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Biomedical subjects

A C Williams

Publications and source records attributed to A C Williams.

At least 19 recordsLinked to original sources
PubMed1995

Sucrose reduces the efficiency of protein denaturation by a chaotropic agent.

Sugars and polyols are used to stabilize proteins. The degree of stabilization conferred on a model protein by sucrose was calculated in terms of the free energy of folding. Phosphoglycerate kinase (PGK) was denatured by guanidine hydrochloride (GuHCl) in different sucrose concentrations. The linear extrapolation method [1,2] was used to calculate the free energy of folding in the absence of denaturant. Although sucrose increased the concentration of GuHCl required to unfold the protein, the free energy of folding in water was unchanged. In order to probe the nature of the stabilizing effect of sucrose, an FT-Raman spectroscopic study of denaturant-polyol systems was undertaken. Investigations of interactions between GuHCl, urea or formamide and polyhydric compounds, revealed no evidence for hydrogen bonding or dipole-dipole associations. Polyhydric compounds caused minor changes in denaturant spectra although the converse was not observed. The structure of deuterated water changed on addition of denaturants. For non-ionic denaturants, addition of polyhydric solutes countered this change in water structure. Thus polyhydric compounds oppose the effect of denaturants on water structure. The observed increase in GuHCl concentration required to unfold PGK in the presence of sucrose may be attributed to this property of sucrose.

Formamides↗
PubMed1995

Mutant p53 is not fully dominant over endogenous wild type p53 in a colorectal adenoma cell line as demonstrated by induction of MDM2 protein and retention of a p53 dependent G1 arrest after gamma irradiation.

To determine whether a single mutational event in one p53 gene is sufficient to confer a significant growth advantage on a colonic epithelial cell, the 143(Ala) p53 mutation was previously expressed in the human colonic adenoma derived cell line AA/C1 (which is wild type for p53) and shown to have no effect on it's in vitro or in vivo growth characteristics. In this investigation, by expressing the 175(His), 248(Trp) or 273(His) mutations in the same AA/C1 cell line, we have shown that this failure to affect the growth of the cells was not mutant specific. We have also demonstrated, using induction of MDM2 protein and the ability of the cells to undergo a p53 dependent G1 arrest, that the 143(Ala), 175(His) or 248(Trp) transfected cells retain functional endogenous wild type p53 activity, and suggest that these p53 mutations would not have a fully dominant negative mode of action in vivo. In contrast, one of the two AA/C1 cell lines transfected with the 273(His) mutation did fail to cell cycle arrest after gamma irradiation, indicating that this mutation can act as a dominant negative. However even loss of wild type p53 function in this cell line was insufficient to directly effect the growth rate of the AA/C1 cells, suggesting that acquisition of the 273(His) mutation may contribute to malignant progression through genomic instability (by inhibiting the G1 arrest) and that other mutations are required before outgrowth of the cell population containing the p53 mutation.

Adenoma↗
PubMed1995

The 'Iceman': molecular structure of 5200-year-old skin characterised by Raman spectroscopy and electron microscopy.

The molecular state of about 5200-year-old skin from the so-called 'Iceman' (Similaun man or Otzi) has been characterised using Fourier transform Raman spectroscopy, and has been compared with that of contemporary man. Contemporary skin was also freeze-dried (to mimic the conditions under which the ancient skin was preserved) and its molecular structure was compared with that of Iceman skin. The results showed that the proteinaceous moiety of the ancient skin had degraded considerably and, although olefinic bonds had probably oxidised, the lipoidal component was largely unaltered. Electron microscopical comparisons of Iceman and contemporary skin showed that the gross structure of Iceman skin had survived essentially intact for five millennia.

Animals↗
PubMed1995

An allelic association study of monoamine oxidase B in Parkinson's disease.

A single-stranded conformational polymorphism in the monoamine oxidase B gene was shown to be A or G, 36 bases upstream from the intron 13-exon 14 boundary. An allelic association study revealed no statistically significant associations between this single-base polymorphism and Parkinson's disease, unlike the results of a previous study.

Adult↗
PubMed1995

Toxicity of sulphur-containing compounds to neuronal cell lines.

Cysteine and its metabolites cysteine sulphinic acid (CSA) and taurine (TA) were shown to be toxic to human and rat neuronal cell lines. However, the mechanisms of action of CSA and TA appeared to be different. As MND/ALS patients have high plasma and CSF cysteine levels, they may have increased levels of neurotoxins in vivo, since cysteine was more toxic than CSA in the assay system used. Cysteic acid, homocysteic acid, BMAA and BOAA were also toxic to the cell lines used.

Animals↗
PubMed1994

Human cysteine dioxygenase type I: primary structure derived from base sequencing of cDNA.

