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Biomedical subjects

M Vos

Publications and source records attributed to M Vos.

At least 19 recordsLinked to original sources
PubMed2003

Comparison of electron and neutron compton scattering from entangled protons in a solid polymer.

We present, for the first time, a direct comparison between electron (ECS) and neutron (NCS) Compton scattering results from protons of a solid polymer. The momentum distributions of hydrogen obtained from ECS and NCS are in excellent agreement. In both experiments, a strong "anomalous" shortfall in the scattering intensity of protons [first detected in liquid water with NCS [Phys. Rev. Lett. 79, 2839 (1997)]]] is found ranging from about 20% up to 50%, depending on the momentum transfer applied. The characteristic times of electron- and neutron-proton collisions lie in the subfemtosecond range. The presented ECS and NCS results provide further direct evidence for this striking effect, which has been ascribed to attosecond quantum entanglement of the protons.

Journal Article↗
PubMed2000

Reactivity of ether- and amine-complexed dimers and tetramers of alkyllithiums towards triphenylmethane.

Kinetics of Lewis base (LB) complexed primary and secondary sigma-alkyllithiums (RLi) with triphenylmethane (TPMH) are reported. RLis in which one or two LB groups (-OMe, -NMe, -NMeR) are part of the molecule form, in benzene, intramolecularly complexed tetramers, for example, 2(4), or dimers, for example, 4(2). They are used as models for their intermolecular congeners R4Li4 x 4LB and R2Li2 x 4LB (LB = NR'3, OR'2). Nonunity reaction orders in [RLi] are in line with reactions via as yet unidentified 1:1 complexes formed in an equilibrium (K(stat. corr.) approximately = 1) between aggregated RLi and TPMH. In some cases, a tetramer/dimer equilibrium mixture undergoes complexation/reaction. Reaction rates correlate linearly with calculated concentrations of the complexes. Relative rates of complexes range from 1 [prim-R4Li4 x 3LB x TPMH (presumed)] to 4250 [sec-R2Li2 x 3LB x TPMH (presumed)]. A major role in the reactivity enhancement owing to LB-induced conversion of tetramers into dimers is ascribed to increased LB participation in LB-richer dimer transition states. Amine and ether complexes have practically equal reactivities. Lithiation of TPMH by dimeric RCH2Li is retarded by a factor of 24000 if a silyl group is linked to the alpha-carbon.

Journal Article↗
PubMed2000

Expression of proadrenomedullin derived peptides in the mammalian pituitary: co-localization of follicle stimulating hormone and proadrenomedullin N-20 terminal peptide-like peptide in the same secretory granules of the gonadotropes.

Expression of proadrenomedullin-derived peptides in the rat, cow and human pituitary was studied by a variety of techniques. Immunocytochemical detection showed a widespread expression of adrenomedullin peptide in the adenohypophysis and the neural lobe, with low expression in the intermediate pituitary. Proadrenomedullin N-20 terminal peptide (PAMP)-immunoreactivity was also present in the anterior pituitary but showed a more marked heterogeneous distribution, with cells going from very strong to negative immunostaining. Lower levels of PAMP were found in the neural lobe. Interestingly, the distribution of adrenomedullin and PAMP immunoreactivity in the anterior pituitary did not completely overlap. In the present study, we concentrated our efforts to determine which cell type of the adenohypophysis expresses PAMP. Paraffin and semithin serial sections immunostained for PAMP and the classical pituitary hormones revealed that a subpopulation of the gonadotropes expresses high levels of PAMP-immunoreactive material. Ultrastructural analysis clearly showed PAMP-immunoreactivity in the follicle stimulating hormone (FSH)-containing large secretory granules of the gonadotropes, suggesting simultaneous secretion of PAMP and FSH by this cell type. Three mouse adenohypophysis-derived cell lines (AtT20, GH3, and alphaT3-1 derived from corticotropes, lacto/somatotropes and gonadotropes, respectively) were also analysed and showed expression of both proadrenomedullin-derived peptides and their mRNA. Functional studies in these three cell lines showed that neither adrenomedullin nor PAMP was able to stimulate cAMP production in our experimental conditions. Taken together, our results support that proadrenomedullin derived peptides are expressed in the pituitary in cell-specific and not overlapping patterns, that could be explained by differences in postranslational processing. Our data showing costorage of PAMP and FSH in the same secretory granules open a way by which PAMP could be involved in the control of reproductive physiology in a coordinated manner with FSH.

Adrenomedullin↗
PubMed1999

Rapid genomic diversification of Helicobacter pylori.

