Mass spectrometric investigation of the sequence selectivity for adduction of heterocyclic aromatic amines on single-strand oligonucleotides

Heterocyclic aromatic amines (HAAs) generated during the cooking of meats are known to be genotoxic substances able to form covalent bonds with DNA bases after metabolic activation. This work aimed at the investigation of the influence of the local environment of nucleobases along the nucleotidic sequence on its modification induced by two different HAAs, namely 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in order to identify possible sequences more susceptible to modification. A systematic study of the neighbouring base effect on the adduction was emphasized. Thus, PhIP and IQ adducts have been synthesized with various T-rich model single-strand oligonucleotides displaying different flanking bases (A, G, C or T) at the 3' or the 5' side of the targeted guanine, which allowed a comparison of the flanking base effects on adduction. Modified oligonucleotides were then analyzed by high-performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry. The localization of the modifications induced by PhIP or IQ along the oligonucleotide sequence was achieved by tandem mass spectrometry, and modification yields of the various model sequences were compared. Results indicate a favouring sequence context effect on the G-C8-IQ adduct formation with the sequence 5'GGG3'. Although higher than IQ, modification yields observed with PhIP showed a less obvious effect of the neighbouring base on the G-C8-PhIP adduct formation, with a preferential sequence 5'GGA/G/T3'.

New insights in the formation of deoxynucleoside adducts with the heterocyclic aromatic amines PhIP and IQ by means of ion trap MSn and accurate mass measurement of fragment ions

The formation of adducts by reaction of active metabolites of two heterocyclic aromatic amines (NHOH-PhIP and NHOH-IQ) at nucleophilic sites of deoxynucleosides has been studied by LC-MS(n) analyses of the obtained reaction mixtures. Sequential MS(3) experiments were carried out on an ion trap mass spectrometer to gain extensive structural information on each adduct detected in the first MS step. Attribution of ions was supported by accurate mass measurements performed on an Orbitrap mass analyzer. Particular attention was given to ions diagnostic of the linking between the heterocyclic aromatic amine (HAA) and the deoxynucleoside. By this way, the structures of five adducts have been characterized in this study, among which two are new compounds: dG-N7-IQ and dA-N(6)-IQ. No depurinating adduct was found in the reactions investigated therein. As expected, the C8 and N(2) atoms of dG were found as the most reactive sites of deoxynucleosides, resulting in the formation of two different adducts with IQ and one adduct with PhIP. An unusual non-depurinating dG-N7-IQ adduct has been characterized and a mechanism is proposed for its formation on the basis of the reactivity of arylamines. A dA-N(6)-IQ adduct has been identified for the first time in this work, showing that HAAs can generate DNA adducts with bases other than dG.

Comparison of genistein metabolism in rats and humans using liver microsomes and hepatocytes

Species differences and metabolism are the most crucial factors in considering the effects of genistein. The aim of this study was to have a better knowledge of the metabolic fate of genistein in humans as compared with rats. For this purpose, radiolabeled genistein was incubated with human and rat liver microsomes and with cryopreserved hepatocytes from both species. Incubations were performed using a wide range of genistein concentrations to analyze the kinetics of formation of the metabolites. Metabolite profiling was obtained using an HPLC system connected to a radioactivity detector. Identification of the metabolites was based on their retention times as compared with those of authentic standards and on LC-MS (ESI-MS/MS) or NMR analyses. In both species, liver microsomes produced the same three hydroxylated metabolites (8-OH, 6-OH and 3'-OH-genistein) whereas cryopreserved hepatocytes produced the same glucurono- and sulfo-conjugates (genistein 4'-O-sulfate 7-O-glucuronide, genistein 7-O-glucuronide, genistein 4'-O-glucuronide, genistein 7-O-sulfate and genistein 4'-O-sulfate). The rate of metabolism varied with species. 3'-Hydroxygenistein was the predominant metabolite produced by rat liver microsomes, whereas in humans 3'-hydroxy and 8-hydroxygenistein were produced in the same range. In both human and rat hepatocyte incubations, genistein 7-O-glucuronide represented more than 50% of the incubated dose. Our results on hepatocytes confirmed the predominance of conjugation reaction compared to oxidative reaction observed in vivo.

