Biomedical subjects

J B Mitchell

Publications and source records attributed to J B Mitchell.

At least 127 records · Page 7Linked to original sources

PubMed1994

Protection against SR 4233 (Tirapazamine) aerobic cytotoxicity by the metal chelators desferrioxamine and tiron.

PURPOSE: Metal chelating agents and antioxidants were evaluated as potential protectors against aerobic SR 4233 cytotoxicity in Chinese hamster V79 cells. The differential protection of aerobic and hypoxic cells by two metal chelators, desferrioxamine and Tiron, is discussed in the context of their potential use in the on-going clinical trials with SR 4233. METHODS AND MATERIALS: Cytotoxicity was evaluated using clonogenic assay. SR 4233 exposure was done in glass flasks as a function of time either alone or in the presence of the following agents: superoxide dismutase, catalase, 5,5-dimethyl-1-pyrroline, Trolox, ICRF-187, desferrioxamine, Tiron (1,2-dihydroxybenzene-3,5-disulfonate), and ascorbic acid. Experiments done under hypoxic conditions were carried out in specially designed glass flasks that were gassed with humidified nitrogen/carbon dioxide mixture and with a side-arm reservoir from which SR 4233 was added to cell media after hypoxia was obtained. Electron paramagnetic resonance studies were also performed. RESULTS: Electron paramagnetic resonance and spectrophotometry experiments suggest that under aerobic conditions SR 4233 undergoes futile redox cycling to produce superoxide. Treatment of cells during aerobic exposure to SR 4233 with the enzymes superoxide dismutase and catalase, the spin trapping agent DMPO, the water-soluble vitamin E analog Trolox, and the metal chelator ICRF-187 provided little or no protection against aerobic SR 4233 cytotoxicity. However, two other metal chelators, desferrioxamine and Tiron, afforded significant protection against aerobic SR 4233 cytotoxicity (protection factors at 50% survival were 3.8 and 3.1, respectively), while exhibiting minimal protection to hypoxic cells treated with SR 4233. CONCLUSIONS: One potential mechanism of aerobic cytotoxicity is redox cycling of SR 4233 with molecular oxygen resulting in several potentially toxic oxidative species that overburden the intrinsic intracellular detoxification systems such as superoxide dismutase, catalase, and glutathione peroxidase. This study identifies two metal chelating agents, desferrioxamine and Tiron, that were able to protect against aerobic but not hypoxic SR 4233 cytotoxicity.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗

PubMed1994

National Cancer Institute (phase II) study of high-grade glioma treated with accelerated hyperfractionated radiation and iododeoxyuridine: results in anaplastic astrocytoma.

PURPOSE: We report the outcome of a Phase II study of a cohort of patients with high-grade glioma treated with accelerated hyperfractionated radiation and the radiation sensitizer, iododeoxyuridine (IdUrd). METHODS AND MATERIALS: Between January 1988 and December 1990, 39 consecutive patients with high-grade glioma were enrolled and treated on a Phase II protocol including hyperfractionated radiation and IdUrd. Thirty-two patients were male and seven were female. Age range was 19 to 71 years with a median age of 38 years. IdUrd (1000 mg/m2 per day) was administered in two separate 14-day courses, the first during the initial radiation field and the second during the final cone-down field. All patients were treated consistently with partial brain technique and received 1.5 Gy/fraction twice daily to a mean total dose of 71.25 Gy (range 66-72 Gy excluding one patient who did not complete treatment). The initial field was treated to 45 Gy followed by a cone-down field covering the tumor volume plus a 1-cm margin to the final dose. Patients were assessed for acute and long-term morbidity and followed for outcome. Two patients had biopsies during the course of treatment. Flow cytometry and high performance liquid chromatography was used to evaluate the labeling index and the percent replacement of IdUrd in the biopsy specimen. RESULTS: Thirty-eight of 39 patients completed therapy. One patient died on treatment at 48 Gy and is included in the survival analysis. No patient was lost to follow-up. Twenty-one patients had Grade 3 (anaplastic astrocytoma) tumors and 18 patients had Grade 4 (glioblastoma multiforme). Median survival for the entire cohort was 23 months. For the glioblastoma multiforme patients, median survival was 15 months. The median survival of the anaplastic astrocytoma patients has not yet been reached. In the patients assessed, the range of IdUrd tumor cell incorporation was only 0-2.4%. CONCLUSION: Accelerated hyperfractionated radiation therapy with IdUrd was administered with acceptable acute toxicity. The major acute side effects of mucositis and thrombocytopenia were related to IdUrd infusion and were dose-dependent. There were no unacceptable acute toxicities referable to the radiation as delivered. With a median potential follow-up of 51 months, the actuarial median survival of the glioblastoma multiforme patients is comparable with the best previously published reports. The outcome of patients with anaplastic astrocytoma compares very favorably with even the most aggressive multi-modality approaches in the recent literature with a minimum of acute morbidity.

