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Biomedical subjects

J A Craft

Publications and source records attributed to J A Craft.

At least 19 recordsLinked to original sources
PubMed2006

Application of SSH and a macroarray to investigate altered gene expression in Mytilus edulis in response to exposure to benzo[a]pyrene.

The lack of genomic resources for aquatic invertebrates restricts their use as sentinel species in coastal environments. It is known that where genomic data are not available, suppression subtractive hybridisation (SSH) can generate cDNA libraries representative of pollutant-responsive gene transcription in aquatic vertebrates. To assess whether the approach was equally suited to aquatic invertebrates, altered gene expression in digestive gland of the mussel, Mytilus edulis, in response to exposure to benzo[a]pyrene (BaP) (1 mg/l) was investigated with SSH and a nylon macroarray. Screening of the subtracted libraries showed 112/250 up-regulated and 25/55 down-regulated clones were positive for differential expression and characterisation of these identified 87 with unique sequence suitable for array on a nylon membrane. The transcripts isolated were from a diverse range of genes involved in general stress, oxidative stress, cell adhesion, transcriptional and translational regulation, transport mechanisms, energy metabolism, cell metabolism, lipid metabolism, protein turnover and activation, lysosomal activity and 22 cryptic clones. Subsequent use of the clones in macroarray format to analyse expression of BaP-responsive genes (0 vs 4 day exposed) showed 0-100-fold increased levels of the forward-subtracted probes and between 0 and 0.1-fold down-regulation of the reverse-subtracted probes. Only 15% of the clones showed less than 2-fold change in expression. The gene ontology of the transcripts isolated demonstrates that BaP elicits a multitude of responses with a major feature being disruption of cellular redox status. The results indicate that the use of SSH and a macroarray is a robust method to discover novel pollutant-responsive genes in aquatic invertebrates.

Animals↗
PubMed2001

Detection of functional PTEN lipid phosphatase protein and enzyme activity in squamous cell carcinomas of the head and neck, despite loss of heterozygosity at this locus.

The human tumour suppressor gene PTEN located at 10q23 is mutated in a variety of tumour types particularly metastatic cases and in the germline of some individuals with Cowdens cancer predisposition syndrome. We have assessed the status of PTEN and associated pathways in cell lines derived from 19 squamous cell carcinomas of the head and neck. Loss of heterozygosity is evident at, or close to the PTEN gene in 5 cases, however there were no mutations in the remaining alleles. Furthermore by Western analysis PTEN protein levels are normal in all of these SCC-HN tumours and cell lines. To assess the possibility that PTEN may be inactivated by another mechanism, we characterized lipid phosphatase levels and from a specific PIP3 biochemical assay it is clear that PTEN is functionally active in all 19 human SCCs. Our data strongly suggest the possibility that a tumour suppressor gene associated with development of SCC-HN, other than PTEN, is located in this chromosomal region. This gene does not appear to be MXI-1, which has been implicated in some other human tumour types. PTEN is an important negative regulator of PI3Kinase, of which subunit alpha is frequently amplified in SCC-HN. To examine the possibility that PI3K is upregulated by amplification in this tumour set we assessed the phosphorylation status of Akt, a downstream target of PI3K. In all cases there is no detectable increase in Akt phosphorylation. Therefore there is no detectable defect in the PI3K pathway in SCC-HN suggesting that the reason for 3q26.3 over-representation may be due to genes other than PI3K110alpha.

Blotting, Western↗
PubMed2001

Clonal origins of human breast cancer.

Tumours are usually considered as the clonal progeny of single transformed cells. An X-chromosome inactivation assay has been applied to exploring clonal relationships in human breast cancer. Analysis of X-inactivation in DNA extracted from microdissected in situ and invasive breast carcinoma by Hpa II restriction and polymerase chain reaction (PCR) of the androgen receptor exon I CAG polymorphism confirmed monoclonality in 105/133 samples of carcinoma cells from 31/32 informative breast cancers. Clonality was identical in seven cases between in situ and invasive carcinoma. Unexpectedly, 4 of 12 cancers (33%) with two or more monoclonal samples available were mosaic (polyclonal) in respect of X-chromosome inactivation between separate morphologically homogeneous tumour cell samples. Concordant clonality supports a common clonal origin of in situ and invasive breast cancers, but frequent apparently mosaic X-inactivation in breast cancer cannot be explained by non-tumour cell contamination. It is concluded that these carcinomas may be genuinely multiclonal. Possible mechanisms of multiclonality include simultaneous transformation of cell groups straddling X-chromosome inactivation patch boundaries, tumour-initiating mutations prior to X-inactivation, or recruitment of bystander stem cells by DNA transfer from necrotic or apoptotic tumour cells. Collision of independent cancers appears implausible at this frequency. Further studies using independent analytical techniques are required to test the important possibility that a significant proportion of mammary carcinomas are not monoclonal.

