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H J Halpern

Publications and source records attributed to H J Halpern.

At least 19 recordsLinked to original sources
PubMed2005

The solution conformation of triarylmethyl radicals.

Hyperfine coupling tensors to 1H, 2H, and natural abundance 13C were measured using X-band pulsed electron nuclear double resonance (ENDOR) spectroscopy for two triarylmethyl (trityl) radicals used in electron paramagnetic resonance imaging and oximetry: methyl tris(8-carboxy-2,2,6,6-tetramethyl-benzo[1,2d:4,5-d']bis(1,3)dithiol-4-yl) and methyl tris(8-carboxy-2,2,6,6-tetramethyl(-d3)-benzo[1,2d:4,5-d']bis(1,3)dithiol-4-yl). Quantum chemical calculations using density functional theory predict a structure that reproduces the experimentally determined hyperfine tensors. The radicals are propeller-shaped with the three aryl rings nearly mutually orthogonal. The central carbon atom carrying most of the unpaired electron spin density is surrounded by the sulfur atoms in the radical and is completely shielded from solvent. This structure explains features of the electron spin relaxation of these radicals and suggests ways in which the radicals can be chemically modified to improve their characteristics for imaging and oximetry.

Electron Spin Resonance Spectroscopy↗
PubMed2001

Tetrahydrobiopterin scavenges superoxide in dopaminergic neurons.

Increased oxidative stresses are implicated in the pathogenesis of Parkinson's disease, and dopaminergic neurons may be intrinsically susceptible to oxidative damage. However, the selective presence of tetrahydrobiopterin (BH(4)) makes dopaminergic neurons more resistant to oxidative stress caused by glutathione depletion. To further investigate the mechanisms of BH(4) protection, we examined the effects of BH(4) on superoxide levels in individual living mesencephalic neurons. Dopaminergic neurons have intrinsically lower levels of superoxide than nondopaminergic neurons. In addition, inhibiting BH(4) synthesis increased superoxide in dopaminergic neurons, while BH(4) supplementation decreased superoxide in nondopaminergic cells. BH(4) is also a cofactor in catecholamine and NO production. In order to exclude the possibility that the antioxidant effects of BH(4) are mediated by dopamine and NO, we used fibroblasts in which neither catecholamine nor NO production occurs. In fibroblasts, BH(4) decreased baseline reactive oxygen species, and attenuated reactive oxygen species increase by rotenone and antimycin A. Physiologic concentrations of BH(4) directly scavenged superoxide generated by potassium superoxide in vitro. We hypothesize that BH(4) protects dopaminergic neurons from ordinary oxidative stresses generated by dopamine and its metabolites and that environmental insults or genetic defects may disrupt this intrinsic capacity of dopaminergic neurons and contribute to their degeneration in Parkinson's disease.

Animals↗
PubMed2001

Electron spin relaxation of triarylmethyl radicals in fluid solution.

Electron spin relaxation times of a Nycomed triarylmethyl radical (sym-trityl) in water, 1:1 water:glycerol, and 1:9 water:glycerol were measured at L-band, S-band, and X-band by pulsed EPR methods. In H(2)O solution, T(1) is 17+/-1 micros at X-band at ambient temperature, is nearly independent of microwave frequency, and exhibits little dependence on viscosity. The temperature dependence of T(1) in 1:1 water:glycerol is characteristic of domination by a Raman process between 20 and 80 K. The increased spin-lattice relaxation rates at higher temperatures, including room temperature, are attributed to a local vibrational mode that modulates spin-orbit coupling. In H(2)O solution, T(2) is 11+/-1 micros at X-band, increasing to 13+/-1 micros at L-band. For more viscous solvent mixtures, T(2) is much shorter than T(1) and weakly frequency dependent, which indicates that incomplete motional averaging of hyperfine anisotropy makes a significant contribution to T(2). In water and 1:1 water:glycerol solutions continuous wave EPR linewidths are not relaxation determined, but become relaxation determined in the higher viscosity 1:9 water:glycerol solutions. The Lorentzian component of the 250-MHz linewidths as a function of viscosity is in good agreement with T(2)-determined contributions to the linewidths at higher frequencies.

Electron Spin Resonance Spectroscopy↗
PubMed1999

Diminished aqueous microviscosity of tumors in murine models measured with in vivo radiofrequency electron paramagnetic resonance.

