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

On elementary flux modes in biochemical reaction systems at steady state

Abstract: A mathematical definition of the concept of elementary mode is given so as to apply to biochemical reaction systems subsisting at steady state. This definition relates to existing concepts of null-space vectors and includes a condition of simplicity. It is shown that for systems in which all flux- have fixed signs, all elementary modes are given by the generating vectors of a convex cone and can, thus, be computed by an existing algorithm. The present analysis allows for the more general case that some reactions can proceed in either direction. Basic ideas on how to compute the complete set of elementary modes in this situation are outlined and verified by way of several examples, with one of them repraenting glycolysis and gluconeogenesis. These examples show that the elementary modes can be interpreted in terms of the particular biochemical functions of the network. The relationships to (futile) substrate cycles are elucidated.

Extensive reorganization of the somatosensory cortex in adult humans after nervous system injury

Abstract: MAGNETIC source imaging revealed that the topographic representation in the somatosensory cortex of the face area in upper extremity amputees was shifted an average of 1.5 cm toward the area that would normally receive input from the now absent nerves supplying the hand and fingers. Observed alterat

Gross worker and job flows in Europe

Abstract: Despite the impression of Eurosclerosis, labor markets in Europe are in fact quite active. Flows into and out of unemployment are large, countercyclical, and highly coherent in four European countries examined. Worker exits from unemployment to employment exhibit a countercyclical pattern similar to that in the United States and Japan. The matching function paradigm is capable of explaining these facts only if the unemployment stock rises sufficiently fast in downturns. We propose an equilibrium model which can deliver a wide range of job and worker flow dynamics. For sufficiently large adverse shocks, the model can generate endogenous layoffs and job destruction which match the stylized facts.

Capillary perfusion of the rat brain cortex. An in vivo confocal microscopy study.

Abstract: Confocal laser-scanning microscopy was used to visualize subsurface cerebral microvessels labeled with intravascular fluorescein in a closed cranial window model of the anesthetized rat. In noninvasive optical sections up to 250 microns beneath the brain surface, plasma perfusion and blood cell perfusion of individual capillaries were studied. Under resting conditions, in all cerebral capillaries the presence of plasma flow as demonstrated by the appearance of an intravenously injected fluorescent tracer within 20 seconds after injection. Plasma flow was verified even in capillaries that contained stationary erythrocytes or leukocytes; 91.1% of the capillaries contained flowing blood cells, 5.2% contained stationary blood cells, and no blood cells were seen in 3.6%. Mean blood cell velocity was 498.3 +/- 443.9 microns/s, and the mean blood cell supply rate was 35.75 +/- 28.01 cells per second. When capillaries were continuously observed for 1 minute, "on" and "off" periods of blood cell flow were noted. During hypercapnia (increase of PCO2 from 33.25 to 50.26 mm Hg), mean blood cell flux increased from 38.6 +/- 17.2 to 55.5 +/- 12.2 per second (P < .005, paired t test of mean values in six animals), and blood cell velocity increased from 519.5 +/- 254.8 to 828.5 +/- 460.8 microns/s (P = .074, paired t test of mean values in six animals). Homogeneity of blood cell flux increased as indicated by the coefficient of variation decreasing from 44.6% to 22.0%, and the portion of poorly perfused capillaries (blood cell flux, < 40 per second) decreased from 59.2% to 22.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Translation of 15-lipoxygenase mRNA is inhibited by a protein that binds to a repeated sequence in the 3' untranslated region.

Abstract: During red blood cell differentiation, the mRNA encoding rabbit erythroid 15-lipoxygenase (LOX) is synthesized in the early stages of erythropoiesis, but is only activated for translation in peripheral reticulocytes. Erythroid LOX, which like other lipoxygenases catalyses the degradation of lipids, is unique in its ability to attack intact phospholipids and is the main factor responsible for the degradation of mitochondria during reticulocyte maturation. Strikingly, rabbit erythroid LOX mRNA has 10 tandem repeats of a slightly varied, pyrimidine-rich 19 nt motif in its 3'-untranslated region (3'-UTR). In this study we demonstrate, using gel retardation and UV-crosslinking assays, that this 3'-UTR segment specifically binds a 48 kDa reticulocyte protein. Furthermore, the interaction between the 3'-UTR LOX repeat motif and the 48 kDa protein, purified to homogeneity by specific RNA chromatography, is shown to be necessary and sufficient for specific translational repression of LOX as well as reporter mRNAs in vitro. To our knowledge this is the first case in which translation, presumably at the initiation step, is regulated by a defined protein-RNA interaction in the 3'-UTR.

