Biomedical subjects

H M Swartz

Publications and source records attributed to H M Swartz.

At least 19 recordsLinked to original sources

PubMed2006

Influence of different anesthetics on skin oxygenation studied by electron paramagnetic resonance in vivo.

The effects of two general anesthetics on skin oxygenation in mice are evaluated by electron paramagnetic resonance oximetry. Up to now no data on the effects of different anesthetics on skin oxygenation could be found. In this study animals were anesthetized with ketamine/xylazine or isoflurane, and partial pressure of oxygen (pO(2)) in the skin, heart rate and hemoglobin oxygen saturation were followed as a function of time and inhaled oxygen concentration. The skin pO(2) significantly increased continuously for about 60 min in mice anesthetized with isoflurane and remained constant after that. During ketamine/xylazine anesthesia, the pO(2) in the skin only slightly decreased. The skin pO(2) increased with higher inspired oxygen concentrations for both anesthetics groups. When breathing 21% oxygen, mice anesthetized with isoflurane had two-fold higher pO(2) in the skin compared to mice anesthetized with ketamine/xylazine. The heart rate was significantly lower in animals anesthetized with ketamine/xylazine, while hemoglobin saturation was almost the same in both groups at all inhaled oxygen concentrations. These results show that the type of anesthesia is an important parameter that needs to be considered in experiments where skin pO(2) is followed.

Anesthetics, Combined↗

PubMed2005

Development and evaluation of biocompatible films of polytetrafluoroethylene polymers holding lithium phthalocyanine crystals for their use in EPR oximetry.

Electron paramagnetic resonance (EPR) oximetry is a powerful technology that allows the monitoring of oxygenation in tissues. The measurement of tissue oxygenation can be achieved using lithium phthalocyanine (LiPc) crystals as oxygen reporters. In order to have biocompatibility for the sensing system and to assure long-term stability in the responsiveness of the system, we developed films of Teflon AF 2400 with embedded LiPc crystals. These systems can be used as retrievable inserts or parts of an implantable resonator or catheter. Atomic force microscopy studies revealed that the surface of the films was regular and planar. The response to oxygen of the sensor (EPR linewidth as a function of pO(2)) remained unchanged after implantation in mice, and was not affected by sterilization or irradiation. The use of resonators, holding LiPc embedded in Teflon AF 2400, implanted in the gastrocnemius muscle of rabbits allowed the monitoring of oxygen during several weeks. Several assays also demonstrated the biocompatibility of the system: (1) no hemolytic effect was noted; (2) no toxicity was found using the systemic injection test of extracts; (3) histological analysis in rabbit muscle in which the films were implanted for 1 week or 3 months was similar to standard polyethylene biocompatible devices. These advanced oxygen sensors are promising tools for future pre-clinical and clinical developments of EPR oximetry. These developments can be applied for other applications of biosensors where there is a need for oxygen permeable membranes.

Absorption↗

PubMed2005

EPR spectrometer for clinical applications.

This article describes an EPR spectrometer specifically designed and constructed for EPR spectroscopy in humans. The spectrometer is based on a permanent magnet, suitable for measurements at 1200 MHz. The magnet has a full 50 cm gap between the poles, which facilitates accurate and comfortable placement of the subject for the EPR measurement at any location on the human body. The bridge includes features to facilitate clinical operations, including an indicator for phasing of the reference arm and a 2 level RF amplifier. Resonators with holders for each type and site of measurement have been developed that comfortably position the resonator and the patient and prevent artifacts due to motion. The initial applications for which the spectrometer has been designed are for oximetry using loops on the surface, oximetry using implanted resonators for measuring deep sites, and measurements in the teeth for determination of exposures to clinically significant doses of ionizing radiation.

Electron Spin Resonance Spectroscopy↗

PubMed2005

Spectrum file size optimization for EPR tooth dosimetry.

