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Biomedical subjects

C Albrecht

Publications and source records attributed to C Albrecht.

At least 19 recordsLinked to original sources
PubMed2001

Elongated multiple electronic cascade and cyclization spacer systems in activatible anticancer prodrugs for enhanced drug release.

The design and synthesis of several novel elongated self-elimination spacer systems for application in prodrugs is described. These elongated spacer systems can be incorporated between a cleavable specifier and the parent drug. Naphthalene- and biphenyl-containing spacers were synthesized but did not eliminate. Prodrugs of the anticancer agents doxorubicin and paclitaxel are reported that contain two or three electronic cascade spacers. A novel catalytic application of HOBt was found for the synthesis of N-aryl carbamates through reacting a 4-nitrophenyl carbonate with an aniline derivative, to connect the 1,6-elimination spacers via a carbamate linkage. In addition, a double spacer-containing paclitaxel prodrug was synthesized, comprising a 1,6-elimination spacer and a bis-amine linker connected to paclitaxel via a 2'-carbamate linkage. Prodrugs in which the novel spacer systems were incorporated between a specific tripeptide specifier and the parent drug doxorubicin or paclitaxel proved to be significantly faster activated by plasmin in comparison with prodrugs containing conventional spacer systems. It is expected that the generally applicable novel spacer systems reported herein will contribute to future development of improved enzymatically activated prodrugs.

Antineoplastic Agents↗
PubMed2001

Fragments of human oncoprotein MDM2 reveal variable distribution within and on cultivated human hepatoma cells.

Human oncoprotein MDM2 reveals a MHC class I binding motif HMDM441 characterizing MDM2 as a potential tumor antigen. To analyze the distribution of MDM2 proteins containing this motif in liver cancer cells we produced rabbit anti-HMDM441 serum. The novel antibodies bound to an MDM2 fragment of approximately 55 kDa which lacked the N-terminal region and was present in lysate and supernatant of a human hepatoma cell line overexpressing normal 90-kDa MDM2. The 55-kDa fragment was detected in the cytoplasm and nucleoli and at the nuclear envelope of hepatoma cells, whereas normal hepatocytes were negative. Double-fluorescence labeling indicated that the MDM2 fragments and MHC class I molecules were coexpressed on the surface of the hepatoma cells. Further studies must clarify whether MDM2 fragments containing motif HMDM441 are novel targets of immunotherapy and immunochemical tumor diagnosis.

Blotting, Western↗
PubMed2001

Quantum interference in artificial band structures.

Magnetotransport experiments on two-dimensional electron systems with an atomically precise, one-dimensional potential modulation reveal striking quantum interference oscillations. Within a semiclassical framework, they are recognized either as self-interference along closed orbits, many of them rendered possible by magnetic breakdown between Fermi contour segments of the artificial band structure, or as interference-enhanced backscattering. The known commensurability oscillations appear as a special case of the latter mechanism.

Journal Article↗
PubMed2001

Evidence of Hofstadter's Fractal Energy Spectrum in the Quantized Hall Conductance.

The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.

Journal Article↗
PubMed2001

[3H]acetycholine release in rat striatal slices is not subject to dopamine heteroreceptor supersensitivity 30 months after 6-hydroxydopamine lesion of the substantia nigra.

