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Biomedical subjects

M G Thomas

Publications and source records attributed to M G Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1999

Trefoil peptides and surgical disease.

BACKGROUND: Trefoil peptides are a family of small proteins that are expressed in a site-specific fashion by certain epithelial tissues. These peptides appear to be important in mucosal healing processes and in neoplastic disease. METHODS: This manuscript reviews the relevant literature obtained by an extensive text word search of the Medline database and a manual search of references from the articles identified. RESULTS AND CONCLUSION: Trefoil peptides are aberrantly expressed by a wide range of human carcinomas and gastrointestinal inflammatory conditions. They impart protection from injury to the gastrointestinal mucosa by possible interaction with mucin glycoproteins. Trefoil peptides influence epithelial cell migration and mucosal restitution following injury. In the future, serum levels of trefoil peptides might be used as markers for both neoplastic and inflammatory diseases. In addition, novel therapies based on such peptides might be used for gastrointestinal inflammatory conditions and to accelerate repair of the gastrointestinal mucosa after surgery.

Biomarkers↗
PubMed1999

Staging of rectosigmoid neoplasia with colonoscopic endoluminal ultrasonography.

BACKGROUND: The accurate staging of colorectal neoplasia may aid the stratification of patients for adjuvant treatment. At present the mural extent of neoplasia proximal to the mid rectum is difficult to determine. Prediction of mural invasion could help identify patients suitable for radical resection, minimal access surgery or endoscopic treatment. Colonoscopic endoluminal ultrasonography (EUS) was used in a prospective study to determine the stage of rectosigmoid neoplasia in 121 patients. METHODS: Mural tumour (T) stage was designated by EUS as uT0/1-uT4 in 121 patients. Nodal (N) staging was performed in 39 cases. EUS staging was compared with histological stage (pT and pN) in 93 patients who underwent resection. RESULTS: Mural staging of disease using colonoscopic EUS showed good correlation with histo-pathological stage (kappa = 0.85 (95 per cent confidence interval 0.76-0.95)). Overall pT and pN stage accuracy of EUS was 92 and 65 per cent respectively. CONCLUSION: EUS accurately assessed tumour stage although node staging remained suboptimal. Colonoscopic EUS may aid the selection of treatment in patients with rectosigmoid neoplasia.

Adult↗
PubMed1999

Protonmotive force, ExbB and ligand-bound FepA drive conformational changes in TonB.

TonB couples the cytoplasmic membrane protonmotive force (pmf) to active transport across the outer membrane, potentially through a series of conformational changes. Previous studies of a TonB transmembrane domain mutant (TonB-delta V17) and its phenotypical suppressor (ExbB-A39E) suggested that TonB is conformationally sensitive. Here, two new mutations of the conserved TonB transmembrane domain SHLS motif were isolated, TonB-S16L and -H20Y, as were two new suppressors, ExbB-V35E and -V36D. Each suppressor ExbB restored at least partial function to the TonB mutants, although TonB-delta V17, for which both the conserved motif and the register of the predicted transmembrane domain alpha-helix are affected, was the most refractory. As demonstrated previously, TonB can undergo at least one conformational change, provided both ExbB and a functional TonB transmembrane domain are present. Here, we show that this conformational change reflects the ability of TonB to respond to the cytoplasmic membrane proton gradient, and occurs in proportion to the level of TonB activity attained by mutant-suppressor pairs. The phenotype of TonB-delta V17 was more complex than the -S16L and -H20Y mutations, in that, beyond the inability to be energized efficiently, it was also conditionally unstable. This second defect was evident only after suppression by the ExbB mutants, which allow transmembrane domain mutants to be energized, and presented as the rapid turnover of TonB-delta V17. Importantly, this degradation was dependent upon the presence of a TonB-dependent ligand, suggesting that TonB conformation also changes following the energy transduction event. Together, these observations support a dynamic model of energy transduction in which TonB cycles through a set of conformations that differ in potential energy, with a transition to a higher energy state driven by pmf and a transition to a lower energy state accompanying release of stored potential energy to an outer membrane receptor.

