Biomedical subjects

R Prior

Publications and source records attributed to R Prior.

At least 19 recordsLinked to original sources

PubMed2000

Effect of fruits, vegetables, or vitamin E--rich diet on vitamins E and C distribution in peripheral and brain tissues: implications for brain function.

Age-related neurodegenerative conditions are the principal cause of declining cognitive and motor function during aging. Evidence support that fruits and vegetables containing generous amounts of antioxidant nutrients are important for neurological function. We investigated the effect of diets enriched with fruits or vegetables but low in vitamin E and a diet high in vitamin E on the distribution of vitamins C and E in the brain and dopamine release of Fischer 344 rat model, over an 8-month period. The low-vitamin E diet resulted in lowered alpha-tocopherol levels in brain and peripheral tissues, whereas the animals that received a diet enriched in vitamin E showed a significant increase, between 500-900%. Vitamin C concentration in plasma, heart, and liver was reduced in the vitamin E-supplemented group. It is concluded that supplementation or depletion of alpha-tocopherol for 8 months results in marked changes in vitamin E levels in brain tissue and peripheral tissues, and varied distribution of alpha-tocopherol throughout the different brain regions examined. In addition, compared to control group, rats supplemented with strawberry, spinach, or vitamin E showed a significant enhancement in striatal dopamine release. These findings suggest that other nutrients present in fruits and vegetables, in addition to the well-known antioxidants, may be important for brain function.

Aging↗

PubMed2000

Apolipoprotein E, smooth muscle cells and the pathogenesis of cerebral amyloid angiopathy: the potential role of impaired cerebrovascular A beta clearance.

Cerebral amyloid angiopathy (CAA) is caused by the deposition of beta-amyloid (A beta) in Alzheimer disease brains. It also occurs isolated, representing a major cause for cerebral hemorrhage in the elderly. The E4 genotype of apolipoprotein E (ApoE) is a risk factor for CAA; however, the molecular mechanism underlying this genetic association is unknown. Various findings suggest that cerebrovascular A beta is derived from the soluble A beta contained in the cortical extracellular space or the cerebrospinal fluid (CSF) that communicates and surrounds small cortical or leptomeningeal vessels. CAA deposits are always intimately associated with smooth muscle cells (SMCs) or SMC-derived pericytes. As we have previously reported, SMCs internalize A beta in vitro via a lipoprotein pathway involving ApoE and the low-density lipoprotein receptor family. Internalized A beta is subsequently located to lysosomes, suggesting its intracellular degradation. We show that A beta is internalized via multiple pathways, because class A and class B scavenger receptors are also colocalized to A beta-containing endosomes in SMCs, and A beta uptake is inhibited by various scavenger receptor antagonists. It has been recently shown for different cell types that the cellular uptake of ApoE is more efficient for the ApoE3 isoform when compared to ApoE4 and that this isoform-specific difference depends on the presence of heparan sulfate proteoglycan (HSPG). HSPG is produced by SMCs and promotes A beta fibrillogenesis. We propose a pathogenetic model of CAA, in which the ApoE- and HSPG-mediated clearance of CSF-derived A beta peptides by SMCs protects the vascular extracellular matrix against critical A beta concentrations. Impairment of this pathway or its reduced efficiency in carriers of the ApoE4 genotype may increase the risk of developing CAA.

Aged↗

PubMed1998

Membrane and receptor modifications of oxidative stress vulnerability in aging. Nutritional considerations.

