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Biomedical subjects

J B Mitchell

Publications and source records attributed to J B Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1998

Anaesthesia for video-assisted thoracoscopic patent ductus arteriosus ligation.

The case notes of children undergoing video-assisted thoracoscopic ligation of a patent ductus arteriosus were reviewed with particular emphasis on the anaesthetic management. All children were managed using one-lung ventilation with no serious adverse sequelae. The lungs could be isolated easily in all cases and no special equipment was required. We describe our initial series of 13 cases and discuss the anaesthetic implications arising from this surgical technique. We also discuss the different ways of monitoring duct closure.

Anesthesia, Inhalation↗
PubMed1998

The multifaceted roles of nitric oxide in cancer.

The roles of nitric oxide (NO) in numerous disease states have generated considerable discussion over the past several years. NO has been labeled as the causative agent in different pathophysiological mechanisms, yet appears to protect against various chemical species such as those generated under oxidative stress. Similarly, NO appears to exert a dichotomy of effects within the multistage model of cancer. Chronic inflammation can lead to the production of chemical intermediates, among them NO, which in turn can mediate damage to DNA. Yet, NO also appears to be critical for the tumoricidal activity of the immune system. Furthermore, NO can also have a multitude of effects on other aspects of tumor biology, including angiogenesis and metastasis. This report will discuss how the chemistry of NO may impact the initiation and progression stages of cancer.

Animals↗
PubMed1998

Influence of carbohydrate status on immune responses before and after endurance exercise.

To determine the effect of carbohydrate (CHO) status on immune responses after long-duration exercise, on two occasions, 10 men completed a glycogen-depleting bout of cycle ergometry followed by 48 h of either a high-CHO diet (HiCHO; 8.0 g CHO/kg) or a low-CHO diet (LoCHO; 0.5 g CHO/kg). After the 48 h, subjects completed a 60-min ride at 75% maximal O2 uptake (EX). Blood samples were taken predepletion, pre-EX, post-EX, and 2 and 24 h post-EX and were assayed for leukocyte number and function, glucose, glutamine, and cortisol. The glucose responses were significantly higher in the HiCHO (4.62 +/- 0.26 mM) vs. the LoCHO (3.19 +/- 0.15 mM) condition post-EX, and glutamine was significantly higher in the HiCHO (0.472 +/- 0.036 mM) vs. the LoCHO (0.410 +/- 0.025 mM) condition throughout. Cortisol levels were significantly greater in the LoCHO (587 +/- 50 nM) vs. the HiCHO (515 +/- 62 nM) condition throughout the trial. Lymphocyte proliferation (phytohemagglutinin) was significantly depressed after exercise. However, there was no difference between conditions, and the depression was not correlated with elevations in cortisol. Circulating numbers of leukocytes, neutrophils, lymphocytes, and lymphocyte subsets were significantly greater in the LoCHO vs. the HiCHO condition at the post-EX and 2 h post-EX time points. These data indicate that the exercise and diet manipulation altered the number of circulating leukocytes but did not affect the decrease in lymphocyte proliferation that occurred after exercise.

Adult↗
PubMed1998

Phase I study of paclitaxel as a radiation sensitizer in the treatment of mesothelioma and non-small-cell lung cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) and dose-limiting toxicities of paclitaxel with concurrent thoracic irradiation in patients with malignant pleural mesothelioma and locally advanced non-small-cell lung cancer (NSCLC) using a 120-hour continuous infusion regimen. A secondary objective was to assess the effect of paclitaxel on the cell cycle through serial tumor biopsies. PATIENTS AND METHODS: Paclitaxel was administered as a 120-hour (5-day) continuous infusion repeated every 3 weeks during the course of radiation therapy. The starting dose of paclitaxel was 90 mg/m2. Doses were escalated at 15-mg/m2 increments in successive cohorts of three patients. In NSCLC patients, radiation was delivered to the primary tumor and regional lymph nodes for a total tumor dose of 6,120 cGy. In mesothelioma patients, hemithoracic irradiation was delivered as the initial treatment field with a conedown to the tumor volume for a total dose of 5,760 to 6,300 cGy. Tumor biopsies were obtained, if possible, before and during paclitaxel treatment. RESULTS: Thirty patients were entered onto this study through three dose levels (from 90 mg/m2 to 120 mg/m2). The MTD was determined to be 105 mg/m2. The dose-limiting toxicity was grade 4 neutropenia (two patients). Grade 2 gastrointestinal (GI) toxicity (nausea and vomiting) was also observed at 120 mg/m2. Three of 30 patients developed a hypersensitivity reaction. Six patients had grade 2 lung injury manifested by a persistent cough that required antitussives. Five patients underwent tumor biopsies. None of the patients showed a significant block of cells in mitosis (G2/M) after paclitaxel infusion. CONCLUSION: The MTD of paclitaxel, when administered as a 120-hour continuous infusion with concurrent radiotherapy, was determined to be 105 mg/m2. The dose-limiting toxicity was neutropenia. Continuous infusion paclitaxel administered with large field irradiation of the lung is well tolerated and deserves continued evaluation.

