Biomedical subjects

M Michaelis

Publications and source records attributed to M Michaelis.

At least 19 recordsLinked to original sources

PubMed2006

Covalent linkage of apolipoprotein e to albumin nanoparticles strongly enhances drug transport into the brain.

Drug delivery to the brain is becoming more and more important but is severely restricted by the blood-brain barrier. Nanoparticles coated with polysorbates have previously been shown to enable the transport of several drugs across the blood-brain barrier, which under normal circumstances is impermeable to these compounds. Apolipoprotein E was suggested to mediate this drug transport across the blood-brain barrier. In the present study, apolipoprotein E was coupled by chemical methods to nanoparticles made of human serum albumin (HSA-NP). Loperamide, which does not cross the blood-brain barrier but exerts antinociceptive effects after direct injection into the brain, was used as model drug. Apolipoprotein E was chemically bound via linkers to loperamide-loaded HSA-NP. This preparation induced antinociceptive effects in the tail-flick test in ICR mice after i.v. injection. In contrast, nanoparticles linked to apolipoprotein E variants that do not recognize lipoprotein receptors failed to induce these effects. These results indicate that apolipoprotein E attached to the surface of nanoparticles facilitates transport of drugs across the blood-brain barrier, probably after interaction with lipoprotein receptors on the brain capillary endothelial cell membranes.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Valproic acid induces extracellular signal-regulated kinase 1/2 activation and inhibits apoptosis in endothelial cells.

The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was recently shown to inhibit angiogenesis, but displays no toxicity in endothelial cells. Here, we demonstrate that VPA increases extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation in human umbilical vein endothelial cells (HUVEC). The investigation of structurally modified VPA derivatives revealed that the induction of ERK 1/2 phosphorylation is not correlated to HDAC inhibition. PD98059, a pharmacological inhibitor of the mitogen-activated protein kinase kinase 1/2, prevented the VPA-induced ERK 1/2 phosphorylation. In endothelial cells, ERK 1/2 phosphorylation is known to promote cell survival and angiogenesis. Our results showed that VPA-induced ERK 1/2 phosphorylation in turn causes phosphorylation of the antiapoptotic protein Bcl-2 and inhibits serum starvation-induced HUVEC apoptosis and cytochrome c release from the mitochondria. Moreover, the combination of VPA with PD98059 synergistically inhibited angiogenesis in vitro and in vivo.

Angiogenesis Inhibitors↗

PubMed2005

Characterization of drug-resistant neuroblastoma cell lines by comparative genomic hybridization.

Three parental neuroblastoma cell lines and nine derived lines resistant to Vincristin, Doxorubicin and Cisplatin, respectively, using CGH were studied. CGH profiles of all three parental cell lines were obtained using DNA from a healthy volunteer as reference DNA. Labeled DNA from each of the drug resistant daughter cell lines and labeled DNA from their parental sensitive cell lines were hybridized to obtain a comparison of gains and losses that accompanied the development of resistance for that particular drug. All three parental cell lines were characterized by typical findings for high risk neuroblastoma: N-myc amplification, gain of 17q, and loss of 1p36.2-36.3. Acquired drug resistance in the neuroblastoma cell lines appeared to be accompanied by a large array of DNA sequence copy number changes. The regions frequently affected in chemo-resistant cell lines included gains of 13q14.1-32, and 7q11.2-31.3, 4 q. Amplifications were seen at 7q 21.1 consistent with MDR1 amplification in UKF-NB-2 VCR, UKF-NB-3 DOXO, UKF-NB-4 VCR, and UKF-NB-4 DOXO, but not in any Cisplatin resistant line. All Cisplatin and Doxorubicin and two Vincristin resistant line (UKF-NB-2 VCR and UKF-NB-4 VCR) had a deletion of part of 19q or the whole 19 chromosome. All lines resistant to Vincristin or Doxorubicin and two Cisplatin resistant lines (UKF-NB-2 CDDP and UKF-NB-4 CDDP) had a deletion of at least part of 17q, UKF-NB-4 DOXO had deletion of the whole chromosome 17. The loss of 17q may cause chemoresistance by deletion of topoisomerase IIalpha gene. Deletion of 19 q in all but one chemo-resistant lines may influence of cytochromes P450 genes which are located on 19q13.2. Also gains of 15q 22, which were detected in UKF-NB-4 VCR, UKF-NB-2 DOXO and UKF-NB-4 DO X O, may affect other cytochromes P450 genes.

