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Decreased clearance of potentially toxic metabolites, due to aging changes, likely plays a significant role in the accumulation of amyloid-beta (Aβ) peptides and other macromolecules in the brain of the elderly and in the patients with Alzheimer's disease (AD). Aging is the single most important risk factor for AD development. Aβ transport receptor proteins expressed at the blood-brain barrier are significantly altered with age: the efflux transporters lipoprotein receptor-related protein 1 and P-glycoprotein are reduced, whereas the influx transporter receptor for advanced glycation end products is increased. These receptors play an important role in maintaining brain biochemical homeostasis. We now report that, in a rat model of aging, gene transcription is altered in aging, as measured by Aβ receptor gene messenger RNA (mRNA) at 3, 6, 9, 12, 15, 20, 30, and 36 months. Gene mRNA expression from isolated cerebral microvessels was measured by quantitative polymerase chain reaction. Lipoprotein receptor-related protein 1 and P-glycoprotein mRNA were significantly reduced in aging, and receptor for advanced glycation end products was increased, in parallel with the changes seen in receptor protein expression. Transcriptional changes appear to play a role in aging alterations in blood-brain barrier receptor expression and Aβ accumulation.

The goals of this research were to describe age-related changes in brain biochemistry and behavior, and the relationships between them. The chronological ages of greatest change are particularly important for targeting interventions. In this experiment, 36 Fischer 344/Brown-Norway rats (3, 12, 20, and 30 months old) were trained in lever boxes on temporal discrimination tasks. The greatest response rate decrease and response pattern change occurred between 12 and 20 months. The biochemical results showed that amyloid-beta peptides (Aβ40 and Aβ42) increased with age. The endothelial expression of the Aβ influx transporter (RAGE) also increased, and the expression of Aβ efflux transporter (LPR-1) decreased, with age. The greatest change in the biochemical measures also were between 12 and 20 months. Twenty additional rats were analyzed for stem cell proliferation, and neurogenesis decreased with age, particularly between about 12 and 20 months. These early changes in brain, biochemistry, and behavior provide opportunity for new therapies or prophylaxis.

Reduced clearance of amyloid β peptides (Aβ) across the blood-brain barrier contributes to amyloid accumulation in Alzheimer disease. Amyloid β efflux transport is via the endothelial low-density lipoprotein receptor-related protein 1 (LRP-1) and P-glycoprotein (P-gp), whereas Aβ influx transport is via the receptor for advanced glycation end products. Because age is the major risk factor for developing Alzheimer disease, we measured LRP-1 and P-gp expression and associated transporter expression with Aβ accumulation in aging rats. Quantitative LRP-1 and P-gp microvessel expression was measured by immunohistochemistry (IHC); LRP-1 and P-gp expression were assessed in microvessel isolates by Western blotting. There was an age-dependent loss of capillary LRP-1 across all ages (3-36 months) by IHC (linear trend p = 0.0004) and between 3 and 20 months by Western blotting (linear trend p < 0.0001). There was a late (30-36 months) P-gp expression loss by IHC (p < 0.05) and Western blotting (p = 0.0112). Loss of LRP-1 correlated with Aβ42 accumulation (p = 0.0121) and very nearly with Aβ40 (p = 0.0599) across all ages. Expression of LRP-1 correlated negatively with the expression of receptor for advanced glycation end products (p < 0.0004). These data indicate that alterations in LRP-1 and P-gp expression seem to contribute progressively to Aβ accumulation in aging.

Aging is the most important single risk factor for developing Alzheimer disease. We measured amyloid-beta peptide (Abeta) levels in rat cerebral cortex and hippocampus during normal aging of Brown-Norway/Fischer rats. Amyloid-beta accumulation was associated with expression of the Abeta influx transporter, the receptor for advanced glycation end-products (RAGEs) at the blood-brain barrier. Rats at selected ages from 3 to 36 months were analyzed by 1) immunohistochemistry for amyloid deposition and quantitative microvessel surface area RAGE expression, 2) ELISA for cortical Abeta40 and Abeta42 concentrations, and 3) Western blotting of microvessel proteins for RAGE expression. Immunohistochemistry showed increasing accumulation of brain Abeta with aging. By ELISA analysis, both Abeta40 and Abeta42 concentrations in cortical homogenates rose sharply from 9 to 12 months. The Abeta42 continued to rise up to age 30 months, whereas Abeta40 stabilized after 12 months. The expression of RAGE initially decreased between 3 and 12 months but then increased between 12 and 34 months by immunohistochemistry. On immunoblotting, RAGE decreased up to 9 months and then progressively increased up to 36 months. These data indicate an association between amyloid and microvessel RAGE during aging. An increase in capillary RAGE expression seems to play a role in the later Abeta accumulation but not in the initial increase.

