Effect of cold acclimation on GSH, antioxidant enzymes and lipid peroxidation in brown adipose tissue

Heme biosynthesis regulates BCAA catabolism and thermogenesis in brown adipose tissue

With age, people tend to accumulate body fat and reduce energy expenditure 1 . Brown (BAT) and beige adipose tissue dissipate heat and increase energy expenditure via the activity of the uncoupling protein UCP1 and other thermogenic futile cycles 2,3 . The activity of brown and beige depots inversely correlates with BMI and age 4-11 , suggesting that promoting thermogenesis may be an effective approach for combating age-related metabolic disease 12-15 . Heme is an enzyme cofactor and signaling molecule that we recently showed to regulate BAT function 16 . Here, we show that heme biosynthesis is the primary contributor to intracellular heme levels in brown adipocytes. Inhibition of heme biosynthesis leads to mitochondrial dysfunction and reduction in UCP1. Although supplementing heme can restore mitochondrial function in heme-synthesis-deficient cells, the downregulation of UCP1 persists due to the accumulation of the heme precursors, particularly propionyl-CoA, which is a product of branched-chain amino acids (BCAA) catabolism. Cold exposure promotes BCAA uptake in BAT, and defects in BCAA catabolism in this tissue hinder thermogenesis 17 . However, BCAAs' contribution to the TCA cycle in BAT and WAT never exceeds 2% of total TCA flux 18 . Our work offers a way to integrate current literature by describing heme biosynthesis as an important metabolic sink for BCAAs.

Multifaceted mitochondrial quality control in brown adipose tissue

Brown adipose tissue (BAT) controls mammalian core body temperature by non-shivering thermogenesis. BAT is extraordinarily rich in mitochondria, which have the peculiarity of generating heat by uncoupled respiration. Since the mitochondrial activity of BAT is subject to cycles of activation and deactivation in response to environmental temperature changes, an integrated mitochondrial quality control (MQC) system is of fundamental importance to ensure BAT physiology. Here, we provide an overview of the conventional and alternative mechanisms through which thermogenic adipocytes selectively remove damaged parts of mitochondria and how macrophages participate in the MQC system by removing extracellular mitochondrial waste to maintain the thermogenic function of BAT.

The multiple facets of mitochondrial regulations controlling cellular thermogenesis

Understanding temperature production and regulation in endotherm organisms becomes a crucial challenge facing the increased frequency and intensity of heat strokes related to global warming. Mitochondria, located at the crossroad of metabolism, respiration, Ca²⁺ homeostasis, and apoptosis, were recently proposed to further act as cellular radiators, with an estimated inner temperature reaching 50 °C in common cell lines. This inner thermogenesis might be further exacerbated in organs devoted to produce consistent efforts as muscles, or heat as brown adipose tissue, in response to acute solicitations. Consequently, pathways promoting respiratory chain uncoupling and mitochondrial activity, such as Ca²⁺ fluxes, uncoupling proteins, futile cycling, and substrate supplies, provide the main processes controlling heat production and cell temperature. The mitochondrial thermogenesis might be further amplified by cytoplasmic mechanisms promoting the over-consumption of ATP pools. Considering these new thermic paradigms, we discuss here all conventional wisdoms linking mitochondrial functions to cellular thermogenesis in different physiological conditions.

A Role of Stress Sensor Nrf2 in Stimulating Thermogenesis and Energy Expenditure

During chronic cold stress, thermogenic adipocytes generate heat through uncoupling of mitochondrial respiration from ATP synthesis. Recent discovery of various dietary phytochemicals, endogenous metabolites, synthetic compounds, and their molecular targets for stimulating thermogenesis has provided promising strategies to treat or prevent obesity and its associated metabolic diseases. Nuclear factor E2 p45-related factor 2 (Nrf2) is a stress response protein that plays an important role in obesity and metabolisms. However, both Nrf2 activation and Nrf2 inhibition can suppress obesity and metabolic diseases. Here, we summarized and discussed conflicting findings of Nrf2 activities accounting for part of the variance in thermogenesis and energy metabolism. We also discussed the utility of Nrf2-activating mechanisms for their potential applications in stimulating energy expenditure to prevent obesity and improve metabolic deficits.

Brown Adipose Tissue Heterogeneity, Energy Metabolism, and Beyond

Brown adipocyte in brown adipose tissue (BAT) specializes in expending energy through non-shivering thermogenesis, a process that produces heat either by uncoupling protein 1 (UCP1) dependent uncoupling of mitochondrial respiration or by UCP1 independent mechanisms. Apart from this, there is ample evidence suggesting that BAT has an endocrine function. Studies in rodents point toward its vital roles in glucose and lipid homeostasis, making it an important therapeutic target for treating metabolic disorders related to morbidities such as obesity and type 2 diabetes. The rediscovery of thermogenically active BAT depots in humans by several independent research groups in the last decade has revitalized interest in BAT as an even more promising therapeutic intervention. Over the last few years, there has been overwhelming interest in understanding brown adipocyte's developmental lineages and how brown adipocyte uniquely utilizes energy beyond UCP1 mediated uncoupling respiration. These new discoveries would be leveraged for designing novel therapeutic interventions for metabolic disorders.

Chronic cold exposure induces autophagy to promote fatty acid oxidation, mitochondrial turnover, and thermogenesis in brown adipose tissue

Autophagy plays an important role in lipid breakdown, mitochondrial turnover, and mitochondrial function during brown adipose tissue (BAT) activation by thyroid hormone, but its role in BAT during adaptive thermogenesis remains controversial. Here, we examined BAT from mice exposed to 72 h of cold challenge as well as primary brown adipocytes treated with norepinephrine and found increased autophagy as well as increased β-oxidation, mitophagy, mitochondrial turnover, and mitochondrial activity. To further understand the role of autophagy of BAT in vivo, we generated BAT-specific Atg5 knockout (Atg5cKO) mice and exposed them to cold for 72 h. Interestingly, BAT-specific Atg5cKO mice were unable to maintain body temperature after chronic cold exposure and displayed deranged mitochondrial morphology and reactive oxygen species damage in their BAT. Our findings demonstrate the critical role of autophagy in adaptive thermogenesis, fatty acid metabolism, and mitochondrial function in BAT during chronic cold exposure.