Helicobacter pylori was cultured from antrum and corpus gastric biopsies from 65 patients originating from two separate groups: (i) a geographically linked group and (ii) a geographically nonlinked group. Genomic DNA was recovered from the clinical isolates and subjected to restriction fragment length polymorphism (RFLP) analysis after digestion with DraI. Southern blots were probed with the oligonucleotide (GTG)5, the riboprobe pKK3535, and the cagA gene probe pMC3. (GTG)5 and cagA DNA fingerprints and ribopatterns suggested that most of the patients were infected with their own unique strain; however, some were infected with multiple strains. Minor genomic differences were detected in many antrum/corpus sample pairs (clonal variants), suggesting rapid evolutionary change in domains detected by (GTG)5. The high degree of genomic diversity detected by (GTG)5 may reflect structural versatility of these domains. The genomic diversity indicates that infection by H. pylori in a defined community does not appear to be limited to certain RFLP types.

Adolescent↗
PubMed1999

Autocrine growth loops dependent on peptidyl alpha-amidating enzyme as targets for novel tumor cell growth inhibitors.

Many small cell lung tumors are dependent in vitro and in vivo on autocrine growth loops. The prototypical small cell lung cancer autocrine growth factor, gastrin-releasing peptide (GRP), is one of many peptide hormones which require post-translational carboxy-terminal alpha-amidation for bioactivity. We have reported that neuroendocrine human lung tumor cell lines express the bifunctional enzyme PAM which catalyzes the biosynthesis of alpha-amidated peptides in a two-step process, and have recently shown that non-small cell lung cancer cell lines and tumors, generally considered to be non-endocrine in nature, also express PAM. We have also shown that two chemical classes of PAM inhibitors, substrate analogues and specific copper chelators, inhibit amidating enzyme activity in cell-free extracts. Here we demonstrate in vitro growth inhibition of lung cancer tumor cell lines by both these classes of PAM inhibitors using the MTT assay and the clonogenic assay. Growth inhibition in a small cell lung cancer cell line can be overcome by exogenous addition of synthetic alpha-amidated GRP. Similar growth-suppressive effects are seen in cell lines stably transfected with a vector expressing antisense PAM RNA. These data support the mechanism of inhibition for a new type of chemotherapeutic/intervention agent, directed at synthesis and activation of peptide growth factors, and support our postulate that alpha-amidated peptide hormones are a common component in lung tumor autocrine growth biology which can be inhibited by targeting the biochemical mechanisms necessary for growth factor synthesis.

Anti-Bacterial Agents↗
PubMed1998

5-Lipoxygenase inhibitors reduce PC-3 cell proliferation and initiate nonnecrotic cell death.

BACKGROUND: Products of the arachidonic acid-metabolizing enzyme, 5-lipoxygenase, stimulate the growth of several cell types. Selective inhibitors of the enzyme, including SC41661A and MK886, reduce PC-3 prostate cell proliferation. With continued culture, cells die, but the mode of death, necrotic or nonnecrotic, has not been established. METHODS: Flow cytometry, laddering after agarose electrophoresis of DNA from inhibitor-treated cells, and light and electron microscopy were employed to examine the type of death in PC-3 prostate cells cultured with either 5-lipoxygenase inhibitor. RESULTS: The inhibitors induced nonnecrotic, programmed cell death. SC41661A-treated cells exhibited "foamy," vacuolated cytoplasm and mitochondria with disrupted cristae and limiting membranes, while some cells contained numerous polysomes and extended hypertrophic Golgi and secretory cisternal networks. A proportion of the treated cells detached and the nuclei of these cells were characteristic of type 1 "apoptotic" programmed cell death. MK886, a 5-lipoxygenase-inhibitor with a different mechanism of action, induced nonnecrotic changes largely confined to the cytoplasm, most consistent with type 2 "autophagic" programmed cell death. In preliminary studies of mechanism, we demonstrated that PC-3 cells express mRNA for 5-lipoxygenase and for 5-lipoxygenase-activating protein. The less active inhibitor, SC45662 neither reduced proliferation nor induced DNA laddering. The antioxidant, N-acetyl-l-cysteine but not butylated hydroxy toluene or alpha tocopherol, partially reduced the inhibition of proliferation from SC41661A. CONCLUSIONS: SC41661A and MK886 inhibit PC-3 cell proliferation and induce a form of type 1 or type 2 programmed cell death, respectively. PC-3 cells contain messenger RNA for 5-lipoxygenase and 5-lipoxygenase-activating proteins. Drug-induced changes included altered redox potential, inferred from the increased survival due to the antioxidant and glutathione precursor, N-acetyl-l-cysteine. PC-3 cells are an appropriate model for studying the mechanism responsible for 5-lipoxygenase inhibitor-induced cellular suicide.

Amides↗
PubMed1998

Transvenous cold mapping and cryoablation of the AV node in dogs: observations of chronic lesions and comparison to those obtained using radiofrequency ablation.

