Soluble IL-6 receptor in vitreous fluid of patients with proliferative diabetic retinopathy

To identify the biological reaction of soluble interleukin-6 receptor (sIL-6R) in the vitreous of patients with proliferative diabetic retinopathy (PDR).

The subjects were 45 patients (45 eyes) with vitreoretinal diseases. The patients were divided into three groups: the PDR group comprised 28 patients (28 eyes) with PDR; the pre-proliferative diabetic retinopathy (PPDR) group comprised seven patients (seven eyes) with PPDR combined with diabetic macular edema; and the nondiabetic group comprised ten patients (ten eyes) with idiopathic macular hole or idiopathic epiretinal membrane. Vitreous samples were obtained at vitrectomy. sIL-6R, vascular endothelial growth factor (VEGF), and protein concentration in vitreous samples were determined by enzyme-linked immunosorbent assay (ELISA). sIL-6R levels in serum were also determined by ELISA in nine of the 28 patients with PDR and in six healthy volunteers as controls.

In vitreous fluid, the levels of sIL-6R in the PDR group, PPDR group, and nondiabetic group were 612.7 +/- 233.8 (mean +/- SD), 746.3 +/- 523.1, and 215.4 +/- 98.3 pg/ml, respectively. Vitreous levels of sIL-6R in the PDR and PPDR groups were significantly higher than those in the nondiabetic group (PDR group, P < 0.0001; PPDR group, P < 0.01). In serum, the levels of sIL-6R were 39.38 +/- 9.43 ng/ml in the PDR group and 22.84 +/- 5.32 ng/ml in the control group. sIL-6R levels in serum in the PDR group were significantly higher than those in the control group (P < 0.01). A partial correlation analysis showed a significant correlation between the levels of sL-6R and VEGF in the vitreous in the PDR group (r = 0.34, P < 0.05).

We conclude that the level of sIL-6R in vitreous fluid can be considered as a biomarker of PDR.