Using very low frequency in vivo electron paramagnetic resonance (EPR), we have compared, for the first time, the average microviscosity of the total aqueous compartment of murine fibrosarcomas and that of normal leg tissue in a living animal. EPR spectra from dissolved nitroxide spin probes report the solvent microviscosity. The tumor aqueous microviscosity, 1.8 +/- 0.1 centipoise, was significantly lower than that of the corresponding normal tissue, 2.9 +/- 0.3 centipoise, a difference of 38 +/- 7%. These results confirm the commonly observed increase in the water proton transverse relaxation times (T2) in magnetic resonance imaging of hyperproliferative states, for example, malignancy. The specificity of the localization of the EPR signal indicates a substantial portion of the T2 increase seen in magnetic resonance imaging derives from decreased bulk-water viscosity. The effect of this microviscosity differences may be the basis of several physiological differences between tumors and normal tissues which could confer a growth rate advantage to tumor tissue.

Animals↗
PubMed1999

Spin trapping of nitric oxide by ferro-chelates: kinetic and in vivo pharmacokinetic studies.

Biologically generated nitric oxide appears to play a pivotal role in the control of a diverse series of physiologic functions. Iron-chelates and low-frequency EPR spectroscopy have been used to verify in vivo production of nitric oxide. The interpretation of in vivo identification of nitric oxide localized at the site of evolution in real time is complicated by the varied kinetics of secretion. The quantitative efficiency of the spectroscopic measurement, so important in understanding the physiology of nitric oxide, remains elusive. The development of a more stable iron-chelate will help better define nitric oxide physiology. In this report, we present data comparing the commonly used ferro-di(N-methyl-D-glucamine-dithiocarbamate) (Fe2+(MGD)2) and the novel chelate ferro-di(N-(dithiocarboxy)sarcosine) (Fe2+(DTCS)2) quantifying the in vitro and in vivo stability of the corresponding spin trapped adducts, NO-Fe(MGD)2 and NO-Fe(DTCS)2. Finally, very low frequency EPR spectroscopy has been used to evaluate the pharmacokinetics of NO-Fe(MGD)2 and NO-Fe(DTCS)2 in mice in real time.

Drug Stability↗
PubMed1996

In vivo spin-label murine pharmacodynamics using low-frequency electron paramagnetic resonance imaging.

A novel, very-low-frequency electron paramagnetic resonance (EPR) technique is used to image the distribution of several nitroxides with distinct pharmacologic compartment affinities in the abdomens of living mice. Image acquisition is sufficiently rapid to allow a time sequence of the distribution for each compound. The spectra and concentrations of these nitroxides are imaged with the use of spectral-spatial imaging to distinguish a single spatial dimension. Liver and bladder of the mouse anatomy are distinguished by this technique. After an intraperitoneal injection of the spin-label probes, a shift in the distribution of the compounds from the upper abdomen (primarily liver) to the lower abdomen (primarily bladder) is observed. The time dependence of the shift in regional distribution depends on the structural properties of the side chain attached to the spin label. These results indicate that this application of in vivo electron paramagnetic resonance imaging will provide a new method of magnetic resonance imaging for determination of pharmacodynamics in the body of an intact animal.

Animals↗
PubMed1996

Measurement of differences in pO2 in response to perfluorocarbon/carbogen in FSa and NFSa murine fibrosarcomas with low-frequency electron paramagnetic resonance oximetry.

We have used very low-frequency electron paramagnetic resonance (EPR) oximetry to measure the change in oxygen concentration (delta pO2) due to change in breathing atmosphere in FSa and NFSa fibrosarcomas implanted in the legs of C3H mice infused with perfluoro-octylbromine (PFOB). Measurements in each tumor were made before and after the administration of the high-density (47% v/v) perfluorocarbon PFOB, perflubron (Alliance Pharmaceutical Corporation, San Diego, CA). Measurements in each tumor were also made, after the administration of the PFOB, both before (PFOB/air) and after the administration of carbogen (95% O2 + 5% CO2, PFOB/carbogen). Large changes (delta p02) relative to PFOB/air oxygenation were seen with the administration of PFOB/carbogen. No significant difference in oxygen concentration was seen between air-breathing mice with and without PFOB. The mean delta pO2 for FSa tumors was 13 +/- 6 torr, while the mean for NFSa fibrosarcomas was 28 +/- 7 torr. There were such large intertumor differences that the trend toward a smaller change in the more hypoxic FSa tumors was not significant (P = 0.13). This paper describes a novel method of measuring differences in oxygenation in tumor tissues. The results of such measurements indicate large differences in pO2 response to different breathing atmospheres in PFOB-infused tumors of similar histology. The intertumor delta pO2 differences may correlate with differences in radiation response.

