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Biomedical subjects

R Wenger

Publications and source records attributed to R Wenger.

At least 19 recordsLinked to original sources
PubMed1992

Molecular mechanisms of immunosuppression.

The immunosuppressive drug cyclosporin A (CsA, Sandimmun, SIM) is currently being evaluated in a variety of autoimmune disorders with some remarkable successes. Despite the wide empiric application of CsA, the precise mechanism of action of this drug remains elusive. To identify the molecular mode of action of CsA in the process of T cell activation, we have compared the biological profile of cyclophilin-binding cyclosporin analogues (CBCA), which lack immunosuppressive properties, with CsA. We have found that CsA binding to its intracellular receptor (cyclophilin) is required but not sufficient for immunosuppression. Moreover, inhibition of the peptidyl-prolyl cis-trans isomerase activity of cyclophilin does not seem to be relevant for the inhibitory effects of CsA. In analogy to the immunosuppressants FK506 and rapamycin, a specific structure at the 'effector' domain of the CsA molecule different from the immunophilin 'binding' domain determines the biological activity. Overall, a significant understanding of the structure-activity relationship of CsA has emerged. This will have a major impact on the identification of the precise mechanism of action of CsA and its side effects in the process of immunosuppression.

Amino Acid Isomerases↗
PubMed1991

Repeatability of transiently evoked otoacoustic emissions in normally hearing humans.

Transiently evoked otoacoustic emissions (TEOAEs) were stimulated using clicks. Responses were measured in each ear of 10 adult subjects during three test sessions separated by 3-day intervals. The purpose was to determine the amount of short-term variability in the amplitude of the emissions when measured under similar test conditions. For each of two modes of determining the stimulus level, mean overall response levels varied approximately 1 dB with repeated measurements. The spectra of the responses were analyzed in discrete frequency bands from 0.7 to 5.8 kHz. Response energy peaked at 1.2 kHz and was reduced markedly above 4 kHz. Variability within individual spectral bands was approximately 1 dB from 0.9 to 4.1 kHz and was slightly greater for 0.7 kHz. The amplitude of TEOAEs is stable over successive short-term measurements. The technique can be used as a sensitive means of monitoring cochlear function.

Adult↗
PubMed1990

Differential effect of insulin and epidermal growth factor on the mRNA translocation system and transport of specific poly(A+) mRNA and poly(A-) mRNA in isolated nuclei.

The efficiency of efflux of rapidly labeled poly(A)-containing mRNA from isolated rat liver nuclei was found to be modulated by insulin and epidermal growth factor (EGF) in a biphasic but opposite way. At physiological concentrations (10 pM insulin and 1 pM EGF), maximal stimulation of the transport rate by insulin (to 137%) and maximal inhibition by EGF (to 69%) were obtained; at higher concentrations (greater than 100 pM and greater than 10 pM, respectively), the amount of poly(A)-containing mRNA released into the postnuclear supernatant was nearly identical with the level found in untreated nuclei (= 100%). Using mRNA entrapped into closed nuclear envelope (NE) vesicles as a model system, it was found that the modulation of nuclear efflux of mRNA by the two growth factors occurs at the level of translocation through the nuclear pore. The NE nucleoside-triphosphatase (NTPase) activity, which is thought to mediate nucleocytoplasmic transport of at least some mRNAs, responded to insulin and EGF in the same manner as the mRNA transport rate. The increase in NTPase activity caused by insulin and the decrease in NTPase activity caused by EGF were found to be due to changes of the maximal catalytic rate; the Michaelis constant of the enzyme remained almost constant. Investigating the effect of the two growth factors on transport of specific mRNAs, poly(A)-containing actin mRNA was found to display the same alteration in efflux rate as rapidly labeled, total poly(A)-containing mRNA. In contrast, efflux of histone H4 mRNA, which lacks a 3'-poly(A) sequence, decreased in response to insulin and reached minimum levels at the same concentration at which maximum levels of actin mRNA transport rate were obtained. Studying the mechanism of action of insulin and EGF on NE mRNA translocation system, insulin was found to cause an enhancement of NE-associated phosphoprotein phosphatase activity, resulting in a dephosphorylation of the NE poly(A) binding site (= mRNA carrier) and, hence, in a decrease in its affinity to poly(A) [the poly(A) binding affinity of the poly(A)-recognizing mRNA carrier within the envelope is increased after phosphorylation]. EGF, on the other hand, stimulated the protein kinase, which phosphorylates the carrier, and, hence increased the NE poly(A) binding affinity. Because the stage of phosphorylation of the mRNA carrier (which is coupled with the NTPase within the intact NE structure) is inversely correlated with the activity of the NTPase, an enhancement of poly(A)-containing mRNA transport rate by insulin and an inhibition by EGF are observed.

