Bioconcentration of xenobiotics in trout bile: a proposed monitoring aid for some waterborne chemicals.

A technique is proposed for the monitoring of certain xenobiotic pollutants in suspect aquatic enviornments by fish bile analysis. Bile removed from rainbow trout (Salmo gairdneri) exposed to nine different radioactive compounds in vivo contained concentrations of radioactivity greater than those in the surrounding water. Bile-to-water radioactivity ratios as high as 10,000: 1 were found after 24-hour exposures. The results of these experiments suggest that analysis of bile of wild or caged fish from a suspect site may be useful as a qualitative monitoring aid for certain types of xenobiotics in water.

Lack of correlation between natural killer activity and tumor growth control in nude mice with different immune defects.

To elucidate the in vivo role of natural killer (NK) cells, the growth of several murine and human tumors was studied in four variants of athymic, nude mice with different levels of NK activity. Beige-nude mice, homozygous for both the beige and the nude genes, had very low levels of NK activity, and their response to the B-cell mitogen, bacterial lipopolysaccharide, was lower than that of high-NK, adult NIH nude mice. Young and adult NIH nudes had different NK levels and showed different response in assays for K-cell, T-cell, and B-cell activity. The B-cell-defective NIH-II mice had slightly lower NK levels than adult NIH animals, but much lower response in the antibody-dependent cell-mediated cytotoxicity assay. No correlation was found between host NK activity and the s.c. growth of various human (LOX, CEM, K562) and murine (YAC-1) tumor cells. Low NK activity was not associated with increased lung colony formation in a metastasis model using i.v.-injected human (LOX) and murine (B16F10) melanoma cells. No relationship was found between host NK activity and the rate of elimination of i.v.-injected 5-iodo-2'-deoxyuridine-labeled LOX, B16F10, and YAC-1 cells from lungs, liver, or spleen. The results fail to support the view that NK cells exert significant direct effects on tumor cells in vivo.

Molecular basis for several drug-induced nephropathies.

A recent clinical advance has been the discovery that many drug-induced hepatic diseases result from the metabolic activation of chemically stable drugs to potent alkylating agents by the liver. In addition to the liver, however, the kidney also contains active enzyme systems capable of metabolically activating drugs and other chemicals. For this reason a systematic investigation of the possible role of metabolic activation in the pathogenesis of several drug-induced renal diseases has been undertaken. These laboratory results are reviewed in the light of the clinical spectrum of the renal injuries, and possible therapeutic implications of these new findings are briefly discussed. The potential use of these models of nephrotoxicity to probe a variety of physiologic and pathophysiologic mechanisms of renal function are noted.

Distribution and metabolism of the pulmonary alkylating agent and cytotoxin, 4-ipomeanol, in control and diethylmaleate-treated rats.

Diethylmaleate (DEM), an agent which depletes tissue glutathione (GSH), increased the covalent binding and toxicity of 4-ipomeanol [1-(3-furyl)-4-hydroxypentanone] in rats. The distribution of unmetabolized 4-ipomeanol-[5-14C] and its metabolites were studied in tissue extracts by high-pressure liquid chromatography (HPLC) in control and DEM-treated rats. At all time periods examined, DEM treatment produced no significant effect on the tissue distribution of unchanged 4-ipomeanol. In both groups, the relative tissue concentrations of unmetabolized 4-ipomeanol were in the order blood greater than lung greater than liver. In control rats, the relative tissue concentrations of nonbound, solvent-extractable 4-ipomeanol metabolites (hereafter referred to simply as "4-ipomeanol metabolites"), as well as the covalently bound 4-ipomeanol metabolites (hereafter referred to as "covalently bound 4-ipomeanol equivalents" to distinguish from all other metabolites) were in the order lung greater than liver greater than blood. The pulmonary levels of both the covalently bound 4-ipomeanol equivalents and the 4-ipomeanol metabolites were increased markedly by DEM treatment at all time periods examined. The total pool of urinary 4-ipomeanol metabolites was significantly decreased by DEM treatment, but the total amounts of excreted ipomeanol-4-glucuronide, the major metabolite of 4-ipomeanol in rats, were not significantly different in the control and DEM-treated rats. These data are consistent with the view that the increased pulmonary covalent binding and toxicity of 4-ipomeanol produced by diethylmaleate treatment in rats are due to the depletion of pulmonary GSH by the DEM and not a major DEM-induced alteration in the tissue distribution of the parent 4-ipomeanol.