INTRODUCTION: Radiofrequency (RF) is the most commonly used energy source for the treatment of cardiac arrhythmias. Surgical experience has shown that cryoablation also is effective for ablating arrhythmias. The aims of this study were to (1) investigate the feasibility of inducing permanent complete AV block (CAVB), (2) investigate the value of cold mapping to select the cryoablation site to produce permanent CAVB, (3) study the macro- and microscopic lesion characteristics 6 weeks later, and (4) compare them to those produced with RF energy. METHODS AND RESULTS: A new steerable 8.5-French bipolar electrode catheter having a thermocouple with a 3-mm tip using N2O as the refrigerant controlled by a cryoconsole was used. Six mongrel dogs were anesthetized, and the catheter was positioned via the femoral vein across the tricuspid valve to record a large low right atrial and a small His-bundle potential. After cold mapping (-15 degrees to -20 degrees C tip temperature) resulted in ECG modifications, cryothermia (-70 degrees C) was given twice, lasting 5 minutes each, to create permanent CAVB (Cryo group). Additionally, RF catheter ablation of the AV node was performed in two anesthetized mongrel dogs (RF group). In the Cryo group, a permanent proximal CAVB was created in four dogs (block occurred within 10 to 20 sec of cryothermia). Permanent right bundle branch block was obtained in one dog and transient CAVB in the remaining dog. In both dogs of the RF group, permanent CAVB was obtained. The cryolesions consisted of well-circumscribed, homogeneous areas of fibrotic tissue without viable cardiomyocytes. Lesions produced with RF were less circumscribed and inhomogeneous, with clear evidence of viable cardiomyocytes and cartilage formation (patchy lesions). CONCLUSIONS: (1) Permanent CAVB can be created by using a steerable cryoablation catheter. (2) Histologically, cryoablated sites were homogeneous and showed fibrotic tissue without signs of chronic inflammation and no evidence of viable myocytes. (3) Lesions created with RF were less homogenous and still contained viable myocytes within the lesion and cartilage formation. (4) The arrhythmogenic significance of these differences requires further study. (5) The technology of using reversible cold mapping has the potential to identify the successful ablation site and warrants further clinical study.

Animals↗
PubMed1998

Expression of heterogeneous nuclear ribonucleoprotein A2/B1 changes with critical stages of mammalian lung development.

Recent reports have demostrated a link between expression of members of the family of heterogeneous nuclear ribonucleoproteins (hnRNPs) and cancer. Overexpression of hnRNP A2/B1 correlated with the eventual development of lung cancer in three different clinical cohorts. We have studied the expression of hnRNP A2/B1 messenger RNA (mRNA) and protein during mammalian development. The expression of hnRNP A2/B1 mRNA and protein are parallel but change dynamically during critical periods in mouse pulmonary development. hnRNP A2/B1 is first detected in the lung in the early pseudoglandular period, peaks at the beginning of the canalicular period, and remains high during the saccular (alveolar) period. In mouse and rat, hnRNP A2/B1 expression is first evident in the earliest lung buds. As lung development progresses, the cuboidal epithelial cells of the distal primitive alveoli show high levels of the ribonucleoprotein, which is almost undetectable in the proximal conducting airways. The expression of hnRNP A2/ B1 is restricted in mature lung. Similar dynamic pattern of expression through lung development was also found in rat and human lung. Upregulated expression of hnRNP A2/B1 at critical periods of lung development was comparable to the level of expression found in lung cancers and preneoplastic lesions and is consistent with hnRNP A2/B1 overexpression playing an oncodevelopmental role.

Animals↗
PubMed1997

Arrhythmia risk: electrophysiological studies and monophasic action potentials.

Shortly after in the introduction of programmed electrical stimulation (PES) of the heart to study and localize cardiac arrhythmias in the intact human heart, the technique was used for risk stratification of the arrhythmia patient. Two decades later we have to conclude that especially in ventricular arrhythmias the technique of PES did not live up to our expectations and the left ventricular function is a better long-term predictor than the induction of ventricular arrhythmias or the ability to find an antiarrhythmic drug able to prevent the initiation of the classically documented ventricular arrhythmia. Another sobering finding came from the analysis of the characteristics of the patient dying suddenly out-of-hospital, which showed that most of those patients could not be classified before the event as being at high risk using noninvasive or invasive testing, not even in those with a previous cardiac history. Monomorphic action potential (MAP) recordings have been of importance in our understanding of torsade de pointe arrhythmias in congenital and acquired QT prolongation. A major problem in case of a less generalized electrophysiological abnormality is the identification of the appropriate place where to put the MAP-electrode.

Action Potentials↗
PubMed1997

Recent molecular advances in the approach to early lung cancer detection and intervention.

Lung cancer is a major contributor to overall cancer mortality. Detecting lung cancer while it is still a localized process is a long-cherished goal for improving the outcome of this disease. Recent developments suggest that we are approaching this capability. We next have to think about how to implement a change in our approach to lung cancer management to derive the benefit of better detection capability. This is an area in which our growing understanding of lung cancer biology is providing clues on improving the inhibition of cancer progression.

