Association between lipid-A-producing oral bacteria of different potency and fractional exhaled nitric oxide in a Norwegian population-based adult cohort

Abstract

Background Lipid A is the primary immunostimulatory part of the lipopolysaccharide (LPS) molecule. The inflammatory response of LPS varies and depends upon the number of acyl chains and phosphate groups in lipid A which is specific for a bacterial species or strain. Traditional LPS quantification assays cannot distinguish between the acylation degree of lipid A molecules, and therefore little is known about how bacteria with different inflammation-inducing potencies affect fractional exhaled nitric oxide (FeNO). We aimed to explore the association between pro-inflammatory hexa- and less inflammatory penta-acylated LPS-producing oral bacteria and FeNO as a marker of airway inflammation. Methods We used data from a population-based adult cohort from Norway (n = 477), a study center of the RHINESSA multi-center generation study. We applied statistical methods on the bacterial community- (prediction with MiRKAT) and genus-level (differential abundance analysis with ANCOM-BC) to investigate the association between the oral microbiota composition and FeNO. Results We found the overall composition to be significantly associated with increasing FeNO levels independent of covariate adjustment, and abundances of 27 bacterial genera to differ in individuals with high FeNO vs. low FeNO levels. Hexa- and penta-acylated LPS producers made up 2.4% and 40.8% of the oral bacterial genera, respectively. The Bray–Curtis dissimilarity within hexa- and penta-acylated LPS-producing oral bacteria was associated with increasing FeNO levels independent of covariate adjustment. A few single penta-acylated LPS producers were more abundant in individuals with low FeNO vs. high FeNO, while hexa-acylated LPS producers were found not to be enriched. Conclusions In a population-based adult cohort, FeNO was observed to be associated with the overall oral bacterial community composition. The effect of hexa- and penta-acylated LPS-producing oral bacteria was overall significant when focusing on Bray–Curtis dissimilarity within each of the two communities and FeNO levels, but only penta-acylated LPS producers appeared to be reduced or absent in individuals with high FeNO. It is likely that the pro-inflammatory effect of hexa-acylated LPS producers is counteracted by the dominance of the more abundant penta-acylated LPS producers in this population-based adult cohort involving mainly healthy individuals.

Fractional exhaled nitric oxide distribution and its relevant factors in the general adult population and its healthy subpopulation

“…Healthy subpopulation 2 had 6.5% with high F eno levels (≥35 ppb), indicating that F eno levels are still distributed in the high range despite this population’s being assumed to be healthy and without type 2 inflammation. This observation suggests that F eno levels are influenced not only by the presence of type 2 inflammation but also by other factors, 32 including the microbiome, 33 , 34 , 35 airway S-nitrosothiol concentration, 36 airway pH, 37 , 38 , 39 and genetic background. 18 , 40 These facts, including our findings, again remind us that F eno is only an adjunctive diagnostic tool in the diagnosis of asthma.…”