The modulation of protein phosphorylation and receptor binding in synaptic membranes by changes in lipid fluidity: implications for ageing

Lipid-lowering medication use and aggression scores in women: a report from the NHLBI-sponsored WISE study

AIM

The aim of this study was to examine the association between the use of lipid-lowering medication and aggressive responding, hostility, cynicism, and depression scores in women undergoing coronary angiography.

METHODS

The cohort included 498 women from the National Heart, Lung and Blood Institute (NHLBI)-sponsored Women's Ischemia Syndrome Evaluation (WISE) study. WISE is a four-center study of women with chest pain who underwent quantitative coronary angiography for suspected myocardial ischemia. The psychosocial indices included the Cook Medley Hostility questionnaire, measuring aggression, hostility, and cynicism, and the Beck Depression Inventory (BDI).

RESULTS

Compared to those not on lipid-lowering medication, women receiving lipid-lowering pharmacotherapy were older (62 vs. 55 years, p < 0.001) and had more hypertension, dyslipidemia, diabetes, and coronary artery disease (CAD, defined as > or =50% stenoses in at least one epicardial artery) (all p < 0.003). Women on lipid-lowering medication had higher aggressive responding scores than those not on medication, 3.0 +/- 1.8 vs. 2.7 +/- 1.7, respectively (age-adjusted p < 0.003). This association persisted after adjustment for coronary risk factors, education, and extent of angiographic disease (CAD) (p < 0.005), and after exclusion of women using psychotropic medications (p < 0.001). Hostility, cynicism, and depression scores did not differ by medication use.

Low plasma cholesterol levels in suicidal males: a gender- and body mass index-matched case-control study of suicide attempters and nonattempters

Findings from animal and human studies suggest an association between low cholesterol levels and suicidal behaviors. The purpose of this case-control study was to test whether cholesterol levels in suicide attempters are lower than in controls without suicide attempt history matched by gender, age, and body mass index (BMI). Suicide attempters (n=177: 68 men and 109 women) and controls (177 blood donors) were assessed. Serum cholesterol levels were significantly lower in suicide attempters than in controls. After gender stratification, the difference remained significant in men, but not in women.

Dietary long chain PUFAs differentially affect hippocampal muscarinic 1 and serotonergic 1A receptors in experimental cerebral hypoperfusion

The chronic dietary intake of essential polyunsaturated fatty acids (PUFAs) can modulate learning and memory by being incorporated into neuronal plasma membranes. Representatives of two PUFA families, the n-3 and n-6 types become integrated into membrane phospholipids, where the actual (n-6)/(n-3) ratio can determine membrane fluidity and thus the function of membrane-bound proteins. In the present experiment we studied hippocampal neurotransmitter receptors after chronic administration of n-3 PUFA enriched diets in a brain hypoperfusion model, which mimics decreased cerebral perfusion as it occurs in ageing and dementia. Male Wistar rats received experimental diets with a decreased (n-6)/(n-3) ratio from weaning on. Chronic experimental cerebral hypoperfusion was imposed by a permanent, bilateral occlusion of the common carotid arteries (2VO) at the age of 4 months. The experiment was terminated when the rats were 7 months old. Three receptor types, the muscarinic 1, serotonergic 1A and the glutaminergic NMDA receptors were labeled in hippocampal slices by autoradiographic methods. Image analysis demonstrated that 2VO increased muscarinic 1 and NMDA receptor density, specifically in the dentate gyrus and the CA3 region, respectively. The increased ratio of n-3 fatty acids in combination with additional dietary supplements enhanced the density of the serotonergic 1A and muscarinic 1 receptors, while n-3 fatty acids alone increased binding only to the muscarinic 1 receptors. Since the examined receptor types reacted differently to the diets, we concluded that besides changes in membrane fluidity, the biochemical regulation of receptor sensitivity might also play a role in increasing hippocampal receptor density.

Systemic effects of dietary n-3 PUFA supplementation accompany changes of CNS parameters in cerebral hypoperfusion

Dietary supplementation with long-chain polyunsaturated fatty acids (PUFAs) has become an attractive possibility to alleviate or prevent cerebrovascular pathophysiology. To characterize the potentially beneficial cerebrovascular action of n-3 PUFAs that predominantly occur in fish oil, we set up an experimental paradigm where rats with chronic cerebral hypoperfusion were supplied with n-3 PUFA-enriched diets. Cerebral hypoperfusion was created by a permanent, bilateral occlusion of the common carotid arteries (2VO) of rats at the age of 4 months, with a survival of 3 months. Simultaneously, the rats were provided with experimental diets from the time of weaning until the termination of the experiments. The control diet was comparable to standard rat chow, while diet 1 contained additional n-3 PUFAs and diet 2 was further enriched with structural phospholipids and neurotransmitter precursors. In summary, the data show that diet 2 improved spatial learning of 2VO rats in the Morris water maze. Both diet 1 and diet 2 augmented blood-brain barrier parameters and increased the density of the M1-type muscarinic cholinergic receptors in the hippocampus independent of the rate of cerebral perfusion. In addition to an overview of these results, changes that were supportive or accompanying those described in the CNS are also presented. Briefly, plasma corticosterone concentration was elevated most explicitly by 2VO, while the relative weight of the liver and spleen increased due to the diets. The data draw attention to changes not only in the CNS, but also in the periphery as a consequence of chronic supplementation with n-3 PUFA-enriched diets.