Antineoplastic Agents↗

PubMed2004

Cytomegalovirus infection blocks apoptosis in cancer cells.

Recent pathological findings reveal a higher frequency of human cytomegalovirus (HCMV) in tumor cells from different tumors compared with surrounding tissues. Experimental investigations suggest possible supportive effects of HCMV for tumor development and progression. One HCMV effect on tumor cells is the inhibition of apoptosis, leading to the promotion of tumor cell survival. Decreased sensitivity to treatment-induced tumor cell death is a major reason for failure of anticancer chemotherapy. HCMV infection interferes with both the intrinsic and extrinsic cellular apoptosis pathways. HCMV promotes cell survival signaling influencing the tumor suppressor p53 and its relative p73, and stimulates the antiapoptotic Ras/Raf/MEK/Erk- and PI-3K-signaling pathways. Antiapoptotic effects mediated by HCMV are inhibited by antiviral treatment in cell culture. Therefore, a better understanding of the influence of HCMV infection on tumor cell apoptosis might translate into improved anti-cancer therapy.

Apoptosis↗

PubMed2004

Infection of cultured intestinal epithelial cells with severe acute respiratory syndrome coronavirus.

To identify a model for the study of intestinal pathogenesis of severe acute respiratory syndrome (SARS) we tested the sensitivity of six human intestinal epithelial cell lines to infection with SARS coronavirus (SARS-CoV). In permissive cell lines, effects of SARS-CoV on cellular gene expression were analysed using high-density oligonucleotide arrays. Caco-2 and CL-14 cell lines were found to be highly permissive to SARS-CoV, due to the presence of angiotensin-converting enzyme 2 as a functional receptor. In both cell lines, SARS-CoV infection deregulated expression of cellular genes which may be important for the intestinal pathogenesis of SARS.

Caco-2 Cells↗

PubMed2002

Antiviral and immunomodulatory activity of the metal chelator ethylenediaminedisuccinic acid against cytomegalovirus in vitro and in vivo.

Antiviral activity of the metal chelator ethylenediaminedisuccinic acid (EDDS) was examined in vitro against human cytomegalovirus (HCMV) wild type strains and strains that are resistant against ganciclovir (GCV) and cidofovir (HPMPC). EDDS inhibited the replication of wild-type as well as GCV- and HPMPC-resistant strains with a 50% effective concentration of 7.4-12 microg/ml. At concentrations of 100 microg/ml EDDS, unlike GCV or HPMPC, suppressed HCMV-induced up-regulation of intercellular adhesion molecule-1 (ICAM-1) and reduced T-cell adhesion to HCMV-infected cells in a monolayer adhesion model. In vitro EDDS inhibited murine cytomegalovirus (MCMV) replication (EC50 8.6 microg/ml) and caused in mice some protection against MCMV induced mortality at a non-toxic dose. Since immunopathological factors may play a significant role in HCMV disease it will be of interest to further study whether EDDS is effective in terms of modulation of inflammatory responses to HCMV infections.

Adjuvants, Immunologic↗

PubMed2001

Modulation of CGRP and PGE2 release from isolated rat skin by alpha-adrenoceptors and kappa-opioid-receptors.

