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D Schenk

Publications and source records attributed to D Schenk.

At least 19 recordsLinked to original sources
PubMed2005

Abeta vaccination effects on plaque pathology in the absence of encephalitis in Alzheimer disease.

The authors report a patient with Alzheimer disease (AD) without encephalitis who was immunized with AN-1792 (an adjuvanted formulation of Abeta-42). There were no amyloid plaques in the frontal cortex and abundant Abeta-immunoreactive macrophages, but tangles and amyloid angiopathy were present. The white matter appeared normal and minimal lymphocytic infiltration in the leptomeninges was observed. This case illustrates the effects of an Abeta-based immunization on AD pathogenesis in the absence of overt meningoencephalitis and leukoencephalopathy.

Aged↗
PubMed2005

Inter- and intralaboratory variation of in vitro diffusion cell measurements: an international multicenter study using quasi-standardized methods and materials.

In vitro measurements of skin absorption are an increasingly important aspect of regulatory studies, product support claims, and formulation screening. However, such measurements are significantly affected by skin variability. The purpose of this study was to determine inter- and intralaboratory variation in diffusion cell measurements caused by factors other than skin. This was attained through the use of an artificial (silicone rubber) rate-limiting membrane and the provision of materials including a standard penetrant, methyl paraben (MP), and a minimally prescriptive protocol to each of the 18 participating laboratories. "Standardized" calculations of MP flux were determined from the data submitted by each laboratory by applying a predefined mathematical model. This was deemed necessary to eliminate any interlaboratory variation caused by different methods of flux calculations. Average fluxes of MP calculated and reported by each laboratory (60 +/- 27 microg cm(-2) h(-1), n = 25, range 27-101) were in agreement with the standardized calculations of MP flux (60 +/- 21 microg cm(-2) h(-1), range 19-120). The coefficient of variation between laboratories was approximately 35% and was manifest as a fourfold difference between the lowest and highest average flux values and a sixfold difference between the lowest and highest individual flux values. Intralaboratory variation was lower, averaging 10% for five individuals using the same equipment within a single laboratory. Further studies should be performed to clarify the exact components responsible for nonskin-related variability in diffusion cell measurements. It is clear that further developments of in vitro methodologies for measuring skin absorption are required.

Clinical Laboratory Techniques↗
PubMed2001

Encapsulation in biodegradable microparticles enhances serum antibody response to parenterally-delivered beta-amyloid in mice.

Poly(lactide-co-glycolide) (PLG) microspheres were tested as a parenteral delivery system for human beta-amyloid (1-42) (Abeta), a potential immunotherapeutic undergoing assessment in Phase 1 studies for Alzheimer's disease (AD). Abeta was successfully encapsulated in PLG microspheres of average sizes of 3 or 15 microm diameter. Swiss Webster (SW) mice were injected by the sub-cutaneous (s.c.) or intra-peritoneal (i.p.) routes with 3-33 microg Abeta. Abeta-PLG microparticles (3 microm) induced dose-dependent antibody responses, which were maximal at 33 microg Abeta, while Abeta in phosphate-buffered saline (PBS) produced weak antibody responses at the same doses by both routes. Significantly increased antibody responses were seen for both small and large particle formulations given by the i.p. route in comparison to the s.c route. It was previously reported that passive immunisation with Abeta-specific antibodies cleared amyloid plaques in a mouse model of AD (Bard F, Cannon C, Barbour R, et al. Peripherally administered antibodies against amyloid beta-peptide enter the nervous system and reduce pathology in a mouse model of Alzheimer disease. Nature Med 2000;6:916-19), an indication that induction of serum antibody is a prerequisite for efficacy.

Amyloid beta-Peptides↗
PubMed2001

BACE knockout mice are healthy despite lacking the primary beta-secretase activity in brain: implications for Alzheimer's disease therapeutics.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulation of amyloid plaques and neurofibrillary tangles in the brain. The major components of plaque, beta-amyloid peptides (Abetas), are produced from amyloid precursor protein (APP) by the activity of beta- and gamma-secretases. beta-secretase activity cleaves APP to define the N-terminus of the Abeta1-x peptides and, therefore, has been a long- sought therapeutic target for treatment of AD. The gene encoding a beta-secretase for beta-site APP cleaving enzyme (BACE) was identified recently. However, it was not known whether BACE was the primary beta-secretase in mammalian brain nor whether inhibition of beta-secretase might have effects in mammals that would preclude its utility as a therapeutic target. In the work described herein, we generated two lines of BACE knockout mice and characterized them for pathology, beta-secretase activity and Abeta production. These mice appeared to develop normally and showed no consistent phenotypic differences from their wild-type littermates, including overall normal tissue morphology and brain histochemistry, normal blood and urine chemistries, normal blood-cell composition, and no overt behavioral and neuromuscular effects. Brain and primary cortical cultures from BACE knockout mice showed no detectable beta-secretase activity, and primary cortical cultures from BACE knockout mice produced much less Abeta from APP. The findings that BACE is the primary beta-secretase activity in brain and that loss of beta-secretase activity produces no profound phenotypic defects with a concomitant reduction in beta-amyloid peptide clearly indicate that BACE is an excellent therapeutic target for treatment of AD.