Cytomegalovirus infection in transplant recipients. The role of tumor necrosis factor.

Abstract: Human cytomegalovirus (CMV) infection is an important cause of morbidity and mortality in transplant recipients. CMV infection commonly results from the reactivation of a latent infection. Using a set of monoclonal anti-CMV antibodies, we found CMV antigen expression in peripheral blood mononuclear cells (PBMNC), particularly in monocytes, in 312 of 816 samples from 190 allograft recipients. The detection of CMV-IE antigens and CMV-IE DNA in PBMNC indicates that positive cells may represent truly infected cells. The relation between increased cytokine plasma levels (particularly following treatment by pan-T cell antibodies) and the appearance of CMV antigens in PBMNC suggests that cytokines may play an important role in the reversal of CMV latency. This hypothesis is supported by our finding that tumor necrosis factor-alpha (TNF) is able to stimulate the activity of the CMV-IE enhancer/promoter region in the human monocytic cell line, HL-60. The interleukins 1, 2, 3, 4, 6, 8 and 10; transforming growth factor-beta; interferongamma; and granulocyte/macrophage colony-stimulating factor did not show any enhancing effect on the CMV promoter activity. Thus, TNF-alpha seems to play a key role in regulating the balance between latency and reactivation of CMV infection. Inhibition of TNF-alpha release or action may be an alternative strategy for preventing CMV-associated morbidity in allograft recipients.

Cyclin D1 expression is regulated by the retinoblastoma protein.

Abstract: The product of the retinoblastoma susceptibility gene, pRb, acts as a tumor suppressor and loss of its function is involved in the development of various types of cancer. DNA tumor viruses are supposed to disturb the normal regulation of the cell cycle by inactivating pRb. However, a direct function of pRb in regulation of the cell cycle has hitherto not been shown. We demonstrate here that the cell cycle-dependent expression of one of the G1-phase cyclins, cyclin D1, is dependent on the presence of a functional Rb protein. Rb-deficient tumor cell lines as well as cells expressing viral oncoproteins (large tumor antigen of simian virus 40, early region 1A of adenovirus, early region 7 of papillomavirus) have low or barely detectable levels of cyclin D1. Expression of cyclin D1, but not of cyclins A and E, is induced by transfection of the Rb gene into Rb-deficient tumor cells. Cotransfection of a reporter gene under the control of the D1 promoter, together with the Rb gene, into Rb-deficient cell lines demonstrates stimulation of the D1 promoter by Rb, which parallels the stimulation of endogenous cyclin D1 gene expression. Our finding that pRb stimulates expression of a key component of cell cycle control, cyclin D1, suggests the existence of a regulatory loop between pRb and cyclin D1 and extends existing models of tumor suppressor function.

Coupling of cerebral blood flow to neuronal activation: role of adenosine and nitric oxide.

Abstract: We studied the role and relationship of the putative mediators of coupling of cerebral blood flow (CBF) and neuronal activation, adenosine (Ado) and nitric oxide (NO) Topical brain application ove

Involvement of 15-lipoxygenase in early stages of atherogenesis.

Abstract: The arachidonate 15-lipoxygenase which is expressed in atherosclerotic lesions is implicated in the oxidative modification of low density lipoproteins during atherogenesis. To obtain experimental in vivo evidence for this hypothesis, we analyzed the structure of oxygenated lipids isolated from the aorta of rabbits fed with a cholesterol-rich diet for different time periods and compared the pattern of oxygenation products with that isolated from low density lipoproteins treated in vitro with the pure rabbit 15-lipoxygenase and with oxygenated lipids isolated from advanced human atherosclerotic lesions. In early atherosclerotic lesions (12-wk cholesterol feeding), specific lipoxygenase products were detected whose structure was similar to those isolated from lipoxygenase-treated low density lipoproteins. The appearance of these products did coincide with the lipid deposition in the vessel wall. In later stages of atherogenesis (26-wk cholesterol feeding) the degree of oxidative modification of the tissue lipids did increase but the share of specific lipoxygenase products was significantly lower, suggesting an increasing overlay of the specific lipoxygenase products by nonenzymatic lipid peroxidation. In advanced human atherosclerotic lesions, large amounts of oxygenation products were detected whose structure suggests a nonenzymatic origin. These data suggest that the arachidonate 15-lipoxygenase is of pathophysiological importance during the early stages of atherogenesis. In later stages of plaque development nonenzymatic lipid peroxidation becomes more relevant.

