Iceland (IS) and Denmark (DK) are ethnically, culturally, and economically closely related Nordic countries, but gastric cancer is much more frequent in Iceland, and other differences in the ...occurrence rates of gastric diseases are also suspected. Therefore a cooperative study was initiated comparing Icelandic and Danish patients with gastric ulcer (GU), duodenal ulcer (DU), and X-ray negative dyspepsia (XND) as regards clinical features, external factors of possible importance for gastritis and cancer, gastroscopic appearance, and histological gastric mucosal changes. The project lasted one year and comprised 93 Icelandic and 88 Danish patients. A large number of comparisons showed a high degree of similarity between Icelandic and Danish patients. Significant differences were found in tobacco consumption (DK greater than IS), duration of symptoms in XND (IS greater than DK), whereas the positon ratio of GU (IS less than DK) and acetylsalicylic acid consumption (DK greater than IS) showed non-significant trends. Significant difference was found between the occurrence of diffuse macroscopic changes of the gastric mucosa (IS greater than DK), which corresponds to the histological differences to be described in a subsequent article.
The potential for human exposure to heterocyclic amine (HAA) mutagens derived from cooking food prompted an evaluation of the disposition and carcinogenicity of three of the HAAs in nonhuman ...primates, especially cynomolgus monkeys. The three HAAs currently under study are 2-amino-3-methylimidazo 4, 5-fquinoline (IQ), 2-amino-3,8-dimethylimidazo4,5-fquinoxaline (8-MeIQx) and 2-amino-1-methyl-6-phenylimidazo 4,5,bpyridine (PhIP). These three HAAs were selected on the basis of several factors including structure, mutagenic activity in vitro, concentration in cooked meat, activity in rodent carcinogenicity tests and availability. Studies on the disposition of IQ demonstrated that it was extensively metabolized in monkeys and excreted in urine and feces as metabolites. These metabolites represent predominantly detoxification products of IQ. The extent of in vivo activation of IQ and PhIP was assessed by measuring DNA adducts in various tissues and white blood cells of monkeys following administration of the compounds. Both compounds form high levels of DNA adducts in a number of organs, particularly the liver, kidney, and heart. The carcinogenicity of IQ, 8-MeIQx and PhIP in nonhuman primates has been under study for 5 years, 24 months, and 7 months, respectively. Thus far, IQ has induced hepatocellular carcinoma in 3 of 20 monkeys at doses of 10 mg/kg daily, 5 days/week and in 10 of 20 monkeys at 20 mg/kg on the same schedule. Thus, IQ is a potent liver carcinogen in nonhuman primates and a potential carcinogen for humans.
The Ames Salmonella plate assay was employed to test urine samples from bladder cancer patients and controls living in Egypt for the presence of chemical mutagens. Urine from five groups of Egyptian ...adults were tested, including individuals with (1) neither bilharziasis nor bladder cancer, (2) urinary bilharziasis and normal urinary cytology, (3) urinary bilharziasis and atypical urinary cytology, (4) carcinoma of the bilharzial bladder, and (5) bladder cancer without bilharziasis. Plates treated with histidine dependent bacteria, S-9 mix, beta-glucuronidases and 0.3 ml sterile urine from all five groups yielded 50 to 150 percent more colonies than plates treated with saline instead of urine. These differences were highly statistically significant for all groups except subjects with bladder cancer without bilharziasis. Gross and microscopic inspection suggested, however, that plates containing urine had heavier bacterial lawns than plates treated with saline. A procedure for quantitating viable bacteria in the lawn was devised which demonstrated that the increase in colonies on urine treated plates could be attributed to increased numbers of viable bacteria in the bacterial lawn on those plates. There was, therefore, no convincing evidence for the presence of mutagenic substances in these urine samples.
The effects of 3-methylcholanthrene (MC) pretreatment on metabolism and mutagenic activation of dimethylnitrosamine (DMN) were studied with liver subfractions from two strains of mice differing ...genetically with respect to aromatic hydrocarbon responsiveness. Both mutagenic activation and DMN N-demethylase activity segregated with aryl hydrocarbon (benzoapyrene) hydroxylase activity as a dominant trait in appropriate crosses between C57BL/6J (Ahb Ahb) and DBA/2J (Ahd Ahd) mice. DMN metabolism and mutagenicity were increased by MC-pretreatment in responsive Ahb Ahb and Ahb Ahd mice, but not in non-responsive Ahd Ahd mice. This indicates the involvement of the Ah locus in the genetic regulation of these activities in mice. Deuteration of DMN reduced mutagenicity and DMN N-demethylase activity by approximately 90 and 50 percent, respectively.
