Development of a screening protocol to identify persons who are responsive to wood smoke particle-induced airway inflammation with pilot assessment of GSTM1 genotype and asthma status as response modifiers

Abstract

Background: We are currently screening human volunteers to determine their sputum polymorphonuclear neutrophil (PMN) response 6- and 24-hours following initiation of exposure to wood smoke particles (WSP). Inflammatory responders (≥10% increase in %PMN) are identified for their subsequent participation in mitigation studies against WSP-induced airways inflammation. In this report we compared responder status (<i>N</i> = 52) at both 6 and 24 hr time points to refine/expand its classification, assessed the impact of the GSTM1 genotype, asthma status and sex on responder status, and explored whether sputum soluble phase markers of inflammation correlate with PMN responsiveness to WSP.

Results: Six-hour responders tended to be 24-hour responders and vice versa, but 24-hour responders also had significantly increased IL-1beta, IL-6, IL-8 at 24 hours post WSP exposure. The GSTM1 null genotype significantly (<i>p</i> < 0.05) enhanced the %PMN response by 24% in the 24-hour responders and not at all in the 6 hours responders. Asthma status enhanced the 24 hour %PMN response in the 6- and 24-hour responders. In the entire cohort (not stratified by responder status), we found a significant, but very small decrease in FVC and systolic blood pressure immediately following WSP exposure and sputum %PMNs were significantly increased and associated with sputum inflammatory markers (IL-1beta, IL-6, IL-8, and PMN/mg) at 24 but not 6 hours post exposure. Blood endpoints in the entire cohort showed a significant increase in %PMN and PMN/mg at 6 but not 24 hours. Sex had no effect on %PMN response.

Conclusions: The 24-hour time point was more informative than the 6-hour time point in optimally and expansively defining airway inflammatory responsiveness to WSP exposure. GSTM1 and asthma status are significant effect modifiers of this response. These study design and subject parameters should be considered before enrolling volunteers for proof-of-concept WSP mitigation studies.

Keywords: Wood smoke particle exposure; airway neutrophil response; responder status.

Figure 1:

Sputum Inflammatory Response to WSP of the Entire Cohort Sputum % PMN (Panel A), PMN/mg sputum (Panel B), $\text{IL-1β}$ (Panel C), IL-6 (Panel D), IL-8 (Panel E) and $\text{TNFα}$ (Panel F) at baseline, 6- and 24-hours post WSP challenge in the total unstratified cohort. . Asterisk denotes mixed model analysis using a compound symmetry covariance matrix where fit used Restricted Maximum Likelihood (REML) to allow for overall and multiple comparisons and missing data.

Figure 2:. Spirometric and blood pressure endpoints at baseline and immediately after WSP challenge of the entire unstratified cohort.

Spirometric and blood pressure endpoints at baseline and immediately after WSP challenge in the total unstratified cohort. Asterisk denotes paired t-test.

Figure 3:. Sputum Inflammatory Response to WSP of responsive volunteers as defined by %PMNs at 6 hours.

Sputum % PMN (Panel A), PMN/mg sputum (Panel B), $\text{IL-1β}$ (Panel C), IL-6 (Panel D), IL-8 (Panel E) and $\text{TNFα}$ (Panel F) at baseline, 6- and 24-hours post WSP challenge in the cohort of volunteers responsive to WSP based on a change from baseline of the 6-hour %PMN of at least 10% (N=30). Asterisk denotes mixed model analysis using a compound symmetry covariance matrix where fit used Restricted Maximum Likelihood (REML) to allow for overall and multiple comparisons and missing data.

Figure 4. Spirometric (Panel A) and blood pressure (Panel B) endpoints at baseline and immediately after WSP challenge of responsive volunteers as defined by %PMNs at 6 hours.

Spirometric and blood pressure endpoints at baseline and immediately after WSP challenge in responders and non-responders defined at 6 hours. Asterisk denotes paired t-test test.

Figure 5. Sputum Inflammatory Response to WSP of responsive volunteers as defined by %PMNs at 24 hours.

Sputum % PMN (Panel A), PMN/mg sputum (Panel B), $\text{IL-1β}$ (Panel C), IL-6 (Panel D), IL-8 (Panel E) and $\text{TNFα}$ (Panel F) at baseline, 6- and 24-hours post WSP challenge in the cohort of volunteers responsive to WSP based on a change from baseline of the 24-hours %PMN of at least 10% (N=28). Asterisk denotes mixed model analysis using a compound symmetry covariance matrix where fit used Restricted Maximum Likelihood (REML) to allow for overall and multiple comparisons and missing data

Figure 6. Spirometric (Panel A) and blood pressure (Panel B) endpoints at baseline and immediately after WSP challenge of responsive volunteers as defined by %PMNs at 24 hours

Spirometric and blood pressure endpoints at baseline and immediately after WSP challenge in responders and non-responders defined at 24 hours. Asterisk denotes paired t-test.