Biomedical subjects

H M Swartz

Publications and source records attributed to H M Swartz.

At least 91 records · Page 5Linked to original sources

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↗

PubMed1995

Use of EPR oximetry with India ink to measure the pO2 in the liver in vivo in mice.

The partial pressure of oxygen (pO2) of the liver in vivo in unanesthetized mice was determined using electron paramagnetic resonance (EPR) oximetry with India ink. The EPR spectra were obtained using a low-frequency (1.2 GHz) EPR spectrometer with a loop gap cavity resonator. The line width of the India ink used in this experiment was reversibly broadened by oxygen and was particularly sensitive to pO2 below 30 torr. After the administration of India ink into the tail vein, the India ink particles were taken up mainly by Kupffer cells in the liver and in part by phagocytes in the spleen. The pO2 measured in the normal liver was about 14 torr and was constant for the 2-week experimental period. The pO2 decreased when measured at 1, 2, and 6 days after treatment with hepatotoxin (carbon tetrachloride (CCl4)); within 2 weeks, it returned almost to the initial level. Measurements by EPR at sacrifice of controls and CCl4-treated mice indicated that more than 90% of the India ink went to the liver; the spleen contained 4.7% of total amount in control mice and 8.8% in CCl4-treated mice when measured 2 weeks after the treatment. These data indicate the usefulness of India ink for measuring the pO2 of the liver in vivo and that the pO2 in the Kupffer cells is decreased when the liver is damaged by CCl4.

Animals↗

PubMed1995

Myocardial oxygen tension and relative capillary density in isolated perfused rat hearts.

Oxygen plays an important role in cardiac function. Many methods have been applied to measure tissue oxygen tension (PO2). Electron paramagnetic resonance (EPR) oximetry appears to have some significant advantages for use in the beating heart. This study presents the serial measurement of myocardial PO2 by EPR oximetry in the isolated crystalloid perfused heart during changes of influent PO2, coronary flow rate, oxygen consumption and end-diastolic pressure. Baseline myocardial PO2 was 198 +/- 12 mmHg (mean +/- S.E.). Myocardial PO2 increased as expected with increased delivery (concentration or flow) or decreased consumption. With increasing flow rate, myocardial PO2 increased in a sigmoid fashion. A critical flow or pressure was reached when myocardial PO2 rapidly increased to a higher level. Increased left ventricular end-diastolic pressure caused local vascular compression and resulted in a decrease of myocardial PO2. Myocardial capillary density in the intact contracting heart was calculated to be 2300 +/- 110/mm2, using local myocardial PO2 and a cylindrical model for oxygen diffusion in tissue. Relative capillary density did not change with mild to moderate hypoxia, increased with increasing flow and increasing oxygen consumption and decreased with elevated diastolic pressure. We conclude that the application of EPR oximetry with LiPc to the isolated heart provides accurate and dynamic evaluation of local myocardial PO2 in the contracting heart. Using various models of oxygen delivery and diffusion in tissue, these data may also be used to serially follow capillary density.

Animals↗

PubMed1995

An analysis of the effects of eddy currents on L-band EPR spectra.

Recently, impressive results have been obtained with EPR studies of living animals and perfused organs using low-frequency EPR. In many instances in such studies, however, there are apparent distortions of the spectra. The shapes of these spectra and theoretical considerations indicate that these effects are due to eddy currents in the moderately conductive biological materials. Therefore the effects of eddy currents produced in biological samples under typical conditions being employed for in vivo EPR studies have been systematically studied in order to determine the extent of these effects and to develop methods for compensating for these effects. The presence of eddy currents was found to decrease the Q factor and distort the shapes of the EPR spectra. The distortion of the spectra led to linewidth broadening, changes in peak heights, and shifts of the apparent center of the lines. These effects could be corrected instrumentally, but this was effective only when signals have a high S/N. The use of appropriate computer simulations, based on linear combinations of the expected absorption and dispersion signals, can effectively correct for the effects of eddy currents and provide accurate data on the parameters of EPR spectra that are needed for most or all of the analyses used in biological studies of animals and tissues at low frequencies.

