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  • 1
    ISSN: 1573-4919
    Keywords: diabetic female rat ; glucose 6-phosphate dehydrogenase ; insulin ; liver ; brain ; adrenaline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were significantly decreased in both diabetic and fasted rats. Treatment of diabetic rats with insulin resulted in liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities that were significantly greater than controls. Insulin promoted an increase in food consumption that was blocked by adrenaline. Insulin, when administered together with adrenaline, restored hepatic glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenas activities of diabetic animals to control values, without altering food consumption. Brain glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were not significantly altered by either dietary restriction, diabetes or insulin treatment. These results demonstrate a dissociation between the action of insulin on hepatic glucose 6-phosphate dehydrogenase activity and its action to increase food intake.
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  • 2
    ISSN: 1573-4919
    Keywords: lactation ; glucose 6-phosphate dehydrogenase ; insulin ; liver ; weaning ; dietary restriction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The activities of the hexose monophosphate dehydrogenases increased in adipose tissue, remained unchanged in liver and decreased in mammary gland following the weaning of rats at mid-lactation (day 14). When dietary intake was restricted at mid-lactation, the activities of the hexose monophosphate dehydrogenases increased in adipose tissue, decreased in liver, but were unaltered in mammary gland. Premature weaning on day 14 postpartum resulted in maternal increases in both plasma insulin and glucose, which peaked at day 16. The plasma insulin levels decreased from day 14 to day 18 postpartum in the normal lactating rat, and a similar trend was observed for animals on a restricted dietary intake. Daily food consumption in the lactating rat decreased from 50 g to 20 g after premature weaning. The live weight of pups raised on dams given a restricted food intake from day 14 had decreased by day 17 postpartum, whereas an increase in daily live weight gain was recorded for the litters from the lactating controls. The results demonstrate that the activities of the hexose monophosphate dehydrogenases are regulated differentially between tissues of the lactating rat.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The activities of the hexose monophosphate pathway enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were measured at autopsy in control and Alzheimer's disease brains. Enzyme activities did not vary between different areas of brain and were unaltered by age. In Alzheimer's disease, the activities of both enzymes were increased, the glucose-6-phosphate dehydrogenase activity being almost double the activity of normal controls. We propose that this increased enzyme activity is a response to elevated brain peroxide metabolism.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The ε4 allele of apolipoprotein E (apoE, protein; APOE, gene) is a major risk factor for Alzheimer's disease (AD). Genetically, the frequency of the ε4 allele is enriched in early-onset sporadic, late-onset familial, and common late-onset sporadic AD. ApoE is found in the extracellular amyloid-β (Aβ) deposits that are characteristic features of AD. In this study, we examined the interaction between Aβ and apoE isoforms. The apoE isoforms used in this study were either produced by stably transfected Chinese hamster ovary cells (CHO) or were from human plasma. We report that when similar concentrations of the apoE isoforms were used, native nonpurified apoE3 from recombinant CHO-derived sources bound Aβ, but apoE4 did not. In fact, in our system, binding of recombinant apoE4 to Aβ was never detectable, even after incubation for 4 days. Furthermore, using the same assay conditions, native apoE2, like apoE3, binds Aβ avidly. Furthermore, when human plasma apoE isoforms are tested in Aβ binding experiments, apoE3 bound Aβ more avidly than apoE4, and a major apoE/Aβ complex (the 40-kDa form) was observed with plasma apoE3 but not apoE4. These data extend our understanding of apoE isoform-dependent binding of Aβ by associating apoE2 with efficient apoE/Aβ complex formation and demonstrate that native apoE3 (whether recombinant or derived from human plasma) forms sodium dodecyl sulfate-stable apoE/Aβ complexes more readily than native apoE4. The different Aβ-binding properties of native apoE4 versus native apoE3 provide insight into the molecular mechanisms by which the APOE ε4 allele exerts its risk factor effects in AD.
