Relative cytotoxicity of psychotropic drugs in cultured rat hepatocytes

Cytotoxicity of 28 MEIC Chemicals to Rat Hepatocytes using Two Viability Endpoints: Correlation with Acute Toxicity Data in Rat and Man

28 of the chemicals on the MEIC list were tested on rat hepatocytes in culture. Firstly, the metabolic capacities of the cell model were characterised, i.e. cytochrome P450 content and conjugation activities. Two independent endpoints, MTT (tetrazolium salt) reduction (for mitochondrial integrity) and neutral red uptake (NRU, for lysosomal integrity), were then used to measure the cytotoxicities of the test compounds after incubation with the cells for 24 hours. The relative toxicities of the test chemicals were measured by the determination of IC50 values for each parameter. Statistical analysis revealed a correlation between the results obtained in the two assays. The NRU assay, however, proved to be more sensitive than the MTT reduction assay. When the in vitro results were compared with those obtained from an in vivo data bank, good agreement was found with the acute toxicities of the test products in rats, with the exception of thioridazine, malathion, copper sulphate (all overestimated) and potassium cyanide (underestimated). In addition, a good correlation between basal cytotoxicity values for rat hepatocytes and LD50 for rats or lethal doses for humans was observed. These results suggest that the MTT reduction and/or NRU assays could be useful indicators of the cytotoxic potential of chemicals in rat hepatocyte cultures and thus provide information on the intrinsic lethal toxicity of compounds and their metabolites to rats and humans.

Comments on the Use of Diverse Cell Systems in Toxicity Testing

To initiate a discussion of the relative merits of various cell systems in acute toxicity testing we have considered the suitability of seven systems in testing three types of toxicity i.e. systemic toxicity in general, systemic toxicity to specific target organs, and local toxicity Available data indicate that systemic toxicity can be predicted by simple systems with non-differentiated cell lines, as well as by primary cultures of hepatocytes. The combined use of both cell systems is probably the method of choice. Specific, cellular, target organ toxicity is often tested in primary cultures of various specific cells. Such use of these cells seems to be irrational, and ought to be replaced by a parallel use of specific and non-specific cell cultures. An analysis of the differential cytotoxicity to both cell types would then point out specific target organ toxicity. It is uncertain whether non-specific cell lines or primary cultures of target-specific cells should be used in tests of local toxicity. Future parallel use of both cell types to produce data on differential cytotoxicity would settle the question.

In vitro and in vivo toxicity evaluation of non-neuroleptic phenothiazines, antitubercular drug candidates

The phenothiazine-derived antipsychotic drugs, such as chlorpromazine and thioridazine, are bactericidal against drug-sensitive and drug-resistant strains of Mycobacterium tuberculosis, but produce undesirable side effects at clinically relevant doses. We have previously modified four novel phenothiazines and maintained their antimycobacterial activity. This study evaluated the pharmacological and toxicity profiles of these novel non-neuroleptic phenothiazines, PTZ3, PTZ4, PTZ31 and PTZ32, for their metabolic stability, kinetic solubility and potential cytotoxic effects in vitro. To further support the safet use of these drug candidates, the in vivo pharmacological and toxicity profiles were assessed in C57BL/6 mice via single or repeated oral gavage. In acute toxicity studies, all four modified phenothiazines showed favourable safety in mice. When treated daily with 100 mg/kg of PTZ3 and PTZ4 for 2 weeks, mice displayed no signs of toxicity. Alternatively, treatment with PTZ31 resulted in 20% mortality with no toxicity evident in biochemical or histological analysis, while exposure to PTZ32 resulted in a 45% survival with increased serum concentrations of uric acid and alkaline phosphatase. The combined non-neuroleptic and antimycobacterial effects of the novel phenothiazines PTZ3, PTZ4, PTZ31 and PTZ32 demonstrated favourable pharmacological and toxicity profiles in this study, highlight the potential of these compounds as suitable anti-tuberculosis drug candidates.

