Search PubMed⌕ Search

Biomedical subjects

K Kühn

Publications and source records attributed to K Kühn.

At least 19 recordsLinked to original sources
PubMed1992

Expression of human collagen type IV genes is regulated by transcriptional and post-transcriptional mechanisms.

The molecules of the basement membrane specific collagen type IV are heterotrimers consisting of two alpha 1(IV) and one alpha 2(IV) polypeptide chains. Comparison of the ratios of transcription by nuclear run-on analysis and mRNAs by RNAse protection assay indicates the involvement of transcriptional as well as post-transcriptional events in the control of overall collagen type IV expression. The relative ratios of transcription of the respective genes COL4A1 and COL4A2 remained near 2:1 in most cells, whereas the ratio of mRNA steady-state levels alpha 1(IV)/alpha 2(IV) varied from 0.3:1 to 1:1 and did not parallel the subunit structure of the protein. Nevertheless, secreted protein shows a 2:1 ratio of the subunit polypeptides. This indicates that post-translational processes during chain selection, aggregation and secretion finally determine the amount of secreted protein.

Cells, Cultured↗
PubMed1992

Long-term therapy with cyclosporin A does not influence serum concentrations of vitamin D metabolites in patients with multiple sclerosis.

Animal studies have shown that cyclosporin A (CyA) stimulates renal 25-hydroxyvitamin D3 [25(OH)D3]-1 alpha-hydroxylase activity; in contrast, studies in renal transplant recipients indirectly suggest that CyA reduces 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] production. To clarify the effect of CyA on vitamin D metabolite concentrations, we measured parameters of calcium metabolism in 37 CyA-treated patients (median trough whole blood levels 171-222 ng/ml) with multiple sclerosis and initially normal kidney function. The patients participated in a randomized double-blind study to assess the efficacy of CyA in multiple sclerosis. An age- and sex-matched control group (n = 39) received azathioprine (Aza). Measurements were made at the end of a 2-year treatment period. The 1,25(OH)2D3 serum concentrations were not significantly different between the two groups, although they were numerically lower in CyA-treated patients [median (range), 28.4 pg/ml (7.8-85.9) vs 41.0 pg/ml (9.2-105.1) in Aza-treated patients]. The 25(OH)D3 levels were comparable in both groups. There was no correlation between the 25(OH)D3 and 1,25(OH)2D3 concentrations. The renal function in both groups was stable in the last 6 months of the study. At the end of the study period, the endogenous creatinine clearance was significantly lower in the CyA-treated group (85 +/- 17 ml/min versus 99 +/- 22 in the Aza-treated group, P less than 0.05). The carboxyterminal parathyroid hormone (C-PTH) was within the normal range in both groups, although CyA-treated patients had significantly higher concentrations (P less than 0.01). The urinary excretion of mineral ions, cations and protein was similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Molecular characterization of cuticle and interstitial collagens from worms collected at deep sea hydrothermal vents.

Two different collagens were isolated and characterized from the body walls of the vestimentiferan tube worm Riftia pachyptila and the annelid Alvinella pompejana, both living around hydrothermal vents at a depth of 2600 m. The acid-soluble cuticle collagens consisted of a long triple helix (2.4 microns for Alvinella, 1.5 microns for Riftia) terminating into a globular domain. Molecular masses of 2600 and 1700 kDa, respectively, were estimated from their dimensions. The two cuticle collagens were also quite different in amino acid composition, in agreement with their different supramolecular organizations within tissues. Interstitial collagens corresponding to cross-striated fibrils underneath the epidermal cells could be solubilized by digestion with pepsin and consisted of a single alpha-chain. They were similar in molecular mass (340 kDa) and length (280 nm) but differed in composition and banding patterns of segment-long-spacing fibrils. This implicates significant sequence differences also in comparison to fibril-forming vertebrate collagens, although all form typical quarter-staggered fibrils. The thermal stability of the worm collagens was, with one exception (interstitial collagen of Riftia), in the range of mammalian and bird collagens (37 to 46 degrees C), and thus distinctly above that of shallow sea water annelids. Yet, their 4-hydroxyproline contents were not directly correlated to this stability. About 20% of Riftia collagen alpha-chain sequence was elucidated by Edman degradation and showed typical Gly-X-Y repeats but only a limited homology (45 to 58% identity) to fibril-forming vertebrate collagens. A single triplet imperfection and the variable hydroxylation of proline in the X position were additional unique features. It suggests that this collagen represents an ancestral form of fibril-forming collagens not directly corresponding to an individual fibril-forming collagen type of vertebrates.

