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Biomedical subjects

S Haas

Publications and source records attributed to S Haas.

At least 109 records · Page 6Linked to original sources
PubMed1996

Interaction of cytostatics and chemosensitizers with the dexniguldipine binding site on P-glycoprotein.

The interaction of cytostatics and chemosensitizers with the dexniguldipine binding site of P-glycoprotein was investigated in photoaffinity labeling experiments. A tritiated azidoderivative of the chemosensitizer dexniguldipine with dihydropyridine structure, [3H]B9209-005, was used to irreversibly label P-glycoprotein. The apparent affinity of cytostatics and chemosensitizers to this binding site was estimated from labeling experiments in the presence of increasing concentrations of compounds. From the cytostatics tested, the vinca alkaloids and taxol showed the highest affinity, anthracyclins possessed moderate affinity while methotrexate, ara C and camptothecin, cytostatics not involved in P-glycoprotein-mediated multidrug resistance, were almost inactive. The chemosensitizers GF 120918, cyclosporin A and SDZ PSC-833 inhibited photoincorporation with the highest potency. Steep dose-inhibition curves were obtained with the cyclic peptides and S9788, indicating that these compounds may bind allosterically to a separate binding site. Compounds with dihydropyridine structure with or without chemosensitizing potency were also tested and some structure-activity relationships could be derived from the data. Our data show that inhibition of photoaffinity labeling by [3H]B9209-005 is a valuable and reliable system for measuring the interaction with and potency of chemosensitizing compounds at P-glycoprotein. Furthermore, data obtained in this test system are well suited to investigate structure-activity relationships for chemosensitizers at P-glycoprotein. In addition cytostatics underlying P-glycoprotein-mediated multidrug resistance can be identified.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Regulation of thrombospondin in the regenerating mouse facial motor nucleus.

Thrombospondin (TSP) is a multifunctional extracellular matrix protein that plays a role in neuronal migration and axonal outgrowth in the developing central nervous system. In the current study we have examined the localization and regulation of TSP immunoreactivity (TSP-IR) during neuronal regeneration in the axotomized facial motor nucleus using Western blotting and light and electron microscopy. Transection of the facial nerve led to a gradual increase in TSP-IR in the regenerating motoneurons, peaking 4-7 days after injury (DAI). In addition to regenerating neurons, axotomy also caused a rapid upregulation of TSP-IR on activated microglia throughout the facial nucleus, with a maximum of 2-3 DAI, and a second increase at 14-21 DAI on microglial aggregates surrounding degenerating motoneurons and in neuronophagic microglia. In summary, injury leads to the induction of thrombospondin on axotomized neurons and activated microglia, peaking at the times of maximal posttraumatic microglial proliferation and during neuronal phagocytosis. Since thrombospondin is a multimodal extracellular matrix protein with a variety of cell attachment sites, thrombospondin might serve to link microglia and injured neurons, followed by microglial proliferation and removal of the neuronal debris.

Animals↗
PubMed1996

Oral immunization with a model protein entrapped in microspheres prepared from derivatized alpha-amino acids.

A model antigen, ovalbumin (OVA), was encapsulated in microspheres prepared from derivatized alpha-amino acids and administered orally to mice. These microspheres are quickly and easily prepared, without the use of organic solvents, high temperatures, or complex purification techniques. Immunological responses included induction of OVA-specific antibodies in both sera (IgG) and in intestinal secretions (sIgA), as well as antigen-dependent proliferation of splenic CD4+ T cells following, in some cases, as little as a single oral priming dose containing 0.1 mg OVA. Oral administration of microspheres was also found to be effective as a secondary immunization following a subcutaneous prime with soluble antigen. In addition, the protective effect of co-encapsulation of cholera toxin, a mucosal adjuvant, was demonstrated in a whole virus model (infectious bursal disease in chickens). These results indicate that oral administration of antigen-loaded derivatized alpha-amino acid microspheres can induce local and systemic antibody production and/or stimulation of effector cells.

