title: Correlation of circulating MMP-9 with white blood cell count in humans: effect of smoking.
abstract: BACKGROUND
  Matrix metalloproteinase-9 (MMP-9) is an emerging biomarker for several disease conditions, where white blood cell (WBC) count is also elevated. In this study, we examined the relationship between MMP-9 and WBC levels in apparently healthy smoking and non-smoking human subjects.
  
  
  METHODS
  We conducted a cross-sectional study to assess the relationship of serum MMP-9 with WBC in 383 men and 356 women. Next, we divided the male population (women do not smoke in this population) into three groups: never (n = 243), current (n = 76) and former (n = 64) smokers and compared the group differences in MMP-9 and WBC levels and their correlations within each group.
  
  
  RESULTS
  Circulating MMP-9 and WBC count are significantly correlated in men (R(2) = 0.13, p<0.001) and women (R(2) = 0.19, p<0.001). After stratification by smoking status, MMP-9 level was significantly higher in current smokers (mean ± SE; 663.3±43.4 ng/ml), compared to never (529.7±20.6) and former smokers (568±39.3). WBC count was changed in a similar pattern. Meanwhile, the relationship became stronger in current smokers with increased correlation coefficient of r = 0.45 or R(2) = 0.21 (p<0.001) and steeper slope of ß = 1.16±0.30 (p<0.001) in current smokers, compared to r = 0.26 or R(2) = 0.07 (p<0.001) and ß = 0.34±0.10 (p<0.001) in never smokers.
  
  
  CONCLUSIONS
  WBC count accounts for 13% and 19% of MMP-9 variance in men and women, respectively. In non-smoking men, WBC count accounts for 7% of MMP-9 variance, but in smoking subjects, it accounts for up to 21% of MMP-9 variance. Thus, we have discovered a previously unrecognized correlation between the circulating MMP-9 and WBC levels in humans.
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Soren
authors.initials: S
authors.lastname: Snitker
authors.forename: Keming
authors.initials: K
authors.lastname: Xie
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Ryan
authors.forename: Daozhan
authors.initials: D
authors.lastname: Yu
authors.forename: Alan R
authors.initials: AR
authors.lastname: Shuldiner
authors.forename: Braxton D
authors.initials: BD
authors.lastname: Mitchell
authors.forename: Da-Wei
authors.initials: DW
authors.lastname: Gong
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000097:blood*; D008875:Middle Aged; D012727:Sex Characteristics; D012907:Smoking / Q000097:blood*; D055815:Young Adult
chemical_list: D020780:Matrix Metalloproteinase 9