Analysis of hemoglobin adducts of acrylamide and glycidamide by liquid chromatography–electrospray ionization tandem mass spectrometry, as exposure biomarkers in French population

The determination of biomarkers of acrylamide exposure in humans from general French population by measurement of hemoglobin adduct levels of acrylamide (AA) and glycidamide (GA) is presented. The analytical procedure included modified Edman degradation and LC-ESI-MS/MS analysis of the final derivatives using deuterated internal standards. Method performances were evaluated in terms of linearity, precision, accuracy, and sensitivity. The method was firstly assessed on rat blood samples and then applied to the study of background adducts levels of AA and GA in 68 human hemoglobin samples, showing mean levels of 33 and 23 pmol/g globin for AA and GA adducts, respectively.

Characterisation of glucosinolates using electrospray ion trap and electrospray quadrupole time-of-flight mass spectrometry

Twelve naturally occurring glucosinolates displaying alkenyl, hydroxylated, methylsulphinyl, aromatic and indole side chains were investigated by both negative and positive ion electrospray ionisation-tandem mass spectrometry (ESI-MS/MS). In order to resolve the MS/MS spectra obtained from the anion and cation molecular ions of glucosinolates, the different fragments were investigated by MSn experiments using an ion trap spectrometer. The MS3 spectra obtained permitted possible fragmentation schemes to be proposed. These were supported by accurate mass measurements of some characteristic diagnostic ions with the help of a quadrupole time-of-flight instrument. The negative ion ESI-MS/MS behaviour of the different glucosinolates investigated in this study confirmed previously described patterns and revealed new interesting structural informative fragments. Some are common to all the glucosinolates and others are highly specific for a type of variable side chain. The positive ion ESI-MS/MS fragments obtained from the [MNa+Na]+ or [MK+K]+ molecular ions did not provide complementary specific diagnostic ions. Nevertheless, when compared with the negative ion mode, the daughter ions appeared more homogenous and with a better relative abundance for all of the 12 compounds studied. Moreover, the positive ion mode appeared to be more efficient than the negative mode for the study of methoxylated glucosinolates and should be useful to detect the glucosinolates present as organic salts in crude plant extracts.

Assessment of metastable atom bombardment (MAB) ionization mass spectrometry for the fast determination of heterocyclic aromatic amines in cooked meat

An investigation of metastable atom bombardment (MAB) ionization mass spectrometry for the fast characterization of mutagenic/carcinogenic heterocyclic aromatic amines (HAAs) formed during heating processes of meats is presented. The aim of our study was to use the selective ionization of MAB to develop a detection method for HAAs in non-purified meat extracts, thus avoiding purification and concentration steps and reducing analysis time. Sample introduction into the MAB ion source was achieved by pyrolysis, allowing the direct and fast insertion of complex food extracts into the mass spectrometer. Analysis conditions were optimized on standard HAAs by using different ionization gases for the MAB process. Metastable nitrogen was selected as the best MAB gas for the analysis of HAAs. Ionization selectivity is shown by the detection of heterocyclic amines in non-purified chicken meat extracts spiked with HAAs. A quantitative approach is also presented by using pyrograms as chromatograms for quantification purposes. HAAs determination using Py-MAB-ToF was finally performed on cooked chicken breast extracts and compared to an LC-APCI-MS/MS method. Although Py-MAB-ToF sensitivity remains to be improved in the present state of development of our prototype device, only 2 h from the cooking were required to obtain quantitative results in good agreement with HAAs concentrations measured by LC-MS/MS in 36 h. Figure Experimental set-up for pyrolysis-MAB-ToF mass spectrometry experiments.

