Antinociceptive and free radical scavenging activities of alkaloids isolated from Lindera angustifolia Chen

Lindera angustifolia Chen is a folk medicine used for the treatment of contusions-induced swelling, rheumatic pains and bellyache in south and the middle part of China. Phytochemical studies showed that aporphine and benzyltetrahydroisoquinoline alkaloids are the characteristic constituents of this plant. In this study, we evaluated the antinociceptive and free radical scavenging properties of six aporphine and two benzyltetrahydroisoquinoline alkaloids isolated from the root of Lindera angustifolia. All alkaloids except magnocurarine exhibited remarkable radical scavenging effects (36–90% scavenging at 25–100 μg/ml) in DPPH radical scavenging test, among them norisocorydine showed the hightest activity (SC50: 14.1 μg/ml). Antinociceptive activities were tested by using acetic acid-induced writhing and formalin test at dose of 20 mg/kg. Norisocorydine exhibited the highest antinociceptive ability with 83.5% writhing inhibition. Boldine, norboldine showed significant antinociceptive activity with 76.3% and 74.6% writhing inhibition respectively. Indomethacin was used as positive control, which showed 67.8% writhing inhibition at dose of 10 mg/kg. Most of the compounds, except N-ethoxycarbonyllaurotetanine and magnocurarine, could significantly inhibit the phase I reaction (P < 0.01), and all of them inhibited the phase II reaction (P < 0.001) in the formalin tests (indomethacin and morphine were used as positive drugs). The antinociceptive effects exhibited a structure–activity relationship similar to that of the free radical scavenging activities. Above results suggested that the alkaloids from the root of Lindera angustifolia possess both free radical scavenging and antinociceptive activities, and the antinociceptive activity seems to be related to the free radical scavenging effect.