Abbas Pezeshk

Vitamin E, membrane fluidity, and blood pressure in hypertensive and normotensive rats

Vitamin E treatment was found to lower blood pressure, and increase membrane fluidity in rats. The objectives of this study were to investigate the effects of the antioxidant, vitamin E, on the blood pressure and erythrocyte membrane fluidity in spontaneously hypertensive (SHR) and normotensive (WKY) rats. Membrane fluidity was assessed using spin labeling technique and electron paramagnetic resonance (EPR) spectroscopy. Two different spin labels were used in this study, 5-doxylstrearic acid (5-SASL) and 16-doxylstearic acid (16-SASL). The rats were given vitamin E, 3 days/week for 3 weeks and blood pressure was measured once weekly, using the tail-cuff method. Subsequently, blood was taken via heart puncture and erythrocytes were prepared for spin labeling. The fluidity of the membrane in the nonpolar region of erythrocytes from hypertensive rats was found quite different from that of normal rats as judged by the spectra of 16-SASL. The values of maximum splitting parameter of the EPR spectra of the spin label 5-SASL incorporated in erythrocyte membrane from both SHR and WKY rats, and the effects of vitamin E on membrane fluidity were compared. The maximum splitting parameter calculated from EPR spectra was larger for SHR than WKY rats. Additionally, the maximum splitting parameter calculated for vitamin E treated SHR and WKY rats were lower than those of their respective controls. As expected, the blood pressure of the SHR rats was found to be higher than that of the WKY rats. Vitamin E treated SHR and WKY rats showed significantly lower blood pressure than their controls.

Transport of spin-labeled tetracycline across model and biological membranes

Electron spin resonance spectra of spin labeled tetracycline (TC-SL) do not show any recognizable partitioning into a lipid bilayer or bulk hydrocarbon solvent, paraffin oil. TC-SL, however, penetrates through the model and biological membranes. It is shown that the rate of permeation depends on membrane composition and increases with temperature. In fluid phase, the rate is greater for saturated dimyristoylphosphatidylcholine than for unsaturated egg yolk phosphatidylcholine membranes. Cholesterol significantly decreases the rate, 30 mol% cholesterol decreases the rate of TC-SL permeation across egg yolk phosphatidylcholine bilayer 8 times at 37 degrees C. The rate of permeation of TC-SL across model membranes is much smaller than the rate for TEMPONE--a compound which slightly partitions into lipid bilayer, and much greater than the rate for TEMPO--choline-a positively charged compound. After addition to the suspension of Ehrlichs ascites tumor cells, the TC-SL is reduced to a non-paramagnetic form. Reduction rate is independent of oxygen concentrations, which led us to suggest that the permeation of TC-SL across the cell plasma membrane is the limiting step of reduction reaction.

Partitional and motional properties of a spin-labeled daunomycin in lipid bilayers. An ESR study

The partition coefficient of a spin-labeled daunomycin (DAU-SL) in dimyristoylphosphatidylcholine membrane has been determined using the electron spin resonance (ESR) method. The experiment was carried out as a function of temperature between 5 degrees C and 35 degrees C, giving partition coefficients between 2 and 6 without abrupt change at the phase transition. The thermodynamic parameters on transferring the DAU-SL from the aqueous phase to the lipid bilayer were also calculated. The calculated values are: delta H = 6.11 kcal/mol and delta S = 23 cal/K mol. The partitioning of the DAU-SL and its motion in the membrane were investigated in a wide range of pH (4-10.3). The data show that pH has no effect on partitioning of the DAU-SL which suggest that the drug exists in the uncharged form in the bilayer.

Drug-metal interactions : spectroscopic studies of copper hydantoin complexes

The preparation and spectral properties of copper(II) complexes of two hydantoins are reported. Complexes of the general formula Cu(hyd)2(py)2, where hyd = phenytoin or nirvanol; and py = pyridine were prepared and characterized by infrared and ESR. Spectral data show that the copper atom is bound to the nitrogen atom of the hydantoin anion and to the nitrogen atom of the pyridine molecule to form 2:2:1 hydantoin:pyridine:copper complexes. The ESR data indicate that both complexes have tetragonal symmetry (g11 greater than g perpendicular greater than g e) with the unpaired electron in the d x2-y2 orbital.

