Biomedical subjects
Publications and source records attributed to S Fischer.
This paper reports on a case of hepatozoonosis of a dog imported from Italy to Germany. A survey of the biology and ecology of the causative agent as well as the pathogenesis, clinics, diagnosis, therapy and prophylaxis of Hepatozoon canis infection is presented.
P56lck is a protein tyrosine kinase of the Src family specifically expressed in T lymphocytes. Triggering of T cells with anti-CD3 or with phorbol 12-myristate 13-acetate (PMA) results in the appearance of slower migrating forms (shift) of p56lck. To investigate the phosphorylation sites on the shifted forms of p56lck and to assess the role of protein kinase C in this phosphorylation, Jurkat cells were treated with a selective inhibitor of this kinase (GF 109203X). This inhibitor completely reversed the shift induced by PMA but only partially reversed the one induced after triggering with anti-CD3. To analyze the shift further, p56lck was immunoprecipitated from in vivo labeled cells treated either with anti-CD3 or with PMA. Tryptic phosphopeptides were generated and analyzed by using a combination of thin layer chromatography, high reticulation polyacrylamide gel electrophoresis, reverse phase chromatography, and phosphopeptide sequencing. We identified serine 158 as a newly phosphorylated site after PMA treatment and tyrosine 192 and serine 194 in the major tryptic phosphopeptide obtained after anti-CD3 triggering. The three sites identified are located in the SH2 domain of p56lck; this suggests that their phosphorylation may regulate the interaction with other proteins or with other internal domains in p56lck.
A detailed mechanism for the catalysis of prolyl isomerization by the rotamase enzyme FKBP is proposed on the basis of a model constructed from the known structure of the FK506/FKBP complex. The model substrate is bound as a type VIa proline turn with the ends exposed to permit longer polypeptide chains (e.g., protein loops) to act as substrates. An ab initio potential for the isomerized imide bond is combined with a molecular mechanics representation of the rest of the system to calculate the reaction path. The resulting activation energy for the enzymatic cis-->trans isomerization is equal to about 6 kcal/mol, in good agreement with experiment. The lowering of the barrier relative to the solution value of 19 kcal/mol is found to arise from a combination of desolvation of the imide carbonyl, ground-state destabilization, substrate autocatalysis, and preferential transition-state binding. Minimal rearrangements are required in the enzyme and the substrate along the reaction path. The enzyme residues that participate in catalysis agree with the available mutation data. The type VIa turn model corresponds to a sequence-specific structural motif commonly found on the surface of proteins. It is likely to have a role in the formation of protein complexes with FKBP-like domains that function as foldases or chaperones.
Stimulation of sensitive cells with erythropoietin results in rapid induction of protein tyrosine phosphorylation. Other than tyrosine phosphorylation of one chain of the erythropoietin receptor, the identities of the remaining tyrosine-phosphorylated proteins are undefined. In this report, we demonstrate that the stimulation of the erythropoietin-sensitive human UT7 cells by erythropoietin rapidly resulted in the appearance of phosphatidylinositol 3-kinase activity in anti-phosphotyrosine immunoprecipitates. Erythropoietin action was rapid, detectable after as early as 1 min stimulation, transient, returning to control level after 30 min stimulation and was observed using the erythropoietin concentrations able to stimulate the cell proliferation. Anti-(phosphatidylinositol 3-kinase) antibodies specifically immunoprecipitated 125I-erythropoietin bound to its receptor, strongly suggesting that phosphatidylinositol 3-kinase associated with a protein complex containing the activated erythropoietin receptor. To confirm this result, phosphatidylinositol 3-kinase was immunoprecipitated from erythropoietin-stimulated cells using mild conditions followed by Western analysis using anti-phosphotyrosine antibodies. Five tyrosine phosphorylated proteins were revealed: the cloned chain of the erythropoietin receptor, the regulatory subunit of phosphatidylinositol 3-kinase and three unidentified proteins of 111, 97 and 64 kDa. None of these tyrosine phosphorylated proteins was detected in anti-(phosphatidylinositol 3-kinase) immunoprecipitates from unstimulated cells. Thus, our results show that phosphatidylinositol 3-kinase associates with a tyrosine-phosphorylated protein complex containing the activated erythropoietin receptor.
alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), an agonist of the non-N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor, was used to imitate glutamate-induced brain injury. A single intracerebroventricular injection of AMPA (9 nmol; 1.7 micrograms) induced convulsive reactions and heavy neurodegeneration in the hippocampal formation. MgSO4 (600 mg/kg), administered 20 min prior to or simultaneously with AMPA exposure, was able to protect completely against this non-NMDA-induced neurotoxicity. Magnesium is suggested to be a hopeful therapeutic principle for glutamate-mediated brain disorders.
