摘要:

AbstractMethyl chloride, bromide, and iodide are used as methylating agents. These compounds are mutagenic in short-term tests and do not require activation by exogenous S9 mix. In DNA-binding studies performed in rats and mice,14C-labeled methyl chloride was given by inhalation, and methylation of DNA bases was examined. The compound did not lead to specific DNA adducts. In particular, methylation of DNA bases was not observed. In contrast, methyl bromide and methyl iodide, upon oral and inhalation administration to rats and mice, caused systemic DNA methylation. Specifically, 3-methyl-adenine, 7-methyl-guanine, and O6- methyl-guanine were formed. Long-term inhalation bioassays have been performed in rats and mice with methyl chloride and methyl bromide. Methyl chloride induced renal tumors, but only in male mice at the highest concentration tested (1000 ppm). Under these special conditions, a number of secondary effects occur subsequent to glutathione depletion in the target tissue, resulting in DNA damage (DNA-protein cross-links and probably DNA single-strand breaks). The particular coincidence of secondary high-dose effects precludes a risk extrapolation to man. Methyl bromide did not induce tumors in rats and mice when administered by inhalation. However, experimental data point to a possible local carcinogenic effect on the rat forestomach when the compound is given by gavage. A factor that accounts for the discrepancy between systemic DNA methylation and apparent noncarcinogenicity upon inhalation might be the preference of 7-N over O6methylation of guanine. An extrapolation of the negative rodent inhalation bioassay of methyl bromide to man might be problematic because rodents metabolize methyl bromide very quickly whereas in humans there is a particular subpopulation that only poorly metabolizes the compound (“nonconjugators”). Such individuals can be characterized by incubation of erythrocytes with methyl chloride or methyl bromide and measurement of the substrate decline. Methyl iodide has been tested, with positive outcome, in early carcinogenicity bioassays not based on modem methodology. However, these results, along with the proven systemic methylating potency of methyl iodide, argue in favor of a carcinogenic effect of the compound.

ISSN:1040-8444    

DOI:10.3109/10408449309105011

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractChromium, like many transition metal elements, is essential to life at low concentrations yet toxic to many systems at higher concentrations. In addition to the overt symptoms of acute chromium toxicity, delayed manifestations of chromium exposure become apparent by subsequent increases in the incidence of various human cancers. Chromium is widely used in numerous industrial processes, and as a result is a contaminant of many environmental systems. Chromium, in its myriad chemical forms and oxidation states, has been well studied in terms of its general chemistry and its interactions with biological molecules. However, the precise mechanisms by which chromium is both an essential metal and a carcinogen are not yet fully clear. The following review does not seek to embellish upon the proposed mechanisms of the toxic and carcinogenic actions of chromium, but rather provides a comprehensive review of these theories. The chemical nature of chromium compounds and how these properties impact upon the interactions of chromium with cellular and genetic targets, including animal and human hosts, are discussed.

ISSN:1040-8444    

DOI:10.3109/10408449309105012

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractDevelopmental toxicity to TCDD-like congeners in fish, birds, and mammals, and reproductive toxicity in mammals are reviewed. In fish and bird species, the developmental lesions observed are species dependent, but any given species responds similarly to different TCDD-like congeners. Developmental toxicity in fish resembles“blue sac disease,”whereas structural malformations can occur in at least one bird species. In mammals, developmental toxicity includes decreased growth, structural malformations, functional alterations, and prenatal mortality. At relatively low exposure levels, structural malformations are not common in mammalian species. In contrast, functional alterations are the most sensitive signs of developmental toxicity. These include effects on the male reproductive system and male reproductive behavior in rats, and neurobehavioral effects in monkeys. Human infants exposed during the Yusho and Yu-Cheng episodes, and monkeys and mice exposed perinatally to TCDD developed an ectodermal dysplasia syndrome that includes toxicity to the skin and teeth. Toxicity to the central nervous system in monkey and human infants is a potential part of the ectodermal dysplasia syndrome. Decreases in spermatogenesis and the ability to conceive and carry a pregnancy to term are the most sensitive signs of reproductive toxicity in male and female mammals, respectively.

ISSN:1040-8444    

DOI:10.3109/10408449309105013

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

ISSN:1040-8444    

DOI:10.3109/10408449309105014

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

ISSN:1040-8444    

DOI:10.3109/10408449309105015

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor