The carcinogenic and other chronic effects of persistent halogenated organic compounds

A case of metastatic adrenocortical carcinoma diagnosed with steroidogenic factor-1 in a sprague-dawley rat

This report describes the morphological and immunohistochemical characteristics of an adrenocortical carcinoma with distant metastasis in a Sprague-Dawley rat. Macroscopically, a single large mass was observed in the adrenal gland, and multiple nodules were noted in the lung, liver and thyroid. Histologically, the adrenal tumor consisted of a solid growth of eosinophilic round cells with nuclear atypia. Vascular invasion was present, and multiple metastatic lesions were also observed in the lungs, liver, and mediastinal lymph nodes. Immunohistochemically, the nuclei of these tumor cells were positive for Steroidogenic Factor-1 (SF-1). In the thyroid, tumor cells histologically resembling adrenal cells were immunohistochemically negative for SF-1 but positive for calcitonin; thus the lesion was diagnosed as thyroid C-cell carcinoma. From these results, the present case was diagnosed as adrenocortical carcinoma with distant metastases. SF-1 could be a valuable marker for the differential diagnosis of adrenocortical tumors versus other endocrine tumors such as C-cell carcinoma.

Chemical disease in humans: problems in comparative toxicology

Difficulties in assessment of the comparative pharmacology of drugs now apply to the effects on humans of foreign compounds from the environment (xenobiotics). Perhaps the most striking change in perspective has been the recognition that a latency of several decades may precede the development of toxic effects. Xenobiotics may persist and accumulate in tissue stores, and estimates of biologically active doses are sometimes complicated by the presence of highly toxic trace contaminants and homologues that have varying biological activity. The effects of chemical exposure on the tissues may be obscured by the absence of the pathognomonic symptoms normally associated with the structural changes of disease. Interactions between two or more xenobiotics or between xenobiotics and genetic and metabolic variables may explain the lack of coherence between carefully defined laboratory observations and the clinical effects of enzyme-inducing xenobiotics. Since we have considerable evidence that biological processes are strikingly similar in different mammalian species, the toxicological significance to humans of enzyme induction and related processes requires careful evaluation.

Adrenal cortical foci and nodules in Sprague-Dawley rats treated with N-nitrosomorpholine. Light and electron microscopic findings

Treatment of male Sprague-Dawley rats with N-nitrosomorpholine (NNM) in the drinking water at a dose of 120 mg/l for 7 weeks resulted in a subsequent enhanced development of focal and nodular lesions in the adrenal cortex. Sequential observation revealed that focal lesions in the zona reticularis/fasciculata or the zona glomerulosa developed both earlier and at a significantly higher incidence in animals treated with carcinogen than in untreated controls. Foci observed within or adjacent to the zona glomerulosa were all of pale cell appearance and contained large numbers of electron-dense cytoplasmic granules similar to those observed in normal granulosa cells. The foci and nodules which arose in the zona reticularis/fasciculata were, in contrast, characterized by a reduction or loss of the dense osmiophilic droplets normally seen in the cells of this region of the adrenal cortex, a pronounced increase in pleomorphic mitochondria of atypical appearance and the development of vacuoles.

Induction of peroxisome proliferation and hepatic tumours in C57BL/6N mice by ciprofibrate, a hypolipidaemic compound

The hepatic effects of ciprofibrate, a potent peroxisome proliferator, were evaluated in male C57BL/6N mice, a mouse strain with very low incidence of spontaneous liver tumour development. Dietary feeding of ciprofibrate (0.0125% or 0.025% w/w) for 2 weeks resulted in a marked proliferation of peroxisomes (9-fold increase) and several-fold increase (8- to 10-fold) in the activity of peroxisomal beta-oxidation enzymes. Feeding ciprofibrate at 0.025% concentration for 15 months followed by a 0.0125% for 6 months led to the development of hepatic adenomas in 8/14 (57%) and hepatocellular carcinomas (HCC) in 3/14 (21%) mice. In mice given 0.0125% ciprofibrate for 18 months 5 of 8 (62%) and 3 of 8 (37%) developed adenomas and HCC respectively. Similar to the findings observed in rats, both the adenomas and HCC were negative for gamma-glutamyltranspeptidase. These results in C57BL/6N mice of hepatocarcinogenic effect of ciprofibrate, a non-genotoxic chemical, indicate that peroxisome proliferation can be used as a reliable parameter to evaluate the carcinogenicity of hypolipidaemic compounds.

