[The action of trimetazidine (TMZ)].
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Coronary Disease↗
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Vasoactivity of trimetazidine on guinea-pig isolated ductus arteriosus.
The effect of trimetazidine (TMZ), an anti-anginal drug, on the mechanical response of the guinea-pig ductus arteriosus placed under conditions of mild hypoxia (PO2 approximately equal to 75 mmHg) was investigated. When the PO2 of the bathing solution was 75 mmHg, TMZ caused a dose-dependent increase in tension. The median effective dose (ED50) for the drug was 8 X 10(-5)M. TMZ-induced increase in tension was not significantly affected by pretreatment of the preparation with adrenoceptor blocking agents, or indomethacin. The amplitude of the PO2-dependent tension was significantly augmented by exposure of the strip to TMZ 10(-4)M, whereas neither the resting tone (low PO2), nor the oxygen-induced contraction (high PO2) were altered. This ability of TMZ to increase the tension response during hypoxia was dependent on the external calcium concentration. Under low PO2 conditions, a contractile activity of 10(-4)M TMZ was unmasked in preparations perfused with 18 mM K+-PSS medium. This response to TMZ disappeared after the removal of calcium from the bath. At the maximally effective dose of 10(-3)M, and during low PO2, the TMZ-induced contractile response changed to a relaxation response when the external K+ concentration was raised more than five fold. The possibility that TMZ stimulates the mechanism by which oxygen normally controls the concentration of free intracellular calcium in the ductus arteriosus is proposed.
Animals↗
Therapeutic value of a cardioprotective agent in patients with severe ischaemic cardiomyopathy.
Trimetazidine (TMZ) has been shown to have anti-ischaemic properties improving exercise tolerance without haemodynamic effects. A 6-month double-blind placebo-controlled study was carried out in 20 patients, mean age 59 +/- 6 years, to examine the benefit of adding 60 mg of TMZ vs placebo to the classical therapy, excluding those previously treated with calcium-antagonists, conversion enzyme inhibitors, vasodilators and antiplatelet agents. All patients had severe ischaemic cardiomyopathy, confirmed by coronary angiography; six were in NYHA class IV; 14 in NYHA class III; four had mild recurrent angina pectoris. assessment included clinical and biological evaluation, electrocardiography (ECG), 24-h ECG monitoring, cardiac volume evaluation with chest X-ray, left ventricular fractional shortening by echocardiography, left ventricular ejection fraction by radionuclide angiography. Baseline characteristics were similar in placebo (11 patients) and TMZ (nine patients) groups. Eighteen patients (nine in each group) were followed up for 6 months. In eight patients of the placebo group, treatment had to be modified (addition of calcium antagonists: four patients, conversion enzyme inhibitors: two patients; digitalics: one patient; diuretics: one patient). In the TMZ group, digitalic therapy was withdrawn in one patient and added in one patient (P less than 0.01). At 6 months, all TMZ group patients were free from angina; dyspnoea was improved in all TMZ patients and in only one placebo patient (P less than 0.001). Ejection fraction, increased by 9.3% in the TMZ group and decreased by 15.6% in the placebo group (P less than 0.018), CV decreased by 7% with TMZ, increased by 4% with placebo. (P = 0.034).(ABSTRACT TRUNCATED AT 250 WORDS)
Angina Pectoris↗
Circadian variation in MGMT promoter methylation and expression predicts sensitivity to temozolomide in glioblastoma.
PURPOSE: Recent studies show that glioblastoma (GBM) is more sensitive to temozolomide (TMZ) in the morning. In cells, inhibiting O6-Methylguanine-DNA-Methyltransferase (MGMT) abolished time-dependent TMZ efficacy, suggesting that circadian regulation of this DNA repair enzyme underlies daily TMZ sensitivity. Here, we tested the hypotheses that MGMT promoter methylation and protein abundance vary with time-of-day in GBM, resulting in daily rhythms in TMZ efficacy. METHODS: We assessed daily rhythms in MGMT promoter methylation in GBM in vitro and retrospectively analyzed MGMT methylation status in human GBM biopsies collected at different times of day. Next, we measured MGMT and BMAL1 protein abundances in GBM cells collected at four-hour intervals. To understand the therapeutic implications of circadian variations in MGMT, we incorporated its daily rhythms into an in vitro mathematical model capturing interactions between MGMT, TMZ, and GBM DNA. RESULTS: We found daily rhythms in MGMT promoter methylation and protein levels in GBM in vitro, and in patient biopsies peaking at midday. Further, MGMT protein levels peaked at CT4, corresponding to the time of maximal TMZ efficacy in vitro. When we incorporated cell-intrinsic circadian rhythms in MGMT protein into a mathematical model for GBM chemotherapy, we found that dosing when daily MGMT levels peaked and began to decline produced maximum DNA damage. CONCLUSION: Our findings suggest that the likelihood of diagnosis of MGMT promoter methylation may vary with time of biopsy in GBM. Furthermore, theoretical modeling predicts that efforts to deliver TMZ after the daily peak of MGMT activity, with exact time being dose-dependent, may significantly enhance its therapeutic efficacy.
