Junko Koyama

Higher radical scavenging activities of polyphenolic antioxidants can be ascribed to chemical reactions following their oxidation

Radical scavenging activities of 34 natural antioxidants were investigated from an electrochemical viewpoint. While the correlation of the oxidation potentials with their DPPH radical scavenging activities (represented by EC(50)) was not high (the correlation coefficient, r=0.73), the number of electrons n required for oxidation of an antioxidant, being obtained by continuous flow-column electrolysis with a slower flow rate (0.05 ml min(-1)), did show a good correlation with EC(50) (1/EC(50)=1.67n+0.50 with r=0.94). The n values of most polyphenols were increased with a decrease in the flow rate, while those of nonpolyphenols were invariant. This suggests that a slower subsequent chemical reaction(s) should be involved in the oxidation of polyphenols, whose higher radical scavenging activities seem to be ascribed to the chemical reactions. In this study, we have proposed a possible mechanism for the oxidation of polyphenols, in which the oxidizable -OH moieties are reproduced through an oxidative dimerization (or more highly polymerization).

Furanonaphthoquinones cause apoptosis of cancer cells by inducing the production of reactive oxygen species by the mitochondrial voltage-dependent anion channel.

The mitochondrial production of reactive oxygen species (ROS) has been implicated in the anticancer activity of furanonaphthoquinone. However, the mechanism of the activation remains elusive. In the current study, we found that treatment of HeLa cells with 2-methyl-5(or -8)-hydroxy-furanonaphthoquinone (FNQ13) induces mitochondrial swelling, followed by apoptosis. This toxic effect of FNQ13 was reduced by the radical scavengers α-tocopherol and trolox. Cytochemical experiments in isolated mitochondria showed that a combination of FNQ13 and NADH induces the production of H2O2 at the exterior mitochondrial membrane surface. This production of H2O2 was reduced by an antibody to the voltage-dependent anion channel (VDAC). Overexpression of the VDAC by transfection with vdac1 cDNA increased the production of H2O2 by HeLa cells, whereas transfection with a small interfering RNA to VDAC reduced FNQ13-induced H2O2 production and cell death due to an almost complete knockdown of VDAC expression. We also found significant correlations between the expression of VDAC and the induction of H2O2 production and cell death by FNQ13 in 11 human cancer cell lines. These results indicate that the anticancer activity of furanonaphthoquinones depends on the production of reactive oxygen species by mitochondrial permeability transition pores (MPTP) including the VDAC.

Anti-infective quinone derivatives of recent patents.

Quinones are important naturally occurring pigments widely distributed in nature and are well known to demonstrate various physiological activities as antimicrobial and anticancer compounds. This review will focus on the preparation, therapeutic application, and administration of several benzoquinones, naphthoquinones, and anthraquinones having anti-infective, e.g. antiviral and antibacterial activities, in recent patents.

Chemopreventive effects of emodin and cassiamin B in mouse skin carcinogenesis

In continuation of our works of natural and synthetic products as cancer chemopreventive agents, we have examined emodin and cassiamin B, which were isolated from Cassia siamea. These compounds exhibited the remarkable anti-tumor promoting effect on two-stage carcinogenesis test of mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter by both topical application. Furthermore, emodin exhibited potent inhibitory activity on two-stage carcinogenesis test of mouse skin tumors induced by nitric oxide donor, (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamide as an initiator and TPA as a promoter.

Inhibitory effects of anthraquinones and bianthraquinones on Epstein-Barr virus activation

Short-term in vitro assays for anti-tumor promoters were carried out for several anthraquinones and bianthraquinones, which were isolated from Cassia siamea and derived from cascaroside A. Anthraquinone monomers showed higher anti-tumor promoting activity than that of bianthraquinones.

Antimicrobial activity of novel furanonaphthoquinone analogs

ABSTRACT Analogs of furanonaphthoquinone (FNQ) from Tecoma ipeMart had MICs ranging from 1.56 to 25 μg/ml against gram-positive bacteria. FNQ showed significantly lower MICs against methicillin-resistant Staphylococcus aureus than against methicillin-sensitive S. aureus. FNQ inhibitedHelicobacter pylori with an MIC of 0.1 μg/ml. Fungi, including pathogenic species, were sensitive to FNQ with MICs similar to those of amphotericin B.

Inhibitory effect of furanonaphthoquinone derivatives on the replication of Japanese encephalitis virus

Japanese encephalitis still occurs in endemic and epidemic forms over a wide area of Asia. Although the vaccine against Japanese encephalitis virus (JEV) is widely used, no antiviral drug has been reported. We used several different kinds of furanonaphthoquinone derivatives and found antiviral activity against JEV. Especially, 2-methylnaphtho[2,3-b]furan-4,9-dione (FNQ3) indicated the highest antiviral activity, followed by 2-(1-hydroxyethyl)-, 5(or 8)-hydroxy-, and 2-methyl-5(or 8)-hydroxy-analogs of naphtho[2,3-b]furan-4,9-dione. In the presence of 3 microg/ml FNQ3, the virus yields in Vero cells were 2 x 10(5) PFU/ml at 24 h after infecting with the virus and 10% of the control level. Western blot analysis using anti-E rabbit sera or anti-NS3 showed that the expression of viral proteins was inhibited by treatment with FNQ3. In addition, Northern blot analysis indicated that the appearance of JEV-RNA was also inhibited by FNQ3. These results suggest that FNQ3 inhibits JEV replication through viral RNA and protein synthesis.

Modified synthesis of monocyclic 1,2,3-triazine and cycloaddition reaction with enamine: the application to the synthesis of alkaloids, tortuosamine, N-formyltortuosamine and N-acetyltortuosamine

Monocyclic 1,2,3-triazines were obtained by periodate oxidation of 1-aminopyrazoles in good reproducibilities and yields. The Diels-Alder reaction of 1,2,3-triazine with several enamines was carried out to afford 2,3-disubstituted pyridines. As an application of this method, we accomplished the synthesis of alkaloids, tortuosamine, N-formyltortuosamine and N-acetyltortuosamine

Correlation between oxidation potentials and inhibitory effects on Epstein-Barr virus activation of flavonoids.

The oxidation potentials of fifteen flavonoids in phosphate buffer at pH 7.2 were determined by cyclic voltammetry. A good correlation was found between these oxidation potentials and the ability of flavonoids to inhibit Epstein-Barr virus early antigen (EBV-EA) activation. Furthermore, multiple regression analysis revealed that the solvent-accessible surface area (SASA) was a useful parameter for estimating the inhibitory effects of flavonoids on EBV-EA activation.

Correlation of redox potentials and inhibitory effects on Epstein-Barr virus activation of 2-azaanthraquinones

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the standard redox potentials of some 2-azaanthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the 2-azaanthraquinones on Epstein-Barr virus early antigen (EBV-EA) activation. It has been further shown that the correlation can be enhanced by introducing an electronic properties, i.e. the atomic charges at the C5 and O12 atoms in the quinone skeleton ring and the HOMO energy as additional parameters.