Adult↗

PubMed1994

Free radical modes of cytotoxicity of adriamycin and streptonigrin.

Free radical modes of cytotoxicity of streptonigrin (STN) and Adriamycin (ADR) in Chinese hamster V79 cells under aerobic conditions were evaluated using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TP), a low molecular weight stable nitroxide free radical with antioxidant properties and desferrioxamine (DF), a transition metal chelator. In addition, exogenous superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6), were tested for cytoprotective effects. EPR studies showed that TP reacts with the semiquinones of both ADR and STN and also with O2- radicals generated during aerobic redox cycling of the respective semiquinone radicals. Pulsed field gel electrophoresis studies confirmed that DNA double-strand breaks (dsb) induced by STN in V79 cells were inhibited completely by TP, whereas ADR-induced DNA dsb were not affected by TP. Clonogenic cell survival studies showed that STN-induced cytotoxicity could be inhibited completely by DF or TP. Both agents were ineffective in inhibiting ADR-induced cytotoxicity. SOD and CAT were ineffective in protecting against both STN and ADR cytotoxicity. Our results are consistent with a mechanism requiring the semiquinone radical intermediate of STN for cytotoxicity and minimal free radical involvement in ADR-induced V79 cell cytotoxicity.

Animals↗

PubMed1994

In vivo radiation protection by nitric oxide modulation.

Drugs that affect blood flow have been shown to be whole body radiation protectors. Using NG-nitro-L-arginine, a specific inhibitor of nitric oxide synthase, and the NO-releasing agent (C2H5)2N[N(O)NO-]Na+ (DEA/NO), we have studied the ability of NO to modulate whole body radiation toxicity in C3H mice. NG-Nitro-L-arginine given to mice between 15 and 60 min prior to radiation afforded significant protection from whole body irradiation, e.g., the estimated whole body irradiation dose required to kill 50% of mice by 30 days after radiation (LD50/30) in mice treated with NG-nitro-L-arginine 60 min before irradiation was 1051 cGy compared with a whole body radiation LD50/30 of 822 cGy in control mice (P < 0.00001). Treatment of mice with DEA/NO prior to whole body irradiation also significantly reduced toxicity; the estimated whole body radiation LD50/30 was 1063 and 945 cGy in mice treated with DEA/NO 10 or 30 min before irradiation, respectively (P < 0.00001 for radiation LD50/30 of either DEA/NO-treated group compared with control). Measurement of [14C]etanidazole binding to bone marrow demonstrated that DEA/NO and NG-nitro-L-arginine exacerbated bone marrow hypoxia. Perturbations of NO levels have profound effects on in vivo radiosensitivity of normal tissues. We hypothesize that alterations in regional blood flow may underlie the changes in radiosensitivity that we have observed.

Amino Acid Oxidoreductases↗

PubMed1994

Changes in radiation survival curve parameters in human tumor and rodent cells exposed to paclitaxel (Taxol).

