PubMed Health⌕ Search

Biomedical subjects

A Astier

Publications and source records attributed to A Astier.

At least 37 records · Page 2Linked to original sources
PubMed1999

Induction of inosine monophosphate dehydrogenase activity after long-term treatment with mycophenolate mofetil.

OBJECTIVES: To study the pharmacologic activity of mycophenolate mofetil in stable kidney transplant recipients receiving mycophenolate mofetil therapy for different periods from 2 months to 3 years. METHODS: Seventeen patients were enrolled during a 9-month period. Blood samples were collected before administration and 1/2, 1, 2, 4, and 6 hours after administration. Mycophenolic acid, the active metabolite of mycophenolate mofetil, was measured in plasma with use of the enzyme multiplication immunoassay technique (EMIT) assay and the activity of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines inhibited by mycophenolate mofetil, was determined in whole blood by the estimation of the 3H-release from [2,8-3H]-hypoxanthine. RESULTS: As the length of mycophenolate mofetil therapy increased, the inhibitory effect of mycophenolate mofetil on IMPDH activity was reduced (0.13+/-0.03 for long-term treatment versus 0.46+/-0.06 for short-term treatment; P = .0006) and a stimulatory effect of mycophenolate mofetil on IMPDH activity was observed (1.16+/-0.56 for long-term treatment, versus 0.03+/-0.01 for short-term treatment; P < .0001). These modifications of IMPDH activity were associated with fluctuations in the pharmacokinetics of mycophenolic acid. CONCLUSION: Long-term treatment with mycophenolate mofetil was associated with an induction of IMPDH activity. Such induction could be deleterious if it is followed by a restoration or a stimulation of the proliferative capacity of lymphocytes. These results strongly suggest that the place of mycophenolate mofetil in long-term treatment of kidney transplant patients needs to be carefully assessed.

Adult↗
PubMed1998

Preconditioning with cromakalim improves long-term myocardial preservation for heart transplantation.

BACKGROUND: Myocardial preservation for heart transplantation relies on hyperkalemic cardiac arrest and hypothermic storage. Our study investigated whether pretreatment with a potassium-channel opener (cromakalim) before prolonged storage in an extracellular fluid improves left ventricular recovery. METHODS: Rabbit hearts were submitted to 6-hours' cold storage and assessed on a blood-perfused isolated heart preparation. Hemodynamic recovery, enzyme release (creatine kinase and lactate dehydrogenase), and adenine nucleotide content were determined. Five groups were tested: control (n=6), no ischemia; UW group (n=7), hearts arrested with and stored in University of Wisconsin solution; STH group (n=5), hearts arrested with and stored in St. Thomas' Hospital solution; cromakalim group (n=6), hearts pretreated with cromakalim (30 microg/kg) before arrest with and storage in St. Thomas' Hospital solution; and glibenclamide group (n=5), hearts pretreated with cromakalim followed by glibenclamide (a potassium-channel blocker) before arrest with and storage in St. Thomas' Hospital solution. RESULTS: Hemodynamic recovery was improved and enzyme release was lower in the UW group than in the STH group. Compared with the STH group, the group pretreated with cromakalim had significantly decreased left ventricular end-diastolic pressures, increased left ventricular developed pressures, increased maximal values of positive and negative rates of rise of left ventricular pressure, and increased time constant of isovolumetric relaxation. Hemodynamic recovery was similar in the UW group and cromakalim groups. Glibenclamide did not abolish the effects of cromakalim. None of the protocols affected myocardial energy stores. CONCLUSION: Pretreatment with cromakalim affords additional protection to that provided by cardioplegic arrest and prolonged cold storage using an extracellular solution. The intracellular mechanisms involved remain to be determined.

Adenine Nucleotides↗
PubMed1998

Leishmania infantum: lack of parasite resistance to amphotericin B in a clinically resistant visceral leishmaniasis.

Amphotericin B (AmB) has been used as a second-line treatment of visceral leishmaniasis, particularly in human immunodeficiency virus-positive patients. AmB median effective doses (ED50s) were determined on an isolate obtained before any treatment and on a second isolate obtained 4 years later from the same AmB-treated patient. ED50s were similar (0.059 and 0.067 mg/kg of body weight, respectively), demonstrating the first evidence of AmB ED50 stability of Leishmania infantum after a long-term drug exposure. An isoenzymatic study was performed in order to verify that the second isolate originated from the same parasite as the first isolate. The present case report showed that treatment failure was not due to parasite resistance in spite of a prolonged exposure to the drug.

