Hemolytic and microbicidal actions of diethyldithiocarbamic acid

Abstract

Micromolar concentrations of diethyldithiocarbamic acid (DDC) kill fungi, bacteria and malaria. DDC forms chelates with copper and the microbicidal effectiveness of this drug is enhanced greatly by small amounts of copper. DDC, in the presence of at least 1 molar equivalent of copper, also causes lysis of human erythrocytes. To explore the cytocidal actions of DDC and copper, we have used human erythrocytes and Escherichia coli as models. We found that: (1) the combination of DDC and copper also lysed E. coli spheroplasts, suggesting a possible common mechanism of hemolytic and microbicidal action; (2) higher ratios of drug: metal (greater than 4:1) diminished hemolytic and, as observed earlier, microbicidal effects; (3) cobalt, known to suppress the microbicidal effects of DDC:Cu, also prevented red cell lysis; (4) despite the necessary involvement of copper in DDC-mediated hemolysis, there was no evidence of oxidative damage to erythrocytes, and both lysis of erythrocytes and killing of E. coli were undiminished in the absence of oxygen; (5) the DDC:Cu chelate preferentially located in organic solvents and in membranes of erythrocytes. The chelate was quite soluble in chloroform but much less so in a C-16 hydrocarbon (hexadecane) which resembled erythrocyte membrane lipid. In hexadecane and at greater than 10(-4) M DDC and 5 x 10(-5) copper, an amphipathic drug:metal complex accumulated at the organic:aqueous interface; and (6) this amphipathic complex may permeabilize the lipid bilayer, causing leakage of ions and cell water and eventuating in colloid osmotic lysis. Red cells and E. coli exposed to the chelate showed early loss of intracellular rubidium (86Rb+). Furthermore, lysis of erythrocytes and E. coli spheroplasts was suppressed by the inclusion of either dextran or sucrose. Thus, it appears that DDC:Cu chelates are cytocidal by virtue of concentrating in the lipid bilayer and, perhaps, forming amphipathic complexes which disrupt membrane integrity. Drugs with similar behavior hold promise for therapy of malaria because metals capable of forming such complexes may accumulate within parasitized red cells.