Animals↗
PubMed1995

In situ detection, by spin trapping, of hydroxyl radical markers produced from ionizing radiation in the tumor of a living mouse.

Hydroxyl radicals are thought to be responsible for the toxicity associated with ionizing radiation in tissues. Measurements of hydroxyl radicals generated by ionizing radiation in cellular systems have failed thus far to elucidate higher-level homeostatic responses to this and other reactive oxygen species. Careful assessment of prior indirect hydroxyl radical assays in living tissues indicates that they are prone to a variety of artifacts, making all but the most qualitative relationships difficult to establish. This paper describes the detection of hydroxyl radicals produced during radiation in the leg tumor of a living mouse, where the free radicals evolve; detection uses low-frequency electron paramagnetic resonance in combination with in vivo spin trapping. To our knowledge, this is the first report of such a direct measurement of free radical production in the tissues of a living animals.

Animals↗
PubMed1994

Oxymetry deep in tissues with low-frequency electron paramagnetic resonance.

We have measured the oxygen concentration in the body water of murine FSa and NFSa fibrosarcomas using a new method for quantitative oxygen concentration determination deep in the tissues of a living animal. The measurement uses unusually low-frequency electron paramagnetic spectroscopy sensitive to substrate 7 cm deep in tissue, partially deuterated spin probes (spin labels of molecular mass 195, approximating that of glucose) whose distribution compartment can be targeted with facile adduct substitution, and novel analytic techniques. We show that the water-compartment oxygen concentration of the tumors decreases as the tumor size increases and also shows a trend to decrease as radiobiologic hypoxia increases. An oxymetric spectral image of the tumor is presented. The technique will improve with larger human tissue samples. It provides the potential to quantitatively assess tissue hypoxia in ischemic or preischemic states in stroke and myocardial infarction. It will allow direct assessment of tumor hypoxia to determine the usefulness of radiation and chemotherapy adjuvants directed to hypoxic cell compartments.

Animals↗
PubMed1992

Beam's eye view volumetrics: an aid in rapid treatment plan development and evaluation.

A well-designed treatment plan fully irradiates the target to the prescribed dose while minimizing radiation to adjacent critical structures. Beam's eye view is an important component of treatment planning systems because it provides the operator with tools needed to achieve this goal. Through interactive manipulation of displays, the planner uses beam's eye view to adequately cover the target volume while geometrically avoiding certain critical, normal structures. A factor not considered in current beam's eye view programs is the fractional volume of each structure irradiated given a specified beam direction. We have incorporated a rapid volume calculation capability in our beam's eye view program, and have applied it to provide a quantitative aid to treatment planning development and evaluation. Treatment planning of lung tumors has been studied using this tool. Volumes of lung and spinal cord treated as a function of portal angle may be calculated much more rapidly than dose volume histograms and yet provide quantitative indices which follow the trends of dose volume histograms as a function of field angle. Plots of normal tissue volume irradiated as a function of field angle identify the optimal angle to minimize irradiated volume of a structure at a glance. For multiple field plans, a bitmap approach identifies areas treated by various combinations of beams. Volumetrics combined with beam's eye view are useful in treatment planning because they (a) provide quantitative information needed in choosing and optimizing portal entry angle (b) provide an interactive approach to understanding the relative merits of different multiple field plans and (c) complement the information provided by the more time consuming generation of dose volume histograms. The clinical application of this tool in treatment planning is presented.

Computer Graphics↗
PubMed1992

Localized prostate cancer: use of serial prostate-specific antigen measurements during radiation therapy.

The serum half-life of prostate-specific antigen (PSA) after radical prostatectomy is about 3 days; to the authors' knowledge, the PSA half-life during radiation therapy (RT) has not been investigated with weekly serial measurements. To determine the rate of decline and the half-life of PSA, serial measurements were obtained during 6-8 weeks of external-beam RT for localized prostate cancer. PSA values were determined immediately before and approximately 24 hours after the first dose of RT; thereafter, weekly measurements were made. There was a downward trend in PSA levels in 19 patients, with a median half-life of 58.5 days; the mean decline was 1.6% per day. However, in four patients, PSA levels either rose and fell to pre-RT values or increased steadily. The effect of digital rectal examination (DRE) on PSA levels was also analyzed. When the dates of DRE and subsequent PSA levels were inspected, no increase in PSA levels subsequent to DRE was found, although three of the four patients in whom PSA levels did not decrease underwent multiple DREs. The authors found a statistically significant (P = .023) transient elevation in the mean PSA values after the first fraction of RT (2 Gy) was administered; the mechanism and importance of which are not known.

