Effect of circulating vasopressin on arterial pressure regulation in rats

It has been hypothesized that moderately increased blood levels of arginine vasopressin (AVP) contribute to the development and/or maintenance of hypertension. In this study, male Sprague-Dawley rats on a fixed 1 meq daily sodium intake received 10-day intravenous infusions of 0.2 and 2.0 ng.kg-1.min-1 AVP. The higher infusion rate was above the acute vasoconstrictor threshold for AVP administration and also produced a maximal antidiuretic effect. During chronic AVP administration, however, daily mean arterial pressure, heart rate, and body fluid composition were not changed, despite a maintained antidiuresis. To test the hypothesis that circulating AVP failed to cause hypertension as a result of sensitization of the baroreflex or a direct sympathoinhibitory effect of the peptide, additional experiments were performed in rats subjected to sinoaortic denervation (SAD) or ablation of the area postrema (APX). Infusion of AVP for 10 days into SAD or APX rats caused a sustained antidiuresis but did not change arterial pressure, heart rate, or body fluid composition. In all groups of rats, the depressor response to ganglionic blockade (20 mg/kg hexamethonium) was used to estimate the autonomic component of resting arterial pressure; no change in autonomic cardiovascular control was found using this method in any of the groups during AVP infusion. Long-term elevation of plasma AVP in rats, therefore, does not cause hypertension or significantly affect autonomic regulation of arterial pressure.

Identification and characterization of the major DNA adduct formed chemically and in vitro from the environmental genotoxin 3-nitrofluoranthene

The genotoxic environmental pollutant 3-nitrofluoranthene (3-NFA) was reduced chemically and allowed to react with calf thymus DNA, yielding one major adduct which was determined to be N-(deoxyguanosin-8-yl)-3-amino-fluoranthene based on Fast Atom Bombardment Mass Spectrometry (FAB-MS), proton nuclear magnetic resonance, ultraviolet-visible wavelength light spectroscopy (UV-VIS), and fluorescence data. Extensive characterization of the isolated adduct by tandem mass spectrometry (MS/MS) was necessary to demonstrate definitively that the adduct isolated was the dG:C8 adduct, and not the isomeric dG:N2 adduct. The extent of modification of the initial calf thymus DNA by chemically reduced 3-NFA was 0.12% (1.2 adducts/10(3) nucleosides), which was sufficient to allow several hundred micrograms of the adduct to be isolated and purified. The chemically synthesized adduct was utilized as a reference standard for comparison to the major adduct isolated from xanthine-oxidase-catalyzed reduction of 3-NFA in vitro. The yield from the in vitro biological system was 2.4 adducts/10(5) nucleosides; the adduct isolated possessed the same mass spectrometric, UV-VIS, and fluorescence characteristics as the purified standard, and co-eluted with the standard on HPLC. No evidence for other adducts was found, either in vitro or in the chemical synthesis, based on FAB-MS examination of whole extracts of the reaction mixture for the presence of ions related to other possible adducts. Therefore, if minor adducts were present they were formed in substantially lesser amounts than N-(deoxyguanosin-8-yl)-3-aminofluoranthene.

Porphinatoiron-mediated oxidation of polycyclic aromatic hydrocarbons

Although porphinatoiron complexes have been used extensively as biomimetic catalysts for oxidation of aliphatic and olefinic hydrocarbons, few oxidations of polycyclic aromatic hydrocarbons (PAH) have been reported. In all cases, heterogeneous iodosobenzene/tetraphenylporphinatoiron(III) systems were employed, oxidations were inefficient and control experiments demonstrating the requirement for catalyst were not described. The current study investigates the oxidation of pyrene, benzo[a]pyrene and benzanthracene in a homogeneous m-chloroperoxybenzoic acid/bifacially hindered porphinatoiron system in which the peroxyacid was shown to be unreactive in the absence of catalyst. Pyrene and benzo[a]pyrene were oxidized efficiently, with pyrene yielding mixtures of 1.6- and 1.8-quinones and benzo[a]pyrene yielding mixtures of phenols and quinones. Benzanthracene was oxidized less efficiently, primarily at the meso positions, to give 7.12-quinone. Initial oxidation of meso carbons of benzo[a]pyrene (confirmed by the presence of the 6-hydroxy derivative as a product) and benzanthracene indicates that PAH-to-catalyst charge transfer may be an important oxidation pathway. Oxidation of pyrene was performed by addition of pyrene to observable oxo iron(V) species as well as in a catalytic reaction where excess peroxyacid was added to a solution of pyrene and catalyst and oxo iron(V) is not generated as an observable intermediate. Yields (based on oxidant consumed), were identical under both conditions, strongly supporting oxo iron(V) as a common intermediate.