The Unity of Redox and Structural Remodeling of Brown Adipose Tissue in Hypothyroidism

Brown adipose tissue (BAT) is important for maintaining whole-body metabolic and energy homeostasis. However, the effects of hypothyroidism, one of the most common diseases worldwide, which increases the risk of several metabolic disorders, on BAT redox and metabolic homeostasis remain mostly unknown. We aimed to investigate the dynamics of protein expression, enzyme activity, and localization of antioxidant defense (AD) enzymes in rat interscapular BAT upon induction of hypothyroidism by antithyroid drug methimazole for 7, 15, and 21 days. Our results showed an increased protein expression of CuZn- and Mn-superoxide dismutase, catalase, glutamyl-cysteine ligase, thioredoxin, total glutathione content, and activity of catalase and thioredoxin reductase in hypothyroid rats, compared to euthyroid control. Concomitant with the increase in AD, newly established nuclear, mitochondrial, and peroxisomal localization of AD enzymes was found. Hypothyroidism also potentiated associations between mitochondria, peroxisomes, and lipid bodies, creating specific structural-functional units. Moreover, hypothyroidism induced protein expression and nuclear translocation of a master regulator of redox-metabolic homeostasis, nuclear factor erythroid 2-related factor 2 (Nrf2), and an increased amount of 4-hydroxynonenal (4-HNE) protein adducts. The results indicate that spatiotemporal overlap in the remodeling of AD is orchestrated by Nrf2, implicating the role of 4-HNE in this process and suggesting the potential mechanism of redox-structural remodeling during BAT adaptation in hypothyroidism.

Protective effects of a unique combination of nutritionally active ingredients on risk factors and gene expression associated with atherosclerosis in C57BL/6J mice fed a high fat diet

Atherosclerosis, an inflammatory disorder of the vasculature and the underlying cause of cardiovascular disease, is responsible for one in three global deaths. Consumption of active food ingredients such as omega-3 polyunsaturated fatty acids, flavanols and phytosterols has many beneficial effects on cardiovascular disease. However, their combined actions on the risk factors for atherosclerosis remains poorly understood. We have previously shown that a formulation containing each of these active components at physiologically relevant doses modulated several monocyte/macrophage processes associated with atherosclerosis in vitro, including inhibition of cytokine-induced pro-inflammatory gene expression, chemokine-driven monocyte migration, expression of M1 phenotype markers, and promotion of cholesterol efflux. The objectives of the present study were to investigate whether the protective actions of the formulation extended in vivo and to delineate the potential underlying mechanisms. The formulation produced several favourable changes, including higher plasma levels of HDL and reduced levels of macrophages and myeloid-derived suppressor cells in the bone marrow. The mRNA expression of liver-X-receptor-α, peroxisome proliferator-activated receptor-γ and superoxide dismutase-1 was induced in the liver and that of interferon-γ and the chemokine (C-X-C motif) ligand 1 decreased, thereby suggesting the potential mechanisms for many beneficial effects. Other changes were also observed such as increased plasma levels of triglycerides and lipid peroxidation that may reflect potential activation of brown fat. This study provides new insights into the protective actions and the potential underlying mechanisms of the formulation in vivo, particularly in relation to risk factors together with changes in systemic inflammation and hepatic lipid alterations associated with atherosclerosis and metabolic syndrome, and supports further assessments in human trials.

Loss of Uncoupling Protein 3 Attenuates Western Diet-Induced Obesity, Systemic Inflammation, and Insulin Resistance in Rats

OBJECTIVE

Uncoupling protein 3 (UCP3) is a mitochondrial carrier related to fatty acid metabolism. Although gene variants of UCP3 are associated with human obesity, their contribution to increased adiposity remains unclear. This study investigated the impact that loss of UCP3 has on diet-induced obesity in rats.

METHODS

Male UCP3 knockout rats (ucp3^-/- ) and wild-type littermates (ucp3^+/+ ) were fed a high-fat, high-carbohydrate Western diet for 21 weeks. Body composition was analyzed by EchoMRI. Whole-body insulin sensitivity and rates of tissue glucose uptake were determined by using hyperinsulinemic-euglycemic clamp. Changes in tissue physiology were interrogated by microscopy and RNA sequencing.

RESULTS

Loss of UCP3 decreased fat mass gain, white adipocytes size, and systemic inflammation. The ucp3^-/- rats also exhibited preserved insulin sensitivity and increased glucose uptake in interscapular brown adipose tissue (iBAT). Brown adipocytes from ucp3^-/- rats were protected from cellular degeneration caused by lipid accumulation and from reactive oxygen species-induced protein sulfonation. Increased glutathione levels in iBAT from ucp3^-/- rats were linked to upregulation of genes encoding enzymes from the transsulfuration pathway in that tissue.

CONCLUSIONS

Loss of UCP3 partially protects rats from diet-induced obesity. This phenotype is related to induction of a compensatory antioxidant mechanism and prevention of iBAT whitening.

Thermogenesis in Adipose Tissue Activated by Thyroid Hormone

Thermogenesis is the production of heat that occurs in all warm-blooded animals. During cold exposure, there is obligatory thermogenesis derived from body metabolism as well as adaptive thermogenesis through shivering and non-shivering mechanisms. The latter mainly occurs in brown adipose tissue (BAT) and muscle; however, white adipose tissue (WAT) also can undergo browning via adrenergic stimulation to acquire thermogenic potential. Thyroid hormone (TH) also exerts profound effects on thermoregulation, as decreased body temperature and increased body temperature occur during hypothyroidism and hyperthyroidism, respectively. We have termed the TH-mediated thermogenesis under thermoneutral conditions “activated” thermogenesis. TH acts on the brown and/or white adipose tissues to induce uncoupled respiration through the induction of the uncoupling protein (Ucp1) to generate heat. TH acts centrally to activate the BAT and browning through the sympathetic nervous system. However, recent studies also show that TH acts peripherally on the BAT to directly stimulate Ucp1 expression and thermogenesis through an autophagy-dependent mechanism. Additionally, THs can exert Ucp1-independent effects on thermogenesis, most likely through activation of exothermic metabolic pathways. This review summarizes thermogenic effects of THs on adipose tissues.

Vitamin E Supplementation and Mitochondria in Experimental and Functional Hyperthyroidism: A Mini-Review

Mitochondria are both the main sites of production and the main target of reactive oxygen species (ROS). This can lead to mitochondrial dysfunction with harmful consequences for the cells and the whole organism, resulting in metabolic and neurodegenerative disorders such as type 2 diabetes, obesity, dementia, and aging. To protect themselves from ROS, mitochondria are equipped with an efficient antioxidant system, which includes low-molecular-mass molecules and enzymes able to scavenge ROS or repair the oxidative damage. In the mitochondrial membranes, a major role is played by the lipid-soluble antioxidant vitamin E, which reacts with the peroxyl radicals faster than the molecules of polyunsaturated fatty acids, and in doing so, protects membranes from excessive oxidative damage. In the present review, we summarize the available data concerning the capacity of vitamin E supplementation to protect mitochondria from oxidative damage in hyperthyroidism, a condition that leads to increased mitochondrial ROS production and oxidative damage. Vitamin E supplementation to hyperthyroid animals limits the thyroid hormone-induced increases in mitochondrial ROS and oxidative damage. Moreover, it prevents the reduction of the high functionality components of the mitochondrial population induced by hyperthyroidism, thus preserving cell function.

