Comparison of cytochrome P450 2A6 polymorphism frequencies in Caucasians and African-Americans using a new one-step PCR-RFLP genotyping method

CYP2A6 (cytochrome P450 2A6), which was first identified as the human coumarin 7-hydroxylase, is the most important enzyme in nicotine C-oxidation. The enzyme also metabolically activates the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in vitro. Polymorphisms in the CYP2A6 gene may thus impact on both smoking behavior and lung cancer susceptibility. Several different genotyping methods have been reported with conflicting results in the frequencies of CYP2A6 polymorphic variants. Thus we decided to perform a sequence analysis of the entire CYP2A6 gene. Sequencing confirmed the published CYP2A6 cDNA sequence. However, intron sequences differed considerably from the reported sequence of the CYP2A6*3 (v2) variant. Our analyses revealed that parts of introns shared homologies with the published sequence of CYP2A13. Based on our sequence data we developed a one step protocol for specific amplification of exon 3 of CYP2A6. The resulting PCR product can be used directly for restriction endonuclease digestion with XcmI and DdeI to determine the frequencies of the reported variant alleles CYP2A6*2 and CYP2A6*3. In a population of 305 African-Americans and 145 Caucasians, we found allele frequencies of 0.003 (2/610) for CYP2A6*2 and 0 (0/610) for CYP2A6*3 in African-Americans and allele frequencies of 0.014 (4/290) and 0 (0/290) in Caucasians. We conclude that both alleles are considerably less frequent in populations than previously reported.

Comparative genomics of the SOX9 region in human and Fugu rubripes: conservation of short regulatory sequence elements within large intergenic regions

Campomelic dysplasia (CD), a human skeletal malformation syndrome with XY sex reversal, is caused by heterozygous mutations in and around the gene SOX9. SOX9 has an extended 5' control region, as indicated by CD translocation breakpoints scattered over 1 Mb proximal to SOX9 and by expression data from mice transgenic for human SOX9-spanning yeast artificial chromosomes. To identify long-range regulatory elements within the SOX9 5' control region, we compared approximately 3.7 Mb and 195 kb of sequence around human and Fugu rubripes SOX9, respectively. We identified only seven and five protein-coding genes in the human and F. rubripes sequences, respectively. Four of the F. rubripes genes have been mapped in humans; all reside on chromosome 17 but show extensive intrachromosomal gene shuffling compared with the gene order in F. rubripes. In both species, very large intergenic distances separate SOX9 from its directly flanking genes: 2 Mb and 500 kb on either side of SOX9 in humans, and 68 and 97 kb on either side of SOX9 in F. rubripes. Comparative sequence analysis of the intergenic regions revealed five conserved elements, E1-E5, up to 290 kb 5' to human SOX9 and up to 18 kb 5' to F. rubripes SOX9, and three such elements, E6-E8, 3' to SOX9. Where available, mouse sequences confirm conservation of the elements. From the yeast artificial chromosome transgenic data, elements E3-E5 are candidate enhancers for SOX9 expression in limb and vertebral column, and 8 of 10 CD translocation breakpoints separate these elements from SOX9.

Longitudinal study of urinary 8-hydroxy-2'-deoxyguanosine excretion in healthy adults

Numerous studies have investigated the urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker for the assessment of oxidative DNA damage in humans. In this study, we performed six consecutive series of measurement of urinary levels of 8-OHdG in 68 healthy probands, in order to provide information on the intra- and inter-individual variability of 8-OHdG and to estimate the influence of smoking, age, sex, body weight and body mass index (BMI) on the excretion of 8-OHdG. The intra-individual coefficient of variation (CV) of urinary 8-OHdG/24 h ranged from 0.18 to 1.06 (mean CV = 0.48). Women excreted significantly lower amounts of 8-OHdG/24 h than men, but the difference lost its significance when the body weight or urinary creatinine were used as covariates. By multiple linear regression analysis significant correlations between the mean individual levels of 8-OHdG/24 h excretion and urinary creatinine (rp = 0.61), and cotinine (rp = 0.27) have been observed, whereas no statistically significant effect of age, body weight and BMI was found. The 8-OHdG/creatinine ratio was found to be significantly increased in 23 smokers (1.95 +/- 0.40 mumol/mol) opposed to 45 non-smoking probands (1.62 +/- 0.50 mumol/mol), which is in good agreement with previously published data. No effect of passive smoking on the excretion of 8-OHdG was found. From our data we conclude that the intra-individual variability of urinary 8-OHdG excretion has been underestimated so far, indicating that values of 8-OHdG measured by single spot monitoring are not representative for individual base levels.