At least two subsets of CD4+ T helper cell lymphocytes termed Th1 and Th2 exist in the mouse and probably in humans. They are characterized by the secretion of different lymphokines and by their functional behavior. Dysregulated expansion of one or the other subset may be one reason for the development of certain diseases. Thus, it is of importance to define the signals involved in the differentiation and activation of the two Th cell subsets. It is known and has been confirmed in this report that the cytokine interleukin (IL)-1 acts on Th2 cells but not on Th1 cells. We now report that a previously identified cytokine which was provisionally termed T cell stimulating factor is identical with IL-12 and exhibits a reciprocal behaviour to IL-1. IL-12 has several effects on Th1 cells. It can induce the proliferation of certain Th1 cells in combination with IL-2. Synthesis of interferon (IFN)-gamma by Th1 cells can be triggered by IL-2 plus IL-12. In contrast to the IFN-gamma production observed after T cell receptor (TcR) CD3 stimulation of Th1 cells with lectin Concanavalin A the IFN-gamma production induced by IL-12 + IL-2 is insensitive to the immunosuppressive drug cyclosporin A. Furthermore, IL-12 enhances the TcR/CD3-induced synthesis of IFN-gamma of several Th1 clones. Finally, IL-12 (+IL-2) induces homotypic cell aggregation of Th1 clones. This type of cell aggregation depends on the participation of LFA-1 and ICAM-1 molecules. In all activation systems with Th1 cells no effect of IL-1 was demonstrable. In contrast, only IL-1 but not IL-12 served as a co-stimulatory signal for several Th2 cell lines activated via the TcR/CD3 complex.
The recently discovered cytokine interleukin (IL)-12 is a heterodimeric protein of two disulfide-bonded subunits of 35 and 40 kDa. IL-12 has multiple effects on T cells and natural killer (NK) cells. In particular it appears to be a major factor for the development of cellular immunity. So far activity of the single subunits alone has not been described, however their expression is regulated independently. In this report we demonstrate for the first time that the mouse IL-12 subunit p40 (IL-12p40) specifically antagonizes the effects of the IL-12 heterodimer in different assay systems. The proliferation of mouse splenocytes activated by phorbol ester and IL-12 was inhibited by IL-12p40, whereas the proliferation induced by phorbol ester and IL-2 was not affected. Furthermore, the synthesis of interferon (IFN)-gamma by mouse splenocytes activated with IL-2 and IL-12 was suppressed by IL-12p40. Purified mouse splenic CD4+ T cells produced IFN-gamma upon activation with plate-bound anti-CD3 monoclonal antibody which was enhanced more than tenfold in the presence of IL-12. In this system IL-12p40 inhibited only the enhancement caused by IL-12 but not IFN-gamma synthesis of CD4+ T cells stimulated with anti-CD3 alone. Moreover, IL-12p40 inhibited the effects of IL-12 on differentiated T helper type 1 (Th1) cells. IFN-gamma production by Th1 cells induced in a T cell receptor-independent way by macrophages and IL-2 or macrophages and IL-12 was greatly reduced by IL-12p40 providing evidence for the endogenous synthesis of IL-12 in the Th1 cell, macrophage and IL-2 co-cultures. The specificity of inhibition was clearly demonstrated in the homotypic aggregation assay of Th1 cells. Incubation of Th1 cells with either IL-2 and IL-12 or IL-2 and tumor necrosis factor induces LFA-1/ICAM-1-dependent aggregation. Only IL-2 + IL-12 but not IL-2 + tumor necrosis factor-induced aggregation was inhibited in a dose-dependent manner by IL-12p40. Thus, the IL-12 subunit p40 appears to be a specific inhibitor for the IL-12 heterodimer.
