The uptake and distribution of [3H]benzo[a]pyrene in the Northern pike (Esox lucius). Examination by whole-body autoradiography and scintillation counting

The uptake and distribution of the polyaromatic hydrocarbon benzo[a]pyrene in Northern pike (Esox lucius) were investigated by whole body autoradiography and scintillation counting. [³H]Benzo[a]pyrene was administered either in the diet or in the water. The levels of this xenobiotic employed corresponded to levels found in moderately polluted water. The uptake and distribution of this compound and its metabolites were followed from 10 hr to 21 days after the initial exposure. The autoradiography patterns observed here with both routes of administration suggest, as expected, that benzo[a]pyrene is taken up through the gastrointestinal system and the gills, metabolized in the liver, and excreted in the urine and bile. Other findings indicate that the gills may not be a major route of excretion for benzo[a]pyrene and its metabolites in the Northern pike; that benzo[a]pyrene may be taken up from the water directly into the skin of this fish; that benzo[a]pyrene and its metabolites are heterogeneously distributed in the kidney of the Northern pike; and that very little radioactivity accumulates in the adipose tissue. With scintillation counting, uptake of radioactivity from the water was found to occur rapidly in all organs, reaching a plateau in most cases after about 0.8 days. The concentrations of radioactivity in different organs ranged between 50 (many organs) and 80,000 (gallbladder + bile) times that found in the surrounding water. Since most of the radioactivity recovered in different organs of the pike after 8.5 days of exposure was in the form of metabolites, we feel that metabolism may play an important role in the bioconcentration of xenobiotics in fish.     

Exposure of two species of deposit-feeding amphipods to sediment-associated [3H]benzo[a]pyrene: Uptake,metabolism and covalent binding to tissue macromolecules

Two species of deposit-feeding marine gammaridian amphipods, Rhepoxynius abronius and Eohaustorius washingtonianus, were exposed to sediment-associated [³H]benzo[a]pyrene (BaP) at 12±1°C. Concentrations of BaP-derived radioactivity increased with time in both E. washingtonianus and R. abronius, and the levels of radioactivity were similar in both species after 7 days of exposure. A significantly (P<0.05) lower proportion (51%) of unconverted BaP was present in R. abronius than in E. washingtonianus (73%) at 1 day. The proportion of unconverted BaP decreased with time in R. abronius (30% at 7 days), but did not vary significantly with time in E. washingtonianus. Reverse-phase high-pressure liquid chromatography (HPLC) of organic solvent-soluble metabolites released from β-glucuronidase and arylsulfatase treated tissue extracts of amphipods showed the presence of metabolites such as 7,8-dihydroxy-7,8-dihydroBaP (BaP-7,8-diol), 9,10-dihydro-9,10-dihydroxyBaP (BaP-9,10-diol), 3-hydroxyBaP and 9-hydroxyBaP. The ratio of BaP-7,8-diol to BaP-9,10-diol obtained from normal-phase HPLC was 1.2 for R. abronius and 0.7 for E. washingtonianus. Moreover, the level of covalent binding of BaP intermediates to macromolecules was significantly (P≤0.01) higher at 7 days in R. abronius (7.00±0.98 pmol BaP equivalents/g-protein) than in E. washingtonianus (4.08±0.51 pmol/g-protein). Thus, using BaP as a representative of sediment-associated polynuclear aromatic hydrocarbons, it was shown that although both amphipod species accumulated similar concentrations of BaP-derived radioactivity, R. abronius converted a higher proportion of BaP into potentially toxic intermediates.     

Metabolism and subsequent covalent binding of benzo[a]pyrene to macromolecules in gonads and liver of ripe English sole (Parophrys vetulus)

1. Ripe English sole (Parophrys vetulus) force-fed [³H]benzo[a]pyrene, contained 1% of the dose in liver, 0.2% in ovary and 0.1% in testis, after 24h. No significant change occurred in levels of radioactivity from 24 to 168h.

2. Gonads and blood contained substantially larger proportions of unchanged benzo[a]pyrene (15–37% of tissue radioactivity) and organic solvent-soluble metabolites (6–35%) than did liver and bile.

