Mitracarpus frigidus (Rubiaceae): potencial farmacológico, avaliação toxicológica e identificação de substâncias bioativas

Abstract

Mitracarpus frigidus (Willd. ex Schult Reem.) K. Schum. (Rubiaceae) is a native species, widely distributed throughout the Brazilian territory, with few reports in the literature on its chemical-biological potential. Previous studies reported that the plant has antimicrobial, antioxidant and leishmanicidal, and that its main constituents are alkaloids, quinones, flavonoids, terpenes and steroids. In order to continue the studies involving this species, this work aimed to evaluate its toxicity and pharmacological potential, as well as to isolate and characterize its bioactive compounds. From the methanolic extract of the aerial parts of M. frigidus (MFM) the triterpenes ursolic acid and methyl ursolate, and the naphthoquinone psycorubrin were isolated. The flavonoids rutin and kaempferol were also identified. Using these compounds as markers, MFM was standardized and evaluated for schistosomicidal, anti-inflammatory, laxative and cytotoxic activity. Moreover, its acute (LD50) and subchronic toxicity were evaluated. The biological potential and chemical composition of the hexane extract and the essential oil of this species were also analyzed. MFM showed both in vitro and in vivo schistosomicidal activity with considerable reduction in parasite burden. Antiinflammatory activity was also observed for the acute and chronic models tested, with a more proeminent acute response. Those results demonstrated that MFM inhibited the inflammation cell mediated migration and also decreased the oxidative process of the organism, as evidenced by the observed low concentration of MDA, catalase and myeloperoxidase. Regarding the expression of cyclooxygenase, MFM inhibited COX 2. Cytotoxic activity against leukemia cells, HL60 and Jurkat, without apoptosis induction was also observed. Furthermore, MFM induced increase of intestinal peristalsis and production of faeces, which can be related to the presence of the anthraquinones identified in MFM. From the acute and subchronic toxicity study of MFM it was possible to verify that the plant has low toxicity (LD50 > 2000 mg/kg) and caused no hematological and biochemical changes during 42 days of experiment. The compounds ursolic acid, methyl ursolate and psycorubrin, isolated from MFM, showed cytotoxicity against different tumor cells and species of Leishmania. Likewise, the hexane extract showed antibacterial and antileishmanial properties, with specificity and selectivity for intracellular forms (amastigotes). The essential oil showed antifungal and leishmanicidal activity. Linalool and eugenol acetate were identified as its major compounds. In conclusion, the species M. frigidus, which has no reports on its use in traditional medicine, could be an alternative source of study for the treatment of various diseases such as those caused by fungi, bacteria and parasites, and pathologies related to inflammatory processes.