Biomedical subjects

H M Swartz

Publications and source records attributed to H M Swartz.

At least 19 recordsLinked to original sources

PubMed1996

The relationship between partial pressure of oxygen and perfusion in two murine tumors after X-ray irradiation: a combined gadopentetate dimeglumine dynamic magnetic resonance imaging and in vivo electron paramagnetic resonance oximetry study.

Changes of partial pressure of oxygen (pO2) and blood perfusion were studied in MTG-B and RIF-1 tumors (n = 5 each) before and after a single 20-Gy dose of X-ray irradiation. Using electron paramagnetic resonance oximetry, we have observed an initial fast decrease of pO2 after irradiation, followed by a slow increase. The time course of these changes was faster in the MTG-B tumors than in the RIF-1 tumors. Gadopentetate dimeglumine (Gd-DTPA) dynamic magnetic resonance imaging studies showed a reduction in uptake of Gd-DTPA at the time of minimum pO2 and a recovery at the time of maximum pO2 in each tumor. Previous work indicates that there is microscopic heterogeneity in tumors, with well-vascularized "capillary regions" being closer to capillaries than poorly vascularized "noncapillary regions." We propose a two-component (slow and fast) model of Gd-DTPA uptake that is designed to quantify the kinetics of these two compartments by analyzing the total tumor uptake kinetics without having to identify specific regions of interest. Total perfusion in the tumors was greatly reduced at the time of minimum oxygenation, and the volume of the slow component increased after irradiation. We conclude that a decrease in blood perfusion is one of the main causes of the decline in pO2 observed after irradiation.

Animals↗

PubMed1996

Detection of free radical metabolite formation using in vivo EPR spectroscopy: evidence of rat hemoglobin thiyl radical formation following administration of phenylhydrazine.

The spin-trapping technique in conjunction with a low-frequency electron paramagnetic (or spin) resonance (EPR or ESR) spectrometer was used to detect the hemoglobin thiyl free radical in living rats using a whole body resonator. The hemoglobin thiyl free radical was formed following the intragastric administration of phenylhydrazine at the LD50 dose of 188 mg/kg. The hemoglobin thiyl free radical was then trapped by preinjected 5,5-dimethyl-1-pyrroline N-oxide (DMPO), which formed the DMPO/hemoglobin thiyl-free radical adduct in the blood. The time course of the in vivo formation and disappearance of the spin adduct was followed. The DMPO/hemoglobin thiyl free radical was detected in blood samples using 9.5 GHz (X-band) and 1.1 GHz (L-band) EPR at room temperature and 77 K. Pretreatment of rats with ascorbate and diethylmaleate (DEM) decreased the signal intensity of the DMPO/hemoglobin thiyl free radical spin adduct. The incubation of ascorbate or DEM at 37 degrees C with rat blood containing preformed DMPO/hemoglobin thiyl radical adduct showed that there was no effect of DEM on the free radical concentration, while ascorbate reduced the radical adduct. This study provided direct evidence of the formation of the DMPO/hemoglobin thiyl free radical in vivo and enabled us to study this formation in living animals free of any artifacts that can occur when using ex vivo methods.

Animals↗

PubMed1996

Evidence for the dissociation of the hepatobiliary MRI contrast agent Mn-DPDP.

These experiments assessed and quantitated the release of free manganese Mn++ from the hepatobiliary contrast agent Mn-DPDP (manganese dipyridoxal diphosphate), using several magnetic resonance techniques (EPR spectroscopy, 31P-NMR spectroscopy, and relaxometry) to differentiate between free Mn++ and Mn++ in complexes in various preparations. The presence of calcium and magnesium in physiological concentrations in aqueous solutions induced the release of Mn++ from the complex, as did incubation of the complex in liver homogenates. After intravenous injection of 15 mumol/kg of Mn-DPDP, both EPR and 31P-NMR spectroscopy demonstrated that Mn-DPDP is partly dissociated (approximately 25%) in the liver. By comparing in vitro and ex vivo data from the liver, we concluded that the dissociation of Mn-DPDP occurs primarily in the liver, whereas a minor portion of the dissociated. Mn found in the liver comes from dissociation of the complex in the blood. Most of the dissociated Mn in liver becomes bound to macromolecules and is responsible for the enhancement of relaxivity observed with this agent.

Animals↗

PubMed1996

Use of nitroxides for assessing perfusion, oxygenation, and viability of tissues: in vivo EPR and MRI studies.

