Nitric oxide, oxidative stress, and apoptosis.

Life demands intra- and intercellular communication in and between cells to respond and adapt to changes in the environment. Among signaling molecules, reactive oxygen (ROS) and nitrogen (RNS) species gained attention in facilitating intracellular communication and causing cell demise during pathology. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic, as well as antagonistic, effects. This is exemplified by using oxidized lipoproteins (oxLDL), or NO donors, in provoking the stabilization of two well recognized transcription factors, such as tumor suppressor p53 and hypoxia-inducible factor-1 alpha (HIF-1 alpha). Radical (i.e., superoxide) (O2-) formation in response to oxLDL is associated with p53, as well as HIF-1 alpha accumulation in human macrophages, a process that is antagonized by NO. On the other side, NO-elicited HIF-1 alpha stabilization is modulated by O2-. Thus, ROS- and RNS-signaling is important in understanding cell physiology and pathology, with the notion that marginal changes in the flux rates of either NO or O2- may shift vital signals used for communication into areas of pathology in close association with human diseases.