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R B Conolly

Publications and source records attributed to R B Conolly.

70 records · Page 4Linked to original sources
PubMed1985

An investigation of the role of microsomal oxidative metabolism in the in vivo genotoxicity of 1,2-dichloroethane.

In vitro studies have demonstrated that two different metabolic pathways, glutathione conjugation mediated by the glutathione S-transferases and microsomal oxidation, may be involved in the genotoxicity and carcinogenicity of 1,2-dichloroethane (DCE). To evaluate the importance of microsomal oxidative metabolism in the bioactivation of DCE in vivo, male B6C3F1 mice were pretreated with piperonyl butoxide (PIB), an inhibitor of microsomal oxidative metabolism, and the effect of this pretreatment on the extent of hepatic DNA damage produced by DCE was determined 4 hr after DCE administration. The in vivo genotoxicity of 2-chloroethanol, a product of the microsomal oxidative metabolism of DCE, was also investigated. Hepatic DNA damage was measured with a sensitive, alkaline DNA unwinding assay for the presence of single-strand breaks and alkali-labile lesions in DNA. Pretreatment of mice with PIB to inhibit microsomal oxidative metabolism significantly potentiated the hepatic DNA damage observed 4 hr after a single, 200-mg/kg, ip dose of DCE. Treatment of mice with single, ip doses of 2-chloroethanol as high as 1.2 mmol/kg failed to produce any evidence of single-strand breaks and/or alkali-labile lesions in hepatic DNA. When diethyl maleate (DEM) was used to deplete hepatic glutathione levels prior to administration of 2-chloroethanol, the acute hepatotoxicity of 2-chloroethanol was potentiated but again there was no evidence of hepatic damage. These results indicate that microsomal, oxidative metabolism of DCE to 2-chloroethanol and/or 2 chloroacetaldehyde is not responsible for the hepatic DNA damage observed in these studies after DCE administration.

Animals↗
PubMed1985

Acute nephrotoxicity of 1,1-dichloroethylene in the rat after inhalation exposure.

A renal toxicity of 4 h inhalation exposure to 1,1-dichloroethylene (vinylidene chloride; VDC) was studied in male Sprague-Dawley rats. Kidney wt./body wt. ratios, serum urea nitrogen and creatinine levels were significantly increased 24 h after exposure to 250 ppm or more of VDC. Histopathologic examination by light microscopy of hematoxylin and eosin (H&E)-stained sections revealed severe tubular necrosis with calcium deposits at the higher exposure concentrations. Specific staining for calcium oxalate was negative, indicating that biotransformation of VDC to oxalate is probably not responsible for its nephrotoxicity. Pretreatment with polychlorinated biphenyl (PCB) induced the level of renal cytochrome P-450. Phenobarbital (PBT) pretreatment did not alter the renal P-450 level, but both PCB and PBT pretreatments antagonized VDC nephrotoxicity. These pretreatments have also been reported to antagonize VDC-induced hepatotoxicity. In summary, inhalation of VDC is nephrotoxic in the rat; the mechanism of nephrotoxicity does not involve calcium oxalate formation, and the magnitude of nephrotoxicity does not correlate directly with the total amount of renal cytochrome P-450.

Animals↗
PubMed1985

Mixed-function oxidase system induction and propylene hepatotoxicity.

Propylene is hepatotoxic to male Charles River COBS Sprague-Dawley rats pretreated with polychlorinated biphenyls (PCB: Aroclor 1254). Four-hour inhalation exposure to 50,000 ppm propylene increased liver weight/body weight ratios and elevated serum enzyme activities in PCB-pretreated animals. Hepatic microsomal cytochrome P-450 content of PCB-pretreated rats dropped profoundly during propylene exposure and remained depressed for at least 24 h. In addition, PCB-pretreated, propylene-exposed rats exhibited a decrease in the specific activity of hepatic microsomal aniline hydroxylase. However, there was no change in activities of either hepatic microsomal aminopyrine demethylase or glucose-6-phosphatase. Propylene exposure of rats pretreated with beta-naphthoflavone (BNF), phenobarbital (PB), or a mixture of BNF and PB was not hepatotoxic. However, there was, in these animals, a substantial decline in hepatic microsomal cytochrome P-450 levels 24 h after the start of propylene exposure. Hence, the propylene-dependent process resulting in hepatic cytochrome P-450 destruction is qualitatively or quantitatively different from the process that causes acute hepatotoxicity. Preexposure fasting had no effect on the hepatotoxicity resulting from a 4-h exposure of PCB-pretreated rats to 50,000 ppm propylene. Administration of SKF-525A to PCB-pretreated rats immediately prior to propylene exposure completely prevented elevations in serum enzyme activities and liver weight/body weight ratios. In vitro incubation of hepatic microsomes prepared from either BNF-, PB-, or PCB-pretreated rats with an atmosphere of 20% propylene/80% air produced in NADPH-dependent decrease in cytochrome P-450 content. These results suggest that PCB pretreatment is a prerequisite for propylene hepatotoxicity in the rat. Cytochrome P-450-dependent bioactivation of propylene is associated with this hepatotoxicity, but further studies are needed to characterize the mechanism of the PCB-propylene interaction.