This study describes histopathological findings in 26 nonhuman primates (cynomolgus and rhesus monkeys) with liver tumors after dosing with IQ for time periods of 27 to 72 months. In most of the ...cases 2-5 well-defined tumor nodules were present in the liver at the time of autopsy. In 5 cases there were numerous nodules occupying most of the liver. Intrahepatic vascular invasion was observed in 14 cases, and lung metastases in 6 cases. The histology of 72 nodules from 21 cases with well-defined tumors and the 5 cases with massive involvement was studied. The majority of the tumors represented well to moderately well-differentiated hepatocellular carcinoma (HCC). Trabecular pattern was most common, followed by solid and pseudoglandular patterns. Five nodules displayed poorly differentiated pleomorphic variant of HCC with large, often multinucleated, tumor cells. Spindle cell and clear cell variants of HCC were seen in one nodule each. Two nodules were classified as cholangiocarcinomas. Immunostaining for cytokeratins 7 and 19 did not prove to be reliable markers for tumors of bile duct origin, since they were also expressed in some of the poorly differentiated HCC. The most common microscopic finding of the noncancerous portions of the liver were clear cell foci, composed of large, glycogen rich hepatocytes with small eccentric nuclei. Other lesions commonly found were dysplastic hepatocyte foci around the central veins and proliferating bile ductular-like (oval) cells along the portal areas and portal tracts.
During the past decade and a half, a number of potent mutagens belonging to the class of heterocyclic aromatic amines (HCA) have been isolated and identified from cooked fish, beef, fowl and other ...meat, and from beef extracts. Several of these HCA mutagens have also been found to be carcinogenic in rodent bioassays, and one of these compounds, 2-amino-3-methylimidazo-4,5-f-quinoline (IQ), has recently been found to cause hepatocellular carcinoma in cynomolgus monkeys. The potential etiological role of these mutagens and carcinogens in human cancer prompted us to evaluate the genotoxicity of these compounds in both nonhuman primates and rodents, with particular emphasis on the formation and tissue distribution of DNA adducts. We selected three compounds for this study based on several factors including chemical structure, mutagenic activity in vitro, concentration in cooked food, and carcinogenic activity in the rodent test system. These were IQ, 2-amino-3,8-dimethylimidazo4,5-f-quinoxaline (8-MeIQx), and 2-amino-1-methyl-6-phenylimidazo-4,5-b-pyridine (PhIP). To maximize the sensitivity of the DNA adduct measurements, we have employed the 32P-postlabeling method to analyze levels and tissue distribution of DNA adducts derived from IQ 8-MeIQx, and PhIP. We have measured DNA adduct formation for all three compounds in various tissues and white blood cells of monkeys following both acute and chronic administration. Both IQ and PhIP form high levels of adducts in a number of organs, particularly liver, kidney, and heart. In contrast, administration of 8-MeIQx to the cynomolgus monkeys results in the formation of only low adduct levels with many tissues showing no detectable levels of adducts. Studies in rodents have also shown that IQ and PhIP from DNA adducts in a number of organs in addition to those that are targets for carcinogenic effects of these agents. Although high DNA adduct levels of HCA are generally found in target organs for HCA induced carcinogenesis the widespread distribution of the adducts in organs not associated with the carcinogenic effects suggest that HCA exposure may be a possible etiological factor in cardiovascular diseases and other degenerative ailments.
The effect of inhibitors of toxicity of N-hydroxyparacetamol (N-OH-pHAA), a postulated proximate metabolite of paracetamol, was studied in isolated rat hepatocytes. Additions of ascorbate, menadione, ...thiol-containing amino acids and glutathione (GSH) led to an increased stability of N-OH-pHAA, reduced the covalent binding of N-OH-pHAA to cellular protein and decreased GSH depletion caused by N-OH-pHAA. Two to three hours elapsed after a 30 min. exposure of the cells to N-OH-pHAA before the cells responded with increased cell permeability. Ascorbate, acetylcysteine, GSH and promethazine were capable of inhibiting this second phase of N-OH-pHAA cytotoxicity in addition to their effects during the initial exposure phase. In contrast, the anti-oxidant tocopherole and phenacetin wee only effective during the second phase. Increasing the incubation medium pH during the second phase of N-OH-pHAA mediated cellular damage resulted in decreases in cytotoxicity. Lipid peroxidation, as measured by accumulation of thiobarbituric acid reactive metabolites, did not seem to be directly correlated with cytotoxicity, since cysteamine or higher concentrations of N-OH-pHAA inhibited lipid peroxidation without decreasing cellular damage.
NIH/3T3 cells transfected with DNA from malignant human tumors produced experimental and spontaneous metastases in nude mice. In contrast, parent or spontaneously transformed NIH/3T3 cells failed to ...metastasize. The transfected clones contained either activated c-Harvey-ras or N-ras oncogenes. A representative clone (T71-17SA
2
) which was used to assess selected cellular and host factors relevant to the metastatic process produced lung metastases in 100% of the NIH nude mice recipients, secreted augmented levels of type IV collagenase, and invaded human amnion basement membrane in vitro. Expression of the metastatic phenotype was not related to decreased sensitivity to natural killer cells or macrophage-mediated cytotoxicity. Analysis of the cellular DNA from the T71-17SA2 transfectant and its corresponding metastases, both of which contained activated N-ras oncogenes, revealed a twofold increase in the N-ras-specific DNA sequences in the metastatic cells. Thus, transfection with human tumor DNA containing activated ras oncogenes can induce the complete metastatic phenotype in NIH/3T3 cells by a mechanism apparently unrelated to immune cell killing.
