Showing papers by "Free University of Berlin published in 1994"

A critical discussion of intraclass correlation coefficients.

Abstract: In general, intraclass correlation coefficients (ICC's) are designed to assess consistency or conformity between two or more quantitative measurements. They are claimed to handle a wide range of problems, including questions of reliability, reproducibility and validity. It is shown that care must be taken in choosing a suitable ICC with respect to the underlying sampling theory. For this purpose a decision tree is developed. It may be used to choose a coefficient which is appropriate for a specific study setting. We demonstrate that different ICC's may result in quite different values for the same data set, even under the same sampling theory. Other general limitations of ICC's are also addressed. Potential alternatives are presented and discussed, and some recommendations are given for the use of an appropriate method.

Resistance to blood flow in microvessels in vivo.

Abstract: Resistance to blood flow through peripheral vascular beds strongly influences cardiovascular function and transport to tissue. For a given vascular architecture, flow resistance is determined by the rheological behavior of blood flowing through microvessels. A new approach for calculating the contribution of blood rheology to microvascular flow resistance is presented. Morphology (diameter and length), flow velocity, hematocrit, and topological position were determined for all vessel segments (up to 913) of terminal microcirculatory networks in the rat mesentery by intravital microscopy. Flow velocity and hematocrit were also predicted from mathematical flow simulations, in which the assumed dependence of flow resistance on diameter, hematocrit, and shear rate was optimized to minimize the deviation between measured and predicted values. For microvessels with diameters below approximately 40 microns, the resulting flow resistances are markedly higher and show a stronger dependence on hematocrit than previously estimated from measurements of blood flow in narrow glass tubes. For example, flow resistance in 10-microns microvessels at normal hematocrit is found to exceed that of a corresponding glass tube by a factor of approximately 4. In separate experiments, flow resistance of microvascular networks was estimated from direct measurements of total pressure drop and volume flow, at systemic hematocrits intentionally varied from 0.08 to 0.68. The results agree closely with predictions based on the above-optimized resistance but not with predictions based on glass-tube data. The unexpectedly high flow resistance in small microvessels may be related to interactions between blood components and the inner vessel surface that do not occur in smooth-walled tubes.

Cardiomyocytes differentiated in vitro from embryonic stem cells developmentally express cardiac-specific genes and ionic currents.

Abstract: Cardiomyocytes differentiated in vitro from pluripotent embryonic stem (ES) cells of line D3 via embryo-like aggregates (embryoid bodies) were characterized by the whole-cell patch-clamp technique during the entire differentiation period. Spontaneously contracting cardiomyocytes were enzymatically isolated by collagenase from embryoid body outgrowths of early, intermediate, and terminal differentiation stages. The early differentiated cardiomyocytes exhibited an outwardly rectifying, transient K+ current sensitive to 4-aminopyridine and an inward Ca2+ current but no Na+ current. The Ca2+ current showed all features of L-type Ca2+ current, being highly sensitive to 1,4-dihydropyridines but not to omega-conotoxin. Cardiomyocytes of intermediate stage were characterized by the additional expression of cardiac-specific Na+ current, the delayed K+ current, and If current. Terminally differentiated cardiomyocytes expressed a Ca2+ channel density about three times higher than that of early stage. In addition, two types of inwardly rectifying K+ currents (IK1 and IK,Ach) and the ATP-modulated K+ current were found. During cardiomyocyte differentiation, several distinct cell populations could be distinguished by their sets of ionic channels and typical action potentials presumably representing cardiac tissues with properties of sinus node, atrium, and ventricle. Reverse transcription polymerase chain reaction revealed the transcription of alpha- and beta-cardiac myosin heavy chain (MHC) genes synchronously with the first spontaneous contractions. Transcription of embryonic skeletal MHC gene at intermediate and terminal differentiation stages correlated with the expression of Na+ channels. The selective expression of alpha-cardiac MHC gene in ES cell-derived cardiomyocytes was demonstrated after ES cell transfection of the LacZ construct driven by the alpha-cardiac MHC promoter region followed by ES cell differentiation and beta-galactosidase staining. In conclusion, our data demonstrate that ES cell-derived cardiomyocytes represent a unique model to investigate the early cardiac development and permit pharmacological/toxicological studies in vitro.

G proteins of the G12 family are activated via thromboxane A2 and thrombin receptors in human platelets.

