Alzheimer Disease: Zlokovic BV

Deane R, Bell RD, Sagare A, Zlokovic BV. · Center for Neurodegenerative and Vascular Brain Disorders, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA. · CNS Neurol Disord Drug Targets. · Pubmed #19275634 No free full text.

Abstract: The main receptors for amyloid-beta peptide (Abeta) transport across the blood-brain barrier (BBB) from brain to blood and blood to brain are low-density lipoprotein receptor related protein-1 (LRP1) and receptor for advanced glycation end products (RAGE), respectively. In normal human plasma a soluble form of LRP1 (sLRP1) is a major endogenous brain Abeta 'sinker' that sequesters some 70 to 90 % of plasma Abeta peptides. In Alzheimer's disease (AD), the levels of sLRP1 and its capacity to bind Abeta are reduced which increases free Abeta fraction in plasma. This in turn may increase brain Abeta burden through decreased Abeta efflux and/or increased Abeta influx across the BBB. In Abeta immunotherapy, anti-Abeta antibody sequestration of plasma Abeta enhances the peripheral Abeta 'sink action'. However, in contrast to endogenous sLRP1 which does not penetrate the BBB, some anti-Abeta antibodies may slowly enter the brain which reduces the effectiveness of their sink action and may contribute to neuroinflammation and intracerebral hemorrhage. Anti-Abeta antibody/Abeta immune complexes are rapidly cleared from brain to blood via FcRn (neonatal Fc receptor) across the BBB. In a mouse model of AD, restoring plasma sLRP1 with recombinant LRP-IV cluster reduces brain Abeta burden and improves functional changes in cerebral blood flow (CBF) and behavioral responses, without causing neuroinflammation and/or hemorrhage. The C-terminal sequence of Abeta is required for its direct interaction with sLRP and LRP-IV cluster which is completely blocked by the receptor-associated protein (RAP) that does not directly bind Abeta. Therapies to increase LRP1 expression or reduce RAGE activity at the BBB and/or restore the peripheral Abeta 'sink' action, hold potential to reduce brain Abeta and inflammation, and improve CBF and functional recovery in AD models, and by extension in AD patients.

Deane R, Sagare A, Zlokovic BV. · Center for Neurodegenerative and Vascular Brain Disorders, University of Rochester, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642, USA. · Curr Pharm Des. · Pubmed #18673201 No free full text.

Abstract: Low-density lipoprotein receptor related protein-1 (LRP) is a member of the low-density lipoprotein (LDL) receptor family which has been linked to Alzheimer's disease (AD) by biochemical and genetic evidence. Levels of neurotoxic amyloid beta-peptide (Abeta) in the brain are elevated in AD contributing to the disease process and neuropathology. Faulty Abeta clearance from the brain appears to mediate focal Abeta accumulations in AD. Central and peripheral production of Abeta from Abeta-precursor protein (APP), transport of peripheral Abeta into the brain across the blood-brain barrier (BBB) via receptor for advanced glycation end products (RAGE), enzymatic Abeta degradation, Abeta oligomerization and aggregation, neuroinflammatory changes and microglia activation, and Abeta elimination from brain across the BBB by cell surface LRP; all may control brain Abeta levels. Recently, we have shown that a soluble form of LRP (sLRP) binds 70 to 90 % of plasma Abeta, preventing its access to the brain. In AD individuals, the levels of LRP at the BBB are reduced, as are levels of Abeta binding to sLRP in plasma. This, in turn, may increase Abeta brain levels through a decreased efflux of brain Abeta at the BBB and/or reduced sequestration of plasma Abeta associated with re-entry of free Abeta into the brain via RAGE. Thus, therapies which increase LRP expression at the BBB and/or enhance the peripheral Abeta "sink" activity of sLRP, hold potential to control brain Abeta accumulations, neuroinflammation and cerebral blood flow reductions in AD.

Zlokovic BV. · Center for Neurodegenerative and Vascular Brain Disorders, Departments of Neurosurgery, University of Rochester Medical School, Rochester, New York 14642, USA. · Neurotherapeutics. · Pubmed #18625452 links to  free full text