Mechanism of sulforaphane-induced cell cycle arrest and apoptosis in human colon cancer cells

Sulforaphane (SFN) is a natural micronutrient found in cruciferous vegetables that has been shown to possess antitumoral properties in carcinogen-treated rats. In vitro, SFN regulates phase II enzymes, cell cycle, and apoptosis. In the present study, we investigated the relationship between SFN induction of apoptosis and cell cycle arrest in HT29 human colon carcinoma cells. In previously published data, a significant increase in the G2/M phase of the cell cycle has been observed in SFN-treated cells that was associated with increased cyclin B1 protein levels. In the present study, our results show that SFN induced p21 expression. Moreover, preincubation of HT29 cells with roscovitine, a specific cdc2 kinase inhibitor, blocked the G2/M phase accumulation of HT29 cells treated with SFN and abolished its apoptotic effect (22.2 +/- 4 of floating cells in SFN-treated cells vs. 6.55 +/- 2 in cells treated with both SFN and roscovitine). These results suggest that the cdc2 kinase could be a key target for SFN in the regulation of G2/M block and apoptosis. Moreover, in SFN-treated cells the retinoblastoma tumor suppressor protein (Rb) is highly phosphorylated. Inhibition of the cdc2 kinase by roscovitine did not change the phosphorylation status of Rb in SFN-treated cells, suggesting that this cyclin-dependent kinase may not be involved. In our study, we did not observe any significant change in the proteasomal activity between control and SFN-treated cells. Moreover, inhibition of proteasomal activity through the use of MG132 diminished SFN-induced HT29 cell death, suggesting that the apoptotic effect of SFN requires a functional proteasome-dependent degradation system. In summary, we have elucidated part of the mechanism of action of SFN in the concomitant regulation of intestinal cell growth and death.

[Carbon monoxide poisoning. Neurologic aspects]

It is most often during winter months that carbon monoxide intoxications occur. Poorly functioning heating systems are the leading cause. We hereby summarize the mechanisms of CO toxicity which leads to treatment basis, and immediate neurological signs of this intoxication. We emphasize the delayed neuropsychiatric syndrome typical of this intoxication, often under or misdiagnosed. Two observations are presented.

Isolation and structure elucidation of a new thermal breakdown product of glucobrassicin, the parent indole glucosinolate

The thermal breakdown of glucobrassicin, the major natural indole glucosinolate present in cruciferous vegetables, has been studied. This study has been conducted using pure synthetic glucobrassicin instead of raw vegetable material to eliminate possible other sources (i.e., enzymatic or chemical) of degradation. After 1 h in aqueous solution at 100 degrees C, 10% of the original glucobrassicin is degraded and yields a unique degradation compound. This compound is described for the first time and has been identified as 2-(3'-indolylmethyl)glucobrassicin on the basis of data obtained by (1)H nuclear magnetic resonance spectroscopy as well as tandem mass spectrometric experiments carried out from positive and negative electrospray produced ions.

[Diagnosis of internal carotid artery dissection. Two case reports]

Two cases of acute internal carotid dissection are presented. Typical symptoms, pathogeny and imaging features are reviewed. Magnetic Resonance is actually the best technique for the diagnosis of internal carotid artery dissection, which should be searched in young patients presenting neurologic and cervico-facial symptoms.

Purification and characterization of a glutathione S-transferase Omega in pig: evidence for two distinct organ-specific transcripts

A cytosolic glutathione S-transferase (GST, EC 2.5.1.18) from the recently characterized Omega class [GSTO; Board et al. 2000, J. Biol. Chem. 275, 24798-24806] has been identified in pig organs. It was found widely distributed in the different tissues investigated and especially abundant in liver and muscle. The hepatic enzyme has been purified to homogeneity by using its selective affinity for S-hexylglutathione over GSH, thus providing a simple method to isolate mammalian GSTO. The dimeric protein has a subunit molecular mass of 27328 Da as measured by electrospray ionization MS. Internal peptide sequencing and complete cDNA sequencing revealed strong similarities with its human recombinant orthologue and two rodent GST-like proteins with the ability to catalyse the GSH-dependent reduction of dehydroascorbate. Additional similarities, including the presence of a specific N-terminal extension and of immunological cross-reactivity, support the results. Moreover, this gene encoding GSTO generates two organ-specific transcripts, suggesting transcriptional mechanisms with a significance that is as yet uncharacterized.