Alzheimer Disease↗
PubMed2001

Accumulation of amyloid beta-protein in the low-density membrane domain accurately reflects the extent of beta-amyloid deposition in the brain.

To learn more about the process of amyloid beta-protein (Abeta) deposition in the brain, human prefrontal cortices were fractionated by sucrose density gradient centrifugation, and the Abeta content in each fraction was quantified by a two-site enzyme-linked immunosorbent assay. The fractionation protocol revealed two pools of insoluble Abeta. One corresponded to a low-density membrane domain; the other was primarily composed of extracellular Abeta deposits in those cases in which Abeta accumulated to significant levels. Abeta42 levels in the low-density membrane domain were proportional to the extent of total Abeta42 accumulation, which is known to correlate well with overall amyloid burden. In PDAPP mice that form senile plaques and accumulate Abeta in a similar manner to aging humans, Abeta42 accumulation in the low-density membrane domain also increased as Abeta deposition progressed with aging. These observations indicate that the Abeta42 associated with low-density membrane domains is tightly coupled with the process of extracellular Abeta deposition.

Adult↗
PubMed2001

Immunotherapy with beta-amyloid for Alzheimer's disease: a new frontier.

Alzheimer's disease (AD) represents the fourth leading cause of death in the U.S. and the leading cause of dementia in the elderly population. Until recently, there was little hope of finding a way to prevent the underlying brain pathology from progressing toward the inevitable conclusion of the disease. However, new immunotherapeutic approaches have been described that are based on vaccination with the beta-amyloid 1-42 peptide (Abeta). The encouraging efficacy and safety of Abeta immunization in reducing neuropathology in animal models of AD has opened up new therapeutic possibilities for patients. Immunization with Abeta is aimed at reducing the Abeta-associated pathology of AD. It is hypothesized that this approach will also reduce the cascade of downstream events leading to neuronal cell loss and, ultimately, dementia. The ensuing articles in this issue describe various aspects of the Abeta immunization strategy and their potential relevance to AD treatment.

Alzheimer Disease↗
PubMed2001

Potential treatment opportunities for Alzheimer's disease through inhibition of secretases and Abeta immunization.

Research over the past ten years on Alzheimer's disease has pursued many opportunities. Notable amongst the various approaches are efforts related to the "amyloid hypothesis." This hypothesis posits that the beta amyloid peptide causes the extensive neuropathology and clinical decline associated with the disease. Extensive research in this area has shown that the beta amyloid peptide is produced by proteases termed "secretases" and it has been shown that blockade of secretase functions reduce the amount of beta amyloid peptide produced. An additional approach to reduce beta amyloid, through an increase in clearance mechanisms, is to immunize with the peptide itself and induce an antibody response. The specifically elicited antibodies then bind to and stimulate clearance of the peptide from the brain. These findings have stimulated several approaches to develop novel therapeutic strategies to treat Alzheimer's disease that either are about or have entered the clinic.

Alzheimer Disease↗
PubMed2000

Effect of the dietary brominated phenol, lanasol, on chemical biotransformation enzymes in the gumboot chiton Cryptochiton stelleri (Middendorf, 1846).

The effects of diet and other non-anthropogenic stressors on biochemical defenses and their relationship to susceptibility have been largely ignored in wildlife populations. Lanosol is a compound found in relatively high amounts in various marine species of Rhodophyta, including Odonthalia dentata. While previous studies demonstrated that lanosol is a feeding deterrent to several marine herbivores, Cryptochiton stelleri readily feeds upon O. dentata. To examine the effects of lanosol on the profile of biochemical defenses in C. stelleri, chitons were gavaged daily with 0, 1, 2.5, 5, or 10 mg/kg of lanosol. After three days of exposure, digestive gland microsomes were probed for expression of homologous isoforms of cytochromes P450 (CYP1A, CYP3A, and CYP2) and phase II enzymatic activities. Expression of a 43 kDa CYP3A-like protein was increased by approximately 45%, over control following 2.5, 5, and 10 mg/kg treatments. Estradiol hydroxylase activity tended to increase with the dose of lanosol. UDP-glucuronosyl transferase activity was highly variable but appeared to increase at the two highest treatments, while sulfotranserase activity was significantly decreased at the three highest doses. Kinetic studies of GST activity showed lanosol is a non-competitive inhibitor of both CDNB and GSH in the GST-mediated conjugation reaction. These results show that dietary exposure to the brominated-phenol, lanosol, may alter expression and activity of some phase I and II biotransformation enzymes in chitons, potentially providing a dietary advantage for the species.