Abstract: Recent findings indicate that neurovascular dysfunction is an integral part of Alzheimer's disease (AD). Changes in the vascular system of the brain may significantly contribute to the onset and progression of dementia and to the development of a chronic neurodegenerative process. In contrast to the neurocentric view, which proposes that changes in chronic neurodegenerative disorders, including AD, can be attributed solely to neuronal disorder and neuronal dysfunction, the neurovascular concept proposes that dysfunction of non-neuronal neighboring cells and disintegration of neurovascular unit function may contribute to the pathogenesis of dementias in the elderly population, and understanding these processes will be crucial for the development of new therapeutic approaches to normalize both vascular and neuronal dysfunction. In this review, I discuss briefly the role of vascular factors and vascular disorder in AD, the link between cerebrovascular disorder and AD, the clearance hypothesis for AD, the role of RAGE (receptor for advanced glycation end products) and LRP (low density lipoprotein receptor related protein 1) in maintaining the levels of amyloid beta-peptide (Abeta) in the brain by controlling its transport across the blood-brain barrier (BBB), and the role of impaired vascular remodeling and cerebral blood flow dysregulation in the disease process. The therapeutic strategies based on new targets in the AD neurovascular pathway, such as RAGE and LRP receptors, and on a few selected genes implicated in AD neurovascular dysfunction (e.g., mesenchyme homeobox gene 2 and myocardin) are also discussed.

Deane R, Zlokovic BV. · Frank P. Smith Laboratory for Neuroscience and Neurosurgical Research, University of Rochester Medical Center, Rochester, NY 14642, USA. · Curr Alzheimer Res. · Pubmed #17430246 No free full text.

Abstract: Cerebrovascular dysfunction contributes to the cognitive decline and dementia in Alzheimer's disease (AD), and may precede cerebral amyloid angiopathy and brain accumulation of the Alzheimer's neurotoxin, amyloid beta-peptide (Abeta). The blood-brain barrier (BBB) is critical for brain Abeta homeostasis and regulates Abeta transport via two main receptors, the low density lipoprotein receptor related protein 1 (LRP1) and the receptor for advanced glycation end products (RAGE). According to the neurovascular hypothesis of AD, faulty BBB clearance of Abeta through deregulated LRP1/RAGE-mediated transport, aberrant angiogenesis and arterial dysfunction may initiate neurovascular uncoupling, Abeta accumulation, cerebrovascular regression, brain hypoperfusion and neurovascular inflammation. Ultimately these events lead to BBB compromise and chemical imbalance in the neuronal 'milieu', and result in synaptic and neuronal dysfunction. Based on the neurovascular hypothesis, we suggest an array of new potential therapeutic approaches that could be developed for AD to reduce neuroinflammation, enhance Abeta clearance and neurovascular repair, and improve cerebral blood flow. RAGE-based and LRP1-based therapeutic strategies have potential to control brain Abeta in AD, and possibly related familial cerebrovascular beta-amyloidoses. In addition, we have identified two vascularly restricted genes, GAX (growth arrest-specific homeobox), which controls LRP1 expression in brain capillaries and brain angiogenesis, and MYOCD (myocardin), which controls contractility of cerebral arterial smooth muscle cells and influences cerebral blood flow. These findings provide insights into new pathogenic pathways for the vascular dysfunction in AD and point to new therapeutic targets for AD.

Zlokovic BV. · Frank P. Smith Laboratories for Neuroscience and Neurological Surgery Research, Department of Neurological Surgery and Division of Neurovascular Biology, University of Rochester Medical Center, Rochester, NY 14642, USA. · Trends Neurosci. · Pubmed #15808355 No free full text.

Abstract: In contrast to traditional neuroncentric views of Alzheimer's disease (AD), recent findings indicate that neurovascular dysfunction contributes to cognitive decline and neurodegeneration in AD. Here, I propose the neurovascular hypothesis of AD, suggesting that faulty clearance of amyloid beta peptide (A beta) across the blood-brain barrier (BBB), aberrant angiogenesis and senescence of the cerebrovascular system could initiate neurovascular uncoupling, vessel regression, brain hypoperfusion and neurovascular inflammation. Ultimately, this would lead to BBB compromise, to chemical imbalance in the neuronal environment and to synaptic and neuronal dysfunction, injury and loss. Based on the neurovascular hypothesis, I suggest an array of new potential therapeutic approaches that could be developed for AD, to enhance A beta clearance and neurovascular repair, and to protect the neurovascular unit from divergent inducers of injury and apoptosis.

Zlokovic BV, Deane R, Sallstrom J, Chow N, Miano JM. · Frank R Smith Laboratories for Neuroscience and Neurosurgical Research, University of Rochester Medical Center, Rochester, NY 14642, USA. · Brain Pathol. · Pubmed #15779240 No free full text.

Abstract: According to the prevailing amyloid cascade hypothesis, the onset and progression of a chronic neurodegenerative condition in Alzheimer disease (AD) is initiated by the amyloid beta-peptide (Abeta) accumulation in brain and consequent neuronal toxicity. Recent emphasis on co-morbidity of AD and cerebrovascular disease and the recognition that cerebrovascular dysregulation is an important feature of AD, has shed new light on neurovascular dysfunction as a possible contributor to cognitive decline and Alzheimer neurodegeneration. In the same time, this association has raised a question as to whether there is a causal relationship between cerebrovascular dysregulation and Abeta-initiated pathology, and whether influencing targets in the neurovasculature may prevent different forms of Abeta brain accumulation and/or lower pre-existing accumulates in a later stage of the disease. Pathogenic cascades which operate to dissociate normal transport exchanges between central and peripheral pools of Abeta, and decreased vascular competence leading to brain hypoperfusion and impaired Abeta clearance are discussed. We suggest that there is a link between neurovascular dysfunction and elevated brain Abeta which provides a new scenario for therapeutic interventions to control Alzheimer mental deterioration.

Zlokovic BV. · Frank P. Smith Laboratories for Neuroscience, Department of Neurological Surgery, University of Rochester Medical Center, New York 14642, USA. · J Neurochem. · Pubmed #15140180 No free full text.

Abstract: According to the amyloid hypothesis, accumulation of amyloid beta-peptide (A beta) in the brain is the primary pathogenic event in Alzheimer's disease (AD). Recent evidence indicates that A beta within the intravascular space is linked to A beta deposited in the brain suggesting that transport of A beta between the brain, blood and cerebrospinal fluid, and across the blood-brain barrier, regulates brain A beta. Thus, understanding A beta exchanges between brain and blood, and vice versa, and developing transport-based systemic A beta-lowering strategies may provide new important insights into pathogenesis and therapeutic control of AD.

Zlokovic BV. · Frank P Smith Laboratories for Neurosurgery and Division of Neurovascular Biology, Center for Aging and Developmental Biology, University of Rochester Medical Center, Rochester, NY 14642, USA. · Adv Drug Deliv Rev. · Pubmed #12453672 No free full text.

Abstract: It is not clear whether Alzheimer's Disease (AD) is primarily a neurodegenerative disorder or not. A body of evidence suggests that vascular disorder in brains of individuals with AD contributes to the extremes of this disease. This raises a question whether Alzheimer's dementia is secondary to vascular dysfunction in the central nervous system (CNS) and, therefore, the neurodegeneration that follows is a consequence of inadequate cerebral blood flow, altered brain metabolism and failure in physiological functions of brain endothelium which represents a site at the blood-brain barrier (BBB). In this paper the evidence for a primary role of the CNS vascular system in pathogenesis of Alzheimer's dementia is reviewed to show how alterations in transport across the BBB contribute to development of cerebral beta-amyloidosis in AD. In addition, vascularly-based therapeutic strategies to limit the development of beta-amyloidosis and to remove amyloid and plaques from the CNS of AD individuals are discussed.

Zlokovic BV. · Department of Neurological Surgery, Division of Neurovascular Biology, University of Rochester Medical Center, NY 14642, USA. · Adv Drug Deliv Rev. · Pubmed #12453670 No free full text.

This publication has no abstract.

Bell RD, Deane R, Chow N, Long X, Sagare A, Singh I, Streb JW, Guo H, Rubio A, Van Nostrand W, Miano JM, Zlokovic BV. · Center for Neurodegenerative and Vascular Brain Disorders, Arthur Kornberg Medical Research Building, University of Rochester School of Medicine & Dentistry, 601 Elmwood Avenue, Rochester, New York 14642, USA. · Nat Cell Biol. · Pubmed #19098903 links to  free full text

Abstract: Amyloid beta-peptide (Abeta) deposition in cerebral vessels contributes to cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD). Here, we report that in AD patients and two mouse models of AD, overexpression of serum response factor (SRF) and myocardin (MYOCD) in cerebral vascular smooth muscle cells (VSMCs) generates an Abeta non-clearing VSMC phenotype through transactivation of sterol regulatory element binding protein-2, which downregulates low density lipoprotein receptor-related protein-1, a key Abeta clearance receptor. Hypoxia stimulated SRF/MYOCD expression in human cerebral VSMCs and in animal models of AD. We suggest that SRF and MYOCD function as a transcriptional switch, controlling Abeta cerebrovascular clearance and progression of AD.

Deane R, Sagare A, Hamm K, Parisi M, Lane S, Finn MB, Holtzman DM, Zlokovic BV. · Center for Neurodegenerative and Vascular Brain Disorders, Department of Neurosurgery, University of Rochester Medical School, Rochester, New York 14642, USA. · J Clin Invest. · Pubmed #19033669 links to  free full text

Abstract: Neurotoxic amyloid beta peptide (Abeta) accumulates in the brains of individuals with Alzheimer disease (AD). The APOE4 allele is a major risk factor for sporadic AD and has been associated with increased brain parenchymal and vascular amyloid burden. How apoE isoforms influence Abeta accumulation in the brain has, however, remained unclear. Here, we have shown that apoE disrupts Abeta clearance across the mouse blood-brain barrier (BBB) in an isoform-specific manner (specifically, apoE4 had a greater disruptive effect than either apoE3 or apoE2). Abeta binding to apoE4 redirected the rapid clearance of free Abeta40/42 from the LDL receptor-related protein 1 (LRP1) to the VLDL receptor (VLDLR), which internalized apoE4 and Abeta-apoE4 complexes at the BBB more slowly than LRP1. In contrast, apoE2 and apoE3 as well as Abeta-apoE2 and Abeta-apoE3 complexes were cleared at the BBB via both VLDLR and LRP1 at a substantially faster rate than Abeta-apoE4 complexes. Astrocyte-secreted lipo-apoE2, lipo-apoE3, and lipo-apoE4 as well as their complexes with Abeta were cleared at the BBB by mechanisms similar to those of their respective lipid-poor isoforms but at 2- to 3-fold slower rates. Thus, apoE isoforms differentially regulate Abeta clearance from the brain, and this might contribute to the effects of APOE genotype on the disease process in both individuals with AD and animal models of AD.

Sagare A, Deane R, Bell RD, Johnson B, Hamm K, Pendu R, Marky A, Lenting PJ, Wu Z, Zarcone T, Goate A, Mayo K, Perlmutter D, Coma M, Zhong Z, Zlokovic BV. · Frank P. Smith Laboratory for Neuroscience and Neurosurgical Research, Department of Neurosurgery, University of Rochester Medical School, Rochester, New York 14642, USA. · Nat Med. · Pubmed #17694066 No free full text.

Abstract: Low-density lipoprotein receptor-related protein-1 (LRP) on brain capillaries clears amyloid beta-peptide (Abeta) from brain. Here, we show that soluble circulating LRP (sLRP) provides key endogenous peripheral 'sink' activity for Abeta in humans. Recombinant LRP cluster IV (LRP-IV) bound Abeta in plasma in mice and Alzheimer's disease-affected humans with compromised sLRP-mediated Abeta binding, and reduced Abeta-related pathology and dysfunction in a mouse model of Alzheimer disease, suggesting that LRP-IV can effectively replace native sLRP and clear Abeta.

Chow N, Bell RD, Deane R, Streb JW, Chen J, Brooks A, Van Nostrand W, Miano JM, Zlokovic BV. · Socratech Research Laboratories L.L.C., Department of Neurosurgery, University of Rochester School of Medicine, 601 Elmwood Avenue, Rochester, NY 14642, USA. · Proc Natl Acad Sci U S A. · Pubmed #17215356 links to  free full text

Abstract: Cerebral angiopathy contributes to cognitive decline and dementia in Alzheimer's disease (AD) through cerebral blood flow (CBF) reductions and dysregulation. We report vascular smooth muscle cells (VSMC) in small pial and intracerebral arteries, which are critical for CBF regulation, express in AD high levels of serum response factor (SRF) and myocardin (MYOCD), two interacting transcription factors that orchestrate a VSMC-differentiated phenotype. Consistent with this finding, AD VSMC overexpressed several SRF-MYOCD-regulated contractile proteins and exhibited a hypercontractile phenotype. MYOCD overexpression in control human cerebral VSMC induced an AD-like hypercontractile phenotype and diminished both endothelial-dependent and -independent relaxation in the mouse aorta ex vivo. In contrast, silencing SRF normalized contractile protein content and reversed a hypercontractile phenotype in AD VSMC. MYOCD in vivo gene transfer to mouse pial arteries increased contractile protein content and diminished CBF responses produced by brain activation in wild-type mice and in two AD models, the Dutch/Iowa/Swedish triple mutant human amyloid beta-peptide (Abeta)-precursor protein (APP)- expressing mice and APPsw(+/-) mice. Silencing Srf had the opposite effect. Expression of SRF did not change in VSMC subjected to Alzheimer's neurotoxin, Abeta. Thus, SRF-MYOCD overexpression in small cerebral arteries appears to initiate independently of Abeta a pathogenic pathway mediating arterial hypercontractility and CBF dysregulation, which are associated with Alzheimer's dementia.

Bell RD, Sagare AP, Friedman AE, Bedi GS, Holtzman DM, Deane R, Zlokovic BV. · Frank P Smith Laboratory for Neuroscience and Neurosurgical Research, Department of Neurosurgery, University of Rochester Medical Center, Rochester, New York 14642, USA. · J Cereb Blood Flow Metab. · Pubmed #17077814 No free full text.