Using the rat model of Parkinson's disease described by Ungerstedt the release of [3H]acetylcholine ([3H]ACh) in the caudatoputamen was investigated to assess possible long-term effects of unilateral dopaminergic denervation on the modulation of cholinergic interneurons. This seemed of interest since rats with 6-hydroxydopamine (6-OHDA) lesions of the left substantia nigra showed an increase in the behavioural susceptibility to small doses of dopamine (DA) D2 receptor agonists 30 months after the lesion. Electrical field stimulation with 3 Hz elicited release of [3H]ACh in slices of both the lesioned and the intact striatum. The DA reuptake blocker nomifensine was ineffective on the lesioned side but diminished the release of [3H]ACh in the intact striatum. This inhibition was reversed by the D2 receptor antagonist domperidone and hence probably due to the effect of endogenously released DA. Single electrical pulses at 0.05 Hz, which neither induced autoinhibition of [3H]ACh release nor heteroinhibition by endogenous DA, elicited a higher release of [3H]ACh on the intact side. Under this stimulation paradigm activation of the D2 heteroreceptor with quinpirole depressed the release of [3H]ACh to a similar extent on both sides, irrespective of the absence or presence of the competitive NMDA receptor antagonist D-CPPene. Also blockade of the NMDA receptor channel by dizocilpine, or of AMPA receptors by NBQX, was ineffective on either side. The NMDA-evoked release of [3H]ACh was higher on the lesioned side. It was equally depressed by quinpirole and by ethanol on both sides. Thus, single electrical pulses and NMDA stimulation per se had opposite effects on the lesioned and the intact side, whereas the modulation of release was similar. Since the lesioned striata were considerably smaller, measurements of mRNA levels of choline acetyltransferase (ChAT) were used to assess the density of cholinergic interneurons and their content of ChAT mRNA. This analysis did not reveal any side difference. In conclusion, the function of D2 heteroreceptors on, and the density and ChAT mRNA content of, cholinergic interneurons are not or no longer altered after long-term DA denervation. Most probably, cholinergic interneurons are not involved in the increased behavioural susceptibility of 6-OHDA-lesioned rats to DA agonists.

Acetylcholine↗
PubMed2001

Regulation of gene expression by muscarinic acetylcholine receptors.

In the brain, muscarinic acetylcholine receptors (mAChRs) are involved in higher cognitive functions including synaptic plasticity and memory. In Alzheimer's disease (AD) patients the cholinergic nervous system is severely damaged. In order to reinforce the cholinergic system, clinical tests were started to use cholinomimetic drugs to treat AD patients. To identify the genes involved in mAChR signalling, we used a differential display approach and found 11 genes that were readily activated by mAChR with 1 hour of activation. These included the transcription factors Egr-1, Egr-2, Egr-3, c-Jun, Jun-D and Gos-3; the growth regulator hCyr61; the signalling factors NGFi-B (nerve growth factor induced gene-B) and Etr101; the unknown gene Gig-2 (for G-protein-coupled receptor induced gene 2); and the acetylcholinesterase gene (ACHE). Our data show that multiple immediate-early genes are under the control of mAChRs, and they suggest that these genes play important roles in coupling receptor stimulation to long-term neuronal responses. The results also suggest a feedback mechanism where up-regulated ACHE expression and accelerated breakdown of acetylcholine (ACh) at the cholinergic synapses limits increases in cholinergic transmission. Three hours after m1 mAChR activation a different pattern of gene expression was demonstrated. It included the novel genes Gig-3 and Gig-4, as well as the LIM-only protein LM04. Like ACHE, these genes are target genes which may be under the control of the above immediate-early genes. Together, our data show that muscarinic receptors induce a complex and sustained pattern of gene expression that may be involved in the regulation of cholinergic transmission as well as the control of cellular functions in post-synaptic cholinergic target cells. These results may contribute to a better understanding of the effects and side effects of cholinomimetic treatment in AD patients.

Alzheimer Disease↗
PubMed2001

Clara-cell hyperplasia after quartz and coal-dust instillation in rat lung.

Bronchiolo-alveolar hyperplasia of type II cells in rat lungs after particle exposure is a well-known preneoplastic lesion. The Clara cell, stem cell of the bronchiolar epithelium and the main carrier of cytochrome P-450 isoenzyme system in the lung, has barely been evaluated with regard to this effect. The aim of this study was to examine Clara-cell hyperplasia after particle exposure and to characterize cell proliferation and its normal function. Female Wistar rats were intratracheally instilled with coal dust samples of variable quartz content, quartz (DQ12), titanium dioxide, or saline solution containing 0.5% Tween 80. After 126-129 wk, all coal mine dust- and quartz-exposed animals developed Clara-cell hyperplasia: up to 0.48% of the total lung area, which was significantly increased compared to titanium dioxide (p <.05) and control (p <.03) animals. Proliferation and hyperplasia of bronchiolar Clara cells by coal dusts was independent of their quartz content. The lack of proliferating cell nuclear antigen staining in most of the hyperplastic Clara cells suggests that following damage of alveolar epithelial cells, Clara cells migrate in and remodulate the alveolar epithelium. After the migration they keep their function in the xenobiotic metabolism, as shown by expansion of CYP2E1 active Clara cells. The minor development of Clara-cell hyperplasia in titanium dioxide-treated rats indicates that this is not a general particle effect, and is possibly due to its lower toxicity to epithelial cells.

