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Influence of ronidazole on chromosomes of the chinese hamster in vivo
Letters
406
INFLUENCE
10 the Ediror
OF RONIDAZOLE ON CHROMOSOMES CHINESE HAMSTER IN VII/O
OF THE
Sir,-The use of ronidazole (a 5-nitroimidazole derivative) for the prevention or treatment of histomoniasis in pigs and poultry raises the possibility of pollution of surface waters or contamination of meat and meat products with its residues. Ronidazole and some related compounds have shown mutagenic activity in bacterial systems (Foster et 01. Br. J. Cancer 1976, 33, 485; Speck et al. J. natn. Cancer Inst. 1976, 56, 283: Voogd et al. Mutation Res. 1974, 26, 483), but we have found no chromosomal damage in the lymphocytes of Chinese hamsters treated with ronidazole. Male and female hamsters, approximately 1 year old (body weight 36-4Og), were given on three successive days an ip injection of either a suspension of ronidazole (99% pure, from Merck & Co.. Rahway, NJ) in 2% aqueous carboxymethylcellulose (CMC) or 2% CMC alone, the daily dose of ronidazole being 130 mg/kg body weight (l/10 of the LDs,, in the mouse). Lymphocytes from blood samples taken before treatment and 3 days after the final dose were cultured as described previously (De Jong & Anders. Experientia 1972, 28, 86; van Went-de Vries et a/. Fd Cosmet. Toxicol. 1975, 13, 415) and chromosome analyses were carried out, again as previously described (van Went-de Vries et al. lot. cit.), 50 metaphases being analysed for each culture. Structural abnormalities were expressed as the minimum number of breakpoints necessary for the formation of the total number of aberrations found in each culture, allowing one for each break or fragment and two for translocations, ring-chromosomes and exchanges. In the incidence of aneuploid and of polyploid cells, none of the ten hamsters treated with ronidazole showed any difference between the post-injection and pre-injection (control) values, and injection of the vehicle alone had a similar lack of effect in each of the ten control hamsters. The variations in the incidence of structural chromosomal abnormalities were great enough for statistical analysis to be undertaken. Using the Freeman and Tukey transformation (De Jonge, Introduction to Medical Statistics: Essay of the Dutch Institute for Preventive Medicine, XLI, part II (1964). p. 688) and a one-sided Student’s t test on the individual differences between the transformed pre- and post-injection values, no significant difference was found between treatment with ronidazole and treatment with the vehicle. [Details of the chromosomal analyses for individual hamsters can be obtained from the undersigned.] When administered to turkeys in feed, ronidazole is rapidly degraded by ring scission followed ultimately by the production of intermediate compounds of amino acid and carbohydrate metabolism (oxalic acid, a-ketoglutaric acid and glutamic acid). Other nitroimidazoles have been reported to resist ring scission: dimetridazole yields seven structurally related metabolites in turkeys, while metronidazole is converted to 5-nitroimidazole-containing compounds in man and mice (Rosenblum et al. J. agric. Fd Chem. 1972. 20, 360). Hite et al. (Mutation Res. 1976, 40, 289) found ronidazole to be mutagenic in the Ames test, but not in the dominant lethal assay, in the micronucleus test or in bone-marrow cells exposed in r,iuo. This lack of mutagenic activity in animal systems, a finding supported by our own results in the hamster, may be due to the rapid breakdown of ronidazole in uiuo. Schinxel & Schmid (ibid 1976, 40, 139) have expressed doubts about the value of this in uiuo lymphocyte system for mutagenicity testing, but Ku&ova (ibid 1976, 41, 123) considers such a test essential for workers exposed to chemicals, and we consider the system satisfactory, having detected chromosome abnormalities in man as well as the hamster months after administration of an active agent (van Went-de Vries et al. lot. cit.). Because the 5-nitroimidazoles exert their toxic activity under predominantly anaerobic conditions, it has been suggested that their cytocidal action is due to their reduction to a toxic intermediate (Eakins et al. Biochem. Pharmac. 1976. 25, 1151). Ronidazole, however, is also mutagenic in aerobic bacterial systems (Hite et al. lot. cit.: Voogd et al. lot. cit.). It is also possible that ronidazole may cause gene mutations rather than chromosome damage. A definite conclusion about the safety of ronidazole as a contaminant of food or water consumed by man for a major part of life must await the results of other mutagenicity tests and of carcinogenicity studies as well as further data on metabolism in man. G. F. VAN WENT, National Institute of Public Health, Laboratory of Pharmacology, P.O. Box I, Bilthouen, The Netherlands
