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

Abstract

Energy restriction (ER), without malnutrition, is the only environmental intervention that consistently increases maximum life span in laboratory rodents. One theory proposes that a reduction in energy expenditure and reactive oxygen species production is the mechanism responsible for this action of ER. To further test this theory, proton leak, H2O2 production, lipid peroxidation, and protein carbonyls were measured in mitochondria from FBNF1 rats fed either a control or 40% ER diet (onset at 6 mo of age). Liver mitochondria were isolated at 7 and 12 mo of age. Liver weight decreased 25 and 36% at 1 and 6 mo of ER, respectively (P < 0.05). ER resulted in an increase (P < 0.05) in percent total polyunsaturates, n-6 polyunsaturates, and total unsaturates (6 mo only) in mitochondrial lipids. These changes, however, were not associated with significant alterations in mitochondrial function. State 4 respiration and membrane potential were not different (P > 0.05) between groups at either assessment period. Similarly, proton leak kinetics were not different between control and ER animals. Top-down metabolic control analysis and its extension, elasticity analysis, were used at the 6-mo assessment and revealed no difference in control of the oxidative phosphorylation system between control and ER rats. H2O2 production with either succinate or pyruvate/malate substrates was also not different (P > 0.05) between groups at either time point. In conclusion, ER did not alter proton leak or H2O2 production at this age or stage of restriction in liver.

Liver mitochondrial properties from the obesity-resistant Lou/C rat

“…28 Nevertheless, the widespread notion of a reduced rate of H 2 O 2 generation by liver mitochondria with CR was recently challenged by some authors. 26,29 Thus, a similar reduction in caloric intake (B40%) for 4-8 weeks was found either to decrease 25 or to enhance 29 mitochondrial H 2 O 2 production. Such discrepancies were also found when CR was extended to 4-6 months 29,35 or 12-18 months.…”

“…26,29 Thus, a similar reduction in caloric intake (B40%) for 4-8 weeks was found either to decrease 25 or to enhance 29 mitochondrial H 2 O 2 production. Such discrepancies were also found when CR was extended to 4-6 months 29,35 or 12-18 months. 26,28 In the present study, we found that isolated liver mitochondria from Lou/C rats, which display an inborn LCI, [1][2][3][7][8][9]14,15 produced more H 2 O 2 than Wistar rats fed ad libitum or even pair-fed.…”

“…The ROS generation in liver is well documented, [25][26][27][28][29][30] and many cellular sources of ROS production have been identified, including plasma membrane NADPH oxidase and xanthine, peroxisomal and endoplasmic reticular oxidases. However, it is now generally accepted that mitochondrial electron transport chain represents the major source of ROS.…”

“…However, it is now generally accepted that mitochondrial electron transport chain represents the major source of ROS. [25][26][27][28][29][30][31] While it was initially thought that complex III was the main or even the only site of ROS generation, 32 recent investigations unequivocally demonstrated that respiratorychain complex I is the major generator of free radicals in liver mitochondria. 16,31 One of the most important finding of our study is the demonstration that in the absence of any inhibitor, hepatic mitochondria energized with G/M/S generated H 2 O 2 to a significant extent (Figure 1).…”

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

“…[51][52][53] Another large body of work demonstrates that ROS release from mitochondria or tissues from CR animals is decreased. 37,[53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] Other publications found no changes in ROS production with CR 46,[68][69][70][71] and many propose that CR-induced decreases in ROS release depend on tissues examined, time on the diet, animal age when the diet was initiated, and gender. No experimental publication was located demonstrating that CR in rodents enhances ROS generation in non-inflammatory tissues.…”