Transcriptomic hepatotoxicity signature of chlorpromazine after short- and long-term exposure in primary human sandwich cultures

Drug-induced liver injury is the most frequent reason for market withdrawal of approved drugs, and is difficult to predict in animal models. Here, we analyzed transcriptomic data derived from short- and long-term cultured primary human hepatocytes (PHH) exposed to the well known human hepatotoxin chlorpromazine (CPZ). Samples were collected from five PHH cultures after short-term (1 and 3 days) and long-term (14 days) repeat daily treatment with 0.1 or 0.2 µM CPZ, corresponding to C(max). Two PHH cultures were additionally treated with 1 µM CPZ, and the three others with 0.02 µM CPZ. Differences in the total number of gene changes were seen between donors and throughout treatment. Specific transcriptomic hepatotoxicity signatures were created for CPZ and consisted of inflammation/hepatitis, cholestasis, and liver proliferation in all five donors, as well as fibrosis and steatosis, which were observed in four of five donors. Necrosis was present in three of five donors, and an indicative signature of cirrhosis was observed after long-term 14-day repeat treatment, also in three of five donors. The inter-donor variability in the inflammatory response to CPZ treatment was associated with variability in the strength of the response of the transcriptomic hepatotoxicity signatures, suggesting that features of inflammation could be related to the idiosyncratic hepatotoxic effects of CPZ in humans.

The liver slice system: An in vitro acute toxicity test for assessment of hepatotoxins and their antidotes

A simple method for rapid and reliable assessment of hepatotoxic agents is described. Liver slices from rats and mice of two age groups were incubated with the test hepatotoxins. Exposure of liver slices from 3-month-old mice to acetaminophen (6.8 mg/ml) resulted in 80% leakage of lactate dehydrogenase into the incubation medium, whereas liver slices from one-day-old mice showed only 12% leakage. Similar results were obtained with rat liver slices. The relative lack of response by livers of newborn rats was also demonstrated with carbon tetrachloride. The in vitro liver slice system has also been used to test the potency of N-acetylcysteine (NAC) as an antidote to acetaminophen toxicity. NAC protected mouse liver slices against acetaminophen toxicity in a dose-dependent manner. Addition of the antidote (10 mm) 20 min following hepatotoxin application reduced enzyme leakage by 75% as compared with the system with acetaminophen only. These findings demonstrate that the liver slice system provides the same type of information about hepatotoxins that is usually obtained by the use of acute in vivo tests on a large number of animals. It can be used for testing potential antidotes against hepatotoxins as well as for demonstration of species and age differences in the toxicity of various substances.

Protective effect of Calligonum comosum on haloperidol-induced oxidative stress in rat

The aqueous and methanolic extracts of Calligonum comosum were investigated for their antioxidant and dopaminergic effects on haloperidol (HL)-induced neuro- and hepatotoxicities in male albino rat model. The total phenolics, flavonoid content and free radical-scavenging activity of the extracts were determined. The results showed that the antioxidant activity of the methanolic extract was higher than the aqueous one. HL significantly reduced GSH and increased MDA in brain and liver tissues. These values were nearly normalized, in the examined tissues, on concomitant administration of C. comosum methanolic extract with HL. Superoxide dismutase activity in the examined tissues was significantly decreased by HL administration that was normalized by the coadministration of the methanolic extract and, to a less extent, the water extract. Determination of the brain neurotransmitter contents revealed a marked decrease in norepinephrine, dopamine and serotonin, which were restored to near control values by concomitant administration of both C. comosum extracts with HL. The results of this study showed that C. comosum methanolic and aqueous extracts ameliorated HL-induced neuro- and hepatotoxicities in rats.

Clozapine-induced hepatotoxicity in rat hepatocytes by gel entrapment and monolayer culture

Clozapine is limitedly used due to its adverse effect including agranulocytosis and hepatotoxicity. However, the mechanism of clozapine toxicity is still not clear. The previous in vitro studies on microsomes proposed a possible mediation of cytochrome P450 (CYP) in producing reactive metabolites. In this paper, clozapine toxicity was, respectively, examined in two cultures of rat hepatocytes. Gel entrapment culture of hepatocytes with higher expression on CYP activities showed higher sensitivity to clozapine treatment than hepatocyte monolayer, indicating the possible involvement of CYP in hepatotoxicity of clozapine. Moreover, in each culture, CYP inhibitors were used to confirm the possible mediation of CYP enzymes. Pretreatment of hepatocytes with CYP 3A inhibitor (ketoconazole), CYP 2E1 inhibitor (diethyldithiocarbamate, DDC) and non-specific inhibitor (cimetidine) significantly reduced the toxicity of clozapine. But the pretreatment with CYP 1A2 inhibitor (fluvoxamine) had no such protective effect indicative of non-function of CYP 1A2 in clozapine toxicity. In addition, glycyrrhizic acid (GA), a scavenger of reactive oxygen species (ROS), also inhibited the adverse response to clozapine, suggesting the positive involvement of oxidant pressure. Thus, it could be concluded that clozapine-induced toxicity was mediated by CYP, particularly CYP 3A and CYP 2E1, and oxidant pressure.

