Biomedical subjects

M Harel

Publications and source records attributed to M Harel.

At least 19 recordsLinked to original sources

PubMed2006

Selective fovea-related deprived activation in retinotopic and high-order visual cortex of human amblyopes.

Amblyopia is a visual disorder starting at early childhood and characterized by reduced visual acuity not of optical origin or due to any eye disease. One expression of such an anomalous early visual experience is abnormal foveal vision. In a previous fMRI study, faces that were presented to amblyopic eyes evoked little response compared to houses in high-order visual areas. Patients also demonstrated reduced recognition of facial expression, raising the possibility that these face-selective abnormalities are related to foveal vision deficit. Whether this deficit originates in low-level processing or is mediated by compromised activation in high-order visual areas is unresolved. In the present functional magnetic resonance imaging (fMRI) study, we explored the impact of amblyopia on the representation of object images presented in foveally biased central versus peripheral retinotopic eccentricities through manipulation of object size. Small and large pictures were correlated to visual acuities of 6/6 and 6/60, respectively. In low-level visual areas, the amblyopic eye showed significantly reduced activation for centrally placed, small pictures than the sound eye, while activation to large pictures was only slightly reduced. Similarly, in high-order visual areas, the amblyopic eye showed marked reduction in activation in the fusiform gyrus, with normal activation in the collateral sulcus. The center/periphery size-related amblyopic outcomes of this study support a "bottom-up" nature of the center-periphery effect observed in high-order visual areas. Taken together, these findings point to the regional extent and functional selectivity of fovea-related cortical reorganization that is related to abnormal visual development of one eye.

Adult↗

PubMed2006

Application of a static fluorescence-based cytometer: the CellScan in clinical immunology.

The CellScan system is a laser scanning cytometer which enables repetitive fluorescence intensity (FI) and polarization (FP) measurements in living cells, as a means of monitoring lymphocyte activation. By monitoring FP changes in peripheral blood lymphocytes (PBL) following exposure to antigenic stimuli, the CellScan may have a role in the diagnosis of autoimmune diseases. Monitoring changes in FI and FP in PBLs from patients with atherosclerosis following exposure to various stimuli, has illustrated the role of the immune system in the atherosclerotic process. The CellScan has also been evaluated as a diagnostic tool for drug-induced allergy, based on FP reduction in PBLs following incubation with the suspected drugs. FI and FP changes in cancer cells have been found to correlate with the cytotoxic effect of different anti-neoplastic drugs, illustrating the potential role of the CellScan system in clinical oncology. In conclusion, the CellScan is a promising new tool with a variety of applications in cell biology, immunology, cancer research and clinical pharmacology.

Atherosclerosis↗

PubMed2004

Synthesis and biological activity of the four stereoisomers of 4-methyl-3-heptanol: main component of the aggregation pheromone of Scolytus amygdali.

Stereoisomers of 4-methyl-3-heptanol are major components of aggregation pheromones of bark beetles and trail pheromones of ants. Recently, (3S,4S)-4-methyl-3-heptanol (I) has been tentatively identified as the main component of the aggregation pheromone of the almond bark beetle, Scolytus amygdali (Coleoptera: Scolytidae). The four stereoisomers of 4-methyl-3-heptanol were prepared and bioassayed. Key steps included preparation of chiral 4-methyl-3-heptanones using SAMP and RAMP reagents, reduction to the corresponding alcohols, and stereospecific transesterification with vinyl acetate with lipase AK catalysis. In field tests, only (3S,4S)-4-methyl-3-heptanol attracted beetles in combination with the synergist (3S,4S)-4-methyl-3-hexanol, whereas (3R,4S)- and (3R,4R)-4-methyl-3-heptanols were inhibitory.

Animals↗

PubMed2004

Sex pheromone of the citrus mealybug Planococcus citri: synthesis and optimization of trap parameters.

A simple synthesis of the pheromone of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), has been developed. Various factors affecting capture of males have been assessed to optimize the trap design and to develop a lure with high efficacy and longevity. Male capture was the same with the racemic and chiral pheromone; technical pheromone (85% purity) was statistically as attractive as pure pheromone (97%). A special formulation was used to determine the actual release rate of the pheromone under field conditions as related to male capture. Generally, plate traps caught more males than delta traps, and large traps caught more than small ones. The effects of aging on the performance of three types of rubber dispensers were evaluated. It was found that the American dispenser displayed the most consistent trapping performance and could be used for monitoring for at least 16 wk with a load of 200 microg of pheromone. The dose-response of the males to sex pheromone was tested within the range of 25-1,600 microg.

Animals↗

PubMed2003

Area-specific amblyopic effects in human occipitotemporal object representations.

The role of early visual experience in the establishment of human high-order visual areas is poorly understood. Here we investigated this issue using human amblyopia--a developmental visual disorder, which manifests a central vision (acuity) deficit. Previous fMRI studies of amblyopes have described abnormal functional activations in early retinotopic areas. Here we report the surprising finding of a selective object-related abnormality in high-order occipitotemporal cortex. Specifically, we found that face-related cortical areas show a severe disconnection from the amblyopic eye, while building-related regions remain essentially normal. The selectivity of the deficit highlights the differential computations performed in the different object-related areas and is compatible with the suggested association of face regions with analysis of fine detail.

Acoustic Stimulation↗

PubMed2003

Sex pheromone of the vine mealybug, Planococcus ficus in Israel: occurrence of a second component in a mass-reared population.

Two pheromonal components were detected in airborne collections from the vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) mass-reared on potato sprouts. The compounds were identified as (S)-lavandulyl senecioate (I) and (S)-lavandulyl isovalerate (II) by GC and GC-MS by comparison with synthetic standards. Chiral GC analysis on a cyclodextrin column established their chirality. Compound I was identified recently as the sex pheromone of P. ficus in California. The attraction of vine mealybug males to both components I and II was demonstrated in a Petri dish bioassay and in a flight assay in the rearing chamber. Indoors, both compounds displayed a similar level of attractiveness to the mass-reared males. However, trials in a vineyard indicated that feral males were attracted only to compound I. Reanalysis of the airborne pheromone indicated that laboratory first generation daughters of females that were collected in the vineyard produce only (S)-lavandulyl senecioate (I). The relative amount of (S)-lavandulyl isovalerate (II) increased gradually in each subsequent generation of P. ficus reared on potatoes. These findings indicate that feral P. ficus mealybugs produce and respond only to (S)-lavandulyl senecioate (I), whereas mealybugs that were reared in the laboratory on potato sprouts produce and respond to both (S)-lavandulyl senecioate (I) and (S)-lavandulyl isovalerate (II).

Alkenes↗

PubMed2002

X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (-)-huperzine B: structural evidence for an active site rearrangement.

Kinetic and structural data are presented on the interaction with Torpedo californica acetylcholinesterase (TcAChE) of (+)-huperzine A, a synthetic enantiomer of the anti-Alzheimer drug, (-)-huperzine A, and of its natural homologue (-)-huperzine B. (+)-Huperzine A and (-)-huperzine B bind to the enzyme with dissociation constants of 4.30 and 0.33 microM, respectively, compared to 0.18 microM for (-)-huperzine A. The X-ray structures of the complexes of (+)-huperzine A and (-)-huperzine B with TcAChE were determined to 2.1 and 2.35 A resolution, respectively, and compared to the previously determined structure of the (-)-huperzine A complex. All three interact with the "anionic" subsite of the active site, primarily through pi-pi stacking and through van der Waals or C-H.pi interactions with Trp84 and Phe330. Since their alpha-pyridone moieties are responsible for their key interactions with the active site via hydrogen bonding, and possibly via C-H.pi interactions, all three maintain similar positions and orientations with respect to it. The carbonyl oxygens of all three appear to repel the carbonyl oxygen of Gly117, thus causing the peptide bond between Gly117 and Gly118 to undergo a peptide flip. As a consequence, the position of the main chain nitrogen of Gly118 in the "oxyanion" hole in the native enzyme becomes occupied by the carbonyl of Gly117. Furthermore, the flipped conformation is stabilized by hydrogen bonding of Gly117O to Gly119N and Ala201N, the other two functional elements of the three-pronged "oxyanion hole" characteristic of cholinesterases. All three inhibitors thus would be expected to abolish hydrolysis of all ester substrates, whether charged or neutral.

Acetylcholinesterase↗

PubMed2002

Kinetic and structural studies on the interaction of cholinesterases with the anti-Alzheimer drug rivastigmine.

Rivastigmine, a carbamate inhibitor of acetylcholinesterase, is already in use for treatment of Alzheimer's disease under the trade name of Exelon. Rivastigmine carbamylates Torpedo californica acetylcholinesterase very slowly (k(i) = 2.0 M(-1) min(-1)), whereas the bimolecular rate constant for inhibition of human acetylcholinesterase is >1600-fold higher (k(i) = 3300 M(-1) min(-1)). For human butyrylcholinesterase and for Drosophila melanogaster acetylcholinesterase, carbamylation is even more rapid (k(i) = 9 x 10(4) and 5 x 10(5) M(-1) min(-1), respectively). Spontaneous reactivation of all four conjugates is very slow, with <10% reactivation being observed for the Torpedo enzyme after 48 h. The crystal structure of the conjugate of rivastigmine with Torpedo acetylcholinesterase was determined to 2.2 A resolution. It revealed that the carbamyl moiety is covalently linked to the active-site serine, with the leaving group, (-)-S-3-[1-(dimethylamino)ethyl]phenol, being retained in the "anionic" site. A significant movement of the active-site histidine (H440) away from its normal hydrogen-bonded partner, E327, was observed, resulting in disruption of the catalytic triad. This movement may provide an explanation for the unusually slow kinetics of reactivation.

Acetylcholinesterase↗

PubMed2002

3D structure of Torpedo californica acetylcholinesterase complexed with huprine X at 2.1 A resolution: kinetic and molecular dynamic correlates.

Huprine X is a novel acetylcholinesterase (AChE) inhibitor, with one of the highest affinities reported for a reversible inhibitor. It is a synthetic hybrid that contains the 4-aminoquinoline substructure of one anti-Alzheimer drug, tacrine, and a carbobicyclic moiety resembling that of another AChE inhibitor, (-)-huperzine A. Cocrystallization of huprine X with Torpedo californica AChE yielded crystals whose 3D structure was determined to 2.1 A resolution. The inhibitor binds to the anionic site and also hinders access to the esteratic site. Its aromatic portion occupies the same binding site as tacrine, stacking between the aromatic rings of Trp84 and Phe330, whereas the carbobicyclic unit occupies the same binding pocket as (-)-huperzine A. Its chlorine substituent was found to lie in a hydrophobic pocket interacting with rings of the aromatic residues Trp432 and Phe330 and with the methyl groups of Met436 and Ile439. Steady-state inhibition data show that huprine X binds to human AChE and Torpedo AChE 28- and 54-fold, respectively, more tightly than tacrine. This difference stems from the fact that the aminoquinoline moiety of huprine X makes interactions similar to those made by tacrine, but additional bonds to the enzyme are made by the huperzine-like substructure and the chlorine atom. Furthermore, both tacrine and huprine X bind more tightly to Torpedo than to human AChE, suggesting that their quinoline substructures interact better with Phe330 than with Tyr337, the corresponding residue in the human AChE structure. Both (-)-huperzine A and huprine X display slow binding properties, but only binding of the former causes a peptide flip of Gly117.

Acetylcholinesterase↗

PubMed2002

Quantitative GC analysis of secondary alcohol pheromones: determination of release rate of red palm weevil, Rhynchophorus ferrugineus, pheromone from lures.

Aliphatic secondary alcohols are components of several aggregation pheromones of important beetle and weevil pests. Some of these pheromones are used frequently for the monitoring and mass trapping of the relevant insects. We encountered severe difficulties in direct GC quantitative analysis of these compounds. Therefore, we developed a simple GC analysis of secondary alcohols convening them to trifluoroacetyl derivatives and using secondary alcohol acetates as internal standards. This method was applied for the quantitative analysis of several secondary alcohols, including the aggregation pheromone components of the almond bark beetle and the red palm weevil. The release rate of the latter pheromone from commercial lures was also determined.

Alcohols↗

PubMed2001

The binding site of acetylcholine receptor as visualized in the X-Ray structure of a complex between alpha-bungarotoxin and a mimotope peptide.

We have determined the crystal structure at 1.8 A resolution of a complex of alpha-bungarotoxin with a high affinity 13-residue peptide that is homologous to the binding region of the alpha subunit of acetylcholine receptor. The peptide fits snugly to the toxin and adopts a beta hairpin conformation. The structures of the bound peptide and the homologous loop of acetylcholine binding protein, a soluble analog of the extracellular domain of acetylcholine receptor, are remarkably similar. Their superposition indicates that the toxin wraps around the receptor binding site loop, and in addition, binds tightly at the interface of two of the receptor subunits where it inserts a finger into the ligand binding site, thus blocking access to the acetylcholine binding site and explaining its strong antagonistic activity.

Amino Acid Sequence↗

PubMed2001

A hierarchical axis of object processing stages in the human visual cortex.

How are objects represented in the human visual cortex? Two conflicting theories suggest either a holistic representation, in which objects are represented by a collection of object templates, or a part-based representation, in which objects are represented as collections of features or object parts. We studied this question using a gradual object-scrambling paradigm in which pictures of objects (faces and cars) were broken in a stepwise manner into an increasing number of blocks. Our results reveal a hierarchical axis oriented anterior--posteriorly in the organization of ventral object-areas. Along this axis, representations are arranged in bands of increasing sensitivity to image scrambling. The axis starts in early visual areas through retinotopic areas V4/V8 and continues into the lateral-occipital sulcus dorsally and the posterior fusiform girus ventrally, corresponding together to the previously described object-related lateral occipital complex (LOC). Regions showing the highest sensitivity to scrambling tended to be located at the most anterior-lateral regions of the complex. In these more anterior regions, breaking the images into 16 parts produced a significant reduction in activation. Interestingly, activation was not affected when images were cut in two halves, either horizontally or vertically. Car images generally produced a weaker activation compared to faces in the lateral occipital complex but showed the same tendency of increased scrambling sensitivity along the anterior--posterior axis. These results suggest the existence of a hierarchical axis along ventral occipito-temporal object-areas, in which the neuronal properties shift from sensitivity to local object features to a more global and holistic representation.

Adult↗

PubMed2001

Application of a gamma model of absorption to oral cyclosporin.

BACKGROUND: Some drugs, such as cyclosporin, exhibit flat and delayed absorption profiles, with a correlation between the delay and the peak width. Such profiles can be described by an absorption model in which the absorption rate is derived from a gamma distribution (of which the classical first-order absorption model is a special case). OBJECTIVE: To develop a model for the pharmacokinetics of extravascular administration of cyclosporin and apply it to a study of the pharmacokinetics of cyclosporin microemulsion in stable renal transplant recipients. PATIENTS AND PARTICIPANTS: 21 renal transplant patients receiving oral cyclosporin microemulsion 75 to 175 mg twice daily. METHODS: The equation of the plasma concentration-time curve after oral administration was expressed as a convolution product between the absorption rate and a multi-exponential impulse response. The convolution integral was computed analytically and expressed in terms of the incomplete gamma function. Cyclosporin was assayed by liquid chromatography/mass spectrophotometry. The model was fitted by nonlinear regression, using a specially developed program. RESULTS: The gamma model yielded a good fit in all of the 21 patients studied. Attempts to fit the same data by a classical exponential with lag-time model failed in most patients. CONCLUSIONS: This model could simplify the Bayesian monitoring of cyclosporin therapy.

Area Under Curve↗

PubMed2000

Specific chemical and structural damage to proteins produced by synchrotron radiation.

Radiation damage is an inherent problem in x-ray crystallography. It usually is presumed to be nonspecific and manifested as a gradual decay in the overall quality of data obtained for a given crystal as data collection proceeds. Based on third-generation synchrotron x-ray data, collected at cryogenic temperatures, we show for the enzymes Torpedo californica acetylcholinesterase and hen egg white lysozyme that synchrotron radiation also can cause highly specific damage. Disulfide bridges break, and carboxyl groups of acidic residues lose their definition. Highly exposed carboxyls, and those in the active site of both enzymes, appear particularly susceptible. The catalytic triad residue, His-440, in acetylcholinesterase, also appears to be much more sensitive to radiation damage than other histidine residues. Our findings have direct practical implications for routine x-ray data collection at high-energy synchrotron sources. Furthermore, they provide a direct approach for studying the radiation chemistry of proteins and nucleic acids at a detailed, structural level and also may yield information concerning putative "weak links" in a given biological macromolecule, which may be of structural and functional significance.

Acetylcholinesterase↗

PubMed2000

Modulation of arachidonate and docosahexaenoate in Morone chrysops larval tissues and the effect on growth and survival.

The extent to which extreme dietary levels of arachidonate (AA) and/or docosahexaenoate (DHA) modulate lipid composition in the body tissues and consequently affect growth and survival in freshwater Morone larvae species was examined. White bass, M. chrysops, larvae (day 24-46) were fed Artemia nauplii enriched with algal oils containing varying proportions of AA and DHA (from 0 to over 20% the total fatty acids). Growth was significantly reduced (P< 0.05) in larvae fed a DHA-deficient Artemia diet. Increases in dietary levels of AA also were associated with a significant growth reduction. However, the inhibitory effect of AA on larvae growth could be suppressed by the dietary addition of DHA (at a level of 21.6% of the total fatty acids in enrichment lipids). Larval brain + eyes tissue accumulated over 10 times more DHA than AA in its structural lipids (phosphatidylcholine, phosphatidylethanolamine) at any dietary ratio. In contrast, DHA accumulation, as compared to AA, in gill lipids declined considerably at higher than 10:1 DHA/AA tissue ratios. DHA and eicosapentaenoic acid (EPA) contents in brain + eyes tissue were most sensitive to competition from dietary AA, being displaced from the tissue at rates of 0.36 +/- 0.07 mg DHA and 0.46 +/- 0.11 mg EPA per mg increase in tissue AA, and 0.55 +/- 0.14 mg AA per mg increase in tissue DHA. On the other hand, AA and EPA levels in gill tissue were most sensitive to dietary changes in DHA levels; AA was displaced at rates of 0.37 +/- 0.11 mg, whereas EPA increased at rates of 0.68 +/- 0.28 mg per mg increase in tissue DHA. Results suggest that balanced dietary DHA/AA ratios (that allow DHA/AA ratios of 2.5:1 in brain + eyes tissue) promote a high larval growth rate, which also correlates with maximal regulatory response in tissue essential fatty acids.

Animals↗

PubMed2000

Structures of recombinant native and E202Q mutant human acetylcholinesterase complexed with the snake-venom toxin fasciculin-II.