Amino Acid Sequence↗
PubMed1991

Characterization of a type IV collagen major cell binding site with affinity to the alpha 1 beta 1 and the alpha 2 beta 1 integrins.

The aim of this investigation was to identify the domains of type IV collagen participating in cell binding and the cell surface receptor involved. A major cell binding site was found in the trimeric cyanogen bromide-derived fragment CB3, located 100 nm away from the NH2 terminus of the molecule, in which the triple-helical conformation is stabilized by interchain disulfide bridges. Cell attachment assays with type IV collagen and CB3 revealed comparable cell binding activities. Antibodies against CB3 inhibited attachment on fragment CB3 completely and on type IV collagen to 80%. The ability to bind cells was strictly conformation dependent. Four trypsin derived fragments of CB3 allowed a closer investigation of the binding site. The smallest, fully active triple-helical fragment was (150)3-amino acid residues long. It contained segments of 27 and 37 residues, respectively, at the NH2 and COOH terminus, which proved to be essential for cell binding. By affinity chromatography on Sepharose-immobilized CB3, two receptor molecules of the integrin family, alpha 1 beta 1 and alpha 2 beta 1, were isolated. Their subunits were identified by sequencing the NH2 termini or by immunoblotting. The availability of fragment CB3 will allow for a more in-depth study of the molecular interaction of a short, well defined triple-helical ligand with collagen receptors alpha 1 beta 1 and alpha 2 beta 1.

Amino Acid Sequence↗
PubMed1991

Abnormal diastolic left ventricular filling by pulsed Doppler echocardiography in patients on continuous ambulatory peritoneal dialysis.

To determine characteristics of diastolic left ventricular (LV) function in patients on continuous ambulatory peritoneal dialysis (CAPD), two groups of CAPD patients without (n = 23; group 1) vs with (n = 25; group 2) LV hypertrophy (greater than 13 mm) were compared with a group of untreated non-renal hypertensive patients with LV hypertrophy (n = 11; group 3) using Doppler-echocardiography. Age and body surface area were comparable in all three groups, mean CAPD-duration (32 +/- 28 vs 26 +/- 23 months; p = NS) was comparable in renal patients. LV systolic function in echocardiography (LVEF: 62 vs 64 vs 63%) and systolic time intervals were normal and comparable in all three groups. Atrial maximum filling velocities (96 +/- 25 vs 91 +/- 25 vs 67 +/- 8 cm/s) were comparably increased, the ratio of maximal early/atrial filling velocities was comparably decreased (0.73 +/- 0.25 vs 0.77 +/- 0.21 vs 0.99 +/- 0.05) in both groups of renal patients as compared to group 3 (p less than 0.05-0.01). Atrial filling fractions were increased in all three groups, more pronounced in group 1 than in group 3 (50 +/- 11 vs 40 +/- 7%; p less than 0.05). The normal correlation of Doppler parameters with age and with LV radius/thickness ratio was altered in renal patients such that high patient age tended to have an additional negative influence on LV diastolic function of hypertrophied, but not of normal myocardium. Isovolumic relaxation time was prolonged in all three groups (134 +/- 38 vs 131 +/- 34 vs 116 +/- 17 ms; p = NS). We conclude that in patients on CAPD, diastolic LV filling is impaired both in normal and hypertrophied myocardium. High age is a factor that further attributes to diastolic dysfunction of hypertrophied myocardium in CAPD.

Age Factors↗
PubMed1990

The primary structure of a triple-helical domain of collagen type VIII from bovine Descemet's membrane.