Apoptosis↗
PubMed1996

Insulin-like growth factor expression in human cancer cell lines.

The insulin-like growth factors (IGFs), IGF-I and IGF-II, are potent mitogens for human lung and other epithelial cancer cell lines. Previous studies in defined medium lacking added IGF or insulin suggest that an IGF-related ligand can act as an autocrine growth factor for many cancer cell lines through action via the type I IGF receptor (IGF-R). Analysis of RNA isolated from human lung and breast cancer cell lines by reverse transcription of mRNA and polymerase chain reaction reveal that IGF-I and IGF-II mRNAs were co-expressed with IGF-R in the majority of cell lines. IGF-I mRNA was detected in 11/12 small cell lung cancer cell lines (SCLC), 13/14 nonsmall cell lung cancer (NSCLC) cell lines, and 1/2 breast cancer cell lines. IGF-II mRNA was detected in 8/10 SCLC, 11/12 NSCLC cell lines, and 2/2 breast lines. All cell lines expressed IGF-R. For analysis of IGF peptide secretion, cell lines were adapted to growth in serum/hormone-free culture medium (R0), and to avoid interference by IGF-binding proteins, secreted IGF peptides were isolated under acidic conditions and analyzed by Western blotting. Based upon measurement of the sensitivity of the anti-IGF antibodies for detection of recombinant human IGFs, IGF peptides accumulated in conditioned medium at greater than picomolar concentrations should have been readily detected. In three cell lines (two lung and one breast) secreted IGF immunoreactivity was detected as three molecular mass species of 23, 14, and 6 kDa. Isolation and NH2-terminal sequencing of each of these species definitively identified them as differentially processed forms of the IGF-II prohormone. Despite the high frequency of IGF-I gene expression detected by reverse transcription-polymerase chain reaction analysis, only one lung cancer cell line, NCI-N417d, was found that unequivocally secreted IGF-I peptide. This direct sequence determination unambiguously identifies IGF-II as the predominant IGF involved in the autocrine growth stimulation of human lung and breast epithelial tumor cell lines and supports a growing body of literature that implicates IGF-II/IGF-R autocrine loops as a common growth mechanism in epithelial carcinogenesis.

Adenocarcinoma↗
PubMed1996

Development of Molecular Approaches to Early Lung Cancer Detection.

Lung cancer has been particularly recalcitrant to standard therapeutic interventions. Improvement in the outcome for this disease requires the ability to identify the disease while it is still localized in the airways. Usually, radiation therapy to eliminate this disease fails because of progression of the cancer outside the radiation treatment ports. This is a failure of the diagnostic modalities to detect the extent of the cancer, not a failure of the radiation. With new epithelial-directed diagnostics, the ability to detect the premetastatic phase of lung cancer is emerging. Evolution of the screening infrastructure will be required to allow percolation of this technology out to the medical community, so that a benefit in cancer mortality reduction can be achieved. Some development issues will have to be resolved. Considering our fragmentary understanding of pulmonary carcinogenesis, the heterogeneity of lung cancer suggests that a panel of biomarkers instead of a single marker will be required to clarify the status of an individual's epithelium. However, the data output from multiplexed bioassays performed on large clinical populations will require better integration of information technology to optimize analysis and reporting of test results. An important new area for outcomes research is the systematic analysis of population screening approaches. With population sampling algorithms, selective screening. This type of research requires careful clinical validation. Finally, the general acceptance of population-based screening will be determined by the availability of effective interventions to complement the new diagnostic tools. New measures to prevent the progression of early cancer will be discussed.

Journal Article↗
PubMed1994

Isolation and functional expression of human pancreatic peptidylglycine alpha-amidating monooxygenase.

Pancreastatin (PST) is processed from chromogranin A and the C-terminal amide of the peptide is an absolute requirement for biological activities. Human pancreatic carcinoma cells QGP-1 which produce both chromogranin A and PST were used to isolate cDNAs encoding two forms of peptidylglycine alpha-amidating monooxygenase (PAM). The two forms are a full length bifunctional enzyme and a variant lacking the transmembrane domain-coding region. When the cDNAs of these two forms were expressed in COS-7 cells, cells transfected with the predicted soluble form released into the culture medium a very much higher amidating activity which converts human chromogranin A-(273-302) to PST-29. The optimal pH for amidating activity was 5.4 and Cu2+, ascorbate and catalase were required as cofactors for the both forms of PAM. Km values for the membrane-bound and the soluble forms of PAM were 15.7 +/- 3.1 microM and 12.4 +/- 1.6 microM, respectively. These results demonstrate that both forms of PAM can function in the posttranslational processing of chromogranin A to PST in the environment of a secretory vesicle.

Amino Acid Sequence↗