Biomedical subjects

J P Tillement

Publications and source records attributed to J P Tillement.

At least 19 recordsLinked to original sources

PubMed1999

Renoprotective effects of trimetazidine against ischemia-reperfusion injury and cold storage preservation: a preliminary study.

BACKGROUND: Initial ischemia-reperfusion injury is associated with organ retrieval, storage, and transplantation adversely affects early graft function and influences the development of chronic graft dysfunction. We have recently shown that the protective agent trimetazidine (TMZ) added to preservation solutions: Euro-collins (EC) and University of Wisconsin (UW) was efficient to protect kidneys from ischemia-reperfusion injury in an isolated perfused kidney model. We extended these observations to investigate the role of this drug in the development and progression of organ dysfunction in the autotransplant pig kidney model. METHODS: Five experimental groups were studied. After 48-hr cold preservation, autotransplantation and immediate controlateral nephrectomy was then performed in group EC (EC+placebo (n=8), EC+TMZ (n=8), UW+placebo (n=7), and (UW+TMZ) (n=7) and compared with control group (uninephrectomized, n=4) during 14 days. Blood and urine samples were collected for the measurement of creatinine and blood urea nitrogen on postoperative days 1, 3, 5, 7, 11, and 14. Histological analysis was performed after reperfusion and at day 14. RESULTS: Survivals were 100% in group B and D versus 42% in group A and 57% in group C. Urine production occurred earlier after autotransplantation from TMZ preserved kidneys than in placebo preserved groups. Peak creat and blood urea nitrogen was significantly greater in groups B and D than in groups A and C. TMZ was also efficient both to reduce ischemia-reperfusion injury and to decrease cellular infiltration. CONCLUSION: These results support the beneficial effect of TMZ against ischemia-reperfusion injury and its early effects on grafts in the form of delayed graft function and decreased graft survival. In addition, TMZ reduces inflammatory cellular infiltration in the renal parenchyma.

Adenosine↗

PubMed1999

Trimetazidine ameliorates the hepatic injury associated with ischaemia-reperfusion in rats.

Ischaemia-reperfusion induces structural and functional damage to hepatocytes. The purpose of this study was to evaluate the protective effect of trimetazidine, an anti- ischaemic drug, in a rat liver model of ischaemia-reperfusion. Male Wistar rats were divided into groups pretreated with different doses of trimetazidine (1, 5, 10 or 20 mg kg-1 day-1) or saline for 7 days. Liver ischaemia was induced for 120 min and blood reflow was subsequently restored for 30, 60, 90 or 120 min. The activities of alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) as well as the bile flow and the liver ATP content were determined. Ischaemia-reperfusion induced major alterations of hepatic functions involving increases of ASAT and ALAT activities, a drop of ATP content and a sharp decrease in bile flow. Trimetazidine pretreatment reduced the liver injury. Indeed, it lowered the increase in ALAT and ASAT activities observed immediately after reperfusion and maintained higher concentrations of hepatic ATP. Simultaneously, bile flow was increased. These effects were dose-dependent and 5 mg kg-1 day-1 seemed to be the lowest effective dose. In this experimental model trimetazidine pretreatment reduced the liver damage induced by ischaemia-reperfusion. Our data suggest that trimetazidine may be a useful drug in liver surgery to prevent ischaemia-reperfusion injury.

Animals↗

PubMed1999

Sympathomimetic effects of Parquetina nigrescens (Periplocaceae) extract in isolated portal vein smooth muscle.

The purpose of this study was to examine the mechanisms underlying the pharmacological effects of the extract of Parquetina nigrescens (Expar) on vascular smooth muscle contractility. To evaluate the Expar effect, the contractile activity of portal veins isolated from Wistar Kyoto rats was isometrically recorded. Isolated portal vein preparations developed rhythmic and spontaneous contractile activity. Expar increased the contractile response of the portal vein preparations in a dose-dependent manner. The maximal effect of the dose-response curve for Expar was prevented by the alpha1-adrenergic blocking agent prazosin at 10 nM and 30 nM concentration dependently. The contractile responses of the muscle to Expar were partly blocked after chemical sympathectomy of the preparations with 6-hydroxydopamine, and those obtained in the same conditions with tyramine were completely abolished, whereas responses to noradrenaline were unaffected by the 6-hydroxydopamine pretreatment. It is concluded that Expar contains principles, which can be characterized as direct and indirect sympathomimetic.

