Accumulation and elimination of dieldrin in muscle tissue of channel catfish

Dieldrin accumulation and elimination in muscle tissue of channel catfish (Ictalurus punctatus) from water and food was determined in the laboratory. Twenty-eight-day exposure of fish 150-225 mm and 350-400 mm long to 75 parts per trillion (ng/liter) dieldrin resulted in the larger catfish consistently accumulating more dieldrin than the smaller fish. After 28 days of elimination, dieldrin levels in both size groups were nearly equal. Catfish exposed to 2 ppm (mg/kg) dieldrin through their diets accumulated significantly more dieldrin in muscle than did fish exposed to 75 pptr in water. When fish were exposed to dieldrin both in food and water, dieldrin from both sources contributed to the total dieldrin load. Large catfish accumulated more dieldrin from food and water than did smaller catfish. After 28 days of elimination, levels of dieldrin were not significantly different in muscles of 150-225 mm and 350-440 mm catfish exposed via both food and water.     

Estrogenic activity of a dieldrin/toxaphene mixture in the mouse uterus, MCF-7 human breast cancer cells, and yeast-based estrogen receptor assays: no apparent synergism

The estrogenic activity of dieldrin, toxaphene, and an equimolar mixture of both compounds (dieldrin/toxaphene) was investigated in the 21-day-old B6C3F1 mouse uterus, MCF-7 human breast cancer cells, and in yeast-based reporter gene assays. Treatment of the animals with 17beta-estradiol (E2) (0.0053 kg/day x3) resulted in a 3.1-, 4.8-, and 7.8-fold increase in uterine wet weight, peroxidase activity, and progesterone receptor binding, respectively. In contrast, treatment with 2.5, 15 and 60 micromol/kg (x3) doses of toxaphene, dieldrin, or dieldrin/toxaphene (equimolar) did not significantly induce a dose-dependent increase in any of the E2-induced responses. The organochlorine pesticides alone and the binary mixture did not bind to the mouse uterine estrogen receptor (ER) in a competitive binding assay using [3H]E2 as the radioligand. In parallel studies, estrogenic activities were determined in MCF-7 cells by using a cell proliferation assay and by determining induction of chloramphenicol acetyl transferase (CAT) activity in MCF-7 cells transiently transfected with plasmids containing estrogen-responsive 5'-promoter regions from the rat creatine kinase B and human cathepsin D genes. E2 caused a 24-fold increase in CAT activity in MCF-7 cells transiently transfected with creatine kinase B and a 3.8-fold increase in cells transiently transfected with the human cathepsin D construct. Treatment of MCF-7 cells with dieldrin, toxaphene, or an equimolar mixture of dieldrin plus toxaphene (10(-8)-10(-5) M) did not significantly induce cell proliferation or CAT activity in the transient transfection experiment with both plasmids. The relative competitive binding of the organochlorine pesticides was determined by incubating MCF-7 cells with 10(-9) M [3H]E2 in the presence or absence of 2 x 10(-7) M unlabeled E2 (to determine nonspecific binding), toxaphene (10(-5) M), dieldrin (10(-5) M), and equimolar concentrations of the dieldrin plus toxaphene mixture (10(-5) M). The binding observed for [3H]E2 in the whole cell extracts was displaced by unlabeled E2, whereas the organochlorine pesticides and binary mixture exhibited minimal to nondetectable competitive binding activity. E2 caused a 5000-fold induction of beta-galactosidase (beta-gal) activity in yeast transformed with the human ER and a double estrogen responsive element upstream of the beta-gal reporter gene. Treatment with 10(-6)-10(-4) M chlordane, dieldrin, toxaphene, or an equimolar mixture of dieldrin/toxaphene did not induce activity, whereas 10(-4) M endosulfan caused a 2000-fold increase in beta-gal activity. Diethylstilbestrol caused a 20-fold increase in activity in yeast transformed with the mouse ER and a single estrogen responsive element upstream of the beta-gal reporter gene. Dieldrin, chlordane, toxaphene, and endosulfan induced a 1.5- to 4-fold increase in activity at a concentration of 2.5 x 10(-5) M. Synergistic transactivation was not observed for any equimolar binary mixture of the pesticides at concentrations of either 2.5 x 10(-5) M or 2.5 x 10(-4) M. The results of this study demonstrate that for several estrogen-responsive assays in the mouse uterus, MCF-7 human breast cancer cells, and yeast-based reporter gene assays, the activities of both dieldrin and toxaphene were minimal, and no synergistic interactions were observed with a binary mixture of the two compounds.     

