished ADP-coupled respiration. CORM-3 restored both cardiac and mitochondrial functions. Size and number of mitochondria increased in the HFD hearts but not in the CORM-3–treated HFD group. CORM-3 modulated HFD-activated mitochondrial fusion and biogenesis signalling. While autophagy was not activated in the HFD group, CORM-3 increased the autophagy marker LC3-II. Finally, ex vivo experiments demonstrated that autophagy inhibition by 3-methyladenine abolished the cardioprotective effects of CORM-3.

Conclusion

CORM-3 may modulate pathways controlling mitochondrial quality, thus leading to improvements of mitochondrial efficiency and HFD-induced cardiac dysfunction.     

Red raspberries suppress NLRP3 inflammasome and attenuate metabolic abnormalities in diet-induced obese mice

The NLR family pyrin domain containing 3 (NLRP3) inflammasome plays a critical role in insulin resistance and the pathogenesis of type 2 diabetes. Red raspberry (RB) contains high amounts of dietary fibers and polyphenolic compounds, which are known for their anti-oxidative and anti-inflammatory effects. This study evaluated the preventive effects of RB supplementation on the NLRP3 inflammasome activation and associated metabolic abnormalities induced by high fat diet (HFD). Wild-type male mice (six weeks old) were randomized into 4 groups receiving a control or typical western HFD supplemented with or without 5% freeze-dried RB for 12 weeks, when mice were sacrificed for tissue collection. HFD feeding substantially increased body weight, which was alleviated by RB supplementation towards the end of the feeding trial. Dietary RB restored the baseline blood glucose level, ameliorating glucose intolerance and insulin resistance, which were aggravated by HFD. Additionally, HFD reduced O₂ expenditure and CO₂ production, which were ameliorated by RB consumption. The liver is the key site for energy metabolism and a key peripheral tissue responsive to insulin. RB supplementation reduced hepatic lipid accumulation in HFD mice. In agreement, RB consumption suppressed hepatic NLRP3 inflammasome activation and reduced interleukin (IL)-1β and IL-18 production in HFD mice, accompanied with normalized mitochondriogenesis. These results suggest that RB consumption improves insulin resistance and metabolic dysfunction in diet-induced obesity, which is concomitant with suppression of NLRP3 inflammasome elicited by HFD. Thus, dietary RB intake is a promising strategy for ameliorating diet-induced metabolic abnormalities.     

Sensitivity of taurine uptake to oxygen-derived reactive substances in MDR and non-MDR cells

Summary. In human KB and LoVo cell lines, high affinity taurine uptake was strongly reduced in both a time and dose-dependent manner by cumene hydroperoxide (CH) and to a lesser extent by hydrogen peroxide (H₂O₂). Uptake-inhibition was greater in multidrug resistant (MDR) cells than in their non-MDR counterparts. Basal taurine efflux was unaffected by the oxidants. Lipid peroxidation levels closely correlated with the uptake inhibition levels, and were greater in MDR cells than in their non-MDR counterparts. The two oxidants reduced the Vmax and, to a lesser extent, the affinity of the transporter for taurine. They also reduced low affinity taurine uptake and, to a lesser extent, taurine diffusion. The composition of the medium used for cell treatment, especially its pyruvate content, greatly affected the H₂O₂ effect. H₂O₂- or CH-induced reduction of the high affinity taurine uptake was unaffected by protein kinase C (PKC) inhibitors and by the calmodulin antagonist W-13, ruling out the involvement of PKC and perhaps of calmodulin kinases in their effect. Received October 2, 2000 Accepted February 13, 2001     

Resistance to high-fat diet in the female progeny of obese mice fed a control diet during the periconceptual, gestation, and lactation periods

With the worldwide epidemic of metabolic syndrome (MetS), the proportion of women that are overweight/obese and overfed during pregnancy has increased. The resulting abnormal uterine environment may have deleterious effects on fetal metabolic programming and lead to MetS in adulthood. A balanced/restricted diet and/or physical exercise often improve metabolic abnormalities in individuals with obesity and type 2 diabetes mellitus (T2D). We investigated whether reducing fat intake during the periconceptual/gestation/lactation period in mothers with high-fat diet (HFD)-induced obesity could be used to modify fetal/neonatal MetS programming positively, thereby preventing MetS. First generation (F1) C57BL/6J female mice with HFD-induced obesity and T2D were crossed with F1 males on control diet (CD). These F1 females were switched to a CD during the periconceptual/gestation/lactation period. At weaning, both male and female second generation (F2) mice were fed a HFD. Weight, caloric intake, lipid parameters, glucose, and insulin sensitivity were assessed. Sensitivity/resistance to the HFD differed significantly between generations and sexes. A similar proportion of the F1 and F2 males (80%) developed hyperphagia, obesity, and T2D. In contrast, a significantly higher proportion of the F2 females (43%) than of the previous F1 generation (17%) were resistant (P<0.01). Despite having free access to the HFD, these female mice were no longer hyperphagic and remained lean, with normal insulin sensitivity and glycemia but mild hypercholesterolemia and glucose intolerance, thus displaying a "satiety phenotype." This suggests that an appropriate dietary fatty acid profile and intake during the periconceptual/gestation/lactation period helps the female offspring to cope with deleterious intrauterine conditions.     

