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.

Plasma coenzyme Q10 concentrations in breast cancer: prognosis and therapeutic consequences

BACKGROUND

Coenzyme Q10 or ubiquinone is a redox component of the respiratory chain, which may be involved in the pathogenesis of cancer.

METHODS

In order to better understand the role of this vitamin in the pathogenesis of breast cancer, a clinical trial including 200 women hospitalized for the biopsy and/or the ablation of a breast tumor was conducted. Ubiquinone plasma concentrations were determined simultaneously with vitamin E plasma concentrations (as antioxidant reference) by HPLC.

RESULTS

A coenzyme Q10 deficiency was noted both in carcinomas (80 patients) and non-malignant lesions (120 patients), while vitamin E concentrations were within the normal range. A correlation was shown between the intensity of the deficiency and the bad prognosis of the breast disease based on high TNM and SBR values or the lack of estrogen receptors. However, neither cathepsin D level nor adenopathy invasion was related to ubiquinone levels.

CONCLUSIONS

Since prooxidants may promote tumorigenesis, ubiquinone supplementation in breast cancer could be relevant.

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.

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.

Potential interest of anti-ischemic agents for limiting cyclosporin A nephrotoxicity

Chronic administration of cyclosporin A induces nephrotoxicity in humans. This is related to a cyclosporin A-induced constriction of afferent glomerular arterioles and mesangial cells, which leads to a decrease in filtration pressure and creatinine clearance. Afterwards, cellular lesions are observed involving mainly tubular atrophy and interstitial fibrosis, both of which are nonspecific. The initial mechanism of its toxicity is not clearly explained. The current pharmacological approach is symptomatic in order to counteract or minimize the consequences of a prime cause, which still remains to be defined. However, cyclosporin A has a deletereous effect on mitochondrial functions and mainly on ATP synthesis, which occurs when Ca2+ accumulates in matrix mitochondria. The effects of trimetazidine, an antischemic drug used in the treatment of angina pectoris, have been assessed. This drug is effective in experimental models of hypoxia induced by cyclosporin A: it restores ATP synthesis previously decreased by Ca2+ and cyclosporin A, and releases a part of Ca2+ excess accumulated by mitochondria at concentrations reached in humans at usual dosage regimens. At higher concentrations, it reverses the mitochondrial permeability transition previously generated (opened) by Ca2+ and a pro-oxidant such as terbutylperoxide (t-BH). It was also observed that trimetazidine does not modify the immunosuppressive effects of cyclosporin A in various models. These data suggest that nephrotoxicity of cyclosporin A is not irrevocably linked to its immunosuppressive effect but that it may be possible to counteract at least partly its nephrotoxic effects without altering its effectiveness in preventing graft rejection.

[Drug prescription and utilization in Morocco]

The aim of this study was to assess drug prescription and utilization in Morocco 8 years after the statement of the Action Program for Essential Drugs. To evaluate the role of essential drugs in these prescriptions, a study of about 600 prescriptions and questionnaires sent to a random sample of 111 prescribers and a series of visits with the investigator as a neutral observer was undertaken. The average number of drugs prescribed was 3.27, which reflected the feelings of most of the clinicians, for whom 3 drugs per patient is the required number. The number of drugs prescribed is lower in the public health structure (2.0 +/- 0.14 depending on the type of institution: hospital or primary health care centre). Specialties from the national list of essential drugs accounted for 15.48 per cent of all drugs which is to be compared with 16.2 per cent of the clinicians stating knowledge of the action programme for essential drugs. In public structures, these prescriptions ranged between 29.8 per cent and 82.4 per cent of the essential drugs (WHO general list). The length of the visit ranged between 3.27 +/- 0.96 min and 4.87 +/- 1.04 min according to the health centres and prescriptions included at least one antibiotic in 47.5 per cent of cases (25 per cent to 64 per cent). At least one antibiotic was prescribed in 43.3 per cent of cases in the study of prescriptions and 17.3 per cent of prescriptions included at least one injectable drug. The average cost of one prescription was 146.25 dirhams (ranging between 4 and 1200 dirhams = US $17). According to 68.6 per cent of the prescribers, the patients felt there to be a strong relation between efficacy and cost. Among the prescription motivations, cost ranked above availability of the drug and after efficacy.

