Increased inositol 1,4,5-trisphosphate accumulation correlates with an up-regulation of bradykinin receptors in Alzheimer's disease

An alteration in signal transduction systems in Alzheimer's disease (AD) would likely be of pathophysiological significance, because these processes control normal brain functions. Previously, a diminished beta-adrenergic-mediated cyclic AMP response was found in cultured fibroblasts from AD patients. Because cross-talk between the phosphoinositide and cyclic AMP pathways exists, the phosphoinositide cascade was studied under conditions that were similar to those for studying the cyclic AMP response. Cells from AD patients and age-matched controls responded to bradykinin (BK) and released inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in a time- and dose-dependent manner. The level of Ins(1,4,5)P3 increased rapidly and transiently in response to BK, peaked at 5 s, but still remained 116-132% above the basal level by 30 s. Although the temporal patterns were similar in both groups, the Ins(1,4,5)P3 concentrations in AD fibroblasts were 73 and 89% above levels in the age-matched controls at 5 and 10 s, respectively. Prostaglandin E1 also increased Ins(1,4,5)P3 formation, but this response was not different between the two groups. Although KD (affinity) values for the BK receptor were similar in both control and AD cells, the number of BK receptors (Bmax) was significantly elevated in AD fibroblasts (186.8 +/- 0.8 fmol/mg of protein) as compared with control fibroblasts (57.2 +/- 15.3 fmol/mg of protein). These results indicate that the elevated Ins(1,4,5)P3 production in response to BK in AD fibroblasts is positively correlated with an increase in the receptor numbers.

Molecular mechanisms of memory and the pathophysiology of Alzheimer's disease

Research on molecular and biophysical mechanisms of associative learning and memory storage identified a number of key elements that are phylogenetically conserved. In both vertebrates and invertebrates, K+ channels, PKC, Cp20, and intracellular Ca2+ regulation play a fundamental role in memory mechanisms. Because memory loss is the hallmark and perhaps the earliest sign of Alzheimer's disease, we hypothesized that these normal memory mechanisms might be altered in AD. With the use of a variety of experimental methodologies, our results revealed that one of the critical elements in memory storage, K+ channels, are dysfunctional in AD fibroblasts. Moreover, beta-amyloid induced the same K+ dysfunction in normal cells. Intracellular Ca2+ release, also associated with molecular memory mechanisms, was found altered in fibroblasts from patients with AD. The results therefore strongly suggest that biophysical and molecular mechanisms of associative learning could be altered in AD and that they may contribute to the memory loss observed early in the disease.

Expression of intracellular calcium-binding proteins in cultured skin fibroblasts from Alzheimer and normal aged donors

Disturbed calcium homeostasis may play a role in the etiology in Alzheimer's and other neurodegenerative diseases. A protective role against cellular degeneration has been postulated for Ca(2+)-binding proteins in certain neuron populations. Recent data suggest that intracellular free calcium regulation is also altered in several non-neuronal cells, including skin fibroblasts, from patients with Alzheimer's disease. In this study we analyzed the expression of several EF-hand Ca(2+)-binding proteins in cultured skin fibroblasts from Alzheimer patients and age-matched normal donors. We detected a strong expression of some members of the S100 Ca(2+)-binding protein family and of calcineurin A. However, no significant differences were found between both types of donors by Northern blot and Western blot analysis. In addition, similar signals were detected on 45Ca(2+)-blots of fibroblasts extracts of Alzheimer patients and control donors. The present findings indicate that the altered level of some intracellular calcium-binding proteins in certain brain areas of Alzheimer patients is not found in skin fibroblasts of these patients.