Humans↗
NR2F6 regulates Temozolomide resistance in glioma via the E2F2-PARP1 pathway.
BACKGROUND: Glioma is the most common primary malignant brain tumor in adults. Temozolomide (TMZ) represents a standard-of-care chemotherapeutic agent in glioblastoma (GBM). However, the development of drug resistance constitutes a significant hurdle in the treatment of malignant glioma. Elucidating the mechanisms of temozolomide (TMZ) resistance in glioma is of critical clinical importance for improving patient prognosis and developing novel therapeutic strategies. METHODS: We obtained RNA sequencing (RNA-seq) data of 648 glioma samples from The Cancer Genome Atlas (TCGA) and 325 samples from the Chinese Glioma Genome Atlas (CGGA) as study cohorts. Additionally, we validated the expression characteristics of the NR2F6 gene in our in-house cohort of glioma patients. Furthermore, we investigated the potential mechanism of NR2F6 in TMZ resistance in glioma by constructing TMZ-resistant cell lines in vitro. Statistical analyses and graphical work were primarily performed using R language and GraphPad Prism software. RESULTS: We observed a significant upregulation of NR2F6 expression in high-grade gliomas, which is associated with an unfavorable prognosis in patients. Concurrently, our findings revealed a significant upregulation of NR2F6 in drug-resistant cells, which induced TMZ resistance in glioma cells via the E2F2-PARP1 axis. CONCLUSION: In brief, NR2F6, as a nuclear transcription factor, enhances the transcription of E2F2.The increased expression of E2F2 enhances PARP1 expression, which in turn facilitates TMZ-mediated DNA damage repair, thereby diminishing glioma sensitivity to TMZ.
Journal Article↗
ERP44 Is Associated With Poor Prognosis and Promotes Proliferation and Temozolomide Resistance in Lower-grade Glioma.
BACKGROUND/AIM: Endoplasmic reticulum resident protein 44 (ERP44), a protein disulfide isomerase family member, has been implicated in tumor biology, but its role in lower-grade glioma (LGG) remains unclear. This study investigated the prognostic significance and biological function of ERP44 in LGG, focusing on proliferation and temozolomide (TMZ) resistance. MATERIALS AND METHODS: ERP44 expression, clinicopathological associations, and prognostic value were analyzed using The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Chinese Glioma Genome Atlas (CGGA) datasets. Time-dependent receiver operating characteristic (ROC) curves, Cox regression, and a prognostic nomogram were constructed. Differential expression, Gene Set Enrichment Analysis (GSEA), Gene Ontology (GO) enrichment, immune infiltration, and drug sensitivity analyses were performed. Functional validation was conducted in SW1088 and SW1783 cells using shRNA-mediated ERP44 knockdown, followed by RT-qPCR, western blotting, CCK-8, colony formation, and TMZ IC50 assays. Subcutaneous xenograft models with or without TMZ treatment were used for in vivo validation. RESULTS: ERP44 was markedly upregulated in LGG and associated with higher WHO grade, IDH wildtype status, 1p/19q non-codeletion, and poor survival in TCGA and CGGA cohorts. ERP44 showed strong prognostic performance and improved risk stratification in a multivariable nomogram. Enrichment analyses linked high ERP44 expression to immune/inflammatory pathways and reduced neuronal functional signatures. ERP44 positively correlated with immune infiltration, proliferation/stemness markers, and predicted TMZ resistance, while its knockdown inhibited proliferation and colony formation, reduced TMZ IC50, suppressed xenograft growth, enhanced TMZ efficacy, and decreased Ki67 positivity. CONCLUSION: ERP44 is a prognostic biomarker that promotes LGG proliferation and TMZ resistance, suggesting its potential as a therapeutic target.
Humans↗
The actions of trimetazidine on nerve and muscle cells in frogs.
