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A Arduini

Publications and source records attributed to A Arduini.

At least 37 records · Page 2Linked to original sources
PubMed1998

Role of acetyl-L-carnitine in rat brain lipogenesis: implications for polyunsaturated fatty acid biosynthesis.

This study was undertaken to explore the metabolic fate of acetyl-L-carnitine in rat brain. To measure the flux of carbon atoms into anabolic processes occurring at regional levels, we have injected [1-(14)C]acetyl-L-carnitine into the lateral brain ventricle of conscious rats. After injection of [1-(14)C]acetyl-L-carnitine, the majority of radioactivity was recovered as 14CO2 expired (60% of that injected). The percentage of radioactivity recovered in brain was 1.95, 1.60, 1.30, and 0.93% at 1, 3, 6, and 22 h, respectively. Radioactivity distribution in various lipid components indicated that the fatty acid moiety of phospholipid contained the majority of radioactivity. The radioactive profile of these fatty acids showed that the acetyl moiety of acetyl-L-carnitine was incorporated into saturated (60%), monounsaturated (15%), and polyunsaturated (25%) fatty acids [mainly present in 20:4 (5.2%) and 22:6 (7.8%)]. Injection in the brain ventricle of radioactive glucose, the major source of acetyl-CoA in the CNS, revealed that glucose was a precursor of saturated (85%) and monounsaturated (15%) but not of polyunsaturated fatty acids. Thus, this study demonstrated distinct fates of glucose and acetyl-L-carnitine following intracerebroventricular injection. In summary, these data implicate acetyl-L-carnitine as an important member of a complex acetate trafficking system in brain lipid metabolism.

Acetylcarnitine↗
PubMed1997

Recognition of cationic species with synthetic receptors.

In the past year progress in the study of cationic species has been made, particularly in our understanding of the factors which control the selective recognition of biologically important cations such as ammonium, alkali and alkaline earth metal ions, and of metal ions used in biomedicine such as lanthanides and iron(III). Based on this knowledge, several new hosts with improved transport, photophysical and biological properties have been designed.

Binding Sites↗
PubMed1997

Addition of L-carnitine to additive solution-suspended red cells stored at 4 degrees C reduces in vitro hemolysis and improves in vivo viability.

BACKGROUND: The role of L-carnitine (LC) as the requisite carrier of long-chain fatty acids into mitochondria is well established. Human red cells (RBCs), which lack mitochondria, possess a substantial amount of LC and its esters. In addition, carnitine palmitoyl transferase, an enzyme that catalyzes the reversible transfer of the acyl moiety from acyl-coenzyme A to LC is found in RBCs. It has recently been shown that LC and carnitine palmitoyl transferase play a major role in modulating the pathway for the turnover of membrane phospholipid fatty acids in intact human RBCs, and that LC improved the membrane stability of RBCs subjected to high shear stress. RBC membrane lesions occur during storage at 4 degrees C; this study investigated whether the addition of LC (5 mM) to a standard RBC preservative solution (AS-3) affected cellular integrity with 42 days' storage. STUDY DESIGN AND METHODS: A paired (n = 10) crossover design was used for RBCs stored in AS-3 with and without LC. Both in vitro RBC properties reflective of metabolic and membrane integrity and in vivo measures of cell viability (24-hour percentage of recovery and circulating lifespan) were measured at the end of the storage. In addition, the turnover of membrane phospholipid and long-chain acylcarnitine fatty acids and the carnitine content of control and LC-stored RBCs were measured. RESULTS: It was shown that LC was irreversibly taken up by RBCs during storage, with a fourfold increase at 42 days. Furthermore, as found by the use of radiolabeled palmitate, the stored RBCs were capable of generating long-chain acylcarnitine. The uptake of LC during storage was associated with less hemolysis and higher RBC ATP levels and by a significantly greater in vivo viability for LC-stored RBCs than for control-stored RBCs: a mean 24-hour percentage of recovery of 83.9 +/- 5.0 vs. 80.1 +/- 6.0 percent and a mean lifespan of 96 +/- 11 vs. 86 +/- 14 days, respectively (p < 0.05). CONCLUSION: A beneficial effect of the addition of LC to RBCs stored at 4 degrees C was evident. This effect may be related to both biophysical and metabolic actions on the cell membrane.

Adenine↗
PubMed1997

Acetyl-L-carnitine flux to lipids in cells estimated using isotopomer spectral analysis.

