HEAT-SHOCK PROTEINS AND MACROPHAGE RESISTANCE TO THE TOXIC EFFECTS OFNITRIC-OXIDE

Nitric oxide (NO) functions as a pathophysiological mediator in mammal ian tissues. Activated macrophages produce NO as a non-specific immune response directed against invading bacteria or micro-organisms. The s ame macrophages that initiate the production of NO also can be toxical ly affected by NO. Incubation of RAW 264.7 macrophages with lipopolysa ccharide (LPS) and/or interferon-gamma (INF-gamma) induced the formati on of NO by the activation of a cytokine-inducible NO synthase (NOS). The viability of these macrophages was inversely correlated with the f ormation of nitrite, a final NO-oxidation product measurable in the in cubation medium. The addition of an NOS inhibitor, N-G-monomethyl-L-ar ginine, diminished NO formation and preserved cell viability in a dose - and time-dependent fashion. Treatment of macrophages with ten cycles of non-lethal doses of LPS and INF-gamma, each followed by subculturi ng of the surviving cells, resulted in cell resistance to the NO toxic insult induced by LPS and INF-gamma. These resistant macrophages show ed a 2-fold increase in the expression of the constitutive heat shock protein (HSC 70) which is known to be involved in protecting cells aga inst the action of various metabolic insults. Our results establish a link between cell resistance to the toxic effects of NO, and the expre ssion of heat shock proteins in RAW 264.7 macrophages.