The EPR spectrum for CuB in cytochrome c oxidase

Incubation of cytochrome c oxidase (CcO) in its resting state in saturated ammonium sulfate, at room temperature overnight, gave EPR signals characteristic of a single Cu(II) center. From the g// and A// values it is concluded that this is a square-planar type 2 copper center, and superhyperfine splitting shows the presence of three nearly equivalent 14N nuclei in the plane. It is suggested that this center, also formed by incubating the enzyme in 10% methanol followed by direct irradiation, must be the CuB center. This type 2 copper EPR spectrum is identical to the EPR spectrum of CuB reported for the isolated cytochrome bo3 complex from Escherichia coli; and to the EPR spectrum reported for the sulfobetaine 12 heat-treated cytochrome c oxidase complex. It is argued that a small perturbation in the system causes decoupling of the magnetic coupling of the heme a3-CuB binuclear center and the appearance of the type 2 EPR signal.

Low-temperature electron paramagnetic resonance studies reveal the structure of thymine dimer radical anions

Electron addition at 77 K to cis-syn pyrimidine dimers yields the monomer radical anion directly, whereas the trans-syn dimer does not split, thus allowing the first observation of the undissociated dimer anion radical species.

Drug-metal interactions: Copper(II) complex of the antidiabetic drug acetohexamide and pyridine

The preparation, spectral properties, and crystal structure of a copper(II) complex of 4-acetyl-N-[(cyclohexylamino)carbonyl]benzenesulfonamide, which is known as acetohexamide, and pyridine are reported. The complex Cu(AH)2(py)2, where AH = acetohexamide and py = pyridine, was prepared and characterized by X-ray and ESR. The complex is monoclinic, space group P2(1)/a, with a = 17.412(6), b = 9.039(2), c = 26.531(10) A, beta = 102.24(2) degrees, and Z = 4. The final refinement used 3892 unique reflections and gave an R value of 0.0646. The copper atom is surrounded by four nitrogen atoms in a square-planar arrangement, two from the acetohexamide ligands (Cu-N = 2.009 A) and two from the pyridine molecules (Cu-N = 2.016 A) in a trans geometry. The ESR data support a similar coordination behavior of the copper (g parallel greater than g perpendicular greater than ge) with the unpaired electron in the dx2-y2 orbital.

Spectroscopic and biological studies of spin-labeled tetracycline

A new nitroxyl labeled tetracycline is synthesized. Proton NMR experiments of tetracycline, spin-labeled tetracycline, and the diamagnetic reduced form in DMSO-d6 are reported. The signals observed in the NMR spectra are all assigned. The NMR data revealed that the spin label is attached to the C-2 amide group on ring A of tetracycline. The spin-labeled tetracycline is also tested in vitro for antitumor activity and is found to be active against leukemia P338/ADR cell line and in melanoma LOX cell line.

ESR studies of molecular interactions of copper (II) nirvanol and copper (II) diisopropylsalicylate with Ehrlich ascites tumor cells

ESR spectra have been obtained after addition of either a cupric phenylhydantoin or a cupric diisopropylsalicylate complex to Ehrlich ascites tumor cells. It is shown that some of the complex remains in the cupric state. Because the ESR parameters of these complexes in the presence of cells differ from the ESR parameters for these complexes in the absence of cells, in the presence of cells either adducts or new cupric complexes are formed. The fast motion of these complexes, as determined from room temperature ESR spectra, is characteristic of complexes with molecular weights less than 1500.

Partitioning and structural effects of the antitumor drug daunomycin on model membranes

The effects of the antitumor drug daunomycin on the phase transition and dynamic properties of phosphatidylcholine membranes were investigated using the electron paramagenetic resonance spin labeling method. Multilamellar liposomes made of saturated dimyristoylphosphatidylcholine and unsaturated egg yolk phosphatidylcholine were used. The main phase transition of saturated bilayer was significantly broadened in the presence of daunomycin. In the fluid phase of saturated membranes, daunomycin caused a decrease in the rotational motion of the spin probe 16-doxylstearic acid (16-SASL). This effect was strongly diminished by raising the temperature. In unsaturated membranes no influence of daunomycin on the rotational motion of 16-SASL was observed. It is proposed that the neutral form of daunomycin can partition into lipid bilayer where it can diffuse into deeper hydrophobic regions of the membrane and decrease the motion of alkyl chains.