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Amyloid b-peptide (Ab) clearance from the central nervous system (CNS) maintains its low levels in brain. In Alzheimer's disease, Ab 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 Ab and of Ab transport proteins, apolipoprotein E (apoE) and apoJ in mice. We show (i) Ab40 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) Ab42 is removed across the BBB at a rate 1.9-fold slower compared with Ab40; (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 125 I-labeled Ab and apolipoproteins were almost identical, but could not be measured at low physiologic levels by mass spectrometry. Amyloid b-peptide 40 binding to apoE3 reduced its efflux rate at the BBB by 5.7-fold, whereas Ab42 binding to apoJ enhanced Ab42 BBB clearance rate by 83%. Thus, Ab, apoE, and apoJ are cleared from brain by different transport pathways, and apoE and apoJ may critically modify Ab clearance at the BBB.

In Alzheimer disease (AD), amyloid β peptide (Aβ) accumulates in plaques in the brain. Receptor for advanced glycation end products (RAGE) mediates Aβ-induced perturbations in cerebral vessels, neurons, and microglia in AD. Here, we identified a high-affinity RAGE-specific inhibitor (FPS-ZM1) that blocked Aβ binding to the V domain of RAGE and inhibited Aβ40-and Aβ42-induced cellular stress in RAGE-expressing cells in vitro and in the mouse brain in vivo. FPS-ZM1 was nontoxic to mice and readily crossed the blood-brain barrier (BBB). In aged APP sw/0 mice overexpressing human Aβ-precursor protein, a transgenic mouse model of AD with established Aβ pathology, FPS-ZM1 inhibited RAGE-mediated influx of circulating Aβ40 and Aβ42 into the brain. In brain, FPS-ZM1 bound exclusively to RAGE, which inhibited β-secretase activity and Aβ production and suppressed microglia activation and the neuroinflammatory response. Blockade of RAGE actions at the BBB and in the brain reduced Aβ40 and Aβ42 levels in brain markedly and normalized cognitive performance and cerebral blood flow responses in aged APP sw/0 mice. Our data suggest that FPS-ZM1 is a potent multimodal RAGE blocker that effectively controls progression of Aβ-mediated brain disorder and that it may have the potential to be a disease-modifying agent for AD.

Spectroscopic parameters for two novel ruthenium complexes on binding to nucleic acids of varying sequences and conformations have been determined. These complexes, R~( b p y )~d p p z~+ and Ru(phen)zdppz2+ (bpy = 2,2'-bipyridine; phen = 1,lO-phenanthroline; dppz = dipyrido[3,2:a-2',3':~]-phenazine) serve as "molecular light switches" for DNA, displaying no photoluminescence in aqueous solution but luminescing intensely in the presence of DNA. The luminescent enhancement observed upon binding is attributed to the sensitivity of the excited state to quenching by water; in DNA, the metal complex, upon intercalation into the helix, is protected from the aqueous solvent, thereby preserving the luminescence. Correlations between the extent of protection (depending upon the DNA conformation) and the luminescence parameters are observed. Indeed, the strongest luminescent enhancement is observed for intercalation into DNA conformations which afford the greatest amount of overlap with access from the major groove, such as in triple helices. Differences are observed in the luminescent parameters between the two complexes which also correlate with the level of water protection. In the presence of nucleic acids, both complexes exhibit biexponential decays in emission. Quenching studies are consistent with two intercalative binding modes for the dppz ligand from the major groove: one in which the metal-phenazine axis lies along the DNA dyad axis and another where the metal-phenazine axis lies almost perpendicular to the DNA dyad axis. Ru(bpy)zdppz2+ and Ru(phen)2dppzz+ are shown here to be unique reporters of nucleic acid structures and may become valuable in the design of new diagnostics for DNA.Considerable attention has been given to the design of small molecules that bind to DNA with site selectivity so as to develop novel therapeutics and chemical probes for nucleic acid sites and structures, as well as novel diagnostic agents targeted to double-helical DNA (Pyle & Dervan, 1986;Moser & Dervan, 1987;Hecht, 1986;Tullius, 1988). Our laboratory has focused in part on the development of transitionmetal complexes as probes of nucleic acid structure (Chow & Barton, 1992;Mei & Barton, 1986;Kirshenbaum et al., 1988;Barton, 1986). We have found that ruthenium complexes serve as very sensitive luminescent reporters of DNA in aqueous solution and may become particularly useful in developing new diagnostics.Ruthenium complexes are ideally suited for application as sensitive noncovalent probes for polymer structure. The complexes are water-soluble, coordinatively saturated, and inert to substitution. Polypyridyl complexes of ruthenium-(11) furthermore are intensely colored owing to a wellcharacterized, localized metal-to-ligand charge transfer (MLCT) transition (Juris et al., 1988). Importantly, this transition is perturbed on binding to DNA, providing a sensitive spectroscopic handle for interactions with nucleic acids (Pyle et al., 1989). Tris( 1 ,IO-phenanthroline)ruthenium(II), Ru-(phen)j2+, has been established, primar...

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