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.     

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.     

Activated microglia do not mediate the early deposition of Abeta in carriers of the apolipoprotein Eepsilon4 allele

Activated microglia are a prominent component of the senile plaques in end-stage Alzheimer's disease, but whether microglia contribute to the initiation of the lesions remains unknown. In a previous postmortem study of non-demented elderly cases, we found that amyloidogenesis is advanced by at least 10 years in carriers of the apoEepsilon4 allele. To determine whether microglia are involved in the initial stages of beta-amyloid pathogenesis and whether apoE genotype influences microglial activation, we quantified HLA-DR-immunoreactive microglia in the medial temporal lobe of 229 non-demented humans of various APOE genotypes who had died between 50 and 91 years of age. Our results show that the number of HLA-DR-immunoreactive microglia increases with advancing age in both the gray matter and the white matter. In contrast to amyloid plaques and neurofibrillary tangles, there is no significant correlation between apoE genotype and density of microglia, although apoEepsilon4 homozygotes tended to have more microglia than did other apoE groups. In sections double-immunostained for Abeta and activated microglia, activated microglia were associated with dense-cored plaques but not with diffuse plaques, suggesting that microglial activation is a relatively late event in the genesis of beta-amyloid. Activation of microglia thus appears not to be the initial impetus for Abeta-deposition in the elderly.     

R 56865 and flunarizine displace Ca2+ from phosphatidylserine monolayers in a stoichiometric manner

The monovalent cationic drugs, R 56865 and flunarizine added to the subphase, displaced Ca2+ from phosphatidylserine (PS) monolayers at pH 5 with EC50 values of 1.2 X 10(-6) and 1.3 X 10(-6) mol/l. The EC50 of flunarizine for the increase in surface pressure due to incorporation of the drug into the PS film was 1.8 X 10(-6) mol/l. The maximal binding of both drugs to PS monolayers was estimated from experiments in which the drug was added to the spreading solution for the monolayer. The maximal molar binding ratio of R 56865 was identical to twice the maximal Ca2+ binding (2 X 0.13 Ca/PS) to the monolayer. The uptake of [14C]R 56865 into PS monolayers could be measured directly and was well described by a Langmuir isotherm in which the EC50 for 45Ca displacement was taken as the concentration for half-maximal binding, and the molar ratio for twice the Ca2+ binding was taken as maximal molar binding ratio. These results show that two molecules of the univalently charged R 56865 displace one molecule of Ca2+. Maximal binding of the cationic drug flunarizine to PS monolayers showed a similar stoichiometry. 45Ca displacement data may thus be useful for predicting monolayer and perhaps also membrane concentrations of the charged species of cationic drugs.     

Intestinale Aminosäurenabsorption bei erblicher Rachitis

Zusammenfassung Ausgehend von der Ähnlichkeit der Transportsysteme für Aminosäuren in Niere und Darm wurde die Frage untersucht, ob bei Rachitis mit Hyperaminoacidurie auch der Aminosäurentransport im Dünndarm gestört ist. In umgestülpten Darmsäckchen wurde die Absorption von ¹⁴C-markierten Aminosäuren bei 2 Ferkeln mit erblicher Pseudomangelrachitis und 7 klinisch gesunden Tieren gemessen. Die Versuche ergaben, daß bei bestehender aktiver Rachitis mit Hyperaminoacidurie die intestinale Aminosäurenabsorption nicht beeinträchtigt ist. Die Absorption nahm dagegen mit dem Alter der Versuchstiere signifikant ab. Das isolierte Auftreten eines Transportschadens für Aminosäuren in der Niere läßt den Schluß zu, daß dieser Defekt nicht durch direkte Einwirkung hämatogener Faktoren (erhöhter PTH-Spiegel oder Mangel an Vitamin D-Metaboliten) auf die Transportsysteme hervorgerufen wird, sondern die Folge vorgeschalteter spezifischer Effekte auf die Tubulusepithelien darstellt.

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Intestinal amino acid absorption in vitamin D dependent rickets

Since structure and specifity of amino acid transport systems are basically similar in kidney and intestines it was suspected that rickets associated with hyperaminoaciduria was linked with defective intestinal amino acid uptake. Therefore amino acid absorption from everted sacs of small intestines was studied in 2 piglets suffering from vitamin D dependent rickets, and 7 healthy piglets using ¹⁴C labelled amino acids. The experiments revealed an unaffected intestinal absorption in the rachitic animals, whereas the uptake decreased significantly with increasing age of the experimental animals. The results from these studies suggest that regulatory factors in the blood system, e. g. increased level of PTH or lack of specific vitamin D metabolites, do not directly affect amino acid transport systems in kidney and intestines. It is concluded that hyperaminoaciduria has to be mediated through specific and thus far unidentified effects at the tubular cell level.

Im Rahmen des Sonderforschungsbereichs 146 Versuchstierforschung finanziell gefördert.     

Inflammatory myopathy with abundant macrophages and dermatomyositis: two stages of one disorder or two distinct entities?

Inflammatory myopathy with abundant macrophages (IMAM) and dermatomyositis (DM) are considered to represent related disorders, since they share inflammatory infiltrates and skin alterations. In order to get more insight into these disorders, we addressed the cellular composition of the inflammatory infiltrates in muscle biopsies of 11 patients with IMAM and DM. In IMAM, inflammatory infiltrates predominantly consisted of CD68+ MRP14+ macrophages which weakly expressed TNF-α, a few CD3+ T cells with a prominent IL-10 expression, and single CD123+ plasmacytoid dendritic cells. In DM, infiltrates were mainly composed of CD3+ CD4+ T cells which expressed IL-10, numerous CD123+ plasmacytoid dendritic cells, and CD20+ B cells. The low number of CD68+ macrophages was of 25F9+ late inflammatory phenotype. Membrane attack complex was expressed in necrotic muscle fibers in IMAM and on endomysial capillaries in DM, respectively. Thus, in IMAM, the inflammatory reaction markedly differed from DM. These observations may lend support to the hypothesis that IMAM and DM are distinct with respect to their pathogenesis. Whether, alternatively, these differences in the cellular composition of the infiltrates and the cytokine profile rather reflect different stages of disease, will require the analysis of a larger series.