The base sequence of cDNA encoding the complete human liver cysteine dioxygenase type I (CDO-I; EC 1.13.11.20) message, and the derived amino-acid sequence are reported. CDO-I is encoded on a single mRNA species (approx. 1.5 kb). Human CDO-I clones were identified by screening a liver cDNA library, and inserts were isolated and sequenced. In addition, human liver total RNA was reverse-transcribed and CDO-I cDNA amplified by PCR using a modified poly-T primer and specific CDO-I primers to give a second source of sequencing template. The CDO-I message encodes a 200 amino-acid residue protein, the sequence of which has greater than 90% homology with the equivalent rat enzyme. The message was not expressed in a human hepatoma cell line (Hep G2).

Amino Acid Sequence↗
PubMed1994

Loss of APC protein expressed by human colonic epithelial cells and the appearance of a specific low-molecular-weight form is associated with apoptosis in vitro.

APC (adenomatous polyposis coli) protein is differentially expressed in the normal colonic crypt and believed to be involved in colonic cell maturation. In this work we investigated whether expression of the APC protein is associated with cell death in colonic epithelial cells. We have previously reported an in vitro system to study apoptosis. Briefly, cells attached to the flask have a low frequency of apoptosis (1-3%), whereas cells that detach from the flask and float in the medium have a high proportion of apoptotic cells (36-96% depending on the cell line). The full-length 300-kDa or truncated APC protein, normally expressed by the attached cells (detected using the FE9 antibody), was found to be lost in the floating apoptotic cells in 8/11 colon tumour cell lines examined. In addition, the APC antibody FE9 detected a 90-kDa protein in the floating apoptotic cells of all cell lines investigated, which was not present in attached cells. Furthermore, loss of full-length APC and gain of the 90-kDa protein was observed in the apoptotic cells of 2 cell lines derived from other tissues: the SV40-transformed fibroblast cell line CMSV40fib and the lymphoblastoid B-cell line BJA-B. In cells repeatedly frozen and thawed, believed to induce necrotic cell death, full-length or truncated APC was also lost, though a 95-kDa protein distinct from that in apoptotic cells was observed. Specific loss of full-length or truncated APC (resulting in a 90-kDa protein in apoptotic cells but a 95-kDa protein in necrotic cells) is therefore associated with cell death. Our findings suggest a possible role for APC in cell survival.

Adenoma↗
PubMed1994

Pathways of cysteine metabolism in MND/ALS.

Analysis of plasma from MND/ALS patients has shown no significant differences in metabolism of cysteine derivatives, although a sub-set of the population has raised glutamate values. Cysteine dioxygenase was found to have reduced activity in vitro, consistent with previous findings of a high plasma cysteine/sulphate ratio.

Adult↗
PubMed1994

Comparison of Fourier transform Raman spectra of mammalian and reptilian skin.

Human skin offers potential advantages for the administration of therapeutic agents for both local and systemic use. However, in studies of transdermal drug delivery, problems with the supply, storage, and use of human tissue have encouraged workers to seek alternative animal materials to model drug diffusion across human skin. We obtained Fourier transform Raman spectra from mammalian (human and pig) and reptilian (snake) skins, and considered structural dissimilarities in the light of differences observed in the diffusion of drugs across the tissues.

Animals↗
PubMed1994

D-penicillamine metabolism in neurodegenerative diseases: an in vivo/in vitro sulphydryl methylation study.

1. D-Penicillamine (125 mg) was administered orally to control (healthy volunteers), Parkinson's and Motor Neurone Disease patients following an overnight fast. 2. Blood was collected at 08:00 h for the preparation of red blood cell membranes used in the in vitro S-methylation studies. Urine was collected from 08:00 to 16:00 h and analysed for D-penicillamine and its metabolites. 3. Metabolism occurred via S-methylation, N-acetylation and disulphide formation. Both the Parkinson's and Motor Neurone Disease patients excreted significantly higher median levels of S-methyl-D-penicillamine in the urine than the controls (177 and 209% more for the Parkinson's and Motor Neurone Disease patients respectively). 4. The in vitro and in vivo production of S-methyl-D-pencillamine was highly correlated in the control (rs = 0.936), Parkinson's (0.986) and Motor Neurone Disease (0.752) populations.

Adult↗
PubMed1992

Specific cytogenetic abnormalities and k-ras mutation in two new human colorectal-adenoma-derived cell lines.

