Methylene blue counteracts cyanide cardiotoxicity: cellular mechanisms

Area of Science:

• Cardiovascular Physiology
• Cellular Electrophysiology
• Toxicology

Background:

• Cyanide poisoning, a significant health risk from industrial exposure and smoke inhalation, can lead to cardiogenic shock.
• Early-stage cyanide exposure impairs myocyte contractility despite normal adenosine triphosphate levels, primarily due to altered calcium (Ca²⁺) homeostasis.
• The oxidation-reduction environment of ion channels is implicated in cyanide-induced cardiac dysfunction.

Purpose of the Study:

• To investigate the effects of sodium cyanide (NaCN) on adult mouse ventricular myocytes.
• To elucidate the mechanisms underlying NaCN-induced cardiotoxicity, focusing on intracellular Ca²⁺ ([Ca²⁺]_i) handling and electrophysiological changes.
• To evaluate the efficacy of methylene blue (MB) as a potential antidote for cyanide cardiotoxicity.

Main Methods:

• Isolated adult left ventricular mouse myocytes were exposed to varying concentrations of NaCN.
• Measurements included contraction amplitude, intracellular Ca²⁺ ([Ca²⁺]_i) transients, L-type Ca²⁺ current ( I_Ca), membrane potential ( E_m), action potentials (AP), K⁺ currents, and mitochondrial membrane potential (ΔΨ_m).
• Cellular adenosine triphosphate levels and superoxide (O₂^·-) production were assessed. The effects of MB administration post-NaCN exposure were analyzed.

Main Results:

• NaCN dose-dependently reduced myocyte contraction and [Ca²⁺]_i transient amplitudes, primarily by altering systolic [Ca²⁺]_i and decreasing I_Ca.
• NaCN also caused membrane depolarization ( E_m), altered AP configuration, and increased superoxide levels, while ATP levels remained unaffected.
• Methylene blue treatment effectively reversed the NaCN-induced abnormalities in contraction, [Ca²⁺]_i homeostasis, electrophysiology, and oxidative stress.

Conclusions:

• NaCN induces cardiotoxicity by disrupting Ca²⁺ homeostasis and excitation-contraction coupling, leading to impaired myocyte function and potential arrhythmias.
• Methylene blue demonstrates significant efficacy in reversing NaCN-induced cardiotoxicity by restoring Ca²⁺ handling, normalizing electrophysiological parameters, and reducing oxidative stress.
• MB's ability to normalize the oxidation-reduction state and Ca²⁺ channel function makes it a promising therapeutic agent for cyanide poisoning.