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: It has previously been reported that amyloid-β (Aβ) peptide is neurotrophic to undifferentiated but neurotoxic to differentiated primary neurons. The underlying reasons for this differential effect is not understood. Recently, the toxicity of Aβ to neurons was shown to be dependent upon the activation of cyclin-dependent kinase 5 (Cdk5), thought to promote tau phosphorylation that leads to cytoskeletal disruption, morphological degeneration and apoptosis. Here we report that Cdk5, tau, and phosphorylated-tau (P-tau) are expressed at very low levels in undifferentiated primary neurons, but that the expression of Cdk5 and tau and the phosphorylation of tau increase markedly between 4 and 8 days of differentiation in vitro. Tau expression decreased after this time, as did the level of P-tau, to low levels by 17 days. Aβ induced tau phosphorylation of neurons only after ≥ 4 days of differentiation, a time that coincides with the onset of Aβ toxicity. Blocking tau expression (and therefore tau phosphorylation) with an antisense oligonucleotide completely blocked Aβ toxicity of differentiated primary neurons, thereby confirming that tau was essential for mediating Aβ toxicity. Our results demonstrate that differentiation-associated changes in tau and Cdk-5 modulate the toxicity of Aβ and explain the opposite responses of differentiated and undifferentiated neurons to Aβ. Our results predict that only cells containing appreciable levels of tau are susceptible to Aβ-induced toxicity and may explain why Aβ is more toxic to neurons compared with other cell types.
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (〉 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the ε4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The ε4 allele of APOE is one of three (ɛ2 ɛ3 and ɛ4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the ɛ4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOEɛ4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the ɛ2/ɛ3/ɛ4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the ɛ2/ɛ3/ɛ4 locus.
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previous studies have shown that a minor glycoform of acetylcholinesterase (AChE) is increased in Alzheimer's disease brain and cerebrospinal fluid. This glycoform can be distinguished from other AChE species by its lack of binding to concanavalin A (Con A). In this study, the temporal relationship between AChE glycosylation and Aβ deposition was examined in Tg2576 mice. There was a significant (p 〈 0.05) difference in AChE glycosylation in Tg2576 mice compared with age-matched background strain control mice at 4 months of age. This difference in glycosylation was also observed in 8- and 12-month-old Tg2576 mice. In contrast, Aβ plaques were only seen in the Tg2576 mice at 12 months of age, and were not detected at 4 and 8 months of age. Soluble human-sequence Aβ was detected as early as 4 months of age in the transgenic mice. The altered AChE glycosylation was due to an increase in a minor AChE isoform, which did not bind Con A, similar to that previously observed to be increased in Alzheimer's disease brain and cerebrospinal fluid. The results demonstrate that in transgenic mice altered AChE glycosylation is associated with very early events in the development of AD-like pathology. The study supports the possibility that glycosylation may also be a useful biomarker of AD.
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  • 8
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Aging and apolipoprotein E (APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid β (Aβ) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEɛ3 or human APOEɛ4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Aβ40 and Aβ42 peptides. Levels of the oxidized lipid F2-isoprostane (F2-isoPs) in the brains of the same animals as those used for the Aβ analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEɛ4 transgenic KO mice. Human APOEɛ3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2-isoPs. In general, the changes in the levels of brain F2-isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Aβ levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Aβ levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEɛ3, but not human APOEɛ4, can apparently prevent the aging-dependent rise in murine brain Aβ levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Aβ/F2-isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2-isoPs can stimulate Aβ generation and aggregation.
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  • 9
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The major component of the amyloid deposition that characterizes Alzheimer's disease is the 4-kDa βA4 protein, which is derived from a much larger amyloid protein precursor (APP). A procedure for the complete purification of APP from human brain is described. The same amino terminal sequence of APP was found in two patients with Alzheimer's disease and one control subject. Two major forms of APP were identified in human brain with apparent molecular masses of 100–110 kDa and 120–130 kDa. Soluble and membrane fractions of brain contained nearly equal amounts of APP in both humans and rats. Immunoprecipitation with carboxyl terminus-directed antibodies indicates that the soluble forms of APP are truncated. Carboxyl terminus truncation of membrane-associated forms of human brain APP was also found to occur during postmortem autolysis. The availability of purified human brain APP will facilitate the investigation of its normal function and the events that lead to its abnormal cleavage in patients with Alzheimer's disease.
    Type of Medium: Electronic Resource
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