Relative perfusion, pO2, and bioreduction were measured simultaneously in vivo in tissues in mice by following changes in the intensity and shape of the EPR spectra of nitroxides injected directly into the tissues, using low frequency (1.1 GHz) localized EPR spectroscopy. Using normal and blood flow restricted gastrocnemius muscles it was shown that the decrease of the EPR signals of the nitroxides in tissues was due principally to perfusion, which redistributed the nitroxides. Changes in pO2 were reflected by changes of the linewidth; only a perdeuterated nitroxide with a narrow line was an adequate indicator for this parameter. This technique was applied experimental murine tumors (MTG-B and RIF-1) to determine the perfusion and pO2 in these relatively hypoxic model tumor systems. Using the paramagnetic properties of the nitroxides to enhance T1-weighted MR images, heterogeneity in perfusion in individual tumors was demonstrated

Animals↗

PubMed1996

Effect of repetitive ischemia on myocardial oxygen tension in isolated perfused and hypoperfused rat hearts.

The objective of this study was to determine the effects of repetitive ischemia on myocardial oxygen tension (pO2), consumption, and delivery in crystalloid normoperfused (perfusion pressure>70 mmHg) and hypoperfused (perfusion pressure approximately 50 mmHg) constant flow isolated rat hearts. EPR oximetry with lithium phthalocyanine was used to measure myocardial pO2. Baseline myocardial pO2 (means +/- SE) was 185 +/- 13 mmHg (normoperfused) and 162 +/- 14 mmHg (hypoperfused). Myocardial pO2 fell to < 1 mmHg during no-flow ischemia. After recovery from repetitive ischemia, myocardial pO2 and coronary resistance increased significantly in all hearts; oxygen consumption and left ventricle work decreased in normoperfused hearts, although not significantly compared with controls, and did not change significantly in hypoperfused hearts. Increased myocardial pO2 in the normoperfused group may be due to decreased oxygen consumption and/or increased local delivery, while increased myocardial pO2 in the hypoperfused hearts is due to increased local oxygen delivery.

Animals↗

PubMed1996

Noninvasive measurement of the pH inside the gut by using pH-sensitive nitroxides. An in vivo EPR study.

The use of pH-sensitive probes permits the measurement of the proton activity in biological systems by EPR spectroscopy. To illustrate the potential of this technique for in vivo purposes, the authors took advantage of the oral administration of nitroxides to monitor the pH value inside the stomach of mice after administration of different antacidics. The results indicate that EPR can be a valuable tool to characterize the pH in vivo in a continuous and noninvasive way.

Animals↗

PubMed1996

Development of biocompatible implants of fusinite for in vivo EPR oximetry.

The development of oxygen-sensitive paramagnetic materials is being actively pursued because of their potential applications for in vivo electron paramagnetic resonance (EPR) oximetry. Among these materials, fusinite is of particular interest because of the high sensitivity of the EPR linewidth to the partial pressure pO2. Although this material has led to a number of very useful results in experimental systems, its potential use in humans is limited by the need to prove that it will not cause deleterious effects. The strategy used in this study to optimize the biocompatibility of the oxygen-sensitive materials was to prepare small silicon implants containing the fusinite. The use of silicon permits the diffusion of oxygen inside the implant while the material does not have contact with the biological environment. Radiosterilization did not affect the pO2 sensitivity of the material. The feasibility of performing pO2 measurement was verified in vivo by periodically inducing ischemia in the gastrocnemius muscle of mice over a period of 6 weeks.

Animals↗

PubMed1996

Interaction of neuromelanin and iron in substantia nigra and other areas of human brain.

Nine areas of the brain were studied by electron paramagnetic resonance spectroscopy and total reflection X-ray fluorescence spectroscopy to measure paramagnetic metal ions, free radicals (neuromelanin), and total metal content. We also determined the extent of accumulation of metal ions by melanins incubated in homogenates of a region of the brain (putamen). The electron paramagnetic resonance spectra of metal ions varied considerably among areas of the brain. There was no correlation between total content of particular metal ions (iron was especially pertinent) and the observed electron paramagnetic resonance spectra, except that the substantia nigra appeared more consistently to have a prominent g = 4 electron paramagnetic resonance signal characteristic of ferric iron in a rhombic state. Only the substantia nigra, and to a lesser extent the locus coeruleus, had a free radical signal consistent with that of neuromelanin. This signal was much more prominent in the unprocessed substantia nigra but when metal ions were removed (reducing the amount of suppression of the electron paramagnetic resonance signal of neuromelanin due to dipole-dipole broadening from nearby metal ions), the electron paramagnetic resonance spectrum of neuromelanin of the locus coeruleus increased much more than that of the substantia nigra. This suggests that the structure of the pigment may differ in these two regions. Incubating synthetic melanins with homogenates of putamen resulted in accumulation of metal ions on the melanins with the concentrations of the three metal ions, relative to their values in the putamen, increasing by factors of 20-30, 3-4, and 25-30, for iron, copper, and zinc, respectively. This suggests that the metal content of isolated neuromelanin may include metal ions which became bound to the neuromelanin during the isolation procedure.