3. T.l.c. revealed the presence of phenols, quinones, 7,8-dihydro-7,8-dihydroxy- and 9,10-dihydro-9,10-dihydroxy-benzo[a]pyrene in liver and gonads.

4. A small proportion (<10%) of the radioactivity in liver and gonads was present as glucuronides and sulphates; bile contained a higher proportion (ca. 20%) of total radioactivity as glucuronides and sulphates.

5. Benzo[a]pyrene intermediates were covalently bound to liver proteins and DNA, and to a lesser extent to gonadal proteins (male and female fish) and gonadal DNA (confirmed for testis only).     

Metabolism of (+)-trans-benzo[a]mpyrene-7,8-dihydrodiol by 3-methylcholanthrene-induced rat liver homogenates

Using a new sensitive reverse-phase HPLC assay with on-line radioactivity detector, metabolism of (+)-trans-benzo[a]pyrene-7,8-dihydrodiol (B[a]P diol) to the ultimate carcinogen benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE) was studied using 3-methylcholanthrene-induced rat liver homogenates. The results demonstrate that the stereoselectivity of B[a]PDE formation is a function of the concentration of the cellular constituents in the incubation media. At more dilute concentrations of the homogenate, the ratio of anti- to syn-B[a]PDE was the highest and decreased as the homogenate protein was increased in the incubation medium. However, there was a marked and parallel decrease of free B[a]PDE and DNA-bound radioactivity with increasing concentrations of cellular constituents in the incubation medium. The decreased DNA-bound radioactivity appears to be due to the preferential binding of B[a]PDE to glutathione and to proteins as the homogenate concentration was increased in the incubation media. These results indicate that liver homogenates, while apparently preserving the function of microsomes, present additional opportunities to study the interrelationship among cytochrome P450 monooxygenase activity, water-soluble conjugates, and binding of B[a]P diol metabolites to macromolecules in the study of benzo[a]pyrene-induced carcinogenesis.     

Effects of naphthalene on benzo[a]pyrene hydroxylase and cytochrome P-450 in Fundulus heteroclitus

Hepatic benzo[a]pyrene (B[a]P) hydroxylase, cytochrome P-450 and cytochrome b₅ were investigated in the mummichog, Fundulus heteroclitus, following acute exposure to naphthalene dissolved in the water. Control experiments revealed that males had significantly higher levels of BaP hydroxylase and cytochrome P-450 compared to females. Significant variation of B[a]P hydroxylase activity was also observed in control fish during a 6-mth period which may reflect seasonal or reproductive influences.Naphthalene at a concentration of 4 mg/l caused a significant reduction of B[a]P hydroxylase activity in males and females. The naphthalene exposure effected significant decreases of cytochrome P-450 in males, but not in females. Addition of naphthalene directly to reaction mixtures containing liver preparation from control fish caused reduced B[a]P hydroxylase activity in vitro. The concentrations of naphthalene necessary to produce in vitro reductions in B[a]P hydroxylase appeared to be much higher than would be realized by in vivo exposures. These data indicate that metabolite formation or other mechanisms such as generalized physiological stress as a result of in vivo exposures may be important factors in reducing B[a]P hydroxylase activity. The nature of the reduction of B[a]P hydroxylase was not elucidated. Cytochrome b₅ concentrations did not change significantly.     

Multidrug resistance protein (MRP) 4 attenuates benzo[a]pyrene-mediated DNA-adduct formation in human bronchoalveolar H358 cells

