Search PubMed⌕ Search

Biomedical subjects

M Levi

Publications and source records attributed to M Levi.

At least 73 records · Page 4Linked to original sources
PubMed2001

Tissue factor pathway inhibitor does not influence inflammatory pathways during human endotoxemia.

Activation of coagulation induces a proinflammatory response in in vitro and animal experiments. Inhibition of the tissue factor-dependent pathway of coagulation inhibits cytokine release and prevents death in gram-negative sepsis models in primates. This study investigated the influence of blocking the coagulation system by tissue factor pathway inhibitor (TFPI) on endotoxin-induced inflammatory responses in healthy humans. Eight men were studied in a double-blind, randomized, placebo-controlled cross-over study. They received a bolus intravenous injection of 4 ng/kg of endotoxin, followed by a 6-h continuous infusion of either TFPI (0.2 mg/kg/h after a bolus of 0.05 mg/kg) or placebo. Endotoxin induced-activation of coagulation was prevented completely by TFPI. In contrast, TFPI did not influence leukocyte activation, chemokine release, endothelial cell activation, or the acute phase response. Thus, complete prevention of coagulation activation by TFPI does not influence activation of inflammatory pathways during human endotoxemia.

Acute-Phase Reaction↗
PubMed2001

Deficiency of urokinase-type plasminogen activator-mediated plasmin generation impairs vascular remodeling during hypoxia-induced pulmonary hypertension in mice.

BACKGROUND: Chronic hypoxia results in the development of pulmonary hypertension and subsequent right heart failure. A role of the plasminogen system in the pathogenesis of pulmonary hypertension and pulmonary vascular remodeling has been suggested. METHODS AND RESULTS: Mice with targeted deficiency of the gene encoding tissue-type plasminogen activator (t-PA(-/-)), urokinase-type plasminogen activator (u-PA(-/-)), u-PA receptor (u-PAR(-/-)), or plasminogen (plg(-/-)) were subjected to hypoxic conditions. Hypoxia caused a significant 2.5-fold rise in right ventricular pressure in wild-type mice. Deficiency of u-PA or plasminogen prevented this increase in right ventricular pressure, t-PA(-/-) mice showed changes that were fully comparable with wild-type mice, and u-PAR(-/-) mice showed a partial response. Hypoxia induced an increase in smooth muscle cells within pulmonary arterial walls and a vascular rarefaction in the lungs of wild-type but not of u-PA(-/-) or plg(-/-) mice. Elastic lamina fragmentation, observed in hypoxic wild-type but not in u-PA or plasminogen-deficient mice, suggested that proliferation of vascular smooth muscle cells was dependent on u-PA-mediated elastic membrane degradation. Hypoxia-induced right ventricular remodeling in wild-type mice, characterized by cardiomyocyte hypertrophy and increased collagen contents, was not seen in u-PA(-/-) and plg(-/-) mice. CONCLUSIONS: Loss of the u-PA or plasminogen gene protects against the development of hypoxia-induced pulmonary hypertension and pulmonary vascular remodeling. These observations point to an essential role of u-PA-mediated plasmin generation in the adaptive response to chronic hypoxia and the occurrence of hypoxic pulmonary vascular disease.

Animals↗
PubMed2001

P0 glycoprotein peptides 56-71 and 180-199 dose-dependently induce acute and chronic experimental autoimmune neuritis in Lewis rats associated with epitope spreading.