Aged↗

PubMed1996

Endotoxin-induced changes in intrarenal pO2, measured by in vivo electron paramagnetic resonance oximetry and magnetic resonance imaging.

Electron Paramagnetic Resonance (EPR) oximetry was used to measure tissue oxygen tension (pO2-partial pressure of oxygen) simultaneously in the kidney cortex and outer medulla in vivo in mice. pO2 in the cortex region was higher compared to that in the outer medulla. An intravenous injection of endotoxin resulted in a sharp drop in pO2 in the cortex and an increase in the medulla region, resulting in a transient period of equal pO2 in both regions. In control kidneys, functional Magnetic Resonance (MR) images showed the cortex region to have high signal intensity (T2*-weighted images), indicating that this region was well supplied with oxygenated hemoglobin, whereas the outer medulla showed low signal intensity. After administration of endotoxin, we observed an immediate increase in signal intensity in the outer medulla region, reflecting an increased level of oxygenated blood in this region. Pretreatment of mice with NG-monomethyl-L-arginine prevented both the changes in tissue pO2 and distribution of oxygenated hemoglobin, suggesting that localized production of nitric oxide has a critical role to play in renal medullary hemodynamics. In combining in vivo EPR with MR images of kidneys, we demonstrate the usefulness of these techniques for monitoring renal pO2 and changes in the distribution of oxygen.

Animals↗

PubMed1996

The measurement of temperature with electron paramagnetic resonance spectroscopy.

An electron paramagnetic resonance (EPR) technique, potentially suitable for in vivo temperature measurements, has been developed based on the temperature response of nitroxide stable free radicals. The response has been substantially enhanced by encapsulating the nitroxide in a medium of a fatty acid mixture inside a proteinaceous microsphere. The mixture underwent a phase transition in the temperature range required by the application. The phase change dramatically altered the shape of the EPR spectrum, providing a highly temperature sensitive signal. Using the nitroxide dissolved in a cholesterol and a long-chain fatty acid ester, we developed a mixture which provides a peakheight ratio change from 3.32 to 2.11, with a standard deviation of 0.04, for a temperature change typical in biological and medical applications, from 38 to 48 degrees C. This translated to an average temperature resolution of 0.2 degree C for our experimental system. The average diameter of the nitroxide mixture-filled microspheres was approximately 2 microns. Therefore, they are compatible with in vivo studies where the microspheres could be injected into the microvasculature having a minimum vessel diameter of the order of 8 microns. This temperature measuring method has various potential clinical applications, especially in monitoring and optimizing the treatment of cancer with hyperthermia. However, several problems regarding temperature and spatial resolution need to be resolved before this technique can be successfully used to monitor temperatures in vivo.

Ascorbic Acid↗

PubMed1995

Chromate-induced chromium(V) formation in live mice and its control by cellular antioxidants: an L-band electron paramagnetic resonance study.

A recent note from our laboratory reported that L-band (1.2 GHz) electron paramagnetic resonance spectroscopy can be utilized in detecting the formation of Cr(V) intermediates from chromate-treated whole mice. Since Cr(V) is thought to be one of the key species in the mechanism of chromate's toxicity, we carried out additional measurements with improved sensitivity. The new spectra show partially resolved hyperfine structure from protons that suggests that the Cr(V) ion is ligated to NAD(P)H moieties via oxygens. Using laboratory-synthesized Cr(V) (K3CrO8) as a standard, the yield of Cr(V) formation was estimated to be 153 +/- 12 nmol after intravenous injection of 100 microliters of 100 mM sodium dichromate into mice. Pretreatment of the mice with ascorbic acid and glutathione significantly reduced the Cr(V) formation yield in a dose-related manner, while pretreatment with NADH had the opposite effect. Injection of ascorbic acid also had the effect of enhancing the rate of Cr(V) disappearance in vivo. By comparing these results with in vitro results utilizing L-band as well as X-band (9.6 GHz) measurements, we conclude that L-band spectroscopy can indeed be effectively utilized for following the metabolism of Cr(V) in live mice and that Cr(V) formation can be controlled by utilizing cellular antioxidants in vivo.