Induction of mammary tumors in virgin female BALB/c mice by single low doses of 7,12-dimethylbenz[a]anthracene

The induction of mammary tumors in virgin female inbred BALB/c mice after administration of 7,12-dimethylbenz[a]anthracene (DMBA) over a wide range of doses was studied. Mice were exposed at 12 weeks of age to single or multiple doses of DMBA ranging from 0.0025 to 12.0 mg by gastric intubation and were checked regularly for mammary tumors. The experiment was terminated when the mice were 800 days of age. In the dose range of 0.0025--0.125 mg DMBA, the incidence of mammary tumors was dose-dependent. At higher doses, the mammary tumor incidence became less dose-dependent and was nearly independent of doses above the 0.25-mg level. Analysis of the data for the rate of appearance of mammary tumors with age of the animals and for the age at death of non-mammary tumor-bearing animals indicated that in the low dose range induction of mammary tumors was the predominant effect of DMBA exposure, whereas at moderate to high doses the toxic and carcinogenic effects of DMBA on other tissues significantly influenced the final incidence of mammary tumors. Greater than 90% of the tumors that resulted from administration of low doses of DMBA were adenocarcinomas. In contrast, adenocarcinomas and adenoacanthomas were found in approximately equal proportions following administration of high doses of DMBA.     

Renal clearance of domoic acid in the rat

The renal clearance (Clr) of the seafood toxin domoic acid (DA) was investigated in the rat. Following cannulation of the right femoral artery, the left femoral vein and the bladder of anaesthetized rats, a single bolus injection of either [3H]DA, [14C]p-aminohippuric acid (PAH) or [3H]inulin was administered through the venous cannula. Blood samples were taken from the arterial cannula at 1, 2, 10, 30, 50, 70, 90, 110 and 130 min following injection, and urine samples were collected at 20-min intervals starting from the time of bolus injection. Based on plasma concentration-time profiles, the total clearances (Clt) for DA, PAH and inulin were 9.12, 33.17 and 7.50 ml/min/kg body weight, respectively. The Clr calculated from urinary excretion rates were not significantly different from the Clt. Probenecid significantly reduced the Clr of PAH but did not affect that of DA. When DA was given at doses of 0.5 ng, 0.5 mg and 2.0 mg/kg body weight, the pharmacokinetic parameters Clt, Clr, elimination-rate constant and apparent volume of distribution at steady state were not statistically different between doses. The entire dose of 3H was recovered in the urine by 160 min after dosing, and analysis of urine samples by HPLC confirmed that the radiolabel (3H) was associated predominantly with the parent form of DA. The results of the present study demonstrate that DA is cleared from plasma primarily through the kidneys. DA clearance occurs primarily by renal glomerular filtration since its Clt is comparable with that of inulin, is less than that of PAH and is not affected by probenecid.     

Inhibition of nicotinic responses by cotinine in bovine adrenal chromaffin cells

We studied the effects of cotinine, the major metabolite of nicotine, on nicotine-induced increase in [3H]phorbol dibutyrate binding, activation of protein kinase C and [3H]noradrenaline release in primary cultured bovine adrenal chromaffin cells. Cotinine (1 mM, 15 min.) and nicotine (10 microM, 5 min.) increased the [3H]phorbol binding by 100% and 150%, respectively. Both a short-term (10 min.) and a long-term (24 hr) pretreatment with cotinine inhibited the effect of nicotine. A 24 hr pretreatment with cotinine (1 mM) also reduced the nicotine-induced increase in membrane-bound protein kinase C activity. Cotinine pretreatment (10 min.) dose-dependently inhibited the release of [3H]noradrenaline induced by nicotine and dimethylphenylpiperazinium. Cotinine pretreatment did not reduce the [3H]noradrenaline release induced by high extracellular potassium (56 mM) or veratrine (10 mg l-1). The results indicate that cotinine inhibits activation of protein kinase C and noradrenaline release induced by nicotinic agonists in primary cultures of bovine adrenal chromaffin cells. The results suggest that pre-existing cotinine could modify responses to acute exposure to nicotine in neural systems.     

