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Biomedical subjects

A Steward

Publications and source records attributed to A Steward.

At least 19 recordsLinked to original sources
PubMed2001

The folding nucleus of a fibronectin type III domain is composed of core residues of the immunoglobulin-like fold.

To identify the contacts that stabilise the rate-limiting transition state for folding of FNfn10 (the tenth fnIII domain of human fibronectin), 42 mutants have been analysed at 29 positions across this domain. An anomalous response to mutation means that structure formation in the A, B and G strands cannot be evaluated by this method. In all the residues analysed, phi-values are fractional and no completely structured region is observed. The analysis reveals that hydrophobic residues from the central strands of the beta-sandwich form a large core of interactions in the transition state. Brønsted analysis shows that the stabilisation energy from the amino acid side-chains in the transition state is approximately 40 % of that in the native state. The protein folds by a nucleation-condensation mechanism, and tertiary interactions within the core make up the folding nucleus. Local interactions, in turns and loops, are apparently much less significant. Comparison with an homologous domain from human tenascin (TNfn3), shows that FNfn10 has a more extended, structured transition state spanning three different "layers" of the beta-sandwich. The results support the hypothesis that interactions in the common structural core guide the folding of these domains.

Fibronectins↗
PubMed2001

Can non-mechanical proteins withstand force? Stretching barnase by atomic force microscopy and molecular dynamics simulation.

Atomic force microscopy (AFM) experiments have provided intriguing insights into the mechanical unfolding of proteins such as titin I27 from muscle, but will the same be possible for proteins that are not physiologically required to resist force? We report the results of AFM experiments on the forced unfolding of barnase in a chimeric construct with I27. Both modules are independently folded and stable in this construct and have the same thermodynamic and kinetic properties as the isolated proteins. I27 can be identified in the AFM traces based on its previous characterization, and distinct, irregular low-force peaks are observed for barnase. Molecular dynamics simulations of barnase unfolding also show that it unfolds at lower forces than proteins with mechanical function. The unfolding pathway involves the unraveling of the protein from the termini, with much more native-like secondary and tertiary structure being retained in the transition state than is observed in simulations of thermal unfolding or experimentally, using chemical denaturant. Our results suggest that proteins that are not selected for tensile strength may not resist force in the same way as those that are, and that proteins with similar unfolding rates in solution need not have comparable unfolding properties under force.

Animals↗
PubMed2000

The folding of an immunoglobulin-like Greek key protein is defined by a common-core nucleus and regions constrained by topology.

TNfn3, the third fibronectin type III domain of human tenascin, is an immunoglobulin-like protein that is a good model for experimental and theoretical analyses of Greek key folding. The third fibronectin type III domain of human tenascin folds and unfolds in a two-state fashion over a range of temperature and pH values, and in the presence of stabilising salts. Here, we present a high resolution protein engineering analysis of the single rate determining transition state. The 48 mutations report on the contribution of side-chains at 32 sites in the core and loop regions. Three areas in the protein exhibit high Phi-values, indicating that they are partially structured in the transition state. First, a common-core ring of four positions in the central strands B, C, E and F, that are in close contact, form a nucleus of tertiary interactions. The two other regions that appear well-formed are the C' region and the E-F loop. The Phi-values gradually decrease away from these regions such that the very ends of the two terminal strands A and G, have Phi-values of zero. We propose a model for the folding of immunoglobulin-like proteins in which the common-core "ring" forms the nucleus for folding, whilst the C' and E-F regions are constrained by topology to pack early. Folding characteristics of a group of structurally related proteins appear to support this model.

Amino Acid Motifs↗
PubMed1999

CYP2D6 is associated with Parkinson's disease but not with dementia with Lewy Bodies or Alzheimer's disease.