Two synthetic peripheral nerve myelin P0 protein peptides, an immunodominant (amino acids 180-199) and a cryptic (amino acids 56-71) one, induced an acute or chronic course of experimental autoimmune neuritis (EAN) in Lewis rats, when given at low dose (50-100 microg/rat) or high dose (250 microg/rat), respectively. Corresponding to the different clinical course, pathological changes and immune responses were found: (1) Onset of clinical signs of P0 peptide 56-71 (P0 56-71) induced EAN was 1-3 days later than in P0 peptide 180-199 (P0 180-199) induced EAN at all immunizing doses, whereas the peak of the disease occurred at a similar time point post immunization (p.i.), i.e. at days 14-16 p.i. in P0 56-71 induced EAN and at day 16 p.i. in P0 180-199 induced EAN. (2) Intramolecular epitope spreading as assessed by delayed type hypersensitivity response occurred in P0 56-71 induced EAN at both low and high antigen doses and in P0 180-199 induced EAN at high antigen dose (250 microg/rat) only. (3) P0 180-199 stimulated higher levels of interferon-gamma production in P0 180-199 induced EAN than in P0 56-71 induced EAN and vice versa. (4) Histopathologic evaluation revealed a similar grade of mononuclear cell infiltration in the sciatic nerves of both types of EAN, but more severe demyelination was found in P0 180-199 induced EAN compared to P0 56-71 induced EAN. The results support the hypothesis that high dose autoantigen immunization induces extensive determinant spreading and chronic course of autoimmune diseases.

Acute Disease↗
PubMed2001

[Long flights and the risk of venous thrombosis].

It is pathophysiologically conceivable that prolonged air travel may lead to blood flow stasis and hypercoagulability of the blood. The available observational and case-control studies do not, however, indicate an increased incidence of venous thromboembolism amongst air travellers. In these studies bias may have been caused by patients visiting their own GP instead of the airport medical services, the omission of an objective test to establish the thrombosis, the selection of control patients with a different travel behaviour or the inclusion of flying times that were too short. If in the future it becomes apparent that patients with an increased likelihood of thrombosis risk developing venous thromboembolism as a result of prolonged air travel then preventive measures may be required. These could include short-term thrombosis prophylaxis or the wearing of special elastic stockings. Furthermore, all air travellers should be advised to keep moving during long flights and to drink plenty, preferably non-alcoholic beverages.

Aerospace Medicine↗
PubMed2001

Successful treatment with recombinant factor VIIa of therapy-resistant severe bleeding in a patient with acquired von Willebrand disease.

We describe an elderly man who presented with life-threatening hematuria and gastrointestinal bleeding caused by acquired von Willebrand disease associated with monoclonal gammopathy of undetermined significance (MGUS). Standard therapy with desmopressin, von Willebrand factor-containing factor VIII concentrate, tranexamic acid, and immunoglobulin failed to achieve adequate hemostasis. However, treatment with recombinant activated factor VII (rFVIIa) arrested the bleeding completely. Since acquired von Willebrand disease can lead to life-threatening hemorrhage, clinicians should consider rFVIIa as an effective treatment option if standard therapy fails.

Aged↗
PubMed2001

Late-onset downregulation of NaPi-2 in experimental Fanconi syndrome.

The pathogenesis of renal phosphate (Pi) leak in Fanconi syndrome is unknown. Disorders of apical membrane transporters, leaky apical membrane, depleted cellular Pi and ATP, and impaired sodium (Na) pumps have been proposed as underlying defects. The present study examined the role of type II Na-Pi cotransport system (NaPi-2) in experimental Fanconi syndrome in rats. Following a single injection of maleic acid (MA), 75 mg/kg body weight i.p., rats were sacrificed after 90 min, 4 h, and 24 h. Renal cortical expression of NaPi-2 mRNA was determined by Northern blotting, and brush border membrane (BBM) NaPi-2 protein by Western blotting. Increased urinary excretion of phosphate was demonstrated as soon as 90 min after MA injection, and was sustained at 4 and 24 h, NaPi-2 mRNA expression and NaPi-2 protein were not decreased after 90 min. NaPi-2 mRNA decreased after 4 h, while NaPi-2 protein decreased only at 24 h. Hence, the immediate phosphaturia in experimental Fanconi syndrome may be independent of NaPi-2 downregulation, possibly resulting from energy depletion or membrane dysfunction. The decrease in NaPi-2 mRNA expression and the subsequent NaPi-2 protein decrease may account for the second-phase phosphaturia.

Animals↗
PubMed2001

Lipid rafts reconstituted in model membranes.

