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RP Barrett, CM Goshgarian, X Huang, LD Hazlett; The Role of iNOS in P. aeruginosa Corneal Infection: A Comparative Study . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1594.
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Purpose: Corneal infection caused by P.aeruginosa induces perforation in B6 (susceptible), but not BALB/c (resistant) mice. The role of inducible nitric oxide synthase(iNOS) in this model system remains unknown and is the purpose of this study. Methods: RT-PCR analysis, determination of viable bacteria in cornea, immunostaining for peroxynitrite, a product of NO and superoxide, iNOS (-/-) mice (B6 only), and treatment of mice (BALB/c only) with aminoguanidine (AMG), an iNOS inhibitor, were used to assess differences between the two strains. Results: RT-PCR analysis revealed no iNOS mRNA expression in the cornea before infection in B6 mice. Unexpectedly, low expression levels were detected constitutively in uninfected BALB/c mouse cornea. At 1 day p.i., iNOS expression levels were significantly elevated (P=0.008), decreased at 3 days (P=0.04) and decreased again (not significantly) at 5 days p.i. (P=0.09) in BALB/c vs. B6 mice. AMG vs. PBS-treatment (ocular topical) of BALB/c mice resulted in corneal perforation and increased bacterial load in the cornea of AMG-treated mice. In infected B6 iNOS -/- vs. wild-type mice, bacterial load in cornea also was elevated (P=0.02, 0.03 at 3 and 5 days p.i., respectively). Peroxynitrite staining in BALB/c vs. B6 cornea was similar at 1 day p.i., heaviest at 3 days p.i. in BALB/c, and heaviest in B6 at 5 days p.i. As expected, reduced peroxynitrite staining was observed in AMG-treated BALB/c cornea and in B6 iNOS -/- mice when compared with appropriate controls. Conclusion: These data provide evidence that in the cornea of B6 and BALB/c infected mice iNOS is important in bacterial killing, but that the kinetics of its upregulation differ between the two mouse strains. Earlier upregulation of iNOS followed by down-regulation favors resistance, while sustained levels of iNOS in cornea favor susceptibility, despite bacteria killing. Support: NIH RO1EY02986 and P30EY04068.
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