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T J Gray

Publications and source records attributed to T J Gray.

At least 37 records · Page 2Linked to original sources
PubMed1994

Mutagenicity and CYP1A induction by azobenzenes correlates with their carcinogenicity.

The genotoxicity of six azobenzenes was evaluated in the Ames test, in the presence of an activation system derived from Aroclor 1254-treated rats. Moreover, the ability of these azobenzenes to induce rat hepatic CYP1A activities and apoprotein levels, and stimulate their own bioactivation to mutagens, was also determined. In the presence of the Aroclor 1254-activation system, o-aminoazotoluene and 3-methoxy-4-aminoazobenzene were potent mutagens, whereas 4-amino-azobenzene and 4-diethylaminoazobenzene failed to elicit a positive mutagenic response. A very weak mutagenic response was induced by 2-methyl-4-dimethylaminoazobenzene and by azobenzene. o-Aminoazotoluene and 3-methoxy-4-aminoazobenzene were potent inducers of CYP1A activities and apoprotein levels, whereas the remaining four compounds displayed either very weak or no induction capability. None of the azobenzenes studied could induce its own activation to mutagens in the Ames test. All six azobenzenes displaced [3H]tetrachlorodibenzo-p-dioxin from the cytosolic Ah receptor, with o-aminoazotoluene and 3-methoxy-4-aminoazobenzene being the most effective. A correlation appears to exist between carcinogenic activity of azobenzenes in the rat on one hand, and of their mutagenic potential and hepatic CYP1 induction on the other. Possible mechanisms accounting for this relationship are discussed.

Animals↗
PubMed1993

Mutagenicity of chrysene, its methyl and benzo derivatives, and their interactions with cytochromes P-450 and the Ah-receptor; relevance to their carcinogenic potency.

The genotoxicity in the Ames test of chrysene, of its six methyl and of two benzo-derivatives, and their ability to induce rat hepatic CYP1A and epoxide hydrolase activities, and stimulate their own bioactivation were determined. The primary objective is to provide a rationale for the higher carcinogenic potency of 5-methylchrysene when compared to that of the parent compound and the other methyl isomers. In the presence of Aroclor 1254-induced hepatic microsomes chrysene, its 5- and 4-methyl derivatives and to a lesser extent the 2- and 3-methyl derivatives and benzo[c]chrysene elicited a positive mutagenic response. Chrysene, all derivatives studied and especially benzo[c]chrysene were potent inducers of rat hepatic CYP1A1 activity as exemplified by the O-deethylation of ethoxyresorufin (30-180-fold when activities are expressed per nmol of total cytochrome P-450). All compounds studied displaced [3H]TCDD from the cytosolic Ah receptor at a concentration of 10(-10)-10(-9) M. Benzo[c]chrysene and to a lesser extent 6-methylchrysene were the only compounds capable of stimulating epoxide hydrolase activity, but the effect was modest. None of the compounds studied could induce its own activation to mutagens in the Ames test. The present findings indicate that the higher carcinogenic potency of 5-methylchrysene cannot be related to its mutagenic potential or its ability to enhance its own activation through induction of CYP1A1 and epoxide hydrolase activities.

Animals↗
PubMed1992

Urinary creatine profiles after administration of cell-specific testicular toxicants to the rat.

Cell-specific testicular toxicants have been used to examine the distribution of creatine within the rat testis, and to examine the potential use of creatinuria as a non-invasive indicator of testicular damage. Groups of rats were administered single doses of various toxicants: a germ cell toxicant (methoxyacetic acid, MAA), one of two Sertoli cell toxicants (di-n-pentyl phthalate, DPP or 1,3-dinitrobenzene, 1,3-DNB), or a Leydig cell toxicant (ethane-1,2-dimethane sulphonate, EDS). Urinary creatine and creatinine levels were monitored in 24 h periods over the following 48 h, after which time the testes were removed, weighed and, after processing, sections were examined by light microscopy. All four treatments resulted in reductions in relative testis weight (RTW) and produced morphological changes similar to those which have been previously reported. In addition, MAA, DPP and 1,3-DNB all caused significant elevations in urinary creatine excretion and the urinary creatine:creatinine ratio (Cr/Crn) within 24 h. EDS had no such effect. We conclude that creatine is associated with the cells of the seminiferous epithelium, and that elevated urinary excretion of creatine may serve as a non-invasive marker for damage to these cells in vivo.

Acetates↗
PubMed1991

The murine local lymph node assay: results of an inter-laboratory trial.