Animals↗

PubMed1995

Assessment of cerebral pO2 by EPR oximetry in rodents: effects of anesthesia, ischemia, and breathing gas.

This report describes experiments designed to assess and illustrate the effectiveness of a new method for the measurement of cerebral interstitial pO2 in conscious rodents. It is based on the use of low frequency electron paramagnetic resonance (EPR) spectroscopy with lithium phthalocyanine as the oxygen sensitive probe. Magnetic resonance imaging was used to document placement of the probe in the brain, and to assess potential cerebral changes associated with the placement. The technique provided accurate and reproducible measurements of localized pO2 in the brains of conscious rodents under a variety of physiological conditions and for time periods of at least 2 weeks. Using this approach we quantitated the depressing effects on cerebral pO2 of three representative anesthetics, isoflurane, ketamine/xylazine, and sodium pentobarbital. The effects of changing the content of oxygen in the breathing gas was investigated and found to change the cerebral pO2. In experiments with gerbils, crystals of lithium phthalocyanine were implanted in each side of the brain and using a one-dimensional magnetic field gradient, simultaneous measurement of pO2 values from normal and ischemic (ischemia induced by unilateral ligation of a carotid artery) hemispheres of the brain were obtained. These results demonstrate that EPR oximetry with lithium phthalocyanine is a versatile and useful method in the measurement of cerebral pO2 under various physiological and pathophysiological conditions.

Anesthetics↗

PubMed1995

Detection of short-lived free radicals by low-frequency electron paramagnetic resonance spin trapping in whole living animals.

We report the direct observation of sulfur trioxide anion free radical (SO3.-) from the body of live mice by using a low-frequency (1.2 GHz, L-band) EPR spin trapping method. Intraperitoneal injection of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (15 mmol/kg) used as trapping agent was followed by sequential iv injections of sodium sulfate (2-5 mmol/kg) and sodium dichromate (0.3 mmol/kg). The mouse was placed in an L-band loop gap resonator. The observed spectra consisted of two superposed components: DMPO/SO3.- (alpha N = 14.0, alpha H = 16.0) and Cr(V) (g = 1.9798). The time course for the generation and reduction of DMPO/SO3.- was followed. The signal intensity reached a maximum at about 7 min. In vitro experiments carried out at 9.15 GHz confirmed the production of SO3.- under the conditions used for in vivo studies; the hyperfine splittings of DMPO/SO3.- produced in the in vitro experiments were the same as those produced in the in vivo studies. The production of SO.-3 is supported by oxygen uptake studies, which show that the prior addition of 300 mM DMPO inhibits oxygen consumption by SO3.-.

Animals↗

PubMed1995

Changes of oxygen tension in experimental tumors after a single dose of X-ray irradiation.

Electron paramagnetic resonance oximetry was used to measure the partial pressure of oxygen (pO2) in two types of tumor in vivo in C3H/HeJ mice. The pO2 in MTG-B (high hypoxic fraction) and RIF-1 (low hypoxic fraction) tumors was monitored prior to and at several time points after a single dose of X-ray irradiation (up to 7 days after treatment). Initial values of pO2 in RIF-1 (8.7 +/- 1.1 mm Hg; n = 14) were higher than that of pO2 in MTG-B (3.3 +/- 0.5 mm Hg; n = 19). The pO2 in both types of unirradiated tumors decreased slowly with tumor growth. Irradiation of tumors had a two-phase effect on pO2: an initial sharp decrease in pO2, followed by slow reoxygenation. After a 20-Gy radiation dose, the pO2 was 2.2 +/- 0.5 mm Hg at 6 h [significantly lower (P < 0.0001) than in control] and 3.2 +/- 0.5 mm Hg at 48 h [significantly higher (P < 0.02) than in control] in MTG-B, and 5.4 +/- 1.2 mm Hg at 24 h and 8.2 +/- 1.0 mm Hg at 72 h in RIF-1. The time course for these changes in pO2 was found to be independent of the doses in use in this study (10, 20, and 40 Gy). The occurrence of radiation-induced changes in pO2 and the different time courses of these changes suggest that repeated monitoring of pO2 in tumors during treatment could be used to enhance the efficacy of clinical treatments.

