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.

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-..

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.

Maximal accumulated oxygen deficit of resistance-trained men

The primary purpose of the study was to compare maximal accumulated oxygen deficit (MAOD) in resistance-trained (RT), endurance-trained (ET), and untrained men (UT). A secondary purpose was to determine the influence of leg muscle mass (MM) on MAOD by examining the relationship between MM and MAOD and by comparing MAOD expressed relative to MM between the groups. MAOD was determined during 2-4 min of constant-load fatiguing cycling. MM, estimated via anthropometric measurements, was higher (p < .05) for RT (mean +/- SE; 25.5 +/- 3.4 kg) compared to ET (20.3 +/- 3.5) and UT (21.6 +/- 3.4). MAOD in liters O2eq was larger in RT (4.75 +/- 0.3) compared to UT (3.07 +/- 0.3) and ET (3.75 +/- 0.3). A significant positive correlation was observed between MAOD (LO2eq) and MM (kg) for RT only (RT, r = .85; ET, r = .55; UT, r = .20). Based on the correlational and mean MM data, the higher MAOD (LO2eq) in RT relative to ET and UT is predominantly the result of their larger leg muscle mass.

Protection from radiation-induced alopecia with topical application of nitroxides: fractionated studies

PURPOSE

Hair loss resulting from irradiation of the head and neck or from whole brain irradiation often leads to cosmetic, social, and psychological problems for the radiotherapy patient. Few successful clinical interventions are available. We have shown that nitroxides (stable free radicals) afford radiation protection against single-dose radiation-induced alopecia in a guinea pig model. Here we determine if topical nitroxide application provides protection from fractionated radiation treatment.

MATERIALS AND METHODS

Two symmetrical and contralateral areas (3 x 5 cm) of skin on the dorsal trunk of guinea pigs were shaved to a hair length of 0.25 cm. A 2 mL solution containing 70 mg/mL nitroxide (Tempo or Tempol) in 70% ethanol was topically applied to the skin surface of one side; 70% ethanol was applied to the contralateral (control) side 10 minutes before irradiation. Animals were placed in a special jig that held skin without decreasing blood flow to the treatment area and fractionated external beam radiation (7 Gy) was delivered daily for eight fractions over 10 days via a 4 MeV linear accelerator. Alopecia (hair density) was scored weekly for 13 to 14 weeks after radiotherapy, using a standardized reference with respect to hair loss and regrowth in the treatment field.

RESULTS

After radiation treatment, dry desquamation and gradual hair loss were observed for both control and nitroxide-treated skin; however, over weeks 4 to 11 postirradiation hair loss was much more pronounced in control animals when compared with nitroxide-treated animals. Hair density measurements for Tempol treatment over weeks 9 to 13 were approximately 75% compared with measurements in controls of approximately 25%. Tempo-treated animals exhibited hair density values of approximately 90% compared with 12% in controls over weeks 11 to 14. Tempol and Tempo treatments resulted in significant radioprotection. Histologic evaluation showed that radiation treatment alone in ethanol controls resulted in a marked decrease in the number of hair follicles and poor development of remaining follicles; however, nitroxide pretreatment resulted in no appreciable decrease in hair follicles and hair follicles appeared mature. This was also observed in unirradiated ethanol controls. Electron paramagnetic resonance studies revealed that topical nitroxide application did not result in measurable systemic concentrations of either drug.

CONCLUSIONS

The results of this study suggest that topical application of nitroxides may be useful in a clinical setting to reduce the undesirable toxicity of radiation-induced alopecia.

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.

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.

Radiation sensitisation by nitric oxide releasing agents

Previous studies have shown that nitric oxide (NO) sensitises hypoxic cells to ionising radiation. In the present study, four different nitric oxide (NO) donor agents were evaluated for both NO release and hypoxic radiosensitisation. The S-nitrosothiol NO donor agents, S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP), were shown to release sustained NO concentrations (microM) and significantly radiosensitise hypoxic cells. The extent of hypoxic radiosensitisation by both of these agents at 1.0 mM concentration was similar to that obtained with molecular oxygen. In contrast, neither 3-morpholinosydnonimine (SIN-1) nor sodium nitroprusside (SNP) released detectable NO concentrations and neither agent enhanced the hypoxic radiation response to the extent of that observed for GSNO or SNAP. NO-mediated hypoxic cell radiosensitisation by NO donor drugs may offer a new approach for clinical consideration, particularly if such agents can be selectively delivered to hypoxic cells.

