Proton leak and hydrogen peroxide production in liver mitochondria from energy-restricted rats

Bioenergetic Status of the Intestinal and Hepatic Cells after Short Term Exposure to Fumonisin B1 and Aflatoxin B1

Fumonisin B1 (FB1) and aflatoxin B1 (AFB1) are frequent contaminants of staple foods such as maize. Oral exposure to these toxins poses health hazards by disrupting cellular signaling. However, little is known regarding the multifaced mitochondrial dysfunction-linked toxicity of FB1 and AFB1. Here, we show that after exposure to FB1 and AFB1, mitochondrial respiration significantly decreased by measuring the oxygen consumption rate (OCR), mitochondrial membrane potential (MMP) and reactive oxygen species (ROS). The current work shows that the integrity of mitochondria (MMP and ROS), that is the central component of cell apoptosis, is disrupted by FB1 and AFB1 in undifferentiated Caco-2 and HepG2 cells as in vitro models for human intestine and liver, respectively. It hypothesizes that FB1 and AFB1 could disrupt the mitochondrial electron transport chain (ETC) to induce mitochondrial dysfunction and break the balance of transferring H⁺ between the mitochondrial inner membrane and mitochondrial matrix, however, the proton leak is not increasing and, as a result, ATP synthesis is blocked. At the sub-toxic exposure of 1.0 µg/mL for 24 h, i.e., a viability of 95% in Caco-2 and HepG2 cells, the mitochondrial respiration was, however, stimulated. This suggests that the treated cells could reserve energy for mitochondrial respiration with the exposure of FB1 and AFB1, which could be a survival advantage.

Is the NDUFV2 subunit of the hydrophilic complex I domain a key determinant of animal longevity?

Complex I, a component of the electron transport chain, plays a central functional role in cell bioenergetics and the biology of free radicals. The structural and functional N module of complex I is one of the main sites of the generation of free radicals. The NDUFV2 subunit/N1a cluster is a component of this module. Furthermore, the rate of free radical production is linked to animal longevity. In this review, we explore the hypothesis that NDUFV2 is the only conserved core subunit designed with a regulatory function to ensure correct electron transfer and free radical production, that low gene expression and protein abundance of the NDUFV2 subunit is an evolutionary adaptation needed to achieve a longevity phenotype, and that these features are determinants of the lower free radical generation at the mitochondrial level and a slower rate of aging of long-lived animals.

Mitochondrial abundance and function in muscle from beef steers with divergent residual feed intakes

The objective of this study was to evaluate the relationship between muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56-day feeding trial was conducted with 81 Angus × Hereford steers (initial BW = 378 ± 43 kg) from the University of California Sierra Foothills Research Station (Browns Valley, CA, USA). All steers were individually fed the same finishing ration (metabolizable energy = 3.28 Mcal/kg DM). Average daily gain (ADG), DM intake (DMI) and RFI were 1.82 ± 0.27, 8.89 ± 1.06 and 0.00 ± 0.55 kg/day, respectively. After the feeding trial, the steers were categorized into high, medium and low RFI groups. Low RFI steers consumed 13.6% less DM (P < 0.05) and had a 14.1% higher G : F ratio (P < 0.05) than the high RFI group. No differences between RFI groups were found in age, ADG or BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to assess mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an oxygraph (Hansatech Instruments Ltd., Norfolk, UK). State 3 and State 4 respiration rates were similar between both groups (P > 0.10). Respiratory control ratios (RCRs, i.e., State 3 : State 4 oxygen uptakes) declined with animal age and were greater in low RFI steers (4.90) as compared to high RFI steers (4.26) when adjusted for age by analysis of covariance (P = 0.003). Mitochondrial complex II activity levels per gram of muscle were 42% greater in low RFI steers than in high RFI steers (P = 0.004). These data suggest that skeletal muscle mitochondria have greater reserve respiratory capacity and show greater coupling between respiration and phosphorylation in low RFI than in high RFI steers.

Caloric restriction induces H2O2 formation as a trigger of AMPK-eNOS-NO pathway in obese rats: Role for CAMKII

Caloric restriction (CR) improves endothelial function through the upregulation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric oxide synthase (eNOS). Moreover, hydrogen peroxide (H₂O₂) is upregulated in yeast subjected to CR. Our aim was to assess if mild short-term CR increases vascular H₂O₂ formation as a link with AMPK and eNOS activation. Twelve-week old Zucker obese (fa/fa) and control Zucker lean male rats were fed a standard chow either ad libitum (AL, n=10) or with a 20% CR (CR, n=10) for two weeks. CR significantly improved relaxation to ACh in fa/fa rats because of an enhanced endogenous production of H₂O₂ in aortic rings (H₂O₂ levels _fa/faAL=0.5 ± 0.05 nmol/mg vs. H₂O₂ levels _fa/faCR=0.76 ± 0.07 nmol/mg protein; p<0.05). Expression of mitochondrial superoxide dismutase (Mn-SOD) and total SOD activity were increased in aorta from fa/fa animals after CR. In cultured aortic endothelial cells, serum deprivation or 2-deoxy-d-glucose induced a significant increase in: i) superoxide anion and H₂O₂ levels, ii) p-AMPK/AMPK and p-eNOS/eNOS expression and iii) nitric oxide levels. This effect was reduced by catalase and strongly inhibited by Ca²⁺/calmodulin-dependent kinase II (CamkII) silencing. In conclusion, we propose that mild short-term CR might be a trigger of mechanisms aimed at protecting the vascular wall by the increase of H₂O₂, which then activates AMPK and nitric oxide release, thus improving endothelium-dependent relaxation. In addition, we demonstrate that CAMKII plays a key role in mediating CR-induced AMPK activation through H₂O₂ increase.