Effects of phenobarbital and 3-methylcholanthrene on the in vivo distribution, metabolism and covalent binding of 4-ipomeanol in the rat; implications for target organ toxicity.

The effects of phenobarbital (PB) and 3-methylcholanthrene (MC) on the distribution, metabolism and covalent binding of 4-ipomeanol were examined in the rat. An analysis of tissue extracts by high-pressure liquid chromatography (HPLC) showed that both treatments markedly decreased the concentrations of unmetabolized 4-ipomeanol at all times examined. PB treatment increased the urinary excretion of nonbound 4-ipomeanol metabolites, while MC treatment did not alter their excretion. Analysis of urine by HPLC indicated that the increased concentration of urinary metabolites found in the phenobarbital-treated rats was attributable primarily to an increased excretion of ipomeanol-4-glucuronide. These data indicate that the decreased pulmonary covalent binding and lethality of 4-ipomeanol in the rat after MC and PB were caused by alterations in the tissue distribution of the parent compound. Pulmonary concentrations of unmetabolized 4-ipomeanol were decreased by MC through an increased metabolism of 4-ipomeanol in the liver, primarily to toxic products that bind covalently in that tissue and lead to hepatoxicity. PB produced a similar decrease in unmetabolized 4-ipomeanol concentrations in lung but by an enhanced in vivo metabolism and clearance of 4-ipomeanol, primarily through a "nontoxic" pathway, glucuronidation, and did not lead to hepatotoxicity.

Protective role of endogenous pulmonary glutathione and other sulfhydryl compounds against lung damage by alkylating agents. Investigations with 4-ipomeanol in the rat.

Because endogenous glutathione is known to participate in the detoxification of highly reactive, hepatotoxic drug metabolites, we studied the role of this substance in the pulmonary toxicity of 4-ipomeanol [1-(3-furyl)-4-hydroxypentanone] in rats. 4-Ipomeanol was an appropriate model for these studies since previous investigations have indicated that an alkylating metabolite, formed in situ, is responsible for selective lung damage by 4-ipomeanol. Toxic doses of 4-ipomeanol preferentially depleted rat lung glutathione. Pretreatment of animals with piperonyl butoxide, an inhibitor of the metabolic activation of 4-ipomeanol, prevented both the depletion of lung glutathione and the pulmonary toxicity of 4-ipomeanol. Prior depletion of lung glutathione by diethylmaleate increased both the pulmonary covalent binding and the toxicity of 4-ipomeanol, whereas administration of cysteine and cysteamine decreased both the covalent binding and the toxicity. These in vivo studies, in conjunction with previous in vitro studies which showed inhibitory effects of sulfhydryl compounds on the covalent binding of 4-ipomeanol, are consistent with the view that pulmonary glutathione plays a protective role against pulmonary alkylation and lung toxicity by 4-ipomeanol, probably by reacting with the toxic metabolite(s) to form nontoxic conjugate(s). Pulmonary glutathione may similarly provide protection against other electrophilic drugs or metabolites that can damage the lungs.

Effects of 3-methylcholanthrene on covalent binding and toxicity of 4-ipomeanol in inducible and non-inducible (B6D2) mice.

The effects of 3-methylcholanthrene (MC) on the covalent binding and toxicity of 4-ipomeanol (1-(3-furyl)-4-hydroxypentanone, IPO) were studied in (C57BL/6N)(DBA/2N)F1 X DBA/2N backcross (B6D2)D2) mice previously segregated into relatively "inducible" or "non-inducible" groups based on zoxazolamine (2-amino-5-chlorobenzoxazole, ZOX) paralysis times following MC treatment. MC decreased the covalently bound IPO metabolite(s) both in the lungs and in the kidneys of "inducible" and "non-inducible" mice when compared to controls not pretreated with MC. On the other hand, concentrations of covalently bound IPO metabolite(s) in liver were increased in "inducible" mice and decreased in "non-inducible" mice by MC pretreatment when compared to non-pretreated heterogenous mice. Associated with MC pretreatment was a significant decrease in the acute lethality of IPO both in the "inducible" and in the "non-inducible" mice when compared to nonpretreated control animals (LD50: 213 +/- 2, 140 +/- 14 and 14 +/- 4 mg/kg, respectively). Hepatic necrosis occurred frequently in the "inducible" mice and occasionally in the "non-inducible" mice given large IPO doses near the respective LD50-values. Hepatic necrosis was never observed in non-pretreated mice receiving near lethal doses of IPO. These results support previous studies indicating that reactive IPO metabolites binding to extrahepatic tissues are formed in situ and do not reflect binding of blood-borne metabolites formed in the liver.

Biliary excretion products of 1-[1-14C]naphthyl-N-methylcarbamate (carbaryl) in rainbow trout (Salmo gairdneri).

Uptake and metabolism of 1-naphthyl-N-methylcarbamate (carbaryl) were studied in rainbow trout (Salmo gairdneri) exposed to 14C-carbaryl in water. A high degree of biliary concentration was indicated by a 24-hr bile to water 14C ratio of nearly 1000:1. Four 14C-labeled compounds were purified from bile and two have been identified with reasonable certainty as unchanged carbaryl and 1-naphthol glucuronide. 5,6-Dihydro-5,6-dihydroxy-1-naphthyl-N-methylcarbamate was tentatively identified by thin-layer chromatography. The results indicate that carbaryl can be metabolized in rainbow trout via pathways similar to those reported in mammals and that bile analysis may be helpful in monitoring fish for exposure to this compound.

The pulmonary clara cell as a target for toxic chemicals requiring metabolic activation; studies with carbon tetrachloride.

Oral administration of carbon tetrachloride to rats or mice caused striking decreases in rat lung microsomal cytochrome P-450 and benzphetamine demethylase activity and in the enzyme-mediated covalent binding of 4-ipomeanol in preparations of rat and mouse lung microsomes, mouse lung slices and isolated whole-mouse lungs. Although it is not yet known whether cytochrome P-450 and benzphetamine demethylase activities are present in substantial amounts in more than one lung cell type in mice or rats, previous studies have indicated that cytochrome P-450 enzymes located in pulmonary bronchiolar Clara cells of these mediate the covalent binding of 4-ipomeanol to lung macromolecules. Histologic examinations of lungs of animals given doses of CCl4, orally or by inhalation, revealed striking morphologic changes in Clara cells, including severe dilation of endoplasmic reticulum and occasional cellular necrosis. Because of cytochrome P-450 enzymes are capable of mediating the formation of highly reactive and potentially toxic-free radicals from CCl4, the present results support the view that pulmonary Clara cells are susceptible to CCl4-induced injury due to their capacity to metabolically activate the chemical.

Covalent binding of metabolites of 4-ipomeanol to rabbit pulmonary and hepatic microsomal proteins and to the enzymes of the pulmonary cytochrome P-450-dependent monooxygenase system.