Effect of neuropeptide-EI on the binding of [3H]SCH 23390 to the dopamine D1 receptor in rat striatal membranes

We have previously demonstrated that neuropeptide-EI, at high doses, stimulates the production of cAMP, in caudate putamen, through the activation of adenylate cyclase coupled to specific D1 receptors. The aim of the present work was to find evidences for a probable interaction between this neuropeptide and the dopamine D1 receptor in the mammalian central nervous system. The present data show that neuropeptide-EI, at high concentrations, affected both the maximum binding and the apparent affinity of [n-methyl-3H] (R)-(+)-8 chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol hemimaleate to the dopamine D1 receptor in a concentration-dependent manner.

The effect of melanotropic peptides on binding of [(3)H]dihydroalprenolol-hydrochloride to hypothalamic membranes

In the present work we studied the interaction of alpha-melanocyte-stimulating hormone (alpha-MSH) and ACTH-(1-24) with beta-adrenergic receptors in hypothalamic membranes from rat brain. Saturation curves for [(3)H]dihydroalprenolol-hydrochloride ([(3)H]DHA) binding in the presence of the peptides revealed a decreased binding capacity (Bmax). The dissociation constant (Kd) was, however, not affected by alpha-MSH or ACTH-(1-24). These data indicate a non competitive interaction between these melanocortin peptides and [(3)H]DHA on beta-adrenergic receptors in hypothalamic membranes.

Biogerontology research in Israel

The article describes the special features of gerontology research that has been expanding for five decades in Israel, and outlines the research in the biology of aging, covering a wide spectrum of areas and topics. A variety of associations, institutes and centers that have been established over the years play an important role in furthering the research and academic training.

Developmental regulation and effect of early undernutrition on phosphorylation of rat cortical synaptic membrane proteins

Undernutrition during early postnatal life was employed in rats by restricting the feeding time. The synaptic membrane fraction from cerebral cortex of normal and undernourished rats of various ages was prepared and endogenous protein phosphorylation studied. Many of the synaptic membrane proteins were found to be phosphorylated in an age-dependent manner. Early undernutrition affects the phosphorylation of various proteins in a complex way; most affected were 48-, 52-, 61- and 74-kDa proteins. These proteins were found to have phosphorylations mainly at tyrosine residues. This finding indicates that tyrosine phosphorylations may be affected most by early undernutrition. Adequate nutrition after early undernutrition removes most of the effects of undernutrition on synaptic protein phosphorylation. To address the question of how undernutrition may affect protein phosphorylation, we studied the lipid content of synaptic membrane fraction as it can affect membrane properties, including the fluidity. We found that undernutrition affects phosphorylation of most of the synaptic membrane proteins in the same manner in which it affects the cholesterol-phospholipid ratio of synaptic membrane and, hence, the fluidity of the membrane. This indicates that lipid biosynthesis is one of the ways by which undernutrition can affect synaptic membrane protein phosphorylation.

Assessing the observed relationship between low cholesterol and violence-related mortality. Implications for suicide risk

Health advocacy groups advise all Americans to restrict their dietary intake of saturated fat and cholesterol as an efficacious and safe way to lower plasma cholesterol concentrations and thus reduce the risk of coronary heart disease and other atherosclerotic disorders. However, accumulating evidence suggests that naturally low or clinically reduced cholesterol is associated with increased nonillness mortality (principally suicide and accidents). Other evidence suggests that such increases in suicide and traumatic death may be mediated by the adverse changes in behavior and mood that sometimes accompany low or reduced cholesterol. These observations provided the rationale for an ongoing series of studies in monkeys designed to explore the hypothesis that alterations in dietary or plasma cholesterol influence behavior and that such effects are potentiated by lipid-induced changes in brain chemistry. In fact, the investigations in monkeys reveal that reductions in plasma cholesterol increase the tendency to engage in impulsive or violent behavior through a mechanism involving central serotonergic activity. It is speculated that the cholesterol-serotonin-behavior association represents a mechanism evolved to increase hunting or competitive foraging behavior in the face of nutritional threats signaled by a decline in total serum cholesterol (TC). The epidemiological and experimental data could be interpreted as having two implications for public health: (1) low-cholesterol may be a marker for risk of suicide or traumatic death and (2) cholesterol lowering may have adverse effects for some individuals under some circumstances.

Role of homocysteine in age-related vascular and non-vascular diseases

Homocysteine (Hcy) may represent a metabolic link in the pathogenesis of atherosclerotic vascular diseases and old-age dementias. Hyperhomocysteinemia is an independent risk factor for coronary artery disease and peripheral vascular disease, and is also associated with cerebrovascular disease; specifically, the risk of extracranial carotid atherosclerosis significantly increases in relation to Hcy levels. Hcy is a reliable marker of vitamin B12 deficiency, a common condition in the elderly which is known to induce neurological deficits including cognitive impairment; a high prevalence of folate deficiency has been reported in psychogeriatric patients suffering from depression and dementia. Both these vitamins occupy a key position in the remethylation and synthesis of S-adenosylmethionine (SAMe), a major methyl donor in CNS; therefore, deficiencies in either of these vitamins lead to a decrease in SAMe and increase in Hcy, which can be critical in the aging brain. Another pathogenetic mechanism linking high Hcy levels to reduced cognitive performances in the elderly might be represented by excitotoxicity, since hyperhomocysteinemia may lead to an excessive production of homocysteic acid and cysteine sulphinic acid, which act as endogenous agonists of NMDA receptors. Considering the reasonably high prevalence in the general population of a genetic predisposition to a thermolabile form of the enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR), hyperhomocysteinemia can be seen as the result of multiple genetic and environmental factors leading to vascular and/or neurodegenerative disorders where age-related involutive phenomena represent a common pathogenetic ground. Systematic studies in different psychogeriatric conditions monitoring Hcy levels and clinical features before and after vitamin supplementation are therefore highly recommended.