Metabolism and DNA binding of 1-nitro[14C]pyrene by isolated rabbit tracheal epithelial cells

The metabolism of 1-nitro[14C]pyrene (1-NP) and the binding of its reactive intermediates to DNA and protein was examined in rabbit tracheal epithelial cells. The tracheal cells isolated by two protease digestion methods had normal cellular morphology and viability. The digestion method which demonstrated the highest rate of 1-NP metabolism and DNA binding used a 1 h incubation of the tracheas with 1% protease at 37 degrees C. Metabolites from the incubation medium and cell lysates were extracted, analyzed and quantitated by h.p.l.c. The majority of the metabolites produced by tracheal cells were EA:AC extractable and were released to the surrounding incubation medium. The predominant metabolites identified and quantified in the medium were the ring oxidation products, a 1-NP-diol, 1-NP phenols (6- or 8-OH-1-NP), 10-OH-1-NP and 3-OH-1-NP. Major metabolites formed by nitroreduction were NAAP and 1-AMP. The metabolites retained by tracheal cells were qualitatively identical to those identified in the medium but were present at one-seventh to one-tenth of the amounts. The rate of both 1-NP metabolism and DNA binding was very high. After 4 h, 62% of the 1-NP was metabolized and 198 DNA adducts/10(6) nucleotides were formed. The rate of [14C]1-NP-DNA adducts formation was highest at 30 min of incubation (124 adducts/10(6) nucleotides/h). These high rates of metabolism and DNA binding are consistent with the possibility that tracheal cells may be a particular target tissue for tumor induction by nitrosubstituted polycyclic aromatic hydrocarbons associated with diesel and other combustion emission particles. The preponderance of highly mutagenic 1-NP phenols as metabolites suggest that ring oxidation as well as nitroreduction may result in intermediates which form DNA adducts.

Synthesis and bacterial mutagenicity of the cyclopenta oxides of the four cyclopenta-fused isomers of benzanthracene

Many polycyclic aromatic hydrocarbons containing peripherally fused cyclopenta rings are believed to be activated primarily by epoxidation of the cyclopenta ring. The cyclopenta epoxides of a series of four cyclopenta benzanthracene derivatives, benz[e]aceanthrylene-5,6-oxide, benz[j]aceanthrylene-1,2-oxide, benz[l]aceanthrylene-1,2-oxide and benz[k]acephenaceanthrylene-4,5-oxide were synthesized from their parent hydrocarbons by formation of the bromohydrin followed by dehydrobromination, and characterized by u.v.-vis, and 1H n.m.r. spectroscopy and mass spectrometry. The mutagenicity of these compounds was investigated in the Ames plate incorporation assay with Salmonella typhimurium strain TA98. All the oxides were active without exogenous metabolic activation (170-320 His+ revertants per nanomole) and also toxic above 0.5 microgram/plate. Addition of S9 protein did not increase, and generally decreased, the mutagenicity of the oxides, while toxicity was largely unchanged. These results are consistent with the postulated role of cyclopenta oxides as major contributors to the mutagenicity of the parent compounds in the Ames assay.

