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Biomedical subjects

G Höfle

Publications and source records attributed to G Höfle.

At least 19 recordsLinked to original sources
PubMed2004

Relationship between various measures of bone mineral density and vertebral fractures in cardiac transplant recipients.

BACKGROUND: The incidence rates of osteoporosis and fractures are increased after cardiac transplantation. METHODS: We performed a cross-sectional analysis of cardiac transplant recipients in a late post-transplantation period (4.4 [2.5] years after cardiac transplantation, n = 27). We measured bone mineral density (BMD) by DXA at the hip and lumbar spine and by quantitative ultrasound (QUS) at the calcaneus. Vertebral fracture (vfx) prevalence was analysed by anterior-posterior and lateral radiographs of the thoracic and lumbar spine. RESULTS: Overall, vfx were present in 13 of 27 patients (48.2%, n = 51 vfx). Vfx were observed in 1 out of 5 patients with normal DXA results, 7 out of 14 osteopenic and 5 out of 8 osteoporotic cardiac transplant recipients. BMD at the femoral neck and more prominently at Ward's triangle were significantly lower in vfx patients compared to patients without vfx, with adjusted mean values (95% CI) of 0.804 [0.750-0.859] vs. 0.915 [0.860-0.969] g/cm2 and 0.573 [0.501-0.646] vs. 0.766 [0.697-0.836] g/cm2, respectively. CONCLUSIONS: These findings suggest an association between DXA measurements of the hip with vertebral fractures in a late post-transplantation period and thus extend knowledge from previous reports on cardiac transplant recipients studied earlier after CTX. In particular, our data pinpoint a potentially interesting role for BMD at Ward's triangle.

Absorptiometry, Photon↗
PubMed2001

Quinolones and their N-oxides as inhibitors of photosystem II and the cytochrome b(6)/f-complex.

4(1H)-quinolones (2-alkyl- (1), 2-alkyl-3-methyl- (2), 2-methyl-3-alkyl- (3), 1-hydroxy-2-methyl-3-alkyl- (4) and 1-hydroxy-2-alkyl- (5)) with n-alkyl side chains varying from C(5) to C(17) have been synthesized and tested for biological activity in photosystem II and the cytochrome b(6)/f-complex. In photosystem II, quinolones 1 and 2 showed only moderate activity, whereas 3<5<4 (increasing activity) were potent inhibitors. Displacement experiments with [(14)C]atrazine indicated that the quinolones share an identical binding site with other photosystem II commercial herbicides. In the cytochrome b(6)/f-complex, only 3<4 showed enhanced activity. Maximal inhibitory potency was achieved at a carbon chain length of 12-14 A. Further increase of the chain length decreased activity. In a quantitative structure-activity relationship inhibitory activity in photosystem II and the cytochrome b(6)/f-complex could be correlated to the physicochemical parameters lipophilicity pi and/or to STERIMOL L.

Binding Sites↗
PubMed2001

New natural epothilones from Sorangium cellulosum, strains So ce90/B2 and So ce90/D13: isolation, structure elucidation, and SAR studies.

In addition to epothilones A (1) and B (2), 37 natural epothilone variants and epothilone-related compounds were isolated from the culture broth of a 700 L fermentation of Sorangium cellulosum, strain So ce90/B2. Of these, only the 12,13-desoxyepothilones, epothilone C (14) and D (15), were produced in significant amounts (3-6 mg/L); the 21-hydroxy derivatives and epothilones E (3) and F (4), in low and variable amounts due to further degradation by the producing organism. Most of the other epothilone variants were produced only in 1-100 microg/L amounts. The new compounds are very similar in structure to the parent compounds 1, 2 and 14, 15 and are presumably the result of the imperfect selectivity of the biosynthetic enzymes for acetate and propionate. Further, epothilones containing an oxazole moiety (10-13) in the side chain instead of a thiazole as well as ring-expanded 18-membered macrolides, epothilones I (30-35), and a ring contracted 14-membered macrolide, epothilone K (36), were found as very minor metabolites. The mutant strain, So ce90/D13, instead of macrolactones, produced short-chain carboxylic acids 40, 41, and 42 bearing the characteristic thiazole side chain. The structures of the new epothilones were elucidated on the basis of comprehensive NMR and MS data. The new epothilone variants were tested in a cytotoxicity assay with mouse fibroblasts (cell line L929), and structure-activity relationships were established. Several new natural epothilones showed activity comparable to 1 and 2, but in no case exceeded that of 2.

Animals↗
PubMed2001

Elevated inferior petrosal sinus levels of PTHrP in a patient with Cushing's disease.