We have isolated and sequenced a fragment of 469 amino acid residues from bovine type VIII collagen. The sequence was composed of a series of Gly-X-Y repeats which was interrupted 8 times by short imperfections. The number and relative location of these interruptions were similar to those of chicken alpha 1(X) and rabbit alpha 1(VIII) chain triple-helical domains. Comparison to published N-terminal sequences to two triple-helical fragments of bovine type VIII collagen and to the cDNA derived sequence of the rabbit alpha 1(VIII) chain showed that this fragment was the triple-helical domain of a second type VIII collagen chain which we designate alpha 2(VIII).

Amino Acid Sequence↗
PubMed1990

Crystals of the NC1 domain of human type IV collagen.

Crystals of the non-collagenous C-terminal region (NC1) of type IV collagen have been obtained from human placenta. These crystals diffract to 2.0 A, and belong to space group P22(1)2(1), with cell dimensions a = 81 A, b = 158 A, c = 138 A, alpha = beta = gamma = 90 degrees. The crystals contain one hexamer in the asymmetric unit; they are very stable with respect to X-rays.

Animals↗
PubMed1990

Cardiac structure and function in continuous ambulatory peritoneal dialysis: influence of blood purification and hypercirculation.

Continuous ambulatory peritoneal dialysis (CAPD) is associated with obvious hemodynamic and blood purification advantages over intermittent hemodialysis. To determine whether this is reflected in favorable left ventricular (LV) structure and function, a group of 55 normotensive patients (aged 58.4 +/- 11.0 years) undergoing CAPD was analyzed by means of echocardiography. Characteristic findings were LV hypertrophy (158 +/- 50 gm/m2), mainly the result of septal thickening (13.3 +/- 2.8 mm), and left atrial dilatation (40.9 +/- 7.4 mm). Mean LV diameter in end diastole and end systole and posterior wall thickness were normal. Parameters of LV systolic function (ejection fraction [EF]: 62.0 +/- 13.0%; velocity of circumferential fiber shortening [Vcf]: 1.58 +/- 0.46 circ/sec) were in the upper normal range at a hyperdynamic circulatory state (cardiac index [CI] 4.67 +/- 1.82 L/min/m2. The amount of LV hypertrophy was related to the amount of hypercirculation (CI: p less than 0.001; hemoglobin: p less than 0.025) and quality of blood purification (creatinine, urea: p less than 0.02) but not to blood pressure, age, or duration of dialysis. Left atrial dilatation was inversely related to LV systolic function (EF, Vcf: p less than 0.001) and directly related to LV muscle mass (p less than 0.02). A low prevalence (13%) of pericardial effusion was independent of blood purification. We conclude that in normotensive patients receiving CAPD, a high prevalence of left atrial dilatation and asymmetric septal hypertrophy is found, the latter being related both to the amount of hypercirculation and the quality of blood purification.

Adult↗
PubMed1990

Significance of portal venous drainage after whole-organ pancreas transplantation for endocrine graft function and prevention of diabetic nephropathy.

The significance of portal venous drainage after whole-pancreas transplantation both for metabolic control and development of diabetic nephropathy was investigated. Streptozotocin-diabetic inbred LEW rats received a duct-ligated pancreas graft with either systemic or portal venous drainage and were followed for up to one year. Normal and untreated diabetic rats (n=18 in each group) served as controls. Irrespective of the route of venous drainage pancreas transplants normalized the diabetic polyuria, polyphagia, and polydipsia. Growth rates and general health did not differ from normal rats. Pancreas transplantation with portal venous drainage furthermore normalized nonfasting blood glucose and peripheral insulin levels, and intravenous glucose tolerance. Pancreas transplantation with systemic venous drainage, however, was associated with peripheral hyperinsulinemia, slightly elevated nonfasting blood glucose levels, and supranormal K-values in intravenous glucose tolerance tests. Though portal venous drainage was associated with better metabolic control than systemic venous drainage, both techniques of pancreas transplantation proved equally effective to prevent the development of diabetic glomerular membrane thickening determined 6 and 12 months posttransplant.

Animals↗
PubMed1990

Skin microcirculation and regional peripheral resistance in patients with chronic renal anaemia treated with recombinant human erythropoietin.

