Succinate increases in the vitreous fluid of patients with active proliferative diabetic retinopathy.

PURPOSE To examine vitreous succinate levels from proliferative diabetic retinopathy (PDR) patients and ascertain their association with PDR activity. DESIGN Comparative case series. METHODS A total of 81 eyes of 72 PDR patients were divided into active PDR (22 eyes), quiescent PDR (21 eyes), and active PDR with intravitreal bevacizumab injection (38 eyes). Twenty epiretinal membrane (ERM) patients (21 eyes) served as controls. RESULTS Mean vitreous succinate levels were 1.27 μM in ERM and 2.20 μM in PDR, with the differences statistically significant (P = .03). When comparing mean vitreous succinate levels (active PDR: 3.32 μM; quiescent PDR: 1.02 μM; active PDR with intravitreal bevacizumab injection: 1.20 μM), significant differences were found between active and quiescent PDR (P < .01) and between active PDR and active PDR with intravitreal bevacizumab injection (P < .01). Even though succinate levels were low, retinopathy activities were very high in patients with active PDR with intravitreal bevacizumab injection. Mean vitreous vascular endothelial growth factor (VEGF) levels (active PDR: 1696 pg/mL; quiescent PDR: 110 pg/mL; active PDR with intravitreal bevacizumab injection: n.d.) were similar to previous reports. Mean vitreous erythropoietin levels (active PDR: 703 mIU/mL; quiescent PDR: 305 mIU/mL; active PDR with intravitreal bevacizumab injection: 1562 mIU/mL) suggested very high retinopathy activities in patients with active PDR with intravitreal bevacizumab injection. CONCLUSIONS Succinate, like VEGF, may be an angiogenic factor that is induced by ischemia in PDR. Although succinate is reported to promote VEGF expression, VEGF inhibition decreases succinate. Thus, VEGF, via a positive feedback mechanism, may regulate succinate.