Genotoxicity testing of extracts from aflatoxin-contaminated peanut meal, following chemical decontamination

One of the most important concerns in the decontamination of aflatoxin-containing feed commodities is the safety of the products for food-producing animals and for human consumption of products derived from these animals. A new method, based on the use of florisil and C18 solid phase extraction columns, was developed for the preparation of extracts from decontaminated peanut meal, which allowed testing with in vitro genotoxicity assays without interference of the residual aflatoxin B1. Recovery of degradation products in the extracts was evaluated by the use of radiolabelled [14C]-aflatoxin B1 (AFB1) added to naturally-contaminated peanut meal (3.5 mg AFB1/kg). The meal was treated by a small-scale version of an industrial decontamination process based on ammoniation. Following decontamination, more than 90% of the label could not be extracted from the meal. AFB1 accounted for about 10% of the radiolabel present in the extractable fraction, indicating a total AFB1 reduction of more than 99%. Decontamination of the meal by a number of other small- and industrial-scale ammonia-based processes resulted in similar efficiencies. Application of the extraction procedure resulted in AFB1-rich and AFB1-poor fractions, the latter containing half of the extractable decontamination products but less than 1% of the residual AFB1. Testing in the Salmonella/microsome mutagenicity assay (TA 100, with S9-mix) of the original crude extracts and AFB1-rich fractions prepared from non-treated and decontaminated meal, showed the positive results expected from the AFB1 contents as determined by HPLC analysis. Analysis and testing of the AFB1-poor fractions showed that the various decontamination processes not only resulted in a successful degradation of AFB1 but also did not produce other potent mutagenic compounds. Slight positive results obtained with these extracts were similar for the untreated and treated meals and may be due to unknown compounds originally present in the meal. Results obtained with an unscheduled DNA synthesis (UDS) and Comet assay with rat hepatocytes supported this conclusion. Positive results obtained with the micronucleus assay, using immortalized mouse hepatocytes (GKB), did not clearly reflect the mycotoxin levels and require further examination. It is concluded that the newly developed extraction procedure yields highly reproducible fractions and hence is very suitable for examining the possible formation of less potent degradation products of aflatoxins in short-term genotoxicity tests.

Absorption, distribution and excretion of aflatoxin-derived ammoniation products in lactating cows