Reorganization of substratum-bound fibronectin on hydrophilic and hydrophobic materials is related to biocompatibility

Abstract: It is a general trend that mammalian cells interact better with wettable surfaces than with non-wettable surfaces. The basis for this difference is still poorly understood. In this study hydrophilic clean glass and hydrophobic octadecyl glass have been used as model surfaces. We show that fibroblasts on hydrophilic surfaces may reorganize fluorescent fibronectin (FN) in an extracellular matrix-like structure whereas on hydrophobic surfaces no rearrangement of FN occurs. This was accompanied by a high proliferation of fibroblasts on clean glass whereas on octadecyl glass no cell growth occurred. Moreover, it was demonstrated that there are striking differences in the morphology of fibroblasts adhering to hydrophilic and hydrophobic surfaces, judged by the overall cell shape, the organization of FN receptors and actin filaments. Indeed, the preadsorption of FN on these surfaces could almost abolish morphological differences between hydrophilic and hydrophobic surfaces. However, preadsorption of FN could not restore the proliferation of fibroblasts on the hydrophobic surface. Taken together, the results suggest that the method of adsorption and reorganization of FN may be critical for the biocompatibility of materials.

Contrast-enhanced MR imaging of liver and spleen: first experience in humans with a new superparamagnetic iron oxide

Abstract: The aim of this prospective study was to obtain the first human safety and magnetic resonance (MR) imaging results with a new formulation of superparamagnetic iron oxide (SPIO) (SHU 555 A). The SPIO was tested at four iron doses, from 5 to 40 mumol/kg. Laboratory tests and clinical measurements were done in 32 healthy volunteers for up to 3 weeks after administration. MR imaging at 1.5 T was performed before and 8 hours to 14 days after fast intravenous injection (500 mumol Fe/min) of the SPIO (six subjects per dose). Results of this phase I study demonstrate that SHU 555 A at a concentration of 0.5 mol Fe/L was well tolerated. A dose-dependent minor increase in activated partial thromboplastin time, which remained within the normal range, was seen. All doses of SPIO caused a signal loss in both liver and spleen (P < .05) with a spin-echo sequence (TR = 2,300 msec, TE = 45 msec). The signal losses in the liver 8 hours after contrast agent injection were 58%, 79%, 82%, and 87% for the 5, 10, 20, and 40 mumol Fe/kg doses, respectively. The corresponding signal losses in the spleen were 23%, 45%, 65%, and 78%, respectively. The doses that reduced signal intensity by half were 3.1 mumol Fe/kg for the liver and 12.8 mumol Fe/kg for the spleen. The results suggest that the new SPIO formulation is a safe and efficient MR contrast agent.

Surface core-level shifts of some 4d-metal single-crystal surfaces: Experiments and ab-initio calculations

Abstract: High resolution measurements are reported of the surface core-level shift of the 3d level for the Rh(111), Rh(110), Pd(111), Pd(110), and Ag(111) single-crystal surfaces. These measurements and earlier ones for the Mo(110), Rh(100), and Pd(100) surfaces are analyzed by ab initio calculations of the surface core-level shift. The calculations are found to reproduce well the trends of the experimental shifts with the 4d metal and with the crystal plane. The comparison between these experimental and theoretical results demonstrates the importance of proper inclusion of final-state effects for accurate calculations of surface core-level shifts. A core hole in a surface atom is found to be better screened than one in a bulk atom for the 4d metals to the left of Pd in the Periodic Table. The use of the Z+1 approximation to describe the core hole is investigated both by explicit use of this approximation and by performing calculations for 1s and 3d core holes, respectively. The Z+1 approximation is found to be well obeyed in the case of Ag whereas for the rest of the 4d transition metals it is less precise, introducing errors of typically 0.1 eV.

Glutathione S-transferase M1 and its variants A and B as host factors of bladder cancer susceptibility: a case-control study.