Adrenergic Agents↗

PubMed1999

The pH-partition profile of the anti-ischemic drug trimetazidine may explain its reduction of intracellular acidosis.

PURPOSE: The anti-ischemic drug trimetazidine (TMZ) acts by a combination of molecular mechanisms which begin to be understood. Thus, it acts in the micromolar range to significantly reduce intracellular acidification during ischemia. To search for a possible physicochemical explanation of this phenomenon, we investigated the transfer mechanisms of the various electrical forms of this dibasic drug. METHODS: The transfer characteristics of TMZ were studied by electrochemistry at the water/1,2-dichloroethane interface. Cyclic voltammetry was used to measure the formal transfer potentials of singly and doubly protonated forms of TMZ (noted TH+ and TH(2)2+, respectively) as a function of aqueous pH, and the partition coefficient of neutral TMZ (log P(T)) was measured by two-phase titration. RESULTS: log P(T) was measured to be 1.04 +/- 0.06, and the acid-base dissociation constants in water were deduced to be pK(w)a1 = 4.54 +/- .02 and pK(w)a2 = 9.14 +/- 0.02. The partition coefficients of TH+ and TH(2)2+ were found to be respectively log P0'TH+ = -3.78 +/- 0.16 and log P0'TH(2)2+ = -9.84 +/- 0.30, which agrees well with the charge being delocalized on two nitrogen atoms in TH+. The pH-partition profile of TMZ was then established in the form of its ionic partition diagram, which showed that the affinity of the ions for the organic phase is pH-dependent and strongly increased by the interfacial potential. CONCLUSIONS: This behavior suggests a physicochemical mechanism whereby efflux of protonated TMZ out of an acidified cell is facilitated, in effect exporting protons to extracellular space.

Acid-Base Equilibrium↗

PubMed1999

Drug transfer across the blood-brain barrier and improvement of brain delivery.

The blood-brain barrier is formed by the endothelial cells of the brain capillaries. Its primary characteristic is the impermeability of the capillary wall due to the presence of complex tight junctions and a low endocytic activity. Essential nutrients are delivered to the brain by selective transport mechanisms, such as the glucose transporter and a variety of amino acid transporters. Although most drugs enter the brain by passive diffusion through the endothelial cells depending on their lipophilicity, degree of ionization, molecular weight, relative brain tissue and plasma bindings, some others can use specific endogenous transporters. In such cases, binding competition on the transporter with endogenous products or nutrients can occur and limits drug transfer. The blood-brain barrier can be a major impediment for the treatment of diseases of the central nervous system, since many drugs are unable to reach this organ at therapeutic concentrations. Various attempts have been made to overcome the limiting access of drugs to the brain, e.g. chemical modification, development of more hydrophobic analogs or linking an active compound to a specific carrier. Transient opening of the blood-brain barrier in humans has been achieved by intracarotid infusion of hypertonic mannitol solutions or of bradykinin analogs. Another way to increase or decrease brain delivery of drugs is to modulate the P-glycoprotein (P-gp) whose substrates are actively pumped out the cell into the capillary lumen. Many P-gp inhibitors or inducers are available to enhance the therapeutic effects of centrally acting drugs or to decrease central adverse effects of peripherally active drugs.

Animals↗

PubMed1999

A GppNHp-insensitivity factor modulates the activation of beta-adrenoceptor-coupled Gs protein in rat cortex and cerebellum.