Mutagenic activity of nitro-substituted cyclopenta-fused polycyclic aromatic hydrocarbons towards Salmonella typhimurium

Cyclopenta-fused isomers of pyrene and benz[a]anthracene, nitrated on the etheno bridge, were synthesized and tested in the Ames plate-incorporation assay. Since enzymatic reduction, if it occurs in these compounds, would form arylhydroxylamines which in turn would form highly stabilized arylnitrenium ions, we hoped to test the hypothesis that the direct-acting mutagenic activity of nitroPAH is correlated with the degree of stabilization of the electrophilic intermediate. We found that these compounds are mutagenic (1-9 rev/nmole in Salmonella typhimurium TA98) and do not require S9 activation. However, this activity is substantially lower than that of other nitroPAH of comparable size such as 1-nitropyrene (250-300 rev/nmole). The reasons for this comparative lack of activity are discussed with reference to current theories regarding structure-activity relationships of nitroPAH.

Metabolism of 1-nitropyrene by cultured rabbit alveolar macrophages and respiratory tract tissues

The metabolism of 1-nitro[14C]pyrene (14C-1-NP; 8.1 microM) was studied in cultured (20 hr) rabbit alveolar macrophages, lung tissue, and tracheal tissue. Metabolites from the incubation medium and from the macrophages and respiratory tract tissues were extracted and then analyzed and quantified by high-pressure liquid chromatography. The following metabolites were detected in the lung and tracheal tissue incubation medium: 1-nitropyrene-4,5-dihydrodiol, N-acetyl-1-aminopyrene, 1-aminopyrene, and 10-hydroxy-1-nitropyrene. Nitropyrene phenols (4-, 5-, 6-, 8- or 9-hydroxy-1-nitropyrene) and 3-hydroxy-1-nitropyrene were only detected in the lung and tracheal tissue and not in the incubation medium for these tissues. Minor amounts of 1-aminopyrene and 10-hydroxy-1-nitropyrene were detected in the macrophage incubation medium, and only minute quantities of 1-nitropyrene-4,5-dihydrodiol, 1-aminopyrene, and 10-hydroxy-1-nitropyrene were detected in macrophages. The total percentage of 1-NP metabolism was significantly greater in the lung and tracheal tissue (28.0 and 23.0% of the recovered 14C, respectively) than in the alveolar macrophages (6.3% of the recovered 14C). The tracheal tissue was found to have the highest activity both in 1-NP metabolism and intracellular metabolite concentration. A major portion of the 1-NP metabolites produced was released into the incubation medium. The majority of the metabolites produced by tracheal and lung tissue, 70 and 84%, respectively, were ethyl acetate extractable. The metabolites retained within the cells or tissues were also predominantly ethyl acetate extractable rather than water soluble (83% for the macrophages and trachea, 95% for the lung tissue). The metabolite profiles obtained demonstrate that metabolism by both nitro reduction and ring oxidation occurs in respiratory tissue, and a degree of tissue specificity in the formation of metabolites exists. Ring oxidation was demonstrated in the lung and tracheal tissue, but very little occurred in the macrophages.

Nitropyrene: DNA binding and adduct formation in respiratory tissues

Binding of 1-nitro (14C)pyrene (NP) or its metabolites to cellular DNA and protein in cultures of rabbit alveolar macrophages, lung tissue, and tracheal tissue was examined. DNA binding in tracheal tissue (136 +/- 18.3 pmole NP/mg DNA) was four to five times the levels measured in either lung tissue (38 +/- 9.4 pmole NP/mg DNA) or macrophages (26 +/- 7.5 pmole NP/mg DNA). Adduct analysis of DNA isolated from lung tissue incubated with 1-nitro[H3]pyrene in vitro resulted in the identification of 2 to 5% of the NP adducts as C8-deoxyguanosine 1-aminopyrene. NP was also bound to cellular protein in tracheal tissue and lung tissue, and at a lower level in macrophages. Cocultivation of the macrophages with lung and tracheal tissue decreased the DNA binding in tracheal tissue by 45%. Following intratracheal instillation of diesel particles (5 mg) vapor-coated with 14C-NP (380 ppm, 0.085 muCi/mg) particles into rats, 5-8% of the radioactivity remained in the lungs after 20 hr. Most of the diesel particles were also deposited in the lung. Examination of DNA and protein binding in this tissue showed 5 to 12% of the pulmonary 14C bound to protein and no detectable levels of 14C bound to DNA.

