Inducible nitric oxide synthase (iNOS) has previously been shown to contribute to atherosclerotic lesion formation and proteinnitration. Micro attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopic imaging was applied ex vivo to analyse lesions in atherosclerotic (ApoE−/−) mice. Histologies of cardiovascular tissue of ApoE−/− mice that contain the gene for iNOS and ApoE−/− mice without iNOS (ApoE−/−iNOS−/− mice) were examined. Spectroscopic imaging of the aortic root revealed that iNOS did not affect the composition of the tunica media; furthermore, irrespective of iNOS presence, lipidesters were found to form the atherosclerotic plaque. ApoE−/− mouse aortic root lesions exhibited a more bulky atheroma that extended into the medial layer; signals characteristic of triglycerides and free fatty acids were apparent here. In ApoE−/−iNOS−/− mouse specimens, lesions composed of free cholesterol were revealed. ATR-FTIR spectra of the intimal plaque from the two mouse strains showed higher lipid concentrations in ApoE−/− mice, indicating that iNOS contributes to lesion formation. The reduction of lesion prevalence in ApoE−/−iNOS−/− mice compared with ApoE−/− mice is consistent with previous data. Moreover, the analysis of the plaque region revealed a change in the spectral position of the amide I band, which may be indicative of proteinnitration in the ApoE−/− mouse, correlating with a more ordered (β-sheet) structure, while a less ordered structure was apparent for the ApoE−/−iNOS−/− mouse, in which proteinnitration is attenuated. These results indicate that micro ATR-FTIRspectroscopic imaging with high spatial resolution is a valuable tool for investigating differences in the structure and chemical composition of atherosclerotic lesions of ApoE−/− and ApoE−/−iNOS−/− mice fed a high-fat Western diet and can therefore be applied successfully to the study of mouse models of atherosclerosis.
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