The effect of trimetazidine (TMZ) on cardiac, skeletal muscle fibres and sympathetic ganglion cells in frogs were studied. In cardiac muscles, the contraction was depressed and the duration of action potentials were shortened by 1.5 mM TMZ. In skeletal muscles, the contraction induced by motor nerve stimulations was depressed by 0.3 mM TMZ, and the amplitude of end-plate potentials was decreased under this condition. The nicotinic transmission in sympathetic ganglia was inhibited by 0.003 mM TMZ, but the muscarinic transmission was not affected by 1.5 mM TMZ. In a Na-free TEA solution, prolonged action potentials (TEA potentials) of sympathetic ganglion cell, which appeared to be produced by an inward Ca movement across the membrane, were shortened by 1.5 mM TMZ. These results suggest that TMZ has a dual action, namely 1) a blocking action of nicotinic transmissions and 2) a blocking action of Ca movement during the generation of action potentials.
Action Potentials↗
Prophylaxis of fever and infection in adult cancer patients. A placebo-controlled trial of oral trimethoprim-sulfamethoxazole plus erythromycin.
Oral trimethoprim-sulfamethoxazole (Bactrim) plus erythromycin (TMZ-E) was tested versus placebo (P) as prophylaxis for bacterial infection in a randomized, double-blind trial in adult cancer patients receiving cytotoxic chemotherapy expected to result in significant neutropenia. The incidence of adverse reactions attributable to TMZ and/or E was higher in drug-treated episodes (18 of 28 vs 3 of 29 for P, P less than 0.0005) resulting in poorer compliance. The incidence of fever was not significantly different between episodes treated with TMZ-E (18/27) and those treated with P (17/29), nor was there a significant difference in the median interval between the onset of neutropenia and the onset of fever. However, 14 of 18 fevers in TMZ-E recipients were without a documented infectious source compared with only 6 of 17 in P recipients (P less than 0.05). The same patterns were apparent even when episodes in which compliance with the regimen was either excellent or good were considered separately. There was no significant difference in the number of deaths from infection between TMZ-E and P recipients (3/27 vs 1/29). It is concluded that TMZ-E prophylaxis is of no practical benefit, may mask the cause of infection in febrile neutropenic cancer patients, and is associated with substantial toxicity.
Adolescent↗
ABCB1 Polymorphisms Influence on Temozolomide Resistance and Overall Survival in Glioblastoma Patients: A Systematic Review of Clinical Evidence.
Glioblastoma (GB), defined as IDH-wildtype CNS WHO grade 4 tumour according to the 2021 WHO classification of CNS tumours, remains a uniformly lethal malignancy in which the efficacy of temozolomide (TMZ) continues to be constrained by both intrinsic tumur biology and the pharmacological barrier imposed by the blood-brain barrier (BBB). Given the central role of the ABCB1 (MDR1/P-glycoprotein) efflux transporter in regulating CNS drug disposition, germline variation in ABCB1 has been proposed as a potential determinant of interindividual variability in TMZ response. This systematic review synthesised clinical evidence from four independent studies, encompassing more than 400 GB patients, evaluating the association between ABCB1 polymorphisms and TMZ efficacy and patients' survival. Across the available literature, the influence of ABCB1 genetic variation emerged as limited and inconsistent. An early study reported a marked survival advantage for carriers of the ABCB1 C1236T C/C genotype treated with TMZ, suggesting reduced efflux and enhanced drug exposure. However, subsequent investigations, including epigenetic analyses, high-quality multivariate survival modelling and a pharmacokinetic study demonstrating genotype-dependent differences in plasma TMZ concentrations, did not replicate a corresponding survival effect. Across the remaining cohorts, common variants such as 1236C>T, 2677G>T/A, 3435C>T and 1199G>A showed no robust association with clinical outcome, indicating that transporter-mediated modulation is likely overshadowed by dominant prognostic drivers, including MGMT methylation, IDH status and tumour heterogeneity. Collectively, current evidence does not support ABCB1 polymorphisms as reliable predictive biomarkers of TMZ response in GB. Nonetheless, the pharmacokinetic signals observed, together with emerging technologies capable of selectively modulating efflux activity at the tumour-BBB interface, point to a continued role for ABCB1 in future therapeutic strategies. Integration of transporter genomics with spatial pharmacokinetics and molecular stratification will be essential to refine drug delivery and improve outcomes in GB.
Humans↗
[Value of trimetazidine in the long-term treatment of cardiomyopathies of ischemic origin].
