Blood, Vol. 95 No. 11 (June 1), 2000:
pp. 3637-3638
CORRESPONDENCE
 |
To the Editor: |
In vivo inhibition of low density lipoprotein receptor-related
protein improves survival of factor VIII in the absence of von
Willebrand factor
We recently reported that administration of recombinant 39 kd
receptor-associated protein (RAP) to von Willebrand factor (vWf) knockout mice induced a significant, sustained rise in endogenous murine factor VIII levels comparable to that induced by the
administration of recombinant vWf.1 RAP is an
antagonist2 of low density lipoprotein receptor-related
protein (LRP), a ubiquitously expressed multifunctional endocytic
receptor.3 In vitro studies show that factor VIII binds to
LRP and that, by specifically blocking LRP, RAP prevents the binding of
factor VIII to LRP.4 Our in vivo data indicated that LRP
facilitates the clearance of endogenous murine FVIII when vWf is
absent. The report also included preliminary data suggesting that
preadministration of RAP slows elimination of infused recombinant human
FVIII (rFVIII) in vWf knockout mice, but the number of animals tested
was too small to allow statistically relevant analysis of the data. We
therefore extended the infusion study to further investigate the effect
of LRP inhibition by RAP on recovery and half-life of infused human
rFVIII in vWf-deficient knockout mice.
vWf knockout mice (with undetectable vWf and FVIII levels of about 20%
due to secondary FVIII deficiency5) were treated with
buffer, human rFVIII (Baxter Hyland Immuno, Thousand Oaks, CA), and RAP
(made as a recombinant fusion protein with glutathione S-transferase),
as described in our original study.1 Briefly, 3 groups were
tested: (1) a control group received 40 mL/kg buffer followed 15 minutes later by a second injection of 20 mL/kg buffer (n = 11); (2)
the rFVIII group received 40 mL/kg buffer followed by 200 U/kg human
rFVIII in a volume of 20 mL/kg (n = 15); (3) the RAP
preadministration group received 40 mg/kg RAP in a volume of 40 mL/kg
followed by 200 U/kg rFVIII in a volume of 20 mL/kg (n = 18). In vivo
recovery was determined at 15 minutes as described,1 and
FVIII levels were measured with an ELISA that is specific for human
FVIII (Immunozym FVIII:Ag, Baxter, Vienna, Austria). Statistical
comparisons were based on repeated measure analysis of variance.
Because of the difficulty in drawing blood at frequent intervals from
vWf knockout mice, sufficient material for analysis was not available
from each animal at each data point and the number of data points was
limited, which allowed only fitting of a 1-compartment model for
calculation of the half-life of rFVIII.6
As expected for detection of a human protein in mice, FVIII levels were
below the limit of detection in all animals before infusion of rFVIII
and in the control group at all time points. Mean recovery
(±SD) was only 5.8% (±3.7%) in the rFVIII group (6 males, 7 females), but 12.6% (±5.9%) in the group with preadministration of
RAP (8 males, 8 females), P = .0023. There was neither an
effect of sex (P > .1) nor an interaction between sex
and group.
FVIII was maintained at higher levels and was detectable in plasma for
a longer period of time with preadministration of RAP (6 hours) than
without preadministration of RAP (3 hours)
(Figure).
View larger version (17K):
[in this window]
[in a new window]
|
Inhibition of LRP by RAP improves survival of infused human
recombinant FVIII in vWf knockout mice.
Animals were treated with 200 U/kg human rFVIII with and without
preadministration of RAP (40 mg/kg). FVIII antigen (FVIII:Ag) was
measured by an ELISA specific for human FVIII. Group means are shown ± SD.
|
|
Blocking LRP by preadministration
of RAP prolonged the half-life of the infused rFVIII from only 42 minutes with rFVIII alone to 67 minutes with preadministration of RAP.
Saenko et al7 reported that RAP slows the clearance of
infused plasma-derived FVIII/vWf in normal mice. Our extended study now
demonstrates that inhibition of LRP by a single bolus administration of
RAP has a significant inhibitory effect on the clearance of infused
FVIII in the absence of vWf, thus further supporting the involvement of
LRP in the clearance mechanisms of FVIII.
Peter L. Turecek
Hans Peter Schwarz
Baxter Hyland Immuno
Vienna, Austria
Bernd R. Binder
University of Vienna
Vienna, Austria
| |
References |
1.
Schwarz HP, Lenting PJ, Binder B, et al.
Involvement of low-density lipoprotein receptor-related protein (LRP) in the clearance of factor VIII in von Willebrand factor-deficient mice.
Blood.
2000;95:1703-1708[Abstract/Free Full Text].
2.
Bu G.
Receptor-associated protein: a specialized chaperone and antagonist for members of the LDL receptor gene family.
Curr Opin Lipidol.
1998;9:149-155[Medline]
[Order article via Infotrieve].
3.
Strickland DK, Ashcom JD, Williams S, Burgess WH, Migliorni M, Argraves WS.
Sequence identity between the 
2-macroglobulin receptor and low density lipoprotein receptor-related protein suggests that this molecule is a multifunctional receptor.
J Biol Chem.
1990;265:17401-17404[Abstract/Free Full Text].
4.
Lenting PJ, Neels JG, van den Berg BMM, et al.
The light chain of factor VIII comprises a binding site for low density lipoprotein receptor-related protein.
J Biol Chem.
1999;274:23734-23799[Abstract/Free Full Text].
5.
Denis C, Methia N, Frenette PS, et al.
A mouse model of severe von Willebrand disease: Defects in hemostasis and thrombosis.
Proc Natl Acad Sci U S A.
1998;95:9524-9529[Abstract/Free Full Text].
6.
Gibaldi M, Perrier D.
Pharmacokinetics. New York, NY: Marcel Dekker; 1982.
7.
Saenko EL, Yakhyaev AV, Mikhailenko I, Strickland DK, Sarafanov AG.
Role of the low density lipoprotein-related protein receptor in mediation of factor VIII catabolism.
J Biol Chem.
1999;274:37685-37692[Abstract/Free Full Text].