Distribution of the alpha-ketoglutarate dehydrogenase complex in rat brain

The alpha-ketoglutarate dehydrogenase complex (KGDHC) is a key enzyme in mitochondrial oxidation that appears critical to neurodegenerative diseases. Its activity in the brain declines in thiamine-deficient animals, Alzheimer's disease, and Wernicke-Korsakoff syndrome. Since selective cell populations are affected in these disorders, understanding the cellular distribution of KGDHC is important in order to define its role in the pathophysiology of these diseases. We used antisera against both bovine KGDHC and its E1k component to determine the immunocytochemical distribution of the enzyme and compare it with that of another mitochondrial enzyme, pyruvate dehydrogenase complex (PDHC) and a cholinergic neuronal marker, choline acetyltransferase (ChAT) in rat brain. Although low levels of immunoreactivity occurred in neurons, glia, and neuropil throughout the brain, some regions displayed relatively high perikaryal KGDHC enrichment. In the cerebral cortex, high immunoreactivity occurred mostly in layers III, V, and VI. The hippocampal pyramidal layer in CA1 and CA2 exhibited more intense staining than CA3. In the mammillary body, intensely labeled cells occurred in the supramammillary and lateral nuclei, while moderately stained cells predominated in the medial nucleus. The basal forebrain, basal ganglia, reticular and midline thalamic nuclei, red nucleus, pons, cranial nerve nuclei, inferior and superior colliculi, and cerebellar nuclei also contained highly immunoreactive neurons. The distribution of KGDHC overlapped with that of PDHC and colocalized to a limited extent with ChAT. These data are the first to demonstrate KGDHC immunoreactivity in discrete areas of rat brain and are vital to our understanding of selective vulnerability to metabolic insults and disease.

Aging and the brain

This review considers some of the changes that occur during aging in the mammalian central nervous system. We focus particularly on neurotransmitter systems, calcium homeostasis, synaptic transmission, oxidative metabolism, amyloid deposition, and other neuropathological and anatomical features. Changes during aging in both humans and nonhuman mammals are discussed.

Selective enrichment of cholinergic neurons with the alpha-ketoglutarate dehydrogenase complex in rat brain

Numerous reports suggest a close interaction between acetylcholine homeostasis and oxidative metabolism. However, the neuroanatomical basis of this relationship has not been established. A previous study showed that a key mitochondrial enzyme, alpha-ketoglutarate dehydrogenase complex (KGDHC) occurs at low levels in neurons, glia and neuropil throughout the rat brain. Some regions including those that are enriched with a cholinergic neuronal marker, choline acetyltransferase (ChAT) show relatively high perikaryal enrichment of KGDHC. The current study utilized double label immunofluorescence to determine whether cholinergic neurons are enriched with KGDHC in rat brain. In cranial nerve nuclei, trapezoid nucleus, nucleus ambiguous and inferior olive, virtually all cholinergic neurons were enriched with KGDHC. However, in basal forebrain nuclei, only a subpopulation of cholinergic cells were intensely immunoreactive for KGDHC. These data provide morphological evidence to support the hypothesized link between cholinergic function and oxidative metabolism in specific brain regions.

Internal Ca2+ mobilization is altered in fibroblasts from patients with Alzheimer disease

The recent demonstration of K+ channel dysfunction in fibroblasts from Alzheimer disease (AD) patients and past observations of Ca(2+)-mediated K+ channel modulation during memory storage suggested that AD, which is characterized by memory loss and other cognitive deficits, might also involve dysfunction of intracellular Ca2+ mobilization. Bombesin-induced Ca2+ release, which is inositol trisphosphate-mediated, is shown here to be greatly enhanced in AD fibroblasts compared with fibroblasts from control groups. Bradykinin, another activator of phospholipase C, elicits similar enhancement of Ca2+ signaling in AD fibroblasts. By contrast, thapsigargin, an agent that releases Ca2+ by direct action on the endoplasmic reticulum, produced no differences in Ca2+ increase between AD and control fibroblasts. Depolarization-induced Ca2+ influx data previously demonstrated the absence of between-group differences of Ca2+ pumping and/or buffering. There was no correlation between the number of passages in tissue culture and the observed Ca2+ responses. Furthermore, cells of all groups were seeded and analyzed at the same densities. Radioligand binding experiments indicated that the number and affinity of bombesin receptors cannot explain the observed differences. These and previous observations suggest that the differences in bombesin and bradykinin responses in fibroblasts and perhaps other cell types are likely to be due to alteration of inositol trisphosphate-mediated release of intracellular Ca2+.