Evidence suggests that oxidative stress (OS) may contribute to the pathogenesis of age-related decrements in neuronal function and that OS vulnerability increases as a function of age. In addition to decreased endogenous protection, increases in OS vulnerability may result from changes in membrane lipids and distribution of receptor subtype. Using a PC-12 cell model system, we have shown that H2O2 or dopamine (DA) exposure induced deficits in the cell's ability to clear (extrude/sequester, E/S) Ca2+ that are similar to those seen in aging. When plasma membrane concentrations of sphingomyelin (SPM) were used, the SPM metabolite, sphingosine-1-phosphate was increased to the same levels as those seen in aging, and enhancement of OS-induced decreases in calcium E/S following KCL depolarization was observed. Differential decreases in CA2+ E/S were also seen following DA-induced OS in COS-7 cells transfected with one of five muscarinic receptor subtypes. Cells transfected with either M1, M2, or M4 receptors showed significantly greater vulnerability to OS (as expressed by greater decrements in calcium E/S and cell death) than those transfected with M3 or M5 receptors. The vitamin E analogue, Trolox, and the nitrone-trapping agent, PBN, were not effective in altering E/S decrements but were effective in preventing cell death 24 h after OS exposure. These findings suggest that putative regional (e.g., striatum and hippocampus) increases in OS vulnerability and loss of neuronal function in aging may be dependent upon membrane SPM concentration and receptor subtype. In related studies, attempts were made to determine whether increased OS protection via nutritional increases in antioxidant levels in rats [using diets supplemented with vitamin E (500IU/kg), strawberry extracts (9.4 g/kg dried aqueous extract, DAE), spinach (6.7 g/kg DAE), or blueberry extracts (10 g/kg DEA for six weeks)] would protect against exposure to 100% O2 (a model of accelerated neuronal aging). Results indicated that these diets were effective in preventing OS-induced decrements in several parameters (e.g., nerve growth factor decreases), suggesting that although there may be increases in OS vulnerability in aging, phytochemicals present in antioxidant-rich foods may be beneficial in reducing or retarding the functional central nervous system deficits seen in aging or oxidative insult.

Aging↗

PubMed1998

Disease incidence and longevity are unaltered by dietary antioxidant supplementation initiated during middle age in C57BL/6 mice.

The ability of augmented antioxidant consumption to alter disease incidence, lesion burden and/or longevity was studied in adult male C57BL/6 mice. Mice were fed modified AIN76 diet or modified AIN76 supplemented with vitamin E, glutathione (GSH), vitamin E and GSH, melatonin or strawberry extract starting at 18 months of age. All the mice in this study were heavier than reference populations of male C57BL/6 mice fed NIH-07 or NIH-31, which were maintained without a mid-life change in diet. Fatty liver, focal kidney atrophy and proteinacious casts in the renal tubules were observed more frequently in this study population than in the reference populations. Lesion burden and incidence of specific lesions observed amongst the various groups in this study did not differ. There were no differences observed for longevity of any of the study groups. The longevity observed in this study was similar to that previously reported for male C57BL/6 mice. Thus, diet supplementation with antioxidants initiated during middle age did not appear to affect age-associated lesions patterns, lesion burden or longevity for ad libitum fed male C57BL/6 mice.

Aging↗

PubMed1998

Overloaded endoplasmic reticulum-Golgi compartments, a possible pathomechanism of peripheral neuropathies caused by mutations of the peripheral myelin protein PMP22.

Nonconservative point mutations of the peripheral myelin protein 22 (PMP22) are associated with Charcot-Marie-Tooth type 1A disease, the most common inherited peripheral neuropathy in humans, and with the Trembler J (TrJ) and Trembler (Tr) alleles in mice. We investigated the intracellular transport of wild-type PMP22 and its TrJ and Tr mutant forms in Schwann cells and in a non-neuronal cell line. In contrast to wild type, mutant proteins were not inserted into the plasma membrane and accumulated in the endoplasmic reticulum and Golgi compartments. Coexpression of each mutant with wild-type PMP22 confirmed the different intracellular distribution of the mutant forms, indicating that neither the TrJ nor Tr protein has a dominant-negative effect on the cellular distribution of wild-type PMP22. Accumulation of PMP22 immunoreactivity in the cell body of myelinating Schwann cells was also observed in nerve biopsies obtained from CMT1A patients carrying the TrJ point mutation. We propose that impaired trafficking of mutated PMP22 affects Schwann cell physiology leading to myelin instability and loss.

Animals↗

PubMed1998

Age-related neurodegeneration and oxidative stress: putative nutritional intervention.