Neurochemical and neurobehavioral effects of repeated gestational exposure to chlorpyrifos in maternal and developing rats

Acute exposure to the organophosphate pesticide chlorpyrifos (CPF) on gestation day 12 (GD12, 200 mg/kg/ml, SC) causes extensive neurochemical changes in maternal brain but lesser changes in fetal brain. In the present study, we examined the relative neurotoxicity of repeated, lower-level CPF exposures during gestation in rats. Pregnant Sprague-Dawley rats were exposed to CPF (6.25, 12.5, or 25 mg/kg per day, SC) from GD12-19 and sampled at either GD16, GD20, or postnatal day 3 (PND3) for measurement of various maternal and developmental neurochemical markers. In contrast to the high acute dose exposure, no maternal toxicity was noted with repeated lower-level dosing. Extensive acetylcholinesterase (AChE) inhibition (83-90%) was noted in maternal brain at all three time points following repeated exposures (25 mg/kg). Higher AChE inhibition (58%) was noted in fetal brain at GD20 compared to 19-25% on PND3 in treated pups cross-fostered to control dams and in control pups cross-fostered to treated dams following repeated exposures (25 mg/kg per day). Whereas similar reductions in brain muscarinic receptor binding were noted at GD20 and PND3 in dams and developing brain between acute and repeated dosing regimens, greater changes in [3H]CD and [3H]cytisine binding were evident following repeated exposures. Righting reflex and cliff avoidance tests were markedly altered following repeated exposures. The results suggest that lower-level repeated exposures to CPF cause extensive neurochemical and neurobehavioral changes in developing rats in the absence of maternal toxicity.     

A rice protein isolate alters 7,12-dimethylbenz[alpha]anthracene-induced mammary tumor development in female rats

The effects of a rice protein isolate (RPI) on 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced mammary tumor progression were investigated in female Sprague-Dawley rats. At 6 weeks of age, rats were fed a casein, RPI or soybean protein isolate (SPI) diet, respectively. After 1 week, DMBA was administered orally at the dose of 30 mg/kg body weight. The mean tumor number per tumor-bearing rat at autopsy was significantly lower only in rats fed RPI than in those fed casein. Palpable tumors at the mid point of the experiment were significantly lower in rats fed RPI and SPI than in those fed casein. Serum estradiol-17 beta concentrations were lower in rats fed the SPI (but not in those fed RPI) than in those fed casein. In a further experiment, no differences were found in hepatic microsomal DMBA-arylhydrocarbon hydroxylase activity after 7 days of feeding the respective diets. These results suggest that RPI exerts its inhibitory effect on DMBA-induced mammary tumorigenesis irrespective of changes in circulating estrogens or modulation of hepatic DMBA metabolism.     

Interleukin-1 alpha gene expression and localization of interleukin-1 alpha protein during tumor promotion

Treatment of the dorsal epidermis of SENCAR mice with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a time- and dose-dependent stimulation of interleukin-1 alpha (IL-1 alpha) gene expression. Levels of IL-1 alpha mRNA were elevated as early as 15 min and peaked at 3-4 h after a single application of TPA (2 micrograms or 10 micrograms). IL-1 alpha gene expression increased in epidermal tissue isolated from SENCAR mice at 1, 3, 6, 10, 16, and 22 wk after a single treatment with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and subsequent twice-weekly application of 2 micrograms TPA. IL-1 alpha-immunoreactive protein was specifically localized within suprabasal keratinocytes in cutaneous tissue isolated from mice treated with DMBA-TPA for 1-22 wk and in nonproliferating cells located within papilloma tissue isolated from SENCAR mice at 22 wk after initiation and promotion. Basal cells within hyperplastic epidermis did not produce IL-1 alpha-immunoreactive protein. DMBA treatment alone did not induce IL-1 alpha gene expression. Injection of IL-1 alpha-specific antibodies (50 micrograms) into SENCAR mice via the tail vein 2 h before treatment with TPA (2 micrograms or 10 micrograms) significantly (P < 0.05) inhibited the skin thickening usually observed 24 h after treatment with TPA. Autoradiography studies showed that injection of anti-IL-1 alpha antibodies inhibited incorporation of [methyl-3H]thymidine by keratinocytes within the epidermis and by cells within hair follicles. It also inhibited neutrophil infiltration into the dermis, which usually results from topical application of TPA. These data suggest that IL-1 alpha is a pivotal cytokine produced by specific subpopulations of epidermal keratinocytes and that IL-1 alpha primarily regulates the epidermal proliferative response of a distinctly separate population of keratinocytes after topical exposure of murine epidermis to TPA and secondarily modulates neutrophil migration into the dermis. Consequently, manipulation of IL-1 alpha may be a way to attenuate or abrogate the cutaneous response to TPA by altering keratinocyte proliferation, the resultant hyperplasia, and a portion of the inflammatory response characterized by dermal infiltration of neutrophils.     