Abstract: Glutathione S -transferase M1 (GSTM1) is a foreign compound-metabolizing enzyme with a heritable complete lack of activity in about 50% of Caucasians. GSTM1 deficiency may predispose individuals to urinary bladder cancer. Thus, a hospital-based case-control study was performed with 296 patients with bladder cancer and 400 controls, investigating this GSTM1 deficiency in relation to environmental risk factors and types of bladder cancer. Frequencies of the GSTM1 gene deletion (genotype, GSTM1*0/0 ) and of the allele variants A (µ) and B (ψ) of the GSTM1-active trait were determined using an internal standard-controlled polymerase chain reaction technique. Moreover, in all patients GSTM1 expression was quantified in blood by an immunoassay. Of the cases, 59.1% had the GSTM1*0/0 genotype, in contrast to 50.7% of the controls (odds ratio, 1.40; 95% confidence limits, 1.02–1.92; P = 0.017). The odds ratio after adjustment for age and gender by logistic regression analysis was 1.54 (95% confidence limits, 1.12–2.13). Occupational risk was defined as previous employment in occupations with known increased bladder cancer risk, but the impact of GSTM1*0/0 was not significantly different in individuals with risk jobs versus those without. The greater proportion of the GSTM1-deficient individuals in the group with cancer was due to a lower frequency of carriers of GSTM1A. The odds ratio for the subgroup of individuals with the GSTM1B phenotype versus carriers of the GSTM1A phenotype in cases versus controls was 1.65 (95% confidence limits, 0.976–2.78; two-tailed Fisher's exact P = 0.057). Analysis of functional GSTM1 activity in a subset of 370 blood samples with the model substrate trans -stilbene oxide confirmed the genetic results and showed that 9 of 10 individuals with µ/ψ heterodimers (genotype, GSTM1*A/B ) had activities above the median of all genetically GSTM1-active individuals (24 pmol/min/1 × 106 lymphocytes; P < 0.01), indicating a gene dose relationship for GSTM1. GSTM1 expression in the urinary bladder endothelium detected by immunoassay and immunohistology corresponded to the genotype of the patients. It may be concluded from this study that the heritable GSTM1 deficiency is responsible for 17% (etiological fraction; 95% confidence limits, 2–30%) of bladder cancer cases.

Assessment of liver metabolic function. Clinical implications.

Abstract: Inter- and intraindividual variability in pharmacokinetics of most drugs is largely determined by variable liver function as described by parameters of hepatic blood flow and metabolic capacity. These parameters may be altered as a result of disease affecting the liver, genetic differences in metabolising enzymes, and various types of drug interactions, including enzyme induction, enzyme inhibition or down-regulation.

Alternative Reproductive Tactics and Reproductive Success in Male Rhesus Macaques

Abstract: Male rhesus macaques on Cayo Santiago use rank-dependent alternative reproductive tactics. High-ranking males can form long-term consorts and guard female mates while low-ranking males frequently resort to quick copulations under the cover of vegetation. No single reproductive tactic provided the Group S males with a definitive reproductive advantage during the one-year study. Males using the long-term tactic and the quick, stealth tactic sired five offspring each, but fewer males used the long-term consort tactic. Males using the long-term reproductive tactic have significantly greater mating success than males using the quick, sneaky tactic, and may have greater reproductive success. The highest-ranking males who form long-term consorts had the greatest degree of reproductive success. This indicates that for the highest-ranking males, forming long-term consorts is the most effective reproductive tactic. The effectiveness of alternative tactics for high-ranking males (i.e. consort disruption and possessive following) was equivocal. Consort disruption had no immediate effect on reproductive success. Possessive following may have resulted in the siring of two offspring by the alpha male, but was ineffective in other cases, where the females were inseminated by subordinate males. The effectiveness of the quick, furtive tactic was demonstrated by the siring of 45% of the infants by males who used this tactic.

Testing a Parametric Model against a Semiparametric Alternative

Abstract: This paper describes a method for testing a parametric model of the mean of a random variable Y conditional on a vector of explanatory variables X against a semiparametric alternative The test is motivated by a conditional moment test against a parametric alternative and amounts to replacing the parametric alternative model with a semiparametric model The resulting semiparametric test is consistent against a larger set of alternatives than are parametric conditional moments tests based on finitely many moment conditions The results of Monte Carlo experiments and an application illustrate the usefulness of the new test

The kinetic basis of threshold effects observed in mitochondrial diseases: a systemic approach

Abstract: Threshold effects in the expression of metabolic diseases have often been observed in mitochondrial pathologies, i.e. the clinical demonstration of the disease appears only when the activity of a step has been reduced to a rather low level. We show experimentally that an inhibition of cytochrome c oxidase activity by cyanide, simulating a defect in this step, leads to a decrease in mitochondrial respiration which then exhibits a threshold behaviour similar to that observed in mitochondrial diseases. We discuss this behaviour in terms of metabolic control theory and construct a mathematical model simulating this behaviour.

