The effects of a combination of tobacco smoke and Lipopolysacharide exposure on lung function in the rat

Mark Freeman, Liz Hardaker, Nicole Dale, Joanie Mok, Ellie Growcott, Parmjit Bahra, Kathy Banner, Chris Poll

Novartis Horsham Research Centre, Horsham, West Sussex, UK

Chronic Obstructive Pulmonary Disease (COPD) is characterised by a predominantly irreversible restriction of airflow and often by acute exacerbations (AECOPD). These exacerbations are defined as a worsening of symptoms that results in a need to change medication and they are associated with a hyper-inflammatory response and a decline in lung function. Tobacco smoking (TS) is widely accepted as the main causative agent for COPD, with the majority of exacerbations being associated with subsequent bacterial or viral infection. Our aim was to develop a model that mimicked certain aspects of the hyper-inflammatory response seen in AECOPD and to determine whether this was associated with impaired lung function. Therefore we combined multiple TS exposures with the administration of the bacteria cell wall component lipopolysaccharide (LPS). Male Sprague Dawley rats were exposed twice daily to 30 minutes of whole body mainstream smoke or room air (RA) for two consecutive days. On the third day animals were exposed to a whole body LPS (0.3mg/ml; E.coli serotype 0111:B4) or isotonic saline aerosol for 30 minutes followed 5 hours later by a further smoke exposure for the same period. Twenty four hours later, animals were terminal anaesthetised (medetomadine/ketamine i.p.) and lung function measured with a forced manoeuvres system. Bronchoalveolar lavage (BAL) was then performed to assess cell influx, total protein and lactate dehydrogenase (LDH) activity levels in the lavage fluid. There was a greater than additive increase in the number of total cells in the BAL of animals exposed to LPS and TS compared to those administered either stimulus alone (see table 1). This increase consisted mainly of neutrophils (354 fold increase, n=8, p<0.001) when compared to the RA/saline group. LDH and total protein levels in the BAL exhibited a similar pattern suggesting increased levels of cytotoxicity and potential oedema in the TS/LPS treated animals. Lung function was only compromised in TS/LPS exposed animals with the forced vital capacity being significantly reduced compared to RA/saline animals (23% decrease, n=8, p< 0.05).

LPS exposure in conjunction with TS exposure produces a pulmonary inflammatory response greater than that observed with either LPS or TS alone and this response is associated with a decline in lung function. This animal model may be suitable for assessing novel drug candidates to treat the inflammation observed during an AECOPD.

Data expressed as mean cells x 103/ml ± sem. (Kruskal-Wallis followed by Dunns post test was used * p<0.05, ** p<0.01, *** p<0.001 compared to RA/Saline control.)