CO-independent modification of K + channels by tricarbonyldichlororuthenium(II) dimer (CORM-2)

Abstract

Although toxic when inhaled in high concentrations, the gas carbon monoxide (CO) is endogenously produced in mammals, and various beneficial effects are reported. For potential medicinal applications and studying the molecular processes underlying the pharmacological action of CO, so-called CO-releasing molecules (CORMs), such as tricabonyldichlororuthenium(II) dimer (CORM-2), have been developed and widely used. Yet, it is not readily discriminated whether an observed effect of a CORM is caused by the released CO gas, the CORM itself, or any of its intermediate or final breakdown products. Focusing on Ca2+- and voltage-dependent K+ channels (KCa1.1) and voltage-gated K+ channels (Kv1.5, Kv11.1) relevant for cardiac safety pharmacology, we demonstrate that, in most cases, the functional impacts of CORM-2 on these channels are not mediated by CO. Instead, when dissolved in aqueous solutions, CORM-2 has the propensity of forming Ru(CO)2 adducts, preferentially to histidine residues, as demonstrated with synthetic peptides using mass-spectrometry analysis. For KCa1.1 channels we show that H365 and H394 in the cytosolic gating ring structure are affected by CORM-2. For Kv11.1 channels (hERG1) the extracellularly accessible histidines H578 and H587 are CORM-2 targets. The strong CO-independent action of CORM-2 on Kv11.1 and Kv1.5 channels can be completely abolished when CORM-2 is applied in the presence of an excess of free histidine or human serum albumin; cysteine and methionine are further potential targets. Off-site effects similar to those reported here for CORM-2 are found for CORM-3, another ruthenium-based CORM, but are diminished when using iron-based CORM-S1 and absent for manganese-based CORM-EDE1.

Mechanisms Responsible for the Anticoagulant Properties of Neurotoxic Dendroaspis Venoms: A Viscoelastic Analysis

“…Lastly, with regard to the inhibition of anticoagulant activity by CORM-2, black mamba venom displayed no inhibition, whereas all three green mamba venoms had anticoagulant activity significantly and completely inhibited in PBS, but not in the presence of 5% human albumin. As with CORM-2-mediated inhibition of bee venom PLA 2 anticoagulant activity [18] and the modification of K + channels [20], albumin served as a "histidine sink" that reacts with a proposed Ru-based radical formed from CORM-2 while CO is being released. Our findings with CORM-2 are critical, as the mechanism by which the Ru-based radical effects its modification of proteins is most likely secondary to its binding to histidine residues or thiol groups, as reviewed in our recent work [18].…”

Ruthenium, Not Carbon Monoxide, Inhibits the Procoagulant Activity of Atheris, Echis, and Pseudonaja Venoms

“…To substantiate this claim, the authors demonstrated that free histidine or albumin, which is resplendent with histidine residues, quenched the inhibition of potassium channels by CORM-2. Furthermore, using mass spectroscopy, the authors demonstrated histidine-Ru-based radical formation following exposure of free histidine with CORM-2 [14]. Lastly, using other various CORMs with other metal centers, the authors demonstrated no CO effects on the channel assessed [14].…”

“…However, cracks in the edifice of this paradigm began to appear in the year 2017 with the publication of a work that demonstrated CO-independent inhibition of K + channels with a putative Ru-based radical formed from CORM-2 during CO release and likely prior to formation of its iRM [14]. To substantiate this claim, the authors demonstrated that free histidine or albumin, which is resplendent with histidine residues, quenched the inhibition of potassium channels by CORM-2.…”

“…Furthermore, using mass spectroscopy, the authors demonstrated histidine-Ru-based radical formation following exposure of free histidine with CORM-2 [14]. Lastly, using other various CORMs with other metal centers, the authors demonstrated no CO effects on the channel assessed [14]. This laboratory became aware of this work recently, and using a similar approach, demonstrated an identical outcome wherein the anticoagulant activity of the purified phospholipase A 2 (PLA 2 ) of Apis mellifera venom was inhibited by CORM-2 in a CO-independent, albumin-inhibitable fashion [15].…”

Acetoxymethyl Concept for Intracellular Administration of Carbon Monoxide with Mn(CO)3‐Based PhotoCORMs

“…In the past, we and others already demonstrated the suitability of facial Mn(CO) 3 units for light-triggered administration of carbon monoxide [16] whereas in ruthenium-based and to al esser extentini ron-basedC ORMs the metal influence interferes with the CO-dependent modification of K + channels. [22] Solubility in aqueous media can be ensuredv ia formation of separated ions as realized for example, in non-toxic [{(OC) 3 Mn} 2 (m-SC 2 H 4 NH 3 ) 3 ]Br 2 (CORM-EDE1), [23] [(OC) 3 Mn{S(C 2 H 4 NH 2 ) 2 }]Br (CORM-EDE3), [18a] and [(OC) 3 Mn{(Pz Me2 ) 2 CHCH 2 OH)]Br (CORM-ONN1). [24] Reduction of the hydrophilicity already showeda nu nspecific uptake by living cells as demonstrated for [(OC) 3 Mn{S(C 2 H 4 NHCH 2 ) 2 }]Br (CORM-EDE4).…”