Biomedical subjects

D Führer

Publications and source records attributed to D Führer.

30 records · Page 2Linked to original sources

PubMed1998

The extracellular thyrotropin receptor domain is not a major candidate for mutations in toxic thyroid nodules.

Constitutive activation of the cyclic adenosine monophosphate (cAMP) cascade by either thyrotropin receptor (TSHR) or gsp mutations is considered to be the major molecular cause of toxic thyroid nodules (TTNs). In a recent study we investigated a consecutive series of 31 TTNs and identified 15 somatic TSHR mutations (n = 14 in exon 10; n = 1 in exon 9) but no mutations in gsp exons 7-10. The purpose of the present study was to determine whether the extracellular TSHR domain would be a candidate for mutations causing TTNs. Therefore, we screened TSHR exons 1-8 in the remaining 16 TTNs without mutations in TSHR exons 9 and 10 and gsp exons 7-10 of our previous study. Except for a known functional polymorphism in exon 1 (Pro 52 Thr) in 2 TTNs and a silent base exchange in exon 7 (187 Asn) in 7 other TTNs no TSHR mutations were identified. To clarify the molecular etiology of TTNs without TSHR or gsp mutations, candidate genes in other steps of the cAMP cascade have to be considered.

Amino Acid Sequence↗

PubMed1998

Clonal origin of toxic thyroid nodules with constitutively activating thyrotropin receptor mutations.

Constitutively activating TSH receptor mutations have recently been detected in toxic nodules. In vitro studies suggest that mutated receptor signaling constitutively elevates cAMP, which causes hyperfunction and proliferation of thyrocytes. Therefore, toxic nodules with constitutively activating somatic TSH receptor mutations should result from clonal expansion of a single mutated cell. To test this hypothesis, we studied the clonal origin of 27 toxic nodules. In 13 of 27 nodules, a somatic mutation in the TSH receptor was identified. A PCR-based clonality assay that analyzes X-chromosome inactivation was used. The assay amplifies a polymorphism located in the androgen receptor gene. Of 27 toxic nodules studied, 23 (85%) were informative for the polymorphism. In the group that contains a somatic mutation in the TSH receptor, 10 of 11 cases showed nonrandom X inactivation, indicating clonal expansion. In only one toxic nodule with a TSH receptor mutation was random X inactivation detected. In the group without detectable mutations in exons 9 and 10 of the TSH receptor and exons 7-10 of the Gs alpha protein, only 6 of 12 toxic nodules show nonrandom X-chromosome inactivation. Therefore, the majority of toxic nodules with constitutively activating TSH receptor mutations are of clonal origin. This finding supports the hypothesis that toxic nodules arise from aberrant growth of a single cell. It is widely accepted that somatic mutations might initiate monoclonal growth. The TSH receptor mutations in these toxic nodules together with Gs alpha mutations in others are the most likely candidates for the initiation of this thyroid tumor. The clonal origin of toxic nodules in the group without detected mutations in the TSH receptor or the Gs alpha protein suggests somatic mutations in genes that are unknown to date.

Female↗

PubMed1997

Somatic mutations in the thyrotropin receptor gene and not in the Gs alpha protein gene in 31 toxic thyroid nodules.

Studies on frequency and distribution pattern of TSH receptor (TSHR) and Gs alpha protein (gsp) mutations in toxic thyroid nodules (TTNs) reported conflicting results, most likely also related to the different screening methods applied and the investigation of only part of exon 10 of the TSHR. Therefore, we screened a consecutive series of 31 TTNs for both TSHR and gsp mutations by direct sequencing of exon 9 and the entire exon 10 of the TSHR gene and exons 7-10 of the gsp gene. Somatic TSHR mutations were identified in 15 of 31 TTNs. TSHR mutations were localized in the third intracellular loop (Asp619Gly and Ala623Val), the sixth transmembrane segment (Phe631Leu and Thr632Ile, Asp633Glu) and the second extracellular loop (Ile568Thr). One mutation was found in the extracellular TSHR domain (Ser281Asn). Two new TSHR mutations were identified. One involves codon 656 in the third extracellular loop (Val656Phe). The other new mutation is a 27-bp deletion in the third intracellular loop resulting in deletion of 9 amino acids at codons 613-621. Transient expression of the new TSHR mutations in COS-7 cells demonstrated their constitutive activity. No mutation was found in exons 7-10 of the gsp gene. This finding was confirmed by an allele-specific PCR for mutations in gsp codons 201 (Arg-->His, Cys) and 227 (Gln-->His, Arg). Our data indicate that constitutively activating TSHR mutations can be found in 48% of TTNs and thus currently represent the most frequent molecular mechanism known in the etiopathogenesis of TTNs. Moreover, the absence of gsp mutations in our series argues for an only minor role of these mutations in TTNs. Constitutive activation of the TSHR by a deletion in a region that might be involved in G protein coupling of the TSHR offers new insights into TSHR activation.

