Alzheimer's disease (AD) brains are characterized by accumulation of amyloid-ß protein (Aβ) and neuroinflammation. Increased blood-to-brain influx and decreased brain-to-blood efflux across the blood-brain barrier (BBB) have been proposed as mechanisms for Aß accumulation. Epidemiological studies suggest that the nonsteroidal anti-inflammatory drug (NSAID) indomethacin slows the progression of AD. We hypothesized that inflammation alters BBB handling of Aß. Mice treated with lipopolysaccharide (LPS) had increased brain influx and decreased brain efflux of Aβ, recapitulating the findings in AD. Neither influx nor efflux was mediated by LPS acting directly on BBB cells. Increased influx was mediated by a blood-borne factor, indomethacin-independent, blocked by the triglyceride triolein, and not related to expression of the blood-to-brain transporter of Aß, RAGE. Serum levels of IL-6, IL-10, IL-13, and MCP-1 mirrored changes in Aß influx. Decreased efflux was blocked by indomethacin and accompanied by decreased protein expression of the brainto-blood transporter of Aß, LRP-1. LPS paradoxically increased expression of neuronal LRP-1, a major source of Aß. Thus, inflammation potentially increases brain levels of Aß by three mechanisms: increased influx, decreased efflux, and increased neuronal production.

Hypertensive encephalopathy occurs when acute changes in blood pressure cause breakdown of the blood-brain barrier (BBB). Angiotensin II (Ang II) plays a role in this pathophysiology. We determined whether Ang II directly regulates endothelial cell function at the BBB. In BBB microvessel endothelial cells (MECs), the Ang II (100 nmol/L; 0 to 6 h) effects on permeability to 125 I-albumin and transendothelial electrical resistance (TEER) were assessed. Angiotensin II (100 nmol/L) caused significant time-dependent changes in both 125 I-albumin permeability (25%) at 2 h and TEER (À8.87 X . cm 2 ) at 6 h. Next, MECs were pretreated with the Ang II type 1 (AT 1 ) receptor blocker telmisartan (1 lmol/L) or the Ang II type 2 (AT 2 ) receptor blocker PD123,319 (1 lmol/L) followed by treatment with Ang II (100 nm). Telmisartan completely inhibited the Ang II-induced increase in 125 I-albumin permeability in MECs whereas PD123,319 had no effect. Using western blot analysis, we showed that MECs express AT 1 receptors but not AT 2 receptors. Treatment with Ang II (100 nmol/L; 0 to 6 h) also increased total protein kinase C activity. In contrast, Ang II had no effect on the expression of occludin, claudin 5, or actin. These results show that Ang II directly modulates transcytotic and paracellular permeability in BBB endothelial cells and could contribute to the pathophysiology of hypertensive encephalopathy.