Polyethylene Glycol Camouflaged Earthworm Hemoglobin.

Vivek P Jani,Alborz Jelvani,David Dantsker,Andre Palmer,Selamawit Moges,Parimala Nacharaju,Joel M Friedman,Pedro Cabrales,Camille Roche

doi:10.1371/journal.pone.0170041

Abstract

Nearly 21 million components of blood and whole blood and transfused annually in the United States, while on average only 13.6 million units of blood are donated. As the demand for Red Blood Cells (RBCs) continues to increase due to the aging population, this deficit will be more significant. Despite decades of research to develop hemoglobin (Hb) based oxygen (O2) carriers (HBOCs) as RBC substitutes, there are no products approved for clinical use. Lumbricus terrestris erythrocruorin (LtEc) is the large acellular O2 carrying protein complex found in the earthworm Lumbricus terrestris. LtEc is an extremely stable protein complex, resistant to autoxidation, and capable of transporting O2 to tissue when transfused into mammals. These characteristics render LtEc a promising candidate for the development of the next generation HBOCs. LtEc has a short half-life in circulation, limiting its application as a bridge over days, until blood became available. Conjugation with polyethylene glycol (PEG-LtEc) can extend LtEc circulation time. This study explores PEG-LtEc pharmacokinetics and pharmacodynamics. To study PEG-LtEc pharmacokinetics, hamsters instrumented with the dorsal window chamber were subjected to a 40% exchange transfusion with 10 g/dL PEG-LtEc or LtEc and followed for 48 hours. To study the vascular response of PEG-LtEc, hamsters instrumented with the dorsal window chamber received multiple infusions of 10 g/dL PEG-LtEc or LtEc solution to increase plasma LtEc concentration to 0.5, then 1.0, and 1.5 g/dL, while monitoring the animals’ systemic and microcirculatory parameters. Results confirm that PEGylation of LtEc increases its circulation time, extending the half-life to 70 hours, 4 times longer than that of unPEGylated LtEc. However, PEGylation increased the rate of LtEc oxidation in vivo. Vascular analysis verified that PEG-LtEc showed the absence of microvascular vasoconstriction or systemic hypertension. The molecular size of PEG-LtEc did not change the colloid osmotic pressure or blood volume expansion capacity compared to LtEc, due to LtEc’s already large molecular size. Taken together, these results further encourage the development of PEG-LtEc as an O2 carrying therapeutic.

Highlights

Both in the United States (US) and globally, the need for red blood cell (RBC) transfusions has steadily increased over the years.[1]
During deoxygenation the O2 tension and %O2 saturation are recorded to obtain an Oxygen equilibrium Curve (OEC), and P50 value
PEGylation of Lumbricus Terrestris erythrocruorin (LtEc) had no statistically significant effect on O2 affinity, (P50, O2 tension at which Hb is 50% saturated with O2)

Summary

Introduction

Both in the United States (US) and globally, the need for red blood cell (RBC) transfusions has steadily increased over the years.[1] Studies indicate that the demand for RBCs in the US relative to the amount collected will create a shortage of 3 million units of RBCs by the year 2030. [7] At least 80% of casualties, who could potentially survive, die from an inadequate supply of RBCs and exsanguinating hemorrhage.[8] The growing demand for RBCs along with the aforementioned issues associated with RBC transfusion justify the need for alternatives to RBCs, that have greater availability, accessibility, shelf life, oxygen (O2) transport capacity, and safety

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Discussion

Conclusion