Biomedical subjects

R Buchholz

Publications and source records attributed to R Buchholz.

At least 19 recordsLinked to original sources

PubMed2005

Synthesis of enantiopure (5R)-hydroxyhexane-2-one with immobilised whole cells of Lactobacillus kefiri.

Whole-cell reduction of (2,5)-hexanedione to yield highly enantiopure (5R)-hydroxyhexane-2-one (enantiomeric excess >99%) with Lactobacillus kefiri DSM 20587 was investigated. Cell immobilisation with sodium cellulose sulphate was chosen as the most suitable encapsulation matrix, giving an immobilisation yield of 40%. Despite the lowered biocatalytic activity from cell immobilisation, the bioreduction process was vastly improved with the help of reaction engineering techniques (batch to a plug flow reactor set-up). High selectivity (95%) and space-time yield (87 g L(-1) day(-1)) were achieved in the plug flow reactor. The biocatalyst remained active (68% residual activity) after 6 days of operation.

Bioreactors↗

PubMed2001

Comparative analysis of the biosorption of cadmium, lead, nickel, and zinc by algae.

Thirty strains of algae were examined for their biosorption abilities in the uptake of cadmium, lead, nickel, and zinc from aqueous solution. A wide range of adsorption capacities between the different strains of algae and between the four metals can be observed. The cyanophyceae Lyngbya taylorii exhibited high uptake capacities for the four metals. The algae showed maximum capacities according to the Langmuir Adsorption Model of 1.47 mmol lead, 0.37 mmol cadmium, 0.65 mmol nickel, and 0.49 mmol zinc per gram of dry biomass. The optimum pH for L. taylorii was between pH 3 and 7 for lead, cadmium, and zinc and between pH 4 and 7 for nickel. Studies with the algae indicated a preference for the uptake of lead over cadmium, nickel, and zinc in a four metal solution. The metal binding abilities of L. taylorii could be improved by phosphorylation of the biomass. The modified biosorbent demonstrated maximum capacities of 2.52 mmol cadmium, 3.08 mmol lead, 2.79 mmol nickel, and 2.60 mmol zinc per gram of dry biomass. Investigations with phosphated L. taylorii indicated high capacities for the four metals also at low pH. The selectivity remained quite similar to the unmodified algae.

Absorption↗

PubMed2000

Enhancement of mass transfer using colloidal liquid aphrons: measurement of mass transfer coefficients in liquid-liquid extraction.

Interphase mass transfer of a sparingly soluble solute is often the rate-limiting step in multiphase biocatalytic processes. Colloidal liquid aphrons (CLA) provide very large interfacial areas, and thus could enhance mass transfer in such processes. The aim of this study was to characterize mass transfer properties of CLA dispersions during transfer of heptanoic acid from water to limonene. The interfacial area per unit volume (a), film mass transfer coefficient (K(L)), and volumetric mass transfer coefficient (K(L)a) values were determined in a stirred-tank reactor. These results were used, along with a literature correlation, to estimate the mass transfer coefficient of the surfactant-stabilized shell surrounding the CLA. The very large increase in a provided by the CLA was only partially offset by a slight increase in the mass transfer resistance of the shell. As a result, the range of K(L)a values obtained using CLA was about an order of magnitude greater than that obtained using a conventional dispersion. The concentration of the aqueous-phase surfactant used to form the CLA strongly affected the Sauter mean diameter of the CLA; however, the concentration of the nonpolar-phase surfactant had little effect. These results suggest that CLA have considerable potential for multiphase biocatalytic applications.

Biotechnology↗

PubMed1998

The Nop60B gene of Drosophila encodes an essential nucleolar protein that functions in yeast.