Adenocarcinoma↗

PubMed1995

Low-frequency EPR study of chromium(V) formation from chromium(VI) in living plants.

The reduction of Cr(VI) by green algae and higher plants was investigated using a low-frequency EPR spectrometer equipped with an extended loop gap resonator. Incubation of algae (Spirogyra and Mougeotia) with Cr(VI) generated both Cr(V) and Cr(III). The maximum Cr(V) signal was observed in about 10 minutes. Incubation of Cr(VI) with oat, soybean, and garlic generated Cr(V). The maximum Cr(V) peak appeared after more than 10 hours of incubation, and Cr(V) was located predominantly in the roots. The Cr(V) peak exhibited hyperfine splittings of about 0.79 gauss, typical of the Cr(V) complexes with diol-containing molecules. The results suggest that the reduction of Cr(VI) to lower oxidation states by living plants may provide a detoxification pathway for Cr(VI) in ecological systems. The results also indicate that low-frequency EPR may be used to investigate the metabolism of paramagnetic metal ions in intact plants.

Chlorophyta↗

PubMed1995

Intraphagosomal oxygen in stimulated macrophages.

A new electron paramagnetic resonance (EPR)-based method was developed to obtain selective information on pO2 in a specific intracellular compartment (phagosomes). This method did not require the use of a broadening agent thereby eliminating one of the potential sources of experimental error with EPR oximetry. An oxygen-sensitive probe (4-(Trimethylammonium) 2,2,6,6-tetramethylpiperidine-d17-1-oxyl iodide (d-Cat1)) which has a net positive charge, was incorporated selectively into the phagosomes of macrophages stimulated with zymosan. Extracellular oxygen was measured by addition of a neutral nitroxide (4-oxo-2,2,6,6-tetramethylpiperidine-d16-1-oxyl (15N PDT)) to this same sample. Measurements based on EPR linewidths showed the average intraphagosomal oxygen concentration to be 11.2 +/- 3.4 microM lower than that measured from the extracellular compartment when the sample was perfused with air, and this was increased on stimulation of mitochondrial consumption or by increasing the oxygen concentration in the extracellular compartment. These experiments provide what we believe to be the first reported measurements of the oxygen concentration in a specific intracellular location (intraphagosomal) and its comparison with the oxygen concentration in the extracellular space. The observed gradient cannot be explained in terms of known coefficients of diffusion, and these results are consistent with previous reports that a gradient in oxygen concentration can occur between the average intracellular and extracellular concentration of oxygen.

Animals↗

PubMed1995

In vivo oximetry using EPR and India ink.

Recent advances in electron paramagnetic resonance (EPR) oximetry have established the use of the particulate materials fusinite and lithium phthalocyanine (LiPc) as probes for measurement of oxygen tensions in tissues in vivo with a sensitivity and accuracy that is relevant for studying pathophysiological processes. India ink, another potentially very useful new probe for EPR oximetry, shares the critical properties of fusinite and LiPc and has the additional advantage of already having been widely used clinically with no apparent toxicity. The line width is particularly sensitive to changes in oxygen tension of less than 30 mmHg; in this range the line broadening/unit of pO2 is much greater than that of fusinite and LiPc. Over the range of biological conditions that can occur in vivo, the response of the EPR spectrum of India ink to pO2 is independent of pH, oxidants, reductants, and the nature of the medium. In this paper we describe the relevant properties of India ink and its use to measure pO2 in vivo in experimental animals and a human subject.

Adenocarcinoma↗

PubMed1995

The apparent diffusion constant measured by MRI correlates with pO2 in a RIF-1 tumor.

As tissue oxygen tension (pO2) is an important variable in cancer therapy, it would be of major clinical benefit to be able to measure pO2 noninvasively. Current methods for determining pO2 in clinical settings are limited to superficial tumors. The authors measured the apparent diffusion constant (ADC) in an implanted murine fibrosarcoma (RIF-1) using magnetic resonance imaging and correlated the ADC with tissue pO2 measured by electron paramagnetic resonance oximetry. The ADC correlates significantly with tissue pO2 in this tumor (r = 0.89; n = 14) and so may provide a noninvasive index of pO2 in tumors.

Animals↗