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H B Matthews

Publications and source records attributed to H B Matthews.

At least 37 records · Page 2Linked to original sources
PubMed1995

Rotenone, an anticarcinogen, inhibits cellular proliferation but not peroxisome proliferation in mouse liver.

In previous National Toxicology Program (NTP) studies, rotenone reduced the background incidence of hepatocellular carcinoma in male B6C3F1 mice. In the present studies, rotenone reduced the basal hepatic labeling index of male B6C3F1 mice in a dose-dependent fashion and inhibited hepatocellular proliferation, but not peroxisome proliferation, induced by the peroxisome proliferator Wy-14,643. These results indicate that reduction of hepatic tumors by rotenone may have been due to decreased liver cell replication, that peroxisome proliferation can be induced in the absence of hepatocellular proliferation and suggest rotenone as a potential tool in studies of relationships of cell proliferation, peroxisomal proliferation and hepatocarcinogenesis.

Animals↗
PubMed1995

Cell proliferation as a determining factor for the carcinogenicity of chemicals: studies with mutagenic carcinogens and mutagenic noncarcinogens.

Recent work in our laboratory has examined mechanisms whereby chemicals produce mutagenicity in short-term in vitro assays yet fail to produce carcinogenesis in 2-year rodent bioassays. These studies have used mutagenic structural analogs of carcinogenic and noncarcinogenic chemicals for comparison. Our previous studies have determined that differences in the metabolism and disposition of these chemicals were not responsible for their observed carcinogenic differences, but that carcinogenicity correlated with the ability of the respective isomer to induce cell proliferation in the target organ. Mutagenic noncarcinogens such as 2,6-diaminotoluene (DAT), 1-nitropropane (NP), dimethoate, dioxathion, and dichlorvos failed to induce an increase in cell turnover in the target organs. An increase in cell proliferation was observed following exposure to the mutagenic carcinogen analogs 2,4-DAT (liver), 2-NP (liver), and tris(2,3-dibromopropyl)phosphate (kidney). Our recent studies have used transgenic (Big Blue) mice to detect in vivo mutagenesis induced by DAT isomers. Results of these studies demonstrate that administration of the carcinogenic isomer, 2,4-DAT, resulted in an increase in in vivo mutation frequency, whereas administration of the noncarcinogenic isomer, 2,6-DAT, failed to do so. These results indicate that cell proliferation may be requisite for expression of chemical-induced mutagenicity in vivo and thereby accommodate expression of carcinogenicity.

Animals↗
PubMed1995

Toxicokinetics of the cholinomimetic compound benzyltrimethylammonium chloride in the male rat and mouse.

1. Benzyltrimethylammonium chloride (BTMAC)-derived radioactivity was rapidly eliminated from the F344 rat and the B6C3F1 mouse following p.o. administration of 0.63-63 mg/kg of [ring-U-14C] BTMAC. Greater than 90% of the radioactivity was excreted in urine and faeces within 24-h post-dosing. 2. BTMAC was poorly to moderately absorbed from the GI tract following p.o. administration. The percent of total dose absorbed did not exceed either 40% in the rat or 15% in the mouse. 3. Absorption was linear, but limited, over time following dermal administration of 63 mg/kg to the rat. Less than 10% of the total dose was absorbed from the skin within 24 h of BTMAC application. 4. Metabolism of BTMAC was minimal in both the rat and mouse. Toxicity (excessive cholinergic stimulation and mortality) appears to be attributable to the parent compound. 5. The limited absorption and rapid elimination of BTMAC should result in little or no bioaccumulation in tissues following repeated exposure to low levels of this compound. The results suggest that greater human health risks may be associated with acute high level exposure rather than chronic low level exposure.

Absorption↗
PubMed1994

Relationship of carcinogenicity and cellular proliferation induced by mutagenic noncarcinogens vs carcinogens. III. Organophosphate pesticides vs tris(2,3-dibromopropyl)phosphate.

