Uptake and accumulation of pentachloronitrobenzene in pak choi and the human health risk

Nowadays, nanocarbon is widely employed to enwrap into fertilizers. However, the influence of nanocarbon on the transportation of contaminants from soil to plants and its mechanism remain unclear. In this study, pentachloronitrobenzene (PCNB), a typical organochlorine fungicide utilized all over the world, was chosen as the target contaminant to investigate the influence of nanocarbon on its transportation in soil-pak choi system. The maximum PCNB concentration in the root and leaf reached to 112 and 86 ng/g, respectively, demonstrating that PCNB would be absorbed by pak choi. The ratio of PCNB between leaf and root indicated that nanocarbon promoted root of pak choi to absorb PCNB. The transportation of PCNB inside plant was inhibited when pak choi was planted in soil containing higher concentration of nanocarbon. Human risk assessment showed that people consuming the pak choi in this study would not experience risk. However, in vitro toxicity test indicated that PCNB could directly impair intestinal epithelial cells (Caco-2 cells) and thus pose a potential risk to human intestine.

Poly(ethylene glycol)-b-poly(lysine) copolymer bearing nitroaromatics for hypoxia-sensitive drug delivery

Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, an amphiphilic block copolymer, composed of poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block, was prepared for hypoxia-sensitive drug delivery. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition, implying high potential as a drug carrier for cancer therapy.

STATEMENT OF SIGNIFICANCE

Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, we developed a novel type of hypoxia-sensitive polymeric micelles (HS-PMs) that can specifically release the drug under the hypoxic conditions. HS-PMs were prepared using poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition. Overall, it is evident that the HS-PMs prepared in this study have the potential to effectively deliver hydrophobic drugs into the hypoxic cells involved in various intractable diseases.

Molecular connectivity indices for predicting bioactivities of substituted nitrobenzene and aniline compounds

Bioconcentration and toxicity of 22 substituted nitrobenzene and aniline compounds to aquatic organisms were assessed with quantitative structure-activity relationship (QSAR). Acute toxicities of aquatic organisms, including daphnia (Daphnia pulex) and carp (Cyprinus carpio), to 22 chemicals have been determined in our previous work. In this study, the bioconcentration factors (BCFs) for carp were further investigated. By the use of multiple-regression analyses, the molecular connectivity indices (MCIs) can describe both acute toxicity and bioconcentration for the test organisms. Applicable QSAR model (0.856<r<0.932 for Eqs. (4)-(7)) can be obtained using only a two- or three-variable regression equation. Using training model for predicting the external dataset, the abilities to predict the acute toxicity on daphnia and carp were validated further. Thus, MCI models may be an accurate, simple, and rapid method for predicting the toxicity of new synthetic or modified substituted nitrobenzenes or anilines and for assessing the hazardous potential of chemicals on environments.

MRP isoforms and BCRP mediate sulfate conjugate efflux out of BeWo cells

The breast cancer resistance protein (BCRP) and the multidrug resistance-associated proteins (MRPs) have the ability to eliminate sulfate conjugates but it is not known if this constitutes one of their roles in the placenta. To determine this, the BeWo cell line was used as a model of placental trophoblast cells and the mechanisms of elimination of sulfate metabolites of two common sulfotransferase substrates, 4-nitrophenol and acetaminophen were examined. At 0.5-200 microM, neither 4-nitrophenyl sulfate nor acetaminophen sulfate affected the accumulation of the BCRP substrates BODIPY FL prazosin or mitoxantrone in BeWo monolayers, indicating a lack of interaction of BCRP with the sulfates. Examination of the effect of BCRP/MRP inhibitors on the efflux of intracellularly generated 4-nitrophenyl sulfate and acetaminophen sulfate, indicated that one or more of the MRP isoforms play a major role in the elimination of 4-nitrophenyl sulfate and acetaminophen sulfate across the basolateral (fetal-facing) and apical (maternal-facing) membranes respectively. BCRP played a minor role in the elimination of these two sulfate conjugates across the apical membrane. This study demonstrates that a yet undetermined role of trophoblast efflux transporters is the elimination of sulfate conjugates.

Permeation of tecnazene through human skin in vitro as assessed by HS-SPME and GC-MS

Permeation of tecnazene into and through human cadaver skin in vitro was assessed using a CC-MS method employing HS-SPME for receptor solution analyses. Two doses of tecnazene dissolved in acetone, corresponding to 103 and 864 microg/cm2 of tecnazene, were applied to skin mounted on Franz diffusion cells and placed in a fume hood. Cells were either occluded with aluminum foil or left unoccluded. Total absorption of tecnazene (dermis + receptor fluid) after 48 h was 2.2-6.1% of the applied dose for the unoccluded treatments and 22-33% for the occluded treatments. Potentially absorbed dose including all tecnazene that may have eventually permeated the skin ranged from 10% unoccluded to 42-53% occluded. Accumulation in the receptor solutions was satisfactorily described by a working diffusion model after upward adjustment of the partition coefficient for tecnazene in all skin layers by a factor of 5-16 versus a priori values. However, residual amounts of tecnazene in both the epidermis and dermis were higher than those estimated from the model, suggesting the existence of tissue binding not accounted for in the calculation. The results indicate that the diffusion model as presently calibrated may significantly underestimate both systemic absorption and skin concentrations of highly lipophilic compounds, as predicted from data generated from in vitro skin permeation assays. Model predictions could be improved by better accounting for partitioning into the epidermis and dermis.

Tissue distribution and elimination of N-methyl-N-2,4,6-tetranitroaniline (tetryl) in rats

The elimination of tetryl was studied using ring-labeled 14C-tetryl. Tetryl was given subcutaneously to male Sprague-Dawley rats at doses of 25, 100, and 300 mg kg(-1), and urine and feces were collected 24 h post-injection. Percent urinary elimination was observed to be 10.02 +/- 2.48, 11.2 +/- 1.66, and 13.24 +/- 5.79 (mean +/- SEM) respectively. Percent fecal elimination was 15.68 +/- 6.13, 9.41 +/- 1.52, and 8.45 +/- 1.81 respectively. At 24 h post-injection, tissues from male Sprague-Dawley rats were collected from animals that received 100 mg kg(-1) 14C-tetryl. Tetryl was found to be poorly absorbed with approximately 65% of the administered dose remaining at the site of subcutaneous injection. Blood was found to be the principal depot of radioactivity, followed by muscle, liver, and kidney. Analysis of the tissue to blood radioactivity ratio revealed that the liver had the highest ratio (1.2), followed by brain (0.45), kidney (0.38), and testes (0.35). All other tissues analyzed had ratios less than 0.30. Urine of animals receiving 14C-tetryl (100 mg kg(-1)) was analyzed using HPLC coupled with UV detection (200-600 nm; 1.2 nm resolution). During HPLC analysis, 1 min fractions were collected and radioactivity measured. Two major peaks of radioactivity were identified at approximately 5 and 14 min retention times, respectively. The 14 min peak had the same retention time and UV spectrum as picric acid and 5 min peak had the same retention time and UV profile as picramic acid. The data presented demonstrates that that there is little retention of tetryl in specific tissue depots and that tetryl is eliminated in roughly equal amounts in both urine and feces. The major urinary metabolites identified picric acid and picramic acid (a known urinary metabolite observed in rabbits). From microsomal fraction studies, a major metabolite, NMPA, was identified. The formation of this metabolite was found to be dependent on at least two enzymes. One enzyme is dependent on NAD+ for NMPA formation and is likely to be NADP(H):quinone oxidoreductase. The second metabolite is NADP+ dependent and is probably related to NADPH:cytochrome-P450 reductase.