The Cbf5 protein of Saccharomyces cerevisiae was originally identified as a low-affinity centromeric DNA-binding protein, and chf5 mutants have a defect in rRNA synthesis. A closely related protein from mammals, NAP57, is a nucleolar protein that coimmunoprecipitates with the nucleolar phosphoprotein Nopp140. To study the function of this protein family in a higher eukaryote that is amenable to genetic approaches, the gene encoding a Drosophila melanogaster homolog, Nop60B, was identified. The predicted Drosophila protein shares a high degree of sequence identity over a 380-residue region with both the mammalian and yeast proteins, and shares several conserved motifs with the prokaryotic tRNA pseudouridine 55 synthases. Nop60B RNA is found at high levels in nurse cells and in the oocyte, and is present throughout development. Nop60B protein is localized primarily to the nucleolus of interphase cells, and is absent from the chromosomes during mitosis. Nop60B mutants were generated and shown to be homozygous lethal. The Drosophila gene can rescue the lethal phenotype of yeast chf5 mutations, showing that the function of this protein has been conserved from yeast to Drosophila.

Amino Acid Sequence↗

PubMed1998

Intrathecal therapy of leptomeningeal CEM T-cell lymphoma in nude rats with anti-CD7 ricin toxin A chain immunotoxin.

We have established a new xenogeneic animal model of leptomeningeal metastasis (LM) by intracisternal inoculation of human CEM T-cell lymphoma into nude rats, and used it to evaluate the anti-lymphoma efficacy of an anti-CD7 ricin A chain immunotoxin (DA7). In vitro incubation with 2 microg/ml DA7 for 72 h inhibited CEM cells by 90% in a trypan blue exclusion assay. To establish its anti-lymphoma activity, one and four days after cisternal inoculation of 10(6) CEM cells, eight animals each were treated cisternally with 10 microg DA7 in 50 microl PBS or sham-treated with 50 microl PBS. Histopathologically, all eight sham-treated and five of eight DA7 treated animals showed typical features of LM with multilayers of tumor cells along the whole subarachnoid space and the ventricular walls, as well as subependymal and diffuse parenchymal tumor cell infiltration. Three DA7 treated animals were free of tumor. Two of these animals were asymptomatic long-term survivors (> 90 days). The third tumor-free animal suddenly died on day 51. Histology revealed viral myocarditis. Median symptom-free survival was 51 days (range 29-90+ days) in DA7 treated and 34 days (range 29-87 days) in sham-treated animals (p = 0.12, log-rank test). Histologically, no signs of neurotoxicity or systemic toxicity was found. However, DA7 treated animals showed a tendency to a slower weight increase on days 6-28 after tumor cell inoculation. Our results indicate that this model is useful in studying leptomeningeal seeding and intracisternal treatment of lymphoma. The demonstrated anti-tumor effect of DA7 treatment deserves further evaluation especially regarding the application of DA7 in early stages of LM from T-cell lymphoma.

Animals↗

PubMed1997

Animal model of human medulloblastoma: clinical, magnetic resonance imaging, and histopathological findings after intra-cisternal injection of MHH-MED-1 cells into nude rats.

To establish an animal model of human medulloblastoma, we have injected human MHH-MED-1 cells into the cisterna magna of nude rats. Tumors grew in 3 out of 4 animals injected with 10(6) medulloblastoma cells. Affected animals showed little or no weight gain and eventually lost weight but did not develop obvious neurological symptoms until the end of observation on day 31 after inoculation. At this time, magnetic resonance imaging (MRI) in tumor-bearing rats revealed contrast enhancement in the region of the fourth ventricle and the cisterna magna. Neuropathological examination demonstrated corresponding leptomeningeal growth in the cisterna magna invading the medulla oblongata, and tumor growth within the fourth ventricle invading the pons. The tumors basically showed the same immunostaining pattern as MHH-MED-1 cells in vitro expressing neuron-specific enolase (NSE) and vimentin, but no neurofilaments (NFs), synapthophysin, or glial fibrillary acidic protein (GFAP). No tumor grew in the fourth animal, which had a normal weight gain and no alteration on MRI. In conclusion (1) the intrathecally injected human medulloblastoma cells spread similar to medulloblastomas in patients, (2) tumor growth is readily detected by MRI, (3) the new animal model is a suitable tool for further experimental research including intrathecal therapeutic studies.

