Nitric Oxide as a Bifunctional Regulator of Apoptosis

t was inevitable that important relationships between two of the most intensely studied topics in biomedical research, apoptosis and nitric oxide (NO), would become apparent. Apoptosis is essential to normal development as well as physiological cell turnover. Although apoptosis in excess can manifest as tissue damage, a failure to undergo apoptosis constitutes pathological cellular overgrowth. It is now evident that NO and its reaction products can either promote or prevent apoptosis in a multitude of settings. The ubiquitous distribution of the NO synthases and the remarkable diffus- ibility and diverse chemical reactivity of NO in biological systems make this molecule unique among the regulators of apoptosis. Understanding the factors that govern the conse- quences of NO exposure on cell viability and identifying the conditions in which NO regulation of apoptosis contribute to pathology are topics of considerable interest and potential importance. In this article, we will review the recent obser-