Neuropathological studies on cycloate-induced neuronal cell death in the rat brain.

The herbicide cycloate (carbamothioic acid, ethyl(cyclohexyl)-S-ethyl ester) given as a single oral dose to rats, caused selective neuronal cell death in two regions in the rat forebrain, the pyramidal neurons of layers II-III throughout the pyriform cortex and in granule cells of the caudal ventro-lateral dentate gyrus. Male Alderley Park rats, 6-8-week-old, were given a single oral dose of either 0 or 2000 mg/kg cycloate and killed for neuropathological investigation 1, 2, 3, 7, 14 or 28 days after dosing, using a regime of perfusion fixation with modified Karnovsky's fixative, followed by routine paraffin embedding. Seven transverse levels of brain were examined from each rat. Cycloate-induced neuronal cell death was seen in the pyriform cortex 1 day after dosing and persisted through to Day 28, the lesion was more marked in the rostral compared to the caudal region of the pyriform cortex. Neuronal cell death was also observed in the ventro-lateral caudal dentate gyrus on Days 1-14, day after dosing. In the early stages, Days 1-3 and to a lesser extent Day 7, the neuronal cell death resembled apoptosis, characterized by condensation of nuclear material, cell shrinkage and strong cytoplasmic eosinophilia. By Days 14 and 28 and to a lesser extent Day 7, the cell death resembled necrosis, i.e. karyorrhectic nuclei with pale irregular cytoplasm. Microglial accumulation was associated with the neuronal cell injury. In control brains, an occasional apoptotic body was seen in both the pyriform cortex and dentate gyrus. Our results demonstrate that cycloate is a novel neurotoxicant, which following a single large oral dose induces a cell specific and highly localized forebrain lesion. The time course data analyzed temporally, suggests that cycloate may cause an up regulation of apoptosis in selected regions of the adult brain.

Safety evaluation of phytosterol esters. Part 2. Subchronic 90-day oral toxicity study on phytosterol esters--a novel functional food.

Phytosterol esters (PE) are intended for use as a novel food ingredient, primarily in margarines and spreads as a functional component with plasma cholesterol lowering activity. Phytosterols and their esters are present naturally in vegetable oils and on average people consume 200 mg/day, but their consumption at this level is not sufficient to lower plasma cholesterol levels. Therefore, through the incorporation of PE into margarines/spreads, the intake can be increased by approximately 10-fold by consuming the PE-containing margarine/spread at normal intake levels. As part of an extensive programme of safety evaluation studies a subchronic rat toxicity study has been conducted in which groups of Alpk:AP(f)SD (Wistar derived) rats (20 males and 20 females/group) were fed diets containing PE at levels of 0, 0.16, 1.6, 3.2 and 8.1% (w/w) in the diet for 90 days. Throughout the study, clinical observations, body weights, and food and water consumption were measured. At the end of the study the rats were subjected to a full post-mortem examination, cardiac blood samples were taken for clinical pathology, selected organs were weighed, and a full tissue list was taken for subsequent histological examination. There were no treatment-related changes that were considered to be of toxicological significance. Therefore, a nominal PE concentration of 8.1% was considered to be the no-observed-adverse- effect level (NOAEL) following daily oral administration to rats for 90 days. This was equivalent to a dose of 6.6 g/kg body weight/day PE or 4.1 g/kg/day phytosterol.

Verrucous carcinoma of the bladder.

Verrucous carcinoma of the bladder unassociated with bilharzial cystitis is an exceedingly rare entity, with only 3 cases reported in the literature. We describe a patient and review the literature concerning verrucous carcinoma.

Eosinophilic cystitis in a renal allograft recipient.

Eosinophilic cystitis is an uncommon condition with an unknown etiology. A case of eosinophilic cystitis in a patient with chronic rejection of a cadaveric renal transplant is presented. The pathogenesis of this disease is discussed.

The detection of cytotoxicity produced by short-lived reactive intermediates: a study with bromobenzene.

1. A V79 cell incubation incorporating rat liver 9000 g supernatant (S9) fractions, used previously to detect the toxicity due to long-lived, stable metabolites of cyclophosphamide, has been used to study the toxicity of short-lived, reactive metabolites generated from bromobenzene. 2. Cytotoxicity was observed in the presence of S9 fractions from rats treated with phenobarbitone but not in the presence of S9 fractions from untreated or beta-naphthoflavone-treated animals. This toxicity was enhanced by depletion of the glutathione in the S9 fraction by prior treatment of the animals with diethyl maleate and was reduced by SKF 525 A, in agreement with results in vivo on the mechanism of bromobenzene-induced hepatotoxicity. 3. This study demonstrates that cytotoxicity due to the generation of short-lived, reactive metabolites can be detected in this system in vitro provided that procedures are used to modify the activating and detoxifying enzyme systems within the S9 fraction.

