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Biomedical subjects

I P Hall

Publications and source records attributed to I P Hall.

At least 19 recordsLinked to original sources
PubMed2002

Asthma.

Asthma is one of the commonest chronic diseases of affluent societies. The striking increase in prevalence of asthma over recent decades and the rarity of this disease in less affluent populations confirms the importance of environmental factors in the cause of asthma--although which environmental factors are responsible is still not clear. Family studies show that genetic factors are also important in determining individual susceptibility to asthma, with results of genetic studies suggesting that there are many genes with moderate effects rather than a few major genes. Asthmatic airways show inflammation and remodelling, with CD4+ helper cells, mast cells, and eosinophils characterising the inflammatory response. Inhaled corticosteroids remain the cornerstone of treatment with the addition of long-acting beta agonists as the next step if symptoms continue. Leukotriene antagonists, the only new drugs to reach the market in the past decade, have modest effects. However, a better understanding of the mechanisms underlying asthma and the genetic and environmental factors that predispose individuals to asthma should lead to better preventative strategies and new therapeutic approaches.

Asthma↗
PubMed2002

The selective CXCR2 antagonist SB272844 blocks interleukin-8 and growth-related oncogene-alpha-mediated inhibition of spontaneous neutrophil apoptosis.

The aims of this study were to investigate the effects of Interleukin-8 (IL-8) and Growth related oncogene-alpha (Gro-alpha) on neutrophil apoptosis and determine the potential for a selective CXCR2 antagonist to inhibit these responses. IL-8 and Gro-alpha both produced dose dependent inhibition of spontaneous human neutrophil apoptosis after 16 hours incubation (59+/-3.5% and 27.5+/-3% respectively; EC50s 2.2+/-1.8 nM, and 0.5+/-0.2 nM respectively). The pro-survival effect of a fixed concentration of agonist (IL-8 or Gro-alpha) on cultured neutrophils was abrogated by a selective CXCR2 antagonist SB272844 (K(D)s 253 nM and 49.9 nM in the presence of IL-8 or Gro-alpha respectively). Our data suggests that the anti-apoptotic effect of Gro-alpha is mediated through CXCR2 as selective CXCR2 blockade with SB272844 can potently abrogate this response. The inhibitory effect of IL-8 may in addition partly be mediated through CXCR1 as SB272844 was less potent in its ability to abrogate the anti-apoptotic effects of IL-8 when this agent was used as an agonist. CXCR2 antagonists may have a therapeutic role in controlling neutrophil-driven inflammation by reducing neutrophil recruitment and restoring neutrophils to the tissue clearance pathway of apoptosis.

Apoptosis↗
PubMed2002

Beta2 adrenoceptor promoter polymorphisms: extended haplotypes and functional effects in peripheral blood mononuclear cells.

BACKGROUND: The beta2 adrenoceptor and its 5' untranslated region contain a number of genetic variants. The aim of this study was to investigate the potential for genetic variation at this locus to influence the expression of beta2 adrenoceptors on circulating peripheral blood mononuclear cells (PBMCs). METHODS: Genotype was determined in 96 individuals with asthma for four polymorphisms at the beta2 adrenoceptor locus. Beta2 adrenoceptor binding and cyclic AMP responses to isoprenaline in PBMCs were determined and the relationship between genotype/haplotype and beta2 adrenoceptor expression and response to isoprenaline examined. RESULTS: Beta2 adrenoceptor promoter polymorphisms were found to be common in white subjects. Strong linkage disequilibrium exists across this locus, resulting in the occurrence of several common haplotypes. No single polymorphism or haplotype was correlated with the level of beta2 adrenoceptor expression or cyclic AMP responses to isoprenaline in vitro. CONCLUSION: Beta2 adrenoceptor polymorphisms, when considered in isolation or by extended haplotypes, do not determine the basal level of expression or coupling of beta2 adrenoceptors in PBMCs from asthmatic subjects.

Adolescent↗
PubMed2001

Mutation screening of the muscarinic M(2) and M(3) receptor genes in normal and asthmatic subjects.