This review describes age-related changes that occur in neuronal function and cites evidence to show that these alterations may be the result of increased sensitivity to oxidative stress (OS). Evidence is presented to show that the abilities to mitigate the OS effects and to repair the damage from OS show decline as a function of age. Results from age- and OS-sensitive tests are given; these results indicate that one of the major sites of action of OS is the membranes, especially if compromised by high amounts of sphingomyelin, and one of the major effects of OS is to further alter the calcium disregulation in aging. It is suggested that attempts to increase antioxidant protection through diets comprised of fruits and vegetables identified as being high in total antioxidant activity might prevent or reverse the deleterious OS effects on neuronal aging.

Aging↗

PubMed1998

Detection of single amyloid beta-protein aggregates in the cerebrospinal fluid of Alzheimer's patients by fluorescence correlation spectroscopy.

Alzheimer's disease is associated with the intraparenchymal growth of plaque-like amyloid deposits. Amyloid plaques are formed by the progressive deposition and transformation of soluble amyloid beta-protein monomers into insoluble and fibrillar aggregates that contain amyloid beta-protein in a beta-pleated sheet conformation. This process is described as 'seeded polymerization' of the monomers with slow-nucleation and fast-growth kinetics. Soluble amyloid beta-protein monomers are present in the cortical extracellular space and in the cerebrospinal fluid, whereas insoluble aggregates so far can be found only by the examination of brain tissue by biopsy or autopsy. Here we present a biophysical method that uses the principle of seeded polymerization in combination with fluorescence correlation spectroscopy, which allowed us to detect single amyloid beta-peptide aggregates in the cerebrospinal fluid samples from Alzheimer's patients. All of 15 Alzheimer's samples but none of the 19 age-matched control samples produced large peaks with fluorescence correlation spectroscopy indicating the rapid aggregation of the fluorescent labelled synthetic amyloid beta-protein probe onto the amyloid beta-protein 'seeds' present in the cerebrospinal fluid. Our method could enable easy in vivo detection of the cerebral amyloid beta-protein pathology of Alzheimer's disease and might be of potential value to facilitate its routine diagnosis.

Aged↗

PubMed1997

Studies on the effects of altered PMP22 expression during myelination in vitro.

Severe inherited dysmyelinating diseases of the peripheral nervous system, the Charcot-Marie-Tooth type1A disease (CMT1A) and the hereditary neuropathy with liability to pressure palsies (HNPP) are associated with a large DNA duplication or deletion of a chromosomal region containing the peripheral myelin protein 22 (PMP22) gene. It has been suggested that a gene dosage effect involving PMP22 is responsible for the pathological phenotype. We investigated if altered PMP22 expression affects the onset of myelin formation and the ultrastructure of myelin. Rat Schwann cell cultures were stably infected with recombinant retrovirus vectors harboring the rat PMP22 cDNA in sense or antisense orientation. Schwann cells over- or underexpressing PMP22 were cocultured with purified DRG neurons under conditions that promote myelination. We examined PMP22 expression and localization in the myelin forming cultures by RT-PCR, immunohistochemistry and confocal microscopy, and we analyzed myelin ultrastructure by electron microscopy. Our results demonstrate that abnormal levels of PMP22 expression do not impair the early stages of myelination and membrane compaction and do not interfere with the expression of other myelin genes. Our observations further indicate that PMP22 is involved more in controlling myelin thickness and stability than in the events determining the initial steps of myelin formation.

