Tsuneo Kada

Detection and chemical identification of natural bio-antimutagens: A case of the green tea factor

A bio-antimutagen, isolated from Japanese green tea (leaves of Camellia sinensis), reduced high spontaneous mutations due to altered DNA-polymerase III in a mutator strain of Bacillus subtilis. Chemical studies showed that the factor was epigallo-catechin-gallate (EGCg).

Rec assay and mutagenicity studies on metal compounds.

We carried out rec assays on 127 metal compounds with Bacillus subtilis to check their DNA-damaging capacity and mutagenicity. Certain compounds of beryllium, cobalt, cesium, iridium, osmium, platinum, rhodium, antimony, tellurium, thallium and vanadium were newly found to be positive in addition to those of known positive metals such as arsenic, cadmium, chromium, mercury, molybdenum and selenium. Reverse mutation assays with Escherichia coli and Salmonella strains showed that compounds of rhodium (RhCl3), tellurium (Na2H4TeO6, Na2TeO3) and platinum (PtCl4, (NH4)2PtCl6) are potent mutagens.

Screening of Environmental Chemical Mutagens by the Rec-Assay System with Bacillus subtilis

For efficient detection and evaluation of environmental chemical mutagens, the assay procedures must be simple and inexpensive. By the use of microorganisms as the repair test, chemicals that damage DNA may be selected very quickly. These DNA-damaging chemicals are likely to be mutagenic and carcinogenic, as well as effectors of chromosome aberrations. Recent developments in techniques and mutagen screening by the rec-assay system using recombination-proficient and -deficient strains of Bacillus subtilis are reviewed in this chapter.

Analysis of the antimutagenic effect of cinnamaldehyde on chemically induced mutagenesis in Escherichia coli

SummaryThe antimutagenic effect of cinnamaldehyde on mutagenesis was investigated using ten kinds of chemical mutagen in Escherichia coli WP2s (uvrA−). In addition, the frequency of mutation induction by each mutagen in an SOS repair deficient (umuC−) strain was compared with that in a wild-type (umuC+) strain. Cinnamaldehyde greatly suppressed the umuC-dependent mutagenesis induced by 4-nitroquinoline 1-oxide (4-NQO), furylfuramide or captan. However, cinnamaldehyde was less effective against the umuC-independent mutagenesis by alkylating agents such as N-methyl-N′-nitro-N-nitrosoguanidine and ethylmethanesulfonate. On the other hand, no inhibitory effect of cinnamaldehyde was observed on prophage induction or tif-mediated filamentous growth. These results suggest that a cinnamaldehyde does not prevent the induction of the SOS functions. Despite the decrease in the number of revertants, a remarkable increase was observed in the survival of 4-NQO-treated WP2s cells after exposure to cinnamaldehyde. The reactivation of survival suggests the promotion of some DNA repair system by cinnamaldehyde. This enhancement of survival was also observed in uvrB, polA, recF or umuC mutants and less in lexA or recB, C mutants. However, it was not observed in recA mutants. Therefore, we assume that cinnamaldehyde may enhance an error-free recombinational repair system by acting on recA-enzyme activity.

Antimutagens and their Modes of Action

Agents suppressing cellular mutagenesis have been known for some time, and their modes of action have been analyzed in the field of bacterial genetics (8, 49). More recently, a number of mutagens have been detected in our environment and their genotoxicities recognized (45). Therefore, it is necessary to have knowledge about antimutagens and their modes of action in order to assess the genotoxic nature of our environment. Crow (9) considers that keeping a low mutation rate in germ cells is important to mankind. For the past several years, we have focused our attention on factors that suppress cellular mutagenesis (19, 22). The word antimutagen has an old origin and has been adopted for factors that reduce the rates of spontaneous and induced mutagenesis by different modes of action. We recently pro-posed a distinction among categories of antimutagens (20, 22) (Fig. 1) as follows: (a) Desmutagens: The frequency of induced mutations will be reduced if mutagens are inactivated by desmutagens in vitro before reaching the cells. There also exist factors that inhibit metabolic activation of chemicals or formation of active forms of mutagens from precursors. “Desmutagens” refers to agents that cause chemical or biochemical modifications of mutagens outside cells (Fig. 2). (b) Bioantimutagens: Factors that interfere with cellular functions which produce genetically stable informative genes from primary damage to DNA should be distinguished from desmutagens and named “bioantimutagens.” Since the word “antimutagens” can be used for factors that reduce the apparent frequencies of mutations, including “desmutagens,” the term bioantimutagens is more specific to those factors that are biologically active (29).

Mutagenicity screening of crude drugs with Bacillus subtilis rec-assay and Salmonella/microsome reversion assay.

This paper describes the screening studies of 104 commercial crude drugs for mutagenicity by the rec-assay with Bacillus subtilis as well as the reversion assay with Ames strains TA98 and TA100 of Salmonella typhimurium. The rec-assays showed that 13 water extracts and 27 methanol extracts of the crude drugs were positive. The Ames assays with or without metabolic activation showed that 24 water extracts and 16 methanol extracts were mutagenic. In total, mutagenic activities were found in 45 samples among the 104 crude drugs tested.

DNA repair enzymes in ataxia telangiectasia and Bloom's syndrome fibroblasts

Ataxia telangiectasia, Blooms syndrome and normal fibroblasts were compared as to the capacity of their cellular extracts to enhance the priming activity of gamma-irradiated colicin E1 DNA for purified DNA polymerase. It was found that an ataxia strain had substantially lower, and a Blooms syndrome strain had slightly lower capacity than a normal strain; while the activities of apurinic site specific endonuclease in these extracts were comparable.

A desmutagenic factor isolated from burdock (Arctium lappa Linne)

A desmutagenic factor was isolated from burdock (Arctium lappa Linne). This factor reduced the mutagenicity of mutagens that are active without metabolic activation, such as 4-NO2-1,2-DAB and 2-NO2-1,4-DAB, as well as mutagens such as ethidium bromide, 2-aminoanthracene, Trp-P-1 and Trp-P-2 requiring S9 for metabolic activation. It is resistant to heat and proteolytic enzymes and sensitive to treatment with MnCl2. The partially purified principles had a molecular weight higher than 300 000 and showed characteristics of a polyanionic substance. An irreversible diminution of the mutagen was confirmed by treatment of 2-NO2-1,4-DAB or Trp-P-2 with the burdock factor.

Antimutagenic effects of germanium oxide on Trp-P-2-induced frameshift mutations in Salmonella typhimurium TA98 and TA1538

A germanium compound, germanium oxide (GeO2) behaved as a potent antimutagen on frameshift-type reverse mutations induced by 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) in strains of Salmonella typhimurium TA98 and TA1538 with and without a plasmid pKM101, respectively. This metal antimutagen seems to work independently of the plasmid, a promotive factor in chemically induced mutagenesis through error-prone DNA repair.

Antimutagenic action of cobaltous chloride on Trp-P-1-induced mutations in Salmonella typhimurium TA98 and TA1538

Abstract Cobaltous chloride worked as a potent antimutagen on Trp-P-1-induced reverse mutations in Salmonella typhimurium , strains TA98 and TA1538. This indicates that this metal antimutagen works independently of the plasmid pKM101. These findings may open new approaches in the analysis of frameshift mutagenesis.