Membrane phospholipids and adrenergic receptor function

We have reviewed the effects on adrenergic receptors by membrane phospholipid alterations secondary to oxidative stress and phospholipases' activity. Experimental evidences indicate that the function of both alpha- and beta-adrenoceptors is regulated by their phospholipid microdomain; however, the underlying mechanism is still undefined. No information seems to be available on the influence of phospholipids on alpha 2-adrenoceptors and on all adrenoceptors' subtypes. Thus, further studies are necessary to clarify the role of membrane phospholipids in regulating the function of each member of the adrenergic receptor superfamily.

Membrane alterations as causes of impaired signal transduction in Alzheimer's disease and aging

Changes in cell-membrane composition in normal aging and in Alzheimer's and other age-related diseases appear to result in impaired neurotransmitter-triggered signal transduction. The impaired signal transduction seems to be related to dysfunctions in the coupling of G proteins to their receptors and effectors. Direct demonstration of altered physiochemical properties of brain tissue of patients with Alzheimer's disease has been achieved by small-angle X-ray diffraction. In this disease, thinner membranes correlate with a 30% decrease in moles of cholesterol:phospholipid. Such changes can affect directly the coupling and uncoupling properties of G proteins, and can account for signal transduction deficits. These findings offer a complementary alternative to the beta-amyloid hypothesis, and an opportunity to consider new types of therapeutic interventions.

Probing membrane bilayer interactions of 1,4-dihydropyridine calcium channel blockers. Implications for aging and Alzheimer's disease

The results of this study demonstrate that the equilibrium nonspecific binding of DHP Ca2+ channel blockers to the membrane bilayer is highly dependent on cholesterol content. The molecular explanation for this observation appears to be related to the fact that cholesterol and DHPs occupy a similar molecular location in the membrane hydrocarbon core (Fig. 4). The membrane location of amlodipine may also be critical for subsequent receptor recognition and binding to voltage-sensitive Ca2+ channels in peripheral and CNS tissue. Finally, changes in the cholesterol content of neural plasma membranes isolated from diseased cortical regions of subjects with AD were reported and may be indicative of a general defect in lipid metabolism. Further studies are underway to characterize in greater detail possible changes in cholesterol content with aging and AD. The implication of these changes for structure/function relationships in the membrane is also being explored.

Signal transduction changes in granulocytes and lymphocytes with ageing

It is well known that the immune response declines with ageing. However, the exact cause of this decline is still unknown. In recent years signal transduction events leading to the transmission of a signal from the cell surface to the nucleus have been extensively studied in various cell systems. These studies have indicated that an alteration in signal transduction occurs with ageing. It is not possible to identify a single age-sensitive step in this sequence, but rather a series of deficiencies contributing to the decline in competency of aged lymphocytes and granulocytes to undergo normal activation. Thus, signal transduction events such as calcium mobilization, phosphatidylinositol breakdown, accumulation of proto-oncogene transcripts, expression of activation markers, and synthesis of new proteins are deficient in the aged. Other events in signal transduction have been much less studied such as protein tyrosine kinase activity and G-protein functions. alterations in these various intracellular signalling events may fundamentally influence the functional activity of lymphocytes and granulocytes in the aged, as suggested by several investigations performed in recent years and reviewed in the subsequent sections. Future study on the signal transduction pathways using well-defined experimental models and healthy individuals should help to elucidate the molecular basis of immunosenescence and to develop effective approaches for reducing age-associated deficits and thereby reducing the incidence of age-associated diseases.

Organic solvents increase membrane fluidity and affect bile flow and K+ transport in rat liver

Following the earlier observation that inhalation of volatile lipid solvents and of narcotic gases causes cholestasis, we studied the effects of various organic solvents on bile flow, plasma membrane fluidity and potassium movement in rat liver. Both in vivo and in the isolated perfused liver, applications of CCl4, CHCl3, dichloromethane, trichloroethylene, halothane, benzene and cyclohexane elicited rapid and sustained but reversible cholestasis. A transient phase of choleresis was observed prior to and after cholestasis, during the increase and fall in liver tissue solvent concentrations, respectively. Tissue concentrations required to produce cholestasis were lower the higher the lipophilicity of the solvent. Membrane fluidity was measured in isolated basolateral liver cell membranes by fluorescence polarization. Fluidity increased with increasing solvent concentration, the increase being associated with either biphasic stimulation and inhibition of membrane enzymes (Na+,K(+)-ATPase, 5'nucleotidase) or with inhibition alone (Mg(2+)-ATPase). In the isolated perfused liver, application of organic solvents caused hepatic uptake of K+ that was followed by K+ release upon withdrawal of the solvent. The magnitude of K+ uptake elicited by the solvent was comparable with the effect of blocking K+ channels with 2 mM Ba2+, but Ba2+ was ineffective in the presence of the solvent. In contrast, application of ouabain caused K+ release in equal amounts in the absence and presence of the solvent, indicating that K+ uptake elicited by the solvent results from inhibition of K+ efflux through K+ channels rather than stimulation of the Na+,K+ pump. The data show that cholestasis elicited by lipid solvents is associated with an increase in membrane fluidity and with disturbance of liver K+ homeostasis. The significance of these observations is discussed with respect to other models of experimental cholestasis.