Amphotericin B↗
PubMed1998

Physicochemical characteristics of pentamidine-loaded polymethacrylate nanoparticles: implication in the intracellular drug release in Leishmania major infected mice.

This work describes the preparation, the physicochemical properties, the tolerance and the intracellular trafficking of pentamidine loaded nanoparticles. Pentamidine was bound to the polymer by ionic interaction. This interaction involved the carboxylic acid functions of methacrylic acid (10% of the polymer) and the amine groups of the drug. Pentamidine fixation and release were pH dependent. An acidic pH led to a decrease of fixation or a release. At pH 5, which is the pH value of lysosomes and parasitophorous vacuoles, the release reached up to 50%. At this pH value, pentamidine is ionized and therefore can not traverse the biological membranes. Unloaded nanoparticles and pentamidine-loaded nanoparticles were tested in vitro on U937 cells and no cytotoxicity was observed. In vivo, in Leishmania infected mice, no significant weight loss was found. Ultrastructural studies showed the different steps of drug loaded nanoparticles trafficking inside Leismania-infected Küpffer cells. The nanoparticle uptake by macrophagic cells led to the location of nanoparticles inside phagocytosis vacuoles which fused with primary lysosomes to form secondary lysosomes. Ultimate fusion of secondary lysosomes containing nanoparticles with parasitophorous vacuoles was also observed. Nanoparticles were identified close to amastigotes but internalization by the parasite was not observed.

Animals↗
PubMed1997

The related adhesion focal tyrosine kinase differentially phosphorylates p130Cas and the Cas-like protein, p105HEF1.

The related adhesion focal tyrosine kinase (RAFTK) is tyrosine-phosphorylated following beta1 integrin or B cell antigen receptor stimulation in human B cells. Two substrates that are tyrosine-phosphorylated following integrin ligation in B cells are p130(Cas) and the Cas family member human enhancer of filamentation 1 (HEF1), both of which can associate with RAFTK. In this report we observed that RAFTK was involved in the phosphorylation of these two proteins. While a catalytically active RAFTK was required for both p130(Cas) and HEF1, phosphorylation of p130(Cas), but not of HEF1, was dependent on an intact autophosphorylation site (Tyr402) on RAFTK. To determine if RAFTK phosphorylated p130(Cas) and HEF1 directly or through an intermediate, we assayed the ability of RAFTK and of a Tyr402 mutant to phosphorylate purified HEF1 and p130(Cas) domains. RAFTK was able to phosphorylate the substrate domains of both p130(Cas) and HEF1, but only the C-terminal domain of p130(Cas). Furthermore, Tyr402, which mediates the binding of RAFTK to c-Src kinase, was required for the phosphorylation of the C-terminal domain of p130(Cas). These data suggest that RAFTK itself is sufficient for HEF1 phosphorylation, whereas a cooperation between RAFTK and Src kinases is required for the complete phosphorylation of p130(Cas).

Adaptor Proteins, Signal Transducing↗
PubMed1997

Regulation of integrin-mediated p130(Cas) tyrosine phosphorylation in human B cells. A role for p59(Fyn) and SHP2.

Engagement of beta1 integrins in terminally differentiated human B cell lines, such as ARH-77, leads to prominent tyrosine phosphorylation of the p130 Crk-associated substrate (Cas). Cas regulates the assembly of several SH2 and SH3 domain-containing proteins into signaling complexes, which are potentially involved in the propagation of downstream signals. We demonstrate here that immunoprecipitated Cas from beta1 integrin-stimulated ARH-77 cells was associated with tyrosine kinase and phosphatase activities and that integrin ligation led to the recruitment of at least p59(Fyn) tyrosine kinase and SHP2 tyrosine phosphatase in Cas immune complexes. Cotransfection studies in COS-7 cells further indicated that Fyn/Cas physical interaction and Fyn-mediated Cas phosphorylation required amino acids 638-889 in the C-terminal region of Cas. This sequence contains both c-Src SH2 and SH3 domain-binding motifs. In vitro binding studies using glutathione S-transferase fusion proteins derived from the SH2 or SH3 domains of Fyn suggested that both Fyn domains can participate in Fyn/Cas interaction. These data implicate Fyn and SHP2 as potential modulators of Cas signaling complexes in B cells.