Background Cognitive deficits in aging, NPH and Alzheimer's disease (AD) are exacerbated by compromised neurogenesis in the dentate gyrus (DG) and subventricular zone (SVZ). We previously found beta-amyloid (Aβ) retention in cortex and hippocampus of aged rats and diseased humans, due to greater RAGE and lesser LRP-1 expression of microvascular transporters for Aβ. Now we focus on the periventricular DG and SVZ that harbor stem cells convertible to new neurons in adults. Working hypothesis: Aβ retention in neurogenic zones harms neural stem cells, leading to reduced cognition.

Background It has been shown that there is an age-related decrease in CSF production in the Fischer rat brain, and that this decrease follows the CNS deposition of amyloid rather than preceding it [1]. We have postulated that amyloid and Tau accumulation in normal aging is multi-factorial, combining early defects in the blood-brain barrier (BBB) efflux transport of amyloid beta-peptide (A-beta) with later changes in CSF production and turnover, as well as up-regulation of A-beta influx transport.

Background Little is known about the cerebellum in NPH. Studies show that neurotransmitter changes in the cerebellum are opposite to the cortex [1,2]. In Kaolin-induced hydrocephalus, increases of A-beta peptides at cortical and hippocampal microvessels were found [3]. Reciprocal changes in BBB receptors, LRP-1, which transports A-beta out of, and RAGE, which transports A-beta into the brain, indicated a defective clearance might be causal. We looked at LRP-1 and RAGE expression changes in the cerebellum vs. the cortex in hydrocephalic and aged rats.

Background Reduced CSF formation in chronic hydrocephalus (NPH) prompts the question of how the expression of choroid epithelial transporters is altered when flow is disrupted. In the Kaolin model of communicating hydrocephalus, we previously demonstrated that choroid plexus chloride transport (proportional to CSF production) is significantly decreased [1]. To investigate the expression of other choroidal transporters that effect CSF homeostasis, we have now analyzed the time course of LRP-1 expression in the plexus at various stages of hydrocephalus. LRP-1 is a transporter that mediates efflux of A-Beta peptide from the CSF. We postulate that LRP-1 in choroid plexus has a key absorptive role that stabilizes A-Beta in the CNS.

Activation of the surface of small diameter polyurethane vascular grafts using radiofrequency glow discharge (RFGD) and covalent linkage of cell attachment oligopeptides may improve graft patency. The effects of RFGD treatment were investigated on a polyurethane-polydimethylsiloxane (PU-PDMS) copolymer (Cardiothane-51; Kontron Cardiovascular, Inc., Everett, MA) membrane fabricated using the spray, phase-inversion technique. RFGD using H2O vapor was used to functionalize the membrane surface, reacted with 1',1 carbonyldiimidazole and covalently bound with oligopeptides (RGDS, RGES). Membranes not subjected to RFGD, either unmodified or with adsorbed fibronectin (Fn), vitro-nectin (Vn), RGDS, RGDV, and RGES, were used as controls. RFGD treated membrane surfaces were evaluated using electron spectroscopy for chemical analysis, which demonstrated a qualitative increase in nitrogen and silicon compared to unmodified PU-PDMS. Indirect confirmation of surface hydroxylation was provided by metallization with palladium and nickel, demonstrating uniform metallization of RFGD treated PU-PDMS surfaces. Human umbilical vein endothelial cells (HUVEC) were seeded at a density of 10(4) cells/cm2 and cell attachment assessed at 3 hr, 24 hr, and 7 days. Untreated PU-PDMS and membrane with adsorbed oligopeptides demonstrated poor HUVEC attachment at all intervals. Adsorbed Fn and Vn had significantly better early cell attachment and growth (p < 0.01). RFGD improved initial attachment and growth over non-RFGD treated controls (p < 0.01) for RGDS bound membranes, which performed as well as Fn controls (N.S.). PU-PDMS membranes can be modified using RFGD to covalently link oligopeptides. RFGD treatment alone, or with covalent linkage of cell attachment oligopeptides, improves HUVEC attachment and growth in a static environment.