Polymorphisms in the human CYP1A1 gene as susceptibility factors for lung cancer: exon-7 mutation (4889 A to G), and a T to C mutation in the 3′-flanking region

Abstract: Genetic differences in the metabolism of carcinogens may codetermine individual predisposition to cancer. Cytochrome P-4501A1 (CYP1A1) metabolically activates precarcinogens in cigarette smoke, such as benzo(a)pyrene, which is also an inducer of CYP1A1. Two point mutations have been reported, m1 in the 3′-flanking region (6235T to C), and m2 within exon 7 (4889A to G), the latter leading to an isoleucine to valine exchange. In the Japanese population ml and m2 are correlated with lung cancer, suggesting an increased susceptibility to cigarette smoking related lung cancer. We studied 142 lung cancer and 171 reference patients in an ethnically homogeneous German group for m1 and m2 mutations by restriction fragment length polymorphism and allele-specific polymerase chain reaction, respectively. No statistically significant difference was found in the distribution of m1 alleles between lung cancer and controls; the frequency was 8.5% and 7.3% of the alleles, respectively (odds ratio = 1.17). A trend to an overrepresentation of ml alleles was observed among 52 squamous cell carcinoma patients (odds ratio = 1.65). In contrast, the frequency of m2 alleles in lung cancer patients was twofold higher (6.7%) than in the reference group (3.2%; odds ratio = 2.16; 95% confidence limits 0.96–5.11, P = 0.033); the odds ratio of m2 alleles in squamous cell carcinoma was 2.51 (95% confidence limits 0.85–7.05, P = 0.05). There was a close genetic linkage of m2 to m1 (10 of 11 reference patients), but a significantly higher number of cancer patients showed no linkage compared to the controls (odds ratio = 8.89, 95% confidence limits 0.83–433, P = 0.04). Thus no association was found between presence of ml alleles and lung cancer, but, in contrast, m2 alleles proved as a hereditary risk factor, especially if not linked with m1 alleles.

Ribosome-deficient plastids affect transcription of light-induced nuclear genes: genetic evidence for a plastid-derived signal

Abstract: Transcription of ten nuclear genes was analysed in the albostrians mutant of barley (Hordeum vulgare L.). The lack of plastid ribosomes in white seedlings of this mutant results in a complex alteration of nuclear gene expression at the transcriptional level. We found a strong reduction in the accumulation of mRNAs transcribed from nuclear genes encoding chloroplast enzymes involved in the Calvin cycle, the chlorophyll a/b binding protein, and the cytosolic enzyme nitrate reductase. In contrast, the levels of transcripts of the genes encoding the cytosolic glycolytic enzymes glyceraldehyde phosphate dehydrogenase and phosphoglycerate kinase were slightly enhanced. Accumulation of chalcone synthase mRNA even reaches much higher levels in white than in green leaves. Ribosome-deficient plastids were combined by crossing with a nuclear genotype heterozygous for the albostrians allele. Analysis of transcript levels in F 1 plants having the same nuclear genotype and differing only with respect to their content of normally developed chloroplasts versus undifferentiated mutant plastids, provided strong genetic evidence for the plastid being the origin of a signal (chain) involved in regulation of nuclear gene expression. Results of run-on transcription in isolated nuclei demonstrated that the plastid signal acts at the level of transcription; it does not interfere with gene regulation in general. Mechanisms triggering nuclear gene expression in response to light operate in white mutant leaves: the very low levels of mRNAs derived from nuclear genes encoding chloroplast proteins and the strongly enhanced level of chalcone synthase mRNA were both light inducible. Also the negative regulation of leaf thionin gene expression by light is observed in white albostrians seedlings. Furthermore, in spite of its low absolute level, the circadian rhythm in the abundance of the cab mRNA is still detectable in plastid ribosome-deficient seedlings. Thus, functional plastid protein biosynthesis and photosynthesis are not preconditions for the circadian oscillations in the level of mRNA transcribed from this gene (family).