Characterization of carbon disulfide binding in blood and to other biological substances

Abstract

Free and bound forms of CS 2 are present in subjects exposed to CS 2. In rats exposed to 2 mg/liter (∼640 ppm) of CS 2 for 4 hr, concentrations of acid-labile CS 2 (AL CS 2, a form of bound CS 2 that can be recovered from biological samples by acid treatment) in plasma and red blood cells (RBCs) increased linearly with exposure time. The majority (90%) of the blood AL CS 2 was present in the RBCs. About 95% of the AL CS 2 in plasma and in RBCs of exposed rats was found in the precipitates after treatment with ammonium sulfate. Incubation of fractionated human RBC lysates with CS 2 showed that CS 2 binding in these fractions was proportional to the hemoglobin concentration. These observations show that in blood, CS 2 binds (in the form of AL CS 2) mainly to hemoglobin and to a small extent to other blood proteins. Binding of CS 2 to small molecules, including amino acids, accounted for only a small fraction of blood AL CS 2. In in vitro studies, CS 2 also bound to human albumin, γ-globulin, and horse heart myoglobin. It was also found that CS 2 binds to amino and sulfhydryl compounds at physiological pH. Plasma incubated with CS 2 was found to chelate copper. Chelation of copper-containing enzyme by the reaction products of CS 2 and biological amines has been observed and has been proposed as one of the mechanisms by which CS 2 induces neurotoxicity ( M. J. McKenna and V. Distefano, 1977b, J. Pharmacol. Exp. Ther. 202, 253–266). Radioisotope studies showed that a substantial portion of the radioactivity could not be released from 14CS 2-treated plasma and serum upon acid treatment at elevated temperature. These studies suggest the existence of non-acid-labile bound CS 2, besides AL CS 2, in plasma and serum treated with CS 2.