Animals↗
PubMed1997

Involvement of p130(Cas) and p105(HEF1), a novel Cas-like docking protein, in a cytoskeleton-dependent signaling pathway initiated by ligation of integrin or antigen receptor on human B cells.

The Crk-associated substrate p130(Cas) (Cas) and the recently described human enhancer of filamentation 1 (HEF1) are two proteins with similar structure (64% amino acid homology), which are thought to act as "docking" molecules in intracellular signaling cascades. Both proteins contain an N-terminal Src homology (SH), three domain and a cluster of SH2 binding motifs. Here we show that ligation of either beta1 integrin or B cell antigen receptor (BCR) on human tonsillar B cells and B cell lines promoted tyrosine phosphorylation of HEF1. In contrast, Cas tyrosine phosphorylation was observed in certain B cell lines but not in tonsillar B cells, indicating a more general role for HEF1 in B cell signaling. Interestingly, pretreatment of tonsillar B cells with cytochalasin B dramatically reduced both integrin- and BCR-induced HEF1 phosphorylation, suggesting that some component of the BCR-mediated signaling pathway is closely linked with a cytoskeletal reorganization. Both HEF1 and Cas were found to complex with the related adhesion focal tyrosine kinase (RAFTK), and when tyrosine phosphorylated, with the adapter molecule CrkL. In addition, the two molecules were detected in p53/56(Lyn) immunoprecipitates, and Lyn kinase was found to specifically bind the C-terminal proline-rich sequence of Cas in an in vitro binding assay. These associations implicate HEF1 and Cas as important components in a cytoskeleton-linked signaling pathway initiated by ligation of beta1 integrin or BCR on human B cells.

Actins↗
PubMed1997

The related adhesion focal tyrosine kinase is tyrosine-phosphorylated after beta1-integrin stimulation in B cells and binds to p130cas.

Integrin ligation initiates intracellular signaling events, among which are the activation of protein tyrosine kinases. The related adhesion focal tyrosine kinase (RAFTK), also known as PYK2 and CAKbeta, is a tyrosine kinase that is homologous to the focal adhesion kinase (FAK) p125FAK. The structure of RAFTK is similar to p125FAK in that it lacks a transmembrane region, does not contain Src homology 2 or 3 domains, and has a proline-rich region in its C terminus. Here we report that RAFTK is a target for beta1-integrin-mediated tyrosine phosphorylation in both transformed and normal human B cells. Ligation of the B cell antigen receptor also induced tyrosine phosphorylation of RAFTK. Phosphorylation of RAFTK following integrin- or B cell antigen receptor-mediated stimulation was decreased by prior treatment of cells with cytochalasin B, indicating that this process was at least partially cytoskeleton-dependent. One of the tyrosine-phosphorylated substrates after integrin stimulation in fibroblasts is p130cas, which can associate with p125FAK. RAFTK also interacted constitutively with p130cas in B cells, since p130cas was detected in RAFTK immunoprecipitates. Although the function of RAFTK remains unknown, these data suggest that RAFTK may have a significant function in integrin-mediated signaling pathways in B cells.

B-Lymphocytes↗
PubMed1997

Activity of pentamidine-loaded methacrylate nanoparticles against Leishmania infantum in a mouse model.