Demonstration and partial characterization of a 7,12-dimethylbenz[alpha]anthracene-binding protein in rat adrenal

Rat adrenal cytosol was found to contain a 7,12-dimethylbenz[a]-anthracene (DMBA)-binding protein which is characterized by a pI of 7.2, a Kd-value of 3 microM and a maximal capacity of about 47 pmol/mg protein. The binding is highly specific for DMBA and is not displaced by 3-methylcholanthrene (MC), benz[a]pyrene (BP) or other polycyclic hydrocarbons. Likewise, various androgens, estrogens or glucocorticoids have no effect on the DMBA binding. It is proposed that the DMBA-binding protein may have a role in the toxic effects of DMBA or DMBA metabolites in adrenal and possibly in other DMBA-sensitive organs as well.     

Evidence that iron-overload promotes 7,12-dimethylbenz(a)anthracene- induced skin tumorigenesis in mice

Iron overload is known to occur in West European and American populations due to the consumption of an iron-rich diet. There are also genetic disorders which lead to body iron overload. It has been shown that iron overload predisposes humans to an increased risk of cancer. In experimental animals, iron overload is known to enhance intestinal, colon, hepatic, pulmonary and mammary carcinogenesis. However, the mechanism by which iron overload enhances chemically-induced carcinogenesis is not known. In this study, we show that iron overload acts as a mild tumor promoter in mouse skin. Female albino swiss mice were given 1 mg iron/mouse parenterally for 2 weeks to induce iron overload. These animals showed a three-fold increase in cutaneous iron concentration as compared to normal mice. Tumors were initiated by topically applying 7,12-dimethylbenz(a)anthracene (DMBA). Appearance of the first tumor (latency period), percent tumor incidence and number of tumors/mouse were recorded. When compared to the control group, iron overload mice showed an increased incidence of tumors, from 25%-55% by week 20, and tumors appeared 4 weeks earlier. The number of tumors per mouse was four-fold higher in the iron overload group. The induction of cutaneous ornithine decarboxylase (ODC) activity and [3H]thymidine incorporation in cutaneous DNA were higher in iron overload groups as compared to normal control animals. Similar to other oxidant tumor promoters, iron overload enhanced cutaneous lipid peroxidation and xanthine oxidase activity and decreased catalase activity. Our results indicate that iron overload exerts a mild tumor promoting activity in mouse skin. Our data also show that oxidative stress generated by iron overload plays an important role in the augmentation of cutaneous tumorigenesis. These data may also have implications for the enhanced risk of cancer-induction following UVB exposure of human populations with iron overload.     

Subchronic toxicity of benzothiophene on rats following dietary exposure

The systemic and neurobehavioral effects of benzo[b]thiophene (routinely referred to as benzothiophene) were studied in rats following 13-wk oral exposure. Male (170 +/- 16 g) and female (146 +/- 12 g) Sprague-Dawley rats (10 animals per group) were fed diet containing 0.5, 5, 50, or 500 ppm benzothiophene for 13 wk. Control animals were given rat feed plus vehicle (corn oil) only. No clinical signs of toxicity and neurobehavioral effects were observed using screening tests that included cage-side observations, righting reflex, open field activities, and forelimb and hindlimb grip strength. Elevated serum aspartate aminotransferase activity and bilirubin level were observed in highest dose females. Except for a statistically significant decrease in hematocrit in the highest dose males, benzothiophene exerted no marked effects on hematological parameters. Benzothiophene exposure did not result in alterations in hepatic alkaline phosphatase activity, or the typical hepatic phase I (aniline hydroxylase, ethoxyresorufin O-deethylase, pentoxyresorufin O-dealkylase, aminopyrine N-demethylase) and phase II (UDP-glucuronosyltransferase, glutathione S-transferase) drug-metabolizing enzyme activities. No significant elevation in urinary ascorbic acid, protein, and N-acetylglucosaminidase activity was detected in the treated animals. Peribiliary fibrosis was the most significant histological change and occurred in the liver of females in the 50 and 500 ppm groups. Mild epithelial hyperplasia in the renal pelvis was detected in the majority of 5 and 50 ppm females, with epithelial hyperplasia in the urinary bladder observed in the 50 ppm females. In males, increased incidence and severity of mild binucleation of hepatocytes and mild thickening of the basement membrane in kidney cortex were observed at 500 ppm. Benzothiophene was not detected in the urine of high-dose animals at the termination of the experiment. Based on the kidney, hepatic, and hematocrit changes, the no-observed-adverse-effect level (NOAEL) in the diet was determined to be 0.5 ppm (0.04 mg/kg/d) for females and 50 ppm (3.51 mg/kg/d) for males.     

