Nitric oxide synthesis by tracheal smooth muscle cells by a nitric oxide synthase-independent pathway

Abstract

Nitric oxide (NO) is known to be synthesized from l-arginine in a reaction catalyzed by NO synthase. Liver cytochrome P-450 enzymes also catalyze the oxidative cleavage of CN bonds of compounds containing a -C(NH2)NOH function, producing NO in vitro. The present study was designed to investigate whether there was evidence of a similar pathway for the production of NO in tracheal smooth muscle cells. Formamidoxime (10−2 to 10−4 M), a compound containing -C(NH2)NOH, relaxed carbachol-contracted tracheal rings and increased intracellular cGMP in cultured tracheal smooth muscle cells, whereasl-arginine had no such effect. NO was detectable in the medium containing cultured tracheal smooth muscle cells when incubated with formamidoxime. Ethoxyresorufin (10−7 to 10−4 M), an alternate cytochrome P-450 substrate, inhibited formamidoxime-induced cGMP accumulation as well as tracheal ring relaxation in cultured tracheal smooth muscle cells. The NO synthase inhibitors N ω-nitro-l-arginine (10−3 M) and N G-monomethyl-l-arginine (10−3 M) had no effect on formamidoxime-induced cGMP accumulation. These results suggest that NO can be synthesized from formamidoxime in tracheal smooth muscle cells, presumably by a reaction catalyzed by cytochrome P-450.

Involvement of NO in the Endothelium-Independent Relaxing Effects ofNω-Hydroxy-l-arginine and Other Compounds Bearing a C=NOH Function in the Rat Aorta

“…In both cases, formation of nitrite was blunted by a P450 inhibitor, supporting the involvement of P450. Exposure of the isolated trachea to formamidoxime caused cGMP accumulation and relaxation (Jia et al, 1998), consistent with the view that the pathway leading to NO formation was functional in the tissue as well as in the cultured tracheal cells. In the present investigation, we hypothesized that this could also be the case in the freshly isolated aorta.…”

“…The existence of an NO synthase-independent pathway capable of oxidizing L-NOHA or another compound with a CϭNOH bond, formamidoxime, to nitrogen oxides has been suggested in cultured smooth muscle cells from the rat aorta (Schott et al, 1994) and from the rat trachea (Jia et al, 1998), respectively. In both cases, formation of nitrite was blunted by a P450 inhibitor, supporting the involvement of P450.…”

A photosensitive vascular smooth muscle store of nitric oxide in mouse aorta: no dependence on expression of endothelial nitric oxide synthase

“…Potential non‐NOS enzymatic sources include cytochrome P 450 (CYP) and xanthine oxidase. CYP, presumably due to its structural similarity to NOS, has been reported to be able to generate NO in smooth muscle in a NADPH and oxygen‐dependent manner (Jia et al ., 1998; Keseru et al ., 2000; Taylor et al ., 2001). Xanthine oxidase is thought to catalyze the reduction of nitrite to generate NO in the presence of NADH (Zhang et al ., 1997; 1998).…”

Amidoximes and Oximes: Synthesis, Structure, and Their Key Role as NO Donors

“…In another study and in order to evaluate the relaxation capacity of amidoximes, Jia et al used formamidoxime in the presence of a tracheal ring previously contracted by carbachol, a cholinomimetic drug. They observed a relaxation effect on the tracheal ring after the incubation along with an accumulation of the cyclic guanosine 3′,5′-monophosphate (cGMP) level after incubation with the tracheal smooth muscle cells [69]. The relation between the production of cGMP and the relaxation of the ring was proved by using a cGMP inhibitor on both the tracheal rings and the smooth muscle cells.…”