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Introduction
Increased rates of population aging are causing the problems associated with aging to attract increasing attention. By the year 2050, the number of individuals over the age of 80 will triple globally (1). More than 70% of individuals over 65 years of age suffer from at least two chronic diseases, such as heart disease, stroke, cancer, arthritis and diabetes (2). Studies of food or medicine as a means of extending longevity have been taking place since ancient times.
The underlying mechanisms of aging remain unknown, despite tremendous progress being made in this area. There is growing evidence to suggest that oxidative stress increases with age (3). The endogenous enzymes, superoxide dismutase (SOD) and catalase (CAT), are involved in the human antioxidant defense network of human (4). Lipofuscin (LF) accumulation, which is deemed to be a hallmark of aging (5), has been shown to be related to the loss of protein homeostasis (6) and the rate of accumulation has been linked to age-dependent mortality (7).
Recently, great interest has arisen in the possibility that antioxidants, particularly naturally occurring antioxidants from edible materials, may reduce the risk of aging (8).
Cordyceps sinensis, one of the most valued edible, medical entomopathogenic fungi, used in traditional Chinese medicine for thousands of years, is commonly used as a tonic for promoting vitality and longevity, as well as a herbal medicine for treating various intractable diseases (9,10). It has been demonstrated to possess multiple pharmacological properties, such as antioxidant (11), immunomodulatory (12) and anti-tumor (13) properties. Furthermore, Cordyceps sinensis extract has been reported to improve learning and memory function in a mouse model of D-galactose-induced aging (14). The aqueous polysaccharides of Cordyceps taii have been shown to possess antioxidant activity in a mouse model of D-galactose-induced aging (15). However, to the best of our knowlewdge, the anti-aging effects of Cordyceps sinensis in vivo, under physiological conditions, have not been confirmed to date.
Cordyceps sinensis oral liquid (CSOL) was studied and manufactured by the Naval Medical Research Institute (Shanghai, China) (16), and has been used as an immunomodulator, an adjunctive therapy during chemoradiation treatment and to ameliorate chronic bronchitis more than twenty years (17). In a previous study of ours, we demonstrated that CSOL inhibited damage induced...