Salivary and plasma levels of matrix metalloproteinase-9 and myeloperoxidase at rest and after acute physical exercise in patients with coronary artery disease

Background: Low-grade systemic inflammation is a predictor of recurrent cardiac events in patients with coronary artery disease (CAD). Plasma proteins such as matrix metalloproteinase (MMP)-9 and myeloperoxidase (MPO) have been shown to reflect basal as well as stress-induced inflammation in CAD. Measurements of MMP-9 and MPO in saliva might pose several advantages. Therefore, we investigated whether salivary levels of MMP-9 and MPO corresponded to plasma levels in patients with CAD, both at rest and after acute physical exercise. Methods: An acute bout of physical exercise on a bicycle ergometer was used as a model for stress-induced inflammation. Twenty-three CAD patients performed the test on two occasions 3-6 months apart. Whole unstimulated saliva was collected before, directly after and 30 min after exercise while plasma was collected before and after 30 min. MMP-9 and MPO in saliva and plasma were determined by Luminex. Results: MMP-9 and MPO levels were 2- to 4-fold higher in saliva than in plasma. Within the saliva compartment, and also to a great extent within the plasma compartments, MMP-9 and MPO showed strong intercorrelations at all time points. However, there were no (or weak) correlations between salivary and plasma MMP-9 and none between salivary and plasma MPO. Conclusion: We conclude that salivary diagnostics cannot be used to assess systemic levels of MMP-9 and MPO in CAD patients, neither at rest nor after acute physical exercise.