[Post-lumbar puncture headache in children. Treatment with epidural autologous blood (blood patch)]

Post-lumbar puncture headaches (PLPH) are uncommon in children, but when they occur treatment is challenging. PLPH in adults have been successfully treated by the use of the epidural blood patch. This treatment has been very rarely reported in children.

CASE REPORT

A 13-year-old boy, weighing 64 kg, had a lumbar puncture as part of a work-up for a 4-day history of right hemithorax pain. This pain was associated with hypoesthesia; there were no cutaneous vesicles. Neurological examination revealed decreased strength in the left upper extremity. A magnetic resonance imaging of the cervicodorsolumbar spine was normal. Three hours after lumbar puncture, the patient complained of bifrontal headaches. The headaches worsened in the upright position and they prevented the boy from ambulating. Treatment with acetaminophen was unsatisfactory. On day 9, the initial symptoms that had motivated the lumbar puncture had disappeared, but PLPH persisted. Therefore, an epidural blood patch was performed (EBP). A 18-gauge 1 Perican needle was introduced into the peridural space at the L3-L4 interspace using the loss of resistance technique. Fifteen milliliters of blood were drawn in a sterile fashion and without anticoagulant from the patient's forearm and injected slowly through the epidural needle. The patient experienced immediate, complete, and definite relief of his PLPH. Follow-up did not show any complication.

CONCLUSION

EBP can be useful in the treatment of PLPH lasting more than 5 days in children.

Role of lipoproteins in the plasma binding of SDZ PSC 833, a novel multidrug resistance-reversing cyclosporin

AIMS

The plasma binding of the cyclosporin D analogue SDZ PSC 833 was investigated in vitro.

METHODS

The plasma total binding constant (corresponding to the bound-to-free concentration or binding ratio) was determined at 37 degrees C by the erythrocyte partitioning technique on plasma samples from three healthy volunteers and three cancer patients. Lipoproteins were also removed from plasma samples from three healthy volunteers by a standard ultracentrifugal technique.

RESULTS

SDZ PSC 833 plasma binding was 97.8 +/- 1.1% and 97.3 +/- 0.2% in samples from three healthy volunteers and three cancer patients respectively. More than 95% of blood SDZ PSC 833 was distributed in plasma. When the original plasma samples of three individuals were delipidated, SDZ PSC 833 binding was strongly decreased (58% bound to plasma proteins) and when lipoproteins were resuspended in the delipidated plasma samples to produce varying lipoprotein plasma concentrations, the binding increased continuously with the fraction of added lipoproteins. When lipoproteins were resuspended to restore the original lipoprotein plasma content, the % plasma-bound SDZ PSC 833 increased to 98.2%, close to the value observed with the original plasma (98.7%).

CONCLUSIONS

These results clearly indicate that SDZ PSC 833 plasma binding is mainly determined by lipoproteins and that in blood, most of SDZ PSC 833 is distributed in plasma.

Trimetazidine does not modify blood levels and immunosuppressant effects of cyclosporine A in renal allograft recipients

AIMS

In renal allograft recipients, trimetazidine (Vastarel) was proposed to be associated with the classic immunosuppressant treatments because it displays anti-ischaemic effects which may protect against cyclosporine A nephrotoxicity. The objective of this work was to assess the possibility of coadministering cyclosporin A, Sandimmun, and trimetazidine.

METHODS

Twelve renal transplant patients were selected on the basis of the stability of their cyclosporine A blood concentrations for the previous 3 months. They received trimetazidine, 40 mg twice daily orally for 5 days. Other coadministered drugs were kept unchanged during the study. Before and after trimetazidine administration, cyclosporine A blood concentrations, plasma interleukin-2 and soluble interleukin-2 receptor levels were measured.

RESULTS

The data showed that neither cyclosporin A blood pharmacokinetic parameters, Cmax, tmax, AUC, nor the concentrations of interleukin-2 and soluble interleukin-2 receptors were significantly modified.