Framework analysis for the carcinogenic mode of action of nitrobenzene

Nitrobenzene (CASRN: 98-95-3) has been shown to induce cancers in many tissues including kidney, liver, and thyroid, following chronic inhalation in animals. However, with a few exceptions, genotoxicity assays using nitrobenzene have given negative results. Some DNA binding/adduct studies have brought forth questionable results and, considering the available weight of evidence, it does not appear that nitrobenzene causes cancer via a genotoxic mode of action. Nitrobenzene produces a number of free radicals during its reductive metabolism, in the gut as well as at the cellular level, and generates superoxide anion as a by-product during oxidative melabolism. The reactive species generated during nitrobenzene metabolism are considered candidates for carcinogenicity. Furthermore, several lines of evidence suggest that nitrobenzene exerts its carcinogenicity through a non-DNA reactive (epigenetic) fashion, such as a strong temporal relationship between non-, pre-, and neoplastic lesions leading to carcinogenesis. In this report, we first describe the absorption, distribution, metabolism, and excretion of nitrobenzene followed by a summary of the available genotoxicity studies and the only available cancer bioassay. We subsequently refer to the mode of action framework of the U.S. Environmental Protection Agency's 2005 Guidelines for Carcinogen Risk Assessment as a basis for presenting possible modes of action for nitrobenzene-induced cancers of the liver, thyroid, and kidney, as supported by the available experimental data. The rationale(s) regarding human relevance of each mode of action is also presented. Finally, we hypothesize that the carcinogenic mode of action for nitrobenzene is multifactorial in nature and reflective of free radicals, inflammation, and/or altered methylation.

Reduction of nitrobenzene and formation of corrosion coatings in zerovalent iron systems

Batch tests were conducted to investigate reduction of nitrobenzene in a zerovalent iron system (Fe0) under various conditions. The results indicated that a limited amount of nitrobenzene (ArNO2) could be reduced to aniline by Fe0, but formation of a lepidocrocite (gamma-FeOOH) coating could significantly slow down the reaction. However, augmenting Fe0 with substoichiometric FeCl2 could dramatically accelerate the reaction. Surface-adsorbed Fe(II), not pH nor Cl-, was found to be responsible for rejuvenating the system. O2 and nitrobenzene could be concomitantly reduced by Fe0 in the presence of Fe2+. In the Fe0 system, both nitrobenzene and O2 favored formation of lepidocrocite; in the presence of aq. Fe(II), a stratified corrosion coating could develop, with magnetite (Fe3O4) as the inner layer and lepidocrocite as the outer layer. Fe2+ was not the main reductant for the reactions, but might accelerate the autoreduction of lepidocrocite to magnetite by the underlying Fe0. Our understanding on the role of Fe(II) in conjunction with a stratified, evolving corrosion coating may be useful for establishing an iron aquatic corrosion model.

Characterization of phenotypes in Gstm1-null mice by cytosolic and in vivo metabolic studies using 1,2-dichloro-4-nitrobenzene

Glutathione S-transferase Mu 1 (GSTM1) has been regarded as one of the key enzymes involved in phase II reactions in the liver, because of its high expression level. In this study, we generated mice with disrupted glutathione S-transferase Mu 1 gene (Gstm1-null mice) by gene targeting, and characterized the phenotypes by cytosolic and in vivo studies. The resulting Gstm1-null mice appeared to be normal and were fertile. Expression analyses for the Gstm1-null mice revealed a deletion of Gstm1 mRNA and a small decrease in glutathione S-transferase alpha 3 mRNA. In the enzymatic study, GST activities toward 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-2,4-dinitrobenzene (CDNB) in the liver and kidney cytosols were markedly lower in Gstm1-null mice than in the wild-type control. Gstm1-null mice had GST activities of only 6.1 to 21.0% of the wild-type control to DCNB and 26.0 to 78.6% of the wild-type control to CDNB. After a single oral administration of DCNB to Gstm1-null mice, the plasma concentration of DCNB showed larger AUC0-24 (5.1-5.3 times, versus the wild-type control) and higher Cmax (2.1-2.2 times, versus the wild-type control), with a correspondingly lower level of glutathione-related metabolite (AUC0-24, 9.4-17.9%; and Cmax, 9.7-15.6% of the wild-type control). In conclusion, Gstm1-null mice showed markedly low ability for glutathione conjugation to DCNB in the cytosol and in vivo and would be useful as a deficient model of GSTM1 for absorption, distribution, metabolism, and excretion/toxicology studies.

Transport of fluorescent chenodeoxycholic acid via the human organic anion transporters OATP1B1 and OATP1B3

This study sought to clarify the contributions of organic anion-transporting polypeptide (OATP) 1B1 and 1B3 to the liver uptake of chenodeoxycholic acid (CDCA). We synthesized a fluorescent version of CDCA, chenodeoxychilyl-(Nepsilon-NBD)-lysine (CDCA-NBD), to characterize transporter-mediated uptake. CDCA-NBD is efficiently transported by OATP1B1 and OATP1B3 with high affinities. The Michaelis-Menten constants for CDCA-NBD uptake by OATP1B1 and OATP1B3 were 1.45 +/- 0.39 microM and 0.54 +/- 0.09 microM, respectively. By confocal laser scanning microscopy, CDCA-NBD, which is taken up by OATP1B1 and OATP1B3, was observed to localize to the cytosol. We also examined the transport of newly synthesized fluorescent bile acids. NBD-labeled bile acids, including cholic acid, deoxycholic acid, lithocholic acid, and ursodeoxycholic acid, were all transported by OATP1B1 and OATP1B3. CDCA-NBD exhibited the highest rate of transport of the five NBD-labeled bile acids examined in OATP1B1- and OATP1B3-expressing cells. Our results suggest that OATP1B1 and OATP1B3 play important roles in CDCA uptake into the liver. Fluorescent bile acids are useful tools to characterize the uptake properties of membrane transporters.

