Biomedical subjects

S Zöllner

Publications and source records attributed to S Zöllner.

10 recordsLinked to original sources

PubMed2001

Synthesis, spectroscopic, and structural properties of spirocyclopropanated bicyclobutylidenes and their radical cations.

The spirocyclopropanated bicyclobutylidenes 3-7 have been prepared by McMurry coupling of the corresponding spirocyclopropanated cyclobutanone (3 and 5), Staudinger-Pfenniger reaction (4), oxidative coupling of a Wittig ylide (4) or Wittig olefination of perspirocyclopropanated cyclobutanone (6 and 7). The structure of the parent 2a and the perspirocyclopropanated bicyclobutylidene 5 was determined by X-ray crystallography which disclosed considerable steric congestion around the double bond. As a result 5 did undergo addition of dichlorocarbene, epoxidation with meta-chloroperbenzoic acid, and cyclopropanation with CH2I2/ZnEt2, but did not add the more bulky dibromocarbene. The reaction of 5 with tetracyanoethene proceeded smoothly, but led to a formal [3+2] cycloadduct across the proximal single bond of one of the inner cyclopropane rings. The consecutive spirocyclopropanation of bicyclobutylidene led to a bathochromic shift in the UV spectra of 12 and 17nm, respectively, for each pair of beta- and alpha-spirocyclopropane groups. In the He(I)-photoelectron spectra of these bicyclobutylidenes, the effect of spirocyclopropanation upon their pi-ionization energies (pi-IE,) was found to be almost additive, leading to a lowering of 0.05 eV per any additional beta-spirocyclopropane, and 0.28-0.22 eV per additional alpha-spirocyclopropane group; this indicates an increasing nucleophilicity of the double bonds in the order 1 < 4 < 3 < 5. Following the radical cations of the three symmetrical bicyclobutylidenes without (2a, b) and with six (5) spiroannelated cyclopropane rings, the radical cations of two symmetrical bicyclobutylidenes with two (4) and four (3) such rings were studied by ESR spectroscopy. Whereas 2b.+, 3.+, and 5.+ could be generated by electrolytic oxidation of the corresponding hydrocarbons in solution, the spectra of 2a.+ and 4.+, with unsubstituted 2,2',4,4'-positions, were observed upon radiolysis of their neutral precursors in a Freon matrix. On going from 2a.+ to 4.+, the coupling constant [aH] of the eight beta protons in the 2,2',4,4'-positions of bicyclobutylidene increases from 2.62 to 3.08 mT, and that of the four gamma protons in the 3,3'-positions changes from 0.27 to 0.049 to 0.401 mT on passing from 2a.+ via 2b.+ to 3.+. Computations by means of the density functional theory (DFT) at the B3LYP/6-311+G*//B3LYP/6-31G* level reproduce well the experimental hyperfine data.

Journal Article↗

PubMed2001

Spirocyclopropanated bicyclopropylidenes: straightforward preparation, physical properites, and chemical transformations.

Perspirocyclopropanated bicyclopropylidene (6) was prepared in three steps from 7-cyclopropylidenedispiro[2.0.2.1]heptane (4) (24% overall) or, more efficiently, through dehalogenative coupling of 7,7-dibromo[3]triangulane (15) (82%). This type of reductive dimerization turned out to be successful for the synthesis of (E)- and (Z)-bis(spiropentylidene) 14 (67%) and even of the "third-generation" spirocyclopropanated bicyclopropylidene 17 (17% overall from 15). Whereas the parent bicyclopropylidene 1 dimerized at 180 degrees C to yield [4]rotane, dimerization of 6 at 130 degrees C under 10 kbar pressure occured only with opening of one three-membered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane derivative 19 (34% yield), and at the elevated temperature the polyspirocyclopropanated 2-cyclopropylidene[3.2.2]propellane derivative 20 (25 % yield). Perspirocyclopropanated bicyclopropylidene 6 and the "third-generation" bicyclopropylidene 17 gave addition of bromine, hydrogen bromide, and various dihalocarbenes without rearrangement. The functionally substituted branched [7]triangulane 28 and branched dichloro-C2v-[15]triangulane 32 were used to prepare the perspirocyclopropanated [3]rotane (D3h-[10]triangulane) 49 (six steps from 6, 1.4% overall yield) and the C2v-[15]triangulane 51 (two steps from 17, 41% overall). Upon catalytic hydrogenation, the perspirocyclopropanated bicyclopropylidene 6 yielded 7,7'-bis(dispiro[2.0.2.]-heptyl) (52) and, under more forcing conditions, 1,1'-bis(2,2,3,3-tetramethylcyclopropyl) (53). The bromofluorocarbene adduct 33 of 17 reacted with butyllithium to give the unexpected polyspirocyclopropanated 1,4-di-n-butyl-2-cyclopropylidenebicyclo[2.2.0]hexane derivative 37 as the main product (55% yield) along with the expected "third-generation" perspirocyclopropanated dicyclopropylidenemethane 38 (21% yield). Mechanistic aspects of this and the other unusual reactions are discussed. The structures of all new unusual hydrocarbons were proven by X-ray crystal structure analyses, and the most interesting structural and crystal packing features are presented.

