Increased nitrotyrosine in the diabetic placenta: Evidence for oxidative stress

OBJECTIVE - To evaluate the presence of nitrotyrosine (NT) residues in placental villous tissue of diabetic pregnancies as an index of vascular damage linked to oxidative stress. RESEARCH DESIGN AND METHODS - Villous tissue was collected and flash frozen after delivery from 10 class C and D IDDM patients (37.9 ± 3.2 weeks) and 10 normotensive pregnant individuals (37.5 ± 3.8 weeks). Serial sections of tissue were immunostained with specific antibodies to NT, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and manganese superoxide dismutase (MnSOD). Sections were scored for intensity of immunostaining (0-3) by three observes blinded to the identity of tissue. RESULTS - All tissues demonstrated immunostaining for eNOS in both syncytiotrophoblast and stem villous vascular endothelium with no apparent differences between groups. Immunostaining for iNOS was seen in the villous stroma, but again was no different between the two groups. Significantly more intense NT staining was apparent in vascular endothelium and villous stroma (both P < 0.02) of diabetic placentas. The endothelium of large villous vessels of diabetic tissues also showed more intense immunostaining for MnSOD (P < 0.01). CONCLUSIONS - In these diabetic pregnancies, we were unable to show increased eNOS, unlike previous findings in preeclamptic pregnancies. The presence of NT may indicate vascular damage in the diabetic placenta due to peroxynitrite action formed from increased synthesis/interaction of nitric oxide and superoxide. The apparently paradoxical increase in MnSOD expression may be an adaptive response to increased superoxide generation.