The covalent binding of metabolites of 4-ipomeanol, a potent lung toxin, to proteins in rabbit pulmonary and hepatic microsomal preparations and in purified monooxygenase systems was investigated. The rate of binding was 12-fold greater in pulmonary preparations than in hepatic preparations. Covalent binding in pulmonary microsomal fractions was inhibited 39 to 49% by antibodies to rabbit pulmonary cytochrome P-450II or P-450I and 90% by antibodies to cytochrome P-450 reductase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and scintillation autoradiography of pulmonary microsomal proteins revealed the presence of heavily labeled bands throughout the molecular weight range (Mr) examined. Two of these bands corresponded in mobility to pulmonary cytochrome P-450I (Mr 52,000) and P-450II (Mr 58,000). In addition, there was a great deal of binding associated with very high molecular weight proteins, probably in the form of cross-linked aggregates which were unable to penetrate the gel matrix. In the absence of cofactor, no binding was observed. Binding was decreased by the addition of the following: antireductase greater than glutathione = NADH (without NADPH) greater than anti-II greater than anti-I. The electrophoretic patterns of the proteins from incubation of [3H]-4-ipomeanol with purified pulmonary P-450-dependent monooxygenase enzymes were also examined. In the complete system, the majority of the binding was associated with high molecular weight species located at the origin and with low molecular weight species that migrated with the tracking dye. In the absence of cofactor, some binding to proteins that corresponded with cytochrome P-450 and P-450 reductase was observed. Protease digestion of incubation mixtures resulted in the migration of all bound material at the dye front.

Ipomeanol 4-glucuronide, a major urinary metabolite of 4-ipomeanol in the rat.

Urinary excretion and metabolism of 4-ipomeanol was studied in rats injected ip with the radiolabeled compound. There was a rapid elimination of radioactivity in the urine, amounting to 47% of the administrated dose within 4hr. One major metabolite was isolated and purified by HPLC. Analysis by analytical HPLC, beta-glucuronidase hydrolysis, and mass spectrometry identified this material as ipo-meanol 4-glucuronide. The large amount of this metabolite excreted suggests that 4-glucuronidation is an important detoxication reaction in vivo for 4-ipomeanol in rats.

Changes in phospholipid methyltransferases and membrane microviscosity during induction of rat liver microsomal cytochrome P-450 by phenobarbital and 3-methylcholanthrene.

Rat liver microsomes contained two methyltransferases which converted phosphatidylethanolamine (PE) to phosphatidylcholine (PC). The first methyltransferase converted PE to phosphatidyl-N-methylethanolamine (PME) and the second methyltransferase converted PME to PC. Previous work has shown that increased PME synthesis decreases membrane microviscosity. Therefore, changes in the rat liver microsomal cytochrome P-450, phospholipid methyltransferases and membrane microviscosity after induction by phenobarbital and 3-methylcholanthrene were studied. Phenobarbital and 3-methylcholanthrene increased cytochrome P-450 levels 2- to 3-fold. At low SAM concentration, the proportion of PME among the total phospholipids formed increased significantly, and at a high SAM concentration, the proportion of PC among the total phospholipids formed decreased significantly in microsomes of treated rats. Treatment of rats with phenobarbital and 3-methylcholanthrene also decreased microviscosities of the microsomal membranes and liposomes which were prepared from phospholipids extracted from the microsomes. In synthetic liposomes containing PE, PME and PC, microviscosity decreased when the proportion of PME was increased or the proportion of PC was decreased. These results suggest that the membrane fluidity increases with phenobarbital and 3-methylcholanthrene treatment, and changes in phospholipid methyltransferases may contribute to the process of enzyme induction. During induction with phenobarbital, all three factors known to increase membrane fluidity (linoleic acid content, the formation of phosphatidyl-N-methylethanolamine, and decreases in the cholesterol/phospholipid ratio) contribute to the decrease in microviscosity. During induction with 3-methylcholanthrene, alterations in phospholipid methylation is possibly the primary cause of the decrease in membrane microviscosity.

Effect of polycyclic aromatic hydrocarbons on hepatic microsomal enzymes and disposition of methylnaphthalene in rainbow trout in vivo.

1. The effects of 3-methylcholanthrene, 2,3-benzanthracene and beta-naphthoflavone on xenobiotic metabolism in rainbow trout were studied. 2. These three polycyclic aromatic hydrocarbons increase hepatic arylhydrocarbon (benzo[alpha]pyrene) hydroxylase activity without altering glucuronyl transferase activity. 3. All three polycyclic aromatic hydrocarbons increased hepatic microsomal cytochrome P-450 levels by approximately 50%. 4. Pretreatment of trout with 2,3-benzanthracene resulted in an increase in the metabolism and biliary excretion of 2-methylnaphthalene in vivo. 5. These studies demonstrate that the induction of mono-oxygenation by polycyclic aromatic hydrocarbons can result in significant effects upon the metabolism and excretion of xenobiotics by fish in vivo.

