The Phospholipase D2 (PLD2) as a potential therapeutic target for the treatment of uveitis

Abstract

Uveitis is a common, sight-threatening inflammatory ocular disease. If left untreated, uveitis can cause irreversible ocular tissue damage and eventually impaired vision and is estimated to account for ~25 % of blindness in developed countries. We previously demonstrated that the phospholipase D (PLD) pathway mediates the inflammatory response of retinal pigment epithelium (RPE) cells induced by lipopolysaccharide (LPS). Objectives This work aims to study the effects of PLD2 inhibition in ocular inflammation using an endotoxin-induced uveitis (EIU) animal model. Methods Female Sprague Dawley rats (~250 g, 6–8 weeks old) were used and EIU was induced by the injection of 0.1 mL of 1 mg/kg LPS of Salmonella typhimurium solution into one footpad. After 2 or 4 h of LPS injection, (1, 4 or 8 mg/kg) of PLD2i (VU0285655-1) were injected intraperitoneally (IP) in 200 μl solution. 6 % DMSO was used as a PLD2i vehicle. PBS was injected instead of LPS in the negative control group of animals and dexamethasone was used as an anti-inflammatory positive control. Ethics approval for this study was obtained from the Animal Experimentation Ethics Committee of the CUHK. To evaluate clinical manifestations of EIU and the effects of PLD2i, rats were quantified using a score from 0 to 4 based in the presence of hyperemia, edema and synachesia, at baseline and 24 h after LPS injection. EIU were considered positive when clinical score >1 in at least one eye. To characterize the influxes of proteins into the aqueous humor (AH) in the different experimental conditions, protein concentrations were measured by the BCA Protein assay. Results After 24 h LPS injection, we observed ocular inflammation indicated by the presence of hyperemia and edema in the iris. The quantitative evaluation of clinical scoring showed a significant reduction by 30 % (p < 0.0001) in animals treated with 8 mg/kg PLD2i at after 2 h of LPS injection. The protein concentration in AH from LPS-treated rats was increased by 116 % (p < 0.001) compared to the negative control animals. Additionally, the elevated AH protein levels were significantly reduced by 33 % (p < 0.01) and by 49 % (p < 0.0001) in rats treated with 4 mg/kg or 8 mg/kg PLD2i, respectively. No statistically significance was ob- served between the 2 PLD2i treated groups and the negative control group. Conclusion Our study reports for first time the promising role of PLD2 inhibition as a potential early treatment for inflammatory ocular diseases.