Search PubMed⌕ Search

Biomedical subjects

N Salem

Publications and source records attributed to N Salem.

At least 91 records · Page 5Linked to original sources
PubMed1996

Quantal acetylcholine release induced by mediatophore transfection.

Mediatophore is a protein of approximately 200 kDa able to translocate acetylcholine in response to calcium. It was purified from the presynaptic plasma membranes of the electric organ nerve terminals. Mediatophore is a homooligomer of a 16-kDa subunit, homologous to the proteolipid of V-ATPase. Cells of the N18TG-2 neuronal line are not able to produce quantal acetylcholine release. We show here that transfection of N18TG-2 cells with a plasmid encoding the mediatophore subunit restored calcium-dependent release. The essential feature of such a release was its quantal nature, similar to what is observed in situ in cholinergic synapses from which mediatophore was purified.

Acetylcholine↗
PubMed1996

Arachidonic and docosahexaenoic acids are biosynthesized from their 18-carbon precursors in human infants.

It is becoming clear that an adequate level of long-chain highly unsaturated fatty acids in the nervous system is required for optimal function and development; however, the ability of infants to biosynthesize long-chain fatty acids is unknown. This study explores the capacity of human infants to convert 18-carbon essential fatty acids to their elongated and desaturated forms, in vivo. A newly developed gas chromatography/negative chemical ionization/mass spectrometry method employing 2H-labeled essential fatty acids allowed assessment of this in vivo conversion with very high sensitivity and selectivity. Our results demonstrate that human infants have the capacity to convert dietary essential fatty acids administered enterally as 2H-labeled ethyl esters to their longer-chain derivatives, transport them to plasma, and incorporate them into membrane lipids. The in vivo conversion of linoleic acid (18:2n6) to arachidonic acid (20:4n6) is demonstrated in human beings. All elongases/desaturases necessary for the conversion of linolenic acid (18:3n3) to docosahexaenoic acid (22:6n3) are also active in the first week after birth. Although the absolute amounts of n-3 fatty acid metabolites accumulated in plasma are greater than those of the n-6 family, estimates of the endogenous pools of 18:2n6 and 18:3n3 indicate that n-6 fatty acid conversion rates are greater than those of the n-3 family. While these data clearly demonstrate the capability of infants to biosynthesize 22:6n3, a lipid that is required for optimal neural development, the amounts produced in vivo from 18:3n3 may be inadequate to support the 22:6n3 level observed in breast-fed infants.

Arachidonic Acid↗
PubMed1996

Artificial rearing of infant rats on milk formula deficient in n-3 essential fatty acids: a rapid method for the production of experimental n-3 deficiency.

Research into the function of docosahexaenoic acid (DHA; 22:6n-3), the predominant polyunsaturated fatty acid (PUFA) in the central nervous system (CNS), is often hindered by the difficulty in obtaining dramatic experimental decreases in DHA in the brain and retina of laboratory rats. In this study, the artificial rearing procedure, whereby infant rats are removed from their mothers, gastrostomized, and fed synthetic formula, was used in an attempt to produce rapid changes in CNS levels of DHA. Female rats were raised, from day 4-5 of life, on one of two formulas-one containing the essential fatty acids of both the n-6 and n-3 series in proportions approximately equal to those of rat milk, and the other containing high levels of 18:2n-6 but very little n-3 fatty acid. At weaning, both groups were given AIN-76A diets modified so that the PUFA content resembled that of the preweaning formula. At eight weeks of age, the n-3-deficient group exhibited decreases of more than 50% in total DHA content in the brain, accompanied by increases in arachidonic acid (AA) (20:4n-6) and, especially, docosapentaenoic acid (22:5n-6). Other artificially-reared rats were mated and their offspring were also maintained on the respective diets. In spite of the fact that they had been reared artificially, the rats mated successfully and reared litters with no obvious abnormalities. At both ten days of age and again at eight weeks, offspring of the n-3-deficient mothers exhibited decreases of more than 90% in total DHA content. Again, the long-chain n-6 PUFA increased proportionately so that total PUFA levels in the brain were not lower. As these differences are greater than those commonly reported, even after 2-3 generations of normal dietary deprivation in rodents, this procedure may be an important tool in the study of the effects of n-3 deficiency on neural development and, subsequently, of the function of DHA in nervous tissue.

