51] Assay of inducible form of nitric oxide synthase activity: Effect of flavonoids and plant extracts

Abstract

This chapter describes a quantitative assay procedure based on the use of radioisotope-labeled arginine for nitric oxide synthase inductive NOS (iNOS) enzyme activity, and summarizes the efficacy of either various purified flavonoids or the folk herbal medicines, Ginkgo biloba extract and Pinus rnarittima proprietary extract. iNOS—which tightly binds calmodulin even in the absence of calcium—is expressed by some cell types following stimulation with proinflammatory mediators such as cytokine or with the bacterial wall component lipopolysaccharide (LPS). Therefore, while the activity of the constitutive isoforms of NOS is mainly regulated by cytosolic calcium levels, iNOS activity depends on the amount of expressed enzyme essentially regulated at the transcriptional or posttranscriptional level. NO overproduction by iNOS is considered as a biological process potentially leading to opposite outcomes, either physiological or pathological, depending on the ability of cells or tissues to control both the expression of iNOS activity and the nonspecific effects of nitric oxide(NO).The chapter concludes with a discussion of the effects of flavonoids and natural plant extracts on iNOS activity.