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.

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.

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.

Using physician claims to identify postoperative complications of carotid endarterectomy

OBJECTIVE

This study develops a methodology for identifying complications following carotid endarterectomy, using physician claims data.

DATA SOURCES/STUDY SETTING

We selected a random 20 percent sample of Medicare patients undergoing carotid endarterectomy in 1991 (n = 8,345) and extracted all of their claims.

STUDY DESIGN

Project neurologists identified the following services as indicative of complications following carotid endarterectomy if they were provided within 30 days of surgery: head CT, head MRI, and surgical exploration of the neck for hemorrhage, thrombosis, or infection.

DATA COLLECTION/EXTRACTION METHODS

Total costs were calculated from all claims associated with the hospitalization and the 30-day postoperative period. Outcomes included mortality (obtained from Medicare eligibility files), length of stay, discharge to an institution, and readmission to an acute care hospital (the latter obtained from claims data).

PRINCIPAL FINDINGS

Surgical complications were identified in one out of every ten endarterectomy patients (10.3 percent). Patients with complications were significantly more likely to die within 30 days of surgery (8.9 percent, compared with 1.1 percent of those not experiencing complications). They also were significantly more likely to be discharged to an institutional setting (24.9 percent versus 2.9 percent), and more likely to be readmitted to acute care hospitals (26.8 percent versus 8.2 percent). Patients with postoperative complications also were significantly more expensive: $22,187 versus $10,892.

CONCLUSION

Our findings suggest that physician claims could be used by PROs or similar entities as a screening tool to identify potential problem hospitals or problem surgeons. First, however, the methodology would need to be clinically validated.

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.

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.

Adaptation to eccentric exercise: effect on CD64 and CD11b/CD18 expression

The primary purpose of the study was to examine circulating neutrophils and monocytes and their plasma membrane expression of CD64, CD11b, and CD18 after two bouts (B1 and B2) of eccentric exercise. Subjects (n = 10) performed 25 forced-lengthened contractions of the forearm flexors on two occasions separated by 3 wk. Blood samples were obtained before exercise and at 1.5, 6, 12, 24, 48, 72, and 96 h of recovery. CD64, CD11b, and CD18 expression was determined via direct immunofluorescence and used as an indicator of neutrophil and monocyte activation. Creatine kinase activity (B1 = 1,390, B2 = 108 U/l), myoglobin (B1 = 163, B2 = 41, ng/dl), and muscle soreness and tenderness were higher (P < 0.01) after B1 compared with B2. Neutrophils at 6, 12, and 96 h were higher (P < 0.05) for B1 vs. B2. CD11b expression on neutrophils was 2.7-fold higher at 72 h for B1 vs. B2. CD64 expression on neutrophils at 72 and 96 h was 1.4- and 1.9-fold higher, respectively, for B1 vs. B2. At 72 and 96 h, CD18 and CD64 expression on monocytes was 1.3-fold higher for B1 vs. B2. The observed changes were not significantly correlated with changes in creatine kinase activity or myoglobin. In conclusion, the adaptation to eccentric arm exercise was associated with a reduction in circulating neutrophils and a lower state of neutrophil and monocyte activation.

Impact of Medicare payment reductions on access to surgical services

OBJECTIVE

This study evaluates the impact of surgical fee reductions under Medicare on the utilization of surgical services.

DATA SOURCES

Medicare physician claims data were obtained from 11 states for a five-year time period (1985-1989).

STUDY DESIGN

Under OBRA-87, Medicare reduced payments for 11 surgical procedures. A fixed effects regression method was used to determine the impact of these payment reductions on access to care for potentially vulnerable Medicare beneficiaries: joint Medicaid-eligibles, blacks, and the very old.

DATA COLLECTION/EXTRACTION METHODS

Medicare claims and enrollment data were used to construct a cross-section time-series of population-based surgical rates from 1985 through 1989.

PRINCIPAL FINDINGS

Reductions in surgical fees led to small but significant increases in use for three procedures, small decreases in use for two procedures, and no impact on the remaining six procedures. There was little evidence that access to surgery was impaired for potentially vulnerable enrollees; in fact, declining fees often led to greater rates of increases for some subgroups.

CONCLUSIONS

Our results suggest that volume responses by surgeons to payment changes under the Medicare Fee Schedule may be smaller than HCFA's original estimates. Nevertheless, both access and quality of care should continue to be closely monitored.

Nitric oxide (NO) protects against cellular damage by reactive oxygen species

Since the discovery of nitric oxide (NO) as an endogenously formed radical, its effect on numerous physiological processes has been intensively investigated. Some studies have suggested NO to be cytotoxic while others have demonstrated it protective under various biological conditions. Though NO shows minimal cytotoxicity to a variety mammalian cell cultures, it does modulate the toxicity of some agents such as reactive oxygen species. Often, NO is generated in the presence of these reactive oxygen species in response to foreign pathogens or under various pathophysiological conditions. We will show that NO can play a protective role under oxidative stress resulting from superoxide, hydrogen peroxide and alkyl peroxides. It was found by measuring the time-concentration profiles of NO released from various NO donor compounds that only microM levels of NO were required for protection against the toxicity of these reactive species. It was found that there are several chemical reactions which may account for these protective effects such as NO preventing heme oxidation, inhibition of Fenton-type oxidation of DNA, and abatement of lipid peroxidation. Taken together, NO at low concentrations clearly protects against peroxide-mediated toxicity.

Nitric oxide potentiates hydrogen peroxide-induced killing of Escherichia coli

Previously, we reported that nitric oxide (NO) provides significant protection to mammalian cells from the cytotoxic effects of hydrogen peroxide (H2O2). Murine neutrophils and activated macrophages, however, produce NO, H2O2, and other reactive oxygen species to kill microorganisms, which suggests a paradox. In this study, we treated bacteria (Escherichia coli) with NO and H2O2 for 30 min and found that exposure to NO resulted in minimal toxicity, but greatly potentiated (up to 1,000-fold) H2O2-mediated killing, as evaluated by a clonogenic assay. The combination of NO/H2O2 induced DNA double strand breaks in the bacterial genome, as shown by field-inverted gel electrophoresis, and this increased DNA damage may correlate with cell killing. NO was also shown to alter cellular respiration and decrease the concentration of the antioxidant glutathione to a residual level of 15-20% in bacterial cells. The iron chelator desferrioxamine did not stop the action of NO on respiration and glutathione decrease, yet it prevented the NO/H2O2 synergistic cytotoxicity, implicating metal ions as critical participants in the NO/H2O2 cytocidal mechanism. Our results suggest a possible mechanism of modulation of H2O2-mediated toxicity, and we propose a new key role in the antimicrobial macrophagic response for NO.

Suppression of LH secretion in food-restricted lactating females: effects of ovariectomy and bromocryptine treatment

It has been shown that restricting food in lactating rats for the first 2 weeks postpartum at a level of 60% of the ad-libitum daily ration increases the length of lactational dioestrus by about 7 days but little is known about correlated changes in hormone levels. In the first experiment we report changes in LH, prolactin (PRL) and ACTH secretion in food-restricted and ad-libitum fed lactating rats at various stages of lactation. Our results demonstrate that food restriction during the first 2 weeks of lactation did not affect PRL or ACTH secretion, but decreased plasma LH levels despite comparable GnRH receptor density between food-restricted and ad-libitum fed females. In the second experiments we investigated a possible causal relationship between the increased secretion of progesterone seen in food-restricted females and the suppression of plasma LH levels, by determining the effects of bromocryptine treatment and ovariectomy on LH secretion in both ad-libitum fed and food-restricted lactating females. LH suppression in food-restricted lactating females was not affected by ovariectomy or bromocryptine treatment, although the latter treatment significantly increased GnRH receptor number. These data suggest that factors other than ovarian steroids, PRL or increased adrenocortical activity modulate LH secretion and the length of lactational dioestrus in food-restricted lactating females.

Nitric oxide protects against alkyl peroxide-mediated cytotoxicity: further insights into the role nitric oxide plays in oxidative stress

Endogenously formed nitric oxide (NO) possesses diverse properties such as regulating physiological functions, exerting specific toxic effects, and protecting against various toxic substances. Recent studies suggest that in the presence of reactive oxygen species, NO can serve as an antioxidant. We show here that NO delivered from the NO donor compound, PAPA/NO (NH2(C3H6)(N[N(O)NO](C3H7)), protects Chinese hamster V79 lung fibroblasts from the cytotoxicity of t-butyl hydroperoxide and cumene hydroperoxide. In contrast, the other end products of PAPA/NO degradation in aqueous solution, NH2(C3H6)NH(C3H7) and nitrite, did not protect. The NONOate DEA/NO releases NO six times faster than PAPA/NO, yet did not afford protection, which implies that NO must be present throughout the alkyl hydroperoxide exposure. Measurements of NO concentrations released from PAPA/NO suggest that micromolar levels protect against cytotoxicity induced by alkyl hydroperoxides. These findings demonstrate that the flux of NO sustained over the duration of the peroxide exposure determines protection and not the total of NO delivered. These results suggest that concentrations of NO produced in the microenvironment of endothelial cells are high enough to protect cells from Fenton-type-mediated toxicity and support the premise that NO may exert a salutary effect in certain diseases associated with membrane damage.

A diffusing sphere which delivers homogeneous laser light for use in photodynamic therapy

Photodynamic therapy (PDT) exploits the selective uptake of a photosensitizer in tumors and other hyperproliferative target tissues, as well as the ability to direct the treatment light beam to a specific region. Since the photodynamic effect depends on light dose, tissue optical properties and photosensitizer concentration, uniform delivery of light is crucial to attain optimal photodynamic effect. Many commonly used methods for delivering laser light during photodynamic therapy, such as a free fiber or microlens, require fiber and laser adjustments to obtain a highly uniform beam. In this study, we test the ability of a diffusing sphere to improve the uniformity of a light field coming from an argon laser coupled to a free fiber, in which no attempt has been made to optimize beam characteristics. Light fields from the free fiber, a microlens and the diffusing sphere are compared for uniformity via light intensity readings. An in vivo comparison between the sphere and the free fiber is also made in guinea pigs given Photofrin-II. The diffusing sphere decreases problems with shielding, allows quick and easy application of light by simply applying the device over the desired treatment area, and optimizes the desired photodynamic effect by producing ad highly uniform beam of light with no necessity to optimize light delivery by vibrating, looping or re-cleaving fibers.

Protection from radiation-induced chromosomal aberrations by the nitroxide Tempol

BACKGROUND

The nitroxide Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) is a stable, free radical that exhibits protection from ionizing radiation damage and from oxidative stress mediated through exposure of cells to superoxide or hydrogen peroxide. Radiation protection has been observed in both in vivo and in vitro models. To understand the mechanism of Tempol-mediated radioprotection better, the production of radiation-induced chromosome aberrations was evaluated. This study analyzed Tempol-mediated radioprotection of human peripheral blood lymphocytes (PBLs).

METHODS

Peripheral blood lymphocytes were exposed to control (0mM), 10 mM (Tp10), and 50 mM (Tp50) concentrations of Tempol for 20 minutes before irradiation with 0, 150, 300, and 450 cGy. One quarter ml whole blood was cultured in F12 medium and phytohemagglutinin at 37 degrees C for 49, 54, 59, and 64 hours. Colcemide was added to each sample for the last 5 hours before harvest. Cells were harvested, treated with hypotonic solution, and fixed before dropping on cold clean slides. Mitotic indices and frequency of dicentric, ring, and triradial chromosomal aberrations were determined at 1000x magnification for each treatment group at each collection point.

RESULTS

Treatment of cells with Tempol alone did not induce the chromosomal aberration frequency above that for unirradiated controls. Radiation dose response curves for total chromosome aberration production revealed radioprotection for Tempol treatment for both 10 and 50 mM exposures. Tempol protection factors (assessed at 0.2 aberrations/cell level) for Tp 10 and Tp 50 were 2.2 and 2.8, respectively.

CONCLUSIONS

Tempol protects against radiation-induced chromosome aberrations in human PBLs. This finding is consistent with and lends support to previous studies in which Tempol was reported to enhance cell survival and reduce radiation-induced DNA double strand breaks.