Distribution and biliary excretion of polychlorinated biphenyls in rats

Absorption, distribution, and excretion of two ³H-labeled polychlorinated biphenyls (PCB), 2,4,5,2′,4′,5′,-hexachlorobiphenyl (HCB) and 2,5,2′,5′-tetrachlorobiphenyl (TCB), were studied in surgically prepared male and female rats. Approximately 3–5 hr after surgery, HCB or TCB (50 mg/kg) was administered into the stomach. Bile, urine, and feces were collected for 24 hr after which the animals were sacrificed and tissues taken for determination of ³H content. The distribution of ³H remaining in the rats, expressed as percentage of dose, was highest in skeletal muscle, skin, liver, and small intestine for both isomers. The major difference observed between the PCBs was in biliary excretion. For HCB, 0.5 ± 0.2% (males, mean ± SE) and 1.1 ± 0.3% (females) of the dose were excreted in bile in 24 hr; for TCB, 42.2 ± 8.5% (males) and 25.7 ± 7.8% (females) were excreted by the same route. The lower biliary excretion of HCB than of TCB cannot be accounted for by a difference in absorption from the gastrointestinal tract and is thought to be due to a slower rate of HCB metabolism. More explicitly, the chlorines in the 4,4′ positions of HCB appear to prevent rapid biliary excretion of the compound by eliminating adjacent unsubstituted carbons which are necessary for rapid metabolism to occur. Urinary excretion of HCB and TCB was of minor importance compared to biliary excretion. Generally, absorption, distribution, and excretion of the PCBs were similar in males and females.     

The influence of pure polychlorinated biphenyl compounds on hepatic function in the rat

Pure biphenyl and isomerically pure mono-, di-, tetra-, hexa-, and octachlorobiphenyls of known chemical composition were injected ip (50 mg/kg/day) into young male Wistar rats for 3 days; the animals were killed 96 hr after the last injection. The potency of the pure PCBs was compared to that of o,p′-DDT and p,p′-DDT and commercial Aroclors (1254, 1260) administered at the same concentrations. Hepatic function was assessed by pentobarbital sleeping times and in vitro assays of hepatic microsomal O-demethylase, N demethylase, aniline hydroxylase, nitroreductase, carboxylesterase and the cytoplasmic bromosulfophthalein-glutathione conjugating enzyme. Biphenyl and 4-monochlorobiphenyl did not cause induction of hepatic drug-metabolizing enzymes. Microsomal mono-oxygenases were induced by hexa- and octachlorobiphenyls and by di- and tetrachlorobiphenyls with chlorines substituted at the 3 and 4 positions. Nitroreductase and carboxylesterase activities were affected only by the highly chlorinated compounds whereas all agents, including biphenyl, caused a marked induction of the bromosulfophthalein-conjugating system.     

Impaired biliary excretion of digitoxin and its metabolites after treatment with polychlorinated biphenyls.

In order to study the effects of polychlorinated biphenyls (PCB), potent inducers of microsomal drug-metabolizing enzymes, on the elimination rate of digitoxin (DT-3), the bile of rats were collected for 4 hr after a single dose of tritiated digitoxin ([³H]DT-3). In comparison to normal rats PCB caused a decrease of elimination by 50% whereas phenobarbital (PB) increased the rate by 36%. After extracting the bile with CHCl₃, measurements of radioactivity revealed that PCB-treated rats excreted only 3.2% of the dose as CHCl₃-soluble compounds. The corresponding fraction of both normal and PB-pretreated rats contained about 10% of the dose. The increased DT-3 elimination produced by PB was due to the large amount of water-soluble metabolites (nearly 24% of the dose). Normal and PCB-pretreated rats excreted about 10% water-soluble metabolites. Further analysis of metabolites showed: (1) In addition to the known metabolites (digoxin, bis-, and monodigitoxosides of both digitoxigenin and digoxigenin) the CHCl₃-soluble fraction contained a more lipophilic fraction. It consisted mainly of the dehydro-bis-digitoxoside of digitoxigenin. (2) Free genins could not be found. (3) Digitoxigenin monodigitoxoside was the main substrate for conjugating enzymes. (4) Nearly 30% of water-soluble metabolites were cardenolide acids presumably formed by hydrolysis of the butenolide. The results suggest that after PCB treatment the decreased DT-3 elimination rate is caused at least in part by an impaired digitoxoside cleavage.     

