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Biomedical subjects

P Kurz

Publications and source records attributed to P Kurz.

At least 19 recordsLinked to original sources

Resolving complex atomic-scale spin structures by spin-polarized scanning tunneling microscopy.

The spin-polarized scanning tunneling microscope (SP-STM) operated in the constant current mode is proposed as a powerful tool to investigate complex atomic-scale magnetic structures of otherwise chemically equivalent atoms. The potential of this approach is demonstrated by successfully resolving the magnetic structure of Cr/Ag(111), which is predicted on the basis of ab initio vector spin-density calculations to be a coplanar noncollinear periodic 120 degrees Néel structure. Different operating modes of the SP-STM are discussed on the basis of the model of Tersoff and Hamann.

Journal Article↗

Three-dimensional spin structure on a two-dimensional lattice: Mn/Cu(111).

Based on first-principles vector spin-density total-energy calculations of the magnetic and electronic structure of Cr and Mn transition-metal monolayers on the triangular lattice of a (111) oriented Cu surface, we propose for Mn a three-dimensional noncollinear spin structure on a two-dimensional triangular lattice as magnetic ground state. This new spin structure is a multiple spin-density wave of three row-wise antiferromagnetic spin states and comes about due to magnetic interactions beyond the nearest neighbors and due to higher order spin interactions (i.e., four spin). The magnetic ground state of Cr is a coplanar noncollinear periodic 120 degrees Néel structure.

Journal Article↗

Increased renal excretion of endothelin-1 in nephrotic patients.

BACKGROUND: Renal function is influenced by direct and indirect action of endothelins. They reduce renal blood flow and glomerular filtration. The aim of the present study was to determine plasma and urinary endothelin-1 (ET-1) in two major categories of renal patients and to compare them with normal subjects. METHODS: Endothelin-1 was measured in the plasma and urine of patients with chronic renal disease and reduced glomerular filtration rate (GFR), and in patients with proteinuria due to glomerular dysfunction with unaffected GFR. A group of healthy subjects was used as a reference. RESULTS: Plasma endothelin-1 was increased in all patients to 60 +/- 13 pg/ml independent of GFR compared to 29 +/- 5 pg/ml in normal subjects (P < 0.001). The endothelin-1 load was decreased to 1190 +/- 450 pg/ml/1.73 m2 in patients with reduced GFR, compared to 2780 +/- 690 pg/ml/1.73 m2 of normal subjects, whereas in patients with glomerular damage and normal GFR, it was increased to 5480 +/- 1910 pg/ml/1.73 m2 (P < 0.01). ET-1 was found to be excreted and reabsorbed by the renal tubules by the same mechanisms as sodium and potassium, because its secretion fraction changes in parallel to those of the above ions. The excreted endothelin increased to 730 +/- 420 and 710 +/- 250 pg/ml/1.73 m2 (P < 0.01) in the two categories of patients respectively, compared to 290 +/- 100 pg/ml/1.73 m2 in the normal group. The excretion fraction of patients with normal GFR was similar to normal subjects, while it appeared to increase in patients with reduced GFR (P < 0.01). CONCLUSIONS: In the development of renal disease the plasma endothelin concentration is independent of the renal filtration capability and endothelin may be involved in functional and anatomical changes of the kidney as a causal factor or resulting from the renal disease.

Adult↗

Increased endothelin-1 content in the platelets of hemodialysed patients.

Patients undergoing hemodialysis, present platelets (PLTs) with physiological dysfunction. Aggregated PLTs stimulate endothelin-1 (ET-1) secretion from endothelial cells. In turn, ET-1 abolishes PLT aggregation. The aim of this study was to determine any presence of ET-1 in the PLTs of hemodialysed patients and to compare its levels with normal subjects. Platelets, isolated from hemodialysed patients, revealed lower aggregation (76 +/- 13%) compared with healthy subjects (96 +/- 2%). Plasma ET-1 was increased in hemodialysed patients 23.5 +/- 3.2 fmol/ml, vs. 10.9 +/- 1.6 fmol/ml in normal subjects. Immunoreactive endothelin-1 was detected in the platelets of both groups. The intraplatelet ET-1 of hemodialysed patients was 13.8 +/- 3.1 fmol/mg protein, vs. 7.9 +/- 1.3 fmol/mg protein in normal individuals. Total RNA was isolated from platelets and reverse transcriptase-mediated polymerase chain reaction (RT-PCR) revealed no presence of the preproET-1 mRNA in either normal or hemodialysed platelets. This suggests that ET-1 is internalized from the plasma. In summary, platelets contain but do not express ET-1. The increased levels of ET-1 in the platelets of the hemodialysed patients may be partly responsible for their lower aggregation.

