Removal of sialic acid from electroporated platelets: effect on platelet survival and potential use as vehicles for targeting drugs to the liver

Basiouny A. El-Gamal
Department of Clinical Biochemistry, College of Medicine, King Khalid University, Abha, Saudi Arabia

Abstract:

Objectives: There has been increasing interests in the use of carrier vehicles for drug delivery in vivo, including the natural transporter, blood platelets (1). Recently (2), a reversible electroporation technique has been developed for introducing drugs and other agents within the cytosolic space of human and animal platelets by exposing cells in suspension containing the drug to be encapsulated to a sequence of high voltage discharges. This will make holes in platelets membrane through which drugs will diffuse. After resealing, platelets show normal function and life-span characteristics when reinfused in vivo. Decreased surface charge and sialic acid content in older platelets are responsible for their removal from circulation after 9-11 days which are taken out by reticulo-endothelial system (RES), particularly the liver. The present study explores the possibility of using platelets for targeting drugs to the liver. It describes the in vitro removal of sialic acid from the surface of rat platelets and investigates the effect of such removal on platelet survival and percentage distribution in different organs (liver, lung and spleen) after labelling with 111indium  oxine and reinfusion into rats.

Methods: Washed platelets were electroporated (7 cycles, 7 KV/cm), resealed (at 37 C for 40 min) , treated with neuraminidase (0.05 u/ml, 60 min), labelled with 111indium oxine "ex vivo", resuspended in platelet-free plasma and reinfused into rats. The total amount of radioactivity in blood and each organ 2 hours after reinfusion was calculated and expressed as percentage of the injected radioactivity.

Results: Treatment of platelets with neuraminidase resulted in  a maximum removal of platelet surface sialic acid after 60 min. Neuraminidase-treated platelets, which have been reversibly electroporated, labelled with 111indium oxine and reinfused into rats, were rapidly removed from the circulation (after 2 hr) and the majority of radioactivity was found in the liver (76%), followed by lungs (4%) and spleen (1.6%). It has been suggested that electroporated/resealed platelets lacking sialic acid on their surface as a result of neuraminidase treatment are recognised as "foreign" and are rapidly taken out of the circulation by the RES, primarily in the liver.

Conclusions: These data suggest that electroporated/resealed platelets lacking sialic on their membrane may be used as vehicles for the direct delivery of drugs and other agents to the liver in various situations. Possible clinical applications may be to deliver macrophage-activating drugs to the liver to kill the cancer cells and cytotoxic drugs to secondary tumors in the liver.

References:

[1] Crawford, N., Chajara, A., Pfliegler, G., El-Gamal, B., Brewer, L. and  Capron, L. (1995) Targeting platelets containing electro-encapsulated iloprost to balloon-injured rat aorta. Thrombosis Haemostasis  73 (3): 535-542.

[2] El-Gamal, B.A.B., Pfliegler, G and Crawford, N. (1992) Effect of platelet  encapsulated iloprost on platelet aggregation and adhesion to collagen and  injured blood vessels in vitro. Thrombosis & Haemostasis 68 (5): 606-614.