Microbial reductive transformation of pentachloronitrobenzene under methanogenic conditions

The reductive transformation of pentachloronitrobenzene (PCNB), an organochlorine fungicide, was investigated with a mixed, methanogenic culture developed from a contaminated estuarine sediment. Batch assays performed with this enrichment culture resulted in the biotransformation of PCNB to pentachloroaniline (PCA), which was then sequentially dechlorinated as follows: PCA --> 2,3,4,5- and 2,3,5,6-tetrachloroaniline (TeCA) --> 2,4,5- and 2,3,5-trichloroaniline (TrCA) --> 2,4-, 2,5-, and 3,5-dichloroaniline (DCA) --> 3- and 4-chloroaniline (CA) (low levels). Glucose fermentation, methanogenesis, and dechlorination were not inhibited at an initial PCNB concentration up to 40 microM, which is 27 times higher than its aqueous solubility. The addition of 25 mM 2-bromoethanesulfonate (BES) to the PCNB-amended culture resulted in the complete inhibition of methanogenesis, but the biotransformation of PCNB to PCA and its sequential dechlorination pathway were not affected. The addition of sodium azide (200 mg/L) to the PCNB-amended culture resulted in complete inhibition of methanogenesis, but did not inhibit the transformation of PCNB to PCA; however, PCA dechlorination was not observed. PCNB was also abiotically transformed to PCA in autoclaved culture media but at much lower rates as compared to the biotic assays. In contrast, the rate of PCNB to PCA transformation in autoclaved culture controls was similar to the rates observed in the azide-amended culture and the active enrichment culture, indicating that biotically derived reductants facilitated the observed transformation of PCNB to PCA. Dechlorination of PCA was not observed in any of the abiotic controls. These findings have significant environmental implications in terms of the fate and transport of PCNB, PCA, and its dechlorination products in subsurface systems.

[Metabolic kinetics of MN9202 in Beagle dog liver microsomes]

AIM

To study the metabolic kinetics of MN9202 in Beagle dog liver microsome.

METHODS

Beagle dog liver microsomes were prepared by using ultracentrifuge method. After incubating 0.4 micromol x L(-1) MN9202 with 1 g x L(-1) microsomes for 30 min at 37 degrees C, the reaction was terminated by adding 0.5 mL alkalization. The RP-HPLC was used to determine the drug in the incubation mixture. The Michaelis-Menten parameters Km, and Vmax in Beagle dog liver microsomes were initially estimated by analyzing Lineweave-Brurk plot. Various selective CYP inhibitors were used to investigate their inhibitory effect on the metabolism of MN9202.

RESULTS

The Km, Vmax and CLint of MN9202 were (22.6 +/- 8.0) micromol x L(-1), (0.54 +/- 0.17) micromol x g(-1) x min(-1) and (0.0242 +/- 0.0009) L x g(-1) x min(-1), respectively. The metabolism of MN9202 was significantly inhibited by ketoconazole (Ket) and troleandomycin (Tro) in Beagle dog liver microsomes. Tranylcypromine (Tra) could inhibit the metabolism of drug as well. While other inhibitors showed little inhibitory effect on the metabolism of MN9202.

CONCLUSION

It was shown that CYP3A and CYP2C19 were involved in MN9202 metabolism. The inhibitors of human CYP3A and CYP2C19 may have potential interaction with MN9202, and this can reduce the metabolism rate and increase the toxicity of MN9202.

Expression of the theta class GST isozyme, YdfYdf, in low GST dogs

We have reported the existence of low glutathione S-transferase (GST) dogs whose GST activity to 1,2-dichloro-4-nitrobenzene (DCNB) as a substrate (GST-D activity) is quite low, and have also reported significant individual differences in dog liver GST-D activity. The dogs were classified as "low", "middle", or "high" GST dogs based on their GST-D activity. In the present study, in order to investigate the causes of quite low GST-D activity in low GST dogs and the individual differences in dog GST-D activity, glutathione (GSH) conjugation of DCNB was kinetically analyzed. Moreover, liver cytosolic proteins whose expression levels were significantly lower in low GST dogs than in high GST dogs were identified by two-dimensional difference gel electrophoresis (2D-DIGE) and LC tandem mass spectrometry (LC/MS/MS). Interestingly, Vmax values for this reaction well reflected their GST-D activities in all groups, i.e. they were 3.8, 80.6, and 169.2 nmol/min/mg protein in the low, middle, and high GST dogs, respectively. However, Km values were almost the same (260.0-283.7 microM) among these groups. These suggest that GSH conjugation of DCNB should be catalyzed by the same enzyme in all the dogs, and individual differences in the GST-D activity should be the result of individual differences in the expression level of the GST isozyme, which catalyzes conjugation of DCNB. In 2D-DIGE, the expression levels of the two protein spots were significantly lower in the low GST dogs than in the high GST dogs. Positive good correlation (r > 0.800) was observed between GST-D activity and expression levels of these two protein spots. Moreover, expression levels were quite low in low GST dogs. These two proteins were both identified as the theta class GST isozyme, YdfYdf, which specifically catalyzes GSH conjugation of DCNB in dog livers. In the present study, we present two novel findings based on an enzyme kinetic study and protein-expression analysis: (1) GSTYdfYdf is expressed at quite a low level in the liver of low GST dogs, and (2) individual differences in dog liver GST-D activity would be due to individual differences in the expression level of GSTYdfYdf. Considering these findings, low GST dogs might have high susceptibility, including an unexpected toxicity at abnormal exposure to chemicals metabolized by GSTYdfYdf.

Degradation of aromatic compounds in plants grown under aseptic conditions

The aim of the work is to investigate the ability of higher plants to absorb and detoxify environmental pollutants - aromatic compounds via aromatic ring cleavage. Transformation of 14C specifically labelled benzene derivatives, [1-6-14C]-nitrobenzene, [1-6-(14)C]-aniline, [1-(14)C]- and [7-(14)C]-benzoic acid, in axenic seedlings of maize (Zea mays L.), kidney bean (Phaseolus vulgaris L.), pea (Pisum sativum L.) and pumpkin (Cucurbita pepo L.) were studied. After penetration in plants, the above xenobiotics are transformed by oxidative or reductive reactions, conjugation with cell endogenous compounds, and binding to biopolymers. The initial stage of oxidative degradation consists in hydroxylation reactions. The aromatic ring can then be cleaved and degraded into organic acids of the Krebs cycle. Ring cleavage is accompanied by 14CO2 evolution. Aromatic ring cleavage in plants has thus been demonstrated for different xenobiotics carrying different substitutions on their benzene ring. Conjugation with low molecular peptides is the main pathway of aromatic xenobiotics detoxification. Peptide conjugates are formed both by the initial xenobiotics (except nitrobenzene) and by intermediate transformation products. The chemical nature of the radioactive fragment and the amino acid composition of peptides participating in conjugation were identified.

Low glutathione S -transferase dogs

Liver and kidney glutathione S-transferase (GST) activities to 1,2-dichloro-4-nitrobenzene (DCNB) as a substrate (GST-D activities) were measured in 280 dogs from five different breeders, and significant individual differences in this activity were observed in both organs. Interestingly, 34 out of the 280 dogs (i.e. 12.1%) were those in which liver GST-D activities were less than 10 nmol/min per mg cytosolic protein, "low GST dogs", and the other dogs were classified as "middle" and "high" GST dogs for which the liver GST-D activities were 10-80 and >80 nmol/min per mg protein, respectively, and occurred at similar percentages (41.4% for the middle GST dog and 46.4% for the high GST dog). Furthermore, the existence of the low GST dogs was not limited to one particular breeder. There was a good correlation (r=0.910) between the liver and kidney GST-D activities, showing low activity in not only the liver but also the kidney in the low GST dogs. Although liver GST activity to 1-chloro-2,4-dinitrobenzene as a substrate (GST-C activity), catalyzed by various GST isozymes in dogs, was significantly correlated with liver GST-D activity, GST-C activity showed more than 450 nmol/min per mg protein even in the low GST dogs. There was no significant difference in cytochrome P450 content, 7-ethoxycoumarin O-deethylase activity or UDP-glucuronosyltransferase activity to p-nitrophenol as a substrate between low GST dogs and the other dogs. Finally, remarkably high plasma concentrations of DCNB were observed in the low GST dogs after single doses of DCNB at 5 or 100 mg/kg. The individual differences in GST-D activity are probably attributable to the content and/or activity of the theta class GST isozyme Yd(f)Yd(f) since it has been reported that glutathione conjugation of DCNB is specifically catalyzed by GSTYd(f)Yd(f) in dogs. In conclusion, we identified a number of low GST dogs in which the GST-D activities were not observed either in vivo or in vitro. The feasibility of using a single low dose of DCNB to phenotype dogs based on GST-D activity was confirmed. It was also suggested that low GST dogs have high susceptibility, including unexpected toxicity or abnormal exposure, to chemicals metabolized by GSTYd(f)Yd(f).