CONCLUSIONS

Therefore, it was suggested that trimetazidine may be coadministered with cyclosporine A without cyclosporine A dosage adjustment.

[Mediators involved in the nephrotoxicity of cyclosporin A]

Cyclosporin A-induced nephrotoxicity is a well known adverse effect but its mechanism remains unclear. The understanding of the toxicity mechanism is necessary since the new generation of immunosuppressant drugs (cyclosporin G, FK 506, rapamycin) demonstrates renal toxicity. A renal vasoconstriction occurs with the first administration of cyclosporin and involves several mediators (prostaglandins, renal sympathetic nerves, dopamine. NO, endothelin) which may explain the limited benefit of antagonists. Furthermore, the vasoconstriction explains only haemodynamic modifications and cannot explain histological lesions. New hypotheses involving an alternation of cellular calcium homeostasis suggest alternative investigations to elucidate cyclosporin A nephrotoxicity.

Population pharmacokinetics of high-dose thiopental in patients with cerebral injuries

Thiopental monitoring was performed in 95 critically ill patients hospitalized for neurologic damage, High-dose thiopental was infused during long-term treatment. Total dose of 333 +/- 144 mg/kg (449 +/- 185 mg/kg for females and 302 +/- 113 mg/kg for men) were given in 125 +/- 43 hours. Plasma concentration-time data were analyzed according to a population pharmacokinetic approach with an initial group of 65 patients. Clearance (CL) and central volume of distribution (Vc) were modeled alone and under the influence of demographic covariates, assuming a two-compartment open model with first-order elimination. The final population models were as follows: CL (L/hr) = 11.7.weight (kg).age (yr)/(2136 + age2) and Vc = 1.52.weight (kg) + 44.8. Mean CL and Vc mean population estimates were 8.01 L/hr (133 ml/min or 2.02 ml/min/kg) and 145 L (2.19 L/kg). The predictive performance of the population modeling and parameters was evaluated with a bayesian fitting procedure in an independent validation set of 30 patients with similar physical and clinical characteristics. There was no statistically significant bias or imprecision between measured and predicted thiopental plasma concentrations in this validation group. Moreover, there was a good adequation (r = 0.939) between individual CL values predicted from the population formula and estimated with the bayesian approach.

Melatonin high-affinity binding to alpha-1-acid glycoprotein in human serum

The binding of 3H-melatonin to human serum proteins was investigated by equilibrium dialysis at 37 degrees C and pH 7.4. The binding to serum was moderate (53%) for physiological melatonin concentrations below 1 nmol/L. alpha 1-Acid glycoprotein and albumin bound melatonin with high 27 +/- 3 and low 1.5 +/- 0.1 (mmol/l)-1 affinity, respectively. Melatonin binding to other serum proteins, gamma-globulins and lipoproteins was not significant. The serum binding was characterized by a saturable and a nonsaturable component. The saturable component resulted from the high-affinity binding to alpha 1-acid glycoprotein and the nonsaturable component resulted from the low-affinity binding to albumin. The number of binding sites was 0.36/molecule of alpha 1-acid glycoprotein, when either pure alpha 1-acid glycoprotein or serum were studied, indicating that only a fraction of alpha 1-acid glycoprotein bound melatonin. The observed binding parameters did not enable simulation of the observed serum binding, and melatonin binding to an alpha 1-acid glycoprotein-albumin mixture was higher than that expected from the binding to each isolated protein. The high-affinity melatonin binding to alpha 1-acid glycoprotein might result from a potentiation of the binding interaction by albumin and the amount of melatonin bound in plasma might vary according to the alpha 1-acid glycoprotein concentration.

Blood-to-brain transfer of various oxicams: effects of plasma binding on their brain delivery

PURPOSE

The objective of this work was to assess the influence of binding to plasma proteins and to serum on the brain extraction of four antiinflammatory oxicams.