PURPOSE: Late G2 and M are the most radiosensitive phases of the cell cycle. Cells exposed to paclitaxel develop a cell cycle arrest in G2/M. These studies were performed to assess the in vitro radiosensitization properties of paclitaxel in human tumor and rodent cell lines. METHODS AND MATERIALS: The effect of paclitaxel on the radiation sensitivity of human breast (MCF-7), lung (A549), ovary (OVG-1) adenocarcinoma and Chinese hamster lung fibroblast V79 cells was determined with clonogenic assays. DNA flow cytometry studies were performed to define the cell cycle characteristics of the cells during irradiation. Survival curve parameters for all cell lines were determined with the use of a computer program which represents cell survival after radiation by a linear-quadratic model. RESULTS: All cell lines developed a G2/M block after exposure to paclitaxel for 24 h. However, the degree of radiosensitization produced by paclitaxel varied among the cell lines. The maximal sensitizer enhancement ratio (SER) of paclitaxel was 1.8 in MCF-7 cells, 1.6 in OVG-1 cells, and 1.7 in V79 cells. However, no concentration of paclitaxel was able to enhance the radiation sensitivity of A549 cells. Paclitaxel increased the linear (alpha) component of the radiation survival curves in all cell lines. The quadratic (beta) component was unaffected by paclitaxel in the rodent cells. High concentrations of paclitaxel (> or = 1000 nM) increased beta slightly in the human cell lines but there was considerable variation in the effect of paclitaxel on beta. The cells which were sensitized to radiation by paclitaxel had a relatively small baseline alpha component, while A549 cells had a large alpha component. CONCLUSION: We conclude that paclitaxel is a modest radiosensitizer in some, but not all, human tumor cells. Paclitaxel appears to cause radiosensitization mainly by increasing the alpha component of radiation survival curves. Cells that normally have a relatively small alpha component should exhibit the most radiosensitization in response to paclitaxel while cells with a large alpha component should show little or no radiosensitization after paclitaxel treatment. Because the greatest effect of paclitaxel is on the linear component of radiation survival curves, these results indicate that paclitaxel may be an effective radiation sensitizer in many human tumors treated at clinically relevant radiation doses of 2 Gy or less.

Animals↗

PubMed1994

Amino/aromatic interactions in proteins: is the evidence stacked against hydrogen bonding?

We investigate the suggestion that aromatic rings can act as hydrogen-bond acceptors in proteins, by an analysis of 55 non-homologous high-resolution protein chain structures. Approximately 10% of interactions between sp2 hybridized nitrogen atoms, from either side-chains or main-chains, and phenylalanine or tyrosine rings have the nitrogen atom positioned above the ring. In these instances, however, the sp2 nitrogen atoms tend to form stacked interactions with the aromatic rings, these geometries outnumbering amino/aromatic hydrogen bonds by around 2.5:1. The statistically expected distribution, in contrast, would have only a few stacked structures and many more with larger interplanar angles, corresponding to amino/aromatic hydrogen bonds. Thus, although we do find some of these unconventional hydrogen bonds, they are clearly disfavoured relative to stacked geometries. In stacked geometries, the nitrogen-bearing groups are observed to fulfil their hydrogen-bonding potential by forming conventional, energetically stronger, hydrogen bonds with other groups in protein or solvent. This may explain the favourability of stacking. Thus, although ab initio calculations of the gas phase interaction energies for three model systems generally favour the amino/aromatic hydrogen-bonded over the stacked geometries, the differences are small enough to be outweighed easily by the additional conventional hydrogen bonding in stacked structures.

Amino Acid Sequence↗

PubMed1994

Bioreductive metabolism of SR-4233 (WIN 59075) by whole cell suspensions under aerobic and hypoxic conditions: role of the pentose cycle and implications for the mechanism of cytotoxicity observed in air.