The effect of a cellular anti-ischemic, trimetazidine (TMZ) in ischemic cardiomyopathies, was evaluated in a double-blind versus-placebo (P) trial, over a period of six months. 20 patients, mean age: 59.5 years, with advanced ischemic cardiomyopathy, demonstrated by left catheterization and coronary angiography, with a past history of myocardial infarction, received either 60 mg per day of TMZ (nine patients) or the placebo (eleven patients) in addition to a basic treatment of digitalis, diuretics and nitrated medications. A complete, clinical, biological and paraclinical evaluation, including chest X-ray, ultrasonography, isotopic ventriculography and 24 h-ECG, was performed upon inclusion in the study; and after three and six months of treatment. Two patients from the placebo group were not reevaluated at six months. The clinical condition, according to the NYHA classification, improved in all patients from the TMZ group, deteriorated in eight on nine patients from the placebo group (p less than 0.001). The isotopic stroke volume is preserved with TMZ, deteriorated with P. The cardiac volume decreases with TMZ, increasing with P. TMZ is beneficial clinically and functionally in advanced ischemic cardiomyopathies.
Analysis of Variance↗
Effect of phenazine methosulfate on electrophysiological activity of the semicircular canal: antioxidant properties of trimetazidine.
Ischemia strokes appear to be the main source of cochleo-vestibular dysfunctions of peripheral origin. The present study aimed to investigate the action of oxygen free radicals on the bioelectric activity of the labyrinthine epithelium, using the frog semicircular canal as an in vitro preparation. We also examined the possible effect of the antianginal drug, trimetazidine (TMZ), under physiological conditions and during the administration of phenazine methosulfate (PMS). The model allows the ionic composition of endolymphatic and perilymphatic fluids bathing the semicircular canal to be dealt with separately. Spontaneous afferent vestibular nerve activity and the endolymphatic potential were recorded under resting conditions. Three additional parameters were investigated during mechanical displacement of the endolymphatic fluid: the ampullar direct current, the nerve direct current and the frequency of the evoked afferent spikes. Addition of TMZ (10(-6) and 10(-5) M, 50 min) into the perilymphatic compartment did not induce significant modifications of the different bioelectrical signals. Generation of oxygen free radicals, through administration of PMS (10(-5) M, 15 min) into the perilymphatic compartment, caused an impairment of all bioelectrical signals, except the ampullar direct current. The spontaneous activity, nerve direct current and frequency of afferent evoked spikes signals were significantly reduced 75 min after the start of PMS administration (-64, -17 and -32%, respectively). In contrast, there was a marked increase of the endolymphatic potential signal (+51%). Addition of TMZ (10(-6) or 10(-5) M) into the perilymph solution reversed the effect of PMS on all bioelectrical signals. These results indicate that TMZ acts as an antioxidant molecule which is capable of protecting the labyrinthine epithelium from the deleterious effect of oxygen radicals. Our data suggest that the protective effect of TMZ on ischemia-induced cochleo-vestibular dysfunctions may be accounted for by the antioxidant properties of this antianginal drug.
Animals↗
Extracellular Vesicles From Glioblastoma Cells Reflect 2D vs. 3D Culture Adaptation and Resistance to Temozolomide.
Glioblastoma (GBM) is an aggressive brain tumor marked by extensive heterogeneity, resistance to therapy, and dismal prognosis. Extracellular vesicles (EVs) have emerged as key players in GBM biology, mediating intercellular communication and therapy adaptation. However, the exact functions and molecular impact of EVs in GBM remain incompletely understood. In this study, we performed a comparative proteomic analysis of U87MG GBM cells grown in two-dimensional (2D) monolayers and three-dimensional (3D) spheroids following temozolomide (TMZ) treatment, alongside characterization of EVs derived from both culture systems. 3D-spheroids secreted more EVs of smaller size and exhibited a more TMZ-resistant, stem-like proteome under TMZ-induced genotoxic stress. In contrast, 2D cell cultures demonstrated greater proteome remodeling, with EVs enriched in protein families involved in DNA repair, oxidative stress adaptation, and methylation processes. Notably, several methyltransferases were decreased intracellularly but selectively retained in EVs, suggesting active sorting to influence the tumor microenvironment or modulate epigenetic states in recipient cells. EVs also carried adhesion molecules and signaling proteins linked to migration, invasion, and Wnt pathway activation, as well as metabolic enzymes connecting serine metabolism and redox control to TMZ resistance. Mapping EV and cellular proteomes onto The Cancer Genome Atlas (TCGA) dataset identified prognostic protein families associated with either poor or favorable patient outcomes. Our data demonstrate that EV cargo composition mirrors TMZ-induced phenotypic adaptation and reveals molecular mechanisms underlying therapeutic resistance. These EV-associated signatures may serve as clinically actionable biomarkers for patient stratification and offer potential targets to overcome chemoresistance in GBM.