Norepinephrine (NE) reduces the release of neuropeptides from central terminals of primary afferent neurones by presynaptic inhibition. We investigated whether NE also affects stimulus-induced intracutaneous calcitonin gene-related peptide (CGRP) and secondary prostaglandin E2 (PGE2) release. For comparison, kappa-opioid effects were examined. Antidromic electrical nerve stimulation resulted in significant increases in the release of CGRP and PGE2. The PGE2 release was prevented by selective activation of alpha2-adrenoceptors whereas the CGRP release was not changed. In contrast, selective kappa-opioid receptor activation diminished electrically evoked release of both CGRP and PGE2. We conclude that NE affected stimulated PGE2 release via alpha2-adrenoceptors on cells other than cutaneous afferents while kappa-opioid receptors are expressed in peripheral terminals of cutaneous afferents and their activation reduced CGRP release and secondary PGE2 formation.

Adrenergic Antagonists↗

PubMed2001

[Psychological and emotional factors of work experience as an issue for occupational medicine practice in the hospital].

The consideration of psychomental and psychological load of employees is not part of the traditional working sphere of occupational physicians. Medical diagnostics and check-up are still regarded as the primary area of responsibility. This fact might be seen as a drawback with regard to the increasing importance of work-related psychomental load on the one hand and the actual requirements for high-quality occupational medicine on the other. The goal of a study in 64 occupational physicians in hospitals was to find out how occupational physicians estimate their own competence for dealing with psychomental problems of their clients, whether employees trust them, and which personal attitudes can be found towards the importance of work-related psychomental strain. The self-estimation of personal competence was--in contradiction to the results of former studies focusing on employees' views--surprisingly positive. A significant influence is the amount of work within the health-care sector compared to others. This might be interpreted as a selective effect and leads to the need for large-scale studies. Agreement could be found concerning the lack of chances for qualification in this sphere. Hence, further education and training in professional work with psychomental problems at the workplace has to be extended.

Adult↗

PubMed2001

Treatment of drug-resistant human neuroblastoma cells with cyclodextrin inclusion complexes of aphidicolin.

Treatment failure in most neuroblastoma (NB) patients is related to primary and/or acquired resistance to conventional chemotherapeutic agents. Aphidicolin (APH), a tetracyclic diterpene, exhibits specific cytotoxic action against NB cells. The purpose of this study was to compare antitumoral efficacy of APH in parental NB cell lines and cell subclones that exhibit drug resistance to vincristine (VCR), doxorubicin (DOX) and cisplatin. Due to poor solubility of APH in water, gamma-cyclodextrin (gamma-CD) inclusion complexes of APH were used for systemic treatment of xenotransplanted parental and VCR-resistant UKF-NB-3 tumours. APH and its gamma-CD inclusion complexes inhibited growth of parental and drug-resistant NB cells at equimolar doses in vitro. Growth of VCR-sensitive and -resistant NB tumors was inhibited at equal doses in a dose-dependent fashion in vivo. These results indicate that the specific cytotoxic activity of APH against NB cells in vitro and in vivo is independent of cellular mechanisms facilitating drug resistance to conventional chemotherapeutic drugs. Hence, taking into account our previous findings that APH acts synergistically with VCR and DOX, APH might be an additive tool for the therapy of NB and is suitable for evaluation in clinical studies of NB treatment protocols.

Animals↗

PubMed2000

Axotomized and intact muscle afferents but no skin afferents develop ongoing discharges of dorsal root ganglion origin after peripheral nerve lesion.

