Biomedical subjects

Louis Scheurer

Publications and source records attributed to Louis Scheurer.

6 recordsLinked to original sources

PubMed2005

Astrogliosis in epilepsy leads to overexpression of adenosine kinase, resulting in seizure aggravation.

Adenosine kinase (ADK) is considered to be the key regulator of the brain's endogenous anticonvulsant, adenosine. In adult brain, ADK is primarily expressed in a subpopulation of astrocytes and striking upregulation of ADK in these cells has been associated with astrogliosis after kainic acid-induced status epilepticus (KASE) in the kainic acid mouse model of temporal lobe epilepsy. To investigate the causal relationship between KASE-induced astrogliosis, upregulation of ADK and seizure activity, we have developed a novel mouse model [the Adktm1(-/-)-Tg(UbiAdk) mouse] lacking the endogenous astrocytic enzyme due to a targeted disruption of the endogenous gene, but containing an Adk transgene under the control of a human ubiquitin promoter. Mutant Adktm1(-/-)-Tg(UbiAdk) mice were characterized by increased brain ADK activity and constitutive overexpression of transgenic ADK throughout the brain, with particularly high levels in hippocampal pyramidal neurons. This ADK overexpression was associated with increased baseline levels of locomotion. Most importantly, two-thirds of the mutant mice analysed exhibited spontaneous seizure activity in the hippocampus and cortex. This was the direct consequence of transgene expression, since this seizure activity could be prevented by systemic application of the ADK inhibitor 5-iodotubercidin. Intrahippocampal injection of kainate in the mutant mice resulted in astrogliosis to the same extent as that observed in wild-type mice despite the absence of endogenous astrocytic ADK. Therefore, KASE-induced upregulation of endogenous ADK in wild-type mice is a consequence of astrogliosis. However, seizures in kainic acid-injected mutants displayed increased intra-ictal spike frequency compared with wild-type mice, indicating that, once epilepsy is established, increased levels of ADK aggravate seizure severity. We therefore conclude that therapeutic strategies that augment the adenosine system after astrogliosis-induced upregulation of ADK constitute a neurochemical rationale for the prevention of seizures in epilepsy.

Adenosine Kinase↗

PubMed2004

Engineering embryonic stem cell derived glia for adenosine delivery.

Based on the anticonvulsant and neuroprotective properties of adenosine, and based on the long-term survival potential of stem cell derived brain implants, adenosine releasing stem cells may constitute a novel tool for the treatment of epilepsy. Pluripotency and unlimited self-renewal make embryonic stem (ES) cells a particularly versatile donor source for cell transplantation. With the aim to test the feasibility of a stem cell-based delivery system for adenosine, both alleles of adenosine kinase (ADK), the major adenosine-metabolizing enzyme, were disrupted by homologous recombination in ES cells. Adk-/- ES cells were subjected to a glial differentiation protocol and, as a result, gave rise to proliferating glial precursors, which could be further differentiated into mature astrocytes and oligodendrocytes. Thus, a lack of ADK does not compromise the glial differentiation potential of ES cells. The Adk-/- ES cells yielded glial populations with an adenosine release of up to 40.1 +/- 6.0 ng per 10(5) cells per hour, an amount considered to be sufficient for seizure suppression. Our findings indicate that Adk-/- ES cells constitute a potential source for therapeutic adenosine releasing grafts.

Adenosine↗

PubMed2004

Overexpression of adenosine kinase in epileptic hippocampus contributes to epileptogenesis.

Endogenous adenosine in the brain is thought to prevent the development and spread of seizures via a tonic anticonvulsant effect. Brain levels of adenosine are primarily regulated by the activity of adenosine kinase. To establish a link between adenosine kinase expression and seizure activity, we analyzed the expression of adenosine kinase in the brain of control mice and in a kainic acid-induced mouse model of mesial temporal lobe epilepsy. Immunohistochemical analysis of brain sections of control mice revealed intense staining for adenosine kinase, mainly in astrocytes, which were more or less evenly distributed throughout the brain, as well as in some neurons, particularly in olfactory bulb, striatum, and brainstem. In contrast, hippocampi lesioned by a unilateral kainic acid injection displayed profound astrogliosis and therefore a significant increase in adenosine kinase immunoreactivity accompanied by a corresponding increase of enzyme activity, which paralleled chronic recurrent seizure activity in this brain region. Accordingly, seizures and interictal spikes were suppressed by the injection of a low dose of the adenosine kinase inhibitor 5-iodotubercidin. We conclude that overexpression of adenosine kinase in discrete parts of the epileptic hippocampus may contribute to the development and progression of seizure activity.