One key tenet of the raft hypothesis is that the formation of glycosphingolipid- and cholesterol-rich lipid domains can be driven solely by characteristic lipid-lipid interactions, suggesting that rafts ought to form in model membranes composed of appropriate lipids. In fact, domains with raft-like properties were found to coexist with fluid lipid regions in both planar supported lipid layers and in giant unilamellar vesicles (GUVs) formed from 1) equimolar mixtures of phospholipid-cholesterol-sphingomyelin or 2) natural lipids extracted from brush border membranes that are rich in sphingomyelin and cholesterol. Employing headgroup-labeled fluorescent phospholipid analogs in planar supported lipid layers, domains typically several microns in diameter were observed by fluorescence microscopy at room temperature (24 degrees C) whereas non-raft mixtures (PC-cholesterol) appeared homogeneous. Both raft and non-raft domains were fluid-like, although diffusion was slower in raft domains, and the probe could exchange between the two phases. Consistent with the raft hypothesis, GM1, a glycosphingolipid (GSL), was highly enriched in the more ordered domains and resistant to detergent extraction, which disrupted the GSL-depleted phase. To exclude the possibility that the domain structure was an artifact caused by the lipid layer support, GUVs were formed from the synthetic and natural lipid mixtures, in which the probe, LAURDAN, was incorporated. The emission spectrum of LAURDAN was examined by two-photon fluorescence microscopy, which allowed identification of regions with high or low order of lipid acyl chain alignment. In GUVs formed from the raft lipid mixture or from brush border membrane lipids an array of more ordered and less ordered domains that were in register in both monolayers could reversibly be formed and disrupted upon cooling and heating. Overall, the notion that in biomembranes selected lipids could laterally aggregate to form more ordered, detergent-resistant lipid rafts into which glycosphingolipids partition is strongly supported by this study.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2001

Enhanced mucosal fibrinolytic activity in gastroduodenal ulcer haemorrhage and the beneficial effect of acid suppression.

BACKGROUND: The high mortality rate in patients with upper gastrointestinal bleeding appears to be particularly related to re-bleeding. The haemostatic mechanisms that may influence the re-bleeding of ulcers are largely unknown. AIM: We studied and analysed fibrinolytic activity in bleeding ulcer patients and the effect of acid suppression on this activity. METHODS: Fibrinolytic activity was analysed in mucosal biopsies from 29 bleeding gastroduodenal ulcer patients and six controls. We analysed levels of D-Dimer, fibrin plate lysis area, plasminogen activator activity, plasminogen activator inhibitor activity, and plasmin antiplasmin complexes. RESULTS: Significantly more fibrinolytic activity was detected in biopsies from patients with bleeding ulcers compared to controls. Moreover, in patients with endoscopic stigmata of recent haemorrhage, mucosal fibrinolytic activity was higher compared to patients without stigmata of recent haemorrhage. In mucosal biopsies of patients that had used acid suppression before admission, a decreased fibrinolytic activity was found compared to patients without such therapy. This effect of acid suppression on fibrinolytic activity was confirmed in nine patients before and after a 24-h ranitidine infusion. CONCLUSIONS: Fibrinolytic activity is enhanced in patients with bleeding gastroduodenal ulcers. Acid suppressive therapy decreases this increased activity, which may be one of the mechanisms explaining the potential beneficial effect of this therapy.

Adult↗
PubMed2001

Interferon-gamma in healthy subjects: selective modulation of inflammatory mediators.

