Long-term toxicity/carcinogenicity of musk xylol in B6C3F1 mice

The long-term toxicity/carcinogenicity of musk xylol, a synthetic nitro musk, was examined in B6C3F1 mice of both sexes. Musk xylol was administered at dietary levels of 0 (control), 0.075 or 0.15% for 80 wk. The overall tumour incidences in all treated groups of both sexes were significantly higher than those in the corresponding controls. Combined malignant and benign liver cell tumours were clearly increased in both sexes, and in males a positive significant trend was also noted for the occurrence of hepatocellular carcinomas. In males the incidence of Harderian gland tumours was also significantly greater in treated groups than in controls. Some other neoplasms, such as lung tumours in both sexes and Harderian gland tumours and lymphomas in females, occurred in greater numbers in the treated groups, although the differences were not statistically significant in comparison with the controls. In addition, the incidences and total numbers of malignant tumours were significantly increased in treated groups of both sexes, although the increases were not dose dependent. The results demonstrated that musk xylol is carcinogenic in B6C3F1 mice when given at dose levels of 0.075 or 0.15% in the diet for 80 wk.     

Toxic effects of benzyl and allyl isothiocyanates and benzyl-isoform specific metabolites in the urinary bladder after a single intravesical application to rats.

Allyl isothiocyanate (AITC) is known to be weakly carcinogenic, whereas benzyl isothiocyanate (BITC) has been suggested to exert carcinogenicity toward the rat urinary bladder. To elucidate direct toxic effects of isothiocyanates (ITCs), BITC, AITC, or BITC-metabolites conjugated either with glutathione, cysteinylglycine, cysteine, or mercapturic acid were intravesically instilled into female F344 rats. Exposure to AITC and BITC at 2.8 mg/kg body weight, and the same mol quantity (37 micromol/kg) of BITC-metabolites was for 2 h. Nineteen hours thereafter, the animals were intravenously administered 5-bromo-2'-deoxyuridine (BrdU) and killed 1 h later. BITC caused more profound toxic damage than AITC. Among the BITC-metabolites, cytotoxicity was evident with intermediate glutathione or cysteinylglycine conjugates, whereas the mercapturic acid, considered to be the major final urinary metabolite, exerted little effects. BrdU labeling was essentially dependent on the degree of cytotoxic potential of each compound. Considering the previous study results demonstrating the generation of free BITC from metabolites in urine, the present results support the idea that cytotoxic activity of orally administered ITCs is derived from free forms cleaved from conjugated metabolite(s) in urine.     

Histopathological and biochemical studies on pancreatic fibrosis in WBN/Kob rats

 We investigated the time-course of changes in pancreatic fibrosis accompanied with pancreatitis in WBN/Kob rats. The areas of fibrosis and fatty replacement were analysed morphometrically, and biochemical measurements of pancreatic and plasma prolyl hydroxylase and of pancreatic collagenase were assessed. Male rats showed acute pancreatitis at 2–3 months of age, lesions that later underwent a transition to widespread fibrosis. The fibrosis then decreased, and the fibrotic tissue was replaced with adipose tissue. Morphometrically, the fibrotic area reached its maximal size when the rats were 4 months old, diminishing thereafter. The fibrosis occurred mainly in the intralobular space, and was principally attributable to type-III collagen. Type-I collagen scarcely appeared throughout the experimental period. α-Smooth muscle actin appeared in and around myofibroblasts that developed in an early stage and diminished later in accordance with the progressive manner of fibrosis. The plasma prolyl hydroxylase level was higher in males than in females from 4 through 10 months of age. Pancreatic collagenase activity in the males also increased during the same period. These findings suggest that pancreatic fibrosis in male WBN/Kob rats is affected by the balance between prolyl hydroxylase and collagenase. Received: 1 October 1998 / Accepted: 2 October 1998     

Development of a new calcium phosphate cement that contains sodium calcium phosphate

A cement powder consisting of sodium calcium phosphate, Na3Ca6(PO4)5, in addition to tetracalcium phosphate and beta-tricalcium phosphate was prepared by pulverizing blocks of 4 wt% sodium-, 11 wt% carbonate-containing apatite samples that were heated at 1700 degrees C for 5 h. When mixed with 30 wt% malic acid or citric acid at a powder liquid ratio of 3:1, the cement set in 3 or 7 min at room temperature with compressive strength being around 52 or 27 MPa. In HeLa-cell cultures, the cement mixed with malic acid was less cytotoxic than the cement mixed with citric acid, which was far less cytotoxic than a commercial carboxylate cement used as a negative control, suggesting malic acid to be superior to citric acid as a liquid in this regard. Similar findings were also obtained with osteoclasts, of which culture experiments clearly suggested that the number of osteoclasts on the cement mixed with malic acid was significantly greater than that on the cement mixed with citric acid. Since osteoclastic response to substrates could be used as a maker in evaluating their bioresorbability associated with osteoclasts, the above finding may suggest that the cement that is to be mixed with malic acid would be more useful as bone substitutes.     