The local lymph node assay is a novel predictive test for the identification of contact allergens. The collaborative study reported here was performed to evaluate the reliability of the method when performed in independent laboratories. Eight chemicals were examined in each of 4 participating laboratories and results compared with predictions of skin-sensitizing activity made from concurrent Magnusson and Kligman guinea-pig maximization tests performed in a single laboratory. The local lymph node assay has as its theoretical basis the fact that contact allergens induce T-lymphocyte proliferative responses. In practice, predictions of contact-sensitizing potential are made following measurement of proliferation in lymph nodes draining the site of exposure to chemical, and derivation of a stimulation index using control values as the comparator. Although in the present study there was some variation between laboratories with respect to the absolute stimulation indices recorded, it was found that with all chemicals each laboratory made the same predictions of sensitizing activity. Six chemicals (2,4-dinitrochlorobenzene, formalin, eugenol, isoeugenol, p-phenylenediamine and potassium dichromate) yielded positive responses, and two (methyl salicylate and benzocaine) were negative, in each laboratory. Furthermore, with 7 of the 8 chemicals tested there was no significant difference between laboratories in terms of the characteristics of the dose-response relationships recorded. With the exception of one chemical (benzocaine), predictions made with the local lymph node assay were in accord with those derived from guinea-pig maximization tests. These inter-laboratory comparisons demonstrate that the local lymph node assay is a robust and reliable method for the identification of at least moderate and strong contact allergens.

Allergens↗
PubMed1990

Efflux of bis-carboxyethyl-carboxyfluorescein (BCECF) by a novel ATP-dependent transport mechanism in epithelial cells.

The efflux of the intracellular pH fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) was quantified in four cultured epithelial cell lines; HCT-8, T84, HGT-1 and MDCK. BCECF efflux was time-dependent, and after 5 h 45-91% of the initial BCECF loaded was extracellular, efflux being greatest in MDCK cells. Depletion of cellular ATP approximately halved BCECF efflux. BCECF efflux was inhibited by indomethacin, vinblastine and verapamil, but not by nifedipine or reserpine. Certain features of BCECF efflux resemble drug efflux in multidrug resistant cells, but inhibition of efflux displays a distinct pharmacological profile suggesting BCECF is a substrate for a novel ATP-dependent transport system.

Adenocarcinoma↗
PubMed1990

The morphogenesis of cyclohexylamine-induced testicular atrophy in the rat: in vivo and in vitro studies.

Male Wistar strain rats were fed a diet providing an intake of 0 or 400 mg cyclohexylamine (CHA)/kg body weight/day for 1, 3, 7, 9, or 13 weeks. At the end of the appropriate feeding period the rats were perfused-fixed with Karnovsky's fixative. The weights of the fixed testes were recorded and the testes, epididymides, and spermatic cord were sampled and processed into methacrylate resin. Histopathological examination of the testes showed changes after 3 weeks of CHA administration. The most frequent and consistent lesion consisted of a focal, basal vacuolation of the Sertoli cell cytoplasm associated with the local loss of spermatocytes and spermatogonia. After a 7-week administration, the Sertoli cell vacuolation was extensive, while the germ cell population showed mild to moderate degeneration and depletion. After longer periods of treatment the lesion was more severe and affected a greater number of tubules leading to general disruption of the germinal epithelium. Cocultures of Sertoli and germ cells were prepared from the testes of Wistar strain rats and exposed to (CHA) or its metabolite 4-aminocyclohexanol (4ACH) at concentrations ranging from 0.1 to 10 mM for periods of 24-72 hr. The cultures were fixed, stained, and examined by light microscopy. Cultures exposed to CHA or 4ACH showed morphological changes comparable with those seen in vivo. Sertoli cell vacuolation was the earliest change with progressive germ cell degeneration and exfoliation from the Sertoli cell monolayer. At equimolar concentrations, CHA produced more marked changes than 4ACH. These results suggest that CHA itself acts directly on the testis and that its primary cellular target is the Sertoli cell.

Aging↗
PubMed1989

Comparative studies on nafenopin-induced hepatic peroxisome proliferation in the rat, Syrian hamster, guinea pig, and marmoset.