A comparative study of the plasma membrane permeabilization and fluidization induced by antipsychotic drugs in the rat brain

We compared the potency of the interaction of three antipsychotic drugs, i.e. chlorpromazine (CPZ), haloperidol (Hal) and sulpiride (Sul), with the plasma membrane in the rat brain. CPZ loading (> or = 100 microM) dose-dependently increased both membrane permeability (assessed as [18F]2-fluoro-2-deoxy-D-glucose-6-phosphate release from brain slices) and membrane fluidity (assessed as the reduction in the plasma membrane anisotropy of 1,6-diphenyl-1,3,5-hexatriene). On the other hand, a higher concentration of Hal (1 mM) was required to observe these effects. However, Sul failed to change membrane permeability and fluidity even at a high concentration (1 mM). These results indicated the following ranking of the potency to interact with the membrane: CPZ>Hal>Sul. The difference among antipsychotic drugs in the potency to interact with the plasma membrane as revealed in the present study may be partly responsible for the difference among the drugs in the probability of inducing extrapyramidal side-effects such as parkinsonism and tardive dyskinesia.

Computational chemistry approach for the early detection of drug-induced idiosyncratic liver toxicity

Idiosyncratic drug toxicity (IDT), considered as a toxic host-dependent event, with an apparent lack of dose response relationship, is usually not predictable from early phases of clinical trials, representing a particularly confounding complication in drug development. Albeit a rare event (usually <1/5000), IDT is often life threatening and is one of the major reasons new drugs never reach the market or are withdrawn post marketing. Computational methodologies, like the computer-based approach proposed in the present study, can play an important role in addressing IDT in early drug discovery. We report for the first time a systematic evaluation of classification models to predict idiosyncratic hepatotoxicity based on linear discriminant analysis (LDA), artificial neural networks (ANN), and machine learning algorithms (OneR) in conjunction with a 3D molecular structure representation and feature selection methods. These modeling techniques (LDA, feature selection to prevent over-fitting and multicollinearity, ANN to capture nonlinear relationships in the data, as well as the simple OneR classifier) were found to produce QSTR models with satisfactory internal cross-validation statistics and predictivity on an external subset of chemicals. More specifically, the models reached values of accuracy/sensitivity/specificity over 84%/78%/90%, respectively in the training series along with predictivity values ranging from ca. 78 to 86% of correctly classified drugs. An LDA-based desirability analysis was carried out in order to select the levels of the predictor variables needed to trigger the more desirable drug, i.e. the drug with lower potential for idiosyncratic hepatotoxicity. Finally, two external test sets were used to evaluate the ability of the models in discriminating toxic from nontoxic structurally and pharmacologically related drugs and the ability of the best model (LDA) in detecting potential idiosyncratic hepatotoxic drugs, respectively. The computational approach proposed here can be considered as a useful tool in early IDT prognosis.

The combined use of human neural and liver cell lines and mouse hepatocytes improves the predictability of the neurotoxicity of selected drugs

The cytotoxicity of amitriptyline (0-100microM), selegiline (0-4.5microM), carbamazepine (0-420microM) and paracetamol (0-10mM) was studied in metabolically competent mouse hepatocytes, metabolically incompetent human hepatoblastoma (HepG2) cells, and in neuroblastoma (SH-SY5Y) and astrocytoma (U-373 MG) cells, by using luminescence-based ATP measurement as an endpoint of cell toxicity. The aim was to evaluate the potential of the selected cell cultures to recognize metabolism-induced toxicity of the test compounds, and to predict further hepatic and neural toxicity. In SH-SY5Y cells amitriptyline was severely toxic, while selegiline and paracetamol failed to show any toxic effect, and carbamazepine was only slightly toxic at the highest concentration. In U-373 MG cells the onset of amitriptyline toxicity started earlier than in SH-SY5Y cells. However, the highest amitriptyline concentration resulted in approximately 100% decrease in the viability of the SH-SY5Y cells, whereas the decrease in the viability of the U-373 MG cells was only approximately 30%. Selegiline, carbamazepine and paracetamol were toxic in mouse hepatocytes (but not in HepG2 cells), which suggests that these drugs may show metabolism-dependent (neuro)toxicity. In conclusion, compared to the use of neurons alone, better estimations of neurotoxicity can be made by the combined use of metabolically competent hepatocytes and glial cells (e.g. U-373 MG) together with neuronal cells (e.g. SH-SY5Y).

