Circadian rhythms (CRs) are intrinsic clocks organizing the behavior and physiology of organisms. These clocks are thought to have coevolved with cellular redox regulation. Metabolism, redox homeostasis, circadian clock, and diet offer insights into aging. Mitochondria play a pivotal role in redox homeostasis, CR, and aging. Melatonin is synthesized in mitochondria, is the key regulator of CRs, and shows substantial antioxidative effects. Melatonin levels tend to decrease significantly with advancing age. Recent reports showed that disruptions of CRs may render aging populations even more susceptible to age-related disorders. Recent and high-quality articles investigating CR, redox homeostasis, aging, and their relationship during aging process were included. Putting special emphasis on the possible effects of melatonin on redox homeostasis and mitochondrial dynamics, recent clinical evidence highlighting the importance of circadian mechanisms was utilized. A deeper understanding of the role of altered mitochondrial redox homeostasis in the pathogenesis of age-related disorders and its relationship with CR could offer novel therapeutic interventions. Chronotherapy, a therapeutic approach considering CR of organisms and best therapeutic times, could potentially reduce side effects and improve therapeutic efficiency. Redox homeostasis, energy metabolism, and CR are all intertwined.

Introduction. The effect of aging on plasma-protein, lipid and DNA oxidation is well documented. However, none of the studies specify the effect of gender. The purpose of this study is to clarify the ambiguity raised in preliminary reports as to gender dependency of oxidative damage in plasma. Methods. In the current study, we investigated the relation between 8-hydroxy-2′-deoxyguanosine levels (8-OHdG), which is a measure of DNA oxidation and protein oxidation parameters such as protein carbonyl (PCO), total thiol (T-SH), and advanced oxidation protein products (AOPP). Our study also covered other oxidative stress parameters, such as lipid hydroperoxides (LHP), malondialdehyde (MDA), erythrocyte glutathione (GSH), superoxide dismutase (Cu-Zn SOD) and the catalase (CAT) activity in plasma of the male and female aged rats. Results. 8-OHdG and MDA levels in male rats were significantly higher than those in the female group (p < 0.01 for both parameters). T-SH levels were found to be higher in female rats than in the male (p < 0.05). Plasma Cu-Zn SOD activities of male rats were significantly higher compared with those of the female rats (p < 0.05). On the other hand, PCO, AOPP, LHP, GSH levels, and CAT activity were not found to be different between genders. Conclusions. We suggest that increased T-SH levels found in female rats may point to an adaptive reaction to oxidative damage, reflecting 8-OHdG and MDA overproduction. We are of the conviction that the increased 8-OHdG and MDA that we have determined in aged male rats may be a risk factor in the extent of oxidation in plasma.