Abstract: Amyloid beta-peptide (Abeta) clearance from the central nervous system (CNS) maintains its low levels in brain. In Alzheimer's disease, Abeta accumulates in brain possibly because of its faulty CNS clearance and a deficient efflux across the blood-brain barrier (BBB). By using human-specific enzyme-linked immunosorbent assays, we measured a rapid 30 mins efflux at the BBB and transport via the interstitial fluid (ISF) bulk flow of human-unlabeled Abeta and of Abeta transport proteins, apolipoprotein E (apoE) and apoJ in mice. We show (i) Abeta40 is cleared rapidly across the BBB via low-density lipoprotein receptor-related protein (LRP)1 at a rate of 0.21 pmol/min g ISF or 6-fold faster than via the ISF flow; (ii) Abeta42 is removed across the BBB at a rate 1.9-fold slower compared with Abeta40; (iii) apoE, lipid-poor isoform 3, is cleared slowly via the ISF flow and across the BBB (0.03-0.04 pmol/min g ISF), and after lipidation its transport at the BBB becomes barely detectable within 30 mins; (iv) apoJ is eliminated rapidly across the BBB (0.16 pmol/min g ISF) via LRP2. Clearance rates of unlabeled and corresponding 125I-labeled Abeta and apolipoproteins were almost identical, but could not be measured at low physiologic levels by mass spectrometry. Amyloid beta-peptide 40 binding to apoE3 reduced its efflux rate at the BBB by 5.7-fold, whereas Abeta42 binding to apoJ enhanced Abeta42 BBB clearance rate by 83%. Thus, Abeta, apoE, and apoJ are cleared from brain by different transport pathways, and apoE and apoJ may critically modify Abeta clearance at the BBB.

Deane R, Sagare A, Hamm K, Parisi M, LaRue B, Guo H, Wu Z, Holtzman DM, Zlokovic BV. · Division of Neurovascular Biology, Department of Neurosurgery, Arthur Kornberg Medical Research Building, University of Rochester Medical Center, Rochester, New York 14642, USA. · J Neurosci. · Pubmed #16354907 links to  free full text

Abstract: The role of blood-brain barrier (BBB) transport in clearance of amyloid beta-peptide (Abeta) by Abeta immunotherapy is not fully understood. To address this issue, we studied the effects of peripherally and centrally administered Abeta-specific IgG on BBB influx of circulating Abeta and efflux of brain-derived Abeta in APPsw(+/-) mice, a model that develops Alzheimer's disease-like amyloid pathology, and wild-type mice. Our data show that anti-Abeta IgG blocks the BBB influx of circulating Abeta in APPsw(+/-) mice and penetrates into the brain to sequester brain Abeta. In young mice, Abeta-anti-Abeta complexes were cleared from brain to blood by transcytosis across the BBB via the neonatal Fc receptor (FcRn) and the low-density lipoprotein receptor-related protein (LRP), whereas in older mice, there was an age-dependent increase in FcRn-mediated IgG-assisted Abeta BBB efflux and a decrease in LRP-mediated clearance of Abeta-anti-Abeta complexes. Inhibition of the FcRn pathway in older APPsw(+/-) mice blocked clearance of endogenous Abeta40/42 by centrally administered Abeta immunotherapy. Moreover, deletion of the FcRn gene in wild-type mice inhibited clearance of endogenous mouse Abeta40/42 by systemically administered anti-Abeta. Our data suggest that the FcRn pathway at the BBB plays a crucial role in IgG-assisted Abeta removal from the aging brain.

Cirrito JR, Deane R, Fagan AM, Spinner ML, Parsadanian M, Finn MB, Jiang H, Prior JL, Sagare A, Bales KR, Paul SM, Zlokovic BV, Piwnica-Worms D, Holtzman DM. · Department of Neurology, Washington University Medical School, St. Louis, Missouri 63110, USA. · J Clin Invest. · Pubmed #16239972 links to  free full text

Abstract: Accumulation of amyloid-beta (Abeta) within extracellular spaces of the brain is a hallmark of Alzheimer disease (AD). In sporadic, late-onset AD, there is little evidence for increased Abeta production, suggesting that decreased elimination from the brain may contribute to elevated levels of Abeta and plaque formation. Efflux transport of Abeta across the blood-brain barrier (BBB) contributes to Abeta removal from the brain. P-glycoprotein (Pgp) is highly expressed on the luminal surface of brain capillary endothelial cells and contributes to the BBB. In Pgp-null mice, we show that [I]Abeta40 and [I]Abeta42 microinjected into the CNS clear at half the rate that they do in WT mice. When amyloid precursor protein-transgenic (APP-transgenic) mice were administered a Pgp inhibitor, Abeta levels within the brain interstitial fluid significantly increased within hours of treatment. Furthermore, APP-transgenic, Pgp-null mice had increased levels of brain Abeta and enhanced Abeta deposition compared with APP-transgenic, Pgp WT mice. These data establish a direct link between Pgp and Abeta metabolism in vivo and suggest that Pgp activity at the BBB could affect risk for developing AD as well as provide a novel diagnostic and therapeutic target.