Multi-drug resistance protein (MRP) 4, an ATP-binding cassette (ABC) transporter, has broad substrate specificity. It facilitates the transport of bile salt conjugates, conjugated steroids, nucleoside analogs, eicosanoids, and cardiovascular drugs. Recent studies in liver carcinoma cells and hepatocytes showed that MRP4 expression is regulated by the aryl hydrocarbon receptor (AhR) and nuclear factor E2-related factor 2 (Nrf2). The AhR has particular importance in the lung and is most commonly associated with the up-regulation of cytochrome P-450 (CYP)-mediated metabolism of benzo[a]pyrene (B[a]P) to reactive intermediates. Treatment of H358, human bronchoalveolar, cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or (−)-benzo[a]pyrene-7,8-dihydro-7,8-diol (B[a]P-7,8-dihydrodiol), the proximate carcinogen of B[a]P, revealed that MRP4 expression was increased compared to control. This suggested that MRP4 expression might contribute to the paradoxical decrease in (+)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-2′-deoxyguanosine ((+)-anti-trans-B[a]PDE-dGuo) DNA-adducts observed in TCDD-treated H358 cells. We have now found that decreased MRP4 expression induced by a short hairpin RNA (shRNA), or chemical inhibition with probenecid, increased (+)-anti-trans-B[a]PDE-dGuo formation in cells treated with (−)-B[a]P-7,8-dihydrodiol, but not the ultimate carcinogen (+)-anti-trans-B[a]PDE. Thus, up-regulation of MRP4 increased cellular efflux of (−)-B[a]P-7,8-dihydrodiol, which attenuated DNA-adduct formation. This is the first report identifying a specific MRP efflux transporter that decreases DNA damage arising from an environmental carcinogen.     

Albumin and hemoglobin adducts of benzo[a]pyrene in humans—Analytical methods,exposure assessment,and recommendations for future directions

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in our environment and can cause cancer. Exposure to PAHs can be assessed by protein adduct dosimetry using benzo[a]pyrene (B[a]P) as a model compound. We present an overview of analytical methods to detect B[a]P- derived protein adducts in humans, their uses in exposure assessment, and recommendations for future research. Two major methodologies, enzyme-linked immunosorbent assay (ELISA) and chemical-specific assays, could be traced in the literature but there remains limitations with both assays. ELISA is nonspecific due to cross-reactivity of the antibody with other PAHs and results are better interpreted in terms of PAH exposure. ELISA is unable to distinguish between exposed and nonexposed persons in the majority of studies. Adduct concentrations are higher by several orders of magnitude compared to those determined by chemical-specific methods. The latter methods mostly analyzed protein adducts derived by (+)-anti-B[a]P-diol epoxide. For this purpose, gas or liquid chromatography in combination with mass spectrometry or fluorescence detection were used. However, the prevalence of positive samples remained low when chemical- specific assays were used mainly due to the lack of sensitivity. Overall, data on B[a]P-derived protein adducts in humans remain inconclusive. Future research should focus on the development and standardization of a sensitive and specific method for B[a]P-derived protein adducts prior to its use in field studies. Finally, exposures of B[a]P at the workplace and via diet, a major route of exposure of the general population, can be studied. The results will contribute to the understanding of B[a]P-induced cancer and will allow for health preventive measures.     

Interaction of [3H]flunitrazepam with the benzodiazepine receptor: Evidence for a ligand-induced conformation change

The interaction of [³H]flunitrazepam with benzodiazepine receptors in rat brain homogenates was studied in the presence of 2 μM endogenous GABA at 0° at pH 7.2. Equilibrium binding experiments showed a dominant component of high affinity with an equilibrium dissociation constant K = 0.86 ± 0.07 nM which accounted for 75% of total binding and another component of lower affinity (K ? 30 nM). The dissociation kinetics of the [³H]flunitrazepam complex at the high affinity site were strictly monophasic with a rate constant k_off = (7.7 ± 0.3) × 10^?4/sec. The association kinetics with the high affinity sites were studied with ligand concentrations [L]₀ in large excess over binding sites. The kinetics were in accordance with a single exponential with a reaction rate τ^?1. In the higher concentration range [L]₀ ? 10 nM, τ^?1 as a function of [L]₀ deviated from linearity and started to level off. The data are compatible with a two-step mechanism where R and L rapidly combine to form a pre-complex RL which then slowly isomerizes to the final complex C:

where $\text{K}{}_1\text{= (}\text{[}\text{R}\text{][}\text{L}\text{]}\text{([}\text{RL}\text{]}\text{)}$ and $\text{[}\text{RL}\text{]}\text{[}\text{C}\text{]}\text{=}\text{k}{}_{\mathrm{?2}}\text{k}{}_2\text{= k}{}_2$. Nonlinear parameter estimation yielded K₁24.2 ± 7.1 nM, k₂ = (2.8 ± 0.5) × 10^?2/sec and k_?2 = (9 ± 2) × 10^?4/sec. The isomerization step might reflect a ligand-induced conformation change of the high affinity site which is involved in the potentiation of GABA-ergic transmission produced by the benzodiazepines.     

Species differences in disposition of benzo[a]pyrene

Comparison of disposition of benzo[a]pyrene (B[a]P) among Sprague-Dawley rats, Gunn rats, hamsters, and guinea pigs was performed. [3H]B[a]P was administered intratracheally to animals, and the rate of excretion of radioactivity into bile, types of metabolites of B[a]P in bile, and distribution of radioactivity among tissues were determined. In Sprague-Dawley rats, Gunn rats, and guinea pigs, the rate of excretion of radioactivity was dependent upon the administered dose. Excretion and tissue distribution of radioactivity were qualitatively similar among these species although quantitative differences were observed. In hamsters, the rate of excretion was essentially independent of dose at the concentrations examined (0.16 and 350 micrograms). The major difference between hamsters and the other species was that increased amounts of radioactivity were retained in lungs of hamsters at the lower dose with a proportional decrease in the amount of radioactivity excreted into bile. The types and relative amounts of conjugated and nonconjugated metabolites of B[a]P were similar in bile of Sprague-Dawley rats and hamsters. Smaller amounts of glucuronides and larger amounts of sulfate conjugates were detected in bile of Gunn rats than in bile of Sprague-Dawley rats or hamsters. Metabolites in bile of guinea pigs were markedly different from those in the other species in that approximately 90% of the metabolites were thioether conjugates. Buthionine sulfoxime was used to reduce tissue levels of glutathione in Sprague-Dawley rats. When liver and lung glutathione levels were reduced to 30% and 82% of control levels, respectively, the amount of radioactivity excreted into bile was not significantly different from controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Importance of CYP1A1 and CYP1B1 in bioactivation of benzo[a]pyrene in human lung cell lines

Polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants classified as carcinogens in humans and rodents. The cytochromes P4501A1 and 1B1 have both shown capacity to carry out bioactivation of the prototype PAH, benzo[a]pyrene (B[a]P) to its ultimate carcinogenic B[a]P-diol-epoxide-I-1 form. The part played by each enzyme in human lung cells, however, has not been clarified. To get further insight into their individual role in the metabolic activation of B[a]P, RNA-interference was used to down-regulate CYP1A1 and/or CYP1B1 gene expression in the human lung cell lines BEP2D and NCIH2009. Fluorescence-HPLC analysis revealed that formation of B[a]P-tetrol-I-1 (hydrolyzed form of the corresponding diol-epoxide) was dependent primarily on CYP1A1. In cells without down-regulation of CYP1A1, the B[a]P-tetrol-I-1 was the major tested isomer formed. In contrast, the B[a]P-cis- and trans-7,8-dihydrodiol isomers were readily formed in cells expressing high levels of either CYP-gene. Simultaneous down-regulation of CYP1A1 and CYP1B1 mRNA resulted in low levels of metabolites overall. Residual unmetabolized B[a]P levels followed the expression of CYP1A1 in an inverse manner. In conclusion, these results indicate a major role of CYP1A1 in the bioactivation of B[a]P to carcinogenic B[a]P-diol-epoxides and in overall metabolism of B[a]P in human lung cell lines. In contrast, both CYP1A1 and CYP1B1 contribute significantly to the formation of the B[a]P-cis- and trans-7,8-dihydrodiol isomers.     