The Effects of Swimming Training in Cold Water on Antioxidant Enzyme Activity and Lipid Peroxidation in Erythrocytes of Male and Female Aged Rats

The aim of this study was to verify whether eight-week-long swimming exercise training would evaluate the level of selected indicators of the pro-oxidant/antioxidant status in response to cold water in comparison with swimming under thermoneutral conditions in sedentary male and female elderly rats. The exercise-trained groups swam four min/day and five days a week during eight weeks of housing. Exercise was performed by swimming in glass tanks containing tap water maintained according to group at 5 °C and 36 °C. At the end of treatment (48 h after the last session), all rats were anaesthetized. The level of chosen biomarkers of oxidative stress and antioxidant enzyme activity was determined in the red blood cells and plasma. The results of study show that female rats seem to be better adapted to changing thermal conditions of the environment, developing not only morphological, but also antioxidant, defense mechanisms, mainly in the form of increased erythrocyte superoxide dismutase (SOD) activity and glutathione (GSH) concentration to restore the pro-oxidant/oxidant balance of the organism. Significantly higher concentrations of GSH were observed in the female rats of the group swimming in cold water (by 15.4% compared to the control group and by 20.5% in relation to the group of female rats swimming at 36 °C). In the group exposed to swimming training exercise in cold water, a significantly higher activity of SOD1 (by 13.4%) was found compared to the control group. On the other hand, the organs of ageing male rats show a reduced capacity to increase the metabolic response to low temperatures compared to female ones. In addition, it was demonstrated that cold exposure leads to an increase in lipid peroxidation in tissues. On the other hand, the repeated exposure to low levels of oxidative stress may result in some adaptive changes in organisms that help them to resist stress-induced damage.

New Advances in Adaptive Thermogenesis: UCP1 and Beyond

Brown and beige adipocytes can catabolize stored energy to generate heat, and this distinct capacity for thermogenesis could be leveraged as a therapy for metabolic diseases like obesity and type 2 diabetes. Thermogenic adipocytes drive heat production through close coordination of substrate supply with the mitochondrial oxidative machinery and effectors that control the rate of substrate oxidation. Together, this apparatus affords these adipocytes with tremendous capacity to drive thermogenesis. The best characterized thermogenic effector is uncoupling protein 1 (UCP1). Importantly, additional mechanisms for activating thermogenesis beyond UCP1 have been identified and characterized to varying extents. Acute regulation of these thermogenic pathways has been an active area of study, and numerous regulatory factors have been uncovered in recent years. Here we will review the evidence for regulators of heat production in thermogenic adipocytes in the context of the thermodynamic and kinetic principles that govern their therapeutic utility.

Thyroid hormone (T3) stimulates brown adipose tissue activation via mitochondrial biogenesis and MTOR-mediated mitophagy

The thyroid hormone triiodothyronine (T₃) activates thermogenesis by uncoupling electron transport from ATP synthesis in brown adipose tissue (BAT) mitochondria. Although T₃ can induce thermogenesis by sympathetic innervation, little is known about its cell autonomous effects on BAT mitochondria. We thus examined effects of T₃ on mitochondrial activity, autophagy, and metabolism in primary brown adipocytes and BAT and found that T₃ increased fatty acid oxidation and mitochondrial respiration as well as autophagic flux, mitophagy, and mitochondrial biogenesis. Interestingly, there was no significant induction of intracellular reactive oxygen species (ROS) despite high mitochondrial respiration and UCP1 induction by T₃. However, when cells were treated with Atg5 siRNA to block autophagy, induction of mitochondrial respiration by T₃ decreased, and was accompanied by ROS accumulation, demonstrating a critical role for autophagic mitochondrial turnover. We next generated an Atg5 conditional knockout mouse model (Atg5 cKO) by injecting Ucp1 promoter-driven Cre-expressing adenovirus into Atg5^Flox/Flox mice to examine effects of BAT-specific autophagy on thermogenesis in vivo. Hyperthyroid Atg5 cKO mice exhibited lower body temperature than hyperthyroid or euthyroid control mice. Metabolomic analysis showed that T₃ increased short and long chain acylcarnitines in BAT, consistent with increased β-oxidation. T₃ also decreased amino acid levels, and in conjunction with SIRT1 activation, decreased MTOR activity to stimulate autophagy. In summary, T₃ has direct effects on mitochondrial autophagy, activity, and turnover in BAT that are essential for thermogenesis. Stimulation of BAT activity by thyroid hormone or its analogs may represent a potential therapeutic strategy for obesity and metabolic diseases. Abbreviations: ACACA: acetyl-Coenzyme A carboxylase alpha; AMPK: AMP-activated protein kinase; Acsl1: acyl-CoA synthetase long-chain family member 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATP: adenosine triphosphate; BAT: brown adipose tissue; cKO: conditional knockout; COX4I1: cytochrome c oxidase subunit 4I1; Cpt1b: carnitine palmitoyltransferase 1b, muscle; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole; DIO2: deiodinase, iodothyronine, type 2; DMEM: Dulbecco's modified Eagle's medium; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; Fabp4: fatty acid binding protein 4, adipocyte; FBS: fetal bovine serum; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FGF: fibroblast growth factor; FOXO1: forkhead box O1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; Gpx1: glutathione peroxidase 1; Lipe: lipase, hormone sensitive; MAP1LC3B: microtubule-associated protein 1 light chain 3; mRNA: messenger RNA; MTORC1: mechanistic target of rapamycin kinase complex 1; NAD: nicotinamide adenine dinucleotide; Nrf1: nuclear respiratory factor 1; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PPARGC1A: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; Pnpla2: patatin-like phospholipase domain containing 2; Prdm16: PR domain containing 16; PRKA: protein kinase, AMP-activated; RPS6KB: ribosomal protein S6 kinase; RFP: red fluorescent protein; ROS: reactive oxygen species; SD: standard deviation; SEM: standard error of the mean; siRNA: small interfering RNA; SIRT1: sirtuin 1; Sod1: superoxide dismutase 1, soluble; Sod2: superoxide dismutase 2, mitochondrial; SQSTM1: sequestosome 1; T₃: 3,5,3'-triiodothyronine; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); ULK1: unc-51 like kinase 1; VDAC1: voltage-dependent anion channel 1; WAT: white adipose tissue.