Age-related changes in maturation of regenerated motor innervation

The dependence of spontaneous transmitter release by regenerated nerve endings on age was studied in rat extensor digitorum longus muscle after sciatic nerve crush during the first year of life. Intracellular recordings were carried out at different times after denervation in muscles of 1.5-, 3- or 12-month-old animals. The frequency of miniature endplate potentials was detected. In order to determine the percentage of multiple innervation, nerve-evoked endplate potentials were recorded. The time course of the percentage of polyinnervated muscle cells was similar in the three groups of animals, but mepp frequency increased more slowly with increasing age. Moreover, by extrapolating the intercept of linear regression for mepp frequency vs days from denervation, a conventional initial time of reinnervation may be computed: the results are consistent with a decrease in the nerve regeneration rate during the first year of life.

Oral choline alfoscerate counteracts age-dependent loss of mossy fibres in the rat hippocampus

Mossy fibres represent a major intrahippocampal associative pathway. They consist of axons of granule cells of the dentate gyrus and show an age-dependent loss as do the granule cells of the dentate gyrus. The present study was designed to assess whether long-term treatment of rats with choline alfoscerate in their drinking water would be effective in countering the loss of mossy fibres and of granule cells occurring with aging. Choline alfoscerate is a precursor in the biosynthesis of brain phospholipids and increases the bioavailability of choline in nervous tissue. Male Sprague-Dawley rats of 18 months of age were divided into two groups. One group received a daily dose of 100 mg/kg choline alfoscerate for 6 months; the other group was used as an untreated control. Twelve-month-old untreated animals were used as a reference group. The area occupied by mossy fibres, as well as their density, was significantly reduced in 24-month-old control rats in comparison with 12-month-old rats. The same is true for the density granule cells of the dentate gyrus which was decreased by about 20% in the oldest animals. In choline alfoscerate-treated rats both the area occupied by mossy fibres and their density were significantly higher than in age-matched controls. Moreover, the number of granule neurons of the hippocampus was higher by about 7% in choline alfoscerate-treated than in control 24-month-old rats. The above data suggest that choline alfoscerate treatment counteracts some anatomical changes of the rat hippocampus occurring in old age.

Brain phosphatidic acid and polyphosphoinositide formation in a broken cell preparation: regional distribution and the effect of age

The effect of age on phosphate incorporation into phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidic acid (PA) was studied. Lysed crude synaptosomal fractions of different brain regions of 3-month-old and 32-month-old Brown Norway rats were used. The brain regions tested were the hippocampus, frontal cortex, occipital/parietal cortex, entorhinal/pyriformal cortex, striatum/septum, thalamus and hypothalamus. The individual specific phosphorylating activities were unevenly distributed within the brain of Brown Norway rats. Strikingly, the distribution of phosphate incorporation into PIP2 was opposite from that of phosphate incorporation into PA. Phosphate incorporation into PA decreased (-15%) with age in almost all brain regions tested, whereas phosphate incorporation into PIP2 decreased with age only in the frontal cortex (-20%) and in the hypothalamus (-8%). The effects of age may reflect a deterioration of phosphoinositide metabolism, with its function in signal transduction coupled to receptors via G-proteins, in the brain regions involved. In addition, there was an age related decrease in protein content and total phospholipid phosphorus content of lysed crude synaptosomal preparations of all brain regions. The high correlation between the changes in these parameters may be indicative of a decrease in the number or size of synaptosomes with age in the brain regions involved.

Evidence for changes in the Alzheimer's disease brain cortical membrane structure mediated by cholesterol

Small angle X-ray diffraction analysis of Alzheimer's disease (AD) lipid membranes extracted from cortical gray matter showed significant, reproducible structure changes relative to age-matched control samples. Specifically, there was an average 4 A reduction in the lipid bilayer width and significant changes in the membrane electron density profiles of AD cortical samples. There were no significant structure differences in the membrane bilayers isolated from an unaffected region (cerebellum) of the AD brain. Lipid and protein analysis of 6 AD and 6 age-matched controls showed that the phospholipid:protein mass ratio was unchanged but that the unesterified cholesterol:phospholipid (C:PL) mole ratio decreased by 30% in the AD temporal gyrus relative to age-matched controls. By contrast, the C:PL mole ratio in the cerebellum did not change significantly. X-ray diffraction analysis of a cholesterol enriched AD sample demonstrated a virtual restoration of the normal membrane bilayer width and electron density profile, suggesting that the cholesterol deficit played a major role in the AD lipid membrane structure perturbation. Alterations in the composition and structure of the membrane bilayer may play an important role in the pathophysiology of AD by altering the activity and catabolism of membrane-bound proteins, including the beta-amyloid precursor protein.

Low serum cholesterol and suicide

Primary prevention trials which have shown that the lowering of serum cholesterol concentrations in middle-aged subjects by diet, drugs, or both leads to a decrease in coronary heart disease have also reported an increase in deaths due to suicide or violence. There has been no adequate explanation for this association. I have reviewed the relevant published work and describe a physiological mechanism that might account for this curious finding. One of the functions of serotonin in the central nervous system is the suppression of harmful behavioural impulses. When mouse brain synaptosomal membrane cholesterol is increased there is a pronounced increase in the number of serotonin receptors. Low membrane cholesterol decreases the number of serotonin receptors. Since membrane cholesterol exchanges freely with cholesterol in the surrounding medium, a lowered serum cholesterol concentration may contribute to a decrease in brain serotonin, with poorer suppression of aggressive behaviour.