Animals↗

PubMed1995

The effects of endotoxin on oxygen consumption of various cell types in vitro: an EPR oximetry study.

We have studied the effects of bacterial endotoxin on the oxygen consumption of a variety of target cells, and found that the rate of utilization of oxygen by treated cells was decreased in a time- and dose-dependent manner. Precise EPR measurement of oxygen concentrations enabled us to demonstrate that this effect was linked to mitochondrial dysfunction and was particular to each cell type. Such detailed knowledge on oxygen utilization by viable whole cells and the varied effects of endotoxin are as yet undocumented. Oxygen consumption was shown to decrease quite markedly in CHO cells and kidney cells from the cortex region. Cells from the kidney medulla region had lower baseline consumption and were stimulated to increased levels of oxygen consumption on addition of similar doses of endotoxin. Macrophages exhibited a dual response in that in addition to inhibiting mitochondrial oxygen consumption, endotoxin pretreatment primed these cells to exhibit an enhanced oxidative burst on stimulation with Zymosan. These results show that endotoxin has a direct effect on normal cellular oxygen consumption and is an important parameter that must be considered when following the early effects on cells and tissues during the septic syndrome.

Animals↗

PubMed1995

In vivo detection of anthralin-derived free radicals in the skin of hairless mice by low-frequency electron paramagnetic resonance spectroscopy.

Free radicals were directly detected in vivo in the skin of hairless mice by low-frequency electron paramagnetic resonance spectroscopy after topical application of anthralin under pertinent therapeutic conditions. The electron paramagnetic resonance signal intensity increased steadily, reaching a maximum after about 1 d and decreased slowly in the following days, probably because of desquamation of the skin. We conclude from the spectroscopic features (single line with a line width of 6 gauss; g = 2.0036) and from the pharmacokinetic pattern that the observed signal arises from the final products of anthralin metabolism (ether-insoluble polymeric structures--"anthralin brown"). Two potential antioxidants, vitamin E and the spin trap tert-butylphenylnitrone, decreased the amount of the anthralin-derived radical that was formed. Neither vitamin E radicals nor tert-butylphenylnitrone spin adducts were observed. We suggest that electron paramagnetic resonance is a valuable tool for the noninvasive and direct in vivo monitoring of drug-induced radical formation in the skin under therapeutic conditions.

Animals↗

PubMed1995

The pO2 in a murine tumor after irradiation: an in vivo electron paramagnetic resonance oximetry study.

Using electron paramagnetic resonance (EPR) oximetry with the oxygen-sensitive paramagnetic material, fusinite, we have measured the partial pressure of oxygen (pO2) in the mouse mammary adenocarcinoma MTG-B. The average pO2 in untreated tumors was low (about 5 mm Hg) and decreased with tumor growth. Magnetic resonance imaging and histological examination were used to localize the position of the fusinite with respect to tumor margins and vascularization. The pO2 was generally higher in the periphery than in the center of the tumors, but there was considerable variation among tumors both during normal growth and after radiation treatment. After a single 20-Gy dose, a characteristic pattern of change in tumor pO2 was observed. In irradiated tumors, there was an initial reduction in pO2 (minimum occurred 6 h postirradiation) which was followed by a transient increase in pO2 to levels higher than the preirradiation pO2 (maximum occurred 48 h postirradiation). This work demonstrates postirradiation changes in pO2 of potential radiobiological significance. Compared to other oxygen assessment techniques, EPR oximetry is very useful because it can assess pO2 in the same region of the tumor over the course of tumor growth and during response to treatment. Thus EPR could be used to identify potentially radioresistant tumors as well as to identify tumors with slow reoxygenation.

Adenocarcinoma↗

PubMed1994

In vivo and in vitro EPR oximetry with fusinite: a new coal-derived, particulate EPR probe.

