Anti-inflammatory cytokine and angiogenic factors levels in vitreous samples of diabetic retinopathy patients

Abstract

Evaluation of cytokines in patients with diabetic retinopathy (DR) is important for the identification of future additive or alternative treatment options. Therefore, vitreous samples were obtained from patients with DR and patients with macular hole or macular pucker (control group) during 23-gauge-vitrectomy (n = 17/group). The levels of three pro-inflammatory (IL-1ß, IL-6, IFN-γ) and pleiotropic cytokines (IL-2, IL-4, IL-13) as well as VEGF, VEGF-A, and PGF were measured using an enzyme linked immunosorbent assay (ELISA). IL-1ß (p = 0.02) and IFN-γ (p = 0.04), two of the three tested pro-inflammatory cytokines, were elevated in the DR patients, while IL-6 (p = 0.51) level was comparable in both groups. Moreover, in DR samples, a trend towards an IL-13 down-regulation (p = 0.36) was observable. The IL-2 (p = 0.62) and IL-4 (p = 0.78) levels were comparable in both groups. All analyzed angiogenetic factors were up-regulated in DR patients (VEGF: p<0.001; VEGF-A: p = 0.002; PGF: p<0.001). The up-regulation of angiogenetic factors underline their importance in DR development. However, the interaction of the other cytokines showed an interesting pattern. Pro-inflammatory cytokines were also up-regulated, which could be evidence for inflammation processes in the diabetic retina. Furthermore, it seems that a counter response of immunomodulatory cytokines is in an initial process, but not strong enough to regulate the processes. Therefore, to support these anti-inflammatory mechanisms might be additive treatment option in the future.

Fig 1. Increased pro-inflammatory cytokine levels in vitreous samples.

A. The pro-inflammatory cytokine IL-1ß (p = 0.02) was significantly up-regulated in compassion to the controls. B. INF-γ (p = 0.04) was also significantly up-regulated. C. In contrast, IL-6 expression level was the same in DR and control patient (p = 0.51). Each symbol depicts an individual patient. The horizontal bar indicates the mean cytokine concentration per group. *: p<0.05.

Fig 2. Contribution of pleiotropic immunomodulatory cytokine levels in vitreous samples.

A. A difference in IL-2 (p = 0.62) level was not measurable between control and DR patients. B. There was no difference in IL-4 level between control and DR patients (p = 0.78). C. A trend for the down-regulation of IL-13 level (p = 0.36) was noted in DR patients. Each symbol depicts an individual patient. The horizontal bar indicates the mean cytokine concentration per group.

Fig 3. Up-regulation of different angiogenic factors in vitreous samples.

A. Total VEGF was significantly up-regulated in vitreous samples of DR patients (p = 0.002). B. VEGF-A was also significantly up-regulated in DR patients (p<0.001). C. Additionally, PGF was upregulated in DR samples compared to controls (p<0.001). Each symbol depicts an individual patient. The horizontal bar indicates the mean cytokine concentration per group. **: p<0.01, ***: p<0.001.