Percutaneous absorption of explosives and related compounds: an empirical model of bioavailability of organic nitro compounds from soil

The percutaneous absorption potentials of (14)C-labeled 2,4,6-trinitrotoluene (TNT), trinitrobenzene, 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene, 2,6-diamino-4-nitrotoluene, N-methyl-N,2,4,6-tetranitrobenzamine, hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and 2,2-thiobis(ethanol) were determined from two soil types, Yolo having 1.9% carbon and Tinker having 9.5% carbon. TNT skin absorption from another low-carbon soil (Umatilla) was also determined. Approximately 10 microg/cm(2) of radiolabeled compound was applied in 5 microl of acetone or 10 mg/cm(2) of soil to excised pigskin mounted in skin penetration-evaporation chambers. Absorption from acetone served as a control. Radiolabel recovered from the dermis and tissue culture media (receptor fluid) was summed to determine the percentage of absorption from the soils. For each compound, percentage absorptions of radiolabel were highest from acetone solution and lowest from Tinker soil, with the results from Yolo soil being intermediate. Skin absorptions of TNT from Yolo and Umatilla soils were similar. For TNT in all vehicles, the penetration rate of radiolabel into the receptor fluid was highest during the 1- to 2-h interval after dosing. HPLC analysis of TNT radiolabel in receptor fluid at maximum flux indicated extensive conversion to monoamino derivatives and other metabolites. For 2,4-DNT and 2,6-DNT applications in Yolo soil, percentage absorptions approached those obtained from acetone applications. After 2,4-DNT and 2,6-DNT applications (acetone and soils), HPLC analysis of radiolabel in receptor fluid during the period of maximum flux revealed no significant metabolites. Skin absorption of the nitro compounds from soils was found to correlate with the compound's water solubility and vapor pressure. These findings formed the basis of an empirical model to predict skin bioavailability.

The mercapturic acid biotransformation pathway of hexachlorobenzene is not involved in the induction of splenomegaly, or skin and lung lesions in the Brown Norway rat

Involvement of the mercapturic acid pathway in the induction of splenomegaly and skin and lung pathology by hexachlorobenzene (HCB) in the rat was investigated by seeking to determine whether pentachloronitrobenzene (PCNB) has the same inflammatory effects as HCB, since both compounds are directly conjugated to glutathione, and further processed into the same mercapturic acid metabolites which are excreted via the urine. Female Brown Norway (BN/SsNO1aHsd) rats at 3 to 4 weeks of age were orally exposed to diets with or without supplementation with 450 mg HCB or equimolar (467 mg) or higher (934 mg) amounts of PCNB per kilogram of diet over 4 weeks. Gross skin lesion development and body weight gains were assessed during exposure and spleen and liver weights as well as histopathologic changes in skin and lung were assessed after exposure. After 3 weeks of exposure, urinary metabolites of the mercapturic acid and oxidative biotransformation pathways were identified using high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). Oral exposure of the rats to 450 mg/kg HCB resulted in an increase in relative spleen and liver weights as well as in the development of skin and lung pathology in the absence of overall liver toxicity. Equimolar or higher concentrations of PCNB caused none of these effects. Urinary levels of the mercapturic acid N-acetyl-S-(pentachlorophenyl)-cysteine (PCP-NAC), were comparable in HCB- and PCNB-treated rats. Levels of closely related methylsulfide derivatives of PCP-NAC, also generated via the same mercapturic acid pathway, appeared to be significantly higher in PCNB- than in HCB-treated rats, whereas the reverse was true for the urinary levels of the oxidative metabolite pentachlorophenol (PCP). Thus, results indicate that metabolites of the mercapturic acid pathway are not involved in the induction of splenomegaly and skin and lung pathology caused by HCB exposure in BN rats and that the main urinary metabolite of HCB in these BN rats is PCP. Since PCP itself, as well as other cytochrome P450-derived metabolites from HCB, are not likely to be involved in the induction of splenomegaly and skin and lung pathology, it is suggested that either the parent compound HCB or as-yet-unidentified non-P450-generated metabolites are involved in these inflammatory effects of HCB.

Taxonomic distribution of plant glutathione S-transferases acting on xenobiotics

Soluble and microsomal glutathione S-transferase activities for five model xenobiotics (nitrobenzene derivatives), two pesticidal xenobiotics (atrazine and fluorodifen), and a natural substrate (cinnamic acid), were determined in 59 different plant species and four plant cell suspension cultures. These enzyme activities were widely distributed over the plant kingdom with certain species showing particularly high activities. Marine macroalgae had a remarkably broad substrate range that included the substrates atrazine and fluorodifen. It is concluded that the evolutionary 'green liver' concept derived for xenobiotic metabolism in higher plant species is also valid for the constitutive soluble and microsomal glutathione S-transferases of lower plant species.

Structural changes of the sarcoplasmic reticulum Ca(2+)-ATPase upon nucleotide binding studied by fourier transform infrared spectroscopy

Changes in the vibrational spectrum of the sarcoplasmic reticulum Ca(2+)-ATPase upon nucleotide binding were recorded in H(2)O and (2)H(2)O at -7 degrees C and pH 7.0. The reaction cycle was triggered by the photochemical release of nucleotides (ATP, ADP, and AMP-PNP) from a biologically inactive precursor (caged ATP, P(3)-1-(2-nitrophenyl) adenosine 5'-triphosphate, and related caged compounds). Infrared absorbance changes due to ATP release and two steps of the Ca(2+)-ATPase reaction cycle, ATP binding and phosphorylation, were followed in real time. Under the conditions used in our experiments, the rate of ATP binding was limited by the rate of ATP release (k(app) congruent with 3 s(-1) in H(2)O and k(app) congruent with 7 s(-1) in (2)H(2)O). Bands in the amide I and II regions of the infrared spectrum show that the conformation of the Ca(2+)-ATPase changes upon nucleotide binding. The observation of bands in the amide I region can be assigned to perturbations of alpha-helical and beta-sheet structures. According to similar band profiles in the nucleotide binding spectra, ATP, AMP-PNP, and ADP induce similar conformational changes. However, subtle differences between ATP and AMP-PNP are observed; these are most likely due to the protonation state of the gamma-phosphate group. Differences between the ATP and ADP binding spectra indicate the significance of the gamma-phosphate group in the interactions between the Ca(2+)-ATPase and the nucleotide. Nucleotide binding affects Asp or Glu residues, and bands characteristic of their protonated side chains are observed at 1716 cm(-1) (H(2)O) and 1706 cm(-1) ((2)H(2)O) and seem to depend on the charge of the phosphate groups. Bands at 1516 cm(-1) (H(2)O) and 1514 cm(-1) ((2)H(2)O) are tentatively assigned to a protonated Tyr residue affected by nucleotide binding. Possible changes in Arg, Trp, and Lys absorption and in the nucleoside are discussed. The spectra are compared with those of nucleotide binding to arginine kinase, creatine kinase, and H-ras P21.