Haemoglobin adducts from aromatic amines in children in relation to area of residence and exposure to environmental tobacco smoke

OBJECTIVE

The influence of area of residence on haemoglobin (Hb) adducts of 4-aminobiphenyl (4-ABP), o-, m-, p-toluidine and o-anisidine was investigated in children from three different-sized Bavarian cities - Munich, Augsburg and Eichstätt, with 1,300,000, 250,000 and 13,000 inhabitants, respectively--and was compared with that of exposure to environmental tobacco smoke (ETS).

METHODS

Blood samples from Munich (n = 34) and Eichstätt (n = 64) were from children attending the Paediatric Clinic of the Technical University of Munich (TUM) or a practice in Eichstätt, respectively. Blood samples (n = 126) together with urine samples (n = 88) were collected from Augsburg children during school medical examination. Personal data including possible sources of ETS exposure were obtained at the interview. Hb adduct levels were analysed by a gas chromatographic method, using mass spectrometry with selected-ion monitoring. Urinary cotinine was determined by radioimmunoassay.

RESULTS

4-ABP Hb adduct levels in children from Munich were 1.5 and 1.2 times higher than those in children from Eichstätt and Augsburg (P < 0.001). Children from Munich also had significantly higher Hb adduct levels of monocyclic aromatic amines than did children from Eichstätt and, except for o-toluidine, children from Augsburg (P < 0.005). Compared with children from Eichstätt, children from Augsburg had higher Hb adduct levels of 4-ABP, o- and m-toluidine (P < 0.01) but not p-toluidine and o-anisidine. In a multivariate analysis, gender, age and body mass index had no consistent influence on Hb adducts. ETS exposure resulted in a slight, nonsignificant increase in 4-ABP Hb adduct levels. In contrast, adduct levels from monocyclic aromatic amines were consistently decreased in ETS-exposed children (significant for o- and m-toluidine, P<0.05).

CONCLUSIONS

Hb adducts from aromatic amines in children were strongly influenced by site of residence, whereas ETS exposure did not significantly increase the adduct levels.JECT

A method for in vitro analysis of the biological activity of complex mixtures such as sidestream cigarette smoke

Studies of the cytotoxicity of air contaminants such as gaseous or particulate compounds and complex mixtures have traditionally used in animal experiments because of the difficulties in exposing cell cultures directly to these substances. New cultivation and exposure techniques enhance the efficiency of in vitro methods, as demonstrated by a new system called CULTEX* which uses a transwell membrane technique for direct exposure of complex mixtures like sidestream cigarette smoke at the air/liquid interface. The factors influencing the susceptibility of human bronchial epithelial cells (e.g. gas flow rate or duration of exposure) were studied and the cells were finally exposed for one hour to clean air or different concentrations of sidestream smoke. The biological parameters estimated were number of cells, metabolic activity and glutathione concentration. After exposure of the cells to sidestream cigarette smoke, dose-dependent effects were measured. Thus, the introduction of these cultivation and exposure techniques offers new testing strategies for the toxicological evaluation of a broad range of airborne and inhalable compounds.

An SRY-negative 47,XXY mother and daughter

Females with XY gonadal dysgenesis are sterile, due to degeneration of the initially present ovaries into nonfunctional streak gonads. Some of these sex-reversal cases can be attributed to mutation or deletion of the SRY gene. We now describe an SRY-deleted 47,XXY female who has one son and two daughters, and one of her daughters has the same 47,XXY karyotype. PCR and FISH analysis revealed that the mother carries a structurally altered Y chromosome that most likely resulted from an aberrant X-Y interchange between the closely related genomic regions surrounding the gene pair PRKX and PRKY on Xp22.3 and Yp11.2, respectively. As a consequence, Yp material, including SRY, has been replaced by terminal Xp sequences up to the PRKX gene. The fertility of the XXY mother can be attributed to the presence of the additional X chromosome that is missing in XY gonadal dysgenesis females. To our knowledge, this is the first human XXY female described who is fertile.

