Sensitive Detection of Oversulfated Chondroitin Sulfate in Heparin Sodium or Crude Heparin with a Colorimetric Microplate Based Assay

Abstract

In this work we describe a 96-well microplate assay for oversulfated chondroitin sulfate A (OSCS) in heparin, based on a water-soluble cationic polythiophene polymer (3-(2-(N-(N'-methylimidazole))ethoxy)-4-methylthiophene (LPTP)) and heparinase digestion of heparin. The assay takes advantage of several unique properties of heparin, OSCS, and LPTP, including OSCS inhibition of heparinase I and II activity, the molecular weight dependence of heparin-LPTP spectral shifts, and the distinct association of heparin fragments and OSCS to LPTP. These factors combine to enable detection of the presence of 0.003% w/w spiked OSCS in 10 μg of heparin sodium active pharmaceutical ingredient (API) using a plate reader and with visual detection to 0.1% levels. The same detection limit for OSCS was observed in the presence of 10% levels of dermatan sulfate (DS) or chondroitin sulfate A (CSA) impurities. In addition, we surveyed a selection of crude heparin samples received by the agency in 2008 and 2009 to determine average and extreme DS, CSA, and galactosamine weight percent levels. In the presence of these impurities and the variable heparin content in the crude heparin samples, spiked OSCS was reliably detected to the 0.1% w/w level using a plate reader. Finally, authentically OSCS contaminated heparin sodium API and crude samples were distinguished visually by color from control samples using the LPTP/heparinase test.