Our laboratory has been examining the mechanisms whereby chemicals produce mutagenicity in short-term in vitro assays yet fail to produce carcinogenesis in 2-year rodent bioassays. Previous studies indicated that some mutagenic hepatocarcinogens increased cell proliferation in the target organ, the liver, while other structurally related mutagens that were noncarcinogenic failed to do so. We demonstrate in this report that another mutagenic carcinogen, tris(2,3-dibromopropyl phosphate), increased cell proliferation that was localized in the outer medulla of the kidney. This was also the target site for carcinogenesis in a 2-year bioassay and is another example of the association between chemically induced cell proliferation and carcinogenesis. This study also reports the absence of increased cell proliferation in the liver or kidney after exposure in the diet to the mutagenic organophosphate insecticides dimethoate, dioxathion, and dichlorvos following dietary exposure for 2 weeks at the same dose levels and routes of exposure that did not increase the tumor incidence in either organ in 2-year carcinogenesis assays. The present studies support the tenet that chemically induced cell proliferation may be a necessary prerequisite for chemical carcinogenesis, since in rat liver and kidney there was neither cell proliferation after 2 weeks nor tumor development after 2 years dietary exposure to the mutagenic organophosphate insecticides dimethoate, dioxathion, and dichlorvos.

Animals↗
PubMed1994

Summary of the National Toxicology Program benzidine dye initiative.

The benzidine dye initiative is a research program established by the National Toxicology Program to generate an integrated body of scientific information regarding the potential health risks associated with exposure to benzidine- and benzidine-congener-derived dyes. Because an in-depth evaluation of each of the hundreds of benzidine-congener-derived dyes was considered impractical, the research program was designed to study the metabolism and disposition, genetic toxicity, and in vivo toxicity and carcinogenicity of two primary benzidine congeners, 3,3'-dimethylbenzidine and 3,3'-dimethoxybenzidine, and a select group of prototypical dyes derived from those amines. It was anticipated that by applying the basic information generated in these extensive studies, it would be possible to make regulatory decisions about other dyes after conducting only a minimal number of experiments such as studies of disposition and metabolism, and in vitro mutagenicity. This paper summarizes the results of studies conducted to evaluate the metabolism, disposition, mutagenicity, toxicity, and carcinogenicity of representative benzidine congeners and derived dyes.

Animals↗
PubMed1993

Toxicity and carcinogenicity of chronic exposure to tris(2-chloroethyl)phosphate.

Previous short-term studies of tris(2-chloroethyl)phosphate (TRCP), a flame retardant used in industrial and consumer products, demonstrated that repeated administration of 350 mg TRCP/kg body wt by oral gavage resulted in necrosis of pyramidal neurons in the CA1 region of the hippocampus of F344 rats, but not in B6C3F1 mice. The 2-year studies reported here were designed to characterize the chronic toxicity and potential carcinogenicity of TRCP in each sex of F344 rats and B6C3F1 mice. Groups of 60 rats per sex received 0, 44, or 88 mg/kg by oral gavage, once per day, 5 days per week, for up to 103 weeks. Groups of 60 mice per sex received 0, 175, or 350 mg/kg by oral gavage on the same dosing schedule. Each of these groups contained 10 animals which were euthanized at 66 weeks. The principal toxic effects of chronic exposure of rats to TRCP occurred in the brain and kidney. In contrast to the findings in the 16-week studies, a hippocampal lesion was not observed in the brain, although degenerative lesions were widely distributed in the gray and white matter of the brain stem and cerebral cortex of high-dose female and, to a lesser extent, male rats. These findings suggest that the hippocampal necrosis may be dependent upon the size of the individual doses or may have a pathogenesis different from that of the lesions in the brain stem and cerebral cortex. The other primary effect of chronic exposure was a dose-dependent increased incidence of renal tubule hyperplasia and adenoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Comparison of lead bioavailability in F344 rats fed lead acetate, lead oxide, lead sulfide, or lead ore concentrate from Skagway, Alaska.