OBJECTIVES: We sought to evaluate whether anticoagulation by an intravenous heparin infusion prevents deterioration of coronary blood flow restored by the novel recombinant plasminogen activator BM 06.022, and to compare the effects of profound fibrinogenolysis with those of an intravenous bolus injection of heparin. BACKGROUND: Recent clinical studies indicate that heparin appears to be effective in reducing reocclusion when combined with recombinant tissue-type plasminogen activator (rt-PA), but that heparin is associated with an increased bleeding incidence. Therefore, the need for heparin has to be critically evaluated in the development of BM 06.022. METHODS: BM 06.022 is an unglycosylated variant of human tissue-type plasminogen activator. Thrombus formation in anesthetized open chest dogs was induced by electrical injury. Left circumflex coronary artery blood flow was monitored for 4 h using an electromagnetic flow probe. Twenty dogs were randomized to receive intravenous heparin (100 IU/kg bolus plus 100 IU/kg per h) in group B or saline solution in group A before an intravenous bolus injection of 200 kU/kg (= 0.34 mg/kg) BM 06.022 1 h after thrombus formation. Another 14 dogs were randomized to receive a single intravenous bolus injection of 200 IU/kg heparin plus 200 kU/kg BM 06.022 in group D or saline solution plus 1,000 kU/kg BM 06.022 in group C. RESULTS: In the absence of a systemic lytic state, heparin infusion prolonged (p < 0.05) the cumulative patency time (sum of time intervals during which the coronary artery was patent) to 204.3 +/- 7.4 min (group B) compared with 34.6 +/- 10.8 min with saline solution (group A), and increased (p < 0.05) the area under the curve for coronary blood flow versus time (AUCFlow) to 34.0 +/- 3.4 ml.h.min-1 compared with 7.7 +/- 4.6 ml.h.min-1. Profound fibrinogenolysis after administration of 1,000 kU/kg BM 06.022 (group C) and a single intravenous heparin injection (group D) did not differ in their effects on the cumulative patency time (182 +/- 30.3 vs. 177.5 +/- 25.4 min) and AUCFlow (36.0 +/- 10.3 vs. 30.5 +/- 4.8 ml.h.min-1), but these values were improved (p < 0.05) compared with those obtained after administration of saline solution plus 200 kU/kg BM 06.022 (group A). CONCLUSIONS: In the absence of a systemic lytic state, intravenous heparin is required as an adjunct to BM 06.022 to maintain coronary blood flow in dogs.
In vivo infection of human T cell lymphocytes by HIV-1 is mediated by the specific binding of the HIV-1 envelope glycoprotein gp120 to the T cell CD4 receptor. One of the post-infection events observed in vivo is the progressive loss of CD4+ T cells. One possible mechanism is the production of infected T cells which are lacking in surface expression of the CD4 receptor protein. We have analysed this possibility utilizing the two HIV-1 chronically-infected CD4- cell lines, 8E5 and ACH-2, both of which are derived from a CD4+ parental strain (A3.01) after HIV-1 infection. In each cell (8E5 and ACH-2) the loss of CD4 surface expression was found to occur by different mechanisms. In ACH-2 cells, neither CD4 protein nor the 3 kb CD4 RNA transcript could be detected. However, treatment of ACH-2 cells with cycloheximide elicited production of the 3 kb transcript suggesting the possibility for a repressor protein(s) to act at the level of transcription and/or stability of the 3 kb mRNA. In contrast, in 8E5 cells the level of the 3 kb CD4 RNA was comparable with that found in the CD4+ A3.01 parental strain. Analysis of the 8E5 strain revealed the presence of a CD4- gp160 bimolecular protein complex sequestered internally in the rough endoplasmic reticulum (RER). Finally, the protein tyrosine kinase p56lck, normally associated with the cellular membrane, appeared to be linked to the RER and bound to the CD4- gp160 proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
To study the penetration of magnesium ions from blood into brain tissue, magnesium content in serum and hippocampus of normal and of excitotoxically affected rats was estimated after a single subcutaneous injection of magnesium sulphate (600 mg kg-1). In normal rats Mg2+ levels in serum rose from 1 to 6 mM, while that of the hippocampus remained constant, provided the brains were perfused before magnesium measurement. Following unilateral intracerebroventricular injection of the excitotoxic glutamate analogues, quinolinate or kainate acid, Mg2+ levels increased up to 38% on the (unaffected) contralateral side. Since magnesium is known to prevent glutamate-mediated neurodegeneration, our findings on the accessibility of exogenously applied magnesium may justify further investigations on the utility of magnesium for a therapeutic approach to limiting excitotoxic brain injury in human patients.
