Abstract

The present study seeks to evaluate the immunoregulatory effects of extracts of the root bark of Cassia sieberiana, a plant used in Ghana for various painful inflammatory conditions, in a modified adjuvant arthritis model induced by administration of very low dose of Mycobacterium tuberculosis (MT) – carrageenan mixture in the rat. A volume of 0.1 mg kg^-1 heat killed MT in paraffin oil was mixed with equal volume of 0.05% (w/v, normal saline) carrageenan. A single intraplantar dose of 0.1 ml of the MT - carrageenan mixture was administered to experimental animals. Groups were administered extracts (20 to 200 mg kg^-1, p.o.), dexamethasone (0.3 mg kg^-1, p.o.) or vehicle an hour prior to the test and daily from test day till the 6th day. Paw volume (ml) of the injected hind limbs were measured using a plethysmometer, while paw withdrawal thresholds were determined using an analgesy meter. Serum levels of IL-1α, IL-6, IL-10 and TNF-α were determined via enzyme linked immunosorbent assay (ELISA). Results showed that the extracts attenuated the inflammation and hyperalgesia caused by the intraplantar injection of MT-carrageenan mixture in the rats in a dose-dependent fashion. Similarly, the extracts reduced the serum levels of IL-1α, IL-6 and TNF- α while increasing the levels of IL-10. It can be concluded that the anti-inflammatory activity of extracts of root bark of C. sieberiana may be attributable to their immunomodulatory effects via suppression of pro-inflammatory cytokines, TNF-α, IL-1α and IL-6; and elevation of the anti-inflammatory cytokine, IL-10 levels, in serum.

Key words: Immunoregulatory, pro-inflammatory cytokines, TNF-α, adjuvant, C. sieberiana, IL-10.