The role of cytosolic free calcium in the regulation of pyruvate dehydrogenase in synaptosomes

Calcium homeostasis and mitochondrial oxidative metabolism interact closely in brain and both processes are impaired during hypoxia. Since the regulation of the pyruvate dehydrogenase complex (PDHC) may link these two processes, the relation of cytosolic free calcium ([Ca2+]i) to the activation state of PDHC (PDHa) was assessed in isolated nerve terminals (i.e. synaptosomes) under conditions that alter [Ca2+]i. K+ depolarization elevated [Ca2+]i and PDHa and both responses required external calcium. Treatment with KCN, an in vitro model of hypoxia decreased ATP and elevated [Ca2+]i and PDHa. Furthermore, in the presence of KCN, PDHa became more sensitive to K+ depolarization as indicated by larger changes in PDHa than in [Ca2+]i. The calcium ionophore Br-A23187 elevated [Ca2+]i, but did not affect PDHa. K+ depolarization elevated [Ca2+]i and PDHa even if [Ca2+]i was elevated by prior addition of ionophore or KCN. Previous in vivo studies by others show that PDHa is altered during and after ischemia. The current in vitro results suggest that hypoxia, only one component of ischemia, is sufficient to increase PDHa. These data also further support the notion that PDHa is regulated by [Ca2+]i as well as by other factors such as ATP. Our results are consistent with the concept that PDHa in nerve endings may be affected by [Ca2+]i and that these two processes are clearly linked.

Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer disease

Since memory loss is characteristic of Alzheimer disease (AD), and since K+ channels change during acquisition of memory in both molluscs and mammals, we investigated K+ channel function as a possible site of AD pathology and, therefore, as a possible diagnostic index as well. A 113-pS tetraethylammonium (TEA)-sensitive K+ channel was consistently absent from AD fibroblasts, while it was often present in young and aged control fibroblasts. A second (166-pS) K+ channel was present in all three groups. Elevated external potassium raised intracellular Ca2+ in all cases. TEA depolarized and caused intracellular Ca2+ elevation in young and aged control fibroblasts but not AD fibroblasts. The invariable absence of a 113-pS TEA-sensitive K+ channel and TEA-induced Ca2+ signal indicate K+ channel dysfunction in AD fibroblasts. These results suggest the possibility of a laboratory method that would diagnostically distinguish AD patients, with or without a family history of AD, from normal age-matched controls and also from patients with non-AD neurological and psychiatric disorders.

Reversible bilateral ureteric obstruction due to a pancreatic pseudocyst

An unusual case of bilateral ureteric obstruction and hydronephrosis due to pancreatic pseudocyst formation, after an episode of acute pancreatitis is reported. All abnormalities resolved with conservative management. Possible reasons for such ureteric obstruction include periureteric fat necrosis by pancreatic enzymes and compression by the inflammatory mass.

Altered beta-adrenergic receptor-stimulated cAMP formation in cultured skin fibroblasts from Alzheimer donors

An alteration in signal transduction systems in Alzheimer's disease would likely be of pathophysiological significance, because these steps are critical to normal brain function. Since dynamic processes are difficult to study in autopsied brain, the current studies utilized cultured skin fibroblasts. The beta-adrenergic-stimulated increase in cAMP was reduced approximately 80% in fibroblasts from Alzheimer's disease compared with age-matched controls. The deficit in Alzheimer fibroblasts in response to various adrenergic agonists paralleled their beta-adrenergic potency, and enhancement of cAMP accumulation by a non-adrenergic agonist, such as prostaglandin E1, was similar in Alzheimer and control fibroblasts. Diminished adenylate cyclase activity did not underlie these abnormalities, since direct stimulation of adenylate cyclase by forskolin elevated cAMP production equally in Alzheimer and control fibroblasts. Cholera toxin equally stimulated cAMP formation in Alzheimer and control fibroblasts. Moreover, cholera toxin partially reduced isoproterenol-induced cAMP deficit in Alzheimer fibroblasts. Pertussis toxin, on the other hand, did not alter the Alzheimer deficits. The results suggest either that the coupling of the GTP-binding protein(s) to the beta-adrenergic receptor is abnormal or that the sensitivity of receptor is altered with Alzheimer's disease. Further, any hypothesis about Alzheimer's disease must explain why a reduced beta-adrenergic-stimulated cAMP formation persists in tissue culture.