METHODS

The brain extraction of isoxicam, tenoxicam, meloxicam and piroxicam was investigated in rats using the carotid injection technique. Blood protein binding parameters were determined by equilibrium dialysis using human serum, human serum albumin (HSA) and alpha-l-acid glycoprotein (AAG) solutions at various concentrations.

RESULTS

All oxicams had low values of brain extraction, between 19% and 39% when dissolved in serum, i.e. under physiological conditions. Brain efflux rate constants calculated from the wash-out curves were the same in the absence or presence of serum. Brain efflux was inversely related to the polarity of the oxicams, such that the higher their H-bonding capacity, the lower their brain efflux. The free dialyzable drug fraction was inversely related to protein concentration. However, rat brain extraction was always higher than expected from in vitro measurements of the dialyzable fraction.

CONCLUSIONS

Except for piroxicam whose brain extraction was partially decreased in the presence of proteins, the serum unbound and initially bound fractions of oxicams both seem available for transfer into the brain. Modest affinities for AAG rule out any related effect. More surprising is the apparent lack of effect on brain transfer of the high-affinity binding to HSA and serum. The enhanced brain uptake of meloxicam in the presence of AAG could be a result of interactions between this globular protein and the endothelial wall.

pH dependent binding of ligands to serum lipoproteins

PURPOSE

The binding interactions of binedaline, nicardipine and darodipine with lipoproteins (HDL, LDL, VLDL) were examined as a function of pH in order to evaluate the role of lipoprotein components and ligand protonation in the binding process.

METHODS

Binding studies were performed by equilibrium dialysis with radiolabeled ligands and differential UV-visible spectroscopy.

RESULTS

Deprotonated ligands had a markedly higher affinity for lipoproteins than the protonated forms, resulting in a concomitant decrease in the pKa of bound ligands, i.e., a decrease in the basicity of the ligand in the bound state. The UV-visible difference spectra generated upon binding of auramine O to lipoproteins also showed that there was a contribution to the binding arising from the deprotonation of the ligand. Ligand binding was related to the phospholipid and cholesteryl ester content and to a lesser degree to the free cholesterol and protein content of lipoproteins, therefore to the surface monolayer components of lipoproteins. This relationship was even more accurate for the deprotonated, high-affinity, than for the protonated species.

CONCLUSIONS

It is suggested that among other possible interactions, ligand binding to lipoproteins involves proton exchange between the reactants and that the high affinity ligand species interact more specifically with the phospholipids of the lipoprotein surface monolayer.

[Value of protecting mitochondrial functions during treatment with cyclosporin A]

The use of cyclosporin A is often limited by its nephrotoxicity. This dose-dependent toxicity can occur in all kinds of transplantation and is reversed with drug withdrawal. Cyclosporin A induces a vasoconstriction leading to an increase of renal vascular resistance and a reduction of glomerular filtration. Histochemical studies show mitochondrial alterations and an excess of cytosolic and mitochondrial calcium leading to a decrease of ATP synthesis. Two strategies can be evoked for limiting cyclosporin-A-induced nephrotoxicity. First, the use of drugs counteracting the vasoconstriction has been proposed. Second, drugs acting by restoration of ATP synthesis could also be of interest. For example, calcium channel blockers may be used for limiting the Ca2+ fluxes into cells. Another way to protect ATP synthesis is to inhibit the cyclosporin-A-induced increase of mitochondrial Ca2+ concentrations; Trimetazidine has shown its efficiency in vitro for protecting mitochondria against these modifications of Ca2+ homeostasis and is under clinical evaluation.

[Mycophenolate mofetil, a new immunosuppressive agent. Is pharmacokinetic monitoring justified?]