Acetyl-L-carnitine is known as a reservoir of activated acetyl units and as a modulator of metabolic function. The objective of this study was to quantify the fate of the acetyl moiety of acetyl-L-carnitine in lipogenic pathways. Lipogenesis was studied in an adipocyte model, differentiated 3T3-L1 cells, and a hepatoma cell, HepG2 cells. Lipogenesis and ketogenesis were examined in rat hepatocytes. Both de novo synthesis and elongation of fatty acids were investigated using gas chromatography/mass spectrometry and [1,2-(13)C]acetyl-L-carnitine. Comparisons were performed with [13C]glucose and [13C]acetate. Isotopomer Spectral Analysis, a stable isotope method for differentiating between the enrichment of the precursor and the amount of synthesis was used to analyze the data. Acetyl-L-carnitine was generally less effective than acetate as a precursor for de novo lipogenesis. The effects of acetyl-L-carnitine were not identical to those of acetate plus carnitine as expected if acetyl-L-carnitine flux to acetyl CoA is controlled by carnitine acetyl transferase. Acetyl-L-carnitine (2 mM) contributed approximately 10% of the lipogenic acetyl-CoA used for synthesis and elongation as well as 6% of the ketogenic acetyl-CoA. No differences were found between the precursor enrichment for de novo lipogenesis and for elongation of saturated fatty acids. Flux of acetyl-L-carnitine to lipid was increased, not decreased, by the ATP citrate lyase inhibitor, -hydroxycitrate. In contrast, flux of glucose to lipid was dramatically decreased by this inhibitor. These results indicate that flux of acetyl-L-carnitine to lipid can bypass citrate and utilize cytosolic acetyl-CoA synthesis.

3T3 Cells↗
PubMed1996

Hypoxanthine and xanthine levels in human aqueous humor from cataractous eyes.

Purine nucleotide degradation products have been determined by HPLC in aqueous humor obtained during cataract surgery and from plasma of 22 patients (12 women). Uric acid, cytosine, guanosine monophosphate, uracyl, guanine, adenosine, adenosine monophosphate, thymine, adenine, inosine, cyclic guanosine monophosphate, hypoxanthine and xanthine were evaluated. Uric acid and the last two were the only compounds detectable in measurable amounts in aqueous humor and in plasma of all patients. Aqueous humor xanthine levels were not significantly different from plasma; aqueous humor hypoxanthine concentrations were lower than those of xanthine and than plasma oxypurine levels. In 8 patients, treated with allopurinol, oxypurinol concentrations in aqueous humor and in plasma were comparable suggesting that oxypurines are transported through the blood-aqueous humor barrier.

Aqueous Humor↗
PubMed1996

L-carnitine and acetyl-L-carnitine in human nerves from normal and diabetic subjects.

Marked reduction in the contents of L-carnitine and acetyl-L-carnitine has been reported in peripheral nerves of rats with experimental diabetes. Since these substances have been claimed to improve a number of signs and symptoms of peripheral neuropathy in controlled clinical trials, this study was aimed at assessing whether nerves from diabetic subjects would also reveal similar decrease in the concentration of L-carnitine and acetyl-L-caritine. To this end, these substances were measured in nerves obtained from 11 patients with diabetic neuropathy, 13 patients with ischemic non-diabetic neuropathy, and 12 normal controls. Nerves from patients with either diabetic neuropathy and ischemic non-diabetic neuropathy showed levels of both carnitines lower than those from normal controls. However, differences among the three groups were not statistically significant, indicating that a reduction in these amino acids probably represents only a co-factor in the development of the variegated clinical picture of human diabetic neuropathy.

Acetylcarnitine↗
PubMed1996

High performance liquid chromatography of long-chain acylcarnitine and phospholipids in fatty acid turnover studies.

In this paper we describe a rapid, isocratic high performance liquid chromatography (HPLC) method for the study of radioactive fatty acid incorporation into complex lipids of human erythrocytes, which allows the simultaneous separation of the major phospholipid classes and long-chain acylcarnitines. The lipid extract of erythrocytes pulsed with radioactive fatty acids was injected into an HPLC system equipped with a silica column. The individual components eluted were monitored by ultraviolet absorption and radioactive emission. With respect to the UV profile, the radioactive profile showed an additional peak between phosphatidyl-choline and phosphatidylethanolamine, which was identified as long-chain acylcarnitine by different experimental approaches. The radioactivity recovered in the long-chain acylcarnitines contains essential information enabling definition of acyl trafficking in red cells.

Carnitine↗
PubMed1995

Effect of propionyl-L-carnitine treatment on membrane phospholipid fatty acid turnover in diabetic rat erythrocytes.

In this work we have examined the effect of the oral administration of propionyl-L-carnitine (PLC) on the membrane phospholipid fatty acid turnover of erythrocytes from streptozotocin-induced diabetic rats. A statistically significant reduction in radioactive palmitate, oleate, and linoleate, but not arachidonate, incorporation into membrane phosphatidylcholine (PC) of diabetic rat erythrocytes with respect to control animals was found. Changes in radioactive fatty acid incorporation were also found in diabetic red cell phosphatidylethanolamine (PE), though they were not statistically significant. Oral propionyl-L-carnitine (PLC) treatment of diabetic rats partially restored the ability of intact red cells to reacylate membrane PC with palmitate and oleate, and reacylation with linoleate was fully restored. The analysis of the membrane phospholipid fatty acid composition revealed a consistent increase of linoleate levels in diabetic rat red cells, a modest decrease of palmitate, oleate and arachidonate. The phospholipid fatty acid composition of diabetic red blood cells was not affected by the PLC treatment. Lysophosphatidylcholine acyl-CoA transferase (LAT) specific activity measured with either palmitoyl-CoA or oleyl-CoA was significantly reduced in diabetic erythrocyte membranes in comparison to controls. In addition, LAT kinetic parameters of diabetic erythrocytes were altered. The reduced LAT activity could be partially corrected by PLC treatment of diabetic rats. Our data suggest that the impaired erythrocyte membrane physiological expression induced by the diabetic disease may be attenuated by the beneficial activity of PLC on the red cell membrane phospholipid fatty acid turnover.

Administration, Oral↗
PubMed1995

Characterization and subcellular localization of L-[3H] carnitine binding sites in rat brain.

In the present study, we investigated the existence of a binding site for L-carnitine in the rat brain. In crude synaptic membranes, L-[3H]carnitine bound with relatively high affinity (KD = 281 nM) and in a saturable manner to a finite number (apparent Bmax value = 7.3 pmol/mg of protein) of binding sites. Binding was reversible and dependent on protein concentration, pH, ionic strength, and temperature. Kinetic studies revealed a Koff of 0.018 min-1 and a Kon of 0.187 x 10(-3) min-1 nM-1. Binding was highest in spinal cord, followed by medulla oblongata-pons > or = corpus striatum > or = cerebellum = cerebral cortex = hippocampus = hypothalamus = olfactory bulb. L-[3H]Carnitine binding was stereoselective for the L-isomers of carnitine, propionylcarnitine, and acetylcarnitine. The most potent inhibitor of L-[3H]carnitine binding was L-carnitine followed by propionyl-L-carnitine. Acetyl-L-carnitine and isobutyryl-L-carnitine showed an affinity approximately 500-fold lower than that obtained for L-carnitine. The precursor gamma-butyrobetaine had negligible activity at 0.1 mM. L-Carnitine binding to rat crude synaptic membrane preparation was not inhibited by neurotransmitters (GABA, glycine, glutamate, aspartate, acetycholine, dopamine, norepinephrine, epinephrine, 5-hydroxytryptamine, histamine) at a final concentration of 0.1 mM. In addition, the binding of these neuroactive compounds to their receptors was not influenced by the presence of 0.1 mM L-carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Evidence for the involvement of carnitine-dependent long-chain acyltransferases in neuronal triglyceride and phospholipid fatty acid turnover.

