Linkage of NAMPT promoter variants to eNAMPT secretion, plasma eNAMPT levels, and ARDS severity.

Background And Objectives: eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel DAMP and TLR4 ligand, is a druggable ARDS therapeutic target with promoter SNPs associated with ARDS severity. This study assesses the previously unknown influence of promoter SNPs on transcription, eNAMPT secretion, and ARDS severity.

Methods And Design: Human lung endothelial cells (ECs) transfected with promoter luciferase reporters harboring SNPs G-1535A, A-1001 C, and C-948A, were exposed to LPS or LPS/18% cyclic stretch (CS) and promoter activity, NAMPT protein expression, and secretion assessed. genotypes and eNAMPT plasma measurements (Days 0/7) were assessed in two ARDS cohorts (DISCOVERY  = 428; ALVEOLI  = 103).

Results: Comparisons of minor allelic frequency (MAF) in both ARDS cohorts with the 1000 Human Genome Project revealed the G-1535A and C-948A SNPs to be significantly associated with ARDS in Blacks compared with controls and trended toward significance in non-Hispanic Whites. LPS-challenged and LPS/18% CS-challenged EC harboring the -1535G wild-type allele exhibited significantly increased promoter activity (compared with -1535A) with the -1535G/-948A diplotype exhibiting significantly increased promoter activity, NAMPT protein expression, and eNAMPT secretion compared with the -1535A/-948 C diplotype. Highly significant increases in Day 0 eNAMPT plasma values were observed in both DISCOVERY and ALVEOLI ARDS cohorts (compared with healthy controls). Among subjects surviving to Day 7, Day 7 eNAMPT values were significantly increased in Day 28 non-survivors survivors. The protective -1535A SNP allele drove -1535A/-1001A and -1535A/-948 C diplotypes that confer significantly reduced ARDS risk (compared with -1535G, -1535G/-1001 C, -1535G/-948A), particularly in Black ARDS subjects. SNP comparisons within the two ARDS cohorts did not identify significant association with either APACHE III scores or plasma eNAMPT levels.

Conclusion: SNPs influence promoter activity, eNAMPT protein expression/secretion, plasma eNAMPT levels, and ARDS severity. genotypes are a potential tool for stratification in eNAMPT-focused ARDS clinical trials.