Negative halothane-caffeine contracture test in mdx (dystrophin-deficient) mice

The genetics of malignant hyperthermia (MH) are ill-understood; however, the association of Duchenne muscular dystrophy (DMD) with MH is well known. A deficiency of dystrophin is common to both the DMD and mdx mouse, an animal model for DMD. Using muscle contracture tests for MH, we have shown that in the mdx mouse there is no MH susceptibility, suggesting the lack of a direct role of the dystrophin in the development of MH syndrome.

Increased toxicity of anthracycline antibiotics induced by calcium entry blockers in cultured cardiomyocytes

Calcium channel blocking drugs have been reported to reduce survival rate of laboratory animals treated with cardiotoxic antitumor anthracyclines. In order to elucidate the mechanisms of this drug interaction, cell toxicity of the anthracyclines, doxorubicin and daunorubicin, was evaluated in primary cultures of cardiac myocytes isolated from neonatal rats. Low concentrations of extracellular calcium ([Ca2+]0) and addition of calcium entry blockers (nifedipine or flunarizine) potentiated myocardial toxicity of anthracyclines as assessed by the release of lactate dehydrogenase from the cells. Accumulation of anthracyclines in the cardiomyocytes was increased by calcium entry blockers (nifedipine, flunarizine, and verapamil) and by low [Ca2+]0; efflux of [3H]daunorubicin from myocardial cells was inhibited by nifedipine. At a dose that exerts only modest calcium channel activity, R-verapamil failed to affect doxorubicin accumulation in cardiomyocytes, whereas the calcium channel activator, (+/-)-Bay K-8644, reduced the retention of anthracyclines; the calcium channel activity is thus required in order to increase the accumulation of anthracyclines in myocardial cells. Calcium channel blockers are also known to increase intracellular retention and toxicity of chemotherapeutic drugs in multidrug resistant tumor cells by inhibiting the efflux of cytotoxic agents from cells; however, the ability of the interacting drugs to inhibit the efflux of chemotherapeutic agents from tumor cells is not dependent on the calcium channel blocking activity. Therefore, the mechanism(s) by which calcium channel blocking drugs increase the accumulation of anthracyclines in resistant tumor cells and myocardial cells may be different. In accordance with previous investigations, the present in vitro study confirmed that anthracycline-induced cardiotoxicity may be potentiated by calcium channel blocking drugs. This indicates that, in the association of antineoplastic drugs with agents that reverse multidrug resistance, the potential exists for enhanced damage of normal cells and tissues; further studies are needed to evaluate the relevance of this adverse interaction.

MPTP-induced ATP depletion and cell death in neuroblastoma X glioma hybrid NG 108-15 cells: protection by glucose and sensitization by tetraphenylborate

The toxic effect of the Parkinsonism-producing neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was investigated using a neuronal cell culture system, namely, neuroblastoma X glioma hybrid NG 108-15. The cells were able to metabolize MPTP into its active metabolite MPP+ (1-methyl-4-phenylpyridinium ion) and to convert its derivative, 2'-methyl MPTP, to the corresponding pyridinium ion. Degenerative changes were observed in NG 108-15 cells when they were examined with a phase-contrast microscope following exposure to MPTP, MPP+, or 2'-methyl MPTP. These compounds also caused an increased leakage of LDH from the treated cells. An enhanced release of [14C]adenine nucleotides was observed from treated cells which were prelabeled with [14C]adenine. The cell death as indicated by the leakage of LDH and the release of adenine nucleotides was markedly reduced in the presence of a high concentration (25 mM) of glucose in the medium. MPTP and MPP+ induced a drastic depletion in cell ATP content prior to cell death. The ATP depletion was also reduced by the presence of a high concentration of glucose. In contrast, tetraphenylborate, a lipophilic anion, highly potentiated the ATP depletion and the subsequent cell death induced by MPTP. Thus, ATP depletion could be a major factor in MPTP-induced neuronal cell death.

