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G Zimmer

Publications and source records attributed to G Zimmer.

At least 55 records · Page 3Linked to original sources
PubMed1997

Learning from our patients: one participant's impact on clinical trial research and informed consent.

This Perspective includes an essay on modifying phase I clinical trials, written by George Zimmer, who was a professor of English and a commentary on that essay. Professor Zimmer was a cancer patient who participated in the phase I clinical trial program at the University of Chicago. His ideas are eloquently expressed and have had a profound effect on our investigational research for anticancer agents. Although at times his suggestions may seem radical, Professor Zimmer urges us to reconsider the 50-year-old Nuremberg paradigm that participants in human research are ignorant and vulnerable and must be protected. Although we must protect patients who have life-threatening diseases from coercive inducements and misplaced hopes, we must also listen carefully and thoughtfully to our patients. This is particularly true when, as research participants in the face of sacrifice and the threat of a life-ending diagnosis, they have made the effort to express their concerns. With the effect of the acquired immunodeficiency syndrome movement on clinical studies and on drug research and development, a precedent has been set that allows patients to reshape their role as participants in research trials. On a personal level, the essay by Professor Zimmer has had a significant effect on our research methods and, indeed, the focus of our research efforts. Thus, it is with a sense of respect and honor that we share George Zimmer's thoughts and our comments about the influence he has had on our research practices.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Clinical evaluation of a method for detecting superficial surgical transitional cell carcinoma of the bladder by light-induced fluorescence of protoporphyrin IX following the topical application of 5-aminolevulinic acid: preliminary results.

BACKGROUND AND OBJECTIVE: In bladder cancer, conventional white light endoscopic examination of the bladder does not provide adequate information about the presence of "flat" urothelial lesions such as carcinoma in situ. In the present investigation, we examine a new technique for the photodetection of such lesions by the imaging of protoporphyrin IX (PpIX) fluorescence following topical application of 5-aminolevulinic acid (ALA). STUDY DESIGN/MATERIALS AND METHODS: Several hours after bladder instillation of an aqueous solution of ALA in 34 patients, a Krypton ion laser or a filtered Xenon arc-lamp was used to excite PpIX fluorescence. Tissue samples for histological analysis were taken while observing the bladder wall either by means of a video camera, or by direct endoscopic observation. RESULTS: A good correlation was found between the PpIX fluorescence and the histopathological diagnosis. On a total of 215 biopsies, 143 in fluorescent and 72 in nonfluorescent areas, all visible tumors on white light cytoscopy appeared in a bright red fluorescence with the photodetection technique. In addition, this method permitted to discover 47 unsuspected carcinomatous lesions on white light observation, among which 40% were carcinoma in situ. CONCLUSION: PpIX fluorescence induced by instillation into the bladder of 5-ALA is an efficient method of mapping the mucosa in bladder carcinoma.

Administration, Cutaneous↗
PubMed1997

The cell receptor level is reduced during persistent infection with influenza C virus.

Persistent influenza C virus infection of MDCK cells perpetuates the viral genome in a cell-associated form. Typically, virus production remains at a low level over extended periods, in the absence of lytic effects of replication. In this study, we demonstrate that persistently infected cells are very restricted in permissiveness for superinfection. By reconstitution experiments, using bovine brain gangliosides as artificial receptors, the degree of super-infection was markedly increased. Analysis of cellular receptor expression revealed reduced concentrations of sialoglycoproteins in general and a limited presentation of the major receptor gp40. Cocultures of persistently infected and uninfected cells (the latter carrying normal receptor levels) initiated a transient rise in virus titers. This kind of induction of virus synthesis appeared to be mainly receptor-linked, since a receptor-deprived subline, MDCK II, did not give rise to a similar effect. Susceptibility of MDCK II cocultures could be partly restored by ganglioside treatment. In accordance to related virus systems, these findings on influenza C virus suggest a role of cell receptor concentrations in the regulation of long-term persistence.

Animals↗
PubMed1997

Electron paramagnetic resonance studies on nitroxide radical 2,2,5,5-tetramethyl-4-piperidin-1-oxyl (TEMPO) redox reactions in human skin.