BACKGROUND: It is suggested that interferon-gamma (IFN-gamma), like other cytokines, is a mediator in the host inflammatory response, which could be of importance in the pathophysiology of sepsis. The role of IFN-gamma in human host inflammatory responses, however, has not been studied. DESIGN: In a placebo-controlled trial we studied the acute effects of IFN-gamma administration on host inflammatory mediators in healthy men: i.e. the cytokine/chemokine cascade system, acute-phase proteins, activation markers of the innate cellular immunity and coagulation/fibrinolysis parameters. RESULTS: IFN-gamma increased plasma levels of interleukin-6 (IL-6), IL-8 and IFN-gamma-inducible protein-10 (IP-10) (P < 0.05), but did not affect plasma levels of other cytokines (IL-4, IL-10, tumour necrosis factor-alpha, IL-12p40/p70). Plasma concentrations of C-reactive protein and secretory phospholipase A2 both increased (P < 0.05). Plasma levels of the leucocyte activation marker elastase-alpha1-antitrypsin complexes increased after IFN-gamma administration (P < 0.05), IFN-gamma increased the percentage of high-affinity Fcgamma-receptor (FcgammaRI) -positive neutrophils (P < 0.05), but did not affect the mean fluorescence intensity of FcgammaRI on neutrophils. Procoagulant and profibrinolytic effects of IFN-gamma were evidenced by increased plasma levels of prothrombin fragment F1 + F2, tissue-plasminogen activator and plasmin-alpha2-antiplasmin complexes (P < 0.05). CONCLUSION: We conclude that IFN-gamma selectively affects host inflammatory mediators in humans.

Acute-Phase Proteins↗
PubMed2001

Gentamicin causes endocytosis of Na/Pi cotransporter protein (NaPi-2).

BACKGROUND: Renal toxicity is a major side-effect of aminoglycoside antibiotics and is characterized by an early impairment in proximal tubular function. In a previous study, we have shown that gentamicin administration to the rat causes an early impairment in sodium gradient-dependent phosphate (Na/Pi) cotransport activity. The purpose of our current study was to determine the molecular mechanisms of the impairment in Na/Pi cotransport activity, specifically the role of the proximal tubular type II Na/Pi cotransporter. METHODS: Rats were treated for one, two, and three days with two daily injections of 30 mg/kg body weight gentamicin or the vehicle. RESULTS: Gentamicin caused a progressive decrease in superficial cortical apical brush-border membrane (SC-BBM) Na/Pi cotransporter activity (856 +/- 93 in control vs. 545 +/- 87 pmol/mg BBM protein in 3-day gentamicin, P < 0.01). Western blot analysis showed a parallel and progressive decrease in SC-BBM Na/Pi cotransporter protein abundance, a 50% decrease after one day of treatment, a 63% decrease after two days of treatment, and an 83% decrease after three days treatment with gentamicin. In contrast, gentamicin treatment had no effect on Na/Pi cotransport activity or Na/Pi cotransporter protein abundance in BBM isolated from the juxtamedullary cortex (JMC-BBM). Immunofluorescence microscopy showed a major decrease in the expression of Na/Pi cotransporter protein in the apical membrane of the proximal convoluted tubule, with progressive intracellular accumulation of Na/Pi protein. Colocalization studies showed that in gentamicin-treated rats, Na/Pi protein was colocalized in the early endosomes and especially in the lysosomes. Northern blot analysis of cortical RNA interestingly showed no reduction in Na/Pi cotransporter mRNA abundance even after three days of gentamicin treatment. CONCLUSION: We conclude that gentamicin inhibits Na/Pi cotransport activity by causing a decrease in the expression of the type II Na/Pi cotransport protein at the level of the proximal tubular apical BBM and that inhibition of Na/Pi cotransport activity is most likely mediated by post-transcriptional mechanisms.

Animals↗
PubMed2001

Glycosphingolipids modulate renal phosphate transport in potassium deficiency.