PTHrP has been found in various tissues, including prolactinomas and growth hormone producing adenomas. The function and clinical importance of PTHrP are poorly understood. We report the case of a 25-year-old female patient with hirsutism. Autonomous ACTH-dependent hypercortisolism was documented by endocrine testing. Magnetic resonance imaging (MRI) revealed a 3-mm intrasellar hypointense lesion in the left side of the pituitary gland. The inferior petrosal sinus sampling disclosed a gradient of ACTH left central/peripheral of 30.5 and right central/peripheral of 2.0 and suggested the diagnosis of a left-sided pituitary ACTH secreting microadenoma. Interestingly, we found elevated PTHrP levels in the left inferior petrosal sinus with a gradient of 4.7 compared to peripheral venous blood and of 3.6 compared to the right sinus. Our results fit very well to the concept of a para-/autocrine secretion of PTHrP which has been proposed recently and suggest a role in the regulation of cell growth of pituitary adenomas.

Adenoma↗
PubMed2001

Studies on the biosynthesis of epothilones: the PKS and Epothilone C/D monooxygenase.

Nonproducer mutants support the assumption that epothilones A and B are synthesized by the same polyketide synthase (PKS). The endproducts of the PKS, epothilones C and D, compete for the active site of a constitutively synthesized monooxygenase which is regulated by product inhibition. The postulated C-13 hydroxy-epothilones as direct precursors of epothilones C and D were not detected.

Binding Sites↗
PubMed2000

The myxochelin iron transport regulon of the myxobacterium Stigmatella aurantiaca Sg a15.

The biosynthetic gene cluster of the myxochelin-type iron chelator was cloned from Stigmatella aurantiaca Sg a15 and characterized. This catecholate siderophore was only known from two other myxobacteria. The biosynthetic genes of 2,3-dihydroxybenzoic acid are located in the cluster (mxcC-mxcF). Two molecules of 2, 3-dihydroxybenzoic acid are activated and condensed with lysine in a unique way by a protein homologous to nonribosomal peptide synthetases (MxcG). Inactivation of mxcG, which encodes an adenylation domain for lysine, results in a myxochelin negative mutant unable to grow under iron-limiting conditions. Growth could be restored by adding Fe3+, myxochelin A or B to the medium. Inactivation of mxcD leads to the same phenotype. A new type of reductive release from nonribosomal peptide synthetases of the 2, 3-dihydroxybenzoic acid bis-amide of lysine from MxcG, catalyzed by a protein domain with homology to NAD(P) binding sites, is discussed. The product of a gene, encoding a protein similar to glutamate-1-semialdehyde 2,1-aminomutases (mxcL), is assumed to transaminate the aldehyde that is proposed as an intermediate. Further genes encoding proteins homologous to typical iron utilization and iron uptake polypeptides are reported.

Amino Acid Sequence↗
PubMed2000

Studies on the biosynthesis of epothilones: the biosynthetic origin of the carbon skeleton.

The biosynthetic origin of the epothilone skeleton was studied by the incorporation of 13C and radioactively labeled precursors by Sorangium cellulosum So ce90. The carbon atoms are derived from acetate, propionate, the methyl group of S-adenosyl-methionine, and cysteine which also introduces the sulfur and nitrogen atoms. Epothilone biosynthesis starts with the formation of the thiazole part from acetate and cysteine. The incorporation of acetate or propionate units results in the formation of epothilones A and B, respectively. To introduce the epoxide function of epothilones A and B molecular oxygen is used.

Carbon↗
PubMed2000

Tubulysins, new cytostatic peptides from myxobacteria acting on microtubuli. Production, isolation, physico-chemical and biological properties.

New cytostatic compounds, tubulysins, were isolated from the culture broth of strains of the myxobacteria Archangium gephyra and Angiococcus disciformis. The compounds are peptides partly consisting of unusual amino acids and are distantly related to the dolastatins. The tubulysins were not active against bacteria and only little against fungi, but showed high cytostatic activity against mammalian cell lines with IC50 values in the picomolar range. An incubation with 50 ng/ml tubulysin A led to a complete disappearance of the microtubuli network of the cells within 24 hours. The more active tubulysin D induced multipolar spindles: At 0.5 ng/ml all mitotic cells showed more than four spindle poles.

Animals↗
PubMed1999

New lessons for combinatorial biosynthesis from myxobacteria. The myxothiazol biosynthetic gene cluster of Stigmatella aurantiaca DW4/3-1.