Administration, Oral↗
PubMed1996

ATP-induced membrane currents in ameboid microglia acutely isolated from mouse brain slices.

Microglial cells were harvested from the surface of corpus callosum slices acutely isolated from the brain of neonatal (five- to seven-day-old) mice. Transmembrane ionic currents were measured employing a standard whole-cell voltage-clamp technique. The extracellular application of 1 mM ATP triggered the generation of a complex membrane current comprising three components: (i) an initial fast inward current which had a reversal potential at about -20 to -15 mV; (ii) this initial component was followed by a steady-state inward current with reversal potential about -50 to -40 mV; and (iii) a delayed inward current with a reversal potential close to 0 mV. The first two components (fast and steady-state) had an activation threshold at 10 microM ATP, and 100 microM ATP evoked an almost maximal response. In contrast, the third component of ATP-induced inward membrane current could be observed only while 1 mM ATP was applied. The increase in concentration of tetra-anionic form of ATP (ATP4-) by removal of divalent cations from the bath solution substantially lowered the activation threshold for the delayed component of ATP-induced membrane current; conversely, lowering the ATP4- concentration (by replacing Ca2+ with Mg2+) resulted in its disappearance. These results suggest that ATP4- acts as a true agonist for the activation of the delayed ATP-induced membrane current. We conclude that microglial cells express several purinoreceptor subtypes. The activation of these receptors might play a role in intracellular signal transduction in brain microglia.

Adenosine Triphosphate↗
PubMed1996

Modulation of P-glycoprotein mediated drug accumulation in multidrug resistant CCRF VCR-1000 cells by chemosensitisers.

P-glycoprotein (PGP) mediated transport of cytostatic drugs out of resistant cancer cells is a major cause of experimental and probably also of clinical multidrug resistance, which often leads to treatment failure during chemotherapy. The broad substrate specificity of PGP strongly restricts effective chemotherapy and diminishes the patients' prognosis. Inhibition of PGP's pumping function by chemosensitisers is one way to restore cellular responsiveness to otherwise ineffective cytostatics. Clinical trials with several chemosensitisers are under way. To date, it is not clear whether a certain chemosensitiser potentiates the action of different cytostatic drugs, transported by PGP equally well, or whether the chemosensitising potency is dependent on the cytostatic drugs used. Therefore, we compared the effects of five potent chemosensitisers on cellular accumulation using [3H]daunomycin, [3H]vincristine and rhodamine-123 as substrates for PGP. The acridonecarboxamide derivative GF 120918 was the most potent compound and a half-maximal effect was seen at concentrations ranging from 5 nM for rhodamine-123 accumulation to 14 and 19 nM for [3H]vincristine or [3H]daunomycin accumulation, respectively. The new chemosensitiser B9203-016 was slightly less effective than GF 120918 in all three test systems. Dexniguldipine was of intermediate potency with half-maximal effects at concentrations between 62 and 194 nM. The cyclic undecapeptide SDZ PSC 833 showed somewhat lower potency ranging from 151 to 331 nM. Cyclosporin A was less potent than SDZ PSC 833. Furthermore, enhancement of drug accumulation produced by each chemosensitiser was similar, regardless of which PGP substrate was measured, that is, the rank order of potency to increase accumulation was the same in each of the assays used. Our data point to similar, if not identical, mechanisms of drug transport by PGP and inhibition of drug transport by chemosensitisers at least for the substrates rhodamine-123, vincristine and daunomycin.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

The role of low-molecular-weight heparins in the prevention of venous thrombosis in surgery with special reference to enoxaparin.