After peripheral nerve lesions, some axotomized afferent neurons develop ongoing discharges that originate in the dorsal root ganglion (DRG). We investigated in vivo which functional types of afferent neurons contributed to this ectopic activity. Six to twelve days after the gastrocnemius soleus (GS) nerve supplying skeletal muscle and the sural (SU) nerve supplying skin had been transected (experimental group E1), 20.4% of afferent neurons with myelinated axons projecting into the GS nerve produced ongoing discharges of irregular or bursting pattern. In contrast, all SU neurons were silent. Additional transection of peroneal and tibial nerves (group E2) induced ongoing activity in a similar percentage of GS neurons (22.1%), but their mean discharge frequency was higher (6.0 vs 2.7 Hz), and more of them exhibited bursting discharges (63 vs 17%). When the GS nerve had been left intact while tibial, peroneal, and SU nerve had been transected (group E3), 18.8% of unlesioned GS neurons developed ongoing discharges at a mean frequency of 6.1 Hz; most of them exhibited a bursting pattern. Without a preceding nerve lesion, almost no GS neuron (1.1%) fired spontaneously. Most afferent neurons with ongoing activity had an axonal conduction velocity of 5-30 m/sec indicating that some of these neurons may have had nociceptive function. These findings provide the first evidence that after peripheral nerve injury both axotomized as well as intact afferent neurons supplying skeletal muscle but not skin afferents generate ongoing activity within the DRG, probably because of a yet unknown signal in the DRG triggered by axotomy.

Animals↗

PubMed2000

Bovine seminal ribonuclease attached to nanoparticles made of polylactic acid kills leukemia and lymphoma cell lines in vitro.

Bovine seminal ribonuclease (BS-RNase) is a protein with a number of biological effects. It shows antitumoral, aspermatogenic, antiembryonic, immunosuppressive and antiviral properties. The cytotoxic effects appear to be specific for tumor cells as non-malignant cells seem to be unaffected in vitro. Unfortunately, the in vivo application of BS-RNase so far was successful only when it was administered intratumorally. Therefore, the objective of the present investigation was to improve the properties of BS-RNase by attachment to nanoparticles made of polylactic acid (PLA-NP) using an adsorption method. This preparation was tested in vitro against leukemia (MOLT-4) and lymphoma (H9) cell lines sensitive and resistant to cytarabine. No difference between the nanoparticle preparation and pure BS-RNase was found in these tests. To examine the in vivo effects, the preparations were tested for their aspermatogenic and antiembryonal efficacy compared to the pure BS-RNase as a rapid test for antitumoral activity. The aspermatogenic and antiembryonal effects were enhanced by the nanoparticle preparation. Consequently, BS-RNase loaded adsorptively to PLA-NP holds promise for the in vivo use as an antitumoral agent. Further research will investigate the efficacy of this preparations in an in vivo tumor model.

Animals↗

PubMed2000

Cytotoxicity of aphidicolin and its derivatives against neuroblastoma cells in vitro: synergism with doxorubicin and vincristine.

Disseminated neuroblastoma diseases are still indicated by a poor outcome despite treatment regimens including radiation therapy and high-dose chemotherapy with stem cell rescue. Therefore, new substances and treatment regimens are of interest. Aphidicolin (APH), a tetracyclic diterpene antibiotic produced by Cephalosporium aphidicola, has a specific toxicity for neuroblastoma cells. Furthermore, it was shown to enhance the effects of X-ray radiation and chemotherapy on malignant cells. To find new substances, 20 APH derivatives were tested for their anti-neuroblastoma efficacy in vitro in UKF-NB-2 cells. Five derivatives had antitumoral activity in neuroblastoma cells. A relationship between the structure and the antitumoral efficacy showed that the hydroxyl groups at C-3 and C-18 are essential for the antitumoral effects. Furthermore, antitumoral effects of APH in combination with doxorubicin and vincristine, both part of commonly used treatment regimens for disseminated neuroblastoma diseases, were tested in the neuroblastoma cell line UKF-NB-2. APH was found to act synergistically with vincristine and synergistically to additive with doxorubicin depending on the molecular ratio of the substances in combination. This may offer the chance to use APH and its derivatives as additional tools in the treatment of neuroblastomas.

Antineoplastic Agents↗

PubMed2000

Spinal nerve injury enhances subthreshold membrane potential oscillations in DRG neurons: relation to neuropathic pain.