An animal model using rats was developed to initiate investigations on the bioavailability of different sources of environmental lead. Lead must be absorbed and transported to target organs like brain, liver, kidney, and bone, before susceptible cells can be harmed. The bioavailability and therefore the toxicity of lead are dependent upon the route of exposure, dose, chemical structure, solubility, particle size, matrix incorporation, and other physiological and physicochemical factors. In the present study male F344 rats were fed < or = 38 microns size particles of lead sulfide, lead oxide, lead acetate, and a lead ore concentrate from Skagway, Alaska, mixed into the diet at doses of 0, 10, 30, and 100 ppm as lead for 30 d. No mortality or overt symptoms of lead toxicity were observed during the course of the study. Maximum blood lead concentrations attained in the 100 ppm groups were approximately 80 micrograms/dl in rats fed lead acetate and lead oxide, and were approximately 10 micrograms/dl in those fed lead sulfide and lead ore concentrate. Maximum bone lead levels in rats fed soluble lead oxide and lead acetate were much higher (approximately 200 micrograms/g) than those seen in rats fed the less soluble lead sulfide and lead ore (approximately 10 micrograms); kidney lead concentrations were also about 10-fold greater in rats fed the more soluble compared to the less soluble lead compounds. However, strong correlations between dose and tissue lead concentrations were observed in rats fed each of the four different lead compounds. Kidney lesions graded as minimal occurred in 7/10 rats fed 30 ppm and in 10/10 rats fed 100 ppm lead acetate, but not at lower doses or from other lead compounds. Similarly, urinary aminolevulinic acid excretion, a biomarker for lead toxicity, was increased in rats fed 100 ppm lead acetate or lead oxide, but was unaffected at lower doses or by the less soluble lead compounds. Although the histological and biochemical responses to lead toxicity were restricted to the more soluble lead compounds in this study, lead from Skagway lead ore concentrate and lead sulfide was also bioavailable, and accumulated in proportion to dose in vulnerable target organs such as bone and kidney. Longer-term studies with different mining materials are being conducted to determine if tissue lead continues to increase, and whether the levels attained are toxic. Data from such studies can be used to compare the toxicity and bioavailability of lead from different sources in the environment.

Administration, Oral↗
PubMed1993

Site-specific cell proliferation in renal tubular cells by the renal tubular carcinogen tris(2,3-dibromopropyl)phosphate.

Our laboratory has been examining the mechanisms whereby chemicals are mutagenic in short-term in-vitro assays yet are not carcinogenic in 2-year rodent bioassays. Previous studies indicated that mutagenic carcinogens increased the amount of cell turnover in the target organ, but that mutagenic noncarcinogens failed to do so. The present study compares the incidence of cell proliferation in specific regions of the kidney, which is the site of carcinogenicity, with cell proliferation induced in a nontarget tissue, the liver, by the mutagenic renal tubular carcinogen tris(2,3-dibromopropyl)phosphate (TRIS). Renal tubular adenocarcinoma induced by TRIS was the only tumor type identified in male F344 rats, and it was localized in the outer medulla. Male F344 rats were fed a diet containing 0, 50, or 100 ppm TRIS for 14 days. These doses were identical to the doses given in the National Toxicology Program cancer bioassay. Replicating cells were labeled with bromodeoxyuridine administered by an osmotic minipump and identified in tissue sections from liver and kidney using immunohistochemical techniques. Examination of liver sections showed no chemically related increases in cell proliferation above control for either dose group. However, in the kidney, TRIS induced significant cell proliferation that was localized in the renal outer medulla region, the target area for carcinogenesis. The labeling index (number of labeled cells/total number of cells counted) in the kidneys of TRIS-exposed rats was increased approximately 4-fold in the outer medulla and was not increased in the cortex or inner medulla. The results of this study suggest an association between the chemically-induced renal cell proliferation and the renal carcinogenicity of TRIS.