Effects of phalloidin on the biliary excretion of cholephilic compounds in rats

Phalloidin is known to cause cholestasis by preventing microfilament depolymerization. In addition, phalloidin is reported to inhibit the vesicular targeting of canalicular transporters. The aim of the present study was to examine the effect of phalloidin on the biliary excretion of substrates typical for various canalicular transporters in rats. Phalloidin decreased the biliary excretion of tracer amounts of taurocholate, leukotriene C(4), pravastatin, and vinblastine. Increases in bile flow and biliary bile acid excretion caused by taurocholate infusion were completely inhibited by phalloidin. These data indicate that, in addition to multidrug resistance protein 2 and P glycoprotein, the vesicular targeting of the bile salt export pump, a major canalicular bile acid transporter, is also impaired by phalloidin. The decrease of biliary excretion of glutathione may also relate to the increase in the bile acid independent canalicular bile flow in phalloidin-treated rats.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the distribution and biliary excretion of polychlorinated biphenyls in rats.

Plasma disappearance, biliary excretion, and tissue distribution of two polychlorinated biphenyls (PCBs), 2,5,2′,5′-[³H]tetrachlorobiphenyl (4-CB) and 2,4,5,2′,4′,5′-[³H]hexachlorobiphenyl (6-CB), was determined in rats 10 days after oral administration of a single 10 or 25 μg/kg dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Plasma disappearance of both PCBs was not altered by TCDD treatment, but biliary excretion was depressed. Associated with the depressed excretion was a reduction in bile flow and concentration of 4-CB- and 6-CB-derived ³H in bile. Treatment with TCDD resulted in less PCB being distributed to the skin and a greater percentage of the dose being accumulated in the liver. The content of PCB-derived ³H in skeletal muscle, adipose tissue, and urine was similar in control and TCDD-treated rats. Extraction of bile with hexane showed that the majority of biliary radioactivity was in the form of polar metabolites and that the proportion of parent PCB (hexane-extractable radioactivity) to polar metabolites was not altered by TCDD treatment. In rats given 4-CB and sacrificed 1 hr later, the majority of radioactivity in the liver was hexane extractable, and the smaller amount of hepatic radioactivity due to polar 4-CB metabolites was greater in the TCDD treatment group than in the control group. When biliary metabolites of 4-CB were administered, biliary excretion of the metabolites was depressed in TCDD-treated animals. Thus, TCDD treatment impairs the initial and main excretory pathway for PCB elimination in the rat—biliary excretion—and alters the distribution of PCBs to the skin and liver.     

Disposition of polychlorinated biphenyl congeners in occupationally exposed persons

Relative concentrations of 37 polychlorinated biphenyl (PCB) congeners and the adipose-plasma partition of 28 PCB congeners were investigated in 26 persons occupationally exposed to various PCBs (20 to 54% chlorine). Concentrations of PCBs in adipose and plasma were related to duration and intensity of exposure in the workplace. PCB concentration in adipose tissue was proportional to that in plasma, with a partition for total PCBs of approximately 190:1 indicated from regression analysis. PCB congeners with chlorines in both 4-positions of the biphenyl ring were the major components in plasma and adipose tissue. Congeners with unsubstituted 3,4-positions (e.g., 2,5-chlorine substitution) on at least one of the biphenyl rings were observed at lower concentrations and had lower adipose-plasma partition than other congeners. In contrast, those compounds with substituents at the 2,4- and/or 3,4-positions on both rings were present in much higher proportions in blood or adipose than in the PCB mixtures in use. These components also had higher adipose-plasma partition than those with unsubstituted 3,4-positions, regardless of the degree of chlorination. PCBs with 2,4-substitution patterns on both rings, including 2,4,4′-tri- and 2,4,5,4′-tetra-CBs, had somewhat higher adipose-plasma partition than congeners with 3,4-substitution on at least one of the biphenyl rings (e.g., 2,4,3′,4′-tetra-CB).     