Spectral acquisition time is one of the limiting factors in electron paramagnetic resonance (EPR) retrospective biodosimetry in teeth. Acquisition times for one sample can be from 2 to 4h. This problem is even more acute for in vivo EPR measurements in L-band. Patients cannot be expected to remain stationary for these lengths of time. In order to overcome this limitation, we investigated the dependence of EPR dose measurements on the number of data points in an EPR spectrum. We have shown that this number could be reduced from 1024 to 256 (factor of 4 reduction in spectral acquisition time) at 5 mT magnetic field sweep without a loss of precision in the dose measurements.

Algorithms↗

PubMed2002

Reduced blood flow and oxygenation in SA-1 tumours after electrochemotherapy with cisplatin.

Electrochemotherapy is an antitumour treatment that utilises locally delivered electric pulses to increase cytotoxicity of chemotherapeutic drugs. Besides increased drug delivery, application of electric pulses affects tumour blood flow. The aim of this study was to determine tumour blood flow modifying effects of electrochemotherapy with cisplatin, its effects on tumour oxygenation and to determine their relation to antitumour effectiveness. Electrochemotherapy of SA-1 subcutaneous tumours was performed by application of electric pulses to the tumours, following administration of cisplatin. Tumour blood flow modifying effects of electrochemotherapy were determined by measurement of tumour perfusion using the Patent blue staining technique, determination of tumour blood volume, and microvascular permeability using contrast enhanced magnetic resonance imaging, and tumour oxygenation using electron paramagnetic resonance oximetry. Antitumour effectiveness was determined by tumour growth delay and the extent of tumour necrosis and apoptosis. Tumour treatment by electrochemotherapy induced 9.4 days tumour growth delay. Tumour blood flow was reduced instantaneously and persisted for several days. This reduction in tumour blood flow was reflected in reduced tumour oxygenation. The maximal reduction in partial oxygen pressure (pO2) levels was observed at 2 h after the treatment, with steady recovery to the pretreatment level within 48 h. The reduced tumour blood flow and oxygenation correlated well with the extent of tumour necrosis and tumour cells apoptosis induced by electrochemotherapy with cisplatin. Therefore, the data indicate that antitumour effectiveness of electrochemotherapy is not only due to increased cytotoxicity of cisplatin due to electroporation of tumour cells, but also due to anti-vascular effect of electrochemotherapy, which resulted in reduced tumour blood flow and oxygenation.

Animals↗

PubMed2001

The effects of ketamine-xylazine anesthesia on cerebral blood flow and oxygenation observed using nuclear magnetic resonance perfusion imaging and electron paramagnetic resonance oximetry.

Ketamine-xylazine is a commonly used anesthetic for laboratory rats. Previous results showed that rats anesthetized with ketamine-xylazine can have a much lower cerebral partial pressure of oxygen (P(t)O(2)), compared to unanesthetized and isoflurane anesthetized rats. The underlying mechanisms for the P(t)O(2) reduction need to be elucidated. In this study, we measured regional cerebral blood flow (CBF) using nuclear magnetic resonance (NMR) perfusion imaging and cortical P(t)O(2) using electron paramagnetic resonance (EPR) oximetry in the forebrain of rats under isoflurane, ketamine, ketamine-xylazine and isoflurane-xylazine anesthesia. The results show that in ventilated rats ketamine at a dose of 50 mg/kg does not induce significant changes in CBF, compared to isoflurane. Ketamine-xylazine in combination causes 25-65% reductions in forebrain CBF in a region-dependent manner. Adding xylazine to isoflurane anesthesia results in similar regional reductions in CBF. EPR oximetry measurements show ketamine increases cortical P(t)O(2) while xylazine decreases cortical P(t)O(2). The xylazine induced reduction in CBF could explain the reduced brain oxygenation observed in ketamine-xylazine anesthetized rats.

Adrenergic alpha-Agonists↗

PubMed2001

Reduced tumor oxygenation by treatment with vinblastine.

