Induction of tetrahydrobiopterin synthesis in rat cardiac myocytes: impact on cytokine-induced NO generation

Abstract

Because tetra-hydrobiopterin (BH4) is an essential cofactor for nitric oxide (NO) formation, we investigated whether BH4 synthesis is required for cytokine-induced NO production in cultured rat cardiac myocytes. The total biopterin content of untreated cardiac myocytes was below our limit of detection. However, treatment with interleukin-1 alpha (IL-1 alpha) + interferon-gamma (IFN-gamma) caused a significant rise in biopterin levels and induced NO synthesis. 2,4-Diamino-6-hydroxypyrimidine (DAHP), a selective inhibitor of GTP cyclohydrolase I (the rate-limiting enzyme for de novo BH4 synthesis), completely abolished the elevation in biopterin levels induced by IL-1 alpha + IFN-gamma. DAHP also caused a concentration-dependent inhibition of (IL-1 alpha + IFN-gamma)-induced NO synthesis. Similarly, N-acetylserotonin, an inhibitor of the BH4 synthetic enzyme sepiapterin reductase, blocked increases in biopterin levels as well as NO synthesis induced by IL-1 alpha + IFN-gamma. Sepiapterin, substrate for BH4 synthesis via the pterin salvage pathway, prevented this inhibition by DAHP or N-acetylserotonin, and this effect was blocked by methotrexate. Sepiapterin and, to a lesser extent, BH4 dose dependently enhanced (IL-1 alpha + IFN-gamma)-induced NO synthesis, suggesting that the concentration of BH4 limits the rate of NO production. Inducible NO synthase mRNA and GTP cyclohydrolase I mRNA were induced by IL-1 alpha + IFN-gamma in parallel. We thus demonstrate that BH4 synthesis is an absolute requirement for induction of NO synthesis by cytokines in cardiac myocytes.

Anoxia/Reoxygenation-Induced Tolerance With Respect to Polymorphonuclear Leukocyte Adhesion to Cultured Endothelial Cells

“…Of particular relevance to the present study is the observation that the gene encoding for GTP-cyclohydrolase I contains an NF-B-binding site in the promoter region. 33 In addition, cytokine-induced NO production by endothelial cells, 21 myocytes, 34 and smooth muscle cells 23 is dependent on GTPcyclohydrolase I activity. Thus, taken together, our findings suggest that NF-B may contribute to the development of A/R tolerance by transactivating the gene encoding GTPcyclohydrolase I.…”

Cardiac Endothelial-Myocardial Signaling: Its Role in Cardiac Growth, Contractile Performance, and Rhythmicity

“…Excessive NO production secondary to the induction of iNOS in failing cardiac tissue would, as in septic shock (460,592), be expected to depress cardiac contraction. This idea has been strengthened further by the observation of high plasma and tissue levels of various cytokines, such as TNF-␣, known to induce iNOS (213,257,499,501,584). Others however, based on studies in pacing-induced cardiac failure in dogs, have questioned the role of plasma cytokines in the pathogenesis of cardiac failure (474).…”

Repression of proinflammatory cytokine and inducible nitric oxide synthase (NOS2) gene expression in activated microglia by N-acetyl-O-methyldopamine: Protein kinase a-dependent mechanism

“…Cytokineinduced NO production requires GTP cyclohydrolase I (GTPCH). GTPCH is the rate-limiting enzyme for synthesis of 6,7, ), an essential cofactor for activation of all isoforms of nitric oxide synthase (NOS) (Kwon et al, 1989;Tayeh and Marletta, 1989;Gross et al, 1991), and availability of BH 4 is known to regulate NOS activity (Werner-Felmayer et al, 1990;Rosenkranz-Weiss et al, 1994;Oddis and Finkel, 1996;Kasai et al, 1997).…”