The peroxisome proliferator-activated receptor agonist pioglitazone and 5-lipoxygenase inhibitor zileuton have no effect on lung inflammation in healthy volunteers by positron emission tomography in a single-blind placebo-controlled cohort study

Abstract

Background: Anti-inflammatory drug development efforts for lung disease have been hampered in part by the lack of noninvasive inflammation biomarkers and the limited ability of animal models to predict efficacy in humans. We used 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) in a human model of lung inflammation to assess whether pioglitazone, a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, and zileuton, a 5-lipoxygenase inhibitor, reduce lung inflammation.

Methods: For this single center, single-blind, placebo-controlled cohort study, we enrolled healthy volunteers sequentially into the following treatment cohorts (N = 6 per cohort): pioglitazone plus placebo, zileuton plus placebo, or dual placebo prior to bronchoscopic endotoxin instillation. 18F-FDG uptake pre- and post-endotoxin was quantified as the Patlak graphical analysis-determined Ki (primary outcome measure). Secondary outcome measures included the mean standard uptake value (SUVmean), post-endotoxin bronchoalveolar lavage (BAL) cell counts and differentials and blood adiponectin and urinary leukotriene E4 (LTE4) levels, determined by enzyme-linked immunosorbent assay, to verify treatment compliance. One- or two-way analysis of variance assessed for differences among cohorts in the outcome measures (expressed as mean ± standard deviation).

Results: Ten females and eight males (29±6 years of age) completed all study procedures except for one volunteer who did not complete the post-endotoxin BAL. Ki and SUVmean increased in all cohorts after endotoxin instillation (Ki increased by 0.0021±0.0019, 0.0023±0.0017, and 0.0024±0.0020 and SUVmean by 0.47±0.14, 0.55±0.15, and 0.54±0.38 in placebo, pioglitazone, and zileuton cohorts, respectively, p<0.001) with no differences among treatment cohorts (p = 0.933). Adiponectin levels increased as expected with pioglitazone treatment but not urinary LTE4 levels as expected with zileuton treatment. BAL cell counts (p = 0.442) and neutrophil percentage (p = 0.773) were similar among the treatment cohorts.

Conclusions: Endotoxin-induced lung inflammation in humans is not responsive to pioglitazone or zileuton, highlighting the challenge in translating anti-inflammatory drug efficacy results from murine models to humans.

Trial registration: ClinicalTrials.gov NCT01174056.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Study design, participant and procedure flow.

Reasons for screen failures were: Elevated alanine aminotransferase level (N = 5); % predicted forced expiratory volume in one second (FEV1) and/or forced vital capacity (FVC) 18F-fluorodeoxyglucose. i.b. = intrabronchial. qD = once per day. Q6hr = once every six hours.

Fig 2. Positron emission tomography (PET) and computed tomography (CT) images from a representative volunteer in each treatment cohort.

White outlines show the volumes of interest (VOIs) used to determine the time-activity curves for the Patlak graphical analysis and standard uptake values. VOIs were sometimes smaller in volume on the left due to the heart.

Fig 3. Patlak graphical analysis results from18F-fluorodeoxyglucose (18F-FDG) PET images in the right and left lungs before and after endotoxin instillation.

Arrows indicate presence of both Asp299Gly and Thr399Ile single nucleotide polymorphisms (SNPs), arrowheads only the Asp299Gly SNP. The arrowhead for the left lung data of the zileuton treatment cohort points to the post-endotoxin data point that decreased slightly after endotoxin. Ki = influx constant describing rate of 18F-FDG uptake into the lung region of interest, determined by Patlak graphical analysis. * = p < 0.05 when comparing post-endotoxin (After) to pre-endotoxin (Before) value.

Fig 4. Mean standard uptake value (SUV) results from18F-fluorodeoxyglucose PET images in the right and left lungs for each treatment cohort.

Arrows indicate presence of both Asp299Gly and Thr399Ile single nucleotide polymorphisms (SNPs), arrowheads only the Asp299Gly SNP. The arrow and arrowhead for the left lung of the placebo cohort point to the top two post-endotoxin data points. * = p

Fig 5. Serum adiponectin and urinary leukotriene E4 (LTE4) levels by treatment cohort.

* = p 4 levels are expressed as pg LTE4/mg creatinine (pg/mg).