Attenuation of polychlorinated biphenyl induced uroporphyria by iron deprivation

A toxic sequel to polyhalogenated aromatic hydrocarbon exposure in humans is the development of porphyria cutanea tarda. In a mouse model (experimental uroporphyria) utilizing an environmentally relevant polychlorinated biphenyl (PCB) mixture, we show that the toxicity can be markedly influenced by nutritional status. In mice made susceptible to uroporphyria through a targeted deletion of one allele of uroporphyrinogen decarboxylase (Uro-D+/−), an iron deficient diet prevented the development of the uroporphyria and the changes in associated parameters normally seen within three weeks following a single exposure to Aroclor 1254. Iron deprivation also completely prevented PCB-induced uroporphyria in mice wild-type at the Uro-D locus (Uro-D+/+), a model that requires δ-aminolevulinic acid administration for the development of uroporphyria. In Uro-D+/− mice consuming δ-aminolevulinic acid, PCB exposure produced a severe uroporphyria that was attenuated, not prevented, by iron deficiency. This attenuation moderated hepatic uroporphyrin and uroporphyrinogen decarboxylase inhibitor levels, but not the depression of cytosolic uroporphyrinogen decarboxylase activity.     

Attenuation of polychlorinated biphenyl induced uroporphyria by iron deprivation

A toxic sequel to polyhalogenated aromatic hydrocarbon exposure in humans is the development of porphyria cutanea tarda. In a mouse model (experimental uroporphyria) utilizing an environmentally relevant polychlorinated biphenyl (PCB) mixture, we show that the toxicity can be markedly influenced by nutritional status. In mice made susceptible to uroporphyria through a targeted deletion of one allele of uroporphyrinogen decarboxylase (Uro-D+/−), an iron deficient diet prevented the development of the uroporphyria and the changes in associated parameters normally seen within three weeks following a single exposure to Aroclor 1254. Iron deprivation also completely prevented PCB-induced uroporphyria in mice wild-type at the Uro-D locus (Uro-D+/+), a model that requires δ-aminolevulinic acid administration for the development of uroporphyria. In Uro-D+/− mice consuming δ-aminolevulinic acid, PCB exposure produced a severe uroporphyria that was attenuated, not prevented, by iron deficiency. This attenuation moderated hepatic uroporphyrin and uroporphyrinogen decarboxylase inhibitor levels, but not the depression of cytosolic uroporphyrinogen decarboxylase activity.     

Inhibition of LPS-induced splenocyte proliferation by ortho-substituted polychlorinated biphenyl congeners

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants, and their ubiquitous nature has prompted studies of their potential health hazards. As a result of their lipophilic nature, PCBs accumulate in breast milk and subsequently affect the health of offspring of exposed individuals. Biological effects of PCBs in animals have mostly been attributed to coplanar congeners, although effects of ortho congeners also have been demonstrated. To investigate the relationship of immunotoxicity and chlorine substitution pattern, the effects of PCB congeners and mixtures of ortho and non-ortho-substituted constituents of Aroclor 1242 on splenocytes from C57B1/6 mice were examined. The immunotoxic endpoints investigated included splenocyte viability, lipopolysaccharide (LPS)-induced splenocyte proliferation, and LPS-induced antibody secretion. Congeners with multiple ortho chlorines preferentially inhibited splenocyte proliferation as compared with non- or mono-ortho-substituted congeners. However, mixtures of non- and mono-ortho-substituted congeners and multi-ortho-substituted congeners inhibited LPS-induced splenocyte proliferation and antibody secretion at similar concentrations. Exposure of splenocytes to these mixtures did not activate the aryl hydrocarbon receptor (AhR) signal transduction pathway. These results suggest individual multi-ortho-substituted congeners preferentially inhibit LPS-induced splenocyte proliferation, while congeners not exhibiting an effect individually may have additive effects in a mixture to produce an immunotoxic response through an AhR-independent pathway.     

