Biomedical subjects

Jean-Paul Tillement

Publications and source records attributed to Jean-Paul Tillement.

14 recordsLinked to original sources

PubMed2004

Role of the permeability transition pore in cytochrome C release from mitochondria during ischemia-reperfusion in rat liver.

Ischemia and reperfusion cause mitochondrial dysfunctions that initiate the mitochondrial apoptosis pathway. They involve the release of cytochrome C and the activation of the caspase cascade but the mechanism(s) leading to cytochrome C release is(are) poorly understood. The aim of this study was to analyse the relation between cytochrome C release and the opening of the permeability transition pore (PTP) during in situ liver ischemia and reperfusion. Liver ischemia was induced for 30, 60 and 120 min and blood re-flow was subsequently restored for 30 and 180 min. Ischemia hugely altered mitochondrial functions, i.e., oxidative phosphorylation and membrane potential, and was accompanied by a time-dependent mitochondrial release of cytochrome C into the cytosol and by activations of caspases-3 and -9. PTP opening was not observed during ischemia, as demonstrated by the absence of effect of an in vivo pre-treatment of rats with cyclosporin A (CsA), a potent PTP inhibitor. Cytochrome C release was due neither to a direct effect of caspases onto mitochondria nor to an interaction of Bax or Bid with the mitochondrial membrane but could be related to a direct effect of oxygen deprivation. In contrast, during reperfusion, CsA pre-treatment inhibits cytochrome C release, PTP opening and caspase activation. At this step, cytochrome C release is likely to occur as a consequence of PTP opening. In conclusion, our study reveals that cytochrome C release, and thus the induction of the mitochondrial cell death pathway, occur successively independently and dependent on PTP opening during liver ischemia and reperfusion, respectively.

Animals↗

PubMed2004

Long-term exposure to nicotine modulates the level and activity of acetylcholine receptors in white blood cells of smokers and model mice.

Long-term consumption of tobacco by smokers causes addiction and increases the level of neuronal nicotinic acetylcholine receptors (nAChRs) in the brain, a phenomenon known as up-regulation. Here, we show that up-regulation of specific nAChR subunits takes place in white blood cells (WBCs) of smokers and mice subjected to long-term administration of nicotine. The basal level of alpha-bungarotoxin binding site, which corresponds to the homomeric alpha7 nAChR subtype, was not affected in WBCs of both smokers and mice administered nicotine. In contrast, epibatidine (EB) binding sites, which correspond to heteromeric nAChR subtypes, were detected in WBCs of smokers but not in WBCs of nonsmokers. The number of EB binding sites significantly decreased after incubation of the smokers' WBCs for 3 days in nicotine-free culture medium. In WBCs of wild-type mice, basal level of EB binding sites was detected before nicotine administration. This basal level is reduced by approximately 60% in knockout mice lacking the genes encoding either the beta2 or the alpha4 receptor subunits. Additional analysis of knockout mice revealed that the remaining approximately 40% do not undergo up-regulation, indicating that the alpha4/beta2 subunits comprise the up-regulated nAChRs. We further found that upregulation in mouse WBCs is accompanied by a significant decrease in the capacity of the up-regulated receptor channels to convey calcium ions. The phenomenon of nAChR up-regulation in WBCs provides a simple tool to evaluate and study tobacco addiction.

Animals↗

PubMed2004

Protection by cyclosporin A of mitochondrial and cellular functions during a cold preservation-warm reperfusion of rat liver.