Action Potentials↗

PubMed2002

Neonatal hepatic steatosis by disruption of the adenosine kinase gene.

Neonatal hepatic steatosis (OMIM 228100) is a fatal condition of unknown etiology characterized by a pale and yellow liver and early postnatal mortality. In the present study, a deficit in adenosine-dependent metabolism is proposed as a causative factor. Physiologically, adenosine is efficiently metabolized to AMP by adenosine kinase (ADK), an enzyme highly expressed in liver. ADK not only ensures normal adenine nucleotide levels but also is essential for maintaining S-adenosylmethionine-dependent transmethylation processes, where adenosine, an obligatory product, has to be constantly removed. Homozygous Adk(-/-) mutants developed normally during embryogenesis. However, within 4 days after birth they displayed microvesicular hepatic steatosis and died within 14 days with fatty liver. Adenine nucleotides were decreased and S-adenosylhomocysteine, a potent inhibitor of transmethylation reactions, was increased in the mutant liver. Thus, a deficiency in adenosine metabolism is identified as a powerful contributor to the development of neonatal hepatic steatosis, providing a model for the rapid development of postnatally lethal fatty liver.

Adenine Nucleotides↗

PubMedDate not supplied

Enhancement of Fas-ligand-mediated programmed cell death by taurolidine.

BACKGROUND: Taurolidine was recently found to have a direct and selective antineoplastic effect on brain tumor cells. The ability of taurolidine to exert antineoplastic action by enhancement of Fas-mediated apoptosis in different malignant glioma cell lines was investigated. MATERIALS AND METHODS: Human derived U373 cells were cultured and incubated with taurolidine and the median inhibitory concentration (IC50) was calculated. Flow cytometric analysis was performed to assess changes in DNA content. The cells were qualitatively and quantitatively examined using light microscopy and electron microscopy. LN-18 and LN-229 cells were incubated in the absence or presence of either Fas-ligand, taurolidine or respective combinations thereof. The cell viability was determined by adding a double concentrated WST-1 reagent. The activity of the mitochondrial succinate reductase was measured in an ELISA reader. RESULTS: The exposure of U373 cells to taurolidine led to a concentration-dependent (IC50 35.8 +/- 2.2 micrograms/ml) loss of cell viability. Flow cytometric analysis demonstrated a concentration-dependent appearance of DNA debris in the sub-Go/G1 region. In the presence of 6.25 vol.% Fas-ligand, LN-18 cells displayed more than 90% loss of cell viability, whereas the viability of LN-229 cells was reduced only at higher concentrations of Fas-ligand. Taurolidine by itself did not appreciably affect the viability of LN-18 cells in the investigated concentration range, but was able to enhance the effect of Fasligand on LN-18 cells. The exposure of LN-229 cells to taurolidine alone caused an appreciable loss of cell viability by about 70% at the highest concentration tested. Cell destruction by Fas-ligand (10 vol.%) was enhanced in the presence of taurolidine. CONCLUSION: The antineoplastic activity of taurolidine seems to be partially based on the enhancement of Fas-ligand-induced apoptosis. In addition, taurolidine was demonstrated to have an antieoplastic effect independent of Fas-ligand. Perhaps taurolidine exerts antineoplastic activity based on different mechanisms.

Antineoplastic Agents↗

PubMedDate not supplied

Taurolidine-Fibrin-Sealant-Matrix using spray application for local treatment of brain tumors.

Malignant gliomas tend to recur in the vast majority of cases. Recurrent gliomas may arise from vital tumor cells present in this zone around the resection margin. It appears promising to combine tumor resection with local chemotherapy using an antineoplastic, but non-toxic agent. Taurolidine exerts a selective antineoplastic effect by induction of programmed cell death and has anti-angiogenic activity. Fibrin sealant is completely degradable and firmly adheres to brain tissue, suggesting that it would provide a suitable matrix for taurolidine delivery--a Taurolidine-Fibrin-Sealant-Matrix (TFM)--in the local treatment of brain tumors. The potential of local delivery of taurolidine out of a fibrin sealant matrix was investigated. Taurolidine could be suspended homogeneously in both the thrombin and the procoagulant protein components of the fibrin sealant. The fibrin sealant matrix was a suitable carrier for the suspension of taurolidine at a concentration that ensured the release of therapeutically effective amounts of the drug over a period of 2 weeks in vitro. The antineoplastic action of taurolidine was not affected by embedding in the fibrin sealant matrix. The described drug delivery system may be suitable for local taurolidine treatment of brain tumors following complete or partial resection or of tumors that are non-resectable because of their location.

Antineoplastic Agents↗