Breast Neoplasms↗
PubMed2001

Measurement of cytochrome P4501A induction in dab (Limanda limanda) and other teleosts with species-specific cDNA probes: isolation and characterisation of dab cDNA and its use in expression studies with beta-naphthoflavone-treated fish.

Induction of cytochrome P4501A (CYP1A) in fish is an important biomarker in marine monitoring programmes but a number of factors complicate interpretation of data based on catalytic activity. To provide additional analytical tools, we have cloned and sequenced entire (dab) and partial cDNAs (flounder, turbot, sand eel) from several fish species. A detailed analysis comparing the new sequences to those on the database (13 sequences) is presented and identifies an invariant, teleost-specific sequence (195-IVVSVANVICGMCFGRRYDH-214) which might be the basis for production of a species cross-reactive antibody. Northern and slot blots of fish RNA (sand eel, plaice, turbot, flounder and dab) showed extensive cross-species hybridisation with each of the cDNAs (sand eel, plaice, turbot, flounder and dab). The exception was turbot RNA, which only gave adequate hybridisation when the turbot probe was used. Attempts to normalise the hybridisation data to GAPDH mRNA were not satisfactory since there were significant species differences in expression of this gene and expression was suppressed (20-40%) by beta-naphthoflavone treatment. The CYP1A probes indicated induction levels relative to untreated dab of: plaice (five-fold); turbot (12-fold); flounder (12-fold); and dab (10-fold). The study demonstrates the relative ease with which species-specific molecular probes can be generated and used.

Amino Acid Sequence↗
PubMed2000

The effect of gender, sexual maturation and xenobiotic treatment on the formation of hydroxymethyl metabolites from 7, 12-dimethylbenz[a]anthracene in rat liver microsomes.

The effects of age, gender, strain, phenobarbital (PB) treatment and pituitary influence on the regioselective metabolism of 7, 12-dimethylbenz[a]anthracene to hydroxmethyl metabolites were investigated. Studies used hepatic microsomal membranes from immature and mature Long Evans (LE) rats and adult Hooded Lister (HL) animals. Hydroxymethyl metabolites were resolved by both normal and reverse phase HPLC with on-line diode array detection. The CYP isoform(s) responsible for oxidation at the 12 methyl position exhibited no gender or developmental regulation and the rate of formation was not altered following hypophysectomy. PB-treatment of adult rats caused a significant increase in the rate of formation of both male and female animals (29 and 41-fold, respectively) suggesting a major contribution from a PB-inducible isoform, such as CYP2B. The rate of formation of 7OHMe12MBA exhibited no gender dependency in immature animals but was 2-fold greater than that observed for 12OHMe7MBA suggesting that steric hindrance resulting from the adjacent 1,2 benzyl ring favours substrate oxidation at the 7-methyl position. Male predominant formation of 7OHMe12MBA was apparent following sexual maturation of the LE rats and was significantly reduced upon hypophysectomy suggesting the involvement of a male-specific GH dependent isoform e.g. CYP2C11.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2000

Gender-specific metabolism of benz[a]anthracene in hepatic microsomes from Long-Evans and Hooded Lister rats.