Tumor promotion in a breast cancer model by exposure to a weak alternating magnetic field

In view of the methodological problems of epidemiological studies on associations between exposures to 50/60 Hz magnetic fields (MF) and increased incidence of cancers, laboratory studies are necessary to determine if 50/60 Hz MF are cancer promoters or can progress cancers. The objective of the present study was to determine if an alternating MF of low flux density exerts tumor-promoting or co-promoting effects in a model of breast cancer in female rats. Mammary tumors were induced by the chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA). A group of 99 rats was exposed to a homogeneous MF of 50 Hz, 100 microT (microtesla), for 24 h/day 7 day/week for a period of 91 days; another group of 99 rats was sham-exposed under the same environmental conditions as the MF-exposed rats. The exposure chambers were identical for MF-exposed and sham-exposed animals. DMBA was administered orally at a dose of 5 mg/kg at the first day of exposure and at weekly intervals thereafter up to a total dose of 20 mg per rat. The animals were palpated once weekly to assess the development of mammary tumors. In controls, DMBA induced tumors in about 40% of the animals within three months of first application. Eight weeks after DMBA application the MF-exposed rats exhibited significantly more tumors than sham-exposed animals. This difference in the rate of tumor development was observed throughout the period of exposure. At the end of the three-month period of MF exposure the tumor incidence in MF-exposed rats was 50% higher than in sham-exposed rats, the difference being statistically significant. Furthermore, the size of tumors as estimated by palpation was significantly larger in the MF-exposed compared to sham-exposed rats. The data demonstrates that long-term exposure of DMBA-treated female rats to an alternating MF of low flux density promotes the growth and increases the incidence of mammary tumors, thus strongly indicating that MF exposure exerts tumor-promoting and/or copromoting effects.     

Attenuation of iron-nitrilotriacetate (Fe-NTA)-mediated renal oxidative stress, toxicity and hyperproliferative response by the prophylactic treatment of rats with garlic oil

Iron nitrilotriacetate (Fe-NTA) is a potent nephrotoxic agent. In this communication we show that Fe-NTA-mediated nephrotoxicity is diminished by 1 wk of oral daily pretreatment of male albino Wistar rats with garlic oil given by gavage at 50 or 100 mg/kg body weight/ml corn oil. Intraperitoneal Fe-NTA treatment at a dose level of 9 mg Fe/kg body weight/10 ml enhances renal microsomal lipid peroxidation and hydrogen peroxide generation which are accompanied by a decrease in the activities of renal antioxidant enzymes (e.g. catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase), and a depletion in the level of renal glutathione. Parallel to these changes, a sharp increase in blood urea nitrogen and serum creatinine has been observed. In addition, Fe-NTA treatment also enhances renal ornithine decarboxylase (ODC) activity and increases [3H]thymidine incorporation into renal DNA. Prophylactic treatment of animals with garlic oil before the administration of Fe-NTA resulted in the diminution of Fe-NTA mediated injury. The enhancement of renal lipid peroxidation and hydrogen peroxide generation was decreased. In addition, there was recovery of glutathione depletion and inhibition of the activities of antioxidant enzymes. Similarly, in animals given the higher dose of garlic oil (100 mg/kg body weight) the enhanced blood urea nitrogen and serum creatinine levels, which are indicative of renal injury, showed a reduction of about 30% and 40%, respectively, in comparison with the group treated with Fe-NTA alone. Pretreatment with garlic oil also ameliorated the Fe-NTA-mediated induction of ODC activity and enhancement of [3H]thymidine incorporation into DNA in a dose-dependent manner. Our data suggest that garlic oil is a potent chemopreventive agent and may suppress Fe-NTA-induced nephrotoxicity.     