Investigation of the cytotoxicity produced by generation of short-lived reactive metabolites in vitro: A study with paracetamol.

A V79 cell incubation, incorporating rat or hamster liver 9000 g supernatant (S-9) or microsomal fraction and used previously to detect the toxicity of reactive metabolites of cyclophosphamide and bromobenzene, has been used to examine the toxicity of short-lived reactive metabolites of paracetamol. Cytotoxicity was observed in the absence of an activating system and did not increase when an activating system was included in the incubation, even when this was derived from the livers of hamsters treated with beta-naphthoflavone (to increase the activity of the cytochrome P-450 form responsible for paracetamol activation) and diethyl maleate (to deplete protective glutathione stores). The failure to detect metabolism-mediated cytotoxicity of paracetamol in this assay system may be related to the high reactivity of the toxic metabolite. This, in turn, suggests that other systems, based on activation within target cells or on the detection of an endpoint closer to the activation event, are required for the in vitro detection of short-lived cytotoxic metabolites.

A comparison of two cytotoxicity assays for the detection of metabolism-mediated toxicity in vitro: a study with cyclophosphamide.

The cytotoxicity to V79 Chinese hamster fibroblasts of cyclophosphamide (CPA) metabolites, generated by rat-liver S9 fractions, has been compared in two assay systems with different endpoints of toxicity, namely, reduction of cloning efficiency and inhibition of cell growth. The two assay systems were found to be equally sensitive in detecting the metabolism-mediated cytotoxicity of CPA and gave similar ID50 values. Further studies confirmed the cytochrome P-450 enzyme requirement for the bioactivation of CPA to cytotoxic metabolites. CPA activation was mediated by phenobarbitone-inducible forms of cytochrome P-450, but not by beta-naphthoflavone-inducible forms.

The FRAME interlaboratory programme on in vitro cytotoxicology.

FRAME (the Fund for the Replacement of Animals in Medical Experiments) has established a research programme in collaboration with four research centres and a number of industrial companies, to determine whether cell cultures can reliably be used to replace live animal procedures in routine tests on the relative acute toxicities of chemicals. Following the development of the test protocol, initial trials were carried out to establish intralaboratory and interlaboratory reproducibility and the criteria for choice of cell types, end-points and metabolizing systems. A set of coded chemicals is being collected for use in blind trials and summaries of existing knowledge of the in vivo toxicity of these compounds are being produced. More recently, FRAME has established an international validation scheme for in vitro alternative methods.

Influence of cytochrome P-450 type on the pattern of conjugation of 7-hydroxycoumarin generated from 7-alkoxycoumarins.

Pretreatment of rats with phenobarbitone increased hepatic microsomal 7-methoxy-and 7-ethoxy-coumarin O-dealkylase activities. Pretreatment with beta-naphthoflavone increased only the 7-ethoxycoumarin O-dealkylase activity. The addition of metyrapone in vitro inhibited the O-dealkylations to different extents. Similar results were obtained with diphenyloxazole and ethanol. These results are taken to indicate that different forms of cytochrome P-450 are involved in the O-dealkylation of these two substrates. The pattern of metabolism (Phase I and Phase II) of each alkoxycoumarin in rat isolated hepatocytes was very similar. The sulphate conjugate was the major metabolite produced, the amount of which approached a plateau as the rate of O-dealkylation increased. It is concluded that the type of cytochrome P-450 involved in the initial Phase I metabolism does not influence the subsequent pattern of conjugation.

Amphibian organ culture in experimental toxicology: the effects of paracetamol and phenacetin on cultured tissues from urodele and anuran amphibians.

Organ cultures of various tissues from urodele amphibians deacetylate paracetamol to p-aminophenol, which polymerises to form a brown precipitate. Paracetamol addition results in a loss of glycogen and lactate dehydrogenase (LDH) from urodele liver cultures and an increase in glucose release, and in LDH loss from kidney cultures. Organ cultures from anuran amphibians are unable to metabolise paracetamol and are not affected by its presence in the culture medium. The addition of unpolymerised p-aminophenol resulted in a loss of LDH from urodele and anuran organ cultures, whilst the addition of polymerised p-aminophenol had no such effects. This suggests that the toxic effects which follow the addition of paracetamol to urodele organ cultures are caused by unpolymerised p-aminophenol, a known toxicant in mammals. Cultures from both urodele and anuran amphibians are able to deacetylate phenacetin to p-phenetidine, but p-phenetidine was found to be much less toxic to amphibian tissues than p-aminophenol, causing LDH loss from kidney cultures only at very high dose levels.