ROS-driven and preferential killing of HepG2 over L-02 cells by a short-term cooperation of Cu(II) and a catechol-type resveratrol analog.

This study was aimed at understanding why dietary polyphenols with a catechol skeleton tend to exhibit cancer chemopreventive activity by using a catechol-type stilbene (3,4-DHS) as a model molecule. Only a short-term cooperation of 3,4-DHS and exogenous Cu(II) exhibited a strong preferential ability to kill HepG2 cells over normal L02 cells. Mechanism studies reveal that this 3,4-DHS/Cu(II) system could produce extracellularly reactive oxygen species (ROS) and o-quinone through two sequential proton loss electron transfer followed by diffusion of ROS into cells, leading to higher intracellular accumulation of ROS, preferential disruption of redox homeostasis and more effective mitochondria-dependent apoptosis as well as necrosis of HepG2 cells than L-02 cells. This work provides further evidence that dietary catechol-type molecules show chemopreventive activity by virtue of their copper-dependent prooxidant action.

Hypohalous acid-mediated halogenation of resveratrol and its role in antioxidant and antimicrobial activities.

The reactions of resveratrol with proinflammatory oxidants including hypochlorous and hypobromous acids in phosphate-buffered saline/methanol solution were carried out and eight halogenated resveratrol derivatives differing in the number and position of halogen atoms, and the configuration of double bond were obtained. Halogenation of resveratrol took place only at the aromatic A ring, and interestingly, the halogenation increased antioxidant activity of this parent molecule in the 2,2'-azobis(2-amidinopropane) hydrochloride-induced RBC haemolysis model. Additionally, antimicrobial activity of the derivatives against Gram-positive bacteria, Gram-negative bacteria and fungi were tested, and toward Candida albicans, 2-chloro-resveratrol and 2-bromo-resveratrol were more active than the unmodified form and the reference compound fluconazole.

Finding more active antioxidants and cancer chemoprevention agents by elongating the conjugated links of resveratrol.

Resveratrol is the subject of intense research as a natural antioxidant and cancer chemopreventive agent. There has been a great deal of interest and excitement in understanding its action mechanism and developing analogs with antioxidant and cancer chemoprevention activities superior to that of the parent compound in the past decade. This work delineates that elongation of the conjugated links is an important strategy to improve the antioxidant activity of resveratrol analogs, including hydrogen atom- or electron-donating ability in homogeneous solutions and antihemolysis activity in heterogeneous media. More importantly, C3, a triene bearing 4,4'-dihydroxy groups, surfaced as an important lead compound displaying remarkably increased antioxidant, cytotoxic, and apoptosis-inducing activities compared with resveratrol.

Hydroxycinnamic acids as DNA-cleaving agents in the presence of Cu(II) ions: mechanism, structure-activity relationship, and biological implications.

The effectiveness of hydroxycinnamic acids (HCAs), that is, caffeic acid (CaA), chlorogenic acid (ChA), sinapic acid (SA), ferulic acid (FA), 3-hydroxycinnamic acid (3-HCA), and 4-hydroxycinnamic acid (4-HCA), as pBR322 plasmid DNA-cleaving agents in the presence of Cu(II) ions was investigated. Compounds bearing o-hydroxy or 3,5-dimethoxy groups on phenolic rings (CaA, SA, and ChA) were remarkably more effective at causing DNA damage than the compounds bearing no such groups; furthermore, CaA was the most active among the HCAs examined. The involvement of reactive oxygen species (ROS) and Cu(I) ions in the DNA damage was affirmed by the inhibition of the DNA breakage by using specific scavengers of ROS and a Cu(I) chelator. The interaction between CaA and Cu(II) ions and the influence of ethylenediaminetetraacetic acid (EDTA), the solvent, and pH value on the interaction were also studied to help elucidate the detailed prooxidant mechanism by using UV/Vis spectroscopic analysis. On the basis of these observations, it is proposed that it is the CaA phenolate anion, instead of the parent molecule, that chelates with the Cu(II) ion as a bidentate ligand, hence facilitating the intramolecular electron transfer to form the corresponding CaA semiquinone radical intermediate. The latter undergoes a second electron transfer with oxygen to form the corresponding o-quinone and a superoxide, which play a pivotal role in the DNA damage. The intermediacy of the semiquinone radical was supported by isolation of its dimer from the Cu(II)-mediated oxidation products. Intriguingly, CaA was also the most cytotoxic compound among the HCAs toward human promyelocytic leukemia (HL-60) cell proliferation. Addition of exogenous Cu(II) ions resulted in an effect dichotomy on cell viability depending on the concentration of CaA; that is, low concentrations of CaA enhanced the cell viability and, conversely, high concentrations of CaA almost completely inhibited the cell proliferation. On the other hand, when superoxide dismutase was added before, the two stimulation effects of exogenous Cu(II) ions were significantly ameliorated, thus clearly indicating that the oxidative-stress level regulates cell proliferation and death. These findings provide direct evidence for the antioxidant/prooxidant mechanism of cancer chemoprevention.

Antioxidant-based lead discovery for cancer chemoprevention: the case of resveratrol.

Resveratrol is a well-known natural antioxidant and cancer chemopreventive agent that has attracted much interest in the past decade. Resveratrol-directed compounds were synthesized, and their antioxidant effects against reactive oxygen species (ROS)-induced DNA damage, their prooxidant effects on DNA damage in the presence cupric ions, and their cytotoxic and apoptosis-inducing effects on human promyelocytic leukemia (HL-60) cells were investigated in vitro. It was found that the compounds bearing o-diphenoxyl groups exhibited remarkably higher activities in inhibiting ROS-induced DNA damage, accelerating DNA damage in the presence cupric ions, and inducing apoptosis of HL-60 cells compared with the ones bearing no such groups. The detail mechanism of the structure-activity relationship was also studied by the oxidative product analysis of resveratrol and its analogues with galvinoxyl radical or cupric ions and UV-visible spectra change in the presence cupric ions. This study reveals a good and interesting correlation between antioxidant and prooxidant activity, as well as cytotoxicity and apoptosis-inducing activity against HL-60 cells, and provides an idea for designing antioxidant-based cancer chemoprevention agents.

4,4'-Dihydroxy-trans-stilbene, a resveratrol analogue, exhibited enhanced antioxidant activity and cytotoxicity.

Resveratrol (3,5,4'-trans-trihydroxystibene) is a natural phytoalexin present in grapes and red wine, which possesses a variety of biological activities including antioxidant activity. In order to find more active antioxidant with resveratrol as the lead compound we synthesized 4,4'-dihydroxy-trans-stilbene (4,4'-DHS). The antioxidant activities of resveratrol and 4,4'-DHS were evaluated by the reaction kinetics with galvinoxyl radical or Cu(II) ions, and the inhibition effects against free-radical-induced peroxidation of human erythrocyte ghosts. It was found that 4,4'-DHS exhibits remarkably higher antioxidant activity than resveratrol. The oxidative products of resveratrol and 4,4'-DHS in the presence of Cu(II) in acetonitrile were identified as the dihydrofuran dimers by spectroscopic method, and the antioxidant mechanism for 4,4'-DHS was proposed. In addition, 4,4'-DHS exhibits remarkably higher cytotoxicity against human promyelocytic leukemia (HL-60) cells than resveratrol.