Bacterial Outer Membrane Proteins↗
PubMed1999

Molecular characterization of eutF mutants of Salmonella typhimurium LT2 identifies eutF lesions as partial-loss-of-function tonB alleles.

The eutF locus of Salmonella typhimurium LT2 was identified as a locus necessary for the utilization of ethanolamine as a sole carbon source. Initial models suggested that EutF was involved in either ethanolamine transport or was a transcriptional regulator of an ethanolamine transporter. Phenotypic characterization of eutF mutants suggested EutF was somehow involved in 1,2-propanediol, propionate, and succinate utilization. Here we provide evidence that two alleles defining the eutF locus, Delta903 and eutF1115, are partial-loss-of-function tonB alleles. Both mutations were complemented by plasmids containing a wild-type allele of the Escherichia coli tonB gene. Immunoblot analysis using TonB monoclonal antibodies detected a TonB fusion protein in strains carrying eutF alleles. Molecular analysis of the Delta903 allele identified a deletion that resulted in the fusion of the 3' end of tonB with the 3' end of trpA. In-frame translation of the tonB-trpA fusion resulted in the final 9 amino acids of TonB being replaced by a 45-amino-acid addition. We isolated a derivative of a strain carrying allele Delta903 that regained the ability to grow on ethanolamine as a carbon and energy source. The molecular characterization of the mutation that corrected the Eut- phenotype caused by allele Delta903 showed that the new mutation was a deletion of two nucleotides at the tonB-trpA fusion site. This deletion resulted in a frameshift that replaced the 45-amino-acid addition with a 5-amino-acid addition. This change resulted in a TonB protein with sufficient activity to restore growth on ethanolamine and eut operon expression to nearly wild-type levels. It was concluded that the observed EutF phenotypes were due to the partial loss of TonB function, which is proposed to result in reduced cobalamin and ferric siderophore transport in an aerobic environment; thus, the eutF locus does not exist.

Amino Acid Sequence↗
PubMed1999

Vitamin D receptor expression in colorectal cancer.

AIMS: To determine whether the vitamin D receptor is expressed in colorectal cancer, and its relation to stage of disease. METHODS: Paraffin embedded sections of colorectal cancer from 30 patients who had undergone surgery were studied. Immunohistochemistry using the specific monoclonal antibody 9A7 gamma directed against the nuclear vitamin D receptor was used to identify receptors for the active metabolite of vitamin D3 (1,25-dihydroxyvitamin D3). RESULTS: Microscopically normal human colorectal epithelium showed vitamin D receptor expression predominantly in the mid and upper crypts. All the colorectal cancer tissue studied showed vitamin D receptor expression, with a median of 25.3 (range 10.1 to 43.7) cells/graticule field (x 400). Although vitamin D receptor staining was heterogeneous within the individual cancers, neither Dukes stage nor the degree of differentiation appeared to influence expression of the receptor. CONCLUSIONS: Colorectal cancer tissue expresses the nuclear vitamin D receptor and this could act as a potential therapeutic target for synthetic vitamin D3 differentiating agents.

Cell Nucleus↗
PubMed1998

Presence of a newly described human DNA virus (TTV) in patients with liver disease.

BACKGROUND: A newly described DNA virus, named transfusion-transmitted virus (TTV), was recently detected with high prevalence in Japanese patients with fulminant hepatitis and chronic liver disease of unknown aetiology. We investigated the presence of this virus in patients with liver disease in the UK to find out whether TTV infection is associated with liver damage. METHODS: We used semi-nested PCR to amplify TTV DNA from serum samples from 126 adults, of whom 72 were patients with a range of chronic liver diseases, 24 had spontaneous resolution of infection with hepatitis C virus (HCV), and 30 were normal controls. Direct DNA sequencing and phylogenetic analysis were used to characterise the TTV isolates. FINDINGS: We detected TTV DNA in 18 (25%) of the 72 patients with chronic liver disease, which was not different from the 10% prevalence in normal controls (p=0.15). The rate of TTV DNA was similar among patients with various liver diseases. The majority of TTV-positive cases had no biochemical or histological evidence of significant liver damage. TTV DNA sequencing of nine isolates showed the same genotypic groups as in Japan: three patients were infected with genotype 1, which showed 4% nucleotide divergence, and six patients were infected with genotype 2 with 15-27% divergence. INTERPRETATION: The high prevalence of active TTV infection in the general population, both in the UK and in Japan, and the lack of significant liver damage, suggest that TTV, similar to hepatitis G virus (HGV), may be an example of a human virus with no clear disease association.