406
INFLUENCE
10 the Ediror
OF RONIDAZOLE ON CHROMOSOMES CHINESE HAMSTER IN VII/O
OF THE
Sir,-The use of ronidazole (a 5-nitroimidazole derivative) for the prevention or treatment of histomoniasis in pigs and poultry raises the possibility of pollution of surface waters or contamination of meat and meat products with its residues. Ronidazole and some related compounds have shown mutagenic activity in bacterial systems (Foster et 01. Br. J. Cancer 1976, 33, 485; Speck et al. J. natn. Cancer Inst. 1976, 56, 283: Voogd et al. Mutation Res. 1974, 26, 483), but we have found no chromosomal damage in the lymphocytes of Chinese hamsters treated with ronidazole. Male and female hamsters, approximately 1 year old (body weight 36-4Og), were given on three successive days an ip injection of either a suspension of ronidazole (99% pure, from Merck & Co.. Rahway, NJ) in 2% aqueous carboxymethylcellulose (CMC) or 2% CMC alone, the daily dose of ronidazole being 130 mg/kg body weight (l/10 of the LDs,, in the mouse). Lymphocytes from blood samples taken before treatment and 3 days after the final dose were cultured as described previously (De Jong & Anders. Experientia 1972, 28, 86; van Went-de Vries et a/. Fd Cosmet. Toxicol. 1975, 13, 415) and chromosome analyses were carried out, again as previously described (van Went-de Vries et al. lot. cit.), 50 metaphases being analysed for each culture. Structural abnormalities were expressed as the minimum number of breakpoints necessary for the formation of the total number of aberrations found in each culture, allowing one for each break or fragment and two for translocations, ring-chromosomes and exchanges. In the incidence of aneuploid and of polyploid cells, none of the ten hamsters treated with ronidazole showed any difference between the post-injection and pre-injection (control) values, and injection of the vehicle alone had a similar lack of effect in each of the ten control hamsters. The variations in the incidence of structural chromosomal abnormalities were great enough for statistical analysis to be undertaken. Using the Freeman and Tukey transformation (De Jonge, Introduction to Medical Statistics: Essay of the Dutch Institute for Preventive Medicine, XLI, part II (1964). p. 688) and a one-sided Student’s t test on the individual differences between the transformed pre- and post-injection values, no significant difference was found between treatment with ronidazole and treatment with the vehicle. [Details of the chromosomal analyses for individual hamsters can be obtained from the undersigned.] When administered to turkeys in feed, ronidazole is rapidly degraded by ring scission followed ultimately by the production of intermediate compounds of amino acid and carbohydrate metabolism (oxalic acid, a-ketoglutaric acid and glutamic acid). Other nitroimidazoles have been reported to resist ring scission: dimetridazole yields seven structurally related metabolites in turkeys, while metronidazole is converted to 5-nitroimidazole-containing compounds in man and mice (Rosenblum et al. J. agric. Fd Chem. 1972. 20, 360). Hite et al. (Mutation Res. 1976, 40, 289) found ronidazole to be mutagenic in the Ames test, but not in the dominant lethal assay, in the micronucleus test or in bone-marrow cells exposed in r,iuo. This lack of mutagenic activity in animal systems, a finding supported by our own results in the hamster, may be due to the rapid breakdown of ronidazole in uiuo. Schinxel & Schmid (ibid 1976, 40, 139) have expressed doubts about the value of this in uiuo lymphocyte system for mutagenicity testing, but Ku&ova (ibid 1976, 41, 123) considers such a test essential for workers exposed to chemicals, and we consider the system satisfactory, having detected chromosome abnormalities in man as well as the hamster months after administration of an active agent (van Went-de Vries et al. lot. cit.). Because the 5-nitroimidazoles exert their toxic activity under predominantly anaerobic conditions, it has been suggested that their cytocidal action is due to their reduction to a toxic intermediate (Eakins et al. Biochem. Pharmac. 1976. 25, 1151). Ronidazole, however, is also mutagenic in aerobic bacterial systems (Hite et al. lot. cit.: Voogd et al. lot. cit.). It is also possible that ronidazole may cause gene mutations rather than chromosome damage. A definite conclusion about the safety of ronidazole as a contaminant of food or water consumed by man for a major part of life must await the results of other mutagenicity tests and of carcinogenicity studies as well as further data on metabolism in man. G. F. VAN WENT, National Institute of Public Health, Laboratory of Pharmacology, P.O. Box I, Bilthouen, The Netherlands