Methylene chloride-induced DNA damage: an interspecies comparison

Abstract

DNA single-strand (ss) breaks were detected in the livers of B6C3F1 mice immediately following exposure to 4000-8000 p.p.m. methylene chloride (MC) for 6 h. This damage was undetectable 2 h after exposure, suggesting an active DNA repair process. Similarly, DNA ss breaks were detected in whole lung homogenates taken from mice exposed to 2000-6000 p.p.m. MC. The DNA of mouse Clara cells incubated in vitro with MC was also damaged at concentrations of 5 mM MC and above. Pre-treatment of mice with the glutathione depletor buthionine sulphoximine (BSO) caused a decrease in the amount of DNA damage detected, suggesting a GST-mediated mechanism. DNA damage was also reduced in Clara cells when incubated in vitro with MC in the presence of BSO. In CHO cells induction of DNA damage was dependent upon exogenous MC metabolism by mouse liver S100 fraction (but not microsomes) in the presence of GSH. DNA ss breaks were not induced by MC in hamster hepatocytes in vitro at concentrations from 5 to 90 mM MC, nor in eight individual samples of normal human hepatocytes exposed to MC at similar concentrations. The ability of MC to induce DNA ss breaks in the four species studied is entirely compatible with the known carcinogenicity of this chemical in animals and offers experimental evidence to suggest that humans would not be susceptible to MC-induced liver cancer. The DNA ss breaks correlate with the metabolism of MC by the GST pathway and provide an explanation for the lack of sensitivity of hamsters and rats to MC-induced liver cancer.

Dichloromethane Metabolism to Formaldehyde and Reaction of Formaldehyde with Nucleic Acids in Hepatocytes of Rodents and Humans with and without Glutathione S-Transferase T1 and M1 Genes

“…The present findings on DPX formation in hepatocytes from mice, rats, hamsters, and humans are consistent with observations of Graves et al (1995) regarding the formation of DNA single-strand (ss) breaks in hepatocytes from these species. These investigators detected DNA ss breaks in mouse hepatocytes incubated with DCM at aqueous concentrations 5= 0.4 mM, which are similar to the concentrations at which DPX were detected in mouse hepatocytes (Fig.…”

“…1). Graves et al (1995) also observed the formation of DNA ss breaks in rat hepatocytes, but only at concentrations 5= 30 mM. According to Graves et al (1995), DCM concentrations above 30 mM are equivalent to in vivo concentrations > 86,000 ppm, which exceed the acute lethal concentration of DCM in rodents.…”

“…Graves et al (1995) also observed the formation of DNA ss breaks in rat hepatocytes, but only at concentrations 5= 30 mM. According to Graves et al (1995), DCM concentrations above 30 mM are equivalent to in vivo concentrations > 86,000 ppm, which exceed the acute lethal concentration of DCM in rodents. Graves et al (1995) did not observe DNA ss breaks in either hamster or human (n = 8) hepatocytes at concentrations as high as 90 or 120 mM, respectively.…”

“…According to Graves et al (1995), DCM concentrations above 30 mM are equivalent to in vivo concentrations > 86,000 ppm, which exceed the acute lethal concentration of DCM in rodents. Graves et al (1995) did not observe DNA ss breaks in either hamster or human (n = 8) hepatocytes at concentrations as high as 90 or 120 mM, respectively. Thus, only mouse hepatocytes were capable of forming either DPX or DNA ss breaks at concentrations below 5 mM.…”

Evidence that human class Theta glutathione S-transferase T1-1 can catalyse the activation of dichloromethane, a liver and lung carcinogen in the mouse: Comparison of the tissue distribution of GST T1-1 with that of classes Alpha, Mu and Pi GST in human

“…Certain of the chemicals that are activated by GST are widely distributed in the environment ; there is therefore justified concern about the risk they pose to human health. For example, DCM, which is a potent hepatic and pulmonary carcinogen in mouse [20,21], is found in paint strippers, aerosol preparations and is used extensively as an industrial solvent [22].…”