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Biomedical subjects

D L Springer

Publications and source records attributed to D L Springer.

At least 19 recordsLinked to original sources
PubMed1992

Changes in adult metabolism of aflatoxin B1 in rats neonatally exposed to diethylstilbestrol. Alterations in alpha-class glutathione S-transferases.

Neonatal exposure of rats to xenobiotics has been shown to produce long-term alterations in hepatic enzyme activities and in levels of DNA adducts following carcinogen exposure. We exposed newborn male rats to diethylstilbestrol (DES), pregnenolone-16 alpha-carbonitrile, 7,12-dimethylbenz[a]anthracene or phenobarbital on days 1, 3 and 5 of age. At five months of age, males were injected with 1 mg/kg of [3H]aflatoxin B1 (AFB1), killed after 2 h and examined for AF-DNA adduction in the liver. Males neonatally exposed to DES showed a 35% decrease in DNA adduction levels. Analysis of the adducted DNA bases failed to show any changes in relative proportions of individual adducts in the DES samples compared to controls. Hepatic glutathione concentrations were unchanged. However, Western blot analysis of alpha-class glutathione S-transferases (alpha GST), enzymes known to inactivate the toxic AFB1-8,9-epoxide, showed a 2-fold increase in subunit levels in the DES-treated males, suggesting that the detoxifying activity of the cytosol may have been increased. To confirm this, in vitro tests were undertaken using butylated hydroxyanisole (BHA) induced mouse microsomes to activate [3H]AFB1 in the presence of treated cytosol and GSH. Analysis of metabolites by HPLC showed that DES-treated males formed 245% of the AFB-SG conjugate relative to vehicle controls. These results indicate that neonatal DES treatment resulted in long-term changes in basal alpha GST levels and suggest that these changes were responsible for lower levels of DNA adduction following adult exposure to AFB1.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1992

DNA polymerase, RNA polymerase and exonuclease activities on a DNA sequence modified by benzo[a]pyrene diolepoxide.

Adducts produced by modification of DNA with benzo[a]pyrene diolepoxide (BPDE) are known to inhibit both DNA and RNA synthesis. This phenomenon has been used as a method for determining the distribution of carcinogen binding within defined DNA sequences. A critical comparison of different enzyme activities on adducted DNA is needed, since different enzymes may process adducted DNA differently. Thus, we compared blocks in DNA polymerase activity with that of an RNA polymerase and with an exonuclease at single base resolution. BPDE adducts blocked the progression of cloned T7 DNA polymerase (Sequenase) in a dose-dependent manner. Although the majority of these blocks were at one base prior to adducted guanines, we also observed some blocks opposite specific guanines, suggesting that in some sequences the polymerase inserted a base opposite the modified guanine. Digestion with T4 DNA polymerase (3'----5') exonuclease activity was also blocked in BPDE-adducted DNA; however, fragments produced by blocks in T4 exonuclease migrated two or more bases longer than the corresponding guanine. Mapping of adduct distributions using both Sequenase and T4 exonuclease gave similar results, demonstrating that a long tract of guanines was preferentially modified, and within a polyguanine sequence, the 5' guanines were more heavily modified than the 3' guanines. Transcription of adducted DNA by SP6 RNA polymerase was also inhibited in a dose-dependent manner. However, adducted bases which posed strong blocks to the DNA polymerase were not always strong blocks to the RNA polymerase. Thus, in terms of adduct distribution, Sequenase and T4 exonuclease provided more consistent results than the RNA polymerase, since blockage of the RNA polymerase correlated poorly with guanines.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1991

Differential sensitivities of murine melanocytes and melanoma cells to buthionine sulfoximine and anticancer drugs.