Nafenopin was administered orally for 21 days to male Sprague-Dawley rats (0.5-50 mg/kg/day), Syrian hamsters (5-250 mg/kg/day), Dunkin-Hartley guinea pigs (50 and 250 mg/kg/day), and marmosets (Callithrix jacchus, 50 and 250 mg/kg/day). With the rat, and to a lesser extent in the hamster, nafenopin treatment produced dose-related increases in liver size and induction of peroxisomal (palmitoyl-CoA oxidation) and microsomal (lauric acid 12-hydroxylase) fatty acid oxidizing enzyme activities. In contrast, in the guinea pig and marmoset, there was no effect on liver size and only comparatively small changes were observed in these enzyme activities. Ultrastructural examination of liver sections from nafenopin-treated rats and hamsters revealed increased numbers of peroxisomes many of which lacked the characteristic crystalline nucleoid. While nafenopin had little effect on peroxisome numbers in either the guinea pig or marmoset, increases in microsomal cytochrome P450 content and mixed function oxidase activities were observed in these species. These results demonstrate marked species differences in nafenopin-induced hepatic peroxisome proliferation with the Syrian hamster being less responsive than the rat and the guinea pig and marmoset being only weakly responsive. As nafenopin is a known hepatocarcinogen in the rat, comparative long-term studies in poorly responsive species, such as the guinea pig and marmoset, may help clarify the role of organelle proliferation in the hepatocarcinogenicity of certain peroxisome proliferators.

Animals↗
PubMed1989

Studies on the mechanism of coumarin-induced toxicity in rat hepatocytes: comparison with dihydrocoumarin and other coumarin metabolites.

Single doses of coumarin (125 mg/kg, ip) produced a depletion of hepatic nonprotein sulfhydryl groups (mainly reduced glutathione; GSH) in young male Sprague-Dawley rats after 2 hr and increased liver weight and produced hepatic centrilobular necrosis after 24 hr. Coumarin also produced time- and dose-dependent toxic effects in primary rat hepatocyte cultures. A marked reduction of GSH levels was also observed in vitro and this was not due either to the formation of oxidized glutathione (GSSG) or to the leakage of GSH and/or GSSG from the hepatocytes. Coumarin-induced toxicity in rat hepatocytes could be inhibited by the cytochrome P450 inhibitors ellipticine and metyrapone and potentiated by depleting hepatocyte GSH levels with diethyl maleate. In contrast to coumarin, dihydrocoumarin--which lacks the 3,4-double bond--produced little toxicity in rat hepatocytes either in vivo (127 and 254 mg/kg, ip) or in vitro. Similarly, coumarin was more toxic to rat hepatocytes than a number of known coumarin metabolites including 3- and 7-hydroxycoumarin and o-hydroxyphenylacetic acid. The results of these studies demonstrate a good in vivo/in vitro correlation for the effects of coumarin and dihydrocoumarin in rat hepatocytes. Furthermore, the data suggest that coumarin hepatoxicity in the rat is due to coumarin bioactivation by cytochrome P450-dependent enzymes to a toxic metabolite(s), which may be a coumarin 3,4-epoxide intermediate. GSH appears to protect against coumarin-induced toxicity possibly by the formation of conjugates with the toxic coumarin metabolite(s).

Animals↗
PubMed1989

Nafenopin, a peroxisome proliferator, depletes hepatic vitamin E content and elevates plasma oxidised glutathione levels in rats.

Male Sprague-Dawley rats were given oral doses of nafenopin (80 mg/kg/d) for up to 28 d. Nafenopin administration resulted in liver enlargement and induction of peroxisomal fatty acid beta-oxidation enzymes (which generate hydrogen peroxide), but little effect was observed on catalase and cytosolic GSH peroxidase was decreased. Hepatic vitamin E levels were depleted to around 50% of control. A small increase in hepatic oxidised glutathione (GSSG) content was paralleled in a time-dependent increase in plasma GSSG. These changes in vitamin E and GSSG levels may represent early indicators of oxidative stress produced in rat hepatocytes by nafenopin and other peroxisome proliferators as a consequence of the increased production of hydrogen peroxide.

Animals↗
PubMed1988

The effects of mono-(2-ethylhexyl)-phthalate on rat Sertoli cell-enriched primary cultures.

There is considerable evidence from in vivo studies that the Sertoli cell is an initial target cell for the actions of phthalates in the rodent testis. Because this metabolically active cell type plays a central role in spermatogenesis, we examined the effects of a toxic phthalate, mono-(2-ethylhexyl)-phthalate (MEHP), on the secretory and synthetic activities of primary testicular cell cultures isolated from 18-day-old rats. These cultures were 78-84% Sertoli cells. Exposure to MEHP decreased cellular ATP by ca. 20%, decreased production of radiolabeled 14CO2 from acetate, and decreased media levels of pyruvate, while it increased media levels of lactate and intracellular lipid. Protein synthesis, evaluated by radiolabeled leucine incorporation, was not affected by MEHP. Mitochondrial succinate dehydrogenase activity was decreased in the presence of MEHP. Michaelis-Menton kinetic analysis indicated this was a mixed inhibition. There was no apparent change in mitochondrial Rhodamine 123 uptake. These data are consistent with the concept that mitochondria are one target for the actions of MEHP in the Sertoli cell.

