Abstract
Purpose: :
Recently, the kallikrein-kinin system (KKS) has been implicated in the pathogenesis of diabetic retinopathy (DR) and diabetic macular edema (DME). This study quantifies the abundance of KKS components in the vitreous of patients with various levels of diabetic retinopathy severity. In addition, the effects of diabetes and hyperglycemia on bradykinin B1 and B2 receptor expression and action in retina and cultured bovine capillary retinal endothelial cells (RECs) are examined.
Methods: :
Human vitreous samples were obtained from patients undergoing pars plana vitrectomy and the concentrations of KKS components including FXII, plasma kallikrein (PK), high molecular weight kininogen, and kininase I which degrades bradykinin (BK, a B2R agonist) into des-Arg-Bradykinin (DABK, a B1R agonist), were analyzed by western blotting. The effects of diabetes and hyperglycemia on B1R and B2R levels in retina from streptozotocin-induced diabetic (DM) rats and nondiabetic (NDM) rats and in cultured RECs as well as the effects of BK and DABK on ERK, p38, and eNOS phosphorylation in RECs were examined by western blotting. Effects of intravitreal injection of BK and DABK on retinal vascular permeability (RVP) were analyzed by vitreous fluorophotometry.
Results: :
The abundance of all components of the KKS were elevated in the vitreous from subjects with proliferative diabetic retinopathy (PDR) and severe nonPDR (NPDR) with DME compared with non-diabetic and those with mild-moderate NPDR. In rat retina after 4 weeks of DM, B1R expression was increased 5 fold compared with NDM control retina, whereas B2R was similarly expressed in DM and NDM rat retina. BK intravitreal injection increased RVP after 40 minutes in both NDM and DM rats. In contrast, intravitreal injection of DABK did not acutely affect RVP but induced a delayed and sustained increase in RVP observed at 48 hrs post injection in DM rats, an effect not observed in NDM controls. Systemic administration of L-NAME, a nitric oxide synthesis inhibitor, significantly suppressed both BK- and DABK-induced hyperpermeability. In vitro, BK rapidly increased ERK, AKT, and eNOS phosphorylation in RECs cultured in 5.5 mM glucose. High glucose (22 mM) increased B1R expression and facilitated DABK-induced p38 phosphorylation, which was not observed in RECs cultured in 5.5 mM glucose.
Conclusions: :
KKS components are increased in the vitreous from people with advance DR. The effects of the KKS on RVP in diabetes involve the combined actions of B1R and B2R, and are mediated at least in part, by nitric oxide.
Keywords: diabetic retinopathy • edema • nitric oxide