High levels of intracellular glutathione (GSH) may result in resistance of tumor cells to cytotoxic drugs. Because of the innate refractory nature of melanoma cells to chemotherapy, we have used a syngeneic murine system consisting of nontumorigenic Mel-ab melanocytes, tumorigenic H-ras-transformed melanocytes (C9.1), and the highly metastatic BL6 melanoma cells to examine the GSH content, glutathione S-transferase (GST) activity, and sensitivity to buthionine sulfoximine (BSO) and other cytotoxic drugs. Compared to the nontumorigenic melanocytes, both C9.1 and BL6 melanoma cells have nearly fivefold higher GSH content, and BL6 cells have increased GST activity. C9.1 and BL6 cells are more resistant to the cytotoxic effects of BCNU and adriamycin; however, the degrees of resistance do not reflect the increased GSH content in these cells. Pretreatment of BL6 melanoma cells with 50 microM BSO depleted over 90% of their GSH content and enhanced the growth-inhibitory effects of L-dopa methylester, BCNU, bleomycin, and dacarbazine. Exposure to BSO alone was not toxic to the tumor cells for up to 24 hr, but was significantly cytotoxic in the melanocytes after 9 hr. The sensitivity of these cells to BSO appears to depend on a critical level of GSH depletion which is not related to the initial GSH content. These studies suggest that the resistance of melanoma cells to cytotoxic drugs is only partially attributed to changes in the GSH system caused during cellular transformation.

Animals↗
PubMed1989

Dichloroacetic acid and trichloroacetic acid-induced DNA strand breaks are independent of peroxisome proliferation.

This study examined whether the induction of single strand breaks in hepatic DNA by dichloroacetic acid (DCA) and trichloroacetic acid (TCA) depends upon peroxisome proliferation. Male B6C3F1 mice were given a single oral dose of either DCA or TCA. At varying times, between 1 and 24 h after administration of the compounds, breaks in DNA were measured using an alkaline unwinding assay. Peroxisome proliferation was monitored at the same time intervals in a parallel experiment by measuring peroxisomal B-oxidation of [14C]palmitoyl-CoA in liver homogenates. Both DCA and TCA significantly increased breaks in DNA at 1, 2, and 4 h post-treatment, with a return to control levels after 8 h. No evidence for an increase in peroxisomal beta-oxidation was produced by either chemical up to 24 h after administration. In a separate experiment, mice were treated with DCA or TCA for 10 days and their livers examined for evidence of peroxisome proliferation. An increase in liver weight was observed, particularly with DCA. Both TCA and DCA increased peroxisomal beta-oxidation in liver homogenates, with TCA-treated animals showing more activity than those treated with DCA. Electron microscopy revealed that the number of peroxisomes were approximately the same in DCA- and TCA-treated animals. However, peroxisomes induced by DCA treatment frequently lacked nucleoid cores. These data indicate that peroxisomes induced by these compounds differ in their concentration of peroxisomal enzymes. Except for a slight hypertrophy, repeated doses of TCA do not produce significant degenerative changes in the liver of mice. Repeated doses of DCA produce multifocal, subcapsular necrotic regions, and a marked hypertrophic response in the liver. Mice treated with TCA for 10 days and sacrificed 24 h after the last dose did not display increased strand breaks in hepatic DNA. This indicates that peroxisomal proliferation does not contribute to the induction of DNA strand breaks.

Acetates↗
PubMed1989

Elevated blood pressure and heart rate in rats exposed to a coal-derived complex organic mixture.

The susceptibility of the cardiovascular system to exposure to a high-boiling coal liquid (heavy distillate, HD) was studied in the rat using an isoproterenol (ISO) myocardial infarction model. Male Fischer rats were exposed to HD by inhalation (0.7 mg/l), 6 h/day, 5 days/week, for 6 weeks. After a 10-day recovery period, sham-exposed and HD-exposed rats were injected subcutaneously with 0, 20, 40 or 60 mg ISO/kg body weight. Blood pressure, heart rate, electrocardiogram and 99mTc uptake by the heart were measured 1 day later. A dose-related increase was observed in the uptake of 99mTc by the hearts of both sham-exposed and HD-exposed animals after ISO injection; however, uptake by the sham-exposed group was significantly greater than that of exposed groups. The most striking observation was a 20% elevation in arterial blood pressure of HD-exposed rats over that of sham-exposed animals when no ISO was injected. These results suggest that the cardiovascular system could be detrimentally affected by exposure to coal-derived complex mixtures and, possibly, to other complex organic mixtures.

