Coagulation protein function. II. Influence of thiols upon acetaldehyde effects

Abstract

It has been reported that prolonged prothrombin time may be a result of the interaction of acetaldehyde (AcH) with clotting proteins to form alkylated inactive products. The current investigation focuses on the influence of l-cysteine (CysH), dl-homocysteine (HC), D-penicillamine, N-acetyl- l-cysteine (NAC), l-serine and l-alanine at 0.01 M concentrations, lactalbumin hydrolysate (2 mg/ml), and 1.0 mM dithiothreitol (DTT) on clotting time as well as their interaction with AcH. The sulfhydryl amino acids, as well as DTT prolonged clotting upon preincubation with plasma. Cysteine and NAC, upon addition to plasma prior to the addition of AcH, exhibited a prolongation of clotting time compared to that of AcH alone. On sequential addition of serine, alanine, or lactalbumin hydrolysate to plasma followed by the addition of acetaldehyde, a prolongation of clotting time comparable to that of AcH alone was exhibited. When HC and penicillamine were added to plasma prior to the addition of AcH, a prolonged clotting time was observed, which was significantly less than that of AcH alone. Premixing of serine, alanine, and lactalbumin hydrolysate with AcH for 20 min prior to addition to the plasma reduced the effectiveness of AcH in prolonging clotting time as compared to successive additions of the amino acid and AcH. Since CysH and penicillamine have been reported to form cyclic adducts with AcH, it is suggested that a similar possibility exists for penicillamine and for HC. The reversible cyclic adduct formation reported for CysH may explain why cysteine did not lower the prolonged clotting time induced by AcH. These results lend further biochemical support to the suggestion that alcoholism may promote prolonged prothrombin times by covalent interaction of AcH with clotting factors. In addition, prolonged clotting times observed with thiols suggest that disulfide interchange can occur between thiol amino acids and the disulfide bridges that are common in many clotting factors. The reduction in clotting times that are seen upon preincubation of HC and penicillamine with AcH leads to the proposal that thiols other than glutathione may detoxify AcH, and that detoxification of AcH by some thiols may minimize potential damage by both compounds.