Endocannabinoid signaling in Alzheimer’s disease: current knowledge and future directions.

The importance of the endocannabinoid system (ECS) in the modulation functions of the central nervous system has been extensively investigated during the last few years. In particular, accumulated evidence has implicated ECS in the pathophysiology of Alzheimer’s disease (AD), that is a progressive, degenerative, and irreversible disorder characterized by the accumulation in the brain of beta-amyloid fragments forming insoluble plaques, and of intracellular neurofibrillary tangles (NTFs) associated with synaptic and neuronal loss. In all the processes involved in the formation of both plaques and NFTs, the key-role played by the ECS has been documented. Here, we review current knowledge and future directions of ECS modulation both in animal models of AD and in human tissues, underlying the role of endocannabinoid signaling in the development of AD hallmarks. Overall, the available data suggest that next generation therapeutics might target distinct ECS elements, for instance CB2 receptor or fatty acid amide hydrolase, as a promising approach to halt or at least to slow down disease progression.

Time-resolved extrinsic fluorescence of aromatic-L-amino-acid decarboxylase.

The coenzyme-linked fluorescence of aromatic-L-amino-acid decarboxylase decays non-exponentially. The decay of both native and NaBH4 reduced samples can only be fitted by two exponentials each roughly accounting for about half of the total fluorescence. Denaturation of the reduced protein with 8 M urea makes the fluorescence decay mono-exponential, like that observed for the reference compound pyridoxamine-5-phosphate. An extra pyridoxyl moiety can be bound to the enzyme after incubation with excess pyridoxal phosphate and reduction with NaBH4. This sample is almost twice as fluorescent and shows also two lifetimes. After denaturation only one fluorescence lifetime is observed. The presence of two non-equivalent pyridoxal sites in the native enzyme can be postulated. The heterogeneous decay behaviour of the pyridoxyl moiety in the enzyme together with the variability of lifetime shown, makes this fluorophore an even more interesting fluorescent probe for proteins.

Evidence for binding of NAD dimers to NAD-dependent dehydrogenases.

The binding of dimers of nicotinamide adenine dinucleotide, (NAD)2, to lactate, malate and alcohol dehydrogenase has been studied by the fluorescence quenching technique. While the alcohol dehydrogenase shows a low binding ability, malate and lactate dehydrogenases have been found to bind (NAD)2 in a specific way with high affinity. Malate dehydrogenase binds (NAD)2 more than NADH. All three dehydrogenases are inhibited by (NAD)2, which behaves as a competitive inhibitor with respect to both NAD+ and NADH. The results show that (NAD)2 is bound to the nucleotide-specific binding site of the dehydrogenases. (NAD)2 was found to stoichiometrically react with ferricyanide at variance with NADH. The specific interactions with the NAD-dependent dehydrogenases and the ability to enter in monoelectronic redox cycles suggest possible physiological roles for (NAD)2.

Hydrogen peroxide release from human blood platelets.

The release of hydrogen peroxide from human blood platelets after stimulation with particulate membrane-perturbing agents has been determined by fluorescence using scopoletin as the detecting agent. Platelet suspensions containing less than 1 polymorphonuclear leukocyte/10(8) platelets showed a significant release of hydrogen peroxide (6.11 nmol/10(9) platelets per 20 min, S.D., 0.26, n = 9) after addition of zymosan or latex particles, compared to unstimulated platelets. The release of hydrogen peroxide was only observed when the scopoletin was added to the platelet suspensions during the stimulation. Any attempt to determine hydrogen peroxide release in the supernatant at the end of the incubation with zymosan or latex failed. A NADH-dependent production of hydrogen peroxide was observed by measuring the difference of oxygen uptake in the presence and absence of catalase (500 units), which was not inhibited by potassium cyanide (1 mM). By this method the NADH-dependent cyanide-insensitive peroxide production and release was 6.0 nmol/10(9) platelets per 20 min from resting platelets (S.D., 2, n = 6) vs 15 nmol/10(9) platelets per 20 min from stimulated platelets (S.D., 2, n = 6).

Electrostatic interactions in Cu,Zn superoxide dismutase. Effects of Ca(II) and of anions not binding to the copper.

Cu,Zn superoxide dismutase (EC 1.15.1.1) from bovine erythrocyte was found to enhance Tb(III) luminescence in a way suggestive of the presence of specific sites binding calcium. Binding of Ca(II) had no effect on the enzyme activity. However, the low-temperature EPR spectra of the enzyme-bound copper were modified into a more axial line shape by Ca(II) and Tb(III), but not by other cations. This effect was not observed by room-temperature EPR and was interpreted as being due to a long-range conformational effect on the copper-binding site occurring on freezing when specific charged amino acid side-chains are neutralized. This interpretation is supported by similar effects observed with anions that neither have inhibitory effect on the activity nor bind to the copper. These results indicate the presence of specific electrostatic interactions of the protein moiety of Cu,Zn superoxide dismutase and the occurrence of changes of the symmetry of the copper site when the protein is frozen under certain conditions.

Lentil root protoplasts: a transient expression system suitable for coelectroporation of monoclonal antibodies and plasmid molecules.

Protoplasts were isolated from lentil (Lens culinaris) roots and their suitability as a transient expression system was investigated. After transfecting the protoplasts with the beta-glucuronidase (GUS) gene by either electroporation or polyethylene glycol (PEG), the specific activity of the reporter enzyme and the cell viability were determined. Electroporation was more effective than PEG treatment as transfection procedure and its efficiency was affected by the plasmid length. The feasibility of electro-transferring at the same time (coelectroporation) inhibitory anti-lipoxygenase monoclonal antibodies and the GUS-carrying plasmid pBI 221 was investigated as well. The amount of transferred immunoglobulins was quantitated by ELISA and the inhibitory ability of monoclonal antibodies on the intracellular target enzyme was determined. Evidence is presented for the successful coelectroporation of immunoglobulins and plasmid DNA into lentil protoplasts, the two types of macromolecules acting independently of each other in the recipient cells.

Adriamycin-catalyzed aerobic photooxidation of NAD dimers to NAD+.

The photooxidation of the dimers of nicotinamide adenine dinucleotide, (NAD)2, is catalyzed by adriamycin under aerobic conditions. (NAD)2 and O2 react in 1:1 molar ratio to yield 2 mol of NAD+. Experiments carried out by irradiating at 340 and 485 nm, corresponding to the absorption maxima of (NAD)2 and adriamycin, respectively, clearly indicate that the process is primed by photoexcitation of adriamycin. The key step of the process is the redox reaction between (NAD)2 and adriamycin with formation of the semiquinone radical anion, identified by the EPR spectrum. The semiquinone is then oxidized back to adriamycin by oxygen with formation of the superoxide radical.

Inhibition of lipoxygenase in lentil protoplasts by expression of antisense RNA.

A number of plasmids were constructed containing chimeric genes consisting of fragments of antisense-oriented lentil lipoxygenase cDNA. The different constructs were tested for their ability to lower lipoxygenase activity in lentil protoplasts. Plasmids containing a full length lentil lipoxygenase cDNA proved to be the most effective, reducing the activity of the target enzyme to 70% of the control value. On the other hand, the full length lentil lipoxygenase cDNA in the sense orientation yielded a 20% increase of lipoxygenase activity.

The primary structure of a lipoxygenase from the shoots of etiolated lentil seedlings derived from its cDNA.

Screening of a cDNA library constructed from the shoots of etiolated lentil seedlings resulted in finding a 2778 bp cDNA sequence, containing an open reading frame coding for a lipoxygenase of 866 amino acid residues. This lipoxygenase appears to be a novel type of vegetative lipoxygenase, different from the seed lipoxygenases of other leguminosae (complete homology < or = 72%).

Changes in the fluorescence and absorbance of lipoxygenase-1 induced by 13-Ls-hydroperoxylinoleic acid and linoleic acid.

1. The addition of 13-Ls-hydroperoxylinoleic acid to lipoxygenase-1 (linoleate: oxygen oxidoreductase EC 1.13.11.12) from soybeans at pH 9 and 25 degrees C causes a quenching of the fluorescence of the enzyme at 328 nm when exciited at 280 nm and gives rise to an increase of the absorbance of the enzyme in the 300 nm to 450 nm region. 2. In the absence of 02, addition of linoleic acid to enzyme treated with 13-Ls-hydroperoxylinoleic acid, causes an increase of the fluorescence at 328 nm and a decrease of the absorbance in the 300 nm to 450 nm region. 3. The fluorescence changes are suggested to be directly coupled to the absorbance changes via a non-radioactive energy transfer process. 4. It is proposed that the observed fluorescence and absorbance changes are related to changes in the formal change of iron in the protein.

The fine structure of luminescence spectra of azurin.

The spectra of azurin absorption, fluorescence, phosphorescence and fluorescence excitation have been measured in aqueous solutions at ordinary and liquid nitrogen temperatures. The fluorescence spectra of azurin even at ordinary temperatures have a well resolved fine vibrational structure. The frequency analysis reveals practically the same wave number distances between the main structure peaks in fluorescence spectra at room and low temperatures and in phosphorescence spectra. The comparison of the protein absorption and excitation spectra shows that all the energy absorbed by tyrosine residues is transferred onto indole chromophore. These data suggest an unusual tryptophan environment in this protein, which is characterized by the absence of any hydrogen bonding or other polar interaction of tryptophan with its environment. The problem of the possibility of contributions of two electronic transitions (1La in equilibrium A and 1Lb in equilibrium A) in absorption and emission spectra of azurin tryptophan arising from their mirror symmetry is discussed.

1H-NMR study and structure determination of 4,4- and 4,6-dimers from electrochemical reduction of NADP+.

The products arising from one-electron electrochemical reduction of the coenzyme nicotinamide adenine dinucleotide phosphate (NADP+) have been studied by HPLC chromatography and 1H-NMR spectroscopy. HPLC and NMR analyses have shown seven dimeric species, the most abundant of which (40%) has been isolated and has resulted to be an NADP 4,4-linked dimer. The other two diastereoisomeric 4,4-dimers present for the 25% and 10%, respectively, have been detected in the crude reaction mixture, but have not been isolated. The 4,4-tetrahydrobipyridine structure and the stereochemistry at the ring-ring junction for these three isomers have been determined on the basis of their NMR parameters. Preparative HPLC chromatography also led to two fractions enriched in another four dimers, present in the crude mixture, which turned out to have a 4,6-tetrahydrobipyridine structure. All the chemical shifts and the H,H coupling constants of the 4,4- and 4,6-tetrahydrobipyridine systems have been obtained for the seven compounds. For the most abundant among the 4,4-dimers the NMR analysis also gave the coupling constant values of the ribose-diphosphate chain.

The endocannabinoid system, anandamide and the regulation of mammalian cell apoptosis.

Endocannabinoids are a new class of lipid mediators, which include amides, esters and ethers of long-chain polyunsaturated fatty acids. Anandamide (N-arachidonoylethanolamine; AEA) and 2-arachidonoylglycerol (2-AG) are the main endogenous agonists of cannabinoid receptors able to mimic several pharmacological effects of Delta-9-tetrahydrocannabinol, the active principle of Cannabis sativa preparations like hashish and marijuana. The pathways leading to the synthesis and release of AEA and 2-AG from neuronal and non-neuronal cells are still rather uncertain. Instead, it is known that the activity of AEA is limited by cellular uptake through a specific membrane transporter, followed by intracellular degradation by a fatty acid amide hydrolase. Together with AEA and congeners these proteins form the 'endocannabinoid system'. Here, the involvement of AEA in apoptosis and the underlying signal transduction pathways will be reviewed, along with the metabolic routes and the molecular targets of this endocannabinoid. Also, recent findings on the apoptotic potential of AEA for neuronal cell differentiation and brain development will be discussed.

Lipoxygenases and their involvement in programmed cell death.

Lipoxygenases are a family of enzymes which dioxygenate unsaturated fatty acids, thus initiating lipoperoxidation of membranes and the synthesis of signaling molecules. Consequently, they induce structural and metabolic changes in the cell in a number of pathophysiological conditions. Recently, a pro-apoptotic effect of lipoxygenase, and of the hydroperoxides produced thereof, has been reported in different cells and tissues, leading to cell death. Anti-apoptotic effects of lipoxygenases have also been reported; however, this has often been based on the use of enzyme inhibitors. Here we review the characteristics of the lipoxygenase family and its involvement in the initiation of oxidative stress-induced apoptosis. Finally, we discuss the role of lipoxygenase activation in apoptosis of animal and plant cells, suggesting a common signal transduction pathway in cell death conserved through evolution of both kingdoms.

A new crystalline modification of the copper enzyme ascorbate oxidase.

The copper enzyme ascorbate oxidase, purified from green zucchini squash, has been crystallized at pH 5.4 employing the organic solvent 2-methyl-2,4-pentanediol. The crystals obtained are larger than one millimetre and belong to the space group P2(1)2(1)2, with unit cell parameters; a = 106.7 A, b = 105.1 A, c = 113.5 A. The crystallographic asymmetric unit contains two subunits of the enzyme (Mr = 140,000) and the solvent content of the crystals is 46% (v/v). The diffraction pattern extends to 2.5 A resolution; this crystal form is suitable for a X-ray structural investigation.

Refined crystal structure of ascorbate oxidase at 1.9 A resolution.

The crystal structure of the fully oxidized form of ascorbate oxidase (EC 1.10.3.3) from Zucchini has been refined at 1.90 A (1 A = 0.1 nm) resolution, using an energy-restrained least-squares refinement procedure. The refined model, which includes 8764 protein atoms, 9 copper atoms and 970 solvent molecules, has a crystallographic R-factor of 20.3% for 85,252 reflections between 8 and 1.90 A resolution. The root-mean-square deviation in bond lengths and bond angles from ideal values is 0.011 A and 2.99 degrees, respectively. The subunits of 552 residues (70,000 Mr) are arranged as tetramers with D2 symmetry. One of the dyads is realized by the crystallographic axis parallel to the c-axis giving one dimer in the asymmetric unit. The dimer related about this crystallographic axis is suggested as the dimer present in solution. Asn92 is the attachment site for one of the two N-linked sugar moieties, which has defined electron density for the N-linked N-acetyl-glucosamine ring. Each subunit is built up by three domains arranged sequentially on the polypeptide chain and tightly associated in space. The folding of all three domains is of a similar beta-barrel type and related to plastocyanin and azurin. An analysis of intra- and intertetramer hydrogen bond and van der Waals interactions is presented. Each subunit has four copper atoms bound as mononuclear and trinuclear species. The mononuclear copper has two histidine, a cysteine and a methionine ligand and represents the type-1 copper. It is located in domain 3. The bond lengths of the type-1 copper centre are comparable to the values for oxidized plastocyanin. The trinuclear cluster has eight histidine ligands symmetrically supplied from domain 1 and 3. It may be subdivided into a pair of copper atoms with histidine ligands whose ligating N-atoms (5 NE2 atoms and one ND1 atom) are arranged trigonal prismatic. The pair is the putative type-3 copper. The remaining copper has two histidine ligands and is the putative spectroscopic type-2 copper. Two oxygen atoms are bound to the trinuclear species as OH- or O2- and bridging the putative type-3 copper pair and as OH- or H2O bound to the putative type-2 copper trans to the copper pair. The bond lengths within the trinuclear copper site are similar to comparable binuclear model compounds. The putative binding site for the reducing substrate is close to the type-1 copper.(ABSTRACT TRUNCATED AT 400 WORDS)

Biotin and biotin analogues specifically modify the fluorescence decay of avidin.

Avidin, a basic tetrameric glycoprotein, isolated from hen egg-white, binds up to four molecules of biotin with exceptionally high affinity. The presence of tryptophanyl residues in the active site pointed out the opportunity of correlating the protein fluorescence with biotin binding. We have performed both steady state and dynamic fluorescence experiments using biotin or biotin-derived molecules (biotinamine, diaminobiotin and iminobiotin) as ligands. The fluorescence decay data can only be fitted by two continuous distributions of lifetimes which may reflect the presence of static or dynamic microheterogeneity in the environment of the tryptophan residues. We observed that the binding of biotin, biotinamine and iminobiotin reduces the widths of both distributions to discrete lifetimes thus indicating a more homogenous environment for the emitting tryptophan residues. Instead, the binding of diaminobiotin, which lacks the imidazolone ring, affects one lifetime distribution only. The binding of biotin also affects the rotational correlation time of avidin, which becomes shorter, suggesting a more compact structure of the ligated protein. The utility of analyzing the fluorescence in terms of distributions appears to be further warranted.

