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Biomedical subjects

J B Mitchell

Publications and source records attributed to J B Mitchell.

At least 91 records · Page 5Linked to original sources
PubMed1997

Nitric oxide enhancement of melphalan-induced cytotoxicity.

The effects of the diatomic radical, nitric oxide (NO), on melphalan-induced cytotoxicity in Chinese hamster V79 and human MCF-7 breast cancer cells were studied using clonogenic assays. NO delivered by the NO-releasing agent (C2H5)2N[N(O)NO]- Na+ (DEA/NO; 1 mM) resulted in enhancement of melphalan-mediated toxicity in Chinese hamster V79 lung fibroblasts and human breast cancer (MCF-7) cells by 3.6- and 4.3-fold, respectively, at the IC50 level. Nitrite/nitrate and diethylamine, the ultimate end products of DEA/NO decomposition, had little effect on melphalan cytotoxicity, which suggests that NO was responsible for the sensitization. Whereas maximal sensitization of melphalan cytotoxicity by DEA/NO was observed for simultaneous exposure of DEA/NO and melphalan, cells pretreated with DEA/NO were sensitized to melphalan for several hours after NO exposure. Reversing the order of treatment also resulted in a time-dependent enhancement in melphalan cytotoxicity. To explore possible mechanisms of NO enhancement of melphalan cytotoxicity, the effects of DEA/NO on three factors that might influence melphalan toxicity were examined, namely NO-mediated cell cycle perturbations, intracellular glutathione (GSH) levels and melphalan uptake. NO pretreatment resulted in a delayed entry into S phase and a G2/M block for both V79 and MCF-7 cells; however, cell cycle redistribution for V79 cells occurred after the cells returned to a level of cell survival, consistent with treatment with melphalan alone. After 15 min exposure of V79 cells to DEA/NO (1 mM), GSH levels were reduced to 40% of control values; however, GSH levels recovered fully after 1 h and were elevated 2 h after DEA/NO incubation. In contrast, DEA/NO (1 mM) incubation did not reduce GSH levels significantly in MCF-7 cells (approximately 10%). Melphalan uptake was increased by 33% after DEA/NO exposure in V79 cells. From these results enhancement of melphalan cytotoxicity mediated by NO appears to be complex and may involve several pathways, including possibly alteration of the repair of melphalan-induced lesions. Our observations may give insights for improving tumour kill with melphalan using either exogenous or possibly endogenous sources of NO.

Animals↗
PubMed1997

The effect of preexercise carbohydrate status on resistance exercise performance.

The purpose of this study was to determine the effect of a high vs. a low preexercise carbohydrate (CHO) diet on performance during multiple sets of resistance exercise. Eleven resistance-trained males performed cycle ergometry to deplete quadriceps muscle glycogen stores, followed by 48 hr of a high (HICHO) or a low (LOCHO) CHO diet. Subjects then performed five sets each of squats, leg presses, and knee extensions (resistance = 15 RM) to failure. Blood samples were taken before and during exercise for determination of glucose and lactate (LA). No differences in performance (repetitions x weight lifted) were observed (HICHO = 15,975 +/- 1,381 and LOCHO = 15,723 +/- 1,231 kg). Blood glucose was significantly higher after exercise for HICHO compared to LOCHO (HICHO = 4.8 +/- 0.2 vs. LOCHO = 3.9 +/- 0.2 mmol.L-1). No differences in LA accumulation were observed. The data indicated that preexercise CHO status did not affect resistance exercise performance. Further, the differences in blood glucose and the similarity in LA responses suggest that glycolysis was maintained in the LOCHO condition, and there may have been an increased reliance on blood glucose when preexercise CHO status was low.

Adult↗
PubMed1997

Access to family planning services: relationship with unintended pregnancies and prenatal outcomes.

Family planning services are important because they can prevent unintended pregnancies and improve prenatal outcomes. This paper uses secondary data to analyze trends in access to family planning services, with a particular focus on poor women and young women. Trends from the 1980s showed a small decline in family planning visits and an upsurge in the percentage of births that were unwanted at the time of conception. These changes were particularly marked for poor women. Over the same decade, public expenditures for contraceptive services declined dramatically. The health insurance system with respect to family planning must be modernized to meet the needs of women and couples today. Future improvements in infant health and survival will depend in large part on ensuring that pregnancies are intended and not the result of lack of access to effective family planning services.

Adolescent↗
PubMed1996

Multiple solution conformations of the integrin-binding cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-). Analysis of the (phi, psi) space available to cyclic pentapeptides.