Administration, Oral↗
PubMed2000

Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of Alzheimer disease.

One hallmark of Alzheimer disease is the accumulation of amyloid beta-peptide in the brain and its deposition as plaques. Mice transgenic for an amyloid beta precursor protein (APP) mini-gene driven by a platelet-derived (PD) growth factor promoter (PDAPP mice), which overexpress one of the disease-linked mutant forms of the human amyloid precursor protein, show many of the pathological features of Alzheimer disease, including extensive deposition of extracellular amyloid plaques, astrocytosis and neuritic dystrophy. Active immunization of PDAPP mice with human amyloid beta-peptide reduces plaque burden and its associated pathologies. Several hypotheses have been proposed regarding the mechanism of this response. Here we report that peripheral administration of antibodies against amyloid beta-peptide, was sufficient to reduce amyloid burden. Despite their relatively modest serum levels, the passively administered antibodies were able to enter the central nervous system, decorate plaques and induce clearance of preexisting amyloid. When examined in an ex vivo assay with sections of PDAPP or Alzheimer disease brain tissue, antibodies against amyloid beta-peptide triggered microglial cells to clear plaques through Fc receptor-mediated phagocytosis and subsequent peptide degradation. These results indicate that antibodies can cross the blood-brain barrier to act directly in the central nervous system and should be considered as a therapeutic approach for the treatment of Alzheimer disease and other neurological disorders.

Alzheimer Disease↗
PubMed2000

Prevention and reduction of AD-type pathology in PDAPP mice immunized with A beta 1-42.

In AD certain brain structures contain a pathological density of A beta protein deposited into plaques. The effect of genetic mutations found in early onset AD patients was an overproduction of A beta 42, strongly suggesting that overproduction of A beta 42 is associated with AD. We hypothesized that an immunological response to A beta 42 might alter its turnover and metabolism. Young PDAPP transgenic mice were immunized with A beta 1-42, which essentially prevented amyloid deposition; astrocytosis was dramatically reduced and there was reduction in A beta-induced inflammatory response as well. A beta 1-42 immunization also appeared to arrest the progression of amyloidosis in older PDAPP mice. A beta immunization appears to increase clearance of amyloid plaques, and may therefore be a novel and effective approach for the treatment of AD.

Alzheimer Disease↗
PubMed1999

Purification and cloning of amyloid precursor protein beta-secretase from human brain.

Proteolytic processing of the amyloid precursor protein (APP) generates amyloid beta (Abeta) peptide, which is thought to be causal for the pathology and subsequent cognitive decline in Alzheimer's disease. Cleavage by beta-secretase at the amino terminus of the Abeta peptide sequence, between residues 671 and 672 of APP, leads to the generation and extracellular release of beta-cleaved soluble APP, and a corresponding cell-associated carboxy-terminal fragment. Cleavage of the C-terminal fragment by gamma-secretase(s) leads to the formation of Abeta. The pathogenic mutation K670M671-->N670L671 at the beta-secretase cleavage site in APP, which was discovered in a Swedish family with familial Alzheimer's disease, leads to increased beta-secretase cleavage of the mutant substrate. Here we describe a membrane-bound enzyme activity that cleaves full-length APP at the beta-secretase cleavage site, and find it to be the predominant beta-cleavage activity in human brain. We have purified this enzyme activity to homogeneity from human brain using a new substrate analogue inhibitor of the enzyme activity, and show that the purified enzyme has all the properties predicted for beta-secretase. Cloning and expression of the enzyme reveals that human brain beta-secretase is a new membrane-bound aspartic proteinase.

Amino Acid Sequence↗
PubMed1999

Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse.

