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Biomedical subjects

M Fiedler

Publications and source records attributed to M Fiedler.

At least 19 recordsLinked to original sources
PubMed2007

Sirolimus improves early microcirculation, but impairs regeneration after pancreatic ischemia-reperfusion injury.

Ischemia and reperfusion injury remains a relevant problem in clinical pancreas transplantation. We investigated the effect of sirolimus (SRL) in a rodent model of 90-min warm pancreatic ischemia. Four groups were studied: (1) sham surgery and vehicle; (2) sham surgery and SRL; (3) warm ischemia and vehicle; (4) warm ischemia and SRL. SRL (1.5 mg/kg/day) and vehicle were administered intraperitoneally for 3 days prior to surgery until the animals were killed. Microcirculation was assessed immediately after reperfusion by means of intravital fluorescence microscopy. Histopathological injury, apoptosis, proliferation and biochemical parameters were analyzed at 2 h, 1 day and 5 days after surgery. Ninety minutes after ischemia, intravital microscopy revealed an improved functional capillary density (p < 0.05) and reduction of adherent leucocytes (p < 0.01) and platelets (p < 0.05) in the SRL-treated group compared to the vehicle-treated controls. In contrast, on day 5 after ischemia, the pancreatic tissue of SRL-treated animals showed a higher grade of histological injury (p < 0.05) and higher rate of apoptotic cells (p < 0.05) than the vehicle controls. In summary, our data indicate that administration of SRL improves microcirculation at a very early stage, but results in an impairment of the recovery phase after pancreatic ischemia-reperfusion injury.

Animals↗
PubMed2006

Immunology of HDV infection.

Hepatitis delta virus (HDV) infection may occur as coinfection with hepatitis B virus (HBV) or as superinfection of a chronically HBV-infected patient. A strong antibody response is mounted, which persists for many years; however, it is not able to modulate the course of infection. In most cases the superinfection takes a chronic course. In patients with inactive disease (HDV PCR negative) an oligospecific T-helper cell immune response and a cytotoxic T-cell response were found, which were absent in patients with persistent viremia. The role of the cellular immune response in liver injury during acute infection has not been investigated. Vaccination strategies tested in the woodchuck model induced specific B- and T-cell responses but failed to protect from HDV infection.

Animals↗
PubMed2006

Disseminated adenovirus infection with respiratory failure in pediatric liver transplant recipients: impact of intravenous cidofovir and inhaled nitric oxide.

Adenoviruses (AdV) are opportunistic pathogens that can lead to severe infections and respiratory failure (acute respiratory distress syndrome, ARDS) with high mortality in immunosuppressed patients. Cidofovir (CDV) has been used in adenoviral disease in bone marrow transplant recipients. Two pediatric liver transplant recipients with disseminated adenoviral disease and ARDS were treated with reduction of immunosuppression, CDV, and inhaled nitric oxide (iNO). CDV 1 mg/kg was given three times per week intravenously with intravenous hydration and oral probenecid. Viral suppression and clinical improvement was achieved. AdV hepatitis did not occur, and graft function was preserved, although acute rejection occurred in both patients. Adverse effects were mild and transient not requiring dose modification. Severe hypoxemia was reversed with iNO 10-20 p.p.m. CDV treatment of AdV infections in organ transplant recipients and other immunocompromised patients should be further investigated in prospective studies.

Adenovirus Infections, Human↗
PubMed2005

Fluctuation of the cytokine expression in the liver during the chronic woodchuck hepatitis virus (WHV) infection is not related to viral load.

The woodchuck together with the woodchuck hepatitis virus (WHV) is an excellent model to study the pathogenesis of hepadnaviral infections. Chronic WHV infection causes severe liver disease and hepatocellular carcinoma in woodchucks. The mechanism of viral clearance is not fully understood, interferons seem to play a major role in down-regulating viral replication prior to elimination of infected hepatocytes. We investigated on the pattern of cytokine and T-cell-marker expression in livers of woodchucks chronically infected with WHV. RNase-protection-assay (RPA) was used to determine mRNA of woodchuck specific genes (TNF-alpha, IFN-gamma, IL-15, CD3, CD4, CD8). Serial liver biopsies were performed daily or weekly in eight chronic WHV-carrier woodchucks. Cytokine/T-cell-marker expression differed significantly between the time points up to +/-50% within each woodchuck. The different expression patterns of cytokines or T-cell-markers did not correlate to the (weak) fluctuations in the viremia but may explain the observed fluctuations in the WHV/HBV-load in chronically infected individuals. Furthermore, we observed associations between cytokine and T-cell-marker expression. The marginal fluctuations in viremia during the chronic infection may indicate, that, once the chronic hepadnaviral infection is established, cytokines/interferons expressed endogenously (i.e. not vector-borne or injected) play only a minor role.