The effect known as the GTP-shift refers to the complete conversion of receptors from the high- to the low agonist-affinity state in the presence of an excess of GTP or one of its analogs. 5'-Guanylylimidodiphosphate (GppNHp) was able to fully suppress the high (-)-isoproterenol-affinity of beta-adrenoceptors (beta AR) in cultured rat brain astrocytes. In contrast, a proportion of beta AR in rat cortex and cerebellum synaptosomes was found to be insensitive to this GTP analog. This GppNHp-insensitivity was due to a membrane-associated factor, presumably interacting with Gs proteins and not present in a functional form in cultured astrocytes. Here we assessed the effect of this factor on the beta AR-mediated activation of Gs proteins. The removal of the GppNHp-insensitivity factor from the synaptosomes was achieved using 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), a mild detergent. The activation of Gs proteins was monitored by the binding of another non-hydrolysable GTP-analog, guanylyl 5'-[gamma-[35S]thio]-triphosphate ([35S]GTP gamma S). The beta AR-Gs protein coupling was at least twofold less efficient in synaptosomes relative to cultured astrocytes. The CHAPS treatment induced a twofold increase in the coupling efficiency in cortex and cerebellum synaptosomes, but had no effect in cultured astrocytes. It undoubtedly indicated the inhibitory effect of the GppNHp-insensitivity factor on the activation of Gs proteins in the synaptosomes. Using CHAPS-soluble material extracted from synaptosomes, it was possible to reconstitute the GppNHp-insensitivity of CHAPS-treated membranes or even to induce it in cultured astrocytes. This effect correlated with the amount of CHAPS-soluble material according to a sigmoid curve, but it was abolished by the heat of CHAPS-soluble material. Successful crossed reconstitutions of the GppNHp-insensitivity suggest that the GppNHp-insensitivity factor is the same regardless of its originating area, and that it might play a general role in the central nervous system. Further investigations should help to identify the GppNHp-insensitivity factor.

Adrenergic beta-Agonists↗

PubMed1999

Effects of resveratrol on the rat brain respiratory chain.

The aim of this work was to investigate the possible effects of resveratrol on the mitochondrial respiratory chain in rat brains. Isolation of mitochondria was performed at 4 degrees C using differential centrifugation. Mitochondrial respiration rate (0.4 mg of protein/ml) was determined by measuring mitochondrial oxygen consumption with a Clark electrode at 37 degrees C. Respiratory control ratio (RCR) was evaluated as the state 3/state 4 ratio of oxidative phosphorylation with substrates adenosine 5'-diphosphate (ADP) and malate plus glutamate, respectively in the presence and in the absence of resveratrol. The rate of oxygen consumption by the different complexes was checked using rotenone (2 microM), malonate (10 mM), antimycin A (1 microM), potassium cyanide (KCN) (0.3 mM) and oligomycin (10 microM) to inhibit complexes II, III, IV, V and I, respectively. Moreover, enzyme activity determinations were checked as follows: the activities of complexes II-III were measured as the rate of cytochrome c reduction at 550 nm (37 degrees C) successively triggered either by succinate (complexes II and III) or by decylubiquinol (DUQH2) (complex III), in the presence and in the absence of resveratrol. Adenosine 5'-triphosphate (ATP) synthase activity was checked as ATP hydrolysis (ATPase) at 37 degrees C for 10 min from purified mitochondria on Percoll gradient. The inorganic phosphate (Pi) concentration was measured by the Fiske and Subbarow method. When complexes I to V were activated by glutamate plus malate, resveratrol (10(-11) - 10(-4) M) significantly decreased RC (p < 0.001) following a biphasic curve with two EC50 values, 0.162 +/- 0.072 microM and 24.5 +/- 4.0 microM, representing about 56% of total oxygen consumption inhibition. We also observed a concentration-dependent effect on state 3 with two EC50 values, 2.28 +/- 0.87 nM and 27 +/- 5 microM respectively. On the other hand, resveratrol inhibited state 4 following a concentration-dependent curve with an EC50 of 37 +/- 11 microM. When complex IV operated alone, resveratrol (100 microM) did not modify oxygen consumption compared with control, indicating that this molecule did not inhibit complex IV. Thus resveratrol inhibits the mitochondrial respiratory chain through complexes I to III. In order to confirm these data, we measured the enzymatic activity of ubiquinol cytochrome c reductase alone and in the presence of resveratrol. In the presence of disrupted mitochondria, after freeze thawing cycles (three times), resveratrol inhibited about 20% of complex III activity. These results suggest that resveratrol and DUQH2 could be competitive on complex III. Resveratrol significantly inhibited ATPase activity (p < 0.001) following a biphasic curve with two EC50 values, 0.39 +/- 0.15 nM and 23.1 +/- 6.4 microM, both representing about 80% of oligomycin-dependent ATPase total activity. Resveratrol was effective as a protecting agent on the three models of oxidation. On lipid peroxidation of brain synaptosomes induced by the Fenton reaction, it was three times more potent than DUQH2. Its effectiveness in reducing 1,1-diphenyl-2-picryl hydrazyl radical (DPPH degrees) showed a stoichiometry of two, indicating that two hydrogen atoms of resveratrol were abstracted by the process. Resveratrol was also able to scavenge the superoxide anion (O2 degrees) generated from rat forebrain mitochondria in a concentration dependent manner. In conclusion, resveratrol can decrease complex III activity by competition with coenzyme Q. This property is especially interesting as this complex is the site where reactive oxygen substances (ROS) are generated. By decreasing the activity of complex III, resveratrol cannot only oppose the production of ROS but can also scavenge them.

