The effect of D-penicillamine on protein-bound homocyst(e)ine in homocystinurics.

There is considerable evidence that homocystine has a direct damaging effect on vascular endothelium and other tissues. The demonstration of the existence of protein-bound homocyst(e)ine has strengthened this hypothesis. In an attempt to remove bound homocyst(e)ine, D-penicillamine was given to three patients with pyridoxine-nonresponsive homocystinuria. Before the clinical trial, it had been demonstrated that 0.1 mumole per ml concentration of D-penicillamine or cysteamine released approximately 50% of the homocyst(e)ine bound to plasma proteins in vitro. Oral D-penicillamine effectively reduced both free and plasma protein-bound homocyst(e)ine in homocystinurics from the second day of treatment. The homocystine excreted in the urine was mainly in the form of homocysteine-penicillamine disulfide. No mixed disulfide was detectable in the plasma, indicating an extremely high renal clearance. These observations suggested that oral D-penicillamine removed a considerable quantity of the bound homocyst(e)ine accumulated in the tissue proteins.