Relationship between Liver Mitochondrial Respiration and Proton Leak in Low and High RFI Steers from Two Lineages of RFI Angus Bulls

The objective of this research is to evaluate liver mitochondrial oxygen consumption and proton leak kinetics in progeny from two lineages of Angus bulls with high and low residual feed intake (RFI). Two Angus bulls were selected based on results from a genetic test for RFI and were used as sires. Eight offspring at 10-11 months of age from each sire were housed in individual pens for 70–105 days following a diet adaptation period of 14 days. Progeny of the low RFI sire had 0.57 kg/d (P = 0.05) lower average RFI than progeny of the high RFI sire. There was no difference in dry matter intake between low and high RFI steers, but low RFI steers gained more body weight (P = 0.02) and tended to have higher average daily gains (P = 0.07). State 3 and State 4 respiration, RCR, and proton leak did not differ between high and low RFI steers (P = 0.96, P = 0.81, P = 0.93, and P = 0.88, resp.). Therefore, the increase in bodyweight gain which distinguished the low RFI steers from the high RFI steers may be associated with other metabolic mechanisms that are not associated with liver mitochondrial respiration and proton leak kinetics.

The influence of dietary fat source on liver and skeletal muscle mitochondrial modifications and lifespan changes in calorie-restricted mice

The Membrane Theory of Aging proposes that lifespan is inversely related to the level of unsaturation in membrane phospholipids. Calorie restriction (CR) without malnutrition extends lifespan in many model organisms, which may be related to alterations in membrane phospholipids fatty acids. During the last few years our research focused on studying how altering the predominant fat source affects the outcome of CR in mice. We have established four dietary groups: one control group fed 95 % of a pre-determined ad libitum intake (in order to prevent obesity), and three CR groups fed 40 % less than ad libitum intake. Lipid source for the control and one of the CR groups was soybean oil (high in n-6 PUFA) whereas the two remaining CR groups were fed diets containing fish oil (high in n-3 PUFA), or lard (high in saturated and monounsaturated fatty acids). Dietary intervention periods ranged from 1 to 18 months. We performed a longitudinal lifespan study and a cross-sectional study set up to evaluate several mitochondrial parameters which included fatty acid composition, H(+) leak, activities of electron transport chain enzymes, ROS generation, lipid peroxidation, mitochondrial ultrastructure, and mitochondrial apoptotic signaling in liver and skeletal muscle. These approaches applied to different cohorts of mice have independently indicated that lard as a fat source often maximizes the effects of 40 % CR on mice. These effects could be due to significant increases of monounsaturated fatty acids levels, in accordance with the Membrane Theory of Aging.

Relationships between residual feed intake and hepatic mitochondrial function in growing beef cattle

The objective of this study was to evaluate the relationship between hepatic mitochondrial function and residual feed intake (RFI) in growing beef cattle. In Trial 1, RFI was measured in 29 Angus heifers (initial BW = 258.0 ± 24.9 kg) from divergent IGF-I selection lines created at the Eastern Agricultural Research Station (The Ohio State University) fed a grain-based diet (calculated ME = 2.85 Mcal/kg DM). In Trial 2, RFI was measured in 119 Santa Gertrudis steers (initial BW = 308.4 ± 28.1 kg) fed a roughage-based diet (calculated ME = 2.21 Mcal/kg DM). At the end of the RFI measurement period, cattle in Trial 1 (n = 7 low RFI and n = 7 high RFI) and in Trial 2 (n = 6 low RFI and n = 8 high RFI) with measures of RFI exceeding 0.5 (Trial 1) or 1.0 (Trial 2) SD from the mean RFI were selected to measure mitochondrial function. Overall ADG, DMI, and RFI were 1.19 ± 0.15, 9.31 ± 1.12, and 0.00 ± 0.63 kg/d and 0.83 ± 0.16, 9.48 ± 1.00, and 0.00 ± 0.86 kg/d in Trial 1 and 2, respectively. Cattle with low RFI consumed 13 and 24% less (P < 0.05) DM and had 14 and 56% greater (P < 0.05) G:F than cattle with high RFI in Trial 1 and 2, respectively, even though ADG and BW were similar (P > 0.10). In Trial 1, cattle with low RFI tended (P = 0.06) to have greater state 3 respiration rates than cattle with high RFI, but state 3 respiration rates were similar (P > 0.10) between cattle with low and high RFI in Trial 2. In both trials, cattle with low RFI had greater (P < 0.05) acceptor control ratios than their high RFI counterparts. The respiratory control ratio tended (P = 0.09) to be greater for cattle with low RFI compared with high RFI cattle in Trial 1, but no difference (P > 0.10) was observed in Trial 2. Proton-leak kinetics were similar (P > 0.05) between cattle with low and high RFI in both trials. These data suggest that ADP has greater control of oxidative phosphorylation in liver mitochondrial of cattle with low RFI compared to their high RFI counterparts.