Journal Article↗

PubMed2001

Sphingosine 1-phosphate activates Akt, nitric oxide production, and chemotaxis through a Gi protein/phosphoinositide 3-kinase pathway in endothelial cells.

Sphingosine 1-phosphate (SPP) binds to members of the endothelial differentiation gene family (EDG) of receptors and leads to diverse signaling events including cell survival, growth, migration and differentiation. However, the mechanisms of how SPP activates these proangiogenic pathways are poorly understood. Here we show that SPP signals through the EDG-1 receptor to the heterotrimeric G protein G(i), leading to activation of the serine/threonine kinase Akt and phosphorylation of the Akt substrate, endothelial nitric-oxide synthase (eNOS). Inhibition of G(i) signaling, and phosphoinositide 3-kinase (PI 3-kinase) activity resulted in a decrease in SPP-induced endothelial cell chemotaxis. SPP also stimulates eNOS phosphorylation and NO release and these effects are also attenuated by inhibition of G(i) signaling, PI 3-kinase, and Akt. However, inhibition of NO production did not influence SPP-induced chemotaxis but effectively blocked the chemotactic actions of vascular endothelial growth factor. Thus, SPP signals through G(i) and PI 3-kinase leading to Akt activation and eNOS phosphorylation.

Animals↗

PubMed2000

A coalescent approach to study linkage disequilibrium between single-nucleotide polymorphisms.

We present the results of extensive simulations that emulate the development and distribution of linkage disequilibrium (LD) between single-nucleotide polymorphisms (SNPs) and a gene locus that is phenotypically stratified into two classes (disease phenotype and wild-type phenotype). Our approach, based on coalescence theory, allows an explicit modeling of the demographic history of the population without conditioning on the age of the mutation, and serves as an efficient tool to carry out simulations. More specifically, we compare the influence that a constant population size or an exponentially growing population has on the amount of LD. These results indicate that attempts to locate single disease genes are most likely successful in small and constant populations. On the other hand, if we consider an exponentially growing population that started to expand from an initially constant population of reasonable size, then our simulations indicate a lower success rate. The power to detect association is enhanced if haplotypes constructed from several SNPs are used as markers. The versatility of the coalescence approach also allows the analysis of other relevant factors that influence the chances that a disease gene will be located. We show that several alleles leading to the same disease have no substantial influence on the amount of LD, as long as the differences between the disease-causing alleles are confined to the same region of the gene locus and as long as each allele occurs in an appreciable frequency. Our simulations indicate that mapping of less-frequent diseases is more likely to be successful. Moreover, we show that successful attempts to map complex diseases depend crucially on the phenotype-genotype correlations of all alleles at the disease locus. An analysis of lipoprotein lipase data indicates that our simulations capture the major features of LD occurring in biological data.

Alleles↗

PubMed2000

Changes of endothelial nitric oxide synthase level and activity during endothelial cell proliferation.

The goal of this study was to investigate the effect of endothelial cell proliferation on the expression and activity of endothelial nitric oxide synthase (eNOS). Bovine atrial endothelial cells (BAtEC) were studied between day 1 and 6 after seeding. During this period the number of cells in S-phase decreased progressively, while cell number and protein content increased, reaching a maximum at confluence (day 4). Expression of eNOS (determined by ELISA) and eNOS activity (determined by L-arginine to L-citrulline conversion) increased with culture duration with a maximum at confluence. Nitric oxide (*NO) release from BAtEC was determined after stimulation with Ca2+ ionophore A23187 (10 microM, 30 min) by .NO chemiluminescence in the absence of a chemical reduction system. Total *NO release (measured in the presence of 100 U/ml superoxide dismutase) did not change with state of cell proliferation/growth, whereas "bioavailable" *NO (measured in the absence of superoxide dismutase) was low in highly proliferating BAtEC. Relative eNOS activity (.NO and L-citrulline production per eNOS protein) was highest in proliferating BAtEC. The novel finding of this study is that the specific eNOS activity is upregulated in proliferating BAtEC and downregulated in quiescent BAtEC. The amount of "bioavailable" *NO is determined by eNOS activity and *NO inactivation (probably by superoxide), both high in proliferating BAtEC.

Animals↗

PubMed1998

PBN spin trapping of free radicals in the reperfusion-injured heart. Limitations for pharmacological investigations.

Post-ischemic reperfusion causes cardiac dysfunction and radical-induced lipid peroxidation (LPO) detectable by ESR spin trapping. This study deals with the applicability of the spin trapping technique to pharmacological investigations during myocardial reperfusion injury. The use of the spin trap phenylbutylnitrone (PBN, 3 mM) in isolated rat hearts demonstrated the release of alkoxyl radicals (aN = 1.39 mT, aHbeta = 0.19 mT) formed particularly within the first 15 min of reperfusion following 30 min of ischemia. The decline of radicals, after 10 min of reperfusion, was accompanied by recovery of function in 80% of the hearts. The radical concentration in the coronary effluent (maximum after 7.5 min) was reduced by the infusion of 1 mM mercaptopropionylglycine (MPG, 2.7+/-0.5 U/ml, p < 0.001) or 5 microM vitamin E (11.7+/-0.8 U/ml, p < 0.001), compared to the (PBN-containing) control (29.7+/-4.3 U/ml). Moreover, functional recovery (left ventricular developed pressure, LVDP 91.6 +/-20% of pre-ischemic level, p < 0.05) was improved by the hydrophilic radical scavenger MPG, compared to the (PBN-containing) control (LVDP 50.5+/-15.7% of baseline). PBN alone led to higher functional recovery (p < 0.05) and reduced VF (duration of ventricular fibrillation; 7.10+/-0.36 min/30 min, p < 0.05), compared to the untreated (PBN-free) control (LVDP 26.6+/-11.8%; VF 19.42+/-3.64 min/30 min). The Ca antagonist verapamil (0.1 microM), MPG, and the lipophilic vitamin E showed cardioprotection in the absence of PBN: post-ischemic recovery of LVDP was 25.4+/-6.8% (p < 0.05), 39.6+/-12.7% (p < 0.05) and 52.4+/-2.6% (p < 0.01), respectively, compared to the corresponding untreated control (13.3+/-6.6%). Whereas verapamil and vitamin E were able to protect the heart when present alone, they offered no additive effect in the presence of PBN. Therefore, PBN can be used to estimate the radical scavenger properties of an agent in the heart. However, because of the protective properties of PBN itself, the results of simultaneous investigations of the effects of other compounds, such as Ca antagonists or lipophilic radical scavengers, on heart function may be limited.

Animals↗

PubMed1997

Nitroxides increase the detectable amount of nitric oxide released from endothelial cells.

Nitroxides are known to exert superoxide dismutase-mimetic properties and to decrease O-2- and H2O2-mediated cytotoxicity. However, the effect of nitroxides on .NO homeostasis has not been studied yet. The present study investigates the effect of nitroxides on the detectable amount of .NO released by 3-morpholinosydnonimine (SIN-1) and cultured endothelial cells. Cultured bovine aortic and atrial endothelial cells stimulated with 10 microM A23187 released a stable flux of .NO, as detected by .NO chemiluminescence. Addition of 100 units/ml SOD or 10 microM of the nitroxides 4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPOL), 3-carboxy-proxyl, and 3-ethoxycarbonyl-proxyl, increased the chemiluminescence signal. The effect of these nitroxides on the amount of .NO released from cell monolayers was dose-dependent, with the highest efficacy between 30 and 100 microM. EPR spin trapping in SIN-1 solutions revealed the formation of .OH adducts from spontaneous dismutation of O-2 and concomitant reaction with H2O2. Both SOD and TEMPOL increased the signal intensity of the .OH adduct by accelerating the dismutation of O-2. The results of this study demonstrate that the SOD-mimetic activity of nitroxides increases the amount of bioavailable .NO in vitro.

Animals↗

PubMed1997

Evaluation of purine nucleotide loss, lipid peroxidation and ultrastructural alterations in post-hypoxic hepatocytes.

1. Hypoxic alterations in isolated rat hepatocytes were demonstrated by a 90% ATP loss during 60 min of ischaemia and temporary increases of nucleotide degradation products. 2. The oxidative stress during reoxygenation was demonstrated in these cells by a decrease in reduced glutathione (GSH) concentration (30%) and a threefold increase in lipid peroxidation products such as 4-hydroxynonenal and thiobarbituric acid-reactive substances (TBA-RSs). The tremendous GSH loss could not be balanced by the slight oxidized glutathione (GSSG) increase during reoxygenation. 3. For the first time the involvement of free radicals was directly demonstrated using electron spin resonance (ESR) spectroscopy in reoxygenated liver cells. Using the spin trap 5,5-dimethylpyrroline-1-oxide (DMPO), a carbon-centred radical and the adduct of the hydroxyl radical could be detected during early reoxygenation. 4. Morphological alteration of cells was observed, beginning during hypoxia and increasing during post-hypoxic reoxygenation. Electron microscopic findings of hypoxic and post-hypoxic cell damage included pyknosis of nuclei, spherical transformation of mitochondria and increased number of vesicles.

Aldehydes↗

PubMed1997

Superoxide-mediated reduction of the nitroxide group can prevent detection of nitric oxide by nitronyl nitroxides.

Nitronyl nitroxides (NN), a class of compounds which react with nitric oxide forming imino nitroxides, were applied in different systems for the detection of nitric oxide. Addition of a NN to planar monolayers of bovine aortic endothelial cells (BAEC) activated by Ca2+ ionophore A23187 immediately resulted in a strong decrease of the ozone-mediated .NO chemiluminescence. Simultaneously, a rapid diminution of the electron spin resonance (ESR) signal intensity of the NN (without detectable formation of the corresponding imino nitroxide) was observed; superoxide dismutase partially inhibited this decrease in the NN concentration. Model experiments using hypoxanthine/xanthine oxidase in aqueous solution and KO2 in dimethylsulfoxide as sources of O2.- revealed that there is a rapid reduction of nitronyl nitroxides by superoxide. The second order rate constant for the reaction of the water soluble NN with O2.- was determined to be 8.8 x 10(5) M-1s-1, which is more than two orders of magnitude higher than the value reported previously for reaction with .NO (Woldman et al., BBRC 202, 195-203, 1994). Reduction of the nitronyl nitroxide was also observed in the presence of glutathione, ascorbic acid or rabbit liver microsomes. Incorporation of both nitronyl and imino nitroxides into liposomes strongly decreased reduction by superoxide and other reductants, however, in the presence of microsomes, there was no protective effect by liposomal encapsulation of NN. The results indicate that in biological systems (in addition to other reducing agents) the presence of superoxide can prevent the detection of nitric oxide using nitronyl nitroxides.

Animals↗

PubMedDate not supplied

Mapping genes through the use of linkage disequilibrium generated by genetic drift: 'drift mapping' in small populations with no demographic expansion.

Linkage disequilibrium has been a powerful tool in identifying rare disease alleles in human populations. To date, most research has been directed to isolated populations which have undergone a bottleneck followed by rapid exponential expansion. While this strategy works well for rare diseases in which all disease alleles in the population today are clonal copies of some common ancestral allele, for common disease genes with substantial allelic heterogeneity, this approach is not predicted to work. In this paper, we describe the dynamics of linkage disequilibrium in populations which have not undergone a demographic expansion. In these populations, it is shown that genetic drift creates disequilibrium over time, while in expanded populations, the disequilibrium decays with time. We propose that common disease alleles might be more efficiently identified by drift mapping - linkage disequilibrium mapping in small, old populations of constant size where the disequilibrium is the result of genetic drift, not founder effect. Theoretical models, empirical data, and simulated population models are presented as evidence for the utility of this approach.

Chromosome Mapping↗