The aqueous solution structure of the cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-) has been determined by two-dimensional 1H-NMR spectroscopy, combined with a conformational search and distance-geometry calculations. As many as five conformers in slow exchange were observed, and the rate of interconversion between components was measured from the build-up rates of exchange peaks. NMR data allowed the structures of the two predominant conformers to be determined. The major component (66%) contained a cis-proline as part of a type-VIa2 beta-turn encompassing residues Asp-Val-cis-Pro-Ser. The second component (16%) contained only trans-amide bonds, and a type-VIII beta-turn formed by residues Val-Pro-Ser-D-Leu. These structures are discussed in relation to the (phi, psi), space available to the cyclic pentapeptide, determined by a conformational search, and in relation to previously published cyclic-pentapeptide structures. The molecule exhibits activity in a scintillation-proximity assay for the inhibition of the interaction between the integrin very-late antigen-4 (VLA-4; alpha 4 beta 1) and vascular-cell-adhesion molecule-1 (VCAM-1). The structure/activity relationship of the LDV sequence is discussed and related to the recently published X-ray structure of VCAM-1. The relevance of the work to the design of anti-inflammatory drugs is discussed.

Amino Acid Sequence↗
PubMed1996

Protein recognition of adenylate: an example of a fuzzy recognition template.

The interaction between protein and adenylate in a non-homologous dataset of 18 high-resolution protein/nucleotide crystal structures is analysed. We find that each constituent of adenylate, adenine, ribose and phosphate, is substantially buried. Adenine has a largely hydrophobic protein interface, while phosphate interacts primarily with hydrophilic residues; ribose is intermediate. A detailed study of hydrogen bonding in these complexes shows hydrogen bonds between protein and adenine to be surprisingly scarce. There does not seem to be a conserved hydrogen-bonding pattern for adenine recognition. The hydrogen bonds that are seen have geometries close to energy minima found in our Distributed Multipole Analysis based model calculations. The experimental hydrogen-bonded geometries have a characteristic signature in our model energy calculations, with a dominant attractive electrostatic term. For stacked interactions, however, the dispersion energy dominates. Finally, we present the concept of a fuzzy recognition template, as a useful means of describing the protein/adenylate interactions presented here, which will also be a valuable concept for characterising other protein/ligand interactions.

Adenine↗
PubMed1996

Stimulation by nitroxides of catalase-like activity of hemeproteins. Kinetics and mechanism.

The ability of stable nitroxide radicals to detoxify hypervalent heme proteins such as ferrylmyoglobin (MbFeIV) produced in the reaction of metmyoglobin (MbFeIII) and H2O2 was evaluated by monitoring O2 evolution, H2O2 depletion, and redox changes of the heme prosthetic group. The rate of H2O2 depletion and O2 evolution catalyzed by MbFeIII was enhanced by stable nitroxides such as 4-OH-2,2,6,6-tetramethyl-piperidinoxyl (TPL) in a catalytic fashion. The reduction of MbFeIV to MbFeIII was the rate-limiting step. Excess TPL over MbFeIII enhanced catalase-like activity more than 4-fold. During dismutation of H2O2, [TPL] and [MbFeIV] remained constant. NADH caused: (a) inhibition of H2O2 decay; (b) progressive reduction of TPL to its respective hydroxylamine TPL-H; and (c) arrest/inhibition of oxygen evolution or elicit consumption of O2. Following depletion of NADH the evolution of O2 resumed, and the initial concentration of TPL was restored. Kinetic analysis showed that two distinct forms of MbFeIV might be involved in the process. In summary, by shuttling between two oxidation states, namely nitroxide and oxoammonium cation, stable nitroxides enhance the catalase mimic activity of MbFeIII, thus facilitating H2O2 dismutation accompanied by O2 evolution and providing protection against hypervalent heme proteins.

Animals↗
PubMed1996

Do nitroxide antioxidants act as scavengers of O2-. or as SOD mimics?

Stable nitroxide radicals were reported to act as SOD mimics and catalyze the dismutation of O2-. through two different catalytic pathways including reductive and oxidative reaction mechanisms (Samuni, A., Krishna, C. M., Riesz, P., Finkelstein, E. & Russo, A. (1988) J. Biol Chem. 263, 17921-17924). Recent studies directly monitoring O2-. and employing kinetics analysis did not reveal SOD activity of nitroxides (Weiss, R. H., Flickinger, A. G., Rivers, W. J., Hardy, M. M., Aston, K. W., Ryan, U. S. & Riley, D. P. (1993) J. Biol. Chem. 268, 23049-23054). Such discrepancy may result in cases where distinction of stoichiometric scavengers from catalytic detoxifiers of O2-. is not readily feasible. Nitroxides are effective antioxidants that protect against oxidative injury in various pathological processes. The distinction of their SOD mimic activity from O2-. scavenging was established by examining the validity of direct and indirect methods employed to assay SOD-like catalytic activity. Kinetics analysis along with direct EPR monitoring were used to study the mechanism underlying nitroxide reactions with O2-.. The nitroxide EPR signal decayed in the presence of NADH but otherwise did not decrease with time, thus substantiating its catalytic role in O2-. dismutation. The catalytic rate constants for O2-., dismutation, determined for the nitroxides tested, were found to increase with [H+], indicating that .OOH rather than O2-. is oxidizing the nitroxide. The results demonstrate the limitations associated with direct kinetics analysis in evaluating SOD mimic activity, underscoring the need for independent assays for valid discrimination of SOD mimics from stoichiometric scavengers of O2-..