The use of drug delivery systems may reduce the toxicity and improve the activity of antileishmanial compounds. In view of such a strategy, we loaded the antileishmanial agent pentamidine on polymethacrylate nanoparticles. The activity of pentamidine-loaded nanoparticles was compared with that of free pentamidine in a BALB/c mice model of visceral leishmaniasis induced by Leishmania infantum. On day 0, mice were infected intravenously with 10(7) promastigotes and then treated via the tail vein on days 14, 16 and 18 with bound pentamidine, free drug or isotonic saline (control group). On day 21, liver parasite burdens were evaluated using the Stauber method. Livers and spleens were removed and weighed. Effective doses (ED) were determined using the Michaelis-Menten representation relating the percentage of parasite suppression to the dose. The ED50 of bound pentamidine was six times lower than that of free pentamidine (0.17 mg kg-1 vs 1.06 mg kg-1). The ED90 value calculated for bound pentamidine was 1 mg kg-1. It was not possible to obtain the ED90 for free pentamidine because the dose-response curve reached a plateau near 60% of parasite suppression. A significant decrease in liver and spleen weights, probably reflecting the leishmanicidal activity, was observed for treated mice with bound pentamidine. These results showed that bound pentamidine was more potent than the free drug against L. infantum in our BALB/c mice model.

Animals↗
PubMed1997

Ultrastructural changes in parasites induced by nanoparticle-bound pentamidine in a Leishmania major/mouse model.

Drug targeting enhances drug efficacy. This principle was tested in the treatment of an experimental visceral leishmaniasis. Using transmission electron microscopy (TEM) we localized pentamidine-loaded polymethocrylate nanoparticles in the liver of mice infected with Leishmania major and compared the ultrastructural changes in the parasites of these mice when they were treated with bound versus free pentamidine. Between days 13 and 17 after infection, loaded nanoparticles treated group were injected i.v. with 3 doses of 0.17 mg/kg bound pentamidine loaded on 2 x 10(11) nanospheres; control groups received 2 x 10(11) unloaded nanospheres. Drug reference control groups received five doses of 200 mg/kg pentavalent antimony (Glucantime) or three doses of free pentamidine (0.17 mg/kg or 2.28 mg/kg). Mice treated with bound pentamidine displayed a 77% reduction in their parasite burden versus the untreated controls. Nanoparticles were located by TEM inside parasitized Küpffer cells, in the phagolysosomes without entering the Leishmania. The low dose of 0.17 mg/kg bound pentamidine damaged the Leishmania to the same extent as 2.28 mg/kg of free pentamidine (the usual dose in human chemotherapy). In the parasites inside the Küpffer cells, TEM showed a swollen mitochondrian with loss of cristae, destruction or fragmentation of the kinetoplast, loss of ribosomes and destruction of parasite structures except for the subpellicular microtubules. This study therefore shows that a dose of bound pentamidine 13 times smaller than the usual dose of free pentamidine has a similar effect on the parasite.

Animals↗
PubMed1997

Activity of pentamidine-loaded poly (D,L-lactide) nanoparticles against Leishmania infantum in a murine model.

The activity of pentamidine-loaded poly(D,L-lactide) nanoparticles was compared, by determination of median effective doses (ED50), to that of free pentamidine in a murine model of visceral leishmaniasis induced by Leishmania infantum. BALB/c mice were infected intravenously on day O with promastigotes and then treated on days 14, 16, and 18. Groups of 5 mice received either 0.57, 1.14 and 2.28 mg/kg of free pentamidine (expressed in pentamidine base) or 0.055, 0.11, 0.22 and 0.44 mg/kg of pentamidine-loaded nanoparticles. In the control group, 12 mice received normal saline. The liver parasite burden was evaluated using the Stauber method 72 h after the last injection and drug levels in livers and spleens were determined. Bound pentamidine was 3.3 times more active than free drug (ED50 value = 0.32 mg/kg versus 1.05 mg/kg for free drug). Drug levels showed a weak accumulation in hepatic and splenic tissues following bound pentamidine administration. A lack of acute toxicity was noted in all groups treated by bound pentamidine. Results obtained with this biodegradable carrier may be of particular interest as no new major antileishmanial compound is today available.

Animals↗
PubMed1997

Reemergence of gentamicin-susceptible strains of methicillin-resistant Staphylococcus aureus: roles of an infection control program and changes in aminoglycoside use.