This study focuses on the potential involvement of carnitine palmitoyltransferase (CPT) on the phospholipid and triglyceride fatty acid turnover in neurons. This category of enzymes, which has been identified in several rat brain tissues, is well known for its role in modulating cellular fatty acid oxidation. Neuronal cell cultures from rat brain cortex incorporated radioactive palmitate or oleate into phospholipids and triglycerides. The largest fraction of radioactive fatty acids was recovered in phosphatidylcholine followed by triglycerides and, to a lesser extent, phosphatidylethanolamine. CPT activity measured in neuronal lysates obtained from neurons treated with 40 microM 2-tetradecylglycidic acid (TDGA) was almost completely abolished. Furthermore, between 2 and 10 microM TDGA CPT activity dropped more rapidly than between 10 and 40 microM. When the cells were pretreated with TDGA, the incorporation process of either radioactive fatty acid into triglycerides was dose-dependently suppressed. Radioactive fatty acid incorporation into phosphatidylcholine was significantly decreased in cells treated with TDGA. In contrast, phosphatidylethanolamine reacylation was essentially not affected by the CPT inhibitor. Similar results on the fatty acid incorporation into triglycerides and phospholipids were observed with neurons treated with palmitoyl-DL-aminocarnitine (PAC), a reversible CPT inhibitor, which does not consume free CoA. These effects do not seem to be the result of an inhibitory activity toward one of the steps involved in the acylation-deacylation process of triglycerides or phospholipids, as cellular lysates from TDGA-treated cells or lysates containing PAC incorporated radioactive fatty acids at rates comparable to controls. Our results suggest that CPT may be an important partner in the pathway of phospholipid and triglyceride fatty acid turnover in neurons.

Animals↗
PubMed1993

Effects of L-carnitine and its acetate and propionate esters on the molecular dynamics of human erythrocyte membrane.

EPR and fluorescence probes were used in this study to define the effects of L-carnitine and its short-chain esters, acetyl-L-carnitine and propionyl-L-carnitine, on the natural fluidity gradient and molecular packing of phospholipid headgroups of erythrocyte membrane in intact cells. Purified erythrocyte suspensions, labeled with different stearic acid derivatives containing a stable doxyl radical ring at the C-5, C-7, C-12 and C-16, were incubated with 0.5-5 mM L-carnitine and its esters for 60 min at 37 degrees C and washed twice with an isosmotic buffer. A decrease in the order parameter, calculated from the EPR spectra of the 5-doxylstearic acid derivative, was observed at all the concentrations of propionyl-L-carnitine and the extent of the decrease was dose and temperature dependent. An increase of the chain length between the doxyl ring and the carboxylic group of the spin label, resulted in a much lower efficacy of propionyl-L-carnitine in decreasing the order parameter. Acetyl-L-carnitine also showed a significant effect of decreasing the molecular order but only at the lower temperatures of red cells labeled with 5-doxyl and treated with the highest concentration of the drug. L-Carnitine did not modify the molecular dynamics at all the temperatures and concentrations used in this study. L-Carnitine and its short-chain derivatives did not alter significantly membrane fluidity of deeper regions of the erythrocyte membrane, measured by means of the excimer/monomer fluorescence intensity ratio of pyrene incorporated into the membrane of intact erythrocytes. However, these compounds were all capable of loosening the molecular packing of the polar head of erythrocyte membrane phospholipids evaluated by the membrane binding fluorescence properties of merocyanine-540. The binding of the fluorescent probe decreased in the order propionyl-L-carnitine > acetyl-L-carnitine > L-carnitine. Our findings suggest that this category of compounds affect the molecular dynamics of a membrane bilayer region close to the glycerol backbone of phospholipids, which might be relevant for the expression of membrane functions.

Acetylcarnitine↗
PubMed1993

The carnitine acyltransferases and their role in modulating acyl-CoA pools.

The role of carnitine via the action of carnitine acyltransferase in buffering CoA availability in the mitochondrial matrix is well known. There is now sufficient evidence to extend this to a general role. Carnitine can buffer the acylation state of the CoA pool for any type of acyl group that is a substrate for the carnitine acyltransferase family of enzymes. Specific carnitine acyltransferases in each organelle or membrane can modulate the reserves of free CoA and acyl-CoA in ways specific to the local metabolic demands. The use of inhibitors of carnitine acyltransferases in complex systems and in vivo now permits exploration of the consequences of this role.

Acyl Coenzyme A↗
PubMed1992

Acyl-trafficking in membrane phospholipid fatty acid turnover: the transfer of fatty acid from the acyl-L-carnitine pool to membrane phospholipids in intact human erythrocytes.

In this work we have investigated the transfer of radioactive palmitic acid between membrane phospholipids and acyl-L-carnitines in intact human erythrocytes. During the incubation period of labeled erythrocyte in non-defatted bovine serum albumin, radioactivity in phosphatidylcholine and phosphatidylethanolamine increased. On the contrary, a decrease of radioactivity in erythrocyte palmitoyl-L-carnitine was observed. 2-Tetradecylglycidic acid, an irreversible erythrocyte carnitine palmitoyltransferase inhibitor, abolished any radioactivity changes in both phospholipids and palmitoyl-L-carnitine. Similar findings were obtained by using erythrocytes labeled with radioactive oleic acid. Our data suggest that in human erythrocytes a carnitine palmitoyltransferase-catalyzed acyl transfer from acyl-L-carnitine to phospholipids, rather than a previously described fatty acid transfer from phosphatidylcholine to phosphatidylethanolamine, is operative.