Adult↗
PubMed1998

Molecular instability in the COII-tRNA(Lys) intergenic region of the human mitochondrial genome: multiple origins of the 9-bp deletion and heteroplasmy for expanded repeats.

We have identified two individuals from Glasgow in Scotland who have a deletion of one of two copies of the intergenic 9-bp sequence motif CCCCCTCTA, located between the cytochrome oxidase II (COII) and lysine tRNA (tRNA(Lys)) genes of the human mitochondrial genome. Although this polymorphism is common in Africa and Asia, it has not been reported in Northern Europe. Analysis of the mitochondrial DNA control region sequences of these two individuals suggests that they belong to a lineage that originated independently of the previously characterized African and Asian 9-bp deleted lineages. Among the Scottish population we have also identified a maternal lineage of three generations exhibiting heteroplasmy for two, three and four copies of the CCCCCTCTA motif. Polymerase chain reaction amplification across the COII-tRNA(Lys) intergenic region of these individuals gives different ratios of the three product lengths that are dependent on the concentration of the DNA-binding dye crystal violet. To investigate whether changes in repeat number were generated de novo, we constructed clones containing known numbers of the CCCCCTCTA motif. In the presence of high concentrations of crystal violet we obtained two, three and four copies of this motif when the amplification template contained only four copies. Various DNA-binding drugs are known to stabilize bulged structures in DNA and contribute to the process of slipped-strand mispairing during DNA replication. These results suggest that the COII-tRNA(Lys) intergenic region is unstable owing to slipped-strand mispairing. Although sequences containing four copies of the CCCCCTCTA motif are less stable in vitro, we observed an increase in the proportion of mitochondrial genomes with four repeats between-a mother and a daughter in the heteroplasmic lineage. From this we conclude that drift in the germ-line lineage is a main factor in the maintenance or loss of heteroplasmy.

Africa↗
PubMed1998

Three-dimensional structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase from Salmonella typhimurium determined to 2.3 A resolution,.

The X-ray structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase (CobU) from Salmonella typhimurium has been determined to 2.3 A resolution. This enzyme of subunit molecular weight 19 770 plays a central role in the assembly of the nucleotide loop for adenosylcobalamin where it catalyzes both the phosphorylation of the 1-amino-2-propanol side chain of the corrin ring and the subsequent attachment of GMP to form the product adenosylcobinamide-GDP. The kinase activity is believed to be associated with a P-loop motif, whereas the transferase activity proceeds at a different site on the enzyme via a guanylyl intermediate. The enzyme was crystallized in the space group C2221 with unit cell dimensions of a = 96.4 A, b = 114.4 A, and c = 106.7 A, with three subunits per asymmetric unit. The structure reveals that the enzyme is a molecular trimer and appears somewhat like a propeller with overall molecular dimensions of approximately 64 A x 77 A x 131 A. Each subunit consists of a single domain that is dominated by a seven-stranded mixed beta-sheet flanked on either side by a total of five alpha-helices and one helical turn. Six of the seven beta-strands run parallel. The C-terminal strand lies at the edge of the sheet and runs antiparallel to the others. Interestingly, CobU displays a remarkable structural and topological similarity to the central domain of the RecA protein, although the reason for this observation is unclear. The structure contains a P-loop motif located at the base of a prominent cleft formed by the association of two subunits and is most likely the kinase active site. Each subunit of CobU contains a cis peptide bond between Glu80 and Cys81 where Glu80 faces the P-loop and might serve to coordinate the magnesium ion of the triphosphate substrate. Interestingly, His46, which is the putative site for guanylylation, lies approximately 21 A from the P-loop and is solvent-exposed. This suggests that the enzyme undergoes a conformational change when the substrates bind to bring these two active sites into closer proximity.