Vinblastine (VLB) previously has been shown to perturb tumor blood flow, but the effect of these perturbations on tissue oxygenation is not known. The recent development of electron paramagnetic resonance (EPR) oximetry now has made it feasible to measure the effects of changes of perfusion on the pO(2) in tumors and normal tissues as a function of time and dose. We measured changes in tumor perfusion by Patent blue staining, tumor blood volume and microvascular permeability by contrast-enhanced magnetic resonance imaging, and tumor oxygenation by EPR in s.c. SA-1 murine tumors. We found that treatment with VLB induced dose-dependent reduction in tumor perfusion. One hour after i.p. treatment of mice with 2.5 mg/kg VLB, tumor perfusion was reduced to 20% of the pretreatment value and returned to close to original values within 48 h. A transient tumor blood flow-modifying effect of VLB was demonstrated also by contrast-enhanced magnetic resonance imaging; reduction of tumor blood volume and microvascular permeability was found. Reduced tumor oxygenation was found as measured by EPR oximetry, with the same time course of changes in tumor blood flow. Tumor oxygenation was reduced to 50% of pretreatment value 1 h after the treatment with 2.5 mg/kg VLB and returned to pretreatment levels within 24 h after the treatment. Although the directions of the changes in perfusion and oxygenation were similar, they were quantitatively different. Reduction in oxygenation of normal tissues, muscle, and subcutis also occurred but was smaller and returned to pretreatment values more quickly compared to the changes induced in the tumors. In conclusion, the present study demonstrates that VLB causes a profound reduction in tumor blood flow and oxygenation, which may have implications in controlling side effects of therapy and the planning of combined treatment with VLB, either with other chemotherapeutic drugs or with radiotherapy.

Animals↗

PubMed2001

Development of biocompatible oxygen-permeable films holding paramagnetic carbon particles: evaluation of their performance and stability in EPR oximetry.

EPR oximetry using paramagnetic particles relies on the measurement of the EPR linewidth, which is directly related to the pO2. It was previously found that some of the paramagnetic materials with optimal EPR spectroscopic properties in vitro may lose their responsiveness to oxygen in tissues (change of the calibration curve of the EPR linewidth as a function of the pO2). We hypothesized that coating paramagnetic particle materials could improve the stability of response, as well as the biocompatibility. In this study, very thin films holding paramagnetic materials were prepared with different biopolymers (cellulose acetate, cellulose triacetate, cellulose nitrate, silicone, and polyurethane) that already are accepted for clinical applications. Their performance was evaluated in EPR oximetry by measuring the stability of the calibration curves (EPR linewidth as a function of pO2) after a prolonged period in an aqueous environment (1 week in saline) or in vivo (implantation for 3 weeks under the skin of mice). We found that one type of silicone film was able to stabilize the responsiveness of an intrinsically unstable carbon material (a wood char).

Animals↗

PubMed2001

High spatial resolution multi-site EPR oximetry. The use of convolution-based fitting method.

We describe a new method to enhance the spatial resolution of multi-site electron paramagnetic resonance (EPR) oximetry. The method is suitable for any shape (density distribution function) of a solid paramagnetic material implanted in tissue. It corrects distortions of lineshapes caused by the gradient and thus overcomes limitations of previous multi-site EPR oximetry methods that restricted the ratio of the particle size to the distance between sites. The new method is based on consecutive applications of magnetic field gradients with the same direction but with a different magnitude and uses a convolution-based fitting algorithm to derive Lorentzian EPR linewidths of each individual peak of the EPR spectrum. The method is applicable for any particulate EPR oxygen sensitive materials whose EPR spectra can be approximated by a Lorentzian function or a superposition of Lorentzian functions. By incorporating this model of the lineshape in the data processing, we are able to decrease significantly the number of parameters needed for the calculations and to recover the oxygen concentration, even from quite noisy spectra. We (i) describe our method and the data-processing algorithm, (ii) demonstrate our approach in model and in vivo experiments, and (iii) discuss the limitations.

Algorithms↗

PubMed2001

The evolution of bioluminescent oxygen consumption as an ancient oxygen detoxification mechanism.