Induction of micronuclei in rat bone marrow by four model compounds

Studies have been performed to determine the dose and sampling time responses of micronuclei after Sprague-Dawley rats were treated with triethylenemelamine, mitomycin C. dimethylbenzanthracene, and vincristine by a single intraperitoneal injection. Three doses were tested for each compound. Animals were sacrificed 24, 48, and 72 h after chemical treatment. Slides prepared from the bone marrow were stained with May-Gruenwald and Giemsa stains. The number of micronucleated polychromatic erythrocytes among 2,000 polychromatic erythrocytes (PCEs) and the ratio of PCEs to normochromatic erythrocytes were determined for each animal. The results show that all four compounds cause micronucleus formation in rat bone marrow. The peak response sampling time, either 24 or 48 h posttreatment, is dependent on the chemical as well as the dose. In all cases, however, an increase in the micronucleated PCEs was detected 24 h after chemical treatment. These results seem to indicate that two sampling times, 24 and 48 h, may be adequate for the micronucleus assay using rat bone marrow cells.

Dimethylnitrosamine-induced micronucleus formation in mouse bone marrow and spleen

The present study was designed to obtain information on the kinetics of micronucleus (MN) formation following dimethylnitrosamine (DMN) treatment in mice. Male mice were injected once intraperitoneally with 50 or 100 mg/kg DMN. Bone marrow and spleen were obtained at various sacrifice time-points and processed for micronucleus analysis. The vehicle control group had 0.6 and 0.9 MN polychromatic erythrocytes (PCEs)/1000 PCEs in bone marrow and spleen, respectively. DMN, at 50 mg/kg, caused 3.8, 7.8, 8.5 and 10.2 MN PCEs/1000 PCEs in bone marrow and 8.0, 9.2, 19.3 and 32.8 MN PCEs/1000 PCEs in spleen at 12, 24, 36 and 48 h sacrifice times, respectively. A similar time-related elevation of micronucleus frequency was noted for 100 mg/kg DMN. At each sacrifice time-point, spleen PCEs had a higher micronucleus frequency than bone-marrow PCEs. In general, DMN decreased the proportion of PCEs to total erythrocytes, suggesting toxicity. Thus, this study demonstrates the clastogenic activity of DMN in both bone-marrow and spleen PCEs of mice and shows a time-related pattern in elevating DMN-induced MN PCE frequency.

Eseroline, a metabolite of physostigmine, induces neuronal cell death

The toxic effects of physostigmine, an anticholinesterase drug, and its metabolite eseroline were investigated in three neuronal cell culture systems, mouse neuroblastoma N1E-115, rat glioma C6, and neuroblastoma-glioma hybrid NG 108-15. Physostigmine and eseroline (0.5 nM) elicited a time-dependent leakage of lactic acid dehydrogenase (LDH) from all three cell types. An increased release of [14C]adenine nucleotides was also detected from cells when they were prelabeled with [14C]adenine. Eseroline was comparatively more toxic than the parent compound, physostigmine. Eseroline elicited a dose- and time-dependent leakage of LDH and release of adenine nucleotides from the neuronal cells. A nonneuronal cell line, rat liver ARL-15, was comparatively the most resistant cell type to eseroline toxicity. The concentrations of eseroline needed for 50% release of adenine nucleotides or 50% leakage of LDH from NG-108-15 and N1E-115 cells in 24 hr ranged from 40 to 75 microM. The concentrations of eseroline needed to obtain similar responses in C6 and ARL-15 cells were much higher and ranged from 80 to 120 microM. Phase contrast microscopy showed extensive damage to three neuronal cell lines at concentrations of eseroline as low as 75 microM. The loss of ATP from N1E-115 cells exceeded 50% when they were treated with 0.3 mM eseroline for 1 hr--at which time the leakage of LDH was not detectable. It seems that eseroline causes neuronal cell death by a mechanism involving loss of cell ATP. Thus, the formation of eseroline may contribute to the toxic effect of physostigmine.

