The effects of water-soluble carbon monoxide-releasing molecules (CO-RMs) on vascular tone
Carbon monoxide (CO) is an important signalling messenger in mammalian cells as it participates in a variety of physiological processes including vessel tone regulation. Dr. Motterlini's group has discovered a new class of molecules which have the ability to carry and deliver CO to physiological systems. These molecules were termed CO-releasing molecules (CO-RMs) and they are an excellent tool to investigate the biological role of CO in the vasculature and other systems. The major focus of the research presented in this report was to evaluate the effects of different water soluble CO-RMs on vascular tone. For this purpose, an aortic ring preparation model was used to assess the vasodilatory properties of CORM-3 and CORM-A1, the first two water-soluble CO-RMs to be identified, and the cellular targets involved in this effect. CORM-3 is a transition metal carbonyl that liberates CO very rapidly (1=1-5 min) in physiological solutions, whereas CORM-A1 is a boron-containing carbonate with a much slower rate of CO release (tvi=21 min at pH=7.4). In the current studies CORM-3 induced a rapid endothelium-dependent vasorelaxation, whereas CORM-A1 elicited gradual endothelium-independent vasorelaxation. The inactive form of both CO-RMs, in which CO has been deliberately depleted, did not exert vasorelaxation indicating a direct involvement of CO liberated from the compounds in the observed vasorelaxation. The vasorelaxation induced by both molecules was enhanced and attenuated by an activator and inhibitor of guanylate cyclase (sGC), respectively. CORM-3-mediated vasorelaxation was completely abolished by non-selective inhibitors of potassium channels (K+), and partially attenuated by inhibition of ATP dependant (Katp) potassium channels. In contrast, CORM-A1 -mediated vasorelaxation was partially attenuated by non selective inhibition of K+ and by inhibition of voltage dependent (Ky) potassium channels. Even at concentrations higher than that used to induce significant vasorelaxation, both CO-RMs had no noticeable effect on the viability of rat aortic smooth muscle cells (A7r5) in vitro. CORM-319, a new water soluble iron containing CO-RM, also induced significant vasorelaxation and was relatively safe to cultured SMCs compared to other non-water soluble iron containing CO-RMs that were extremely toxic. In summary, our data reveal that the CO-RMs examined in this project are promising CO carriers that could be further modified for optimal therapeutic applications. In addition, our data demonstrate the significant effect imposed by the chemical structure and kinetics of CO release on the pharmacological activity of various CO-RMs.