Age-related anatomical changes in the rat hippocampus: retardation by choline alfoscerate treatment

The age-related anatomical changes in the rat hippocampus were evaluated in male Sprague-Dawley rats of 3 (young), 12 (mature) and 24 (aged) months by counting the number of nerve cells in the CA1 and CA3 fields and in the dentate gyrus and by measuring the density of Nissl bodies in the cytoplasm of the pyramidal and granule neurons of the above areas. Moreover, the effect of 3 months choline alfoscerate treatment on the anatomical parameters examined was evaluated. The number of pyramidal neurons of the CA1 field and of granule neurons of the dentate gyrus was not significantly changed between young and mature animals, but it was decreased in aged rats. The number of pyramidal neurons of the CA3 field showed a progressive age-dependent reduction. The density of Nissl bodies was the highest in the cytoplasm of pyramidal or granule neurons in mature rats followed in descending order by young and aged animals. Choline alfoscerate treatment counteracted the age-related loss of nerve cells in the 3 hippocampal portions examined and slow-drown the decrease of Nissl bodies in the cytoplasm of pyramidal or of granule neurons in the hippocampus. The significance of changes induced by choline alfoscerate in the hippocampus of aged rats and the possible mechanism of action of the compound are discussed.

ACTH/MSH-like peptides inhibit the binding of dopaminergic ligands to the dopamine D2 receptor in vitro

ACTH-(1-24) decreased the binding of the dopamine D2 receptor agonist, [3H]N-propylnorapomorphine ([3H]NPA), to rat striatal membranes in a concentration-dependent manner, with a Ki of 5 x 10(-7) M. Saturation curves for [3H]NPA binding in the presence of increasing concentrations of ACTH-(1-24) were performed. Scatchard analysis in the presence of ACTH-(1-24) revealed an increased dissociation constant (Kd), while the binding capacity (Bmax) was not affected by the peptide, suggesting an apparent competitive interaction between ACTH-(1-24) and [3H]NPA. ACTH-(1-24) also reduced the binding of the dopamine D2 receptor antagonist [3H]spiperone to striatal membranes, with a Ki of 10(-6) M. Much higher concentrations of ACTH-(1-24), up to 10(-4) M, were needed for the displacement of appropriate radiolabelled ligands from dopamine D1 receptors, serotonin 5-HT1A, serotonin 5-HT1B, muscarinic M1 acetylcholine and histamine H1 receptors. ACTH-(1-24) also inhibited the binding of [3H]spiperone to dopamine D2 receptors in membranes of the pituitary gland, the septum and the substantia nigra. ACTH-(1-39) and most ACTH fragments and analogs were less potent than ACTH-(1-24) in displacing [3H]NPA from the dopamine D2 receptor in striatal membranes. In general there was a relationship between displacing potency and chain length. ACTH-(7-16)-NH2 and benzyloxycarbonyl-ACTH-(8-16)-NH2, however, were more potent than ACTH-(1-24) in reducing the binding of [3H]NPA to dopamine D2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Action of organic solvents on protein kinase C

The action of organic solvents on the biochemical and biophysical properties of protein kinase C (PKC) was measured in a defined lipid vesicle system. Chloroform, benzyl alcohol and ethanol all partially activated PKC. They had no effect on the Ca(2+)- or anionic phospholipid-, phosphatidylserine-dependence. Their ability to activate PKC correlated with their lipid perturbing effect as measured by the decrease in fluorescence anisotropy. Chloroform was the most potent activator stimulating PKC phosphotransferase activity up to a level 40% of that obtained by the endogenous activator, diacylglycerol. The three fluidizers induced a more hydrophobic environment for at least one PKC tryptophan residue. This may have been due to insertion of an additional or different region of protein kinase C into the lipid bilayer as demonstrated by a blue shift in tryptophan fluorescence, providing an explanation for their inability to act as competitors of PKC binding of phorbol esters. Higher concentrations of the organic solvents resulted in a lipid bilayer that was too fluid to support membrane activity. This study demonstrates that these anesthetics and alcohols modulate lipid structure which subsequently induces PKC to undergo a different protein-lipid interaction in comparison to the endogenous activator, diacylglycerol. This supports the proposal that the biophysical state of the membrane plays a significant role in modulating PKC activity.

Modulation of the beta-adrenergic stimulation of cyclic AMP accumulation in rat prostatic epithelial cells by membrane fluidity

1. The influence of membrane lipid composition on the beta-adrenergic stimulation of cyclic AMP accumulation in rat prostatic epithelial cells was assessed after treating the cells with cholesteryl hemisuccinate (ChH). 2. ChH treatment resulted in a 40% inhibition of the beta-adrenergic response after 30 min of lipid preincubation at 37 degrees C. 3. The inhibitory effect of ChH was dose-dependent and was accompanied by an increase of microviscosity as measured by a fluorescence polarization technique with the probe diphenylhexatriene. 4. Experiments with increasing concentrations of isoproterenol indicated that the efficiency, but not the potency, of the beta-adrenergic response was affected by the increasing of the cholesterol content in the cell membrane.

