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.

Association of ABCB1 genetic variants 3435C>T and 2677G>T to ABCB1 mRNA and protein expression in brain tissue from refractory epilepsy patients.

PURPOSE: There is evidence from studies in rodents that P-glycoprotein (P-gp) overexpression is implicated in the causation of refractory epilepsy. Genetic variants in the human ABCB1 (MDR1) gene were shown to affect the expression levels of the transporter in various tissues and to be associated with refractory epilepsy. However, the effect of the genetic variants on the P-gp level in epileptogenic brain tissue is poorly investigated. In the present study, we examined the impact of putatively functional polymorphisms 3435C>T and 2677G>T in the ABCB1 gene on the ABCB1 mRNA expression and P-gp content in human brain tissue from epileptogenic foci of the patients with refractory epilepsy. METHODS: Fresh brain tissue specimens were obtained from therapy-refractory epilepsy patients during neurosurgery of the epileptogenic focus. We determined the ABCB1 mRNA expression in 23 samples using 5' exonuclease-based real-time polymerase chain reaction (PCR) as well as the P-gp content in 32 samples determined by immunohistochemistry, genotyping was performed by PCR/restriction fragment length polymorphism (RFLP). RESULTS: There was lack of association of 3435C>T and 2677G>T as well as diplotype configurations on ABCB1 mRNA expression and P-gp content in epileptogenic brain tissues. CONCLUSIONS: We cannot exclude an association of ABCB1 variants on P-gp function, but our results suggest that brain ABCB1 mRNA and protein expression is not substantially influenced by major ABCB1 genetic variants thus explaining in part results from case-control studies obtaining lack of association of ABCB1 polymorphisms to the risk of refractory epilepsy.

Disposition and antimuscarinic effects of the urinary bladder spasmolytics propiverine: influence of dosage forms and circadian-time rhythms.

Propiverine extended release is expected to be better tolerated compared to immediate release tablets because of slower drug release and reduced formation of active metabolites in the colon. CYP3A4 and ABCC2, the major variables in pharmacokinetics of propiverine, are less expressed in the colon. Therefore, disposition and pharmacodynamics of propiverine were measured in a double-blind, double-dummy, crossover study with administration of 15 mg immediate release 3 times daily for 7 days compared to 45 mg extended release once daily for 7 days in 24 healthy subjects. Twelve subjects also received 15 mg propiverine intravenously. Serum and urine propiverine levels were measured repeatedly following oral administration on day 7 for up to 72 hours and correlated to duodenal expression of CYP3A4, ABCB1, and ABCC2. Propiverine immediate release 3 times daily was not different to extended release once daily in areas under the serum concentration-time curve (0-24 hours) and peak-trough fluctuation. The areas under the serum concentration-time curve of propiverine immediate release was circadian-time-dependent, with the lowest values during the night. Disposition of intravenous propiverine and propiverine immediate release administered in the night was influenced by intestinal expression of ABCC2. We concluded that oral absorption of propiverine is site-dependent and influenced by dosage form and circadian-time-dependent elimination processes.

MDR1-P-Glycoprotein (ABCB1) Mediates Transport of Alzheimer's amyloid-beta peptides--implications for the mechanisms of Abeta clearance at the blood-brain barrier.

Amyloid-beta (Abeta) is the major component of the insoluble amyloid plaques that accumulate intracerebrally in patients with Alzheimer's disease (AD). It has been suggested that MDR1-P-glycoprotein (ABCB1, P-gp) plays a substantial role in the elimination of Abeta from the brain. In the present study, MDR1-transfected LLC cells growing in a polarized cell layer were used to characterize the interaction of Abeta1-40/1-42 with P-gp. In this system, P-gp-mediated transport can be followed by the efflux of the fluorescent dye rhodamine-123, or of Abeta itself from the cells into the apical extracellular space. Abeta significantly decreased the apical efflux of rhodamine-123, and the transcellular transport of Abeta1-40 and Abeta1-42 into the apical chamber could be demonstrated using both ELISA and fluorescence (FITC)-labeled peptides. This transport was inhibited by a P-gp modulator. Furthermore, ATP-dependent, P-gp-mediated transport of the fluorescence-labeled peptides could be demonstrated in isolated, inside-out membrane vesicles. Our data support the concept that P-gp is important for the clearance of Abeta from brain, and thus may represent a target protein for the prevention and/or treatment of neurodegenerative disorders such as AD.

Cerebrovascular P-glycoprotein expression is decreased in Creutzfeldt-Jakob disease.

The abnormal conformation and assembly of proteins in the central nervous system is increasingly thought to be a critical pathogenic mechanism in neurodegenerative disorders such as Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease (AD). CJD is marked primarily by the buildup of misfolded prion protein (PrP(Sc)) in brain, whereas the accrual of beta-amyloid protein (Abeta) and tau protein are characteristic for AD. Prior studies have shown that the ATP-binding cassette transporter P-glycoprotein (P-gp) is a cellular efflux pump for Abeta, and that age-associated deficits in P-gp may be involved in the pathogenesis of Alzheimer's disease. In the present study, we investigated the relationship between P-gp and idiopathic CJD, and found that CJD, like AD, is associated with a decrease in the expression of cerebrovascular P-gp. In some instances, Abeta and PrP deposits coexist in cases of CJD, suggesting the possibility of pathogenic interactions. Since there is, to date, no evidence that PrP itself is a substrate for P-gp, we hypothesize that the age-related deficits in P-gp could promote the accumulation of PrP(Sc) either by promoting the buildup of Abeta (which could act as a seed for the aggregation of PrP(Sc)), or by overloading the ubiquitin-proteasomal catabolic system, and thereby facilitating the accumulation of PrP. Alternatively, the loss of P-gp could be a non-specific response to neurodegenerative changes in the central nervous system. In either case, dysfunction of this critical toxin-elimination pathway in CJD and AD suggests that selectively increasing cerebrovascular P-gp function could open new therapeutic pathways for the prevention and/or treatment of a number of proteopathic disorders of the central nervous system.

The ATP-binding cassette transporter ABCG2 (BCRP), a marker for side population stem cells, is expressed in human heart.

Efforts to improve severely impaired myocardial function include transplantation of autologous hematopoietic side population (SP) stem cells. The transmembrane ABC-type (ATP binding cassette) half-transporter ABCG2 (BCRP) serves as a marker protein for SP cell selection. We have recently shown that other ABC transport proteins such as ABCB1 and ABCC5 are differentially expressed in normal and diseased human heart. Here we investigated localization and individual ABCG2 expression in 15 ventricular (including 10 cardiomyopathic) and 51 auricular heart tissue samples using immunohistochemistry, confocal laser scanning fluorescence microscopy, and real-time RT-PCR. Individual genotypes were assigned using PCR-restriction fragment length polymorphism (RFLP) analysis and subsequently correlated to ABCG2 mRNA levels. ABCG2 was localized in endothelial cells of capillaries and arterioles of all samples. Ventricular samples from cardiomyopathic hearts exhibited significantly increased levels of ABCG2 mRNA (ABCG2/18S rRNA: 1.08 +/- 0.30 x 10(-7); p=0.028 (dilative cardiomyopathy) and 1.16 +/- 0.46 x 10(-7); p=0.009 (ischemic cardiomyopathy) compared with 0.44 +/- 0.26 x 10(-7) in nonfailing hearts). The individual haplotypes were not associated with altered mRNA expression. ABCG2 is variably expressed in endothelial cells of human heart, where it may function as a protective barrier against cardiotoxic drugs such as anthracyclines or mitoxantrone. ABCG2 expression is induced in dilative and ischemic cardiomyopathies.

Modulation of multidrug resistance P-glycoprotein 1 (ABCB1) expression in human heart by hereditary polymorphisms.

OBJECTIVES: Variable expression of the ABC-type multidrug resistance membrane protein P-glycoprotein (P-gp, MDR1, ABCB1) in human heart is a potential modulator of drug effects or drug-induced cardiotoxicity. Expression of P-gp is known to be affected by single nucleotide polymorphisms in the MDR1 gene. Therefore, genotype-dependent expression of P-gp could be an important modulator of action of cardiac drugs. METHODS: Heart tissue (auriculum) from 51 patients undergoing coronary artery bypass graft surgery was screened for genotype-dependent P-gp expression. P-gp was identified by immunoblotting and localized using immunohistochemistry. MDR1 mRNA was quantified by real-time PCR and immunohistochemistry and related to the MDR1 genotypes G2677T/A (Ala893Ser/Thr) and C3435T. RESULTS: MDR1/18S rRNA mRNA copy numbers in heart auriculum were 3.48 +/- 2.25 x 10(-6) compared to 4.56 +/- 0.58 x 10(-6) in non-failing ventricular samples studied before. While the exon 26 C3435T genotype did not influence MDR1 mRNA expression, we found significantly elevated MDR1 mRNA expression in 10 patients carrying the exon 21 2677 AT or TT genotype as compared to 12 patients carrying the GG-variant with intermediate MDR1 mRNA expression in 29 heterozygous samples. P-gp was detected in the endothelial wall. Quantitative immunohistochemistry of protein expression, however, did not reveal significant influence of the studied SNPs. CONCLUSION: The present study based on auricular samples suggests that genetic factors play a rather limited role in modulating P-gp expression in human heart. Therefore, the substantial interindividual variability in cardiac P-gp expression is likely related to environmental or disease related factors.