Amino Acid Sequence↗

PubMed1997

Identification of a new thyrotropin receptor germline mutation (Leu629Phe) in a family with neonatal onset of autosomal dominant nonautoimmune hyperthyroidism.

Constitutively activating germline mutations in the TSH receptor (TSHR) gene have been identified as a cause of autosomal dominant nonautoimmune hyperthyroidism and sporadic congenital hyperthyroidism. We report a 10-yr-old boy and his 31-yr-old mother, both presenting with a history of recurring toxic thyroid hyperplasia and no evidence for autoimmune thyroid disease. In the boy, onset of hyperthyroidism and goiter was neonatal. In the mother, onset of thyroid disease dates back to early childhood. There was no history of thyroid disease in the rest of the family. Screening for germline mutations in exon 10 of the TSHR was performed by direct sequencing of genomic DNA extracted from peripheral blood leukocytes of both patients. In the boy and his mother, an identical heterozygous TSHR mutation was identified, exchanging leucine for phenylalanine at residue 629 of the TSHR (TTG-->TTT). Transient expression of the mutated TSHR construct in COS-7 cells confirmed the constitutive activity of the new TSHR germline mutation. This is the second family displaying congenital manifestation of hyperthyroidism in familial nonautoimmune hyperthyroidism.

Adult↗

PubMed1997

Identification of constitutively activating somatic thyrotropin receptor mutations in a subset of toxic multinodular goiters.

Constitutively activating mutations in the TSH receptor (TSHR) gene and in the Gs alpha gene are frequent molecular causes for solitary toxic nodules of the thyroid. However, the etiology of toxic multinodular goiter is still largely unknown. Therefore, DNA from nodular and quiescent surrounding tissue of six patients with toxic multinodular goiters was screened for mutations in exons 9 and 10 of the TSHR gene and exons 7-10 of the Gs alpha gene by direct automated sequencing. In one patient, two different somatic TSHR mutations were identified in two different toxic nodules (L632I and F631L). In another patient, two different toxic nodules harbored the same TSHR mutation (I630L), whereas only one TSHR mutation (F631L) was identified in one of the two toxic nodules of an additional patient. In the other three patients, no mutations could be found in exons 9 and 10 of the TSHR gene or in exons 7-10 of the Gs alpha gene. Our results demonstrate that not only solitary toxic adenomas but also toxic multinodular goiters can be caused by constitutively activating mutations of the TSHR. In addition to mutations in the TSHR and possibly in Gs alpha, there are probably other still unknown mechanisms that cause hot nodules in toxic multinodular goiters.

Amino Acid Sequence↗

PubMed1996

Constitutively activating mutations of the thyrotropin receptor and thyroid disease.

Recent advances in the understanding of the molecular biology of the TSH receptor had a considerable impact on several aspects of thyroidology. Identification and functional characterization of somatic mutations in the TSH receptor gene that activate the receptor ligand-independently. Provide an explanation for the molecular pathomechanisms of solitary toxic thyroid adenomas. Moreover, we have recently demonstrated, that multiple hyperfunctioning adenomas in the same thyroid gland can be caused by identical or different somatic Thyrotropin receptor mutations. Furthermore, germline mutations with similar characteristics have been reported in the TSH receptor gene of families with autosomal dominant forms of non-autoimmune hyperthyroidism and in two cases of sporadic congenital non-autoimmune hyperthyroidism. Interestingly, constitutively activating Thyrotropin receptor alterations have also been identified in differentiated thyroid carcinoma, thus implying a possible role of the constitutively active TSH receptor in the aetiopathology of both benign and malignant thyroid neoplasia.

Amino Acid Sequence↗

PubMed1996

Omega-3 lipid infusion in a heart allotransplant model. Shift in fatty acid and lipid mediator profiles and prolongation of transplant survival.

