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PubMed2004

Analysis of Deinococcus radiodurans's transcriptional response to ionizing radiation and desiccation reveals novel proteins that contribute to extreme radioresistance.

During the first hour after a sublethal dose of ionizing radiation, 72 genes were upregulated threefold or higher in D. radiodurans R1. Thirty-three of these loci were also among a set of 73 genes expressed in R1 cultures recovering from desiccation. The five transcripts most highly induced in response to each stress are the same and encode proteins of unknown function. The genes (ddrA, ddrB, ddrC, ddrD, and pprA) corresponding to these transcripts were deleted, both alone and in all possible two-way combinations. Characterization of the mutant strains defines three epistasis groups that reflect different cellular responses to ionizing radiation-induced damage. The ddrA and ddrB gene products have complementary activities and inactivating both loci generates a strain that is more sensitive to ionizing radiation than strains in which either single gene has been deleted. These proteins appear to mediate efficient RecA-independent processes connected to ionizing radiation resistance. The pprA gene product is not necessary for homologous recombination during natural transformation, but nevertheless may participate in a RecA-dependent process during recovery from radiation damage. These characterizations clearly demonstrate that novel mechanisms significantly contribute to the ionizing radiation resistance in D. radiodurans.

Deinococcus↗
PubMed2006

The role of hydration in the distribution of free radical trapping in directly ionized DNA.

The purpose of this study was to elucidate the role of hydration (Gamma) in the distribution of free radical trapping in directly ionized DNA. Solid-state films of pUC18 (2686 bp) plasmids were hydrated to Gamma in the range 2.5 < or = Gamma < or = 22.5 mol water/mol nucleotide. Free radical yields, G(Sigmafr), measured by EPR at 4 K are seen to increase from 0.28 +/- 0.01 micromol/J at Gamma = 2.5 to 0.63 +/- 0.01 micromol/J at Gamma= 22.5, respectively. Based on a semi-empirical model of the free radical trapping events that follow the initial ionizations of the DNA components, we conclude that two-thirds of the holes formed on the inner solvation shell (Gamma < 10) transfer to the sugar-phosphate backbone. Likewise, of the holes produced by direct ionization of the sugar-phosphate, about one-third are trapped by deprotonation as neutral sugar-phosphate radical species, while the remaining two-thirds are found to transfer to the bases. This analysis provides the best measure to date for the probability of hole transfer (approximately 67%) into the base stack. It can thus be predicted that the distribution of holes formed in fully hydrated DNA at 4 K will be 78% on the bases and 22% on the sugar-phosphate. Adding the radicals due to electron attachment (confined to the pyrimidine bases), the distribution of all trapped radicals will be 89% on the bases and 11% on the sugar-phosphate backbone. This prediction is supported by partitioning results obtained from the high dose-response curves fitted to the two-component model. These results not only add to our understanding of how the holes redistribute after ionization but are also central to predicting the yield and location of strand breaks in DNA exposed to the direct effects of ionizing radiation.

Computer Simulation↗
PubMed2002

Enhancement of antitumor activity of ionizing radiation by combined treatment with the selective epidermal growth factor receptor-tyrosine kinase inhibitor ZD1839 (Iressa).