Animals↗
PubMed1993

Relationship between the time of sustained ethyl acrylate forestomach hyperplasia and carcinogenicity.

Chronic administration of ethyl acrylate (EA) by gavage at 100 or 200 mg/kg/day resulted in a significant dose-dependent increase in the incidence of forestomach (FS) squamous cell papillomas and carcinomas in both sexes of F344 rats and B6C3F1 mice. Subsequent work in this laboratory was designed to investigate the relationship between EA-induced FS hyperplasia and carcinogenicity. Current studies have focused on determining the time required for sustained FS hyperplasia to produce neoplastic transformation. Results of these studies demonstrated that gavage administration of EA to male F344 rats at 200 mg/kg/day for 6 or 12 months caused a sustained increase in FS epithelial hyperplasia for as long as exposure to EA continued. However, FS hyperplasia regressed, and no neoplasms developed when animals receiving EA for 6 months were allowed to recover until they were sacrificed at 24 months of age. In contrast, rats treated for 12 months and allowed 9 months recovery developed FS squamous cell carcinomas (3/13) and papillomas (1/13) for a combined incidence of 4/13. No gross lesions were detected in the liver of any of the rats treated with EA or corn oil vehicle, confirming the tissue specificity in the relationship between EA-induced FS hyperplasia and carcinogenesis. In conclusion, the present work has demonstrated that FS hyperplasia is selectively sustained at the site of EA-induced carcinogenicity for as long as EA is administered and has also demonstrated a temporal relationship between FS mucosal hyperplasia and the development of FS neoplasia by EA.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylates↗
PubMed1992

Development of tolerance to 2-butoxyethanol-induced hemolytic anemia and studies to elucidate the underlying mechanisms.

Early work demonstrated that a single administration of 2-butoxyethanol (BE) causes acute hemolytic anemia in rats. Current studies were undertaken to investigate the effect of repetitive daily dosing of BE on the hematologic parameters of male F344 rats. Treatment of rats with BE daily (125 mg/kg/day) for 1 to 3 consecutive days resulted in a time-dependent increase in the hemolysis of erythrocytes. However, when daily treatment with BE continued beyond 3 days, the number of erythrocytes began to rebound and approached pretreatment levels within 12 days despite continued daily exposure, suggesting development of tolerance to the hemolytic effect of BE. In vivo and in vitro studies were designed to investigate the underlying mechanism(s) of tolerance to the hematotoxicity of BE. Rats were treated with 125 mg BE/kg/day for 3 days followed by a 7-day recovery. At the end of this recovery period, rats were challenged with a single 125 or 250 mg BE/kg dose and the hematologic profiles were assessed at 2, 8, and 24 hr later. A significant decline in the sensitivity of BE-pretreated/recovered rats compared to vehicle-pretreated rats was observed. Further, in vitro incubation of blood obtained from BE-pretreated/recovered with the hematotoxic metabolite of BE, 2-butoxyacetic acid (BAA), revealed that erythrocytes obtained from these rats were significantly less sensitive to BAA than those obtained from normal rats. These studies suggested that tolerance is due, at least in part, to the lesser sensitivity of young erythrocytes formed during the regeneration process. In another study, rats were rendered anemic by bleeding followed by a 7-day recovery. BE administration to bled/recovered rats demonstrated that these rats were less sensitive than rats which were not subjected to bleeding. In vitro incubation of blood obtained from the bled/recovered animals with BAA demonstrated that erythrocytes were significantly less sensitive to BAA than those obtained from control rats. This further confirmed that young erythrocytes, formed during the regeneration process, were less sensitive to BAA than older erythrocytes. Current data also suggested that it is unlikely that tolerance is caused by modification of BE metabolism in rats repetitively exposed to this chemical. In conclusion, chronic exposure to BE would be expected to result in tolerance to BE-induced hemolytic anemia. The mechanisms responsible are likely related to the fact that older cells are more susceptible to BE and BAA and that hemolysis of these cells during the initial exposure followed by their replacement with less susceptible younger cells may account for tolerance development.