The cytochrome P450 isoforms responsible for the regio-selective metabolism of benz[a]anthracene (BA) are poorly defined but as with other polycyclic aromatic hydrocarbons (PAHs) may include members of the CYP2C sub-family. Since the expression of some of these is regulated in a gender-specific manner and may be altered by age, rat strain or by phenobarbital treatment, the effects of these variables on metabolism of BA to diols was investigated. These studies used hepatic, microsomal membranes from immature and adult Long-Evans rats and adult Hooded Lister rats. BA-diols were resolved by normal phase HPLC into three discrete peaks identified as benz[a]anthracene-5,6-diol (BA-5,6-diol), benz[a]anthracene-10, 11-diol (BA-10,11-diol) and a mixture of benz[a]anthracene-3,4- and -8,9-diols (BA-3,4-diol and BA-8,9-diol and termed Peak(3/8)). Significant gender-related differences were found in the rates of diol formation in adults of both the Long-Evans and Hooded Lister rat strains. Formation of BA-10,11-diol and to a lesser extent the components of Peak(3/8) were greater in the male compared to female animals by factors of at least 14 and two, respectively. An age-dependent effect is also observed in the Long-Evans rat since these differences are still apparent in prepubertal animals but to a lesser extent (gender ratio male:female BA-10,11-diol 9X; Peak(3/8) 1.4X). In contrast BA-5,6-diol was formed at similar rates by membranes from female and male rats whether mature (Long-Evans and Hooded Lister) or immature (Long-Evans). Phenobarbital treatment of the adult Long-Evans rats resulted in a moderate increase in the formation of each diol other than at the 10,11-position and the induction was not gender specific. The rate of formation of BA-10, 11-diol was decreased in phenobarbital-treated male rats suggesting modulation of a male specific isoform. Measurement of microsomal epoxide hydrolase revealed no gender or age differences and suggests that this enzyme is not rate limiting in BA-diol formation and thus is not responsible for the differences in BA-diol formation observed. The results suggest that CYP2C11 along with a male-specific isoenzyme not regulated by age are important in the formation of BA-10,11-diol and a component(s) of Peak(3/8) in males. CYPs 2B2 and/or 2C6 appear to be involved in formation of BA-5,6-diol in male and female. Identification of the CYPs involved in the regio-selective metabolism of BA may lead to an explanation of the lower carcinogenic potency of this PAH compared to dimethylbenz[a]anthracene and this study provides novel clues concerning the identities of the CYPs, which are important.

Age Factors↗
PubMed1998

The association of flowering time quantitative trait loci with duplicated regions and candidate loci in Brassica oleracea.

A population of 150 doubled haploid lines of rapid cycling Brassica oleracea, derived from an F1 from a var. alboglabra x var. italica cross, was scored for flowering time in two trials. Using information on 82 mapped molecular markers, spread evenly across the nine linkage groups, QTL were identified at six locations; one each on linkage groups O2 and O3 and two each on linkage groups O5 and O9. In total, these QTL explained 58 and 93% of the genetical variation in the two trials. Three of these QTL, on linkage groups O2, O3, and O9, were situated in regions showing considerable homology both with each other and with chromosome regions of B. nigra that have been shown to affect flowering time. These same regions are all homologous to a single tract of Arabidopsis chromosome 5, which contains a number of the flowering-related genes, one or more of which may be candidates for the QTL found in Brassica.

Brassica↗
PubMed1996

Metabolism of benz[alpha]anthracene by human bone marrow in vitro.

The metabolism of polycyclic aromatic hydrocarbons by bone marrow, mononuclear cells from normal donors and leukaemia patients in remission has been investigated. When benz[alpha]anthracene (BA) was included with marrow under cell culture conditions, it was converted to materials which were resolved into three peaks by normal phase HPLC, and which had the chromatographic characteristics of BA-dihydrodiols. Formation of hydroxymethyl-or dihydrodiol-derivatives of 7, 12-dimethylbenz[alpha]anthracene were not detected under the same conditions. The BA-metabolites were identified as BA-5,6-dihydrodiol, BA-10,11-dihydrodiol and BA-8,9-dihydrodiol. The identification was based upon chromatographic properties of the metabolites during normal and reverse phase chromatography and on UV spectral and fluorometric characterization. It was not possible to detect the formation of BA-3,4-dihydrodiol since this dihydrodiol co-elutes with BA-8,9-dihydrodiol and BA-10,11-dihydrodiol during normal phase and reverse phase chromatography, respectively. the UV spectra of BA-3,4-dihydrodiol does not have features which enable it to be readily identified in the presence of these other compounds. Formation of the dihydrodiol-metabolites was dependent on cell number and temperature. Two general cytochrome P450 inhibitors, carbon monoxide and piperonyl butoxide, blocked the formation of metabolites but the cyclooxygenase inhibitor, indomethacin had no effect. Large variations were observed in the capacity of marrow from different individuals to form benz[alpha]anthracene-dihydrodiols but, in each sample where dihydrodiols were formed, the relative amount of each metabolite was BA-8,9-dihydrodiol >> BA-5,6-dihydrodiol > BA-10,11-dihydrodiol. Factors which may contribute to this variation, including disease status, genetic and environmental agents, are considered.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1994

Comparison of oxygenation measurements in pediatric patients during sickle cell crises.