Peanut meal naturally contaminated with 3.5 mg/kg aflatoxin B1 (AFB1) was spiked with radiolabelled AFB1 (meal 14C-I0) and decontaminated by a small-scale copy of an industrial ammoniation process (meal 14C-I1). During the process 15% of the radioactivity was lost, whereas 90% of the remaining radiolabel could not be extracted from the meal. In the extractable part, AFB1 accounted for 10% of the radiolabel, consistent with a total AFB1 reduction of more than 99%. No degradation products were observed in the extracts. Four lactating cows were fed with a diet containing 15% of either meal 14C-I0 or 14C-I1 for 10 days. On day 9 of this treatment, respectively 23 and 67% of the radiolabel was excreted in the urine and faeces of cows fed meal 14C-I0, as compared with 2 and 101% in the case of cows fed meal 14C-I1. Milk contained respectively 1.35 (meal 14C-I0) and 0.25% (meal 14C-I1) of the radiolabel. Milk samples taken during the equilibrium stage contained respectively 5 and 0.5 ng/ml of AFB1-derived compounds. Aflatoxin M1 (AFM1) accounted for 50-80% of these compounds in the case of milk from cows fed 14C-I0, as compared with 6-20% in the case of 14C-I1. AFB1 to AFM1 carry-over rates for 14C-I0 or 14C-I1 were estimated to be respectively 0.5 and 5.9%. Only liver and kidney samples contained detectable levels of the radiolabel, being respectively 260 and 37 micrograms/kg for cows fed meal 14C-I0, and 10 and 3 micrograms/kg for those fed meal 14C-I1. In the latter case, more than 55% of the radiolabel in the liver could not be extracted, as compared with 90% in the group fed meal 14C-I1. A small part of the extractable radiolabel in the livers of cows fed meal 14C-I0 could be attributed to AFB1 and AFM1 (less than 1% of total radioactivity). In the case of the animals fed 14C-I1 there were indications for the presence of AFB1 and AFM1 (6% of total radioactivity). Decontamination of the highly contaminated (non-radiolabelled) peanut meal by two different industrial ammoniation processes, resulted in a similar reduction of the initial AFB1 levels of 3.5 mg/kg to 15 micrograms/kg. Feeding of diets containing 15% of the non-treated and two treated peanut meals to cows for a period of 10 days, resulted in AFM1 levels in milk of respectively 2.1, 0.04 and 0.07 ng/ml. AFB1 to AFM1 carry-over rates were calculated to be respectively 0.5, 2.0, and 3.6%. It is concluded that the efficient reduction of aflatoxin levels by ammoniation of contaminated peanut meal results in a strong reduction of aflatoxin-related residues in milk and meat of cows, most likely caused by a decreased bioavailability of the degradation products.

Sulforaphane, a naturally occurring isothiocyanate, induces cell cycle arrest and apoptosis in HT29 human colon cancer cells

Sulforaphane is an isothiocyanate that is present naturally in widely consumed vegetables and has a particularly high concentration in broccoli. This compound has been shown to block the formation of tumors initiated by chemicals in the rat. Although sulforaphane has been proposed to modulate the metabolism of carcinogens, its mechanism of action remains poorly understood. We have previously demonstrated that sulforaphane inhibits the reinitiation of growth and decreases the cellular viability of quiescent human colon carcinoma cells (HT29). Moreover, the weak effect observed on differentiated CaCo2 cells suggests a specific anticancer activity for this compound. Here we investigated the effect of sulforaphane on the growth and viability of HT29 cells during their exponentially growing phase. We observed that sulforaphane induced a cell cycle arrest in a dose-dependent manner, followed by cell death. This sulforaphane-induced cell cycle arrest was correlated with an increased expression of cyclins A and B1. Moreover, we clearly demonstrated that sulforaphane induced cell death via an apoptotic process. Indeed, a large proportion of treated cells display the following: (a) translocation of phosphatidylserine from the inner layer to the outer layer of the plasma membrane; (b) typical chromatin condensation; and (c) ultrastructural modifications related to apoptotic cell death. We also showed that the expression of p53 was not changed in sulforaphane-treated cells. In contrast, whereas bcl-2 was not detected, we observed increased expression of the proapoptotic protein bax, the release of cytochrome c from the mitochondria to the cytosol, and the proteolytic cleavage of poly(ADP-ribose) polymerase. In conclusion, our results strongly suggest that in addition to the activation of detoxifying enzymes, induction of apoptosis is also involved in the sulforaphane-associated chemoprevention of cancer.

Flavonoids and the inhibition of PKC and PI 3-kinase

Flavonoids provide a large number of interesting natural compounds that are consumed daily and exhibit more or less potent and selective effects on some signaling enzymes as well as on the growth and proliferation of certain malignant cells in vitro. Among the identified signal transducers, phosphoinositide 3-kinase (PI 3-kinase) and protein kinase C (PKC) are now considered key players in many cellular responses including cell multiplication, apoptosis, and transformation. Despite their lack of strict specificity, some flavonoids provide valuable bases for the design of analogues that could be used to specifically block particular isoforms of PI 3-kinase or PKC and their downstream-dependent cellular responses.