High-performance liquid chromatographic-tandem mass spectrometric determination of 3-hydroxypropylmercapturic acid in human urine

A sensitive and specific high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) method was developed for the determination of 3-hydroxypropylmercapturic acid (3-HPMA) in human urine. Samples were extracted using ENV+ cartridges and then injected onto a C8 Superspher Select B column with acetonitrile and formic acid as eluent (5:95, v/v). N-Acetylcysteine was used as internal standard for HPLC-MS-MS. Linearity was given in the tested range of 50-5000 ng/ml urine. The limit of quantification was 50 ng/ml. Precision, as C.V., in the tested range of 50-5000 ng/ml was 1.47-6.04%. Accuracy ranged from 87 to 114%. 3-HPMA was stable in human urine at 37 degrees C for 24 h. The method was able to quantify 3-HPMA in urine of non-smokers and smokers.

Three novel SRY mutations in XY gonadal dysgenesis and the enigma of XY gonadal dysgenesis cases without SRY mutations

Mutations in the Y-located testis-determining gene SRY are one cause for XY sex reversal. We have previously identified four SRY mutations in a total of 45 sex-reversed females with XY gonadal dysgenesis (XY GD). In a new sample of 16 XY GD cases, three previously undescribed SRY mutations were identified. Two are point mutations that lead to amino acid substitutions in the HMG domain of SRY, M64R, and F67V. The third SRY mutation is a single base insertion 5' to the HMG box within codon 43, converting this lysine codon to a stop codon (K43X). A total of 33 SRY mutations have so far been described that account for only 10-15% of XY GD females. A further 10-15% of these cases result from deletion of SRY due to aberrant X/Y interchange. The etiology of the remaining 70-80% of XY GD cases is still enigmatic. Possible explanations for these XY sex-reversal cases are discussed.

Acampomelic campomelic dysplasia with SOX9 mutation

Acampomelic campomelic dysplasia is a rare clinical variant of the more commonly encountered campomelic dysplasia (CMD1), characterized by absence of long bone curvature (acampomelia). We present a patient with acampomelic CMD1 with a de novo SOX9 missense mutation and report his clinical course to age one year, thereby contributing to genotype-phenotype correlation in CMD1. 2000.

Sensitization to death receptor cytotoxicity by inhibition of fas-associated death domain protein (FADD)/caspase signaling. Requirement of cell cycle progression

Upon binding of their ligands, death receptors belonging to the tumor necrosis factor (TNF) receptor family initiate a signaling pathway leading to the activation of caspases and ultimately apoptosis. TNF, however, in parallel elicits survival signals, protecting many cell types from cell death that can only be induced by combined treatment with TNF and inhibitors of protein synthesis. Here, we report that in NIH3T3 cells, apoptosis in response TNF and cycloheximide is not inhibited by the broad spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD. fmk). Moreover, treatment with zVAD.fmk sensitizes the cells to the cytotoxic action of TNF. Sensitization was also achieved by overexpression of a dominant-negative mutant of Fas-associated death domain protein and, to a lesser extent, by specific inhibition of caspase-8. A similar, but weaker sensitization of zVAD.fmk to treatment with the TNF-related apoptosis-inducing ligand (TRAIL) or anti-CD95 antibody was demonstrated. The unexpected cell death in response to TNF and caspase inhibition occurs despite the activation of nuclear factor kappaB and c-Jun N-terminal kinases. The mode of cell death shows several signs of apoptosis including DNA fragmentation, although activation of caspase-3 was excluded. TNF/zVAD.fmk-induced cell death is preceded by an accumulation of cells in the G(2)/M phase of the cell cycle, indicating an important role of cell cycle progression. This hypothesis is further strengthened by the observation that arresting the cells in the G(1) phase of the cell cycle inhibited TNF/zVAD.fmk-induced cell death, whereas blocking them in the G(2)/M phase augmented it.

