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PubMed2004

Two analytical solutions for a model of pulsed arterial spin labeling with randomized blood arrival times.

A fairly general theoretical model for pulsed arterial spin labeling perfusion methods has been available for some time but analytical solutions were derived for only a small number of arterial blood input functions. These mostly assumed a sudden and simultaneous arrival of the tagged blood into the imaged region. More general cases had to be handled numerically. We present analytical solutions for two more realistic arterial input functions. They both allow the arrival times of the molecules of tagged arterial blood to be statistically distributed. We consider cases of (1) a uniform distribution on a finite time interval and (2) a normal distribution characterized by its mean and standard deviation. These models are physiologically meaningful because the statistical nature of the arrival times reflects the distribution of velocities and path lengths that the blood water molecules undertake from the tagging region to the imaged region. The model parameters can be estimated from the measured dependency of the perfusion signal on the tag inversion time.

Algorithms↗
PubMed2003

Pediatric perfusion imaging using pulsed arterial spin labeling.

PURPOSE: To test the feasibility of pediatric perfusion imaging using a pulsed arterial spin labeling (ASL) technique at 1.5 T. MATERIALS AND METHODS: ASL perfusion imaging was carried out on seven neurologically normal children and five healthy adults. The signal-to-noise ratio (SNR) of the perfusion images along with T1, M(0), arterial transit time, and the temporal fluctuation of the ASL image series were measured and compared between the two age groups. In addition, ASL perfusion magnetic resonance (MR) was performed on three children with neurologic disorder. RESULTS: In the cohort of neurologically normal children, a 70% increase in the SNR of the ASL perfusion images and a 30% increase in the absolute cerebral blood flow compared to the adult data were observed. The measures of ASL SNR, T1, and M(0) were found to decrease linearly with age. Transit time and temporal fluctuation of the ASL perfusion image series were not significantly different between the two age groups. The feasibility of ASL in the diagnosis of pediatric neurologic disease was also illustrated. CONCLUSION: ASL is a promising tool for pediatric perfusion imaging given the unique and reciprocal benefits in terms of safety and image quality.

Adult↗
PubMed1982

Spin-labeled phorbol esters and their interaction with cellular membranes.

A series of homologous spin-labeled fatty acid analogs of the type 12-O-FASL (n,m)-phorbol-13-acetate [(n,m)PA] of 12-O-tetradecanoylphorbol-13-acetate (TPA) with variable chain length N of the fatty acid moiety and various positions of the nitroxide group were synthesized. Their irritant doses 50 (ID50) on the ear and their initiation-promoting activities on the back skin of NMRI mice were determined. The irritancy 1/ID50 of the (n,m)PA follows the simple linear relation ln(1/ID50) = alpha N + beta. In an "equilibrium" approach, the electron paramagnetic resonance (EPR) spectra measured in absence and in presence of erythrocytes (E) were used to determine the partition coefficients KM,0 between the erythrocyte membrane (M) and the extracellular solution (o). The KM,0 depend on the chain length N of the fatty acid moieties following the equation ln KM,0 = aN + b and show that the (n,m)PA are accumulated preferentially in the erythrocyte membrane. In a "kinetic" approach, the decay rate J(t)/J(o) of the EPR signal intensity of (n,m)PA molecules in absence and in presence of equilibrated E was measured during oxidation with ferricyanide and reduction with ascorbate, respectively. From the data obtained by the "kinetic" approach, a "two-compartmental model" is shown to be the most simple approximation to describe the system, in which finite concentrations of the (n,m)PA are postulated for the extracellular and the membrane compartment only. EPR data indicate that generally the (n,m)PA are buried with their acyl chain in the E membrane with the phorbol moiety close to the outer membrane surface. Apparently only in case of (1,12)PA is the acyl chain long enough to be anchored in the lipid layer of the membrane in a way similar to the tetradecanoyl residue of TPA. A possible relationship with biological activities is discussed.

Animals↗
PubMed1996

Structural features and light-dependent changes in the cytoplasmic interhelical E-F loop region of rhodopsin: a site-directed spin-labeling study.

Thirty consecutive single cysteine substitution mutants in the amino acids Q225-I256 of bovine rhodopsin have been prepared and modified with a sulfhydryl specific nitroxide reagent. This sequence includes the E-F interhelical loop, a transducin interaction site. The accessibilities of the attached nitroxides to collisions with hydrophilic and hydrophobic paramagnetic probes in solution were determined, and the electron paramagnetic resonance spectra analyzed in terms of side chain mobility, both in the dark and after photoactivation. Accessibility cata shows that the rhodopsin polypeptide chain crosses an aqueous/ hydrophobic boundary in the range V227-K231 and again in the range V250-V254. In the hydrophobic segments, both the accessibility and mobility data are consistent with helical structures. In the regions of the sequence located within the aqueous phase, periodic variation in both accessibility and mobility of the spin-labeled side chains indicates that the E-F interhelical loop is largely alpha-helical, being formed by regular extensions of the E and F helices by about 1.5 and 3 turns, respectively. Judging from nitroxide mobilities, the putative extension of helix E in the aqueous phase is more dynamic than that of helix F. Changes in the electron paramagnetic resonance characteristics of the spin-labeled rhodopsin upon photoactivation indicate that chromophore isomerization results in patterns of structural changes that can be interpreted in terms of movements of helices that extend into the aqueous loop regions.