The serotonin transporter (SLC6A4) is present in B-cell clones of diverse malignant origin: probing a potential anti-tumor target for psychotropics

Following our previous description of the serotonin transporter (SERT) acting as a conduit to 5-hydroxytryptamine (5-HT)-mediated apoptosis, specifically in Burkitt's lymphoma, we now detail its expression among a broad spectrum of B cell malignancy, while exploring additional SERT substrates for potential therapeutic activity. SERT was readily detected in derived B cell lines with origins as diverse as B cell precursor acute lymphoblastic leukemia, mantle cell lymphoma, diffuse large B cell lymphoma, and multiple myeloma. Concentration and timecourse kinetics for the antiproliferative and proapoptotic activities of the amphetamine derivatives fenfluramine (an appetite suppressant) and 3,4-methylenedioxymethamphetamine (MDMA; "Ecstasy") revealed them as being similar to the endogenous indoleamine. A tricyclic antidepressant, clomipramine, instead mirrored the behavior of the selective serotonin reuptake inhibitor fluoxetine, both being effective in the low micromolar range. A majority of neoplastic clones were sensitive to one or more of the serotonergic compounds. Dysregulated bcl-2 expression, either by t(14;18)(q32;q21) translocation or its introduction as a constitutively active transgene, provided protection from proapoptotic but not antiproliferative outcomes. These data indicate a potential for SERT as a novel anti-tumor target for amphetamine analogs, while evidence is presented that the seemingly more promising antidepressants are likely impacting malignant B cells independently of the transporter itself.

Modulation of glucose uptake in glial and neuronal cell lines by selected neurological drugs

Glucose is the main energy source of brain cells. The transport of glucose across the cell membrane is the first step of its utilization. Any modification in glucose uptake capacity may cause deleterious effects on neural cell functions. In the present study, 3-O-methyl-D-glucose (3-OMG) uptake and its modulation by selected neurological drugs (amitriptyline, selegiline, carbamazepine and phenytoin) were studied in differentiated (with retinoic acid and 12-O-tetradecanoyl phorbol 13-acetate) and undifferentiated neuroblastoma SH-SY5Y and astrocytoma U-373 MG cell lines, using tracer methods. The expression of glucose transporters was studied by immunocytochemistry. SH-SY5Y and U-373 MG cells showed differences both in their glucose uptake properties and in the modulation of glucose uptake by the drugs, which might reflect different specialization of neuronal and glial cells in vivo. While selegiline and amitriptyline had a minor and variable effect on 3-OMG uptake in all cell cultures, the anticonvulsants carbamazepine and phenytoin increased 3-OMG uptake in U-373 MG cells, but decreased that in SH-SY5Y cells. Differentiated SH-SY5Y cells were more sensitive to the effects of the anticonvulsants than undifferentiated SH-SY5Y cells. The results suggest that, the cell lines are promising neural models for the evaluation of drug side effects due to disturbances in glucose uptake.

Effect of enzyme induction on Sandimmun (cyclosporin A) biotransformation and hepatotoxicity in cultured rat hepatocytes and in vivo

This study was designed to examine the relationship between the extent of Sandimmun (cyclosporin A, SIM) metabolism and SIM-induced hepatotoxicity both in vivo and in primary cultures of rat hepatocytes. Firstly, SIM (50 mg/kg p.o.) was administered daily to male Wistar rats for 10 days with or without co-administration of Aroclor 1254. SIM-induced hepatotoxicity appeared after 4 days of treatment and was enhanced after 10 administrations of SIM. Total plasma proteins were decreased and hyperbilirubinemia as well as increased levels of plasma bile salts were prominent. Aroclor 1254 stimulated total hepatic cytochrome P-450 3.7-fold, and markedly increased the rate of SIM metabolism and plasma elimination as determined by both HPLC and RIA techniques. However, this induction did not change the degree of SIM-induced hepatotoxicity. Secondly, short-term cultures of hepatocytes obtained from normal rats and from rats pretreated with either Aroclor 1254 or dexamethasone, a specific inducer of the cytochrome P-450 III gene family responsible for the formation of the primary SIM metabolites M1, M17 and M21, were incubated with various concentrations of SIM for up to 17 hr. At 1 microM SIM, both inducers greatly increased the rate of SIM metabolism in vitro, producing, however, different metabolite patterns. In the hepatocyte cultures, SIM inhibited the incorporation of amino acids into proteins. In addition, a small fraction of [3H]-labeled SIM was covalently bound to hepatocellular macromolecules. Although the fraction of covalently bound SIM was markedly increased in cells from dexamethasone-treated rats, the degree of inhibition of hepatocellular protein synthesis was not changed in cells from induced rats. In contrast to SIM-induced nephrotoxicity, these results suggest that increased rates of SIM biotransformation by inducers of drug metabolism are not associated with an attenuation of hepatotoxicity both in vivo and in vitro.