1. Muscarinic receptors are important in the development of airway hyperresponsiveness, and dysfunction of these receptors has been suggested to be present in asthma. 2. The human muscarinic M(2) and M(3) receptor genes were screened for polymorphic variation using single-stranded conformation polymorphism (SSCP) analysis, complemented by direct fluorescent sequencing. Forty-six random DNA samples and 46 respiratory physician diagnosed asthmatic samples were used as a template for analysis. 3. Within the muscarinic M(2) receptor gene, we identified two degenerate single base substitutions (1197T-->C, Thr-->Thr and 976A-->C, Arg-->Arg) in one random and one asthmatic sample respectively. Analysis of the 3' UTR region revealed an additional 'A' at bp 1793 (c.f. ATG). This was present in all of 49 samples analysed by sequencing or BsmI digest, suggesting that the published sequence (GenBank Accession NO: M16404) is incorrect. A common 3' UTR polymorphism (T-->A) was found at bp 1696 (c.f. ATG) (allelic frequency=65%, n=60), but this does not alter transcription factor recognition sites. 4. We were unable to identify any polymorphic variation within the muscarinic M(3) coding region or the flanking regions investigated, using the methods described. 5. The coding regions for the human muscarinic M(2) and M(3) receptor genes are both highly conserved. These data suggest that polymorphic variation within these coding sequences is unlikely to account for inter-individual variability in response to methacholine or anticholinergic therapy. The potential functional significance of the muscarinic M(2) receptor 3' UTR polymorphism (bp 1696) remains to be determined.

3' Untranslated Regions↗
PubMed2001

Linkage analysis of the 5q31-33 candidate region for asthma in 240 UK families.

Atopy and asthma are complex genetic diseases resulting from the interactions of a number of genetic and environmental factors. We had previously reported allelic association between the IL9 marker on chromosome 5q31-33 and atopy. In order to further investigate the role of susceptibility genes on 5q31-33 in the development of atopy and asthma we have studied 240 UK families comprising 131 families selected at random, 60 multiplex families with affected sib pairs, and 49 single proband nuclear families. Polymorphic markers on 5q31-33 were genotyped and both single and multipoint linkage analysis was undertaken using the BETA program. We have used both affection status and quantitative scores for atopy and asthma for phenotypic variables, combining data into scores for asthma and atopy. The strongest suggestion of linkage using multipoint analysis was centred around D5S410 with a maximum Lod of 1.946 at location 171.3 cM and a standard error of 3.3 for the asthma quantitative score. There was no evidence of linkage with atopy, the atopy quantitative score or total serum IgE.

Asthma↗
PubMed2001

Human airway smooth muscle expresses 7 isoforms of adenylyl cyclase: a dominant role for isoform V.

Adenylyl cyclases are a nine-member family of differentially regulated enzymes responsible for the synthesis of cAMP. cAMP is an important second messenger that contributes to the regulation of airway smooth muscle tone. However, little is known regarding the expression and regulation of adenylyl cyclase isoforms in airway smooth muscle cells. Nondegenerate specific primers were designed for all nine known isoforms of human adenylyl cyclase. RT-PCR experiments were performed using total RNA extracted from whole human brain (positive control), whole rat brain (negative control), whole human trachea, human airway smooth muscle, and primary cultures of human airway smooth muscle cells. Seven of the nine known isoforms of adenylyl cyclase (isoforms I, III-VII, and IX) were expressed at the mRNA level in both human airway smooth muscle and primary cultures of human airway smooth muscle cells. Immunoblot and adenylyl cyclase functional assay indicated that isoform V is likely among the functionally predominant isoforms of adenylyl cyclase in human airway smooth muscle. These results suggest that multiple isoforms of adenylyl cyclase enzymes are coexpressed in human airway smooth muscle cells and that isoform V is among the functionally important isoforms.

Adenylyl Cyclases↗
PubMed2001

Mechanisms of cytokine effects on G protein-coupled receptor-mediated signaling in airway smooth muscle.