Bacterial mutagenicity of aceanthrylene: a novel cyclopenta-fused polycyclic aromatic hydrocarbon of low molecular weight

Aceanthrylene, a non-alternant cyclopenta-fused hydrocarbon, was shown to be weakly mutagenic without S9 and strongly mutagenic with S9 in the Ames Salmonella plate incorporation assay. The compound was most active in strain TA100 (35 revertants/nmole in the presence of 0.3 mg of S9 protein), and less active in strains TA98, TA1537 and TA1538 (20, 10 and 3.1 rev/nmole respectively, + S9). Strain TA1535 was unresponsive, suggesting that this compound induces frameshift mutations rather than base-pair substitutions. The mutagenic potency of aceanthrylene is consistent with predictions of its activity based on the relatively large delocalization energy (delta E deloc/beta = 0.931) of the carbonium ion which would result from oxirane ring opening of the 1,2-epoxide, a potential active metabolite.

Metabolism of 1-nitro[14C]pyrene in vivo in the rat and mutagenicity of urinary metabolites

The metabolic fate of the bacterial mutagen, environmental pollutant and potential carcinogen 1-nitropyrene (NP) has been investigated in the rat. Over half of an i.p. dose (10 mg/kg) of 1-nitro[14C]pyrene was excreted within 24 h of dosing, 15% of the dose in urine and 40% in the faeces. After 96 h greater than 80% of the dose had been recovered. The urinary and fecal metabolites of NP were separated and quantitated by h.p.l.c., then identified by high resolution gas chromatography/mass spectrometry (h.r.g.c./m.s.) and comparison with synthetic reference compounds, where available. Very little (less than 5%) of the dose was excreted unchanged. Urinary metabolites were all excreted in conjugate form, mainly with glucuronic acid. Among the principal metabolite fractions identified were 3-hydroxy-1-nitropyrene and 8-hydroxy-1-nitropyrene (already known as hepatic in vitro metabolites of 1-nitropyrene) and the hitherto unreported metabolites 6-hydroxy-N-acetyl-1-aminopyrene and 8-hydroxy-N-acetyl-1-aminopyrene. Mutagenic activity was detected, by means of the Ames Salmonella (strain TA 98) plate incorporation assay, in the urine of rats dosed with NP. This mutagenicity, unlike that of NP itself, required exogenous metabolic activation. It was predominantly associated with 6-hydroxy-N-acetyl-1-aminopyrene and with the nitropyrene phenols (specific mutagenicity 600 and 700 rev/nmol respectively in the presence of 0.6 mg of S9 protein per plate). The majority of the residual metabolites were polar, refractory to enzymic hydrolysis, and of low mutagenicity. The major proportion of the 14C in feces was not extractable or amenable to enzymic hydrolysis; the extractable fecal metabolites were similar in nature to those in urine.

Mutagenicity of derivatives and metabolites of 1-nitropyrene: activation by rat liver S9 and bacterial enzymes

The mutagenicity and activation requirements of purified synthetic derivatives and potential metabolites of 1-nitropyrene have been characterized in the Ames plate incorporation assay with the Salmonella tester strains TA98, TA98NR and TA98/1,8-DNP6, in the presence or absence of exogenous metabolic activation provided by Aroclor-induced rat liver S9. All the compounds tested (1-aminopyrene, N-acetyl-1-aminopyrene, N-hydroxy-N-acetyl-1-aminopyrene, 3-hydroxy-1-nitropyrene, 6-hydroxy-1-nitropyrene, and 8-hydroxy-1-nitropyrene) exhibited mutagenic activity under one or more assay conditions. 1-Nitropyrene was metabolized to 3-hydroxy-1-nitropyrene, 6- or 8-hydroxy-1-nitropyrene, 1-aminopyrene, N-acetyl-1-aminopyrene and other unidentified products (including some bound to protein) by an S9 preparation analogous to that used for exogenous metabolic activation in the Ames assay. 1-Nitropyrene and 3-hydroxy-1-nitropyrene were activated primarily by the 'classical' nitroreductase, while the other compounds, particularly in the presence of S9 metabolic activation, were dependent on transesterification for expression of their mutagenicity.

