Influence of aging on the circadian patterns of thiobarbituric acid reactive substances and antioxidants in Wistar rats

Therapeutic effects of hydro-alcoholic leaf extract of Withania somnifera on age-induced changes in daily rhythms of Sirt1, Nrf2 and Rev-erbα in the SCN of male Wistar rats

The temporal expression pattern of the circadian clock genes are known to be altered/attenuated with advance in age. Withania somnifera (WS) essentially consists of numerous active constituents including withanolides is known to have antioxidant, anti-inflammatory and adaptogenic properties. We have earlier demonstrated therapeutic effects of hydro-alcoholic leaf extract of WS on the age-induced alterations in the levels and daily rhythms of various clock genes such as rBmal1, rPer1, rPer2 and rCry1. We have now studied effects of hydro-alcoholic leaf extract of WS on the age-induced alterations in the levels and daily rhythms of expression of SIRT1 (an NAD⁺ dependent histone deacetylase and a modulator of clock) and NRF2 (a clock controlled gene and a master transcription factor regulating various endogenous antioxidant enzymes) in addition to rRev-erbα in SCN of adult [3 months (m)], middle-aged (12 m) and old-aged (24 m) male Wistar rats. The daily rhythms of rNrf2 expression showed 6 h phase delay in middle age and 12 h phase advance in old age. WS restored rSirt1 daily rhythms and phase in old age whereas it restored the phase of rNrf2 in the SCN of both middle and old aged animals. At protein level, SIRT1 expression showed phase advances in 12 m and 24 m whereas NRF2 daily rhythms were abolished in both the age groups. WS restored the phase and daily rhythms of SIRT1 as well as NRF2 in 12 m old rats. However, rRev-erbα expression was found insensitive to WS treatment in all the age groups studied. Pairwise correlation analysis demonstrated significant stoichiometric interactions among rSirt1, rNrf2 and rRev-erbα in 3 m which altered with aging significantly. WS treatment resulted in differential restorations of such interactions.

Aging modifies daily variation of antioxidant enzymes and oxidative status in the hippocampus

BACKGROUND

Aging is a complex and multifactorial biological process that leads to the progressive deterioration of physiological systems, including the circadian system. In addition, oxidative stress has been associated with the aging of the normal brain and the development of late-onset neurodegenerative diseases. Even though, functional weakening of circadian rhythms and antioxidant function has been observed during aging, the mechanisms by which the circadian system signaling and oxidative stress are interrelated have not yet been elucidated. The objectives of this study were to evaluate the consequences of aging on the temporal organization of the antioxidant defense system and oxidative status as well as to analyze the endogenous clock activity, in the hippocampus of aged rats.

METHODS

Young adults (3-month-old) or older (22-month-old) male Holtzman rats were maintained under constant darkness conditions, during 15days before the sacrifice. Levels of catalase (CAT) and glutathione peroxidase (GPx) mRNA and activity, reduced glutathione (GSH), lipoperoxidation (LPO) and BMAL1 protein were analyzed in hippocampus samples isolated every 4h during a 24-h period. Locomotor activity was recorded during 20days before the experiment.

RESULTS

Our results show that aging modifies temporal patterns of CAT and GPx expression and activity in the hippocampus in a different way. On the one hand, it abolishes the oscillating CAT expression and specific enzymatic activity while, on the other, it increases the mesor of circadian GPx activity rhythm (p<0.01). Additionally, we observed increased GSH (p<0.05) and reduced LPO (p<0.01) levels in the hippocampus of aged rats. Moreover, the nocturnal locomotor activity was reduced in the older animals in comparison to the young adult rats (p<0.01). Interestingly, the 22month-old animals became arrhythmic and showed a marked fragmentation as well as a significant decline in daily locomotor activity when they were maintained under constant darkness conditions (p<0.05). Aging also abolished circadian rhythms of the core clock BMAL1 protein.

CONCLUSION

The loss of temporal organization of the antioxidant enzymes activity, the oxidative status and the cellular clock machinery could result in a temporally altered antioxidant defense system in the aging brain. Learning about how aging affects the circadian system and the expression of genes involved in the antioxidant defense system could contribute to the design of new strategies to improve the quality of life of older people and also to promote a healthy aging.

Molecular mechanisms of the circadian clockwork in mammals

Circadian rhythms enable organisms to co-ordinate biological processes with the predictable 24 h cycle of day and night. Given that molecular clocks that coordinate such biological timing have evolved in almost all organisms, it is clear that being synchronous with the external environment confers competitive advantage. Conversely, it is apparent that being out of phase is detrimental, resulting in a number of clinical conditions, many of which are linked to metabolic dysfunction. The canonical clockwork involves a core set of genes that negatively regulate themselves through a so-called transcription translation feedback loop. However, recent studies describing evolutionarily conserved oscillations in redox reactions link circadian rhythms to metabolic processes, and in particular, redox pathways. In this review we describe the evidence for the interaction between transcriptional loops, redox and metabolism in mammals and suggest the clock may be potential target for the treatment of disease.

Melatonin administration differentially affects age-induced alterations in daily rhythms of lipid peroxidation and antioxidant enzymes in male rat liver

A central clock/pacemaker, suprachiasmatic nuclei of the hypothalamus coordinates and entrains circadian oscillations in the peripheral tissues such as the liver, kidney, heart, lungs etc. called peripheral clocks. These also have endogenous circadian oscillations. The circadian rhythms of antioxidants present in cytosol signify redox state of the cell during day/night cycle. The liver has a major impact on homeostasis through its control on serum protein composition and plays a pivotal role in the metabolism of nutrients, drugs, hormones, and metabolic waste products and undergoes substantial changes in structure and function upon aging. In present study, the temporal patterns of oxidative stress indicators in liver were studied. Daily rhythms of lipid peroxidation end products, reduced glutathione (GSH), oxidized glutathione (GSSG) and antioxidant enzymes such as glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) were studied in liver at variable time points (Zeitgeber Time (ZT) 0, 6, 12 and 18) in three age groups: 3 (adult), 12 and 24 months old male Wistar rats. There was increase in oxidative stress in 12 and 24 months old rats indicated through a significant increase in lipid peroxidation, decrease in GSH/GSSG ratio and antioxidant enzyme activities. In 3 months old rats, lipid peroxidation was maximum at ZT-12 whereas GSH, SOD and CAT activities were minimum at ZT-12. The maximum level in 24 h i.e., acrophases of lipid peroxidation, GPx, SOD and CAT activities in liver cell free extracts altered upon aging. As melatonin, messenger of darkness, an endogenous synchronizer of rhythm, an antioxidant and an antiaging drug, declines with aging we studied the effects of melatonin on activities of these antioxidant enzymes in aging rats. Melatonin administration resulted in differential restoration of acrophases, amplitude, mean as well as daily rhythms of lipid peroxidation and antioxidants in liver of 12 and 24 months old rats.