Heparinase reactor

The RTD (residence time distribution) of the heparinase reactor was studied using a large-molecule (MW 2,000,000) blue dextran, which is... 

Fig. t2. Concentration profile of blue dextran in effluent of heparinase reactor during washout experiment. Inlet flow rate 120 mL/min. Concentration is normalized by initial concentration of dye in the reactor, and time is normalized by mean residence time in the reactor as determined by best fit to data. Line is theoretical prediction for washout of dye from CSTR [from Bernstein et al. (50)]. 

The heparinase reactor was modeled as an ideal CSTR for which a steady-state mass balance for heparin is given by... 

Figure 1. Proposed heparin circuit. The extracorporeal device could be a renal dialysis unit or a pump-oxygenator. The heparinase reactor could be part of a blood filter to be used either continuously (in which case heparin would, be added, continuously at the start of the circuit) or at the end of an operation. Heparin could thus be confined to the extracorporeal circuit.

The development of the heparin removal system is still at an early stage. Work currently is being directed toward (1) completing the purification of heparinase, (2) immobilizing heparinase to additional supports, and (3) testing the blood compatibility and effectiveness of heparinase reactors in vitro and in vivo. 

In developing a reactor such as the one just described, it is important to understand important design parameters, such as the radial distribution of the enzyme within the catalyst particles, the kinetics of heparin degradation catalyzed by immobilized heparinase, the flow properties in the reactor, and the effect of in vivo factors such as blood proteins which bind to the substrate. These parameters and how they can be evaluated are now discussed. 

The degradation of heparin by the reactor is a multistep process. Heparin and the heparin-antithrombin complex must first diffuse from the bulk phase to the surface of the immobilized enzyme particle. The two species diffuse into the agarose particles where they encounter immobilized heparinase. The heparin-anti thrombin complex is assumed to be sterically inhibited from binding to immobilized heparinase, and under these conditions only unbound heparin is enzymatically degraded. As unbound heparin is consumed, heparin dissociates from the heparin-antithrombin complex to generate more free heparin. The breakdown of heparin is given by the following chemical reaction ... 

Several other reactors for immobilized heparinase have been designed (53,54). The initial reactor (47) caused no more blood damage than conventionally used extracorporeal devices such as the artificial kidney machine (54a). By controlling the mode of immobilized enzyme bead suspension, all blood damage can be essentially eliminated (54). The FDA... 

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