Introduction and Objective: Early diabetic retinopathy (DR) is associated with inflammation and retinal neurodegeneration, which begin prior to overt microvascular pathology. Cannabinoid (CB) receptor 2 agonism has been shown to have anti-inflammatory and neuroprotective properties in the central nervous system. This study tested the potential of CB2-selective agonists HU-308 and CB65 to reduce inflammation and increase the survival of retinal photoreceptors in diabetic retinopathy.Methods: Primary photoreceptors were harvested from C57BL/6J mouse retinas via papain dissociation followed by passage through magnetic columns. Photoreceptors in culture were stimulated with the inflammatory cytokine IL-1β (1 ng/ml) for 6 hours. The CB2 agonists used in this study were HU-308 (0.1 μM) and CB65 (0.1 μM). The endogenous CB2 agonist 5,6-EET (0.5 μM) was used as a positive control. The streptozocin (STZ) -induced mouse model was used as the in vivo model of diabetes. Some STZ mice received daily i.p. injections of vehicle or HU-308 (5 mg/kg) for 4 weeks beginning 6 weeks post-STZ injection, others received 1 intravitreal injection of 1 μL vehicle or HU-308 (5 μmol/L) 10 weeks post-STZ injection, 1 day before tissue collection. TUNEL staining was performed on cells and retinal sections. Quantitative RT-PCR was employed according to the manufacturer’s instructions for detecting mRNA levels of cytokine transcripts.Results: CB2 agonism decreased the expression of IL-1β (8-fold decrease, p=0059), IL-6 (2-fold decrease, p<0.001), and TNFα (2-fold decrease, p<0.001). A significantly higher number of photoreceptors underwent apoptosis when exposed to inflammation in vitro, and in the STZ model. Upon treatment with CB2 agonists, the number of apoptotic cells returned to control levels.Conclusion: CB2 agonism reduced cytokine expression in response to diabetes-relevant stimuli, and improved retinal photoreceptor survival. These results demonstrate that CB2 agonism has significant anti-inflammatory and neuroprotective potential in early DR.
I. De La Huerta: None.
NIH (K08EY032620)
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