Adult↗

Liver hemorrhage during laparotomy in patients with necrotizing enterocolitis.

UNLABELLED: Major liver hemorrhage (LH) without obvious iatrogenic injury was recently observed in several patients during operation for necrotizing enterocolitis (NEC). The purpose of this study was to determine the incidence and risk factors associated with the development of LH in patients with NEC. METHODS: The hospital charts of patients with NEC who underwent surgical exploration during a 5-year period (1989-1994) were reviewed. The patients in whom LH developed without obvious significant iatrogenic liver injury were compared with those who did not have LH. RESULTS: Eight of the 68 patients reviewed had LH. The survival rate for those with LH was 13%, compared with 88% for those without LH (P < .001). The patients with LH had a younger gestational age (28 +/- 3 weeks v 32 +/- 5 weeks) and a lower birth weight (1,262 +/- 489 g v 1,649 +/- 666 g); however, the differences were not significant. The patients with LH had significantly lower preoperative mean arterial blood pressure (35 +/- 1 mm Hg v 46 +/- 3 mm Hg; P < .001) and required greater fluid intake (272 +/- 28 mL/kg/d v 186 +/- 9 mL/kg/d; P < .01) for the 24 hours preceding surgery. CONCLUSION: LH is as an important and lethal complication associated with laparotomy in very small infants with NEC. The presence of hypotension and the administration of large amounts of volume in the preoperative period appear to be risk factors. Earlier surgical intervention and restoration of blood pressure using inotropic agents, once a particular level of fluid administration has been achieved, my be preventive.

Birth Weight↗

Interleukin-1 beta stimulates glucose uptake of human peritoneal mesothelial cells in vitro.

To investigate whether the glucose uptake (GU) of human peritoneal mesothelial cells (HPMC) is mediated by glucose transporters and whether this uptake is influenced by interleukin 1-beta (IL-1 beta), we measured 2-deoxy-(3H)-GU of HPMC in vitro, after exposing the cells for different times (two and 12 hours) to increasing concentrations (0.1, 1.0, and 2.0 ng/mL) of IL-1 beta. To exclude a noncarrier-mediated transport, GU was also tested in the presence of cytochalasin B. All experiments were performed in triplicate in the cells of two donors. Cytochalasin B inhibits GU of HPMC almost completely. GU of HPMC is not stimulated by insulin. GU is stimulated by IL-1 beta in a dose-dependent manner. These data indicate a GU of HPMC, which is mediated by a glucose transporter and stimulated by IL-1 beta. The increased uptake of glucose from the dialysate in patients with peritonitis may be mediated by a (cytokine-induced) increased activity of HPMC glucose transporters.

Blood Glucose↗

Differences in calcium kinetic pattern between CAPD and HD patients.

To assess the effect of different dialysis modalities on calcium turnover, we studied 57 patients on maintenance hemodialysis treatment (HD) and 38 patients on continuous ambulatory peritoneal dialysis (CAPD) with tracer kinetic studies using two calcium isotopes (45Ca by mouth and 47Ca intravenously). The two groups were comparable in age, sex and prevalence of diabetes. The groups did not differ in their serum concentrations of intact parathyroid hormone (iPTH), calcium, inorganic phosphate and 1,25-dihydroxyvitamin D. 25-hydroxy-vitamin D and alkaline phosphatase were found to be significantly higher in HD patients. Despite these similarities, CAPD patients showed a significantly lower calcium kinetic response as measured by calcium retention and plasma calcium efflux than HD patients. Mean calcium retention was 39.5% in HD patients compared to 31.2% in the CAPD group (p < 0.05). Plasma calcium efflux was significantly lower in the CAPD group (2.7 vs 3.2 respectively; p < 0.01). iPTH correlated with calcium retention and plasma calcium efflux in HD patients (r = 0.69 and r = 0.67 respectively). In CAPD patients, the correlation coefficient between iPTH and calcium retention was markedly lower (r = 0.54), whereas no correlation was found between iPTH and plasma calcium efflux (r = 0.08). In addition, the slope of the correlation curve were higher in HD patients (p < 0.01 and p < 0.001, respectively), indicating a better response of this patient group to the action of parathyroid hormone. Our data are in accordance with recently published results showing that the dialysis modality has a major impact on bone turnover and on the progression of uremic bone disease. It has been shown that CAPD is an independent risk factor for the development of the adynamic form of renal bone disease. This finding may be explained by the lower response of calcium turnover to the action of PTH as shown here with tracer kinetic studies.

