In vitro and in vivo comparison of sulfur donors as antidotes to acute cyanide intoxication.

Antidotes for cyanide (CN) intoxication include the use of sulfane sulfur donors (SSDs), such as thiosulfate, which increase the conversion of CN to thiocyanate by the enzyme rhodanese. To develop pretreatments that might be useful against CN, SSDs with greater lipophilicity than thiosulfate were synthesized and assessed. The ability of SSDs to protect mice against 2LD50 of sodium cyanide (NaCN) administered either 15 or 60 min following administration of an SSD was assessed. To study the mechanism of action of the SSD, the candidate compounds were examined in vitro for their effect on rhodanese and 3-mercaptopyruvate sulfurtransferase (MST) activity under increasing SSD concentrations. Tests were conducted on nine candidate SSDs: ICD1021 (3-hydroxypyridin-2-yl N-[(N-methyl-3-aminopropyl)]-2-aminoethyl disulfide dihydrochloride), ICD1022, (3-hydroxypyridin-2-yl N-[(N-methyl-3-aminopropyl)]-2-aminoethyl disulfide trihydrochloride), ICD1584 (diethyl tetrasulfide), ICD1585 (diallyl tetrasulfide), ICD1587 (diisopropyl tetrasulfide); ICD1738 (N-(3-aminopropyl)-2-aminoethyl 2-oxopropyl disulfide dihydrochloride), ICD1816 (3,3'-tetrathiobis-N-acctyl-L-alanine), ICD2214 (2-aminoethyl 4-methoxyphenyl disulfide hydrochloride) and ICD2467 (bis(4-methoxyphenyl) disulfide). These tests demonstrated that altering the chemical substituent of the longer chain sulfide modified the ability of the candidate SSD to protect against CN toxicity. At least two of the SSDs at selected doses provided 100% protection against 2LD50 of NaCN, normally an LD99. All compounds were evaluated using locomotor activity as a measure of potential adverse behavioral effects. Positive hypoactivity relationships were found with several disulfides but none was found with ICD1584, a tetrasulfide. Separate studies suggest that the chemical reaction of potassium cyanide (KCN) and cystine forms the toxic metabolite 2-iminothiazolidine-4-carboxylic acid. An alternative detoxification pathway, one not primarily involving the sulfur transferases. may be important in pretreatment for CN intoxication. Although studies to elucidate the precise mechanisms are needed. it is clear that these newly synthesized compounds provide a new rationale for anti-CN drugs, with fewer side-effects than the methemoglobin formers.