Mitochondrial reactive oxygen species and adipose tissue thermogenesis: Bridging physiology and mechanisms

Brown and beige adipose tissues can catabolize stored energy to generate heat, relying on the principal effector of thermogenesis: uncoupling protein 1 (UCP1). This unique capability could be leveraged as a therapy for metabolic disease. Numerous animal and cellular models have now demonstrated that mitochondrial reactive oxygen species (ROS) signal to support adipocyte thermogenic identity and function. Herein, we contextualize these findings within the established principles of redox signaling and mechanistic studies of UCP1 function. We provide a framework for understanding the role of mitochondrial ROS signaling in thermogenesis together with testable hypotheses for understanding mechanisms and developing therapies.

Stress turns on the heat: Regulation of mitochondrial biogenesis and UCP1 by ROS in adipocytes

Reactive oxygen species (ROS) production and oxidative stress (OS) in adipose tissue are associated with obesity and insulin resistance (IR). The nature of this relationship i.e., cause and effect or consequence has not been clearly determined. We provide evidence that elevated mitochondrial ROS generated by adipocytes from mice with diet-induced obesity (DIO) represents an adaptive mechanism that precipitates fatty acid oxidation, mitochondrial biogenesis, and mitochondrial uncoupling in an effort to defend against weight gain. Consistent with that, mice with adipocyte-specific deletion of manganese superoxide dismutase (MnSOD) exhibit increased adipocyte superoxide generation and are protected from weight gain and insulin resistance which otherwise develops in wild-type (WT) mice that consume an obesogenic diet. The defense mechanism displayed by MnSOD-deficiency in fat cells appears to be mediated by a dual effect of ROS on inefficient substrate oxidation through uncoupling of oxidative phosphorylation and enhanced mitochondrial biogenesis. The aim of this commentary is to summarize and contextualize additional evidence supporting the importance of mitochondrial ROS in the regulation of mitochondrial biogenesis and the modulation of uncoupling protein 1 (UCP1) expression and activation in both white and brown adipocytes.

Oxidative stress during courtship affects male and female reproductive effort differentially in a wild bird with biparental care

Oxidative stress has been suggested as one of the physiological mechanisms modulating reproductive effort, including investment in mate choice. Here, we evaluated whether oxidative stress influences breeding decisions by acting as a cost of or constraint on reproduction in the brown booby (Sula leucogaster), a long-lived seabird with prolonged biparental care. We found that during courtship, levels of lipid peroxidation (LP) of males and females were positively associated with gular skin color, a trait presumably used in mate choice, while levels of reactive oxygen species (ROS) were higher as laying approached and in early breeding pairs. Evidence of a constraining effect of oxidative stress for females was suggested by the fact that females with higher ROS during courtship laid smaller first eggs and had chicks with lower rates of body mass gain, and higher female LP was associated with lower offspring attendance time. No evidence of an oxidative cost of parental effort was found; from courtship to parental care male and female' ROS decreased, and changes in LP levels were non-significant. Finally, using a cross-fostering experiment we found that offspring ROS was unrelated to rearing and genetic parents' ROS. Interestingly, offspring LP was positively associated with the LP during courtship of both the rearing parents and the genetic father, suggesting that offspring LP might have both a genetic and an environmental component. Hence, in the brown booby oxidative stress may be a cost of investment in reproductive traits before egg laying and constrain females' investment in eggs and parental care.

Growth performance and antioxidant enzyme activities in rainbow trout (Oncorhynchus mykiss) juveniles fed diets supplemented with sage, mint and thyme oils

This study evaluated effects of dietary supplementation of sage (Salvia officinalis), mint (Mentha spicata) and thyme (Thymus vulgaris) oils on growth performance, lipid peroxidation level (melondialdehyde, MDA) and liver antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; glucose-6-phosphate dehydrogenase, G6PD; glutathione reductase, GR; glutathione-S-transferase, GST and glutathione peroxidase, GPx) in rainbow trout (Oncorhynchus mykiss) juveniles. For this purpose, triplicate groups of rainbow trout were fed daily ad libitum with diets containing sage, mint and thyme oils at 500, 1,000 and 1,500 mg kg(-1) for 60 days. While weight gain percentage of fish fed the diets containing sage and thyme oils was significantly higher than the control group, that of fish fed mint oil was the lowest. Similarly, specific growth rate was found to be the highest in all groups of the sage and thyme oil feeding and the lowest in the mint groups. Moreover, feed conversion ratio was significantly higher in the mint oil administered groups. Survival rate was also significantly reduced in the fish fed the diet containing mint oil. It was observed that SOD, G6PD and GPx activities were significantly increased in liver tissues of all the treated fish groups compared to that of control diet-fed group. However, CAT, GST and GR activities were significantly decreased in experimental diet-fed fish groups at the end of the experiment. On the other hand, a significant reduction was found in MDA levels in the fish fed the diets with sage and thyme oils compared to control and mint diets on the 30th and 60th days of experiment. Overall, dietary inclusion of sage and thyme oils is effective in enhancing rainbow trout growth, reduction in MDA and least changing antioxidant enzyme activities at a low level of 500 mg kg(-1) diet, and they can be used as important feed supplements for rainbow trout production.

ROS production in brown adipose tissue mitochondria: the question of UCP1-dependence

Whether active UCP1 can reduce ROS production in brown-fat mitochondria is presently not settled. The issue is of principal significance, as it can be seen as a proof- or disproof-of-principle concerning the ability of any protein to diminish ROS production through membrane depolarization. We therefore undertook a comprehensive investigation of the significance of UCP1 for ROS production, by comparing the ROS production in brown-fat mitochondria isolated from wildtype mice (that display membrane depolarization) or from UCP1(-/-) mice (with a high membrane potential). We tested the significance of UCP1 for glycerol-3-phosphate-supported ROS production by three methods (fluorescent dihydroethidium and the ESR probe PHH for superoxide, and fluorescent Amplex Red for hydrogen peroxide), and followed ROS production also with succinate, acyl-CoA or pyruvate as substrate. We studied the effects of the reverse electron flow inhibitor rotenone, the UCP1 activity inhibitor GDP, and the uncoupler FCCP. We also examined the effect of a physiologically induced increase in UCP1 amount. We noted GDP effects that were not UCP1-related. We conclude that only ROS production supported by exogenously added succinate was affected by the presence of active UCP1; ROS production supported by any other tested substrate (including endogenously generated succinate) was unaffected. This conclusion indicates that UCP1 is not involved in control of ROS production in brown-fat mitochondria. Extrapolation of these data to other tissues would imply that membrane depolarization may not necessarily decrease physiologically relevant ROS production. This article is a part of a Special Issue entitled: 18th European Bioenergetics Conference (Biochim. Biophys. Acta, Volume 1837, Issue 7, July 2014).