Prophylaxis with low-dose heparin has contributed significantly to the reduction in thromboembolic complications in surgery. Without prophylaxis, the rate of deep-vein thrombosis is about 30% in patients undergoing general surgery, rising up to 70% in orthopedic and trauma surgery. According to Collins et al. [N Engl J Med 1988; 318: 1162-1172] and Clagett and Reisch [Ann Surg 1988; 208: 227-240] heparin prevented at least 60% of deep-vein thromboses. Meanwhile, various heparin fragments have become available for clinical use and the question arises whether these low-molecular-weight heparins are equal or even superior to unfractionated heparin in preventing thromboembolic complications. Because of the pharmacological heterogeneity of low-molecular-weight heparins and variations in administered doses, this question can only be partially answered by meta-analysis. However, in summary it can be said that despite the difficulties of and concerns about general assessments, single daily injections of low-molecular-weight heparin are at least as efficacious as multiple daily doses of unfractionated heparin. In particular, enoxaparin 40 mg once a day and enoxaparin 30 mg twice a day seem to be superior to unfractionated heparin in high-risk patients, and adverse drug reactions occur less frequently when this prophylaxis is used.

Dose-Response Relationship, Drug↗
PubMed1996

Activity of the DNA repair protein O6-methylguanine-DNA methyltransferase in human tumor and corresponding normal tissue.

The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is a main determinant of resistance of cells towards the cytostatic effect of N-nitrosoureas. Here we report the activity of MGMT in different types of human tumors. Colorectal tumors showed the highest mean of MGMT activity (481 +/- 258 fmol/mg protein) followed by ovarian tumors (437 +/- 291 fmol/mg), breast (306 +/- 204 fmol/mg), testicular (299 +/- 179 fmol/mg), and brain tumors (55 +/- 44 fmol/mg). Only in breast and brain tumors were MGMT-deficient samples found, with a frequency of 3 and 5%, respectively. No significant difference in mean MGMT activity was observed between breast tumors of grading I, II, and III. For brain tumors there was a tendency of MGMT to decline with increasing grading. Breast and colorectal carcinomas were compared with the corresponding normal tissue obtained from the same patient. The data showed for 11 out of 12 pairs of breast tissue and for 13 out of 15 pairs of colorectal tissue that MGMT activity in the tumor was equal to or, more frequently, higher than the activity found in the corresponding normal tissue. Thus, it appears that in these groups of tumors, increase of MGMT activity during tumor formation and progression is the rule rather than the exception.

Brain Neoplasms↗
PubMed1996

ECT-induced seizure durations.

Electroconvulsive therapy (ECT) efficacy is related to the stimulus intensity and clinically associated with the duration of the induced seizure. Convulsions lasting 30 to 60 seconds are conventionally considered to be of optimal length, and generally are achieved by applying routine ECT technique. An ictus slightly shorter or longer is usually also therapeutically satisfactory. In our study, seizures lasting between 30 and 60 seconds produced a favorable clinical outcome. A very similar effect was observed in all cases where the duration was within 16 to 120 seconds. However, subjects experiencing intal periods of less than 15 seconds and those over 120 seconds resulted in less favorable response. Detailed records as to medicinal and electrical stimulus doses, seizure timings, etc, were excellent guides for subsequent ECT to achieve appropriate convulsion durations and a safe, satisfactory outcome.

Adult↗
PubMed1996

Growth-state-dependent radiation-induced expression of the proto-oncogene c-fos in NIH 3T3 cells.

Expression of the proto-oncogene c-fos in response to ionizing radiation has been observed in some but not all cell lines tested. Here we report on delayed, transient c-fos expression in NIH 3T3 cells induced by 60Co gamma rays in the dose range 2-5 Gy. Induction of c-fos was significantly increased in cells irradiated in the density-arrested quiescent state compared to irradiation in the exponential growth phase. The enhancement correlated with the transition to quiescence as measured by the proliferation markers, proliferating cell nuclear antigen and bromodeoxyuridine. The observation of growth-state-dependent expression of c-fos after irradiation might indicate a functional relationship between c-fos and growth control in the DNA damage response, e.g. a potential role of c-fos in the control of replicative proteins.

3T3 Cells↗
PubMed1995

Microsphere formation in a series of derivatized alpha-amino acids: properties, molecular modeling, and oral delivery of salmon calcitonin.

