Regulation of nitric oxide synthesis by proinflammatory cytokines in human umbilical vein endothelial cells. Elevations in tetrahydrobiopterin levels enhance endothelial nitric oxide synthase specific activity.

Abstract

We have examined cytokine regulation of nitric oxide synthase (NOS) in human umbilical vein endothelial cells (HUVEC). 24-h treatment with IFN-'y (200 U/ml) plus TNF (200 U/ml) or IL-1,8 (5 U /ml) increased NOS activity in HUVEC lysates, measured as conversion of I '4C IL-arginine to Essentially, all NOS activity in these cells was calcium dependent and membrane associated. Histamine-induced nitric oxide release, measured by chemiluminescence, was greater in cytokine-treated cells than in control cells. Paradoxically, steadystate mRNA levels of endothelial NOS fell by 94±2.0% after cytokine treatment. Supplementation of HUVEC lysates with exogenous tetrahydrobiopterin (3 ,M) greatly increased total NOS activity, and under these assay conditions, cytokine treatment decreased maximal NOS activity. IFN-y plus TNF or IL-1,8 increased endogenous tetrahydrobiopterin levels and GTP cyclohydrolase I activity, the rate-limiting enzyme oftetrahydrobiopterin synthesis. Intracellular tetrahydrobiopterin levels were higher in freshly isolated HUVEC than in cultured cells, but were still limiting. We conclude that inflammatory cytokines increase NOS activity in cultured human endothelial cells by increasing tetrahydrobiopterin levels in the face of falling total enzyme; similar regulation appears possible in vivo.

Methylene Blue for Distributive Shock: A Potential New Use of an Old Antidote

“…Further evidence to support the role of the NO-cGMP pathway in anaphylaxis is demonstrated by the finding that increased histamine results in upregulation of eNOS gene expression with increased production of NO leading to vasodilation through increased activity of GC. Inhibition of GC reduces vasodilation induced by histamine [53][54][55]. This evidence provides support that histamine-induced vasodilation is at least partly mediated through the NO-cGMP pathway and that inhibition of this pathway reverses the vasodilation.…”

Induction of Endothelial Nitric Oxide Synthase Expression by IL-17 in Human Vascular Endothelial Cells: Implications for Vascular Remodeling in Transplant Vasculopathy

“…In support of the first possibility, IL-17 is a weaker activator of NF-kB than TNF-a (43). Interestingly, attenuation of eNOS expression by TNF-a is somewhat offset by increased eNOS enzymatic activity caused by this cytokine in human umbilical vein ECs (12). Increased eNOS enzymatic activity in this setting is due to a TNF-a-mediated increase in the production of the eNOS cofactor tetrahydrabiopterin.…”

“…eNOS-derived NO also regulates inflammation, immune responses, and angiogenesis (9). Inflammatory cytokines alter the expression and activity of eNOS, and the effects of different inflammatory and immunological conditions on eNOS may be distinct depending on the cytokine milieu (10)(11)(12).…”

Interactive role of nitric oxide and superoxide anion in neutrophil-mediated endothelial cell injury

“…Treatment of EC with the combination of cytokines, IFN-␥ and TNF-␣, demonstrated an additive effect in terms of NO generation. There have been extensive discussions on the ability of cytokines, either alone or in combination, to induce NOS expression [29,30]. The discrepancies in the pattern of inducible NOS (iNOS) expression might be attributed to the functional heterogeneity of vascular EC, depending on their source of isolation and calcium dependence of the NOS.…”