Animals↗
PubMed2003

High prevalence of human metapneumovirus infection in young children and genetic heterogeneity of the viral isolates.

RNA of the newly identified human metapneumovirus (HMPV) was detected in nasopharyngeal aspirates of 11 of 63 (17.5%) young children with respiratory tract disease. Markers of infection caused by another member of the Pneumovirinae subfamily of the family Paramyxoviridae, respiratory syncytial virus (RSV), were identified in 15 of these patients (23.8%). Three patients were simultaneously infected with HMPV and RSV. Studies of the clinical characteristics of HMPV-infected children did not reveal any difference between HMPV-infected patients and a control population of RSV-infected patients with regard to disease severity, but the duration of symptoms was significantly shorter for HMPV-infected patients. Phylogenetic analysis of the amplified viral genome fragments confirmed the existence and simultaneous circulation within one epidemic season of HMPV isolates belonging to two genetic lineages.

Genetic Variation↗
PubMed2002

5-Aminoimidazole-4-carboxamide ribonucleoside treatment improves glucose homeostasis in insulin-resistant diabetic (ob/ob) mice.

AIMS/HYPOTHESIS: The 5'AMP-activated protein kinase is an important mediator of muscle contraction-induced glucose transport and a target for pharmacological treatment of Type II (non-insulin-dependent) diabetes mellitus. The 5'AMP-activated protein kinase can be activated by 5-aminoimidazole-4-carboxamide ribonucleoside. We hypothesised that 5-aminoimidazole-4-carboxamide ribonucleoside treatment could restore glucose homeostasis in ob/ob mice. METHODS: Lean and ob/ob mice were given 5-aminoimidazole-4-carboxamide ribonucleoside (1 mg.g body wt(-1).day(-1) s.c) or 0.9 % NaCl (vehicle) for 1-7 days. RESULTS: Short-term 5-aminoimidazole-4-carboxamide ribonucleoside treatment normalised glucose concentrations in ob/ob mice within 1 h, with effects persisting over 4 h. After 1 week of daily injections, 5-aminoimidazole-4-carboxamide ribonucleoside treatment corrected hyperglycaemia, improved glucose tolerance, and increased GLUT4 and hexokinase II protein expression in skeletal muscle, but had deleterious effects on plasma non-esterified fatty acids and triglycerides. Treatment with 5-aminoimidazole-4-carboxamide ribonucleoside increased liver glycogen in fasted and fed ob/ob mice and muscle glycogen in fasted, but not fed ob/ob and lean mice. Defects in insulin-stimulated phosphatidylinositol 3-kinase and glucose transport in skeletal muscle from ob/ob mice were not corrected by 5-aminoimidazole-4-carboxamide ribonucleoside treatment. While ex vivo insulin-stimulated glucose transport was reduced in isolated muscle from ob/ob mice, the 5-aminoimidazole-4-carboxamide ribonucleoside stimulated response was normal. CONCLUSION/INTERPRETATION: The 5-aminoimidazole-4-carboxamide ribonucleoside mediated improvements in glucose homeostasis in ob/ob mice can be explained by effects in skeletal muscle and liver. Due to the apparently deleterious effects of 5-aminoimidazole-4-carboxamide ribonucleoside on the blood lipid profile, strategies to develop tissue-specific and pathway-specific activators of 5'AMP-activated protein kinase should be considered in order to improve glucose homeostasis.

Aminoimidazole Carboxamide↗
PubMed2002

An engineered IN-1 F(ab) fragment with improved affinity for the Nogo-A axonal growth inhibitor permits immunochemical detection and shows enhanced neutralizing activity.

The myelin axonal growth inhibitor NI-220/250 (Nogo-A) has attracted considerable attention in elucidating the mechanisms that account for the lack of plasticity in the adult central nervous system. The cognate monoclonal antibody IN-1, which was obtained prior to the molecular characterization of its Nogo-A antigen, has played a crucial role in this respect. However, this murine IgM/kappa antibody does not only provide an inappropriate format for in vivo studies, its low antigen affinity has also hampered the thorough structure-function analysis of its neutralizing effect toward the Nogo-A inhibitor on a molecular basis. We describe here the affinity maturation of a bacterially produced functional IN-1 F(ab) fragment via protein engineering. A soluble fragment of Nogo-A derived from the central exon 3 of its gene, which was prepared by secretion into the periplasm of Escherichia coli, served as a target in these experiments. After repeated cycles of site-directed random mutagenesis and screening, the mutant II.1.8 of the IN-1 F(ab) fragment was obtained, carrying five side chain substitutions within CDR-L3. Its dissociation constant for the complex with the recombinant Nogo-A fragment was determined in surface plasmon resonance measurements as approximately 1 microM. The affinity of the unmutated IN-1 F(ab) fragment was 8-fold lower. The engineered F(ab) fragment appeared to be well suited for the specific detection of Nogo-A in immunochemical assays and for the histochemical staining of myelin-rich tissue sections. Most importantly, its concentration-dependent neutralizing effect on the Nogo-A inhibitory activity was significantly enhanced in cell culture. This study confirms Nogo-A to be the antigen of the IN-1 antibody and it demonstrates increased potential of the engineered F(ab) fragment as a reagent for promoting axonal regeneration in vivo.

