Bioassay-Guided Isolation of Constituents of Piper sarmentosum Using a Mitochondrial Transmembrane Potential Assay

Abstract

Bioassay-guided fractionation was conducted on a chloroform-soluble extract of the aerial parts of Piper sarmentosum collected in Vietnam, monitored by a mitochondrial transmembrane potential assay using HT-29 human colon cancer cells. This led to the isolation of four new C-benzylated dihydroflavones, sarmentosumins A–D (1–4), as well as 14 known compounds. The structures of the new compounds were elucidated on the basis of spectroscopic data interpretation. Among these compounds, 1–4 as well as five known C-benzylated dihydroflavones (5–9) and a piperamide, pipercallosine (11), were found to induce apoptosis in HT-29 cells by moderately reducing the mitochondrial transmembrane potential (ΔΨm), with ED₅₀ values ranging from 1.6 to 13.6 μM. Furthermore, 7-methoxydichamanetin (8) and pinocembrin (10) exhibited proteasome inhibitory activities in a human 20S proteasome bioassay with IC₅₀ values of 3.45 ± 0.18 and 2.87 ± 0.26 μM, respectively. This is the first time that C-benzylated dihydroflavones have been reported to demonstrate an apoptotic effect associated with disruption of the mitochondrial transmembrane potential.