Sensitivity of Syrian golden hamster fetal lung cells to benzo[a]pyrene and other polycyclic hydrocarbons in vitro

Dose responses were compared of cultured fetal Syrian golden hamster lung cells (FSHL) to the toxic and transforming effects of benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), benz[a]anthracene (B[a]a) indeno[1,2,3-c,d]pyrene (I[c,d]P), benzo[k]fluoranthene (B[k]F) and benzo[e]pyrene (B[e]P). Effort was first given to standardising the techniques for evaluating B[e]P dose-responses. These polycyclic aromatic hydrocarbons (PAH) were then tested at concentrations of up to 1 μg/ml, and only B[a]P showed clear cytotoxicity. The transforming effects of B[b]F, B[a]A and I[c,d]P at 1 μg/ml appeared comparable to those of B[a]P at 0.05 μg/ml.     

Characteristics of [3H]fentanyl binding to the opiate receptor

The present study characterises the binding of the highly lipophilic opiate agonist [³H]fentanyl to homogenates of the rat central nervous system. At 25°C, association of [³H]fentanyl with its binding site was rapid ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 2.5}\text{min}$). Dissociation from the binding site was biphasic ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{'}\text{s}\text{= 4.0}\text{and}\text{100}\text{min}$) suggesting the existence of high and low affinity binding sites. Scatchard plots of saturation isotherms were curvilinear, confirming the presence of high (K_D = 0.46 nM) and low K_D = 4.26 nM) affinity binding sites. Increasing temperature and the concentration of sodium ion decreased the [³H]fentanyl binding. Opiate agonists, antagonists and mixed agonist-antagonists were all potent (IC₅₀'s < 20 nM) in displacing [³H]fentanyl and displacement by levorphanol and dextrorphan indicated that [³H]fentanyl binding was stereospecific. The μ and δ selective peptides, morphiceptin and [D-Ala²,D-Leu⁵]enkephalin, had IC₅₀ values of 87 and 9.2 nM respectively. The regional distribution of [³H]fentanyl binding was in the rank order striatum ? midbrain > hypothalamus > cortex > hippocampus > brainstem > spinal cord > cerebellum. Comparison of [³H]fentanyl, [³H]naloxone and [³H-d-Ala², d-Leu⁵]enkephalin binding in the hypothalamus-thalamus (μ-enriched) compared with the frontal cortex-striatum (δ-enriched) indicated that the pattern of [³H]fentanyl labelling was similar to that obtained with [³H]naloxone, but differed from that obtained with [³H-d-Ala²,d-Leu⁵]enkephalin. These characteristics suggest that [³H]fentanyl binds to the μ-opiate receptor. These findings are discussed in relation to the high lipid solubility of fentanyl as compared with morphine.     

Temperature-dependent disposition of [14C]benzo(a)pyrene in the spiny lobster, Panulirus argus

[¹⁴C]Benzo(a) pyrene (BP) (1 mg/kg) was administered by intracardiac injection to groups of spiny lobsters which were killed at various times up to 7 weeks after dosing. Tissues and fluids were evaluated for BP-derived radioactivity. Two studies were conducted in successive summer and winter seasons, when seawater temperatures throughout were 26.5 to 29.0 and 13.5 to 16.5°C, respectively. Highest concentrations of BP-derived radioactivity were found in the hepatopancreas, stomach, intestine, intestinal contents, and the green gland. After an initial distribution phase, the dose was lost from the lobsters in a log linear manner. The elimination half-lives for overall elimination of BP-derived radioactivity were 1.11 weeks in the warmer (summer) and 2.25 weeks in the colder (winter) water. Similarly, for individual organs, elimination was more rapid in the warmer water. For the hepatopancreas, green gland, intestine, and tail muscle, respective $\text{t}\text{1}\text{2}$ values (week) were 1.02, 1.26, 1.71, and 1.42 in the summer and 2.50, 1.50, 5.04, and 2.11 in the winter. There was no suggestion of tissue accumulation of BP-derived radioactivity. HPLC analysis of hepatopancreas samples showed that, in summer, unmetabolized BP concentrations fell rapidly, accounting for only 5% of the total label in the hepatopancreas by 3 days. The fall in unmetabolized BP was accompanied by approximately equal increases in the percentages of both polar metabolites and conjugates. Although the time curve for metabolism of BP in the hepatopancreas was not studied in winter, the metabolic capacity was such that, by 3 days after the dose, only 5% of the ¹⁴C present in hepatopancreas was unmetabolized BP. Thus, it appears that, for this dose of BP, the more rapid elimination of ¹⁴C in summer was due to a more rapid excretion of metabolites, and not to increased metabolism of BP.     

