Oxidative Stress, Cancer and Antioxidant: A symbiosis?

Abstract

The imbalance production of free radicals and reactive metabolites known as reactive oxygen species (ROS) and their elimination, will developed oxidative stress. ROS are playing dual roles as deleterious or beneficial species. At low level, they act as messengers in cell signaling and play a role in maintaining homeostasis whereas at higher concentration will cause cellular redox imbalance. This event is commonly occurred in cancer cells compared to normal cells. The oxidative DNA damage occurs as a result of elevated level of ROS causing single or double strand DNA breaks, replication errors, base modification, base oxidation, DNA cross-linking which leads to cell dysfunction and cell death. Taking antioxidant such as polyphenolic compounds is believed to exert anticancer effect due to ROS manifestations. Studies with flavonoids compounds exerted anticancer activity through modulation of ROS-scavenging enzyme activities, cell cycle arrest, induction of apoptosis, autophagy, and suppression of cancer cell proliferation and invasiveness. However, the mechanisms responsible for this anticancer effect have not been fully understood. Most of the laboratory and animal studies exhibited increased levels of exogenous antioxidants which prevent the types of free radical damage associated with cancer development. Few clinical studies in human were conducted with aim to observe possibilities of lowering risk of developing or dying from cancer upon taking dietary supplements. The dietary antioxidant supplements which were tested on human subjects were beta carotene, tocopherol, alpha tocopherol, vitamin C, selenium and zinc. These studies have yielded mixed results. In some preclinical studies, antioxidants have been found to promote tumor growth and metastasize. In tumor-bearing mice the supplements given had increased the ability to circulate tumor cells to metastasize. In conclusion, the mechanism of antioxidant action in cancer treatment is poorly understood. Many factors need to be considered before taking or giving antioxidant supplement since there were reports pertaining to benefits and disadvantages of antioxidant in cancer treatment.