Animals↗

PubMed1997

Cerebrovascular smooth muscle cells internalize Alzheimer amyloid beta protein via a lipoprotein pathway: implications for cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) is caused by the cerebrovascular deposition of Alzheimer amyloid beta protein (Abeta) and shows an increased incidence in carriers of the apolipoprotein E (APOE) epsilon4 genotype. To study the pathogenesis of CAA, primary cultures of human and canine smooth muscle cells from leptomeningeal vessels were incubated with fluorescein- and biotin-conjugated amyloid beta-protein. In the presence of human serum or cerebrospinal fluid, A beta1-40 and Abeta1-42 were rapidly internalized and appeared within endosomal and lysosomal vesicles. The accumulation of intracellular Abeta was enhanced by chloroquine and blocked by cycloheximide and brefeldin A and pretreatment with trypsin, suggesting that the internalization of Abeta occurs by receptor-mediated endocytosis. The internalization of Abeta was also inhibited by lipoprotein-deficient serum or by incubation with the 39-kd receptor-associated protein, indicating that Abeta is internalized via a receptor of the low-density lipoprotein receptor family. A lipoprotein pathway was confirmed by colocalization of cell surface-bound or internalized Abeta with APOE and low-density lipoprotein receptor-related protein. We propose a pathogenetic model of CAA, in which Abeta-APOE-complexes contained within the cerebrospinal fluid or the extracellular fluid of the brain are internalized and accumulated in cerebrovascular smooth muscle cells. Such a model could explain the preferential localization of CAA to the outer and middle layers of cortical and leptomeningeal arterioles, while indicating a mechanism by which the APOE genotype might determine the risk of CAA.

Amino Acid Sequence↗

PubMed1996

Loss of vessel wall viability in cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) is a neuropathological feature of Alzeheimer's disease and an important cause of cerebral haemorrhage in the elderly. CAA is characterized by the deposition of Alzheimer amyloid beta protein (A beta) in cerebral and leptomeningeal vessel walls. In order to study the effect of cerebrovascular A beta deposits in vivo, living canine leptomeninges obtained from old dogs affected by CAA were analysed by confocal laser scanning microscopy after immunofluorescence staining for A beta and viability staining with fluorescein diacetate (FDA). Simultaneous detection of the two signals showed a segmental loss of leptomeningeal vessel wall viability at some site of A beta deposition. Many of the non-viable vessels segments were also dilated, suggesting that A beta-induced vascular cell death creates the loci minores resistentiae for the development of cerebral haemorrhage in CAA.

Animals↗

PubMed1996

Canine leptomeningeal organ culture: a new experimental model for cerebrovascular beta-amyloidosis.

Cerebral amyloid angiopathy (CAA) is a neuropathological feature of Alzheimer's disease and a common cause of cerebral hemorrhage in the elderly. The pathogenetic mechanisms leading to the deposition of Alzheimer amyloid beta-protein (A beta) in cortical and leptomeningeal vessel walls are unknown. There are no experimental models which reproduce the pathological changes of CAA. In this study, leptomeninges from young and old dogs with pre-existing CAA were cultured in cell culture medium or cerebrospinal fluid and their viability, histological appearance and metabolic activity were analyzed during the culture. In addition, living leptomeninges of old and young dogs were incubated with fluorescein-conjugated A beta and the uptake of A beta was studied by fluorescence microscopy. Leptomeninges from young and old dogs were viable up to 8 weeks in culture. They contain many small- and medium-sized arterioles, the main vessel type affected by CAA. Histology and immunohistochemistry showed excellent preservation of the vessel wall microarchitecture up to 4 weeks in culture. The cultures were metabolically active as shown by the de novo production of beta-amyloid precursor protein. Exogenously added A beta was focally deposited in the vessel walls of old, but not young dogs. In conclusion, the organ culture of canine leptomeninges is easy to perform and appears suitable to investigate the pathogenesis and the progression of CAA.

Amyloid beta-Protein Precursor↗

PubMed1996

Selective binding of soluble Abeta1-40 and Abeta1-42 to a subset of senile plaques.

Alzheimer's disease is characterized by the progressive accumulation of amyloid-beta protein (Abeta) in senile plaques and cerebral amyloid angiopathy. It is not known whether the plaque growth is a continuous and homogeneous process or whether some plaques have a more rapid evolution. As plaques grow by the deposition of Abeta, we used an in situ binding technique to analyze the deposition of fluorescein-conjugated and biotinylated Abeta1 40 and Abeta1-42 in cryosections of brains from Alzheimer's disease patients. Only a subset of senile plaques but all cerebrovascular Abeta deposits were labeled by both Abeta1-40 and Abeta1-42. Striking differences in binding were observed among adjacent plaques. Quantitative analysis showed that on average 60% of all plaques were labeled with Abeta1-42 and 31% of all plaques were labeled with Abeta1-40 (n=7; P<0.001). Confocal laser scanning microscopy of double-labeled sections revealed that the newly deposited Abeta was only partially co-localized to pre-existing Abeta and apolipoprotein E and was not co-localized to heparan sulfate proteoglycan. Abeta binding was preserved after glycolytic pretreatment with periodic acid. Our results suggest that at a given time point only a subset of active senile plaques accumulate A(beta) and that plaque growth may be conditioned by the presence of other distinct plaque components different from Abeta, apolipoprotein E or heparan sulfate proteoglycan.