Animals↗

PubMed1996

Morphological analysis of yeast cells using an automated image processing system.

In order to control the growth of the yeast Saccharomyces cerevisiae during cultivations, a fully-automated sampling and analysing system has been developed. Based on the microscopic appearance of cells, a detailed characterization of yeast suspensions from the bioreactor is available, presenting data of current cell concentrations, distributions of process-dependent cell structures and parts of cells containing vacuoles. This measuring system combines quantitative and qualitative analysis methods in a digital image processing technique, which offers the possibility of on-line estimation of cell development that approximates real-time. Perturbations within the process are detectable in time and regulative actions can be done without any delay.

Bioreactors↗

PubMed1996

Intrathecal treatment of C6 glioma leptomeningeal metastasis in Wistar rats with interleukin-2.

The efficacy of intrathecal treatment of leptomeningeal metastasis (LM) with interleukin-2 (IL-2) was evaluated in an animal model using Wistar rats inoculated intracisternally with 10(7) C6 glioma cells. Prior to the in vivo experiments the antiproliferative effects of human IL-2, and of murine IFN-gamma and TNF-alpha which are cytokines induced by IL-2 were tested in a colony forming assay. Only IFN-gamma caused a dose-dependent inhibition of colony formation. Twelve animals were treated intracisternally with either 10(5) IU IL-2 or control medium on day 0, 2, and 5 after tumor cell inoculation. Both IL-2 treated and sham-treated animals developed LM with a symptom-free survival of 7 to 9 days. There was no significant difference between treated and untreated animals regarding time to onset of symptoms and pattern of tumor growth. Infiltration of the tumor tissue with ED-1+ monocytes and macrophages, and CD8+ lymphocytes, however, was slightly increased in IL-2 treated animals. In a second experiment 4 non tumor-bearing Wistar rats were intracisternally injected with a single dose of 10(5) IU IL-2. These animals also showed slightly enhanced leptomeningeal infiltration with CD8+ lymphocytes compared to controls. We conclude that intrathecal application of high-dose IL-2 although eliciting a slight immune reaction within the leptomeninges does not inhibit leptomeningeal tumor growth or prolong symptom-free survival in our animal model of LM. These results raise doubt about the clinical efficacy of intrathecal IL-2 treatment in patients with LM.

Animals↗

PubMed1995

Repeated decompressive craniectomy after head injury in children: two successful cases as result of improved neuromonitoring.

BACKGROUND Decompressive craniectomy in the treatment of posttraumatic brain swelling is not generally accepted. Until now the efficacy of operative decompressive craniectomy in posttraumatic brain swelling of children appeared more promising. However, the criteria for such procedures remain unclearly defined. METHODS We present two children who had repeated decompressive craniectomy following head injury, in order to control intracranial pressure (ICP) sufficiently. Our indications for performing a decompressive craniectomy in the presence of conservatively uncontrollable raised ICP are: (1) Patient is between the ages of 3 and 35 years. (2) An initial Glasgow Coma Scale (GCS) ranging between 4 and 8. (3) Three criteria have to be fulfilled at the same time: The cerebral perfusion pressure (CPP) has to drop to values of less than 60 mm Hg. It is impossible to control the ICP values (up to 45 mm Hg) conservatively. The diastolic velocity of the transcranial doppler sonography (TCD) has to decrease until only a systolic flow pattern is obtained. (4) No other mass lesion should be detected on cranial computed tomography (CCT) that could account for the rise in pressure. In both cases we performed bifrontal decompressive craniectomies. RESULTS Both patients survived. Seven months after the accident, patient No. 1 was oriented and could walk on her own with a mild right-side hemiparesis. Patient No. 2 could attend school 12 months postinjury. Both patients developed hygromas after the craniectomy. A shunt operation, however, was not necessary. CONCLUSIONS ICP monitoring, together with CCT examination, simultaneous recording of TCD, and systemic parameters, will reveal a patient at risk at a time when impending damage due to uncontrollable ICP may still be prevented. The simultaneous assessment of cerebral blood flow by transcranial doppler (TCD), in this situation, proves most valuable. It improves the guidelines of patient selection for decompressive craniectomy, in the presence of conservatively uncontrollable ICP.