Synaptosomal plasma and mitochondrial membrane potentials during anoxia

The precise mechanism by which altered oxidative metabolism impairs neuronal function is unknown. Previous indirect studies suggest that anoxia's effects on the mitochondrial membrane potentials may underlie anoxia's actions. Twenty minutes of anoxia reduced the mitochondrial membrane potential of intact synaptosomes by 38-59 mV, but diminished the plasma membrane potential by only 4-10 mV. Anoxia did not alter the response of the plasma or mitochondrial membrane potentials to K+, nor did anoxia affect the reaction of the plasma membrane potential to valinomycin. However, anoxia diminished the response of the mitochondrial membrane potential to valinomycin by 50%. Thus, partial collapse of the mitochondrial membrane potential may be an important mediator of hypoxia-or anoxia-induced changes in neuronal function.

Cytosolic free calcium in lymphoblasts from young, aged and Alzheimer subjects

Altered cellular calcium homeostasis may be important in the pathophysiology of aging and Alzheimer's disease. Calcium transport by freshly isolated lymphocytes declines with Alzheimer's disease compared with age-matched controls. To determine if these changes occur in the absence of complications due to drugs, diet or any of the other variables that are dependent upon the state of the patients, cytosolic free calcium ([Ca2+]i) was determined in cultured lymphoblasts from young and aged control subjects, as well as from Alzheimer patients. Lymphoblast [Ca2+]i was determined with the fluorescent probe fura-2 in either the presence or absence of serum. In cells that were grown in serum free medium, neither growth rates nor [Ca2+]i varied between groups. Growing cells in serum containing medium doubled growth rates and [Ca2+]i. However, [Ca2+]i from young, aged and Alzheimer groups were still similar. Thus, an age- or Alzheimer-related alteration in [Ca2+]i does not occur in cultured lymphoblasts.

Nonneural markers in Alzheimer disease

Nonneural tissues are now widely used to search for abnormalities in genes as well as for other markers of dementia of the Alzheimer type (DAT). Studies of nonneural tissues can experimentally circumvent problems inherent in the study of autopsy brain, but to be meaningful, abnormalities identified in the periphery must be correlated with abnormalities in the brain, which is the tissue of clinical interest. Among the topics in DAT research that can be readily studied in nonneural cells (including tissue cultures) are molecular genetics, amyloid precursor protein formation and metabolism, systemic manifestations of immunological and inflammatory mechanisms, proteolysis, membranes, signal transduction, and mitochondria and metabolism. Although phenomena suggesting the possibility of cytoskeletal abnormalities in nonneural DAT cells have been described, the tau molecules involved in paired helical filament formation are relatively brain-specific. Since the neuropathological diagnosis of DAT depends on recognizing a pattern of changes rather than any single abnormality, it seems unlikely that any one laboratory abnormality in peripheral tissues will correlate precisely with the clinicopathological entity of DAT. However, abnormalities found in nonneural DAT cells that correlate with the existence of similar abnormalities in the brain are likely to be informative about the disease process in the patients in whom they occur.

Thiamin and Alzheimer's disease

Because of clinical and neuropathological overlap between the characteristics of dementia of the Alzheimer type (DAT) and of a human thiamin deficiency syndrome (Wernicke-Korsakoff syndrome), thiamin pyrophosphate (TPP) dependent processes have been studied in DAT brain and other tissues. The activities of 3 TPP-dependent enzymes are reduced in DAT brain: transketolase (TK), the pyruvate dehydrogenase complex (PDHC), and the alpha-ketoglutarate dehydrogenase complex (KGDHC). Quantitatively, the most marked reductions are in KGDHC (to less than 20% of normal). In cultured skin fibroblasts, KGDHC activity is reduced to 50-60% of normal, TK activity to 80-90% of normal, and PDHC is normal. Structural and molecular studies of the DAT and non-DAT enzymes are in process. A lesion of KGDHC may be related to the pathogenesis of DAT. Treatment with large doses of thiamin has not been beneficial, but the data are not totally negative. Further studies of thiamin-dependent mechanisms in DAT seem justified.