X-ray crystal structure of the blue oxidase ascorbate oxidase from zucchini. Analysis of the polypeptide fold and a model of the copper sites and ligands.

Two crystal forms of the multi-copper protein ascorbate oxidase from Zucchini have been analysed at 2.5 A (1 A = 0.1 nm) resolution and a model of the polypeptide chain and the copper ions and their ligands has been built. Crystal forms M2 and M1 contain a dimer of 140,000 Mr and a tetramer of 280,000 Mr, respectively, in the asymmetric unit. The crystallographic analysis proceeded by multiple isomorphous replacement in M2 followed by solvent flattening and averaging about the local dyad axis. M1 was solved by Patterson search techniques using the M2 electron density. M1 was fourfold averaged. M1 and M2 were combined and the process of averaging repeated in cycles. An atomic model was built into the resulting electron density map and refinement initiated. The current R values of M2 and M1 are 24.5% and 32.6%, respectively. Excellent stereo chemistry was maintained, with root-mean-square deviations of bond lengths and bond angles from average values of 0.02 A and 3.1 degrees, respectively. Each subunit of about 550 amino acid residues has a globular shape with dimensions of 49 A x 53 A x 65 A. It is built up by three domains arranged sequentially on the polypeptide chain and tightly associated in space. The folding of all three domains is of a similar beta-barrel type. It is distantly related to plastocyanin. Each subunit has four copper atoms bound as mononuclear and trinuclear species. The mononuclear copper has two histidine, a cysteine, and a methionine ligand and represents the type-1 copper. It is located in the third domain. The trinuclear cluster has eight histidine ligands. It may be subdivided into a pair of copper atoms with six histidine ligands arranged trigonal prismatic. The pair probably represents the type-3 copper. The remaining copper has two histidine ligands. Its third site of co-ordination is formed by the pair of copper atoms. The fourth ligand may be OH- represented by a small protrusion of electron density. This copper probably is the type-2 copper. The symmetry of the trinuclear cluster is C2 and the ligands are supplied symmetrically by domains 1 and 3. However, domain 1 does not contain a type-1 copper and lacks the characteristic ligands. The unprecedented trinuclear cluster probably represents the oxygen binding and electron storage site.

Stimulated platelets release factor(s) affecting the in vitro response of human polymorphonuclear cells.

The metabolic and functional responses of human polymorphonuclear cells (PMNs) to thrombin-activated platelet supernatants were studied. The incubation of PMNs with supernatants from stimulated platelets (SPS) caused a 50% decrease in both killing of Staphylococcus aureus and luminol-enhanced chemiluminescence (CL) by PMNs stimulated by opsonized-zymosan (OZ), Concanavalin A (Con A), or calcium ionophore A23187. The levels of PMN intracellular fluorescence measured by flow cytometry, using the fluorochrome dichlorofluorescein diacetate (DCF-DA), were considerably less in the presence of SPS than in resting platelet supernatants (RPS). No influence of platelet supernatant on O2 consumption and O2- generation by OZ-activated PMNs was observed. The incubation of PMNs with SPS caused a significant increase in the rate of chemotaxis and aggregation elicited by Con A, OZ, and phorbol myristate acetate (PMA). The supernatant from resting platelets did not show any of the above-reported effects. Platelets previously degranulated by thrombin were unable to inhibit CL when activated with agonists. Studies on the differential release of the granules by platelets showed that the CL-quenching activity paralleled the discharge of lysosomal content. The release of myeloperoxidase (MPO) from PMNs elicited by OZ was reduced in the presence of SPS. The platelet supernatant did not affect the MPO activity if PMNs were lysed with Triton X-100. The leakage of lactate dehydrogenase (LDH) from platelets was less than 3%, and no catalase or superoxide dismutase was released. This activity withstood lyophilization, but was destroyed by 10 min heating at 100 degrees C or by treatment with proteolytic enzymes.