Development and evaluation of a fluorescence microplate assay for quantification of heparins and other sulfated carbohydrates

Due to their complex composition, quantification of heparins is difficult. On the one hand there are many biological tests, which only indirectly detect effects of the antithrombin-binding material. On the other hand direct quantitative methods are available but they are often insensitive, challenging, time-consuming or expensive. The aim of this study was to develop a sensitive, rapid, simple as well as inexpensive direct quantification assay suitable for routine analysis. Based on Polymer-H, a novel heparin complexing, fluorescent labeled synthetic polymer (λ(ex) 320 nm, λ(em) 510 nm), a microplate assay was developed and optimized. The specificity of the assay was evaluated by structure–assay response relationships studies using structurally defined glucan sulfates, heparins, and other natural and synthetic sulfated carbohydrates. The fluorescence intensity of Polymer-H (7.5 μg/ml) showed to be concentration-dependently amplified by heparins as well as by other sulfated carbohydrates. The best sensitivity, accuracy and linearity were observed in a range from 0.63 to 5.0 μg/ml heparins. No differences in the fluorescence between various heparins were observed, so that only one calibration curve is needed. In addition, all types of carbohydrates with a degree of sulfation (DS) > ∼1.2 and a Mr > 3000 can be quantified as well. By own calibration curves also other sulfated carbohydrates like fondaparinux or other glycosaminoglycans (DS > 0.4) can be determined