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Biomedical subjects

M Levi

Publications and source records attributed to M Levi.

At least 271 records · Page 15Linked to original sources
PubMed1993

Lipid phases in renal brush border membranes revealed by Laurdan fluorescence.

Steady-state fluorescence properties of 6-dodecanoyl-2-dimethylaminonapththalene (Laurdan) have been used to determine the coexistence of separate lipid-phase domains in apical brush border membrane vesicles isolated from the rat renal cortex. The temperature dependence of generalized polarization has been utilized to quantitate the lipid phases. Finally, the effect of cholesterol enrichment on these parameters has been studied. The results indicate the coexistence of lipid-phase domains in brush border membranes based on the values of the generalized polarization and assuming that the membrane state can be described by coexistence of gel and liquid crystalline state. At 37 degrees C, approximately 19-32% of the brush border membrane lipids are in the gel phase, and cholesterol enrichment causes a further concentration-dependent increase in the gel phase of brush border membrane lipids.

2-Naphthylamine↗
PubMed1993

Phosphonoformic acid blunts adaptive response of renal and intestinal Pi transport.

Parenteral administration of phosphonoformic acid (PFA) results in phosphaturia, but the effects of oral PFA on Pi handling are not known. To assess this effect, PFA was administered in drinking water for 5 days to rats stabilized on normal (NPD) or low (LPD) phosphorus diets. In renal brush-border membrane vesicles (BBMV), kinetic studies showed a higher apparent Vmax for Pi in rats on LPD compared with rats on NPD (1,840 +/- 274 vs. 1,111 +/- 192 pmol.mg-1.5 s-1, respectively, P < 0.05, n = 5). In LPD rats, PFA reduced the apparent Vmax for Pi to 1,047 +/- 191 pmol.mg-1.5 s-1 (P < 0.05, n = 5) with no change in the apparent Km. Similarly, there was a higher apparent Vmax for Pi in intestinal BBMV from rats on LPD compared with rats on NPD. In LPD rats, PFA reduced the apparent Vmax for Pi with no change in the apparent Km. Oral PFA had no effect on the kinetics of Pi transport in renal or intestinal BBMV from rats on NPD. Pi-protectable [14C]PFA binding was lower in renal BBMV from PFA-treated LPD rats, but membrane fluidity was not different. Orally administered PFA can blunt the adaptive response of the renal and intestinal BBM to an LPD. The downregulation of Na(+)-Pi cotransport is mediated through a reduction in the number of Na(+)-Pi cotransporters.

Absorption↗
PubMed1993

The activation of factor X and prothrombin by recombinant factor VIIa in vivo is mediated by tissue factor.

The human coagulation system continuously generates very small quantities of Factor Xa and thrombin. Current evidence suggests that basal level activation of the hemostatic mechanism occurs via Factor VIIa-dependent activation of Factor X, but direct proof has not been available for the participation of tissue factor in this pathway. To examine this issue, we infused relatively high concentrations of recombinant Factor VIIa (approximately 50 micrograms/kg body wt) into normal chimpanzees and observed significant increases in the plasma levels of Factor IX activation peptide, Factor X activation peptide, and prothrombin activation fragment F1+2. Metabolic turnover studies with radiolabeled Factor IX activation peptide, Factor X activation peptide, and F1+2 indicate that elevated levels of the activation peptides are due to accelerated conversion of the three coagulation system zymogens into serine proteases. The administration of a potent monoclonal antibody to tissue factor, which immediately neutralizes function of the Factor VIIa-tissue factor complex in vitro, abolishes the activation of Factor X and prothrombin mediated by the infused recombinant protein, and also suppresses basal level activation of Factor IX and Factor X. The above results suggest that recombinant Factor VIIa functions as a prohemostatic agent by interacting with endogenous tissue factor sites, but definitive proof will require studies in hemophilic animals using relevant hemostatic endpoints.

Animals↗
PubMed1993

Effects of adjuvants and multiple antigen peptides on humoral and cellular immune responses to gp160 of HIV-1.