Amino Acid Sequence↗
PubMed1979

Spin labeling studies of the interactions of P815 mouse mastocytoma cells with antiserum to histocompatibility antigens, H-2d.

The effect of antiserum to histocompatibility antigens on the membrane organization of murine neoplastic mast cells (P815) has been studied by spin labeling. Incubation of in vivo passaged cells, labeled with a nitroxide derivative of methyl stearate, with antiserum to membrane carried histocompatibility antigens, H-2d, resulted in an apparent decrease in membrane fluidity that was accompanied by histamine release. This electron spin resonance (esr) detectable change was found to be temperature, time, and dose dependent. Treatment of the cells with cytochalasin B, a drug disrupting microfilament structure, inhibited the effects induced by H-2d antiserum. In contrast, vinblastine, which disrupts microtubules, did not modulate the effect of this antiserum. Other data presented here suggest that some of the large spectral change observed on treatment of the cells with anti-H-2d serum may result from hydrolysis of the spin label fatty acid ester via activation of a membrane-associated esterase. The relationship of these results to other immunologically induced membrane phenomena is discussed.

Animals↗
PubMed2003

Quantitative tissue perfusion measurements in head and neck carcinoma patients before and during radiation therapy with a non-invasive MR imaging spin-labeling technique.

PURPOSE: Tumor blood flow, tumor tissue perfusion and oxygen supply have substantial influence on the responsiveness of tumors to radiotherapy. This study was aimed at implementing and evaluating a non-invasive functional magnetic resonance (MR) imaging spin-labeling technique at a main magnetic field strength of 2T for measuring tissue perfusion changes in head and neck carcinoma patients before and during radiotherapy. METHODS: Tissue perfusion was determined quantitatively in ten patients with head and neck cancer. Five patients were investigated twice during radiation therapy. For perfusion measurements, a non-invasive MR spin-labeling technique was employed: The longitudinal relaxation time T(1) was measured with segmented Snapshot-FLASH imaging after either slice-selective or non-selective spin inversion. Perfusion values were calculated pixelwise employing a two-compartment tissue model. With this technique no contrast agents are required so that repetitive measurements are possible. Perfusion images with a slice thickness of 10mm and an in-plane resolution of 1.9x2.8mm(2) were acquired at a total scan time of 8:30min per scan. RESULTS: With the non-invasive MR imaging technique it was possible to visualize tumor and normal tissue perfusion as well as perfusion changes in the course of radiotherapy with a spatial resolution of less than 3mm. Among the investigated subjects measured tumor perfusion and changes in perfusion were heterogenous. In 4/5 patients studied at the start and end of radiotherapy, perfusion decreased, while in one patient there was an increase. CONCLUSIONS: A method is presented that allows non-invasive and repetitive characterization of tissue perfusion. This parameter may be used for treatment stratification, especially in treatments that use vasomodulation or anti-angiogenic agents.

Algorithms↗
PubMed1975

Spin label evidence for the role of lysoglycerophosphatides in cellular membranes of hibernating mammals.

The phospholipid composition of ground squirrel heart muscle changes during hibernation: more lysoglycerophosphatides are found in the hibernating state than in the active state. Phase transitions inferred from spin label motion occur in the usual manner typical of mammalian mitochondria for the mitochondria and mitochondrial lipids from active squirrels. However, a conspicuous absence of a spin label-detectable phase transition is observed in equivalent preparations from hibernating animals. The addition of lysolecithin to preparations from active squirrels removes the break and induces a straight line in the Arrhenius plot. The lack of a spin label-detectable phase transition in hibernating animals, therefore, is attributed to an increased content of lysoglycerophosphatides present in the phospholipids during hibernation.

Adaptation, Physiological↗
PubMed1977

Drug tolerance in biomembranes: a spin label study of the effects of ethanol.

Ethanol in vitro increased the fluidity of spin-labeled membranes from normal mice. Membranes from mice that had been subjected to long-term ethanol treatment were relatively resistant to this fluidizing effect. The data suggest that the membranes themselves had adapted to the drug, a novel form of drug tolerance.