Effect of several compounds on biliary excretion of paclitaxel and its metabolites in guinea-pigs

The objective of this study was to evaluate the in vivo metabolic profile of paclitaxel and to examine the effect of potential co-administered drugs on the biliary secretion of paclitaxel and its metabolites in guinea-pigs. We first investigated in vitro paclitaxel metabolism using liver microsomes obtained from various species to identify the most suitable animal model with a similar metabolism to humans. Then, in vivo paclitaxel metabolism was investigated in male guinea-pigs. The levels of paclitaxel and its metabolites were measured by high-performance liquid chromatography in bile samples from guinea-pigs after paclitaxel i.v. injection (6 mg/kg). We further evaluated the effects of various drugs (quercetin, ketoconazole, dexamethasone, cotrimoxazole) on the biliary secretion of paclitaxel and its metabolites in guinea-pigs. This work demonstrated significant in vitro interspecies differences in paclitaxel metabolism. Our findings showed both in vitro and in vivo similarities between human and guinea-pig biotransformation of paclitaxel. 6alpha-Hydroxypaclitaxel, the main human metabolite of paclitaxel, was found in guinea-pig bile. After paclitaxel combination with ketoconazole or quercetin in guinea-pigs, the cumulative biliary excretion of paclitaxel and its metabolites up to 6 h was significantly decreased by 62 and 76%, respectively. The co-administration of cotrimoxazole or pretreatment with dexamethasone did not alter significantly cumulative biliary excretion. The guinea-pig is a suitable model to study metabolism and biliary excretion of paclitaxel, and to investigate in vivo drug interactions.     

Cytotoxic effects of polychlorinated biphenyl hydroquinone metabolites in rat hepatocytes

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that exhibit various toxic effects in animals and exposed human populations. The molecular mechanisms of PCB toxicity have been attributed to the toxicological properties of its metabolites, such as hydroquinones, formed by cytochrome‐P‐450 oxidation. The effects of PCB hydroquinone metabolites towards freshly isolated rat hepatocytes were investigated. Hydroquinones can be oxidized to semiquinones and/or quinone metabolites. These metabolites can conjugate glutathione or can oxidize glutathione as a result of redox cycling. This depletes hepatocyte glutathione, which can inhibit cellular defence mechanisms, causing cell death and an increased susceptibility to oxidative stress. However in the following, glutathione‐depleted hepatocytes became more resistant to the hydroquinone metabolites of PCBs. This suggested that their glutathione conjugates were toxic and that there was a third type of quinone toxicity mechanism which involved a hydrogen peroxide‐accelerated autoxidation of the hydroquinones to form toxic electrophilic quinone and semiquinone–glutathione conjugates. Copyright © 2009 John Wiley & Sons, Ltd.     

多氯联苯118对大鼠甲状腺自身免疫反应的影响

目的探讨多氯联苯118(PCB118)对大鼠甲状腺功能及自身免疫反应的影响。方法Wistar大鼠40只均分为四组:A组为空白对照;B、C、D组分别给予PCB118 10、100、1000μg.kg-1.d-1腹腔注射,每周5次。13周后检测血清游离三碘甲状腺原氨酸(FT3)、游离甲状腺素(FT4)、促甲状腺激素(TSH)、甲状腺球蛋白(TG)、甲状腺球蛋白抗体(TGAb)、过氧化物酶抗体(TPOAb)水平,甲状腺组织过氧化物酶(TPO)mRNA表达水平,观察甲状腺组织病理学改变。结果甲状腺组织病理学检查显示B、C、D组均可见滤泡腔塌陷、上皮脱落、间质纤维化、小血管增生,B、C组可见间质淋巴细胞浸润。随着PCB118剂量增加,B、C、D组血清FT3、FT4、TG浓度逐渐降低;D组FT3浓度明显低于A、B组(P<0.05);B、C、D组血清FT4、TSH浓度明显低于A组(P<0.05);C、D组血清TG水平明显低于A组(P<0.05)。与A组比较,B、C组血清TGAb、TPOAb浓度显著升高(P<0.05);C组TPO mRNA表达水平明显高于A组(P<0.05)。结论 PCB118可导致大鼠甲状腺组织形态和功能异常,激活甲状腺自身免疫反应。     