Carnitine O-Palmitoyltransferase↗
PubMed1992

Role of carnitine and carnitine palmitoyltransferase as integral components of the pathway for membrane phospholipid fatty acid turnover in intact human erythrocytes.

The deacylation and reacylation process of phospholipids is the major pathway of turnover and repair in erythrocyte membranes. In this paper, we have investigated the role of carnitine palmitoyltransferase in erythrocyte membrane phospholipid fatty acid turnover. The role of acyl-L-carnitine as a reservoir of activated acyl groups, the buffer function of carnitine, and the importance of the acyl-CoA/free CoA ratio in the reacylation process of erythrocyte membrane phospholipids have also been addressed. In intact erythrocytes, the incorporation of [1-14C]palmitic acid into acyl-L-carnitine, phosphatidylcholine, and phosphatidylethanolamine was linear with time for at least 3 h. The greatest proportion of the radioactivity was found in acyl-L-carnitine. Competition experiments using [1-14C]palmitic and [9,10-3H]oleic acid demonstrated that [9,10-3H]oleic acid was incorporated preferentially into the phospholipids and less into acyl-L-carnitine. When an erythrocyte suspension was incubated with [1-14C]palmitoyl-L-carnitine, radiolabeled palmitate was recovered in the phospholipid fraction, and the carnitine palmitoyltransferase inhibitor, 2-tetradecylglycidic acid, completely abolished the incorporation. ATP depletion decreased incorporation of [1-14C]palmitic and/or [9,10-3H]oleic acid into acyl-L-carnitine, but the incorporation into phosphatidylcholine and phosphatidylethanolamine was unaffected. In contrast, ATP depletion enhanced the incorporation into phosphatidylcholine and phosphatidylethanolamine of the radiolabeled fatty acid from [1-14C]palmitoyl-L-carnitine. These data are suggestive of the existence of an acyl-L-carnitine pool, in equilibrium with the acyl-CoA pool, which serves as a reservoir of activated acyl groups. The carnitine palmitoyltransferase inhibition by 2-tetradecylglycidic acid or palmitoyl-D-carnitine caused a significant reduction of radiolabeled fatty acid incorporation into membrane phospholipids, only when intact erythrocytes were incubated with [9,10-3H]oleic acid. These latter data may be explained by the differences in rates and substrates specificities between acyl-CoA synthetase and the reacylating enzymes for palmitate and oleate, which support the importance of carnitine palmitoyltransferase in modulating the optimal acyl-CoA/free CoA ratio for the physiological expression of the membrane phospholipids fatty acid turnover.

Acylation↗
PubMed1992

Possible mechanism of inhibition of nitrite-induced oxidation of oxyhemoglobin by ergothioneine and uric acid.

The time course of oxyhemoglobin oxidation by nitrite consisted of a kinetic lag followed by a transition phase which progressed into a rapid autocatalytic phase. The imidazolthione and imidazolone derivatives, ergothioneine and uric acid, respectively, caused an increase in the duration of the lag phase in a concentration-dependent manner, without affecting the onset and rate of the autocatalytic phase. Neither compound reacted with H2O2 or nitrite, oxidizing species required in the initiation steps of oxyhemoglobin oxidation. On the other hand, both compounds reduced effectively and at comparable rates the high oxidation state of hemoglobin, i.e., ferrylhemoglobin, which is an intermediate species occurring in the autocatalytic phase. In addition, the rate of ergothioneine oxidation, upon its reaction with ferrylmyoglobin, was accelerated by nitrite, thus suggesting a reaction between the thione and nitrogen dioxide. Nitrogen oxide and ferrylhemoglobin are key species in the free radical chain propagation leading to oxyhemoglobin oxidation by nitrite. These data support the view that ergothioneine and urate delay oxyhemoglobin oxidation by nitrite upon the temporary removal of the propagating species, i.e., nitrogen dioxide and, secondarily, ferrylhemoglobin, and within a mechanism encompassing alterations of the nitrite in equilibrium with nitrogen dioxide and ferrylhemoglobin in equilibrium with methemoglobin redox transitions.

Adult↗