Maitotoxin-induced myocardial cell injury: calcium accumulation followed by ATP depletion precedes cell death

Maitotoxin, the most potent marine toxin, is known to increase the uptake and the accumulation of Ca2+ into cells, and was used in the present study to investigate the mechanisms of myocardial cell damage induced by Ca2+ overload. In cultured cardiomyocytes, isolated from 2-day-old rats, maitotoxin affected cell viability, as indicated by the leakage of the cytosolic enzyme lactate dehydrogenase (LDH) and of radiolabeled adenine nucleotides into the extracellular medium. Maitotoxin-induced leakage of LDH steadily increased between 30 min and 24 hr, and was preceded by a marked depletion of intracellular ATP. Addition of maitotoxin resulted in a rapid influx of extracellular Ca2+, as detected by preincubating the cells in the presence of 45Ca; this effect evolved in a few minutes, thus preceding the signs of cell death. Cytosolic levels of free Ca2+ ([Ca2+]i) were monitored by loading freshly isolated, suspended cardiomyocytes with the intracellular fluorescent probe fura-2; in these cells, maitotoxin induced a dose-dependent increase in [Ca2+]i, with a lag phase of less than a minute. All these effects of maitotoxin were inhibited by reducing Ca2+ concentration in the culture medium or by incubating the cells with the calcium-channel blocking drug verapamil. It is thus demonstrated that maitotoxin-induced cardiotoxicity is secondary to an inordinate influx of Ca2+ into the cells. It is also suggested that, in those conditions that lead to an inordinate accumulation of Ca2+ into myocardial cells, the unmatched demands of energy and the depletion of ATP play a primary role in the irreversible stage of cell damage.

Sister-chromatid exchange studies on direct- and indirect-acting clastogens in mouse primary cell cultures

An in vitro sister-chromatid exchange (SCE) assay using mouse primary bone marrow and spleen cells was conducted with both direct- and indirect-acting genotoxic agents. 2,4,7-Trinitrofluorenone, a direct-acting genotoxic agent, induced a significant dose-related increase in SCEs. In both bone marrow and spleen cells, 2.0 micrograms/ml caused an approx. 3-fold increase in SCE level over control values. Cyclophosphamide, an indirect-acting genotoxicant which requires metabolic activation for its clastogenicity, induced a significant increase in SCEs in the presence of S9 from liver of rats pretreated with Aroclor-1254. A dose of 2 micrograms/ml resulted in a 2-fold increase in bone marrow and a greater than 5-fold increase in spleen cells. Benzo[a]pyrene, another indirect-acting genotoxicant, also induced significant dose-related SCE responses in both cell types. It seems that primary bone marrow and spleen cell culture systems can detect both direct- and indirect-acting genotoxicants and may be useful for routine and/or comparative cytogenetic studies.

Tumoral calcinosis

Tumoral calcinosis is an interesting clinical entity. It is not uncommon in certain countries. We report our experience with 22 patients with this condition seen over a 7-year period and review in detail the modalities of clinical presentation, theories of etiogenesis, histological appearances, and treatment modalities.

Maitotoxin-induced liver cell death involving loss of cell ATP following influx of calcium

Maitotoxin, one of the most potent marine toxins known, produced cell death in cultures of rat hepatocytes with a TD50 of 80 pM at 24 hr. The cell death, as indicated by a dose- and time-dependent leakage of lactate dehydrogenase (LDH), was also associated with the leakage of [14C]adenine nucleotides from hepatocytes prelabeled with [14C]-adenine. The toxic effect of maitotoxin was completely abolished by the omission of calcium from the culture medium. The cell death induced by maitotoxin increased with increasing concentrations of calcium in the medium. Treatment of hepatocytes with low concentrations of the toxin (less than 0.5 ng/ml) resulted in increases in 45Ca influx into the cells. At higher concentrations of maitotoxin (greater than 1ng/ml), the initial increase in 45Ca influx was followed by the release of the 45Ca from the cells into the medium. Since the 45Ca release paralleled the LDH leakage, the release of calcium was due to cell death. The 45Ca influx, [14C]adenine nucleotide leakage, and LDH leakage were effectively inhibited by verapamil, a calcium channel blocker. Maitotoxin also induced a time- and dose-dependent loss of ATP from hepatocytes, which preceded the [14C]adenine nucleotide and LDH leakage. Thus, it appears that the cell death resulting from maitotoxin treatment is caused by the elevated intracellular calcium, which in turn inhibits mitochondrial oxidative phosphorylation causing depletion of cell ATP. Loss of cell ATP may be the causative event in the maitotoxin-induced cell death.