The effects of dietary restriction on oxidative stress in rodents

Oxidative stress is observed during aging and in numerous age-related diseases. Dietary restriction (DR) is a regimen that protects against disease and extends life span in multiple species. However, it is unknown how DR mediates its protective effects. One prominent and consistent effect of DR in a number of systems is the ability to reduce oxidative stress and damage. The purpose of this review is to comprehensively examine the hypothesis that dietary restriction reduces oxidative stress in rodents by decreasing reactive oxygen species (ROS) production and increasing antioxidant enzyme activity, leading to an overall reduction of oxidative damage to macromolecules. The literature reveals that the effects of DR on oxidative stress are complex and likely influenced by a variety of factors, including sex, species, tissue examined, types of ROS and antioxidant enzymes examined, and duration of DR. Here we present a comprehensive review of the existing literature on the effect of DR on mitochondrial ROS generation, antioxidant enzymes, and oxidative damage. In a majority of studies, dietary restriction had little effect on mitochondrial ROS production or antioxidant activity. On the other hand, DR decreased oxidative damage in the majority of cases. Although the effects of DR on endogenous antioxidants are mixed, we find that glutathione levels are the most likely antioxidant to be increased by dietary restriction, which supports the emerging redox-stress hypothesis of aging.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following eight months of calorie restriction

Calorie restriction (CR) has been shown to decrease reactive oxygen species (ROS) production and retard aging in a variety of species. It has been proposed that alterations in membrane saturation are central to these actions of CR. As a step towards testing this theory, mice were assigned to 4 dietary groups (control and 3 CR groups) and fed AIN-93G diets at 95 % (control) or 60 % (CR) of ad libitum for 8 months. To manipulate membrane composition, the primary dietary fats for the CR groups were soybean oil (also used in the control diet), fish oil or lard. Skeletal muscle mitochondrial lipid composition, proton leak, and H(2)O(2) production were measured. Phospholipid fatty acid composition in CR mice was altered in a manner that reflected the n-3 and n-6 fatty acid profiles of their respective dietary lipid sources. Dietary lipid composition did not alter proton leak kinetics between the CR groups. However, the capacity of mitochondrial complex III to produce ROS was decreased in the CR lard compared to the other CR groups. The results of this study indicate that dietary lipid composition can influence ROS production in muscle mitochondria of CR mice. It remains to be determined if lard or other dietary oils can maximize the CR-induced decreases in ROS production.

Calorie restriction influences key metabolic enzyme activities and markers of oxidative damage in distinct mouse liver mitochondrial sub-populations

AIMS

The purpose of the study was to establish if enzyme activities from key metabolic pathways and levels of markers of oxidative damage to proteins and lipids differed between distinct liver mitochondrial sub-populations, and which specific sub-populations contributed to these differences.

MAIN METHODS

Male C57BL/6J mice were fed non-purified diet for one month then separated into two groups, control and calorie-restricted (CR). The two groups were fed semi-purified diet (AIN93G), with the CR group receiving 40% less calories than controls. After two months, enzyme activities and markers of oxidative damage in mitochondria were determined.

KEY FINDINGS

In all mitochondrial sub-populations, enzyme activities and markers of oxidative damage, from control and CR groups, showed a pattern of M1>M3>M10. Higher acyl-CoA dehydrogenase (β-oxidation) and β-hydroxybutyrate dehydrogenase (ketogenesis) activities and lower carbonyl and TBARS levels were observed in M1 and M3 fractions from CR mice. ETC enzyme activities did not show a consistent pattern. In the Krebs cycle, citrate synthase and aconitase activities decreased while succinate dehydrogenase and malate dehydrogenase activities increased in the M1 mitochondria from the CR versus control mice.

SIGNIFICANCE

CR does not produce uniform changes in enzyme activities or markers of oxidative damage in mitochondrial sub-populations, with changes occurring primarily in the heavy mitochondrial populations. Centrifugation at 10,000 g to isolate mitochondria likely dilutes the mitochondrial populations which show the greatest response to CR. Use of lower centrifugal force (3000 g or lower) may be beneficial for some studies.

The influence of dietary lipid composition on liver mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of CR (calorie restriction), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and the CR groups were fed diets containing soya bean oil (also in the control diet), fish oil or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak and H₂O₂ production were measured in liver mitochondria following 1 month of CR. The results indicate that mitochondrial phospholipid fatty acids reflect the PUFA (polyunsaturated fatty acid) profile of the dietary lipid sources. CR significantly decreased the capacity of ROS (reactive oxygen species) production by Complex III but did not markedly alter proton leak and ETC (electron transport chain) enzyme activities. Within the CR regimens, the CR-fish group had decreased ROS production by both Complexes I and III, and increased proton leak when compared with the other CR groups. The CR-lard group showed the lowest proton leak compared with the other CR groups. The ETC enzyme activity measurements in the CR regimens showed that Complex I activity was decreased in both the CR-fish and CR-lard groups. Moreover, the CR-fish group also had lower Complex II activity compared with the other CR groups. These results indicate that dietary lipid composition does influence liver mitochondrial phospholipid composition, ROS production, proton leak and ETC enzyme activities in CR animals.

Cardiovascular redox and ox stress proteomics

SIGNIFICANCE

Oxidative post-translational modifications (OPTMs) have been demonstrated as contributing to cardiovascular physiology and pathophysiology. These modifications have been identified using antibodies as well as advanced proteomic methods, and the functional importance of each is beginning to be understood using transgenic and gene deletion animal models. Given that OPTMs are involved in cardiovascular pathology, the use of these modifications as biomarkers and predictors of disease has significant therapeutic potential. Adequate understanding of the chemistry of the OPTMs is necessary to determine what may occur in vivo and which modifications would best serve as biomarkers.