Amyloid-beta peptide (Abeta) seems to have a central role in the neuropathology of Alzheimer's disease (AD). Familial forms of the disease have been linked to mutations in the amyloid precursor protein (APP) and the presenilin genes. Disease-linked mutations in these genes result in increased production of the 42-amino-acid form of the peptide (Abeta42), which is the predominant form found in the amyloid plaques of Alzheimer's disease. The PDAPP transgenic mouse, which overexpresses mutant human APP (in which the amino acid at position 717 is phenylalanine instead of the normal valine), progressively develops many of the neuropathological hallmarks of Alzheimer's disease in an age- and brain-region-dependent manner. In the present study, transgenic animals were immunized with Abeta42, either before the onset of AD-type neuropathologies (at 6 weeks of age) or at an older age (11 months), when amyloid-beta deposition and several of the subsequent neuropathological changes were well established. We report that immunization of the young animals essentially prevented the development of beta-amyloid-plaque formation, neuritic dystrophy and astrogliosis. Treatment of the older animals also markedly reduced the extent and progression of these AD-like neuropathologies. Our results raise the possibility that immunization with amyloid-beta may be effective in preventing and treating Alzheimer's disease.

Alzheimer Disease↗
PubMed1999

Appearance of sodium dodecyl sulfate-stable amyloid beta-protein (Abeta) dimer in the cortex during aging.

We previously noted that some aged human cortical specimens containing very low or negligible levels of amyloid beta-protein (As) by enzyme immunoassay (EIA) provided prominent signals at 6 approximately 8 kd on the Western blot, probably representing sodium dodecyl sulfate (SDS)-stable Abeta dimer. Re-examination of the specificity of the EIA revealed that BAN50- and BNT77-based EIA, most commonly used for the quantitation of Abeta, capture SDS-dissociable Abeta but not SDS-stable Abeta dimer. Thus, all cortical specimens in which the levels of Abeta were below the detection limits of EIA were subjected to Western blot analysis. A fraction of such specimens contained SDS-stable dimer at 6 approximately 8 kd, but not SDS-dissociable A(beta) monomer at approximately 4 kd, as judged from the blot. This A(beta) dimer is unlikely to be generated after death, because (i) specimens with very short postmortem delay contained the A(beta) dimer, and (ii) until 12 hours postmortem, such SDS-stable A(beta) dimer is detected only faintly in PDAPP transgenic mice. The presence of A(beta) dimer in the cortex may characterize the accumulation of A(beta) in the human brain, which takes much longer than that in PDAPP transgenic mice.

Adult↗
PubMed1998

High cerebrospinal fluid tau and low amyloid beta42 levels in the clinical diagnosis of Alzheimer disease and relation to apolipoprotein E genotype.

OBJECTIVE: To evaluate cerebrospinal fluid (CSF) levels of amyloid beta protein ending at amino acid 42 (Abeta42) and tau as markers for Alzheimer disease (AD) and to determine whether clinical variables influence these levels. DESIGN: Cohort study. SETTING: Six academic research centers with expertise in dementia. SUBJECTS: Eighty-two patients with probable AD, including 24 with very mild dementia (Mini-Mental State Examination score >23/30) (AD group); 60 cognitively normal elderly control subjects (NC group); and 74 subjects with neurological disorders, including dementia (ND group). MAIN OUTCOME MEASURES: Levels of Abeta42 and tau were compared among AD, NC, and ND groups. Relationships of age, sex, Mini-Mental State Examination score, and apolipoprotein E (Apo E) genotype with these levels were examined using multiple linear regression. Classification tree models were developed to optimize distinguishing AD from NC groups. RESULTS: Levels of Abeta42 were significantly lower, and levels of tau were significantly higher, in the AD group than in the NC or ND group. In the AD group, Abeta42 level was inversely associated with Apo E epsilon4 allele dose and weakly related to Mini-Mental State Examination score; tau level was associated with male sex and 1 Apo E epsilon4 allele. Classification tree analysis, comparing the AD and NC subjects, was 90% sensitive and 80% specific. With specificity set at greater than 90%, the tree was 77% sensitive for AD. This tree classified 26 of 74 members of the ND group as having AD. They had diagnoses difficult to distinguish from AD clinically and a high Apo E epsilon4 allele frequency. Markers in CSF were used to correctly classify 12 of 13 patients who later underwent autopsy, including 1 with AD not diagnosed clinically. CONCLUSIONS: Levels of CSF Abeta42 decrease and levels of CSF tau increase in AD. Apolipoprotein E epsilon4 had a dose-dependent relationship with CSF levels of Abeta42, but not tau. Other covariates influenced CSF markers minimally. Combined analysis of CSF Abeta42 and tau levels discriminated patients with AD, including patients with mild dementia, from the NC group, supporting use of these proteins to identify AD and to distinguish early AD from aging. In subjects in the ND group with an AD CSF profile, autopsy follow-up will be required to decide whether CSF results are false positive, or whether AD is a primary or concomitant cause of dementia.

Adult↗