Adenosine Triphosphatases↗

PubMed1998

Glucocorticoids decrease cytochrome c oxidase activity of isolated rat kidney mitochondria.

The importance of mitochondria is rising as a target in pathologic processes such as ischemia. We have investigated the effects of hydrocortisone, prednisolone, dexamethasone and triamcinolone on oxidative phosphorylation, Ca2+ fluxes, swelling and membrane potentials in isolated kidney mitochondria. The measurement of respiration state 3 showed a significant decrease in presence of glucocorticoids whereas the other respiration states were not modified. When mitochondria were uncoupled and either the complexes III and IV or the complex IV were stimulated, the O2 consumption was decreased by glucocorticoids. These results suggest the cytochrome c oxidase is a target of the glucocorticoid effect on the respiratory chain. Indeed, the other mitochondrial functions investigated were unchanged, ruling out a direct effect on Ca2+ fluxes or swelling. A regulation of cytochrome c oxidase activity by glucocorticoids will be of particular interest in pathology involving metabolic insult.

Animals↗

PubMed1998

Study of the expression of the genetic variants of human alpha1-acid glycoprotein in healthy subjects using isoelectric focusing and immunoblotting.

Human alpha1-acid glycoprotein (AAG) exists as an heterogeneous population of two or three genetic variants (ORM1 F1 and/or S and ORM2 A) in the plasma of most individuals. The ORM1 and ORM2 variants have a separate genetic origin. AAG belongs to the acute-phase proteins, which, under conditions of inflammation, increase several-fold in concentration. Additionally, there is evidence to suggest that it is not only the concentration but also the distribution of the two gene products of AAG (ORM1 and ORM2) that alter in such conditions. Variations of the relative concentrations of the AAG variants in certain diseases, such as cancer, can only be shown by reference to data collected in healthy people. In this study, we have investigated a group of 74 healthy subjects (42 men and 32 women) for AAG concentrations, AAG phenotypes and relative proportions of genetic variants in plasma. The specific assay of AAG was carried out by an immunonephelometric method and the phenotyping was performed, after desialylation of AAG, by analytical isoelectric focusing. Detection of the AAG variants was made by immunoblotting and their relative proportions were determined by laser densitometry analysis. The AAG plasma concentrations in the healthy group ranged between 0.28 and 0.92 g/l (mean value 0.50+/-0.14 g/l). The relative proportions of the variants derived from the two genes of AAG were variable, depending on the individual, but the amount of ORM1 variants almost always exceeded that of the ORM2 variant. No sex-related differences were observed in respect either in the total AAG level nor the relative proportions of the ORM1 and ORM2 variants. The data collected in this study may serve as a reference towards the investigation of possible changes in the expression of the genetic variants of AAG in chronic inflammatory diseases.

Adult↗

PubMed1998

Role of bilirubin in the regulation of the total peroxyl radical trapping antioxidant activity of plasma in sickle cell disease.