Endogenous reductants such as hydrogen sulfide and alkylthiols provided free radical scavenging systems during the early evolution of life. The development of oxygenic photosynthesis spectacularly increased oxygen levels, and ancient life forms were obliged to develop additional antioxidative systems. We develop here the hypothesis of how "prototypical" bioluminescent reactions had a plausible role as an ancient defense against oxygen toxicity through their "futile" consumption of oxygen. As oxygen concentrations increased, sufficient light would have been emitted from such systems for detection by primitive photosensors, and evolutionary pressures could then act upon the light emitting characteristics of such systems independently of their use as futile consumers of oxygen. Finally, an example of survival of this ancient mechanism in present-day bioluminescent bacteria (in the Euprymna scolopes-Vibrio fischeri mutualism) is discussed. Once increasing ambient oxygen levels reached sufficiently high levels, the use of "futile" oxygen consumption became too bioenergetically costly, so that from this time the evolution of bioluminescence via this role was made impossible, and other mechanisms must be developed to account for the evolution of bioluminescence by a wide range of organisms that patently occurred after this (e.g., by insects).

Adaptation, Physiological↗

PubMed2001

Microencapsulation of carbon particles used as oxygen sensors in EPR oximetry to stabilize their responsiveness to oxygen in vitro and in vivo.

The electron paramagnetic resonance (EPR) spectra of some paramagnetic materials exhibit a pO2 (partial pressure of oxygen)-dependent linewidth. By recording the EPR linewidth in vivo using low-frequency EPR spectrometers, it is possible to measure the partial pressure of oxygen in tissues. It has been found, however, that some of the paramagnetic materials with optimal spectroscopic properties in vitro may lose or change their responsiveness to oxygen in tissues. The aim of this study was to microencapsulate paramagnetic particles by biopolymers in order to stabilize their responsiveness to oxygen. Carbohydrate char particles (Bubinga) were encapsulated with different biopolymers: cellulose acetate or cellulose triacetate, silicone and polyurethane. The performance of the materials was evaluated in vitro and in vivo. X-band EPR spectroscopy was used to test the variation of the calibration curve (EPR linewidth as a function of the pO2) after incubation in saline and after prolonged residence in tissues. The stability of the responsiveness to PO2 in vivo was carried out by L-band EPR spectroscopy using mice that received injection of the oxygen sensors in the muscles. After residence in saline and prolonged residence in tissues, only the calibration curve of the silicone-coated (coating weight of 0.5% (w/w)) paramagnetic materials remained unchanged, while those of oxygen sensors coated with cellulose acetate, cellulose triacetate and polyurethane changed.

Animals↗

PubMed2001

Firefly flashing is controlled by gating oxygen to light-emitting cells.

Although many aspects of firefly bioluminescence are understood, the mechanism by which adult fireflies produce light as discrete rapid flashes is not. Here we examine the most postulated theory, that flashing is controlled by gating oxygen access to the light-emitting cells (photocytes). According to this theory, the dark state represents repression of bioluminescence by limiting oxygen, which is required for bioluminescence; relief from this repression by transiently allowing oxygen access to the photocytes allows the flash. We show that normobaric hyperoxia releases the repression of light emission in the dark state of both spontaneously flashing and non-flashing fireflies, causing continual glowing, and we measure the kinetics of this process. Secondly, we determine the length of the barriers to oxygen diffusion to the photocytes in the aqueous and gas phases. Thirdly, we provide constraints upon the distance between any gas-phase gating structure(s) and the photocytes. We conclude from these data that the flash of the adult firefly is controlled by gating of oxygen to the photocytes, and demonstrate that this control mechanism is likely to act by modulating the levels of fluid in the tracheoles supplying photocytes, providing a variable barrier to oxygen diffusion.

Adenosine Monophosphate↗

PubMed2001

Estimation of oxygen distribution in RIF-1 tumors by diffusion model-based interpretation of pimonidazole hypoxia and eppendorf measurements.

