Patterns of chloroform-induced regenerative cell proliferation in BDF1 mice correlate with organ specificity and dose-response of tumor formation

• Published in: Carcinogenesis (New York) Vol. 19; no. 1; pp. 187 - 193
• Main Authors: TEMPLIN, M. V, CONSTAN, A. A, WOLF, D. C, WONG, B. A, BUTTERWORTH, B. E
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 1998; Oxford Publishing Limited (England)
• Subjects: Adenoma - chemically induced; Adenoma - pathology; Animals; Biological and medical sciences; Body Weight - drug effects; Carcinogenesis, carcinogens and anticarcinogens; Carcinogens - toxicity; Carcinoma - chemically induced; Carcinoma - pathology; Cell Division - drug effects; Chemical agents; Chloroform - toxicity; Dose-Response Relationship, Drug; Female; Liver - drug effects; Liver - pathology; Liver - physiology; Liver Neoplasms - chemically induced; Liver Neoplasms - pathology; Liver Regeneration - drug effects; Male; Medical sciences; Mice; Organ Size - drug effects; Sex Characteristics; Time Factors; Tumors; Cell proliferation; Chlorination; Toxicity; Liver; Hepatic disease; Carcinogenesis; Kidney; Dose activity relation; Organochlorine compounds; Organ specificity; Mechanism of action; Kidney disease; Volatile compound; Urinary system disease; Chloroform; Rodentia; Malignant tumor; Inhalation; Carcinogen; Vertebrata; Mammalia; Mouse; Animal; Digestive diseases; By product
• ISSN: 0143-3334; 1460-2180; 1460-2180
• DOI: 10.1093/carcin/19.1.187

It has been reported that chloroform administered to BDF1 mice by inhalation for 2 years at concentrations of 5, 30 or 90 p.p.m. for 6 h/day, 5 days/week induced an increase in renal cell tumors in male but not female mice exposed to the doses of 30 and 90 p.p.m. A small increase in liver tumors was statistically significant in the female mice at 90 p.p.m. if the incidences of carcinomas and adenomas were combined. Because chloroform is not a DNA reactive mutagen, a 13-week time-course and dose-response study was conducted under conditions of the original bioassay to examine whether regenerative cell proliferation was an underlying mechanism of carcinogenesis. Mice were given bromodeoxyuridine via infusion during the last 3.5 days prior to necropsy to label cells in S-phase. Chloroform induced pathology and regenerative cell proliferation, measured as the labeling index (LI, percentage of cells in S-phase), were assessed microscopically and immunohistochemically. Male mice exposed to 30 and 90 p.p.m. exhibited a dose-dependent increase in regenerating tubules within the renal cortex and up to a 31-fold increase in LI. No renal lesions or increased LI were observed in females. Increased centrilobular to midzonal hepatocyte degeneration and vacuolation and a 7-fold increase over controls in the hepatocyte LI were observed in the female mice at 90 p.p.m. at 13 weeks. Males exhibited similar pathology, but the increase in LI was not sustained. The observed correlations between cytolethality and regenerative cell proliferation with tumor formation supports extensive evidence that chloroform induces cancer via a non-genotoxic-cytotoxic mode of action. A concentration of 5 p.p.m. is the no-observed-adverse-effect level for nephrotoxicity, cell proliferation and cancer. An appropriate safety factor applied to this value is a straightforward approach to cancer risk assessment that is consistent with the mode of action of chloroform.