Acetylcholine formation from glucose following acute choline supplementation

The effects of choline administration on acetylcholine metabolism in the central nervous system are controversial. Although choline supplementation may elevate acetylcholine (ACh) content in brain, turnover studies with labelled choline precursors suggest that systemic choline administration either has no effect or actually diminishes brain ACh synthesis. Since choline supplementation elevates brain choline levels, the apparent decreases in previous turnover studies may reflect dilution of the labelled choline precursor pool rather than altered ACh formation. Therefore, brain ACh formation from [U-14C]glucose was determined after choline supplementation. A two to three fold elevation of brain choline did not alter ACh levels or [U-14C]glucose incorporation into ACh in the cortex, hippocampus or striatum. Although atropine stimulated ACh formation from [U-14C]glucose in hippocampus, two to three fold increases in brain choline did not augment ACh synthesis or content in atropine pretreated animals. Atropine depressed brain regional glucose utilization and this effect was not reversed by choline treatment. These results suggest that short-term elevation of brain choline does not enhance ACh formation from [U-14C]glucose, and argue against enhanced presynaptic cholinergic function after acute, systemic choline administration.

Inositol phosphates and intracellular calcium after bradykinin stimulation in fibroblasts from young, normal aged and Alzheimer donors

Several studies suggest that alterations in the receptor-mediated phosphoinositide cascade and cytosolic free calcium concentration ([Ca2+]i) are involved in the pathophysiology of aging and Alzheimer's disease. Therefore, the phosphoinositide cascade and [Ca2+]i were determined under resting conditions and after stimulation with bradykinin (100 nM) in cultured human skin fibroblasts from young (21 +/- 3 years), normal aged (59 +/- 6 years) and Alzheimer subjects (58 +/- 6 years). The inositol polyphosphates (IP3, IP2 and IP) were monitored after prelabeling the cells with [3H]inositol in serum free medium. [Ca2+]i was determined with the fluorescent probe, fura-2AM, under exactly analogous conditions. The bradykinin-induced formation of IP3 and IP2 increased significantly in fibroblasts from normal aged and Alzheimer donors compared to young subjects, but did not differ from each other. Bradykinin-induced IP3 formation was 63-117% above the young group at time points between 10-60 s in normal aged or Alzheimer donors. Bradykinin-induced IP2 formation was 49-59% above the young group at time points between 10-60 s in normal aged or Alzheimer subjects. Neither the basal [Ca2+]i, nor the bradykinin-stimulated [Ca2+]i, differed among fibroblasts from young, normal aged and Alzheimer donors. The precise molecular basis and pathophysiological significance of the enhanced bradykinin-induced phosphoinositide cascade in fibroblasts from aged donors remains to be determined.

Interactions between inositol phosphates and cytosolic free calcium following bradykinin stimulation in cultured human skin fibroblasts

The inositol triphosphate (IP3) that results from hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) is generally accepted to be responsible for the mobilization of intracellular calcium. However, some studies suggest that low concentrations of agonists elevate cytosolic free calcium concentration ([Ca2+]i) without IP3 formation. Thus, in the present studies, a comparison of the temporal response of inositol phosphates (IP3, IP2 and IP) and [Ca2+]i to a wide range of bradykinin concentrations was used to examine the relation of these two signal transduction events in cultured human skin fibroblasts (GM3652). In addition, the effects of alterations in internal or external calcium on the response of these second messengers to bradykinin were determined. Bradykinin stimulated accumulation of inositol phosphates and a rise of [Ca2+]i in a time- and dose-dependent manner. Decreasing the bradykinin concentration from 1 microM to 0.1 microM increased the time until the IP3 peak, and when the bradykinin concentration was reduced to 0.01 microM IP3 was not detected. [Ca2+]i was examined under parallel conditions. As the bradykinin concentration was reduced from 1 microM to 0.01 microM, the time to reach the peak of [Ca2+]i increased progressively, but the magnitude of the peak was unaltered. These two second messengers were variably dependent on external calcium. Although the bradykinin-stimulated initial spike of [Ca2+]i did not depend on extracellular calcium, the subsequent sustained levels of [Ca2+]i were abolished in calcium free medium. The bradykinin-stimulated inositol phosphate formation was not dependent on the extracellular calcium nor on the elevation of [Ca2+]i that was produced with Br-A23187. These results demonstrate that bradykinin-induced IP3 formation can be independent of [Ca2+]i and of external calcium, whereas changes in [Ca2+]i are partially dependent on external calcium.