Plasma reactive oxygen metabolites and non-enzymatic antioxidant capacity are not affected by an acute increase of metabolic rate in zebra finches

Understanding the sources of variation in oxidative stress level is a challenging issue due to the implications of oxidative stress for late age diseases, longevity and life-history trade-offs. Reactive oxygen species that cause oxidative stress are mostly a by-product of energy metabolism and it is therefore often assumed that oxidative stress is proportional to energy consumption. In mammals, an increased metabolic rate induced by cold exposure generally increases oxidative stress. However, compared to mammals, birds generate fewer free radicals per ATP produced and hence it is not obvious that, in birds, a cold-induced increase of metabolic rate increase oxidative stress. We tested whether cold-induced increase in metabolic rate increased oxidative stress in zebra finches by exposing individuals to cold and warm overnight temperatures. We registered metabolic rate and plasma levels of non-enzymatic antioxidants and reactive oxygen metabolites (ROMs), a measure of oxidative damage. Metabolic rate was on average 88 % higher in cold compared to warm temperature, with females being stronger affected than males. However, temperature had no effect on plasma antioxidants or our measure of oxidative damage. Middle-age birds had higher levels of plasma antioxidants than younger and older birds, but age was unrelated to ROMs. Birds showed repeatability of plasma ROMs across temperatures but not of non-enzymatic antioxidants. In contrast to similar studies in mammals, our results do not show evidence of increased oxidative stress in plasma after an acute cold-induced increase of metabolic rate but research in more bird species is needed to assess the generality of this pattern.

Mitochondrial ('mild') uncoupling and ROS production: physiologically relevant or not?

During the last decade, the possibility that 'mild' uncoupling could be protective against oxidative damage by diminishing ROS (reactive oxygen species) production has attracted much interest. In the present paper, we briefly examine the evidence for this possibility. It is only ROS production from succinate under reverse electron-flow conditions that is sensitive to membrane potential fluctuations, and so only this type of ROS production could be affected; however, the conditions under which succinate-supported ROS production is observed include succinate concentrations that are supraphysiological. Any decrease in membrane potential, even 'mild uncoupling', must necessarily lead to large increases in respiration, i.e. it must be markedly thermogenic. Mitochondria within cells are normally ATP-producing and thus already have a diminished membrane potential, and treatment of cells, organs or animals with small amounts of artificial uncoupler does not seem to have beneficial effects that are explainable via reduced ROS production. Although it has been suggested that members of the uncoupling protein family (UCP1, UCP2 and UCP3) may mediate a mild uncoupling, present evidence does not unequivocally support such an effect, e.g. the absence of the truly uncoupling protein UCP1 is not associated with increased oxidative damage. Thus present evidence does not support mild uncoupling as a physiologically relevant alleviator of oxidative damage.

Crucial yet divergent roles of mitochondrial redox state in skeletal muscle vs. brown adipose tissue energetics

Reduced glutathione (GSH) is the major determinant of redox balance in mitochondria and as such is fundamental in the control of cellular bioenergetics. GSH is also the most important nonprotein antioxidant molecule in cells. Surprisingly, the effect of redox environment has never been examined in skeletal muscle and brown adipose tissue (BAT), two tissues that have exceptional dynamic range and that are relevant to the development of obesity and related diseases. Here, we show that the redox environment plays crucial, yet divergent, roles in modulating mitochondrial bioenergetics in skeletal muscle and BAT. Skeletal muscle mitochondria were found to naturally have a highly reduced environment (GSH/GSSG≈46), and this was associated with fairly high (∼40%) rates of state 4 (nonphosphorylating) respiration and decreased reactive oxygen species (ROS) emission. The deglutathionylation of uncoupling protein 3 (UCP3) following an increase in the reductive potential of mitochondria results in a further increase in nonphosphorylating respiration (∼20% in situ). BAT mitochondria were found to have a much more oxidized status (GSH/GSSG≈13) and had basal reactive oxygen species emission that was higher (∼250% increase in ROS generation) than that in skeletal muscle mitochondria. When redox status was subsequently increased (i.e., more reduced), UCP1-mediated uncoupling was more sensitive to GDP inhibition. Surprisingly, BAT was found to be devoid of glutaredoxin-2 (Grx2) expression, while there was abundant expression in skeletal muscle. Taken together, these findings reveal the importance of redox environment in controlling bioenergetic functions in both tissues, and the highly unique characteristics of BAT in this regard.

Glutathionylation acts as a control switch for uncoupling proteins UCP2 and UCP3

The mitochondrial uncoupling proteins 2 and 3 (UCP2 and -3) are known to curtail oxidative stress and participate in a wide array of cellular functions, including insulin secretion and the regulation of satiety. However, the molecular control mechanism(s) governing these proteins remains elusive. Here we reveal that UCP2 and UCP3 contain reactive cysteine residues that can be conjugated to glutathione. We further demonstrate that this modification controls UCP2 and UCP3 function. Both reactive oxygen species and glutathionylation were found to activate and deactivate UCP3-dependent increases in non-phosphorylating respiration. We identified both Cys(25) and Cys(259) as the major glutathionylation sites on UCP3. Additional experiments in thymocytes from wild-type and UCP2 null mice demonstrated that glutathionylation similarly diminishes non-phosphorylating respiration. Our results illustrate that UCP2- and UCP3-mediated state 4 respiration is controlled by reversible glutathionylation. Altogether, these findings advance our understanding of the roles UCP2 and UCP3 play in modulating metabolic efficiency, cell signaling, and oxidative stress processes.

Oxidative stress in cold-induced hyperthyroid state

Exposure of homeothermic animals to low environmental temperature is associated with oxidative stress in several body tissues. Because cold exposure induces a condition of functional hyperthyroidism, the observation that tissue oxidative stress also happens in experimental hyperthyroidism, induced by 3,5,3'-triiodothyronine (T(3)) treatment, suggests that this hormone is responsible for the oxidative damage found in tissues from cold-exposed animals. Examination of T(3)-responsive tissues, such as brown adipose tissue (BAT) and liver, shows that changes in factors favoring oxidative modifications are similar in experimental and functional hyperthyroidism. However, differences are also apparent, likely due to the action of physiological regulators, such as noradrenaline and thyroxine, whose levels are different in cold-exposed and T(3)-treated animals. To date, there is evidence that biochemical changes underlying the thermogenic response to cold as well as those leading to oxidative stress require a synergism between T(3)- and noradrenaline-generated signals. Conversely, available results suggest that thyroxine (T(4)) supplies a direct contribution to cold-induced BAT oxidative damage, but contributes to the liver response only as a T(3) precursor.

A urinary marker of oxidative stress covaries positively with hostility among midlife community volunteers

OBJECTIVE

Although not all findings are consistent, growing evidence suggests that individuals high in dispositional hostility are at elevated risk for cardiovascular disease and all-cause mortality; however, the mechanisms of these associations remain unclear. One possibility is that hostility is associated with oxidative stress. Here, we explore relationships between hostility and a measure of systemic oxidative stress among a mid-life sample.