Skin microcirculation and regional peripheral resistance were studied in 14 patients with renal anaemia during therapy with recombinant human erythropoietin. Haematocrit was raised from 20.0 to 31.3% after 10-12 weeks of treatment and remained stable over another period of 12 weeks. Antihypertensive treatment had to be intensified in five patients. Regional calf blood flow decreased significantly; accordingly, calculated peripheral vascular resistance was increased by more than 100%. However, transcutaneous oxygen pressure (37 degrees C and 44 degrees C) increased significantly. The pathological vasoconstrictor response of skin capillaries was not influenced. There were no significant differences of any parameter between the patients requiring reinforced antihypertensive therapy and those with stable blood pressure. In conclusion skin oxygenation may be improved by erythropoietin treatment to a large extent despite an increase in calculated total limb vascular resistance.

Adult↗
PubMed1990

Binding of the J1 adhesion molecules to extracellular matrix constituents.

The J1 glycoproteins can be obtained in multiple forms in the soluble fraction of developing and adult mouse brain tissue. They are recovered as two forms of apparent molecular weights of 160,000 and 180,000 (J1-160) from adult mouse brain and as forms of apparent molecular weights of 200,000 and 220,000 (J1-220) from developing brain. J1-160 and J1-220 share common epitopes but are considered as separate entities, with J1-220 being immunochemically closely related if not identical to tenascin. Based on the observation that J1 immunoreactivity appears on basement membrane and interstitial collagens after denervation of the neuromuscular junction in adult rodents, we became interested in investigating the binding properties of J1 glycoproteins to extracellular matrix constituents in vitro. Both J1-160 and J1-220 bound to collagens type I-VI and IX but not to laminin, fibronectin, bovine serum albumin, or gelatin under hypotonic buffer conditions. Under isotonic buffer conditions, J1-220 bound to all collagen types, whereas J1-160 bound only to collagen types V and VI with values that could be examined by Scatchard analysis. Binding of J1-220 to collagens displayed two binding constants (KD) between 1.5 and 4.4 X 10(-9) and 1.8 and 5.5 X 10(-8) M, respectively, under hypotonic buffer conditions and a single KD of 2.1-8.0 X 10(-8) M under isotonic buffer conditions. Binding of J1-160 to collagens had an apparent KD of 1.9-8.0 X 10(-9) M under hypotonic buffer conditions. Under isotonic buffer conditions, binding constants of J1-160 to collagen types V and VI were approximately 2 X 10(-8) M. Binding of J1-220 to collagen type I could be inhibited by J1-220, J1-160, and collagen type VI but not by fibronectin or gelatin. Conversely, binding of J1-160 was inhibited by J1-220, J1-160, and collagen type VI (in order of decreasing efficacy of competition). J1-160 and J1-220 were retained on a heparin-agarose column and eluted in a salt gradient at approximately 0.5 M NaCl. The formation of the J1-heparin complexes was inhibited 100-fold more efficiently by heparin than by chondroitin sulfate. These experiments show that J1 glycoproteins resemble in many respects the extracellular matrix constituents fibronectin, laminin, vitronectin, and von Willebrand factor.

Animals↗
PubMed1990

Fibroblast-derived J1 adhesion glycoproteins show binding properties to extracellular matrix constituents different from those of central nervous system origin.

The J1 extracellular adhesion molecule from mouse brain consists of several immunochemically related glycoproteins of different molecular weights and distinct functional properties. Like the brain J1 glycoproteins, the fibroblast-derived J1 glycoproteins interact with all collagen types tested (collagen G and types I-IV and IX), as measured by binding of 125I-labeled J1 glycoproteins to immobilized collagens. As tested for collagen type I, this binding can be inhibited more effectively by chondroitin sulfate than by heparin. After electrophoretic separation and transfer to nitrocellulose, fibroblast-derived J1 only binds to a limited number of collagen types (collagen types I, VI, and IX and G), whereas brain-derived J1 glycoproteins bind to all collagen types tested (collagen types I-VI and IX and G). These results show that fibroblast-derived J1 glycoproteins, although immunochemically related to J1 glycoproteins from brain, differ from these in their binding specificities to extracellular matrix constituents.

Animals↗
PubMed1990

Regulation of divergent transcription of the genes coding for basement membrane type IV collagen.

