Peroxisome Proliferator-Activated Receptor-gamma: a novel therapeutic target for asthma?

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Scientific Abstract|This study will translate molecular pathophysiology studies from our group identifying peroxisome proliferator-activated receptor (PPAR) -gamma as a potential drug target in asthma. The key question is whether stimulation of PPAR-gamma receptors produce measurable biological airway and clinical responses in patients with asthma that would justify exploring PPAR-gamma stimluation as a novel therapeutic modality|DESIGN - Randomized, double blind, placebo controlled two parallel group clinical trial |SETTING - Nottingham University Hospitals NHS Trust|TARGET POPULATION - People aged 18-75 of either sex with a clinical diagnosis of asthma, FEV1 60 % predicted or higher and an increase in FEV1 of greater than 12 % following inhaled salbutamol 400mcg or PEF variability > 12 % during run-in taking 0 to 800 mcg inhaled beclometasone diproprionate or equivalent and as required short acting beta agonist. The exclusion criteria will be inability to produce a sputum sample on induction, current smoking, > 10 pack years smoking history, treatment with leukotriene antagonists, liver or cardiovascular disease, oral steroid treatment or exacerbation within 6 weeks, females who are pregnant, lactating or not using adequate contraception, any contra-indication to pioglitazone and lactose intolerance. |INTERVENTIONS BEING EVALUATED - Active intervention: 30 mg pioglitazone daily for 4 weeks, increasing to 45 mg pioglitazone daily for 8 weeks. Placebo intervention: placebo matching 30 mg pioglitazone daily for 4 weeks followed by placebo matching 45 mg pioglitazone daily for 8 weeks. Participants will be randomised to one or other intervention using a web-based randomisation system and allocation concealed by blinding of participants and investigators. |MEASUREMENT OF CLINICAL OUTCOMES AND DURATION OF FOLLOW-UP - Primary outcome: FEV1 at 12 weeks. Secondary outcomes: daily asthma symptoms, mean morning and evening PEF, Juniper Asthma Control Questionnaire and Asthma Quality of Life Questionnaire scores, exhaled nitric oxide level, bronchial hyper-responsiveness, induced sputum cell counts & analysis detailed below, BMI, glucose & adverse effects. Follow up will take place at 0, 4, 8, 12, & 16 weeks for data collection. |ADDITIONAL LABORATORY OUTCOMES - Our previous studies have suggested that the mechanism of action of PPAR-gamma agonists in vitro involves effects on gene transcription. Gene transcription is a complex process involving binding of transcription factors to their recognition sequences on gene promoters. Access to these recognition sequences requires DNA to unravel and this process is controlled by covalent modification of core histone molecules around which DNA is wrapped. |The most important covalent modification is acetylation of histone H4 which is regulated by two competing groups of enzymes, histone acetyl transferases (HATs) and histone deacetylases (HDACs). HATs increase transcription whereas HDACs reduce it. In our studies of eotaxin we found that acetylation of histone H4 was reduced by PPAR agonists but we have not determined whether this is due to a reduced HAT or increased HDAC activity. |To examine things further we will perform studies in cells obtained from induced sputum to analyse 1) HDAC and HAT activities by HDAC Fluorescent Activity Assay Kit (BIOMOL) and HAT Assay Kit (Upstate Biotechnology). We have shown from preliminary experiments that we can obtain enough cells from induced sputum for these assays. 2) PPAR-gamma activation (nuclear translocation) by western blotting. |This will be conducted on a subset of samples from each group to confirm the effect of pioglitazone. We will also perform studies in supernatant obtained from induced sputum to analyse 1) the concentration of chemokines (eotaxin, MCP-1, IP-10) and growth factors (VEGF) by ELISA; 2) effector mediators (cyst-leukotriens, eosinophil cationic protein (ECP) and histamine) by radio-immuno assay. |These analyses will be conducte