Scoring of Cytotoxicity by Image Analysis using Animal Cell Cultures

The estimation and assessment of toxic effects can be made clearer by direct observation of the target object — the living cell. Following this approach we continuously assess the reactions of cell cultures (at a range of densities) by using image analysis equipment. The parameters evaluated are: growth rate, alteration of cell cycle time, cell progeny, and mortality rate. The use of multi-well culture plates during the observation period enables the effects of different agents at different concentrations to be examined simultaneously under the same experimental conditions. The automatic observation of the fate of many individual cells permits the accurate quantification and characterisation of cytotoxic effects for the exposed cells and their progeny. Using this method, we have examined ethyl methanesulfonate (EMS), cetyltrimethyl-ammonium chloride (CTAC), and Na-aciclovir (NaA), and we demonstrate the distinction between reversible and irreversible cell damage.

In vitro screens from CNS, liver and kidney for systemic toxicity

The development and evaluation of in vitro systems from target organs for preliminary assessments of the potential for systemic toxic effects has been receiving increased attention. This review presents a synopsis of progress made in developing toxicity screens for three common target organs and identifies further work needed for more complete validation.

In vitro toxicity assessment of cyclosporin A and its analogs in a primary rat hepatocyte culture model

The cytotoxicity of cyclosporin A (CsA), a widely used immunosuppressant drug, was evaluated in primary cultures of rat hepatocytes. Furthermore, the concentration-dependent (10(-7) to 10(-5) M) cytotoxic effects of the cyclosporin analogs, CsG, CsH, CsF, and of a major metabolite of CsA, CsA/M17, were assessed in an attempt to classify the different cyclosporin analogs according to their in vitro hepatotoxic potential. All compounds invariably inhibited the net release of taurocholate (de novo synthesized from cholate added to the extracellular medium). This sensitive functional marker did not discriminate between the structural analogs. In addition, all compounds inhibited, to various extents, the biosynthesis and secretion of proteins without affecting the uptake rate of the nonmetabolizable amino acid, alpha-aminoisobutyric acid. These functional changes occurred in the absence of overt irreversible cell damage (no leakage of lactic dehydrogenase up to 10(-5) M cyclosporin during 17 hr of incubation). The relative toxic potential of the drug congeners (CsG greater than CsA greater than CsH = CsF = CsA/M17) correlated well with the degree of their accumulation in the hepatocytes during exposure to equimolar drug concentrations.

Factors regulating the secretion of lysophosphatidylcholine by rat hepatocytes compared with the synthesis and secretion of phosphatidylcholine and triacylglycerol. Effects of albumin, cycloheximide, verapamil, EGTA and chlorpromazine

1. The synthesis and secretion of glycerolipid by monolayer cultures of rat hepatocytes was measured by determining the incorporations of [3H]glycerol, [3H]oleate and [14C]choline and by the absolute concentration of triacylglycerol. 2. The presence of albumin in the medium stimulated the accumulation of lysophosphatidylcholine in the medium by 11-13-fold. 3. Cycloheximide did not significantly alter the accumulation of lysophosphatidylcholine. 4. This process was particularly sensitive to inhibition by chlorpromazine and verapamil, compared with the secretion of triacylglycerol and phosphatidylcholine. By contrast, it was relatively less sensitive to EGTA. 5. It is suggested that intracellular Ca2+ may be important in the production of lysophosphatidylcholine, which then accumulates in the medium by binding to albumin. In vivo this lysophosphatidycholine may be a means of delivering choline and polyunsaturated fatty acids to other organs.