Abstract: Using subtype-specific antisera, we were able to identify the recently described alpha subunits of G12 and G13 in platelet membranes as 43-kDa proteins. Activation of the thromboxane A2 and the thrombin receptors in platelet membranes led to increased incorporation of the photoreactive GTP analogue [alpha-32P]GTP azidoanilide into immunoprecipitated alpha 12 and alpha 13, indicating that both receptors couple to G12 and G13. In addition, both activated receptors were demonstrated to couple to one or more members of the Gq family. In the absence of receptor agonists, incorporation of [alpha-32P]GTP azidoanilide into alpha 12 and alpha 13 was low over a long time period (up to 45 min) due to an obviously low basal nucleotide exchange rate, whereas an agonist-stimulated photolabeling of alpha 12 and alpha 13 could be observed after 4-8 min and reached a maximum after 30-45 min. Effective activation of G12 and G13 via the thromboxane A2 and the thrombin receptors was not dependent on the presence of GDP. Our results provide evidence that G12 and G13 play a functional role in transmembrane signal transduction and suggest that both proteins are involved in pathways leading to platelet activation.

Structure of the Tet repressor-tetracycline complex and regulation of antibiotic resistance

Abstract: The most frequently occurring resistance of Gram-negative bacteria against tetracyclines is triggered by drug recognition of the Tet repressor. This causes dissociation of the repressor-operator DNA complex and enables expression of the resistance protein TetA, which is responsible for active efflux of tetracycline. The 2.5 angstrom resolution crystal structure of the homodimeric Tet repressor complexed with tetracycline-magnesium reveals detailed drug recognition. The orientation of the operator-binding helix-turn-helix motifs of the repressor is inverted in comparison with other DNA binding proteins. The repressor-drug complex is unable to interact with DNA because the separation of the DNA binding motifs is 5 angstroms wider than usually observed.

Syncope : a videometric analysis of 56 episodes of transient cerebral hypoxia

Abstract: To investigate the clinical features of transient cerebral hypoxia, syncope was induced in 56 of 59 healthy volunteers through a sequence of hyperventilation, orthostasis, and Valsalva maneuver. All events were monitored on video by two cameras. Complete syncope with falling and loss of consciousness was observed in 42 subjects, lasting 12.1 ± 4.4 seconds. Myoclonic activity occurred in 38 of these 42 episodes (90%). The predominant movement pattern consisted of multifocal arrhythmic jerks both in proximal and distal muscles. Superposition of generalized myoclonus was common. Additional movements such as head turns, oral automatisms, and righting movements occurred in 79%. Eyes remained open throughout syncope in most subjects and initial upward deviation was common. Sixty percent reported visual and auditory hallucinations. Thirteen subjects had incomplete syncope with falls but partially preserved consciousness. These episodes were shorter and usually not accompanied by myoclonus and hallucinations. Transient amnesia and unresponsiveness without falling occurred in 1 subject.

Optimism, Vulnerability, and self-beliefs as health-related cognitions: A systematic overview

Abstract: This paper disentangles a number of closely related cognitions by dividing them into the categories of defensive and functional optimism. Optimistic biases in risk perception are discussed that may represent barriers in the adoption of preventive health behaviors. Instead of defensive optimism, some sense of vulnerability is seen as indispensable for behavioral change operating jointly with beliefs about positive health outcomes, instrumental actions, and appropriate coping resources. A distinction is made between three kinds of functional optimism that depend either on attributional style, outcome expectancies, or personal agency. Findings are presented that corroborate the strength of these constructs in predicting health outcomes. In terms of health behavior change, it is argued that optimistic self-beliefs are the most beneficial because of their operative power that helps to set goals, initiate actions, and maintain motivation.

Crossover from in-plane to perpendicular magnetization in ultrathin ni/cu(001) films

Abstract: The easy axis of magnetization in Ni/Cu(001) films exhibits a crossover from in-plane to perpendicular orientation with increasing film thickness. This reorientation at \ensuremath{\approxeq}7 monolayers, observed by ferromagnetic resonance, is substantially different from previous findings for Fe and Co films and can be extrapolated from thin-film data. The artificial lattice structure of Ni on Cu yields within magnetoelasticity theory a volume anisotropy of 29 \ensuremath{\mu}eV/atom agreeing perfectly with experiment. In thinner films the surface anisotropy of -77 \ensuremath{\mu}eV/atom dominates.