The genes coding for the two polypeptide chains, alpha 1(IV) and alpha 2(IV), which form together the molecule of the basement membrane type IV collagen, were found to have a special and unusual genomic arrangement. The two genes are very closely linked, they are transcribed in opposite directions, and they apparently use a common and bidirectional promoter with a length of 127 bp. This region is characterized by a symmetrical arrangement of typical elements and by the palindromic structure of the sequence. In accordance with the symmetry of the promoter itself, a symmetrical organization of sequence motifs (SP1, CCAAT) was also observed in flanking regions. For the promoter and the flanking regions we could detect specific binding of nuclear factors that indicates their involvement in transcriptional activation. This suggests that the intrinsic symmetry of the type IV collagen promoter and its flanking regions may be a structural prerequisite for its bidirectional function. In transient gene expression systems no significant activity of the type IV collagen promoter was observed in either direction. This implies that additional enhancing elements are essential for the efficient and tissue-specific transcription of both type IV collagen genes. The screening for such controlling elements within the alpha 1(IV) and the alpha 2(IV) gene led to the observation that the transcription in direction of the alpha 2(IV) gene is activated by an element located in the first intron of the alpha 2 gene. Its enhancing effect is strictly dependent on the intact genomic structure of this region. Alternation of orientation and distance to the promoter destroys its activity completely. This element, located about 100-600 bp downstream from the start site of alpha 2(IV) transcription, seems to form a synergistically acting unit with the common promoter, essential for transcriptional activity in alpha 2 direction. We have not found additional enhancing elements in other regions of both genes. Explanations for the discrepancy with previous data, which define an enhancing element within the first intron of the alpha 1(IV) gene of mouse, are only speculative at present.

Base Sequence↗
PubMed1989

[Effect of captopril therapy on sodium and water excretion in patients with liver cirrhosis and ascites].

UNLABELLED: Ascites in patients with cirrhosis of the liver frequently is refractory to diuretic treatment. It was postulated that vasoconstriction of the renal cortex, mediated by activation of the renin-angiotensin-aldosterone-system (RAAS), may be one course of the disturbed sodium- and water-excretion in these patients. We therefore investigated in 14 cirrhotic patients with ascites under constant diuretic treatment the effects of low-dose captopril therapy on urinary sodium- and potassium-excretion, body weight, abdominal girth, serum-sodium, -potassium, creatinine-clearance, plasma-renin-activity (PRA), plasma-aldosterone (PA) and mean arterial pressure (MAP). After a control period of 4 days the patients received 2 x 6.25 mg/d captopril for 5 days and 4 x 6.25 mg/d for further 5 days. Treatment was followed by a second control period without captopril. PRA increased significantly after 2 days of captopril treatment. 2 x 6.25 mg/d captopril induced a significant increase in sodium excretion and a significant decrease of body weight. MAP decreased slightly but significantly without clinical signs of hypotension. 4 x 6.25 mg/d captopril resulted in a further reduction of body weight and a further enhancement of sodium excretion. Three days after withdrawal of captopril sodium output was significantly reduced again. CONCLUSION: In cirrhotic patients low-dose captopril seems to be efficient in the treatment of ascites resistant to diuretics without causing major side effects.

Adult↗
PubMed1989

Characterization of gelatinase from pig polymorphonuclear leucocytes. A metalloproteinase resembling tumour type IV collagenase.

The metalloproteinase 'gelatinase' stored in the granules of pig polymorphonuclear leucocytes has been purified in the latent form. The enzyme is secreted as an Mr 97,000 proenzyme that can be activated in the presence of 4-aminophenylmercuric acetate (APMA) by self-cleavage to generate lower-Mr species, of which an Mr 88,000 form was the most active. Trypsin-initiated activation generated different Mr gelatinases of much lower specific activity. Activation was slowed but not prevented by the presence of the tissue inhibitor of metalloproteinases, TIMP. The activated gelatinase formed a stable complex (Mr 144,000) with TIMP, in a Zn2+- and Ca2+-dependent manner, and complex formation was inhibited by the presence of the substrate gelatin. Similar to the human granulocyte gelatinase, the organomercurial-activated pig enzyme degraded gelatin and TCA and TCB fragments of type I collagen, as well as elastin and types IV and V collagen. The degradation of type IV collagen was shown, both by polyacrylamide-gel electrophoresis and by electron microscopic analysis, to generate 3/4 and 1/4 fragments as described for mouse tumour type IV collagenase. Furthermore, an antiserum raised to mouse type IV collagenase recognized the pig granulocyte gelatinase. An antiserum to the pig polymorphonuclear leucocyte gelatinase recognized other high-Mr gelatinases, including those from human granulocytes, pig monocytes and rabbit connective tissue cells, but not the Mr 72,000 enzyme from connective tissue cells. These data suggest that there are two distinct major forms of gelatinolytic activity that also cause specific cleavage of type IV collagen. These enzymes are associated with a wide variety of normal connective tissue and haemopoietic cells, as well as many tumour cells.