Adenosine Triphosphate↗
PubMed1991

Relationship of hepatocarcinogenicity and hepatocellular proliferation induced by mutagenic noncarcinogens vs carcinogens. II. 1- vs 2-nitropropane.

2-Nitropropane (2-NP) is mutagenic in a number of short-term mutagenicity assays in vitro and in vivo, and is a potent hepatocarcinogen in rats. A structural isomer, 1-nitropropane (1-NP), is mutagenic in V79 cells and can induce unscheduled DNA synthesis in rat hepatocytes, yet did not induce tumors in rats following chronic exposure. We examined the correlation of cell proliferation and hepatocarcinogenesis induced by this mutagenic noncarcinogen-carcinogen pair in a rat liver proliferation model. Rats were exposed to gavage doses of 0.5, 1, or 2 mmol/kg of 1-NP or 2-NP daily for 10 days; the highest two dose groups were similar to the doses used in the carcinogenesis bioassay. Cell proliferation was quantitated by incorporation of bromodeoxyuridine, detected immunohistochemically, into newly synthesized DNA. Animals exposed to the vehicle exhibited a labeling index (LI) of approximately 1.9% and animals exposed to CCL4 had a LI of approximately 30%. Rats exposed to the hepatocarcinogen 2-NP exhibited a dose-related increase in LI to 6.3 and 11% at the 1 and 2 mmol/kg doses, respectively, and no increase above control at the 0.5 mmol/kg exposure level. Animals exposed to the noncarcinogenic isomer 1-NP showed no statistically significant increase in LI above controls at any dose level tested. Serum chemistries were consistent with mild to moderate decreases in hepatocellular function, cholestasis, and necrosis following 2-NP exposure, but only minimal effects were observed, probably due to slight dehydration resulting from 1-NP exposure. These data indicate a positive association between increased cell proliferation and hepatocarcinogenesis induced by these two nitropropane isomers.

Alanine Transaminase↗
PubMed1991

Correlation of hepatocellular proliferation with hepatocarcinogenicity induced by the mutagenic noncarcinogen:carcinogen pair--2,6- and 2,4-diaminotoluene.

2,4-Diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT) are equally genotoxic in the Ames/Salmonella assay and are both readily absorbed, metabolized, and excreted and metabolites of both compounds are mutagenic with metabolic activation. However, there are marked differences in the results of chronic rodent bioassays with these two compounds. 2,4-DAT is a potent hepatocarcinogen whereas 2,6-DAT failed to produce an increased incidence of tumors in any tissue even when administered at a dose higher than that of 2,4-DAT. In an effort to elucidate the source of these apparently discordant results, the present studies were designed to determine the effects of these two chemicals on cell proliferation in the liver when administered at the dose levels comparable to those used in the original bioassays. This study utilized repeated oral dosing, osmotic minipumps to deliver bromodeoxyuridine (BrDU) for 8 days, and immunohistochemistry to quantitate BrDU incorporation into hepatic DNA, CCl4 (0.4 ml/rat, single ip dose) or vehicle control groups were included as positive and negative controls, respectively. The degree of cell proliferation was quantified by the labeling index from at least 1000 hepatocytes. Results from the control studies indicate that approximately 1.1% of the hepatocytes from vehicle-treated animals replicated during the exposure period whereas approximately 50% replicated in the positive controls. The carcinogen 2,4-DAT produced a dose-dependent increase in cell proliferation of approximately 10% and 20% in livers of animals exposed to 12.5 and 25.0 mg/kg/day, respectively, whereas the noncarcinogen 2,6-DAT produced no increase in cell turnover compared to vehicle control following treatment with 25.0 or 50.0 mg/kg/day. These results indicate a positive correlation between increased cell proliferation and hepatocarcinogenesis induced by these two isomers of diaminetoluene.

Animals↗
PubMed1991

Effects of sulfhydryl modulation on ethyl acrylate-induced forestomach toxicity.