The cellular basis of delirium and its relevance to age-related disorders including Alzheimer's disease

A wide variety of conditions lead to delirium (i.e., metabolic encephalopathies) in human beings and animals. Despite the varied etiology the clinical consequences are relatively stereotyped which suggests that the diverse insults that cause delirium may act by common metabolic and cellular "final pathways." Related molecular and cellular mechanisms may be involved in aging and Alzheimer's disease, conditions that predispose to the development of delirium. Animal models of delirium better reflect age-related disorders such as Alzheimer's disease than those that impair a single neurotransmitter system such as the cholinergic system; the metabolic encephalopathies produce global cognitive disturbance, which is more typical of these disorders. Thus, research related to delirium has far-reaching implications for normal and abnormal brain function.

Dopamine and serotonin in rat striatum during in vivo hypoxic-hypoxia

Dopamine and serotonin were determined in extracellular fluid of rat striatum by semiderivative in vivo voltammetry during normoxia and a single or repeated exposure to 15% O2 (i.e., mild hypoxia) or 12.5% O2 (i.e., moderate hypoxia). A single exposure to 15% oxygen increased extracellular dopamine 76%. With reintroduction of air to the animals, dopamine values returned to baseline. During a second episode of 15% oxygen, dopamine increased 63% and remained elevated even during a final exposure to air. On the other hand, serotonin was unaffected by 15% oxygen. Moderate hypoxia (12.5% oxygen) increased dopamine (79%) and serotonin (26%) and both remained elevated even after the initial reintroduction of air. These studies demonstrate that in vivo hypoxia increases rat striatal extracellular dopamine and, to a lesser extent, extracellular serotonin. Furthermore, after repeated, mild hypoxic episodes or moderate hypoxia, the increases in rat striatal extracellular dopamine and serotonin continue even during normoxia. These studies further support a role for dopamine and serotonin in hypoxic-induced changes in brain function. The hypoxic-induced elevation of these two neurotransmitters during normoxia may be important in the production of hypoxic/ischemic-induced cell damage.

Cytosolic-free calcium and neurotransmitter release with decreased availability of glucose or oxygen

Exposing brain slices to reduced oxygen tensions or impairing their ability to utilize oxygen with KCN decreases acetylcholine (ACh) but increases dopamine (DA) and glutamate in the medium at the end of a release incubation. To determine if these changes are due to alterations in the presynaptic terminals, release from isolated nerve endings (i.e. synaptosomes) was determined during histotoxic hypoxia (KCN). KCN reduced potassium-stimulated synaptosomal ACh release and increased dopamine and glutamate release. Since several lines of evidence suggest that altered calcium homeostasis underlies these changes in release, the effects of reducing medium calcium concentrations from 2.3 to 0.1-mM were determined. In low calcium medium, KCN still increased dopamine and glutamate release, but had no effect on ACh release. Hypoxia increased cytosolic-free calcium in both the normal and low calcium medium, although the elevation was less in the low calcium medium. Thus, the effects of histotoxic hypoxia on cytosolic free calcium concentration paralleled those on glutamate and dopamine release. Reducing the glucose concentration of the medium also increased cytosolic-free calcium. The data are consistent with the hypothesis that hypoxia and hypoglycemia increase cytosolic-free calcium, which stimulates the release of dopamine and glutamate, whose excessive release may lead to subsequent cellular damage postsynaptically.