Humans↗
Myocardial protection during percutaneous transluminal coronary angioplasty: effects of trimetazidine.
Trimetazidine (TMZ) has recently been shown to improve anginal symptoms without altering haemodynamic variables. A randomized, double-blind, placebo-controlled study was conducted in 20 patients to study the effects of TMZ on the severity of myocardial ischaemia during PTCA of the left anterior descending coronary artery. Five minutes after a first successful dilatation (D0), a control balloon inflation (D1) was performed until onset of ischaemic signs on both the intracoronary (i.c.) and precordial ECG. Two minutes later, patients received either TMZ 6 mg or placebo i.c. Another inflation (D2) was performed 5 min after D1. No differences were found between the two groups regarding responses in heart rate, systemic and i.c. pressures during the study. TMZ decreased the maximum ST-segment shift at D2 compared with D1 (0.8 +/- 0.1 vs 1.4 +/- 0.3 mV, P = 0.023) and delayed its onset (46 +/- 4 vs 36 +/- 5 s, P = 0.024). TMZ also decreased maximum T-wave changes (1.06 +/- 0.24 vs 2.19 +/- 0.3 mV, P = 0.001), and significantly reduced the area under the curve (mv s-1) of the i.c. ST-segment and T-wave changes during balloon inflation (P = 0.042 and P = 0.009 respectively). The placebo had no effect on these parameters. These results support the hypothesis that trimetazidine has a direct anti-ischaemic effect on human myocardial cells.
Angioplasty, Balloon, Coronary↗
Inhibitory effects of trimetazidine dihydrochloride on aggregation, serotonin release and malondialdehyde production in rabbit platelets.
Aggregation, serotonin release and malondialdehyde (MDA) production via cyclooxygenase and thromboxane A2 synthetase were investigated in rabbit platelets. Trimetazidine dihydrochloride (TMZ) attenuated the collagen-induced aggregation more strongly than the arachidonic acid (AA)-, thromboxane A2 agonist (U-46619)-, Ca2+-ionophore (A-23187)- and ADP-induced aggregation: IC50 values were 1.0 +/- 0.1, 4.4 +/- 0.3, 4.3 +/- 0.4, 4.1 +/- 0.7 and 3.3 +/- 0.2 mM, respectively. TMZ decreased dose-dependently the serotonin release induced by collagen and A-23187, but did not decrease that induced by AA. TMZ also decreased the MDA production induced by collagen and A-23187 (IC50: 0.3 +/- 0.03 and 1.0 +/- 0.1 mM, respectively), but did not decrease the production induced by AA. Furthermore, TMZ decreased dose-dependently the MDA production induced by exogenous phospholipase A2. On the other hand, indomethacin (10 microM) attenuated the aggregation induced by collagen and AA, but not by the other agents, and decreased the serotonin release and the MDA production induced by collagen, A-23187 and AA. The present results suggest that TMZ may inhibit the process preceding the cyclooxygenase pathway in the AA cascade, and subsequently may attenuate the aggregation and the serotonin release via thromboxane A2 production from endogenous AA.
Animals↗
Diazepam metabolism by rat and human liver in vitro: inhibition by mephenytoin.
1. Diazepam metabolism and its association with mephenytoin hydroxylase were studied in vitro using human and rat livers. 2. Enzyme kinetic parameters were obtained for the formation of p-hydroxydiazepam (p-hydroxy-DZP), N-desmethyldiazepam (NDZ), and temazepam (TMZ) from diazepam (DZP) in rat liver fractions. The Km values for formation in rat of p-hydroxy-DZP, NDZ and TMZ were 14 +/- 3 (SEM) microM, 44 +/- 4 and 63 +/- 8, respectively; clearance values calculated from Vmax/Km were 5.7, 3.2 and 4.9 ml/g per min, respectively. 3. Mephenytoin (MP) competitively inhibited, in rat liver, the formation of NDZ, but not the formation of p-hydroxy-DZP or TMZ; in human liver neither NDZ nor TMZ formation was inhibited by MP. 4. In seven different human livers the formation of p-hydroxy-DZP represented a minor pathway compared to the formation of NDZ and TMZ.