SOX9 mutation in a previously published case of campomelic dysplasia without overt campomelia

An SOX9 mutation in a previously published case of campomelic dysplasia is described. This case did not have overt campomelia of the femora or tibiae although campomelic dysplasia has subsequently been confirmed by gene analysis.

Biomonitoring of exposure to polycyclic aromatic hydrocarbons of nonoccupationally exposed persons

In a field study with 69 subjects, we investigated the influence of smoking, exposure to environmental tobacco smoke (ETS), diet, and location of residence on biomarkers for polycyclic aromatic hydrocarbons (PAH), including urinary excretion of 1-hydroxypyrene and benzo[a]pyrene (BaP) adducts of hemoglobin and albumin. The self-reported smoking status and the extent of ETS exposure were verified by urinary cotinine measurements. ETS exposure was quantified by nicotine and 3-ethenylpyridine measurements on personal samplers worn by the nonsmokers over 5 or 7 days before blood and urine samples were collected. Smokers (n = 27), on average, excreted 0.346 microg/24 h 1-hydroxypyrene, whereas the corresponding value for nonsmokers (n = 42) was 0.157 microg/24 h. Average BaP adduct levels with hemoglobin and albumin were 0.105 fmol/mg and 0.042 fmol/mg, respectively, for smokers, and 0.068 fmol/mg and 0.020 fmol/mg, respectively, for nonsmokers. The differences, except for the hemoglobin adducts, were statistically significant. Of the 42 nonsmokers, 19 were classified as passive smokers. There was no significant difference in the PAH biomarkers between nonsmokers exposed to ETS and those not or rarely exposed to ETS. Total dietary BaP intake, as calculated from questionnaire data, did not correlate with any of the PAH biomarkers (r < 0.1). Subjects living in the suburbs tended to have higher BaP-protein adduct levels than subjects living in the city. Our findings suggest that diet and smoking are major sources for PAH exposure of persons not occupationally exposed to PAH, whereas the influence of ETS exposure is negligible. The lack of correlation between the dietary PAH intake and the PAH biomarkers may be due to the inaccuracy of the estimate for the dietary PAH intake.

Male specific expression suggests role of DMRT1 in human sex determination

Sex determination in mammals is controlled by various transcription factors. Following the identification of SRY on the Y chromosome, several other factors have been identified. They can normally be identified as being involved in sex determination by the identification of sex reversal mutations or deletions, functional studies, and also by male-specific expression patterns in embryos. Here, it is shown that DMRT1, recently demonstrated to be deleted in 9p monosomies associated with sex reversal, is specifically expressed during sex determination in the genital ridge of human male, but not female, embryos, similar to SRY.

Fast quantification of the urinary marker of oxidative stress 8-hydroxy-2'-deoxyguanosine using solid-phase extraction and high-performance liquid chromatography with triple-stage quadrupole mass detection

Exogenous and endogenous oxidants constantly cause oxidative damage to DNA. Since the reactive oxidants itself are not suitable for analysis, oxidized bases like 8-hydroxy-2'-deoxyguanosine (8OHdG) are used as biomarkers for oxidative stress, either in cellular DNA or as elimination product in urine. A simple, fast and robust analytical procedure is described for urinary 8OHdG as an indicator of oxidative damage in humans. The adduct was purified from human urine by applying a single solid-phase extraction step on LiChrolut EN. After evaporation of the eluate, the residue was resolved and an aliquote was injected into a HPLC system with a triple quadrupole mass spectrometer. The limit of detection was 0.2 ng ml(-1) (7 fmol absolute) when using one product ion as quantifier and two further product ions as qualifier. The coefficient of variation was 10.1% (n=5 at 2.8 ng ml(-1) urine). The sample throughput was about 50 samples a day. Thus, this method is more sensitive and much faster than the common method using HPLC with electrochemical detection. The results of a study with nine volunteers investigated at six time-points each over 5 days are presented. The mean excretion of 8OHdG was 2.1 ng mg(-1) creatinine (range 0.17-5.9 ng mg(-1) creatinine; 4 of 53 samples were below the LOD). A relatively large intra- (relative SD 66%) and inter-individual (relative SD 71%) variation in urinary 8OHdG excretion rates was found.

