Composition and cytotoxic and antioxidant activities of the oil of Piper aequale Vahl

Background: Piper aequale Vahl is a small shrub that grows in the shadow of large trees in the Carajás National Forest, Municipality of Parauapebas, Para state, Brazil. The local people have used the plant against rheumatism and inflammation.

Methods: The essential oil of the aerial parts was extracted and analyzed by GC and GC-MS. The MTT colorimetric assay was used to measuring the cytotoxic activity of the oil against human cancer lines. The determination of antioxidant activity of the oil was conducted by DPPH radical scavenging assay.

Results: The main constituents were δ-elemene (18.92 %), β-pinene (15.56 %), α-pinene (12.57 %), cubebol (7.20 %), β-atlantol (5.87 %), and bicyclogermacrene (5.51 %), totalizing 65.63 % of the oil. The oil displayed a strong in vitro cytotoxic activity against the human cancer cell lines HCT-116 (colon) and ACP03 (gastric) with IC₅₀values of 8.69 μg/ml and 1.54 μg/ml, respectively. The oil has induced the apoptosis in a gastric cancer cells in all tested concentration (0.75-3.0 μg/ml), after 72 h of treatment, when compared to negative control (p < 0.001). Also, the oil showed a significant antioxidant activity (280.9 ± 22.2 mg TE/ml), when analyzed as Trolox equivalent, and a weak acetylcholinesterase inhibition, with a detection limit of 100 ng, when compared to the physostigmine standard (1.0 ng).

Conclusion: The higher cell growth inhibition induced by the oil of P. aequale is probably due to its primary terpene compounds, which were previously reported in the proliferation inhibition, in stimulation of apoptosis and induction of cell cycle arrest in malignant cells.