Effect Of Purified Poloxamer 188  and Various Dextrans On Erythrocyte Sedimentation Rate In Healthy Subjects and Patients With Sickle Cell Disease

Purified poloxamer188 (P188) (Mast Therapeutics) is a non-ionic, linear block copolymer composed of a central chain of hydrophobic polyoxypropylene and two flanking chains of hydrophylic polyoxyethylene (MW 8.5 kDa). This agent has hemorheologic properties which result in improved microvascular blood flow. P188 has been investigated in a number of indications and is currently under study in an international phase 3 clinical trial in sickle cell patients with vaso-occlusive crisis. Dextrans represent branched polysaccharides of 10-70 kDa that have been used as antithrombotic agents and plasma expanders. Sickle cell disease (SCD) represents a complex hemorheologic condition due to RBC aggregation and cell-fibrin/fibrinogen interactions. The erythrocyte sedimentation rate (ESR) is reflective of RBC and plasma interactions. This study was designed to compare the effect of P188 and dextrans on ESR’s in blood obtained from healthy subjects and patients with sickle cell disease who were seen at Loyola University Medical Center clinics.

Whole EDTA blood collected from normal individuals (n=8) and sickle cell patients confirmed by electrophoresis (n=11) were supplemented with P188 or dextran 10K, 18K , 40K and 70K at various concentrations (or saline control). ESR was measured using standard laboratory technique.

The ESR’s for sickle cell patients (26.4 ± 7.1 mm/hr) were significantly higher in comparison to the ESR’s for healthy subjects (14.6 ± 2.1 mm/hr). Supplementation of P188 decreased ESR’s in both populations. Normal blood ESR’s decreased to 9.1 ± 1.3 mm/hr (38%), whereas the sickle cell patient values decreased to 14.1 ± 4.6 mm/hr (47%).  At comparable concentrations, none of the dextrans changed ESR’s in healthy subjects or patients with sickle cell disease.

These results demonstrate that ESR in SCD patients are elevated compared to healthy subjects. P188 supplementation decreased (up to 50%) ESR’s in both the healthy subjects and sickle cell patients. This may be due to the inhibition of rouleaux formation resulting from P188 effects on RBC membranes or cell-protein interactions. None of the dextrans produced a similar decrease, suggesting that the observed lowering of ESR by P188 is unlikely to be due to a non-specific effect related to polymer molecular weight.

P188 is a potential therapeutic agent which may facilitate blood flow and reduce cell-fibrin/fibrinogen interactions in a variety of hemorrheologic disorders. The observed decrease in ESR both in normal and sickle cell blood samples by P188 may primarily be due to increased membrane hydration, fibrinogen dispersion and anti-adhesive effects of this agent.

Emanuele:Mast Therapeutics: Employment. Fareed:Mast Therapeutics: Research Funding.