Adenosine Triphosphate↗
PubMed1998

Schizophrenia susceptibility loci on chromosomes 13q32 and 8p21.

Schizophrenia is a common disorder characterized by psychotic symptoms; diagnostic criteria have been established. Family, twin and adoption studies suggest that both genetic and environmental factors influence susceptibility (heritability is approximately 71%; ref. 2), however, little is known about the aetiology of schizophrenia. Clinical and family studies suggest aetiological heterogeneity. Previously, we reported that regions on chromosomes 22, 3 and 8 may be associated with susceptibility to schizophrenia, and collaborations provided some support for regions on chromosomes 8 and 22 (refs 9-13). We present here a genome-wide scan for schizophrenia susceptibility loci (SSL) using 452 microsatellite markers on 54 multiplex pedigrees. Non-parametric linkage (NPL) analysis provided significant evidence for an SSL on chromosome 13q32 (NPL score=4.18; P=0.00002), and suggestive evidence for another SSL on chromosome 8p21-22 (NPL=3.64; P=0.0001). Parametric linkage analysis provided additional support for these SSL. Linkage evidence at chromosome 8 is weaker than that at chromosome 13, so it is more probable that chromosome 8 may be a false positive linkage. Additional putative SSL were noted on chromosomes 14q13 (NPL=2.57; P=0.005), 7q11 (NPL=2.50, P=0.007) and 22q11 (NPL=2.42, P=0.009). Verification of suggestive SSL on chromosomes 13q and 8p was attempted in a follow-up sample of 51 multiplex pedigrees. This analysis confirmed the SSL in 13q14-q33 (NPL=2.36, P=0.007) and supported the SSL in 8p22-p21 (NPL=1.95, P=0.023).

Adult↗
PubMed1998

Gonadotropin-releasing hormone secretion into third-ventricle cerebrospinal fluid of cattle: correspondence with the tonic and surge release of luteinizing hormone and its tonic inhibition by suckling and neuropeptide Y.

Objectives of the current studies were to characterize the pattern of GnRH secretion in the cerebrospinal fluid of the bovine third ventricle, determine its correspondence with the tonic and surge release of LH in ovariectomized cows, and examine the dynamics of GnRH pulse generator activity in response to known modulators of LH release (suckling; neuropeptide Y [NPY]). In ovariectomized cows, both tonic release patterns and estradiol-induced surges of GnRH and LH were highly correlated (0.95; p < 0.01). Collectively, LH pulses at the baseline began coincident with (84%) or within one sampling point after (100%) the onset of a GnRH pulse, and all estradiol-induced LH surges were accompanied by corresponding surges of GnRH. A 500- microg dose of NPY caused immediate cessation of LH pulses and lowered (p < 0.001) plasma concentrations of LH for at least 4 h. This corresponded with declines (p < 0.05) in both GnRH pulse amplitude and frequency, but GnRH pulses were completely inhibited for only 1.5-3 h. In intact, anestrous cows, GnRH pulse frequency did not differ before and 48-54 h after weaning on Day 18 postpartum, but concentrations of GnRH (p < 0.05) and amplitudes of GnRH pulses (4 of 7 cows) increased in association with weaning and heightened secretion of LH. We conclude that the study of GnRH secretory dynamics in third-ventricle CSF provides a reasonable approach for examining the activity and regulation of the hypothalamic pulse generator in adult cattle. However, data generated using this approach must be interpreted in their broadest context. Although strong neurally mediated inhibitors of LH pulsatility (suckling; NPY) had robust effects on one or more GnRH secretory characteristics in CSF, only high doses of NPY briefly abolished GnRH pulses. This implies that the GnRH signal received at the hypophyseal portal vessels under these conditions may differ quantitatively or qualitatively from those in CSF, and theoretically would be undetectable or below a biologically effective threshold when LH pulses are absent.