Liver transplantation is an effective therapeutic option for end-stage liver disease, but initial poor graft function still occurs, often related to cold preservation-warm reperfusion (CPWR) conditions. Damages to mitochondria could be implicated in hepatocyte cell death since opening of the permeability transition pore (PTP) can lead to necrosis and apoptosis. The purpose of this study was to test the hypothesis that inhibition of mitochondrial permeability transition by cyclosporin A could improve rat liver mitochondrial and hepatocellular parameters after 24-h cold preservation followed by a warm reperfusion in Krebs-Henseleit Buffer. Mitochondrial functions were assessed by measuring respiratory parameters, swelling, cytochrome c release and caspases activation. Hepatocyte injury was assessed by evaluation of ATP energetic charge, lactate dehydrogenase (LDH) leakage, apoptosis and necrosis. Results show that CPWR induces liver mitochondrial and cellular damages. CPWR induced damages on the mitochondrial respiratory chain, leading to mitochondrial swelling. The consequences are the loss of ATP energetic charge, the initiation of apoptosis through cytochrome c release and the activation of caspases. Cyclosporin A partially protects respiratory chain integrity and totally prevents mitochondrial swelling, allowing better recovery of energetic charge. It also partially limits the activation of the apoptotic machinery and subsequent cell death by apoptosis in both the organ and isolated hepatocytes. Inhibition of permeability transition thus provides only partial protection against CPWR. However, this target can be considered as a promising adjunct therapeutic approach to improve the primary function of the grafted liver after transplantation.

Animals↗

PubMed2004

Fluoride curcumin derivatives: new mitochondrial uncoupling agents.

The mitochondrial effects of two fluoride curcumin derivatives were studied. They induced the collapse of mitochondrial membrane potential (DeltaPsi), increased mitochondrial respiration, and decreased O(2)*- production and promoted Ca(2+) release. These effects were reversed by the recoupling agent 6-Ketocholestanol, but not by cyclosporin A, an inhibitor of the permeability transition pore (PTP), suggesting that these compounds act as uncoupling agents. This idea was reinforced by the analysis of the physico-chemical properties of the compounds indicating, that they are mainly in the anionic form in the mitochondrial membrane. Moreover, they are able to induce PTP opening by promoting the oxidation of thiol groups and the release of cytochrome c, making these two molecules potential candidates for induction of apoptosis.

Animals↗

PubMed2004

Effects of curcumin and curcumin derivatives on mitochondrial permeability transition pore.

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is a natural compound with antiproliferative properties. Recent studies suggest that these properties might be due to the ability of curcumin to induce apoptosis in tumor cells by increasing the permeability of the mitochondrial membrane. In the present study, we confirm these observations and provide a molecular mechanism for the action of curcumin in rat liver mitochondria. Curcumin induced mitochondrial swelling, the collapse of Deltapsi, and the release of cytochrome C, events associated with the opening of the permeability transition pore (PTP). Experiments were performed with chemically substituted curcumin derivatives. Some derivatives were obtained by modification of groups on the terminal aromatic rings, and others were obtained by substitution of the diketone function with the cyclohexanone function. They demonstrated that phenol and methoxy groups were essential to promote PTP opening. Curcumin and curcumin derivatives that open the PTP were able to oxidize thiol groups. In addition, PTP opening was abolished in medium devoid of O2 and decreased in the presence of catalase, ferrozine, o-phenanthroline, mannitol, or N-ethylmaleimide. These data suggest that the mechanism by which curcumin promotes PTP opening involves the reduction of Fe3+ to Fe2+, inducing hydroxyl radical (HO*) production and oxidation of thiol groups in the membrane, leading to pore opening.

Animals↗

PubMed2003

Glycosylation study of the major genetic variants of human alpha1-acid glycoprotein and of their pharmacokinetics in the rat.

Human alpha1-acid glycoprotein (AAG) is a mixture of at least two genetic variants, the A variant and the F1 and/or S variant or variants, which are encoded by two different genes. AAG is also an extensively glycosylated protein which possesses five N-linked glycans exhibiting substantial heterogeneity in their structures. The first objective of this study was to investigate the glycosylation of the two major gene products of AAG, i.e. the A variant and a mixture of the F1 and S variants (F1*S). To this end, we combined a chromatographic method for the fractionation of the AAG variants with a lectin-binding assay to characterise the glycosylation of purified glycoproteins. Secondly, because the oligosaccharides can influence the disposition of AAG, a kinetic study of the AAG variants was carried out in the rat. After intravenous administration of whole human AAG, the separation and quantification of the AAG variants in plasma was performed by application of specific methods by isoelectric focusing and immunonephelometry. The binding studies carried out on a panel of lectins showed significant differences in the lectin-binding characteristics of the separated F1*S and A variants, accounting for differences in the degree of branching of their glycan chains and substitution with sialic acid and fucose. The plasma concentration-time profiles of the F1*S and A variants were biphasic, and only small differences were observed between the variants for their initial and terminal half-lives, clearance and distribution volume. This indicates that the structural differences between the two AAG gene products do not affect their pharmacokinetics in the rat. Specific drug transport roles have been previously demonstrated for the F1*S and A variants, calling for further investigations into their effects on the disposition of drugs they bind in plasma. The present study shows that such investigations are possible without being complicated by kinetic differences between these variants.

