Introduction: The aims of the present study were to characterize the day/night variation of matrix metalloproteinase (MMP)-9 in patients who have developed ST-segment elevation myocardial infarction (STEMI), in response to light/dark differences in circulating melatonin and to assess whether melatonin, a day/night variation regulator, modulates the nocturnal inflammatory changes in patients who have STEMI.
Methods: The study included 75 patients diagnosed with STEMI and 75 control subjects. Each subject was studied under strictly controlled light/dark conditions. Blood samples for measurement of MMP-9 and melatonin were collected at 09:00 a.m. (light period) and 02:00 a.m. (dark period).
Results: In patients with STEMI, melatonin concentrations maintained a light/dark variation but the difference between nocturnal and diurnal levels was smaller than that in controls (p<0.001). In contrast to melatonin, serum MMP-9 concentrations showed no day/night variation in control subjects. MMP-9 concentrations were significantly higher in patients with STEMI than in control subjects. In the STEMI subjects, MMP-9 serum concentrations in the light period were significantly higher than those during the dark phase (291.1+/-59.5 vs. 261.8+/-57.8 ng/ml, p<0.01). Furthermore in the control subjects there was no correlation between MMP-9 and melatonin levels, while in the STEMI group there was a significant correlation between these parameters (Pearson's r=0.40, p<0.0004).
Conclusions: Our results suggest that the light/dark variations in endogenous MMP-9 production in patients who have STEMI might be associated, at least in part, to the day/night variation of melatonin.