The origin of the major cystic fibrosis mutation (ΔF508) in European populations

Abstract: delta F508 is the most frequent cystic fibrosis (CF) mutation and accounts for approximately 70% of CF chromosomes worldwide. Three highly polymorphic microsatellite markers have been used to study the origin and evolution of delta F508 chromosomes in Europe. Haplotype data demonstrate that delta F508 occurred more than 52,000 years ago, in a population genetically distinct from any present European group, and spread throughout Europe in chronologically distinct expansions, which are responsible for the different frequencies of delta F508 in Europe.

Use of dynamic magnetic resonance imaging with fast imaging in the detection of early and advanced sacroiliitis in spondylarthropathy patients

Abstract: Objective. To evaluate the new magnetic resonance imaging (MRI) method of dynamic MRI with fast imaging in the diagnosis of sacroiliitis among patients with spondylarthropathy. Methods. Fifteen patients with a history of inflammatory back pain without radiographic evidence of grade II or greater sacroiliitis (group 1), 25 patients with definite ankylosing spondylitis (group 2), and 12 patients with noninflammatory spinal pain (controls) (group 3) were examined. Dynamic MRI with fast imaging was performed after intravenous bolus injection of the contrast agent gadolinium—diethylenetriamine pentaacetic acid. The degree of enhancement was graded as representing acute sacroiliitis, latent sacroiliitis, or no sacroiliitis. Results. Acute sacroiliitis was detected in 22 of 30 sacroiliac (SI) joints in group 1 patients and in 27 of 50 SI joints in group 2 patients; latent sacroiliitis was seen in 25 of 80 SI joints in patients from groups 1 and 2. No group 3 patient was found to have sacroiliitis. Conclusion. Early sacroiliitis can be demonstrated by dynamic MRI in spondylarthropathy patients in whom abnormalities are not revealed by conventional radiography.

Weekly variation of acute myocardial infarction. Increased Monday risk in the working population.

Abstract: BACKGROUNDSeasonal and circadian variations in the occurrence of myocardial infarction and sudden cardiac death have been documented, suggesting that triggering factors may play a role in the causa...

The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family

Abstract: We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log λ n , where λ n is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional χ (2) 2 -distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio λ n are possible and the asymptotic distribution of 2 log λ n is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the χ2-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (θ≤0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log λ n are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2α)100 percentiles of χ (1) 2 . In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log λ n is pivotal. Selected (1−α) 100 percentiles are presented and shown to differ between the two models.

Mutation of His-105 in the beta 1 subunit yields a nitric oxide-insensitive form of soluble guanylyl cyclase

Abstract: Soluble guanylyl cyclase [GTP pyrophosphate-lyase (cyclizing); EC 4.6.1.2] is a hemoprotein that exists as a heterodimer; the heme moiety has been proposed to bind nitric oxide, resulting in a dramatic activation of the enzyme. Mutation of six conserved His residues reduced but did not abolish nitric oxide stimulation whereas a change of His-105 to Phe in the beta 1 subunit yielded a heterodimer that retained basal cyclase activity but failed to respond to nitric oxide. Heme was not detected as a component of the mutant heterodimer and protophorphyrin IX failed to stimulate enzyme activity. The activity of the His mutant was almost identical to that of the wild-type enzyme in the presence of KCN, suggesting that disruption of heme binding is the principal effect of the mutation. Thus, the mutation provides a means to inhibit the nitric oxide-sensitive guanylyl cyclase signaling pathway.

Emergence of fluconazole-resistant strains of Candida albicans in patients with recurrent oropharyngeal candidosis and human immunodeficiency virus infection.

Abstract: After repeated use of fluconazole for therapy of oropharyngeal candidosis, the emergence of in vitro fluconazole-resistant Candida albicans isolates (MIC, > or = 25 micrograms/ml) together with oral candidosis unresponsive to oral dosages of up to 400 mg of fluconazole were observed in patients with human immunodeficiency virus (HIV) infection. Antifungal susceptibility testing was done by broth microdilution and agar dilution techniques on C. albicans isolates recovered from a cohort of patients with symptomatic HIV infection who were treated repeatedly with fluconazole for oropharyngeal candidosis. In vitro findings did show a gradual increase in the MICs for C. albicans isolates recovered from selected patients with repeated episodes of oropharyngeal candidosis. Primary resistance of C. albicans to fluconazole was not seen. Cross-resistance in vitro occurred between fluconazole and other azoles (ketoconazole, itraconazole), but to a lesser extent. The results of the study suggest that the development of clinical resistance to fluconazole could be clearly correlated to in vitro resistance to fluconazole. Itraconazole may still serve as an effective antifungal agent in patients with HIV infection and oropharyngeal candidosis nonresponsive to fluconazole.

