Submitted on October 17, 2006
Accepted on August 25, 2007
Profound Biopterin Oxidation and Protein Tyrosine Nitration in Tissues of ApoE-null Mice on an Atherogenic Diet: Contribution of Inducible Nitric Oxide Synthase
Rita K. Upmacis1*, Mark J. Crabtree2, Ruba S. Deeb1, Hao Shen1, Paul B. Lane2, Lea Esther S. Benguigui1, Nobuyo Maeda3, David P. Hajjar1, and Steven S. Gross4
1 Pathology and Laboratory Medicine, Weill Medical College of Cornell University, New York, New York, United States
2 Pharmacology, Weill Medical College of Cornell University, New York, New York, United States
3 Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina, United States
4 Pharmacology, Weill Medical College of Cornell University, New York, New York, United States; Center of Vascular Biology, Weill Medical College of Cornell University, New York, New York, United States
* To whom correspondence should be addressed. E-mail: rupmacis{at}med.cornell.edu.
Diminished nitric oxide (NO) bioactivity and enhanced peroxynitrite formation have been implicated as major contributors to atherosclerotic vascular dysfunctions. Hallmark reactions of peroxynitrite include the accumulation of 3-nitrotyrosine (3-NT) in proteins and oxidation of the NO synthase (NOS) cofactor, tetrahydrobiopterin (BH4). The present study sought to: (i) quantify the extent to which 3-NT accumulates and BH4 becomes oxidized in organs of ApoE-/- atherosclerotic mice, and (ii) determine the specific contribution of inducible NOS (iNOS) to these processes. Whereas protein 3-NT and oxidized BH4 were undetected or near the detection limit in heart, lung and kidney of 3-week old ApoE-/- mice or ApoE-/- mice fed a regular chow diet for 24 weeks, robust accumulation was evident after 24 weeks on a Western (atherogenic) diet. Since 3-NT accumulation was diminished 3- to 20-fold in heart, lung and liver in ApoE-/- mice missing iNOS, iNOS-derived species are involved in this reaction. In contrast, iNOS-derived species did not contribute to elevated protein 3-NT formation in kidney or brain. iNOS deletion also afforded marked protection against BH4 oxidation in heart, lung and kidney of atherogenic ApoE-/- mice, but not brain or liver. These findings demonstrate that iNOS-derived species are increased during atherogenesis in ApoE-/- mice and that these species differentially contribute to protein 3-NT accumulation and BH4 oxidation in a tissue-dependent manner. Since BH4 oxidation can switch the predominant NOS product from ·NO to superoxide, we predict that progressive NOS uncoupling is likely to drive atherogenic vascular dysfunctions.