Structural requirements for anthracycline-induced cardiotoxicity and antitumor effects

By employing rat cardiac myocytes in culture and mouse L-1210 leukemia cells, we have compared different anthracycline analogs with respect to their ability to kill cardiac myocytes and tumor cells. Anthracyclines induced a decrease in cellular ATP and glutathione from both cardiac myocytes and L-1210 cells in a time- and concentration-dependent fashion. Moreover, the decrease in ATP in cardiac myocytes was followed by release of the cytoplasmic enzyme lactic acid dehydrogenase and of adenine nucleotides after anthracycline treatment. At very low concentrations of anthracyclines, at which ATP and glutathione were not affected, the drugs induced complete cessation of the growth of L-1210 cells. Some structural alterations in the anthracycline molecule resulted in parallel changes in antitumor activity and in cardiotoxicity. But other structural alterations resulted in dissimilar changes in antitumor activity and cardiotoxicity. Although the results indicate that the structural requirements for inducing cardiotoxicity and antitumor activity may be different, they also indicate that the mechanisms by which anthracycline causes cell death in tumor cells and cardiac myocytes may be the same.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine inhibits proton motive force in energized liver mitochondria

It is known that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like disease in primates and humans, depletes hepatocytes of ATP and subsequently causes cell death. Incubation of rat liver mitochondria with MPTP and 1-methyl-4-phenyl pyridinium ion (MPP+) significantly inhibited incorporation of 32Pi into ATP.MPTP and MPP+ inhibited the development of membrane potential and pH gradient in energized rat liver mitochondria, suggesting that reduction of the proton motive force may have reduced ATP synthesis. Since deprenyl, an inhibitor of monoamine oxidase, prevented the formation of MPP+ and inhibited the decrease in membrane potential caused by MPTP, but not that caused by MPP+, these effects of MPTP, as well as cell death, probably were mediated by MPP+. This mechanism may play a role in the specific loss of dopaminergic neurons resulting in MPTP-induced Parkinson's disease.

Use of the cytokinesis-block method for the analysis of micronuclei in V79 Chinese hamster lung cells: results with mitomycin C and cyclophosphamide

The cytochalasin B (CYB)-blocked binucleated cell assay has been explored to analyze micronuclei and cell cycle kinetics using 2 known mutagenic carcinogens in V79 Chinese hamster lung cells. To determine the optimum time to obtain the maximum number of binucleated cells for micronucleus analysis, duplicate cultures of exponentially growing cells were treated with 3 micrograms/ml CYB for varying durations (8-48 h). A peak appearance of binucleated cells at 16 h in the presence of CYB suggested this as an optimum time for micronucleus analysis in binucleated V79 cells. To evaluate the capacity for induction of micronuclei in V79 cells, 2 mutagenic carcinogens, mitomycin C (0.125-1.0 micrograms/ml) and cyclophosphamide (2-12 micrograms/ml) were tested in duplicate cultures. Mitomycin C, a direct-acting alkylating agent, caused approximately an 18-fold increase in micronucleus frequency over controls at the highest concentration tested (1.0 micrograms/ml), and this increase occurred in a dose-related manner (r = 0.92). The concentrations of mitomycin C tested also caused a significant dose-related cell cycle delay, thus suggesting cytotoxicity to V79 cells. Cyclophosphamide, an indirect-acting alkylating agent, requiring the presence of S9 mix, caused approximately a 17-fold increase in micronucleus frequency over controls at the highest tested concentration (12 micrograms/ml), with a clear dose response (r = 0.99). The various concentrations of cyclophosphamide also caused cytotoxicity in a dose-related fashion. Thus, this study demonstrates the usefulness of the cytokinesis-block method in V79 cells as a possible screen to analyze micronucleus induction and cytotoxicity. Because this approach is much less labor intensive than conducting a structural chromosomal analysis, this assay has great potential both as an initial screen for clastogenic activity and as a tool for investigating the underlying mechanisms for clastogenicity.

