Reactive nitrogen intermediates in human neuropathology: an overview
Abstract
Nitric oxide (NO) is a recently recognized messenger molecule that has been shown to possess pleiotropic properties, including vasodilation, neurotransmission, cytotoxicity and antimicrobial activity. Constitutive and inducible forms of NO synthase (NOS) have been identified. Activation of cNOS releases relatively low levels of NO for short periods of time whereas induction of iNOS releases high levels of NO for extended periods of time. In rodents, iNOS is predominantly found in cells of the monocyte/macrophage series, including microglia, where it is induced by a combination of bacterial products and cytokines. cNOS and iNOS have also been reported in rodent astrocytes. Activation of iNOS in the CNS could be toxic to many different cell types, including neurons and oligodendrocytes. iNOS, however, has been difficult to demonstrate in human peripheral blood cells, suggesting that the regulation of expression of this enzyme in humans is different from that found in rodents. In this overview, we show that in human glial cells cultured in vitro, astrocytes, but not microglia, can be induced by cytokines to express NO-like activity. Bacterial products are without effect, but a combination of IL-1 and TNF alpha or IFN gamma is a po...Continue Reading
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