METHODS

In a community sample of 223 adults aged 30 to 54 years (86% white, 50% female), oxidative stress was measured as the 24-hour urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG). An abbreviated Cook Medley Hostility Scale was used to measure dimensions of hostility.

RESULTS

Regression analyses controlling for demographic characteristics and cardiovascular risk factors showed a positive relationship of 8-OHdG with total hostility (beta = 0.003, p = .03) and hostile affect (beta = 0.018, p < .001).

CONCLUSIONS

These findings provide evidence that dispositional hostility, and in particular, hostile affect, covary positively with systemic oxidative stress, raising the possibility that oxidative stress contributes to the pathogenicity of hostile attributes.

Effect of cold acclimation on antioxidant status in cold acclimated skaters

We investigated whether cold acclimation leads to increased activity of the antioxidant defense enzymes and muscle injury. Comparisons were between short track skaters (n=6) and inline skaters (n=6) during rest and at submaximal cycling (65% VO2max) in cold (ambient temperature: 5+/-1 degrees C, relative humidity: 41+/-8%) and warm conditions (ambient temperature: 21+/-1 degrees C, relative humidity: 35+/-5%), during 60 min, respectively, and during the recovery phase. Erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHpx), reduced glutathione (GSH), thiobarbituric substance acid (TBARS), serum creatine kinase (CK), lactate dehydrogenase (LDH), plasma myoglobin (Mb) and cortisol were determined. Activities of CAT and GSHpx and the level of GSH and TBARS in erythrocyte and the level of LDH in serum were elevated in cold acclimated subjects. We suggested that the compensatory increase in antioxidative defense enzymes resulting from long-term cold exposure may reflect the elevated reactive oxygen species (ROS) production and muscle injury at this environment acclimation.

The impact of experimentally elevated energy expenditure on oxidative stress and lifespan in the short-tailed field vole Microtus agrestis

Life-history theory assumes that animal life histories are a consequence of trade-offs between current activities and future reproductive performance or survival, because resource supply is limited. Empirical evidence for such trade-offs in the wild are common, yet investigations of the underlying mechanisms are rare. Life-history trade-offs may have both physiological and ecological mediated costs. One hypothesized physiological mechanism is that elevated energy metabolism may increase reactive oxygen species production, leading to somatic damage and thus compromising future survival. We investigated the impact of experimentally elevated energy expenditure on oxidative damage, protection and lifespan in short-tailed field voles (Microtus agrestis) maintained in captivity to remove any confounding ecological factor effects. Energy expenditure was elevated via lifelong cold exposure (7+/-2 degrees C), relative to siblings in the warm (22+/-2 degrees C). No treatment effect on cumulative mortality risk was observed, with negligible effects on oxidative stress and antioxidant protection. These data suggest that in captive animals physiologically mediated costs on life history do not result from increased energy expenditure and consequent elevations in oxidative stress and reduced survival.

Antioxidative and metabolic responses to extended cold exposure in rats

In this work, we investigated whether extended cold exposure increases oxidative damage and susceptibility to oxidants of rat liver, heart, kidney and lung which are metabolically active tissues. Moreover in this study the effect of cold stress on some of the lipid metabolic mediators were studied in rat experimental model. Male albino Sprague-Dawley rats were randomly divided into two groups: The control group (n=12) and the cold-stress group (n=12). Tissue superoxide dismutase (SOD), catalase (CAT), glutathion S-transferase (GST) and glutathion reductase (GR) activities and glutathion (GSH) were measured using standard protocols. The biochemical analyses for total lipid, cholesterol, trigliceride, HDL, VLDL and LDL were done on autoanalyzer. In cold-stress groups SOD activity was decreased in the lung whereas it increased in the heart and kidney. CAT activity was significantly decreased (except liver) in all the tissues in treated rats. GST activity of cold-induced rats increased in liver and heart while decreased in the lung. GR activity was significantly decreased (except in liver) in all the tissues in cold-stressed rats. GSH level was significantly increased in the heart but decreased in the lung of animals exposed to cold when compared to controls. It was found that among the groups trigliceride, total lipid, HDL and VLDL parameters varied significantly but cholesterol and LDL had no significant variance. In this study, we found that exposure of extended (48 h) cold (8 degrees C) caused changes both in the antioxidant defense system (as tissue and enzyme specific) and serum lipoprotein profiles in rats.

Vitamin E attenuates cold-induced rat liver oxidative damage reducing H2O2 mitochondrial release

Vitamin E is a major chain-breaking antioxidant which is able to reduce liver oxidative damage without modifying aerobic capacity in T(3)-treated rats. We investigated whether vitamin E has similar effects in hyperthyroid state induced by cold exposure. Cold exposure increased aerobic capacity and O(2) consumption in homogenates and mitochondria and tissue mitochondrial protein content. Vitamin E did not modify aerobic capacity and mitochondrial protein content of cold liver, but increased ADP-stimulated respiration of liver preparations. Succinate-supported H(2)O(2) release rates were increased by cold during basal and stimulated respiration, whereas the pyruvate/malate-supported ones increased only during basal respiration. Vitamin administration to cold-exposed rats decreased H(2)O(2) release rates with both substrates during basal respiration. This effect reduced ROS flow from mitochondria to cytosol, limiting liver oxidative damage. Cold exposure also increased mitochondrial capacity to remove H(2)O(2), which was reduced by vitamin treatment, showing that the antioxidant also lowers H(2)O(2) production rate. The different effects of cold exposure and vitamin treatment on H(2)O(2) generation were also found in the presence of respiration inhibitors. Although this can suggest that the cold and vitamin induce opposite changes in mitochondrial content of autoxidizable electron carriers, it is likely that vitamin effect is due to its capacity to scavenge superoxide radical. Finally, vitamin E reduced mitochondrial oxidative damage and susceptibility to oxidants, and prevented Ca(2+)-induced swelling elicited by cold. In the whole, our results suggest that vitamin E is able to maintain aerobic capacity and attenuate oxidative stress of hepatic tissue in cold-exposed rats modifying mitochondrial population characteristics.