Two new human epithelial cell lines from sporadic colorectal adenomas designated S/RR and S/BR are reported. Both cell lines have extended growth capacities in vitro, reaching passages 38 and 40 respectively and show no sign of senescence. S/RR and S/BR cell lines have retained the ability to differentiate in vitro, as shown by mucin production from goblet-like cells. S/BR was derived from a large colonic tubular villous adenoma (3 to 4 cm), whereas S/RR was derived from a small rectal adenoma (< 1 cm), and may represent a relatively early-stage adenoma. The parent S/RR cell line has given rise to a clonogenic variant, designated S/RR/Cl, which also has shown no sign of senescence and has currently reached passage 43. Both the S/BR and the S/RR cell lines had mutations in codon 12 of the K-ras gene, while retaining one normal allele. The presence of this mutation, particularly in the cell line S/RR derived from a small adenoma, is consistent with ras mutation being a relatively early event in colorectal carcinogenesis and is perhaps involved in the ability of the adenoma cells to progress and to give rise to an immortal cell line in vitro. The clonal derivatives of the S/RR cells have an isochromosome 1q and abnormalities of chromosome 13 which include an isochromosome 13q. The S/BR cells have a deletion on the short arm of chromosome 1 and trisomy 7. The common abnormality for S/RR and S/BR cells involves chromosome 1. The involvement of different chromosomes in the 2 cell lines also suggests different pathways for malignant progression of the premalignant adenoma cells.

Adenoma↗
PubMed1992

A single human colonic adenoma cell line can be converted in vitro to both a colorectal adenocarcinoma and a mucinous carcinoma.

In a previous study, using a chemical carcinogen, we converted in vitro a non-tumorigenic cell line derived from a human colorectal diploid adenoma, designated PC/AA, into a tumorigenic cell line which, when inoculated into athymic nude mice, produced progressively growing adenocarcinomas. We now report that continuous in vitro passage of the PC/AA adenoma cell line resulted in its spontaneous transformation to a mucinous carcinoma with a modal karyotype of 51, XY, +i(Iq), +8, +9, +13, +i(13q), -21, +mar. These studies show that a single adenoma can be converted along 2 independent pathways, giving rise to either a mucinous carcinoma or an adenocarcinoma, and provide further experimental evidence for the adenoma-carcinoma sequence. Cytogenetic changes which occur along both pathways to tumorigenicity include abnormalities of chromosome I and multiple copies of chromosome 13. These abnormalities may be important in tumour development and progression in colorectal carcinogenesis.

Adenocarcinoma↗
PubMed1992

Debrisoquine hydroxylase gene polymorphism and susceptibility to Parkinson's disease.

The pathogenesis of Parkinson's disease may be influenced by genetic and environmental factors. Cytochrome P450 mono-oxygenases help to protect against toxic environmental compounds and individual variations in cytochrome P450 expression might, therefore, influence susceptibility to environmentally linked diseases. The frequency of mutant CYP2D6 alleles was studied in 229 patients with Parkinson's disease and 720 controls. Individuals with a metabolic defect in the cytochrome P450 CYP2D6-debrisoquine hydroxylase gene with the poor metaboliser phenotype had a 2.54-fold (95% Cl 1.51-4.28) increased risk of Parkinson's disease. Determination of CYP2D6 phenotype and genotype may help to identify those at greatest risk of Parkinson's disease and may also help to identify the environmental or metabolic agents involved in the pathogenesis of this disease.

Cytochrome P-450 CYP2D6↗
PubMed1992

Hyperproinsulinaemia in patients with myotonic dystrophy.

Hyperinsulinaemia is a reported feature of the inherited multisystem disorder myotonic dystrophy. This phenomenon has been attributed to a compensatory beta cell response to tissue insulin resistance. In this study, circulating concentrations of insulin, proinsulin, and split proinsulin molecules were determined after an overnight fast in ten patients with myotonic dystrophy using two-site monoclonal antibody-based immunoradiometric assays. Results were compared with ten healthy control subjects matched for age, gender, and body mass index. Oral glucose tolerance (75 g), as defined by World Health Organization criteria, was normal in all subjects. Fasting plasma immunoreactive insulin concentration, as determined using a conventional radioimmunoassay, was almost three times higher (p < 0.005) in the myotonic dystrophy patients than the healthy control subjects. By contrast, fasting concentrations (mean +/- SEM) of C-peptide (0.75 +/- 0.09 vs 0.52 +/- 0.03 nmol/l, p = 0.07) and immunoradiometrically-determined insulin (60 +/- 12 vs 38 +/- 4 pmol/l, p = 0.09) were not significantly different between the groups. Fasting concentrations of proinsulin (10.3 +/- 2.9 vs 1.6 +/- 0.3 pmol/l, p < 0.01), and 32-33 split proinsulin (7.8 +/- 2.5 vs 2.9 +/- 0.4 pmol/l, p < 0.05) were significantly elevated in the patients with myotonic dystrophy. Accordingly, the mean fasting proinsulin:insulin ratio, expressed as a percentage, was significantly increased in the myotonic patients (20 +/- 5 vs 4 +/- 1%, p < 0.01). The overall C-peptide response to the oral glucose challenge was significantly greater in the myotonic patients compared with the healthy control subjects (p < 0.001). These results provide corroborative evidence of increased beta-cell secretion in myotonic dystrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

C-Peptide↗