The peak-to-peak line width (LW) of the first derivative electron spin resonance (EPR) spectrum of the coal maceral fusinite is reversibly broadened by O2. The extent of broadening per unit of partial pressure of oxygen (pO2) is unusually large, exceeding that of nitroxides by almost two orders of magnitude. This paramagnetic property of fusinite, combined with its very stable physicochemical properties and low toxicity, is shown to be of utility in the measurement of pO2 in vitro and in vivo. Fusinite particles are endocytosed by chinese hamster ovary (CHO) cells in vitro; this is useful for intracellular O2 measurements with commercially available EPR spectrometers operating at 9.1-9.3 GHz. For measurement of oxygen in vivo using low frequency EPR (1.1-1.3 GHz), fusinite provides a sensitive and persistent means to measure pO2 in tissues. Particles implanted into the gastrocnemius muscle of A/J mice remained interstitially in the same position for months with undiminished sensitivity to pO2 and no specific toxic effects.

Adsorption↗

PubMed1994

India ink: a potential clinically applicable EPR oximetry probe.

Using a material that already is in widespread use in humans, India ink, the first EPR measurements in a human have been made, using the India ink in a pre-existing tattoo. The EPR spectra of India ink are very sensitive to the partial pressure of oxygen (pO2), thereby making it feasible to use this approach to measure pO2 in tissues in patients. This potentially provides a means to measure this parameter directly with a sensitivity, accuracy, and repeatability that have not been available previously, and thereby to be able to individualize and guide treatment of diseases such as cancer and peripheral vascular insufficiency.

Animals↗

PubMed1994

Measurement of the intracellular concentration of oxygen in a cell perfusion system.

[O2] was measured in the embedding material (alginate) in a typical apparatus for conducting studies of viable cells with NMR, using low frequency EPR. In suspension cultures respiration was independent of [O2] in the perfusing media down to about 1 microM while in alginate beads, the comparable value was 70 microM, indicating that the alginate was a very substantial barrier to the free diffusion of oxygen. With knowledge of [O2] in the various compartments, [O2] in the perfusing medium can be increased and the full power of NMR can be used to provide information on metabolism under various conditions. These results also provide evidence supporting the feasibility and usefulness of EPR techniques using nitroxides to measure [O2] in macroscopic samples such as NMR perfusion tubes. This technique is rapid, apparently nonperturbing, and enables one to differentiate between the concentrations of oxygen in different compartments.

Alginates↗

PubMed1994

Low-frequency EPR detection of chromium(V) formation by chromium(VI) reduction in whole live mice.

Measurements by direct low frequency EPR spectroscopy provide the first evidence that Cr(V) is generated in one-electron reduction of Cr(VI) in live mice. The Cr(V) yield reached a maximum about 10 min following Cr(VI) intravenous injection and then decayed slowly with a life time of approximately 37 min. The time for the Cr(V) EPR signal to reach maximum intensity increased with the dose of Cr(VI). A discernible EPR signal was still observable at a dose as low as 0.1 mmol/kg. The Cr(V) was found predominantly in the liver, with a small amount in the blood. No Cr(V) signal was detectable in heart, spleen, kidney, and lung. Pretreatment of the animals with metal ion chelators, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and 1,10-phenanthroline significantly reduced the intensity of the Cr(V) signal that was observed.

Animals↗

PubMed1994

Physical and instrumental considerations in the use of lithium phthalocyanine for measurements of the concentration of the oxygen.

The use of crystals of lithium phthalocyanine (LiPc) to measure the concentration of oxygen in vivo and in vitro by electron paramagnetic resonance leads to experimental constraints due to the very narrow EPR lines that may occur (as narrow as 11-13 mG in the absence of O2), distortions induced by the automatic frequency control system, anisotropy in the spectra (orientation-dependent linewidth is 11-17 mG in the absence of O2), microwave power saturation, and the effect of physiological motion. These constraints can be overcome if recognized. This article highlights the experimental and theoretical basis of these properties of the EPR signal of LiPc and suggests some technical solutions. It is most important to recognize that paramagnetic species such as LiPc present problems that are not commonly encountered in EPR spectroscopy.

Electron Spin Resonance Spectroscopy↗