Animals↗

PubMed2003

[3H]BHDP as a novel and selective ligand for sigma1 receptors in liver mitochondria and brain synaptosomes of the rat.

The binding profile of [(3)H]BHDP ([(3)H]N-benzyl-N'-(2-hydroxy-3,4-dimethoxybenzyl)-piperazine) was evaluated. [(3)H]BHDP labelled a single class of binding sites with high affinity (K(d)=2-3 nM) in rat liver mitochondria and synaptic membranes. The pharmacological characterization of these sites using sigma reference compounds revealed that these sites are sigma receptors and, more particularly, sigma1 receptors. Indeed, BHDP inhibited [(3)H]pentazocine binding, a marker for sigma1 receptors, with high affinity in a competitive manner. BHDP is selective for sigma1 receptors since it did not show any relevant affinity for most of the other receptors, ion channels or transporters tested. Moreover, in an in vitro model of cellular hypoxia, BHDP prevented the fall in adenosine triphosphate (ATP) levels caused by 24 h hypoxia in cultured astrocytes. Taken together, these results demonstrate that [(3)H]BHDP is a potent and selective ligand for sigma1 receptors showing cytoprotective effects in astrocytes.

Adenosine Triphosphate↗

PubMed2003

Compared pharmacological characteristics in humans of racemic cetirizine and levocetirizine, two histamine H1-receptor antagonists.

The potent histamine H(1)-receptor antagonist cetirizine (Zyrtec) is a racemic mixture of levocetirizine (now available under the trademark Xyzal and dextrocetirizine. In this Commentary, we examine some biological properties of cetirizine and levocetirizine, namely enantioselectivity in pharmacological activity and pharmacokinetic properties, with emphasis on the possibility of racemization, the compared behavior of the two enantiomers, and the potential for interactions with other drugs. Recent data demonstrate that the antihistaminergic activity of the racemate is primarily due to levocetirizine. Levocetirizine is rapidly and extensively absorbed, poorly metabolized, and not subject to racemization. Its pharmacokinetic characteristics are comparable after administration alone or in the racemate. Its apparent volume of distribution is smaller than that of dextrocetirizine (0.41 L kg(-1) vs. 0.60 L kg(-1)). Moreover, the non-renal (mostly hepatic) clearance of levocetirizine is also significantly lower than that of dextrocetirizine (11.8 mL min(-1) vs. 29.2 mL min(-1)). Our conclusion is that levocetirizine is indeed the eutomer of cetirizine. The evidence reviewed here confirms preclinical findings and offers a rationale for the chiral switch from the racemate to levocetirizine.

Acetates↗

PubMed2003

Anoxia-reoxygenation-induced cytochrome c and cardiolipin release from rat brain mitochondria.

Rat brain mitochondria were successively submitted to anoxia and reoxygenation. The main mitochondrial functions were assessed at different reoxygenation times. Although the respiratory control ratio decreased, the activity for each one of the enzymes participating in the respiratory chain was not affected. However, during reoxygenation, mitochondrial membrane lipoperoxidation quickly increased and was proportional to the decrease seen in membrane fluidity. Under the same conditions, cytochrome c and cardiolipin were released from mitochondria and their rate of release increased with reoxygenation time. The release of cytochrome c and cardiolipin was followed by the collapse of the membrane potential and it was not inhibited by cyclosporin A. Addition of the antioxidant alpha-tocopherol abolished all these reoxygenation-induced changes. These data indicate that, in this model, reoxygenation promotes the uncoupling of respiratory chain, and cytochrome c and cardiolipin releases. These events are not related to the membrane potential collapse but to an oxidative stress.

