Complement activation in vitro by the red cell substitute, liposome-encapsulated hemoglobin: mechanism of activation and inhibition by soluble complement receptor type 1.
BACKGROUND
Liposome-encapsulated hemoglobin (LEH) has been developed as an emergency blood substitute, yet its effect on human complement has never been explored. Considering that complement activation is a major pathogenic factor in the respiratory distress syndrome that often develops in trauma and shock, LEH-induced complement activation may be a critical safety issue.


METHODS
Various LEH and corresponding empty liposomes were incubated with normal human sera, and various markers of complement activation (serum levels of C4d, Bb, SC5b-9, and CH50; C5a-induced granulocyte aggregation; membrane deposition of C3b) were measured. Incubations were also performed in the presence of (ethylene-bis[oxyethylenenitrilo]tetraacetic acid) (EGTA) and Mg++ (EGTA/Mg++) and soluble complement receptor type 1.


RESULTS
LEH and liposomes activated human complement, as indicated by significant changes in one or more markers. The effect was primarily due to the presence of the phospholipid vehicle; small, unilamellar, highly homodispersed vesicles induced the greatest degree of complement activation. Complement activation was partially inhibited by EGTA/Mg++. The latter finding, together with the parallel increases in serum C4d and Bb, suggests activation of both the classical and alternative pathways. Soluble complement receptor type 1 (0.05-20 micrograms/mL) efficiently inhibited all vesicle-induced complement activation.


CONCLUSIONS
Because of complement activation, the use of LEH for transfusion may require careful evaluation of safety. Soluble complement receptor type 1 may be useful as a prophylactic agent for complement activation-related complications of liposome infusions.
Szebeni
J
J
Department of Membrane Biochemistry, Walter Reed Army Institute of Research, Washington, DC, USA.
Wassef
N M
NM
Hartman
K R
KR
Rudolph
A S
AS
Alving
C R
CR
D001802:Blood Substitutes / Q000494:pharmacology*; D003167:Complement Activation / Q000187:drug effects*; D003181:Complement C4 / Q000494:pharmacology; D003182:Complement C5 / Q000494:pharmacology; D003183:Complement C6 / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004337:Drug Carriers; D004533:Egtazic Acid / Q000494:pharmacology; D006454:Hemoglobins / Q000008:administration & dosage*; D006801:Humans; D008081:Liposomes; D008274:Magnesium / Q000494:pharmacology; D011951:Receptors, Complement / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D012995:Solubility
D001802:Blood Substitutes; D003181:Complement C4; D003182:Complement C5; D003183:Complement C6; D004337:Drug Carriers; D006454:Hemoglobins; D008081:Liposomes; D011951:Receptors, Complement; D011994:Recombinant Proteins; D004533:Egtazic Acid; D008274:Magnesium