Animals↗
PubMed1996

Essential fatty acid uptake and metabolism in the developing rodent brain.

Studies were carried out to determine whether the brain takes up and metabolizes essential fatty acids during early postnatal development in rodents. Rats and mice were dosed with deuterium-labeled linoleic and linolenic acids either by intraperitoneal injection or by gavage. Animals were killed at different times thereafter, and organs were removed. Brains, livers, and blood were analyzed by gas chromatography--negative-ion-mass spectrometry for labeled fatty acids. To determine whether fatty acids were present in the brain apart from cerebral blood, a subset of animals was exsanguinated by perfusion with buffered saline, and the brain was then fractionated into subcellular components. Results demonstrated that the brain took up both labeled essential fatty acids within 8 h from the time of dosing. There was on average a greater uptake of linolenic acid into the cerebellum than into the cerebral cortex during the first 8 d of life in rats. The amount of linoleic acid taken into either region was similar, however. Docosahexaenoic acid intermediates, 20:5n-3 and 22:5n-3, were also found labeled in the brain. Time-course labeling experiments indicated that these intermediates may be converted to 22:6n-3 within the brain. A rise of labeled 22:6n-3 in the brain at 24 h appeared to be due to uptake of this fatty acid from the blood. The amount of labeled 22:6n-3 in the brain continued to increase beyond 24 h, and this did not appear to be correlated with its blood concentration. These results suggest that, during development in the rodent, different regions within the brain may vary in their capacity to synthesize 22:6n-3, and this may be correlated with regional growth rates.

Administration, Oral↗
PubMed1996

Losses of arachidonic acid in rat liver after alcohol inhalation.

This paper presents an animal model of alcoholism in which rats were exposed to alcohol by inhalation and were fed a diet that simulated the poor diet of some alcoholics. It is hypothesized that some of the pathophysiological effects of alcohol are related to its effects on essential fatty acid metabolism and composition of vital organs. A diet that contains no 20- and 22-carbon essential fatty acids and has low levels of 18-carbon essential fatty acids was used as a dietary challenge. Addition of a second metabolic challenge, i.e., alcohol, led to loss of tissue polyunsaturates, particularly liver arachidonate. A method of cycling alcohol inhalation for 12 h/d was also presented, which was also shown to lower liver arachidonic acid content.

Administration, Inhalation↗
PubMed1996

The structure-activity relationship of lipoxygenase products of long-chain polyunsaturated fatty acids: effects on human platelet aggregation.

The effect of hydroperoxy and hydroxy derivatives of various fatty acids on human platelet aggregation was determined to delineate potencies and structure-activity function. In this regard, the 22-carbon n-3 fatty acids are the most potent inhibitors in comparison to the n-6 lipoxygenase derivatives. Submicromolar levels of the docosapentaenoic (22:5) and especially docosahexaenoic (22:6) n-3 hydroperoxy and hydroxy derivatives specifically antagonize the platelet aggregating effect to arachidonic acid (AA, 20:4n-6) but not that of ADP or collagen. Chain length (22-C > 20-C), double-bond position (n-3 > n-6), and double-bond number (6 > 5 > 4) influence the degree of inhibition of AA-induced aggregation of human platelets. Moreover, significant differences in potency were associated with specific structural aspects of 22:6n-3 lipoxygenase derivatives of 22:6n-3 as follows: functional group (OOH > OH) and positional isomer (14-OOH, 14-OH, 20-OOH > 11-OOH, 17-OOH > 10-OOH > 11-OH, 8-OOH, 7-OOH > 4-OOH).

Arachidonic Acid↗
PubMed1996

Docosahexaenoic acid block of neuronal voltage-gated K+ channels: subunit selective antagonism by zinc.