Metabolism of clenbuterol in rats

The metabolic fate of [14C]clenbuterol was studied in male and female Wistar rats. After a single oral dose of 200 microgram/kg [14C]clenbuterol, in an 8-day study period, approximately 60% of the radioactivity was eliminated in urine; 20 and 30% of the radioactivity was excreted in feces by male and female rats, respectively. HPLC coupled to on-line radioactivity detection allowed the separation and quantitation of clenbuterol metabolites, some of which were found to be poorly stable in urine. Most of the urinary and fecal metabolites of clenbuterol were isolated and identified using various MS techniques. Analytical methods were also developed to establish the metabolic profiles in feces and tissues, up to 72 hr after clenbuterol administration. Clenbuterol was mainly metabolized by N-dealkylation (secondary amine), as well as N-oxidation and sulfate conjugation (primary amine). Gender-related differences in the rates of clenbuterol N-dealkylation were observed. 4-N-Hydroxylamine was the major metabolite detected in urine, whereas more than one half of the radioactivity in feces was associated with clenbuterol sulfamate.

Selective cytostatic and cytotoxic effects of glucosinolates hydrolysis products on human colon cancer cells in vitro

Glucosinolates hydrolysis products are attracting increasing attention since many studies have suggested that they may be involved in the anticarcinogenic property of cruciferous vegetables. In this study, we show that diindolylmethane (DIM) and sulforaphane, produced during the hydrolysis of glucobrassicin and glucoraphanin, respectively, exert a dose-dependent cytotoxicity on human colon adenocarcinoma HT29 cells. Moreover, these products are able to inhibit quiescent cells to re-enter the cell cycle. Interestingly, our results clearly show that low doses of DIM and sulforaphane, although very effective on undifferentiated intestinal HT29 cells, do not affect the viability of the differentiated CaCo2 cells. The reversibility of their effects has also been tested and is discussed.

Comparative metabolism of clenbuterol by rat and bovine liver microsomes and slices

The metabolism of clenbuterol by liver microsomal fractions and precision-cut liver slices was studied in rats and cattle using a 14C-labeled molecule and radio-HPLC quantitation of the resulting metabolites. 4-N-Oxidation of clenbuterol was found to be an extensive in vitro metabolic pathway in both species. Clenbuterol hydroxylamine was by far the major metabolite characterized from microsomal and slice incubation media. Trace amounts of 4-nitro-clenbuterol were also detected. Another important microsomal biotransformation of clenbuterol, resulting in the production of 4-amino-3,5-dichlorobenzoic acid, was observed only when the drug was incubated with bovine liver microsomes. The corresponding glycine conjugate, namely 4-amino-3,5-dichlorohippuric acid, was detected when clenbuterol was incubated with bovine or rat liver slices. Structural characterization of the major metabolites was performed using electrospray ionization-mass spectrometry, either coupled to liquid chromatography or with direct infusion of collected samples. In addition to these compounds, only quantitatively minor metabolites were detected in bovine (but not rat) microsomal incubation media. Analysis of incubation media from liver slices also allowed the quantitation of a few additional metabolites, some of which were shown to be conjugated compounds.

Evidence for a new and major metabolic pathway clenbuterol involving in vivo formation of an N-hydroxyarylamine

Clenbuterol is a beta-adrenergic agonist widely but illegally used in cattle as a growth promoter. The metabolic fate of this drug remains unknown in the main target species, i.e. the bovine, and only limited data have been published concerning its biotransformations in laboratory animals. A metabolic study has been carried out in the rat using 3H- and 14C-labeled clenbuterol. Urine appeared to be the major excretion pathway. Using a soft technique for urine preparation, extraction, and purification, as well as adequate analytical tools in order to preserve labile metabolites, N-oxidation products of the parental drug on the primary amine function were identified for the first time. Clenbuterol hydroxylamine was the major compound, but 4-nitroclenbuterol was also detected. The metabolic pathway leading to the formation of clenbuterol hydroxylamine prevails at high dosages. Clenbuterol hydroxylamine (but not 4-nitroclenbuterol) was also formed extensively when the drug was incubated with rat liver microsomal fractions in aerobic conditions. It is concluded that oxido reduction during urine preparation have previously impaired the identification of this toxicologically important clenbuterol metabolic route.