Wu Z, Guo H, Chow N, Sallstrom J, Bell RD, Deane R, Brooks AI, Kanagala S, Rubio A, Sagare A, Liu D, Li F, Armstrong D, Gasiewicz T, Zidovetzki R, Song X, Hofman F, Zlokovic BV. · Frank P. Smith Laboratories for Neuroscience and Neurosurgical Research, University of Rochester Medical Center, Arthur Kornberg Medical Research Building, 601 Elmwood Avenue, Box 670, Rochester, New York 14642, USA. · Nat Med. · Pubmed #16116430 No free full text.

Abstract: Neurovascular dysfunction substantially contributes to Alzheimer disease. Here, we show that transcriptional profiling of human brain endothelial cells (BECs) defines a subset of genes whose expression is age-independent but is considerably altered in Alzheimer disease, including the homeobox gene MEOX2 (also known as GAX), a regulator of vascular differentiation, whose expression is low in Alzheimer disease. By using viral-mediated MEOX2 gene silencing and transfer, we show that restoring expression of the protein it encodes, GAX, in BECs from individuals with Alzheimer disease stimulates angiogenesis, transcriptionally suppresses AFX1 forkhead transcription factor-mediated apoptosis and increases the levels of a major amyloid-beta peptide (Abeta) clearance receptor, the low-density lipoprotein receptor-related protein 1 (LRP), at the blood-brain barrier. In mice, deletion of Meox2 (also known as Gax) results in reductions in brain capillary density and resting cerebral blood flow, loss of the angiogenic response to hypoxia in the brain and an impaired Abeta efflux from brain caused by reduced LRP levels. The link of MEOX2 to neurovascular dysfunction in Alzheimer disease provides new mechanistic and therapeutic insights into this illness.

Deane R, Wu Z, Zlokovic BV. · Frank P. Smith Laboratories for Neuroscience and Neurosurgical Research, Department of Neurological Surgery and Division of Neurovascular Biology, University of Rochester Medical Center, Rochester, NY, USA. · Stroke. · Pubmed #15459432 links to  free full text

Abstract: Accumulation of amyloid beta-peptide (Abeta) in the central nervous system (CNS) may initiate pathogenic cascades mediating neurovascular and neuronal dysfunctions associated with the development of cerebral beta-amyloidosis and cognitive decline in patients with Alzheimer disease (AD) and with related familial cerebrovascular disorders. Whether Abeta-related pathology in the CNS is reversible or not and what key therapeutic targets are controlling Abeta/amyloid levels in the aging brain remain debatable. In this article, we summarize recent evidence why the receptor for advanced glycation end products and low-density lipoprotein receptor related protein 1 in the vascular CNS barriers are critical for regulation of Abeta homeostasis in the CNS and how altered activities in these 2 receptors at the blood-brain barrier may contribute to the CNS Abeta accumulation resulting in neuroinflammation, disconnect between the cerebral blood flow and metabolism, altered synaptic transmission, neuronal injury, and amyloid deposition into parenchymal and neurovascular lesions. We briefly discuss the potential of advanced glycation end products and low-density lipoprotein receptor related protein 1-based therapeutic strategies to control brain Abeta in animal models of AD and ultimately in patients with AD and related familial cerebrovascular beta-amyloidoses.

LaRue B, Hogg E, Sagare A, Jovanovic S, Maness L, Maurer C, Deane R, Zlokovic BV. · Department of Neurosurgery, Frank P. Smith Neurosurgical Research Laboratory, Center of Aging & Developmental Biology, University of Rochester Medical Center, 601 Elmwood Avenue, Box 670, Rochester, NY 14642, USA. · J Neurosci Methods. · Pubmed #15325132 No free full text.

Abstract: The role of transport exchanges of neuroactive solutes across the blood-brain barrier (BBB) is increasingly recognized. To take full advantage of genetically altered mouse models of neurodegenerative disorders for BBB transport studies, we adapted a brain perfusion technique to the mouse. During a carotid brain perfusion with a medium containing sheep red blood cells and mock plasma, the physiological parameters in the arterial inflow, regional cerebral blood flow (14C-iodoantipyrine autoradiography), ultrastructural integrity of the tissue, barrier to lanthanum, brain water content, energy metabolites and lactate levels remain unchanged. Amyloid-beta peptides (Abeta) were iodinated by lactoperoxidase method. Non-oxidized mono-iodinated Abeta monomers were separated by HPLC (as confirmed by MALDI-TOF spectrometry) and used in transport measurements. Transport of intact 125I-Abeta40 across the BBB was time- and concentration-dependent in contrast to negligible 14C-inulin uptake. In 5-6 months old Alzheimer's Tg2576 mice, Abeta40 BBB transport was increased by >eight-fold compared to age-matched littermate controls, and was mediated via the receptor for advanced glycation endproducts. We conclude the present arterial brain perfusion method provides strictly controlled environment in cerebral microcirculation suitable for examining transport of rapidly and slowly penetrating molecules across the BBB in normal and transgenic mice.