Chemoprevention of heterocyclic amine-induced mammary carcinogenesis in rats

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is one of the most prevalent carcinogenic heterocyclic amines in the environment, targeting the colon, prostate, pancreas, and mammary gland in rodents. Chemopreventive effects of synthetic and naturally occurring compounds on PhIP-induced rat mammary carcinogenesis were investigated in a series of experiments. In a PhIP feeding model, groups of 20-21 female F344 rats each, were treated with 0.02% PhIP alone or PhIP plus 0.5% 1-O-hexyl-2,3,5-trimethylhydroquinone (HTHQ), 1% green tea catechins, 1% alpha-tocopherol, 0.1% ellagic acid, or 1% chlorophyllin, each in the diet, or 0.1% caffeine in drinking water for 52 weeks. To assess the mechanism of HTHQ and caffeine inhibition of PhIP-induced carcinogenesis, effects of these compound on the in vitro metabolic activation of PhIP were examined in the presence of S9 mix. In the next series of experiments, the PhIP intragastric dose model was applied to allow separate investigation of the effects of chemicals during the initiation and postinitiation periods. In these experiments, female Sprague-Dawley rats were given eight intragastric doses of 100 mg/kg body weight during the first 4-8 weeks for initiation. Either during initiation or after initiation, or only after initiation, animals were treated with either corn or perilla oil at doses of 5 and 20%, conjugated fatty acid derived from safflower oil (CFA-S) or perilla oil (CFA-P) at a dose of 1%, arctiin at doses of 0.02 and 0.2% in the diet, or sodium nitrite (NaNO(2)) at a dose of 0.2% in drinking water. In the PhIP feeding model, administration of PhIP alone for 52 weeks induced adenocarcinomas in 40% of rats, but the incidence was remarkably reduced to 5% by the simultaneous treatment with 0.5% HTHQ, a strong lipophilic phenolic antioxidant, or to 10% by 0.1% caffeine. Administration of 1% chlorophyllin exerted similar, albeit weaker, effects. alpha-Tocopherol at a dose of 0.5% only reduced the multiplicity of carcinomas, and 1% green tea catechins only the mean size of mammary tumors. In a metabolic activation study of PhIP, HTHQ and caffeine clearly inhibited the formation of metabolites. In the PhIP gastric dose model, among the naturally occurring compounds examined, a plant lignan arctiin, perilla oil, which contains a large amount of n-6 alpha-linolenic acid, and CFA-S or CFA-P inhibited mammary tumor development, particularly in the postinitiation period, although a clear dose response was not observed. Treatment with 0.2% NaNO(2) in the initiation period was found to lower the volume of mammary tumors. The present results indicate that a number of compounds may be candidate chemopreventive agents against PhIP-induced mammary carcinogenesis, acting through different mechanisms and depending on the stage of carcinogenesis.     

Pathological Effects of Matebrnal Hypoglycemia on Fetal Development in Cats

The pathogenesis of fetal brain damage caused by acute maternal hypoglycemia was investigated experimentally in cats: profound hypoglycemia (blood glucose concentration:less than 30 mg/dl) was induced in 12 pregnant cats at various stages of gestation by intravenous bolus injections of insulin. Maximal hypoglycemia was attained within 2 3 h, although the grade and duration in individual cats varied. The EEGs of all of seven maternal cats examined showed an increased frequency of slow high-voltage waves as hypoglycemia progressed, eventually becoming flat in 3 for a maximum period of 20 min. Some fetuses showed severe neuropathological changes, such as infarction or intrauterine death. Subventricular soften ing, cortical hemorrhage and ischemic neuronal changes also occurred, being distributed symmetrically in the para-sagittal areas of the cerebrum, basal ganglia, thalamus and tegrnentum of the brainstem. In general, these patho logical changes were more marked in fetuses and neonates than in the maternal cats, in which only ischemic neuronal changes were present, and may have been due to fetal systemic hypotension and cerebral ischemia induced by hypoglycemia. In maternal cats, the distribution of neu rons showing ischemic changes was widest in the cerebral cortex, and some were also present in the dentate gyri of the hippocampus. Moreover, ultrastructural examination of the ischemic neurons in maternal cats, unlike those of the fetuses, showed no mitochondrial swelling. Therefore, the distribution and ultrastructural nature of the ischemic neurons found in the maternal cats were considered to be characteristic of hypoglycemia, as proposed by Agardh et al . (1980). Acta Pathol Jpn 42 : 316–324, 1992.