Adaptation, Physiological↗
PubMed1985

Reduction of the spin-label TEMPONE by ubiquinol in the electron transport chain of intact rabbit spermatozoa.

When the hydrophilic spin label TEMPONE (deuterated 2,2,6,6-tetramethylpiperidine-N-oxyl) was incubated with intact rabbit spermatozoa at concentrations greater than 0.3 X 10(9) cells/ml, the electron spin resonance signal height decreased with time. This loss of signal amplitude was reversed by the oxidizing reagent potassium dichromate, indicating that the signal loss was due to a reduction of the paramagnetic nitroxide species to the nonparamagnetic hydroxylamine. Using inhibitors that act on the respiratory chain, we observed that, relative to controls, the rate of TEMPONE reduction was decreased in the presence of rotenone, but increased in the presence of antimycin A and potassium cyanide (KCN). Parallel studies measuring oxygen consumption showed decreases with all three inhibitors. We interpret these observations to mean that TEMPONE is reduced by ubiquinol in the respiratory chain. Supporting this conclusion is the observation that the midpoint potential of TEMPONE was determined by be +48mV, which is close to the midpoint potential of +40 mV for the ubiquinone/ubiquinol couple. Furthermore, in a cell-free test system, ubiquinol reduced TEMPONE, but ubiquinone, NADH, and succinate did not.

Animals↗
PubMed1987

Spin-label studies on the specificity of interaction of cardiolipin with beef heart cytochrome oxidase.

The selectivity of interaction of various cardiolipin analogues with beef heart cytochrome oxidase in reconstituted complexes with dimyristoylphosphatidylcholine has been studied by electron spin resonance spectroscopy, using lipids spin-labeled in the acyl chains. No difference in selectivity is observed between cardiolipin and its monolyso derivative, and similarly no selectivity is observed between phosphatidylcholine and lysophosphatidylcholine. Removal of the cardiolipin charge by methylation of the phosphate groups reduces but does not eliminate selectivity relative to phosphatidylcholine. The dependence of the lipid selectivity on head group and chain composition is in the order cardiolipin approximately equal to monolysocardiolipin greater than acylcardiolipin greater than dimethylcardiolipin greater than phosphatidylcholine approximately equal to lysophosphatidylcholine, where acylcardiolipin has the spin-label chain attached at the center -OH of the head group. The degree of association of the negatively charged cardiolipin derivatives with cytochrome oxidase decreases with increasing salt concentration, to a level comparable to that for dimethylcardiolipin. At high ionic strength there is still a marked selectivity relative to phosphatidylcholine. Li+ ions are more effective in screening the interaction than are Na+ ions, and divalent ions are more effective than monovalent ions. The selectivity for cardiolipin is only slightly reduced on titrating the protein to high pH. Alkylation of the protein with N-ethylmaleimide has little effect on the titration behavior. Covalent modification of the protein by reaction with citraconic anhydride decreases the selectivity of interaction with cardiolipin. It is concluded that cardiolipin possesses an additional specificity of interaction with cytochrome oxidase other than that of purely electrostatic origin.

Animals↗
PubMed1999

Fingerprint patterns from laser-induced azido photochemistry of spin-labeled photoaffinity ATP analogs in matrix-assisted laser desorption/ionization mass spectrometry.

The photochemical reaction of azide derivatives induced by ultraviolet (UV) laser in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) is reported. A novel synthesized class of azide aromatic derivatives, spin-labeled photoaffinity non-nucleoside adenosine triphosphate (ATP) analogs which are useful probes in study of muscle contraction mechanism, is used in this investigation. In the negative ion MALDI spectra of these ATP analogs, "fingerprint" peaks corresponding to [M - 10 - 1]-, [M - 12 - 1]-, [M - 16 - 1]-, [M - 26 - 1]-, [M - 28 - 1]-, [M - 41 - 1]-, and [M - 42 - 1]- were observed with relative intensities depending on the MALDI matrix. Only the [M - 16 - 1]- is present in the similar mass spectra of the analog in which the azido group is replaced by a hydrogen. A model is suggested for the photochemical reactions of azide derivatives under UV laser irradiation. The photoreaction fingerprint information is diagnostically useful in characterization of azido compounds, especially for spin-labeled photoaffinity non-nucleoside ATP analogs.

Adenosine Triphosphate↗
PubMed1985

Measurement of intracellular oxygen concentration using the spin label TEMPOL.