Primary sensory neurons with myelinated axons were examined in vitro in excised whole lumbar dorsal root ganglia (DRGs) taken from adult rats up to 9 days after tight ligation and transection of the L(5) spinal nerve (Chung model of neuropathic pain). Properties of subthreshold membrane potential oscillations, and of repetitive spike discharge, were examined. About 5% of the DRG neurons sampled in control DRGs exhibited high-frequency, subthreshold sinusoidal oscillations in their membrane potential at rest (V(r)), and an additional 4.4% developed such oscillations on depolarization. Virtually all had noninflected action potentials (A(0) neurons). Amplitude and frequency of subthreshold oscillations were voltage sensitive. A(0) neurons with oscillations at V(r) appear to constitute a population distinct from A(0) neurons that oscillate only on depolarization. Axotomy triggered a significant increase in the proportion of neurons exhibiting subthreshold oscillations both at V(r) and on depolarization. This change occurred within a narrow time window 16-24 h postoperative. Axotomy also shifted the membrane potential at which oscillation amplitude was maximal to more negative (hyperpolarized) values, and lowered oscillation frequency at any given membrane potential. Most neurons that had oscillations at V(r), or that developed them on depolarization, began to fire repetitively when further depolarized. Spikes were triggered by the depolarizing phase of oscillatory sinusoids. Neurons that did not develop subthreshold oscillations never discharged repetitively and rarely fired more than a single spike or a short burst, on step depolarization. The most prominent spike waveform parameters distinguishing neurons capable of generating subthreshold oscillations, and hence repetitive firing, was their brief postspike afterhyperpolarization (AHP) and their low single-spike threshold. Neurons that oscillated at V(r) tended to have a more prolonged spike, with slower rise- and fall-time kinetics, and lower spike threshold, than cells that oscillated only on depolarization. The main effects of axotomy were to increase spike duration, slow rise- and fall-time kinetics, and reduce single-spike threshold. Tactile allodynia following spinal nerve injury is thought to result from central amplification ("central sensitization") of afferent signals entering the spinal cord from residual intact afferents. The central sensitization, in turn, is thought to be triggered and maintained in the Chung model by ectopic firing originating in the axotomized afferent neurons. Axotomy by spinal nerve injury enhances subthreshold membrane potential oscillations in DRG neurons, augments ectopic discharge, and hence precipitates neuropathic pain.

Action Potentials↗

PubMed2000

Tamoxifen-bound estrogen receptor (ER) strongly interacts with the nuclear matrix protein HET/SAF-B, a novel inhibitor of ER-mediated transactivation.

The estrogen receptor (ER) is a ligand-dependent transcription factor that acts in a cell- and promoter-specific manner. Evidence suggests that the activity of the ER can be regulated by a number of other stimuli (e.g. growth factors) and that the effects of the ER are modulated by nuclear factors termed coregulators. While the interplay among these factors may in part explain the pleiotropic effects elicited by the ER, there are several other less well described mechanisms of control, such as interactions with the nuclear matrix. Here we report that the nuclear matrix protein/scaffold attachment factor HET/SAF-B is an ER-interacting protein. ER and HET/SAF-B interact in in vitro binding assays, with HET binding to both the ER DNA-binding domain and the hinge region. Coimmunoprecipitation experiments reveal that HET/SAF-B and ER associate in cell lines in the presence or absence of estradiol, but binding is increased by the antiestrogen tamoxifen. HET/SAF-B enhances tamoxifen antagonism of estrogen-induced ER-mediated transactivation, but at high concentrations can inhibit both estrogen and tamoxifen-induced ER activity. HET/SAF-B-mediated repression of ER activity is dependent upon interaction with the ER-DBD. While the existence of high-affinity binding sites for the ER in the nuclear matrix has been known for some time, we now provide evidence of a specific nuclear matrix protein binding to the ER. Furthermore, our data showing that HET/SAF-B binds to ER particularly strongly in the presence of tamoxifen suggests that it may be important for the antagonist effect of tamoxifen.

Adenocarcinoma↗

PubMed1999

Simple and efficient method for the detection of diethylenetriaminepentaacetic acid.