Drug protein conjugates—I. A study of the covalent binding of [14C]captopril to plasma proteins in the rat

The metabolism of [¹⁴C]captopril has been investigated in vitro and in vivo in male Wistar rats. The formation of conjugates of [¹⁴C]captopril with plasma proteins was observed both in vitro and in vivo: 180 min after intravenous infusion of [¹⁴C]captopril 35 ± 5% of total radioactivity was covalently bound to plasma proteins. The fate of [¹⁴C]captopril-plasma protein conjugates was investigated in vivo. [¹⁴C]Captopril was incubated in vitro with rat and human plasma and the resulting captopril-protein conjugates were infused into male rats. The plasma concentration of [¹⁴C]captopril-rat plasma protein conjugates declined monoexponentially with a half-life of 71.1 ± 2.2 min. After 180 min 28 ± 3% of the radioactivity was excreted in urine, largely as [¹⁴C]captopril-cysteine mixed disulphide (67%). Thus although captopril readily forms covalent bonds with plasma proteins the resulting conjugates dissociate in vivo. The toxicological implications of these findings are discussed.     

Quantitative microspectrofluorimetry study of the “blocking effect” of 6-aminochrysene on benzo[a]pyrene metabolism using single living cells

By microspectrofluorimetry on single living cells (murine fibroblasts 3T3), we have obtained monoexponential decreases of fluorescence intensity for benzo[a]pyrene (B[a]P) and 6-aminochrysene (6a-chrysene) metabolism. These kinetics are characteristics of B[a]P and 6a-chrysene metabolism and histograms can be drawn from the rate constants. We have studied the influence of 6a-chrysene on B[a]P metabolism. Using different methods of incubation, it has been observed that the presence of 6a-chrysene leads to modifications of the histogram profiles during B[a]P metabolism. Polycyclic aromatic hydrocarbons (PAH) are used to induce B[a]P metabolism. Whatever the experimental conditions we never detected such a phenomenon with 6a-chrysene. On the contrary we have observed an inhibition of B[a]P metabolism by 6a-chrysese, which can reach 80% of the aryl hydrocarbon hydroxylase (AHH) activity when 6a-chrysene remains constant in the cells. Compared with the results previously observed “in vitro” (which presented 50% mean inhibition) we show that inhibiyion acts in an all-or-nothing mechanism at the cellular level.     

Temperature-induced alterations in the metabolic activation of benzo[a]pyrene to DNA-binding metabolites in the Bluegill fry cell line BF-2

Many carcinogenic chemicals such as the environmental pollutant benzo[a]pyrene (B[a]P) require metabolic activation to reactive DNA-binding intermediates in order to induce cancer formation. To determine whether the temperature of incubation affects the proportion of B[a]P metabolized to DNA-binding metabolites as well as the amount of B[a]P metabolized, cultures of the Bluegill (Lepomis macrochirus) fry cell line BF-2 maintained at 23°C and 35°C were exposed to [³H]B[a]P. Exposure at 35°C resulted in an increase in the amount of B[a]P metabolized by 61% at 24 h compared with cultures incubated at 23°C. The amount of B[a]P-9,10-diol present in the medium was similar at both temperatures, but the amount of water-soluble metabolites was greater in the cultures maintained at 35°C. The amount of B[a]P bound to DNA in cultures exposed to B[a]P at 35°C was 97% greater at 24 h and 61% greater at 48 h than in cultures exposed at 23°C. The increase in the major B[a]P-deoxyribonucleoside adduct, (+)-anti-B[a]P-7,8-diol-9,10-epoxide (B[a]PDE; the isomer with the epoxide and benzylic hydroxyl on opposite faces of the molecule)-deoxyguanosine at 35°C, was 314% and 100% at 24 h and 48 h, respectively. There was no significant change in the amount of syn-B[a]PDE (the isomer with the epoxide and benzylic hydroxyl on the same face of the molecule)-deoxyguanosine. These results indicate that although the amount of B[a]P metabolized by BF-2 cell cultures is 60% greater at 35°C than at 23°C, the amount of B[a]P bound to DNA through the (+)-anti-B[a]PDE increased by more than 300%. Thus increased temperature can increase the proportion of B[a]P metabolized to an ultimate carcinogenic metabolite in BF-2 cells in culture.     