Measurements of the saturation of arterial blood with oxygen (SaO2) were compared in 24 children during sickle cell crises. Simultaneous pulse oximetry (Nellcor N-100 pulse oximeter) and arterial blood analysis showed that SaO2 measured by pulse oximetry overestimated cooximeter-measured SaO2 (mean bias, 6.9%; p < 0.001). The blood gas machine-calculated SaO2 also overestimated cooximeter-measured SaO2 (p < 0.001). The bias increased with increasing age (p = 0.002) and carboxyhemoglobin level (p = 0.005) but was not related to methemoglobin, total hemoglobin, percentage of hemoglobin S, or percentage of hemoglobin F.

Adolescent↗
PubMed1992

Steroid 21-hydroxylase is a major autoantigen involved in adult onset autoimmune Addison's disease.

An adrenal-specific protein reacting with autoantibodies in the sera of patients with adult onset Addison's disease has been purified from human adrenal glands. The protein, mol.wt. 55K, has the biochemical characteristics of steroid 21-hydroxylase and reacts on Western blots with rabbit antibodies to recombinant 21-hydroxylase. Absorption of the native human 55K adrenal protein with human adrenal autoantibodies prevented the subsequent reaction of the 55K protein with rabbit antibodies to 21-hydroxylase in Western blot analysis. In addition, human adrenal autoantibodies reacted with recombinant 21-hydroxylase expressed in yeast. These data indicate that the adrenal specific enzyme steroid 21-hydroxylase is a major autoantigen involved in adult onset autoimmune Addison's disease.

Addison Disease↗
PubMed1991

The role of specific cytochromes P450 in the formation of 7,12-dimethylbenz(a)anthracene-protein adducts in rat liver microsomes in vitro.

The role of specific cytochrome P450 (P450) isoforms in the formation of adducts of 7,12-dimethylbenz(a)anthracene metabolites and membrane proteins has been investigated in vitro with microsomal fractions prepared from rats pretreated with various isoenzyme selective inducers. The effects of isoenzyme selective inhibitors were also evaluated. Adduct formation was shown to be mediated by P450 catalysed reactions but was unaltered, relative to untreated animals, in membranes from pyrazole- and clofibrate-treated animals suggesting that CYP2E1 and CYP4A1 are not involved in this process. However, adduct formation was significantly increased in microsomes from Sudan III-, phenobarbital- and dexamethasone-treated rats, suggesting the involvement of the CYP1A, CYP2B and CYP3A subfamilies, respectively. These conclusions were further supported by the finding that adduct formation in these microsomes could be inhibited by the isoenzyme-selective inhibitors alpha-naphthoflavone, metyrapone and troleandomycin, respectively.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

Metabolism of 7,12-dimethylbenz[a]anthracene in hepatic microsomal membranes from rats treated with isoenzyme-selective inducers of cytochromes P450.

Previous work has shown that member(s) of the cytochrome P450IIC sub-family play significant roles in the formation of diols of 7,12-dimethylbenz[a]anthracene (DMBA) and are particularly important in formation of the proximate carcinogen (DMBA-3,4-diol). To further characterize the role of members of this subfamily in DMBA-diol formation and to assess the part played by other P450s, DMBA metabolism has been investigated in microsomes prepared from animals pre-treated with isoenzyme selective inducers. The rates of formation of DMBA-diols in membranes from phenobarbital-treated rats were very low when NADH was used as reductant and rates were not altered when NADPH and NADH were used in combination rather than using NADPH alone. This suggests that cytochrome b5 is not involved in DMBA-diol formation in these membranes. Treatment of animals with clofibrate, pyrazole and dexamethasone produced regio-selective alterations in the rates of formation of DMBA-diols at the -3,4-, -5,6- and -8,9- positions. However, none of the inducers caused increases in the rates of DMBA-diol formation of any great magnitude suggesting that the isoforms which are the major induced proteins (P450IVA1, P450IIE1 and P450IIIA1) do not play a significant role in diol formation. The content of other P450s in these membrane are also altered and these were investigated by Western blot using antibodies to P450IIC6, P450IIB1 and P450IIIA1. The results of the Western blots show that the effects of the inducing agents on DMBA-diol formation can be explained by alterations of members of the P450IIC and P450IIB subfamilies.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

The contribution of specific cytochromes P-450 in the metabolism of 7,12-dimethylbenz[a]anthracene in rat and human liver microsomal membranes.