Adult↗
PubMed1998

Development of functional electron paramagnetic resonance imaging.

The potential use of electron paramagnetic resonance imaging (EPRI) to obtain physiological information noninvasively is reviewed. EPR, a spectroscopic technique similar to nuclear magnetic resonance (NMR), is useful in detecting and characterizing free radical species. The ability to obtain information about tissue redox and oxygen status using nontoxic free radical spin probes is presented. The capability to encode this information spatially using magnetic field gradients, similar to magnetic resonance imaging (MRI), gives this technique the ability to overlay functional information of tissue with anatomic information. The noninvasive and quantitative nature of EPRI makes it a potentially useful technique for obtaining physiological information from tumors. The requirements for the magnetic field strengths are approximately 600 times lower than that for proton MRI at an identical frequency, making this a low-cost diagnostic tool.

Journal Article↗
PubMed1998

Interaction of gemcitabine with paclitaxel and cisplatin in human tumor cell lines.

We have used clonogenic survival assays and flow cytometry of human lung A549, breast MCF7 and pancreas adenocarcinoma P-SW cell lines to examine the effects of gemcitabine (2'-deoxy-2', 2'-difluorocytidine) in combination with cisplatin, paclitaxel or radiation. Additive cell killing was observed for all cell lines when they were treated with cisplatin for 1 h followed by varying concentrations of gemcitabine for 24 h. Likewise, additive cell killing was noted in all cell lines when treated with gemcitabine for 24 h followed by varying doses of radiation. When A549 cells were exposed to gemcitabine for 24 h followed by a 1 h exposure to cisplatin, synergistic effects were noted. Using the latter regimen, MCF7 cells demonstrated additive cell kill, while the P-SW cells showed a more complex relationship with additive killing below 50 nM gemcitabine and less than additive effect above 50 nM gemcitabine. All three cell lines were also tested with various gemcitabine/paclitaxel combinations. When gemcitabine and paclitaxel were incubated concurrently, gemcitabine antagonized the cell kill produced by paclitaxel. All cell lines showed less than additive killing when either gemcitabine incubation preceded the paclitaxel incubation or the paclitaxel incubation preceded the gemcitabine incubation. Our results show that gemcitabine acts as a radiation sensitizer to increase the effects of radiation. Likewise, we demonstrate that the only uniformly beneficial drug combination schedule in all three cell lines was when cisplatin incubation preceded gemcitabine incubation. The gemcitabine/paclitaxel combinations were much more disturbing with respect to potential clinical trials. Our results would caution any planned clinical trials combining paclitaxel with gemcitabine to be reconsidered because of the potential for less than additive and even antagonistic effects of the combination.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

The role of nitric oxide chemistry in cancer treatment.

Over the last decade the role of nitric oxide (NO) in various disease states has become apparent. In cancer, NO plays a variety of roles which are at times contradictory. On one hand, NO is involved in different etiological mechanisms as well as promoting tumor growth. Yet, NO derived from leukocytes plays a seminal role in their tumoricidal activity. In cancer treatment, NO also has diverse effects. Whereas in vitro, NO can enhance the cytotoxic efficacy of some chemotherapeutic agents as well as radiation, NO donors can provide whole body protection against these same agents. This manuscript will discuss some mechanisms involved with NO and cancer treatment modalities and the potential application of these findings to cancer therapy.

Animals↗
PubMed1997

Qualitative and quantitative analysis of DNA fragmentation using digital imaging.

Apoptosis is an important and common pathway of cellular death. Differentiation from cellular necrosis and quantitation of apoptosis within the milieu of necrosis are analytical challenges. We describe the use of the RIT120 digital imaging software package for quantitative and qualitative analysis of apoptotic DNA ladders induced by a variety of agents, such as serum, tumor necrosis factor-alpha, transforming growth factor-beta1, and nitric oxide. Autoradiographs of DNA ladders are densitometrically scanned to yield a set of curves with peaks corresponding to specific DNA fragments, thereby allowing quantitative subtraction of concurrent DNA degradation from necrotic death. Integration of the areas specifically under the peaks yields a quantitative measure of apoptosis. We provide a useful, rapid, and objective means to quantitate apoptosis, using relatively inexpensive hardware and software.