The role of P-glycoprotein in cerebral amyloid angiopathy; implications for the early pathogenesis of Alzheimer's disease.

It has been shown in vitro that beta-amyloid (Abeta) is transported by P-glycoprotein (P-gp). Previously, we demonstrated that Abeta immunoreactivity is significantly elevated in brain tissue of individuals with low expression of P-gp in vascular endothelial cells. These findings led us to hypothesize that P-gp might be involved in the clearance of Abeta in normal aging and particularly in Alzheimer's disease (AD). As we were interested in the early pathogenesis of Abeta deposition, we studied the correlation between cerebral amyloid angiopathy (CAA) and P-gp expression in brain tissue samples from 243 non-demented elderly cases (aged 50 to 91 years). We found that endothelial P-gp and vascular Abeta were never colocalized, i.e., vessels with high P-gp expression showed no Abeta deposition in their walls, and vice versa. Abeta deposition occurred first in arterioles where P-gp expression was primarily low, and disappeared completely with the accumulation of Abeta. At this early stage, P-gp was upregulated in capillaries, suggesting a compensatory mechanism to increase Abeta clearance from the brain. Capillaries were usually affected only at later stages of CAA, at which point P-gp was lost even in these vessels. We hypothesize that Abeta clearance may be altered in individuals with diminished P-gp expression due, e.g., to genetic or environmental effects (such as drug administration). The impairment of Abeta clearance could lead to the accumulation and earlier deposition of Abeta, both in the walls of blood vessels and in the brain parenchyma, thus elevating the risk of CAA and AD.

Deposition of Alzheimer's beta-amyloid is inversely correlated with P-glycoprotein expression in the brains of elderly non-demented humans.

Deposition of the beta-amyloid peptide (Abeta) in the brain occurs during normal ageing and is substantially accelerated in patients with Alzheimer's disease. Since Abeta is continuously produced in the brain, it has been suggested that a clearance mechanism should exist to prevent its accumulation and subsequent aggregation. Until now, little attention has been paid to the possible role of P-glycoprotein (P-gp), a member of the ATP binding cassette superfamily of transporter proteins, in the pathogenesis of Alzheimer's disease. A recent study demonstrated that Abeta40 and Abeta42 interact directly with P-gp. We therefore hypothesized that Abeta accumulation in the brain would correlate inversely with the degree of vascular P-gp expression. To study early pathogenetic factors that influence the deposition of Abeta, at routine autopsies, brain tissue samples were taken from 243 non-demented subjects who died between the ages of 50 and 91 years. Vascular P-gp expression and the number of Abeta40- and Abeta42-positive senile plaques were assessed immunohistochemically in the medial temporal lobe. In addition, the apolipoprotein E (apoE) genotypes, as well as multiple drug resistance gene 1 ( ) polymorphisms (exon 2, G-1A; exon 21, G2677T/A; exon 26, C3436T), were also determined for each case. P-gp expression was not correlated with genotypes, but we found a significant inverse correlation between P-gp expression and the deposition of both Abeta40 and Abeta42 in the medial temporal lobe. Our results provide the first evidence in human brain tissue that the accumulation of Abeta may be influenced by the expression of P-gp in blood vessels, and suggest that P-gp may influence the elimination of Abeta from brain.

August 2001: Sellar/suprasellar mass in a 59-year-old woman.

The August 2001 COM. Symptomatic granular cell tumors (GCTs) of the neurohypophysis are rare lesions. They are generally regarded as benign neoplasms, although detailed descriptions of the natural course of the tumors are limited to a few cases. We report on a 59-year-old woman with a large GCT of the neurohypophysis and rapid onset of symptoms. Although lacking definitive signs of malignancy, the tumor showed nuclear polymorphism, proliferative activity, evidence of a mutation of the tumor suppressor gene p53 as well as expression of the apoptosis-inhibiting protein bcl-2. These indices may be useful in defining more precisely the clinicopathological prognosis for neurohypophyseal GCTs.