Life-long vitamin C supplementation in combination with cold exposure does not affect oxidative damage or lifespan in mice, but decreases expression of antioxidant protection genes

Oxidative stress is suggested to be central to the ageing process, with endogenous antioxidant defence and repair mechanisms in place to minimize damage. Theoretically, supplementation with exogenous antioxidants might support the endogenous antioxidant system, thereby reducing oxidative damage, ageing-related functional decline and prolonging life- and health-span. Yet supplementation trials with antioxidants in animal models have had minimal success. Human epidemiological data are similarly unimpressive, leading some to question whether vitamin C, for example, might have pro-oxidant properties in vivo. We supplemented cold exposed (7+/-2 degrees C) female C57BL/6 mice over their lifespan with vitamin C (ascorbyl-2-polyphosphate), widely advocated and self administered to reduce oxidative stress, retard ageing and increase healthy lifespan. No effect on mean or maximum lifespan following vitamin C treatment or any significant impact on body mass, or on parameters of energy metabolism was observed. Moreover, no differences in hepatocyte and lymphocyte DNA oxidative damage or hepatic lipid peroxidation was seen between supplemented and control mice. Using a DNA macroarray specific for oxidative stress-related genes, we found that after 18 months of supplementation, mice exhibited a significantly reduced expression of several genes in the liver linked to free-radical scavenging, including Mn-superoxide dismutase. We confirmed these effects by Northern blotting and found additional down-regulation of glutathione peroxidase (not present on macroarray) in the vitamin C treated group. We suggest that high dietary doses of vitamin C are ineffective at prolonging lifespan in mice because any positive benefits derived as an antioxidant are offset by compensatory reductions in endogenous protection mechanisms, leading to no net reduction in accumulated oxidative damage.

Activity of 20S proteosomes and content of oxidized proteins in rat liver after long-term cold exposure

We studied the effect of long-term (5 and 10 days) cold exposure (4 degrees C) on oxidative damage to proteins and proteosomal activity in the liver of Wistar rats. It was shown that core temperature on the 10th day of cold exposure decreased by 1.1 degrees C. The content of oxidized proteins increased at this term. Chymotrypsin-like and peptidylglutamyl peptide hydrolyzing activities increased, while trypsin-like activity decreased during cold exposure.

Differential effects of experimental and cold-induced hyperthyroidism on factors inducing rat liver oxidative damage

Thyroid hormone-induced increase in metabolic rates is often associated with increased oxidative stress. The aim of the present study was to investigate the contribution of iodothyronines to liver oxidative stress in the functional hyperthyroidism elicited by cold, using as models cold-exposed and 3,5,3'-triiodothyronine (T3)- or thyroxine (T4)-treated rats. The hyperthyroid state was always associated with increases in both oxidative capacity and oxidative damage of the tissue. The most extensive damage to lipids and proteins was found in T3-treated and cold-exposed rats, respectively. Increase in oxygen reactive species released by mitochondria and microsomes was found to contribute to tissue oxidative damage, whereas the determination of single antioxidants did not provide information about the possible contribution of a reduced effectiveness of the antioxidant defence system. Indeed, liver oxidative damage in hyperthyroid rats was scarcely related to levels of the liposoluble antioxidants and activities of antioxidant enzymes. Conversely, other biochemical changes, such as the degree of fatty acid unsaturation and hemoprotein content, appeared to predispose hepatic tissue to oxidative damage associated with oxidative challenge elicited by hyperthyroid state. As a whole, our results confirm the idea that T3 plays a key role in metabolic changes and oxidative damage found in cold liver. However, only data concerning changes in glutathione peroxidase activity and mitochondrial protein content favour the idea that dissimilarities in effects of cold exposure and T3 treatment could depend on differences in serum levels of T4.

UCP1 and Defense against Oxidative Stress

Uncoupling proteins have been ascribed a role in defense against oxidative stress, particularly by being activated by products of oxidative stress such as 4-hydroxy-2-nonenal (HNE). We have investigated here the ability of HNE to activate UCP1. Using brown fat mitochondria from UCP1+/+ and UCP1-/- mice to allow for identification of UCP1-dependent effects, we found that HNE could neither (re)activate purine nucleotide-inhibited UCP1, nor induce additional activation of innately active UCP1. The aldehyde nonenal had a (re)activating effect only if converted to the corresponding fatty acid by aldehyde dehydrogenase; the presence of a carboxyl group was thus an absolute requirement for (re)activation. The UCP1-dependent proton leak was not increased by HNE but HNE changed basal proton leak characteristics in a UCP1-independent manner. In agreement with the in vitro results, we found, as compared with UCP1+/+ mice, no increase in HNE/protein adducts in brown fat mitochondria isolated from UCP1-/- mice, irrespective of whether they were adapted to thermoneutral temperature (30 degrees C) or to the cold (4 degrees C). The absence of oxidative damage in UCP1-/- mitochondria was not due to enhanced activity of antioxidant enzymes. Thus, HNE did not affect UCP1 activity, and UCP1 would appear not to be physiologically involved in defense against oxidative stress. Additionally, it was concluded that at least in brown adipose tissue, conditions of high mitochondrial membrane potential, high oxygen tension, and high substrate supply do not necessarily lead to increased oxidative damage.

Effect of experimental and cold exposure induced hyperthyroidism on H2O2 production and susceptibility to oxidative stress of rat liver mitochondria

To investigate the iodothyronine role in liver responses to cold, we examined metabolic and oxidative mitochondrial changes in cold-exposed, T3-treated, and T4-treated rats, which exhibit different T4 serum levels. All treatments increased mitochondrial respiration which reached the highest and lowest values after T3 and cold treatment, respectively. The T3- and T4-induced changes agreed with the respective increases in Complex IV activities, while those elicited by cold were inconsistent with increased activities of respiratory complexes. Mitochondrial capacity to produce H2O2 was the highest in T3-treated rats, whereas it was similar in T4-treated and cold-exposed rats. The effects of respiratory inhibitors suggested that T3 and T4 mainly increase the mitochondrial content of autoxidizable electron carrier of Complex I and Complex III, respectively. The indices of oxidative modifications of proteins exhibited increases consistent with the treatment effects on H2O2 production. The increases in indices of lipid peroxidation were also dependent on changes in lipid composition. The increased protein damage in treatment groups was confirmed using immunoblotting analysis, which also showed oxidative damage in a 133 kDa fraction, which was not expressed in T3-treated rats. Antioxidant levels were not related to the extent of oxidative damage as only mitochondrial GSH levels decreased in T3-treated rats. Mitochondrial susceptibility to in vitro oxidative challenge and Ca2+-induced swelling was increased by all treatments, but was the highest in T3-treated rats. In the whole, our results indicate T3 as main responsible for the changes in the mitochondrial population associated with cold exposure. However, a significant role is also played by T4, which appears to acts mainly modulating T3 effects, but also inducing some effects different from the T3 ones.