The biosynthetic mta gene cluster responsible for myxothiazol formation from the fruiting body forming myxobacterium Stigmatella aurantiaca DW4/3-1 was sequenced and analyzed. Myxothiazol, an inhibitor of the electron transport via the bc(1)-complex of the respiratory chain, is biosynthesized by a unique combination of several polyketide synthases (PKS) and nonribosomal peptide synthetases (NRPS), which are activated by the 4'-phosphopantetheinyl transferase MtaA. Genomic replacement of a fragment of mtaB and insertion of a kanamycin resistance gene into mtaA both impaired myxothiazol synthesis. Genes mtaC and mtaD encode the enzymes for bis-thiazol(ine) formation and chain extension on one pure NRPS (MtaC) and on a unique combination of PKS and NRPS (MtaD). The genes mtaE and mtaF encode PKSs including peptide fragments with homology to methyltransferases. These methyltransferase modules are assumed to be necessary for the formation of the proposed methoxy- and beta-methoxy-acrylate intermediates of myxothiazol biosynthesis. The last gene of the cluster, mtaG, again resembles a NRPS and provides insight into the mechanism of the formation of the terminal amide of myxothiazol. The carbon backbone of an amino acid added to the myxothiazol-acid is assumed to be removed via an unprecedented module with homology to monooxygenases within MtaG.

Amino Acid Sequence↗
PubMed1999

Changes in the volume of residual pituitary adenomas in patients with adult-onset growth hormone deficiency during replacement therapy with the recombinant human growth hormone.

In the course of a prospective study concerning recombinant human growth hormone replacement therapy in adult-onset growth hormone deficiency, we determined the volumes of residual tumors in six patients with pituitary macroadenomas who had formerly been treated with surgery alone or surgery and external radiotherapy. Pituitary CT scans in direct coronal views were obtained at baseline, and at 6, 12 and 18 months. The volumes of the residual tumors were calculated from the tumor diameters assuming that the tumors had an ellipsoid shape. Tumor volumes did not change in one patient and were reduced in two patients. In three patients, clinically non-significant tumor expansion by a median of 23.6 +/- 13.2% (range, 21.1-62.0%) was noted after 12 to 18 months. This tumor expansion did not cause signs or symptoms of a mass effect and did not influence further treatment. One of the six patients discontinued treatment and no further change in tumor size, as determined by MRT, was noted over a mean follow up of 34 months. Treatment was continued for up to 38 months in five patients. In four of these five patients no further change in tumor size was detected. However, treatment with the growth hormone was stopped in one patient since a 30% expansion in tumor volume, elevating the optic chiasm, was noted on MRT. None of the patients developed deterioration of visual fields. Interestingly, tumor invasion of the cavernous sinus had been present initially in all three who displayed tumor expansion while on rhGH. This first study in which diameters of residual pituitary adenomas in patients on growth hormone replacement therapy were prospectively and carefully measured, permits no conclusion regarding a causal relationship between growth hormone and tumor expansion, owing to the small number of patients. However, the observed incidence is not much different from that in former studies without growth hormone replacement therapy. Nevertheless, a close observation of the pituitary by imaging studies at regular intervals appears to be mandatory, particularly in patients with invasive residual adenomas.

Adenoma↗
PubMed1999

Melithiazols, new beta-methoxyacrylate inhibitors of the respiratory chain isolated from myxobacteria. Production, isolation, physico-chemical and biological properties.

New antibiotic compounds, melithiazols, were isolated from the culture broth of strains of the myxobacteria Melittangium lichenicola, Archangium gephyra, and Myxococcus stipitatus. The compounds belong to the group of beta-methoxyacrylate (MOA) inhibitors and are related to the myxothiazols. The melithiazols show high antifungal activity, but are less toxic than myxothiazol A and its methyl ester in a growth inhibition assay with mouse cell cultures. The melithiazols inhibit NADH oxidation by submitochondrial particles from beef heart. Melithiazol A blocks the electron transport within the bc1-segment (complex III) and causes a red shift in the reduced spectrum of cytochrome b.

Acrylates↗
PubMed1998

Oxidative and reductive transformations of epothilone A.

The C7 hydroxy group of cytotoxic epothilone A was selectively oxidized using PDC. A selective oxidation of the C3 hydroxy group was accomplished with Me2S/(PhCO2)2 after in situ protection of C7-OH. Reduction of epothilone A or of a C5, C7 dioxo derivative with NaBH4 proceeded at the C5 carbonyl group. Oxidation and hydrogenation of the C16-C17 double bond proved to be difficult but it was easily cleaved with ozone and the resulting keto derivative was transformed to epothilone analogs with different side chains.