Alkenes↗
PubMed1984

An in vivo-in vitro alkaline DNA unwinding assay for hepatic DNA damage: comparison with the alkaline sucrose gradient centrifugation technique.

An in vivo-in vitro alkaline DNA unwinding assay for single-strand breaks and/or alkali-labile lesions in hepatic DNA is described. The assay involves isolation of hepatic nuclei from mice, alkaline denaturation and unwinding of hepatic DNA, separation of single- and double-stranded DNA by hydroxylapatite batch chromatography, and quantitation of DNA in chromatographic fractions by a fluorometric assay. The method allows for the sensitive detection of hepatic DNA damage following in vivo administration of xenobiotics. Using this procedure, DNA fragmentation was demonstrated in alkali after administration of as little as 0.5 mg/kg of N-nitrosodimethylamine (DMN) to male B6C3F1 mice. A comparison of this technique with a similar alkaline sucrose density gradient centrifugation assay demonstrated comparable limits of sensitivity for the two procedures.

Alkalies↗
PubMed1984

In vivo genotoxicity and acute hepatotoxicity of 1,2-dichloroethane in mice: comparison of oral, intraperitoneal, and inhalation routes of exposure.

The in vivo genotoxicity of 1,2-dichloroethane (DCE) was studied in the liver of male C57BL/6 X C3H F1 (hereafter called B6C3F1) mice after single p.o., i.p., and inhalation exposures. The acute hepatotoxicity of DCE was also examined in order to determine nonnecrogenic exposure levels for each route of administration. Single-strand breaks and/or alkali-labile lesions were demonstrated by alkaline DNA-unwinding/hydroxylapatite chromatography in hepatic DNA at 4 hr after p.o. or i.p. administration of nonnecrogenic doses (100 mg/kg, p.o.; 150 mg/kg, i.p.) of DCE to groups of four to six mice. No evidence of hepatic DNA damage was found immediately following 4-hr inhalation exposures of mice to a nonnecrogenic (150 ppm) or necrogenic (500 ppm) concentration of DCE. Four-hr inhalation exposures of mice to concentrations of DCE causing high mortality within 24 hr (1000 to 2000 ppm) produced evidence of hepatic DNA damage at 4 hr, but the possibility that this damage was due to the acute necrogenic effects of the exposures could not be excluded. A significant fraction of the hepatic DNA damage observed 4 hr after i.p. administration of DCE (200 mg/kg) was still evident after 24 hr, indicating the persistence of unrepaired lesions in the DNA. These findings are consistent with the seemingly contradictory results of the two long-term carcinogenicity bioassays, in which DCE was found to be carcinogenic to Osborne-Mendel rats and B6C3F1, mice when administered by gavage but nontumorigenic to Sprague-Dawley rats and Swiss mice after chronic inhalation exposure. Therefore, our results provide additional evidence for the importance of a route of administration effect in the in vivo genotoxicity and carcinogenicity of DCE.

Administration, Intranasal↗
PubMed1983

Comparative in vivo genotoxicity and acute hepatotoxicity of three 1,2-dihaloethanes.

Hepatic DNA damage was demonstrated by alkaline DNA unwinding/hydroxylapatite batch chromatography in male B6C3F1 mice treated with non-necrogenic doses of 1,2-dichloroethane, 1-bromo-2-chloroethane, and 1,2-dibromoethane. Intraperitoneal administration of 0.5 mmol/kg of 1-bromo-2-chloroethane and 1,2-dibromoethane produced similar levels of DNA damage. A 4-fold higher dose of 1,2-dichloroethane (2.0 mmol/kg) was required to produce a comparable effect.

Animals↗
PubMed1977

Acute hepatotoxicity of ethylene and halogenated ethylenes after PCB pretreatment.