Animals↗
PubMed1997

Superoxide modulates the oxidation and nitrosation of thiols by nitric oxide-derived reactive intermediates. Chemical aspects involved in the balance between oxidative and nitrosative stress.

Thiol-containing proteins are key to numerous cellular processes, and their functions can be modified by thiol nitrosation or oxidation. Nitrosation reactions are quenched by O-2, while the oxidation chemistry mediated by peroxynitrite is quenched by excess flux of either NO or O-2. A solution of glutathione (GSH), a model thiol-containing tripeptide, exclusively yielded S-nitrosoglutathione when exposed to the NO donor, Et2NN(O)NONa. However, when xanthine oxidase was added to the same mixture, the yield of S-nitrosoglutathione dramatically decreased as the activity of xanthine oxidase increased, such that there was a 95% reduction in nitrosation when the fluxes of NO and O-2 were nearly equivalent. The presence of superoxide dismutase reversed O-2-mediated inhibition, while catalase had no effect. Increasing the flux of O-2 yielded oxidized glutathione (GSSG), peaking when the flux of NO and O-2 were approximately equivalent. The results suggest that oxidation and nitrosation of thiols by superoxide and NO are determined by their relative fluxes and may have physiological significance.

Free Radicals↗
PubMed1997

Mammalian DNA topoisomerase I mediates the enhancement of radiation cytotoxicity by camptothecin derivatives.

The role of DNA topoisomerase I as a biochemical mediator of radiosensitization in cultured mammalian cells by camptothecin derivatives was studied. We found that, in Chinese hamster DC3F cells, camptothecin enhanced the cytotoxicity of radiation in a schedule-dependent manner. At 4 microM, a sensitizer enhancement ratio of 1.45 was observed when radiation was used concurrently with or immediately after drug treatment. By comparison, no enhancement was obtained if radiation preceded camptothecin treatment. Consistently, in human breast cancer MCF-7 cells, sensitizer enhancement ratios of 1.43, 1.38, and 1.05 were observed when radiation was used concurrently with, immediately after, or prior to treatment with 20(S)-10,11-methylenedioxycamptothecin (MDCamp). Three studies indicated that an intact stereospecific interaction between camptothecin derivatives and DNA topoisomerase I is essential in the induction of radiosensitization: (a) higher concentrations of camptothecin were required to radiosensitize the camptothecin-resistant DC3F/C-10 cells; (b) a newly identified topoisomerase 1-targeting Hoechst 33342 also radiosensitized DC3F cells; and (c) 20(S)-methylenedioxycamptothecin, but not its noncytotoxic 20(R)-stereoisomer, radiosensitized MCF-7 cells by obliterating the "shoulder" of the radiation survival curve. The mechanism of radiosensitization was investigated in DC3F cells. We found that camptothecin only minimally enhanced the cytoxic effect of radiation in G1-phase cells obtained by a mitotic shake-off technique as well as in plateau-phase cells arrested by growing to confluency. Our data suggest a potential development of topoisomerase I drugs as radiosensitizers in treating human malignancies.

Animals↗
PubMed1997

Non-randomness in side-chain packing: the distribution of interplanar angles.

We analyze the distributions of interplanar angles between interacting side chains with well-defined planar regions, to see whether these distributions correspond to random packing or alternatively show orientational preferences. We use a non-homologous set of 79 high-resolution protein chain structures to show that the observed distributions are significantly different from the sinusoidal one expected for random packing. Overall, we see a relative excess of small angles and a paucity of large interplanar angles; the difference between the expected and observed distributions can be described as a shift of 5% of the interplanar angles from large (> or = 60 degrees) to small (< 30 degrees) values. By grouping the residue pairs into categories based on chemical similarity, we find that some categories have very non-sinusoidal interplanar angle distributions, whereas other categories have distributions that are close to sinusoidal. For a few categories, observed deviations from a sinusoidal distribution can be explained by the electrostatic anisotropy of the isolated pair potential energy. In other cases, the observed distributions reflect the longer range effects of different possible interaction geometries. In particular, geometries that disrupt external hydrogen bonding are disfavored.

Amides↗
PubMed1997

In vivo imaging of a stable paramagnetic probe by pulsed-radiofrequency electron paramagnetic resonance spectroscopy.

Imaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin-spin relaxation times, typically under 1 microsecond, of most biologically relevant paramagnetic species. Recent advances in radiofrequency (RF) electronics have enabled the generation of pulses of the order of 10-50 ns. Such short pulses provide adequate spectral coverage for EPR studies at 300 MHz resonant frequency. Acquisition of free induction decays (FID) of paramagnetic species possessing inhomogenously broadened narrow lines after pulsed excitation is feasible with an appropriate digitizer/averager. This report describes the use of time-domain RF EPR spectrometry and imaging for in vivo applications. FID responses were collected from a water-soluble, narrow line width spin probe within phantom samples in solution and also when infused intravenously in an anesthetized mouse. Using static magnetic field gradients and back-projection methods of image reconstruction, two-dimensional images of the spin-probe distribution were obtained in phantom samples as well as in a mouse. The resolution in the images was better than 0.7 mm and devoid of motional artifacts in the in vivo study. Results from this study suggest a potential use for pulsed RF EPR imaging (EPRI) for three-dimensional spatial and spectral-spatial imaging applications. In particular, pulsed EPRI may find use in vivo studies to minimize motional artifacts from cardiac and lung motion that cause significant problems in frequency-domain spectral acquisition, such as in continuous wave (cw) EPR techniques.

Animals↗
PubMed1997

Nitric oxide and some nitric oxide donor compounds enhance the cytotoxicity of cisplatin.

A major emphasis in cancer therapy research is finding mechanisms to enhance the effectiveness of clinically used chemotherapeutic agents. In this report, we show the effects of direct NO exposure or NO delivery agents such as NONOate NO donors, DEA/NO ((C2H5)2N[N(O)NO]-Na+) and PAPA/ NO (NH2(C3H6)(N[N(O)NO]C3H7)), or S-nitrosothiol NO donors (GSNO, S-nitrosoglutathione, and SNAP, S-nitroso-N-acetylpenicillamine) on the cytotoxicity of cisplatin with Chinese hamster V79 lung fibroblast cells. Cells pretreated with bolus NO or NO delivered from NONOate NO donors were markedly sensitized to subsequent cisplatin treatment, whereas S-nitrosothiol NO donors exerted little effect. The enhancement in cisplatin cytotoxicity from pretreatment with DEA/NO and PAPA/ NO persisted for approximately 180 and 240 min, respectively; thereafter cytotoxicity returned to a level consistent with cisplatin treatment alone. Pretreatment of cells with GSNO or SNAP did not enhance cisplatin cytotoxity. To discern why there were differential effects among the different NO donors, formation of NO over the time course of the experiment was assessed by the nitrosation of 2,3-diaminonaphthylene. Bolus NO, DEA/NO, and PAPA/NO produced more reactive nitrogen oxide species (RNOS) than did treatment with GSNO or SNAP. Previously reported electrochemical studies revealed that temporal NO concentrations measured from DEA/NO and PAPA/NO (1 mM) were greater than 5 microM. It appears that the flux of NO, as well as the amount of RNOS, is important in the NO-mediated enhancement of cisplatin cytotoxicity. Our results demonstrate the importance of NO delivery systems in the enhancement of cisplatin cytotoxicity and may provide insights into strategies for participation of NO donors and nitric oxide synthase with cisplatin therapy.

Animals↗
PubMed1997

The effects of gonadal steroids on brain stimulation reward in female rats.

The present study examined possible estrogen and/or progesterone effects on the mesolimbic dopamine (DA) system using brain stimulation reward (BSR). It is well known that BSR with electrical stimulation of the medial forebrain bundle (MFB) depends on the functioning of the mesolimbic DA system. If estrogen affects this system in a manner similar to its effects on the nigrostriatal DA system, reward measures would be expected to vary across the estrous cycle. Cycling female rats were trained to bar press for electrical stimulation to the MFB. Animals were tested at each stage of the estrous cycle, after ovariectomy and 4, 24, 48, 72 and 96 h after hormone replacement with estradiol (10 micrograms, s.c.), estradiol and progesterone (0.5 mg, s.c.), or oil (s.c.). The rewarding value of the stimulation and the maximum rate of bar pressing increased during estrus, but not during proestrus or metestrus, as compared with diestrus. Hormone replacement had differing effects on reward and motor performance. Motor performance increased 4 and 24 h after estrogen alone and 24 h after estrogen with the addition of progesterone 4 h before testing. The rewarding value of the stimulation increased only 24 h after estrogen together with an injection of progesterone 4 h before testing. These results indicate that gonadal steroids affect the functioning of the mesolimbic DA system.

Animals↗
PubMed1997

Direct evidence for in vivo nitroxide free radical production from a new antiarrhythmic drug by EPR spectroscopy.

The new Class I anti-arrhythmic agent 2,2,5,5-tetramethyl-3-pyrroline-1-carboxamide derivative, is currently being evaluated in clinical trials in patients with a high risk for cardiac arrhythmias. In this study we show that this antiarrhythmic drug can be chemically converted to the nitroxide free radical analog. Further, using an in vivo Electron Paramagnetic Resonance (EPR) spectroscopy model by detecting free radicals in the distal portion of the tail of an anesthetized mouse, we demonstrate that the drug is oxidized to the corresponding nitroxide. In vitro studies using Chinese hamster V79 cells suggest that the oxidation products of the drug, namely, the hydroxylamine and the nitroxide protect against oxidative damage induced by hydrogen peroxide (H2O2). Taken together, our results suggest that, in addition to the antiarrhythmic effects of the parent drug, sufficient levels of nitroxides may accumulate from the parent drug in vivo to provide antioxidant defense to cardiac tissue that may be subject to ischemia and oxidation-driven injury.

Animals↗
PubMed1997

Evaluation of tempol radioprotection in a murine tumor model.

Tempol, a stable nitroxide free radical compound, is an in vitro and in vivo radioprotector. Previous studies have shown that Tempol protects C3H mice against whole-body radiation-induced bone marrow failure. In this study, the radioprotection of tumor tissue was evaluated. RIF-1 tumor cells were implanted in female C3H mice 10 d prior to radiation. Groups of mice were injected intraperitoneally with Tempol (275 mg/kg) or PBS followed 10 min later by a single dose of radiation to the tumor bed. Tumor growth curves generated after 10 and 33.3 Gy doses of radiation showed no difference in growth between the Tempol- and PBS-treated animals. A full radiation dose-response experiment revealed a tumor control dose in 50% of the animals in 30 d (TCD(50/30)) value of 36.7 Gy for Tempol-treated mice and 41.8 Gy for saline-treated mice suggesting no protection of the RIF-1 tumor by Tempol. Tumor pharmacokinetics were done to determine why Tempol differentially protected bone marrow and not tumor cells. Differential reduction of Tempol in the RIF-1 tumor and bone marrow was evaluated with EPR spectroscopy 10, 20, and 30 min after injection. Bioreduction of Tempol to its corresponding hydroxylamine (which is not a radioprotector) occurred to a greater extent in RIF-1 tumor cells compared to bone marrow. We conclude that the differences in radioprotection may result from enhanced intratumor bioreduction of Tempol to its nonradioprotective hydroxylamine analogue. The nitroxides as a class of compounds may provide a means to exploit the redox differences between normal tissues and tumors.

Animals↗
PubMed1997

Tempol inhibits neutrophil and hydrogen peroxide-mediated DNA damage.

Inflammatory conditions characterized by neutrophil activation are associated with a variety of chronic diseases. Reactive oxygen species are produced by activated neutrophils and produce DNA damage which may lead to tissue damage. Previous studies have shown that activated murine neutrophils induce DNA strand breaks in a target plasmacytoma cell, RIMPC 2394. We studied the effect of a water soluble nitroxide anti-oxidant, Tempol, on murine neutrophil induction of DNA strand breaks in this system. Murine neutrophils were isolated from the peritoneal cavity of BALB/cAn mice after an i.p. injection of pristane oil. Neutrophils were activated by the phorbol ester PMA and co-incubated with RIMPC 2394 cells. Control alkaline elution studies revealed progressive DNA strand breaks in RIMPC cells with time. The addition of Tempol to the incubation mixture prevented DNA damage in a dose dependent fashion. Five mM Tempol provided complete protection. Tempol protection against DNA strand breaks was similar for both stimulated neutrophils and exogenously added hydrogen peroxide. Measurement of hydrogen peroxide produced by stimulated neutrophils demonstrated that Tempol did not decrease hydrogen peroxide concentration. Oxidation of reduced metals, thereby interfering with the production of hydroxyl radical, is the most likely mechanism of nitroxide protection, although superoxide dismutase (SOD) like activity and scavenging of carbon-based free radicals may also account for a portion of the observed protection. The anti-oxidant activity of Tempol inhibited DNA damage by activated neutrophils. The nitroxides as a class of compounds may have a role in the investigation and modification of inflammatory conditions.

Animals↗