RECENT ADVANCES

By using mass spectrometry, advanced labeling techniques, and antibody identification, OPTMs have become accessible to a larger proportion of the scientific community. Advancements in instrumentation, database search algorithms, and processing speed have allowed MS to fully expand on the proteome of OPTMs. In addition, the role of enzymatically reversible OPTMs has been further clarified in preclinical models.

CRITICAL ISSUES

The identification of OPTMs suffers from limitations in analytic detection based on the methodology, instrumentation, sample complexity, and bioinformatics. Currently, each type of OPTM requires a specific strategy for identification, and generalized approaches result in an incomplete assessment.

FUTURE DIRECTIONS

Novel types of highly sensitive MS instrumentation that allow for improved separation and detection of modified proteins and peptides have been crucial in the discovery of OPTMs and biomarkers. To further advance the identification of relevant OPTMs in advanced search algorithms, standardized methods for sample processing and depository of MS data will be required.

Caloric restriction and redox state: does this diet increase or decrease oxidant production?

Calorie restriction (CR) is well established to enhance the lifespan of a wide variety of organisms, although the mechanisms are still being uncovered. Recently, some authors have suggested that CR acts through hormesis, enhancing the production of reactive oxygen species (ROS), activating stress response pathways, and increasing lifespan. Here, we review the literature on the effects of CR and redox state. We find that there is no evidence in rodent models of CR that an increase in ROS production occurs. Furthermore, results in Caenorhabditis elegans and Saccharomyces cerevisiae suggesting that CR increases intracellular ROS are questionable, and probably cannot be resolved until adequate, artifact free, tools for real-time, quantitative, and selective measurements of intracellular ROS are developed. Overall, the largest body of work indicates that CR improves redox state, although it seems improbable that a global improvement in redox state is the mechanism through which CR enhances lifespan.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of calorie restriction (CR), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and fed diets containing soybean oil (also in the control diet), fish oil, or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak, and H(2)O(2) production were measured in muscle mitochondria following 1 month of CR. The results indicate that phospholipid fatty acids reflected the polyunsaturated fatty acid profile of the dietary lipid sources. Capacity for Complex I- and III-linked H(2)O(2) production was decreased with CR, although there was no difference between CR groups. The CR lard group had lower proton leak than all other groups. The results indicate that a decreased degree of unsaturation in muscle mitochondrial membranes is not required for reduced H(2)O(2) production with CR. However, dietary lipids do have some influence on proton leak with CR.

Regulation of cell physiology and pathology by protein S-glutathionylation: lessons learned from the cardiovascular system

SIGNIFICANCE

Reactive oxygen and nitrogen species contributing to homeostatic regulation and the pathogenesis of various cardiovascular diseases, including atherosclerosis, hypertension, endothelial dysfunction, and cardiac hypertrophy, is well established. The ability of oxidant species to mediate such effects is in part dependent on their ability to induce specific modifications on particular amino acids, which alter protein function leading to changes in cell signaling and function. The thiol containing amino acids, methionine and cysteine, are the only oxidized amino acids that undergo reduction by cellular enzymes and are, therefore, prime candidates in regulating physiological signaling. Various reports illustrate the significance of reversible oxidative modifications on cysteine thiols and their importance in modulating cardiovascular function and physiology.

RECENT ADVANCES

The use of mass spectrometry, novel labeling techniques, and live cell imaging illustrate the emerging importance of reversible thiol modifications in cellular redox signaling and have advanced our analytical abilities.

CRITICAL ISSUES

Distinguishing redox signaling from oxidative stress remains unclear. S-nitrosylation as a precursor of S-glutathionylation is controversial and needs further clarification. Subcellular distribution of glutathione (GSH) may play an important role in local regulation, and targeted tools need to be developed. Furthermore, cellular redundancies of thiol metabolism complicate analysis and interpretation.

FUTURE DIRECTIONS

The development of novel pharmacological analogs that specifically target subcellular compartments of GSH to promote or prevent local protein S-glutathionylation as well as the establishment of conditional gene ablation and transgenic animal models are needed.

Mitochondrial energetics in liver and skeletal muscle after energy restriction in young rats

The present study investigated the effect of 2 weeks of energy restriction on whole body, liver and skeletal muscle energy handling. We measured whole-body oxygen consumption, as well as mitochondrial protein mass, respiratory capacity and energetic coupling in liver and skeletal muscle from food-restricted (FR) rats, age- and weight-matched controls. We also assessed markers of oxidative damage and antioxidant defences. The present results show that, in response to energy restriction, an adaptive decrease in whole-body energy expenditure is coupled with structural and functional changes in mitochondrial compartment, both in liver and skeletal muscle. In fact, liver mitochondrial mass per g of liver significantly increased, whereas total hepatic mitochondrial oxidative capacity was lower in FR than in control rats, because of a significant decrease in liver contribution to total body weight. In skeletal muscle, sub-sarcolemmal (SS) mitochondrial respiratory capacity, as well as SS and inter-myofibrillar (IMF) mitochondrial protein mass per g of tissue, was significantly lower in FR rats, compared to controls. Finally, a decrease in oxidative damage was found in liver but not in skeletal muscle mitochondria from FR rats, whereas an increase in antioxidant defence was found in both tissues. From the present results, it appears that skeletal muscle is involved in the decrease in energy expenditure induced by energy restriction. Energy sparing is achieved through changes in the activity (SS), mass (SS and IMF) and efficiency (IMF) of mitochondrial compartment.