A series of benzoylated and phenylsulfonylated amino acids are novel, low molecular weight, self-assembling molecules. At low pH, these compounds form microspheres that dissolve readily under neutral conditions. In a given synthetic series, those molecules with low aqueous solubility formed microspheres more readily than did the molecules possessing high water solubility, suggesting that the hydrophobicity of these compounds contributes to the ability to form microspheres. In addition, molecular modeling studies on selected compounds have shown that microsphere formation may depend also on various aromatic ring and dipole-dipole interactions, which could effect the extent and types of favorable stacking conformations between molecules. The microspheres prepared from these compounds have been used to effect the oral delivery of salmon calcitonin, a model protein drug, in both rodents and primates.

Administration, Oral↗
PubMed1995

N-acylated alpha-amino acids as novel oral delivery agents for proteins.

A series of N-acylated alpha-amino acids were synthesized and shown to improve the oral delivery of two protein drugs, salmon calcitonin (sCT) and interferon-alpha. Forty-five compounds in this series were tested in vivo in rats and primates. A significant positive correlation was found between the log P of the acylated amino acids and the decrease in serum calcium following oral dosage of sCT in rats. Such a correlation was not found for interferon-alpha. These derivatized amino acids only weakly inhibited the activity of trypsin or leucine aminopeptidase. Histological examinations of rat intestinal tissue after oral dosing of acylated amino acid/protein combinations revealed no detectable pathology.

Acylation↗
PubMed1995

Identification of a sequence-specific single-stranded DNA binding protein that suppresses transcription of the mouse myelin basic protein gene.

The myelin basic protein (MBP) gene is expressed only in oligodendrocytes and Schwann cells, and expression follows a tightly regulated developmental time course. Cell type- and developmental stage-specific expression of the MBP gene appears to be regulated by a series of cis-acting elements located upstream of the transcription start site. The proximal element of the MBP regulatory region (MB1), located between nucleotides -14 and -50, is one of several elements participating in the programmed expression of MBP. In this report, we describe the molecular cloning and characterization of myelin gene expression factor-2 (Myef-2), a protein isolated from mouse brain that binds specifically to single-stranded DNA derived from the MB1 element and represses transcription of the MBP gene in transient transfection assay. Myef-2 mRNA is developmentally regulated in mouse brain; its peak expression occurs at postnatal day 7, prior to the onset of MBP expression. The developmental pattern of Myef-2 mRNA expression coincides with that previously described for SCIP, a POU domain transcription factor that also represses myelin basic protein expression. The myef-2 gene maps to mouse chromosome 2. The relevance of these findings for regulation of MBP gene expression and oligodendrocyte differentiation is discussed.

Aging↗
PubMed1995

O6-methylguanine-DNA methyltransferase activity in breast and brain tumors.

The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is a main determinant of resistance of tumor cells to the cytostatic activity of chemotherapeutic alkylating agents (methylating and chloroethylating nitrosoureas) and is effective in protecting normal cells against genotoxic and carcinogenic effects resulting from DNA alkylation. Therefore, the level of expression of MGMT is significance for the response of both the tumor and the non-target tissue following application of nitrosoureas in tumor therapy. To determine the expression of MGMT in tumor tissue, we have assayed MGMT activity in 68 breast carcinomas and 38 brain tumors. There was a wide variation of MGMT expression in breast carcinomas ranging from below the level of detection up to 863 fmol/mg protein. About 4% of breast tumors did not display detectable MGMT, 15% had activity lower than 100 fmol/mg protein, and 26% expressed more than 500 fmol/mg. The mean level of expression was 321 fmol/mg. In brain tumors (astrocytoma WHO grade I, II, and III, and glioblastoma WHO grade IV) the MGMT activity was generally lower than in breast tumors, ranging from below the level of detection up to 238 fmol/mg. The mean level of expression was 55 fmol/mg. Five percent of the brain tumors had no detectable MGMT activity. The MGMT repair activity correlated well with the amount of MGMT protein present in tumor samples, as shown by Western-blot analysis, indicating that loss of MGMT repair activity is due to inability of these tumor cells to synthesize the protein.

Adult↗