Amino Acid Substitution↗
PubMed2001

Immunization of woodchucks (Marmota monax) with hepatitis delta virus DNA vaccine.

We investigated the DNA immunization approach in order to induce a protective immune response against hepatitis delta virus (HDV) superinfection of chronically woodchuck hepatitis virus (WHV) infected woodchucks. The animals were immunized with an expression vector encoding HDAg by gene gun. T cell and humoral immune responses induced by this protocol were determined and compared with those induced by HDAg immunization using a CpG oligonucleotide as an adjuvant. After immunization the woodchucks were challenged with 10(6) genome equivalents of HDV. The protein immunization with HDAg induced good humoral and T helper cell responses in the woodchucks, but did not protect them from HDV superinfection. The DNA immunized woodchucks were also not protected from HDV superinfection, however, the course of infection was modified: HDV viremia occurred later, the typical fluctuation of the HDV RNA titer with several peaks was absent, and antibodies to HDV were not detectable.

Animals↗
PubMed2001

proBA complementation of an auxotrophic E. coli strain improves plasmid stability and expression yield during fermenter production of a recombinant antibody fragment.

The proline-auxotrophic Escherichia coli K12 strain JM83 harbouring an expression vector providing the proBA gene in trans was utilized for the fermenter production of the partially humanized IN-1 antibody F(ab) fragment. Thus, plasmid-mediated complementation of the chromosomal proBA deletion was employed as a second selection mechanism, together with a chloramphenicol resistance, in order to (i) abolish plasmid loss and (ii) benefit from E. coli JM83 as an expression strain with approved periplasmic protein secretion characteristics in the presence of a minimal medium. Starting from the generic vector pASK75, which makes use of the tightly regulated and chemically inducible tet promoter for foreign gene expression, a set of new vectors carrying the entire or part of the proBA operon was constructed and compared concerning their capability of functional Delta proBA complementation as well as recombinant protein yield. As a result, the vector pMF1 was developed, where transcription of the proBA operon is controlled by its own constitutive promoter and terminator sequences, permitting the transformed JM83 strain to grow under glucose/ammonia minimal culture conditions. When pMF1 was used for the fermenter production of the IN-1 F(ab) fragment, no plasmid loss was observed during the growth and induction phases, and the yield of functionally purified recombinant protein was found to be considerably improved.

Aldehyde Oxidoreductases↗
PubMed2001

Large nontransplanted hepatocellular carcinoma in woodchucks: treatment with adenovirus-mediated delivery of interleukin 12/B7.1 genes.

BACKGROUND: Cytokine-based gene therapy strategies efficiently stimulate immune responses against many established transplanted tumors, leading to rejection of the tumor. In this study, we investigated the therapeutic potential of cancer immunotherapy in a clinically more relevant model, woodchucks with primary hepatocellular carcinomas induced by woodchuck hepatitis virus. METHODS: Large (2-5 cm), established intrahepatic tumors were given an injection once with 1 x 10(9) plaque-forming units of AdIL-12/B7.1, an adenovirus vector carrying genes for murine interleukin 12 and B7.1, or of AdEGFP, the control virus, and regression of the tumors was then monitored. Five animals were used in total. RESULTS: In four tumor-bearing animals, the antitumor response was assessed by autopsy and histologic analysis within 1-2 weeks after treatment. In all animals treated with AdIL-12/B7.1 therapy versus AdEGFP therapy, we observed substantial tumor regression (P =.006; two-sided unpaired Student's t test) accompanied by a massive infiltration of T lymphocytes. These tumors also contained increased levels of CD4(+) and CD8(+) T cells and interferon gamma (IFN gamma). In continuously growing tumor nodules given an injection of the control virus or in nontumoral liver, no such effects (i.e., tumor regression and increased levels of CD4(+) and CD8(+) T cells and IFN gamma) were detected. In the fifth animal, monitored for long-term antitumor efficacy by magnetic resonance imaging (MRI) after intratumoral vector administration by MRI guidance, the tumor was almost completely eliminated (> or = 95%) 7 weeks after treatment. CONCLUSION: Adenovirus vector-based immunotherapy appears to be an effective treatment of large nontransplanted (orthotopic) tumors that acquire malignant characteristics in a stepwise process, reflecting the real-world scenario of hepatocellular carcinoma in humans.