The similarities between the clinical and pathological findings of dementia with Lewy Bodies (DLB) with Alzheimer's disease and Parkinson's disease are complex, and their significance for pathogenesis is unresolved. It is likely that DLB shares common disease determinants with both Alzheimer's disease and Parkinson's disease. Clinically DLB shows the presence of dementia similar, though not identical, to that found in Alzheimer's disease. A parkinsonian movement disorder is present in a proportion of DLB cases. Pathologically DLB shows senile plaques, as with Alzheimer's disease, and also substantia nigra neurone loss and Lewy bodies, as with Parkinson's disease. At a genetic level, DLB shows an elevated Apolipoprotein E epsilon4 frequency as described in Alzheimer's disease, but this is absent in Parkinson's disease. An elevated frequency of the CYP2D6*4 allele has been found in Parkinson's disease and we have therefore genotyped a large series of clinically and neuropathologically confirmed cases of DLB, Alzheimer's disease, Parkinson's disease and age-matched control individuals for the CYP2D6*4 allele. Whilst an elevated frequency of the CYP2D6*4 allele was found in Parkinson's disease, no such elevations were found in DLB or Alzheimer's disease. Stratification of the CYP2D6*4 allele with respect to the Apolipoprotein E epsilon4 also did not show any significant associations with the CYP2D6*4 allele. The CYP2D6*4 allele is not a major genetic determinant of DLB and the results place DLB with Alzheimer's disease rather than Parkinson's disease on a genetic level.

Aged↗
PubMed1998

Co-administration of polyanions with a phosphorothioate oligodeoxynucleotide (CGP 69846A): a role for the scavenger receptor in its in vivo disposition.

The effects of co-administering polyanions on the pharmacokinetics of a 20-mer phosphorothioate oligodeoxynucleotide (CGP 69846A), and the role of scavenger receptors in its in vivo disposition, have been investigated. Following i.v. administration, CGP 69846A was rapidly cleared from the plasma and distributed amongst high (e.g. kidney, liver, spleen), low (e.g. skeletal muscle) and negligible (e.g. brain) accumulating tissues. In addition it was shown that: 1) dextran sulphate co-administration has a dose-dependent effect on the disposition of CGP 69846A; 2) CGP 69846A undergoes renal filtration and renal accumulation largely results from tubular reabsorption; 3) cross-inhibition studies are consistent with CGP 69846A being recognized by scavenger receptors in vitro and in vivo; and 4) the scavenger receptor may be an important determinant for the in vivo disposition of CGP 69846A in mice. These studies contribute toward an increased understanding of the mechanism underlying the pharmacokinetic behaviour of phosphorothioate oligodeoxynucleotides.

Animals↗
PubMed1998

CYP2D6 phenotype-genotype relationships in African-Americans and Caucasians in Los Angeles.

CYP2D6 genotyping (CYP2D6*3, CYP2D6*4, CYP2D6*5, CYP2D6*13, CYP2D6*16 alleles and gene duplications) was previously performed on 1053 Caucasian and African-American lung cancer cases and control individuals and no significant difference in allele frequencies between cases and control individuals detected. We have carried out additional genotyping (CYP2D6*6, CYP2D6*7, CYP2D6*8, CYP2D6*9, CYP2D6*10, CYP2D6*17 alleles) and debrisoquine phenotyping on subgroups from this study to assess phenotype-genotype relationships. African-Americans showed significant differences from Caucasians with respect to frequency of defective CYP2D6 alleles, particularly CYP2D6*4 and CYP2D6*5. The CYP2D6*17 allele occurred at a frequency of 0.26 among 87 African-Americans and appeared to explain higher average metabolic ratios among African-Americans compared with Caucasians. CYP2D6*6, CYP2D6*8, CYP2D6*9 and CYP2D6*10 were rare in both ethnic groups but explained approximately 40% of higher than expected metabolic ratios among extensive metabolizers. Among individuals phenotyped with debrisoquine, 32 out of 359 were in the poor metabolizer range with 24 of these (75%) also showing two defective CYP2D6 alleles. Additional single strand conformational polymorphism analysis screening of samples showing large phenotype-genotype discrepancies resulted in the detection of three novel polymorphisms. If subjects taking potentially interfering drugs were excluded, this additional screening enabled the positive identification of 88% of phenotypic poor metabolizers by genotyping. This sensitivity was comparable with that of phenotyping, which identified 90% of those with two defective alleles as poor metabolizers.