Relationship of electrophilic stress to aging

This review begins with the premise that an organism's life span is determined by the balance between two countervailing forces: (i) the sum of destabilizing effects and (ii) the sum of protective longevity-assurance processes. Against this backdrop, the role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses. Because most biological macromolecules contain nucleophilic centers, electrophiles are particularly reactive and toxic in a biological context. The majority of cellular electrophiles are generated from polyunsaturated fatty acids by a peroxidation chain reaction that is readily triggered by oxygen-centered radicals, but propagates without further input of reactive oxygen species (ROS). Thus, the formation of lipid-derived electrophiles such as 4-hydroxynon-2-enal (4-HNE) is proposed to be relatively insensitive to the level of initiating ROS, but to depend mainly on the availability of peroxidation-susceptible fatty acids. This is consistent with numerous observations that life span is inversely correlated to membrane peroxidizability, and with the hypothesis that 4-HNE may constitute the mechanistic link between high susceptibility of membrane lipids to peroxidation and shortened life span. Experimental interventions that directly alter membrane composition (and thus their peroxidizability) or modulate 4-HNE levels have the expected effects on life span, establishing that the connection is not only correlative but causal. Specific molecular mechanisms are considered, by which 4-HNE could (i) destabilize biological systems via nontargeted reactions with cellular macromolecules and (ii) modulate signaling pathways that control longevity-assurance mechanisms.

Calorie restriction modifies ubiquinone and COQ transcript levels in mouse tissues

We studied ubiquinone (Q), Q homologue ratio, and steady-state levels of mCOQ transcripts in tissues from mice fed ad libitum or under calorie restriction. Maximum ubiquinone levels on a protein basis were found in kidney and heart, followed by liver, brain, and skeletal muscle. Liver and skeletal muscle showed the highest Q(9)/Q(10) ratios with significant interindividual variability. Heart, kidney, and particularly brain exhibited lower Q(9)/Q(10) ratios and interindividual variability. In skeletal muscle and heart, the most abundant mCOQ transcript was mCOQ7, followed by mCOQ8, mCOQ2, mPDSS2, mPDSS1, and mCOQ3. In nonmuscular tissues (liver, kidney, and brain) the most abundant mCOQ transcript was mCOQ2, followed by mCOQ7, mCOQ8, mPDSS1, mPDSS2, and mCOQ3. Calorie restriction increased both ubiquinone homologues and mPDSS2 mRNA in skeletal muscle, but mCOQ7 was decreased. In contrast, Q(9) and most mCOQ transcripts were decreased in heart. Calorie restriction also modified the Q(9)/Q(10) ratio, which was increased in kidney and decreased in heart without alterations in mPDSS1 or mPDSS2 transcripts. We demonstrate for the first time that unique patterns of mCOQ transcripts exist in muscular and nonmuscular tissues and that Q and COQ genes are targets of calorie restriction in a tissue-specific way.

Caloric restriction influences hydrogen peroxide generation in mitochondrial sub-populations from mouse liver

Calorie restriction (CR) has been shown to decrease H(2)O(2) production in liver mitochondria, although it is not known if this is due to uniform changes in all mitochondria or changes in particular mitochondrial sub-populations. To address this issue, liver mitochondria from control and CR mice were fractionated using differential centrifugation at 1,000 g, 3,000 g and 10,000 g into distinct populations labeled as M1, M3 and M10, respectively. Mitochondrial protein levels, respiration and H(2)O(2) production were measured in each fraction. CR resulted in a decrease in total protein (mg) in each fraction, although this difference disappeared when adjusted for liver weight (mg protein/g liver weight). No differences in respiration (State 3 or 4) were observed between control and CR mice in any of the mitochondrial fractions. CR decreased H(2)O(2) production in all fractions when mitochondria respired on succinate (Succ), succ+antimycin A (Succ+AA) or pyruvate/malate+rotenone (P/M+ROT). Thus, CR decreased reactive oxygen species (ROS) production under conditions which stimulate mitochondrial complex I ROS production under both forward (P/M+ROT) and backward (Succ & Succ+AA) electron flow. The results indicate that CR decreases H(2)O(2) production in all liver mitochondrial fractions due to a decrease in capacity for ROS production by complex I of the electron transport chain.

Complex I-associated hydrogen peroxide production is decreased and electron transport chain enzyme activities are altered in n-3 enriched fat-1 mice

The polyunsaturated nature of n-3 fatty acids makes them prone to oxidative damage. However, it is not clear if n-3 fatty acids are simply a passive site for oxidative attack or if they also modulate mitochondrial reactive oxygen species (ROS) production. The present study used fat-1 transgenic mice, that are capable of synthesizing n-3 fatty acids, to investigate the influence of increases in n-3 fatty acids and resultant decreases in the n-6:n-3 ratio on liver mitochondrial H(2)O(2) production and electron transport chain (ETC) activity. There was an increase in n-3 fatty acids and a decrease in the n-6:n-3 ratio in liver mitochondria from the fat-1 compared to control mice. This change was largely due to alterations in the fatty acid composition of phosphatidylcholine and phosphatidylethanolamine, with only a small percentage of fatty acids in cardiolipin being altered in the fat-1 animals. The lipid changes in the fat-1 mice were associated with a decrease (p<0.05) in the activity of ETC complex I and increases (p<0.05) in the activities of complexes III and IV. Mitochondrial H(2)O(2) production with either succinate or succinate/glutamate/malate substrates was also decreased (p<0.05) in the fat-1 mice. This change in H(2)O(2) production was due to a decrease in ROS production from ETC complex I in the fat-1 animals. These results indicate that the fatty acid changes in fat-1 liver mitochondria may at least partially oppose oxidative stress by limiting ROS production from ETC complex I.