Alpha-tocopherol and bilirubin antioxidant properties were evaluated in sickle cell disease. The total peroxyl radical trapping antioxidant activity of plasma (TRAP) was measured with a polarographic method using hemin as oxidative stress initiator. The TRAP was not correlated with plasma alpha-tocopherol concentration. The TRAP was correlated with plasma total bilirubin concentration [TRAP = 8.1 (total bilirubin) +363.7 (r = 0.67)] and the correlation was even better with the sum (alpha-tocopherol + total bilirubin) plasma concentration [TRAP = 9.1(alpha-tocopherol + total bilirubin)+ 170.5(r = 0.77)]. The alpha-tocopherol contribution in the antioxidant capacity of plasma was significant but bilirubin level acted as the limiting factor of plasma antioxidant capacity in sickle cell anemia. This result can be explained by the antioxidant property of bilirubin but also by coantioxidant activity towards oxidized alpha-tocopherol.

Anemia, Sickle Cell↗

PubMed1998

Structure-property relationships of trimetazidine derivatives and model compounds as potential antioxidants.

Twenty-five compounds (trimetazidine derivatives and other compounds, mostly having a free phenolic group) were examined for their radical scavenging and antioxidant properties. Their reaction with DPPH (2,2-diphenyl-1-picrylhydrazyl) as a measure of radical scavenging capacity was assessed by two parameters, namely EC50 (the concentration of antioxidant decreasing DPPH by 50%), and log Z, a kinetic parameter proposed here and derived from initial second-order rate constants and antioxidant/DPPH ratios. Antioxidant activities were determined by the inhibition of lipid peroxidation and albumin oxidation. The most active compounds were derivatives having a trolox or hydroquinone moiety. Physicochemical and structural properties were determined by molecular modeling as lipophilicity (virtual log P calculations) and H-Surf (solvent-accessible surface of hydroxyl hydrogen) and by quantum mechanical calculations (deltaH(ox) = oxidation enthalpy; deltaH(abs) = enthalpy of hydrogen abstraction). QSAR models were derived to identify molecular mechanisms responsible for the reactivity toward the DPPH radical and for the inhibition of lipid peroxidation. A useful prediction of antioxidant capacity could be achieved from calculated molecular properties and the kinetic parameter developed here.

Antioxidants↗

PubMed1998

Dose-related inversion of cinnarizine and flunarizine effects on mitochondrial permeability transition.

We investigated the effects of cinnarizine and flunarizine on mitochondrial permeability transition, ATP synthesis, membrane potential and NAD(P)H oxidation. Both drugs were effective in inhibiting the mitochondrial permeability transition induced either by Ca2+ alone or in the presence of tert-butylhydroperoxide. This protective effect occurred at low concentrations (< 50 microM) of these drugs and was accompanied by the inhibition of NAD(P)H oxidation and the restoration of the mitochondrial membrane potential decreased by a high concentration of Ca2+ (25 microM). However, at higher concentrations (> 50 microM) of cinnarizine and flunarizine and in the absence of both tert-butylhydroperoxide and Ca2+, their effects on the mitochondria were reversed as follows: mitochondrial permeability transition was generated, mitochondrial NAD(P)H was oxidized and membrane potential collapsed. These deleterious effects were not antagonized by cyclosporine A, the most potent inhibitor of the mitochondrial permeability transition, but by 2,6-di-tert-butyl-4-methylphenol, a known antioxidant agent. This mitochondrial effect was neither accompanied by an increase in malondialdehyde production nor by an increase in H2O2 generation, which attested that the effect of both drugs was not due to an increase in reactive oxygen species production. The dual effects of both cinnarizine and flunarizine on mitochondrial functions is discussed with regard to both the protective effect afforded by these drugs against ischemia-reperfusion injury and their side effect observed in some therapeutic situations where an overdosage seems likely.

Animals↗

PubMed1998

Molecular properties and pharmacokinetic behavior of cetirizine, a zwitterionic H1-receptor antagonist.