Neurochemical and behavioral characterization of potential antidepressant properties of indeloxazine hydrochloride

The potential antidepressant properties of indeloxazine hydrochloride were examined in vitro and in vivo. Indeloxazine showed preferential affinity for both [3H] citalopram (Ki: 22.1 nM) and [3H]nisoxetine binding sites (Ki: 18.9 nM) in membranes of the rat cerebral cortex. In microdialysis studies, intraperitoneal injection of indeloxazine (3 and 10 mg/kg) dose-dependently increased the extracellular level of both serotonin and norepinephrine in rat frontal cortex of freely moving rats. Amitriptyline was almost equivalent to indeloxazine in these two assays with the exception of a much weaker effect on extracellular serotonin levels. Spontaneous [3H]serotonin release from rat cortical synaptosomes was significantly enhanced by indeloxazine (10-1000 nM). In behavioral studies, indeloxazine increased the number of wheel rotations in forced swimming tests in both ICR mice (50 mg/kg, p.o.) and SAMP8//YAN, a substrain of senescence-accelerated mouse (20 and 30 mg/kg, p.o.). Indeloxazine (3-10 mg/kg p.o.) also inhibited the incidence of muricide in raphe-lesioned rats. These results suggest that indeloxazine is an inhibitor of serotonin and norepinephrine uptake and has potential antidepressant properties. In addition, the drug-induced enhancement of serotonin release may contribute to its potent effects on the serotonergic system in vivo.     

Effect of pyridostigmine pretreatment, HI-6 and Toxogonin treatment on rat tracheal smooth muscle response to cholinergic stimulation after organophosphorus inhalation exposure

The ex vivo contraction response of the rat tracheal smooth muscle was examined after 10 min in vivo inhalation of soman and/or pretreatment with pyridostigmine and/or post-exposure treatment with HI-6 ([[[(4-aminocarbonyl)pyridinio]methoxy]methyl]-2[(hydroxy imino) methyl]pyridinium dichloride) or Toxogonin (1,1'-[oxybis-(methylene)]bis[4-[(hydroxyimino)methyl]-py rid inium] dichloride). In vivo pretreatment with pyridostigmine was achieved by subcutaneous (s.c.) implantation of an osmotic pump that delivered pyridostigmine continuously (0.01 mg/h) in the neck region of the rat 18 h before soman exposure. The ex vivo cholinergic tracheal smooth muscle response increased during the first 60 min after soman exposure in animals pretreated with pyridostigmine. The amplitude of the contraction response in pyridostigmine pretreated animals was about 60% of control, compared to 15% of control without pyridostigmine pretreatment. Pyridostigmine pretreatment also produced significant recovery of the total cholinesterase (ChE) activity in plasma, but not in trachea and lung. Intraperitoneal (i.p.) injection of HI-6 or Toxogonin (50 mg/kg), immediately after 10 min inhalation exposure to soman, also significantly improved the ex vivo cholinergic contraction response of the trachea (decapitation 15 min after oxime administration). The recovery of the physiological response with Toxogonin was, however, not stable. HI-6 was superior to Toxogonin with respect to the initial airway contraction response, and the response increased up to a stable level not significantly different from control. There was no significant reactivation of the ChE activity after treatment with the oximes. Combination of pyridostigmine pretreatment and oxime treatment enhanced the recovery of the tracheal contraction response and the ChE activity in the trachea compared to treatment with oximes alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Black tea and mammary gland carcinogenesis by 7,12-dimethylbenz[a]anthracene in rats fed control or high fat diets

Epidemiological studies suggest that tea may reduce cancer risk, and in laboratory rodents, chemopreventive effects of tea or purified extracts of tea have been demonstrated in lung, gastrointestinal tract and skin. There is some evidence of chemoprevention by tea in the mammary gland, but the data are not conclusive. In order to evaluate more fully the possible influence of black tea on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary gland tumors in the female S-D (Sprague-Dawley) rat, three large studies were performed: experiment 1, tumorigenesis in rats fed AIN-76A diet and given 25 mg/kg DMBA and 1.25 or 2.5% whole tea extract or water to drink; experiment 2, tumorigenesis in rats given 15 mg/kg DMBA and the same diet and fluids as in experiment 1; experiment 3, tumorigenesis in rats fed control or HF (high fat, corn oil) diet and given 15 mg/kg DMBA and 2% tea or water to drink. Tea was given throughout the experiment; DMBA was given by gastric gavage at 8 weeks of age. There was no consistent effect of tea on tumorigenesis in rats fed AIN-76A diet; there was, however, evidence in experiment 3 of a reduction of tumorigenesis by tea in rats fed the HF diet. In experiment 3, rats fed the HF diet and given water showed the expected increase in tumor burden (number and weight) compared with rats fed control diet. However, rats fed the HF diet and given 2% tea showed no increase in tumor burden; their tumor burden was significantly lower than in rats fed the HF diet and given water (P < 0.01) and was not different from rats fed control diet and given water or tea. In addition, in experiment 3, the number of malignant tumors per tumor-bearing rat was increased by the HF diet in water-drinking rats (P < 0.01) but not in tea-drinking rats. Therefore, it appears that tea partially blocked the promotion of DMBA-induced mammary tumorigenesis by the HF diet.     