Mutagenicity of 1-nitropyrene metabolites from lung S9

The mutagenicity of 1-nitropyrene metabolites from rabbit lung S9 incubates was evaluated using the Salmonella typhimurium plate incorporation assay with strain TA98, with and without Aroclor-induced rat liver S9. The following metabolites were isolated, identified and quantitated by HPLC: 1-nitropyrene -4,5- or -9,10-dihydrodiol (K-DHD), N-acetyl-1-aminopyrene ( NAAP ), 1-aminopyrene (1-AMP), 10-hydroxy-1-nitropyrene, 4-, 5-, 6-, 8- or 9-monohydroxy-1-nitropyrene (phenols) and 3-hydroxy-1-nitropyrene. The predominant metabolites formed by lung S9 incubates were K-DHD, 3-OH-1-nitropyrene and phenols. All of the metabolites were mutagenic in the absence of the exogenous rat liver S9 metabolic activation system, and several, including two unidentified metabolites were more potent than the parent 1-nitropyrene. The mutagenicity of 3 of the metabolites ( NAAP , 10-OH-1-nitropyrene and phenols) were enhanced by S9 while most of the other metabolites were less mutagenic in the presence of S9. These results indicate that lung tissue is capable of both oxidative and reductive metabolism which produced mutagenic metabolites, several of which were more potent than the parent compound, 1-NP.

Binding of 1-nitro[14C]pyrene to DNA and protein in cultured lung macrophages and respiratory tissues

Binding of 1-nitro[14C]pyrene (1-NP) or its metabolites to cellular DNA and protein in cultures of rabbit alveolar macrophages and lung and tracheal tissues was examined. DNA binding was highest in tracheal tissue (136.9 +/- 18.3 pmol 1-NP/mg DNA). DNA binding in macrophages and lung tissue was one-fifth of the level observed in tracheal tissue. Also, 1-NP was bound to cellular protein in tracheal and lung tissues, and at a lower level in macrophages. Co-cultivation of the macrophages with lung and tracheal tissues decreased the DNA binding in tracheal tissue and increased the protein binding in macrophages. This study shows that lung cells and tissue are capable of binding 1-NP or its metabolites to DNA and protein.

A rapid technique for estimating DNA binding, used to evaluate 1-nitropyrene adduct formation

A simple and rapid procedure for estimating binding of radio-labelled material to DNA and protein is described. Protein was extracted from lysed rabbit alveolar macrophages with chloroform: iso-amyl-alcohol:phenol extraction. Nucleic acids were precipitated from the lysate, and hydrolysed with protease and NaOH to remove residual protein and RNA respectively. Bound radioactivity was quantitated by precipitation of DNA onto glass fiber filters. Protein labelled with 3H-leucine and DNA and RNA adducts formed from 1-nitro[14C]pyrene by xanthine oxidase were used to define this procedure. 14C was shown to be bound to endogeneous protein and DNA isolated from rabbit alveolar macrophages that had been incubated with 1-nitro[14C]pyrene.