Synthesis of caged peptides using caged lysine: application to the synthesis of caged AIP, a highly specific inhibitor of calmodulin-dependent protein kinase II

N(alpha)-Fmoc-N(epsilon)-(2-nitrobenzyloxycarbonyl)-lysine has been prepared and used in the solid-phase synthesis of caged peptides. The synthesized caged AIP (cagedKcagedKALRRQEAVDAL) showed characteristics required for caged peptides including a significantly reduced inhibitory activity to calmodulin-dependent protein kinase II and instantaneous recovery of the activity with photo-irradiation.

DT-diaphorase catalyzes N-denitration and redox cycling of tetryl

Rat liver DT-diaphorase (EC 1.6.99.2) catalyzed reductive N-denitration of tetryl (2,4,6-tri-nitrophenyl-N-methylnitramine) and 2,4-dinitrophenyl-N-methylnitramine, oxidizing the excess of NADPH. The reactions were accompanied by oxygen consumption and superoxide dismutase-sensitive reduction of added cytochrome c and reductive release of Fe2+ from ferritin. Quantitatively, the reactions of DT-diaphorase proceeded like single-electron reductive N-denitration of tetryl by ferredoxin:NADP+ reductase (EC 1.18.1.2) (Shah, M.M. and Spain, J.C. (1996) Biochem. Biophys. Res. Commun. 220, 563-568), which was additionally checked up in this work. Thus, although reductive N-denitration of nitrophenyl-N-nitramines is a net two-electron (hydride) transfer process, DT-diaphorase catalyzed the reaction in a single-electron way. These data point out the possibility of single-electron transfer steps during obligatory two-electron (hydride) reduction of quinones and nitroaromatics by DT-diaphorase.

Intermediary metabolism of pentachloronitrobenzene in the control and germ-free rat and rat with cannulated bile ducts

1. Nearly 70% of single oral doses of 14C-labelled pentachloronitrobenzene (PCNB) was excreted in bile within 24 h. 2. The characterized biliary metabolites of PCNB were either mercapturic acid pathway metabolites or catabolites thereof (thiols, methylthiols, S-glucuronides). 3. A major biliary metabolite was S-(aminotetrachlorophenyl)glutathione. 4. Conjugation with glutathione with subsequent catabolism to bis-methylthiotetrachlorobenzene was the major pathway in the control rat. 5. Germ-free experiments showed that only nitro- group displacement occurred, and no nitro- group reduction was detected.

[The protective action of tocopherol acetate in simultaneous administration with nitrobenzene and its chloro derivatives]

In experiments in albino rats, effects were studied of nitrobenzene and its chloro derivatives in intragastric administration with tocoferolum acetatum. Changes in the process of lipid peroxidation in blood serum, liver, and spleen which were characteristic of xenobiotics themselves have been shown to be less pronounced in this setting. Tocoferolum acetatum being administered at the same time is actively drawn into the metabolism. Normalization of the antioxidant activity of the tissues under investigation was to be observed, with lipid peroxidation and the antioxidant system being in equilibrium. Tocoferolum acetatum administered with xenobiotics has been shown to have a protective action. Tocoferolum acetatum is recommended to be included into diets for workers engaged in chemical industry on a prophylactic basis.

Comparison of CoMFA models for Salmonella typhimurium TA98, TA100, TA98 + S9 and TA100 + S9 mutagenicity of nitroaromatics

Comparative Molecular Field Analysis (CoMFA) was applied to a comprehensive data set of heterogeneous nitroaromatics tested in Salmonella typhimurium TA98 and TA100 with and without S9 microsomal activation. The four CoMFA models developed agree with postulated mechanisms of mutagenicity, and explain over 70% of the corresponding mutagenic variance The standard deviation coefficient contours common in the four models included high electronic density regions equivalent to C4-C5 in the pyrene ring, and an electron deficient site equivalent to C6. These areas are associated with high mutagenicity. Electron deficient areas may be related with the nitroreductive bioactivation of nitroaromatics. Electron rich sites may be involved with oxidative mechanisms analogous to the bioactivation pathway of polycyclic aromatic hydrocarbons. The contribution of steric factors to mutagenicity follows the order TA98 + S9 > TA98 > TA100 + S9 > TA100. The models indicated that increasing bulk perpendicular to the aromatic plane would decrease mutagenicity, but increasing the aromatic ring system along a region corresponding to C6-C7 in 1-nitropyrene would increase mutagenicity.

Hepatic uptake of p-nitrophenyl sulfate by transporter that acetaminophen sulfate shares for uptake: sulfate moiety as a vector for metabolite transport

Hepatic uptake of the sulfate conjugate of p-nitrophenol (p-NPsul) has been studied. Uptake clearance of p-NPsul by isolated rat hepatocytes was dependent on p-NPsul concentration, suggesting carrier-mediated transport. The uptake of p-NPsul by isolated rat hepatocytes was inhibited by acetaminophen sulfate (APAPsul), the uptake of which had been previously reported to be inhibited by p-NPsul. The hepatic uptake of p-NPsul was also inhibited by bromosulfophthalein (BSP) or dibromosulfophthalein (DBSP), which had been reported to inhibit hepatic uptake of APAPsul in the previous study. These inhibitory effects were observed in isolated perfused liver experiments as well as in isolated hepatocyte experiments. Therefore, it was concluded that hepatic uptake of p-NPsul was mediated by a transporter, which mediates hepatic uptake of APAPsul as well as BSP or DBSP. It is suggested that sulfate moiety may have a key role as a vector for the hepatic transport of sulfate conjugate metabolites. Interaction between sulfate conjugate metabolites in hepatic uptake may also be expected.

Structure-activity relationships for the glutathione conjugation of 2-substituted 1-chloro-4-nitrobenzenes by rat glutathione S-transferase 4-4

In the present study structure--activity relationships (SAR's) are described for the experimentally determined kinetic parameters (Km, kappa cat, and kappa cat/Km) of the GST 4-4-catalyzed reaction between GSH and 10 2-substituted 1-chloro-4-nitrobenzenes. Steric, lipophilic, and electronic parameters were correlated with the kinetic parameters. Moreover, charge distributions and several energy values were calculated for the substrates and the corresponding Meisenheimer intermediates with MeS- as a model nucleophile for the thiolate anion of GSH and used in the regression analyses. The correlations obtained were compared with the corresponding SAR's for the base-catalyzed GSH conjugation reaction at pH 9.2. A high correlation coefficient was found between the kinetic parameter kappa s for the base-catalyzed reaction and the Hammett substituent constant (sigma p). Much lower correlation coefficients were obtained with kappa cat and sigma p and with kappa cat/Km and sigma p. Moreover, the reaction constant rho was significantly higher for the base-catalyzed than for the enzyme-catalyzed reaction. Also, high correlations were found between the kinetic parameters and the charges on the p-nitro substituent in the substrates. When kappa s was plotted against these charges, a linear relationship was found in which the slope was larger than the slope of a corresponding plot with kappa cat/Km. The Hammett sigma p can be divided into an inductive (F) and a resonance (R) component. With multiple regression between the kinetic parameters and F and R, higher correlation coefficients were obtained than with sigma p alone. Our observations suggest that the transition states for the base-catalyzed and the GST 4-4-catalyzed GSH conjugation reaction are different. Moreover, single classical physiochemical and computer-calculated molecular parameters and combinations of them can be an alternative approach for examining SAR's for spontaneous and GST-catalyzed GSH conjugation reactions.