Characterization of pig liver glutathione S-transferases using HPLC-electrospray-ionization mass spectrometry

We have characterized 11 porcine liver cytosolic glutathione S-transferase (GST) subunits from their precise molecular mass, immunoreactivity and partial amino acid sequence. Four Alpha-, six Mu- and one unexpected Pi-class GST subunits were found with average molecular masses of 24.984-25.228 kDa, 25.039-25.657 kDa and 23.510 kDa respectively. Molecular masses were established using electrospray-ionization mass spectrometry, with a precision of +/- 3-4 mass units. Glutathione (GSH) and S-hexylglutathione (ShGSH) were tested as affinity ligands in the purification procedure. The binding selectivity of GSH was better than that of ShGSH, although non-GST proteins were retained on both matrices. As already described in other studies, a number of non-GST proteins bound to the affinity resins. Two of them were tentatively identified as mevalonate kinase and carbonyl reductase. The characterization of pig liver cytosolic GST subunits pattern achieved in this work should constitute a useful tool for rapid evaluation of these enzymes' expression in modulation studies.

Optimization of the separation of beta-agonists by capillary electrophoresis on untreated and C18 bonded silica capillaries

The conditions of the separation of ten beta-agonists by capillary zone electrophoresis were studied. Several buffers were tested at different ionic strengths and different pH values. The experiments were carried out on two different supports, i.e. an untreated fused-silica capillary and a C18 covalently bonded silica capillary. The results showed that the optimum pH value was the same for the two capillaries. Separation efficiencies were slightly better for the fused-silica capillary whereas better selectivity and repeatability were obtained with the C18 bonded capillary, under optimal conditions.

Electrospray ionization-mass spectrometry as a tool for characterization of glutathione S-transferase isozymes

Reversed-phase high-performance liquid chromatography coupled to electrospray ionization-mass spectrometry (ESI-MS) was used for the first time to determine the molecular masses of nine rat liver cytosolic glutathione S-transferase (GST) subunits. The precision of the measurements was +/- 3-4 mass units which, in practice, allowed discrimination between monomers differing by more than 8 Da. Mass accuracy was improved by replicates in the measurements. Comparison of experimental values to cDNA or protein-deduced data available reveals slight differences. N-terminal sequence analyses and interstrain mass comparisons tend to show that primary structures of liver cytosolic GSTs are well conserved from Sprague-Dawley to Wistar rats. Moreover, ESI-MS analysis enabled identification of two minor additional subunits present in both strains, one of which belongs to the mu-class. In addition to rapid and accurate mass determination of GST monomers, and direct determinations achieved on heterodimeric forms, this technique provides precise information on minor structural differences or modifications of these proteins. As such, it constitutes a useful tool for rapid characterization of purified GSTs in comparative studies.

Evidence for new metabolic pathways of chloramphenicol in the duck

Following subcutaneous administration of [3H]chloramphenicol (CP) to duck, HPLC and TLC analyses showed that the two most important metabolites in 0- to 24-hr excreta were CP-oxamic acid and CP-alcohol, which together accounted for about one-third of the radioactivity therein. The remainder was due to unchanged CP (15% dose), CP-base (5% dose), and various metabolites representing < 4% dose each. Among these, CP-glucuronide and CP-sulfate have been previously isolated in mammals. In addition to these metabolites, several previously unreported in vivo CP biotransformation products were identified in this study by HPLC and MS comparison with synthetic reference compounds. These new metabolites were unequivocally identified as 1-O-monoacetyl CP, CP-1,3-diacetate, N-acetyl CP-base, CP-oxamylglycine, and CP-oxamylethanolamine. Besides these formally identified compounds, the CP-phosphate structure was tentatively assigned to a conjugate metabolite resistant to beta-glucuronidase and sulfatase hydrolysis. The possible origin of these metabolites is discussed extensively.

