K. Dobashi et al., MODULATION OF ENDOGENOUS ANTIOXIDANT ENZYMES BY NITRIC-OXIDE IN RAT C-6 GLIAL-CELLS, Journal of neurochemistry, 68(5), 1997, pp. 1896-1903
To understand the possible mechanism of nitric oxide (NO)-mediated cyt
otoxicity, we investigated the effect of NO on the endogenous antioxid
ant enzymes (AOEs) catalase, glutathione peroxidase (GPX), and CuZn- a
nd Mn-superoxide dismutases (SODs) in rat C-6 glial cells under condit
ions in which these cells expressed oligodendrocyte-like properties as
evidenced by the expression of 2',3'-cyclic-nucleotide 3'-phosphohydr
olase. The 24-h treatment with S-nitroso-N-acetylpenicillamine (SNAP),
a NO donor, decreased the activities and the protein levels of catala
se, GPX, and Mn-SOD in a dose-dependent manner. Alternatively, the act
ivity and the protein level of CuZn-SOD were increased. 2-Phenyl-4,4,
5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), a NO scavenger, bloc
ked the effect of SNAP. Moreover, the treatment of C-6 cells with sodi
um nitroprusside, another NO donor, or with a combination of lipopolys
accharide (LPS) and interferon-gamma (IFN-gamma), which induce excessi
ve production of NO, also significantly modulated the AOE activities i
n a manner similar to that seen with SNAP treatment. The compounds/enz
ymes that inhibit the production of NO (e.g., N-nitro-L-arginine methy
l ester hydrochloride, arginase, and PTIO) blocked the effects of LPS
and IFN-gamma on the activities of AOEs. Treatment with SNAP and a com
bination of LPS and IFN-gamma also modulated the mRNA levels of AOEs,
parallel to the changes in their protein levels and activities, except
for Mn-SOD where the combination of LPS and IFN-gamma markedly stimul
ated the mRNA expression. In spite of the stimulation of mRNA level, L
PS and IFN-gamma significantly inhibited the activity of Mn-SOD within
the first 24 h of incubation; however, Mn-SOD activity gradually incr
eased with the increase in time of incubation. These results suggest t
hat alterations in the status of AOEs by NO may be the basis of NO-ind
uced cytotoxicity in disease states associated with excessive NO produ
ction.