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Biomedical subjects

C Ropars

Publications and source records attributed to C Ropars.

At least 19 recordsLinked to original sources
PubMed1998

Engineered erythrocytes: influence of P50 rightward shift and oxemia on oxygen transport to tissues.

The red blood cell (RBC) membrane may be reversibly opened using a lysis-resealing continuous flow method. The technology was adapted to the internalisation of an allosteric effector of haemoglobin, Inositol-Hexaphosphate (IHP). This molecule, occupying the allosteric site of 2,3 Bis-Phosphoglycerate with a very large affinity, induces a rightward shift of the oxyhaemoglobin dissociation curve (ODC). From ODC parameters in human volunteers, the potential effect of P50 (oxygen pressure at 50% haemoglobin saturation) on oxygen exchangeable fraction (OEF%), for various oxygen partial pressures (oxemia) was evaluated. For hyperoxic or normoxic arterial oxygen pressure (paO2), rightward shift greatly improved OEF%. In optimised conditions, engineered erythrocytes were potentially able to deliver two to three times more oxygen than normal cells. For patients with decreased paO2, as observed in chronic obstructive pulmonary deficiency (COPD), the reduction in arterial oxygen saturation (saO2%) reduces the benefit of the treatment for paO2 values between 60 and 80 mmHg. Below 60 mmHg, the saO2% reduction cannot be compensated by a corresponding reduction in svO2%, particularly for organs with physiologically low svO2%. In these organs, deleterious effects could be observed for a very large rightward shift of the ODC. Such engineered cells have unique properties for oxygen transport improvement and may be used for the treatment of patients suffering from diseases associated with hypoxia and ischemia.

Erythrocytes↗
PubMed1996

Improved pharmacodynamics of L-asparaginase-loaded in human red blood cells.

To evaluate the modification of pharmacodynamic parameters induced by the administration of L-asparaginase loaded into red blood cells, 13 patients received a single dose of L-asparaginase internalised into the carrier. The enzyme was loaded using a reversible lysis-resealing process. The dose per patient ranged from 30 to 200 i.u. kg-1. Considerable heterogeneity occurred between patients. the level of L-asparaginase circulating after 24 h represented 47% of the total injected dose as compared to 74.8% for red blood cells (RBCs). However, the half-life of the enzyme remaining in the circulation was very similar to that of the RBC carrier, i.e. 29 days and 27 days, respectively, compared with 8-24 h for the free enzyme. Sustained elimination of plasma L-asparagine occurred, the duration of which was dependent on the injected dose. A single injection of 30.i.u.kg-1 was sufficient to eliminate plasma L-asparagine over 10 days. With 150-200 IU.kg-1 the elimination period was extended to 50 days. These data show that the use of RBCs as carriers of L-asparaginase greatly improves the pharmacodynamic parameters of the drug.

Adolescent↗
PubMed1996

Tolerance evaluation of L-asparaginase loaded in red blood cells.

OBJECTIVE: A pilot clinical study was conducted to evaluate the toxicity of a single dose of L-asparaginase loaded in red blood cells (RBCs). METHODS: Thirteen patients received a single dose of L-asparaginase in the range 30-200 i.u.kg-1. The enzyme was loaded in one autologous blood unit using a lysis-resealing process. A control population of 33 patients receiving L-asparaginase intravenously were tested in parallel. IgG, IgM and IgE class anti-L-asparaginase antibodies were detected using specific radioimmunoassays. RESULTS: L-Asparaginase pharmacodynamic parameters may be greatly improved by administration of the drug after internalisation in RBCs as compared to intravenous injection of free drug. The drug elimination was prolonged and similar to that of circulating carrier. After one injection of 30 i.u.kg-1, plasma L-asparagine was eliminated in 10 days and this was extended to 50 days for 150-200 i.u.kg-1. The drug was well tolerated and only transient variations were observed for some of the biological parameters measured. We did not reach the maximum tolerable dose (MTD) of L-asparaginase loaded in RBCs. No significant clinical toxicity was detected. In particular, no immune adverse effects were observed. CONCLUSION: This study opens new perspectives for the clinical utilisation of L-asparaginase. This mode of administration of the drug is able to improve pharmacodynamic parameters and enzymic efficacy and to increase the general tolerance of the treatment.

Adolescent↗
PubMed1996

Internalization and distribution of inositol hexakisphosphate in red blood cells.