Numerous in vitro and in vivo studies have implicated the cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) as mediators of airway inflammation and therefore potentially important substances in the pathogenesis of asthma. In this study, we examined the mechanisms by which IL-1 beta and TNF-alpha affect inhibition of cell growth, G protein-coupled receptor (GPCR) desensitization, and the recently reported adenylyl cyclase sensitization in human airway smooth muscle (HASM) cultures. Our findings demonstrate that adenylyl cyclase sensitization is independent of cytokine-mediated cyclooxygenase type 2 (COX-2) and prostaglandin E(2) (PGE(2)) induction, whereas COX-2 induction appears to be required for both growth inhibition and GPCR desensitization. However, GPCR desensitization was highly dependent on the presence of EGF during chronic treatment with cytokines, which could be explained by a synergistic effect of EGF on cytokine-mediated COX-2 and PGE(2) induction. Interestingly, various agents (including inhibitors of p42/p44 and p38 mitogen-activated protein kinase signaling) were significantly more effective in inhibiting cytokine-mediated PGE(2) induction, GPCR desensitization, and cell growth inhibition than in inhibiting COX-2 induction. These data demonstrate disparity in the requirement and sufficiency of COX-2 induction in promoting different functional effects of IL-1 beta and TNF-alpha in HASM.

Adenylyl Cyclases↗
PubMed2001

Interleukin-1beta and rhinovirus sensitize adenylyl cyclase in human airway smooth-muscle cells.

Rhinovirus (RV) is a major cause of wheezing in asthmatics and has been reported to cause beta2 adrenergic receptor hyporesponsiveness in human airway smooth muscle (HASM) via cellular secretion of interleukin (IL)-1beta. We studied the effects of IL-1beta and RV on cyclic adenosine monophosphate (cAMP) production in HASM cells. Chronic incubation with IL-1beta or RV caused a significant increase (approximately 3- and approximately 2-fold, respectively) in forskolin (FSK)-stimulated cAMP production, suggesting a sensitization of adenylyl cyclase (AC). The observed augmentation of FSK-stimulated cAMP formation by IL-1beta was completely abrogated by pretreatment with an IL-1 receptor antagonist or cycloheximide, demonstrating that the effect is mediated via the IL-1 receptor 1 (IL-1R1) and that de novo protein synthesis is required. In contrast, RV-induced AC sensitization was not mediated via the IL-1R1 but was observed to be protein kinase C-dependent. We suggest that the sensitization of AC observed after exposure to IL-1beta or RV infection is a cellular defense mechanism to promote pathways that induce relaxation in the inflamed airway.

Adenylate Cyclase Toxin↗
PubMed2001

Effects of growth factors and extracellular matrix on survival of human airway smooth muscle cells.

Airway remodeling complicates longstanding asthma. It is characterized by an increase in the number of airway smooth muscle cells (SMCs) as well as an increase in and alteration of the type of extra-cellular matrix (ECM) in the airways. Although the number of SMCs in the airways depends on the balance of cell proliferation and cell death, studies to date have concentrated on factors affecting SMC proliferation. Here we report the first study on airway SMC survival factors: these cells receive a strong survival signal, which is not dependent on the known growth factor mitogens. We identified the ECM factors fibronectin, laminin, and collagens I and IV as important anti-apoptotic elements, and characterized the expression of the ECM receptors (integrins) on cultured SMC. Functionally blocking antibody and peptide studies revealed the alpha(5)beta(1) integrin to be an important transducer of the ECM-derived survival signal in these cells. Confocal microscopy confirmed the striking effects that discrete ECM factors have on SMC phenotype, notably the cytoskeleton. In summary, our data improves the understanding of the mechanisms underlying airway remodeling by outlining the key survival factors for airway SMC and by highlighting the impact of the cell-matrix interactions on cell death and phenotype.

Apoptosis↗
PubMed2001

Peripheral blood neutrophils are hyperresponsive to IL-8 and Gro-alpha in cryptogenic fibrosing alveolitis.

