Repletion of antioxidant status by EGCG and retardation of oxidative damage induced macromolecular anomalies in aged rats
Introduction
Ageing is a process that results in the loss of cellular function with resultant increase in mortality and represents the major risk factor for a plethora of age related diseases (Squier, 2001). It was proposed 51 years ago that free radicals are one of the major factors involved in the ageing process (Harman, 1956). The main notion was that ageing is caused by the accumulation of free radical-elicited oxidative damage to various biological molecules in tissue cells. It is known that small, but significant amount of electrons which leak from the electron transport chain generate reactive oxygen species (ROS) as hydroxyl radicals (Leeuwenburgh et al., 1999) and the superoxide radicals (Cadenas et al., 1977). ROS mediated lipid peroxidation and DNA damage is associated with a variety of chronic health problems (Marnett, 2000). Under normal physiological conditions, the ROS generated by the respiratory chain is scavenged by enzymic and non-enzymic antioxidant systems to prevent deleterious oxidative damage to the cell.
As the organism ages, ROS production increases, while antioxidants status declines, leading to accumulation of age associated damaged macromolecules, which further enhances ROS production. This vicious cycle cannot be terminated, while it can be interrupted by intervention of antioxidants supplementation. Plant and food derived antioxidants have been found beneficial in protecting against several diseases and hence antioxidant therapy has become an attractive therapeutic strategy (Rice-Evans and Diplock, 1993). Tea (Camellia sinensis) has been widely consumed as beverage besides water. Green tea and its constituent catechins namely (−)-epicatechin (EC), (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin-3-gallate (EGCG), catechin and gallocatechin are best known for their antioxidant properties, which have led to their evaluation in a number of diseases associated with ROS. The health benefits of green tea are mainly attributed to its antioxidant properties and abilities of its polyphenolic catechins to scavenge ROS (Yang, 1999).
The potent antioxidative actions of green tea are associated with ECG and EGCG because their chemical structures have galloyl moieties, which is absent in other catechins. Moreover, only EGCG has two triphenolic groups in its chemical structure. Therefore, these specific structural characteristics must affect antioxidative potency (Osada et al., 2001). Numerous in vitro studies reveal that, EGCG scavenges a wide range of free radicals including singlet oxygen, superoxide anions, peroxyl radicals and also the most active hydroxyl radicals, which initiates lipid peroxidation (Nanjo et al., 1996, Jovanovic and Simic, 2000). Hence, the present study was initiated with a notion to identify tea as an anti-senescent beverage, and to extend its beneficial effects to retard age associated derangements.
Section snippets
Source of chemicals
EGCG and bovine serum albumin (BSA) were purchased from Sigma chemicals, St. Louis, MO, USA. All other chemicals used were of analytical and reagent grade.
Animals
Male albino Wistar rats weighing approximately 130–160 g (young, 3–4 months old) and 380–410 g (aged, 24 months old) were used. Animals were maintained as per national guidelines and protocols, approved by the Institutional Ethical Committee (IAEC No.: 02/079/07). The animals were housed two per cage in large spacious cages under conditions of
Liver
Table 1 reveals the effect of EGCG on the levels of hepatic LPO in young and aged rats. A significant increase in LPO levels were observed in aged rats when compared with young rats. The hepatic tissue of aged control rats showed a 2.2, 1.7 and 1.5-fold increase in basal LPO, ferrous sulphate induced LPO and ascorbate induced LPO respectively. EGCG supplementation to aged rats brought down the levels of LPO by approximately 49% (basal LPO), 37% (ferrous sulphate induced LPO) and 30% (ascorbate
Discussion
The present study was aimed to evaluate the modulatory role of EGCG in alleviating age associated oxidative disturbances in various biological molecules, with special emphasis on mitotic tissue-liver and post-mitotic tissue-skeletal muscle.
A significant increase in basal, ferrous sulphate as well as ascorbate induced LPO were observed in the liver and skeletal muscle of aged rats. This is in agreement with the report by Sagai and Ichinose (1980) and Savitha et al. (2005). Increased free radical
Conclusion
It can be concluded from the above study that EGCG has a potency in mitigating age associated oxidative disturbances, by reducing LPO and protein carbonyl content. On the other hand, it enhances the antioxidant status and glutathione redox system in aged rats. This botanical supplement with immense potential can complement the depleted antioxidant status associated with ageing and have a check on augmentation of dysfunction in mitotic and post-mitotic organs.
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