Urinary metabolites of dodecylcyclohexane in Salmo gairdneri: evidence of aromatization and taurine conjugation in trout

1. The urinary metabolites of 3H-dodecylcyclohexane were investigated in rainbow trout, Salmo gairdneri R. after a single intragastric dose. In 72 h, 14% of the ingested radioactivity was excreted in urine. 2. Cyclohexylacetic acid, 1-hydroxy-, 3-hydroxy- and 4-hydroxy-cyclohexylacetic acids were present in the unconjugated fraction. 3. In the glucuronide fraction (1.2% dose) labelled aglycones were cyclohexylacetic acid and phenylacetic acid. 4. More than 30% of the urinary 3H was present as phenylacetic and cyclohexylacetic acids conjugated with taurine.

Growth reduction in trout induced by naphthenic and isoprenoid hydrocarbons (Dodecylcyclohexane and pristane)

Rainbow trout were fed a diet containing 1% dodecylcyclohexane or pristane for 9 weeks. Feed intake was recorded daily and weight gain every 3 weeks. These animals were compared with fish receiving a hydrocarbon-free diet (groups fed ad libitum and pair-fed groups for which the ration provided was the amount of food consumed by the hydrocarbon-contaminated fish, the day before). The total food ingested by the pristane and dodecylcyclohexane groups amounted to 66 and 70%, respectively, of that eaten by the controls. The final mean weight of the controls was twofold their initial weight. The average weight gain of the dodecylcyclohexane and pristane groups was 37 and 25%. During the same period the fish of the pair-fed groups gained approximately 70% of their initial weight. Significant effects of hydrocarbon consumption on food conversion factors, viscerosomatic index, hepatosomatic index, and liver lipid concentration were observed. The results are discussed in relation to the possible causes of such changes.

[Oxidation of a naphthenic hydrocarbon, dodecylcyclohexane, in the rat]

Naphthenic hydrocarbons, mainly of fossil origin, are widespread in our environment, and contaminate the food chains; they are also used as food additives. Their fate in mammals is unknown, except for the fact that they are absorbed and accumulate in tissues. Only a few microorganisms have been shown capable or oxidising n-alkyl substituted cycloparaffins. In this study, dodecylcylohexane has been chosen as a typical monocycloparaffin, and has been administered orally to rats. The GLC and GLC-MS analysis of the methylesters of body and hepatic fatty acids led to the identification of cyclohexyldodecanoic and its decanoïc and octanoïc homologs. The alkyl chain undergoes a terminal oxidation followed by the classical beta-oxidation process. After administration of one 200 mg dose, or incorporation of 0.1% of the cycloparaffin in the diet for 2 months, these acids were found at low levels in neutral lipids and phospholipids. Their subsequent metabolic pathway and their possible interaction with the biochemical mechanisms involving phospholipids are under investigation.

[Course of the level of aliphatic and naphtenic hydrocarbons and of 3,4-benzopyrene in mussels taken in a coast area polluted by a fuel spill]

After a fuel spillage, a coastal zone was polluted and wild Mussels were contaminated by paraffinic and naphtenic hydrocarbons and 3,4-benzopyrene. The evolution of this contamination was followed. Normal levels were re-established after a month and a half. Normal paraffins were metabolised faster.

[The effect of prolonged injestion of paraffin oil in pigs: selective retention and interference with cholesterol metabolism]

Hydrocarbons administered to the pig as paraffin oil fix preferentially in the liver, and the existence of a selective filtration mechanism can be supposed. Moreover a significant increase of the level of squalene is observed in adipose tissue and liver; it could correspond to an inhibition of the cholesterol synthesis following vitamin A deficiency due to perturbation of intestinal absorption.