Metabolism of 2,3,5,6-tetrachloronitrobenzene (tecnazene) in rat

1. The metabolic fate of [U-14C]-2,3,5,6-tetrachloronitrobenzene (tecnazene) has been determined in the male and female rat following a single dose of 1 mg/kg and in surgically prepared, bile-duct-cannulated rats following a single oral dose of 135 mg/kg. 2. Radioactivity in the female rat was excreted mainly in urine (82%). The male rat, however, excreted approximately equal amounts of radioactivity in urine and faeces (the latter via bile). 3. The principal metabolic pathway was conjugation with glutathione (GSH) and concomitant nitro-displacement. The GSH-conjugate and related metabolites were excreted in the bile and ultimately in the urine as the mercapturic acid conjugate. The cysteine conjugate underwent beta-lyase-mediated metabolism to yield a thiol that underwent subsequent methylation to the thioanisole followed by S-oxidation. 4. A novel tetrachloromethyldisulphide metabolite was also formed.

Different metabolic pathways of 2,5-difluoronitrobenzene and 2,5-difluoroaminobenzene compared to molecular orbital substrate characteristics

The in vivo metabolite patterns of 2,5-difluoroaminobenzene and of its nitrobenzene analogue, 2,5-difluoronitrobenzene, were determined using 19F NMR analysis of urine samples. Results obtained demonstrate significant differences between the biotransformation patterns of these two analogues. For the aminobenzene, cytochrome P450 catalysed aromatic hydroxylation presents the main metabolic pathway. 2,5-Difluoronitrobenzene was predominantly metabolised through glutathione conjugation leading to excretion of 5-fluoro-2-(N-acetylcysteinyl)-nitrobenzene and fluoride anions, and, to a minor extent, through cytochrome P450 catalysed hydroxylation and nitroreduction. Pretreatment of the rats with various inducers of cytochrome P450 enzymes, known also to influence glutathione S-transferase enzyme patterns, followed by exposure to the 2,5-difluoroamino- or 2,5-difluoronitrobenzene, generally resulted in metabolite patterns that varied only to a small (< or = 12%) extent. Based on these results it was concluded that the biotransformation enzyme pattern is not the predominant factor in determining the metabolic route of these two model compounds. Additional in vitro microsomal and cytosolic incubations with 2,5-difluoroaminobenzene and 2,5-difluoronitrobenzene qualitatively confirmed the in vivo results. NADPH/oxygen supported microsomal cytochrome P450 catalysed hydroxylation was observed only for 2,5-difluoroaminobenzene whereas cytosolic GSH conjugation occurred only in incubations with 2,5-difluoronitrobenzene as the substrate. Outcomes from molecular orbital calculations provided a working hypothesis that can explain the difference in metabolic pathways of the nitro- and aminobenzene derivative on the basis of their chemical characteristics. This hypothesis states that the chances for a nitro- or aminobenzene derivative to enter either a cytochrome P450 or a glutathione conjugation pathway are determined by the relative energy levels of the frontier orbitals of the compounds. The aminobenzene derivative has relatively high energy molecular orbitals leading to an efficient reaction of its highest occupied molecular orbital (HOMO) with the singly occupied molecular orbital of the cytochrome P450 (FeO)3+ intermediate, but a low reactivity of its lowest unoccupied molecular orbital (LUMO) with the HOMO of glutathione. The nitrobenzene, on the other hand, has molecular orbitals of relatively low energy, explaining the efficient interaction, and, thus, reaction between its LUMO and the HOMO electrons of glutathione, but resulting in low reactivity with the SOMO electron of the cytochrome P450 (FeO)3+ reaction intermediate.

[Accident in the Hoechst AG company 22 February 1993. 2. Public health evaluation]

A major chemical accident occurred on 22 February 1993 at plant Griesheim of Hoechst AG Frankfurt/Germany during which approximately 11.8 tons of a chemical mixture containing mostly chlorinated nitroarenes were emitted leading to serious contaminations in Schwanheim/Goldheim, a nearby housing area. Numerous inhabitants of the contaminated area complained of irritation of eyes, skin and mucous membranes, headache and nausea, and 92 persons with moderate symptoms were reported to the National Health Department. Urine samples were collected from the inhabitants of the affected area a few days after the accident and analysed for o-nitrophenol as a representative metabolite to assess the actual uptake of pollutants. O-nitrophenol, however, was also detected in the urine of not knowingly exposed control subjects, an observation not hitherto described in literature. The median levels of o-nitrophenol were three times higher in the exposed population than in the controls. Taking into account the data on pollution measured in the environment, the reported intoxication symptoms, the results of biomonitoring, and the published literature on the components of the mixture, the following conclusions were drawn: (1) The exposure was not high enough to cause severe acute toxic effects. (2) Although the emitted mixture contained carcinogenic components according to animal experiments, the transient exposure to these chemicals does not increase the tumour risk to any measurable extent, i.e. demonstrable by epidemiological methods, especially if weighed against the permanent exposure to "normal" urban pollution.

Toxicity of monocyclic and polycyclic nitroaromatic compounds in a panel of mammalian test cell lines

The cytotoxicity of polycyclic and monocyclic nitroarenes was tested in cell lines V79/NH, H4IIEC3/G-, 5L and BWI-J, which are distinguished by their specific expression of xenobiotic metabolizing enzymes. The results show that polycyclic nitroarenes differentially affect the test cell lines suggesting that some compounds, such as 1,3-dinitropyrene, are activated by cytochrome P4501A1, others, such as 1,6-dinitropyrene, by reductase(s) and acetyltransferase. No such cell specific responses were seen for 13 monocyclic nitroarenes tested. This group of chemicals apparently is activated by an enzyme(s) other than the polycyclic nitroarenes tested.

Improved oral absorption of enteric coprecipitates of a poorly soluble drug

An anticancer agent, N-[[[4-(5-bromo-2-pyrimidinyloxy)-3-chlorophenyl]amino]carbonyl]-2 - nitrobenzamide (HO-221, 1), shows poor oral absorption and is only slightly soluble in water (0.055 microgram/mL at 37 degrees C). The coprecipitates with polyvinylpyrrolidone or a vinylpyrrolidone and vinylacetate copolymer (copolyvidone) showed a marked increase of the dissolution rate and attainment of temporary supersaturation of 1. The oral bioavailability of these preparations in dogs at a dose of 1 of 5 mg/kg was approximately 60%, which was 3.5 times greater than that of a micronized preparation. Further, the enteric coprecipitate with hydroxypropyl methylcellulose phthalate 200731, which showed a dissolution profile similar to that of the copolyvidone preparation at pH 6.5 but no dissolution at pH 1.2, revealed the almost complete oral absorption. Because intraduodenal administration of the copolyvidone coprecipitate showed a higher absorption than that of per oral administration, it was suggested that the partial precipitation of crystallites in the nonenteric coprecipitates occurred before reaching the absorption site, the small intestine.