Brain Edema↗

PubMed1994

Investigation of oxygen transfer through the membrane of polymer hollowspheres by oxygen micro-electrodes.

Estimation of oxygen transfer from an aqueous solution into polymer hollow spheres, as used for encapsulation of microorganisms, requires detection of the dissolved oxygen concentration inside the hollow sphere. Using microcoaxial needle electrodes, oxygen kinetics in different penetration depths within single cellulose-sulfate hollow spheres loaded with and without living yeast cells could be measured. Based on the reaction kinetics the diffusion coefficient for oxygen and the oxygen-uptake rate have been calculated. The diffusion coefficient DO2 within the thin membrane of cell-free spheres was in the order of 10(-10)m2s-1. Due to the liquid core of the hollow sphere the corresponding diffusion coefficient DO2 is in the range of the value for water. The oxygen-uptake rate QO2 in cell containing spheres could be estimated to 90 mmol l-1 h-1, which corresponds to a specific oxygen-uptake rate qO2 of 10 mmol g-1 h-1. It is to conclude that oxygen supply of the microorganisms inside the hollow spheres was, in this case, not critically influenced by the thin polymeric wall of the capsules.

Diffusion↗

PubMed1993

Comparative study of transcranial color duplex sonography and transcranial Doppler sonography in adults.

To determine whether the frequency shift recorded in basal cerebral arteries corresponds to "true" flow velocities, a prospective comparative study of transcranial color duplex sonography (TCCD) and transcranial Doppler sonography (TCD) was performed. A 2.0-MHz transducer of a computerized TCCD system and a TCD device were used. The middle cerebral artery (MCA) and anterior cerebral artery (ACA) were examined by TCCD in 49 healthy volunteers (mean age 35 +/- 12 years). In 45 of the same volunteers a comparative TCD examination was possible. The studies were carried out blindly by different examiners at separate appointments. Peak systolic flow velocity, end-diastolic maximum flow velocity, time-averaged maximum flow velocity, and the pulsatility index were measured by both techniques. Additionally, for TCCD, time-averaged flow velocity was assessed, the resistance index and a spectral broadening index were calculated, and the energy output required for reliable measurement was analyzed. The TCCD signals were recorded in 98% of both MCA's and ACA's; with TCD, signals were recorded in 98% of MCA's and 87% of ACA's. Although in both vessels the angle-corrected peak systolic and time-averaged maximum velocities were approximately 10% to 15% higher in TCCD than in TCD measurements, correlation of flow velocities between both techniques was significant (p < 0.0001); differences between sides and age-dependency of flow velocities corresponded as well. In a reproducibility study, TCCD was repeated in 27 subjects by a third examiner with significant correlation (p < 0.0001) of both TCCD examinations. It is concluded that the advantage of TCCD is associated more with a qualitative aspect than a quantitative one. The additional visual dimension of TCCD can open new diagnostic possibilities in cerebrovascular disorders.

Adult↗

PubMed1992

MR imaging of experimental meningeal melanomatosis in nude rats.

MR imaging of the rat brain has become an increasingly frequently used method in experimental neuroradiology. On a generally available 1.5 T whole body tomograph, supplemented with an individually made small coil and a special SE sequence we obtained fairly fine images of the structures of the rat brain. With gadolinium-DTPA, we were able to visualize posterior fossa and cervical leptomeningeal growth of intrathecally injected B16 melanoma in nude rats. Using MRI to follow experimental leptomeningeal metastasis, may provide a new means for diagnostic evaluation and preclinical testing of treatment modalities.