The capacity of five different adjuvants, AlPO4, a muramyldipeptide formulation (MDP.TSL), Freund's adjuvant, immunostimulating complex and its matrix components to elicit humoral and cellular responses in rabbits immunized with the human immunodeficiency virus type 1 (HIV-1) envelope protein rgp160IIIB was compared. The highest antibody titers against gp160 and gp41/gp120 epitopes were seen with rgp160 in MDP.TSL or Freund's adjuvant, whereas the broadest responses were seen in rabbits immunized with rgp160 in matrix or MDP.TSL. The broadest spectrum of high-avidity antibodies was also induced by rgp160 in MDP.TSL. Neutralizing titers against HIV-1IIIB, low titers to HIV-1MN, and the most efficient inhibition of viral cell-to-cell spread was seen with rgp160 in MDP.TSL. The strongest and most persisting cellular responses were induced by rgp160 in AlPO4 or MDP.TSL. Using MDP.TSL as the adjuvant, we also improved the immune response against gp120 epitopes by boosting rgp160-primed rabbits with rgp160, multiple antigenic peptides (MAPs), or unconjugated peptides. The MAPs induced high neutralizing titers and were superior to rgp160 alone in inducing both humoral and cellular reactivity. MAPs are therefore strong candidates for inclusion into future HIV-1 vaccines.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1992

Plasminogen activation in vivo upon intravenous infusion of DDAVP. Quantitative assessment of plasmin-alpha 2-antiplasmin complex with a novel monoclonal antibody based radioimmunoassay.

Infusion of desamino-d-arginine vasopressin (DDAVP) results in an increase in plasma plasminogen activator activity. Whether this increase results in the generation of plasmin in vivo has never been established. A novel sensitive radioimmunoassay (RIA) for the measurement of the complex between plasmin and its main inhibitor alpha 2-antiplasmin (PAP complex) was developed using monoclonal antibodies preferentially reacting with complexed and inactivated alpha 2-antiplasmin and monoclonal antibodies against plasmin. The assay was validated in healthy volunteers and in patients with an activated fibrinolytic system. Infusion of DDAVP in a randomized placebo controlled crossover study resulted in all volunteers in a 6.6-fold increase in PAP complex, which was maximal between 15 and 30 min after the start of the infusion. Hereafter, plasma levels of PAP complex decreased with an apparent half-life of disappearance of about 120 min. Infusion of DDAVP did not induce generation of thrombin, as measured by plasma levels of prothrombin fragment F1+2 and thrombin-antithrombin III (TAT) complex. We conclude that the increase in plasminogen activator activity upon the infusion of DDAVP results in the in vivo generation of plasmin, in the absence of coagulation activation. Studying the DDAVP induced increase in PAP complex of patients with thromboembolic disease and a defective plasminogen activator response upon DDAVP may provide more insight into the role of the fibrinolytic system in the pathogenesis of thrombosis.

Adult↗
PubMed1992

Deep vein thrombosis in obstetric patients: diagnosis and risk factors.

This study was performed to assess the prevalence of deep vein thrombosis (DVT) in consecutive obstetric patients with clinical symptoms of DVT, using impedance plethysmography (IPG) as the diagnostic method and to establish the safety of withholding anticoagulant therapy in patients with a repeatedly normal IPG. In addition, in patients with DVT the prevalence of coagulation and fibrinolytic disorders, which may explain the occurrence of venous thrombosis was investigated. Of the 77 obstetric patients with symptoms of DVT, 32 (42%) had an abnormal IPG. The remaining 45 patients had a repeatedly normal IPG and showed no venous thromboembolism during a 6 months follow-up period. Twenty percent (six patients) of the patients with an abnormal IPG had a coagulation or fibrinolytic abnormality. These observations suggest that serial IPG can be used effectively in the management of obstetric patients with clinically suspected DVT and that hemostatic abnormalities are frequently found in those patients with DVT.

Adolescent↗
PubMed1992

The fortuitous diagnosis of cholera in a two-year-old girl.

We are reporting the fortuitous diagnosis of a case of cholera and the unusual failure of the commercial bacteriologic media that led to the unexpected isolation of Vibrio cholerae. The case demonstrates the need for communication between the medical staff and laboratory personnel when an uncommon disease, such as cholera, is suspected. This case also alerts the clinician to the possibility of multiple enteric pathogens coinfecting a traveller.

Animals↗
PubMed1992

Bisacylphosphonates inhibit hydroxyapatite formation and dissolution in vitro and dystrophic calcification in vivo.