3H]Rilmenidine-labelled imidazoline-receptor binding sites co-localize with [3H]2-(benzofuranyl)-2-imidazoline-labelled imidazoline-receptor binding sites and monoamine oxidase-B in rabbit, but not rat, kidney

The distribution and relative densities of imidazoline-receptor binding sites (I-RBS) and monoamine oxidase (MAO)-A and -B enzyme(s) in rat and rabbit kidney were compared autoradiographically using fixed nanomolar concentrations of [3H]rilmenidine and [3H]2-(benzofuranyl)-2-imidazoline ([3H]2-BFI) to label I-RBS, and [3H]RO41-1049 and [3H]RO19-6327 to label MAO-A and -B isoenzymes, respectively. In rat kidney, high densities of I-RBS labelled by [3H]rilmenidine were observed in the cortex and outer stripe (120-280 fmol/mg tissue), in contrast to low I-RBS densities labelled by [3H]2-BFI (<4 fmol/mg). A relatively high density of [3H]RO41-1049 binding to MAO-A enzyme was present in all regions of the rat kidney (160-210 fmol/mg) compared with a low density of [3H]RO19-6327 binding to MAO-B (< 25 fmol/mg). Comparison of MAO-A and -B distributions with that of [3H]rilmenidine-labelled I-RBS strongly suggests a lack of association in rat kidney. Similarly, the extremely low densities of [3H]2-BFI-labelled I2-RBS in rat kidney contrasts with the density of MAO-A, but is consistent with the low density of MAO-B. Rabbit kidney cortex and outer stripe contained high relative densities of [3H]rilmenidine-labelled I-RBS (200-215 fmol/mg) and [3H]2-BFI-labelled I2-RBS (45-60 fmol/mg) with lower densities in the inner stripe and inner medulla (< or = 100 and 30 fmol/mg respectively). A high density of MAO-A binding was observed in the inner stripe (515 fmol/mg) with lower levels in the cortex and outer stripe (100-240 fmol/mg), while high densities of MAO-B binding were observed in the cortex and outer stripe (290-450 fmol/mg) with lower levels in the inner stripe (65 fmol/mg). The correlation between the localization of [3H]rilmenidine-labelled I-RBS and [3H]RO19-6327-labelled MAO-B in rabbit kidney (r = 0.87, P = 0.057) suggest that [3H]rilmenidine may label a binding site co-existent with MAO-B, but not MAO-A (n.s.), in this tissue, but rilmenidine did not inhibit [3H]RO41-1049 or [3H]RO19-6327 binding. The distribution of [3H]2-BFI-labelled I2-RBS overlapped the combined distributions of both MAO-A and -B isoenzymes, suggesting that [3H]2-BFI may label sites on both enzymes in the rabbit, but [3H]2-BFI binding only correlated with [3H]RO19-6327 (r = 0.84, P = 0.07), not [3H]RO41-1049 binding (n.s.). Moreover, 2-BFI only inhibited [3H]RO19-6327, not [3H]RO41-1049 binding. These data are consistent with reports that I2-RBS are located on MAO-B and allosterically influence the catalytic site. The relationship of [3H]rilmenidine- and [3H]2-BFI-labelled I-RBS and the identity of non-MAO-associated [3H]rilmenidine-labelled I-RBS requires further investigation.     

