Vector-mediated delivery of 125I-labeled beta-amyloid peptide A beta 1-40 through the blood-brain barrier and binding to Alzheimer disease amyloid of the A beta 1-40/vector complex.

Abstract

The brain amyloid of Alzheimer disease (AD) may potentially be imaged in patients with AD by using neuroimaging technology and a radiolabeled form of the 40-residue 18-amyloid peptide A81-40 that is enabled to undergo transport through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo.Transport of 125I-labeled A31-40 (125I-A31B-40) Alzheimer disease (AD) is a severe neurodegenerative disorder, and presently there is no premortem diagnostic test for this disease (1). The dementia of AD correlates with the deposition in brain of amyloid (2), which is principally composed of the 42-to 43-amino acid (3-amyloid peptide, A1(3'42/43 (3,4). One possible diagnostic approach to AD is the development of a premortem brain scan that would allow for semiquantitation of the AP3 amyloid burden in human brain. Previous studies have shown that 125I-labeled A(31-40 (125I-A3'-40) binds to preexisting amyloid plaques in frozen sections of AD brain (5). The delivery to brain of radiolabeled A,f1-40 in conjunction with the use of standard neuroimaging modalities such as single photon emission computed tomography (SPECT) may allow for quantitation of AB3 amyloid in AD brain. Therefore, the present studies examine whether 125I-A3l-40 undergoes significant transport through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, by using both intravenous/pharmacokinetic and internal carotid artery perfusion techniques. These studies then measure the extent to which BBB transport of 125I-AI3-40 is enhanced with the use of a vector-mediated drug delivery system (6). The latter is composed of a conjugate of streptavidin (SA) and the OX26 monoclonal antibody (mAb) to the transferrin receptor (7), which undergoes receptor-mediated transcytosis through the BBB (6); 125I-A31-40 is monobiotinylated (bio), and 125I,bio-Af140 is then conjugated to the SA-OX26 vector. Since conjugation of 125I-Af3'-40 to the vector-mediated delivery system may inhibit binding of A1'-40 to amyloid plaques, the present studies also examine the saturable binding of 125I-A31-40 to amyloid in AD brain after conjugation to the delivery system. Conjugate Synthesis. The OX26 was conjugated to SA by a thioether linkage as described previously (7,8 Abbreviations: Af31-40, 13-amyloid peptide residues 1-40; BBB, bloodbrain barrier; AD, Alzheimer disease; SA, streptavidin; mAb, monoclonal antibody; 0X26, murine mAb to the rat transferrin receptor; NHS, N-hydroxysuccinimide; SPECT, single photon emission computed tomography; bio, biotinylated; VD, brain volume of distribution; PS, permeability-surface area; AUC, area under the plasma concentration curve; TCA, trichloroacetic acid; TFA, trifluoroacetic acid; %ID, percent of the injected dose. MATERIALS AND METHODS

Clearance of Alzheimer’s amyloid-β1-40 peptide from brain by LDL receptor–related protein-1 at the blood-brain barrier

“…Our findings further suggest that if the levels of Aβ in brain extracellular space exceed the transport capacity of the clearance mechanism across the BBB, or if the vascular transport of the peptide were impaired, for example by downregulation of LRP-1, this would result in accumulation of Aβ in the brain, and possibly formation of amyloid plaques. Previous studies from our laboratory and others have demonstrated a major role of the BBB in determining the concentrations of Aβ in the CNS by regulating transport of circulating Aβ (33,39,(49)(50)(51)(62)(63)(64)(65)(66). This study extends this hypothesis by showing that vascular transport out of the brain across the BBB may represent a major physiological mechanism that prevents accumulation of Aβ and amyloid deposition in the brain.…”

“…In addition, the apoJ system that transports blood-borne Aβ into the brain is saturated under the physiological conditions (64) that may facilitate the efflux of Aβ from the brain. Previous studies have shown that circulating free Aβ is also metabolized during its transport across the BBB (48,49,65,66), possibly by pericytes, which represent a major enzymatic barrier for the transport of several peptides and proteins across the BBB (67).…”

Cerebrovascular Accumulation and Increased Blood‐Brain Barrier Permeability to Circulating Alzheimer's Amyloid β Peptide in Aged Squirrel Monkey with Cerebral Amyloid Angiopathy

“…Plasma aliquots were counted for total and TCA (12.5%)-precipitable radioactivities to determine the fraction of 251.. sA/3 1_40 that was not degraded (Saito et al, 1995). Brain was removed from the skull, leptomeningeal vessels were carefully isolated, and brain cortical tissue was subjected to microvascular depletionby dextran density gradient centrifugation (Triguero et al, 1990) to determine the fraction of radiolabeled peptide tightly bound to the BBB (Zlokovic, 1995).…”

“…of terminal plasma), respectively. The BBB permeability surface area (PS) product was determined as follows (Saito et al, 1995;Z!okovic, 1995): …”

Blood–brain barrier delivery of protein and non-viral gene therapeutics with molecular Trojan horses

“…The Aβ 1-40 peptide rapidly binds pre-existing amyloid plaque [23], and Aβ 1-40 could be used as a peptide radiopharmaceutical for imaging brain amyloid with standard external detection modalities such as positron emission tomography (PET) or single photon computed emission tomography (SPCET). However, Aβ does not cross the BBB [24]. Conjugation of Aβ to the TfRMAb allowed for BBB transport of the peptide radiopharmaceutical, and for imaging brain amyloid in a transgenic mouse model of Alzheimer's disease (AD) [25].…”