Treatment of psoriasis with topical NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis

A double blind left, right comparative study was carried out in 17 psoriatic subjects to examine the influence of a topically applied inhibitor of nitric oxide (NO) synthesis on the pathogenic events of psoriasis. The inhibitor NG-monomethyl-L-arginine (L-NMMA) in aqueous cream BP was applied to one plaque while aqueous cream BP alone served as control. Compared with the control, the L-NMMA-treated side showed significant (77%) inhibition of NO production and a reduction in blood flow, confirming its bioavailability. L-NMMA significantly reduced staining for endothelial cells and intercellular adhesion molecule 1, while CD1a-positive Langerhans cells and CD8-positive suppressor cytotoxic T cells increased. CD4-positive lymphocytes and epidermal proliferation, as indicated by Ki-67 staining, were unaffected by this degree of inhibition of NO synthesis, and correspondingly significant clinical improvement was not found.