Biomedical subjects

A Liebetrau

Publications and source records attributed to A Liebetrau.

4 recordsLinked to original sources

PubMed2002

[Fusion implants of carbon fiber reinforced plastic].

Carbon fiber reinforced plastics (CFRP) are used in the medical field when high mechanical strength, innovative design, and radiolucency (see spinal fusion implants) are needed. During the manufacturing process of the material CFRP carbon fibers are embedded into a resin matrix. This resin material could be thermoset (e.g., epoxy resin EPN/DDS) or thermoplastic (e.g., PEAK). CFRP is biocompatible, radiolucent, and has higher mechanical capabilities compared to other implant materials. This publication demonstrates the manufacturing process of fusion implants made of a thermoset matrix system using a fiber winding process. The material has been used clinically since 1994 for fusion implants of the cervical and lumbar spine. The results of the fusion systems CORNERSTONE-SR C (cervical) and UNION (lumbar) showed no implant-related complications. New implant systems made of this CFRP material are under investigation and are presented.

Adult↗

PubMed2000

Cellular immune responses persist and humoral responses decrease two decades after recovery from a single-source outbreak of hepatitis C.

As acute hepatitis C virus (HCV) infection is clinically inapparent in most cases, the immunologic correlates of recovery are not well defined. The cellular immune response is thought to contribute to the elimination of HCV-infected cells and a strong HCV-specific T-helper-cell (Th) response is associated with recovery from acute hepatitis C (ref. 2). However, diagnosis of resolved hepatitis C is based at present on the detection of HCV-specific antibodies and the absence of detectable HCV RNA, and detailed comparison of the humoral and cellular immune response has been hampered by the fact that patient cohorts as well as HCV strains are usually heterogeneous and that clinical data from acute-phase and long-term follow-up after infection generally are not available. We studied a cohort of women accidentally exposed to the same HCV strain of known sequence and found that circulating HCV-specific antibodies were undetectable in many patients 18-20 years after recovery, whereas HCV-specific helper and cytotoxic T-cell responses with an interferon (IFN)-gamma-producing (Tc1) phenotype persisted. The data indicate these HCV-specific CD4 + and CD8+ T cells are biomarkers for a prior HCV exposure and recovery. Because of undetectable antibodies against HCV, the incidence of self-limited HCV infections and recovery may be underestimated in the general population.

Antibody Specificity↗

PubMed1991

Adenosine receptor-coupled adenylate cyclase in the caudate nucleus of the rat brain.

5'-(N-Ethylcarboxamido)adenosine (NECA) and N6-[(R)-(phenylisopropyl)]adenosine (PIA) were incubated in an adenylate cyclase assay with a particulate fraction of caudate-putamen tissue of the rat, in order to examine the effect of kainic acid and a 6-hydroxydopamine-induced lesion on adenosine receptor coupled adenylate cyclase in vitro. There was an enhancement of formation of cyclic AMP induced by NECA, that was mediated by A2 adenosine receptors. Phenylisopropyl adenosine also stimulated adenylate cyclase in the striatum, with a maximum increase at 0.1 mM. At smaller concentrations, PIA inhibited the basal activity, which was previously described to be an effect mediated by A1 adenosine receptors. In caudate-putamen tissue from rats receiving a unilateral lesion, induced with kainic acid, basal and maximally NECA- and PIA-stimulated activity of adenylate cyclase was decreased. The maximum stimulatory effects of both substances were also significantly decreased, whereas no change of the inhibitory effect of PIA was observed. After unilateral lesion induced with 6-OHDA, basal and maximally NECA- and PIA-activated adenylate cyclase was increased; however, no inhibitory effect of PIA was seen. These results suggest that A2 adenosine receptor-coupled adenylate cyclase was located on neurones intrinsic to the neostriatum and probably postsynaptic to the dopaminergic input. The A1 adenosine receptors seem to be associated with the nigrostriatal pathway implying a presynaptic localization on dopaminergic afferents. In addition, since after both kainic acid- and 6-OHDA-induced lesions, respectively, in caudate-putamen tissue of the contralateral side, PIA no longer inhibited the activity of adenylate cyclase, contralateral structures also appeared to be involved in the regulation of A1 adenosine receptors.

Adenosine↗

PubMed1987

Dopamine and somatostatin modulated adenylate cyclase activity in the rat caudate-putamen following unilateral cortical ablation.

Dopamine and somatostatin-14 (SRIF) were incubated with a membrane fraction of rat caudate-putamen (CP) tissue in an adenylate cyclase assay in order to examine the D-1-receptor coupled adenylate cyclase activity 5 days and 3 weeks after unilateral ablation of the left frontal and lateral cortex. Five days after decortication the ipsilateral basal and dopamine stimulated adenylate cyclase activity was increased by about 30% compared to that of the contralateral side. Three weeks after decortication no significant difference could be seen. On either side basal and dopamine stimulated adenylate cyclase activity was not significantly decreased compared to sham operated controls. Somatostatin (10(-7) mol/l) reduced basal adenylate cyclase activity of the ipsilateral CP five days following lesioning and reduced the maximal stimulation induced by dopamine. The effects of somatostatin were most marked in the absence and at low concentrations of dopamine (10(-7)-10(-6) mol/l). The effects of somatostatin in the lesioned CP were no longer apparent three weeks following surgery. These results do not favour a presynaptic localization of D-1-receptors on cortico-striate projection fibers and suggest that somatostatin is involved in the interaction of the cortico-striate and nigro-striatal projection systems and may play a role in the regulation of D-1-receptor linked adenylate cyclase.

Adenylyl Cyclases↗