Increased levels of IL-6, sIL-6R, and sgp130 in the aqueous humor and serum of patients with diabetic retinopathy

PURPOSE Trans-signaling of interleukin (IL)-6 through its soluble receptor (sIL-6R) is critically involved in the promotion of chronic inflammatory diseases. The aim of the present study was to estimate IL-6, sIL-6R, and soluble gp130 (sgp130, a natural antagonist of IL-6 trans-signaling) concentrations in the serum and aqueous humor (AqH) of patients with diabetic retinopathy (DR). METHODS Paired AqH and serum samples were collected from 152 consecutive diabetic patients (105 with DR and 47 without DR, NDR) and 51 healthy controls. The IL-6, sIL-6R, and sgp130 concentrations were measured with multiplex bead immunoassay. RESULTS The sgp130 concentrations in the serum and AqH were statistically significantly elevated in patients with DR compared with the NDR patients and the healthy controls (p<0.001). The sgp130 concentrations in the serum and AqH increased as the DR severity increased (p = 0.008, p<0.001, respectively). Higher serum and AqH concentrations of IL-6 and sIL-6R were also observed in patients with DR when compared with the NDR patients and the healthy controls (p<0.001). The AqH concentration of sgp130 was found to be statistically significantly correlated with sIL-6R and IL-6. Similarly, the IL-6 concentration in the AqH was statistically significantly correlated with sIL-6R (p<0.001). Elevated sgp130, sIL-6R, and IL-6 concentrations in the AqH were associated with longer disease duration and higher body mass index, plasma glucose, and glycosylated hemoglobin (HbA1c). CONCLUSIONS The sgp130, IL-6, and sIL-6R concentrations were statistically significantly elevated in patients with DR, suggesting a probable contributing role of the IL-6 trans-signaling pathway to the pathophysiology of DR.