Absence of uncoupling protein-3 leads to greater activation of an adenine nucleotide translocase-mediated proton conductance in skeletal muscle mitochondria from calorie restricted mice

Calorie restriction (CR), without malnutrition, consistently increases lifespan in all species tested, and reduces age-associated pathologies in mammals. Alterations in mitochondrial content and function are thought to underlie some of the effects of CR. Previously, we reported that rats subjected to variable durations of 40% CR demonstrated a rapid and sustained decrease in maximal leak-dependent respiration in skeletal muscle mitochondria. This was accompanied by decreased mitochondrial reactive oxygen species generation and increased uncoupling protein-3 protein (UCP3) expression. The aim of the present study was to determine the contribution of UCP3, as well as the adenine nucleotide translocase to these functional changes in skeletal muscle mitochondria. Consistent with previous findings in rats, short-term CR (2 weeks) in wild-type (Wt) mice resulted in a lowering of the maximal leak-dependent respiration in skeletal muscle mitochondria, without any change in proton conductance. In contrast, skeletal muscle mitochondria from Ucp3-knockout (KO) mice similarly subjected to short-term CR showed no change in maximal leak-dependent respiration, but displayed an increased proton conductance. Determination of ANT activity (by measurement of inhibitor-sensitive leak) and protein expression revealed that the increased proton conductance in mitochondria from CR Ucp3-KO mice could be entirely attributed to a greater acute activation of ANT. These observations implicate UCP3 in CR-induced mitochondrial remodeling. Specifically, they imply the potential for an interaction, or some degree of functional redundancy, between UCP3 and ANT, and also suggest that UCP3 can minimize the induction of the ANT-mediated 'energy-wasting' process during CR.

Compromised respiratory adaptation and thermoregulation in aging and age-related diseases

Mitochondrial dysfunction and reactive oxygen species (ROS) production are at the heart of the aging process and are thought to underpin age-related diseases. Mitochondria are not only the primary energy-generating system but also the dominant cellular source of metabolically derived ROS. Recent studies unravel the existence of mechanisms that serve to modulate the balance between energy metabolism and ROS production. Among these is the regulation of proton conductance across the inner mitochondrial membrane that affects the efficiency of respiration and heat production. The field of mitochondrial respiration research has provided important insight into the role of altered energy balance in obesity and diabetes. The notion that respiration and oxidative capacity are mechanistically linked is making significant headway into the field of aging and age-related diseases. Here we review the regulation of cellular energy and ROS balance in biological systems and survey some of the recent relevant studies that suggest that respiratory adaptation and thermodynamics are important in aging and age-related diseases.

Effect of aging, caloric restriction, and uncoupling protein 3 (UCP3) on mitochondrial proton leak in mice

Mitochondrial proton leak may modulate reactive oxygen species (ROS) production and play a role in aging. The purpose of this study was to determine proton leak across the life span in skeletal mitochondria from calorie-restricted and UCP2/3 overexpressing mice. Proton leak in isolated mitochondria and markers of oxidative stress in whole tissue were measured in female C57BL/6J mice fed ad-libitum (WT-Control) or a 30% calorie-restricted (WT-CR) diet, and in mice overexpressing UCP2 and UCP3 (Positive-TG), their non-overexpressing littermates (Negative-TG) and UCP3 knockout mice (UCP3KO). Proton leak in WT-CR mice was lower than that of control mice at 8 and 26 months of age. The Positive-TG mice had greater proton leak than the Negative-TG and UCP3KO mice at 8 months of age, but this difference disappeared by 19 and 26 months. Lipid peroxidation was generally lower in WT-CR vs. WT-Control mice and UCP3KO mice had greater concentrations of T-BARS (thiobarbituric acid reactive substances, a measure of lipid peroxidation) than did Positive-TG and Negative-TG. The results of this study indicate that sustained increases in muscle mitochondrial proton leak are not responsible for alterations in life span with calorie restriction or UCP3 overexpression in mice. However, UCP3 may contribute to the actions of CR through mechanisms distinct from increasing basal proton leak.

Mitochondrial metabolism in hibernation and daily torpor: a review

Hibernation and daily torpor involve substantial decreases in body temperature and metabolic rate, allowing birds and mammals to cope with cold environments and/or limited food. Regulated suppression of mitochondrial metabolism probably contributes to energy savings: state 3 (phosphorylating) respiration is lower in liver mitochondria isolated from mammals in hibernation or daily torpor compared to normothermic controls, although data on state 4 (non-phosphorylating) respiration are equivocal. However, no suppression is seen in skeletal muscle, and there is little reliable data from other tissues. In both daily torpor and hibernation, liver state 3 substrate oxidation is suppressed, especially upstream of electron transport chain complex IV. In hibernation respiratory suppression is reversed quickly in arousal even when body temperature is very low, implying acute regulatory mechanisms, such as oxaloacetate inhibition of succinate dehydrogenase. Respiratory suppression depends on in vitro assay temperature (no suppression is evident below approximately 30 degrees C) and (at least in hibernation) dietary polyunsaturated fats, suggesting effects on inner mitochondrial membrane phospholipids. Proton leakiness of the inner mitochondrial membrane does not change in hibernation, but this also depends on dietary polyunsaturates. In contrast proton leak increases in daily torpor, perhaps limiting reactive oxygen species production.

