The fruit extract of Xylopia aethiopica (dunal) a. rich. (annonaceae) and its principal constituent, Xylopic acid, modulate inflammation

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Xylopia aethiopica extract is traditionally employed, among other uses, in the treatment of inflammatory conditions. This study aimed at investigating the anti-inflammatory properties of the aqueous ethanol (70% v /v) extract of the dried fruit of Xylopia aethiopica and its principal constituent, xylopic acid. The anti-inflammatory effect of the extract and xylopic acid were preliminarily established by in vitro assay employing the albumen denaturation method. The extract and xylopic acid showed a concentration-dependent inhibition of protein denaturation at the concentration ranges 6.25 - 200 µg ml -1 with IC50 of 10.12 µg ml -1 and 15.55 µg ml -1 respectively. The in vivo acute anti-inflammatory effect of the extract (30, 100, 300 mg kg -1 ) and xylopic acid (10, 30, 100 mg kg -1 ) were established using the carrageenan-induced acute inflammation model in mice. The inhibition of inflammation obtained were significant, with the highest dose suppressing oedema to 48.13 ± 10.90% and 60.81 ± 3.25% by the extract in both prophylactic and therapeutic models; and 56.58 ± 3.91% and 68.11 ± 3.59% by xylopic acid in the prophylactic and therapeutic models respectively of the inflamed control response. In the allergy studies, passive cutaneous anaphylactic and systemic anaphylactic studies were conducted. Pinnal inflammation reaction model and compound 48/80-induced passive cutaneous anaphylaxis model were employed in the passive cutaneous anaphylaxis studies. The antigen-induced inflammation was significantly suppressed by both the extract and xylopic acid with maximum suppression of 62.83 ± 0.83% and 77.62 ± 2.26% respectively. The extract and xylopic acid inhibited mast cell degranulation and caused a reduction in the extent of mast cell degranulation and skin tissue damage. Compound 48/80-induced systemic anaphylaxis and Lipopolysaccharide (LPS)-induced septic shock models were employed in the systemic anaphylaxis studies. The extract (30, 100, 300, 1000 mg kg -1 ) and xylopic acid (10, 30, 100, 300 mg kg -1 ) offered 40 - 100% and 40 – 90% survival proportion in the compound 48/80-induced systemic anaphylaxis respectively. In the LPS-induced septic shock, the intraperitoneal administration of LPS caused significant mortality in vehicle-treated animals. In the extract-treated animals, there was dose-dependent protection against endotoxic shock with maximum protection of 70%, xylopic acid also gave a maximum of 70% protection from endotoxic shock. In the chronic inflammatory study, the role of reactive oxygen species inhibition in the chronic inflammatory process was investigated using the acetic acid-induced colitis model in rats. The extract and xylopic iv acid showed anti-oxidant activity in acetic acid-induced colitis by decreasing the activity of myeloperoxidase and lowering lipid peroxidation as well as increasing the activities of catalase, superoxide dismutase and ascorbate peroxidase in vivo hence affecting the generation of reactive oxygen species which are involved in the inflammatory process and affects cellular activity and proliferation during the inflammatory process. The anti-arthritic property of the extract and xylopic acid were investigated using adjuvant-induced arthritis model in rats. The extract, at the highest dose, reduced the total limb swelling over 28 days in the ipsilateral limb to 41.07 ± 4.71% prophylactically and 42.90 ± 5.60% therapeutically of the arthritic control rats; with xylopic acid showing a maximal reduction in total limb swelling in the ipsilateral limb to 51.29 ± 8.34% prophylactically and 62.21 ± 11.85% therapeutically of the arthritic control rats with its highest dose administered. The extract and xylopic acid also showed inflammation alleviation in the other indices monitored. With the mechanism elucidation studies carried out, the extract and xylopic acid showed anti-histaminic activity with inhibitory effect on histamine-induced inflammation, indirect anti-histaminic activity in the clonidine-induced catalepsy model and possible competitive H1 receptor blockade. The extract and xylopic acid also showed effect on serotonergic, bradykinin and phospholipid/arachidonate pathways of inflammation with inhibitory effect on expression of intercellular adhesion molecule 1 and cellular component recruitment in the inflammatory process. Xylopic acid was identified to inhibit the serum expression of pro-inflammatory cytokines, IL-6 and TNF-alpha, in chronic inflammation. These novel findings show the anti-inflammatory property of the aqueous ethanol extract of the dried fruit of Xylopia aethiopica and its principal constituent, xylopic acid, obtained from the bio-fractionation of the petroleum ether extract of the dried fruit of Xylopia aethiopica.
A thesis submitted to the Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, College of Health Sciences in fulfilment of the requirements for the degree of Doctor Of Philosophy.