Antioxidants↗
PubMed1996

The effect of various nitric oxide-donor agents on hydrogen peroxide-mediated toxicity: a direct correlation between nitric oxide formation and protection.

The role that nitric oxide (NO) plays in various degenerative and disease states has remained a mystery since its discovery as a biological messenger, prompting the question, "NO, friend or foe?" Some reports have suggested that NO is cytotoxic, and yet others have shown that it possesses protective properties against reactive oxygen species (ROS). Many studies have used various NO donor complexes arriving at seemingly different conclusions. This report will address the effects of various NO donor compounds on ROS-mediated toxicity. Consistent with our previous study, the NO donor compound, DEA/NO ((C2H5)2N[N(O)NO]-Na+), afforded protection against hydrogen peroxide-mediated cytotoxicity in V79 Chinese hamster lung fibroblasts at concentrations as low as 10 microM DEA/NO. Furthermore, a survey of other NO donor complexes revealed that some either protected or potentiated hydrogen peroxide-mediated cytotoxicity. 3-Morpholinosynodiomine.HCl (SIN-1) and sodium nitroprusside (SNP) enhanced hydrogen peroxide-mediated cytotoxicity, while S-nitrosoglutathione (GSNO), and S-nitroso-N-acetylpenicillamine (SNAP) afforded protection. Electrochemical detection of NO in cell culture medium revealed that neither 1000 microM SIN-1 nor SNP yielded appreciable NO concentrations (<0.3 microM). In contrast, DEA/NO, SNAP, and GSNO yielded fluxes of NO >1.0 microM. Thus, a direct correlation between inhibition of hydrogen peroxide cytotoxicity and NO production was observed: agents that release NO during hydrogen peroxide treatment afford significant protection, whereas agents that do not release NO do not protect. Similar results were observed for NO donors studied when hypoxanthinesolidusxanthine oxidase was used as the source for ROS, although the S-nitrosothiol agents were much less protective. These results demonstrate that NO possesses properties which protect against ROS toxicity and demonstrate how the use of different NO donor compounds can lead to different conclusions about the role that NO can play in the cytotoxicity of ROS.

Animals↗
PubMed1996

Convenient colorimetric and fluorometric assays for S-nitrosothiols.

S-nitrosothiols have been shown to affect a number of physiological functions. Several techniques have been used to detect these species in biological systems, primarily by methods utilizing chemiluminescence. Since the apparatus required for measurement of chemiluminescence are not readily available in most laboratories, methods employing more conventional techniques such as uv-vis and fluorescence spectroscopy may be of greater use. Herein, we report the development of colorimetric and fluorometric methods for the reliable quantitation of S-nitrosothiols. Solutions containing sulfanilamide/N-(1-naphthyl)- ethylenediamine dihydrochloride or 2,2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid), when exposed to S-nitrosoglutathione (GSNO), S-nitrosocysteine, or S-nitrosoacteylpenicillamine, resulted in no absorbance changes in the range of 400-800 nm. Exposure to HgCl2 or Cu(acetate)2 resulted in release of nitric oxide (NO) from the S-nitrosothiols. The liberated NO reacted subsequently with oxygen and formed a chemical species which reacted with either analysis solution, resulting in an increase in absorption between 400 and 800 nm. A plot of RSNO versus absorbance was linear for both mercury(II) and copper(II) ions where the slope in the presence of mercury ion was significantly greater than that for copper ion. The sensitivity was as low as 5 microM RSNO using HgCl2. The fluorometric method using 2, 3-diaminonaphthalene as the scavenger of the NOsolidusO2 products gave a sensitivity of 50 nM for GSNO. In addition, S-nitrosylated proteins were quantitated using the fluorometric technique. These methods provide accurate determination of low concentrations of S-nitrosothiols, utilizing conventional spectroscopic techniques available in most laboratories.

Benzothiazoles↗
PubMed1996

Electron paramagnetic resonance imaging of rat heart with nitroxide and polynitroxyl-albumin.

