Constituents of Mediterranean Spices Counteracting Vascular Smooth Muscle Cell Proliferation: Identification and Characterization of Rosmarinic Acid Methyl Ester as a Novel Inhibitor

Abstract

Scope: Aberrant vascular smooth muscle cell (VSMC) proliferation is involved in atherosclerotic plaque formation and restenosis. Mediterranean spices have been reported to confer cardioprotection, but their direct influence on VSMCs has largely not been investigated. This study aims at examining rosmarinic acid (RA) and 11 related constituents for inhibition of VSMC proliferation in vitro, and at characterizing the most promising compound for their mode of action and influence on neointima formation in vivo.

Methods and results: RA, rosmarinic acid methyl ester (RAME), and caffeic acid methyl ester inhibit VSMC proliferation in a resazurin conversion assay with IC₅₀ s of 5.79, 3.12, and 6.78 µm, respectively. RAME significantly reduced neointima formation in vivo in a mouse femoral artery cuff model. Accordingly, RAME leads to an accumulation of VSMCs in the G₀ /G₁ cell-cycle phase, as indicated by blunted retinoblastoma protein phosphorylation upon mitogen stimulation and inhibition of cyclin-dependent kinase 2 in vitro.

Conclusion: RAME represses PDGF-induced VSMC proliferation in vitro and reduces neointima formation in vivo. These results recommend RAME as an interesting compound with VSMC-inhibiting potential. Future metabolism and pharmacokinetics studies might help to further evaluate the potential relevance of RAME and other spice-derived polyphenolics for vasoprotection.

Keywords: Mediterranean spices; neointima formation; rosmarinic acid; rosmarinic acid methyl ester; vascular smooth muscle cells.