Adult↗

In vitro effect of vegetable and fruit juices on the mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline.

The antimutagenic potencies of the juices of 28 fruits and 34 vegetables commonly consumed in Germany were investigated with respect to the mutagenic activities induced by 2-amino-3-methyl[4,5-f]-quinoline (IQ), and in part by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in Salmonella typhimurium TA98 and TA100. With IQ, weak to strong antimutagenic activities were found in 68% of the fruits and 73% of the vegetables that were tested. In fruits, strong antimutagenic activities were detected in bananas, blackberries, blueberries, sweet and sour cherries, blackcurrants and redcurrants, pineapple and watermelon. Moderate antimutagenic activities were detected in greengage, kiwi, mangos, honeydew melons and plums. Weak antimutagenic activities were detected in apple, apricot, mirabelle, pears, peaches and strawberries, whereas white and red grapes and raspberries were inactive, and gooseberries and citrus fruits in general possessed marginal or no antimutagenic activities. In vegetables, strong to moderate antimutagenic activities were found for all cruciferous vegetables, except Chinese cabbage, which had only weak antimutagenic activity. Other vegetables with strong antimutagenic activities were beets, chives, horseradish, onions, rhubarb and spinach. Moderate antimutagenic activities were found with green beans and tomatoes, weak activities in eggplant, garden cress, many lettuces, leeks, mangold, cucumber, pumpkin, radish and summer squash. Asparagus, carrots, fennel leaves, parsley, green peppers and radishes were inactive. When fruit and vegetable juices were heated, a considerable reduction of antimutagenic potencies was seen with apple, apricot, kiwi, pineapple, beets, cabbage (Chinese, Savoy, red and white), cauliflower, leafy lettuce, cucumber, onions, radish and rhubarb. Antimutagenic factors in blackberries, blueberries, sweet and sour cherries, honeydew melons, mirabelle, plums, strawberries, Brussels sprouts, chicory greens, eggplant, garden cress, mangold, pumpkin, lamb's lettuce and spinach were, however, remarkably heat stable. Antimutagenic potencies in bananas, blackcurrants and redcurrants, greengages, gooseberries, mangos, watermelon, green beans, kohlrabi, horseradish, tomatoes and chives were partially reduced. Antimutagenic activities in the juices of eight apple cultivars were moderate in two, weak in four, and marginal or absent in two. No major differences, however, were detected in five batches of oranges and three batches each of grapefruits, asparagus, green beans, broccoli, cauliflower, spinach and tomatoes. No (or only minor) differences were seen between IQ, MeIQ and MeIQx and tester strains TA98 and TA100. Pineapple and celeriac juices inhibited the enzymatic system responsible for the activation of IQ, but had no desmutagenic activity. Peroxidase activity found to be present in broccoli, cauliflower, green beans and tomatoes may contribute to antimutagenic activities in these vegetables.

Animals↗

Evidence for abnormal calcium homeostasis in patients with adynamic bone disease.