High Dietary Fat Selectively Increases Catalase Expression within Cardiac Mitochondria

Obesity is a predictor of diabetes and cardiovascular disease. One consequence of obesity is dyslipidemia characterized by high blood triglycerides. It has been proposed that oxidative stress, driven by utilization of lipids for energy, contributes to these diseases. The effects of oxidative stress are mitigated by an endogenous antioxidant enzyme network, but little is known about its response to high fat utilization. Our experiments used a multiplexed quantitative proteomics method to measure antioxidant enzyme expression in heart tissue in a mouse model of diet-induced obesity. This experiment showed a rapid and specific up-regulation of catalase protein, with subsequent assays showing increases in activity and mRNA. Catalase, traditionally considered a peroxisomal protein, was found to be present in cardiac mitochondria and significantly increased in content and activity during high fat feeding. These data, coupled with the fact that fatty acid oxidation enhances mitochondrial H₂O₂ production, suggest that a localized catalase increase is needed to consume excessive mitochondrial H₂O₂ produced by increased fat metabolism. To determine whether the catalase-specific response is a common feature of physiological conditions that increase blood triglycerides and fatty acid oxidation, we measured changes in antioxidant expression in fasted versus fed mice. Indeed, a similar specific catalase increase was observed in mice fasted for 24 h. Our findings suggest a fundamental metabolic process in which catalase expression is regulated to prevent damage while preserving an H₂O₂-mediated sensing of diet composition that appropriately adjusts insulin sensitivity in the short term as needed to prioritize lipid metabolism for complete utilization.     

The essential function of CARD9 in diet‐induced inflammation and metabolic disorders in mice

Inflammation and metabolic disorder are common pathophysiological conditions, which play a vital role in the development of obesity and type 2 diabetes. The purpose of this study was to explore the effects of caspase recruitment domain (CARD) 9 in the high fat diet (HFD)‐treated mice and attempt to find a molecular therapeutic target for obesity development and treatment. Sixteen male CARD9^?/? and corresponding male WT mice were fed with normal diet or high fat diet, respectively, for 12 weeks. Glucose tolerance, insulin resistance, oxygen consumption and heat production of the mice were detected. The CARD9/MAPK pathway‐related gene and protein were determined in insulin‐responsive organs using Western blotting and quantitative PCR. The results showed that HFD‐induced insulin resistance and impairment of glucose tolerance were more severe in WT mice than that in the CARD9^?/? mice. CARD9 absence significantly modified O₂ consumption, CO₂ production and heat production. CARD9^?/? mice displayed the lower expression of p38 MAPK, JNK and ERK when compared to the WT mice in both HFD‐ and ND‐treated groups. HFD induced the increase of p38 MAPK, JNK and ERK in WT mice but not in the CARD9^?/? mice. The results indicated that CARD9 absence could be a vital protective factor in diet‐induced obesity via the CARD9/MAPK pathway, which may provide new insights into the development of gene knockout to improving diet‐induced obesity and metabolism disorder.     

Mitochondrial Biosvnthesis Controls the Sensitivitvy of Chinese Hamster Cells to Hydrogen Peroxide

The mechanism of H₂O₂-resistance of Hpr-4, a variant of Chinese hamster V79 cells, was investigated. The effect of H₂O₂ on the mitochondria of the parental and Hpr-4 cells was compared. First, both biochemical and ultrastructural results showed that mitochondria in the parental cells were damaged by exposure to H₂O₂, while those in Hpr-4 cells recovered from the damage. Second, the H₂O₂ resistance of Hpr-4 cells was reversibly reduced or recovered by the addition or removal of inhibitors of mitochondrial biosynthesis, respectively. Third, the parental cells were auxotrophic to pyruvate after exposure to H₂O₂. Fourth, H₂O₂-sensitivity of the parental cells was also enhanced by the inhibition of mitochondrial biosynthesis. From these results, it was concluded that the mitochondria of Hpr-4 cells apparently had a greater resistance to H₂O₂ than those of the parental cells and that functional mitochondria were involved in the recovery of Chinese hamster V79 cells from H₂O₂-induced damage.     

Angiotensin AT2 Receptor Contributes towards Gender Bias in Weight Gain

Obesity is a major disease condition, in turn leading to pathological changes collectively recognized as metabolic syndrome. Recently angiotensin receptor AT₂R has been associated negatively with body weight (BW) gain in male mice. However, the gender differences in AT₂R and BW changes have not been studied. To understand the gender based role of AT₂R involving BW changes, we fed male and female wild type (WT) and AT₂R knock out (AT₂KO) mice with C57BL6 background with high fat diet (HFD) for 16 weeks. The male AT₂KO had higher HFD calorie intake (WT: 1280±80; AT₂KO:1680±80 kcal) but gained less BW compared with the WT (WT: 13; AT₂KO: 6 g). Contrary to the male animals, the female AT₂KO mice with equivalent caloric intake (WT: 1424±48; AT₂KO:1456±80 kcal) gained significantly more BW than the WT mice (WT: 9 g; AT₂KO: 15 g). The male AT₂KO on HFD displayed lower plasma insulin level, less impaired glucose tolerance (GT), and higher plasma T3 compared with WT males on HFD; whereas the female AT₂KO mice on HFD showed elevated levels of plasma insulin, more impaired GT, lower plasma T3 and higher free fatty acid and hepatic triglycerides compared with WT females on HFD. Interestingly, compared with WT, AT₂KO female mice had significantly lower estrogen, which was further reduced by HFD. These results suggest that AT₂R in female mice via potentially regulating estrogen may have protective role against BW gain and impaired glucose tolerance and lipid metabolism.     

Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement

The deleterious effects of H₂O₂ on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H₂O₂ resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H₂O₂ on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H₂O₂ on respiratory complexes was almost completely recovered by β-mercaptoethanol treatment. H₂O₂ treatment resulted in full resistance to Q_O site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (Q_O) of complex III is the target for H₂O₂. H₂O₂ did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H₂O₂ addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria.