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Biomedical subjects

M Tabak

Publications and source records attributed to M Tabak.

At least 37 records · Page 2Linked to original sources
PubMed1995

Effect of hydration upon the fluidity of intercellular membranes of stratum corneum: an EPR study.

The principal mechanisms controlling the molecular permeability through the skin are associated to the intercellular membranes of stratum corneum (SC), the outermost layer of mammalian skin. It is generally accepted that an increase in fluidity of these membranes leads to a reduction of the physical barrier exerted by SC with a consequent enhancement in permeation of different compounds. It is known that water diffusion in SC increases with the increase in the water content in SC. Using the spin labeling method we evaluate the effect of hydration on the fluidity of intercellular membranes at three depths of the alkyl chain. Increase in the water content in SC leads to a drastic increase in membrane fluidity especially in the region near the membrane/water interface; the effect decreases on going deeper inside the hydrophobic core. Analysis of electron paramagnetic resonance (EPR) parameters as a function of temperature showed that the rotational motion at depth of the 16th carbon atom of the chain experienced a phase transition at 45 and 60 degrees C. These phase transition temperatures were not altered by changes in the water content of SC. A phase transition between 28 and 48 degrees C was observed from the segmental motion in the region near the polar headgroup (up to 12th carbon in the chain) and was strongly dependent upon the hydration of SC. Our results give a better characterization of the fluidity of SC, the main parameter involved in the mechanisms that control the permeability of different compounds through skin.

Animals↗
PubMed1995

Proton relaxation and spin label studies of papaverine localization in ionic micelles.

The localization of papaverine (PAV) in micelles of zwitter-ionic N-hexadecyl-N, N-dimethyl-3-ammonio-1-propanesulfonate (HPS), cationic cetyltrimethylammonium chloride (CTAC), and anionic sodium dodecyl sulfate (SDS) in D2O was studied by 1H NMR and ESR in the presence and absence of 5-doxyl- or 12-doxyl-stearic acid. PAV, surfactants, and spin probes are characterized by restricted anisotropic motion in micelles. The rotational correlation time of doxyl fragment was in the range of 0.2 to 0.5 nanoseconds. Binding of PAV to micelles decreases the mobility of both probes, suggesting the localization of PAV inside the hydrophobic part of micelles near the micelle-water interface. According to the NOE data, the methoxy groups of PAV are located in the vicinity of the nitrogen atom in CTAC and HPS micelles, the methoxy groups of the PAV heterocycle being immersed slightly deeper inside the micelle. The T1 relaxation enhancements by two different spin probes show that the H5 and methoxy substituents of the PAV heterocycle are in close proximity to the alpha-CH2 of acyl chains in all types of micelles, whereas H3 and H12 are the most distant from the alpha-CH2. No significant differences were found for the protonated and neutral PAV in SDS micelles at pD 4.9 and 11.2. These data show that the geometry of the PAV-micelle complex is practically independent of the PAV charge and surfactant head-group.

Electron Spin Resonance Spectroscopy↗
PubMed1995

Interaction of primaquine and chloroquine with ionic micelles as studied by 1H NMR and electronic absorption spectroscopy.

The characteristics of binding of primaquine (PQ) and chloroquine (CQ) to micelles of surfactants with different charge of headgroups were studied by 1H-NMR and optical absorption spectroscopy. Cetyltrimethylammonium chloride (CTAC) was used as a cationic surfactant, sodium dodecylsulfate (SDS) as an anionic surfactant and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane-sulfonate (HPS) as zwitterionic. The pK values and binding constants were estimated. Interaction with SDS significantly increases an apparent pK of PQ and CQ. However, chemical shift patterns and values of binding constants in the presence of different surfactants show that mode of interaction of charged drugs with micelles is nonspecific, since the complexes formed are similar for different types of surfactants. Electrostatic forces alter the affinity between drugs and micelles bearing charged groups. Interaction of drugs with cationic micelles is prevented if the drug has two positive charges. HPS interacts with charged drugs in the same manner as CTAC rather than SDS.

Cetrimonium↗
PubMed1995

Stratum corneum intercellular lipid as compared to erythrocyte ghosts: an ESR study of thermotropic behavior and nitroxide reduction. Electron Spin Resonance.

Intercellular membranes of Stratum Corneum and erythrocyte ghosts were studied through partition of Tempo nitroxide spin label. Stratum Corneum presents a phase transition-monitored by the spin label at 58 degrees C--that is in agreement with data obtained through the use of other techniques. A reduction of the nitroxide is observed. Erythrocyte ghosts at protein concentrations higher than the values generally used in ESR studies (above 15 mg/ml) also show the partition and reduction of Tempo. Experimental data suggest that the reduction mechanism might be common to both types of membranes involving probably the membrane lipoperoxidation as well as protein oxidation.

Animals↗
PubMed1994

Charge- and pH-dependent binding sites for dibucaine in ionic micelles: a fluorescence study.

Binding of micromolar concentrations of the local anesthetic dibucaine to micelles of cationic, zwitterionic and anionic detergents was studied using the fluorescence emission of dibucaine. Difference in quantum yields for charged and neutral dibucaine allowed to obtain shifts of pKa values due to binding. Estimates for the electrostatic potential affecting the tertiary amine of dibucaine were obtained from the pKa shifts. Change of fluorescence emission upon binding allowed to obtain the binding constants of both charged and neutral dibucaine to the micelles. The binding constant for the neutral form is essentially independent of micelle charge and of specific differences in detergent structure. Consistency between the ratio of neutral to cationic dibucaine binding constants and the measured pKa shift was tested. For LPC micelles complete agreement was found. For CTAC, however, the ratio of binding constants does not explain the pKa shift. The discrepancy between the results is used to estimate the errors involved upon neglecting non-coulombic electrostatic interactions of drugs to charged membrane surfaces. Fluorescence quenching with sodium iodide and nitroxide stearic acid derivatives allowed a depth profiling of the drug in the micelles.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1994

Depth profiling of dibucaine in sarcoplasmic reticulum vesicles by fluorescence quenching.

The location of molecules of the local anesthetic dibucaine in sarcoplasmic reticulum vesicles (SRV) was determined using the quenching of its intrinsic fluorescence by iodide and by nitroxide-labeled stearic acids (SASL) with the nitroxide group at different positions of the fatty acyl chain. The molar ratios of dibucaine to Ca(2+)-ATPase in the samples were less than 1. The acid-base titration of membrane bound dibucaine revealed a pK of 9.1, showing a negligible shift upon binding. The quenching data were obtained at pH 6.8 and are therefore related to protonated dibucaine. Quenching by iodide showed SRV-bound dibucaine to be more protected from collisions with iodide anion than dibucaine in buffer or even in neutral micelles. This shows the influence of negatively charged lipids in keeping iodide away from the ionic diffuse layer of the membrane surface where the dibucaine tertiary amine might be located. Analysis of the SASL quenching data indicates that dibucaine molecules are at a shallow position in the membrane bilayer. Their average depth was found to be at most that of the fourth carbon atom of the fatty acyl chain. The results do not exclude a preferential site for dibucaine in Ca(2+)-ATPase, but if there is such site it must be located at the protein/lipid interface.

Animals↗
PubMed1994

Interaction of papaverine with micelles of surfactants with different charge studied by 1H-NMR.

The interaction of the vasodilator drug papaverine (PAV) with micelles of surfactants with different charge of headgroups as well as the properties of PAV in D2O solution were studied by 1H-NMR. At pD values above 6.4 deprotonated PAV molecules tend to precipitate, the signals of the heterocycle protons of solubilized PAV molecules being shifted to high field. At PAV concentration above 1 mM its protons experience upfield shifts which increase with pD value and are due to the stacking of aromatic rings. Incorporation into micelles caused shifts of all resonances. This effect is due to changes in the local chemical environment of PAV rather than to stacking, and, possibly, involves the deprotonation of the N atom of PAV heterocycle. Line broadening of PAV protons at the molar ratio surfactant/PAV > 16 indicated their restricted mobility. Different complexes were formed due to interaction between the heterocycle of PAV and polar headgroups of cationic cetyltrimethylammonium chloride (CTAC) or anionic sodium dodecylsulfate (SDS). The binding of PAV to zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) is similar to that of PAV to CTAC. Association constants were estimated from NMR data as 20, 60 and 350 M-1 at pD = 4.9 +/- 0.1 for HPS, CTAC and SDS, respectively. Thus, the mode of binding of PAV to HPS is defined by the cationic dimethylammonium headgroup fragment, whereas the negative fragment attenuates the effective charge of HPS headgroup.

Electrochemistry↗
PubMed1994

Binding of peptide fragments from a seven helix membrane receptor to lipid bilayers and to micelles.

Membrane proteins influence the organizational and motional properties of lipids, while the conformation and function of these proteins (receptors, channels, enzymes, pumps) are affected by the lipid environment. Model systems consisting of peptides and lipids can provide information at a molecular level about the interactions between proteins and lipids in biological membranes. We have synthesized peptides (residues 253-266 (EYWSTFGNLHHISL) from the seven-helix receptor expressed by the mas oncogene), having free or blocked N- and C-terminals. An analog was obtained by linking a spin-labeled amino acid to the N-terminal via a peptide bond. Several spectroscopic techniques were employed to study the interaction between the peptides and lipophilic systems (zwitterionic and negatively charged phospholipid bilayers, and negatively charged, positively charged, zwitterionic and nonionic micelles). Peptide conformational changes were monitored by circular dichroism (CD). The peptides acquired an increased secondary structure upon binding to the lipid systems. Additional evidence for peptide incorporation into micelles came from fluorescence measurements which indicated a blue shift of the tryptophan's emission wavelength, and from ESR spectra of the spin-labeled analog. While narrow lines were obtained in the aqueous phase, line broadening indicative of slower motion was observed in the presence of the lipophilic aggregates. The slow exchange between the two media allowed the evaluation of partition coefficients. The spectra in aqueous solution were also sensitive to conformational changes as a function of pH, allowing the determination of the N-terminal pK. ESR spectra of lipid spin probes incorporated into phospholipid bilayers indicated that the lipids became more immobilized upon binding of the peptides.

Amino Acid Sequence↗
PubMed1993

[Identification systems for dental prostheses using fluorescence techniques].

The dental description of unknown or missing persons in case of mass disasters such as fire, drowning and individual accidents is a very successful odontological mean of identification in forensic research. Difficulties arise if the natural dentition is gone for one reason or another or has been replaced by a dental prothesis. From a dental-prosthetic point of view, this can be prevented by using denture marking in order to give this registration a more personal character, an application from the fluorescence technique was chosen, enabling to mark the denture base with an adequate and inconspicuous code when fabricating the prothesis. This preventive registration may be read in the visible spectrum with the proper equipment at a specific frequency. In view to an increase in the percentage of old people and inherently an increased use of prosthetic appliances with this population, registration by means of the fluorescence technique will be most useful to the forensic odontologist in his identification research. Other useful indications are patients in hospitals, parental homes, nursing-homes and mental homes. To prevent exchange or the loss of prosthetics.

Aged↗
PubMed1992

Interaction of dipyridamole with micelles of lysophosphatidylcholine and with bovine serum albumin: fluorescence studies.