Pharmacokinetic study of p-chloronitrobenzene in rat

The pharmacokinetics of p-chloronitrobenzene (p-CNB) was evaluated in rats to propose an index for monitoring p-CNB exposure of humans exposed to it. After a single dose of 30, 100, or 333 mg/kg body weight, p-CNB was administered intraperitoneally to male Sprague-Dawley rats; blood and urine were collected periodically. p-CNB in plasma and its five major metabolites--2-chloro-5-nitrophenol, N-acetyl-S-(4-nitrophenyl)-L-cysteine,2,4-dichloroaniline,p-chloroanilin e, and 2-amino-5-chlorophenol--in urine were measured by reversed-phase HPLC methods. Pharmacokinetics was evaluated by moment analysis and compartment model analysis of the p-CNB concentration in plasma vs. time curves and of the urinary excretion rate of its metabolites vs. time curves. Urinary excretion was considered to be the most important pathway for disappearance of p-CNB, because the fraction of p-CNB metabolites excreted in urine was ca.2/3 of the dose level. N-Acetyl-S-(4-nitrophenyl)-L-cysteine was the most abundant urinary metabolite of p-CNB and comprised ca.1/2 of the total amount of the five metabolites excreted into the urine. The urinary excretion of N-acetyl-S-(4-nitrophenyl)-L-cysteine was considered to be proportional to the dose of p-CNB over a wide range of doses, because the process of metabolism of p-CNB to N-acetyl-S-(4-nitrophenyl)-L-cysteine was linear in the dose range studied. Consequently, urinary N-acetyl-S-(4-nitrophenyl)-L-cysteine was considered to be suitable as an index for monitoring p-CNB exposure.

Pharmacokinetic study of p-chloronitrobenzene in humans suffering from acute poisoning

The pharmacokinetics of p-chloronitrobenzene (p-CNB) in human subjects suffering from acute poisoning was studied from the urinary excretion of p-CNB metabolites. The time course for excretion of five metabolites--2-chloro-5-nitrophenol,N-acetyl-S-(4-nitrophenyl)- L-cysteine, 2,4-dichloroaniline, p-chloroaniline, and 2-amino-5-chlorophenol-were determined by reversed-phase HPLC analysis of urine collected from six subjects during their hospitalization after accidental exposure to p-CNB. The cumulative excretion amount at infinite time (X infinity) and mean residence time for each metabolite were estimated by moment analysis of excretion rate vs. the time curve. The rate constants for p-CNB metabolism were calculated by nonlinear least squares fitting of the time course data using a one-compartment model. The results indicated that the average values of the ratio of excreted amount of each metabolite to the total amount of the five metabolites (X infinity metabolite/X infinity Total) and mean residence time in the six subjects were, respectively: 12.2% and 6.7 days for 2-chloro-5-nitrophenol, 48.0% and 7.0 days for N-acetyl-S-(4-nitrophenyl)-L-cysteine, 1.2% and 3.7 days for 2,4-dichloroaniline, 29.9% and 10.0 days for p-chloroaniline, and 8.7% and 6.0 days for 2-amino-5-chlorophenol. The average values of rate constants in the metabolism of p-CNB to 2-chloro-5-nitrophenol, N-acetyl-S-(4-nitrophenyl)-L-cysteine, and p-chloroaniline were 0.021, 0.082, and 0.067 day-1, respectively. Similarly those in further metabolism of p-chloroaniline for C-chlorination, C-hydroxylation, and N-conjugation were 0.205, 1.206, and 3.526 day-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of a micronized, poorly water-soluble drug, HO-221, in experimental animals

N-[[[4-(5-Bromo-2-pyrimidinyloxy)-3-chlorophenyl]amino]carbonyl] - 2-nitrobenzamide (HO-221) is presently under development as an oral anticancer agent with a novel mode of action. However, HO-221 exhibits extremely poor bioavailability after oral administration because it is only slightly soluble in water (0.055 micrograms/ml at 37 degrees C). Our previous study revealed that the micronization of HO-221 to the submicron region improved this oral bioavailability. In this study, the oral pharmacokinetics of this micronized HO-221 was investigated in rats, dogs and monkeys. After oral administration, the agent was moderately absorbed with the Tmax of 6.5-8.0, 17.3-20.0 and 12.0 h, and eliminated with the terminal half-lives of 11.9-15.0, 66.8-78.3 and 42.3 h in rats, dogs and monkeys, respectively. The bioavailability was incomplete (3.7-21.4%). In rats, the plasma concentration did not increase proportionally with increasing oral doses. In dogs, food enhanced the bioavailability 2.2-fold with a standard meal and 3.6-fold with a high fatty meal as compared with fasting conditions.

Nitroxyl analogs as inhibitors of aldehyde dehydrogenase. C-nitroso compounds

We previously postulated that the catalase-mediated oxidation of cyanamide leads to the formation of the unstable intermediate, N-hydroxycyanamide, which spontaneously decomposes to nitroxyl, the putative inhibitor of aldehyde dehydrogenase (EC 1.2.1.3; AlDH). Since it was not possible to provide direct evidence for the inhibition of AlDH by nitroxyl, we examined the activity of three representative substituted nitroxyls (C-nitroso compounds), viz. nitrosobenzene (NB), 1-nitrosoadamantane (NA), and 2-methyl-2-nitrosopropane (MNP), as direct inhibitors of yeast AlDH in vitro. While NB and NA were highly effective inhibitors in this system exhibiting IC50 values of 2.5 and 8.6 microM, respectively, MNP was considerably less effective with an IC50 of 0.15 mM. When tested in vivo, NA did not show any inhibitory activity on the hepatic AlDH, possibly due to the lack of site-specific delivery of the active monomeric form of this compound. However, NB at a low dose did inhibit hepatic AlDH as reflected by an increase in blood acetaldehyde levels. These results attest to the abilities of NB and NA to act as direct inhibitors of AlDH analogous to nitroxyl itself.

Radioiodinated 2-nitrobenzyl carbamates as bioreductive alkylating agents for tissue hypoxia

Three N-methylcarbamates of iodonitrobenzyl alcohols (4-iodo-2-nitrobenzyl alcohol 2, 5-iodo-2-nitrobenzyl alcohol 3 and 4-iodo-2,6-dinitrobenzyl alcohol 4) bearing [125I] have been prepared and characterized for their lipophilicity, their reduction potentials and the in vivo liability of the radioiodine in healthy mice. Based upon these results, 2 and 4 were tested in tumour-bearing mice showing limited uptake of radioactivity in tumours and a tumour-to-blood ratio of less than 1. Consequently these particular carbamates are not satisfactory as hypoxia imaging agents.

