Bioassay-guided isolation of anti-inflammatory and antinociceptive compound from Plumbago zeylanica leaf

Plumbago zeylanica Linn. (Plumbaginaceae) is used in the treatment of various inflammatory ailments in traditional medicines. In order to validate these ethnobotanical practices, the anti-inflammatory and antinociceptive activities of various leaf extracts (petroleum ether (60-80 degrees ), chloroform, acetone, ethanol, and aqueous) were studied using in vivo experimental models at two dose levels (200 and 400 mg/kg, p.o.). Anti-inflammatory activity was tested using the carrageenan induced rat hind paw edema method while analgesic activity was studied using the hot plate and formalin induced models. Diclofenac (100 mg/ kg) was used as the reference standard in both anti-inflammatory and analgesic models and morphine (10 mg/ kg, i.p.) was used as the reference standard in the formalin induced analgesic model. The acetone extract significantly (p < 0.01) reduced inflammation in the rats when compared to the control group. As for the analgesia effect, the acetone and petroleum ether extracts significantly (p < 0.01) decreased the pain stimulus only in the later phase of the formalin test, suggesting that the drug could be peripherally acting. Bioassay-guided fractionation of the acetone extract led to the isolation and identification of plumbagin. Structure elucidation of plumbagin confirmed it as 5-hydroxy-2-methyl-1,4-naphthoquinone, a naphthaquinone derivative, through spectral techniques.