© 1994 Oxford University Press
research-article |
Encapsulation of Rhodanese and Organic Thiosulfonates by Mouse Erythrocytes
Department of Medical Pharmacology and Toxicology, Texas A&M University, College of Medicine, College Station Texas 77843-1114
Received May 17, 1993; accepted October 28, 1993
A series of organic thiosulfonates were synthesized and studied as sulfur donor substrates for rhodanese encapsulated within murine carrier erythrocytes. Previous studies have indicated that resealed erythrocytes containing rhodanese (CRBC) and sodium thiosulfate can rapidly metabolize cyanide to the less toxic thiocyanate. This thiosulfate-rhodanese system was very efficacious as a new conceptual approach to antagonize cyanide intoxication both in vitro and in vivo. However, its potential is restricted because of the limited availability of thiosulfate due to its poor permeability through RBC membrane. Present studies suggest that there are advantages in using alternative sulfur donors, i.e., organic thiosulfonates in this rhodanese-containing resealed erythrocyte system, since these compounds have higher lipid solubility than inorganic thiosulfates and can readily penetrate the red blood cell membrane. Therefore, this system could provide a virtually unlimited amount of sulfur donor to the encapsulated rhodanese even if the substrates are in solution out side the cells. Moreover, the rhodanese reaction rate of any of these organic thiosulfonates is much faster than the rate ob served with the classic cyanide antidote, sodium thiosulfate. This CRBC system will continue to detoxify cyanide even when these encapsulated sulfur donors are depleted, as the lipid soluble organic thiosulfonate outside the cells will diffuse past the membrane into the cell to replenish the sulfur donor. The en capsulation efficiency for rhodanese is about 30°h, and the velocity of the rhodanese reaction increases linearly with the volume of enzyme-laden erythrocytes. Similarly, reaction velocity in creases linearly with substrate concentration. These results further establish the use of resealed erythrocytes as biodegradable drug carriers, particularly since the sulfur donor is now no longer limiting in this system.