The SOX8 gene is located within 700 kb of the tip of chromosome 16p and is deleted in a patient with ATR-16 syndrome

SOX proteins are transcription factors that are characterized by a common DNA-binding motif known as the HMG domain. We describe the 5. 4-kb human SOX8 gene that codes for a 446-amino-acid protein and that is expressed strongly in brain and less abundantly in other tissues. SOX8 shows an overall identity of 47% to SOX9 and SOX10. The latter two possess a C-terminal transactivation domain, whereas in SOX8, this domain is located in the central part of the protein. We have mapped SOX8 within 700 kb of the telomeric repeats of band 16p13.3. Hemizygosity for 1 Mb from this region causes the ATR-16 syndrome characterized by alpha-thalassemia and mental retardation. We show that SOX8 is deleted in an ATR-16 patient, and from its location, we deduce that it should be deleted in all previously described cases. Thus, SOX8 is a good candidate gene contributing to the mental retardation phenotype seen in ATR-16 patients.

Genomic sequencing reveals the structure of the Kcnk6 and map3k11 genes and their close vicinity to the sipa1 gene on mouse chromosome 19

In this report we present the analysis of two overlapping mouse cosmid clones that contain the entire Kcnk6, Map3k11 and Pcnxl3 genes, as well as part of the Sipa1 gene. The sequence and genomic organisation of the Kcnk6 and Map3k11 genes are described in detail. Sipa1 and Map3k11, which have independently been mapped with low resolution to the centromeric region of mouse chromosome 19, are shown here to lie close to each other and to the Kcnk6 gene, which has not previously been mapped. This gene cluster maps to the vicinity of the Dancer (Dc) mutation, which involves inner ear abnormalities and circling phenotypes. Since potassium channels have been implicated in deafness disorders, we have analysed the Kcnk6 gene, which encodes a two-P domain potassium channel, in the Dc mutant. No Dc-causing mutation in the Kcnk6 coding region could be identified. However, we detected a polymorphism in the Kcnk6 gene that leads to a C-terminal extension of the encoded protein by eight amino acids.

Spontaneous and chemically induced point mutations in HPRT cDNA of the metabolically competent human lymphoblastoid cell line, MCL-5

Thioguanine-resistant clones of the human lymphoblastoid cell, MCL-5, which carries two recombinant plasmids expressing xenobiotic metabolizing enzymes, were obtained spontaneously and after treatment with 0.1 microgram/ml benzo[a]pyrene (BaP), 1.0 microgram/ml 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), and 10 micrograms/ml cigarette smoke condensate (CSC). Treatment with the chemicals reduced the cloning efficiency (CE) of MCL-5 cells from about 30% in untreated cultures to about 10% after treatment with NNK and to about 1% or to less than 1% after treatment with CSC or BaP, respectively. At the same time, the mutant frequencies were increased about sevenfold above those of untreated cultures. Among a total of 138 independent mutant clones that had resulted from 55 separate cultures, 60 point mutations were identified within the hypoxanthine guanine phosphoribosyltransferase (HPRT) reading frame by sequencing full-size reverse transcription polymerase chain reaction (RT-PCR) products from thioguanine-resistant clones. The identified 53 coding errors were distributed among 33 locations and types. Among the 30 types of single basepair substitutions leading to coding errors, 12 had not been described before. In the present set of point mutations, the distribution of base substitution types as well as of mutated sites appeared to be influenced by the treatment with the chemicals. Thus, the ratio of G to T transversions increased from 3 among 19 spontaneous point mutations in the HPRT coding region to 9 among 21 BaP-induced point mutations. The G119T and G208T transversions were found three times each, exclusively after treatment with BaP, while the accumulation of two to eight incidences of the G97T, CG142/3TA, C508T, T583A and G599A mutations was split among different treatments. All eight identified point mutations identified after NNK treatment were at G or T residues on either strand that were followed by additional G or T residues.