Metabolism of benzo(a)pyrene and benzo(a)pyrene 4,5-oxide in rabbit lung

For several years our laboratory has been investigating the biotransformation of various environmental pollutants by lung. Studies have been performed with pulmonary subcellular fractions, purified monooxygenase and glutathione transferase enzymes, and preparations having intact cellular structure including the isolated perfused lung and cell fractions enriched in alveolar macrophages, Clara cells and alveolar type II cells. Collectively, these investigations have identified several metabolic factors which may contribute to the pulmonary toxicity mediated by certain polycyclic aromatic hydrocarbons (PAH). First, although lung has low overall cytochrome P-450-dependent monooxygenase activity for many substrates, relative to liver, this activity is localized in only a few cell types and specific activity in certain cell types, such as the non-ciliated bronchiolar epithelial (Clara) cell, can be high. Second, oxidative metabolites of benzo(a)pyrene tend to accumulate in pulmonary tissue due, at least in part, to the low ability of lung (relative to liver) to conjugate and detoxify phenolic, dihydrodiol and epoxide metabolites. Thus, products such as benzo(a)pyrene 7,8-dihydrodiol are available for further cytochrome P-450-dependent oxidation to ultimate carcinogens and cytotoxins. Moreover, the lung is efficient in removing benzo(a)pyrene 4,5-oxide and presumably other oxidized PAH metabolites, from the bloodstream. Consequently, the uptake of relatively stable electrophilic metabolites released by the liver may also contribute to pulmonary toxicity.

Intestinal absorption of nutrients in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Impairment of active intestinal absorption of glucose and leucine was observed in rats 2-3 wk after oral treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (5 and 100 mg/kg). At the higher dose level used this response was complicated by the effects of severely reduced food consumption. Malabsorption of specific nutrients may help occasion the body wasting seen in many animals after acute exposure to TCDD.

Metabolism and biliary excretion of benzo[a]pyrene 4,5-oxide in the rat

The excretion and biliary metabolites of intravenously administered benzo[a]pyrene 4,5-oxide were studied in the rat at two dose levels. After administration of 4.5 or 0.47 mumol, half of the dose was excreted in the bile in 60 min. Biliary metabolites were separated by reverse-phase high-pressure liquid chromatography and identified by cochromatography with biosynthetic standards, beta-glucuronidase hydrolysis, ultraviolet spectrophotometry and, in the case of the thioether conjugates, identification of the constituent amino acids. The major biliary metabolite was a mixture of isomeric glutathione conjugates. Some cysteine conjugate was also present, but no cysteinylglycine conjugate was detected. Hydration to transbenzo[a]pyrene-4,5-dihydrodiol followed by glucuronidation was also a quantitatively important metabolic pathway. Although benzo[a]pyrene-4,5-dihydrodiol glucuronide was more readily excreted by the liver than was benzo[a]pyrene 4,5-oxide:glutathione conjugate, the rate of glucuronidation of the dihydrodiol was low, resulting in its accumulation in the liver and possible release into the circulation. Therefore, the glutathione S-transferases may provide a more efficient mechanism for the removal of benzo[a]pyrene 4,5-oxide from the body than is provided by expoxide hydrolase.

Benzo(a)pyrene oxidation, conjugation and disposition in the isolated perfused rabbit lung: role of the glutathione S-transferases

The isolated perfused rabbit lung metabolised 7--11 % of 20 mumol of [14C]-benzo(a)pyrene added in the perfusion medium in 1 h. The major metabolite formed was 3-hydroxybenzo(a)pyrene, both free (30--40 % of the total metabolites) and conjugated (4 % of total metabolites). Quinones comprised 15 % of the total and metabolism at the 9, 10 position accounted for a further 10 %. Forty per cent of the water-soluble metabolites was chromatographically identical to the glutathione conjugate of benzo(a)pyrene 4,5-oxide. Sulphate and glucuronide conjugates were formed in small but detectable amounts, principally from phenols, but also from dihydrodiols. After 1 h the more water-soluble conjugates had diffused from the lung into the perfusion medium, but the majority (60--90 %) of the metabolic products were still concentrated within the lung. The lung's limited ability to conjugate its major metabolites of benzo(a)pyrene with sulphuric or glucuronic acid, coupled with slow elimination of the products formed, particularly dihydrodiols may contribute to the susceptibility of this organ to polycyclic aromatic hydrocarbon-induced carcinogenesis.