Purpose: Elevated levels of C-reactive protein (CRP), a proinflammatory marker, are associated with systemic vascular disorders. In addition, clinical studies have implicated that elevated CRP is an independent risk factor for diabetic retinopathy and age-related macular degeneration. However, the direct effect of CRP on ocular microvascular reactivity remains unknown. The authors examined whether CRP can affect endothelium-dependent nitric oxide (NO)-mediated dilation of retinal arterioles and whether oxidative stress and distinct protein kinase signaling pathways are involved in the CRP-mediated effect.
Methods: Porcine retinal arterioles (internal diameter, 71 +/- 2 microm) were isolated and pressurized without flow for in vitro study. Diameter changes were recorded using videomicroscopic techniques. Dihydroethidium (DHE) was used to detect superoxide production.
Results: Intraluminal treatment with a clinically relevant concentration of CRP (7 microg/mL, 60 minutes) significantly attenuated arteriolar dilation to endothelium-dependent NO-mediated agonists bradykinin and A23187 but not to endothelium-independent NO donor sodium nitroprusside. In the presence of superoxide scavenger TEMPOL, NAD(P)H oxidase inhibitor apocynin, p38 kinase inhibitor SB203580, simvastatin, or Rho-kinase inhibitor Y-27632, the detrimental effect of CRP on bradykinin-induced dilation was prevented. DHE staining showed that CRP produced TEMPOL-sensitive superoxide production in the arteriolar endothelium.
Conclusions: CRP inhibits endothelium-dependent NO-mediated dilation in retinal arterioles by producing superoxide from NAD(P)H oxidase, which appears to be linked with p38 kinase and RhoA/Rho-kinase activation. By impairing endothelium-dependent NO-mediated vasoreactivity, CRP can potentially facilitate the development of retinal vascular diseases. In addition, statins are beneficial by preserving endothelial function, possibly through inactivation of the RhoA/Rho-kinase pathway.