Aged↗

PubMed1996

The Alzheimer's disease-associated presenilins are differentially phosphorylated proteins located predominantly within the endoplasmic reticulum.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the deposition of extracellular senile plaques composed of amyloid beta-peptide (A beta). Whereas most cases of AD occur sporadically, about 10% of AD cases are inherited as a fully penetrant autosomal dominant trait. Mutations in the recently cloned Presenilin genes (PS-1 and PS-2) are by far the most common cause of early onset familial AD. MATERIALS AND METHODS: Cellular expression of endogenous and overexpressed PS proteins was analyzed by immunocytochemistry and metabolic labeling followed by immunoprecipitation. In vivo phosphorylation sites of PS proteins were analyzed by extensive mutagenesis. RESULTS: PS-1 as well as PS-2 proteins were localized predominantly within the endoplasmic reticulum (ER). However, small amounts of the PS proteins were detected within the Golgi compartment, where they colocalize with the beta-amyloid precursor protein (beta APP). The PS-2 protein was found to be highly phosphorylated, whereas very little phosphorylation was observed for PS-1. The selective phosphorylation of PS-2 occurs exclusively on serine residues. In vivo phosphorylation of PS-2 was mapped to serine residues 7, 9, and 19 within an acidic stretch at the N terminus, which is absent in PS-1. casein kinase (CK)-1 and CK-2 were shown to phosphorylate the N terminus of PS-2 in vitro. CONCLUSIONS: The majority of PS proteins were detected in the ER where little if any proteolytic processing of beta APP was reported. ER retention of PS proteins might occur by intramolecular aggregation. Small amounts of PS proteins were also detected in the Golgi where they colocalized with beta APP. This might suggest that potential interactions between PS proteins and beta APP could occur within the Golgi. Selective phosphorylation of PS-2 proteins within the acidic domain missing in PS-1 indicates differences in the biological functions and regulation of the two highly homologous proteins.

Alzheimer Disease↗

PubMed1995

Experimental deposition of Alzheimer amyloid beta-protein in canine leptomeningeal vessels.

To study the pathogenesis of cerebral amyloid angiopathy (CAA), organ cultures of canine leptomeninges were incubated with fluorescein-conjugated amyloid beta-protein (FA beta, residues 1-40; 10 nM to 200 microM). Fluorescence microscopy showed focal and dose-dependent FA beta binding to blood vessels affected by CAA at FA beta-concentrations as low as 10 nM. The new A beta deposits appeared to be extracellular and were localized to the middle and outer layers of leptomeningeal arterioles. FA beta partially co-localized with apolipoprotein E (ApoE) as revealed by confocal microscopy, suggesting that A beta in situ binds to ApoE. Young dogs or old dogs without CAA showed no deposition of FA beta. Our results indicate that after initiation of CAA pathology, physiological concentrations of soluble A beta are sufficient to sustain its further deposition and therefore the progression of CAA.

Alzheimer Disease↗

PubMed1995

Hyperhomocysteinemia and traditional cardiovascular disease risk factors in end-stage renal disease patients on dialysis: a case-control study.