BACKGROUND: omega-3 Fatty acids may have a major impact on immune responses involved in heart transplant rejection. We compared the effects of posttransplant intravenous supplementation with omega-3-rich versus omega-6-rich lipid emulsions on graft survival, plasma fatty acid profiles, and levels of arachidonic acid versus eicosapentaenoic acid-derived lipid mediators. METHODS AND RESULTS: Inbred PVG and Wistar-Kyoto rats were used as donors and recipients, respectively, in a model of heterotopic heart transplantation. Animals received 9 g/kg body wt per day of either fish oil-derived (n = 8) or soybean oil-derived fat (n = 7) in the form of a continuously infused lipid emulsion; controls were sham-infused with saline (n = 8). Graft rejection was assessed by loss of activity of the transplant. The fish oil-derived preparation but not that originating from soybean oil caused an increase in total and free plasma fatty acids. Substantial quantities of eicosapentaenoic acid and docosahexaenoic acid appeared in the free fatty acid fraction, surpassing those of arachidonic acid. Ex vivo stimulation of neutrophils with the Ca2+ ionophore A23187 demonstrated an increase in 5-series leukotriene (LT) generation in animals undergoing omega-3 lipid infusion (LTB5, omega-oxidation products of LTB5, LTA5 secretion), with 5-series/4-series LT ratios ranging between 0.08 and 0.36. Ratios of TX B3/B2 liberated from ex vivo stimulated platelets even approached 1:1 in omega-3 supplemented rats. Graft survival was 7.6 +/- 0.3 (mean +/- SEM) days in saline-infused, 10.4 +/- 0.7 in omega-6 lipid-infused, and 12.9 +/- 0.4 in omega-3 lipid-infused animals. CONCLUSIONS: Posttransplant intravenous alimentation with fish oil-derived lipid emulsions prolongs heart transplant survival in excess to omega-6 lipids. Profound changes in fatty acid profiles and lipid mediator generation may underlie this finding.

Animals↗

PubMed1996

Acceleration of experimental diabetic retinopathy in the rat by omega-3 fatty acids.

Omega-3 fatty acids exert several important biological effects on factors that may predispose to diabetic retinopathy. Potential pathogenetic mechanisms include platelet dysfunction, altered eicosanoid production, increased blood viscosity in association with impaired cell deformability and pathologic leucocyte/endothelium interaction. Therefore, we tested whether a 6-month administration of fish oil (750 mg Maxepa, 5 times per week), containing 14% eicosapentaenoic acid (EPA) and 10% docosahexaenic acid, could inhibit the development of experimental retinopathy of the streptozotocin-diabetic rat. The efficiency of fish oil supplementation was evaluated by measuring EPA concentrations in total, plasma and membrane fatty acids and by measuring the generation of lipid mediators (leukotrienes and thromboxanes). Retinal digest preparations were quantitatively analysed for pericyte loss, and the formation of acellular capillaries. Omega-3 fatty acid administration to diabetic rats resulted in a twofold increase of EPA 20:5 in total fatty acids, and a reduction of the thromboxane ratio from 600 (untreated diabetic rats) to 50 (treated diabetic rats). Despite these biochemical changes, diabetes-associated pericyte loss remained unaffected and the formation of acellular, occluded capillaries was increased by 75% in the fish oil treated diabetic group (115.1 +/- 26.8; untreated diabetic 65.2 +/- 15.0 acellular capillary segments/mm2 of retinal area). We conclude from this study that dietary fish oil supplementation may be harmful for the diabetic microvasculature in the retina.

Animals↗

PubMed1995

Hydrolysis of fatty acid esters by Malassezia furfur: different utilization depending on alcohol moiety.

The lipophilic yeast Malassezia furfur belongs to the resident skin flora but has been implicated in various skin diseases. While topical oily preparations may support its growth, their formulation may be altered by yeast-dependent enzymatic degradation. Different synthetic fatty acid (mono-)esters used as refatting agents were mixed with 10(4), 10(5) and 5 x 10(5) yeasts/microliters, respectively, and incubated at 35 degrees C for a maximum of 48 h on selective agar for pathogenic fungi (Merck). The amount and pattern of generated free acids were evaluated by densitometric and gas chromatographic analysis, while yeast density was determined in a Neubauer chamber. Depending on the inoculum, yeast-dependent hydrolysis occurred immediately and was best effected in ethyl esters, followed by isopropyl esters, whereas hydrolysis of decyl oleate was only limited. Of the fatty acids released, unsaturated fatty acids were more stimulative to growth than saturated fatty acids; no toxic effects were observed. In conclusion, yeast-dependent hydrolysis of these synthetic fatty acid (mono-)esters was critically dependent on alcohol moiety, while growth promotion was best effected by unsaturated fatty acids. These results may help to improve the compatibility of topical formulations, especially in seborrheic areas.

Alcohols↗

PubMed1995

[Immunosuppressive effect of parenteral fat emulsions in defined immunostimulation].