Inositol hexakisphosphate (InsP6), an allosteric effector of haemoglobin, is able to modify the oxyhaemoglobin dissociation curve. The rightwards shift of the curve increases the in vivo oxygen delivery to tissues. Such an exogenous substance may be internalized into red blood cells (RBC) using a reversed lysis-resealing process following a hypoosmotic shock, resulting in InsP6-RBC with modified oxygen transport capacity. The efficacy of the process depends on various physicochemical parameters which can be fixed during the experimental protocol. The variability of InsP6 internalization from one sample to another appeared to be mainly due to the natural variation in osmotic fragility of RBC. This factor was also modified during the storage of RBC units before the lysis-resealing process. The separation of InsP6-RBC on a density gradient revealed a wide heterogeneity of internalized InsP6 concentration, varying with the degree of osmotic shock. The control of these various parameters will result in resealed InsP6-RBC in reproducible conditions suitable for in vivo use.

Biological Transport, Active↗
PubMed1994

Density gradient separation of L-asparaginase-loaded human erythrocytes.

L-Asparaginase has been encapsulated in human red blood cells using a hypotonic dialysis process. Erythrocytes loaded with L-Asparaginase were separated into eight fractions using a discontinuous Percoll density gradient. A minor cell subpopulation of low density cells and a major subpopulation of denser erythrocytes was obtained after hypotonic dialysis treatment, in both the absence or presence of L-Asparaginase. The encapsulated L-Asparaginase activity per resealed erythrocyte was higher in low-density cells and decreased progressively with increasing in cellular density.

Asparaginase↗
PubMed1992

Erythrocytes as carriers of new anti-opioid prodrugs: in vitro studies.

In using a reversed hypoosmotic lysis and resealing process, internalization of Naloxone or Naltrexone prodrugs as new opioid antagonists into red blood cells (RBC) can be obtained. We describe the entrapment method and haematological parameters of such RBC carriers. Percentages of internalization range between 35% and 70%, depending on the prodrug. The stability of the different prodrugs within RBC, after in vitro internalization have been compared at 4 degrees C and 37 degrees C. These studies were performed in order to screen and choose the most interesting prodrugs for in vivo studies. Some prodrugs tested appeared to be stable after 24 hours of incubation, but others were not. The intracellular ATP and 2,3 BPG concentrations of RBC carriers were similar to the control.

Drug Carriers↗
PubMed1992

Acetaldehyde, ethanol and acetone concentrations in blood of alcohol-treated mice receiving aldehyde dehydrogenase-loaded erythrocytes.

Blood levels of acetaldehyde (ACh), ethanol and acetone were investigated in mice treated with ethanol for 6 months and receiving compatible erythrocytes (RBCs) overloaded with aldehyde dehydrogenase (AlDH). Following an acute dose of ethanol, ACh levels were significantly lower in these animals than in alcohol-treated mice receiving AlDH-unloaded RBCs, and were similar to the ACh levels of normal mice. The peak ethanol concentration was higher in normal mice than in both groups of alcohol-treated animals, while acetone concentrations were not significantly different in the three groups of animals.

Acetaldehyde↗
PubMed1992

Enhanced O2 transportation during cardiopulmonary bypass in piglets by the use of inositol hexaphosphate loaded red blood cells.

A continuous lysing and resealing of erythrocytes permitted internalization of inositol hexaphosphate (IHP), a strong allosteric effector of Hb, leading to significant rightward shifts of the HbO2 dissociation curve. Twelve piglets were put on cardiopulmonary bypass (CPB) with the heart beating, cooled to 25 degrees C then rewarmed to 37 degrees C before weaning off CPB. AoP, LV pressure, PAP, and cardiac output (CO) were monitored. Blood samples were taken before CPB, at 25 degrees C, at 30 degrees C, at 37 degrees C and after CPB for assessment of blood gases, arterio-venous difference in O2 content, lactates, P50 (partial pressure of O2 at 50% Hb saturation), and ionogram. Control group I included five pigs where the CPB circuit was primed with Ringer's lactate solution and porcine blood. In group II (n = 5), priming was done with Ringer's lactate solution and IHP loaded erythrocytes. P50 was significantly higher during CPB than before surgery in group II (20%), but not in group I (1%). There was a significant increase in VO2 in group II (6.02 ml/min) compared to group I (4.03 ml/min) (p less than 0.05) after CPB. Hemodynamics improved after CPB in group II (mean AoP 42 mmHg and syst LVP 70 mmHg) compared to group I (AoP 25 mmHg and syst LVP 22.5 mmHg). These preliminary results show that O2 transportation at the end of CPB is enhanced and myocardial function is improved in piglets with the use of IHP erythrocytes.