Electron paramagnetic resonance (EPR) is currently being explored for the study of living biological systems. Among biophysical and biochemical applications, the study of nitroxide radical interactions with tissue antioxidants and oxidants is of growing interest. Skin is a target organ of the EPR methodology and is frequently exposed to oxidative stress. We investigated the piperidine-type nitroxide 2,2,5,5-tetramethyl-4-piperidin-1-oxyl (TEMPO) because it is skin permeable and readily accepts electrons in biological systems. TEMPO is readily scavenged on the surface of cultured human skin. Pretreatment of skin cultures with butylhydroperoxide, which decreases intracellular ascorbate and glutathione, causes inhibition of nitroxide scavenging. Exposure of skin cultures to dehydroascorbate, which is internalized and converted to ascorbate, leads to stimulation of nitroxide scavenging. In human keratinocytes and fibroblasts, the TEMPO radical is reversibly reduced to the hydroxylamine depending on the oxygen concentration and the availability of intracellular glutathione and ascorbate. Cell exposure to the glutathione synthetase inhibitor buthionine-sulfoximine depleted intracellular glutathione and inhibited nitroxide reduction; exposure to dehydroascorbate or glutathione-monoethylester increased intracellular ascorbate or glutathione concentration and stimulated nitroxide reduction. Quantitative considerations indicate that the major reduction site of TEMPO in skin and skin cells is the cytosol ascorbate/glutathione redox cycle. We suggest that analysis of TEMPO radical scavenging by the EPR technique is a convenient method for measuring skin ascorbate and thiol-dependent antioxidant activity in vitro and in vivo.

Antioxidants↗
PubMed1996

Determination of rate constants of the reactions of thiols with superoxide radical by electron paramagnetic resonance: critical remarks on spectrophotometric approaches.

Two new EPR approaches were developed for determination of rate constants of reaction glutathione (GSH), N-(2-mercaptopropionyl) glycine (MPG), dihydrolipoic acid (BNL), and tetranor-dihydrolipoic acid (TNL) with superoxide radical. In both cases the competition between thiols and spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) for superoxide radical was used. In the first method the dependence of amplitude of EPR spectrum of DMPO-OOH spin adduct on concentration of thiols in a superoxide-generating system was studied. In the second approach the changes in reduced thiol concentration due to reaction with superoxide radical were measured by nitroxide biradical containing disulfide bond. Observed rate constants were the following: GSH, 1.8 x 10(5) M-1s-1; MPG, 2.2 x 10(5) M-1s-1; TNL, 1.2 x 10(5) M-1s-1; BNL, 2.5 x 10(5) M-1s-1; DHL, 4.8 x 10(5) M-1s-1. The determination of the rate constants of reaction of superoxide radical with thiols by spectrophotometrical cytochrome C assay could result in an underestimation of the values due to the reduction of cytochrome C by thiols. Use of epinephrine for this purpose could lead to an overestimation of experimental rate constants because the adrenochrome formed in the reaction of epinephrine with superoxide radical reacts with thiols.

Adrenochrome↗
PubMed1996

T cell responses in calcineurin A alpha-deficient mice.

We have created embryonic stem (ES) cells and mice lacking the predominant isoform (alpha) of the calcineurin A subunit (CNA alpha) to study the role of this serine/threonine phosphatase in the immune system. T and B cell maturation appeared to be normal in CNA alpha -/- mice. CNA alpha -/- T cells responded normally to mitogenic stimulation (i.e., PMA plus ionomycin, concanavalin A, and anti-CD3 epsilon antibody). However, CNA alpha -/- mice generated defective antigen-specific T cell responses in vivo. Mice produced from CNA alpha -/- ES cells injected into RAG-2-deficient blastocysts had a similar defective T cell response, indicating that CNA alpha is required for T cell function per se, rather than for an activity of other cell types involved in the immune response. CNA alpha -/- T cells remained sensitive to both cyclosporin A and FK506, suggesting that CNA beta or another CNA-like molecule can mediate the action of these immunosuppressive drugs. CNA alpha -/- mice provide an animal model for dissecting the physiologic functions of calcineurin as well as the effects of FK506 and CsA.

Animals↗
PubMed1996

Comparative study on four enzyme-linked immunosorbent assays and a cocultivation assay for the detection of antigens associated with the bovine viral diarrhoea virus in persistently infected cattle.

Four commercially available ELISAs for detection of antigens associated with the bovine viral diarrhoea virus in persistently infected cattle have been compared. The tests are equally specific (100%) and the sensitivity of three ELISAs is comparable with that of a conventional cocultivation assay. Performing ELISA on samples from young animals that received colostrum may yield false negative results because of interference of maternal antibodies in the tests. It is concluded that ELISA can be a valuable tool in eradications programs when large numbers of cattle are to be monitored.

Animals↗
PubMed1996

Virus entry into a polarized epithelial cell line (MDCK): similarities and dissimilarities between influenza C virus and bovine coronavirus.

We have analysed the uptake of influenza C virus and bovine coronavirus (BCV) by a polarized epithelial cell line, Madin-Darby canine kidney (MDCK) cells. Both viruses use N-acetyl-9-O-acetylneuraminic acid as a receptor determinant for attachment to cells. Virus binding assays with immobilized proteins indicated that a glycoprotein of 40 kDa is the major surface protein containing the receptor determinant for the two viruses. MDCK cells grown on filters for permeable support were found to have differential sensitivity to infection by these viruses. Both viruses were able to initiate infection via the apical domain of the plasma membrane, but only influenza C virus also accomplished infection via the basolateral plasma membrane. The resistance of MDCK cells to BCV infection from the basal filter chamber was overcome when the cell polarity was abolished by maintaining the cells in calcium-free medium. This finding indicates that the resistance to basolateral infection by BCV is a property of the cell line and not due to a technical problem related to the use of filters. Our results indicate that two viruses which use the same receptor for attachment to cells may differ in their ability to enter polarized cells. The possible involvement of an accessory molecule in the entry of BCV is discussed.

Animals↗
PubMed1996

Digestive leishmaniasis in acquired immunodeficiency syndrome: a light and electron microscopic study of two cases.

An increased incidence of visceral leishmaniasis in patients infected with the human immunodeficiency virus (HIV) is observed in areas in which both infectious diseases are endemic. Intensive worldwide traveling has also resulted recently in an increasing number of leishmanial and HIV coinfections in nonendemic areas. We describe the clinical, light microscopic, and ultrastructural features of two cases of imported, HIV-related, visceral leishmaniasis involving the alimentary tract, including the esophagus, the stomach, the duodenum, the ileum, the colon, and the rectum. We also discuss the differentiation of leishmanial infections from other HIV-related gastrointestinal opportunistic infections.

Acquired Immunodeficiency Syndrome↗
PubMed1996

[Controlled reperfusion of the extremities for preventing local and systemic damage after prolonged ischemia. An experimental study with the swine model].

Our previous studies in isolated rat hindlimbs using crystalloid perfusion solutions have shown that control of the initial reperfusion reduces postischemic complications. However, no experimental study has been undertaken to evaluate the concept of controlled limb reperfusion experimentally in an in-vivo blood-perfused model and to assess the local as well as systemic effects of normal blood reperfusion and controlled limb reperfusion. Of twenty pigs undergoing preparation of the infrarenal aorta and iliac arteries, six were observed for 7.5 hours and served as controls. Fourteen other pigs underwent 6 hours of complete infrarenal occlusion. Thereafter, embolectomy was stimulated in 8 pigs by removing the aortic clamp and establishing normal blood reperfusion at systemic pressure. In 6 other pigs, control of the composition of the reperfusate and control of the conditions of reperfusion was done during the first 30 min, followed by normal blood reperfusion. Six hours of infrarenal aortic occlusion lead to a severe decrease in high energy phosphates and muscle temperature and a slight increase in creating kinase (CK) and potassium in the systemic circulation. Normal blood reperfusion resulted in severe reperfusion injury: massive edema developed (80.6% vs. 76.6%, p < 0.0009), the tissue showed a marked decrease in oxygen consumption (7.3 +/- 1.1 vs. 14.3 +/- 2.5 mL )2/100 g/min, p < 0.02), glucose consumption (0.19 +/- 0.06 vs. 0.51 +/- 0.03 mg/100 g/min, p < 0.06), tissue ATP (18.3 +/- 1.9 vs. 36.1 +/- 0.9 mumol/g protein, p < 0.000001), total adenine nucleotides (26.3 +/- 2.6 vs. 45.8 +/- 1.5 mumol/g protein, p < 0.00001), muscle pH (5.9 +/- 0.1 vs. 7.3 +/- 0.1, p < 0.000006) and total calcium in the femoral vein (2. +/- 0.1 vs. 2.7 +/- 0.1 mmol/L, p < 0.002). Furthermore, a massive increase was seen in CK concentration (12,743 +/- 2,562 vs. 513 +/- 80 U/L, p < 0.0003), potassium (7.9 +/- 0.3 vs. 4.4 +/- 0.2 mmol/L, p < 0.000001) and muscle rigidity (60 +/- 11 vs. 122 +/- 1 degree, p < 0.00008). In sharp contrast, initial treatment of the ischemic skeletal muscle by controlled limb reperfusion resulted in normal water content (77.6 +/- 0.4 vs. 76.8 +/- 0.3%), oxygen consumption (13.2 +/- 1.6 vs. 14.9 +/- 3.2 mL O2/100 g/min), glucose consumption (0.58 +/- 0.18 vs. 0.46 +/- 0.11 mg/100 g/min), flow (5.4 +/- 1.1 vs. 4.6 +/- 4.6 +/- 0.5 mL/100 g/min) and muscle rigidity (106 +/- 4 vs. 122 +/- 1 degree). Furthermore, controlled limb reperfusion resulted in higher total adenine nucleotides content (78% vs. 57% of control), less tissue acidosis (6.6 +/- 0.2 vs. 5.9 +/- 0.1, p < 0.002), severely reduced CK release (2,618 +/- 702 vs. 12,743 +/- 2.562, p < 0.02) and potassium release (5.1 +/- 0.3 vs. 7.9 +/- 0.3 mmol/L, p < 0.0002) as compared to normal blood reperfusion. In conclusion this study shows that 6 hours of acute infrarenal aortic occlusion will result in a severe reperfusion injury (postischemic syndrome) if normal blood at systemic pressure is given in the initial reperfusion phase. In contrast, initial treatment of the ischemic skeletal muscle by controlled limb reperfusion reduces the metabolic, functional and biochemical alterations.

Animals↗
PubMed1996

Interaction of glucose and metformin with isolated red cell membrane.

Isolated human erythrocyte membranes (red blood cell (RBC) ghosts) were incubated with glucose at 5, 10, 20 and 100 mmol/l concentrations, with insulin (0.01 to 200 mU/l) and metformin (CAS 657-24-9) 0.5 up to 50.0 mumol/l). Binding studies with 14C-glucose and subsequent gel electrophoresis revealed 60% of the radioactivity around ban 4.2-4.5 at 5 mmol/l, whereas a random distribution of radioactivity over all protein bands of the RBC membrane was found at 20 mmol/l concentration after incubation for 30 min or 48 h. Metformin does not bind covalently to RBC membranes, however, after photochemical linkage of 14C-metformin via the aminoreactive linker azidophenylglyoxal the highest radioactivity (21%) was counted in the range of band 4.2-4.5. In parallel with an increase of order parameters of 5-doxyl-stearic acid the thiol status of the membranes decreases as determined by monobromobimane fluorescence. 20 and 100 mmol/l concentrations of glucose decrease the reactivity of membrane thiols towards bromobimane significantly to 73 and 62% of the controls. Concomitantly, membrane fluidity at polar sites is diminished as measured by order parameters of spin label 5-doxyl stearic acid. In RBC membranes pretreated with 20 mmol/l glucose the decreased fluorescence is significantly raised again by insulin and metformin. This effect is even more pronounced, if insulin and metformin are incubated together. Reaction of membrane thiols with a maleimido spin label detects modification in the ratio of mobile and immobilized spin label populations in the electron paramagnetic resonance signal under the above conditions, indicative of conformational changes of membrane proteins.

Bridged Bicyclo Compounds↗
PubMed1995

Decrease of red cell membrane fluidity and -SH groups due to hyperglycemic conditions is counteracted by alpha-lipoic acid.

Human red cell membranes (ghosts) were treated by 5 min of incubation with fasting or hypo- and hyperglycemic concentrations of D-glucose. This simulation of nondiabetic or diabetic conditions revealed an influence on membrane fluidity and on protein -SH reactivity. Protein -SH groups, measured with Ellman's reagent, generally behave in the same way as membrane fluidity determined with diphenylhexatriene. Maximal values were obtained with 5 mM D-glucose, whereas decrease was observed above 10 mM D-glucose. Addition of alpha-lipoic acid (4 nmol/mg protein) resulted in a significant increase in membrane fluidity and titratable -SH groups at glucose concentrations of 10 mM and above. Dithiothreitol diminished titrable-SH groups and did not restore membrane fluidity. 2-Mercaptopropionylglycine was only effective in restoration of -SH groups. By contrast to D-glucose, other sugars such as L-glucose, D-fructose, or sucrose revealed no comparable changes on membrane fluidity and titratable membrane -SH groups between concentrations of 5 and 10 mM. The hyperglycemic effects of D-glucose were corroborated with isolated, reconstituted membrane proteins and erythrocyte glucose carrier, indicating that, in general, the observed divergent biochemical/biophysical changes of the red cell membrane are influenced by the glucose transport protein GluT1. The natural R-form and the S-form of alpha-lipoic acid were compared with racemic R-/S-forms for their efficiencies in alterations of red cell membrane fluidity. Decreased fluidities in presence of 10 mM glucose were found to be influenced in differentiated ways: the S-form was highly active in increasing fluidity at 4 nmol/mg and increasingly less active up to 20 nmol/mg protein. By contrast the R-form of lipoic acid was moderately efficient in increasing fluidity through a larger concentration range between 4 and 80 nmol/mg protein.

Dithiothreitol↗
PubMed1995

ATP synthesis by purified ATP-synthase from beef heart mitochondria after coreconstitution with bacteriorhodopsin.

An ATP-synthase complex active in ATP synthesis was isolated from beef heart mitochondria by solubilization of submitochondrial particles with dodecyl-beta-D-maltoside and purified in a one-step procedure by subsequent ion-exchange chromatography. The electrophoretic analysis resulted in 14 subunits for the F0 F1 complex. ATP hydrolysis activity of the purified enzyme was 25 mumol ATP min-1 mg-1F0F1. ATP hydrolysis could be stimulated by addition of lipid vesicles. Further stimulation was observed in the presence of uncoupler. The inhibitors dicyclohexylcarbodiimide and oligomycin reduced hydrolytic activity to 70 and 40%, respectively. The preservation of ATP synthesis capability was demonstrated by reconstitution of the purified enzyme together with the light-driven proton pump bacteriorhodopsin. Upon illumination of ATP-synthase/bacteriorhodopsin proteoliposomes ATP synthesis activity was detectable for at least 7 min. At reduced temperature this time could be increased to 20 min. The maximum synthesis rate of 58 nmol ATP min-1 mg-1 F0F1 was obtained after reconstitution into liposomes made from crude soy bean lecithin by a detergent dialysis procedure using octyl-beta-D-glucopyranoside and monomeric bacteriorhodopsin. ATP synthesis was partially inhibited by oligomycin or dicyclohexylcarbodiimide and was completely abolished in the presence of uncoupler. The ability of the purified enzyme to synthesize ATP shows that the described isolation procedure results in an ATP-synthase complex which is intact in structure and function.

Adenosine Triphosphate↗