Diethylenetriaminepentaacetic acid (DTPA) is a commonly used chelating agent. Its antiviral, antibacterial and immunomodulatory effects are well documented. DTPA forms a highly stable complex with lead (II) with an increased absorption coefficient and a bathochromic shift of the absorption maximum compared to pure DTPA. Based on this complex a high-performance liquid chromatographic method for the quantitative detection of DTPA in biological fluids was developed. A calibration curve was prepared and linearity was shown in the concentration range between 10 mg l(-1) and 1000 mg l(-1) DTPA. The recovery in water and in human plasma showed the method to be suitable for routine use.

Adsorption↗

PubMed1999

Membrane potential oscillations in dorsal root ganglion neurons: role in normal electrogenesis and neuropathic pain.

Abnormal afferent discharge originating at ectopic sites in injured primary sensory neurons is thought to be an important generator of paraesthesias, dysaesthesias, and chronic neuropathic pain. We report here that the ability of these neurons to sustain repetitive discharge depends on intrinsic resonant properties of the cell membrane and that the prevalence of this characteristic increases after nerve injury. Recording from primary sensory neurons in excised rat dorsal root ganglia, we found that some cells show subthreshold oscillations in their membrane potential. The amplitude, frequency, and coherence of these oscillations were voltage sensitive. Oscillations gave rise to action potentials when they reached threshold. Indeed, the presence of oscillations proved to be a necessary condition for sustained spiking both at resting membrane potential and on depolarization; neurons without them were incapable of sustained discharge even on deep depolarization. Previous nerve injury increased the proportion of neurons sampled that had subthreshold oscillations, and hence the proportion that generated ectopic spike discharge. Oscillatory behavior and ectopic spiking were eliminated by [Na(+)](o) substitution or bath application of lidocaine or tetrodotoxin (TTX), under conditions that preserved axonal spike propagation. This suggests that a TTX-sensitive Na(+) conductance contributes to the oscillations. Selective pharmacological suppression of subthreshold oscillations may offer a means of controlling neuropathic paraesthesias and pain without blocking afferent nerve conduction.

Afferent Pathways↗

PubMed1999

Distribution of sensory properties among axotomized cutaneous C-fibres in adult rats.

A few hours after peripheral axons of cutaneous afferent neurons have been transected, some of their novel endings become excitable by physical or chemical stimuli. It has been assumed that these axon endings preferentially respond to those stimuli which have excited their previous receptive endings. We studied the prevalence of sensory properties among 784 unmyelinated sural nerve fibres which had been axotomized 2-24 h before, by applying mechanical and thermal forces to the nerve lesion site. Among 126 responding C-fibres, the majority was unimodal, responding exclusively to mechanical (31%), cold (23%) or heat (18%) stimuli. The remainder were either mechano-heat sensitive (10%), mechano-cold sensitive (6%) or heat and cold sensitive (12%). The distribution of sensory properties among acutely axotomized sural nerve C-fibres is therefore largely similar to the recently published distribution of receptor types among intact sural nerve C-fibre afferents. Thus, the hypothesis that responses of axotomized afferent fibres reflect their original receptive properties is corroborated. Knowledge of underlying transduction mechanisms may lead to specific pharmacological tools for suppression of ectopic discharges in unmyelinated axotomized afferents, which probably contribute to neuropathic pain states.

Age Factors↗

PubMed1999

Interobserver reproducibility of quantitative cartilage measurements: comparison of B-spline snakes and manual segmentation.

The objective of this work was to develop a segmentation technique for thickness measurements of the articular cartilage in MR images and to assess the interobserver reproducibility of the method in comparison with manual segmentation. The algorithm is based on a B-spline snakes approach and is able to delineate the cartilage boundaries in real time and with minimal user interaction. The interobserver reproducibility of the method, ranging from 3.3 to 13.6% for various section orientations and joint surfaces, proved to be significantly superior to manual segmentation.

Cartilage, Articular↗