The binding of colchicine and its derivatives to bovine and human serum albumin and human plasma.

The protein binding of colchicine and its derivatives demecolcine and desacetylcolchiceine was studied by equilibrium dialysis at 22 degrees C and pH 7.38 in bovine and human serum albumin and human plasma. Colchicine and demecolcine (2 X 10(-4) -5 X 10(-4) mol/l) is not bound to proteins. The binding of desacetylcholchiceine was 60--80% in the range 10(-4)-5 X 10(-4) mol/l. The association constant for a single binding site was 8.03 X 10(3) 1/mol for human serum albumin and 13.20 X 10(3) 1/mol for human plasma. The binding profiles for desacetylcholchiceine were quite similar in human serum albumin (4% conc.) and human plasma (3.8% conc. of albumin fraction). We suggest that desacetylcolchiceine was likely to be bound predominantly to albumin. Salicylic acid in vitro, at clinical concentrations (1.8--14.5 X 10(-4) mol/l), significantly decreases the binding of desacetylcolchiceine to human serum albumin.