Protective Effect of High Molecular Weight Protein Sub-fraction of Calotropis procera Latex in Monoarthritic Rats

BACKGROUND: Proteins present in the latex of Calotropis procera have been shown to produce anti-inflammatory effect and to afford protection in various disease models. OBJECTIVES: To determine the efficacy of high molecular weight protein sub-fraction (LP(PI)) of latex of C. procera in ameliorating joint inflammation and hyperalgesia in a preclinical model of arthritis. MATERIALS AND METHODS: Monoarthritis was induced in rats by intra-articular injection of Freund's complete adjuvant (FCA) and the effect of two doses of LP(PI) (5 and 25 mg/kg) and diclofenac (5 mg/kg) was evaluated on joint swelling, stair climbing ability, motility, and dorsal flexion pain on day 3. The rats were sacrificed on day 3 to measure tissue levels of reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS). Evaluation of joint histology was also made. RESULTS: Intra-articular injection of FCA produced joint swelling and difficulty in stair climbing ability, motility, and pain on flexion of the joint as revealed by scores obtained for these functional parameters. LP(PI) produced a dose-dependent decrease in joint swelling and improved joint functions. Arthritic rats also revealed altered oxidative homeostasis where joint tissue GSH levels were decreased and TBARS levels were increased as compared to normal rats. The levels of these oxidative stress markers were near normal in arthritic rats treated with LP(PI). Moreover, treatment with LP(PI) also maintained the structural integrity of the joint. The protective effect of LP(PI) was comparable to the standard anti-inflammatory drug, diclofenac. CONCLUSION: The findings of the present study show that LP(PI) fraction comprising high molecular weight proteins could be used for the alleviation of arthritic symptoms. SUMMARY: High molecular weight protein sub-fraction of latex of Calotropis procera (LP(PI)) reduced joint swelling and hyperalgesia in arthritic rats. LP(PI) produced a significant improvement in stair climbing ability and motility in arthritic rats. LP(PI) normalized the levels of oxidative stress markers in the arthritic joints. Treatment with LP(PI) reduced neutrophil influx and edema in the arthritic joints. Abbreviations used: FCA: Freund's complete adjuvant, GSH: Glutathione, TBARS: Thiobarbituric acid reactive substances, TBA: Thiobarbituric acid, MDA: Malondialdehyde, LP(PI): Latex protein fraction PI.