Administration, Inhalation↗
PubMed1989

Complex mixture effects on the dermal absorption of benzo[a]pyrene and other polycyclic aromatic hydrocarbons from mouse skin.

To study the dermal penetration of benzo[a]pyrene (BAP) in relation to other polycyclic aromatic hydrocarbons (PAHs), a complex mixture of PAHs was applied to the backs of CD-1 mice, and the dermal residence times of BAP and eleven other PAHs were determined using gas chromatography. The dermal penetration of BAP was found to be representative of the other PAHs studied, with a dermal half-life of 6.7 h. Half-lives of the other eleven PAHs ranged from 5.0 to 8.8 h. The dermal half-life of BAP applied in a volatile organic solvent, rather than a PAH mixture, was 3.0 h. The effects of five complex organic mixtures, with boiling points ranging from 300-700 degrees F to greater than 850 degrees F, on the dermal residence time of BAP was studied by adding radiolabeled BAP to the mixtures, and applying them to the backs of mice. All of the mixtures studied increased the dermal residence time of BAP by amounts ranging from 1.8-fold to 6.9-fold.

Animals↗
PubMed1989

Comparison of fetotoxic effects of a dermally applied complex organic mixture in rats and mice.

A high-boiling (288-454 degrees C), coal-derived complex organic mixture (COM) has been shown to be teratogenic in rats following inhalation and oral routes of exposure. To determine whether similar changes also occur after dermal exposure to this COM, pregnant rats and mice were exposed during periods of organogenesis (Days 11 to 15 of gestation). Shaved backs were painted with 0, 500, or 1500 mg/kg of the COM (control, low, or high dose, respectively); the exposed area was not occluded. Maternal weight gain during the gestation period decreased with increasing dose in rats but not in mice. Examination of rat fetuses on Day 20 of gestation showed that resorptions had occurred in more than 90% of low- and high-dose litters (vs 6% in the control group). In mice, fetal examinations on Day 18 of gestation showed that resorptions occurred in 71% of litters from both exposure groups (vs 14% in the controls). Fetal measurements indicated that both the weight and the length of rat fetuses decreased with increasing dose, but mouse fetuses were unaffected. Cleft palates, absent in the control groups, were observed in 50 to 55% of the high-dose group and 5 to 8% of the low-dose fetuses of both species. Small fetal lungs occurred in nearly 100% of the exposed rat fetuses and in 25% of the high-dose mice; the incidence of small lungs was 1% in control animals. Other variations observed in exposed groups included edema and reduced ossification in the rat and renal pelvic cavitation in the mouse.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗
PubMed1989

Inhibition of benzo[a]pyrene-7,8-diol formation in vitro by complex organic mixtures.

Coal-derived complex organic mixtures [COM] with boiling points greater than or equal to 370 degrees C (greater than or equal to 700 degrees F) are known to inhibit both mouse skin tumor initiation by benzo[a]pyrene [BAP], and BAP-induced bacterial mutagenesis. We have examined the effects of 5 COM, with boiling points of 149-370 degrees C (300-700 degrees F), 370-398 degrees C (700-750 degrees F), 398-426 degrees C (750-800 degrees F), 426-454 degrees C (800-850 degrees F), and greater than 454 degrees C (greater than 850 degrees F), on both the rate and the route of BAP metabolism by rat liver homogenates in vitro. When co-metabolized in 40:1 excess with BAP, all of the COM reduced the rate of BAP metabolism. The 149-370 degrees C (300-700 degrees F) COM reduced the initial rate of BAP metabolism to 34% of the rate for BAP alone, while the four higher-boiling COM reduced it to 6.3-9.3% of the rate for BAP alone. In addition, the 2 highest-boiling COM (426-454 degrees C and greater than 454 degrees C boiling points) were found to reduce the percentage of BAP metabolized to BAP-7,8-diol, in comparison to incubations using BAP alone. The 370-398 degrees C and 398-426 degrees C COM did not alter the percentage of BAP metabolized to BAP-7,8-diol, while the 149-370 degrees C COM increased it. Both the general inhibition of BAP metabolism (by all of the COM), and the specific inhibition of BAP-7,8-diol formation (by the highest-boiling COM) may play a role in the inhibition of formation of BAP-induced skin tumors by these materials.