Aiding troubled employees: the prevalence, cost, and characteristics of employee assistance programs in the United States

Bilirubin neurotoxicity can be mediated by numerous mechanisms due to its increased permeability in neuronal membranes. The present study tests the hypothesis that a prolonged bilirubin infusion modifies the N-methyl-D-aspartate (NMDA) receptor/ ion channel complex in the cerebral cortex of newborn piglets. Studies were performed in seven control and six bilirubin-exposed piglets, 2-4 d of age. Piglets in the bilirubin group received a 35 mg/kg bolus of bilirubin followed by a 4-h infusion (25 mg/kg/h) of a buffer solution containing 0.1 N NaOH, 5% human albumin, and 0.055 Na2HPO4 with 3 mg/mL bilirubin. The final mean bilirubin concentration in the bilirubin group was 495.9 +/- 85.5 mumol/L (29.0 +/- 5.0 mg/dL). The control group received a bilirubin-free buffer solution. Sulfisoxazole was administered to animals in both groups. P2 membrane fractions were prepared from the cerebral cortex. [3H]MK-801 binding assays were performed to study NMDA receptor modification. The Bmax in the control and bilirubin groups were 1.20 +/- 0.10 (mean +/- SD) and 1.32 +/- 0.14 pmol/mg protein, respectively. The value for Kd in the control brains was 6.97 +/- 0.80 nM compared with 4.80 +/- 0.28 nM in the bilirubin-exposed brains (p < 0.001). [3H]Glutamate binding studies did not show a significant difference in the Bmax and Kd for the NMDA-specific glutamate site in the two groups. The results show that in vivo exposure to bilirubin increases the affinity of the receptor (decreased Kd) for [3H]MK-801, indicating that bilirubin modifies the function of the NMDA receptor/ion channel complex in the brain of the newborn piglet. We speculate that the affinity of bilirubin for neuronal membranes leads to bilirubin-mediated neurotoxicity, resulting in either short- or long-term disruption of neuronal function.     

Coenzyme Q10 and adriamycin toxicity in mice

Pretreatment for four days with coenzyme Q10 (CoQ10) significantly lowered the acute toxicity in female C3H/HeNCrlBR mice given moderately lethal (15.0 and 20.0 mg/kg) i.p. doses of adriamycin as well as in male ICR/Hla mice given 12.5 mg/kg i.p. adriamycin. In both strains of mice, CoQ10 pretreatment did not protect the mice at higher i.p. adriamycin dose levels. When adriamycin was administered by the clinically-used i.v. route, CoQ10 pretreatment did not reduce acute toxicity at moderately lethal doses in either strain. At higher i.v. adriamycin dose levels, CoQ10 pretreatment significantly enhanced acute toxicity. CoQ10 pretreatment did not alter the antitumor effectiveness of adriamycin (i.p. or i.v.) against the Dunn osteosarcoma.     

Vitamin E modulation of hepatic focal lesion growth in mice

The effect of DL-alpha-tocopherol acetate (vitamin E) on hepatic focal lesion growth in male B6C3F1 mice previously treated with diethylnitrosamine (DEN) was investigated. After hepatic focal lesions were formed, mice were placed into one of the following dose groups: 0 mg vitamin E/kg NIH-07 diet, 50 mg vitamin E/kg NIH-07 diet (control diet), 250 mg vitamin E/kg NIH-07 diet, and 450 mg vitamin E/kg NIH-07 diet. Mice were euthanized after either 30 or 60 days of dietary treatment. In normal (nonlesion) liver, vitamin E deficiency (0 mg/kg diet) increased hepatic DNA synthesis. In addition, vitamin E supplementation (450 mg/kg diet) decreased the incidence of hepatic apoptosis, while vitamin E deficiency (0 mg/kg diet) increased the incidence of hepatic apoptosis. The effect of vitamin E-induced lesion growth was examined by measuring the number of focal lesions per liver and the relative focal lesion volume. High-dose vitamin E supplementation (450 mg/kg diet) appeared to enhance the growth of hepatic focal lesions. In particular, basophilic lesions appeared to be the most sensitive to high-dose vitamin E modulation (450 mg/kg diet) as evidenced by increased number, volume, and labeling index of hepatic focal lesions. Vitamin E deficiency also appeared to enhance the growth of hepatic focal lesions, though to a lesser extent than vitamin E supplementation (450 mg/kg diet). In the present study, both vitamin E supplementation (450 mg/kg diet) and deficiency (0 mg/kg diet) appeared to enhance focal lesion growth albeit neither treatment enhanced lesion growth as dramatically as known nongenotoxic hepatocarcinogens (e.g., phenobarbital and dieldrin). The data presented here suggest that oxidative stress in focal hepatocytes may be a component of the liver tumor promotion process.