Alzheimer's dementia and binding to alpha 2 adrenoreceptors in platelets

Seventy-five patients with probable Alzheimer's disease were screened for binding of alpha 2 receptors (A2R) to their platelet membranes; the results were compared with 51 age- and sex-matched controls. Receptor binding assays were performed using [3H] Yohimbine as the radioligand. The results showed a higher binding capacity in the demented population as compared to the control group (2.18 +/- 0.15 fmol/mg protein, as compared to 1.73 +/- 0.13, P less than 0.03). This increased binding to platelets in the demented patients was more prominent in demented females: 34% higher binding as compared with female controls (2.06 +/- 0.5 vs 1.54 +/- 0.04). The difference between demented and normal males was less (2.34 +/- 0.05 vs 1.88 +/- 0.05). The results indicate an involvement of the A2R system, either primarily or secondarily, in the disease process. Since there is an overlap between results from the patients with Alzheimer's disease and the normal subjects, A2R may serve as only a supportive marker for Alzheimer's disease.

ACTH modulation of nerve development and regeneration

(1) The availability of short amino acid sequences of the naturally occurring ACTH 1-39 molecule has made it possible to separate the corticotropic characteristics of the parent molecule from its neurotrophic effects. Potent neurotrophic fragments are ACTH 4-10, an analog of ACTH 4-9 (Org 2766), and alpha-MSH (ACTH 1-13), peptide fragments that do not evoke corticosteroid secretion, yet clearly affect both the development and regeneration of peripheral nerve. (2) Early postnatal administration of either ACTH 4-10 or Org 2766 accelerates the neuromuscular development of the immature rat, increasing the contractile strength of the EDL muscle and inducing more rapid muscle contractions. Grasping strength and motor activity are increased; these are all changes indicative of more rapid neuromuscular maturation. Prenatal peptide treatment elicits a more complex pattern of response since administration early in gestation (GD 3-12) accelerates neuromuscular development whereas later administration (GD 13-21) decelerates maturation. (3) ACTH peptides have a similar accelerating effect on the morphology of the developing neuromuscular junction. At two weeks of age, nerve arborization is conspicuously increased by postnatal administration of either ACTH 4-10 or Org 2766, as is nerve terminal branching within the endplate itself. However, this is preceded by an initial depression of nerve branching in the 7-day-old rat pup. We conclude that while the developing neuromuscular system is sensitive to ACTH peptides, this susceptibility is age-related. The crucial role of these peptides may be limited to very brief, defined periods during which the peptides may interact with trophic or growth-associated substances, each of which may have its own decisive, circumscribed time frame of influence. (4) Perinatal administration of ACTH peptides affects CNS development. One measurable indication of this is an acceleration of eye opening. Early exposure to ACTH peptides has long-lasting effects on behavior, apparent when these animals are tested as adults. Increased spontaneous motor activity, heightened states of arousal and agitation, and changes in social behavior have been reported. Certain avoidance responses and tests of visual discrimination in male rats are improved by neonatal treatment with alpha-MSH. Overall motor activity is increased and the normal period of hyperactivity is initiated earlier. Male sexual behavior is decreased and sexually dimorphic behaviors in males are eliminated. alpha-MSH may alter the development of its own dopaminergic feedback circuitry while ACTH affects serotonin levels in the preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Age-dependent deterioration of neuronal membranes and the pathogenesis of Alzheimer's disease: a hypothesis

Senile dementia of the Alzheimer's type (SDAT) is considered either a specific pathological condition unrelated to normal aging or an accumulation of brain aging alterations leading to clinical dysfunction. In the present paper a hypothesis is formulated to reconcile these two issues to a common denominator, i.e. the increased age-dependent deterioration of the neuronal membrane. If this holds true, normal aging and SDAT may be considered as two different aspects of the same problem and specific interventions to slow down the former can delay the onset of the latter to older ages.

AL721, a novel membrane fluidizer

AL721, which is a novel lipid mixture extracted from egg yolks, is believed to be a therapeutic pharmacologic agent. AL721 interacts with membranes of various types of cells with a common mode of action. AL721 modifies cellular membrane composition and fluidity through passive extraction and/or exchange of cholesterol. Physiologically diminished cell function due to rigidification of its membrane is reversible both in vitro and in vivo by AL721. Fluidization of aged membranes with AL721 has been shown to restore brain serotonin receptor function both in vitro and in vivo. AL721 can also successfully restore deficient immune responsiveness of lymphocytes to mitogen stimulation in aged subjects. Drug tolerance to morphine and ethanol develops upon elevation of the viscosity of neuronal cell membranes in order to counteract the fluidization effect of the drug. Treatment of rigidified cellular membranes with AL721 in vivo can markedly reduce withdrawal symptoms. The virucidal effect of AL721 on the human immunodeficiency virus is believed to operate by lowering of viral membrane cholesterol thus interfering with the binding of the viral antigen to the host cell. Non-toxicity of AL721 is clearly demonstrated in animal and human safety studies.

Neuropharmacology of S-adenosyl-L-methionine

The metabolite S-adenosyl-L-methionine (SAMe), when prepared as the stable p-toluene-sulfonate complex of its sulfate salt and given parenterally in high doses, appears to have mood-elevating effects in depressed adults. The material is remarkably well tolerated when given by injection or intravenous infusion for this purpose, even in elderly or demented patients. Assuming that the toluene sulfonate component is inert, SAMe appears to have central neuropharmacologic effects after systemic injection in high doses. Nevertheless, the functional consequences of these remain unclear and, indeed, the ability of exogenous SAMe to reach the brain, and especially neuronal cytoplasm, is limited. SAMe has small effects on monoamine metabolism and, after injection, appears to have effects on the microviscosity of cell membranes that may be related to stimulation of phospholipid synthesis. The recent introduction of an orally administered form of SAMe for use in the treatment of osteoarthritis promises to stimulate further study of SAMe in disease-associated depression, major depressive disorder, and other neuropsychiatric conditions.