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in our hospital in the 1980s correlated with increasing acquisition of resistance to antibiotics including gentamicin, rifampin, and fluoroquinolones. During the period 1993-1995, there was a major change in clinical MRSA isolates: the percentage of aminoglycoside-resistant MRSA isolates decreased from 75% to 52%, while the proportion of heterogeneous MRSA strains susceptible to gentamicin, rifampin, and tetracycline increased gradually from 4.9% to 27.5%. We used five epidemiological markers (i.e., antibiotyping, phage typing, pulsed-field gel electrophoresis, and restriction analysis of PCR amplified coagulase and protein A genes) to characterize recent isolates. With use of these techniques, we confirmed the persistence of the aminoglycoside-resistant MRSA clone and identified a clone of erythromycin-susceptible strains among the gentamicin-susceptible isolates and found that the remaining strains were diverse. These changes were due to the introduction of various MRSA strains from outside the hospital, while implementation of infection control measures in 1991 could have led to reduced transmission of the aminoglycoside-resistant MRSA strain. Changes in antibiotic prescribing patterns that resulted in reduced selective pressure from gentamicin may have contributed to the spread of gentamicin-susceptible MRSA strains.

Anti-Bacterial Agents↗
PubMed1997

Infection risk and cost-effectiveness of commercial bags or glass bottles for total parenteral nutrition.

OBJECTIVE: To determine whether the greater daily expense of administering total parenteral nutrition (TPN) via plastic bags changed once daily, compared to glass bottles changed thrice daily, could be offset by savings from a reduction in nosocomial infections. DESIGN: The costs and potential benefits of commercially available TPN bags and TPN in glass containers were compared. Costs were computed from the viewpoint of the hospital, first in a general model and then for two specific examples, Crohn's disease and intensive-care unit (ICU) patients. The extra cost of using bags was $20 per day. The total cost of nosocomial bacteremia was estimated at $6,000. The monetary benefits of using TPN bags were $6,000XT, where XT was the percentage of nosocomial infections averted. We also considered that reduction in intravenous (IV)-line manipulation could reduce bacteremia-related mortality and computed a cost-per-life-saved ratio. RESULTS: Modeling showed that TPN in bags could yield a net benefit when the absolute reduction in the daily risk of nosocomial bacteremia reached the threshold value of 0.3%. Such a reduction could not be attained in patients with Crohn's disease, and corresponded to a 50% to 60% reduction of infection rates in ICU patients. Varying the risk of mortality attributable to IV-line-related infection from 1% to 13% resulted in a cost effectiveness of using TPN bags ranging from $90,000 to $7,000 per life saved in ICU, assuming a two-thirds reduction in IV-line infections, and from $180,000 to $14,000 if the infection rate was reduced by one third. CONCLUSION: The baseline cost-minimization analysis concluded that the extra cost of TPN bags was not justified by the extra savings. The cost-effectiveness analysis, however, found that the cost per life saved fell within the accepted range of public health interventions, provided a large fraction of infections are averted using TPN bags.

Cost-Benefit Analysis↗
PubMed1997

Activity of a new liposomal formulation of amphotericin B against two strains of Leishmania infantum in a murine model.

The efficacy of a new liposomal formulation of amphotericin B was compared to that of amphotericin B deoxycholate (Fungizone) in a murine model of visceral leishmaniasis induced by Leishmania infantum. Median effective doses (ED50) were determined with two different strains: strain 1 was obtained from an untreated patient, and strain 2 was obtained from a patient who had received 12.5 g of amphotericin B over 3 years. BALB/c mice were infected intravenously on day 0 with promastigotes and then treated on days 14, 16, and 18 (strain 1) or on days 21, 23, and 25 (strain 2) with the liposomal formulation of amphotericin B (five doses were tested for each strain: 0.05, 0.1, 0.5, 0.8, and 3 mg/kg of body weight) or with conventional amphotericin B (four doses were tested for each strain: 0.05, 0.1, 0.5, and 0.8 mg/kg). Mice in the control group received normal saline solution. The liposomal amphotericin B formulation was about three times more active than the conventional drug against both strains. ED50 of the liposomal formulation were 0.054 (strain 1) and 0.194 (strain 2) mg/kg. ED50 of conventional amphotericin B were 0.171 (strain 1) and 0.406 (strain 2) mg/kg. Determination of drug tissular levels, 3 days after the last drug administration, showed a drug accumulation in hepatic and splenic tissues much higher after administration of liposomal amphotericin B than after conventional amphotericin B. A lack of toxicity was noted in all groups treated with the liposomal formulation.

Amphotericin B↗