Mycophenolate mofetil is a new immunosuppressive agent which is indicated in combination with cyclosporin A and a corticosteroid for the prophylaxis of acute transplant rejection in patients receiving allogenic renal transplants. It is an ester prodrug rapidly hydrolysed to mycophenolic acid, an active metabolite. The mechanism of action of mycophenolic acid is different from that of other known immunosuppressive drugs: it inhibits the activity of inosine monophosphate deshydrogenase, an enzyme responsible for the de novo pathway of guanosine nucleotide synthesis in B and T lymphocytes and slows down their proliferative response. Should mycophenolic acid plasma concentrations be monitored? To date, all available data are assessed and more particularly:--the doses of 1 or 1.5 g administered twice daily,--a pilot, open-label multicentre study which showed a decreased incidence of acute rejection episodes in patients with steady state AUC0-12 h plasma levels < 40 micrograms.ml-1.h.--adverse events (mainly gastrointestinal, blood and lymphatic disorders) which appear more frequently in patients receiving 3 g/day than in patients receiving 2 g/day and which do not seem to be correlated with plasma concentrations of mycophenolic acid. The examination of these data clearly shows that additional investigations are necessary to better clarify the relationship between plasma mycophenolic acid concentration and side effects in order to provide a scientific rationale for monitoring the plasma concentrations on a regular basis.

In vitro targeting and specific transfection of human neuroblastoma cells by chCE7 antibody-mediated gene transfer

We developed a new vector for gene targeting of neuroblastoma (NB) cells, based on the utilization o a monoclonal antibody (chCE7) covalently linked to polylysine (PL). In the presence of chloroquine, chCE7-PL-DNA complexes transfected NB cells as efficiently as DOTAP, transfectam, TF-X50, or lipofectamine. This was demonstrated by transfection of the luciferase or beta-galactosidase reporter genes in three different NB cell lines. This transfection was specific, since it was inhibited in the presence of competing unconjugated chCE7 antibody (Ab), and was not observed in cell lines negative for the CE7 antigen. We tested the potential biological activity of a plasmid coding for gamma-interferon (gamma IFN) transfected with chCE7-PL. HLA ABC expression on NB cells was induced after transfection with pCMV-gamma IFN at a higher level than after incubation with 1000 IU/ml of purified gamma IFN. Moreover, these HLA ABC-positive NB cells were able to activate autologous cytotoxic T lymphocytes in vitro. Thus chCE7-PL is able to target a plasmid to NB cells and to allow the expression of the transfected gene in a biologically active form.

[The Cochrane Collaboration, support of therapeutic information]

Today, prescribers need to distinguish between the clinical practices based on randomized clinical trialing information and those based on animal physiological data or theory. Now the information on therapeutics is becoming more dense, more complex and less available to the clinicians. Information sources are numerous and varied, including data whose quality differs. These data are unhierarchised in terms of methodological quality and clinical relevance. It will be optimal if each prescriber could himself collect and analyse scientific information. In fact this situation cannot be effective in private physician's practices. An international collaboration, the Cochrane Collaboration, including volunteers, university researchers, and clinical investigators has the following objective: to prepare, maintain and disseminate systematic reviews of the effects of health care. The Cochrane Collaboration is thus the most adapted intermediairy between scientifically actualized data and clinical practitioners.

Prednisolone and azathioprine worsen the cyclosporine A-induced oxidative phosphorylation decrease of kidney mitochondria

We investigated the effects of cyclosporine A, prednisolone and azathioprine on respiration rates, Ca2+-induced swelling and Ca2+ fluxes of rat kidney mitochondria. The three drugs significantly decreased the succinate induced-respiration rates according to concentration-dependent processes. Each drug inhibited about 10% of the respiratory control ratio, with EC50 of 3.7 x 10(-7) M, 5.8 x 10(-9) M for cyclosporine A and azathioprine respectively. Prednisolone was the most effective (19.2%) acting by a two-step process with EC50 of 9.2 x 10(-12) M and 1.9 x 10(-8) M. The combination of the three drugs developed a higher significant decrease of respiratory control ratio than that of each drug but lower than the sum of their respective effects. Inhibitions of swelling and Ca2+ fluxes through mitochondrial membrane due to the combination were not different from those induced by cyclosporine A alone. The action mechanisms of cyclosporine A and prednisolone were total and partial Ca2+ dependent respectively. Azathioprine appears to act by a Ca2+-independent one. It is concluded that azathioprine and prednisolone may worsen cyclosporine A-induced renal mitochondrial alteration of oxidative phosphorylation.