Complexes of metals other than platinum as antitumour agents.

Abstract: The earliest reports on the therapeutic use of metals or metal-containing compounds in cancer and leukemia date from the sixteenth and nineteenth centuries. They were forgotten until the 1960s, when the anti-tumour activity of the inorganic complex cis-diammine-dichloroplatinum(II) (cisplatin) was discovered. This led to the development of other types of non-organic cytostatic drugs. Cisplatin has developed into one of the most frequently used and most effective cytostatic drugs for the treatment of solid carcinomas. Numerous other metal compounds containing platinum, other platinum metals, and even non-platinum metals were then shown to be effective against tumours in man and experimental tumours in animals. These compounds comprise main-group metallic compounds of gallium, germanium, tin, and bismuth, early-transition metal complexes of titanium, vanadium, niobium, molybdenum, and rhenium, and late-transition metal complexes of ruthenium, rhodium, iridium, platinum, copper, and gold. Several platnium complexes and four non-platnium-metal antitumour agents have so far entered early clinical trials. Gallium trinitrate and spirogermanium have already passed phase II clinical studies and have shown limited cytostatic activity against certain human carcinomas and lymphomas. The two early-transition metal complexes budotitane and titanocene dichloride have just reached the end of phase I clinical trials and have been found to have an unusual pattern of organ toxicity in man. Titanocene dichloride will soon enter phase II clinical studies.

Mapping of the Gene for Autosomal Recessive Polycystic Kidney-disease (arpkd) To Chromosome 6p21-cen

Abstract: Autosomal recessive polycystic kidney disease (ARPKD) is one of the major hereditary nephropathies in children predominantly presenting in early childhood. The clinical picture is variable but there is a fatal outcome in many cases. We have performed linkage analysis in 16 ARPKD families and localized the ARPKD gene to chromosomal region 6p21-cen with no evidence for genetic heterogeneity among different clinical phenotypes. Linkage was confirmed using six adjacent microsatellite markers and the highest lod score of 7.42 was obtained with D6S272 at theta = 0.00. Our findings should lead to more accurate forms of prenatal diagnosis than those currently available using ultrasound.

The effect of epoetin beta (recombinant human erythropoietin) on the need for transfusion in very-low-birth-weight infants

Abstract: Background. Anemia of prematurity is characterized by low reticulocyte counts and inadequate erythropoietin response, for which many very-low-birth-weight infants receive multiple blood transfusions. We investigated whether early treatment of such infants with recombinant human erythropoietin would reduce their need for transfusions. Methods. We performed a controlled, blinded trial in 241 infants with very low birth weights at 12 centers in six European countries. When three days old, the infants were randomly assigned either to the epoetin group or to the control group. Those in the epoetin group received 250 IU of epoetin beta per kilogram of body weight subcutaneously three times a week from day 3 to day 42 (for a total of 17 doses); those in the control group did not receive this drug. Infants in both groups received oral iron (2 mg per day) from day 14 onward. Results. The control infants needed a mean of 1.25 transfusions each, as compared with 0.87 transfusion for epoetin-treated infants (P = 0.013). The median cumulative volume of blood transfused per kilogram per day was 0.41 mi in the control group (first quartile, 0 ml; third quartile, 0.8 ml) and 0.09 ml in the epoetin group (first quartile, 0 ml; third quartile, 0.8 ml) (P = 0.044). The rate of success, defined as an absence of need for transfusions and a hematocrit that never fell below 32 percent, was 4.1 percent in the control group and 27.5 percent in the epoetin group (P = 0.008). Epoetin was most beneficial in boys with birth weights of 1200 g or more and a base-line hematocrit of 48 percent or more. No toxic effects were observed in the epoetin group; as compared with the control group, the epoetin group had an increased incidence of septicemia (14 vs. 7 episodes, P not significant) and reduced weight gain (520 vs. 571 g, P = 0.02). Conclusions, Infants with very low birth weights have less need of transfusions if given epoetin beta during the first six weeks of life (250 IU per kilogram three times a week). We recommend early epoetin treatment for all such infants, but further studies of nutrition and iron supplementation during treatment are needed.

