S. Tanaka et al., IMMUNOLOGICAL ABNORMALITY ASSOCIATED WITH THE AUGMENTED NITRIC-OXIDE SYNTHESIS IN ADJUVANT-INDUCED ARTHRITIS, International journal of immunopharmacology, 20(1-3), 1998, pp. 71
Excessive nitric oxide (NO) synthesis by inducible NO synthase (iNOS),
has been implicated in the pathogenesis of inflammatory diseases such
as rheumatoid arthritis. We investigated the pathophysiological role
of NO using an adjuvant-induced arthritis model. Kinetics of iNOS mRNA
expression in paw and spleen showed that it was induced from an early
stage of the disease. To further characterize the pathophysiological
relevance of iNOS induction in spleen, the mitogenic response of splee
n cells was examined. ConA-induced proliferation of spleen cells from
arthritic rats was completely suppressed in comparison to normal fats.
Elevation of nitrite, which could be converted from NO, was also obse
rved in the culture supernatants. Addition of three NOS inhibitors, S-
(2-aminoethyl) isothiouronium bromide (ITU), aminoguanidine (AG) and L
NG-nitroarginine methyl ester (L-NAME) all reduced the nitrite level a
nd restored the proliferative response dose-dependently. These NOS inh
ibitors also showed anti-arthritic effects. Daily subcutaneous adminis
tration of either ITU at 50 mg/kg or AG at 200 mg/kg suppressed the pa
w swelling by 50% in arthritic rats on day 18. Oral administration of
L-NAME at 30 mg/kg showed a tendency to suppress the development of ar
thritis from day ii to day 15. However, drug-induced hypertension was
observed with L-NAME due to poor selectivity for iNOS isozyme. These r
esults suggest that augmented NO synthesis, via iNOS induction, may be
partly involved in the pathogenesis of adjuvant-induced arthritis by
causing defects in lymphocyte function. Thus, selective inhibition of
iNOS might be beneficial for the treatment of immunological abnormalit
ies associated with inflammatory diseases. (C) 1998 International Soci
ety for Immunopharmacology. Published by Elsevier Science Ltd. All rig
hts reserved.