To investigate whether the derangements in calcium kinetics in patients with renal osteodystrophy are similar in the various histologic forms of this metabolic bone disease, 43 patients on chronic maintenance dialysis underwent calcium kinetic studies using the double isotope technique, iliac crest bone biopsies for mineralized bone histology and histomorphometry and determinations of serum indices of calcium and bone metabolism. Intestinal calcium absorption was not different among the three histologic groups. However, women exhibited lower calcium absorption in each histologic form (P < 0.01). Patients with predominant hyperparathyroid bone disease showed plasma calcium efflux, calcium accretion rate and calcium retention markedly above normal values. Patients with low turnover bone disease exhibited a normal or slightly decreased plasma calcium efflux and calcium accretion rate together with a disproportionately low calcium retention. Patients with mixed uremic osteodystrophy presented with a calcium kinetic profile intermediary to the two other forms. Good relationships existed between plasma calcium efflux, calcium accretion rate, calcium retention and histomorphometric parameters of bone turnover as well as serum levels of parathyroid hormone. However, no serum parameter could indicate with certainty the underlying bone disease. These findings demonstrate that adynamic bone disease does not merely represent an academic finding but is characterized by a very low bone capacity to buffer calcium and inability to handle an extra calcium load. This is particularly relevant for the daily care of end-stage renal failure patients presently receiving higher than ever amounts of vitamin D and calcium salts.

Adolescent↗

Decrease in peritonitis rate by integrated disconnect system in patients on continuous ambulatory peritoneal dialysis.

The prevention of peritonitis is of major concern for successful long-term continuous ambulatory peritoneal dialysis (CAPD) treatment. The effect of a Y-system on peritonitis incidence and patient morbidity was observed in a comparative, retrospective single-center analysis over a period of 5 years. The integrated disconnect system prolonged the peritonitis-free period from 1:11 patient-months, observed with the conventional system, to greater than 1:50 patient-months. The rate of hospitalization was reduced by 45%.

Humans↗

Effect of recombinant human erythropoietin on iron balance in maintenance hemodialysis: theoretical considerations, clinical experience and consequences.

Iron deficiency is the main reason for insufficient response to rEPO therapy. Serum ferritin and transferrin saturation give valuable information on storage iron and iron transport. Iron demand for correction of anemia can easily be estimated after HCT (vol%) x average blood volume (dl) = mg iron. Inadequate iron supply of the bone marrow in the presence of sufficient storage iron in the RES develops frequently under rEPO, possibly explaining the improvement of bone marrow response to rEPO by concomitant intravenous iron supply. The reasons of functional iron deficiency are still speculative.

Anemia↗

Bactericidal activity of human peritoneal macrophages from patients undergoing peritoneal dialysis.

Peritoneal macrophages (PM) play an essential role in the pathogenesis of bacterial peritonitis, the main complication of peritoneal dialysis (PD). We determined the antibacterial activity of PM from 31 PD patients using gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and gram-negative (Escherichia coli, Pseudomonas aeruginosa) test organisms. In an 8-hour test assay, PM revealed the highest antibacterial activity against E. coli [median bactericidal index (Bi) = 5.46 representing 0.74 log growth inhibition compared to controls] and the lowest against P. aeruginosa (Bi = 1.63, 0.21 log growth inhibition, p less than 0.05). The antibacterial activity against S. aureus (Bi = 1.99, 0.3 log growth inhibition) and S. epidermidis (Bi = 2.0, 0.31 log growth inhibition) was within this range. When compared to peripheral blood polymorphonuclear leukocytes, PM reached only 4% (S. aureus) and 8.1% (E. coli) of their antibacterial activity (p less than 0.05). Using E. coli as a test organism, PM isolated after a 4-hour dialysis period revealed the highest antibacterial activity when compared to PM isolated after longer dialysis periods (p less than 0.05). Increasing the duration of PD to 6 and 8 h subsequently decreased the antibacterial activity of PM, suggesting that unphysiologic concentrations of toxic metabolites in the peritoneal effluent might have a harmful influence on PM functions.

Bacteria↗

CAPD in elderly patients with cardiovascular risk factors.

Twenty-nine elderly patients (greater than 70 years) on CAPD treatment were compared with 30 younger patients (less than 55 years). Biochemical parameters did not differ between the two groups, apart from blood sugar which was higher in the older patient group. Ultrafiltration rates were almost identical. CAPD-specific complications also did not differ in the two patient groups. Arterial hypertension was well-controlled on CAPD and the proportion of patients requiring antihypertensives fell significantly. 8% of the old patients and 52% of the young patients required antihypertensive medication after 12 months of therapy compared to 38% and 81% before commencement of CAPD. Improvement of hemodynamic parameters was especially pronounced in older patients, who had cardiac risk factors in a high percentage of cases. Age and cardiac risk factors had the highest impact on the outcome, thus explaining the higher mortality in the older patient group. Older patients with renal insufficiency can be treated with CAPD leading to equally good results as those documented for younger patients.