Animals↗
PubMed2001

Expression of putative anticancer targets in familial adenomatous polyposis and its association with the APC mutation status.

Several substances interfering with colorectal carcinogenesis may reduce or prevent adenoma formation in familial adenomatous polyposis (FAP), an inherited predisposition to colorectal cancer. This study determined the expression of genes coding for putative anticancer targets (COX-2, iNOS, MMP-7, ODC, PKCbeta, PPARgamma, RXRalpha, RXRbeta, RXRgamma) in FAP patients to provide one of the rationales for the design of chemotherapy and -prevention strategies. Gene expression was assessed by TaqMan analysis in colonic tissue of 9 FAP patients with mutations in the APC gene (APCpos), 5 FAP patients without identified genetic defect (APCneg), and 3 healthy individuals. Among the examined genes, PKCbeta and MMP-7 were most consistently altered in adenoma tissue relative to matched mucosa. Intriguingly, ODC was clearly overexpressed in polyps from APCpos but not APCneg patients. Furthermore, PKCbeta, MMP-7, ODC, and COX-2 as well as all RXRs displayed altered expression in apparently healthy FAP mucosa as opposed to that of healthy individuals. Our data suggests PKCbeta and MMP-7 to be the most suited as anticancer targets among the genes studied.

Adenomatous Polyposis Coli↗
PubMed2000

Muscarinic acetylcholine receptors induce the expression of the immediate early growth regulatory gene CYR61.

In brain, muscarinic acetylcholine receptors (mAChRs) modulate neuronal functions including long term potentiation and synaptic plasticity in neuronal circuits that are involved in learning and memory formation. To identify mAChR-inducible genes, we used a differential display approach and found that mAChRs rapidly induced transcription of the immediate early gene CYR61 in HEK 293 cells with a maximum expression after 1 h of receptor stimulation. CYR61 is a member of the emerging CCN gene family that includes CYR61/CEF10, CTGF/FISP-12, and NOV; these encode secretory growth regulatory proteins with distinct functions in cell proliferation, migration, adhesion, and survival. We found that CYR61, CTGF, and NOV were expressed throughout the human central nervous system. Stimulation of mAChRs induced CYR61 expression in primary neurons and rat brain where CYR61 mRNA was detected in cortical layers V and VI and in thalamic nuclei. In contrast, CTGF and NOV expression was not altered by mAChRs neither in neuronal tissue culture nor rat brain. Receptor subtype analyses demonstrated that m1 and m3 mAChR subtypes strongly induced CYR61 expression, whereas m2 and m4 mAChRs had only subtle effects. Increased CYR61 expression was coupled to mAChRs by both protein kinase C and elevations of intracellular Ca(2+). Our results establish that CYR61 expression in mammalian brain is under the control of cholinergic neurotransmission; it may thus be involved in cholinergic regulation of synaptic plasticity.

Animals↗
PubMed1999

Identification of genes regulated by muscarinic acetylcholine receptors: application of an improved and statistically comprehensive mRNA differential display technique.