Animals↗
PubMed1989

Influences of complex organic mixtures on tumor-initiating activity, DNA binding and adducts of benzo[a]pyrene.

Co-incubation of benzo[a]pyrene (BaP) and coal-derived complex organic mixtures has been shown to decrease the metabolism and mutagenic activity of BaP. Because of these influences, five mixtures were co-administered dermally to mice to initiate tumor development. Results from these studies demonstrated that BaP tumor-initiating activity was decreased substantially by four of the five mixtures. When one of the mixtures was separated into chemical class fractions, the polycyclic aromatic hydrocarbon (PAH) and nitrogen-containing polycyclic aromatic compound fractions were the most effective, and the aliphatic and hydroxy-PAH fractions were the least effective as inhibitors of BaP-induced tumor initiation. Binding of [3H]BaP to epidermal DNA under conditions identical to those used for tumor initiation was decreased by co-administration of all five mixtures. Calculations of the number of tumors produced/micrograms BaP bound to DNA demonstrated that co-administration of this carcinogen with the mixtures consistently increased the effectiveness of the bound BaP at producing tumors by approximately a factor of 2. The HPLC radioactivity profiles of enzyme-hydrolyzed, adducted DNA indicated that, in the presence of the mixtures, the predominant adducts were derived from BaP-diol epoxide (BPDE); however, the mixtures decreased the ratios of the anti-BPDE-deoxyguanosine to syn-BPDE-deoxy-guanosine adducts. These data indicate that the prevailing influences of the mixtures (i.e. decreased DNA binding and adduct shifts) were similar to those observed with other bioassays following co-administration of binary mixtures. Furthermore, the data demonstrate that both DNA binding and adduct profiles are important in determining the contribution of a known carcinogen to tumor initiation by complex organic mixtures.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1989

Preparation of microgram quantities of BaP-DNA adducts using isolated rat hepatocytes in vitro.

The analysis of carcinogen-DNA adducts generally requires the preparation (by chemical or biological means) of DNA adduct standards, in amounts sufficient for chemical characterization. We have established conditions for the in vitro biological preparation of microgram quantities of DNA adducts derived from benzo[a]pyrene (BaP), fluoranthene and 7,12-dimethylbenzanthracene, using isolated rat hepatocytes. The metabolic activation of 180 microM BaP by isolated rat hepatocytes in a calf-thymus-DNA (CT-DNA)-supplemented medium resulted in the formation of 2.9 micrograms of BaP adducted to 56.7 mg of DNA. The average level of binding in this experiment was 148 +/- 8 pmol BaP bound/1 mg DNA, which compares favorably to the 10-30 pmol BAP/1 mg DNA which is typical of mouse skin adducts in vivo. In another experiment, BaP-DNA adduct formation in calf-thymus DNA added to hepatocyte incubations was further increased to 327 +/- 27 pmol/mg DNA, by physical shearing of the DNA prior to the incubation. The HPLC profile of the BaP adducts produced using hepatocytes plus CT-DNA is virtually indistinguishable from that produced by tumor-initiating doses of BaP applied to mouse skin in vivo, and the major DNA adduct formed by the hepatocytes co-elutes with the (+)-anti-diol-epoxide adduct of deoxyguanosine. Similar experiments using fluoranthene and 7,12-dimethylbenzanthracene also resulted in substantial DNA adduct formation; however, incubations using dibenz[a,h]anthracene did not. These results indicate that isolated rat hepatocytes in vitro can be useful for the preparation of DNA adducts of a number of polycyclic aromatic hydrocarbons, in quantities sufficient for chemical characterization.

Animals↗
PubMed1987

Phenotypically selective promotion of diethylnitrosamine-initiated altered hepatocyte foci by dietary phenobarbital or a topically applied coal-derived organic mixture in male and female rats.