BACKGROUND: In the heterotopic rat heart allotransplant model we have previously shown that intravenous fat emulsions are to a various extent immunosuppressive or immunoneutral, dependent on their n-3/n-6 fatty acid ratio. Safflower oil (n-3: n-6 = 1:370), fish oil (7.6:1) and soybean oil (1:6.5) prolonged the transplant survival time to 13.3, 12.3 and 10.4 days compared to 6.7 days (oil control group; 1.2.1) and 7.8 days (saline control group) (p < 0.01), respectively. This study presents a correlation of graft survival to immunohistological, cell biological and biochemical parameters. MATERIALS AND METHODS: 20% emulsions of safflower oil, fish oil, soybean oil and a 1:1 mixture of safflower and fish oil (oil control group) were continuously infused (9 g fat/kg body weight/day; n = 10 each group) after transplantation. Subpopulations of infiltrating and circulating immunocompetent cells and leukotriene B4 and B5 release of circulating mononuclear cells were analyzed (on the 4th postoperative day). RESULTS: In the 2 groups with the highest prolongation of graft survival the number of infiltrating cells was reduced by up to 40% and the peripheral blood mononuclear cell interleukin-6 release by up to 45%. Beyond that, circulating T cells were reduced in the fish oil group. Leukotriene B4 was released in all groups to the same extent, leukotriene B5 exclusively in the fish oil group. CONCLUSIONS: Intravenous fat emulsions show a varying immunomodulatory effect in dependence of the n-3/n-6 fatty acid ratio. Both n-6 and n-3 fatty acids, if applied as main fatty acid source, exert immunosuppressive effects by a diminished infiltration and mobilisation of immunocompetent cells. Soybean oil with a more balanced n-3/n-6 fatty acid ratio than safflower oil is significantly less immunosuppressive than safflower oil, and fat emulsions with a n-3/n-6 fatty acid ratio of 1:2 are immunologically neutral.

Animals↗

PubMed1993

A double-blind, randomized, placebo-controlled trial of n-3 fatty acid based lipid infusion in acute, extended guttate psoriasis. Rapid improvement of clinical manifestations and changes in neutrophil leukotriene profile.

Twenty patients hospitalized for acute psoriasis guttata with a minimum 10% of body surface area involvement (range 10-90%) completed a 10-day trial in which they were randomly allocated to receive daily infusions with either an n-3 fatty acid based lipid emulsion [100 ml/day with 2.1 g eicosapentaenoic (EPA) and 21 g docosahexaenoic acid (DHA)] or a conventional n-6 lipid emulsion (EPA + DHA < 0.1 g/100 ml). The severity of disease was evaluated by scoring daily erythema, infiltration, and desquamation and by a subjective scoring of clinical manifestations offered by the patients. Leukotriene (LT) and platelet-activating factor (PAF) generation were investigated in ionophore-stimulated neutrophils obtained on days 0, 1, 3, 5, 10, and 40. Moderate improvement in clinical manifestations was noted in the n-6 group (changes in score systems between 16-25% from baseline within 10 days). In contrast, the severity of disease markedly decreased in all patients of the n-3 group, with improvements in all score systems ranging between 45% and 76% within 10 days (P < 0.05 for each variable). The difference in response to the two regimens was evident within 4-7 days after onset of lipid infusion. A more than ten fold increase in neutrophil EPA-derived 5-lipoxygenase product formation (LTB5, its omega-oxidation products, non-enzymatic degradation products of LTA5 and 5-hydroxyeicosapentaenoic acid) was noted in the n-3 group but not in the n-6 group. Neutrophil PAF generation increased in the n-6 group but decreased in the n-3 group. In conclusion, modulation of eicosanoid metabolism by intravenous n-3 fatty acid supplementation appears to exert a rapid beneficial effect on inflammatory skin lesions in acute guttate psoriasis.

Acute Disease↗

PubMed1993

Influence of intravenous n-3 lipid supplementation on fatty acid profiles and lipid mediator generation in a patient with severe ulcerative colitis.

N-3 fatty acids were supplied to a 36-year-old female patient suffering from ulcerative colitis and severe steroid side-effects, in a sequence of parenteral and enteral administration. During a moderately active period of disease, 200 ml d-1 fish oil-derived lipid emulsion (eicosapentaenoic acid [EPA], 4.2 g; docosahexaenoic acid [DHA], 4.2 g) was infused for 9 days, in parallel with rapid tapering of the steroid dose. Disease activity declined rapidly, and the patient was subsequently provided with 16 fish oil capsules per day (EPA, 2.9 g; DHA, 1.9 g) for 2 months. At the end of this period of therapy, severe colitis recurred with intestinal and extraintestinal manifestations. The n-3 lipid emulsion was then used for intravenous alimentation (29 days, maximum dose 300 ml per day); during this time, marked improvement of the inflammatory bowel disease was noted. During both periods of parenteral n-3 lipid administration, total plasma EPA and DHA contents increased several-fold, surpassing that of arachidonic acid; this plasma n-3 fatty acid enrichment was only maintained to a minor extent during the intermediate period of dietary fish oil supplementation. The intravenously administered EPA-containing triglycerides were rapidly hydrolyzed, as evidenced by the appearance of substantial quantities of EPA in the plasma free fatty acid fraction. Platelet and neutrophil total membrane content of EPA and DHA as well as n-3 fatty acid/AA membrane ratios similarly increased during the periods of intravenous n-3 lipid administration and declined during oral fish oil uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