Adenosine Triphosphate↗
PubMed1990

Binding of Tat protein to TAR region of human immunodeficiency virus type 1 blocks TAR-mediated activation of (2'-5')oligoadenylate synthetase.

The TAR sequence of the 5' leader of HIV-1 long terminal repeat-directed mRNA was found to be able to bind to and to activate double-stranded RNA-dependent (2'-5')A synthetase. Binding of TAR to the purified synthetase in vitro was abolished by addition of HIV-1 Tat protein, which binds to this sequence with a high affinity. Inhibition of TAR-mediated activation of (2'-5')A synthetase by Tat was prevented in the presence of the Zn2+ and Cd2+ chelators o-phenanthroline and penicillamine, which did not impair TAR-synthetase interaction. Transient expression assays of bacterial chloramphenicol acetyltransferase (CAT) gene in HeLa cells revealed that the levels of both CAT mRNA and CAT protein decreased after treatment of the cells with interferon, if CAT gene was linked to HIV-1 TAR segment. Cotransfection of the cells with a tat sequence containing plasmid rendered CAT gene expression insensible to the action of interferon.

2',5'-Oligoadenylate Synthetase↗
PubMed1990

Effect of nonviable preparations from human immunodeficiency virus type 1 on nuclear matrix-associated DNA polymerase alpha and DNA topoisomerase II activities.

In a previous paper, we determined that treatment of lymphocytes with nonviable preparations of human immunodeficiency virus type 1 (HIV-1) results in an impairment of the phosphatidylinositol/protein kinase C pathway, most likely due to an inhibition of the cleavage of phosphatidylinositol bisphosphate into inositol trisphosphate and diacylglycerol, mediated by phospholipase C. Here we show that one consequence of these changes is a reduced phosphorylation of nuclear matrix-associated DNA topoisomerase II, resulting in an inhibition of the activity of this enzyme. Antibodies to the viral proteins suppressed the inhibitory effects caused by the HIV-1 preparation. Furthermore, the phytohemagglutinin A-caused augmentation of nuclear matrix-associated DNA polymerase alpha and beta activities was found to be abolished by coincubation with the HIV preparation or with the HIV-1 gp120. The phytohemagglutinin A-enhanced matrix association and processivity of DNA polymerase alpha was determined to be reduced if the lymphocytes were in contact with HIV-1 preparation. These results suggest that the reduced proliferative response of lymphocytes to phytohemagglutinin A in the presence of disrupted HIV-1 preparation is due to inhibition of at least two, perhaps separate, pathways, one involving protein kinase C resulting in a reduced phosphorylation of DNA topoisomerase II and the other changing the state of matrix association of DNA polymerase alpha and beta.

DNA Polymerase II↗
PubMed1979

[Relationship between vitamin status (A, B1, B2, B6, and C), clinical features and nutritional habits in a population of old people (author's transl)].

112 patients in a medical ward were examined clinically and biochemically with regard to their vitamin status (plasma vitamin A, plasma vitamin C, blood glutathione reductase, vitamin B1, vitamin B2, N-methyl nicotinic acid amide and pyridoxic acid excretion). The nutritional habits were assessed by means of a questionnaire. The results of these two examinations were correlated with the clinical findings. The assessment of the vitamin B2 status showed a deficiency in 8 cases and a marginal vitamin B2 supply in a further 4 cases. The thiamine intake was insufficient in 43 cases and marginal in 42 cases. The biochemical assessment of vitamins C, B1 and PP indicated a deficiency of these vitamins. Dermatological signs pointed to a deficiency of vitamins A and B2. There was a significant correlation between the plasma vitamin A level and the serum iron level. The importance of milk and vegetables in the diet is stressed and also the association between milk consumption and the serum cholesterol level.

Aged↗
PubMed1976

[Postoperative endocardial fibrosis following mitral valve prosthesis].

Uncommon observation of endocardial fibroelastosis of the left auricle and ventricle found at autopsy. The 46-year-old female patient had her mitral valve replaced 15 months ago because of mitral stenosis (and slight incompetence). The left auricle with certainty did not show endocardial fibrosis at the time of operation. The therefore acquired postoperative fibroelastosis of the left auricle is probably caused mechanically resp. by hypoxia since postoperatively valvular incompetence and restenosis with severe thrombosis of the artificial valve developed. There are no reasons to assume an inflammatory etiology. It must remain open if the fibroelastosis of the left ventricle was congenital. Its possible etiology - if it was also acquired - is discussed.

Autopsy↗