Relative frequencies of diethylnitrosamine (DEN)-initiated foci of altered hepatocytes appearing in response to promotion by either dietary phenobarbital or a topically applied coal-derived organic mixture (CDM) were investigated in male and female rats. The focus population was examined for two histochemical markers, elevated gamma-glutamyl transpeptidase [GG(+)] and iron exclusion [FE(-)], giving rise to 3 detectable focus phenotypes, i.e., GG(+) foci, FE(-) foci, and GG(+)/(FE(-) foci. Frequencies of the 3 phenotypes were quantitated through the use of serial frozen sectioning and computer-assisted image analysis. In agreement with our prior observations, cutaneous exposure to CDM or dietary phenobarbital promoted the expression of DEN-initiated foci. However, the current data showed that this promoting effect of CDM occurred only in females and was restricted to foci with the GG(+)/FE(-) phenotype. Dietary phenobarbital, on the other hand, promoted both the GG(+) and GG(+)/FE(-) phenotypes and was effective in both males and females, although a sex-related differential in the promoting efficiency of phenobarbital was also observed. The pronounced heterogeneity in the responses of the 3 focus phenotypes suggests that each phenotype is the consequence of a specific type of genomic alteration with a specific capacity to undergo phenotypic expression in response to a given promoting stimulus.

Administration, Topical↗
PubMed1987

Effects of subchronic inhalation exposure of mice to a high-boiling coal liquid.

Mice (CD-1) were exposed to aerosol concentrations of 0.0, 0.03, 0.14, or 0.69 mg/liter of heavy distillate (HD), a high-boiling coal liquid from the solvent-refined coal (SRC)-II process. Exposures were for 6 hr/day, 5 days/week for 13 weeks. Particle sizes ranged between 1.6 and 1.8 micron, mass median aerodynamic diameter, with a geometric standard deviation range of 1.9-2.5. Growth for high-dose males was significantly less than that of the control group. Compared to controls, weights of liver were significantly higher and those of ovaries and thymus significantly lower; these changes were significant on both absolute and relative weight bases. The number of red blood cells, volume of packed red cells, and hemoglobin concentration for animals from the high-dose group were significantly lower than those of controls. Microscopic examination of organ sections showed focal hepatic necrosis and nonspecific hepatopathy. Additionally, olfactory epithelial degeneration occurred in a dose-dependent manner. Results from this study indicated that exposure to HD caused adverse effects at the high dose and that these changes were either less severe or absent in middle-dose group mice. Comparison of these results with those for rats indicated that with rats the biological effects were more severe and present at lower doses than was observed for mice.

Administration, Inhalation↗
PubMed1987

Cardiovascular effects in rats following exposure to a high-boiling coal liquid.

In previous work, increased blood pressure was observed in anesthetized rats following a subchronic aerosol exposure to solvent-refined coal heavy distillate (HD). To determine if this increase is a permanent, dose-related response, 11-week-old male rats were exposed by inhalation to 0, 0.24, or 0.70 mg/liter (control, low-exposure, and high-exposure groups, respectively) of HD for 6 hr/day, 5 days/week, for 6 weeks. In addition to blood pressure, select cardiovascular parameters were measured to obtain information on other possible toxic effects of the HD and also to gain some insight into potentially altered regulatory mechanisms that could be affecting the blood pressure. The angiotensin-aldosterone hormonal system, body fluid regulation, cardiac function and regulation, and pulmonary gas-exchange capabilities were examined. Two weeks after the end of exposure, mean blood pressures and heart rates of anesthetized animals in the low-and high-exposure groups were elevated relative to the controls. Plasma angiotensin concentrations decreased with increasing dose, whereas aldosterone concentrations were unaffected. In the high-dose group, blood and plasma volumes were 20 and 28%, respectively, higher than those of controls. Seven weeks after exposure, all measured cardiovascular parameters were similar to control values. Results from this study show that a 6-week exposure to HD resulted in dose-dependent, transient changes in a variety of physiological factors considered important in cardiovascular function.