Actuarial Analysis↗

Selective blockade of the antigen-receptor-mediated pathway of T cell activation in patients with impaired primary immune responses.

We investigated impaired cellular immune responses of individuals on chronic hemodialysis by using monoclonal antibodies that trigger differential pathways of T cell activation. Reduced cellular reactivity, which exists in a high proportion of such patients, can be attributed to a failure of the monocyte population to support the process of primary T cell activation in vitro. This defect results in a lack of interleukin 2 production, which is critically dependent on a monocyte-derived signal. In contrast, T lymphocyte function was found to be physiologic. Perhaps more important, the degree of monocyte dysfunction in vitro correlated with the same patients' in vivo responses to hepatitis B vaccination. Addition of recombinant human interleukin 2 fully reconstituted their deficient immune response in vitro.

Adult↗

Impaired cellular immune responses in chronic renal failure: evidence for a T cell defect.

Cellular immune responses in vitro were studied in 24 patients on chronic hemodialysis and 16 healthy volunteers with normal kidney function. Patients on maintenance hemodialysis had lymphopenia with diminished numbers of both T4+ and T8+ T-lymphocytes. The T4/T8 ratios were within the normal range. Peripheral blood lymphocytes (PBL) showed a diminished proliferative response upon stimulation with concanavalin A, phytohemagglutinin and pokeweed mitogen. When cell surface antigens were used for stimulation (mixed lymphocyte culture) uremic lymphocytes also showed a lower proliferation rate. Although without statistical conformation, there was a tendency by uremic PBL to produce less IL-2 as compared to healthy controls. Moreover, in a PWM driven system, peripheral blood lymphocytes from uremics produced significantly less IgG than PBL from normals. These results support the notion that a profound defect in lymphocyte function accounts at least, in part, for the observed immunodeficiency of uremic patients.

Adult↗

Alterations in microsomal drug metabolism and heme oxygenase activity in isolated hepatic parenchymal and sinusoidal cells in Murphy-Sturm lymphosarcoma-bearing rats.

Previous studies have demonstrated that Murphy-Sturm lymphosarcoma-bearing rats have significantly decreased hepatic microsomal cytochrome P-450 and NADPH-cytochrome c reductase activity, a consequent decreased capacity for oxidative microsomal drug metabolism, and increased microsomal heme oxygenase activity. Splenic microsomes obtained from tumor-bearing rats did not display similar changes. To define the cellular locus of these changes, preparations of hepatic parenchymal and hepatic sinusoidal cells were obtained from control and Murphy-Sturm lymphosarcoma-bearing rats and examined for alterations in microsomal parameters of drug metabolism and heme oxygenase. In hepatic parenchymal cell populations, heme oxygenase activity was significantly increased in tumor-bearing rats (0.046 nmol/mg/min vs. 0.019 nmol/mg/min, control, p less than 0.01) while other microsomal parameters were all significantly decreased in activity (cytochrome P-450, 0.25 nmol/mg vs 0.70 nmol/mg, control, p less than 0.001; NADPH-cytochrome c reductase, 24.4 nmol/mg/min vs 42.6 nmol/mg/min, control, p less than 0.005; benzo(a) pyrene hydroxylase, 0.230 nmol/mg/min vs. 0.518 nmol/mg/min, control, p less than 0.001). These results are similar to those obtained with microsomes from whole liver. Conversely, while hepatic sinusoidal cell preparations also demonstrated increased heme oxygenase activity (0.134 nmol/mg/min vs 0.079 nmol/mg/min, control, p less than 0.01), all other hepatic sinusoidal cell microsomal parameters were not appreciably altered in tumor-bearing animals. The results indicate that the major effect of the tumor-bearing state on hepatic microsomal heme and drug metabolism is on the parenchymal cell, and not the sinusoidal cell population.

Animals↗