The role of specific cytochrome P-450 isoenzymes in the regio-selective metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) has been studied in microsomal membranes from rat and human liver. An antibody inhibition study using membranes from phenobarbital-treated rats demonstrates that a member(s) of the CYP2C family accounts for up to 90% of the formation of the proximate carcinogen, DMBA-3,4-diol, and makes significant contributions to the formation of DMBA-5,6-diol and DMBA-8,9-diol. In these membranes the formation of DMBA-5,6-diol can be entirely accounted by the combined activity of members of the CYP2C and CYP2B families. The metabolism of DMBA has been investigated in human using microsomes from 10 individuals and the metabolites formed by these membranes were found to be mainly hydroxymethyl- and -diol products. The rates of formation of each metabolite show considerable interindividual variation and there was no correlation between these rates for any pairing of metabolites. The CYP content in these membranes of specific members of families 1, 2, 3 and 4 did correlate with the rates of formation of individual metabolites. Surprisingly there was no correlation between the content of CYP2C and formation of DMBA-3,4-diol but an antibody to rat CYP2C6 partially inhibited the formation of this metabolite. The results indicate that in human both inducible sub-families of CYPs, particularly of the PB-type, and constitutively expressed CYPs may be important in DMBA metabolism and that each metabolite may be produced by the combined activity of several CYP isoforms.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1990

Membrane topology of epoxide hydrolase.

The amino acid sequences of epoxide hydrolase from rat, rabbit and human have been subjected to hydropathy analysis and a novel model for the membrane topology of this enzyme is presented. The enzyme would appear to be retained in microsomal membranes by a single transmembrane segment located at the N-terminus and the majority (96%) of the protein is exposed at the cytosolic membrane surface. This model is significantly different from a scheme suggested by analysis of the rat enzyme alone which proposed six transmembrane domains (Porter et al. (1988) Arch. Biochem. Biophys. 248, 121-129). Experiments with rat microsomal membranes were conducted to distinguish between the two models and used proteolytic enzymes and non-permeant chemical probes. Epoxide hydrolase of intact and permeabilised membranes was resistant to digestion by a number of proteinases. However, this is likely to be related to a compact fold of the protein rather than membrane association since purified, delipidated enzyme preparations were also resistant to proteolysis. While the use of proteinases did not provide useful membrane topological information, experiments with the fluorescent probe, 3-azido-2,7-naphthalenedisulphonate strongly support the view that the majority of the protein is indeed exposed at the cytosolic surface of the membranes. The analysis illustrates the caution which must be employed in the formulation of topological models based on hydropathy plots alone and the value of considering homologous proteins.

Animals↗
PubMed1990

Changes in hepatic xenobiotic-metabolising enzymes in mouse liver following infection with Leishmania donovani.

Infection of mice with Leishmania donovani resulted in decreased activities of several liver enzymes involved in the metabolism of xenobiotics. Microsomal membranes from infected livers contained reduced amounts of cytochromes P450 and b5 and NADPH-cytochrome P450 reductase. Several cytochrome P450 isoenzymes (P450-PB1, P450-PB3, P450-PCN and P450-UT1) and P450-mediated reactions (aminopyrine demethylase, aniline hydroxylase, benzphentamine demethylase and ethoxycoumarin deethylase) were affected similarly. The metabolism of two carcinogens (nitrosodimethylamine and 7,12-dimethylbenz[a]anthracene) by liver microsomal membrane preparations was also reduced. Leishmania infection caused an increase of cytosolic epoxide hydrolase and microsomal epoxide hydrolase and NADH-cytochrome b5 reductase were unaffected. The results suggest that Leishmania-infected animals are likely to have altered responses to exogenous toxins compared to uninfected animals.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

Induction of microsomal epoxide hydrolase by nitrosamines in rat liver. Effect on messenger ribonucleic acids.

Nitrosomethylethylamine and nitrosomethylpropylamine were found to be more potent inducers of rat liver microsomal epoxide hydrolase (styrene oxide hydrolase) than nitrosodiethylamine or nitrosodimethylamine. The time course of induction following a single administration of nitrosodimethylethylamine, nitrosomethylpropylamine or nitrosodiethylamine each showed a delay of 24 hr during which enzyme activity was unaltered. After that time activity increased and reached a maximum at between 72 and 120 hr. Increased enzyme activity following NDEA was paralleled by changes in the content of epoxide hydrolase in microsomes as measured by Western blots. Nitrosamines caused an increase of mRNA for epoxide hydrolase which was detected by probing Northern blots with a [32]-P labelled epoxide hydrolase cDNA and by in vitro translation of polyadenylated mRNA. Both methods showed a maximal increase at 72 hr after nitrosodiethylamine treatment but a significant increase was also observed at 24 hr although at this time no increase in enzyme activity was apparent.

Animals↗