Some geminal bisphosphonates are used clinically for a number of important bone/calcium related diseases; however, side effects and lack of selectivity impede their wide use. This work reports the synthesis and evaluation of bisacylphosphonates (e.g., adipoyl- and suberoylbisphosphonate). These compounds were found to inhibit significantly hydroxyapatite formation and dissolution in vitro and the calcification of bioprosthetic tissue implanted subdermally in rats. These are the first instances of nongeminal bisphosphonates [P-(C)n-P, n greater than or equal to 2] that have been reported to be active in calcium-related disorders. The reported bisacylphosphonates possess apparent lower toxicity, and their calcium complexes/salts have improved solubility properties. Therefore, they are of potential importance for clinical applications.

Animals↗
PubMed1992

Streptococcal toxic shock syndrome due to noninvasive pharyngitis.

Serious infections due to group A beta-hemolytic streptococcus (GABHS) have been reported with increasing frequency in recent years. We report a case of toxic shock syndrome (TSS) due to GABHS pharyngitis in an otherwise healthy 14-year-old boy. The organism was found to produce toxin A. To our knowledge, this is the second reported case of streptococcal TSS associated with the production of toxin A that is not associated with an invasive disease and the first case associated with a documented rise in the level of antibody to the streptococcal toxin itself. Clinicians must be especially vigilant for this entity in patients who have streptococcal pharyngitis because early recognition and institution of aggressive supportive therapy can be lifesaving.

Adolescent↗
PubMed1992

Impaired fibrinolysis in cyclosporine-treated renal transplant patients. Analysis of the defect and beneficial effect of fish-oil.

Cyclosporine treatment has been associated with thrombotic vascular complications. We investigated the activity of the fibrinolytic system and its capacity to respond upon DDAVP stimulation in a group of 20 cyclosporine-treated patients as compared with a group of 9 azathioprine-treated patients. Furthermore, the effect of the administration of fish-oil to these patients on the endogenous fibrinolytic activity was studied in a double-blind randomized, placebo-controlled cross-over study. The cyclosporine-treated patients showed a significantly reduced plasminogen activator activity and plasmin generation response upon the infusion of DDAVP as compared with the azathioprine group. In the cyclosporine group 60% of the patients had an impaired fibrinolytic response, whereas this was found in only 11% of the azathioprine-treated patients (P < 0.05). The impairment of the endogenous fibrinolysis activity could be attributed either to a defective release of plasminogen activator from the vessel wall (67% of patients) or to high plasma levels of plasminogen activator inhibitor 1 (33% of patients). Administration of fish-oil resulted in a significant improvement of the impaired fibrinolysis in the cyclosporine group. Particularly, in patients with a defective release of plasminogen activator from the vessel wall, fish-oil treatment resulted in a normalization of the fibrinolytic activity. These results indicate that cyclosporine treatment induces an impaired fibrinolysis that may contribute to the frequent occurrence of thromboembolic complications and eventually the impairment of renal function in cyclosporine-treated patients. The beneficial effect of the administration of fish-oil on the endogenous fibrinolysis may result in a reduction of the adverse events associated with cyclosporine treatment.

Cyclosporine↗
PubMed1992

Inhibition of plasminogen activator inhibitor-1 activity results in promotion of endogenous thrombolysis and inhibition of thrombus extension in models of experimental thrombosis.

BACKGROUND: We investigated the effect of inhibition of plasminogen activator inhibitor-1 (PAI-1) activity by a murine monoclonal anti-human PAI-1 antibody (MAI-12) on in vitro thrombolysis and on in vivo thrombolysis and thrombus extension in an experimental animal model for thrombosis. METHODS AND RESULTS: Thrombolysis, mediated by recombinant tissue-type plasminogen activator (rt-PA), was studied in an in vitro system consisting of fibrinogen, plasminogen, and thrombin. Addition of purified platelets during clot formation inhibited rt-PA-mediated thrombolysis in a dose-dependent manner. Platelet-dependent thrombolysis resistance could be completely neutralized by the monoclonal antibody MAI-12, supporting the notion that the observed resistance is due to PAI-1 released from alpha-granules of platelets. Subsequently, we monitored in vivo thrombolysis and thrombus extension of human whole blood thrombi that were allowed to form in rabbit jugular veins. During thrombus formation, either MAI-12 or an irrelevant antibody was incorporated. Thrombolysis and thrombus extension were simultaneously measured during endogenous thrombolysis or upon administration of different dosages of rt-PA. We observed that endogenous thrombolysis was enhanced in the presence of MAI-12 compared with the control antibody. Significantly, thrombus extension was partially prevented by MAI-12 and not by the control antibody irrespective of whether exogenous rt-PA was systematically administered. CONCLUSIONS: These observations further confirm the essential role of PAI-1 in the regulation of the thrombolytic system and support the exploration of adjunctive therapy based on inhibition of PAI-1 activity in thrombolytic strategies.