Phosphatidylinositol metabolism during in vitro hypoxia

The effects of in vitro histotoxic hypoxia (0.5 mM KCN) on potassium-stimulated phosphatidylinositol turnover were determined. In rat cortical slices that were prelabeled with [2-3H]inositol, depolarization with 60 mM KCl increased [2-3H]inositol monophosphate and [2-3H]inositol bisphosphate accumulation in a Ca2+-dependent manner. At early times (10 s and 1 min), histotoxic hypoxia enhanced potassium-stimulated [2-3H]inositol monophosphate and inositol bisphosphate accumulation. Under basal conditions, hypoxia did not alter the accumulation of [2-3H]inositol phosphates. These results are consistent with the following hypothesis. The hypoxic-induced increase in cytosolic free calcium that we reported previously may lead to the early stimulation of inositol phosphates formation during hypoxia through activation of phospholipase C. The impairment of inositol phosphates formation during more prolonged hypoxia may be due to negative feedback regulation of the phosphatidylinositol cascade by protein kinase C or to a reduction in ATP levels.

Effects of in vitro hypoxia on depolarization-stimulated accumulation of inositol phosphates in synaptosomes

The effects of potassium and in vitro histotoxic hypoxia (i.e. KCN) on phosphatidylinositol turnover in rat cortical synaptosomes were determined. [2-3H] Inositol prelabelled rat synaptosomes were prepared from cerebral cortex slices that had been incubated with [2-3H] inositol. Depolarization with 60 mM KCl increased [2-3H] inositol phosphates in a time dependent manner. Depolarization with 60 mM KCl increased [2-3H] inositol trisphosphate transiently at 5 s. K+ induced rapid formation of [2-3H]-inositol bisphosphate and maintained an elevated level for at least 5 min. K+ stimulated gradual formation of [2-3H] inositol monophosphate with time. One minute of hypoxia enhanced potassium-stimulated [2-3H] inositol bisphosphate formation. However, 30 min of hypoxia impaired potassium-stimulated accumulation of [2-3H] inositol phosphates. The effects of histotoxic hypoxia were all dependent upon calcium in the medium and on K+-depolarization. Thus, hypoxia altered the K+-induced accumulation of inositol phosphates in prelabelled synaptosomes in a time dependent, biphasic manner that was calcium dependent.

Changes in cytosolic free calcium with 1,2,3,4-tetrahydro-5-aminoacridine, 4-aminopyridine and 3,4-diaminopyridine

The effects of 1,2,3,4-tetrahydro-5-aminoacridine (THA), 4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP) on cytosolic free calcium (Ca2+i) were determined. Both 4-AP and THA have been used to treat Alzheimer's disease. THA is a structural analog of the aminopyridines, which alter calcium homeostasis in nerve terminals. The structural similarities between these compounds suggest a common mechanism of action. The aminopyridines raised Ca2+i concentrations in non-depolarized synaptosomes, whereas THA had no effect. Neither the aminopyridines nor THA had any effect on Ca2+i concentrations in potassium-depolarized synaptosomes. These results suggest that the beneficial effects of THA may be mediated by other mechanisms (i.e. neurotransmitter degradative enzyme inhibition), whereas those of 4-AP and 3,4-DAP may be due, at least in part, to their elevation of Ca2+i, which may enhance neurotransmitter release or other calcium-dependent processes.

Reduced activities of thiamine-dependent enzymes in the brains and peripheral tissues of patients with Alzheimer's disease

A report of cell loss in the nucleus basalis of Meynert in patients with Wernicke-Korsakoff disease prompted the examination of thiamine pyrophosphate (TPP)-dependent enzymes in the brain and peripheral tissues of patients with Alzheimer's disease. In these brains, the activities of the 2-ketoglutarate dehydrogenase complex were reduced more than 75% and those of transketolase more than 45%. Decreases occurred in histologically damaged and in relatively undamaged areas. Small but statistically significant abnormalities of transketolase, but not of 2-ketoglutarate dehydrogenase complex, were identified in red blood cells and cultured fibroblasts. Previous studies have shown deficiencies in the brain and variable effects in peripheral tissues on another TPP-dependent enzyme--the pyruvate dehydrogenase complex. Activities of TPP-dependent enzymes appear to be deficient in the brain and perhaps in some peripheral tissues in patients with Alzheimer's disease.