Adenoviridae↗
PubMed2001

5-aminoimidazole-4-carboxy-amide-1-beta-D-ribofuranoside treatment ameliorates hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice.

AIM/HYPOTHESIS: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside increases 5'-AMP-activated kinase activity in insulin-sensitive tissues known to control glucose homeostasis. We hypothesised that 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment could have a beneficial effect on glucose homeostasis in KKAy-CETP mice, a model of Type II (non-insulin-dependent) diabetes mellitus. Our aim was to examine potential effects of acute and chronic (7-day) 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment on glucose homeostasis in KKAy-CETP diabetic mice. METHODS: Female KKAy-CETP mice were treated with 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside by a single daily injection for 7 days (100, 300, or 500 mg. kg-1. day-1). RESULTS: After 7 days of treatment with 500 mg. kg-1. day-1 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside, blood glucose and plasma insulin concentrations were reduced (p < 0.01). Body weight and food intake were also reduced after treatment (p < 0.01 and p < 0.05, respectively). Glucose and insulin tolerance were improved (p < 0.05), whereas endogenous glucose production was suppressed (p < 0.05). The beneficial effect of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside on hyperglycaemia and hyperinsulinaemia was due to an inhibition of endogenous glucose production, since in vivo and in vitro basal and insulin-stimulated glucose uptake in skeletal muscle was not affected by 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside. Other features of the treatment included increased plasma of free fatty acid concentration (1.9-fold, p < 0.01) and triglycerides (1.3-fold, p < 0.05). CONCLUSION/INTERPRETATION: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment attenuated hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice, a model of Type II diabetes. The blood glucose lowering effects of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside occurs mainly as a consequence of reduced endogenous glucose production because insulin-stimulated skeletal muscle glucose uptake has not been altered.

Aminoimidazole Carboxamide↗
PubMed2001

Vaccination against hepatitis delta virus infection: studies in the woodchuck (Marmota monax) model.

Hepatitis delta virus (HDV) superinfection of hepatitis B virus carriers causes severe liver disease and results in a high rate of chronicity. So far, neither sufficient therapy nor vaccines to prevent HBV carriers from superinfection are available. A good model to test vaccine candidates is the woodchuck chronically infected with the woodchuck hepatitis virus (WHV); the woodchuck can be superinfected with HDV and shows a course of infection similar to that of patients. Different strategies have been investigated to establish a protective vaccine against HDV superinfection. Both proteins of HDV (HDAg p24 and p27), which differ only in the C-terminal amino acid sequence, have been used as vaccine candidates. Synthetic peptides derived from B cell epitopes of HDAg and HDAg p24 expressed in Escherichia coli, yeast, or baculovirus have been used to immunize woodchucks. The protein immunization induced a specific antibody response, however, no protection from HDV superinfection was achieved. Vaccinations with vaccinia virus expressing HDAg p24 or p27 and DNA immunization with vectors expressing p24 were also not able to induce a protective immune response, but seemed to modulate the course of HDV superinfection. Thus, new strategies to develop a vaccine to prevent HDV superinfection are needed.

Animals↗
PubMed2000

Regeneration of lesioned corticospinal tract fibers in the adult rat induced by a recombinant, humanized IN-1 antibody fragment.

Axons in the CNS of higher vertebrates generally fail to regenerate after injury. This lack of regeneration is crucially influenced by neurite growth inhibitory protein constituents of CNS myelin. We have shown previously that a monoclonal antibody (mAb IN-1) capable of binding and neutralizing Nogo-A, a myelin-associated inhibitor of neurite growth, can induce long-distance axonal regeneration and increased structural plasticity with improved functional recovery in rat models of CNS injury. In this paper we demonstrate that a partially humanized, recombinant Fab fragment (rIN-1 Fab) derived from the original mAb IN-1, was able to promote long-distance regeneration of injured axons in the spinal cord of adult rats. When infused into a spinal cord injury site, regrowth of corticospinal fibers in 11 of 18 animals was observed after a survival time of 2 weeks. Regenerating fibers grew for >9 mm beyond the lesion site and arborized profusely in the distal cord. Regenerated fibers formed terminal arbors with varicosities in the spinal cord gray matter, strongly resembling synaptic points of contact to neurons in the spinal cord distal to the lesion. In animals that had received a bovine serum albumin solution or a recombinant IN-1 fragment that had been mutated in the antigen binding site (mutIN-1 Fab), no significant growth beyond normal lesion-induced sprouting was observed. Neutralization of endogenous nerve growth inhibitors represents a novel use of recombinant antibody technology with potential therapeutic applications after traumatic CNS lesions.