Platelet membrane abnormality in Alzheimer's disease

Fluorescence studies of membrane fluidity were conducted double-blind using platelet and red cell membranes prepared from 24 demented patients with probable Alzheimer's disease and 36 neurologically healthy subjects. The fluidity of the hydrocarbon and lipid-aqueous interface regions of cell membranes was determined at 37 degrees C by fluorescence spectroscopy using the lipid probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), respectively. The rotation rate of TMA-DPH in labeled platelet membranes did not differ between the groups. In contrast, the rotation rate of DPH in labeled platelet membranes from the demented patients (2.15 +/- 0.24 X 10(8)/sec, SD) was greater than that for the normal controls (1.93 +/- 0.13 X 10(8)/sec, SD, p = 3.8 X 10(-5)). This difference was reflected by a reduction in the steady-state anisotropy of DPH in labeled platelets from the demented group (0.1887 +/- 0.0085, SD) when compared to the respective mean for the controls (0.2000 +/- 0.0060, SD; p = 1.3 X 10(-7)). Abnormal membrane fluidity was significantly correlated with severity of dementia, but not with duration of illness or apparent age of onset. The findings do not support the hypothesis that Alzheimer's disease results from a pathological acceleration of the normal aging process, since normal aging is associated with decreased fluidity of cell membranes from platelets, as well as from lymphocytes, hepatocytes, and neurons.

Effect of combined or separate administration of piracetam and choline on learning and memory in the rat

Different groups of rats received combined or separate administration of different doses of piracetam (P1:100, P2:200, and P4:400 mg/kg) and choline (C1:100 and C2:200 mg/kg). Compared to control treatment, C1 significantly improved performance in a delayed alternation (DA) task, while P1, P2, P4 or P1C1 had no effect. Moreover, rats receiving P2C1 and P4C1 were significantly inferior in acquiring DA to rats receiving the vehicle or separate administration of P1, P2 or C1. The different treatments with combined or separate administration of P and C had no effect on spontaneous locomotor activity and two-way avoidance conditioning. In a recognition-task only groups C1 and P4 were able to discriminate between familiar and new objects. The combined or separate administration of P1 and C1 on NA, DA, DOPAC, 5-HT, 5-HIAA levels, CAT activity and choline uptake were measured in frontal cortex and hippocampus: the only significant effect was a 5-HT increase in the hippocampus of rats treated with C1.

Hippocampal membrane alteration in Alzheimer's disease

The biophysical properties of hippocampal membrane preparations from patients with Alzheimer's disease were examined by fluorescence spectroscopy using the membrane lipid probe 1,6-diphenyl-1,3,5-hexatriene (DPH) and its cationic derivative 1-[4-(trimethylamino)-phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH). Results of these experiments suggest that Alzheimer's disease is associated with a biophysical alteration in superficial regions of brain cell membranes, as reflected by the mobility of TMA-DPH. In contrast, no change in the mobility of DPH, which preferentially localizes to the hydrocarbon core, was observed. Although a trend was observed for TMA-DPH mobility to parallel histopathologic severity in hippocampal specimens, the biophysical changes did not appear to reflect a loss of neuronal membranes relative to glial membranes or the presence of senile plaques or neurofibrillary tangles.

In vitro interaction of ACTH with rat brain muscarinic receptors

ACTH-(1-24) inhibits the in vitro binding of the muscarinic antagonist [3H]QNB to membranes from rat brain. The magnitude of inhibition is dependent on the concentration of ACTH-(1-24). Kinetic analysis indicates a pure competitive inhibition which is suggestive of a reversible interaction of ACTH with muscarinic receptors. A mechanism involving an interaction of ACTH-(1-24) with the phospholipid core of the receptors is suggested. Structure activity studies point to a relation with reported effects of intracerebroventricularly administered ACTH on the turnover rate of acetylcholine and the ACTH-induced stretching and yawning syndrome.

Melanocortins, neural plasticity and aging

Peptides derived from ACHT and alpha-MSH are known to exert trophic influences on peripheral and central nervous structures. Age-related brain diseases may in part be related to loss of neural plasticity. Melanocortins improve adaptional abilities of the nervous system. Chronic treatment with melanocortins may counteract age-related brain pathology.

Membrane fluidity and adenylate cyclase activity in the lacrimal glands of rats fed diets containing trans fatty acids

The effects of feeding a diet containing trans fatty acids on the fatty acid composition of plasma membrane phospholipids, fluorescence polarization of diphenylhexatriene (DPH) and adenylate cyclase activity in the exorbital lacrimal glands of rats were studied. Three groups of male, weanling rats were fed semipurified diets containing 20% corn oil (CO), 20% partially hydrogenated soybean oil (PHSBO) (a source of trans fatty acids) and 19% PHSBO + 1% CO. Plasma membranes of the lacrimal glands from rats fed 20% PHSBO showed higher adenylate cyclase activity and lower fluidity as shown by a lower double bond index of the fatty acids of their phospholipids and higher fluorescence polarization of DPH. When 1% CO was included with the diet containing PHSBO, the adenylate cyclase activity and membrane fluidity tended to be normal. The results suggest that feeding of a diet containing trans fatty acids in the absence of sufficient linoleic acid (18:2) can result in a decrease in membrane fluidity and an increase in adenylate cyclase activity in the lacrimal glands.