MPTP and MPTP analogs induced cell death in cultured rat hepatocytes involving the formation of pyridinium metabolites

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) which has been shown to produce a Parkinson-like syndrome in humans and monkeys also causes cell death in cultures of rat hepatocytes. Treatment of cells with MPTP or its metabolite MPP+ (1-methyl-4-phenyl pyridinium ion), resulted in leakage of lactic acid dehydrogenase and 14C-labeled adenine nucleotides, as well as marked depletion of ATP and glutathione. Deprenyl, a specific inhibitor of monoamine oxidase-B, the enzyme catalyzing the oxidation of MPTP into MPP+, blocked the lethal effect of MPTP, but gave no protection from MPP+-induced cell death. The 4'-fluoro and 4'-chloro analogs of MPTP evoked toxicities similar to that of the parent compound, while N-butyl-PTP, 4'-amino-MPTP, and 2'-methyl-MPTP were relatively less toxic. N-Acetylamino-MPTP was found virtually nontoxic. The cell death produced by these analogs was also associated with leakage of [14C]adenine nucleotides, which is an indicator of loss of ATP from cells. All these compounds except the N-acetylamino analog were converted to corresponding pyridinium metabolites by liver cells when analyzed by high-pressure liquid chromatography and plasma desorption mass spectrometry. MPTP and its analogs also served as substrates for rat liver mitochondrial monoamine oxidase to varying degrees. Toxicity of various analogs, with the noticeable exception of 2'-methyl-MPTP, was inhibited by deprenyl. These findings indicate that the conversion of MPTP and its analogs to corresponding pyridinium metabolites is essential for the expression of toxicity.

Sister-chromatid exchanges induced by triethylenemelamine: in vivo and in vivo/in vitro studies in mouse and Chinese hamster bone marrow and spleen cells

This study was designed to obtain sister-chromatid exchange (SCE) frequencies in bone marrow and spleen cells of mice and Chinese hamsters under in vivo and in vivo/in vitro systems following treatment of animals with varying doses (15-405 micrograms/kg) of triethylenemelamine (TEM). A dose-related SCE response was found in both species, tissues, and systems analyzed following TEM treatment. In vivo, similar responses were noted for both tissues in both species. However, in vivo/in vitro, the response was lower than in vivo and it varied with the tissue. The spleen cells were more sensitive and gave higher numbers of SCEs than bone marrow of both species at the two highest doses tested (135 and 405 micrograms/kg). These differences may be attributed to cell-culturing effects, type of cells analyzed, species and tissue specificities, and pharmacokinetic properties of the chemical. This study lends support to recently established in vivo/in vitro cell culture methodologies employing mice and Chinese hamsters for comparative cytogenetic analysis.

In vivo and in vivo/in vitro kinetics of cyclophosphamide-induced sister-chromatid exchanges in mouse bone marrow and spleen cells

In several acute and chronic exposures to various chemicals in vivo and in vitro, the average sister-chromatid exchange (SCE) frequencies in human, mouse, rat, and rabbit lymphocytes generally decrease with time following treatment. The rate of this decline varies, but little data have been published pertaining to the comparative kinetics of SCEs both in vivo and in vivo/in vitro (exposure of animals to the test compound and culturing of cells) simultaneously in the same tissues. In this study, a single dose of cyclophosphamide (40 mg/kg) was injected for varying periods (6-48 h) and its effects, as assessed by the induction of SCEs, were analyzed under both in vivo and in vivo/in vitro conditions in mouse bone marrow and spleen cells. In vivo, the cyclophosphamide-induced SCEs increased with increasing time up to 12 h, stayed at approximately the same level until 24 h, and then decreased with increase in post-exposure time. However, the SCE levels remained significantly higher than controls at 48 h post-exposure time in both bone marrow and spleen cells. Under in vivo/in vitro conditions, the SCEs in bone marrow decreased with increase in post-exposure time until reaching control values by 48 h post exposure. However, in spleen cells, the decrease in SCE level was gradual, and by 48 h post-exposure time, the cells still had approximately 6 times higher SCEs than the control values. These results suggest that there are pharmacokinetic differences for cyclophosphamide in mouse bone marrow and spleen. Also, there is a differential SCE response to cyclophosphamide under in vivo and in vivo/in vitro conditions.