Glutathione-dependent biliary excretion of arsenic

This study aimed to clarify whether glutathione (GSH) plays a role in the hepatobiliary transport of arsenic. For this purpose, the biliary excretion of 74As was measured in urethane-anaesthetized rats for 2 hr after the administration of labelled sodium arsenite (50 mumol/kg, i.v.) or arsenate (150 mumol/kg, i.v.) and under the influence of sulfobromophthalein (BSP), indocyanine green (ICG) or diethyl maleate (DEM) which are known to diminish hepatobiliary transport of GSH. Although the biliary excretion of arsenic was different after arsenite and arsenate administration in terms of quantity (19% vs 6% of dose in 2 hr, respectively) and time course, arsenic excretion responded similarly to BSP (50 mumol/kg, i.v.), ICG (25 mumol/kg, i.v.) or DEM (4 mumol/kg, i.p.) irrespective of the injected arsenical. Initially the biliary excretion of arsenic in rats with either arsenite or arsenate was significantly reduced, but then moderately increased by BSP and, more lastingly, depressed by ICG, whereas it was virtually abolished by DEM. The responses of arsenic excretion to BSP, ICG and DEM were related, both proportionally and temporally, to the effects exerted by these agents on the hepatobiliary transport of GSH, as assessed by the biliary excretion of non-protein thiols. These findings indicate that the biliary excretion of arsenic after the administration of either arsenite or arsenate is dependent on the hepatobiliary transport of GSH. Transport of arsenic as a GSH complex may account for the GSH dependence of biliary arsenic excretion.     

Enhanced polychlorinated biphenyl lesions in Moloney leukemia virus-infected mice.

The hepatic toxicity produced by polychlorinated biphenyls (PCB) was enhanced in mice that were inoculated with an oncogenic virus, Moloney leukemia virus (MLV). Whenever there was neoplastic involvement of the spleen by MLV, the hepatic lesions produced by PCB were more pronounced than in those of non-MLV inoculated mice. Mice were exposed to PCB Aroclors, 1254, 1242, and 1221 for six months. Aroclors 1254 and 1242 were hepatotoxic with Aroclor 1254 causing death. Aroclor 1221 did not affect the mice. Liver weights in mice that were fed PCBs for six months and then maintained on a PCB-free diet for an additional three months were comparable with those of non-PCB exposed mice. These results suggest that the PCB-produced hepatic lesions (noncirrhotic) regenerate after removal of PCB from the diet. Polychlorinated biphenyls did not affect (promote or induce) the oncogenesis of MLV in this study.     

Effects of single or repeated treatment with several anticholesterolemic compounds on biliary excretion of cholesterol

The effects of single or repeated treatments with nicotinic acid, 3-pyridineacetic acid, inositol hexanicotinate, Na-phenylbutyrate, betaine phenylbutyrate, 1:4-dicaffeylquinic acid and sodium dehydrocholate on biliary excretion of cholesterol were studied in the rat. After a single intravenous administration, among the drugs experimented only 1:4-dicaffeylquinic acid at the highests doses examined and phenylbutyrates, these at the lowest doses, increased the biliary excretion of cholesterol. After repeated administrations by the intraperitoneal route none of the compounds examined succeeded in modifying in a statistically significant manner the biliary excretion of cholesterol.     

Hepatic uptake and biliary excretion of organic cations--I. Characterization of three new model compounds