Up-regulation of a thioredoxin peroxidase-like protein, proliferation-associated gene, in hibernating bats

Two-dimensional gel electrophoresis was used to assess differential protein expression between euthermic and hibernating states in heart of Myotis lucifugus. A hibernation-induced protein was identified by mass spectrometry as a thioredoxin peroxidase-like protein known as PAG. Western blotting confirmed up-regulation (>2-fold) and RT-PCR also revealed up-regulation (>5-fold) of pag mRNA. Cloning revealed a highly conserved sequence suggesting a conserved function for PAG. Oxidative stress markers, p-IkappaB-alpha (Ser 32) and p-HSP27 (Ser 78/82), were also up-regulated in heart and skeletal muscle during hibernation. Although there are selected increases in gene/protein expression during hibernation, general translation inhibition occurs as part of metabolic rate depression. This was confirmed by elevated levels of the inactive forms of the eIF2alpha (Ser 51) in both heart and skeletal muscle (2- to 5-fold higher than in euthermia) and the eEF2 (Thr 51) in skeletal muscle (a 15-fold increase). This study suggests that hibernators may use up-regulation of specific proteins to counteract oxidative stress.

Cold-induced hyperthyroidism produces oxidative damage in rat tissues and increases susceptibility to oxidants

In this work, we investigated whether cold exposure-induced hyperthyroidism increases oxidative damage and susceptibility to oxidants of rat liver, heart and skeletal muscle. All tissues exhibited gradual increases in hydroperoxide and protein-bound carbonyl levels. Glutathione peroxidase activity increased in all tissues after 2 days and further increased in the muscle after 10 days of cold exposure. Liver glutathione reductase activity increased after 10 days of cold exposure, while heart and muscle activities were not modified. Vitamin E levels were not affected by cold, while coenzyme Q9 and coenzyme Q10 levels decreased in heart and muscle after 2-day cold exposure and were not further modified after 10 days. Liver coenzyme Q9 levels increased after 2 days whereas coenzyme Q10 levels increased after 10 days in the cold. The whole antioxidant capacity was lowered, while parameters positively correlated with susceptibility to oxidants were increased by cold. Lipid fatty acid composition was modified in all tissues. In particular, fatty acid unsaturation degree increased in heart and muscle. Cytochrome oxidase activity increased, suggesting an increased content of hemoproteins, which are able to generate .OH radical. This view was supported by the observation that the tissue susceptibility to H(2)O(2) treatment, which is strongly correlated to iron-ligand content, increased after cold exposure. In this frame, it is apparent that the increase in oxidative capacity, necessary for homeotherm survival in low temperature environments, has potential harmful effects, because it results in increased susceptibility to oxidative challenge.

Cold-stress-induced modulation of antioxidant defence: role of stressed conditions in tissue injury followed by protein oxidation and lipid peroxidation

The aim of this study was to determine the effects of cold stress on antioxidant enzyme activities and examine protein oxidation and lipid peroxidation in various tissues (brain, liver, kidney, heart and stomach). Twenty male Wistar rats (3 months old) weighing 220 +/- 20 g were used. The rats were randomly divided into two groups of ten: the control group and the cold stress group. Cold stress was applied to the animals by maintaining them in a cold room (5 degrees C) for 15 min/day for 15 days. Blood samples were taken for measuring plasma corticosterone levels. Tissues were obtained from each rat for measuring the antioxidant enzyme activities, protein oxidation and lipid peroxidation. Corticosterone levels were increased in the cold stress group. Copper, zinc superoxide dismutase activities were increased in the brains, livers and kidneys, whereas they decreased in the hearts and stomachs of rats in the cold stress group. Catalase activities were increased in the brains, livers, kidneys and hearts, whereas they decreased in the stomachs of rats in the cold stress group. Selenium-dependent glutathione peroxidase activities were increased in the brain, liver, heart and stomach. Reduced glutathione levels were decreased, while levels of protein carbonyl, conjugated diene and thiobarbituric-acid-reactive substances were increased in all tissues of the cold stress group. These results lead us to conclude that cold stress can disrupt the balance in an oxidant/antioxidant system and cause oxidative damage to several tissues by altering the enzymatic and non-enzymatic antioxidant status, protein oxidation and lipid peroxidation.

Effect of cold-induced hyperthyroidism on H2O2 production and susceptibility to stress conditions of rat liver mitochondria

Previous studies have shown that T3 treatment and cold exposure induce similar biochemical changes predisposing rat liver to oxidative stress. This suggests that the liver oxidative damage observed in experimental and functional hyperthyroidism is mediated by thyroid hormone. To support this hypothesis we investigated whether middle-term cold exposure (2 and 10 days), like T3 treatment, also increases H2O2 release by liver mitochondria. We found that the rate of H2O2 release increased only during State 4 respiration, but faster flow of reactive oxygen species (ROS) from mitochondria to the cytosolic compartment was ensured by the concomitant increase in tissue mitochondrial proteins. Cold exposure also increased the capacity of mitochondria to remove H2O2. This indicates that cold causes accelerated H2O2 production, which might depend on enhanced autoxidizable carrier content and should lead to increased mitochondrial damage. Accordingly, mitochondrial levels of hydroperoxides and protein-bound carbonyls were higher after cold exposure. Levels of low-molecular weight antioxidants were not related to the extent of oxidative damage, but susceptibility to both in vitro oxidative challenge and Ca2+-induced swelling increased in mitochondria from cold exposed rats. The cold-induced changes in several parameters, including susceptibility to swelling, were time dependent, because they were apparent or greater after 10 days cold exposure. The cold-induced increase in swelling may be a feedback mechanism to limit tissue oxidative stress, purifying the mitochondrial population from ROS-overproducing mitochondria, and the time course for such change is consistent with the gradual development of cold adaptation.

Chronic cold exposure affects the antioxidant defense system in various rat tissues

BACKGROUND

Chronic exposure to stress alters the normal body homeostasis and, hence, leads to the development of various human pathologies, which might involve alterations in the antioxidant defense system. We studied the effect of chronic cold exposure on oxidative stress and antioxidant defense system in various rat tissues.

METHODS

Male albino rats (Wistar strain), 2-3 months old, were exposed to 3 weeks of cold treatment. Antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) were measured in addition to the antioxidants, ascorbic acid (AsA) and glutathione (GSH), and the prooxidants, lipid peroxides (LPO) and xanthine oxidase (XOD), in brain, heart, kidney, liver and small intestine using standard protocols.

RESULTS

Chronic cold exposure resulted in a significant increase in LPO in all the tissues studied while XOD was increased in the brain and intestine. Total SOD activity was significantly decreased in all the tissues, whereas CAT activity was significantly increased in the kidney and decreased in heart, liver and intestine in the animals exposed to cold. GPx activity was increased only in the brain and intestine of stressed rats. Chronic cold exposure resulted in significant decrease in GR activity in heart, liver and intestine. GST activity was increased (except heart) and GSH was significantly decreased in all the tissues in treated rats. AsA was increased in kidney and intestine but decreased in heart of stressed animals.

CONCLUSIONS

The observed changes in the antioxidant defense system are tissue specific, but it is evident that chronic exposure to cold leads to oxidative stress by displacing the prooxidant-antioxidant balance of this defense system by increasing the prooxidants while depleting the antioxidant capacities.