Antineoplastic Agents↗
PubMed1998

Derivatization of the C12-C13 functional groups of epothilones A, B and C.

Epothilone A reacted with hydrohalic acids to C12-C13 halohydrin regioisomers (ratios: 2:1-4:1), whereas epothilone B gave under the same conditions the isomerically pure C12 halo C13 hydroxy derivative. With non-nucleophilic Brønstedt acids and with Lewis acids a highly solvent dependent product distribution and some unexpected rearrangement products were observed. Epothilone C bearing a double bond between C12 and C13 was regioselectively dihydroxylated or hydrogenated at that position.

Antineoplastic Agents↗
PubMed1998

Surgery combined with dopamine agonists versus dopamine agonists alone in long-term treatment of macroprolactinoma: a retrospective study.

We retrospectively analysed the long-term treatment results (median 8 years) of 31 patients with macroprolactinoma. 17 patients were treated by pituitary surgery (group 1) followed by long-term dopamine agonist therapy whereas 14 patients received long-term dopamine agonist therapy alone (group 2). 2 patients of group 1 and 1 patient of group 2 had external pituitary irradiation because of progressive disease. The two groups were comparable with respect to age, gender and initial prolactin (PRL) levels. At the end of the observation period dopamine agonist dosage could be reduced by 50% in group 1 and by 39.3% in group 2. Pituitary function did not change substantially during therapy. Complete remissions (no visible tumour in CT or MRI, normal PRL levels under current dopamine agonist medication) were achieved in 23.5% of group 1 vs. 21.4% of group 2, partial remissions (reduction of PRL and tumour size) in 35.3% vs. 64.3%, stable disease in 23.5% vs. 7.1% and progressive disease in 17.7% vs. 7.1% (differences not significant). Visual field defects showed 28.4% remissions (complete and partial) in group 1 versus 50% in group 2. Dopamine agonist therapy could be stopped definitively in only 1 patient of group 2 with an invasive macroprolactinoma. Initial surgical reduction of tumour load followed by medical therapy does not seem to guarantee a better long-term outcome than dopamine agonist therapy alone if the patient responds to and tolerates dopamine agonist therapy. Surgery should be reserved for non-responders, drug-intolerant or non-compliant patients, and for those with acute severe neurological compromise.

Adolescent↗
PubMed1998

Adrenocortical carcinoma evolving after diagnosis of preclinical Cushing's syndrome in an adrenal incidentaloma. A case report.

A 43-year-old female patient underwent abdominal ultrasonography and CT scan because of uncharacteristic abdominal pain. A 3-cm homogeneous adrenal tumor was diagnosed. The endocrine tests revealed an adrenal preclinical Cushing's syndrome (PCS). Due to the latent hormone excess we decided to operate on the adrenal tumor. Since the tumor was small, laparoscopic adrenalectomy was performed. Histological evaluation showed an adrenocortical tumor of undetermined nature. Four months later the patient presented with a metastasizing cortisol- and androgen-producing adrenocortical carcinoma (ACC). After pretreatment with ketoconazole to suppress the biosynthesis of adrenal steroids under substitution with hydrocortisone, we reduced the tumor load by surgery. Postoperatively we continued ketoconazole and started o, p'-dichlorodiphenyldichloroethane as well as chemotherapy with doxorubicin and suramin. However, the patient died from ACC 7 months after adrenalectomy. It is known from several reports that PCS may persist clinically silently or may progress to full-blown Cushing's syndrome. This is the first time a malignant course of PCS is described. Independent of the initial therapeutic strategy of PCS, i. e. surgery or regular follow-up visits, we must be aware that also relatively small adrenal tumors can harbor malignancy.

Adrenal Cortex Neoplasms↗
PubMed1998

Apicularens A and B, new cytostatic macrolides from Chondromyces species (myxobacteria): production, physico-chemical and biological properties.

A novel macrolide, apicularen A, was produced by several species of the genus Chondromyces. Initially it was discovered by bioassay-guided RP-HPLC-fractionation of culture extracts of Chondromyces robustus, strain Cm a13. Apicularen A showed no antimicrobial activity, but was highly cytotoxic for cultivated human and animal cells, with IC50 values ranging between 0.1 and 3 ng/ml. A cometabolite of apicularen A, the N-acetylglucosamine glycoside apicularen B, was distinctly less cytotoxic with IC50 values between 0.2 and 1.2 microg/ml, and showed weak activity against a few Gram-positive bacteria. Apicularen A is chemically closely related to the salicylihalamides A and B from the marine sponge Haliclona sp.

Animals↗