Hyperhomocysteinemia occurs frequently in end-stage renal disease (ESRD), but its prevalence in comparison with traditional cardiovascular disease (CVD) risk factors is unknown. Fasting total plasma homocysteine, potential determinants of plasma homocysteine (i.e., plasma B-vitamins and serine), total and HDL cholesterol, glucose, and creatinine, were determined in 24 ESRD patients on dialysis, and 24 age, gender, and race matched Framingham Offspring Study controls with normal renal function. Presence of clinical CVD and CVD risk factors was established by standardized methods. Mean plasma homocysteine was markedly higher in the ESRD patients versus controls (22.7 vs. 9.5 mumol/l). ESRD patients were 33 times more likely than controls to have hyperhomocysteinemia (> 15.8 mumol/l) (95% confidence interval, 5.7-189.6). Hyperhomocysteinemia persisted in the ESRD patients despite normal to supernormal B-vitamin status. Plasma serine levels below the tenth percentile of the control distribution were found in 75% of the ESRD patients. Oral serine supplementation caused a 37% increase in mean plasma serine, but had no effect on plasma homocysteine in four ESRD patients with supernormal plasma folate, low plasma serine, and hyperhomocysteinemia. Given its unusually high prevalence, improved management of hyperhomocysteinemia might reduce CVD sequelae in ESRD.

Adult↗

PubMed1992

Identification and differential expression of a novel alternative splice isoform of the beta A4 amyloid precursor protein (APP) mRNA in leukocytes and brain microglial cells.

The gene for the beta A4-amyloid precursor protein (APP) consists of 19 exons which code for a typical N- and O-glycosylated transmembrane protein with four extracellular domains followed by the transmembrane domain and a short cytoplasmic domain. The beta A4-amyloid sequence is part of exons 16 and 17. Several APP isoforms can be generated by alternative splicing of exons 7 and 8, encoding domains with homologies to Kunitz-type protease inhibitors and the MRC OX-2 antigen, respectively. The mechanism by which the pathological beta A4 is generated is unknown, it is however a critical event in Alzheimer's disease and is distinct from the normally occurring cleavage and secretion of APPs within the beta A4 sequence. We report here for the first time considerable APP mRNA expression by rat brain microglial cells. In addition we showed by S1 nuclease protection and polymerase chain reaction analysis of reverse transcribed RNA (RT-PCR) that T-lymphocytes, macrophages, and microglial cells expressed a new APP isoform by selection of a novel alternative splice site and exclusion of exon 15 of the APP gene. This leads to a transmembrane, beta A4 sequence containing APP variant, lacking 18 amino acid residues close to the amyloidogenic region. The use of this novel alternative splice site alters the structure of APP in close proximity to the beta A4 region and thus may determine a variant, potentially pathogenic processing of leukocyte-derived APP in brain.

Amyloid beta-Protein Precursor↗

PubMed1992

Occlusive microangiopathy by immunoglobulin (IgM-kappa) precipitation: pathogenetic relevance in paraneoplastic cryoglobulinemic neuropathy.

Histological, immunohistochemical and ultrastructural sural nerve and skin biopsy findings in a case of cryoglobulinemia secondary to an IgM-kappa-producing non-Hodgkin lymphoma are described. The main finding was an occlusive microangiopathy present in both the sural nerve and the skin. Widespread cryoglobulin deposits of the proliferated vasa nervorum were associated with pronounced changes probably evoked by ischemia. Moderate perivascular inflammation, but no florid vasculitis was additionally present. Our observations indicate that occlusive microangiopathy by precipitated cryoglobulins may be a relevant pathogenetic factor in cryoglobulinemic peripheral neuropathy.

B-Lymphocytes↗

PubMed1991

Localization of Alzheimer beta A4 amyloid precursor protein at central and peripheral synaptic sites.

We have recently shown that the amyloid beta A4 precursor protein (APP) is synthesized in neurons and undergoes fast axonal transport to synaptic sites [Koo et al., Proc. Natl. Acad. Sci. U.S.A., 87 (1990) 1561-1565]. Using immunofluorescence, laser confocal microscopy and immunoelectron microscopy with simultaneous detection of APP and synaptophysin, we now report a preferential localization of APP at synaptic sites of human and rat brain and at neuromuscular junctions. APP is further found on vesicular elements of neuronal perikarya, dendrites and axons. The synaptic localization of APP implies (1) a role of APP in physiological synaptic activity and (2) a potential and early impairment of central synapses when synaptic APP is converted to beta A4 amyloid during the pathological evolution of Alzheimer's disease and Down's syndrome.

Amyloid beta-Protein Precursor↗