Aerosols↗
PubMed1986

Lung development and postnatal survival for rats exposed in utero to a high-boiling coal liquid.

Previous studies performed in this laboratory indicated that exposure of rat fetuses to high-boiling coal liquids from 12-14 days of gestation (dg) induced a number of major malformations, including cleft palate, diaphragmatic hernia and small lungs. The study reported here was designed to determine postnatal viability and development of survivors following in utero exposure to Harmarville process solvent (HPS), a wide-boiling-range (150 to greater than 455 degrees C) coal liquid. For this study, 0.74 g kg-1 of the coal liquid was administered (by intragastric intubation) to rats from 12 to 14 dg. Offspring were evaluated for postnatal survival, growth and lung and thymus weights. Randomly selected pups from control and treated litters were killed and necropsied at 1, 3, 7 and 21 days postpartum. In addition, data for control pups were obtained at 0.25 and 0.5 days postpartum for comparison with body, lung and thymus weights of pups that died during this interval. Fifty-four per cent of the exposed pups and 9% of the control pups died between birth and 3 days postpartum. Of the treated pups that died, 10% (6/5; pups/litters) had cleft palate, 27% (17/9) had small lungs and 33% (21/8) had both cleft palate and small lungs. No gross malformations were observed in the remaining 30% of the dead pups. Microscopic examination of lungs from HPS-treated pups revealed no evident histological abnormalities. Body, lung and thymus weights for treated animals that died were significantly less than those of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Effects of inhalation exposure to a high-boiling (288 to 454 degrees C) coal liquid.

Coal liquids have been evaluated in a variety of short-term toxicological assays; however, few studies have been conducted to determine the systemic effects after inhalation exposure to these materials. To extend the data base on potential health effects from coal liquefaction materials, we performed a study with solvent refined coal (SRC)-II heavy distillate (HD). Fischer-344 rats were exposed for 6 hr/day, 5 days/week for 5 or 13 weeks to an aerosol of HD (boiling range, 288 to 454 degrees C) at concentrations of 0.69, 0.14, 0.03, or 0.0 mg/liter of air for the high, middle, low, and control groups, respectively. Survival through 13 weeks of exposure was greater than 90% for all groups; body weights for exposed animals were decreased in a dose-dependent manner. Significant increases in liver weights and decreases in thymus and ovary weights were observed for treated animals compared with controls. There were also significant treatment-related decreases in erythrocytes, hemoglobin, volume of packed red blood cells, lymphocytes, eosinophils, and total white blood cells. After 5 weeks of exposure serum cholesterol concentrations increased in a dose-dependent manner for both sexes and serum triglyceride amounts decreased for males but not for females. After 13 weeks of exposure, high-dose animals had significant increases in cholesterol (males only), triglycerides, blood urea nitrogen, and serum glutamic pyruvic transaminase (SGPT; males) and significant decreases in albumin, SGPT (females), and lactate dehydrogenase (LDH). Examination of bone-marrow preparations from exposed animals demonstrated consistent decreases in the degree of cellularity, suggesting that this organ is a target for HD. Microscopic evaluation of organ sections indicated exposure-related changes for nasal mucosa, pulmonary macrophages, thymus, liver, kidney, bone marrow, ovaries, and cecum. Results from this study indicated dose-dependent increases in the severity of the lesions observed, with few effects in the low-exposure group that were attributable to the exposure.

Animals↗
PubMed1985

Promotion of preneoplastic changes in liver by coal-derived organic mixtures applied to skin.

The promotion of preneoplastic hepatocyte foci was observed in rats neonatally initiated by a single intraperitoneal injection of benzo[a]pyrene (BP) or diethylnitrosamine (DEN) and exposed, from weaning, to repeated topical applications of coal-derived complex organic mixtures that are carcinogenic for mouse skin. Topical application of these mixtures in the absence of prior initiation did not cause significant induction of hepatocyte foci. These observations indicate the advantage of the neonatal rat hepatocarcinogenesis system for detecting promoting activity in carcinogenic mixtures and identify the existence of systemic tumorigenic risk from cutaneous contact with promoting agents.

Administration, Topical↗