Dietary Protein Restriction Decreases Oxidative Protein Damage, Peroxidizability Index, and Mitochondrial Complex I Content in Rat Liver

Caloric restriction (CR) decreases oxidative damage, which contributes to the slowing of aging rate. It is not known if such decreases are due to calories themselves or specific dietary components. In this work, the ingestion of proteins of Wistar rats was decreased by 40% below that of controls. After 7 weeks, the liver of the protein-restricted (PR) animals showed decreases in oxidative protein damage, degree of membrane unsaturation, and mitochondrial complex I content. The results and previous information suggest that the decrease in the rate of aging induced by PR can be due in part to decreases in mitochondrial reactive oxygen species production and DNA and protein oxidative modification, increases in fatty acid components more resistant to oxidative damage, and decreased expression of complex I, analogously to what occurs during CR. Recent studies suggest that those benefits of PR could be caused, in turn, by the lowered methionine intake of that dietary manipulation.

Energy expenditure and restriction of energy intake: could energy restriction alter energy expenditure in companion animals?

The treatment of obesity in companion animals frequently focuses on restriction of energy intake. One important question with this treatment is whether dietary energy restriction (ER) produces a sustained decrease in mass-adjusted energy expenditure (EE), which prevents further weight loss and promotes rapid regain of body weight during lapses in dietary ER. This review summarizes studies that investigated the effects of dietary ER on EE at the whole-animal, organ, and cellular level. Whole-animal studies indicate that long-term dietary ER either decreases or does not affect mass-adjusted EE. The reason for this discrepancy between studies is not entirely clear, although analysis of data pooled from multiple studies suggests that a reduction in mass-adjusted EE with long-term ER would be observed if the sample size were sufficiently large and appropriate methods were used to adjust EE for body size. At the organ level, attempts were made to determine whether alterations in organ mass can entirely explain changes in EE with dietary ER. However, these studies were not conclusive, and it remains to be determined whether changes in EE exceed those that would be predicted from ER-induced alterations in organ mass. At the cellular level, there is evidence that dietary ER may induce sustained decreases in substrate oxidation, mitochondrial proton, and Na+-K+-ATPase activity in at least some tissues. These results are consistent with the idea that dietary ER may induce decreases in cellular EE. However, future studies integrating measurements at the whole-animal, organ, and cellular level will be required to determine definitively whether dietary ER produces sustained decreases in tissue or cellular EE.

Bioenergetics of aging and calorie restriction

Aging is a physiological process that involves a multi-factorial set of deleterious changes. These alterations are caused by an exponential increase in damage to macromolecules. This process is likely due to the cumulative effects of oxidative stress over time. One area of ongoing research in gerontology has focused on determining why there is an age-dependent decrease in cellular bioenergetics. The aim of this review is to summarize the recent findings on the effects of aging and calorie restriction on energy metabolism. The effect of calorie restriction on age-associated changes in bioenergetic parameters will be examined.

Energy expenditures & physical activity in rats with chronic suboptimal nutrition

BACKGROUND

Sub-optimally nourished rats show reduced growth, biochemical and physiological changes. However, no one has assessed metabolic rate adaptations in rats subjected to chronic suboptimal nutrition (CSN). In this study energy expenditure (EE; kcal/100 g body weight) and physical activity (PA; oscillations in weight/min/kg body weight) were assessed in rats subjected to three levels of CSN.

RESULTS

Body weight gain was diminished (76.7 +/- 12.0 and 61.6 +/- 11.0 g) in rats fed 70 and 60% of the ad-libitum fed controls which gained more weight (148.5 +/- 32.3 g). The rats fed 80% gained weight similarly to controls (136.3 +/- 10.5 g). Percent Fat-free body mass was reduced (143.8 +/- 8.7 and 142.0 +/- 7.6 g) in rats fed 70 and 60% of ad-libitum, but not in those fed 80% (200.8 +/- 17.5 g) as compared with controls (201.6 +/- 33.4 g). Body fat (g) decreased in rats fed 80% (19.7 +/- 5.3), 70% (15.3 +/- 3.5) and 60% (9.6 +/- 2.7) of ad-libitum in comparison to controls (26.0 +/- 6.7). EE and PA were also altered by CSN. The control rats increased their EE and PA during the dark periods by 1.4 +/- 0.8 and 1.7 +/- 1.1 respectively, as compared with light the period; whereas CSN rats fed 80 and 70% of ad-libitum energy intake had reduced EE and PA during the dark periods as compared with the light period EE(7.5 +/- 1.4 and 7.8 +/- 0.6 vs. 9.0 +/- 1.2 and 9.7 +/- 0.8; p < 0.05, respectively), PA(3.1 +/- 0.8 and 1.6 +/- 0.4 vs. 4.1 +/- 0.9 and 2.4 +/- 0.4; p < 0.05) and RQ (0.87 +/- 0.04 and 0.85 +/- 0.5; vs. 0.95 +/- 0.03 and 0.91 +/- 0.05 p < 0.05). In contrast, both light (7.1 +/- 1.4) and dark period (6.2 +/- 1.0) EE and PA (3.4 +/- 0.9 and 2.5 +/- 0.5 respectively) were reduced in rats fed 60% of ad-libitum energy intake.