Uptake and displacement of [3H]dihydroalprenolol, [3H]epinephrine and [3H]clonidine in isolated perfused rabbit lung

Uptake and displacement of three adrenergic receptor ligands, [³H]dihydroalprenolol ([³H]DHA), [³h]epinephrine ([³H]EPI) and [³H]clonidine ([³H]CLON), were examined in isolated rabbit lungs by recirculating perfusion. Removal of [³h]DHA was the most extensive (85% uptake; 6.6 $\text{ml}\text{min}$ clearance), [³H]CLON removal was intermediate (50%; 3.8 $\text{ml}\text{min}$), and [³H]EPI removal was the lowest (33%; 1.2 $\text{ml}\text{min}$). Specific displacement of each radioligand from lung was attempted using several competing agents. Both (?)- and (+)-propranolol equally displaced [³H]DHA from lung. Phentolamine, (?)-phenylephrine and (?)-epinephrine were unable to displace 10 nM [³H]EPI from lung, although the latter two agents did produce concentration-dependent increases in perfusion pressure. High concentrations of (?)-epinephrine, which produced near maximal physiological responses, inconsistently displaced 30–40 nM [³H]EPI from lung. [³H]Clonidine was displaced by unlabeled clonidine at concentrations that caused increases in perfusion pressure. Pretreatment of lungs with either 10 μM phentolamine or phenoxybenzamine did not alter the total amount of [³H]CLON displaced by clonidine, suggesting that [³H]CLON was displaced predominantly from non-specific sites, perhaps preventing detection of [³H]CLON displacement from specific (receptor) sites. Alternatively, these results may be interpreted as inhibition of uptake of each radioligand. Thus, both (?)- and (+)-propranolol interfered with [³H]DHA removal, suggesting a common mechanism for uptake and/or retention for these two β-adrenergic receptor antagonists. Inhibition of ³H]EPI removal was observed only at high concentrations of (?)-epinephrine which indicates that pulmonary removal of epinephrine occurs through a low affinity uptake system. [³H] Clonidine removal was effectively inhibited by the same (μM) concentrations of unlabeled clonidine that produced physiological responses. Neither phentolamine nor phenoxybenzamine was able to interfere with pulmonary removal of [³H]CLON. Therefore, uptake and displacement of these adrenergic receptor radioligands showed no correlation with pharmacological effects produced by these agents in isolated perfused rabbit lung. The results are more closely associated with inhibition of removal and/or non-specific retention of the radioligands examined.     

Inflammatory mediators accelerate metabolism of benzo[a]pyrene in rat alveolar type II cells: The role of enhanced cytochrome P450 1B1 expression