The interaction of the coronary vasodilator dipyridamole with biological systems, protein and membranes has been studied through optical absorption and fluorescence spectroscopies. Using the analysis of the spectra and fluorescence intensity of dipyridamole (DIP) in solution, the interaction of this compound with the transport protein albumin (BSA) and with a model of cell membranes, namely micelles of lysophosphatidylcholine (L-PC), was investigated. Measurements were performed at pH 5.0 and pH 7.0 where the molecule of DIP is fully protonated and partially protonated, respectively. The quenching of fluorescence with nitroxide-stable radicals 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as well as with acrylamide and iodide allowed the localization of the drug in the polar interface of micelles. Quenching by acrylamide and iodide in L-PC micelles demonstrated the effect of micelle protonation which increased the accessibility of iodide to the chromophore. An effective association constant was obtained both at pH 7.0 (7.5 x 10(3) M-1) and pH 5.0 (2.5 x 10(3) M-1) and a very good agreement with the proposed binding model was observed. The quantum yields of fluorescence data agree very well with the fluorescence lifetimes. The measurement of lifetimes was important to understand the kinetic data obtained from Stern-Volmer plots both of radical, acrylamide and iodide quenching of fluorescence. It was observed that, in the presence of micelles, the kq value increased for TEMPO while decreased for TEMPOL. This result, together with the vanishing solubility of DIP in saturated hydrocarbons and the preferential partition of TEMPO in micelles, suggested the localization of DIP in the polar micellar interface. This is also supported by the enhanced iodide quenching at pH 5.0, constancy of acrylamide quenching in the range of pH 7.0-5.0 and the partition of TEMPO and TEMPOL in SDS micelles. The association constant of DIP to BSA was also estimated both at pH 7.0 (2 x 10(4) M-1) and pH 5.0 (4 x 10(3) M-1). Quenching studies with nitroxide radicals, acrylamide and iodide also suggested the binding of the drug to a hydrophobic region of the protein. At pH 5.0, the protein undergo a conformational change which leads to a loosening of the overall structure so that the accessibility of the nitroxide radicals for DIP is increased at this pH. The differences in kq values at pH 7.0 and pH 5.0 suggested that at pH 7.0 the chromophore is protected in the protein site.(ABSTRACT TRUNCATED AT 400 WORDS)

Dipyridamole↗
PubMed1991

The lymphocyte transformation test with type II collagen as a diagnostic tool of autoimmune sensorineural hearing loss.

Immunological disorders of the cellular type can be diagnosed by the lymphocyte transformation test (LTT). An autoimmune mechanism of certain cases of sensorineural hearing loss (SNHL) can be evaluated by using human inner ear tissue as an antigen. Recent studies have shown that type II collagen plays an important role, not only in some autoimmune mediated rheumatoid diseases, but also as an antigenic substrate of inner ear tissue in autoimmune sensorineural hearing loss. This paper deals with results of the lymphocyte transformation test using type II collagen as antigen in 68 patients with progressive sensorineural hearing loss (PSNHL) and 68 healthy volunteers. Thirty-four patients showed a strong stimulation in the lymphocyte transformation test, in contrast to only four volunteers in the control group, two of whom had a history of rheumatoid arthritis.

Adult↗
PubMed1990

An ESR study of pathologic red blood cell membranes (RBCM).

A comparative study of red blood cell membranes from normal subjects and beta-thalassemia and sickle cell anemia patients was performed by spin labeling at the lipidic and protein phase. The results show that the quantity of bound spin label is the same for sickle, thalassemic, and normal membranes. The data from 5-doxyl stearic acid suggest an increase in fluidity for the thalassemic membrane.

Adult↗
PubMed1990

Effect of low mole fraction of trehalose dicorynomycolate from Corynebacterium diphtheriae on water permeability and electrical capacitance of lipid bilayer membranes.

The effect of incorporation of different proportions of trehalose dicorynomycolates (TDC) into lecithin bilayer membranes was studied. It was found that TDC, induces a 14% decrease of water osmotic permeability (42.6 +/- 3.9 to 36.8 +/- 2.7 microns/s) at 1.6 mole%, suggesting that this substance leads to an increase of the degree of packing of the constituent lipid molecules. A condensing effect of TDC was also apparent from membrane electrical capacitance (Cm) measurement. By incorporating TDC into bilayer membranes, the value of Cm experienced a decrease of 29% at 1.6% mole fraction. This finding was taken to reflect an increase in membrane thickness, known in many examples, to be related to the condensing effect.