Adenocarcinoma↗
PubMed1991

Measurement of bioreduction rates of cells with distinct responses to ionizing radiation and cisplatin.

A low frequency electron paramagnetic resonance (EPR) spectrometer has been used to measure the bioreduction rate of an exogenously added nitroxide free radical species. Measurements have been made in a well controlled, in vitro system using an X-ray and cisplatin sensitive Chinese hamster ovary (CHO) cell line, xrs-5, and partial revertants which display wild-type levels of sensitivity to X-rays but retain xrs-5 levels of cisplatin sensitivity. The xrs-5 cells reduce this radical species at a rate which is approx. 50% that of the wild-type CHO cell line, K1. The partial revertants maintain this defect in bioreduction despite their decrease in radiosensitivity. However, the bioreduction rate observed in these cells correlates with their sensitivity to the chemotherapeutic drug cisplatin. Low frequency EPR allows measurements and imaging of living tissue and may be of value as a predictive assay of human tumor response to chemotherapy.

Animals↗
PubMed1991

Optimization of radical radiotherapy with beam's eye view techniques for non-small cell lung cancer.

The presence of vital and sensitive organs such as the spinal cord, heart, and lungs makes curative radiotherapy of non-small cell lung cancer difficult to implement and necessitates use of oblique portals. Defining the target volumes in oblique portals is very difficult. We now show, for non-small cell lung cancer, how beam's eye view-based radiotherapy can be used for accurate delineation of treatment volumes and for avoidance of real or dosimetric geographic misses. Furthermore, the beam's eye view-based method enables one to project accurately a 2-dimensional image of 3-dimensional disease extension, especially in oblique fields, thus facilitating the design of accurate customized blocking and avoiding inadvertent blocking of the tumor or unnecessary irradiation of normal tissues. Beam's eye view volumetric analysis is helpful for devising a customized treatment plan for each patient. Such customization may minimize local failure, which is one cause of poor results of radiotherapy in this site. Beam's eye view-based radiotherapy has the potential of improving local control and hence may improve the survival of patients with non-small-cell lung cancer.

Carcinoma, Non-Small-Cell Lung↗
PubMed1991

Use of a low-frequency ESR spectrometer: implications for spin-trapping free radicals, in situ.

We have adapted the low-frequency ESR spectrometer, designed and built by H.J. Halpern, to the physiologic needs of organ preparations operating at 250 MHz. Initial studies have allowed us to detect nitroxides in an isolated perfused heart. These in situ measurements were made with nitroxides specifically designed to mimic the lipophilic nature of 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH). These spin labels provided information about the influence of dynamic factors of the heart, such as flow rate, different cell populations and unequal distribution between compartments on our ability to conduct and interpret spin trapping experiments. They also clarified the sacrifice in sensitivity involved in operating at the lower frequencies. To deal with this later problem, we have increased the sensitivity of the spin trapping method by synthesizing a family of 15N- and deuterium-containing DMPO analogs and by determining their ability to spin trap free radicals generated by the model superoxide system of xanthine/xanthine oxidase. Finally, since activated neutrophils are one of the few cells known to generate free radicals as part of their physiologic function, we used these phagocytic cells, as a source of superoxide.

Animals↗
PubMed1990

Radiation therapy in the treatment of cervical cancer: the University of Chicago/Michael Reese Hospital experience.

A retrospective analysis was conducted on 307 patients referred for radiation therapy at The University of Chicago and Michael Reese Hospital between 1971 and 1986. Median follow-up was 6.4 years. Treatment techniques varied during the time of the study. Actuarial disease-free survivals were 78%, 64%, 55%, 33%, 41%, and 60% for stage IB, IIA, IIB, IIIA, IIIB, and IVA, respectively. Stage, size of the cervical lesion, and hemoglobin level during treatment were prognostic factors. Treatment technique as well as time dose factors were analyzed with respect to survival, failures, and complications.

Adult↗