BACKGROUND: Potassium (K) deficiency (KD) and/or hypokalemia have been associated with disturbances of phosphate metabolism. The purpose of the present study was to determine the cellular mechanisms that mediate the impairment of renal proximal tubular Na/Pi cotransport in a model of K deficiency in the rat. METHODS: K deficiency in the rat was achieved by feeding rats a K-deficient diet for seven days, which resulted in a marked decrease in serum and tissue K content. RESULTS: K deficiency resulted in a marked increase in urinary Pi excretion and a decrease in the V(max) of brush-border membrane (BBM) Na/Pi cotransport activity (1943 +/- 95 in control vs. 1184 +/- 99 pmol/5 sec/mg BBM protein in K deficiency, P < 0.02). Surprisingly, the decrease in Na/Pi cotransport activity was associated with increases in the abundance of type I (NaPi-1), and type II (NaPi-2) and type III (Glvr-1) Na/Pi protein. The decrease in Na/Pi transport was associated with significant alterations in BBM lipid composition, including increases in sphingomyelin, glucosylceramide, and ganglioside GM3 content and a decrease in BBM lipid fluidity. Inhibition of glucosylceramide synthesis resulted in increases in BBM Na/Pi cotransport activity in control and K-deficient rats. The resultant Na/Pi cotransport activity in K-deficient rats was the same as in control rats (1148 +/- 52 in control + PDMP vs. 1152 +/- 61 pmol/5 sec/mg BBM protein in K deficiency + PDMP). These changes in transport activity occurred independent of further changes in BBM NaPi-2 protein or renal cortical NaPi-2 mRNA abundance. CONCLUSION: K deficiency in the rat causes inhibition of renal Na/Pi cotransport activity by post-translational mechanisms that are mediated in part through alterations in glucosylceramide content and membrane lipid dynamics.

Animals↗
PubMed2001

Evidence for a PTH-independent humoral mechanism in post-transplant hypophosphatemia and phosphaturia.

BACKGROUND: Patients undergoing successful kidney transplantation often manifest overt hypophosphatemia associated with exaggerated phosphaturia during the early post-transplant period (2 weeks to 3 months). The mechanism for this phenomenon has not been fully elucidated. We tested the hypothesis that a circulating serum factor [non-parathyroid hormone (non-PTH)], which operates during chronic renal failure (CRF) to maintain phosphate (Pi) homeostasis, can increase fractional excretion of Pi (FE(PO4)) in normal functioning kidney grafts during the early post-transplant period, thereby causing phosphaturia and hypophosphatemia. METHODS: Five groups of patients were studied: control subjects (group 1, N = 16), "early" (2 weeks to 1 month) post-transplant patients (group 2, N = 22), "late" (9 to 12 months) post-transplant patients (group 3, N = 14), patients with advanced CRF (glomerular filtration rate = 30 to 40 mL/min; group 4, N = 8), and patients who suffered from end-stage renal failure and were treated by chronic hemodialysis (group 5, N = 14). Group 2 manifested significant hypophosphatemia and phosphaturia when compared with groups 1 and 3 (Pi = 0.9 +/- 0.003 mg/dL, FE(PO4) = 68+/- 5%, P < 0.0005 vs. groups 1 and 3). Sera were taken from each of the five subject groups and applied to the proximal tubular opossum kidney (OK) cells. The activity of Na/Pi-type 4 (that is, OK-specific type II transporter) was evaluated by measuring Na(+)-dependent (32)Pi flux. The expression of Na/Pi type II mRNA and the abundance of Na/Pi protein were determined by Northern and Western blot assays, respectively. RESULTS: When compared with sera from groups 1 and 3, 10% sera taken from groups 2, 4, and 5 (incubated overnight with OK cells) inhibited (32)Pi flux by 25 to 30% (P < 0.0003). Both Na/Pi mRNA and the expression of Na/Pi protein were markedly augmented under the same conditions (P < 0.05 groups 2, 4, and 5 vs. groups 1 and 3). Time-course analysis revealed that the up-regulation of Na/Pi protein by sera from groups 2, 4, and 5 was observed as early as four hours of incubation, whereas augmented abundance of Na/Pi mRNA was only seen after eight hours of incubation. The addition of PTH (1-34) to sera from groups 2, 4, and 5 abolished the augmented expression of NaPi protein. We labeled OK cell surface membrane proteins with N-hydroxysuccinimide bound to biotin (NHS-SS-biotin). Biotinylated transporters incubated with the different sera were precipitated by strepavidin and identified by Western blot analysis. Cells incubated in sera from group 2 showed increased membrane bound transporter when compared with control sera, whereas the intracellular pool of the transporter was comparable between the two groups. CONCLUSION: A non-PTH circulating serum factor (possibly phosphatonin) that increases FE(PO4) during CRF is also responsible for phosphaturia and hypophosphatemia in the early period following successful kidney transplantation. The putative factor inactivates Na/Pi activity along with inhibition of the transporter trafficking from the cell membrane into the cytosol.

