Effect of TNF and LTA polymorphisms on biological markers of response to oxidative stimuli in coal miners: a model of gene-environment interaction. Tumour necrosis factor and lymphotoxin alpha

INTRODUCTION

Interaction between genetic background and oxidative environmental stimuli in the pathogenesis of human lung disease has been largely unexplored.

METHODS

A prospective epidemiological study was undertaken in 253 coal miners. Intermediate quantitative phenotypes of response to oxidant exposure, including erythrocyte glutathione peroxidase (GSH-Px) and catalase activities, were studied. Oxidant exposures studied were smoking habits and cumulative dust exposure assessed by job history and ambient measures. Disease phenotypes included subclinical computed tomography score at the first survey and x ray profusion grades twice, five years apart, to assess established coal workers' pneumoconiosis (CWP). Miners were genotyped for common functional polymorphisms in the gene for tumour necrosis factor alpha (TNF) and lymphotoxin alpha (LTA), two proinflammatory cytokines that have been implicated in the pathogenesis of chronic lung diseases.

RESULTS

Regarding gene-environment interaction on intermediate phenotypes, results showed interaction of a promoter polymorphism at the -308 position in TNF with occupational exposure on erythrocyte GSH-Px activity with a significant association in those with high exposure (p=0.003), whereas no association was observed among those with low exposure (interaction p=0.06). Regarding gene intermediate phenotype interaction on clinical outcome, results showed an association of CWP prevalence with an NcoI polymorphism in LTA in those with low catalase activity (p=0.05), whereas no association was observed in those with high activity (interaction p=0.03). No other significant association was observed.

CONCLUSION

The results suggest that interactions of genetic background with environmental exposure and intermediate response phenotypes are important components in the pathogenesis of CWP.

Modified control of breathing in genetically obese (ob/ob) mice

Attenuated hypercapnic chemosensitivity and hypoventilation are characteristics periodically associated with human obesity. We tested the hypothesis that ventilatory control is altered by genetic determinants and age-dependent factors that influence the obese phenotype. To this end, the magnitude and pattern of breathing were examined before and associated with the development of obesity in C57BL/6J mice homozygous and heterozygous at the ob gene locus. Breathing frequency and tidal volume were measured using whole body plethysmography, and minute ventilation was assessed during acute hypoxic and hypercapnic challenges with intermittent room air exposures. In age- and weight-matched mice before pronounced obesity, significant (P < 0.05) reductions in hypercapnic ventilatory sensitivity occurred in mutant (ob/ob) mice relative to wild-type (+/+) homozygotes primarily because of an attenuated tidal volume. Longitudinal studies indicated that mutant ob mice developed rapid baseline breathing relative to the wild type, accompanying a twofold greater increase in body mass. Early differences between homozygotes in hypercapnic ventilatory sensitivity were maintained through 230 days. These data demonstrate that genetic determinants at or closely linked to the ob locus influence hypercapnic ventilation before the emergence of pronounced obesity, whereas changes in baseline breathing appear due to age-dependent increases in body weight.