Adult↗
PubMed1992

Contact system dependent fibrinolytic activity in vivo: observations in healthy subjects and factor XII deficient patients.

The contribution of activation of the contact system to activation of the fibrinolytic system in vivo was investigated in healthy volunteers and in factor XII deficient patients. The plasminogen activating activity in normal plasma was only partially blocked (for 77%) with specific antibodies to tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). The residual activity could be quenched by a monoclonal antibody that inhibits factor XII activity and was not present in patients with a factor XII deficiency. The formation of plasmin upon the DDAVP stimulus as reflected by circulating plasmin-alpha 2-antiplasmin (PAP) complexes was lower in factor XII deficient patients than in healthy volunteers. These results indicate that in vivo the plasminogen activating activity is partially dependent on activation of the contact system. This fibrinolytic activity is impaired in factor XII deficient patients which may explain the occurrence of thromboembolic complications in these patients.

Adult↗
PubMed1991

Deep vein thrombosis and fibrinolysis. Defective urokinase type plasminogen activator release.

In the present study 57 consecutive patients with a first episode of venographically proven deep vein thrombosis were investigated to evaluate the release of tissue-type plasminogen activator (t-PA) and of urokinase-type plasminogen activator (u-PA) in response to DDAVP stimulation as well as the resting plasminogen activator inhibitor (PAI) concentration, comparing this to the results obtained in 66 similar patients with a clinical suspicion of thrombosis but with a normal venogram. All assays were performed without knowledge of the patient's status. Four patients in the deep vein thrombosis-group (7%) had an absent u-PA antigen response upon DDAVP infusion, while a normal response was observed in all control subjects. Patients and controls showed similar increases in t-PA antigen level upon DDAVP. High resting PAI antigen levels were encountered in 5 patients in the deep vein thrombosis-group (9%) and in 6 subjects in the control group (9%). The results from this controlled study indicate that a defective release of u-PA may occur in patients with deep vein thrombosis and may have pathogenetic significance. Furthermore it is concluded that elevation of PAI levels cannot be considered as a specific risk factor for venous thrombosis.

Antigens↗
PubMed1991

Fibrinolytic response to tumor necrosis factor in healthy subjects.

Tumor necrosis factor (TNF) may be involved in the disturbance of the procoagulant-fibrinolytic balance in septicemia, leading to microvascular thrombosis. To assess the dynamics of the fibrinolytic response to TNF in humans, we performed a crossover saline-controlled study in six healthy men, investigating the effects of a bolus intravenous injection of recombinant human TNF (50 micrograms/m2) on the stimulation and inhibition of plasminogen activation as well as on plasmin activity and inhibition. TNF induced a brief fourfold increase in the overall plasma plasminogen activator (PA) activity peaking after 1 h (p less than 0.0001), which was associated with rises in the antigenic levels of urokinase-type plasminogen activator (p less than 0.0001) and tissue-type plasminogen activator (p less than 0.0001). Plasminogen activator inhibitor type I antigen remained unchanged in the first hour, but showed a rapid eightfold increase thereafter (p less than 0.0001), which coincided with the decrease in PA activity. Generation of plasmin activity in the first hour was signified by an 11-fold rise in D-dimer levels (p less than 0.0001); inhibition of plasmin was reflected by a 36-fold rise in plasmin-alpha 2 antiplasmin complexes (p less than 0.0001), as well as by a transient 16% decrease in alpha 2-antiplasmin activity (p less than 0.01). In conclusion, TNF induced an early activation of the fibrinolytic system becoming maximal in 1 h, with a rapid inhibition thereafter. Earlier observations in the same subjects showed sustained coagulation activation for 6-12 h. The observed disbalance between the procoagulant and fibrinolytic mechanisms after TNF injection confirms the in vivo relevance of the effects of TNF on vascular endothelium in vitro and may explain the tendency towards microvascular thrombosis in septicemia.

