Catherine Charles

An Overview of Cancer Chemopreventive Potential and Safety of Proanthocyanidins

Cancer is a major public health problem worldwide. Over two-thirds of cancer-related deaths could most probably be prevented through lifestyle modification, particularly through dietary means. Proanthocyanidins (PAs), the most abundant polyphenolic substances after lignin in the plant kingdom, have been widely investigated for their chemopreventive potential. The PAs literature has, however, been mostly concerned with positive cardiovascular activities, and recent reviews about cancer chemoprevention are scarce. The present review highlights a series of in vitro and in vivo studies indicating (1) that PAs can act as anticarcinogenic agents through their antioxidant, apoptosis-inducing, immuno-modulating, and/or enzyme modulating properties, effects on epigenetics; and (2) that PAs could be particularly safe dietary compounds. These convergent data encourage further research to better understand the many aspects of cancer chemoprevention by PAs.

Measurement of the influence of flavonoids on DNA repair kinetics using the comet assay

The complexity of DNA repair mechanisms infers that xenobiotics, derived from food and medicinal plants, may interfere in the process, activating or inhibiting repair. Different flavonoids were investigated, at the highest non-toxic concentration, for their capacity to modulate DNA repair 12, 24 and 48 h after a non-reactive oxygen species (ROS) treatment involving ethylmethanesulfonate (2mM; 2h). After 12h, DNA fragmentation is substantially increased by quercetin; this effect disappears at subsequent sampling times. At 24h, fragmentation is reduced in the presence of apigenin and slightly increased by sakuranetin. None of the flavonoids tested inhibited repair, which seems complete at 48 h. Ex vivo comet experiments were then performed to assess the excision capabilities of protein extracts obtained from flavonoid-treated cells. Quercetin increases non-specific endonuclease activity, apigenin and epicatechin increase the excision of damages and sakuranetin increases both non-specific and specific enzymatic activities. Combining direct repair and ex vivo experiments yields complementary data that may lead to characterizing mechanisms.

Effects of chemopreventive natural products on non-homologous end-joining DNA double-strand break repair.

Double-strand breaks (DSBs) may result from endogenous (e.g., reactive oxygen species, variable (diversity) joining, meiotic exchanges, collapsed replication forks, nucleases) or exogenous (e.g., ionizing radiation, chemotherapeutic agents, radiomimetic compounds) events. DSBs disrupt the integrity of DNA and failed or improper DSBs repair may lead to genomic instability and, eventually, mutations, cancer, or cell death. Non-homologous end-joining (NHEJ) is the major pathway used by higher eukaryotic cells to repair these lesions. Given the complexity of NHEJ and the number of proteins and cofactors involved, secondary metabolites from medicinal or food plants might interfere with the process, activating or inhibiting repair. Twelve natural products, arbutin, curcumin, indole-3-carbinol, and nine flavonoids (apigenin, baicalein, chalcone, epicatechin, genistein, myricetin, naringenin, quercetin, sakuranetin) were chosen for their postulated roles in cancer chemoprevention and/or treatment. The effects of these compounds on NHEJ were investigated with an in vitro protocol based on plasmid substrates. Plasmids were linearized by a restriction enzyme, generating cohesive ends, or by a combination of enzymes, generating incompatible ends; plasmids were then incubated with a nuclear extract prepared from normal human small-intestinal cells (FHS 74 Int), either treated with these natural products or untreated (controls). The NHEJ repair complex from nuclear extracts ligates linearized plasmids, resulting in plasmid oligomers that can be separated and quantified by on-chip microelectrophoresis. Some compounds (chalcone, epicatechin, myricetin, sakuranetin and arbutin) clearly activated NHEJ, whereas others (apigenin, baicalein and curcumin) significantly reduced the repair rate of both types of plasmid substrates. Although this in vitro protocol is only partly representative of the in vivo situation, the natural products appear to interfere with NHEJ repair and warrant further investigation.

On-chip microelectrophoresis for the study of in vitro nonhomologous end-joining DNA double-strand break repair.

Oligomerization of linearized plasmids by nuclear proteins extracts, a recognized measure of nonhomologous end-joining (NHEJ) repair capacity, is typically assessed through agarose gel electrophoresis, a labor-intensive procedure. In the current study, a more convenient NHEJ assay was developed using microchips that allow scaled-down separation and quantification. This microchip method allows a considerable reduction in sample amount and analysis time with similar costs and comparable or slightly better precision. Data obtained with quercetin and wortmannin show that the method can be applied to the screening of food components and natural products for positive and negative modulators of NHEJ, potential chemopreventive and indirect genotoxic compounds, respectively.