Synergy of nitric oxide and azoles against Candida species in vitro

The candidacidal activity of nitric oxide (NO) as delivered by a class of compounds termed diazeniumdiolates has been investigated. Diazeniumdiolates are stable agents capable of releasing NO in a biologically usable form at a predicted rate, and three such compounds were examined for activity. One compound, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1, 2-diolate (DETA-NO), proved to be most suitable for examining NO activity due to its relatively long half-life (20 h) and because of limited candidacidal activity of the uncomplexed DETA nucleophile. DETA-NO was active against six species of Candida for which the MICs necessary to inhibit 50% growth (MIC50s) ranged from 0.25 to 1.0 mg/ml. C. parapsilosis and C. krusei were the most susceptible to the compound. In addition to a determination of NO effects alone, the complex was utilized to investigate the synergistic potential of released NO in combination with ketoconazole, fluconazole, and miconazole. Activity was investigated in vitro against representative strains of Candida albicans, C. krusei, C. parapsilosis, C. tropicalis, C. glabrata, and C. dubliniensis. Determination of MIC50, MIC80 and MICs indicated that DETA-NO inhibits all strains tested, with strains of C. parapsilosis and C. krusei being consistently the most sensitive. The combination of DETA-NO with each azole was synergistic against all strains tested as measured by fractional inhibitory concentration indices that ranged from 0.1222 to 0.4583. The data suggest that DETA-NO or compounds with similar properties may be useful in the development of new therapeutic strategies for treatment of Candida infections.