PURPOSE: The epidermal growth factor receptor (EGFR) is expressed in the majority of human epithelial cancers and has been implicated in the development of cancer cell resistance to cyotoxic drugs and to ionizing radiation. EXPERIMENTAL DESIGN: We used ZD1839, a selective small molecule EGFR tyrosine kinase inhibitor currently in clinical development. We tested the antiproliferative and the proapoptotic activity of ZD1839 in combination with ionizing radiation in human colon (GEO), ovarian (OVCAR-3), non-small cell lung (A549 and Calu-6), and breast (MCF-7 ADR) cancer cell lines. The antitumor activity of this combination was also tested in nude mice bearing established GEO colon cancer xenografts. RESULTS: With ionizing radiation or ZD1839, a dose-dependent growth inhibition was observed in all of the cancer cell lines growing in soft agar. A cooperative antiproliferative and proapoptotic effect was obtained when cancer cells were treated with ionizing radiation followed by ZD1839. This effect was accompanied by inhibition in the expression of the antiapoptotic proteins bcl-xL and bcl-2, and by a suppression of the activated (phosphorylated) form of akt protein. Treatment of mice bearing established human GEO colon cancer xenografts with radiotherapy (RT) resulted in a dose-dependent tumor growth inhibition that was reversible upon treatment cessation. Long term GEO tumor growth regressions were obtained after RT in combination with ZD1839. This resulted in a significant improvement in survival of these mice as compared with the control group (P < 0.001), the RT-treated group (P < 0.001), or the ZD1839-treated group (P < 0.001). The only mice alive 10 weeks after tumor cell injection were in the RT-plus-ZD1839 group. Furthermore, 10% of mice in this group were alive and tumor-free after 26 weeks. Similar results were obtained in mice bearing established human A549 lung adenocarcinoma xenografts. Finally, the combined treatment with RT plus ZD1839 was accompanied by a significant potentiation in the inhibition of transforming growth factor alpha, vascular epidermal growth factor, and basic fibroblast growth factor expression in cancer cells, which resulted in significant antiangiogenic effects as determined by immunohistochemical count of neovessels within the GEO tumors. CONCLUSION: This study provides a rationale for evaluating in cancer patients the combination of ionizing radiation and selective EGFR tyrosine kinase inhibitors such as ZD1839.

Animals↗
PubMedDate not supplied

[Ionization chambers with preamplifiers for X-ray exposure metering systems].

Ionization chambers with preamplifiers available from SpektrAp, Ltd., are described. The ionization chambers are intended for use in X-ray automatic exposure systems of diagnostic X-ray apparatuses. The ionization chambers provide automated matching of their sensitivity to the sensitivity of modern intensifying screens. The preamplifier provides direct integration of the ionization chamber current. It can operate within the entire dose rate range of the roentgenographic mode and meets the requirements of modern diagnostic X-ray detectors to the dose range. Special techniques for increasing the noise immunity of preamplifiers are described. Performance specifications of the ionization chambers and preamplifiers are given.

Air Ionization↗
PubMed1990

The influence of electromagnetic interference and ionizing radiation on cardiac pacemakers.

Adverse effects of the ionizing and non-ionizing electromagnetic fields on five pacemaker models have been tested. The study consisted of three parts: 1. measurement of magnetic fields in a radiotherapy room (microtron MM14), 2. the application of non-ionizing electromagnetic fields on pacemakers in a test laboratory (1...1000 microT, 10...10000 Hz), and 3. the application of ionizing radiation of different types of radiotherapy devices on the pacemakers. The magnetic field strength in the microtron treatment room was found to be under 7.5 microT, which is one order of magnitude lower than the tolerance level obtained for the pacemakers in the test laboratory. All the tested pacemakers tolerated the ionizing radiation dose levels (less than 60 Gy) which are used in the radiotherapy.

Electromagnetic Fields↗
PubMed1981

Ionized calcium in acute pancreatitis and its relationships with total calcium and serum lipase.

Serial measurements of serum amylase, lipase and ionized calcium were made in a prospective study of 17 patients with acute pancreatitis. The mean serum ionized calcium was significantly below the normal range for the first 24 h and had returned to normal after 48 h. There was no correlation between serum ionized calcium and paired calcium corrected for albumin during the first 36 h of the study, but they were correlated for the remainder of the investigation. Serum lipase and ionized calcium levels were just significantly correlated over the first 3 days (r = -0.44; t = 2.3; P less than 0.05; d.f. 22), but failed to reach correlation over the whole period of study (r = -0.34; t = 2.0; d.f. 31). These data establish a significant drop in directly measured ionized calcium early in an attack of pancreatitis, which is not seen in the paired corrected calcium values. Furthermore, the drop is correlated with serum lipase, although this is weak and other factors must be involved in the hypocalcaemia.

Acute Disease↗
PubMed1976

Chemical ionization and high resolution electron impact mass spectra of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide and three of its metabolites.

