Maerua angolensis Extract Reduces Allodynia and Hyperalgesia in a Mouse Model of Vincristine-Induced Peripheral Neuropathy.

Allodynia and hyperalgesia comprise the main and frequent symptoms suffered by patients with neuropathic pain, which responds poorly to therapy. An earlier study reported that stem bark extracts of Maerua angolensis exhibited dose-dependent anti-nociceptive effect against the neurogenic and inflammatory phases of the formalin test. The current study evaluated the effect of petroleum ether/ethyl acetate stem bark extract of Maerua angolensis on vincristine-induced neuropathy. Neuropathic pain was induced by intraperitoneal injection of vincristine (0.1 mg/kg/day) using a 5-day-on, 2-day-off schedule over 12 days. On day 15, baseline responses were measured in the Randall-Selitto mechanical hyperalgesia test and paw withdrawal tests (using Von Frey filaments and cold water at 4.5 °C) and mice that developed allodynia/hyperalgesia were randomly assigned into 7 groups. Normal saline (i.p.), pregabalin (10, 30, and 100 mg/kg, p.o.) and extract (3, 10, and 20 mg/kg, p.o.) were administered to the individual groups. Allodynia/hyperalgesia was measured hourly for 5 hours post treatment. The extract produced significant (P<0.05) and dose-dependent inhibition of vincristine-induced mechanical hyperalgesia, tactile and cold allodynia responses. In all, the study shows that oral administration of Maerua angolensis stem bark extract inhibits vincristine-induced neuropathy in mice suggesting that it may exert analgesic effect in cancer patients with vincristine-induced neuropathic pain.

Evaluation of Analgesic Property of Petroleum Ether/Ethyl Acetate Stem Bark Extract and Fractions of Maerua angolensis in Murine Models of Pain.

This study investigated the possible antinociceptive action of the petroleum ether/ethyl acetate extract and fractions prepared from the stem barks of Maerua angolensis. The acetic acid-induced abdominal writhing, formalin–induced nociception, prostaglandin E2–induced mechanical hyperalgesia, bradykinin– and epinephrineinduced thermal hyperalgesia tests as well as Paw withdrawal test using Hargreaves thermal hyperalgesia model were used to assess the antinociceptive effects of the extract and the fractions after oral administration in rodents. Diclofenac and morphine were used as reference analgesic agents. Mice were submitted to the rotarod test in order to assess any non–specific muscle–relaxant effect of the extract and the fractions. The petroleum ether/ethyl acetate extract and the fractions of Maerua angolensis produced significant (P < 0.05) and dose-dependent antinociceptive effects in the acetic acid, formalin, prostaglandin E2, bradykinin, epinephrine and paw withdrawal tests. The extract and the fractions of Maerua angolensis (3 and 10 mg/kg) did not compromise the motor coordination of animals in the rotarod test, suggesting lack of central depressant effect. The petroleum ether/ethyl acetate extract and fractions of Maerua angolensis stem bark produced dose-dependent antinociception in murine models of chemical, mechanical and thermal nociception suggesting peripheral and central analgesic action.