L-arginine metabolites regulate DNA synthesis and nitric oxide synthase activity in cultured human dermal microvascular endothelial cells--potential positive and negative regulators of angiogenesis derived from L-arginine.
Human dermal microvascular endothelial cell (HDMVEC) growth and proliferation is important for skin angiogenesis. Our data support the hypothesis that a regulatory switch from an angiogenic to a nonangiogenic stimulus involves a change in l-arginine metabolism from polyamines (PAs) to nitric oxide (NO) and, conversely, a change to an angiogenic stimulus is expected to drive l-arginine metabolism in favor of PA synthesis. Current studies with cultured HDMVECs demonstrated that NO inhibited, whereas the PA putrescine stimulated DNA synthesis. The nitric oxide synthase (NOS) inhibitor NG-nitro l-arginine methyl ester stimulated DNA synthesis with a significant increase from control at 2.5 and 5 mM (p < 0.05); in contrast, the ornithine decarboxylase (ODC) inhibitor alpha-difluoromethyl ornithine (DFMO) inhibited DNA synthesis with a significant decrease from control at 19.65, 29.48, and 39.48 microM (p < 0.05). NO donors sodium nitroprusside dihydrate, S-nitroso-N-penicillamine, and l-hydroxy-2-oxo-3(3-aminopropyl)-3-propyl-triazine all inhibited DNA synthesis. There was a significant increase in NOS activity with DFMO treatment (p < 0.05) and a less pronounced decrease in NOS activity with direct PA treatment. In summary, NO and PAs are important mediators of HDMVEC growth and PAs downregulate NOS activity in these cells. NOS and ODC enzyme products may not only be important components in the regulation of angiogenesis in the skin but they may also regulate their own synthesis via feedback mechanisms.