PURPOSE: Measurement of pentose cycle (PC) activity is shown to be a noninvasive means for monitoring the reduction of SR-4233 in whole cells. Comparing these measurements to the actual measurements of drug loss under aerobic and hypoxic conditions helps to define the mechanism for the associated aerobic toxicity. METHODS AND MATERIALS: SR-4233 is activated to a toxic species by bioreductive metabolism. NADPH is required for the activation of the drug by purified enzymes, cell homogenates and whole cells. In vivo the NADPH:NADP+ ratio is maintained by the oxidation of glucose via the oxidative limb of the pentose cycle. By measuring radiolabeled 14CO2 released as a product of this oxidation one can get an accurate measurement of the rate of drug metabolism in whole cells. These results are compared to measurements of drug consumption under aerobic and hypoxic conditions using an HPLC assay. RESULTS: SR-4233 stimulates pentose cycle activity to a greater extent in air then under hypoxia, however, in the presence of added catalase, pentose cycle activity is stimulated to a similar extent under both conditions. The higher levels of PC activity observed in air are due to the production of hydrogen peroxide by the nitroxide free radical undergoing futile redox cycling. The contribution of H2O2 to the observed aerobic cytotoxicity of SR-4233 is minimal however, since toxicity is only slightly reduced in the presence of exogenous catalase and antioxidants such as vitamin E. The level of PC stimulation by SR-4233 suggests that the rate of electron addition to the drug is independent of O2 concentration. The loss of drug from the incubation medium, i.e., conversion to a stable intermediate species, occurs approximately five times faster under nitrogen than in air for A549 cells. It is the rate of drug loss from the cell and not the rate of reduction which best correlates with the observed aerobic and hypoxic toxicity. CONCLUSION: Toxicity in air and in nitrogen is directly related to the rate of drug reduction, i.e., at equivalent levels of drug loss we observe equal levels of cytotoxicity.

Aerobiosis↗

PubMed1994

Potential use of nitroxides in radiation oncology.

The identification of radioprotectors is an important goal for those involved in radiation oncology and for those interested in the investigation of the mechanisms of radiation cytotoxicity. Recently, a new class of in vitro and in vivo radioprotectors, the nitroxides, has been discovered. The nitroxides are low-molecular-weight stable free radicals which are freely membrane permeable and which have been shown to act as superoxide dismutase mimics. Further investigation of these compounds has shown that a water-soluble nitroxide, Tempol, protects cultured Chinese hamster V79 cells from the cytotoxicity caused by superoxide, hydrogen peroxide, and t-butyl hydroperoxide. Tempol and five other water-soluble nitroxides have also been shown to protect V79 cells against radiation-induced cytotoxicity. Potential mechanisms of protection by the nitroxides include oxidation of reduced transition metals, superoxide dismutase-like activity, and scavenging of oxy- and carbon-based free radicals. In vivo studies reveal that Tempol protects C3H mice from the lethal effects of radiation with a dose causing 50% lethality within 30 days of 9.97 Gy and 7.84 Gy in Tempol-treated and saline-treated mice, respectively, and a dose modification factor of 1.3. The nitroxides represent a new class of non-thiol radioprotectors which may also have application as general antioxidants. Additional work is necessary to screen other nitroxides for in vivo radioprotection and toxicity as well as to fully evaluate the extent to which these compounds protect tumors.

Animals↗

PubMed1994

In vitro studies of Taxol as a radiation sensitizer in human tumor cells.

BACKGROUND: Cells exposed to paclitaxel (Taxol) develop a cell cycle arrest in G2/M. It has long been recognized that late G2 and M are the most radiosensitive phases of the cell cycle. PURPOSE: These studies were performed to assess the in vitro radiosensitization properties of paclitaxel in human tumor cell lines. METHODS: The effect of paclitaxel at concentrations ranging from 0 to 10,000 nM on the radiation sensitivity (from 0 to as much as 10 Gy in certain experiments) of human breast (MCF-7), lung (A549), ovary (OVG-1), and pancreas (PC-Sh) adenocarcinoma cells was determined using clonogenic assays. DNA flow cytometry studies were performed to define the cell cycle characteristics of populations of cells that had been treated for 6-72 hours with 0, 100, 1000, or 10,000 nM paclitaxel. RESULTS: All cell lines developed a G2/M block after exposure to 100-10,000 nM paclitaxel for 24 hours. However, the degree of radiosensitization produced by paclitaxel varied among the cell lines. The sensitizer enhancement ratio (SER) of paclitaxel at 10% survival was 1.8 in MCF-7 cells and 1.6 in OVG-1 cells. However, paclitaxel at any concentration was unable to enhance the radiation sensitivity of A549 cells. PC-Sh cells demonstrated a complex and inconsistent radiosensitization response to paclitaxel. At 10% survival, an SER of 1.5 was observed in PC-Sh cells. However, at 1% survival, no radiosensitization was observed in PC-Sh cells. Maneuvers that prevented paclitaxel from producing a G2/M block, including coincident treatment with cycloheximide or treatment of cells in plateau phase of growth, completely abrogated the radiosensitization afforded by paclitaxel in MCF-7 cells. CONCLUSIONS: Paclitaxel is a modest radiosensitizer in some, but not all, human tumor cells. The degree of radiosensitization that we have observed with paclitaxel is similar to what has been found with other chemotherapeutic agents. The absence of radiosensitization by paclitaxel in MCF-7 cells grown to plateau phase or treated with cycloheximide implies that the development of a G2/M block is a necessary condition for paclitaxel radiosensitization. However, the inability of paclitaxel to radiosensitize A549 cells despite the presence of a G2/M block in those cells demonstrates that a G2/M block is not a sufficient condition for paclitaxel radiosensitization. IMPLICATIONS: Paclitaxel can radiosensitize to a modest degree some, but not all, human cell lines by a mechanism that requires the production of a G2/M cell cycle block. Additional studies are needed to define more clearly the mechanism by which paclitaxel radiosensitizes cells.

Cell Cycle↗

PubMed1994

New directions for free radical cancer research and medical applications.

The nitroxides are stable, low molecular weight free radical compounds which are freely membrane permeable. These properties make the nitroxides valuable for the study of and possible protection against oxidative stresses. It is becoming increasingly clear that oxidative stress is important to the pathogenesis of cancer as well as to the development of treatments for cancer. Several nitroxides have been shown to interrupt the toxicity of oxidative stress with the protection against H2O2 toxicity and possibly ischemia/reperfusion injury being of primary importance. With respect to radiation, the nitroxides have afforded both in vitro and in vivo protection. The redox activity of the nitroxides may allow for the differential activity of these agents in normal versus tumor tissues. Further study of these compounds may yield a nitroxide with clinical applications as well as provide insight into the mechanisms of radiation cytotoxicity. Finally, the nitroxides have allowed us to explore the mechanisms of action of several chemotherapeutic agents. Understanding these processes is important to the process of ameliorating the toxicity of therapies and to the rationale design of future agents.

Animals↗

PubMed1994

The influence of Cremophor EL on the cell cycle effects of paclitaxel (Taxol) in human tumor cell lines.

We have performed DNA flow analysis, mitotic index studies, time-lapse photography, and paclitaxel uptake studies of human tumor cell lines exposed to paclitaxel. DNA flow analysis demonstrated that cells began accumulating in G2/M within 6 hrs of exposure to paclitaxel; by 12 hrs over 50% of cells accumulated in G2/M at all concentrations tested. After 24 hrs of exposure to 10 nM paclitaxel, cells underwent non-uniform mitotic division resulting in multinucleated cells. Of cells treated with 30 nM to 1000 nM paclitaxel, 75% to 85% remained blocked in G2/M for up to 72 hrs. Although a large proportion of cells treated with higher concentrations of paclitaxel (10,000 nM) was blocked in G2/M, a significant proportion (10% to 40%) of these cells was also in G1. Cells exposed to lower concentrations of paclitaxel (10 nM to 1000 nM) in medium containing 0.135% (v/v) Cremophor EL also had a relatively large proportion in G1. Mitotic index studies demonstrated that the paclitaxel-induced G2/M block was initially a mitotic block and that cells remained in mitosis for up to 24 hrs. With additional time of exposure to paclitaxel, mitotic index and time-lapse studies indicated that cells attempted to complete mitosis; however, cytokinesis was inhibited and cells became multinucleated. Time-lapse photography revealed that paclitaxel markedly prolonged the time in mitosis from 0.5 hr to 15 hr. High levels of Cremophor EL (0.135% v/v) markedly reduced the number of cells in mitosis but did not alter the mitotic delay induced by paclitaxel. 3H-paclitaxel uptake studies revealed that high concentrations of Cremophor EL did reduce the rate of uptake of paclitaxel into cells but had little effect on total paclitaxel accumulation. These results confirm that paclitaxel has striking effects on the cell cycle and show that high concentrations of Cremophor EL are capable of inducing a cell cycle block distinct from the mitotic block seen with paclitaxel. These results also demonstrate that cells exposed to paclitaxel for longer than 24 hours attempt to complete mitosis but the process of cytokinesis is inhibited. Together with cytotoxicity data, these results indicate that entry into and exit out of mitosis are prerequisites for paclitaxel cytotoxicity.

Adenocarcinoma↗

PubMed1994

Pharmacokinetic properties of nitroxide-labeled albumin in mice.

We have conjugated bovine serum albumin (BSA) with a pyrrolidinyl nitroxide and report on the in vivo pharmacokinetic properties of this conjugate in mice. In vivo EPR measurements of nitroxide were obtained after intravenous injection of 30 mg of labeled BSA by analysis of the nitroxide signal from the tails of mice. Following in vivo nitroxide measurements, the animals were sacrificed by exsanguination and organs were removed for determination of nitroxide levels. The level of nitroxide as determined by in vivo measurements declined exponentially with time and had a half-life (t1/2) of 7 hours. Blood nitroxide levels also declined exponentially with time with an initial t1/2 of 70 minutes and a terminal t1/2 of 10 hours. Nitroxide concentration varied among different organs; no nitroxide was detected within brain whereas lung had high concentrations of nitroxide. Liver and kidney both had relatively low levels of oxidized nitroxide, though total nitroxide (reduced plus oxidized) accumulated in the kidneys with time. Nitroxide-labeled BSA was well tolerated by the mice, is relatively stable, and is mainly confined to the intravascular space. Nitroxide-labeled albumin may be useful as a contrast agent for MRI or EPR imaging.

Animals↗

PubMed1994

Costs and outcomes of inpatient versus outpatient hernia repair.

This study sought to compare treatment costs and outcomes for a large number of Medicare patients undergoing inpatient versus outpatient hernia repair around the country. Medicare physician and hospital claims were obtained for all Medicare enrollees residing in eleven states in 1987 and 1988, in order to take advantage of geographic variation in treatment location. All patients undergoing uncomplicated inguinal hernia repair were identified from the surgeon's bill; the location of surgery was then validated by the facility bill (n = 27,036). Over one-third of all hernia repairs in our sample were performed on an ambulatory basis, but with tremendous variation across states, ranging from 89.9% of cases in Washington in outpatient settings to almost none (6.3%) in Georgia. Treatment costs were 56% higher for hernias repaired on an inpatient basis, $2341 versus $1505 for those performed in outpatient settings. There were no detectable differences between inpatients and outpatients along such outcomes as complication rates, deaths and hernia recurrence, but readmission rates were higher for inpatients. The dramatic differences in costs, along with the apparent absence of adverse outcomes, suggests that Medicare should actively encourage surgeons to perform more hernia repairs on an outpatient basis.

Aged↗

PubMed1994

Suxamethonium apnoea and the isolated leg.

The anaesthetic management of a patient with an unsuspected homozygous atypical pseudocholinesterase genotype is described. Suxamethonium was administered after an arterial tourniquet had been applied to the patient's right leg. After release of the tourniquet and termination of the anaesthetic it was noted that the patient was able to move his right leg but no other part of his body. This observation was confirmed by the use of a peripheral nerve stimulator and by the patient's own recollections. It is suggested that this occurrence shows that the slow offset of neuromuscular block in patients with atypical pseudocholinesterases who have received suxamethonium is caused by long lasting effects at the neuromuscular junction rather than the continuing presence of suxamethonium in the plasma.

Adult↗

PubMed1994

Healing impairment of open wounds by skin irradiation.

BACKGROUND: Ionizing radiation is frequently used for the treatment of malignancy. Sequelae of therapeutic radiation frequently present clinical problems in the form of poor wound healing and easy injury of treated tissue in response to mild trauma. OBJECTIVE: We describe a radiation-impaired wound healing model in guinea pigs, developed to determine the effect of cutaneous irradiation on wound contraction. METHODS: Guinea pigs were anesthetized and a flap of skin was isolated and treated with x-rays to 18 Gy. Circular wounds of identical size were made in irradiated and control skin, and average wound size was recorded. RESULTS: Our results demonstrate that a statistically significant wound healing deficit is produced in open wounds by surface irradiation of skin. CONCLUSION: Radiation of skin results in slower healing of open wounds, and provides an in vivo system for evaluation of topical dressings and growth factors in radiation-impaired wounds.

Animals↗

PubMed1994

Hydrogen peroxide effects on rat mast cell function.

Oxidant exposure of the airway mucosa may play a significant role in the pathophysiology of asthma and allergic rhinitis. Mast cells play an important role in asthma, and oxidant exposure has been reported to cause direct mast cell degranulation as well as augment immunoglobulin E (IgE)-mediated responses in vivo. H2O2 is an oxidant generated by inflammatory cells and by the interaction of ozone with lipids or aqueous solutions. In this study, the RBL-2H3 mast cell line was used to investigate the ability of H2O2 to induce mast cell responses as well as to effect mast cell responses to IgE and the calcium ionophore A23187. Although cytotoxicity of RBL-2H3 cells at the membrane level was not observed with any concentration of H2O2, DNA damage resulted from exposure to 0.2 and 2.0 mM H2O2, and cell proliferation was inhibited by 0.075-0.2 mM H2O2. RBL cell prostaglandin D2 generation was enhanced after 60- and 120-min exposure to 0.2-20 mM H2O2. Direct serotonin release required 120-min exposures to 2.0 mM and 60-min exposures to 20 mM H2O2. However, degranulation responses induced by either IgE or A23178 were diminished after exposure to 0.2-2.0 mM H2O2. Lesser amounts (0.005-0.02 mM) had no effect on mast cell function. In summary, H2O2-induced responses of RBL cells, as well as modification of responses to IgE and A23187, occurred only at high concentrations of H2O2, which also induced both intracellular damage and inhibition of cell proliferation. Concentrations of H2O2 more likely to be physiologically relevant had no effect on mast cell responses or cytotoxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Regulation of the adrenomedullary catecholaminergic system after mild, acute stress.

The time course of regulation of rat adrenomedullary phenylethanolamine N-methyltransferase (PNMT) and tyrosine hydroxylase (TH) activity was studied after a single episode of 20-min restraint stress. Significant increases in PNMT and TH activity were observed 18 h after the beginning of the stress. The time course of acute stress-induced regulation of PNMT and TH was examined for the influence of neural and hormonal input. Unilateral denervation was performed, and the animals were exposed to a single episode of restraint. PNMT activity increased similarly in both the innervated and denervated adrenals, with a significant increase observed at 36 h after the stress. TH activity was similar in both denervated and innervated adrenals, with a significant increase observed at 24 and 36 h after stress. Finally, suppression of endogenous corticosterone with dexamethasone delayed the stress-induced increase in activity of PNMT but not TH. The present study indicates that increases in catecholamine biosynthetic enzymes can be observed after a single episode of mild, acute stress. In addition, glucocorticoids appear to be important in the time course of the stress-induced increase in PNMT but not TH activity, whereas neural input does not seem to affect the time course of these increases.

Acute Disease↗

PubMed1994

Broken screws.

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Bone Screws↗