Factor VIII heavy chain polypeptides in plasma and concentrates

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Abstract
Factor VIIK polypeptides in plasma and FVIII concentrates have been analysed by an electrophoretic technique based on that of Weinstein et al (1981). Samples were complexed with radiolabeled anti-FVIII Fab'', and the immunocomplexes visualized by SDS-polyacrylamide electrophoresis. The technique visualized FVIII heavy chain polypeptides in all types of samples, including plasma, without further purification. Fresh or frozen normal plasma (collected into protease inhibitors) contained a range of polypeptides with the largest dominant band at an apparent Mr of 250-300 kDa, and the smallest at 80-90 kDa: no bands were produced from samples of severe haemophilic plasma. Cryoprecipitate had a similar polypeptide distribution to normal plasma, but intermediate purity FVIII concentrates showed more degraded patterns which varied between products: the 250-300 kDa bands were reduced or absent, the 80-90 kDa bands were more pronounced than in plasma, and in one product a polypeptide was seen at approximately 40-50 kDa. In some products heat treatment for viral inactivation increased the proportion of smaller FVIII polypeptides. Highly-purified FVIII concentrate derived from plasma was also degraded relative to plasma FVIII, and two products obtained by recombinant DNA technology both showed degraded, through slightly different, profiles. The native structure of FVIII in fresh plasma appears heterogeneous with a predominance of higher Mr forms; these are degraded to a greater or lesser extent during concentrate production, dependent on the manufacturing processes used.

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