Abstract
Purpose: :
Early diabetic retinopathy is associated with microglial activation and increased levels of inflammatory cytokines. We have previously shown that cannabidiol (CBD), a non-psychoactive cannabinoid, possesses anti-inflammatory property in Streptozotocin (STZ)-induced diabetic model. However, the underlying mechanism still remains unclear. In this study, we investigated the effect of CBD on microglia activation during diabetes. We examined the role of microglia in retinal inflammation and tested the ability of CBD to inhibit microglial activation in the diabetic retina and in isolated cells.
Methods: :
Diabetes was induced by STZ in Sprague Dawley rats. After diabetes was established for two weeks, a single intravitreal injection of CBD or vehicle was performed. Forty-eight hours later, retinas were processed for TNF-α and microglia marker (Iba-1) expression by Quantitative Real Time-PCR. Vitreous samples were analyzed for TNF-α release by Enzyme-linked Immunosorbent Assay. To study the signaling pathways associated with inflammation, retinal microglial cells isolated from newborn rats were cultured and analyzed under diabetic conditions. Cells were treated with glycated albumin, a risk factor of diabetes, in the presence or absence of CBD. Thereafter, Reactive oxygene species (ROS) formation, TNF-α release, and MAP kinase activation were determined.
Results: :
Dramatic up-regulation of TNF-α and Iba-1 expression with a very suggestive correlative evidence (R=0.876, p<0.001) were observed in 2-weeks diabetic rats. In the CBD-treated diabetic animals, Iba-1 expression and TNF-α expression and release were all significantly reduced compared to the un-treated diabetic controls. This inflammation is associated with early events including ROS formation and the subsequent activation of ERK and P38 MAP kinases. CBD represses TNF-α expression and release and inhibits ERK and P38 activation in the activated microglial cells by its ROS-scavenging ability.
Conclusions: :
These data reveal a previously unrecognized role for CBD in attenuating diabetes-induced retinal inflammation by interfering with inflammatory signaling that occurs in activated microglia. Moreover, these data present new thoughts as to how compounds similar to CBD may suppress retinal complications associated with diabetes.
Keywords: microglia • antioxidants • diabetic retinopathy