Animals↗
PubMed1990

In vivo accelerated acetaldehyde metabolism using acetaldehyde dehydrogenase-loaded erythrocytes.

Human erythrocytes were loaded with homogeneous acetaldehyde dehydrogenase (AcDH) purified from Alcaligenes Eutrophus (an enzyme species with an apparent Km for acetaldehyde similar to the mitochondrial enzyme), using an encapsulation procedure based on hypotonic haemolysis, isotonic resealing and reannealing. The AcDH-overloaded erythrocytes contained 1.55 +/- 0.25 I.U. of AcDH activity per ml of packed erythrocytes, a value 12-15 times higher than that of corresponding unloaded or native red cells. The AcDH-loaded erythrocytes were found to metabolize 4 +/- 0.8 mumol of acetaldehyde/hr/ml of red blood cells, whereas the glycolytic activity was almost unmodified. Estimates of intracellular adenine nucleotides showed 50% ATP decay in the AcDH-loaded cells when incubated in the presence of acetaldehyde concentrations higher than 50 microM, whereas the [NAD+]/[NADH] ratio was strongly decreased but to the same extent as in control cells, suggesting that this was due to the acetaldehyde itself and not to the presence of encapsulated AcDH. Similar results were obtained using mouse erythrocytes. AcDH-overloaded mouse red blood cells from donor animals were also injected intraperitoneally into compatible recipients (Balb/C) and 80 to 85% of these were found to enter into circulation within 24 hr and to circulate with a half-life of 6-7.3 days (normal half-life 11 days). Following an acute dose of ethanol (2g/kg intraperitoneally), blood levels of acetaldehyde were significantly lower in mice receiving the AcDH-loaded erythrocytes than in controls. Blood levels of ethanol were also lower in the treated mice compared to controls. These results show that AcDH-overloaded erythrocytes can perform in vitro and in vivo as bioreactors improving alcohol and acetaldehyde metabolism, and suggest that administration of these cells to alcoholic patients could be of value in restoring to normal, or improving, alcohol and acetaldehyde metabolism.

Acetaldehyde↗
PubMed1990

Erythrocytes as carriers for L-asparaginase. Methodological and mouse in-vivo studies.

L-Asparaginase has been encapsulated in Swiss mouse or human erythrocytes by hypotonic haemolysis followed by isotonic resealing and reannealing. The details of incorporation and properties of carrier erythrocytes are presented. When L-asparaginase loaded into 51Cr-labelled erythrocytes, was infused intravenously, the same half-life was found for asparaginase and 51Cr. In addition, L-asparaginase loaded into erythrocytes was much more effective in eliminating plasma asparagine compared with the same dose of free L-asparaginase injected in solution, during a sustained period (14 days).

Animals↗
PubMed1990

Several aspects of red blood cell engineering: potential therapeutic applications.

Erythrocytes can be used to entrap drugs, enzymes or other molecules with active properties, with various encapsulation procedures. The method of internalization we are using includes an hypotonic dialysis step. Carrier erythrocytes survival depends on the dialysis process and the carried molecule. Research has led us to perform preclinical trials on animals for several drugs and enzyme therapies and for the improvement of oxyphoric capacity of erythrocytes. There exist many potential clinical applications for each kind of internalized molecules.

Animals↗
PubMed1989

Modification of partial pressure of oxygen (P50) in mammalian red blood cells by incorporation of an allosteric effector of hemoglobin.

Internalization of inositol hexaphosphate (IHP) in mammalian red blood cells (RBC) produces a modification of the hemoglobin-oxygen affinity, leading to a rightward shift of the dissociation curve. The process of incorporation, based on an osmotic shock, has been tested on RBC of different species. Two dialysis protocols have been defined to transform RBC, the first one for small volumes in a cellulose bag and the other for larger volumes using a commercially available dialysis device. Different optimal conditions must be used for each species. Most of the cellular characteristics of the transformed RBC having encapsulated IHP are similar to those of native cells. For several species, such modified RBC could be reinfused and used for physiological studies.

Allosteric Regulation↗