The omega-3 polyunsaturated fatty acid docosahexaenoic acid is highly enriched in neuronal membranes, and several studies suggest that DHA is critical for neuronal development. We have investigated the effects of exogenously applied DHA on voltage-gated K+ channels using patch-clamp techniques. DHA produced a concentration-dependent inhibition of the sustained outward current in isolated neocortical neurons. This blocking action was examined in more detail with two cloned neuronal K+ channels (Kv1.2 and Kv3.1a) expressed in mammalian fibroblasts. DHA produced a potent inhibition of depolarization-activated K+ currents from cells expressing these channels (Kd values, 1.8 +/- 0.1 muM and 690 +/- 60 nM, for Kv1.2 and Kv3.1a, respectively, at +40 mV). The DHA block of both channel types was rapidly reversed (approximately 2 sec) by bovine serum albumin, which binds the fatty acid. Micromolar concentrations of extracellular Zn2+ non-competitively antagonized DHA inhibition of Kv1.2 channels, whereas there was little effect on DHA block of Kv3.1a channels. Experiments with membrane patches from Kv1.2 transfected cells demonstrated that the DHA block occurred from the outside, suggesting that the fatty acid interacts directly with an external domain of the ion channel. DHA may serve as a local messenger molecule that selectively modulates the activity of certain voltage-gated K+ channels in a Zn2(+)-dependent fashion.

Animals↗
PubMed1996

Anandamide, an endogenous cannabinoid, inhibits Shaker-related voltage-gated K+ channels.

Anandamide has been identified in porcine brain as an endogenous cannabinoid receptor ligand and is believed to be a counterpart to the psychoactive component of marijuana, delta 9-tetrahydrocannabinol (delta 9-THC). Here we report that anandamide directly inhibits (IC50, 2.7 muM) Shaker-related Kv1.2 K+ channels that are found ubiquitously in the mammalian brain. Delta 9-THC also inhibited Kv1.2 channels with comparable potency (IC50, 2.4 muM), as did several N-acyl-ethanolamides with cannabinoid receptor binding activity. Potassium current inhibition occurred through a pertussis toxin-insensitive mechanism and was not prevented by the cannabinoid receptor antagonist SR141716A. Utilizing excised patches of Kv1.2 channel-rich membrane as a rapid and sensitive bioassay, we found that phospholipase D stimulated the release of an endogenous anandamide-like K+ channel blocker from rat brain slices. Structure-activity studies were consistent with the possibility that the released blocker was either anandamide or another N-acyl-ethanolamide.

Animals↗
PubMed1996

Evoked acetylcholine release expressed in neuroblastoma cells by transfection of mediatophore cDNA.

Transmitter release was elicited in two ways from cultured cells filled with acetylcholine: (a) in a biochemical assay by successive addition of a calcium ionophore and calcium and (b) electrophysiologically, by electrical stimulation of individual cells and real-time recording with an embryonic Xenopus myocyte. Glioma C6-Bu-1 cells were found to be competent for Ca(2+)-dependent and quantal release. In contrast, no release could be elicited from mouse neuroblastoma N18TG-2 cells. However, acetylcholine release could be restored when N18TG-2 cells were transfected with a plasmid coding for mediatophore. Mediatophore is a protein of nerve terminal membranes purified from the Torpedo electric organ on the basis of its acetylcholine-releasing capacity. The transfected N18TG-2 cells expressed Torpedo mediatophore in their plasma membrane. In response to an electrical stimulus, they generated in the myocyte evoked currents that were curare sensitive and calcium dependent and displayed, discrete amplitude levels, like in naturally occurring synapses.

Acetylcholine↗
PubMed1996

A gene responsible for a sensorineural nonsyndromic recessive deafness maps to chromosome 2p22-23.

The recessive mode of transmission accounts for approximately 75% of inherited non syndromic deafness cases. We have previously designed the conditions for linkage studies of this highly heterogeneous disorder [Guilford et al. (1994) Nature Genet. 6, 24-28]. Here, using a similar approach, we have studied the segregation of a gene responsible for congenital, profound and fully penetrant sensorineural deafness in a consanguineous family living in an isolated region of Lebanon. A maximum lod score of 8.03 (theta = 0.00) was detected with a new polymorphic marker, AFMa052yb5 (D2S2144). Observed recombinants and homozygosity mapping define a maximum interval of 2 cM for this gene, DFNB6, which lies between AFMb346ye5 (a new polymorphic marker) (D2S2303) and AFM254vc9 (D2S174) on chromosome 2p22-23.

Base Sequence↗
PubMed1996

Mapping of DFNB12, a gene for a non-syndromal autosomal recessive deafness, to chromosome 10q21-22.