Previous studies from our laboratory have shown that ethylene, vinyl fluoride monomer (VFM), vinyl chloride monomer (VCM), and vinyl bromide monomer (VBM) are all acutely hepatotoxic in rats pretreated with polychlorinated biphenyl (PCB). The time course of hepatic injury development after exposure and several parameters, environmental and chemical, affecting this toxicity were evaluated in the work reported here. Liver injury, as measured by serum alanine-alpha-ketoglutarate transaminase (SAKT) or sorbitol dehydrogenase (SDH), develops progressively over a 24-hr period following a 4-hr inhalation exposure of PCB-pretreated rats to ethylene or VCM. Environmental temperature during exposure to VCM does not affect hepatotoxicity or mortality below 30.3 degrees C. At 33.8 degrees C, however, mortality and SAKT are dramatically increased. Overnight fasting, which depletes hepatic glutathione (GSH) of PCB-pretreated rats before exposure to ethylene or VCM, significantly increases the hepatotoxicity of these compounds as measured by SDH. The combined effects of fasting and of trichloropropane epoxide (TCPE), an inhibitor of epoxide hydrase (EH), were also examined. TCPE treatment of fasted PCB-pretreated rats immediately before exposure was synergistic in increasing the acute toxicity of ethylene and VCM. TCPE increased mortality in fed or fasted rats exposed to VFM, but there was no effect of fasting alone. Both fasting and TCPE increased the sensitivity of PCB-pretreated rats to VBM, but there was not a clearly synergistic effect of fasting plus TCPE. These data suggest that the acute toxicity of these compounds is mediated through epoxide intermediates.

Animals↗
PubMed1975

Short-term inhalation toxicity of halogenated hydrocarbons: effects on fasting rats.

Male rats, fasted overnight (18 hours), and exposed to various materials in inhalation were more sensitive to the hepatotoxic effects of carbon tetrachloride, 2-chlorobutadiene, 1,1-dibromoethylene, and 1,1-dichloroethylene (DCE). Vinyl chloride monomer and 1,1-difluoroethylene were not acutely hepatotoxic in fed or fasted rats at any concentration tested. Vinyl chloride monomer when administered simultaneously with DCE prevented the injury associated with DCE inhalation in fasted rats. This prevention of injury may be a result of a competitive interaction since the effect was concentration dependent.

Aerosols↗
PubMed1975

Biochemical toxicology of unsaturated halogenated monomers.

Previous inhalation toxicity studies from our laboratory have shown that 1,1-dichloroethylene (1,1-DCE), 1,1-dibromoethylene (1,1-DBE), and 2-chloro-1,3,-butadiene (2-CBD) are more toxic to fasted rats than to fed rats. Vinyl chloride monomer (VCM) and 1,1-difluoroethylene (1,1-DFE) were not acutely hepatotoxic at 46,500 and 82,000 ppm, respectively, in normal male rats, whether fed or fasted. On a molar basis, 1,1-DBE and 1,1-DCE have similar toxicities while 2-CBD is less toxic. All three compounds produce similar elevation of serum transaminase and bloody ascites, although at differing times following differing exposure concentrations. 1,1-DCE produces massive midzonal hepatic necrosis with hepatic thrombosis and chromatolysis within 2 hr after a 4 hr exposure of fasted rats to 200 ppm. Subsequent to formation of this midzonal lesion, the central portion of the lobule collapses, accompanied by congestion, ascites, and in increased hematocrit in the rat. Serum transaminase and sorbital dehydrogenase are greatly elevated at 6 hr. This effect in fasted rats is associated with glutathione (GSH) depletion. Diethyl maleate (DEM) which depletes GSH in fed rats potentiates the injury associated with 1,1-DCE exposure as well as that produced by 2-CBD. Rats fed ad libitum and exposed to 1,1-DCE or 2-CBD at night, a time of low hepatic GSH concentration, exhibit enhancement of hepatotoxic response when compared to animals exposed during the day when GSH is high.

Alanine Transaminase↗
PubMedDate not supplied

Ototoxicity of toluene in rats.

Toluene is a major industrial solvent and substance of abuse which is ototoxic in rats as shown by both behavioral testing and measurement of brainstem auditory evoked response (BAER) thresholds. The objective of this investigation was to examine the morphological (hair cell loss) and functional (BAER threshold elevations) changes resulting from toluene administration. In the preliminary experiment, 5 male Sprague-Dawley rats were dosed by gavage to 0.5 ml toluene/kg body weight/day in corn oil for 21 days then consecutively to 1.0 ml toluene/kg/day for 21 days. In the main experiment, eight male Sprague-Dawley rats were dosed by gavage for eight weeks with 1.0 ml toluene/kg body weight/day in corn oil. Five and six control rats, respectively, received corn oil only. BAER thresholds were recorded from four toluene-treated and four control rats prior to dosing (main experiment) and from all rats after dosing (both experiments). Loss of outer hair cells occurred in all toluene-treated rats in the middle and basal turns of the organ of Corti, with the greatest loss in the third row and progressively less in the second and first rows. This loss was more severe in toluene-treated rats that demonstrated elevated BAER thresholds in midfrequency regions, typically 2-8 kHz. These experiments demonstrate that auditory changes are associated with cochlear hair cell loss in toluene-treated rats. These ototoxic effects of toluene contrast with those of other known ototoxicants, e.g., aminoglycoside antibiotics, in terms of the position of hair cell lesion in the organ of Corti and in the pattern of hair cell loss.

Animals↗