Base Sequence↗
PubMed1996

An improved animal model for studying desferrioxamine.

A hamster model has been developed for studying desferrioxamine. The hamster shows many similarities to man in terms of plasma stability and metabolites formed from desferrioxamine. The [59Fe]ferritin derived from rats has been shown to be sequestered into liver parenchymal cells when injected intravenously into hamsters. The technique has proved sufficiently sensitive to enable detection of differences of < 1% of the radioactivity administered in the elimination of iron. Alterations in iron excretion were seen when dosing desferrioxamine via different routes. The principal route of iron excretion was into the intestines. The effectiveness of the dosing routes for desferrioxamine in removing iron were subcutaneous (10.5%) > intravenous (6.25%) > oral (3.66%) > control (2.19%). A dose-response relationship was demonstrated using the intravenous dose route. The model offers a simple method for comparing the efficacy of administration routes for determining the optimal use of desferrioxamine.

Animals↗
PubMed1995

The transmucosal absorption of recombinant human interferon-alpha B/D hybrid in the rat and rabbit.

For therapeutic proteins such as interferon-alpha B/D, a non-parenteral route of delivery is desirable. Possible sites of administration include the various regions of the gastrointestinal tract and airways, and this paper reports the bioavailability of interferon-alpha B/D via these routes in the rat and rabbit. Apart from the stomach, detectable levels of interferon-alpha B/D in the serum were achieved via all routes. Bioavailabilities were less than 1%, except from the lung (6.8% in the rat) and nasal cavity (2.9% in the rabbit). Absorption from the gastrointestinal tract was similar for both species, but in the nasal cavity of the rabbit was sixfold that of the rat, and in the lung of the rat was tenfold that in the rabbit. Absorption from all routes, except the buccal cavity, resulted in detectable biochemical changes in the liver of the rabbit. Comparison with reports from other groups show differences in the extent of absorption of interferon-alpha B/D and of natural or homologous recombinant interferon-alpha. The non-parenteral delivery of biochemically active amounts of interferon-alpha B/D is thus demonstrated.

Absorption↗
PubMed1992

Effects of androgens in models of rheumatoid arthritis.

Testosterone and its metabolite 5 alpha-dihydrotestosterone (DHT) were compared with dexamethasone 21-acetate in two different animal models of arthritis and found to have effects on cartilage breakdown and inflammation. In the mouse air pouch, at the three dose levels used, significant effects were obtained with DHT and were more pronounced on cartilage breakdown than on inflammation. At the lowest dose of 0.3 mg kg-1 there was a 64% inhibition of collagen breakdown and 18% inhibition of glycosaminoglycans (GAGs) breakdown. In the antigen-induced arthritis mouse model testosterone had significant inhibitory effects on inflammation (synovial hyperplasia) and cartilage erosion.

Animals↗
PubMed1988

A modified mouse air pouch model for evaluating the effects of compounds on granuloma induced cartilage degradation.

1. Employing rat femoral head cartilage implanted in a 6 day old mouse air pouch, the effects of inflammatory stimuli (i.e. cotton pellets, carrageenan, zymosan) on the loss of proteoglycan and collagen and granuloma formation have been studied. 2. Wrapping of the cartilage in cotton resulted in granuloma formation with accelerated loss of proteoglycan and collagen over the 14 day implantation period. The amount of loss increased with increasing weight of cotton. 3. The effects of different classes of anti-rheumatic drugs on granuloma formation and proteoglycan and collagen loss from cotton wrapped femoral head cartilage in the mouse air pouch have been studied. 4. Non-steroidal anti-inflammatory drugs (NSAIDs) had no influence on granuloma formation, but in general accelerated the rates of proteoglycan and collagen loss. 5. Dexamethasone and prednisolone significantly reduced granuloma formation and had a marked protective effect on cartilage breakdown. 6. Of the slow acting anti-rheumatic drugs examined, only gold sodium thiomalate (GSTM) and dapsone significantly decreased cartilage loss, with an accompanying modest decrease in granuloma formation. 7. The immunosuppressants cyclophosphamide and methotrexate, but not azathioprine, reduced cartilage degradation, but had no effect on granuloma formation. 8. The results for the different classes of anti-inflammatory and anti-rheumatic drugs are discussed in relation to their effects in other animal models and their reported therapeutic activities in man. It is concluded that the mouse air pouch method as described offers advantages as an animal model over existing procedures to predict therapeutic efficacy in man.