In order to identify genes that are regulated by muscarinic acetylcholine receptors, we developed an mRNA differential display technique (DD) approach. By increasing redundancy and by evaluating optimised reagents and conditions for reverse transcription of total RNA, PCR and separation of PCR products, we generated a DD protocol that yields highly consistent results. A set of 64 distinct random primers was specifically designed in order to approach a statistically comprehensive analysis of all mRNA species in a defined cell population. This modified DD protocol was applied to total RNA of HEK293 cells stably expressing muscarinic m1 acetylcholine receptors and cells stimulated with the receptor agonist carbachol were compared to identical but non-stimulated cells. In 81 of 192 possible PCR experiments, 38 differential bands were identified. Sequence analysis followed by northern blot analyses confirmed differentially expressed genes in 19 of 23 bands analysed. These represented 10 distinct immediate-early genes that were up-regulated by m1AChR activation: Egr-1, Egr-2, Egr-3, NGFi-B, ETR101, c- jun, jun -D, Gos-3 and hcyr61, as well as the unknown gene Gig-2. These data show that this improved DD protocol can be readily applied to reliably identify differentially expressed genes.

Base Sequence↗
PubMed1999

Evaluation of autoreceptor-mediated control of [(3)H]acetylcholine release in rat and human neocortex.

In order to assess the autoinhibitory control of endogenous acetylcholine (ACh) in rat and human neocortex, slices of these tissues were prelabelled with [(3)H]choline, superfused continuously and stimulated electrically using various frequencies in the presence or absence of drugs. The autoinhibitory feedback control of [(3)H]ACh release was operative - despite the absence of blockers of ACh esterase - at stimulation frequencies >/= 3 Hz in rat and >/= 6 Hz in human neocortex tissue. At these frequencies the muscarinic antagonist atropine (0.1 microM) disinhibited the release of [(3)H]ACh in both species. Estimation of the biophase concentration of ACh near the autoreceptor in the rat neocortex from concentration-response curves of the muscarinic agonist oxotremorine revealed that at 3 Hz about 25% of the autoreceptors were activated by endogenously released ACh. This estimation is consistent with an increase in [(3)H]ACh release to about 120% of control values by complete blockade of autoreceptors with atropine. The observation that in human neocortical tissue presynaptic autoinhibition of [(3)H]ACh release is operative at stimulation frequencies >/= 6 Hz suggests that selective blockade of autoinhibition may also increase ACh release in the cortex of Alzheimer's disease patients, without additional blockade of the enzyme acetylcholinesterase.

Acetylcholine↗
PubMed1999

Atosiban, an oxytocin receptor blocking agent: pharmacokinetics and inhibition of milk ejection in dairy cows.

Plasma concentrations of the oxytocin receptor blocking agent Atosiban were measured at 2, 4, 10, 15 and 20 min after injection of 5, 10, 20 and 50 micrograms Atosiban/kg body weight in six dairy cows. The half life of Atosiban was 18 min and the total body clearance was 3301 ml/min. Intramammary pressure (IMP) within the teat cistern was measured in six cows before and after i.v. injection of 0 or 20 micrograms Atosiban/kg body weight and repeated injections of 0.2 or 0.5 i.u. oxytocin. IMP was also measured in eleven cows after injection of 0, 10 or 50 micrograms Atosiban/kg body weight: in seven during oxytocin infusions, in four after oxytocin injections in successively increasing dosages (0.05, 0.1, 0.2, 0.5, 1 and 10 i.u.). The occurrence of milk ejection was indicated by a rise in IMP. After injection of 20 micrograms Atosiban/kg body weight, 0.2 i.u. oxytocin did not induce an IMP rise before 48 min, whereas 0.5 i.u. oxytocin induced an IMP rise within 4 min. The time from the start of infusion until the beginning of the IMP rise and the duration of IMP rise during oxytocin infusions both increased, whereas the IMP rise itself was diminished by increasing Atosiban dosages. The amount of injected oxytocin necessary to induce an IMP response increased with increasing Atosiban dosages. Atosiban was shown to have a powerful effect in inhibiting milk ejection in dairy cows.

Animals↗
PubMed1999

Long-term effects on sexual function and fertility after treatment of testicular cancer.