3T3 Cells↗
PubMed2000

The role of technical, biological, and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. VII. Seasonal influences on anticonvulsant drug actions in mouse models of generalized seizures.

Seasonal or circannual rhythms have been reported in various physiologic, biochemical, pharmacological, and toxicological studies in mice and rats despite laboratory conditions with standardized and controlled light cycle, temperature, humidity, and food. This may either be explained by the existence of innate, free-running circannual rhythms or by the existence of seasonally varying environmental factors ('zeitgeber') which are detected by the animals despite controlled laboratory conditions. In the present study, it was evaluated whether circannual rhythms affect the anticonvulsant activity of phenobarbital, carbamazepine, or valproate in two mouse models of generalized seizures, i.e. the threshold for generalized tonic seizures in the maximal electroshock seizure (MES) test and the threshold for different types of generalized seizures induced by the chemical convulsant pentylenetetrazol (PTZ). A study protocol was used with data sampling in separate groups of mice per month (using each group only once) over a period of 13 months beginning and ending in late summer (September), so that data collected in the other seasons could be compared with summer values of 2 subsequent years. With all three anticonvulsants, marked seasonal variation was observed in both seizure models with lowest anticonvulsant efficacy and potency in March and April, i.e. in late winter and early spring. The most marked loss of anticonvulsant activity in this period of the year was observed with valproate. Analysis of drug levels in plasma and brain indicated that the seasonal variation in phenobarbital's and carbamazepine's anticonvulsant effect was predominantly due to alterations in drug metabolism leading to reduced brain levels in March and April, while the seasonal rhythm in valproate's activity appeared to be mainly related to altered pharmacodynamic activity. These findings indicate that the time of the year is an important variable in the experimental evaluation of anticonvulsant drugs. Furthermore, the present data add to the accumulating evidence that endogenous circannual rhythms should be considered during animal experiments under controlled laboratory conditions.

Animals↗
PubMed2000

Repeated acute testing of anticonvulsant drugs in amygdala kindled rats: increase in anticonvulsant but decrease in adverse effect potential.

PURPOSE: Because preparation of kindled rats is laborious, time-consuming, and expensive, such animals are often used for several experiments in the evaluation of anticonvulsant drugs (AEDs). Furthermore, for comparison with data on new drugs, often "historical" data on standard drugs obtained in previous experiments in other groups of kindled rats are used. Without knowing how factors such as repeated drug testing or seasonal variation in drug responses affect drug potencies in the kindling model, false conclusions and predictions might be drawn from such comparisons. In this study, we examined the anticonvulsant and adverse effects of the three clinically established AEDs carbamazepine (CBZ), phenobarbital (PB), and valproate (VPA) once per month in the same two groups of amygdala-kindled rats over a period of 9 (group 1) or 6 (group 2) consecutive months. To evaluate the possible effect of the season, experiments in group 1 were started in autumn, and experiments in group 2 in spring. METHODS: For quantification of anticonvulsant activity, the focal seizure threshold (threshold for afterdischarges; ADT) was determined after each acute drug treatment and compared with a control ADT determined 2-3 days before. RESULTS: The repeated acute (single-dose) drug testing in the same groups of amygdala-kindled rats led to three pronounced alterations in the animals: (a) a significant decrease in ADT, (b) a marked potentiation of AED effects on ADT, and (c) a striking reduction in ataxia produced by drug treatments. Drug levels in plasma, which were determined in each drug trial, showed only moderate variation over the period of the experiments, so that the observed alterations in drug responses were certainly not due to pharmacokinetic factors. PB and VPA, but not CBZ, showed a more potent anticonvulsant effect when experiments were started in October (group 1) compared with April (group 2), but this difference was rapidly overridden by the marked and progressive potentiation of anticonvulsant activity on repeated drug testing. CONCLUSIONS: These data demonstrate that repeated use of the same kindled rats for acute drug testing significantly alters the sensitivity of the animals to the anticonvulsant and adverse effects of drugs. Because the anticonvulsant potency increases, whereas the adverse effect potential decreases during repeated acute drug testing, this may lead to false-positive data on a test compound. The mechanisms involved in these observations deserve further studies.

Amygdala↗