Animals↗
Anti-ischemic effects of trimetazidine: 31P-NMR spectroscopy in the isolated rat heart.
The effects of trimetazidine (TMZ) on ischemia-induced metabolic damage were evaluated by 31P-NMR spectroscopy in the isolated rat heart. Isolated rat hearts underwent retrograde perfusion (37 degrees C, 9.81 kPa, pH 7.4, bicarbonate buffer) and were subjected to either partial global ischemia (24 min, 0.2 ml.min-1 residual coronary flow) or total global ischemia (12 min, no flow). 31P-NMR spectra (132 accumulations, 45 degrees, 101.3 MHz) were recorded every 3 min. Changes in cardiac ATP, PC and Pi were followed, and intracellular pH was estimated from the chemical shift of Pi. Trimetazidine (TMZ) was added to the perfusion fluid at the beginning of the perfusion. The drug was used at 2 concentrations: 6.10(-7) M, with no effect upon cardiac contractility under normoxic conditions, and 6.10(-4) M, which significantly depresses cardiac work. When TMZ was used at a concentration of 6.10(-7) M, intracellular acidosis at the end of the 24 min low-flow ischemia protocol was lower than in control hearts (6.6 vs 6.0). During reperfusion, restoration of phosphorylation (as expressed by ATP/Pi ratios) was accelerated by the drug. Similar but more pronounced effects were seen following 12 min total ischemia when TMZ was used at a concentration (6.10(-4) M) which brings about a reduction in cardiac work. In this case, myocardial ATP content was also protected during ischemia. It is concluded that restoration of phosphorylation processes upon reperfusion is more rapid under the effects of trimetazidine than in control hearts. Protection of the mechanisms or structures involved in energy transfer could be due to a reduction in ischemia-induced intracellular acidosis under the effect of TMZ.
Adenosine Triphosphate↗
Effect of oral contraceptives on triazolam, temazepam, alprazolam, and lorazepam kinetics.
The effects of low-dose estrogen oral contraceptives (OC) on the elimination of the oxidized benzodiazepines triazolam (TRZ) and alprazolam (ALP) and the conjugated benzodiazepines temazepam (TMZ) and lorazepam (LOR) were studied in two parallel crossover studies of 20 women each. Women taking OC steroids containing low doses of estrogen and women matched for age, weight, and cigarette smoking received single oral doses of TRZ (0.5 mg) and TMZ (30 mg) or ALP (1 mg) and LOR (2 mg). Kinetics were determined as plasma concentrations during 48 hr after dosing. OCs inhibited the metabolism of ALP: The AUC increased and the elimination rate constant was greater in users of OCs. For TRZ, which has an intermediate extraction ratio, the AUC was increased by OCs but not significantly so. In contrast, OCs decreased the AUC for TMZ and the elimination rate constants for LOR and TMZ. The AUC of LOR was not affected by OCs. Low-dose estrogen OCs may therefore inhibit the metabolism of some oxidized benzodiazepines and accelerate the metabolism of some conjugated benzodiazepines.
Administration, Oral↗
[A cellular anti-ischemic agent, trimetazidine prevents the deleterious effects of oxygen free-radicals on the internal ear].
Improvement of cochleovestibular symptoms induced by trimetazidine (TMZ) has been evidenced by clinical studies. However, a poor knowledge of the physiopathology and the scarcity of experimental models contributed to making determination of the mode of action of the drugs difficult. We studied the effect, in vitro, of TMZ on the production of oxygen-derived free radicals using, as a biological model, the isolated semicircular canal of the frog. This model allows to exert separate control over the ionic composition of the endo- and perilymphatic fluids. The spontaneous activity of the afferent nerve fibers, as well as the endolymphatic potential, were recorded at rest. Three additional parameters were analyzed, while the semicircular canal was subjected to mechanical stimulation, i.e., ampulla potential, nerve potential and the evoked frequency of action potentials. Free radical generation induced by the administration of phenazine methosulfate (PMS, 10(-5) M, 15 min) into the perilymphatic compartment, leads to a deterioration of the production of endolymph and the release of this afferent neuromediator. Inversely, PMS has no influence whatsoever on the mechanisms of mechanical-electrical transduction. The addition of TMZ (10(-6) or 10(-5) M) in the perilymphatic compartment counteracts the harmful effects of free radicals on the various bioelectric activities. These results suggest that the beneficial action of TMZ observed during treatment of cochleovestibular disorders is due, at least in part, to the anti-oxidizing properties of the molecule of interest.
Action Potentials↗