Adult↗
PubMed1991

Variable effects of radiological contrast media on thrombus growth in a rabbit jugular vein thrombosis model.

We studied the effect of an ionic high osmolar contrast medium (Ioxitalamate), an ionic low osmolar contrast medium (Ioxaglate) and various nonionic low osmolar contrast media (Iopamidol, Iopromide and Iohexol) on thrombus growth in a rabbit jugular vein thrombosis model. Thrombus growth was determined by the accretion of 125I-labeled fibrinogen onto autologous preformed thrombi in rabbit jugular veins at various time-intervals from 15 min up to 10 h after infusion of the study solution. The ionic low osmolar contrast medium markedly inhibited thrombus growth whereas all nonionic low osmolar contrast media promoted thrombus growth. The ionic high osmolar, contrast medium inhibited thrombus growth, but less than the ionic low osmolar contrast medium. Within the group of nonionic contrast media, the Iopamidol associated promotion of thrombus growth was significantly higher than the Iopromide or Iohexol associated effects. The simultaneous administration of the apparently most potent thrombus growth promoting contrast medium (i.e. Iopamidol) and heparin resulted in complete abolishment of the increase in thrombus growth. These results support the claims of prothrombotic properties of nonionic as compared to ionic contrast media and could explain the clinically encountered thromboembolic complications after the use of nonionic low osmolar contrast media.

Animals↗
PubMed1991

Technique for drawing blood for cultures: is changing needles truly necessary?

After drawing blood for culture, medical students and house officers are often taught to change needles before inoculating the culture media. Data to support this practice have been scarce. We obtained simultaneous blood cultures on 75 hospital patients using two techniques: changing needles (C) or not changing needles (NC) before inoculating the cultures. Positive cultures judged to be contaminants were obtained in 4/75 patients in the NC group (5.3%) and in 1/75 patients in the C group (1.3%). This difference was not statistically significant. The practice of changing needles after drawing blood for culture may not be necessary, thus reducing the risk of needlestick injury.

Adult↗
PubMed1991

Dietary NaCl modulates Na(+)-H+ antiporter activity in renal cortical apical membrane vesicles.

An apical membrane Na(+)-H+ antiporter mediates proximal tubule NaCl and NaHCO3 reabsorption. The present studies examined whether chronic changes in dietary NaCl intake lead to an adaptation of the Na(+)-H+ antiporter. Rats were maintained either on a low-salt (LS, 0% NaCl) or a high-salt (HS, 2% NaCl) diet for 4 days. Na(+)-H+ antiporter was assayed using the acridine orange fluorescence method in apical membrane vesicles prepared by Mg2+ aggregation. Rats on LS diet exhibited a higher maximal activity (Vmax) for antiporter activity (0.109 +/- 0.008 s-1) compared with rats on HS diet (0.090 +/- 0.008 s-1; P less than 0.01), whereas Na activity (KNa) was similar (13.1 +/- 1.5 and 14.2 +/- 0.8 mM in HS and LS groups, respectively). The modulation of Na(+)-H+ antiporter activity was amiloride sensitive. Proton permeability, Na(+)-dependent [3H]glucose uptake, and vesicle enrichments were similar in both groups. In addition, the dietary protocols were not associated with any systemic acid-base disturbances, K+ deficiency, or hyperfiltration, conditions that have previously been demonstrated to alter Na(+)-H+ antiporter activity. Acute differences in extracellular fluid volume, induced by 10% body weight isohydric expansion failed to affect Na(+)-H+ antiporter activity. Thus chronic alterations in dietary NaCl intake alter the maximal activity (Vmax) of the Na(+)-H+ antiporter. This adaptation may contribute to decreased NaCl reabsorption in extracellular fluid volume expansion, enhanced NaCl reabsorption in extracellular fluid volume depletion, and enhanced NaHCO3 reabsorption in chronic metabolic alkalosis associated with volume contraction.

Animals↗