Campomelic dysplasia translocation breakpoints are scattered over 1 Mb proximal to SOX9: evidence for an extended control region

Campomelic dysplasia (CD), a skeletal malformation syndrome with or without XY sex reversal, is usually caused by mutations within the SOX9 gene on distal 17q. Several CD translocation and inversion cases have been described with breakpoints outside the coding region, mapping to locations >130 kb proximal to SOX9. Such cases are generally less severely affected than cases with SOX9 coding-region mutations, as is borne out by three new translocation cases that we present. We have cloned the region extending 1.2 Mb upstream of the SOX9 gene in overlapping bacterial-artificial-chromosome and P1-artificial-chromosome clones and have established a restriction map with rare-cutter enzymes. With sequence-tagged-site-content mapping in somatic-cell hybrids, as well as with FISH, we have precisely mapped the breakpoints of the three new and of three previously described CD cases. The six CD breakpoints map to an interval that is 140-950 kb proximal to the SOX9 gene. With exon trapping, we could isolate five potential exons from the YAC 946E12 that spans the region, four of which could be placed in the contig in the vicinity of the breakpoints. They show the same transcriptional orientation, but only two have an open reading frame (ORF). We failed to detect expression of these fragments in several human and mouse cDNA libraries, as well as on northern blots. Genomic sequence totaling 1,063 kb from the SOX9 5'-flanking region was determined and was analyzed by the gene-prediction program GENSCAN and by a search of dbEST and other databases. No genes or transcripts could be identified. Together, these data suggest that the chromosomal rearrangements most likely remove one or more cis-regulatory elements from an extended SOX9 control region.

Smoking behaviour and compensation: a review of the literature

RATIONALE

Compensation or compensatory smoking, accurately defined, deals with the question of whether switching to cigarette brands with different smoke yields is associated with a change in smoke uptake proportional to the change in machine-derived yields. The issue of compensation is important because it bears on whether switching to "lighter" brands means lower overall smoke intake or not.

OBJECTIVES

The present review investigated whether and to what extend low yield cigarettes are smoked more intensively. In addition, published data on whether nicotine, "tar", or any other smoke constituent or property influence compensational smoking are summarized.

METHODS

The studies on compensation were classified as follows: (1) studies on smoking behaviour in relation to cigarette yields (with and without brand switching); (2) studies on compensation for nicotine (switching between cigarettes which differ "only" in their nicotine yield, nicotine supplementation, manipulation of renal nicotine excretion, administration of nicotine agonists or antagonists); (3) studies on compensation for other factors (influence of tar, taste, irritation, draw resistance). In order to quantify the degree of compensation, an index is defined and applied to selected brand switching studies. This compensation index determines, in relative units, the degree to which a smoker responds to a change in smoke yields with a change in smoke uptake measured by suitable biomarkers. The role of vent blocking is also briefly discussed.

RESULTS

Most of the studies which compare the smoking behaviour when smoking cigarettes with different smoke yields supply evidence for "partial" compensation, suggesting that cigarettes with lower yields are smoked more intensively than those with higher yields. These studies also show that a change in the daily number of cigarettes is not a common mechanism of compensation. Effective vent blocking during smoking is a rare event and can therefore also be regarded as an uncommon mechanism of compensation. Evaluation of a suitable subset of brand-switching studies revealed an average compensation of 50-60% of the nicotine yield. Compensation tended to be more complete when changing to cigarettes with higher yields than when changing to cigarettes with lower yields. In general, brand-switching studies do not supply information on the underlying causal factors responsible for compensatory smoking. Results of the nicotine supplementation studies are not conclusive: some report evidence of nicotine titration, others do not. A general problem with this type of investigation is that continuous nicotine application does not mimic the spike-wise application with cigarette smoking, and may lead to nicotine tolerance. There is limited evidence that cigarettes were smoked more intensively when the urinary clearance of nicotine was increased. A small number of studies provide some evidence that smoking intensity increased after smokers were administered a nicotine antagonist. Several reports indicate that tar, taste and sensory properties of the smoke as well as the draw resistance of the cigarette may play a role in compensatory smoking. Low-yield cigarettes usually have reduced pressure drops which smoke researchers have suggested leads to increased puff volume. This effect seems to be independent of the smoke yield of the cigarette. There is also some evidence that some smokers maintain a consistent pattern of smoking which works independent of any changes in nicotine or tar yields, taste or design features of the cigarette ("functional autonomy").

