The circulating level of MMP-9 and its ratio to TIMP-1 as a predictor of severity in patients with community-acquired pneumonia

Background: Here, we have examined the plasma levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1), the MMP-9/TIMP-1 molar ratio, the TIMP-1 single nucleotide polymorphisms (SNPs) 372C/T and the susceptibility to community-acquired pneumonia (CAP). Methods: An enzyme-linked immunosorbent assay (ELISA) was used to measure plasma MMP-9 and TIMP-1 concentrations in 60 patients with CAP and 60 healthy individuals. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was used to detect the TIMP-1 SNPs 372C/T. Results: The plasma MMP-9, TIMP-1 levels and the MMP-9/TIMP-1 molar ratio were significantly increased in patients with CAP compared to normal controls. The MMP-9/TIMP-1 molar ratio decreased significantly in patients with CAP after treatment. Furthermore, the plasma TIMP-1 concentration was positively correlated with the pneumonia severity index (PSI), the CURB score, the results of the acute physiology and chronic health evaluation II (APACHE II) and the length of the hospital stay. No significant difference was found in the genotype distribution of TIMP-1 372C/T between patients with CAP and normal controls. Conclusions: We hypothesize that MMP-9 levels and the MMP-9/TIMP-1 molar ratio play a role in the development of CAP and are related to the severity of CAP. Based on our data, we suggest that incorporating plasma MMP-9 levels and the MMP-9/TIMP-1 molar ratio into a clinical evaluation will aid in CAP diagnosis. ™Plasma TIMP-1 levels and the MMP-9/TIMP-1 ratio were increased in CAP.™TIMP-1 levels positively correlated with severity of CAP scores.™TIMP-1 levels positively correlated with the length of the hospital stay.™MMP-9/TIMP-1 ratio should be a biomarker for assessing CAP severity.