Acute administration of a single dose of ethyl acrylate (EA) to F344 rats by gavage caused time- and dose-dependent forestomach edema. Evidence from our laboratory and others suggested that EA is hydrolyzed to acrylic acid (AA) and ethanol both in vivo and in vitro. The major metabolites detected in teh urine of rats treated with EA were derivatives of the glutathione conjugates of EA and AA. The current work was undertaken to investigate the effects of sulfhydryl-depleting agents (diethylmaleate and fasting) and sulfhydryl-containing agents (cysteine and cysteamine) on EA-induced forestomach edema. Results presented in this report revealed that pretreatment of rats with sulfhydryl-containing chemicals such as cysteine or cysteamine has potentiated EA-induced forestomach edema. In contrast, depletion of indigenous sulfhydryls by fasting of rats or pretreatment with diethylmaleate (DEM) protected against EA-induced forestomach edema. Furthermore, repetitive daily administration of EA by gavage induced mucosal forestomach hyperplasia. Co-administration of cysteamine and EA resulted in a significant enhancement of the severity of EA-induced forestomach mucosal hyperplasia. In conclusion, current data suggest that modulation of indigenous sulfhydryls play a role in EA-induced forestomach toxicity; however, the exact mechanism underlying this role remains to be characterized.

Acrylates↗
PubMed1991

Sustainability of forestomach hyperplasia in rats treated with ethyl acrylate for 13 weeks and regression after cessation of dosing.

In a chronic study conducted by the National Toxicology Program (NTP), gavage administration of 100 or 200 mg ethyl acrylate (EA)/kg/day, 5 days/week, to F344 rats and B6C3F1 mice resulted in a significant dose-dependent increase in the incidence of squamous cell papillomas and carcinomas of the forestomach of both sexes of rats and mice. No increase in the incidence of tumors was observed at any other site in these rats. Chemically-induced cell proliferation is currently thought to play a role in the development and progression of chemically-induced neoplasia. Therefore, a stop-study was initiated where 100 or 200 mg EA/kg (in corn oil) was administered daily, 5 days/week, for 13 weeks. Rats sacrificed at the end of the treatment regimen had severe epithelial hyperplasia of the forestomach. No lesions were observed in the glandular stomach or liver of EA-treated rats. Forestomach hyperplasia induced by EA included upward and downward cell proliferation. However, forestomachs of rats treated for 13 weeks and sacrificed 8 weeks after the last EA dose exhibited a significant decline in the incidence and severity of forestomach mucosal hyperplasia. Histopathologic evaluation of forestomachs of EA-treated rats (13 weeks) which were allowed a 19-month-recovery (with no exposure to EA) showed further decline in the incidence and severity of mucosal cell hyperplasia. These results indicate that gavage administration of EA to rats results in extensive and sustained forestomach mucosal hyperplasia. The sustainability of forestomach hyperplasia is apparently dependent on the continued exposure of rats to ethyl acrylate, and regressed after cessation of dosing. Furthermore, although enough post-treatment time was allowed for tumors to develop after cessation of EA administration, forestomachs exhibited a nearly complete recovery with no increased incidence of papillomas or carcinomas. It, therefore, remains to be determined what duration of exposure or other factors are critical for reversibility or progression of EA-induced forestomach mucosal hyperplasia to neoplasia.

Acrylates↗
PubMed1990

Acute exposure to tris(2-chloroethyl)phosphate produces hippocampal neuronal loss and impairs learning in rats.

