Lack of P-glycoprotein Results in Impairment of Removal of Beta-Amyloid and Increased Intraparenchymal Cerebral Amyloid Angiopathy after Active Immunization in a Transgenic Mouse Model of Alzheimer's Disease.

BACKGROUND: Immunization against beta-amyloid (Aß) reduces cerebral Aß deposits and improves cognitive capacities in transgenic mouse models, and thus has been considered a promising disease- modifying therapeutic approach for Alzheimer's disease (AD). Although clinical trials in AD patients have yielded evidence for clearance of parenchymal Aß plaques, Aß increases in blood vessels of treated patients. We hypothesize that an age-related decline in the mechanisms that clear Aß from the brain might be at least in part responsible for the failure to purge and re-distribute Aß. The expulsion of Aß via the blood-brain barrier is mediated by specialized transport proteins such as P-glycoprotein (P-gp, ABCB1/MDR1). OBJECTIVE: The objective of this study is to investigate the influence of the absence of P-gp at the bloodbrain barrier on the effectiveness of Aß peptide immunization in APP/PS1+/- P-gp ko mice. METHODS: Male APP/PS1+/- P-gp wt (n = 8) and APP/PS1+/- P-gp ko (n = 8) mice were actively immunized with human Aß42. After behavioral testing animals were sacrificed at the age of 395 days (+/- 5 days) and antibody titres against Aß were measured. Brains were dissected and soluble/insoluble cerebral Aß was quantified, additionally the number of amyloid plaques and severity of amyloid angiopathy were evaluated. RESULTS: In immunized mice with intact P-gp, our results showed a significant reduction of soluble and insoluble Aß40 and Aß42. Furthermore, immunization significantly reduced Aß plaque burden. In contrast, immunized APP/PS1+/- P-gp ko mice lacking functional P-gp did not show a reduction of Aß40 or Aß42 accumulation in the brain except for the soluble form of Aß42. Furthermore, after active immunization these mice displayed a stronger intracerebral amyloid angiopathy. CONCLUSION: The results show that the absence of P-gp results in a significant disturbance of Aß removal from the brain and increased intraparenchymal cerebral amyloid angiopathy after immunization against Aß. Our data indicate that the selective up-regulation of P-gp could enhance the efficacy of Aß immunization in the treatment or prevention of AD.

St. John's Wort reduces beta-amyloid accumulation in a double transgenic Alzheimer's disease mouse model-role of P-glycoprotein.

The adenosine triphosphate-binding cassette transport protein P-glycoprotein (ABCB1) is involved in the export of beta-amyloid from the brain into the blood, and there is evidence that age-associated deficits in cerebral P-glycoprotein content may be involved in Alzheimer's disease pathogenesis. P-glycoprotein function and expression can be pharmacologically induced by a variety of compounds including extracts of Hypericum perforatum (St. John's Wort). To clarify the effect of St. John's Wort on the accumulation of beta-amyloid and P-glycoprotein expression in the brain, St. John's Wort extract (final hyperforin concentration 5%) was fed to 30-day-old male C57BL/6J-APP/PS1(+/-) mice over a period of 60 or 120 days, respectively. Age-matched male C57BL/6J-APP/PS1(+/-) mice receiving a St. John's Wort-free diet served as controls. Mice receiving St. John's Wort extract showed (i) significant reductions of parenchymal beta-amyloid 1-40 and 1-42 accumulation; and (ii) moderate, but statistically significant increases in cerebrovascular P-glycoprotein expression. Thus, the induction of cerebrovascular P-glycoprotein may be a novel therapeutic strategy to protect the brain from beta-amyloid accumulation, and thereby impede the progression of Alzheimer's disease.

Association of ATP-binding cassette transporter variants with the risk of Alzheimer's disease.

