Análise fitoquímica de frações do extrato aquoso de Echinodorus macrophyllus e de seu potencial antinociceptivo

Abstract

Echinodorus macrophyllus (Kunth) Mich. species, of the Alismataceae family, is a medicinal plant popularly known as chapéu de couro and used as a diuretic and anti-inflammatory agent. This study aimed to perform the fractionation and phytochemical characterization of the aqueous extract and fractions of Echinodorus macrophyllus and evaluate the in vivo antinociceptive potential. The EAEm was obtained by the leaves infusion in distilled water (50 g p.s./L, 100°C), followed by filtration and lyophilization. EAEm was fractionated in Sephadex LH-20, generating fractions Fr20 and Fr40, as well as by liquid-liquid extraction yielding fractions FHex, FDCM, FAcE, FBut, and FAq. All fractions originating from EAEm were analyzed by TLC or HPTLC on a silica gel 60 plate and by HPLC-DAD on a C18 column. The in vivo nociception models used were hot plate and formalin, which evaluate responses to thermal and chemical nociceptive stimuli, respectively, using male SW mice (25-30 g). In the hot plate model, the animals were previously treated (v.o.) with EAEm (25 mg/kg), Fr20 and Fr40 (25 and 100 mg/kg), and vehicle, and morphine (10 mg/kg, i.p.). In the formalin model, the animals were previously treated (v.o.) with FAcE and FBut (25 and 50 mg/kg), dipyrone (50 mg/kg v.o.), vehicle (control) and morphine (10 mg/kg i.p.). This model is biphasic: 0 - 5 min, phase 1 (neurogenic); and 15 - 25 min, phase 2 (inflammatory). Fr40, FAcE, and FBut fractions showed profiles with a similar yellow band when evaluated by TLC or HPTLC and revealed for flavonoids, which suggests the presence of this class of compounds in the fractions. The orientin, isoorientin, vitexin, and isovitexin flavones were used as standards. Based on the colorations and Rf values, it is possible to suggest that isoorientin and isovitexin are present in EAEm, FAcE, and FBut, while vitexin in EAEm, FBut, and FAq. Regarding the evaluation of antinociceptive action, using the hot plate model, Fr20 was able to increase the latency time by 30 min (25 mg/kg) and by 60 min (25 and 100 mg/kg), and the Fr40 at a dose of 100 mg/kg, in 30 and 60 min. In the formalin model, FAcE (25 mg/kg) showed a reduction in bite and licked time in phase 1 (neurogenic), while FBut reduced it with both doses in this same phase. In phase 2 (inflammatory), FBut reduced bite and lick time only with the 25 mg/kg dose. Concerning the antinociceptive activities observed with the EAEm samples, such activities may be associated with the inhibition of central/peripheral pain mechanisms, mediated by nociceptors activated by thermal and chemical stimuli. In conclusion, the fractionation of EAEm by liquid-liquid partition was reproducible and increased the yield of fractions with antinociceptive action, which allows the study of these fractions to continue. Besides, Fr40, FAcE, and FBut fractions showed phytochemical profiles compatible with flavonoids, which must be associated with the important antinociceptive action observed.