Adult female, Fischer-344 rats were exposed to 275 mg/kg of tris(2-chloroethyl)phosphate (TRCP) by gavage. TRCP produced consistent signs of convulsive activity within 60-90 min after dosing and extensive loss of CAT hippocampal pyramidal cells when examined 7 days after dosing. At the light microscopic level, toxic effects of TRCP on pyramidal cells in the CA3 and CA4 regions and on granule cells in the dentate gyrus were less severe than those on the CA1 cells. The seizure-related and neurohistological effects of TRCP were significantly attenuated by pretreatment with atropine or chlordizepoxide, suggesting that the hippocampal damage was related to the seizures produced by TRCP. In a second experiment designed to assess the potential health risk associated with TRCP, exposed rats were mildly impaired in the acquisition of a reference memory task in a water maze. However, TRCP-exposed rats were consistently impaired in performing a repeated acquisition task in the water maze. These data underscore the potential health risk associated with exposure to TRCP and support the conclusion that the hippocampus is intimately involved in spatial memory in rats.

Animals↗
PubMed1990

Comparison of the hematologic effects of 2-butoxyethanol using two types of hematology analyzers.

Earlier reports from this laboratory indicated that 2-butoxyethanol (BE) causes acute hemolytic anemia in rats as evidenced by a time- and dose-dependent decrease in the number of red blood cells, in hemoglobin concentrations, and in hematocrits (HCT). Subsequent studies showed that treatment with BE causes an early increase in HCT and mean cell volume (MCV). Since this effect went undetected in our early work and resulted in the publication of inaccurate information, present studies were designed to reinvestigate the hematologic effects of BE using the laser-based hematology analyzer which was used in the early studies and an impedance-based hematology analyzer, simultaneously. Packed cell volumes (PCV; spun HCT) were also performed on all blood samples. Male F344 rats were treated with 0, 125, 250, or 500 mg BE/kg (po) and blood was collected from the retro-orbital venous plexus at 1, 2, 4, 8, and 24 hr after dosing. Hematology profiles of BE-treated rats obtained from the impedance-based analyzer showed an early dose- and time-dependent increase in HCTs and MCVs. In contrast, analysis of the same blood samples using the laser-based analyzer showed a dose- and time-dependent decrease in HCTs with little or no change in MCVs. Changes observed in PCVs were consistent with results obtained from the impedance-based analyzer. Therefore, under the experimental conditions of this and previous studies, the laser-based analyzer was unable to detect early increases in HCTs and MCVs in rats treated with BE. Finally, these data explain the different principles utilized to measure cell size by both instruments as they relate to the hematologic effects of BE. Moreover, present data show that BE-induced hemolysis of erythrocytes is preceded by a quantitatively unique and massive swelling suggesting the erythrocyte membrane as the target.

Animals↗
PubMed1990

Evidence for an acetoxyarylamine as the ultimate mutagenic reactive intermediate of the carcinogenic aromatic amine 2,4-diaminotoluene.

2,4-Diaminotoluene (2,4-DAT) is a mutagenic and hepatocarcinogenic aromatic amine, requiring metabolic activation. We have found that the mutagenic potency of 2,4-DAT in Salmonella TA98 is similar when activated by either Aroclor-1254-induced rat primary hepatocytes or 9000 x g supernatant. Previous work has demonstrated that 2,4-DAT is activated by cytochrome P450. The present report describes an investigation of the role of acetyltransferase in 2,4-DAT activation. Substitution of TA98 with the acetyltransferase-deficient strain TA98/1,8-DNP6 resulted in an approximately 90% decrease in the mutagenic potency for 2,4-DAT using S9 activation. The newly engineered acetyltransferase-enhanced Salmonella tester strain YG1024 (TA98(pYG219] demonstrated greatly enhanced sensitivity to the mutagenicity of 2,4-DAT. Inhibition of O-acetyltransferase activity, either with the selective acetyltransferase inhibitor thiolactomycin, or by competitive inhibition with an alternative substrate for the enzyme, reduced the mutagenicity of 2,4-DAT in this acetyltransferase-enhanced bacterial strain. From these data we conclude that following 2,4-DAT activation by N-hydroxylation by cytochrome P450, the resulting hydroxylamino intermediate is further activated in the bacteria via O-acetylation to form the ultimate reactive intermediate, which is postulated to be 4-acetoxyamino-2-aminotoluene.

Acetylation↗