Structures of recombinant wild-type human acetylcholinesterase and of its E202Q mutant as complexes with fasciculin-II, a 'three-finger' polypeptide toxin purified from the venom of the eastern green mamba (Dendroaspis angusticeps), are reported. The structure of the complex of the wild-type enzyme was solved to 2.8 A resolution by molecular replacement starting from the structure of the complex of Torpedo californica acetylcholinesterase with fasciculin-II and verified by starting from a similar complex with mouse acetylcholinesterase. The overall structure is surprisingly similar to that of the T. californica enzyme with fasciculin-II and, as expected, to that of the mouse acetylcholinesterase complex. The structure of the E202Q mutant complex was refined starting from the corresponding wild-type human acetylcholinesterase structure, using the 2.7 A resolution data set collected. Comparison of the two structures shows that removal of the charged group from the protein core and its substitution by a neutral isosteric moiety does not disrupt the functional architecture of the active centre. One of the elements of this architecture is thought to be a hydrogen-bond network including residues Glu202, Glu450, Tyr133 and two bridging molecules of water, which is conserved in other vertebrate acetylcholinesterases as well as in the human enzyme. The present findings are consistent with the notion that the main role of this network is the proper positioning of the Glu202 carboxylate relative to the catalytic triad, thus defining its functional role in the interaction of acetylcholinesterase with substrates and inhibitors.

Acetylcholinesterase↗

PubMed2000

Three-dimensional structures of Drosophila melanogaster acetylcholinesterase and of its complexes with two potent inhibitors.

We have crystallized Drosophila melanogaster acetylcholinesterase and solved the structure of the native enzyme and of its complexes with two potent reversible inhibitors, 1,2,3,4-tetrahydro-N-(phenylmethyl)-9-acridinamine and 1,2,3,4-tetrahydro-N-(3-iodophenyl-methyl)-9-acridinamine--all three at 2.7 A resolution. The refined structure of D. melanogaster acetylcholinesterase is similar to that of vertebrate acetylcholinesterases, for example, human, mouse, and fish, in its overall fold, charge distribution, and deep active-site gorge, but some of the surface loops deviate by up to 8 A from their position in the vertebrate structures, and the C-terminal helix is shifted substantially. The active-site gorge of the insect enzyme is significantly narrower than that of Torpedo californica AChE, and its trajectory is shifted several angstroms. The volume of the lower part of the gorge of the insect enzyme is approximately 50% of that of the vertebrate enzyme. Upon binding of either of the two inhibitors, nine aromatic side chains within the active-site gorge change their conformation so as to interact with the inhibitors. Some differences in activity and specificity between the insect and vertebrate enzymes can be explained by comparison of their three-dimensional structures.

Acetylcholinesterase↗

PubMed1999

Crystal structures of aged phosphonylated acetylcholinesterase: nerve agent reaction products at the atomic level.

Organophosphorus acid anhydride (OP) nerve agents are potent inhibitors which rapidly phosphonylate acetylcholinesterase (AChE) and then may undergo an internal dealkylation reaction (called "aging") to produce an OP-enzyme conjugate that cannot be reactivated. To understand the basis for irreversible inhibition, we solved the structures of aged conjugates obtained by reaction of Torpedo californica AChE (TcAChE) with diisopropylphosphorofluoridate (DFP), O-isopropylmethylphosponofluoridate (sarin), or O-pinacolylmethylphosphonofluoridate (soman) by X-ray crystallography to 2.3, 2.6, or 2.2 A resolution, respectively. The highest positive difference density peak corresponded to the OP phosphorus and was located within covalent bonding distance of the active-site serine (S200) in each structure. The OP-oxygen atoms were within hydrogen-bonding distance of four potential donors from catalytic subsites of the enzyme, suggesting that electrostatic forces significantly stabilize the aged enzyme. The active sites of aged sarin- and soman-TcAChE were essentially identical and provided structural models for the negatively charged, tetrahedral intermediate that occurs during deacylation with the natural substrate, acetylcholine. Phosphorylation with DFP caused an unexpected movement in the main chain of a loop that includes residues F288 and F290 of the TcAChE acyl pocket. This is the first major conformational change reported in the active site of any AChE-ligand complex, and it offers a structural explanation for the substrate selectivity of AChE.

Acetylcholinesterase↗