Keratin 9 Gene Mutations in Epidermolytic Palmoplantar Keratoderma (EPPK)

Abstract: We have isolated the gene for human type I keratin 9 (KRT9) and localised it to chromosome 17q21. Patients with epidermolytic palmoplantar keratoderma (EPPK), an autosomal dominant skin disease, were investigated. Three KRT9 mutations, N160K, R162Q, and R162W, were identified. All the mutations are in the highly conserved coil 1A of the rod domain, thought to be important for heterodimerisation. R162W was detected in five unrelated families and affects the corresponding residue in the keratin 14 and keratin 10 genes that is also altered in cases of epidermolysis bullosa simplex and generalised epidermolytic hyperkeratosis, respectively. These findings provide further evidence that mutations in keratin genes may cause epidermolysis and hyperkeratosis and that hyperkeratosis of palms and soles may be caused by different mutations in the KRT9 gene.

Nephrotoxicity following orthotopic liver transplantation. A comparison between cyclosporine and FK506.

Abstract: Nephrotoxicity represents a serious side effect of immunosuppression following liver transplantation. In order to compare the nephrotoxic action of CsA and FK506 in a clinical setting, we evaluated the incidence of early and late nephrotoxicity in 121 patients, 60 of whom were randomly assigned to CsA- and 61 to FK506-based immunosuppression. Early postoperative renal insufficiency (between PODs 0 and 30; SCr 1.5-3 mg/dl) was observed to a similar extent in patients treated with CsA (38.3%) and FK506 (42.6%). Early postoperative acute renal failure (ARF) (SCr > 3 mg/dl) was observed in 18.0% of patients in the FK506 treatment group and 18.3% of patients receiving CsA therapy. Approximately half the patients with ARF required hemodialysis (CsA: 11.7%; and FK506: 8.2%). All patients with early postoperative ARF requiring hemodialysis survived for more than one year. New onset of late ARF (between PODs 30 and 365) was observed in 6.6% of patients receiving FK506 therapy and in 1.7% in the CsA treatment group as a result of severe infection with multiple organ failure syndrome (MOFS). There was 100% mortality in patients with late ARF requiring hemodialysis. Etiology and prognosis of early and late ARF seem to be completely different. Early ARF was associated with severe coagulopathy and a rise in bilirubin and free hemoglobin, and was accompanied by impaired liver function. Mean onset of hemodialysis in CsA-treated patients was POD 1 and in FK506-treated patients POD 6, which disclosed a different time course of drug-specific nephrotoxicity of CsA and FK506 in early ARF. In contrast, late ARF occurred in both treatment groups only as a part of the MOFS in association with severe infections, an observation consistent with the assumption of overimmunosuppression rather than a primary nephrotoxic effect. Late renal insufficiency appeared in 23.3% of CsA- and in 29.4% of FK506-treated patients, and represented a slowly progressing form of drug-specific nephrotoxicity of CsA and FK506. These preliminary results demonstrate a similar outcome in terms of both early and late nephrotoxicity, but longer follow-up will delineate the overall efficacy and toxicity in humans.

Atopic diseases in infancy. The German multicenter atopy study (MAS-90).

Abstract: Atopic diseases are complex multifactorial in origin (1). A genetic background predisposes vulnerable individuals to develop IgE-mediated reactions to environmental allergens. Since the classical work by Goner et al. (2) many studies have shown that atopic vulnerability can be recognized at birth and atopic disease predicted by family history and cord blood IgE values (3). However, the predictive value especially of cord blood IgE has been questionned recently (4-8). The rising public concern about environmental pollution and many reports of the increasing prevalence of atopic diseases in affluent societies have initiated a new series of investigations on the predictability and early prevention of atopic disorders. Effective prevention and early intervention strategies are priority research objectives. However, our knowledge about the relative contribution of genetic and environmental factors for the manifestation, seventy, duration and impact of atopic diseases is still unsatisfactory. The German Multicenter Atopy Study (MAS-90) was initiated to evaluate the predictive value of various clinical and immunological parameters as well as the significance of early environmental exposures to allergens and trigger factors for the development of atopic diseases in early childhood.