Electron paramagnetic resonance (EPR) imaging utilizing stable nitroxyl radicals is a promising technique for measuring free radical distribution, metabolism, and tissue oxygenation in organs and tissues [Kuppusamy, P., Chzhan, M., Vij, K., Shteynbuk, M., Lefer, D. J., Giannella, E., & Zweier, J. L. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 3388-3392]. However, the technique has been limited by the rapid reduction of nitroxide in vivo to its hydroxylamine derivative, a diamagnetic, EPR-inactive species. In this report a novel, polynitroxylated derivative of human serum albumin is shown to be capable of reoxidizing the hydroxylamine back to nitroxide in vivo. Polynitroxyl-albumin (PNA) is shown to be effective in maintaining the signal intensity of the nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL or TPL) in the ischemic isolated rat heart, allowing the acquisition of high-resolution three-dimensional (3D) EPR images of the heart throughout a prolonged 2.5 h period of global cardiac ischemia. In serial transverse sections of the 3D image, TPL intensity maps of the heart showed cardiac structure with submillimeter resolution. TPL intensities in coronary arteries and myocardium showed that nitroxide concentration decreases with increasing distance from large blood vessels. These results demonstrate that EPR imaging in vivo is possible using nitroxides in conjunction with PNA. In addition to its utility in the emerging technology of EPR imaging, the greatly prolonged half-life of TPL observed in the presence of PNA may facilitate the therapeutic application of nitroxides in a variety of disease processes.

Animals↗
PubMed1996

Remaking health care in America.

Academic medical centers, vulnerable populations, rural health. Each represents the fragmentation of the current health care delivery system. Not surprisingly, the challenge of achieving cost-effective integrated delivery raises complex issues for each. These issues are explored in Remaking Health Care in America, based on research by Stephen Shortell, Ph.D., and his colleagues at Northwestern University, in partnership with KPMG's National Health Care & Life Sciences practice and 11 integrated health care systems. Hospitals & Health Networks presents an exclusive preview of the book.

Academic Medical Centers↗
PubMed1996

Radiation biology of lung cancer.

The enormous problem that is lung cancer still defies satisfactory therapeutic strategy. This article summarizes some of the more important laboratory efforts directed at understanding the biology of this complex disease. The radiation sensitivities of established lung cancer cell lines are outlined. The effect of radiation dose rate and chemotherapy is explored. The emerging biology of oncogenetic alterations is explored as it relates to radiation sensitivity in general, and lung cancer in particular. Finally, novel therapeutic approaches including photodynamic therapy are introduced.

Antineoplastic Agents↗
PubMed1996

The effect of moderate aerobic training on lymphocyte proliferation.

The purpose of this study was to determine the effect of 12 wks of aerobic training on resting lymphocyte number and proliferation, and immunoglobulin and cytokine levels. Eleven college-aged males (training group = EX) performed 30 min of cycling at 75% of VO2peak, 3 days/wk with VO2peak assessment and blood samples taken at 0,8 and 12 wks. A group of 10 sedentary controls (CT) underwent the same testing protocol. Lymphocyte proliferation response to phytohemagglutinin (PHA) and pokeweed mitogen (PWM) was quantified as a stimulation index (SI) based on the ratio of stimulated versus control cultures, and as total counts per min (CPM). Immunoglobulin (Ig) levels (IgG, IgA, and IgM), and lymphocyte counts were also determined. There was a significant increase in VO2 in the EX group (41.0 +/- 1.8 vs. 46.3 +/- 1.4 ml.kg-1.min-1 pre and post training, respectively). Training had no effect on the PHA SI for the EX group (23.9 +/- 3.3, 27.7 +/- 4.1, and 26.3 +/- 4.0 at 0, 8 and 12 wks, respectively), or the responses of the CT group (28.8 +/- 6.0, 23.9 +/- 3.1, and 30.6 +/- 4.3). No changes were observed for the PWM SI. Significant increases were observed in the CPM for both groups. No differences in the Ig or lymphocyte levels were found during the study. These data indicate that 12 wks of moderate endurance training did not alter resting immune function as determined by mitogen stimulated lymphocyte proliferation, total circulating lymphocytes, or Ig levels.

Adult↗
PubMed1996

Evaluation of commercial vancomycin agar screen plates for detection of vancomycin-resistant enterococci.

Brain heart infusion-6-micrograms/ml vancomycin agar plates obtained from five commercial sources (B-D Microbiology Systems, Carr-Scarborough Microbiologicals, MicroBio Products, PML Microbiologicals, and REMEL) were evaluated with 714 enterococci for detection of vancomycin resistance. All 465 (100%) vancomycin-resistant enterococci (MIC > or = 32 micrograms/ml) were detected by each manufacturer's agar screen plate, and each manufacturer's agar screen plate detected at least 99% of the 177 vancomycin-susceptible enterococci (MIC < or = 4 micrograms/ml). Detection of the 72 vancomycin-intermediate enterococci (MIC = 6 to 16 micrograms/ml) ranged from 94% for B-D Microbiology Systems to 99% for PML Microbiologicals.

Anti-Bacterial Agents↗