We have developed a noninvasive method with general applicability for measuring intracellular oxygen using the spin label TEMPOL (2,2,6,6,-tetramethypiperidine-N-oxyl-4-ol) which has superhyperfine structure in its electron spin resonance spectra that is broadened in the presence of oxygen. This broadening is linear over a range of 1 to 6 ppm oxygen which covers the important physiological range of oxygen concentration. Viscosity, TEMPOL concentration, and instrument modulation intensity also can affect superhyperfine structure but the contributions from these effects can be determined. The TEMPOL distributes equally into the intra- and extracellular compartments but its intracellular signal can be studied selectively by addition of transition metal ions such as potassium ferricyanide and potassium tris(oxalato)chromiate, which broaden away the signal from extracellular TEMPOL and do not cross the cell membrane to affect the intracellular TEMPOL. Results with a cell culture line (mouse thymus-bone marrow) indicate that under our experimental conditions these cells may maintain an average intracellular oxygen concentration lower than the extracellular oxygen concentration, and that there is not a constant relationship between extracellular and intracellular oxygen concentrations.

Animals↗
PubMed1989

A spin labeling study of pig cardiac tropomyosin.

Tropomyosin (TM) extracted from pig cardiac muscle was spin-labeled with 2,2,6,6-tetramethyl-4-(dichlorotriazin)-aminopiperidine-1-oxyl. The ESR spectra of the product (SL-TM) were of a type of weak immobilization. Effects of three means for the denaturation were observed on the above spectra. The ESR spectrum obtained for SL-TM after enzymatic degradation was found to be analogous to that for the label itself in a dilute solution and thereby the quantity of labels bound in SL-TM estimated. The Arrhenius plots attained through variable temperature measurement for SL-TM's exhibited two inflexion points (the conformational transition temperatures for TM) around 45 degrees C and 74-75 degrees C, the latter temperature having not been reported in literature so far. However, the enzymatic degradation product from SL-TM behaved quite differently from it in the response to microwave power saturation and temperature variation.

Animals↗
PubMed1984

Spin-labeling study of phosphatidylcholine-cardiolipin binary mixtures.

Electron paramagnetic resonance spectra of the spin-label probe 2,2,6,6-tetramethylpiperidinyl-1-oxy have been used to study the phase behavior of binary mixtures of different phosphatidylcholines (dipalmitoyl, distearoyl, and dioleoyl) with cardiolipin, using either calcium-free or calcium-containing cardiolipin (with a calcium:cardiolipin ratio of 1:2) samples. Results show that the nature of the fatty acid chains of the phosphatidylcholines (chain length and unsaturation) may influence the coexistence of different phases as well as does the nature of the cation linked to the cardiolipin.

Animals↗
PubMed1999

MR perfusion imaging of pulmonary parenchyma using pulsed arterial spin labeling techniques: FAIRER and FAIR.

Magnetic resonance imaging of pulmonary parenchyma perfusion using pulsed arterial spin labeling (ASL) techniques is presented. ASL uses magnetically labeled water as an endogenous, freely diffusible tracer. Presented are comparative results of ASL methods called Flow sensitive Alternating Inversion Recovery (FAIR), and FAIR with an Extra Radiofrequency pulse (FAIRER). Six healthy human volunteers were imaged. Perfusion-weighted images at different time delays, TI, were calculated from the subtraction of the control and tag images, which were acquired within a single breathhold. Detailed pulmonary structures can be visualized with negligible cardiac or respiratory motion artifacts. Different patterns of signal enhancement between the pulmonary vessels and parenchyma are shown in the perfusion images acquired at different TIs.

Adult↗
PubMed1985

Measurement of erythrocyte orientation in flow by spin labeling III--erythrocyte orientation and rheological conditions.

The measurements of erythrocyte orientation, obtained through a spin labeling technique, are compared with a phenomenological model. Several rheological conditions are varied: hematocrit, suspending medium viscosity, blood age, artificial reversible aggregation. We found that the onset of orientation is very sensitive to any variation of these conditions, and that its measurement would be a good method to assess erythrocyte deformability. A critical shear rate for the orientation process is then determined and compared to the corresponding parameter obtained from viscosity measurements of identical suspensions. A close qualitative relationship is found between the two sets of values of the critical shear rate.

Biomechanical Phenomena↗
PubMedDate not supplied

[Spin-labeled nucleosides, nucleoside-5'-mono-, di-, and triphosphates].

A general method of synthesis of spin-labeled nucleosides, nucleoside-5'-mono-, di- and triphosphates is developed. It is based on the acyllation of ribose OH-group with N-(2,2,5,5-tetramethyl-3-carbonylpyrollin-1-oxyl)-imidasole. Their ESR and UV-spectra are studied. While studying the products of interaction between nucleoside mono-, di- and triphosphates and N-(2,2,5,5-tetramethyl-3-carbonylpyrrolin-1-oxyl)-imidasole along with the formation of monoradicals due to the acyllation of 2'(3')-OH-groups of ribose in the case of AMP, GMP and GDP acyllation by the phosphate group with the formation of biradicals has been also observed.

Cyclic N-Oxides↗