Mackic JB, Bading J, Ghiso J, Walker L, Wisniewski T, Frangione B, Zlokovic BV. · Department of Neurological Surgery, USC School of Medicine, Los Angeles, CA 90033, USA. · Vascul Pharmacol. · Pubmed #12529925 No free full text.

Abstract: 1. We studied cerebrovascular sequestration and blood-brain barrier (BBB) permeability to [125I]- or [123I]-labeled amyloid-beta peptides (A beta) in aged rhesus and aged squirrel monkey, the nonhuman primate models of cerebral beta-amyloidosis and cerebrovascular amyloid angiopathy (CAA), respectively. 2. In aged rhesus, the half-time of elimination of [125I]A beta 1-40, t1/2e, was faster by 1.34 h, the systemic clearance, Clss, increased by 4.21 ml/min/kg and the mean residence time of intact peptide in the circulation shortened by 2 h. 3. Cerebrovascular sequestration of [125I]A beta 1-40 was significant in aged squirrel monkey (20.8 ml/g x 10(2)), but undetectable in the rhesus. 4. The permeability surface area product, PS, for [14C]inulin was low in both species (0.11-0.18 ml/g/s x 10(6)) indicating an intact barrier. 5. The BBB permeability to A beta 1-40 was 34.8- and 13.7-fold higher than for [14C]inulin in aged squirrel and rhesus, respectively, suggesting a specialized A beta transport across the BBB. 6. The single photon computed emission tomography studies confirmed a saturable [123I]A beta 1-40 transport at the BBB in primates (Km = 40 nM). 7. Brain autoradiographic analysis of [125I]A beta 1-42 or [125I]A beta 1-40 after intracarotid infusions of radiotracers confirmed co-localization of the signal with A beta-immunoreactive plaques in rhesus monkeys. 8. Metabolism of [125I]A beta 1-40 in brain and plasma was slower in aged squirrel compared to aged rhesus, by 2.9- and 2.6-fold, respectively. 9. Thus, transport of circulating A beta across the BBB contributes to brain parenchymal accumulation of amyloid in aged nonhuman primates. Negligible capillary binding, rapid systemic and brain degradation, and accelerated body elimination of blood-borne A beta, may prevent the development of CAA in rhesus in contrast to squirrel monkeys.

Giri R, Selvaraj S, Miller CA, Hofman F, Yan SD, Stern D, Zlokovic BV, Kalra VK. · Department of Biochemistry and Molecular Biology, Keck School of Medicine, University of Southern California, Los Angeles 90033, USA. · Am J Physiol Cell Physiol. · Pubmed #12176746 links to  free full text

Abstract: During normal aging and amyloid beta-peptide (Abeta) disorders such as Alzheimer's disease (AD), one finds increased deposition of Abeta and activated monocytes/microglial cells in the brain. Our previous studies show that Abeta interaction with a monolayer of normal human brain microvascular endothelial cells results in increased adherence and transmigration of monocytes. Relatively little is known of the role of Abeta accumulated in the AD brain in mediating trafficking of peripheral blood monocytes (PBM) across the blood-brain barrier (BBB) and concomitant accumulation of monocytes/microglia in the AD brain. In this study, we showed that interaction of Abeta(1--40) with apical surface of monolayer of brain endothelial cells (BEC), derived either from normal or AD individuals, resulted in increased transendothelial migration of monocytic cells (HL-60 and THP-1) and PBM. However, transmigration of monocytes across the BEC monolayer cultivated in a Transwell chamber was increased 2.5-fold when Abeta was added to the basolateral side of AD compared with normal individual BEC. The Abeta-induced transmigration of monocytes was inhibited in both normal and AD-BEC by antibodies to the putative Abeta receptor, receptor for advanced glycation end products (RAGE), and to the endothelial cell junction molecule, platelet-endothelial cell adhesion molecule-1 (PECAM-1). We conclude that interaction of Abeta with the basolateral surface of AD-BEC induces cellular signaling, promoting transmigration of monocytes from the apical to basolateral direction. We suggest that Abeta in the AD brain parenchyma or cerebrovasculature initiates cellular signaling that induces PBM to transmigrate across the BBB and accumulate in the brain.

Bading JR, Yamada S, Mackic JB, Kirkman L, Miller C, Calero M, Ghiso J, Frangione B, Zlokovic BV. · Department of Radiology, USC School of Medicine, Los Angeles, CA 90033, USA. · J Drug Target. · Pubmed #12164385 No free full text.