Improved oral absorption of a poorly water-soluble drug, HO-221, by wet-bead milling producing particles in submicron region

N-[[[4-(5-Bromo-2-pyrimidinyloxy)-3-chlorophenyl]amino]carbonyl]-2 -nitrobenzamide (HO-221) is being developed as an anticancer agent with a novel mode of action. HO-221 shows poor oral absorption and is only slightly soluble in water (0.055 micrograms/ml at 37 degrees C). In this study, it was shown that the reduction in particle size of HO-221 to the submicron region (0.453 microm, mean by volume) could be achieved by a wet milling in a decaglycerin monolaurate aqueous solution with small glass beads. The wet milling suspension obtained showed improved dissolution rate and oral absorption in rats. A solid dosage form could also be made from that suspension with addition of sucrose palmitate which prevented aggregation caused by the hydrophobic interaction. The solid dosage form thus obtained showed twice as much oral absorption in dogs as the preparation made by dry milling.

Identification of urinary metabolites of human subjects acutely poisoned by p-chloronitrobenzene

1. Urinary metabolites from human subjects acutely poisoned with p-chloro-nitrobenzene (p-CNB) were identified by g.l.c.-mass spectrometry. 2. Eight substances, namely, a very large amount of N-acetyl-S-(4-nitrophenyl)-L-cysteine, relatively large quantities of p-chloroaniline, 2-chloro-5-nitrophenol and p-chloroformanilide produced by pyrolysis of a substance originating from p-CNB, small amounts of 2-amino-5-chlorophenol and 2,4-dichloroaniline, and traces of p-chloroacetanilide and 4-chloro-2-hydroxyacetanilide, were detected in urine samples. 3. All of the absorbed p-CNB was metabolized prior to excretion, as the parent compound was not found in urine. 4. N-Acetylated metabolites of p-chloroaniline and 2-amino-5-chlorophenol, resulting from p-CNB by metabolism, were found in only one of eight individuals indicating that this pathway is weak or may be absent in some humans. 5. A scheme for the pattern of metabolic pathways of p-CNB is proposed, and chlorination was considered to be a possible novel metabolic pathway.

Reduction of nitroaromatic compounds mediated by Streptomyces sp. exudates

Exudates from Streptomyces griseoflavus Tü 2484 effectively mediated electron transfer between hydrogen sulfide and various nitrobenzenes. In general, pseudo-first-order kinetics were observed, except for the initial phase of the reaction at higher pH values. Under fixed pH and Dh conditions, linear free energy relationships were found between the logarithms of the reaction rate constants and the one-electron reduction potentials of the nitroaromatic compounds. No competition was observed between various compounds. Comparison of the results of this study with the results of experiments conducted with model quinones and an iron porphyrin suggest that the secondary metabolites cinnaquinone and dicinnaquinone, excreted by strain Tü 2484 on the order of 100 mg/liter, are responsible for the catalytic activity of the exudate. Further support for this hypothesis comes from the facts that the catalytic activity of the exudate became prominent only after the growth phase of the microorganisms and that the mediating substances have a molecular weight of less than 3,000.

Effect of dose on the percutaneous absorption of 2- and 4-chloronitrobenzene in rats

The effect of dose on the dermal absorption of 2- and 4-chloronitrobenzene (2- and 4-CNB) has been investigated in rats following nonocclusive protective dermal application on an area of 4 cm2 per animal at approximately 0.0325, 0.325, and 3.25 mg/cm2 (0.65, 6.5, and 65 mg/kg, respectively). At the three-dose levels, 33-40% and 51-62% of the dose of 2- and 4-CNB, respectively, was absorbed from the skin within 72 hr. The balance of the dose was recovered in the protective device and the organic trap (i.e. that portion unavailable for dermal absorption). The absorbed radioactivity was excreted in urine (21-28% of dose, 2-CNB; 43-45%, 4-CNB) and feces (11-15%, 2-CNB; 5-12%, 4-CNB). The extent and rate of dermal absorption and urinary and fecal excretion of 2-CNB were linear over the 0.65-65 mg/kg dose range; for 4-CNB they were linear over the 0.65-6.5 mg/kg dose, and nonlinear at the 65 mg/kg dose.

[EPR studies and the role of the electron structure of the heterocycle in the metabolic denitrosation of 5-nitrofuran]

The ESR method revealed that the reduction of 5-nitrofuran and nitrobenzene in liver homogenate is accomplished by the appearance of the nitro anion radicals. ESR spectrum of nitroxyl radical for nitrobenzene was recorded. Metabolic denitrosation in liver homogenate and the formation of hemoprotein nitrosyl complexes were present for 5-nitrofuran and were absent for nitro- and nitrosobenzene. Quantum chemical calculations of the electron structure for the molecules of 5-nitrosofuran and nitrosobenzene showed that the electronegative oxygen atom in the aromatic system turns to increase the positive charge of C atom bonded to NO group. The process of denitrosation in the molecules of 5-nitrosofuran and 5-N-furylhydroxylamine was proposed to include the reaction of nucleophilic NO group substitution.

Kinetics of [18F]1-fluoro-2,4-dinitrobenzene, a potential probe for the glutathione detoxification system, in perfused working rat heart

[18F]1-Fluoro-2,4-dinitrobenzene (FDNB), a substrate for the detoxification enzyme glutathione-S-transferase, was prepared by 18F-Cl exchange. It was administered as a rapid bolus in the perfused working rat heart and the kinetics of the label were followed by external coincidence detection and by analysis of the coronary effluents and tissue homogenates. The data suggest that part of the extracted tracer was released, part was dehalogenated and part was reversibly incorporated into a large tissue pool of FDNB that was not a substrate for defluorination. The rates of the specific processes, estimated from the residue data, may be sensitive to changes in the glutathione detoxification system and therefore applicable to investigation of the compromised myocardium.

Tissue distribution of epimucosally applied 3H DNFB: an autoradiographic study

The distribution of 3H-labeled 2,4-dinitrofluorobenzene (DNFB) has been autoradiographically investigated in buccal mucosa after topical application to sensitized or nonsensitized rats. The rats were killed between 3 min and 24 h after challenge. No significant labeling pattern differences were found between plastic embedded and frozen sections. Surface epithelium was heavily labeled and labeled cells were observed in the lamina propria shortly (3-6 min) after application. These cells were clearly dendritic. Specific accumulation of hapten in epithelial Langerhans cells (LC) could not be clearly demonstrated. The connective tissue labeling gradually diminished and at 24 h post-elicitation, remaining label could be detected only in the epithelial surface layers.

Control of the immune response to contact sensitizing chemicals by cutaneous antigen-presenting cells

The fate of 2,4-dinitrochlorobenzene, a potent contact sensitizing chemical, and 2,4-dichloronitrobenzene, a non-sensitizer, was compared following their application to the skin of BALB/c mice. Although both chemicals were able to bind to protein in vitro and were capable of being absorbed across mouse skin in vivo, only 2,4-dinitrochlorobenzene was able to bind to cells in the skin and to induce the movement of these cells from the epidermis into the dermis and ultimately into the draining lymph nodes. The sensitization potential of a chemical may therefore be dependent on its ability to associate with and stimulate the efflux of cutaneous antigen-presenting cells.