Nitric Oxide, LPS and the Pathogenesis of Asthma - Phase II

(IRB# Pro00005035)

The purpose of the study is to determine the role of nitric oxide (NO) in asthma and to characterize the symptoms associated with inhaled endotoxin in normal subjects. The effect of inhaled endotoxin on exhaled NO is determined in healthy African Americans, with and without NOS2 promoter polymorphisms. The protocol involves the use of NIH Clinical Center Reference Endotoxin which has been approved by the FDA under IND BB-IND-10035.

Background & significance: Asthma is a significant cause of morbidity and mortality for African Americans and asthma is increasing in prevalence. Both environmental and genetic factors contribute to the pathogenesis of asthma. In addition to allergens, environmental lipopolysaccharide (LPS) or endotoxin plays an important role in the chronic inflammation associated with asthma. There is convincing evidence that endotoxin exacerbates airflow obstruction and airway inflammation in allergic asthmatics. Endotoxin increases inducible nitric oxide synthase (NOS2) expression and nitric oxide (NO) production in vitro and in vivo in humans.

In asthma, NOS2 expression is upregulated in several cell types including bronchial epithelium, macrophages and other inflammatory cells. The increase in NOS2 expression is associated with increases in exhaled NO in individuals with asthma as compared to healthy individuals.

This prompted our search for NOS2 single nucleotide polymorphisms (SNPs) and the subsequent identification of three NOS2 promoter SNPs. Two of the SNPs are associated with increased systemic NO levels. Another SNP creates a predicted binding site for the human homolog of delta EF1, which is a transcriptional repressor and we predicted that this SNP would be associated with low NO levels. Importantly, the three NOS2 promoter SNPs are not linked, do not segregate together and are present primarily in individuals of African ancestry.