Animals↗

PubMed1992

Intrathecal ACNU treatment of B16 melanoma leptomeningeal metastasis in a new athymic rat model.

To evaluate new cytotoxic drugs for intrathecal treatment we developed an experimental model of leptomeningeal metastasis by intracisternal injection of 10(4) B16-F10 melanoma cells in nude rats. One hour in vitro incubation with 20 micrograms/ml ACNU (area under the drug concentration-time curve = 1200 microgramsxmin/ml) induced a 4-log kill of B16 melanoma cells. A single or repeated non-toxic dose of 1 mg/kg was injected into the cisterna magna of rats inoculated with tumor (area under the drug concentration-time curve assuming an even cerebrospinal fluid distribution greater than 7000 microgramsxmin/ml). Median survival free of symptoms was 16 days (range 14-27) for controls (n = 9) and 18 days (range 17-23) for rats treated with ACNU on day 4 (n = 9). Animals treated both on day 2 and 8 (n = 8) developed symptoms on day 21 (range 13-35). Neurological symptoms and neuropathological examination in animals with increased survival indicated local suppression of tumor growth in the cisterna magna but increased spinal seeding and mass growth. From these results and the available pharmacokinetic data on ACNU it is concluded that bolus injection of ACNU--although locally effective--is not a sufficient treatment of widespread leptomeningeal metastasis. An increased therapeutic efficacy might be achieved by ventriculolumbar perfusion.

Animals↗

PubMed1989

A comparison of reference method values for calcium, lithium and magnesium with method-dependent assigned values.

Commercially available control sera were analysed by the reference methods for calcium, lithium and magnesium. Calcium: The mean deviation of the target values for routine flame atomic absorption spectrometry from the reference method values was -1.2%, in the case of flame atomic emission spectrometry -0.1%. The assigned values of determinations by methylthymol blue and cresolphthalein showed a positive bias: +2.3 and +2.2%. Lithium: Target values for routine flame atomic absorption spectrometry and flame atomic emission spectrometry were in generally good agreement with the reference method values (deviation +1.7% and +0.7%), although the differences were dependent on concentration. Magnesium: The assigned values for routine flame atomic absorption spectrometry yielded a mean bias of -0.4% from the reference method value. The target values for absorption spectrometry after reaction with Magon and Calmagite, however, differed by +8.2% and +9.3% on average. These methods seem to be less suitable for the determination of magnesium in serum than FAAS and would have failed several times to meet the requirements of quality assessment.

Calcium↗

PubMed1986

Effects of alloxan-induced diabetes mellitus on the metabolism of the rat placenta.

Biochemical changes in the placenta were studied using alloxan-induced diabetes mellitus in the female rat. In comparison with a control group (n = 13) the placentas of the diabetic animals (n = 12) had significantly higher glucose, glycogen and protein levels. It was, however, shown that this supply of substrate was inadequately utilised for energy, as ATP/ADP quotient was lower and the ADP content was significantly higher. Metabolism still appeared to take place under aerobic conditions, as evidenced by the unchanged lactate levels. In terms of the protein content of the placentas, the activity of the enzymes we investigated (GOT, GPT, LDH, G-6-PDH, MDH, ICDH) was lowered by 25-44%. These results support the idea of global placental insufficiency in diabetics.

Adenosine Diphosphate↗

PubMed1986

In vivo formation of diiodotyrosine by extrathyroidal thyroxine ether-link cleavage and effects of mononitrotyrosine on this pathway in the rat.

