nitroarginine and baicalin

Stress induced by ultraviolet-B (UV-B) irradiation stimulates the accumulation of various secondary metabolites in plants. Nitric oxide (NO) serves as an important secondary messenger in UV-B stress-induced signal transduction pathways. NO can be synthesized in plants by either enzymatic catalysis or an inorganic nitrogen pathway. The effects of UV-B irradiation on the production of baicalin and the associated molecular pathways in plant cells are poorly understood. In this study, nitric oxide synthase (NOS) activity, NO release and the generation of baicalin were investigated in cell suspension cultures of Scutellaria baicalensis exposed to UV-B irradiation. UV-B irradiation significantly increased NOS activity, NO release and baicalin biosynthesis in S. baicalensis cells. Additionally, exogenous NO supplied by the NO donor, sodium nitroprusside (SNP), led to a similar increase in the baicalin content as the UV-B treatment. The NOS inhibitor, Nω-nitro-l-arginine (LNNA), and NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) partially inhibited UV-B-induced NO release and baicalin accumulation. These results suggest that NO is generated by NOS or NOS-like enzymes and plays an important role in baicalin biosynthesis as part of the defense response of S. baicalensis cells to UV-B irradiation.

Topics: Benzoates; Cells, Cultured; Enzyme Inhibitors; Flavonoids; Imidazoles; Molecular Structure; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Plant Cells; Scutellaria baicalensis; Signal Transduction; Time Factors; Ultraviolet Rays

We previously reported that oroxylin A, a polyphenolic compound, was a potent inhibitor of lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In the present study, three oroxylin A structurally related polyphenols isolated from the Chinese herb Huang Qui, namely baicalin, baicalein, and wogonin, were examined for their effects on LPS-induced nitric oxide (NO) production and iNOS and COX-2 gene expressions in RAW 264.7 macrophages. The results indicated that these three polyphenolic compounds inhibited LPS-induced NO production in a concentration-dependent manner without a notable cytotoxic effect on these cells. The decrease in NO production was in parallel with the inhibition by these polyphenolic compounds of LPS-induced iNOS gene expression. However, these three compounds did not directly affect iNOS enzyme activity. In addition, wogonin, but not baicalin or baicalein, inhibited LPS-induced prostaglandin E2 (PGE2) production and COX-2 gene expression without affecting COX-2 enzyme activity. Furthermore, N-nitro-L-arginine (NLA) and N-nitro-L-arginine methyl ester (L-NAME) pretreatment enhanced LPS-induced iNOS (but not COX-2) protein expression, which was inhibited by these three polyphenolic compounds. Wogonin, but not baicalin or baicalein, similarly inhibited PGE2 production and COX-2 protein expression in NLA/LPS or L-NAME/LPS-co-treated RAW 264.7 cells. These results indicated that co-treatment with NOS inhibitors and polyphenolic compounds such as wogonin effectively blocks acute production of NO and, at the same time, inhibits expression of iNOS and COX-2 genes.

Topics: Animals; Antioxidants; Blotting, Western; Cells, Cultured; Cyclooxygenase 2; Dinoprostone; Drug Interactions; Drugs, Chinese Herbal; Enzyme Inhibitors; Flavanones; Flavonoids; Gene Expression; Isoenzymes; Lipopolysaccharides; Macrophages; Mice; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Prostaglandin-Endoperoxide Synthases

To examine the role of endothelium in the vascular responses to flavonoids, baicalein, baicalin, cardamonin, alpinetin, and to purified jasmine green tea (-)epicatechin in the isolated rate mesenteric artery rings.. The isometric contraction was measured by Grass force-displacement transducers.. Both baicalein and baicalin enhanced the phenylephrine-induced contractile response in the endothelium-intact rings. This enhancement was abolished by pretreatment with the nitric oxide inhibitor NG-nitro-L-arginine or in the absence of the endothelium. Both flavonoids also inhibited the acetylcholine-induced endothelial nitric oxide-dependent relaxation. In contrast, cardamonin, alpinetin or (-)epicatechin induced both endothelium-dependent and -independent relaxation. NG-nitro-L-arginine meyhyl ester or endothelium denudation attenuated the endothelium-dependent relaxation to the same extent.. Baicalein and baicalin enhanced the phenylephrine-induced contraction most likely through inhibiting production or/and release of endothelial nitric oxide. Whilst, cardamonin-, alpinetin- or (-)epicatechin-induced endothelium-dependent relaxation is primarily mediated through endothelial nitric oxide.

Topics: Animals; Catechin; Endothelium, Vascular; Flavanones; Flavonoids; In Vitro Techniques; Male; Mesenteric Arteries; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley