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Biomedical subjects

A Alexandrov

Publications and source records attributed to A Alexandrov.

At least 19 recordsLinked to original sources
PubMed2006

Towards hematopoietic stem cell-mediated protection against infection with human immunodeficiency virus.

The failure of pharmacological approaches to cure infection with the human immunodeficiency virus (HIV) has renewed the interest in gene-based therapies. Among the various strategies that are currently explored, the blockade of HIV entry into susceptible T cells and macrophages promises to be the most powerful intervention. For long-term protection of both of these lineages, genetic modification of hematopoietic stem cells (HSCs) would be required. Here, we tested whether HSCs and their progeny can be modified to express therapeutic levels of M87o, a gammaretroviral vector encoding an artificial transmembrane molecule that blocks fusion-mediated uptake of HIV. In serial murine bone marrow transplantations, efficient and multilineage expression of M87o was observed for more than 1 year (range 37-75% of mononuclear cells), without signs of toxicity related to the transmembrane molecule. To allow enrichment of M87o-modified HSCs after transplant, we constructed vectors coexpressing the P140K mutant of O(6)-methylguanine-DNA-methyltransferase (MGMT-P140K). This clinically relevant selection marker mediates a survival advantage in HSCs if exposed to combinations of methylguanine-methyltransferase (MGMT) inhibitors and alkylating agents. A bicistronic vector mediated sufficient expression of both M87o and MGMT to confer a selective survival advantage in the presence of HIV and alkylating agents, respectively. These data encourage further investigations in large animal models and clinical trials.

AIDS Vaccines↗
PubMed2006

Chemical activity of photoinduced Ti3+ centers in titanium oxide gels.

We report on the chemical activity of trapped electrons in wet titanium oxide gels. These electrons are generated under the band gap irradiation of gels in the spectral range between 3.25 and 4.4 eV and stored as Ti3+ centers that absorb in the visible. Chemical processes in photoirradiated gels are generally similar to those earlier reported in TiO2 colloids; however, peculiarities exist. In particular, a high internal surface of gels strongly enhances interface reactions. Measurements of UV-visible absorption kinetics allow conclusions to be made about extremely high available traps concentration and the activity of all trapped electrons toward nitrate and nitrite anion reduction according to a heterogeneous photocatalytic mechanism.

Journal Article↗
PubMed2005

Light-induced charge separation and storage in titanium oxide gels.

We report on the interaction of light with a particular class of media--wet gels, which in contrast to sols of nanoparticles possess a macroscopic bulk structure, and which differ from conventional solids by the existence of the internal liquid-solid interface. We show, taking an absorption cross section of trapped electrons from Safrany, Gao, and Rabani [J. Phys. Chem. B 104, 5848 (2000)], that a separation of charges with quantum efficiency as high as 46% appears under the band-gap irradiation of titanium oxide gels: electrons are stored in the gel network as Ti3+ centers, whereas holes are stored in the liquid phase. Under a prolonged UV-laser irradiation, more than 14% of Ti4+ centers can be converted into Ti3+ . Their lifetime can be extremely long and exceeds months at room temperature. The trapped electrons are responsible for a "dark" absorption continuum covering the spectral range from 350 nm to 2.5 mum .

Journal Article↗
PubMed2001

Structure of an RNA hairpin from HRV-14.

The 5' noncoding region of the picornaviral genome begins with a cloverleaf which is required for viral replication, due at least in part to an interaction with the viral RNA polymerase as part of a fusion with the predominant viral protease. The necessary region of the cloverleaf has previously been narrowed to a highly conserved stem-loop. The solution structure of a 14-nucleotide RNA hairpin, which is part of the conserved stem-loop from human rhinovirus isotype 14, is presented here. The secondary structure of the hairpin is identical to predictions: a five base pair stem is bounded by a triloop with sequence UAU. However, the fold of the triloop is novel, with stacking of the second loop base onto the closing base pair of the stem, and deviations from A form geometry are introduced into the stem regions bordering the triloop, particularly on the 3' side. These deviations and the associated triloop structure could help to explain the distinct sequence conservation and mutational analysis data observed for the stem region of the hairpin, as compared to a second sequentially similar stem in the intact stem-loop.

5' Untranslated Regions↗
PubMed2001

Role of excitons in electron- and photon-stimulated desorption of neutrals from alkali halides.

Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields I2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the gamma3/2-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 with hyperthermal velocity and is in competition with self-trapping. Spin memory of the gamma-exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides.

Journal Article↗
PubMed2001

pH-induced folding of an apoptotic coiled coil.

Par-4 is a 38-kD protein pivotal to the apoptotic pathways of various cell types, most notably prostate cells and neurons, where it has been linked to prostate cancer and various neurodegenerative disorders including Alzheimer's and Huntington's diseases and HIV encephalitis. The C-terminal region of Par-4 is responsible for homodimerization and the ability of Par-4 to interact with proposed effector molecules. In this study, we show that the C-terminal 47 residues of Par-4 are natively unfolded at physiological pH and temperature. Evidence is rapidly accumulating that natively unfolded proteins play an important role in various cellular functions and signaling pathways, and that folding can often be induced on complexation with effector molecules or alteration of environment. Here we use primarily CD studies to show that changes in the environment, particularly pH and temperature, can induce the Par-4 C terminus to form a self-associated coiled coil.

Amino Acid Sequence↗
PubMed2000

alpha(1)-adrenoceptor subtypes differentially couple to growth promotion and inhibition in Chinese hamster ovary cells.

We have compared the coupling of human alpha(1A)-, alpha(1B)-, and alpha(1D)-adrenoceptors (expressed at approximately 2000 fmol/mg protein in Chinese hamster ovary cells) to cellular growth promotion (as assessed by [(3)H]thymidine incorporation) and related signaling mechanisms. Maximum elevation of intracellular Ca(2+) by the three subtypes occurred with the rank order alpha(1A) (1691 nM) > alpha(1D) (1215 nM) > alpha(1B) (360 nM). In contrast, activation of the ERK, JNK, and p38 forms of mitogen-activated protein kinases occurred with the rank order alpha(1D) > alpha(1A) > alpha(1B). alpha(1A)-Adrenoceptor stimulation inhibited basal and growth factor-stimulated [(3)H]thymidine incorporation by 74%, and this was mitigated by p38 inhibition. In contrast, alpha(1D)-adrenoceptor stimulation enhanced cellular growth by 136%, and this was blocked by two distinct inhibitors of ERK activation. We conclude that within a given cell type alpha(1)-adrenoceptor subtypes can have opposite effects on cellular growth, although their proximal signal transduction displays only quantitative differences.

Animals↗
PubMed2000

Inconsistent relation of MAPK activation to infarct size reduction by ischemic preconditioning in pigs.

The importance of the activation of mitogen-activated protein kinases (MAPK) for the cardioprotection achieved by ischemic preconditioning (IP) is still controversial. We therefore measured infarct size and p38, extracellular signal-regulated kinase (ERK), and c-Jun NH(2)-terminal kinase (JNK) MAPK phosphorylation (by biopsies) in enflurane-anesthetized pigs. After 90 min low-flow ischemia and 120 min reperfusion, infarct size averaged 18.3 +/- 12.4 (SD)% (group 1, n = 14). At similar subendocardial blood flows, IP by 10 min ischemia and 15 min reperfusion (group 2, n = 14) reduced infarct size to 6.2 +/- 5.1% (P < 0.05). An inconsistent increase in p38, ERK, and p54 JNK phosphorylation (by Western blot) was found during IP; p46 JNK phosphorylation increased with the subsequent reperfusion. At 8 min of the sustained ischemia, p38, ERK, and p54 JNK phosphorylation were increased with no difference between groups (medians: p38: 207% of baseline in group 1 vs. 153% in group 2; ERK: 142 vs. 144%; p54 JNK: 171 vs. 155%, respectively). MAPK phosphorylation and reduction of infarct size by IP were not correlated, thus not supporting the concept of a causal role of MAPK in mediating cardioprotection by IP.

Animals↗
PubMed1999

Differential regulation of 46 and 54 kDa jun N-terminal kinases and p38 mitogen-activated protein kinase by human alpha(1A)-adrenoceptors expressed in Rat-1 cells.

We have investigated the alpha(1A)-adrenoceptor-mediated activation of 46 and 54 kDa isoforms of c-jun N-terminal kinase (JNK) and of p38 mitogen-activated protein kinase. The alpha(1)-adrenoceptor agonist phenylephrine activated all three kinases but with different time courses and maximal effects. Activation of all three kinases was insensitive to the phosphatidylinositol-3-kinase inhibitor wortmannin but was enhanced by the protein kinase C inhibitor bisindolylmaleimide I; a protein kinase C-activating phorbol ester inhibited JNK but not p38 activation. Activation of 54 kDa JNK, but not of the other two kinases, was inhibited by pertussis toxin and the phospholipase C inhibitor U 73,122. We conclude that alpha(1)-adrenoceptor stimulation activates 46 kDa JNK, 54 kDa JNK and p38 but uses at least partly different pathways to do so.

Adrenergic alpha-Agonists↗
PubMed1998

Axial synergies in parkinsonian patients during voluntary trunk bending.

During upper trunk movements, the axial kinematic synergies (opposite movements of upper and lower segments) preserve the balance by minimizing the antero-posterior center of gravity (CG) shift due to the movement. Forward and backward upper trunk movements were analyzed in a population of parkinsonian patients (PD) that were subject to falling, in order to determine whether an impaired control of the kinematic synergies might explain the falling. Ten PD (stage III-IV of the Hoehn and Yahr classification; Hoehn MM, Yahr MD. Parkinsonism: onset, progression and mortality. Neurology 1967;17;427-432) were compared to seven age-matched control subjects (CS). Kinematic analysis and force platform recordings were carried out. Principal Component (PC) analysis was performed to measure the coupling between hip, knee and ankle joint angles during the movement. (1) In both PD and CS, the first principal component (PC1) was found to account for 98% or more of the joint angles changes, which indicates that there exists a strong coupling between the angles during the movement; however, the part of the movement not accounted for by PC1 was twice as high in PD as in CS. (2) The intertrial variability between the angle ratios was about twice as high in PD as in CS. (3) The absolute value of the antero-posterior CG shift occurring during the movement significantly increased in PD in the case of backward movements, both fast and slow. (4) As a high correlation was found between actual CG shift and its estimation based on the observed interjoint coordination, the increased CG shift in PD was related to unproper set of ratios between joint angles. It was concluded that the control of the kinematic synergy is preserved on the whole in PD, with an increased variability and unproper set of the ratios between joint angular changes. This may lead to CG shifts to beyond the support surface, especially in backward bending. Copyright 1998 Elsevier Science B.V.

Journal Article↗
PubMed1998

Axial synergies during human upper trunk bending.

Upper trunk bending movements were accompanied by opposite movements of the lower body segments. These axial kinematic synergies maintained equilibrium during the movement performance by stabilizing the center of gravity (CG), which shifted on average across all the subjects by 1 +/- 4 cm in the anteroposterior direction and thus always remained within the support area. The aim of the present investigation was to provide an insight into the central control responsible for the performance of these synergies. The kinematic analysis was performed by the method of principal components (PC) analysis applied to the covariation between ankle, knee and hip joint angles and compared with CG shifts during upper trunk bending. Subjects were asked to perform backward or forward upper trunk bending in response to a tone. They were instructed to move as fast as possible or slowly (2 s), with high or low movement amplitudes. PC analysis showed a strong correlation between hip, knee and ankle joint changes. The first principal component (PC1) representing a multijoint movement with fixed ratios between joint angular changes, accounted, on average, for 99.7% +/- 0.2% of the total angular variance in the forward trunk movements and for 98.4% +/- 1.4% in the backward movements. The instructed voluntary regulation of the amplitude and velocity of the movement was achieved by adapting the bell-shaped profile of the velocity time course without changes in interjoint angular relations. Fixed ratios between changes in joint angles, represented by PC1, ensured localization of the CG within the support area during trunk bending. The ratios given by PC1 showed highly significant dependence on subjects, suggesting the adaptability of the central control to each subject's biomechanical peculiarities. Subject's intertrial variability of PC1 ratios was small, suggesting a stereotyped automatic interjoint coordination. When changing velocity and amplitude of the movement, the ratios remained the same in about half the subjects while in others slight variations were observed. A weak second principal component (PC2) was shown only for fast movements. In forward movements PC2 reflected the early knee flexion that seems related to the disturbances caused by the passive interaction between body segments, rather than to the effect of a central command. In fast backward movements, PC2 reflected the delay in hip extension relative to the movement onset in the ankle and knee that mirrors intersubject differences in the initiation process of the axial synergy. The results suggest that PC1 reflects the centrally controlled multijoint movement, defining the time course and amplitude of the movement and fixing the ratios between changes in joint angles. They support the hypothesis that the axial kinematic synergies result from a central automatic control that stabilizes the CG shift in the anteroposterior direction while performing the upper trunk bending.

Adaptation, Physiological↗
PubMed1998

Stimulation of alpha1A-adrenoceptors in Rat-1 cells inhibits extracellular signal-regulated kinase by activating p38 mitogen-activated protein kinase.

In Rat-1 fibroblasts, endothelin-1 and a protein kinase C-stimulating phorbol ester stimulated extracellular signal-regulated kinase (ERK), whereas phenylephrine, acting at stably transfected human alpha1A-adrenoceptors, inhibited basal and endothelin-1- and phorbol ester-stimulated ERK. On the other hand, phenylephrine stimulated p38 mitogen-activated protein kinase (MAPK). Anisomycin caused p38 activation and ERK inhibition quantitatively similar to those produced by phenylephrine. SB 203,580, an inhibitor of p38, significantly attenuated phenylephrine- and anisomycin-induced ERK inhibition. The ERK inhibition by phenylephrine was not affected by the cytosolic phospholipase A2 inhibitor arachidonyltrifluoromethyl ketone or the cyclooxygenase inhibitor indomethacin but was significantly attenuated by a combination of the phosphatase inhibitors Na3VO4 and okadaic acid. Neither SB 203,580 nor the phosphatase inhibitors significantly affected ERK inhibition by the adenylyl cyclase activator forskolin. We conclude that there is a previously unrecognized interaction between ERK and p38 MAPK, in which activation of p38 causes inhibition of ERK; this may at least partly involve MAPK phosphatases that inactivate ERK.

Animals↗
PubMed1997

Repair pattern in the beta-globin gene cluster of human fibroblasts after ultraviolet irradiation.

We have developed a novel technique to determine repair of structurally different DNA lesions. It was used to address the question of whether DNA repair in the absence of transcription occurs in a uniformly random manner or with preferences for certain regions. Human fibroblasts were exposed to ultraviolet light (3-10 J/m2) and treated with 7.5 mM hydroxyurea to inhibit replicative DNA synthesis. During the first hours after irradiation cells were treated with 5-bromodeoxyuridine to label the regions undergoing repair, with the presumption that the regions that have been more efficiently repaired would incorporate more of the nucleoside. A 155-kb DNA sequence containing the entire human beta-globin domain was reconstructed using sequences deposited in the EMBL gene bank. Twelve uniformly long single-copy RNA probes spanning the beta-globin cluster were synthesised in vitro and immobilized on microtiter plates. They were hybridized with DNA from the irradiated cells. The amount of 5-bromodeoxyuridine, incorporated as a result of repair in the DNA fractions hybridized to the different RNA probes, was determined immunochemically using antibody to this nucleoside. By this technique we registered increased repair efficiency in the zone of the permanent scaffold attachment region at the 5'-end of the beta-globin domain during the first hours after ultraviolet irradiation. This result was confirmed and by the more conventional T4 endonuclease V technique detecting the removal of cyclobutane pyrimidine dimers.

Bromodeoxyuridine↗
PubMed1996

Is the center of gravity controlled during upper trunk movements?

The question was addressed in this study as to whether the kinematic synergy responsible for equilibrium control during upper trunk movements may involve an actual evaluation of the weight of the body segments. Five adult subjects were asked to bend the upper trunk forward or backward to an angle of about 35 degrees, first without any load and then with a 10 kg load fixed to their shoulders. The center of gravity (CG) shift in the sagittal direction which occurred at the end of the movement was compared versus without a load. Two patterns of CG shift were identified. In the first pattern shown by three subjects in forward and three in backward trunk bending, the CG shift remained the same, while in the other pattern (two subjects for forward and two for backward trunk bending), the CG shift increased by an amount corresponding to the purely mechanical effect of the load. These results indicate that the actual weight of the segments may be evaluated on the basis of sensory inputs and may be responsible for a change in the kinematic synergy which preserves the CG control during the upper trunk movement.

Adaptation, Physiological↗
PubMed1996

mRNA stabilization in continuous flow translation system.

In contrast with standard in vitro translation systems, where 1 to 2 copies of polypeptide per mRNA molecule are produced, the continuous flow cell-free translation system is able to synthesize hundreds of polypeptide molecules per one mRNA molecule. Our investigations have shown that the poor yield obtained in the standard analytical system is due to rapid mRNA decay as opposed feedback inhibition by low molecular weight translation by products. In contrast, continuous flow system was found to stabilize mRNA for up to two-three days. RNAse activity can not be removed from wheat germ extract unless mRNA is added and compartmentalization of the translational machinery occurs.

Cell-Free System↗