Adenosine Triphosphate↗
PubMed1988

The effect of mono-(2-ethylhexyl) phthalate and other phthalate esters on lactate production by Sertoli cells in vitro.

Sertoli cells produce lactate and pyruvate as energy substrates for the developing germ cells in the testis. Since the Sertoli cells are thought to be the initial target for phthalate esters causing testicular atrophy, the effect of some phthalates on lactate and pyruvate production by primary Sertoli cell-enriched cultures was studied. Mono-(2-ethylhexyl) phthalate (0.1-200 microM) produced a concentration-dependent stimulation of lactate, but not pyruvate production over a 24 h treatment period and an increase in the ratio of lactate/pyruvate concentration in the culture medium. Di-(2-ethylhexyl) phthalate and 2-ethylhexanol (200 microM) had no such effects. Other phthalate monoesters known to cause testicular atrophy also increased Sertoli cell lactate production and the lactate/pyruvate ratio, whereas monoesters not associated with testicular damage in vivo had no such effects. The results suggest that loss of germ cells in phthalate-induced testicular atrophy is not due to inhibition of energy substrate production by the Sertoli cells and that stimulation of lactate production may be a useful in vitro marker for phthalate esters and related compounds that cause testicular injury.

Animals↗
PubMed1987

The ultrastructural effects of di-n-pentyl phthalate on the testis of the mature rat.

A sequential morphological study has been carried out to examine the ultrastructural effects of di-n-pentyl phthalate (DPP) on the mature rat testis. A single oral dose of 2.2 g DPP/kg body wt was administered, and testes, perfuse-fixed 3-48 hr after dosing, were examined by transmission electron microscopy. By 3 hr, rarefaction of the basal Sertoli cell cytoplasm was seen and the basal plasma membranes separating adjacent Sertoli cells were thrown into a series of convoluted profiles with the appearance of interdigitating cell processes. The subjacent ectoplasmic specializations that normally face these membranes were disrupted, and by 12 hr the inter-Sertoli junctions showed numerous membrane discontinuities. The lateral processes of Sertoli cell cytoplasm, which separate germ cells, showed retraction and fragmentation, resulting in direct contact between adjacent germ cells or the isolation of germ cells unapposed by Sertoli cell plasma membrane. In addition, the ectoplasmic specializations associated with Sertoli-spermatid and Sertoli-pachytene spermatocyte junctions were often disrupted or absent. The mitochondria in the Sertoli cells were enlarged and, in some tubules, increased in number. The changes seen were restricted to tubules in the successive stages XI-XIV, I, and II of the spermatogenic cycle. Elongating spermatids (steps 12-15) showed cytoplasmic condensation and vacuolation by 12 hr and were necrotic by 24 hr. A small proportion of zygotene and early pachytene spermatocytes showed necrosis by 24 hr after dosing. By 48 hr, the cytoplasmic rarefaction and convoluted plasma membranes had regressed and ectroplasmic specializations had reformed along Sertoli-Sertoli junctions.

Animals↗
PubMed1987

Effect of prolonged administration of clofibric acid and di-(2-ethylhexyl)phthalate on hepatic enzyme activities and lipid peroxidation in the rat.

Male Sprague-Dawley rats were fed diets containing either 0.5% clofibric acid (CA) or 2% di-(2-ethylhexyl)phthalate (DEHP) for 2 years. Both compounds produced liver enlargement which was accompanied by the formation of liver nodules. Hepatic peroxisomal and microsomal fatty acid oxidising enzyme activities were induced in both large nodules and host tissue (i.e. tissue remaining after removal of large nodules) preparations from CA and DEHP treated rats. In contrast, little change in catalase activity was observed and the activities of cytosolic GSH peroxidase and GSH S-transferases were markedly reduced. Increased lipid peroxidation was observed by measurement of conjugated dienes in host tissue homogenates from CA and DEHP treated rats. Microsomal NADPH-dependent lipid peroxidation was also stimulated. Histological examination revealed extensive lipofuscin deposition in non-nodular, but not in nodular, tissue sections from treated rats. These results demonstrate that prolonged peroxisome proliferation can result in lipid peroxidation and that certain enzymes which metabolise hydrogen peroxide and organic hydroperoxides are either little affected or markedly inhibited.

Animals↗