The ionization and lipophilicity behavior of the antihistamine (H1-receptor antagonist) cetirizine was investigated, showing the drug to exist almost exclusively as a zwitterion in the pH region 3.5-7.5. In this pH range, its octanol/water lipophilicity is constant and low compared to cationic antihistamines (log D = log PZ = 1.5), whereas its H-bonding capacity is relatively large (delta log PZ > or = 3.1). Conformational, electronic, and lipophilicity potential calculations revealed that zwitterionic cetirizine experiences partial intramolecular charge neutralization in folded conformers of lower polarity. Pharmacokinetic investigations have shown the drug to be highly bound to blood proteins, mainly serum albumin, and to have a low brain uptake, explaining its lack of sedative effects. As such, cetirizine does not differ from "second-generation" antihistamines. In contrast, its very low apparent volume of distribution in humans (0.4 L kg-1, smaller than that of exchangeable water) implies a low affinity for lean tissues such as the myocardium and is compatible with the absence of cardiotoxicity of the drug. The zwitterionic nature and modest lipophilicity of cetirizine may account for this pharmacokinetic behavior. The suggestion is offered that cetirizine and analogous zwitterions, whose physicochemical, pharmacokinetic, and pharmacodynamic properties differ from those of "first-" and "second-generation" drugs in this class, could be considered as "third-generation" antihistamines.

Alkanes↗

PubMed1998

Efficiency of trimetazidine in renal dysfunction secondary to cold ischemia-reperfusion injury: a proposed addition to University of Wisconsin solution.

Nonspecific injury in cadaveric renal transplants adversely affects early graft function and influences long-term graft survival after organ transplantation. Trimetazidine (TMZ) has been reported to exert a protective action against normothermic ischemia and reperfusion injury in several experimental and clinical studies. In an isolated perfused pig kidney model, we investigated the effects of TMZ added to University of Wisconsin solution (UW) during 48 or 72 h of cold storage (CS) and the consequence during reperfusion. Under all conditions tested renal perfusate flow rate (PFR), renal functions, and tubular injury markers were determined during a 120-min perfusion period. Lipid peroxidation and histological examination (optical and electron microscopy) were also determined after CS and reperfusion. The addition of TMZ (10(-6) M) to the UW solution improved dramatically the quality of preserved kidneys and consequently the functional recovery during reperfusion. TMZ + UW also significantly had a protecting role against reperfusion injury and lipid peroxidation when compared to UW alone. These results were correlated with both a better preservation of the proximal brush border membrane and reduced cellular and mitochondrial swelling. These results also suggested that the TMZ-induced renoprotection correlated well with the observed decrease membrane lipid peroxidation. Therefore, trimetazidine may be useful for clinical kidney graft preservation.

Adenosine↗

PubMed1998

Evidence for the stabilisation of the high-affinity state of beta-adrenoceptors by an endogenous factor in rat brain.

Inhibition of binding of the labelled antagonist (-)[3H]CGP 12177 by the full agonist (-)isoproterenol results in shallow competition curves, characteristic of the presence of both high- and low-affinity states of beta-adrenoceptors (betaAR). When in excess, the GTP analog 5'-guanylylimidodiphosphate (GppNHp) is expected to convert all receptors in the high-affinity state to the low-affinity state. However, in the rat cortex and cerebellum synaptosomes, a proportion of the betaAR in the high-affinity state was GppNHp-insensitive. This apparent GppNHp-insensitivity decreased with decreasing temperature of incubation. Moreover, it was totally abolished by the gentle treatment of membranes with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). We propose that a protein factor interacts with the betaAR/Gs protein complex and that it induces the GppNHp-insensitivity. This factor would be released by CHAPS in a functional form because it may regenerate the GppNHp-insensitivity after concentration and reconstitution with CHAPS-treated membranes. It is likely that the factor acts as a stabiliser of betaAR in the high-affinity state.

Animals↗

PubMed1998

Lipid peroxidation after cold storage and normothermic reperfusion: the effect of trimetazidine.

