Analgesic effects of main indole alkaloid of kratom, mitragynine in acute pain animal model

• Published in: Behavioural brain research 2023-02, Vol.439, p.114251-114251, Article 114251
• Main Authors: Mat, Noorul Hamizah, Bakar, Siti Najmi Syuhadaa, Murugaiyah, Vikneswaran, Chawarski, Marek C., Hassan, Zurina
• Format: Article
• Language: English
• Subjects: Acute Pain - drug therapy; Analgesics; Analgesics - pharmacology; Animals; Anti-inflammatory agents; Female; Indomethacin; Male; Mitragyna; Mitragynine; Models, Animal; Pain; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Secologanin Tryptamine Alkaloids - pharmacology; TRPV1 receptor
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2022.114251

Mitragynine exerts its analgesic effect mainly via opioid receptors activation. Additionally, the effect may be mediated via mitragynine’s anti-inflammatory property and non-opioid receptor pain pathways, namely through the TRPV1 receptor. No studies identify hitherto, hence, the current study aimed to investigate the mitragynine’s analgesic effect via the anti-inflammatory property, non-opioid receptor (TRPV1) and the effective dose (ED) to alleviate pain. Male and female Sprague Dawley rats were pre-treated intraperitoneally with either mitragynine (1, 5, 10, 13, 15 or 30 mg/kg), vehicle, or indomethacin (1 mg/kg) 30 min before inducing inflammatory pain using acetic acid. The writhes and pain-related withdrawal behaviour occurrence were counted within a 1-h duration. Percentage of writhes inhibition, pain-related withdrawal behaviour aggregate, ED50 and ED95 were determined. The body temperature was recorded and TRPV1 expression in the rats' brains was measured. Mitragynine (except 1 mg/kg) significantly reduced the number of writhes compared with the vehicle administered group. Mitragynine (30 mg/kg) demonstrated 99.5% inhibition of writhing behaviour and low withdrawal behaviour score compared with vehicle and indomethacin and successfully blocked the hypothermia induced by acetic acid. The overall ED50 and ED95 values of mitragynine were 3.62 and 20.84 mg/kg, respectively. The percentage of writhing inhibition and withdrawal behaviour were similar in both genders. Mitragynine (15 and 30 mg/kg) significantly reduced the TRPV1 expression in the brain of the rats. Mitragynine alleviated pain-like behaviour and showed analgesic effects via anti-inflammatory and non-opioid receptor pathways. The findings also suggest that mitragynine might regulate some physiological functions of the rat. •Mitragynine fully attenuated the writhing behaviour.•Mitragynine displayed a significantly lower cumulative withdrawal score.•Mitragynine maintain the normal body temperature even after the acetic acid injection.•Mitragynine-treated rats expressed lower TRPV1 expression in the brain.