Nitroglycerin upregulates matrix metalloproteinase expression by human macrophages

OBJECTIVES This study aimed to determine whether nitroglycerin (NTG) treatment affects matrix metalloproteinase (MMP) gene expression and activities in human macrophages. BACKGROUND Nitroglycerin is one of the most frequently used therapeutic agents for the symptomatic relief of stable or unstable coronary artery disease; however, its effects on vascular biology are poorly characterized. Despite its powerful vasodilator activity, NTG has not been shown to improve outcomes in coronary disease. We now describe evidence that NTG has potentially pro-inflammatory effects in human monocyte-derived macrophages (MDMs). METHODS Human monocytes were isolated from whole blood by elutriation and allowed to differentiate into macrophages over eight to 10 days. The MDMs were then treated for 4 or 24 h with control media, pharmacologically relevant doses of NTG or other nitric oxide donors. Matrix metalloproteinase activity was measured by zymography, protein levels measured by enzyme-linked immunosorbent assay and messenger ribonucleic acid (mRNA) levels were quantified by competitive reverse transcription-polymerase chain reaction. RESULTS The major MMP expressed by MDMs was MMP-9. Nitroglycerin treatment stimulated a dose-dependent increase in MMP-9 mRNA levels (NTG 200 pmol: 193 +/- 6% and NTG 2,000 pmol: 372 +/- 9% compared to controls, p < 0.005) and MMP-9 activity (NTG 200: 142 +/- 5.5% and NTG 2,000: 167 +/- 11% compared to controls, p < 0.005). Nitroglycerin 2,000 pmol also increased MMP-2 and MMP-7 mRNA levels to 187 +/- 8% and 183 +/- 21% of control values, respectively (p < 0.05). Furthermore, tissue inhibitor of metalloproteinase (TIMP)-1 (the major tissue inhibitor of MMPs) mRNA and protein levels were decreased in NTG 2,000 pmol-treated MDMs compared with control cells (mRNA: 67 +/- 7%, p < 0.005; protein: 45 +/- 5%, p < 0.005). CONCLUSIONS Nitroglycerin in pharmacologically relevant concentrations activates MMP but represses TIMP expression in human macrophages. The subsequent imbalance in MMP/TIMP expression associated with NTG treatment could promote matrix degradation, with potentially adverse effects on plaque stability.