Three quaternary ammonium compounds (QACs) with different lipophilicity, triethylmethyl ammonium iodide (TEMA), tripropylmethyl ammonium iodide (TPMA) and tri-n-butylmethyl ammonium iodide (TBuMA) were given as a bolus injection of 10 mumole and 1 mumole in an isolated perfused liver. TPMA and TBuMA exhibited saturation kinetics at a dose of 10 mumole, but not when 1 mumole of the agents was given. Biliary clearance of TEMA was equal to the bile flow (0.010 ml/min), whereas for TPMA and TBuMA much higher values of 0.8 ml/min and 2.2 ml/min were found respectively. Partition coefficients of TEMA, TPMA and TBuMA between n-octanol and Krebsbicarbonate solution were 0.0013, 0.013 and 0.14 respectively. Liver-to-plasma concentration ratios were 4, 16 and 30 in the post-distribution phase, whereas bile-to-liver ratios were calculated to be 0.1, 1.3 and 14 respectively. The latter parameter varied roughly proportionally to the lipophilicity of the compounds. The liver/plasma concentration ratios corrected for intracellular binding exceeded a value of 12 indicating that accumulation in the liver of these agents cannot soley be explained by passive equilibration according to the membrane potential. Transport from liver into the bile of TPMA and TBuMA presumably also occurred against an electrochemical gradient. It was inferred that the small molecular weight compounds such as TEMA, can be transported from plasma into bile paracellularly by a passive process. Rapid uptake into the liver of such compounds may not lead to an appreciable biliary output and can even reduce the rate of biliary excretion. QACs with intermediate or high lipophilicity are transported by carrier mediated processes both at the level of hepatocyte uptake and bile canalicular transport. The influence of choleresis on hepato-biliary transport of the three QACs was investigated by giving sodium taurocholate (Tc) by constant infusion of 60 mumole/hr, increasing bile flow from 9 to 16 microliter/min. The biliary output of TEMA appeared to be basically unaffected, whereas the biliary excretion of TPMA and TBuMA was clearly elevated when the bile flow was increased. The stimulatory influence of taurocholate on the biliary output of the latter organic cations is explained by an increased net uptake of these agents into the liver and an increased net canalicular transport. This effect is proposed to be due to a reduced reabsorption from the biliary tree as a consequence of the higher bile flow and/or biliary micelle binding. Taurocholate increased liver-to-plasma ratios.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vitro reproductive toxicity of polychlorinated biphenyl congeners 153 and 126

Abstract<195>This study was conducted to investigate the applicability of an in vitro technique for maturation, fertilization, cleavage, and growth to blastocysts of bovine oocytes to investigate reproductive toxicologic effects. During maturation, the oocytes were exposed to the di-ortho-substituted PCB congener 2,2′,4,4′,5,5′-CB (PCB 153) in the three concentrations 0.84 ng/mL, 8.4 ng/mL, and 84 ng/mL or to the non-ortho-substituted PCB congener 3,3′4,4′,5-CB (PCB 126) in the three concentrations 1.006 pg/mL, 10.06 pg/mL, and 100.6 pg/mL and compared with control groups. PCB 153 had no effect on maturation but resulted in a reduced proportion of oocytes that cleaved at the highest concentration. There were no differences in blastocyst development among groups. PCB 126 resulted in a reduction in maturation percentage at the highest concentration and in blastocyst development at all concentrations. These results demonstrated adverse effects of PCB congeners on bovine oocytes and showed that this system can be used to evaluate toxic effects on oocytes and preimplantation-stage embryos.     

Pathology of chronic polychlorinated biphenyl (PCB) feeding in rats

The hepatocarcinogenic effect of Clophen A 30 and Clophen A 60 was tested in male weanling rats by long-term feeding over a period of 832 days. The mortality rate was investigated in 100-day intervals. In the first 800 days liver carcinoma accounted for 21% of necropsies in the Clophen A 60 group but only 2% of the necropsies in the Clophen A 30 group and none in the control animals. The tumors were first observed after 700 days. After 800 days hepatocellular carcinoma was the most common lesion observed in the Clophen A 60 animals (61%) whereas it was only observed in 3% of animals in the Clophen A 30 group and 2% in the controls. Preneoplastic lesions, such as foci of hepatocellular alterations and neoplastic nodules, were first observed after Day 500. The incidence of foci predominated in all time intervals, but an increase in neoplastic nodules and hepatocellular carcinomas was observed with increased time. There was a marked trend from foci to neoplastic nodule to hepatocellular carcinoma with time. The total mortality rate and the incidence of thymoma, inflammatory lesions of the urogenital tract, in the experiment were significantly reduced by Clophen administration. Whether this protective effect could be induced by polychlorinated biphenyls (PCBs) is discussed.