Prediction of Rodent Carcinogenesis: An Evaluation of Prechronic Liver Lesions as Forecasters of Liver Tumors in NTP Carcinogenicity Studies

Abstract

Nicotine, a toxic tobacco component, plays an important role in the development of cardiovascular and lung diseases in smokers. Our objective was to investigate the effects of the intraperitoneal (i.p.) nicotine treatment in lung morphology. Wistar male rats (3-4 months old) were divided in five groups, a control one, and other groups treated with nicotine (1 mg/kg/day) for 8 days and sacrificed after 24, 48, 96, and 192 h. Morphometry was used to estimate the lung alveolar parenchyme and septal elastic fibers changes, and immunohistochemistry was performed to detect macrophage metalloelastase (MMP-12) and quantify vessels by immunolabelling with alpha-smooth muscle cells. Thickening of the alveolar septa was present in all nicotine groups, and associated with mononuclear cell infiltration, angiogenesis, and irregular areas of collapse. After 96 h, rat lungs showed macrophage, expressing MMP-12, that was also present after 192 h of recovery. Pleural and parenchyma inflammation, fibrosis and macrophage were also seen after 192 h. Intraperitoneal nicotine treated rats exhibited an increase of the volume fraction of alveolar parenchyme, a reduction of volume and surface fraction septal elastic fibers, and an increase of the numerical fraction of microvasculature vessels compared to control ones. MMP-12 was detected in groups of macrophages Wistar rats lung exhibited a progressive morphological damage after 192 hours of recovery, after 8 daily doses of 1 mg/kg body weight on i.p. nicotine.

Liver Hypertrophy

“…In a survey of 138 chemicals used in the agrochemical industry, a relative increase in liver weight of !150% of control values after 1 year of treatment was positively correlated with the induction of liver tumors in mice (Carmichael et al 1997). Similarly, in another survey of mouse NTP studies where correlations between liver weight increases and histological parameters and carcinogenesis were assessed, the authors concluded that ''the best single predictor of liver cancer in mice was hepatocellular hypertrophy'' (Allen et al 2004). This study demonstrates a highly significant relationship between increases in liver weight and the future outcome of hepatic neoplasia (p < .001; Table 2).…”

“…This study demonstrates a highly significant relationship between increases in liver weight and the future outcome of hepatic neoplasia (p < .001; Table 2). In a similar review of the rat, a less statistically significant relationship (p ¼ .018) between liver weight and hepatocarcinogenesis was also noted, whereby liver weight increases alone correctly predicted eight of the eleven liver carcinogens (but overpredicted twenty-six false positives and failed to predict three true positives; Allen et al 2004). …”

“…Increases in liver weights have been shown to be associated with the induction of increased incidences of hepatocellular neoplasia in 2-year carcinogenicity studies in rodents (Allen et al 2004;Carmichael et al 1997) and while considered to be of little relevance to man for some chemicals (Butler and Newberne 1975;Ito and Sugano 1991;McClain et al 1995;Stevenson et al 1990), dose levels of a chemical inducing this degree of liver weight increase would be considered to carry an increased risk of inducing hepatic neoplasms in these types of study. In a survey of 138 chemicals used in the agrochemical industry, a relative increase in liver weight of !150% of control values after 1 year of treatment was positively correlated with the induction of liver tumors in mice (Carmichael et al 1997).…”

“…The practice of fasting rodents before necropsy was one that was debated at the workshop but because of the differing experiences of the group a recommendation was made for a comparison dose-response study with a known hepatotrophic agent, such as sodium phenobarbitone, in the rat where TABLE 2.-Correlation between liver toxicity and carcinogenesis in mouse National Toxicology Program studies (adapted from Allen et al 2004 groups would be fasted and the results obtained compared to non-fasted groups. The NOEL for the histopathology of hepatocellular hypertrophy would then be compared between the fasted and non-fasted groups.…”

Commentary on “Evaluation of Possible Carcinogenic Risk to Humans Based on Liver Tumors in Rodent Assays

“…A basic premise of Dr. Cohen's argument is that all key events associated with development of liver neoplasms in rodents can be detected in shorter term (thirteen-week) studies (Allen et al 2004). This is likely correct, at least for all key events identified to date.…”