AIM: A number of studies have demonstrated that ABCB1 and BCRP (ABCG2) actively transport Aß. We aimed to investigate the association of genetic variants of selected multidrug transporters with Alzheimer's disease (AD) in histopathologically confirmed AD cases and controls. MATERIALS & METHODS: DNA from brain tissue of 71 AD cases with Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropathological stages B/C and 81 controls was genotyped for selected variants in ABCA1, ABCA7, ABCB1, ABCC2 and ABCG2. In addition, the APOE4 status was analyzed. RESULTS: The novel ABCA7 SNP, rs3752246, tended to be associated with AD in our study. Variants in ABCB1 were significantly less frequent in AD cases older than 65 years of age and among females. This association of ABCB1 2677G>T (rs2032582) was more pronounced in APOE4-negative cases (p = 0.005). However, only ABCC2 3972C>T (rs3740066) was significantly associated with AD risk after logistic regression analysis including all variants. Other transporters showed a lack of association. CONCLUSION: Our results support the hypothesis that ABCB1 and possibly other ABC-transporters are involved in the process of Aß accumulation in the aging brain and may modulate the risk for AD in an allele-specific manner, and thus might represent a new target for prevention and treatment of AD.

The role of the ATP-binding cassette transporter P-glycoprotein in the transport of ß-amyloid across the blood-brain barrier.

The blood-brain barrier (BBB) protects the brain against endogenous and exogenous compounds and plays an important part in the maintenance of the microenvironment of the brain. In particular, the importance of brain-to-blood transport of brain-derived metabolites across the BBB has gained increasing attention as a potential mechanism in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease, which is characterized by the aberrant polymerization and accumulation of specific misfolded proteins, particularly ß-amyloid (Aß). There is growing evidence that the ABC transport protein P-glycoprotein (P-gp), a major component of the BBB, mediates the efflux of Aß from the brain. In this review, we discuss the possible role of P-gp in Alzheimer's disease and other neurodegenerative disorders, and consider how a fuller understanding of this function might promote the development of more effective treatment strategies.

Beta-Amyloid Downregulates MDR1-P-Glycoprotein (Abcb1) Expression at the Blood-Brain Barrier in Mice.

Neurovascular dysfunction is an important component of Alzheimer's disease, leading to reduced clearance across the blood-brain barrier and accumulation of neurotoxic ß-amyloid (Aß) peptides in the brain. It has been shown that the ABC transport protein P-glycoprotein (P-gp, ABCB1) is involved in the export of Aß from the brain into the blood. To determine whether Aß influences the expression of key Aß transporters, we studied the effects of 1-day subcutaneous Aß1-40 and Aß1-42 administration via Alzet mini-osmotic pumps on P-gp, BCRP, LRP1, and RAGE expression in the brain of 90-day-old male FVB mice. Our results demonstrate significantly reduced P-gp, LRP1, and RAGE mRNA expression in mice treated with Aß1-42 compared to controls, while BCRP expression was not affected. The expression of the four proteins was unchanged in mice treated with Aß1-40 or reverse-sequence peptides. These findings indicate that, in addition to the age-related decrease of P-gp expression, Aß1-42 itself downregulates the expression of P-gp and other Aß-transporters, which could exacerbate the intracerebral accumulation of Aß and thereby accelerate neurodegeneration in Alzheimer's disease and cerebral ß-amyloid angiopathy.

A comprehensive proteome map of bovine cerebrospinal fluid.

Cerebrospinal fluid (CSF) is considered as the most promising body fluid target for the discovery of biomarkers for early diagnosis of neurodegenerative diseases such as Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cattle. For the recognition of disease-associated changes in bovine CSF protein patterns, a detailed knowledge of this proteome is a prerequisite. The absence of a high-resolution CSF proteome map prompted us to determine all bovine CSF protein spots that can be visualised on 2-D protein gels. Using state-of-the-art 2-DE technology for proteome mapping of bovine ante mortem CSF combined with sensitive fluorescent protein staining and MALDI-TOF/TOF MS for protein identification, a highly detailed 2-DE map of the bovine CSF proteome was established. Besides the proteins mapped by earlier studies, this map contains 66 different proteins, including 58 which were not annotated in bovine 2-DE CSF maps before.