Porphyrins and hepatotoxicity

Human porphyrias are rare inborn disorders of porphyrin metabolism. Porphyria cutanea tarda is one such disorder, which may occur spontaneously after the ingestion of drugs and alcohol. This is the "constitutional" type and is associated with a deficiency of uroporphyrinogen decarboxylase in the liver. This constitutional type must be differentiated from the "acquired" type, which occurred in hundreds of people poisoned by hexachlorobenzene in Turkey. Morphological changes observed in the livers of animals and humans vary greatly. Porphyria cutanea tarda may be associated with very little liver pathology or with very pronounced changes, depending on the agent causing the porphyria. Usually, the liver has an increased iron load, and mitochondria contain a crystalline material.

Effect of PCB on some MFO enzyme activities in pregnant and virgin rabbits

Fenclor 64 (a PCB's commercial mixture) was administered twice i.p. to virgin and pregnant New Zealand rabbits at the dose of 100 mg/Kg to evaluate its inducing properties on the following hepatic microsomal MFO activities: p-nitro-anisole-O-demethylase, amino-pyrine-N-demethylase, acetanilide-hydroxylase and aryl-hydrocarbons-hydroxylase. The results indicate that Fenclor 64 evoked a "mixed type" induction in virgin as well as in pregnant rabbits since it increased liver weight, cytochrome P-450 levels, as well as p-nitro-anisole-O-demethylase and acetanilide-hydroxylase. Pregnancy by itself affects only amino-pyrine-N-demethylase levels.

Effects of PCBs and related compounds on hepatocarcinogenesis in rats and mice

Commercial mixtures of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) can cause hepatocellular carcinoma in rats and mice. Present evidence indicates that these chemicals act as promoters and not initiators of hepatocarcinogenesis. Our results show that Firemaster BP-6 (FM) and its nontoxic major congener, 2,2', 4,4', 5,5'-hexabromobiphenyl (HBB), act as promoters in the two-stage model for hepatocarcinogenesis devised by Pitot and associates. A toxic congener, 3,3', 4,4', 5,5'-HBB, also was assessed for tumor-promoting activity. This congener, though not in FM, is similar to TCDD, in that both cause 3-methylcholanthrene (MC)-type induction of hepatic microsomal enzymes and produce similar toxic responses. FM contains several congeners which are mixed-type inducers in that they induce MC-type and phenobarbital (PB)-type enzymes. The toxicity of FM is most likely associated with its congeners which are mixed-type inducers and not to relatively nontoxic congeners such as 2,2', 4,4', 5,5'-HBB which are strictly PB-type inducers. Congener 3,3', 4,4', 5,5'-HBB acted as a tumor promoter only at a dose that was hepatotoxic. A synergistic effect on tumor promoting ability was produced by combining a nontoxic and nonpromoting dose of 3,3', 4,4', 5,5'-HBB with a promoting dose of 2,2', 4,4', 5,5'-HBB. Our results suggest that synergism between toxic and nontoxic congeners in FM may explain why mixtures such as FM have greater promoting ability than individual congeners. Our results also indicate that with PBB, toxicity and carcinogenicity are not necessarily related.