Numerical simulations of oxygen diffusion from the capillaries in tumor tissue were used to predict the capillary oxygen supply within and near hypoxic regions of the RIF-1 tumor. A finite element method to simulate the oxygen distribution from a histology section is presented, along with a method to iteratively estimate capillary oxygen concentrations. Pathological structural data for these simulations came from sections of the tumor stained with hematoxylin and eosin and were used to define the capillary positions and shapes, while overlapping regions of low oxygen concentration were defined by the hypoxia marker pimonidazole. These simulations were used to calculate spatial maps of the oxygen concentration and were tested for their ability to reproduce Eppendorf pO(2) histograms from the same tumor line. This simulation study predicted that capillary oxygen concentrations ranged from zero to above 20 microM, with a dominant peak in the hypoxic regions showing 78% of capillaries with less than 1 microM oxygen concentration, compared to only 12% in the non-hypoxic regions. The results were not highly sensitive to the metabolic oxygen consumption rate, within the range of 2 to 16 microM/s. This numerical method for oxygen capillary simulation is readily adaptable to histology sections and provides a method to examine the heterogeneity of oxygen within the capillaries and throughout the tumor tissue section being examined.

Animals↗

PubMed2001

Response to radioimmunotherapy correlates with tumor pO2 measured by EPR oximetry in human tumor xenografts.

The efficacy of radiation treatment depends upon local oxygen concentration. We postulated that the variability in responsiveness of tumor xenografts to a fixed dose of radioimmunotherapy might be related to the tumor pO2 at the time that radioimmunotherapy was administered. We evaluated the growth of xenografts of CALU-3 tumors, a non-small cell lung carcinoma, in response to an 8.9-MBq dose of 131I-RS-7-anti-EGP-1 and correlated tumor growth rate with initial tumor pO2 measured by EPR oximetry. The greatest growth delay in response to radioimmunotherapy had the highest initial pO2, and the fastest-growing tumors had the lowest initial pO2. We then determined the dynamic effect of radioimmunotherapy on tumor pO2 by serial measurements of pO2 for 35 days after radioimmunotherapy. This information could be important for ascertaining the likelihood that a tumor will respond to additional doses as part of a multiple dose scheme. Serial tumor pO2 measurements may help identify a window of opportunity when the surviving tumor regions will be responsive to a second round of radioimmunotherapy or a second therapeutic modality such as chemotherapy or an anti-vascular agent. After radioimmunotherapy, there was an increase in tumor pO2 followed by a decrease below initial levels in most mice. Thus defined times may exist when a tumor is more or less radiosensitive after radioimmunotherapy.

Animals↗

PubMed2000

In vivo EPR of topical delivery of a hydrophilic substance encapsulated in multilamellar liposomes applied to the skin of hairless and normal mice.

In vivo low frequency EPR was used to measure the enhancement of topical delivery of hydrophilic substances by use of multilamellar liposomes. The contribution of transepidermal or/and transfollicular routes of transport was investigated using hairless and normal mice. Two liposome dispersions that previously had been shown to have different enhancement properties on ex vivo skin were used. The kinetics of the reduction of hydrophilic spin probe GluSL (N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-2,3,4,5, 6-pentahydroxy-hexaneamide) applied to the skin encapsulated into the liposomes was measured. To distinguish the reduction of GluSL on the skin surface from its reduction inside the skin, the oxidizing agent potassium ferricyanide (KFeCN) was used. This does not penetrate into the skin and therefore it oxidizes hydroxylamines back to nitroxide only on the surface of the skin. We observed significant differences in the properties of the two types of liposomes with respect to their stability when in contact with skin and their transport characteristics. The results measured in vivo are consistent with those obtained ex vivo, indicating that in vivo L-band EPR is a powerful technique for following pharmacokinetics in the skin of live animals. The results also show that clearance by blood flow and possible alterations of skin after sacrifice of animal do not influence the results of penetration of liposome entrapped substances into the skin during the time of our experiment (typically around 60 min). The reduction of GluSL in the skin of hairless vs. normal mice was similar, indicating that the transfollicular penetration was not of major importance in vivo in this experimental model.

Administration, Topical↗

PubMed2000

Electronically tunable surface-coil-type resonator for L-band EPR spectroscopy.