Adult↗
PubMed2001

Pathogenesis and treatment of disseminated intravascular coagulation in the septic patient.

The incidence of sepsis and complications stemming from septicemia has remained constant in recent years despite improved levels of monitoring and care. Disseminated intravascular coagulation (DIC), a syndrome that occurs frequently in septic patients, is associated with increased mortality. Organ dysfunction is also a common sequela that is strongly correlated with DIC. Cytokines released early in the course of sepsis stimulate a procoagulant state that causes development of intravascular fibrin deposition. In a later stage of DIC, bleeding may occur in parallel because of consumption of clotting factors and inhibitors. Therapeutic strategies to attenuate or reverse these conditions have focused on multiple stages of the molecular cascade of events, including preventing cytokine induction, inhibiting coagulation processes, and promoting fibrinolysis. Recent clinical trials have supported the use of antithrombin and activated protein C supplementation in DIC associated with severe sepsis. Studies of other novel therapeutic avenues are still ongoing. Future efforts may be directed at combining 2 or more agents to achieve prompt and successful reversal of DIC.

Antithrombins↗
PubMed2001

Advances in the understanding of the pathogenetic pathways of disseminated intravascular coagulation result in more insight in the clinical picture and better management strategies.

Disseminated intravascular coagulation (DIC) is a syndrome characterized by systemic intravascular activation of coagulation leading to widespread deposition of fibrin in the circulation. There is ample experimental and pathological evidence that the fibrin deposition contributes to multiple organ failure. The massive and ongoing activation of coagulation may result in depletion of platelets and coagulation factors, which may cause bleeding (consumption coagulopathy). Recent knowledge on important pathogenetic mechanisms that may lead to DIC has resulted in novel preventive and therapeutic approaches to patients with DIC. DIC is not a disease in itself but is a complication of a variety of disorders. However, the pathogenesis of DIC follows similar pathways in almost all of these situations, with a pivotal role of proinflammatory cytokines. The cornerstone of the management of DIC is the specific and vigorous treatment of the underlying disorder. Strategies aimed at the inhibition of coagulation activation may theoretically be justified and have been found to be beneficial in experimental and initial clinical studies. These strategies comprise inhibition of tissue factor-mediated activation of coagulation and restoration of physiological anticoagulant pathways by means of the administration of (activated) protein C concentrate or antithrombin concentrate.

Disseminated Intravascular Coagulation↗
PubMed2001

Regulatory role of cytokines in disseminated intravascular coagulation.

Disseminated intravascular coagulation (DIC) can complicate a number of diseases. DIC in the setting of sepsis is considered to result from strong activation of the coagulation system and concurrent inhibition of fibrinolysis and other anticoagulant pathways. Cytokines have been implicated as important mediators in these hemostatic alterations. This article summarizes recent insights into which cytokines are likely to be involved in the procoagulant response to systemic infection.

Animals↗
PubMed2001

Anticoagulant factor concentrates in disseminated intravascular coagulation: rationale for use and clinical experience.

Natural inhibitors of coagulation, in other words, antithrombin (AT), the protein C system, and tissue factor pathway inhibitor (TFPI), play an important role in controlling the activation of coagulation during disseminated intravascular coagulation (DIC). Furthermore, they may not only influence coagulation but also attenuate inflammatory responses during sepsis. Low circulating levels of AT and protein C have been associated with poor outcome. Replacement therapy with AT, activated protein C (APC), and TFPI has been shown to attenuate thrombin generation and to reduce mortality in experimental sepsis models. Experience with AT and APC in patients is promising. Data from large phase III trials of AT and APC as treatment of patients with severe sepsis will soon be available. Recombinant TFPI is currently in phase II clinical trials for severe sepsis.

Antithrombins↗