Nitric Oxide Theory of Aging

Interesting information on NO is oral cavity and gastric mucosa, and the role of bacteria in digestion of NO - which Andrea does a great job explaining as well. 

NO does appear to have beneficial qualities in allowing blood vessel dilation and increase blood flow to occur at needed times. On the other hand, these effects seem to be needed at times in cases due to disruption in normal function - such as by viral or endotoxin exposure (1,2). The NO theory of aging  suggests that repeated infections create progressive oxidative damage leading to coronary disease and neurodegenerative conditions (1,2). The principal mechanism tested is when bacterial lipopolysaccharides (LPS) injected, NO Synthetase is induced (via an IL-1) mediator within 2-4 hours (2). The blood brain barrier does not appear to keep LPS out of the central nervous system (3), and an intense NO response is seen in the brain (1,2). The effect of NO is to inactivate enzymes which leads to cell death of invading virus as well as host cells (1). Antioxidant vitamin C and E appear to be beneficial in attenuating the NO oxidant effect (1,2). 

Sources:

1/ McCann S et al. The nitric oxide theory of aging revisited. Ann N Y Acad Sci. 2005 Dec;1057:64-84.

2/McCann S et al. The nitric oxide hypothesis of aging. Exp Gerontol. 1998 Nov-Dec;33(7-8):813-26.

3/Wei-Ye L et al. Increasing the Permeability of the Blood–brain Barrier in Three Different Models in vivo. CNS Neuroscience & Therapeutics. 21 (2015) 568-574.