Animals↗
PubMed1989

An increase in the ratio of thromboxane A2 to prostacyclin in association with increased blood pressure in patients on cyclosporine A.

The aim of this study was to determine the effect of two years of treatment with cyclosporine A on blood pressure and the rates of secretion into the circulation of the vasoconstrictor thromboxane A2 and the vasodilator prostacyclin. Seven patient suffering from multiple sclerosis took part. Their blood pressures and urinary concentrations of 2,3-dinor-thromboxane A2 (a major urinary metabolite of thromboxane A2) and of 2,3-dinor-6-keto-prostaglandin F1 alpha (the major urinary metabolite of prostacyclin) were determined at the end of two years of treatment with cyclosporine A, and once again three months after cessation of this treatment. No other drugs were given during or after cyclosporine A. Mean arterial blood pressure was 113 +/- 5 mmHg (mean +/- SEM) during the cyclosporine A treatment, but fell to 94 +/- 4 mmHg after the three-month's wash-out period. Urinary excretion of the thromboxane metabolite decreased slightly from 674 +/- 150 pg.mg-1 creatinine during cyclosporine A therapy to 503 +/- 90 pg.mg-1-creatinine after the end of therapy. At the same time the prostacyclin metabolite increased significantly from 82 +/- 17 pg.mg-1 creatinine to 113 +/- 23 pg.mg-1 creatinine (P less than 0.05). The ratio of 2,3-dinor-thromboxane B2 to 2,3-dinor-6-keto-prostaglandin F1 alpha (taken as a measure of vasoconstrictor prostanoid activity) fell significantly from 8.4 +/- 0.8 4.7 +/- 0.6 (P less than 0.005). The shift in prostanoid production observed during cyclosporine A treatment could be one causal factor for the hypertensive and thromboembolic events associated with the use of this drug.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

LTB4 in nephrotoxic serum nephritis in rats.

We studied leukotriene B4 (LTB4) synthesis in isolated glomeruli of rats with nephrotoxic serum nephritis. This nephritis was induced in male Sprague Dawley rats by injecting one proteinuric dose of nephrotoxic serum (rabbit anti-rat-GBM serum) after prior immunization of the rats with rabbit IgG. Histological and analytical examinations were performed in kidneys perfused until free of blood 6, 12, 24, 48 and 72 hours after induction of the disease. To investigate LTB4 production, glomeruli were isolated and incubated for one hour in the presence of Ca++-ionophore A23187. The supernatants were analyzed for LTB4. The peak comigrating on reverse-phase high performance liquid chromatography (RP-HPLC) with reference LTB4 was isolated. The ethyl ester trimethylsilyl ether derivative of this peak was analyzed by gaschromatography-mass spectrometry (GC/MS). Identical spectra of the glomerular samples and of reference LTB4 in the positive and in the negative ion chemical ionization mode provided unequivocal evidence that the substance released from the nephritic glomeruli was indeed LTB4. Six hours after injection of nephrotoxic serum, glomerular LTB4 release was highest with 5.52 +/- 0.50, then declining to 2.20 +/- 0.10 ng/mg glomerular protein at 12 hours. At 24, 48 and 72 hours no statistically significant difference from control animals was found. No metabolism of LTB4 to 20-hydroxy- or 20-carboxy-LTB4 was detected during the incubation period. Albuminuria developed during the first 24 hours after nephrotoxic serum challenge and rose steadily throughout the observation period up to 277 +/- 25 mg/24 hr after 72 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Albuminuria↗