Intact human lymphocyte membranes respond to muscarinic receptor stimulation by oxotremorine with marked changes in microviscosity and an increase in cyclic GMP

The muscarinic agonist oxotremorine produced a linear dose-dependent increase in membrane fluidity of intact and viable human lymphocytes in vitro. This effect proved to be receptor-mediated because preincubation with 10(-5)M atropine shifted the dose-response curve one order of magnitude rightward. Pirenzepine preincubation did not affect membrane fluidity variation. A cGMP increase was also found after oxotremorine treatment. The results are discussed in terms of possible modulation of guanyl cyclase and adenyl cyclase through membrane fluidity variations.

Neurochemical aspects of depression: the past and the future?

The role of aberrant neurochemical substrates in the etiology of depression and the neurochemical mechanisms of antidepressant therapies have been the subjects of many hypotheses in the last 30 years. Pharmacological studies of early antidepressant drugs indicated that brain monoamines were significantly affected by these drugs and these led to the formulation of the biogenic amine hypothesis of depression. Although this hypothesis has been of heuristic value in the study of drug mechanisms and has provided a basis for screening drugs for antidepressant potential, deficiencies in it have become apparent. Neuroanatomical and neurochemical considerations favour the view that brain noradrenaline and serotonin systems may serve as bias adjusting systems for each other and numerous other neural systems. As a consequence of such a relationship, a primary defect in some other neural system would appear amplified in measurements of serotonin or noradrenaline. A possible site for this primary defect may be in membrane composition and function. Recent studies have found that typical and other antidepressant therapies have a pronounced effect on membrane lipids. Thus, in view of the important functions of membrane lipids and the fact that they have been linked to the initiation and development of a number of other disease processes, it is now suggested that consideration be given to them as playing primary causal roles in the etiology of depression and as a site of action for antidepressant drugs.

Chronic dietary choline modulates synaptic plasticity in the cerebellar glomeruli of aging mice

A morphometric investigation was carried out on ethanolic phosphotungstic acid (E-PTA) stained synaptic junctions in the cerebellar glomeruli of adult, old, old choline-deficient and old choline-supplemented mice. Numerical (Nv) and surface (Sv) density as well as average length (L) of the synapses were calculated on 100 pictures per group. A significant reduction of Nv and Sv, as well as an increase of L was found during aging. Choline deficient animals did not show any change as compared to old animals of the same age. In choline supplemented mice Nv and Sv were significantly increased and L significantly decreased, respectively, as compared to old control littermates. No difference was found between adult and choline supplemented mice. In the cerebellar glomeruli only a small fraction of fibers are cholinergic, therefore the present findings support the idea that dietary choline can influence systems other than cholinergic. The possible role of choline supplementation in the modulation of synaptic plasticity via the synthesis and/or turnover of neuronal membrane choline phospholipids, is discussed.

Effects of dietary choline on memory and brain chemistry in aged mice

The purpose of this study was to investigate in more detail the characteristics of the age-related extension of the retrograde amnesia gradient previously demonstrated in a passive avoidance task [6]. In Experiment 1, it was found that while 2-3 month old mice were susceptible to the amnesic effects of anisomycin (ANI) only when given prior to 15 min post-training, memory of 14-16 month old mice was susceptible to disruption when ANI was given as late as 20 min post-training, and retention of 17-20 month old mice was impaired when ANI was injected even as late as 30 min after training. Experiment 2 examined whether the age-related change in susceptibility to the effects of ANI could be ameliorated by chronic pretreatment with a choline-enriched diet. Results showed that ANI injected 20 min after training did not induce amnesia in choline treated mice (14.5 month old), but did induce amnesia when injected 15 min post training. Subsequent assay of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) activity showed that choline treatment significantly reduced ChAT activity but did not affect TH activity. It appears that dietary choline treatment can render new long-term memories less susceptible to disruption following training.

Effect of ethanol and aging on histamine release and membranes of mast cells

The effects of ethanol on histamine release from mast cells were compared to ethanol's effects on membrane order of mast cell membranes and synaptosomes in young (6 month) and old (24 month) Fischer 344 rats. Concanavalin A (con A) stimulated histamine release in a concentration dependent manner. Ethanol (10-500 mM) inhibited con A stimulated release while having no effect on nonstimulated release in both young and old rats. Ethanol's effect on membrane order of synaptosomes and mast cell plasma membranes was estimated by measuring the fluorescence polarization of diphenylhexatriene. Ethanol (10-500 mM) decreased the polarization of synaptosomes to the same degree in young and old rats. The polarization of mast cell membranes was also decreased by ethanol but to a greater degree than synaptosomes. The ethanol induced changes in polarization correlated (r2 = 0.99) with ethanol's inhibition of con A stimulated histamine release from mast cells. These findings suggest that mast cells may be more sensitive to membrane disordering by ethanol than synaptosomes. In addition, we have demonstrated that mast cells may be a useful model system for studying ethanol effects on stimulus-secretion coupling. No differences were found between rats 6 and 24 months for histamine release (with or without ethanol) or membrane order of mast cells or synaptosomes.

Effects of aging on the lipid order and composition of rat adipocyte ghosts

An analysis of the cholesterol/phospholipid ratio of adipocyte ghosts from rat epididymal fat pads shows a significant increase with age (P less than 0.005). An attempt to correlate these changes with the order of the lipid matrix was made using the stearic acid spin label 2-(3-carboxypropyl)-4, 4-dimethyl-2-tridecyl-3-oxazolidinyloxyl [I(12,3)]. Although order was negatively correlated with temperature in preparations from both 6- and 24-month-old rats, no effect of age could be detected.