Cryptogenic fibrosing alveolitis (CFA) is characterized by increased pulmonary recruitment of peripheral blood neutrophils (PBNs) by interleukin (IL)-8 and other chemotactic mediators. This study investigated whether, in CFA, the PBN motility response is primed by IL-8 and growth-related oncogene (Gro)-alpha, as demonstrated in other neutrophilic inflammatory diseases, and whether the motility response of PBNs to IL-8 and Gro-alpha can be abrogated using a selective antagonist for the neutrophil receptor for IL-8 and Gro-alpha, CXCR2. The percentage of PBNs to undergo shape change (%SC), spontaneously and in response to IL-8 and Gro-alpha, was measured in patients with CFA (n=10) and controls (n=10), and the effect of the CXCR2 antagonist SB272844 studied. Plasma levels of IL-8, and Gro-alpha were measured using an enzyme-linked immunosorbent assay (ELISA). The %SC of unstimulated PBNs and the potency of Gro-alpha and IL-8 to produce neutrophil polarization was greater in CFA than in controls; dose which produces 50% of maximal effect (EC50) of IL-8 was 3.6 +/- 0.7 nM for CFA versus 6.3 +/- 1.0 nM for controls; p<0.05. SB272844 inhibited Gro-alpha induced but not IL-8 induced neutrophil shape change (equilibrium constant (KD) 123 +/- 18 nM). Plasma concentrations of Gro-alpha were increased in patients with CFA. PBNs are spontaneously activated and undergo a greater motility response to IL-8 and Gro-alpha in CFA. Interleukin-8 and growth-related oncogene-alpha, circulating in substimulatory amounts in cryptogenic fibrosing alveolitis, may prime the peripheral blood neutrophils motility response, thus increasing their capacity for migration to the lung. Selective CXCR2 antagonists may be useful to block the Gro-alpha-induced priming response whilst preserving neutrophil functions mediated by CXCR1, the alternative neutrophil receptor for interleukin-8.

Aged↗
PubMed2000

A first trial of retrospective collaboration for positional cloning in complex inheritance: assay of the cytokine region on chromosome 5 by the consortium on asthma genetics (COAG).

The central problem of complex inheritance is to map oligogenes for disease susceptibility, integrating linkage and association over samples that differ in several ways. Combination of evidence over multiple samples with 1,037 families supports loci contributing to asthma susceptibility in the cytokine region on 5q [maximum logarithm of odds (lod) = 2.61 near IL-4], but no evidence for atopy. The principal problems with retrospective collaboration on linkage appear to have been solved, providing far more information than a single study. A multipoint lod table evaluated at commonly agreed reference loci is required for both collaboration and metaanalysis, but variations in ascertainment, pedigree structure, phenotype definition, and marker selection are tolerated. These methods are invariant with statistical methods that increase the power of lods and are applicable to all diseases, motivating collaboration rather than competition. In contrast to linkage, positional cloning by allelic association has yet to be extended to multiple samples, a prerequisite for efficient combination with linkage and the greatest current challenge to genetic epidemiology.

Asthma↗
PubMed2000

Interleukin-4 receptor alpha gene variants and allergic disease.

The interleukin-4 (IL-4) signalling cascade has been identified as a pathway potentially important in the development of asthma. Genetic variants within this signalling pathway might contribute to the risk of developing asthma in a given individual. A number of polymorphisms have been described within the IL-4 receptor alpha (IL-4Ralpha) gene. In addition polymorphism occurs in the promoter for the IL-4 gene itself. This commentary accompanies a paper by C Ober et al describing the contribution of IL-4Ralpha polymorphism to susceptibility to asthma and atopy in the Hutterite population and other outbred populations collected during the collaborative studies on the genetics of asthma (CSGA) programme.

Genetic Variation↗
PubMed2000

Second messengers, ion channels and pharmacology of airway smooth muscle.

The airway smooth muscle cell is the chief effector cell governing the control of airway calibre in the human lung. The contractile state of the airway smooth muscle cell is predominantly influenced by the balance of constrictor and relaxant stimuli. Agents such as histamine and acetylcholine cause airway smooth muscle cells to contract through activation of specific cell surface receptors and engagement of signal transduction pathways and/or ion channels. The predominant pathway mediating constriction is activation of phospholipase C, with release of inositol 1,4,5-triphosphate and elevation of intracellular calcium levels. Relaxation is brought about predominantly by stimulation of adenylyl cyclase-coupled receptors (e.g. the beta2-adrenoceptor) resulting in elevation of cell cyclic adenosine monophosphate content. Complex crosstalk occurs between both of these pathways and also ion channels expressed on the airway smooth muscle cell membrane, leading to careful regulation of airway smooth muscle tone. A greater understanding of the mechanisms governing control of these pathways will lead to the identification of novel therapeutic targets which will in turn lead to new agents for the treatment of asthma.