Animals↗
PubMed1997

Tuberculosis in those with HIV infection.

AIMS: To determine the incidence, demography, clinical features, treatments and outcome for patients with tuberculosis and human immunodeficiency virus (HIV) infection in Auckland. METHODS: We reviewed the notes of all patients with HIV infection and tuberculosis seen by the Infectious Disease Unit, at Auckland Hospital since the onset of the HIV epidemic in New Zealand in 1984 until 31 December 1995. RESULTS: Eleven patients have had HIV infection and tuberculosis, 2.4% of all those with HIV infection cared for by this unit. Ten were male and eight homosexual. The median age was 30 years (range 24-57). The incidence in Pakeha was 1.2% (3 of 234), in Maori 20% (5 of 25) and in African 27% (3 of 11). Until 1990 we saw one case every two years and since then one or two cases per year. Six patients had normal chest x-rays and five had abnormal chest x-rays; of the latter, three were typical of tuberculosis and two atypical. Ten of the eleven strains of Mycobacterium tuberculosis cultured were fully sensitive but one was resistant to both rifampicin and isoniazid. Conventional treatment regimens were used. Seven patients have died of HIV infection, three continue treatment and one returned to Africa. One patient relapsed with fully sensitive tuberculosis. Three patients had major side effects to rifampicin necessitating alternative treatment. CONCLUSIONS: Tuberculosis is uncommon amongst those with HIV infection in Auckland but the incidence has risen in recent years. The risks amongst Maori and Africans are high. Multidrug resistant tuberculosis is uncommon. Those caring for patients with tuberculosis need to be mindful of HIV infection: those caring for patients with HIV infection need to be increasingly alert for tuberculosis.

AIDS-Related Opportunistic Infections↗
PubMed1997

Villous adenoma of the distal appendix.

Villous adenoma confined to the distal appendix has not been previously reported in conjunction with acute apendicitis. The presence of an adenoma indicates a need for further investigation due to an association with neoplasia elsewhere.

Acute Disease↗
PubMed1997

The steroid vitamin D3 reduces cell proliferation in human duodenal epithelium.

1. The active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3, controls calcium absorption in the human duodenum, an effect that is mediated by mucosal vitamin D receptor expression. Functional vitamin D receptor signalling in the human colon is suggested by the reduced colonic mucosal cell proliferation seen in response to 1,25-dihydroxyvitamin D3. Thus 1,25-dihydroxyvitamin D3 might be expected to reduce cell proliferation in the small-bowel epithelium. 2. We have used an organ-culture system combined with the metaphase arrest technique to study the effects of 1,25-dihydroxyvitamin D3 on human duodenal mucosal proliferation. To validate our technique, multiple human mucosal explants were established in organ culture and vincristine (0.6 micrograms/ml) was added at 10 h. Explants were removed sequentially from 10 to 15 h and metaphase arrest figures were demonstrated by using the Feulgen reaction. The mean number of metaphase arrest figures was plotted against time in culture to show a linear accumulation of metaphases between 11 and 15 h (correlation coefficient = 0.93, r2 = 0.87, P < 0.0001). The mean crypt cell production rate was 2.01 (0.27) cells/h per crypt. 3. Paired normal duodenal mucosal biopsies from six patients were then established in organ culture with or without 10(-10) mol/l (100 pmol/l) 1,25-dihydroxyvitamin D3. The crypt cell production rate was determined between 12 and 15 h after vincristine-induced metaphase arrest. 1,25-Dihydroxyvitamin D3 reduced the median crypt cell production rate from 2.42 (1.15-4.82) to 1.41 (0.03-2.05) cells/h per crypt (P < 0.05). Thus, vitamin D3 reduces human duodenal epithelial cell proliferation.

Aged↗