We report here, the localization of a new recessive non-syndromal deafness gene (DFNB12) to 10q21-22 by linkage analysis, of a Sunni family. Affected individuals suffer from congenital profound sensorineural hearing loss. A maximum LOD score of 6.40 (theta = 0.00) was obtained with locus D10S535. Analysis of patients carrying recombinations mapped the gene distal to D10S529 and proximal to D10S532, delineating an interval between 11 and 15 cM. Three deaf mouse mutants Jackson circler (jc), Waltzer (v) and Ames waltzer (av) have been localized to the homologous murine region on chromosome 10. Each of these mouse mutants is a candidate mouse model for the DFNB12-associated hearing impairment.

Adolescent↗
PubMed1996

Is dietary arachidonic acid necessary for feline reproduction?

A study was carried out to determine whether corn oil-based diets devoid of arachidonic acid, 20:4(n-6), are capable of supporting feline reproduction. One group of four adult female felines were acclimated to a 10 weight% (wt%) fat diet consisting of 1 wt% corn oil and 9 wt% hydrogenated coconut oil for 1 mo before mating. One female produced two live offspring, and the other three females delivered either stillborn fetuses or offspring that were severely deformed and died shortly after birth. Two of these females were subsequently placed on a 1 wt% corn oil diet that was supplemented with 20:4(n-6) (200 mg/ kg of diet), and after 2 mo they were mated. Offspring resulting from the second mating were healthy. A third group of females that were maintained on a 10 wt% fat diet consisting of 3 wt% corn oil were also mated. The offspring from these matings appeared healthy at birth. Neonates from each diet group were killed, and the fatty acyl composition of the livers, plasma and brains was analyzed. In the offspring livers and plasma, the level of 20:4(n-6) from both the 1 wt% or 3 wt% corn oil diet groups was about half that of offspring from those receiving 20:4(n-6) in the diet. There were no differences in the level of 20:4(n-6) in the neonate brains among any of the groups. This study suggests that nutritional factors unrelated to the tissue accumulation of arachidonic acid in the offspring may be responsible for the high percentage of stillbirths and deformities associated with maternal diets containing low amounts of essential fatty acids but that diets that contain a higher percentage of corn oil can support feline reproduction.

Animals↗
PubMed1996

Is docosahexaenoic acid necessary in infant formula? Evaluation of high linolenate diets in the neonatal rat.

Neural accretion of docosahexaenoic acid (DHA) is thought to play an important role in the neural development of human infants. The lack of DHA in infant formulas contributes to the lowered neural accretion of DHA observed in formula-fed infants relative to those breast-fed. We hypothesized that lowering the dietary linoleic acid (LA) to alpha-linolenic acid (LNA) ratio may lead to increases in the level of DHA in the developing brain and retina. Lowering the LA to LNA ratio from 10:1 to 1:1 and to 1:12 in the artificially reared (AR) neonatal rat pup resulted in a significant increase in the percentage of brain DHA between AR dietary groups. The brain level of DHA in the AR group fed a 1:12 ratio was similar to that of a dam-reared reference group. However, levels of DHA in the retina of all AR groups were significantly lower than that of the (chow fed) dam-reared group. It appears that LNA may serve as an adequate substrate for the accretion of DHA in the brain, but not the retina of the developing rat. In both the brain and the retina, levels of arachidonic acid in the AR pups fed the 1:1 ratio were similar to that of the dam-reared group. However, levels in the 1:12 group were significantly reduced. The addition of long chain n-3 polyunsaturates such as DHA to infant formula may therefore be necessary for adequate neural DHA accretion and optimal neural development.

Animal Feed↗
PubMed1995

Hydroxylated 22-carbon fatty acids in platelet and vascular smooth muscle function: interference with TXA2/PGH2 receptors.

Sub-micromolar levels of the lipoxygenase products of n-3 fatty acids specifically antagonize both the contractile effects of thromboxane (U46619) and its platelet aggregating effect. In addition, OH-22:6n3 inhibits thromboxane-induced decreases in cerebral blood flow of the rat. Analysis of binding parameters indicates these derivatives induce a marked decrease in the affinity of the TXA2/PGH2 receptor for thromboxane with a mild change in the number of receptor sites. The 22-carbon n-3 hydroxy fatty acids are the most potent biological antagonists of thromboxane in comparison to the n-6 hydroxy fatty acids and their parent fatty acids. Dietary permutations modify the hydroxy fatty acid profile and correlate with changes in thromboxane-mediated responses.