Long-term deregulated inflammation represents one of the key factors contributing to lung cancer etiology. Previously, we have observed that tumor necrosis factor-α (TNF-α), a major pro-inflammatory cytokine, enhances genotoxicity of benzo[a]pyrene (B[a]P), a highly carcinogenic polycyclic aromatic hydrocarbon, in rat lung epithelial RLE-6TN cells, a model of alveolar type II cells. Therefore, we analyzed B[a]P metabolism in RLE-6TN cells under inflammatory conditions, simulated using either recombinant TNF-α, or a mixture of inflammatory mediators derived from activated alveolar macrophage cell line. Inflammatory conditions significantly accelerated BaP metabolism, as evidenced by decreased levels of both parent B[a]P and its metabolites. TNF-α altered production of the metabolites associated with dihydrodiol-epoxide and radical cation pathways of B[a]P metabolism, especially B[a]P-dihydrodiols, and B[a]P-diones. We then evaluated the role of cytochrome P450 1B1 (CYP1B1), which is strongly up-regulated in cells treated with B[a]P under inflammatory conditions, in the observed effects. The siRNA-mediated CYP1B1 knock-down increased levels of B[a]P and reduced formation of stable DNA adducts, thus confirming the essential role of CYP1B1 in B[a]P metabolism under inflammatory conditions. TNF-α also reduced expression of aldo-keto reductase 1C14, which may compete with CYP1B1 for B[a]P-7,8-dihydrodiol and divert it from the formation of ultimate B[a]P dihydrodiol epoxide. Together, the present data suggests that the CYP1B1-catalyzed metabolism of polycyclic aromatic hydrocarbons might contribute to their enhanced bioactivation and genotoxic effects under inflammatory conditions.     

Toxicity and DNA repair in normal human keratinocytes co-exposed to benzo[a]pyrene and sunlight

Skin has the potential to be exposed to both solar UV radiation and polycyclic aromatic hydrocarbons, especially in occupational environments. In the present work, we investigated how benzo[a]pyrene (B[a]P) modulates cellular phototoxicity and impacts formation and repair of pyrimidine dimers induced by simulated sunlight (SSL) in normal human keratinocytes (NHK). We were especially interested in determining whether the aryl hydrocarbon receptor (AhR) was involved since it was recently shown to negatively impact repair. Addition of 1 μM B[a]P after exposure to 2 minimal erythemal doses of SSL had little impact on NHK. The inverse protocol involving incubation with B[a]P followed by irradiation led to a strong increase in phototoxicity. Repair of DNA photoproducts was drastically impaired. Using agonists and antagonists of AhR allowed us to conclude that this factor was not involved in these results. Observation of a strong increase in the level of the oxidative marker 8-oxo-7,8-dihydroguanine in the protocol involving B[a]P treatment followed by exposure to SSL strongly suggested that a photosensitized oxidative stress was responsible for cell death and inhibition of DNA repair. Accordingly, both adverse effects were diminished with a lower concentration of B[a]P and a lower SSL dose, leading to less oxidative stress.     

Drug-protein conjugates-VII: Disposition of [3H]-Ethinylestradiol-protein conjugates in the rat

[³H]17α-Ethinylestradiol ([³H]EE₂; 5 μg/kg, 98.5 μCi) was administered to a female rat. After 18 hr less than 0.02% of the dose was present per ml plasma. Approximately 60% of radioactivity present in plasma was irreversibly bound to proteins, as determined by exhaustive solvent extraction and by high performance ion exchange chromatography of proteins after removal of unbound metabolites with activated charcoal. After chronic administration of [³H]EE₂ (5 μg/kg; 2 μCi per day) for 22 days, there was a three- to fourfold accumulation of radioactivity in the plasma, together with an accumulation of radioactivity in the lung, liver, kidney, spleen and brain, compared to animals receiving a single dose. The spleen showed the greatest ( >tenfold) significant (P < 0.001) accumulation of radioactivity. There was a greater increase in radioactivity irreversibly bound to the soluble fraction than to the microsomal fraction of the liver. [³H]EE₂ was conjugated to rat serum proteins by incubation with rat microsomes in vitro. Upon administration to female rats, the [³H]EE₂-rat serum protein conjugate had a small volume of distribution (12.5 ± 0.5 ml), and its plasma concentration declined slowly $\text{(}\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 450 ± 140}\text{min}\text{)}$. Immunization of male New Zealand White rabbits with a chemically synthesized conjugate of 2-hydroxyethinylestradiol (2-OH-EE₂) and human serum albumin produced antibodies which bound EE₂ and 2-OH-EE₂ but not estrone. These data indicate that although reactive metabolite formation represents a minor biotransformation, drug protein conjugates may accumulate during chronic administration.