Impact of exercise, reactive oxygen and reactive nitrogen species on tumor growth

Abstract

Physical activity results in numerous health benefits. Specifically, regular exercise reduces the risk of developing cardiovascular disease, metabolic syndrome, and cancer. The exercise-induced health benefits are attributed to alterations in hormone levels, growth factors, decreased obesity, and/or decrease in pro-in flammatory mediators. In addition to these factors, exercise-induced reactive oxygen species (ROS) and reactive nitrogen species (RNS) production has drawn a lot of attention in recent years. In this regard, during exercise the production of ROS and RNS increases in the body. It is now well accepted that physiological levels of ROS/RNS produced during exercise play an important role in cells including the control of gene expression and regulation of cell signaling pathways. However, high levels of ROS/RNS can damage cellular components. For example, excessive ROS and RNS can directly damage DNA by causing DNA base modifications leading to carcinogenesis. Although the production of ROS/RNS increases during muscular contractions, exercise also promotes the upregulation of several antioxidant enzymes that can counteract the increased production of these oxidants. Therefore, exercise can have differential effects on carcinogenesis. For example, moderate physical activity increases the expression of endogenous antioxidants that may protect against a carcinogenic event. In contrast, regular bouts of exhaustive exercise have been shown to impair the immune system and could reduce immune-surveillance and increase the risk of some cancers. Therefore, identifying the optimal amount of physical activity that can lead to cancer-preventive effects is of paramount importance.