The automatic frequency control (AFC) circuit in conventional electron paramagnetic resonance (EPR) spectrometers automatically tunes the microwave source to the resonance frequency of the resonator. The circuit works satisfactorily for samples stable enough that the geometric relations in the resonance structure do not change in a significant way. When EPR signals are measured during in vivo experiments with small rodents, however, the distance between the signal source and the surface-coil detector can change rapidly. When a conventional AFC circuit keeps the oscillator tuned to the resonator under those conditions, the resultant frequency change may exceed +/-5 MHz and markedly shift the position of the EPR signal. Such a shift results in unacceptable effects on the spectra, especially when the experimenter is dealing with narrow EPR lines. The animal movement also causes a mismatching of the resonator and the 50-ohm transmission line. Direct results of this mismatching are increased noise; shifts in the position of the baseline; and a high probability of overdriving the signal preamplifier with consequent loss of the EPR signal. We therefore designed, built, and tested a new surface-coil resonator using varactor diodes for tuning the resonance frequency to the fixed frequency oscillator and for capacitive matching of the resonator to the 50-ohm transmission line. The performance of the automatic matching system was tested in vivo by measuring EPR spectra of lithium phthalocyanine implanted in rats. Stability and sensitivity of the spectrometer were evaluated by measuring EPR spectra with and without the use of the automatic matching system. The overall experimental performance of the spectrometer was found to significantly improve during in vivo experiments using the automatic matching system. Excellent matching between the 50-ohm transmission line and the resonator was maintained under all experimental circumstances that were tested. This should allow us now to carry out experiments that previously were not possible.

Animals↗

PubMed2000

Kinetics of chromium(V) formation and reduction in fronds of the duckweed Spirodela polyrhiza--a low frequency EPR study.

The uptake of chromate by the duckweed Spirodela polyrhiza was investigated with atomic absorption spectroscopy and the reduction of Cr(VI) to Cr(V) was measured using low frequency EPR spectroscopy. The biphasic kinetics of the uptake was fitted to parameters of a proposed kinetic model. Another model was developed to simulate chromate reduction. The first step of chromate reduction was found to be much faster than the uptake of Cr(VI) from the free space. Most probably, this step occurs already in the cell wall or on the cell membrane surface. Further reduction of Cr(V) to Cr(III) was estimated to be slower. The disappearance of the Cr(V) signal, following transfer of the plants into a Cr-free solution, lasted several tens of hours; the kinetics was mono- or biexponential depending on the length of Cr loading. The rate constants for Cr reduction in living plants were determined for the first time.

Chromium↗

PubMed2000

In vivo EPR dosimetry of accidental exposures to radiation: experimental results indicating the feasibility of practical use in human subjects.

Low frequency electron paramagnetic resonance (EPR) provides the potential advantage of making accurate and sensitive measurements of absorbed radiation dose in teeth in situ, i.e. without removing the teeth from the potential victim. The potential limiting factors for making such measurements are: (1) whether low frequency EPR is sufficiently sensitive to detect radiation-induced signal in human teeth; (2) whether sufficient sensitivity can be maintained under in vivo conditions. In this manuscript, we summarize results indicating that this approach is feasible. Using 1.2 GHz EPR spectroscopy, we found that the lower limit for these measurements in isolated human teeth is 0.2 Gy or lower. Measurements of radiation-induced EPR signals in the teeth of living rats were achieved with sufficient sensitivity to indicate that, when taking into consideration the larger mass of human teeth, similar measurements in human teeth in situ would provide sensitivity in the dose range for potential accidental exposures. We estimate that the current lower limit for detecting radiation doses in human teeth in situ (in vivo) is 0.5-1.0 Gy; this would be sufficient for determining if a person has been exposed to potentially life threatening doses of ionizing radiation. The limiting factor for sensitivity appears to be background signals rather than signal/noise, and there are feasible means to overcome this problem and further increase sensitivity. The additional instrumental developments required to make an effective in vivo EPR dosimetric spectrometer for the measurements in teeth in human subjects in situ, seem quite achievable.

Animals↗