CONCLUSIONS

The available data suggest that smokers partially compensate for a different smoke yield. While the factors and their interaction responsible for compensational smoking are not fully understood, there are data suggesting that a subgroup of smokers may partially compensate for nicotine. Even in this subgroup of smokers, however, the relative importance of the pharmacological versus

Determination of sorbic acid in urine by gas chromatography-mass spectrometry

The average daily uptake of the common food preservative sorbic acid is estimated to range from 0.01 to 1.1 mg kg-1. Sorbic acid mainly is metabolised to carbon dioxide. Minor amounts are converted to trans,trans-muconic acid (ttMA) as well as excreted unchanged into the urine. Since urinary ttMA is a biomarker for the occupational and environmental exposure to benzene, there is an additional need for monitoring the uptake of sorbic acid, particularly at low, environmental benzene exposure levels. For this purpose, a simple, robust and rapid method for the determination of sorbic acid in urine at trace levels was developed. After addition of 10 ml of water and 5 ml of 8 M hydrochloric acid to 10 ml of the thawed urine, the sample was water steam distilled using an automated distillation device. A total of 100 ml of the distillate were solid-phase extracted. After washing, the sorbic acid was eluted with 4 ml methanol. The eluate was reduced under a stream of nitrogen to a volume of 300 microliters. After addition of 500 microliters boron trifluoride in methanol and incubation for 1 h at 60 degrees C, the resulting sorbic acid methyl ester was extracted three times with 1 ml heptane. To the combined heptane layers, sorbic acid ethyl ester was added as an internal standard. After reducing to a volume of 100 microliters in a stream of nitrogen, the final analysis was performed by GC-MS using the fragment ions m/z 126 for the analyte and m/z 140 for the internal standard. The limit of detection was 0.7 ng ml-1 urine and the R.S.D. of 69 duplicate determinations was 7.5%. In a controlled, experimental study and in a field study, we were able to show that urinary sorbic acid is a marker for the dietary uptake of sorbic acid and that sorbic acid is converted to ttMA. On average, 0.1% of the dietary sorbic acid is excreted unchanged into the urine. Excretion is complete within 24 h. We found that, on average, 0.23% of the oral dose of sorbic acid is excreted as urinary ttMA. There was a significant correlation between urinary excretions of sorbic acid and ttMA (r = 0.74, n = 69). We conclude that urinary sorbic acid can be used to correct the urinary ttMA level in order to determine the portion related to benzene exposure. This appears to be necessary particularly at low, environmental benzene levels.

Impaired neutral sphingomyelinase activation and cutaneous barrier repair in FAN-deficient mice

The WD-40 repeat protein FAN binds to a distinct domain of the p55 receptor for tumor necrosis factor (TNF) and signals the activation of neutral sphingomyelinase (N-SMase). To analyze the physiological role of FAN in vivo, we generated FAN-deficient mice by targeted gene disruption. Mice lacking a functional FAN protein do not show any overt phenotypic abnormalities; in particular, the architecture and cellular composition of lymphoid organs appeared to be unaltered. An essential role of FAN in the TNF-induced activation of N-SMase was demonstrated using thymocytes from FAN knockout mice. Activation of extracellular signal-regulated kinases in response to TNF treatment, however, was not impaired by the absence of the FAN protein. FAN-deficient mice show delayed kinetics of recovery after cutaneous barrier disruption suggesting a physiological role of FAN in epidermal barrier repair. Although FAN exhibits striking structural homologies with the CHS/Beige proteins, FAN-deficient mice did not reproduce the phenotype of beige mice.