Anti-Asthmatic Agents↗
PubMed2000

Association analysis of beta2 adrenoceptor polymorphisms with hypertension in a Black African population.

OBJECTIVE: To determine whether or not beta2 adrenoceptor polymorphism is a risk factor for the development of hypertension in a Black South African population. BACKGROUND: Attenuated vasodilator responses to endogenous catecholamines may contribute to the aetiology of hypertension. Downregulation of beta2 adrenoreceptors (beta2AR) following stimulation with agonists is determined in part by variation at the beta2AR gene locus. The Glu27 beta2AR genotype results in attenuated downregulation compared with the wild-type Gln27 receptor, whereas Gly16 exhibits enhanced down-regulation compared to Arg16. Possible racial differences in the prevalence of the beta2AR polymorphisms may be an explanation for the blunted responses to isoprenaline and the increased prevalence of hypertension in Black African populations. METHODS: One hundred and ninety-two unrelated hypertensives and 123 normotensives of Black South African origin were studied. Hypertensives were recruited from hospital hypertension clinics in the province of Gauteng and if on treatment, had a 2-4 week washout period before 24-h ambulatory blood pressure assessment Normotensive controls were recruited from the same community. RESULTS: There was no significant association between either the Arg-Gly16 polymorphism or the Gln-Glu27 polymorphism and hypertension status. Furthermore, in the hypertensives, no significant association was seen between beta2AR genotype at either site and clinical blood pressure, 24-h blood pressure or left ventricular mass. A significant association was seen between Arg16 homozygotes and lower body mass index in hypertensives (P = 0.007) although this was not a primary end point. Interestingly, the Glu27 polymorphism was much rarer in this population (allelic frequency 17%) compared to a Caucasian population. CONCLUSION: These data suggest that beta2AR polymorphism is not a risk factor for hypertension per se in this defined population. The possibility that the decreased prevalence of Glu27 in black South African populations explains blunted vasodilator responses to isoprenaline requires further study.

Adrenergic beta-Agonists↗
PubMed2000

Beta(2)-adrenoceptor polymorphism determines vascular reactivity in humans.

Altered beta-adrenergic regulation has been reported in individuals with hypertension. The variability in vascular responsiveness to beta-agonists, such as isoproterenol, observed in humans may be explained partially by beta(2)-adrenoceptor polymorphism. Individuals with the Gln27 form of the receptor may show reduced vascular reactivity because of downregulation expression of the receptor in the vasculature. We screened 127 normotensive white subjects, 37 of whom were homozygous for these alleles. Thirty-two subjects (17 Gln27 and 15 Glu27) agreed to receive brachial artery infusions of isoproterenol at doses of 1 to 300 ng. min(-1); forearm blood flow was measured by using venous occlusion plethysmography. Of these subjects, 25 (12 Glu27 and 13 Gln27) received local doses of isoproterenol (0.3 to 30.0 ng. min(-1)) via a dorsal hand vein preconstricted with norepinephrine. Compared with subjects homozygous for the Glu27 allele, subjects with the Gln27 substitution had lower baseline blood flow and, in response to isoproterenol, had a significantly attenuated increase in forearm blood flow. This pattern was more marked in veins. We also studied the relationship between the position 16 polymorphism and vascular reactivity. Homozygotes for Arg16 had significantly lower basal blood flow and attenuated increases in forearm blood flow compared with the Gly16 homozygotes. This was significant in veins but not in arteries. Thus, beta(2)-adrenoceptor genotype determines vascular responses to isoproterenol in forearm resistance vessels and in capacitance vessels. Further studies are necessary to establish whether beta(2)-adrenoceptor polymorphisms are important in the genesis of hypertension.

Adrenergic beta-Agonists↗