The formation of DIT from T4 was quantitatively studied in thyroidectomized (T) rats given 16 micrograms synthetic T4 daily. Measurement of the elimination of radioiodinated DIT and T4 tracers from serum yielded MCRs of 19.0 ml/h X 100 g body weight for DIT and 0.65 ml/h X 100 g body weight for T4. Mean serum concentrations +/- SD (nanomoles per liter; n = 8) measured by RIA 24 and 48 h after the last T4 administration were as follows: DIT, 0.243 +/- 0.130 and 0.150 +/- 0.070, respectively; T4, 173 +/- 34 and 97 +/- 20, respectively. In T rats which had not received T4, DIT and iodothyronines in serum were undetectable. From the results of kinetic studies and RIA measurements, the fraction of circulating T4 converted to DIT was calculated to be 3.9-4.3%. After administration of the iodotyrosine inhibitor 3-nitro-L-tyrosine (MNT) to T4-treated T rats at a dosage of 50 mumol/day for 1 week or longer, it was possible to observe, on the one hand, the expected delay of DIT tracer elimination from serum resulting in a decreased MCR of 9.9 ml/h X 100 g body weight. On the other hand, MNT treatment led to a strong decline of DIT serum levels below the detection limit in all animal groups. This effect of MNT on the peripheral T4-to-DIT conversion requires further studies using other experimental systems for confirmation and elucidation of its mechanism. It is concluded that peripheral DIT formation in the animal model used occurs via ether-link cleavage of administered T4 and/or some of its iodothyronine metabolites. On the basis of data from recent studies, the peripheral DIT turnover resulting from iodothyronine degradation can be estimated to be about 35% in intact rats. Our data confirm the in vivo generation of extrathyroidal DIT from T4 in the rat. Although the experiments were performed at unphysiologically high T4 serum levels and our quantitative data, therefore, cannot be applied to euthyroid conditions with absolute certainty, the results suggest that ether-link cleavage of T4 yielding DIT is not an insignificant pathway of peripheral T4 metabolism in the rat.

Animals↗

PubMed1985

Oxygen transfer from gas bubble into liquid.

Oxygen transfer from a gas bubble into the surrounding liquid is examined by measuring oxygen pressure with Po2-needle electrodes at different distances from the bubble. From there, the mass transfer coefficient can be calculated. First measurements yielded results in the range to be expected.

Ethylene Glycol↗

PubMed1983

Effects of iodotyrosine deiodinase inhibition on serum concentrations and turnover of diiodotyrosine (DIT) and thyroxine (T4) in the rat.

Serum concentrations and metabolic clearance rates (MCR) of diiodotyrosine (DIT) and thyroxine (T4) have been measured by radioimmunoassay and tracer kinetic technique in both normal rats and rats treated with 3-nitro-L-tyrosine (MNT), a potent inhibitor of iodotyrosine deiodinase. In normal rats, DIT serum levels were 0.27 +/- 0.12 nmol/l (mean +/- SD); MCR was 15.9 ml/h . 100 g body weight (bw), and the turnover rate was 4.3 pmol/h . 100 g bw. Inhibition of iodotyrosine deiodination by treatment with 50 mumol MNT per day for 1 week caused a highly significant elevation of DIT serum levels to 4.80 +/- 3.30 nmol/l, a decrease of MCR to 9.0 ml/h . 100 g bw and a ten-fold increase of the DIT turnover rate to 43.2 pmol/h . 100 g bw. Serum concentrations of T4 and T3 decreased slightly, whereas the T4 turnover rate (37.5 vs 37.8 pmol/h . 100 g bw) and rT3 serum levels remained unchanged under MNT treatment. The study demonstrates the presence of measurable DIT serum concentrations in the normal rat. Inhibition of intra- and extrathyroidal iodotyrosine deiodinase leads to a situation in which circulating iodotyrosines play an equally important role in peripheral iodine turnover as the iodothyronines. Since DIT serum levels in normal and enzyme-blocked rats were comparable to those in normal human subjects and patients with iodotyrosine deiodinase defect respectively, MNT-treated rats afford a suitable experimental model for this disease.

Animals↗