Aroclor 1254 increases the genotoxicity of several carcinogens to liver primary cell cultures

The genotoxicity of both direct-acting and precarcinogenic chemicals was evaluated in liver primary cell cultures (LPCC) from untreated and Aroclor 1254 (Ar) pretreated rats. Hepatocytes were isolated from partially hepatectomized rats and their DNA was labeled in vitro with [3H] dThd; the molecular weight of single-stranded DNA was determined by alkaline sucrose sedimentation. Two parameters of DNA damage were defined: the mean effective dose (ED50), i.e., the carcinogen concentration that decreased the DNA molecular weight to half the original, and the DNA breaking potency (DBP), i.e., the number of breaks per DNA molecule produced by 2 h exposure to 1 mM concentration of the chemical. Two hours exposure of LPCC from untreated rats to the direct-acting alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) (6.8-340 microM) and to the precarcinogens benzo[a]pyrene (BaP) (0.05-0.33 mM) and dimethylnitrosamine (DMN) (0.45-16 mM) produced a concentration-dependent decrease in the molecular weight of DNA. Pretreatment of rats with Ar decreased significantly the sedimentation velocity of DNA and increased five, three, and two times the DBP of MNNG, BaP, and DMN, respectively. These results show that Ar-pretreatment of rats increases the genotoxicity of both direct-acting and precarcinogenic chemicals and suggest that Ar might increase the genotoxicity of chemical carcinogens perhaps by enhancing their metabolic activation, by producing direct genotoxic effects, or both. Our results also emphasize the carcinogenic risk that the environmental pollution by polychlorinated biphenyls might represent to humans.

Pathology of chronic polychlorinated biphenyl (PCB) feeding in rats

The hepatocarcinogenic effect of Clophen A 30 and Clophen A 60 was tested in male weanling rats by long-term feeding over a period of 832 days. The mortality rate was investigated in 100-day intervals. In the first 800 days liver carcinoma accounted for 21% of necropsies in the Clophen A 60 group but only 2% of the necropsies in the Clophen A 30 group and none in the control animals. The tumors were first observed after 700 days. After 800 days hepatocellular carcinoma was the most common lesion observed in the Clophen A 60 animals (61%) whereas it was only observed in 3% of animals in the Clophen A 30 group and 2% in the controls. Preneoplastic lesions, such as foci of hepatocellular alterations and neoplastic nodules, were first observed after Day 500. The incidence of foci predominated in all time intervals, but an increase in neoplastic nodules and hepatocellular carcinomas was observed with increased time. There was a marked trend from foci to neoplastic nodule to hepatocellular carcinoma with time. The total mortality rate and the incidence of thymoma, inflammatory lesions of the urogenital tract, in the experiment were significantly reduced by Clophen administration. Whether this protective effect could be induced by polychlorinated biphenyls (PCBs) is discussed.

Carcinogen testing: current problems and new approaches

The classic procedures for testing potential carcinogens in animals have basically not changed in the past 50 years. Considerable knowledge of the mechanisms of carcinogenesis has accrued in the last 20 years, particularly concepts on the metabolic activation of chemicals to reactive electrophilic compounds that can interact with nucleophilic including DNA. These developments, in turn, have yielded a framework for integrating into carcinogen testing the determination of genetic effects of chemicals. A systematic decision point approach to carcinogen testing has been developed which entails a sequential decision-making process as specific tests are performed and evaluated prior to initiation of higher order, more complex tests. Compared to conventional bioassays in rodents, this approach provides knowledge based on mechanisms of carcinogenesis, yields a substantial amount of data at minimal cost, and forms a solid base for eventual heath risk assessment.

Evidence for an epigenetic mode of action in organochlorine pesticide hepatocarcinogenicity: a lack of genotoxicity in rat, mouse, and hamster hepatocytes

Genotoxicity was not elicited by any of a variety of organochlorine pesticides tested in the hepatocyte primary culture (HPC)/DNA repair assay utilizing hepatocytes from the rat, mouse, and hamster. DNA repair was observed in response to the positive control in all three systems. Thus the tumorigenicity of the organochlorine pesticides appears to reflect an epigenetic mechanism, probably involving a promotional effect resulting from a disruption in intercellular communication.