S-nitrosylated human alpha(1)-protease inhibitor

alpha(1)-Protease inhibitor (alpha(1)PI) is an acute phase plasma protein, and possesses a single cysteine residue at position 232. A single cysteinyl sulfhydryl of human alpha(1)PI is found to be readily S-nitrosylated by ni tric oxide (NO) in vitro without affecting the inhibitory capacity against bovine trypsin or elastase, a major target protease of alpha(1)PI in vivo. S-Nitroso-alpha(1)PI (S-NO-alpha(1)PI) was also formed by the reaction of a lpha(1)PI with NO produced excessively by a murine macrophage cell line (RA W264 cells) upon infection with Salmonella typhimurium and in an ex vivo pe rfusion system of the liver obtained from lipopolysaccharide-treated rats. S-NO-alpha(1)PI (10(-9)-10(-6) M) induces a dose-dependent relaxation of th e ring preparation of rabbit aorta. Also, S-NO-alpha(1)PI but not alpha(1)P I shows a potent inhibitory effect on platelet aggregation. Unprecedented o bservation is that S-NO-alpha(1)PI showed a potent bacteriostatic effect ag ainst a wide range of bacteria at the concentration of 1-10 mu M, which was 10-1000-fold stronger than that of NO and other S-nitrosylated compounds i ncluding S-nitrosylated albumin and S-nitrosylated glutathione. These resul ts suggest that S-NO-alpha(1)PI is produced as an NO sink under inflammator y conditions. where production of both alpha(1)PI and NO is highly up-regul ated, and it may function as a soluble Factor which consists of an innate d efense system through not only the protease inhibitory activity but also it s antibacterial activity and facilitating the peripheral blood flow. Theref ore, S-nitrosylation of alpha(1)PI occuring under physiological conditions in vivo should diversify the biological functions contributing; to cytoprot ective effects of alpha(1)PI. (C) 2000 Elsevier Science B.V. All rights res erved.