CONCLUSION

CSN rats adapt to mild energy restriction by reducing body fat, EE and PA mainly during the dark period while growth proceeds and lean body mass is preserved. At higher levels of energy restrictions there is decreased growth, body fat and lean mass. Moreover EE and PA are also reduced during both light and dark periods.

Lack of effect of caloric restriction on bioenergetics and reactive oxygen species production in intact rat hepatocytes

To investigate the hypothesis that caloric restriction alters mitochondrial function in situ, intact hepatocytes were isolated from fully fed and calorie-restricted (55% of control food intake, 4 months duration) male Brown-Norway rats at 6 months of age, and various parameters were determined. Overall, the production of reactive oxygen species was not affected by caloric restriction, neither were the mitochondrial membrane potential, oxygen consumption driving proton leak, or oxygen consumption driving ATP turnover. It is concluded that while isolated mitochondria from liver tissue of calorie-restricted animals display a reduction in the generation of reactive oxygen species, it was not possible to confirm this effect in isolated hepatocytes. Further work is required to establish what effect, if any, caloric restriction has on the rate of generation of reactive oxygen species in intact cells and tissues and importantly at the whole-animal level.

Kinetics and control of oxidative phosphorylation in rat liver mitochondria after dexamethasone treatment

The present investigation was undertaken in order to evaluate the contributions of ATP synthesis and proton leak reactions to the rate of active respiration of liver mitochondria, which is altered following dexamethasone treatment (1.5 mg/kg per day for 5 days). We applied top-down metabolic control analysis and its extension, elasticity analysis, to gain insight into the mechanisms of glucocorticoid regulation of mitochondrial bioenergetics. Liver mitochondria were isolated from dexamethasone-treated, pair-fed and control rats when in a fed or overnight fasted state. Injection of dexamethasone for 5 days resulted in an increase in the fraction of the proton cycle of phosphorylating liver mitochondria, which was associated with a decrease in the efficiency of the mitochondrial oxidative phosphorylation process in liver. This increase in proton leak activity occurred with little change in the mitochondrial membrane potential, despite a significant decrease in the rate of oxidative phosphorylation. Regulation analysis indicates that mitochondrial membrane potential homoeostasis is achieved by equal inhibition of the mitochondrial substrate oxidation and phosphorylation reactions in rats given dexamethasone. Our results also suggest that active liver mitochondria from dexamethasone-treated rats are capable of maintaining phosphorylation flux for cellular purposes, despite an increase in the energetic cost of mitochondrial ATP production due to increased basal proton permeability of the inner membrane. They also provide a complete description of the effects of dexamethasone treatment on liver mitochondrial bioenergetics.

Metabolism of normothermic woodchucks during prolonged fasting

The energy metabolism of hibernators has not been characterized for normothermic fasting, and our goal was to quantify oxidative fuel selection of non-hibernating woodchucks Marmota monax during prolonged food deprivation. Indirect calorimetry and nitrogen excretion measurements were used to assess changes in metabolic rate(V̇O2), fuel selection and composition of nitrogen wastes, as well as seasonal differences. For reference, matching experiments were also performed on rabbits. The results show that woodchucks have a higher metabolic rate in summer (271μmol O2 kg-1 min-1) than in spring (200μmol O2 kg-1 min-1) and that fasting-induced metabolic depression is only possible in summer (-25% in 14 days). The metabolic rate of rabbits is high at all times (383 μmol O2 kg-1 min-1), but they show a more rapid depression in response to fasting (-32% in 7 days). Woodchucks have a naturally low reliance on proteins in the fed state (accounting for 8%V̇O2 in spring;17% V̇O2 in summer; vs 28%V̇O2 in rabbits)and are able to decrease it even further during fasting (spring, 5%V̇O2; summer, 6%V̇O2; vs20% V̇O2 in rabbits). This study shows that, apart from their notorious capacity for hibernation, woodchucks are particularly well adapted for normothermic fasting. Their ability to cope with prolonged food deprivation is based on a series of integrated responses eliciting deep metabolic depression and a rapid change in fuel selection to spare limited protein reserves. Information presently available on prolonged fasting suggests that such an ability for metabolic depression, possibly down to minimal levels still compatible with normothermic life, may be common among mammals. In contrast, the extreme protein sparing demonstrated in woodchucks is a unique metabolic feature of fasting champions.

Ageing, oxidative stress, and mitochondrial uncoupling

Mitochondria are a cell's single greatest source of reactive oxygen species. Reactive oxygen species are important for many life sustaining processes of cells and tissues, but they can also induce cell damage and death. If their production and levels within cells is not effectively controlled, then the detrimental effects of oxidative stress can accumulate. Oxidative stress is widely thought to underpin many ageing processes, and the oxidative stress theory of ageing is one of the most widely acknowledged theories of ageing. As well as being the major source of reactive oxygen species, mitochondria are also a major site of oxidative damage. The purpose of this review is a concise and current review of the effects of oxidative stress and ageing on mitochondrial function. Emphasis is placed upon the roles of mitochondrial proton leak, the uncoupling proteins, and the anti-ageing effects of caloric restriction.