Antidotal Effects of the Phenothiazine Chromophore Methylene Blue Following Cyanide Intoxication

Abstract

Our study was aimed at (1) determining the efficacy of the dye methylene blue (MB), following a rapidly lethal cyanide (CN) intoxication in un-sedated rats; (2) clarifying some of the mechanisms responsible for the antidotal properties produced by this potent cyclic redox dye. Sixty-nine awake rats acutely intoxicated by CN (IP, KCN 7 mg/kg) received saline, MB (20 mg/ kg) or hydroxocobalamin (HyCo, 150 mg/kg) when in deep coma. Survival in this model was very low, reaching 9% at 60 min without any treatment. Methylene blue significantly increased survival (59%, p < .001) at 60 min, versus 37% with HyCo (p < .01). In addition, 8 urethane-anesthetized rats were exposed to a sublethal CN intoxication (KCN, 0.75 mg/kg/min IV for 4 min); they received MB (20 mg/kg, IV) or saline, 5 min after the end of CN exposure. All MB-treated rats displayed a significant reduction in hyperlactacidemia, a restoration of pyruvate/lactate ratio-a marker of NAD/NADH ratio-and an increase in CO 2 production, a marker of the activity of the TCA cycle. These changes were also associated with a 2-fold increase in the pool of CN in red cells. Based on series of in vitro experiments, looking at the effects of MB on NADH, as well as the redox effects of MB on hemoglobin and cytochrome c, we hypothesize that the antidotal properties of MB can in large part be accounted for by its ability to readily restore NAD/NADH ratio and to cyclically re-oxidize then reduce the iron in hemoglobin and the electron chain complexes. All of these effects can account for the rapid antidotal properties of this dye following CN poisoning.

Methylene blue and monosodium glutamate improve neurologic signs after fluoroacetate poisoning

“…43 As a medical therapeutic, MB is FDA approved for the treatment of methemoglobinemia and has also shown efficacy in treating hypoxia, hypotension, and cyanide intoxication. [44][45][46][47] MSG is metabolized to alphaketoglutarate, a substrate of the citric acid cycle that would bypass the aconitase blockade following 1080 poisoning. By supporting glutamine metabolism, MSG may circumvent the bottleneck in the citric acid cycle that prevents pyruvate oxidation.…”

Antidotal effects of methylene blue against cyanide neurological toxicity: in vivo and in vitro studies

“…17,18 We have recently revisited the effects of MB, which was briefly proposed in the 1930s [19][20][21][22] as a treatment of CN intoxication, and found that this molecule exerts potent antidotal effects against CN toxicity through a unique modality of action that results from its distinctive cyclic redox properties. [23][24][25] These properties are currently used to treat the excessive formation of ferric iron in hemoglobin (methemoglobin), restoring the ability of hemoglobin to carry O 2 in patients with methemoglobinemia. 17,18,26,27 After being administrated, MB is immediately reduced into its leucoform, leucomethylene blue (LMB), 28 by reducing agents present in blood and cells, such as NAD(P)H. 29 reoxidized into MB by molecules with a higher redox potential (such as O 2 or most metallocompounds), giving up to two electrons in the process (Fig.…”

“…29 Diffusing rapidly into the cytoplasm and in the mitochondria of any cells, including neurons, 30 the MB/LMB couple can restore the TCA cycle and the glycolytic activity by oxidizing NADH and decreasing the NADH/NAD ratio, 31 rescuing the TCA cycle when inhibited by the accumulation of NADH, like for instance during an impediment of the electron chain activity by CN or H 2 S intoxication. 25,28 The reestablishment of the TCA cycle can, in turn, lead to the production of ATP via succinyl-CoA synthase-the mitochondrial substrate-level phosphorylation 31 independently of the integrity of the mitochondrial ATPase activity. Also, MB/LMB redox properties appear to be able to restore the mitochondrial membrane potential, depressed by CN, through mechanisms that are not fully understood.…”

“…Also, MB/LMB redox properties appear to be able to restore the mitochondrial membrane potential, depressed by CN, through mechanisms that are not fully understood. 25,28 Indeed, recent studies have shown a decrease, by MB, of postanoxic brain injury, [32][33][34][35][36] as well as in various conditions associated with altered mitochondrial functions. [37][38][39][40][41] It has been proposed that LMB could interact directly with the mitochondrial electron chain, 42 providing electrons to the complexes I and III and allowing a partial resuscitation of the mitochondrial electron chain.…”

“…Although such a mechanism would be difficult to reconcile with the effects of CN intoxication, which result, if anything, in a reduction of the electron chain complexes, MB does restore the mitochondrial membrane potential and decrease the production of reactive O 2 species in cells intoxicated by CN. 24,25 These effects translate into a drastic decrease in mortality following MB administration after lethal CN intoxication in the rat. 24,25 This increased survival is mediated through the rescue of cardiac contractility, 23,43 an effect also observed with other mitochondrial poisons.…”