Yin yang

oxidative Medicine and celluar Longevity 227 Derived from classical Chinese philosophy and with frequent applications in Chinese medicine, " yin yang " has grown into an interesting concept that may have a number of applications. The term is usually used to depict the existence of polarizing or opposing forces in nature. Yet, the concept of " yin yang " can be much more involved, especially in biological systems, and pertain to events that not only are intimately connected, but also have significant repercussions upon each other. Interestingly, one does not need to search far in biology and medicine to learn of the concept of " yin yang. " For example, nicotinamide, which is the amide form of vitamin B3 (niacin), is a robust cytoprotectant that can scavenge reactive oxygen species during oxidative stress and increase survival of both neuronal and vascular cells during multiple injury paradigms that include anoxia, excitotoxicity, ethanol toxicity, and elevated glucose. Furthermore, nicotinamide also may limit inflammatory injury, protect against trauma, and improve cognition under some conditions. However, there is another side to nicotinamide that is relevant to the concept of " yin yang " and involves opposing forces with sirtuins. It appears that reduced concentrations of nicotinamide may be necessary to increase cell longevity to permit activity of sirtuins. Elevated concentrations of nicotinamide block the activity of sirtuins, agents that have been tied to increases in longevity and cellular protection such as during metabolic disorders with diabetes mellitus. Therefore, in relation to the biology of cell survival and cell longevity, a complex relationship exists between nicotinamide and sirtuins that require a careful balance to maximize cell survival and extend cell longevity. In this issue of Oxidative Medicine and Cellular Longevity, we present a unique group of papers that bring home the role of " yin yang " for our readers. In the review paper by Bouayed and Bohn, the authors take direct aim at the concept of " yin yang " in bringing to light the sometimes unrecognized and unexpected effects of exogenous antioxidants. Exogenous dietary antioxidants, such as vitamin C, vitamin E, carotenoids, and polyphenols, are necessary for the proper functioning of the endogenous cellular antioxidant system, but under certain conditions exogenous agents also may yield pro-oxidant behavior. As a result, the authors outline the intimate connections between oxidant and antioxidant pathways and the need to better align these systems. In the next review …