Vol. 275, Issue 6, H2258-H2265, December 1998
Osteopontin inhibits inducible nitric oxide synthase activity
in rat vascular tissue
Jeremy A.
Scott1,3,4,
M. Lynn
Weir2,5,
Sylvia M.
Wilson2,5,
Jim W.
Xuan2,5,
Ann F.
Chambers2,5, and
David G.
McCormack1,3,4
1 A. C. Burton Vascular Biology
Laboratory, 2 London Regional
Cancer Centre, London Health Sciences Centre, and Departments of
3 Medicine,
4 Pharmacology and Toxicology,
and 5 Oncology, University of
Western Ontario, London, Ontario, Canada N6A 4G5
We tested the hypothesis that osteopontin
(OPN) can inhibit the induction of inducible nitric oxide synthase
(iNOS) in vascular tissue. iNOS activity was induced in rat thoracic
aortas by incubation of the tissue with lipopolysaccharide (LPS) and
measured by conversion of
L-[3H]arginine
to
L-[3H]citrulline.
Addition of 
1 nM recombinant OPN protein significantly reduced the
LPS-induced increase in iNOS activity. Western blotting and the RT-PCR
were used to determine the effect of LPS with and without OPN on tissue
levels of iNOS protein and RNA, respectively. LPS resulted in an
increase in iNOS protein and RNA, whereas OPN dose-dependently reduced
tissue levels of iNOS activity, protein, and RNA. Mutated OPN proteins,
in which the integrin-binding RGD amino acid sequence was deleted or
mutated to RGE, resulted in complete and partial loss, respectively, of
the ability of OPN to inhibit LPS-induced iNOS activity, implicating
integrin binding in the effect. These results indicate that OPN can
prevent induction of iNOS in vascular tissue.
lipopolysaccharide; sepsis; endotoxin