The aim of this study was to evaluate the biotransformation of orally administered ursodeoxycholic acid in man. The distribution of ursodeoxycholic acid and its metabolites in gallbladder bile, in serum and in urine with emphasis on separation of their unconjugated, amidated and sulfated species in particular, was investigated. Seven gallstone patients were given 750 mg of ursodeoxycholic acid daily for 2-3 weeks. Six gallstone patients who did not receive ursodeoxycholic acid served as controls. Ursodeoxycholic acid became the major bile acid in gallbladder bile contributing 43% to total bile acids. 2% of biliary ursodeoxycholic acids were in the unconjugated form, 87% in the amidated form and 11% in the sulfated form. Iso-ursodeoxycholic acid was found in bile in small amounts and was present only as the sulfated species and not as the amidated one. Other metabolites of ursodeoxycholic acid tentatively identified in bile were 1 beta, 12 beta, 6 alpha- and 21,22-hydroxylated derivatives of ursodeoxycholic acid. Lithocholic acid in bile tended to increase under ursodeoxycholic acid treatment and was positively correlated to ursodeoxycholic acid. The concentration of cholic acid in bile decreased significantly whereas the levels of deoxycholic acid and chenodeoxycholic acid did not change. Total bile acid concentration in serum and excretion of bile acids in urine increased from 5.4 +/- 1.1 to 18.4 +/- 9.5 mumol l-1 (mean +/- SD, P < 0.005) and from 5.6 +/- 1.3 to 13.1 +/- 7.9 mumol g-1 creatinine (mean +/- SD, P < 0.05) after ursodeoxycholic acid ingestion mainly due to spillover and excretion of ursodeoxycholic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
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The C-terminal src kinase (Csk) is responsible for the phosphorylation of the carboxy-terminal tyrosine of several tyrosine kinases of the Src family. This phosphorylation site has a negative regulatory function. Csk is unique among the members of the protein tyrosine kinase family because it lacks the conserved tyrosine autophosphorylation site and has been thought to be devoid of autophosphorylation activity. Using the glutathione S-transferase (GST) bacterial expression system, we have produced large amounts of a chimeric rat Csk protein. We have determined that the GST-Csk fusion protein isolated from bacteria is autophosphorylated on tyrosine residue(s). GST-Csk and purified Csk are capable of undergoing autophosphorylation on tyrosine residue(s) in vitro. The GST-Csk fusion protein also phosphorylates exogenous substrates, including the heteropolymer poly-Glu/Tyr and enolase. This is the first indication that Csk is autophosphorylated on tyrosine residue(s) both in vivo in bacteria expressing Csk cDNA and in vitro. These findings suggest that the autophosphorylation of Csk might play a role in the regulation of its kinase activity as well as its binding to other cellular proteins.
Anorexia and emaciation are symptoms which can be found in many diseases either singly or in combination with other unspecific clinical signs such as diarrhea and vomiting. Therefore accurately assessing the medical history, performing a thorough clinical examination and carrying out laboratory tests are all necessary steps in establishing a diagnosis. Further specific examinations such as radiography, ultrasonography or endoscopy may also have to be performed. Since anorexia and emaciation can result in severe consequences for the organism, establishing a definitive diagnosis is important to enable the appropriate therapy to be applied without delay.
Activity of fecal lysozyme was determined in healthy cats and cats with chronic diarrhea. The established reference value ranged from 0 up to 2.6 micrograms/g feces. Mean activity of the control group was 1.3 +/- 0.9 micrograms/g feces, mean activity of the patient group was 3.4 +/- 3.3 micrograms/g. There was a statistically significant difference between these two values. Nevertheless it was not possible to classify various diseases by evaluating lysozyme activity. In addition to endoscopy and histological examination, determination of lysozyme can be used as screening test and means of assessment for treatment and progress in cats with chronic diarrhea.
A case of successful operative repair of a previously unknown aortic dissection type A after intrapericardial rupture is presented. Under resuscitative measures an inferior pericardiotomy was done, followed by sternotomy to control bleeding under then stabilized circulation. Without detailed diagnostic evaluation, immediate operation with resection of the aneurysm and supracoronary prosthesis interposition was carried out. The diagnostic methods and problems, the differential diagnosis, and comparable cases from the literature are discussed.
The BT-PABA/Xylose test was used in 10 healthy cats and 49 cats with chronic diarrhea. In seven cats the test was performed three times in order to investigate individual variability. There was a statistically significant difference between the control group and the patients in the mean peak concentration of xylose, but no difference between groups of different diseases. The mean peaks of PABA were not significantly different between the control group and the patient group. Due to high individual variation in healthy cats the BT-PABA/Xylose test cannot be considered to be a useful test in feline diagnosis.
Polyclonal antibodies have been raised against two synthetic peptides reproducing the 48-64 and 353-369 sequences of CSK, a protein tyrosine kinase implicated in the down-regulation of src-related protein kinases. Both antibodies specifically recognize recombinant CSK and a CSK-related 49 kDa protein tyrosine kinase present in spleen but they do not cross-react with purified TPK-IIB, a spleen protein tyrosine kinase sharing with CSK catalytic activity toward src kinases and incapability to autophosphorylate. CSK and TPK-IIB once resolved from each other by heparin-Sepharose affinity chromatography, display opposite specificities toward synthetic peptides reproducing the sequences around the main phosphoacceptor residues of pp60c-src, namely Tyr-416 and Tyr-527. These data support the view that TPK-IIB and CSK may exert opposite effects on the activity of src-related protein tyrosine kinases.