Animals↗

PubMed2003

Tacrolimus and sirolimus decrease oxidative phosphorylation of isolated rat kidney mitochondria.

1. Tacrolimus and sirolimus are potent immunosuppressors used in transplantation. Tacrolimus has been suspected to alter mitochondrial respiration of different tissues but sirolimus has not been evaluated. 2. We evaluated the in vitro effect of tacrolimus and sirolimus on oxidative phosphorylation of isolated rat kidney mitochondria. 3. Oxygen consumption was measured with a Clark-type electrode. Tacrolimus and sirolimus increased the resting rate (state 4) and had no significant effect on ADP-stimulated respiration (state 3). The decrease of respiratory control ratio was concentration-dependent with a biphasic curve for tacrolimus. The EC(50)s were 3.4 x 10(-11) M and 2.3 x 10(-8) M for tacrolimus and 4.4 x 10(-10) M for sirolimus. The maximal inhibition was 20 and 14% for tacrolimus and sirolimus, respectively. 4. Tacrolimus and sirolimus had an uncoupling effect on oxidative phosphorylation related to a decrease of the inner membrane fluidity. At the opposite of cyclosporin A, no effect on swelling or Ca(2+) fluxes was observed. 5. All events occurred at therapeutic concentrations and then could appear during long-term treatment. Cellular consequences such as chronic nephrotoxicity with tacrolimus are suggested. The risk of cyclosporin A nephrotoxicity potentiation by sirolimus is discussed.

Animals↗

PubMed2002

Resveratrol-induced limitation of dysfunction of mitochondria isolated from rat brain in an anoxia-reoxygenation model.

Resveratrol protection on the main functions of purified rat brain mitochondria submitted to anoxia-reoxygenation was investigated. Resveratrol (<0.1 microM) reversed partly (23.3%) the respiratory control ratio (RCR) decrease by protecting both states 3 and 4. This effect was both observed when resveratrol was added before anoxia or reoxygenation. Resveratrol fully inhibited the release of cytochrome c in a concentration-dependent manner and significantly decreased the superoxide anion (O2(0-)) production at a concentration of 1 nM. The mitochondrial membranes damaged after the anoxia-reoxygenation were partly protected (about 70%) by resveratrol at 0.1 microM. The oxygen consumption of mitochondria in presence of NADH and cytochrome c was significantly inhibited by resveratrol with a low EC50 of 18.34 pM. Resveratrol inhibited the CCCP-induced uncoupling from about 20%. The effects of resveratrol on oxidative phosphorylation parameters were also investigated in rats after pretreatment (0.4, 2 and 10 mg/kg/day) for one week. After the isolation of brain mitochondria, the RCR was significantly less decreased in the resveratrol group compared to the control group. These results showed that resveratrol could preserve the mitochondrial functions with at least three mechanisms: antioxidant properties, action on complex III and a membrane stabilizing effect.

Animals↗

PubMed2002

Evidence for sigma-1-like receptors in isolated rat liver mitochondrial membranes.

1. Sigma (sigma) receptors have generated a great deal of interest on the basis of their possible roles in various pathologies, including cytoprotection. Although the exact function of sigma-1 (sigma(1)) receptors is not yet known, their role in the regulation of intracellular Ca(2+) levels and sterol biosynthesis, functions that could be assigned to mitochondria, are the only mechanisms described. 2. Using preparations of purified rat liver and brain mitochondria we demonstrate herein the presence of sigma-like binding sites. [(3)H](+)-pentazocine, a sigma(1) radioligand was used to label these sites. 3. In the liver, [(3)H](+)-pentazocine labelled one class of binding sites with high affinity (K(d)=3 nM), similar to that observed in liver microsomes and synaptic membranes. These sites were located on the outer mitochondrial membranes and displayed high affinity for other sigma(1) ligands namely, haloperidol, ifenprodil, carbetapentane or 1,3-di(2-tolyl)guanidine (DTG). 4. The presence of sigma(1) receptors on liver mitochondria was confirmed using double fluorescence immunostaining. 5. [(3)H](+)-pentazocine binding sites were also found on brain mitochondria but they appeared pharmacologically distinct to the liver ones as [(3)H](+)-pentazocine and typical sigma(1) ligands displayed lower affinities for these sites. Nevertheless, [(3)H](+)-pentazocine binding on both liver and brain mitochondria was modulated by progesterone, a putative endogenous ligand for sigma receptors. 6. Our data demonstrates the presence of [(3)H](+)-pentazocine binding sites with pharmacological characteristics identical to sigma(1) receptors on rat liver mitochondrial membranes. The pharmacological significance of these sites and their role on mitochondrial function remain unknown.