The electron impact and the hydrogen and methane chemical ionization mass spectra of 5,6-dihydro-2-methyl-1,4-oxathin-3-carboxanilide, the sulfoxide and sulfone derived therefrom, and 2-(2-hydroxyethylthio)-acetoacetanilide enol have been determined. All four compounds show abundant molecular ions in the electron impact spectra and abundant [MH]+ ions in the methane chemical ionization spectra (along with the expected [M + C2H5]+ and [M + C3H5]+ ions), but relatively low [MH]+ ion signals in the hydrogen chemical ionization spectra. From high resolution mass measurements and metastable transitions determined by metastable ion refocusing, electron impact fragmentation mechanisms have been established. For 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide, 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide-4-oxide and 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide-4,4-dioxide the major fragmentation mode involves loss of the anilino radical from [M]+, followed by loss of C2H4. Fragmentation to form the aniline molecular ion increases in importance with increasing oxidation state of the sulfur. In the chemical ionization of these three compounds fragmentation of [MH]+ proceeds in a similar fashion by loss of neutral aniline and by formation of protonated aniline. The electron impact mass spectrum of 2-(2-hydroxyethylthio)acetoacetanilide is dominated by the molecular ion and the aniline molecular ion. However, in the chemical ionization mass spectra characteristic fragment ions involving loss of water and loss of aniline from [MH]+, as well as protonated aniline, are observed and serve to characterize the compound.

Acetanilides↗
PubMed1978

Electrohydrodynamic ionization mass spectrometry of biochemical materials.

Electrohydrodynamic ionization mass spectrometry has been applied to a range of biochemical materials dissolved in glycerol with NaI as electrolyte. Sugars (glucose, sucrose, raffinose), nucleosides (adenosine, thymidine, uridine), a tripeptide (glutathione) and an aminocyclitol antibiotic (neomycin) have been analyzed. Unambiguous analysis of a multicomponent solution has been demonstrated. All samples yielded several quasimolecular ions involving either proton or cation attachment to clusters of sample and/or solvent molecules. Unlike other techniques such as field desorption, electrohydrodynamic ionization is not observed to cause fragmentation of sample molecules. The mass spectrometer was operated so as to analyze only those ion clusters which had not undergone decomposition processes; under these conditions, most materials are ionized with similar efficiencies if the total abundance of all characteristic quasimolecular ions is considered. Information regarding the amino acid sequence of glutathione was obtained by thermal pretreatment of the glycerol solution before mass analysis. Positive and negative ion spectra give complementary information which can resolve potential ambiguities regarding the exact composition of quasimolecular ions. Electrohydrodynamic ionization mass spectrometry should be applicable to materials which cannot be ionized by other methods.

Carbohydrates↗
PubMed1988

Modulation of serum parathyroid hormone and ionized calcium concentrations during reproduction in rats fed a low calcium diet.

Moderate dietary restriction of calcium (0.1% Ca) was used to accentuate the changes in serum immunoreactive parathyroid hormone (iPTH) that had been reported earlier in lactating rats fed 0.4% Ca diet. In addition, the effects of this low-Ca diet on serum total and ionized Ca and iPTH during pregnancy, extended lactation, and weaning were examined. The positive correlation between serum total and ionized Ca was highly significant (r = 0.88, p less than 0.001, n = 120). Serum iPTH was significantly higher (36%) in pregnant rats on the day of parturition compared to nonmated controls, and there was a concomitant decrease in both total and ionized serum Ca. Within 1 day after parturition, however, serum Ca had risen to the control level. Serum iPTH remained significantly elevated during the first 2 weeks of lactation, and increased further during the third week of lactation to a level more than twice that of nonlactating controls. Serum Ca fell gradually during the second week of lactation. The high serum iPTH levels were maintained for another 2 weeks when lactation was extended with foster litters. Within 6 hr of removal of the suckling pups on day 16 of lactation, maternal serum ionized and total Ca had risen and serum iPTH had fallen; all three parameters were at levels similar to those of nonmated controls by 24-48 hr after weaning. The data suggest that serum ionized Ca is a major factor contributing to the hyperparathyroid state during lactation in rats fed a low-Ca diet.

Aging↗
PubMed2005

Surface-activated chemical ionization ion trap mass spectrometry in the analysis of drugs in dilute urine samples. Part II: analysis of morphine and other street drugs.

The new ionization method, called surface-activated chemical ionization (SACI), was employed for the analysis of fives drugs (morphine, codeine, 6-monoacetylmorphine (6-MAM), benzoylecgonine and cocaine) by ion trap mass spectrometry. The results so obtained have been compared with those achieved by using atmospheric pressure chemical ionization (APCI), no-discharge-APCI and electrospray ionization (ESI) clearly showing that SACI is the most sensible one mainly due to the high ionization efficiency and the lower chemical noise. The performance of SACI in terms of sensitivity and linearity was compared with the sensitivity and linearity obtained using APCI, no-discharge-APCI and ESI, showing that the new SACI approach gives rise to the best results. Then, SACI was used to analyze morphine, codeine, 6-MAM, benzoylecgonine and cocaine in urine samples. After the optimization of the instrumental parameters for a mixture of the standard compounds, eight urine samples were analyzed. They were strongly diluted (1 : 20 and 1 : 100) in order to prevent the chromatographic column damage due to the matrix composition. Furthermore, the diluted urine samples were directly analyzed, without pretreatment, through LC-MS and LC-MS/MS, and the obtained results are reported.

Cocaine↗
PubMed1986

Kinetics of sorption of ionizable solutes by plastic infusion bags.

Aqueous solutions of several ionizable substances were stored in plastic infusion bags and the sorption of the substances monitored with time. The substances used were p-nitrophenol, p-toluidine, warfarin sodium [3-(alpha-acetonylbenzyl)-4-hydroxycoumarin sodium salt] and trifluoperazine hydrochloride (10-[3-(4-methyl-1-piperazinyl)propyl]-2-(trifluoromethyl)phenothiazine dihydrochloride). The rate and extent of sorption for each substance varied with pH and was consistent with a preferential uptake of the un-ionized species. The uptake of p-nitrophenol and p-toluidine was adequately described by a diffusion model derived assuming that sorption is rate-controlled by the diffusivity of the solute in the plastic matrix, and that only the un-ionized species was sorbed by the plastic matrix. However, the uptake of warfarin sodium and trifluoperazine hydrochloride was described more accurately by a diffusion model in which the diffusional resistance of the plastic matrix and of an interfacial resistance barrier both contributed to the diffusional resistance encountered in the sorption process. It appeared that the rate of uptake of the un-ionized form of these solutes was diminished due to the influence of interfacial or aqueous diffusional barriers. Solute lipophilicity and degree of ionization appeared to be important factors determining the relative contribution of the respective barriers to the overall diffusional resistance.

Absorption↗
PubMed1986

Ionization and surface properties of verapamil and several verapamil analogues.

We have investigated the ionization and surface properties of verapamil (5-[(3,4-dimethoxyphenethyl)methylamino]-2-(3, 4-dimethoxyphenyl)-2-isopropylvaleronitrile, 1) and several verapamil analogues since these properties appear to be involved in the biologic activities of these compounds. Our results show that verapamil and its analogues are surface-active and bind to amphiphilic surfaces. The affinity toward, as well as the capacity of, an amphiphilic surface for verapamil and its ionizable analogues is pH dependent, with the surface having both higher affinity and capacity for the neutral form of the molecules. Thus, verapamil exists as protonated and neutral forms, both of which are free in solution and adsorbed to the interface, and the ionization of verapamil at an interface changes with respect to its ionization in solution. From analyses of the pH dependency of surface binding and of solution and interfacial ionizations, we determined the values of the four equilibrium constants. These equilibrium constants permit correlative studies between the pH-dependent abundance of each species and biologic activity. We discuss preliminary studies which indicate that the negative inotropic effect of verapamil is mediated by the membrane-bound neutral form of the drug.

Absorption↗
PubMed1985

Mechanisms of altered myocardial contractility during hemodialysis: importance of changes in the ionized calcium to plasma potassium ratio.

Hemodialysis is associated with alterations in myocardial contractility, but duration and precise determinants responsible for these changes are unknown. We investigated the effect of several variables, established to influence left ventricular (LV) contractility, which normally changed during dialysis: the plasma concentrations of ionized calcium, potassium, bicarbonate, and magnesium and the removal of uremic toxins. The influence of three different isovolemic bicarbonate-dialysis procedures in 16 patients with normal (group 1) and hypertrophied myocardium (group 2) was assessed by echocardiography prior to and up to 44 h following each dialysis. During the first procedure, ionized calcium and potassium concentration decreased, but LV performance remained unchanged in both groups. The second procedure with increased ionized calcium and decreased potassium concentration resulted in an improvement of mean circumferential fiber shortening (VCF from 1.15 to 1.56 circ/s (P less than 0.001) in group 1 and from 1.05 to 1.16 circ/s (P less than 0.05) in group 2. The positive inotropic effect declined gradually up to 12 h (group 1) and 2.5 h (group 2) respectively. In the third procedure when ionized calcium was increased and potassium concentration remained unchanged contractility did not improve. Removal of uremic toxins, decrease in magnesium, and increase in bicarbonate concentrations were comparable during each procedure. These results suggest that the ionized calcium to potassium ratio is the important determinant of dialysis-related augmentation in LV contractility. In LV hypertrophy the expected contractile response is diminished indicating a depressed inotropic state.

Adult↗
PubMed2003

Ionized calcium changes during living-donor liver transplantation in patients with and without administration of blood-bank products.

Exogenous citrate load from blood transfusion during orthotopic liver transplantation is thought to be the main cause of ionized hypocalcemia, which may result in hemodynamic instability. This implies that if no blood is transfused, chelation of free ionized calcium (Ca(++)) by citrate is avoided and supplemental calcium need not be given. For this study, we divided 39 pediatric living-donor liver transplant patients into two groups according to the blood component replacement given: group I received packed red blood cells and fresh frozen plasma with and without 5% albumin, and group II received 5% albumin alone. The intra-operative serial ionized calcium level was recorded, and the amount of calcium chloride replacement to maintain acceptable blood Ca(++) levels was compared between the groups. The mean serum ionized calcium level changes of both groups could be maintained within lower-to-normal limits intra-operatively. The amount of supplemental calcium chloride required to correct the hypo-ionized calcium was not significantly different between the groups. We can conclude that if an exogenous citrate load is eliminated by the avoidance of blood transfusion and 5% albumin infusion is used, instead, to replace the blood and ascites loss during OLT, the risk of ionic hypocalcemia still persists. Serum Ca(++) monitoring and adequate replacement are, therefore, still required in this setting.

Adult↗
PubMed1999

Permanently reduced plasma ionized magnesium among renal transplant recipients on cyclosporine.

Hypomagnesemia is common after kidney transplantation. Until recently, only the determination of total plasma magnesium was possible, whereas the assessment of ionized magnesium has since become practicable. One hundred and nine renal transplant patients on cyclosporine with allografts functioning stably for more than 6 months and plasma creatinine levels of less than 200 micromol/l entered the study. Total and ionized circulating magnesium were assessed among these 109 patients, as well as among 15 renal transplant patients not on cyclosporine and 21 healthy volunteers. Cyclosporine patients showed significantly lower total and ionized circulating magnesium values than the two control groups. Plasma total and ionized magnesium levels were also significantly lower among cyclosporine patients treated concurrently with insulin or oral hypoglycemic agents than among those who were not. No correlation was noted between time after transplantation and plasma magnesium with respect to patients on cyclosporine. In conclusion, the study demonstrates that a large subset of renal transplant patients treated with cyclosporine have permanent deficiencies of ionized and total magnesium. The tendency towards hypomagnesemia is also more pronounced among patients with diabetes mellitus.

Adolescent↗
PubMed1999

Ionized calcium and bone turnover in the estrogen-deficient rat.

The long-term effects of high bone resorption on blood ionized calcium and calciotropic hormone levels following oophorectomy in 6-month-old Sprague-Dawley female rats were investigated. Fasting urine and blood samples were collected from 16 sham and 16 oophorectomized (oophx) rats preoperatively and up to 130 days postoperatively. From 50 days postoperation, daily injections of 17-beta estradiol (E2) (20 microg/kg body weight) were administered subcutaneously to eight of the oophx rats. Urine hydroxyproline excretion (OHPrE) and serum osteocalcin were significantly elevated (P < 0.001) as a result of oophorectomy and normalized within 6 days of E2 replacement. Urine deoxypyridinoline and total serum alkaline phosphatase were significantly elevated (P < 0.001) following oophorectomy and suppressed to control levels after 37 days of E2 replacement. Blood ionized calcium was significantly reduced in oophx rats (P < 0.001) compared with sham rats and was normalized by E2 replacement at 55 days posttreatment. Serum 1,25 dihydroxyvitamin D (1,25(OHD)2D3) was significantly elevated (P < 0.001) in oophx rats and again was normalized by E2 at 55 days posttreatment. Serum parathyroid hormone (PTH) was unaffected by oophorectomy. These data indicate that despite increased bone resorption following oophorectomy, blood ionized calcium levels are decreased. The increased bone turnover in oophx rats was rapidly suppressed by E2 replacement before ionized calcium levels were normalized, suggesting a direct effect of estrogen on the modulation of bone cell activity. The depression of blood ionized calcium levels following oophorectomy, which is not mediated by calciotropic hormones, suggests an effect of estrogen on intestinal calcium absorption, renal handling of calcium, or a combination of both.

Alkaline Phosphatase↗
PubMed2004

Catecholamine-induced regulation in vitro and ex vivo of intralymphocyte ionized magnesium.

Despite the importance of the adrenergic activity and of the metabolism of magnesium in some important cardiovascular pathologies, very little is known about how intracellular ionized magnesium (Mgi2+) is regulated by catecholamines. We made an in-vitro study of the variations in the concentration of ionized magnesium in human lymphocytes using the fluorescent probe furaptra in response to different catecholamines. We also made an ex-vivo study of the changes in intracellular ionized magnesium in lymphocytes in 20 subjects with essential arterial hypertension, 10 treated with 120 mg/d of propranolol and 10 with placebo. Norepinephrine and isoproterenol significantly decrease Mgi2+ and this effect is blocked by beta-blockers but not by alpha-blockers. The EC50 of the effect of norepinephrine is within the range of concentrations physiologically present in plasma. The substitution of extracellular sodium with choline blocks the decrease in intracellular ionized magnesium induced by norepinephrine, which leads us to suppose that the magnesium-reducing effect of catecholamines is a result of the activation of a Na+-Mg2+ exchanger. We were not able to demonstrate any change in intracellular ionized magnesium after 1 and 17 days of active treatment in essential hypertensives. The impossibility of demonstrating ex vivo the mechanism of catecholamine-mediated regulation that is evident in vitro is perhaps due to our experimental conditions or to substances which in vivo inhibit the action of the catecholamines on magnesium, such as insulin and/or glucose.

Adrenergic alpha-Agonists↗
PubMed2001

Ionization properties of titratable groups in ribonuclease T1. II. Electrostatic analysis.

The experimental NMR data for the individual titratable groups in ribonuclease T1 presented in the preceding paper were analysed by means of a continuum dielectric model. The role of two factors, the alteration of hydrogen loci on the ionizable groups and the conformational flexibility, were analysed. It was suggested that the position of the titratable hydrogen is essential mainly for strongly interacting groups. For groups which are accessible to the solvent and whose ionization is not coupled with the ionization of neighbouring groups, this factor can be neglected. The influence of the conformational flexibility on the electrostatic interactions becomes apparent for the environment of K25. For some strongly interacting groups, non-sigmoidal ionization curves were calculated. On this basis the pH dependence of the NMR chemical shift of the 13Cepsilon2 resonance of H27, whose ionization is coupled with E82, was reproduced.

Hydrogen↗