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Biomedical subjects

S L Waters

Publications and source records attributed to S L Waters.

At least 19 recordsLinked to original sources
PubMed1997

Depletion of endoplasmic reticulum calcium stores protects against hypoxia- and mitochondrial inhibitor-induced cellular injury and death.

We have shown previously that intracellular Ca+2 chelation and calpain inhibitors block the influx of extracellular Ca+2 and Cl- during the late phase of cell injury in renal proximal tubules (RPT) exposed to the mitochondrial inhibitor antimycin A. Since the endoplasmic reticulum (ER) is the major intracellular Ca+2 storage site, ER Ca+2 release/depletion may mediate the Ca+2 influx and cell death. Treatment of RPT suspensions with thapsigargin, an ER Ca+2-ATPase inhibitor, increased cytosolic free Caf+2 (Ca+2) levels from 122 +/- 7 to 322 +/- 55 nM within 10 sec of addition followed by a return to control levels within 3 min. A 5-min pretreatment of RPT suspensions with thapsigargin blocked antimycin A- and hypoxia-induced influx of extracellular Ca+2 and Cl- and the resulting cell death/lysis. These data suggest that ER Ca+2 release/depletion during cell injury may trigger a signaling cascade that causes extracellular Ca+2 influx followed by Cl- influx, cell swelling, and ultimately cell death/ lysis.

Animals↗
PubMed1997

Neurosteroid inhibition of cell death.

Diverse gamma-aminobutyric acid (GABAA) receptor modulators exhibited novel cytoprotective effects and mechanisms of action in rabbit renal proximal tubules subjected to mitochondrial inhibition (antimycin A) or hypoxia. Cytoprotective potencies (50% effective concentration, EC50) were 0.3 nM allopregnanolone (AP) > 0.4 nM 17 alpha-OH-allopregnanolone (17 alpha-OH-AP) > 30 nM dehydroepiandrosterone sulfate (DHEAS) = 30 nM pregnenolone sulfate (PS) > 500 nM pregnenolone (PREG) > 30 microM muscimol > 10 mM GABA following antimycin A exposure. Maximal protection with AP and 17 alpha-OH-AP was 70%, whereas DHEAS, PS, PREG, and muscimol produced 100% cytoprotection. Experiments with AP, PS, and muscimol revealed the return of mitochondrial function and active Na+ transport following hypoxia/reoxygenation. Muscimol inhibited the antimycin A-induced influx of both extracellular Ca2+ and Cl- that occurs during the late phase of cell injury, whereas the neurosteroids only inhibited influx of Cl-. Radioligand binding studies with AP and PS did not reveal a specific binding site; however, structural requirements were observed for cytoprotective potency and efficacy. In conclusion, we suggest that the GABAA receptor modulators muscimol and neurosteroids are cytoprotective at different cellular sites in the late phase of cell injury; muscimol inhibits Ca2+ and subsequent Cl- influx, whereas the neurosteroids inhibit Cl- influx.

Alkaloids↗
PubMed1997

Calpains mediate calcium and chloride influx during the late phase of cell injury.

The role of Ca++ in cell death is controversial. Extracellular Ca++ influx and calpain activation occurred during the late phase of renal proximal tubule cell injury produced by the mitochondrial inhibitor antimycin A. Chelation of intracellular Ca++, extracellular Ca++, the calcium channel blocker nifedipine, calpain inhibitor 1 and the dissimilar calpain inhibitor PD150606 blocked antimycin A-induced influx of extracellular Ca++ and cell death. The calcium channel blocker verapamil was ineffective. Calpain inhibitor 1 and PD150606 were cytoprotective also against tetrafluoroethyl-L-cysteine-, bromohydroquinone-, oxidant (t-butylhydroperoxide)- and calcium ionophore (ionomycin)-induced cell death. Extracellular Ca++ influx was associated with the translocation of calpain activity from the cytosol to the membrane and was prevented by calpain inhibitor 1, PD150606 and nifedipine. Finally, nifedipine, calpain inhibitor 1, PD150606 and the Cl- channel inhibitors [5-nitro-2-(3-phenylpropylamino)-benzoate, niflumic acid, diphenylamine-2-carboxylate, and indanyloxyacetic acid] blocked the increase in Cl- influx that occurs during the late phase of cell injury and triggers terminal cell swelling and death. These data suggest that Ca++ and calpains play a common and critical role in renal proximal tubule cell death produced by diverse agents. In addition, calpain activation appears to play a dual role during the late phase of cell injury. Initial calpain activation elicits extracellular Ca++ influx through a nifedipine-sensitive pathway, resulting in calpain translocation to the membrane and in turn Cl- influx.

Acrylates↗
PubMed1996

Extracellular acidosis and chloride channel inhibitors act in the late phase of cellular injury to prevent death.

Extracellular acidosis is cytoprotective in several models against anoxia/hypoxia and a variety of toxicants. The goal of this study was to determine the temporal relationships among toxicant exposure, the initiation of extracellular acidosis, Cl. Influx, Cl- channel inhibition and the onset of cellular death in rabbit renal proximal tubule suspensions. Extracellular acidosis was produced by adding HCl or H2SO4 to renal proximal tubule suspensions to decrease the extracellular buffer pH to 6.4 or by resuspending renal proximal tubules in a pH 6.4 buffer. The initiation of extracellular acidosis 15 min after the mitochondrial inhibitors antimycin A or carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone addition, a time point in which adenosine triphosphate levels are depleted and intracellular K+ is decreased, ameliorated lactate dehydrogenase release, a marker of necrotic cellular death. The initiation of extracellular acidosis 120 min after the addition of the toxicants tetrafluoroethyl-L-cysteine or t-butyl hydroperoxide decreased lactate dehydrogenase release 120 min later. Increased Cl- influx is an important step during the late phase of toxicant-induced cellular injury. Therefore, we determined if extracellular acidosis cytoprotection was associated with inhibition of Cl- influx and whether the Cl- channel inhibitors indanyloxyacetic acid (1.0 mM). niflumic acid (100 microM) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (100 microM) decreased Cl- influx and cellular death in renal proximal tubules exposed to antimycin A. Indeed, all three Cl- channel inhibitors significantly decreased 38Cl- influx and cellular death. In contrast, extracellular acidosis did not decrease 38Cl- influx but did prevent lactate dehydrogenase release. These results demonstrate that extracellular acidosis cytoprotection occurs during the late phase of cellular injury at a site distal to Cl- influx. Furthermore, the Cl- influx that occurs during the late phase of cellular injury and is critical for cellular swelling and lysis is sensitive to 5-nitro-2-(3-phenylpropyl-amino)-benzoic acid, niflumic acid and indanyloxyacetic acid.

Acidosis↗
PubMed1995

PET radiopharmaceuticals in Europe: current use and data relevant for the formulation of summaries of product characteristics (SPCs).

The increasing use of radiopharmaceuticals for positron emission tomography (PET) has come to the attention of regulatory bodies. In order to help authorities in all aspects, the EANM has formed a task group for licensing PET radiopharmaceuticals; this group has surveyed the use of these compounds in Europe by a questionnaire. The number of PET centres that responded to the questionnaire was 26, which included more than 90% of the larger European PET centres. The survey showed that 2-[18f]fluoro-2-deoxyglucose is by far the most important pet radiopharmaceutical with more than 200 applications per week, followed by [15o]water, [15o]carbonmonoxide, [13n]ammonia, [11c]-l-methionine, and l-6-[18f]fluoro-dopa. More than 25 other PET radiopharmaceuticals are in regular use, however, at rather low application frequencies. The data were used by the European Pharmacopoeia Commission for its priority rating for requesting the formulation of monographs. Since it is likely that group registrations will be issued by authorities for the PET radiopharmaceuticals, relevant data on toxicity and dosimetry for the formulation of summaries of product characteristics have been collected by the task group as well.

Data Collection↗
PubMed1995

Disposition of inhaled 1,1,1,2-tetrafluoroethane (HFA134A) in healthy subjects and in patients with chronic airflow limitation. Measurement by 18F-labeling and whole-body gamma-counting.

HFA134a (1,1,1,2-tetrafluoroethane) is a nonozone-depleting candidate to replace the chlorofluorocarbons used as propellants in metered-dose inhalers (MDIs) for pharmaceuticals that are widely used in the treatment of respiratory tract disease. As a means for ensuring the safety of such a compound for human use, it is necessary to establish that there is no excessive or unexpected accumulation in the body and in selected regions. A sensitive whole-body gamma-counting technique has been used with 18F-labeled HFA134a to measure the whole-body and regional absorption, distribution, and retention of HFA134a after administration in humans by single-breath inhalation. In seven healthy subjects, labeled HFA134a was rapidly eliminated by ventilation during the first few minutes, with an average of 9.6% of the radioactivity retained in the body at 5 min. This radioactivity cleared with an apparent terminal half-life of 1.5-4.2 hr to leave, on average, < 1% of the administered dose (< 750 micrograms, approximately 0.2 microCi) retained in the body at 5.8 hr. Disposition of radioactivity was independent of the position of label. Thus, there was no evidence of any significant degradative metabolism. On average, only 0.0056% of the administered dose appeared in the urine within the first 2 hr. Later samples contained no significant radioactivity. Inhaled HFA134a first distributed to all regions of the body and then cleared without evident accumulation in any specific region.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1993

Radioligands for PET studies of central benzodiazepine receptors and PK (peripheral benzodiazepine) binding sites--current status.

The status of the radiochemical development and biological evaluation of radioligands for PET studies of central benzodiazepine (BZ) receptors and the so-called peripheral benzodiazepine binding sites, here discriminated and referred to as PK binding sites, is reviewed against current pharmacological knowledge, indicating those agents with present value and those with future potential. Practical recommendations are given for the preparation of two useful radioligands for PET studies, [N-methyl-11C]flumazenil for central BZ receptors, and [N-methyl-11C]PK 11195 for PK binding sites. Quality assurance and plasma metabolite analysis are also reviewed for these radioligands and practical recommendations are given on methodology for their performance.

Animals↗
PubMed1991

Asymmetric synthesis of a precursor for the automated radiosynthesis of S-(3'-t-butylamino-2'-hydroxypropoxy)-benzimidazol-2-[11C]one (S-[11C]CGP 12177) as a preferred radioligand for beta-adrenergic receptors.

S-[1-(2,3-Diaminophenoxy)]-3'-(N-t-butylamino)propan-2'-ol has been synthesized in three steps from 2,3-dinitro-phenol and the chiral auxiliary, S-glycidyl-3-nitrobenzenesulphonate, to provide a precursor for labelling S-(3'-t-butylamino-2'-hydroxypropoxy)-benzimidazol-2-one (S-CGP 12177) with the short-lived positron-emitting radionuclide, carbon-11 (t 1/2 = 20.4 min; beta+ = 99.8%). Reaction of the diamine with [11C]phosgene, itself derived from no-carrier-added cyclotron-produced [11C]methane, provides radiochemically and chemically pure S-[carbonyl-11C]CGP 12177 in greater than 95% enantiomeric excess after HPLC. Automated apparatus is described for safely producing up to 5.9 GBq (160 mCi) of S-[11C]CGP 12177 with high sp. act. (20-40 GBq/mu mol or 0.54-1.08 Ci/mu mol) in a form suitable for human intravenous injection at only 30 min from the end of radionuclide production. S-[11C]CGP 12177 is preferred to the formerly described racemate as a radioligand for the study of beta-adrenergic receptors in vivo by positron emission tomography.

Adrenergic beta-Antagonists↗
PubMed1990

Labelled agents for PET studies of the dopaminergic system--some quality assurance methods, experience and issues.

Practical methods are described for the quality assurance of three labelled agents (L-6-[18F]fluoro-DOPA, S-[N-methyl-11C]nomifensine and [O-methyl-11C]raclopride) now produced regularly for PET studies of the dopaminergic system in man. These include indirect methods for the initial determination of label position (e.g. 13C-NMR spectroscopy) and also direct methods for the assessment of chiral purity (TLC and HPLC) and the routine determination of radiochemical purity, chemical purity and specific activity (HPLC). Mass spectrometry has been used to identify some impurities. L-6-hydroxy-DOPA (a precursor in vivo of the neurotoxin, L-6-hydroxydopamine) has been detected by HPLC in some preparations of L-6-[18F]fluoro-DOPA. Formulated S-[N-methyl-11C]nomifensine has been found to decrease in radiochemical purity with storage, whereas formulated [O-methyl-11C]raclopride has been found to be stable. Some quality assurance issues are discussed in relation to experience in the application of the described methods and the obtained results.

Carbon Radioisotopes↗
PubMed1987

Experience with a 82Sr/82Rb generator for clinical use.

A 82Sr/82Rb generator system is described which is shown to be suitable for continuous intravenous infusion in man. The breakthrough of the 82Sr parent has been closely monitored and remained less than 18.5 Bq mL-1 of infusate. A method using a 0.05% solution of sodium hypochlorite to disinfect the generator resulted in a sterile and pyrogen free eluate. Recommendations are made for the setting up of the generator to ensure the maintenance of its pharmaceutical integrity.

Humans↗
PubMed1984

PAC studies of 111In binding to transferrin, tropolone and acetylacetone in aqueous solutions.

Time integral and time-differential PAC measurements have been made over a wide temperature range in aqueous solutions of [111In]tropolonate and [111In]acetylacetonate. The quadrupole frequency in the latter is approximately 30% higher than that in the former and the molecular volumes derived from rotational correlation times show the expected differences. Apo-transferrin was separately added to the two 111In-chelates and the transfer of activity from chelate to transferrin followed as a function of relative molar concentrations. Very much larger molar ratios of transferrin to tropolone than of transferrin to acetylacetone were required before substantial transfer of 111In from chelate to transferrin took place. This difference in affinity for transferrin could be one significant factor in explaining the enhanced ability of [111In]tropolonate to label blood cells in the presence of plasma. The determination of PAC parameters in [111In]transferrin over a range of temperatures showed that the values of quadrupole frequency obtained depended on the number of binding sites assumed. For only one 111In site per molecule, the quadrupole frequency increases by over 50% as the temperature is reduced below the freezing point of the solution. If two 111In sites are assumed there appears to be a change in the percentage occupancy of the two sites on either side of the transition.

Cycloheptanes↗
PubMed1983

Radioassay problems associated with the clinical use of a 82Rb radionuclide generator.

The short-lived positron emitting radionuclide 82Rb (t1/2 1.27 min) is conveniently available from a 82Sr/82Rb generator system. The parent nuclide (t1/2 25.5d) produced from the spallation of molybdenum, has associated with it varying quantities of other long-lived strontium radionuclides, namely 85Sr, 89Sr and 90Sr. It is important therefore in the clinical use of such material that the levels of strontium radionuclides being administered to patients is carefully assayed and controlled. The problems associated with these measurements are discussed with special reference to the radiation dose received by the patient and the problems in resolving overlapping peaks with different FWHMs.

Humans↗