Animals↗

PubMed2002

Blood distribution of levocetirizine, a new non-sedating histamine H1-receptor antagonist, in humans.

The aim of the present study was to determine (1) the extent of levocetirizine binding to human blood cells, plasma and individual plasma proteins; (2) the parameters for levocetirizine binding to individual plasma proteins both at their physiological concentrations and, for human serum albumin (HSA), at a lower saturating concentration; and (3) to simulate levocetirizine distribution in human blood using the information obtained at physiological haematocrit (H) for blood cells and at physiological concentrations for individual plasma proteins. The nature of the main binding sites of HSA, i.e. site I (warfarin) and site II (diazepam), preferentially involved in levocetirizine binding was also investigated. Over the range of therapeutic concentrations and multiples thereof, levocetirizine is extensively bound to blood components, the free fraction remaining constant (6.45%) and the fraction bound to blood cells and to plasma proteins accounting for 27.43 and 66.11%, respectively. The binding of levocetirizine to HSA in the presence of physiological concentrations of non-esterified fatty acids (NEFAs) is the main interaction of levocetirizine in blood (50.68% of overall blood binding). This interaction is fatty acid sensitive, with decreasing concentrations of NEFA increasing the amount of bound drug and vice versa. Levocetirizine is also bound to alpha1-acid-glycoprotein and high-density lipoproteins (5.17 and 6.89% of overall blood binding, respectively). The displacement of levocetirizine by diazepam is consistent with the binding of this drug to HSA at site II, as diazepam is a specific marker for this site. The binding of levocetirizine to HSA at site II being characterized by a low association constant, other drugs sharing the same site with high association constants cannot displace levocetirizine except at very high plasma concentrations. In any case, at therapeutic concentrations of levocetirizine and at physiological protein concentrations, the observation that none of the levocetirizine binding proteins is saturated suggests that very little or no variation of the free fraction will occur although a different distribution of its bound forms is possible.

Acetates↗

PubMed2000

Trimetazidine reduces renal dysfunction by limiting the cold ischemia/reperfusion injury in autotransplanted pig kidneys.

Ischemia/reperfusion injury leads to delayed graft function, which is a major problem in kidney transplantation. This study investigated the effects of adding trimetazidine (TMZ) to the perfusate of cold-stored kidneys on the function of reperfused autotransplanted pig kidney. The left kidney was removed and cold-flushed with Euro-Collins (EC), or University of Wisconsin (UW) solutions with or without 10(-6)M TMZ and stored for 48 h at 4 degrees C. The kidneys were then autotransplanted and the contralateral kidneys were removed. Several parameters were analyzed over the 14 d after transplantation. The survival rate was 57% in pigs transplanted with kidneys cold-flushed with UW and 43% for those flushed with EC solution; it was 100% for pigs having kidneys cold-flushed with TMZ-supplemented UW and EC solutions. The functions of the transplanted kidneys were also better preserved after cold flush with TMZ-supplemented solutions than with TMZ-free solutions. Creatinine clearance was higher and the urinary excretion of trimethylamine-N-oxide and dimethylamine, used as markers of renal medulla injury, were lower in animals transplanted with kidneys cold-flushed with TMZ-supplemented solutions than with TMZ-free solutions. The cytoprotective action of TMZ also reduced interstitial and peritubular inflammation and the numbers of infiltrating mononuclear CD45+and CD3+ T cells. These results indicate that the tissue damage due to ischemia/reperfusion injury may be prevented, at least in part, by adding TMZ to preservation solutions.

Animals↗