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.