Effects of vitamin E on the distribution and metabolism of nitrofurantoin in rats.

Previous studies have shown a significant increase in the pulmonary toxicity of nitrofurantoin (NF) in animals fed a diet lacking vitamin E. The authors have therefore examined the pharmacokinetics of NF in control and vitamin E-deficient male Sprague-Dawley rats. NF was rapidly absorbed following subcutaneous injection and was cleared from all tissues examined (blood, lung, liver and kidney) in a biphasic manner. Substantial metabolism of the drug was observed, and the disposition of NF metabolites was qualitatively similar to that of the parent compound. The most apparent difference between control and vitamin E-deficient animals was a significant increase in tissue metabolite levels 4-16 hr after treatment. Unchanged NF was also elevated in all tissues examined 16 hr after treatment in the vitamin E-deficient animals. Urinary excretion of NF and metabolites accounted for 68% of the total dose in control rats and 35% in vitamin E-deficient rats. This study illustrates a marked alteration in NF disposition in animals fed a diet lacking vitamin E when compared with controls. The observed alterations appear to be related to a decreased renal clearance of both NF and metabolites.

In vitro metabolic activation of the pulmonary toxin, 4-ipomeanol, in nonciliated bronchiolar epithelial (Clara) and alveolar type II cells isolated from rabbit lung.

The metabolism and covalent binding of 4-ipomeanol (IPO), a pulmonary toxin, were investigated in pulmonary cells isolated from rabbit. 3H-labeled IPO was incubated with freshly, isolated, intact alveolar type II cells (83% purity), nonciliated bronchiolar epithelial (Clara) cells (77% purity) and alveolar macrophages (greater than 90% purity). Covalent binding of radioactive material to type II and Clara cells was observed by autoradiography and by a biochemical method. IPO binding to cells was almost totally prevented by 1 mM piperonyl butoxide, an inhibitor of the cytochrome P-450-dependent metabolism of IPO. No covalent binding was observed with alveolar macrophages in the presence or absence of piperonyl butoxide. The maximal rates of enzyme-mediated covalent binding of IPO to protein were greater in the Clara cells (135 pmol/10(6) cells/min) than in the type II cells (13 pmol/10(6) cells/min). Incubation of either sonicated Clara or type II cell fractions with [3H]IPO, glutathione and NADPH (20 min, 37 degrees C) resulted in the formation of two distinct radiolabeled glutathione conjugates.

The relationship between the catalytic activities of rabbit pulmonary cytochrome P-450 isozymes and the lung-specific toxicity of the furan derivative, 4-ipomeanol.

Metabolism of the pulmonary toxin, 4-ipomeanol, in microsomal preparations from rabbit liver and lung and in purified cytochrome P-450-dependent monooxygenase systems was investigated. The rate of formation of reactive electrophilic products from 4-ipomeanol was estimated by measuring covalent binding to protein or glutathione. Pulmonary microsomal preparations were much more active than hepatic preparations in mediating these reactions. Both of the rabbit pulmonary cytochrome P-450 isozymes, P-450I and P-450II, were active in the metabolism of 4-ipomeanol. In the assay for covalent binding to protein, P-450I was slightly more active than P-450II at high substrate concentrations and significantly more active at low substrate concentrations. Incubation of either isozyme with 4-ipomeanol produced two glutathione conjugates but at quite different ratios. Rates of metabolism determined by conjugate formation in the purified systems were about 3 times the rates determined by covalent binding to protein, whereas both determinations gave the same values in the microsomal preparations. The relationship between the activities of P-450I and P-450II in the metabolism of 4-ipomeanol and the pulmonary toxicity of 4-ipomeanol is discussed.