This retrospective study evaluates the types and incidences of sexual disturbances and fertility distress in patients cured from testicular cancer and examines whether there is an effect resulting from different treatment modalities. A self-reported questionnaire was sent to 124 randomly selected patients who were treated at Hanover University Medical School between 1970 and 1993. Ninety-eight patients were included in the study, representing a response rate of 78%. All patients had been in complete remission (CR) for at least 24 months. The median age at diagnosis was 28 years (range 17-44). The median follow-up at the time of study was 12.0 years (range 2.8-25.6). Twenty patients (20%) had been treated for seminomatous and 78 patients (80%) for non-seminomatous germ cell tumours. Treatment included surveillance (7%), primary retroperitoneal lymph node dissection (RPLND) (13%), chemotherapy (CT) (33%), CT + secondary resection of residual retroperitoneal tumour mass (SRRTM) (43%) and infradiaphragmatic radiotherapy (4%). Patients receiving two treatment modalities (CT+SRRTM) reported more frequent an unfulfilled wish for children. Inability of ejaculation was clearly associated with RPLND and SRRTM. Subjective aspects of sexuality, like loss of sexual drive and reduced erectile potential, occurred only in a minority of patients after treatment. No abnormalities were observed concerning the course of pregnancies of partners. In conclusion, sexual dysfunction and infertility are common long-lasting sequelae in testicular cancer survivors affecting approximately 20% of patients. The relative risk for infertility appeared to be elevated for patients treated with the combination of CT+SRRTM. Twenty-one of 40 patients were able to fulfil their wish for children, and no congenital abnormalities were observed in these children.

Adolescent↗
PubMed1999

Time-course analysis of type II cell hyperplasia and alveolar bronchiolization in rats treated with different particulates.

In this study, we compared the morphological reaction patterns in rat lungs following a single intratracheal instillation of 20 mg quartz, 20 mg coal mine dust (15.3% quartz), or 25 mg talc. Control animals received a single dose of 0.5 ml saline solution intratracheally. Investigations by light microscopy, morphometry, and DNA image cytometry were carried out 3, 6, 12, and 18 mo after dust administration. During the investigation period, we observed a temporary increase in the number, area, and proliferative activity of the type II cells, which differed in intensity among the three dusts. After 18 mo, however, type II cells in treated animals did not differ from control animals. On the other hand, the expansion of a multifocal alveolar bronchiolization as putative preneoplastic lesion had progressed enormously by the end of the test (1-3% of the investigated lung area). Consistent with this, the proliferative activity of the epithelial cells in terminal bronchi of the coal mine dust- and quartz-treated animals was enhanced by the end of the 18-mo investigation period, while the reaction to talc was minimal (0.2% of totally investigated lung area). Our data suggest that in bronchiolo-alveolar regions, especially in the epithelium of terminal bronchi, there is an overshoot regeneration after cell damage that leads to an alveolar bronchiolization.

Air Pollutants↗
PubMed1998

Muscarinic acetylcholine receptors activate expression of the EGR gene family of transcription factors.

In order to search for genes that are activated by muscarinic acetylcholine receptors (mAChRs), we used an mRNA differential display approach in HEK293 cells expressing m1AChR. The zinc-finger transcription factor genes Egr-1, Egr-2, and Egr-3 were identified. Northern blot analyses confirmed that mRNA levels of Egr-1, Egr-2, and Egr-3 increased readily after m1AChR stimulation and that a maximum was attained within 50 min. At that time, Egr-4 mRNA was also detectable. Western blots and electromobility shift assays demonstrated synthesis of EGR-1 and EGR-3, as well as binding to DNA recognition sites in response to m1AChR activation. Activation of m1AChR increased transcription from EGR-dependent promoters, including the acetylcholinesterase gene promoter. Activity-dependent regulation of Egr-1 mRNA expression and EGR-1 protein synthesis was also observed in cells expressing m2, m3, or m4AChR subtypes. Increased EGR-1 synthesis was mimicked by phorbol myristate acetate, but not by forskolin, and receptor-stimulated EGR-1 synthesis was partially inhibited by phorbol myristate acetate down-regulation. Together, our results demonstrate that muscarinic receptor signaling activates the EGR transcription factor family and that PKC may be involved in intracellular signaling. The data suggest that transcription of EGR-dependent target genes, including the AChE gene, can be under the control of extracellular and intracellular signals coupled to muscarinic receptors.

Cell Line↗