Ischemia reperfusion injury is still a leading cause of early graft dysfunction after transplantation. Trimetazidine (TMZ) has been postulated to be protective against renal damage from oxygen free radicals. The aim of this study was to assess the effect TMZ during cold storage (CS) and normothermic reperfusion in an isolated perfused pig kidney model. Three groups were studied: control group, immediately perfused (G0), 48 h CS in Euro-Collins solution (G1), and 48 h CS in Euro-Collins solution plus TMZ (G2). Glomerular filtration rate (GFR) and fractional sodium reabsorption (FRNa+) were calculated during reperfusion from urine and perfusate samples. Lipid peroxidation was determined by the renal tissue level of Schiff bases (SB) and malondialdehyde (MDA) after reperfusion. A histological evaluation was performed after reperfusion. Renal function was significantly improved and lipid peroxidation reduced after preservation in Euro-Collins solution plus TMZ. Functional data were closely related to histological damage. In conclusion, TMZ is a useful protective agent against renal damage induced by CS.

Animals↗

PubMed1998

The genetic variant A of human alpha 1-acid glycoprotein limits the blood to brain transfer of drugs it binds.

The objective of this work was to check the effects of alpha-1 acid glycoprotein (AAG) and of its components, A and F1/S genetic variants, on the brain transfer of drugs they bind in plasma. The relevant extractions of six basic drugs, highly bound to AAG, were measured. We chose three drugs selectively bound to the A variant, disopyramide, imipramine and methadone, one drug mainly bound to the mixture F1/S, mifepristone, and two drugs which were simultaneously bound to the variant A and the mixture F1/S, propranolol and chlorpromazine. Their brain extraction were investigated in rats using the carotid injection technique and the capillary depletion method. Injected drugs were dissolved either in buffer, either in native AAG containing the three variants (A, F1 and S), either in variant A or in variant F1/S solutions. Brain extractions of disopyramide, imipramine and methadone were significantly reduced by native AAG and by variant A. Drug's plasma retention was related to their preferential and almost exclusive binding to A variant, both of them exhibiting the same decrease in brain transfer as compared to a buffered solution. At the opposite, there were no significative differences between the extraction either in buffer, either in AAG or in F1/S solutions, of drugs both bound to A variant and F1/S mixture (chlorpromazine and propranolol) or to the F1/S mixture (mifepristone). In serum, the retentional effect of the A variant on the extraction of disopyramide and imipramine was counteracted by the presence of albumin and lipoproteins, which simultaneously bind these two drugs at a high extent and act as permissive binders. We conclude that AAG binding decreases brain drug transfer when the A variant is mainly and almost exclusively involved in the binding. On the contrary, the entire fraction of the tested drugs when bound exclusively or partly to the mixture F1/S is available for transfer into the brain.

Animals↗

PubMed1998

Tacrolimus decreases in vitro oxidative phosphorylation of mitochondria from rat forebrain.

The effects of tacrolimus (FK 506) on brain phosphorylation have been investigated in vitro using mitochondria isolated from rat brain. Respiratory control ratio (RCR), oxygen consumption, ATP synthesis and enzymatic activities of involved complexes have been measured to assess the mechanisms of action of tacrolimus. Our data show that this drug decreases RCR and ATP synthesis. This effect is quantitatively limited after a single application of the drug (14%), concentration-dependent and biphasic, the respective effect 50%-concentration (EC50) being 0.129 and 247 nM, each step corresponding to 50% of the total oxygen consumption inhibition. Tacrolimus acts mainly as an inhibitor of ubiquinol-cytochrome c reductase (complex III), competing at least partly with antimycin A or myxothiazol, the corresponding EC50 being 0.27 and 103 nM respectively. Tacrolimus inhibits also complex V i.e. ATPase activity (40%) and ATP synthase activity (30%) in a concentration-dependent manner, the relevant EC50 being 78 and 394 nM respectively. These data may be relevant for the protective effect of tacrolimus observed in ischemia-reperfusion, which may be due to its inhibition of both complex III, where Reactive Oxygen Species (ROS) are generated, and complex V, where ATP is depleted by ATPase activation. It may also be related to neurotoxicity occurring along chronic administration of tacrolimus in humans.

Adenosine Triphosphate↗