Animals↗
PubMed1995

Ethanol exposure causes a decrease in docosahexaenoic acid and an increase in docosapentaenoic acid in feline brains and retinas.

Alcohol altered the fatty acyl composition of the liver, brain, and retina of domestic felines that were maintained on a diet having low, but adequate, amounts of essential fatty acids. For 8 mo, seven adult cats were provided a diet with 10% fat (by wt), consisting of 9:1 ratio of hydrogenated coconut oil:corn oil. During 6 of these 8 mo, four of the cats were given oral daily doses of a 95% ethanol solution (1.2 g.kg-1.d-1). Cats were killed and the fatty acyl composition of tissues were determined. In the plasma and livers of the alcohol-exposed animals, there were significant decreases in the concentrations of 18:2 omega 6, 20:4 omega 6, 22:5 omega 3, and 22:6 omega 3 and increases in the concentrations of the nonessential fatty acids 16:1 omega 7, 18:1 omega 9, and 20:3 omega 9. In the brains and retinas of the alcohol-exposed animals, 22:6 omega 3 decreased by 17% and there was a compensatory increase in 22:5 omega 6. In the retinas, the concentration of 22:5 omega 6 increased by 250%. The reciprocal change in the ratio of 22:6 omega 3 to 22:5 omega 6 is known to be associated with a loss in nervous system function and may provide a biochemical mechanism underlying some of the neuropathology associated with alcoholism.

Animals↗
PubMed1995

Dietary polyunsaturated fatty acids and depression: when cholesterol does not satisfy.

Recent studies have both offered and contested the proposition that lowering plasma cholesterol by diet and medications increases suicide, homicide, and depression. Significant confounding factors include the quantity and distribution of dietary n-6 and n-3 polyunsaturated essential fatty acids that influence serum lipids and alter the biophysical and biochemical properties of cell membranes. Epidemiological studies in various countries and in the United States in the last century suggest that decreased n-3 fatty acid consumption correlates with increasing rates of depression. This is consistent with a well-established positive correlation between depression and coronary artery disease. Long-chain n-3 polyunsaturate deficiency may also contribute to depressive symptoms in alcoholism, multiple sclerosis, and post-partum depression. We postulate that adequate long-chain polyunsaturated fatty acids, particularly docosahexaenoic acid, may reduce the development of depression just as n-3 polyunsaturated fatty acids may reduce coronary artery disease.

Cholesterol↗
PubMed1995

Time- and voltage-dependent block of delayed rectifier potassium channels by docosahexaenoic acid.

Docosahexaenoic acid (22:6n3) acts at an extracellular site to produce a voltage- and time-dependent block of the delayed rectifier current (IK) similar to that classically described for intracellularly applied quaternary ammonia compounds. In dissociated cells from the pineal gland, some long-chain polyunsaturated fatty acids reduced both late sustained (IK) (for 22:6n3, IC50 = 2.5 +/- 0.3 microM) and early transient (IA) (IC50 = 2.0 +/- 0.1 microM) components of potassium current when applied extracellularly, whereas the monounsaturate oleic acid had minimal efficacy. From comparisons of other related fatty acids, it was determined that there is a structural requirement for polyunsaturation to block IK. In contrast, chain-elongated 22-carbon polyunsaturates acted similarly to their precursor 20-carbon fatty acids (arachidonic acid and eicosapentanoic acid). Block of IK by 22:6n3 was accompanied by a dose-dependent acceleration of the current decay in both whole-cell and outside-out membrane patches, and 22:6n3 increased the macroscopic inactivation rate of IA. The combined "eicosanoid" inhibitor eicosatetraenoic acid, when included in the patch pipette, did not antagonize the action of 22:6n3. Instead, eicosatetraenoic acid produced a direct block of IK when applied extracellularly at high concentrations (25 microM). Analyses of voltage- and time-dependent block by 22:6n3 support the hypothesis that certain fatty acids directly interact with and preferentially block the open state of some potassium channels. We also describe an interaction between fatty acid block and zinc; 22:6n3 failed to block either IA or IK in the presence of zinc or cadmium, whereas extracellular calcium did not affect the response. These studies suggest a possible biological function for 22:6n3 in the nervous system, which may underlie its essential role during neural development.

Animals↗