Abstract: Squirrel monkey is a valuable model to study pathogenesis of cerebrovascular amyloid angiopathy (CAA). Previous studies suggested that circulating amyloid-beta40 peptide (Abeta40) crosses the blood-brain barrier (BBB) and may therefore enhance cerebrovascular amyloidosis in aged squirrel monkeys. In the present study, we used single photon emission computed tomography (SPECT) to determine elimination of 123I-Abeta40 and 99mTc-DTPA, an extracellular marker, from the brain in squirrel monkeys at different age. Following intracerebral microinfusions, the time-activity brain clearance curves indicated bi-exponential removal of 123I-Abeta40 with an initial rapid washout (1.1 < or = t 1/2 < or = 2.7 h). This, plus the observed appearance of 123I-radioactivity in plasma suggest significant brain-to-blood transport. In contrast, 99mTc-DTPA was removed slowly by brain interstitial fluid bulk flow (monoexponential decay with 6.8 < or = t 1/2 < or = 16.8 h). A comparison of three middle aged (11-16 years old) vs. two old (22 yrs old) monkeys was consistent with an age-related decline in the BBB capacity to remove 123I-Abeta from the brain. This correlated with an age-dependent increase in A1beta40/42 cerebrovascular immunoreactivity and amyloid deposition. Thus, vascular clearance plays an important role in reducing Abeta levels in the squirrel monkey brain and impaired Abeta40 elimination across the BBB may contribute to the development of CAA.

Monro OR, Mackic JB, Yamada S, Segal MB, Ghiso J, Maurer C, Calero M, Frangione B, Zlokovic BV. · Department of Neurosurgery, University of Southern California, Los Angeles, CA, USA. · Neurobiol Aging. · Pubmed #11959403 No free full text.

Abstract: A point mutation of G to C at codon 693 of the amyloid-beta (Abeta) precursor protein gene results in Glu to Gln substitution at position 22 of the Abeta (AbetaQ22) associated with hereditary cerebrovascular amyloidosis with hemorrhage Dutch type. Factors that regulate AbetaQ22 levels in the central nervous system (CNS) are largely unknown. By using ventriculo-cisternal perfusion technique in guinea pigs, we demonstrated that clearance from the cerebrospinal fluid and transport from the CNS to blood of [(125)I]-AbetaQ22 (1 nM) were reduced by 36% and 52%, respectively, in comparison to the wild type Abeta(1-40) peptide. In contrast to significant uptake and transport of Abeta(1-40) across the brain capillaries and leptomeningeal vessels, AbetaQ22 was not taken up at these CNS vascular transport sites, which was associated with its 53% greater accumulation in the brain. The CNS clearance of Abeta(1-40) was half-saturated at 23.6 nM; AbetaQ22 had about 6.8-fold less affinity for the CNS efflux transporters and its elimination relied mainly on transport across the choroid plexus. Thus, the Dutch mutation impairs elimination of Abeta from brain by reducing its rapid transport across the blood-brain barrier and the vascular drainage pathways, which in turn may result in accumulation of the peptide around the blood vessels and in brain.

Shibata M, Yamada S, Kumar SR, Calero M, Bading J, Frangione B, Holtzman DM, Miller CA, Strickland DK, Ghiso J, Zlokovic BV. · Department of Neurological Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. · J Clin Invest. · Pubmed #11120756 links to  free full text

Abstract: Elimination of amyloid-ss peptide (Ass) from the brain is poorly understood. After intracerebral microinjections in young mice, (125)I-Ass(1-40) was rapidly removed from the brain (t(1/2) </= 25 minutes), mainly by vascular transport across the blood-brain barrier (BBB). The efflux transport system for Ass(1-40) at the BBB was half saturated at 15.3 nM, and the maximal transport capacity was reached between 70 nM and 100 nM. Ass(1-40) clearance was substantially inhibited by the receptor-associated protein, and by antibodies against LDL receptor-related protein-1 (LRP-1) and alpha(2)-macroglobulin (alpha(2)M). As compared to adult wild-type mice, clearance was significantly reduced in young and old apolipoprotein E (apoE) knockout mice, and in old wild-type mice. There was no evidence that Ass was metabolized in brain interstitial fluid and degraded to smaller peptide fragments and amino acids before its transport across the BBB into the circulation. LRP-1, although abundant in brain microvessels in young mice, was downregulated in older animals, and this downregulation correlated with regional Ass accumulation in brains of Alzheimer's disease (AD) patients. We conclude that the BBB removes Ass from the brain largely via age-dependent, LRP-1-mediated transport that is influenced by alpha(2)M and/or apoE, and may be impaired in AD.