Elevated intravitreal interleukin-6 levels in patients with proliferative diabetic retinopathy.

BACKGROUND

We conducted this study to elucidate the possible role of interleukin-6 (IL-6) in the pathogenesis of proliferative diabetic retinopathy (PDR).

METHODS

Together with pertinent clinical and laboratory data, intravitreal and serum concentrations of IL-6 were determined in 8 patients with PDR by means of enzyme-linked immunosorbent assay (ELISA). The results were compared with data from 8 nondiabetic control subjects undergoing vitrectomy.

RESULTS

Significantly higher intravitreal IL-6 concentrations were found in patients with PDR (mean [SD], 755 [177] pg/mL) compared with control subjects (93 [151] pg/mL) (p = 0.001). The serum IL-6 levels in the PDR group were lower than the measurable threshold of the ELISA kit (<0.16 pg/mL). Diabetic patients with macular edema had a higher mean (SD) level of intravitreal IL-6 (896 [73] pg/mL) compared with patients without macular edema (613 [119] pg/mL) (Mann-Whitney U test, p = 0.03). Correlation analysis did not reveal any significant association between intravitreal IL-6 levels and patient age, duration of either diabetes mellitus or vitreous hemorrhage, panretinal photocoagulation, type of current medical therapy, hyperglycemia, or the biochemical indicators of renal function.

INTERPRETATION

IL-6, a proinflammatory cytokine, may have a role in PDR. Intraocular production of IL-6 appears to be responsible for the elevated intravitreal levels observed.