Animals↗
PubMed1988

Proteoglycan biosynthesis as a determinant of patella damage in the murine antigen-induced arthritis model.

The incorporation of 35SO4 into cartilage proteoglycan has been employed as a measure of patella damage in the murine antigen-induced arthritis model. In a preliminary set of experiments, where both the proteoglycan concentration and 35SO4 incorporation were determined in control and arthritic patella over a 2 day to 6 day week period, the arthritic joint contained significantly higher levels of radioactivity compared with the controls. A subsequent study over an extended period of 10 weeks confirmed the earlier results, and indicated that the 6 week samples showed the greatest difference (71%) in 35SO4 incorporation between the arthritic and control patella.

Animals↗
PubMed1988

The serum amyloid P response in the mouse air pouch.

Levels of the acute phase reactant serum amyloid P (SAP) have been measured in the mouse pouch model of rheumatoid arthritis. Implantation of cartilage resulted in a significant and rapid elevation in the SAP concentration, which remained high for the duration of the experiment (14 days). Initial studies with several clinically employed antirheumatic drugs indicated that dexamethasone and cyclosporin A had a marked inhibitory effect.

Air↗
PubMed1986

The determination of receptor constants for histamine H2-agonists in the guinea-pig isolated right atrium using an irreversible H2-antagonist.

From measurements of chronotropy in the guinea-pig isolated right atrium, a compound (E1309) was found which behaved as an irreversible antagonist at the histamine H2 receptor. E1309 was used to block irreversibly a proportion of the H2 receptors and the dissociation constants, relative efficacies and receptor reserves of four H2-agonists were determined. The calculated dissociation constants were similar to the Ki values reported from H2-radioligand binding studies but different from the observed EC50 values. The order of potency for the four H2-agonists was impromidine much greater than histamine greater than dimaprit greater than 4-methylhistamine. The order of relative efficacy was 4-methylhistamine greater than dimaprit greater than histamine greater than impromidine, the natural agonist not being the most efficacious. This atypical finding is discussed in relation to other receptor classes.

Animals↗
PubMed1985

In vitro histamine H2-antagonist activity of the novel compound HUK 978.

Histamine stimulated adenylate cyclase from guinea-pig fundic mucosa and 3H-tiotidine binding in guinea-pig cerebral cortex were used to assess the in-vitro histamine H2-activity of the novel H2-antagonist HUK 978. The results showed that HUK 978 was a more potent H2-antagonist than either cimetidine or ranitidine. HUK 978 was also shown to be devoid of activity at the histamine H1-receptor, the muscarinic receptor and the alpha and beta-adrenergic receptors.

Adenylyl Cyclases↗
PubMed1985

Anti-secretory activity of the novel H2-antagonist, HUK 978, in rat, guinea-pig and dog.

The anti-secretory activity of the competitive H2-antagonist HUK 978 was determined in rat, guinea-pig and dog. In all systems examined, HUK 978 was more potent than cimetidine and ranitidine both intravenously and orally. In addition, the compound at approximately equipotent doses as these established H2-antagonists exhibited a significantly longer inhibitory profile following oral and systemic administration. Data from these pharmacological studies and the in vitro investigations previously reported, suggest that HUK 978 is a highly specific H2-antagonist and inhibits acid secretion for longer periods than other competitive compounds.

Administration, Oral↗