Cord Factors↗
PubMed1990

Effect of hydration in metHb: reversible changes monitored by ESR of iron.

The dehydration of human and bovine methemoglobins was monitored using ESR spectroscopy of the iron signal. The interconversion of the Fe(III) signal between the high spin form (at g approximately 6) in solution and low spin form (at g approximately 2) was quantitatively studied as a function of hydration. The dehydration process leads also to a loss of paramagnetism resulting in the appearance of about 40% Fe(II) below 0.40 grH2O/grHb. The remaining 60% of Fe(III) ESR signal is distributed as the residual high spin form (at g approximately 6, 5%) and low spin form (hemichromes H and P, 55%). The formation of hemichrome P was explained as resulting from the coordination of the cysteine residue at beta 93 with the iron atom which follows the rupture of the proximal histidine bond. Experiments with hemoglobins where the sulphur atom of cysteine beta 93 was blocked (N-ethylmaleimide) did not showed the hemichrome P, confirming the involvement of the sulphur atom. This implies that the dehydration process induces displacements and torsion of the F helix, drastically changing the iron coordination at proximal site. In agreement with this proposition the Fe(II) symmetry is pentacoordinated with the disrupted bond to the proximal histidine at fifth coordination. This is also supported by ESR experiments with nitrosyl complex at low hydrations. All conformational changes were reversibly modulated by hydration degree and partially by lyophilization rate. A one-cycle dehydration of bovine hemoglobin followed by solubilization shows 100% reversibility of hemichrome P. Increasing the number of cycles of dehydration-hydration reduces the reversibility degree. With three cycles a reversibility of 70%-75% is observed. The level of 0.40 grH2O/grHb was the critical hydration for the molecules to return to aquo met form and correspond also to a minimal water content necessary to cover all protein surface as obtained from other techniques.

Animals↗
PubMed1988

pH-dependent phase transition of chlorpromazine micellar solutions in the physiological range.

The effects of pH and drug concentration on aggregation properties of chlorpromazine-HCl (CPZ) are examined. The critical micelle concentration (cmc) changes from 0.2 mM at pH 7.3 to 2 mM at pH 5.6 as estimated from the stearic acid spin label solubility measurements. For concentrations above the cmc CPZ micelles undergo a concentration-, temperature- and pH-dependent transition leading to phase separation. This phase transition is followed by a sudden increase of light scattering. The phase diagram pH vs. concentration is obtained by observation of the cloud point for concentrations ranging from 0.01 to 10 mM. The intramicellar environment is probed at pH ranging from 5.5 to 8.0 using a stearic acid spin label. The intramicellar compactness increases smoothly with increasing pH suggesting the weakening of polar heads repulsion due to charge decrease. The reported results indicate that pH effects are relevant and should be properly taken into account in the performance and interpretation of experiments with CPZ.

Chlorpromazine↗
PubMed1988

The mechanism of reaction of nitrosyl with met- and oxymyoglobin: an ESR study.

In this ESR work we have studied the pentacoordinate symmetry in horse, whale and sperm-whale myoglobin (Mb) in different physical states such as solution and powder. Experiments were performed in which the following parameters were varied: the sample temperature, pH, reaction time with NO, and NO concentration. The results enabled us to explain the NO reaction mechanism in the oxy and met forms of myoglobin. The study of powder samples at different degrees of hydration allowed us to identify the diamagnetic intermediate species existent in the reaction of NO with met-Mb proposed in the literature. The results presented explain adequately the pH effect and temperature dependence observed in the ESR spectra obtained using the met-Mb sample solutions from Sigma Chemical Co., which consist of a mixture (13%) of Mb-O2.

Electron Spin Resonance Spectroscopy↗