Valproic acid-induced increase in carnitine acetyltransferase in rat hepatocytes is not due to an induction of peroxisomes

Valproic acid induced a dose-dependent increase in carnitine acetyltransferase (CAT) activity in rat hepatic mitochondrial fractions isolated by differential centrifugation. An increase in CAT and carnitine palmitoyltransferase (CPT) also occurred in cultured rat hepatocytes in a concentration-and time-dependent fashion. A maximal increase of 8-fold in the activity of CAT and 2-fold in the activity of CPT was induced by 3 mM valproic acid in 72 h. Valproic acid had no effect on cytochrome P-450 levels in cultured rat hepatocytes. Electron-microscopic examination of rat hepatocytes showed that there was no increase in the number of peroxisomes but there was a marked proliferation of mitochondria in parallel with an increase in glutathione level and succinic dehydrogenase in the liver cells after incubation with valproic acid in vitro.

Characterization of ciprofibrate and clofibric acid as peroxisomal proliferators in primary cultures of rat hepatocytes

We have determined the comparative activities of peroxisomal proliferators, ciprofibrate and clofibric acid on various hepatic parameters associated with endoplasmic reticulum, mitochondria and peroxisomes in primary cultures of rat hepatocytes. We have measured the activities of carnitine acetyltransferase and fatty acylCoA oxidase, and the amount of 60 and 80 kD polypeptides as biochemical markers of the peroxisomal function; laurate hydroxylase and cytochrome P-450 as markers of the endoplasmic reticulum; and carnitine palmitoyltransferase as a marker of mitochondria in primary cultures of hepatocytes. Ciprofibrate (0.01 to 0.3 mM) and clofibric acid (0.1 to 3 mM) produced similar changes in several components of cultured hepatocytes within 72 hr. Increases of protein (18 and 11%), carnitine palmitoyltransferase (23 and 97%), cytochrome P-450 (37 and 49%), carnitine acetyltransferase (484 and 614%), fatty acylCoA oxidase (529 and 931%) and laurate hydroxylase (624 and 671%) were obtained in hepatocytes after a 72-hr exposure to 0.1 mM ciprofibrate and 1.0 mM clofibric acid, respectively. In cultured hepatocytes, ciprofibrate was about 30-fold more active than clofibric acid for the stimulation of carnitine acetyltransferase, laurate hydroxylase and fatty acylCoA oxidase activities. Ciprofibrate was also more potent than clofibric acid as an inducer of the 60 and 80 kD proteins in hepatocytes. The maximal drug-induced increases in carnitine acetyltransferase activity were not additive, and the induction of carnitine acetyltransferase by ciprofibrate was blocked by addition (1 micrograms per ml) of cycloheximide or actinomycin D. Changes in protein and RNA synthesis preceded the drug-induced increases of carnitine acetyltransferase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Daunomycin inhibits the uptake of adenine, amino acids, and glucose into cardiac myocytes

Daunomycin and adriamycin are widely used antitumor agents which induce dose-dependent cardiotoxicity. The mechanisms by which daunomycin causes cardiotoxicity have been investigated in neonatal rat cardiac myocytes maintained in tissue culture. Daunomycin inhibited the uptake of adenine, amino acids, and deoxyglucose in a dose-dependent fashion. The uptake of both adenine and methionine was inhibited without any delay while the glucose uptake (deoxyglucose) was inhibited after a delay of 2 hr. Since daunomycin affected the uptake of both adenine and amino acids without any delay and since daunomycin did not affect the incorporation of adenine into nucleotide and amino acids into proteins once these were transported into the cell, it is possible the daunomycin exerted these effects by acting directly on the cell membrane. Thus, one of the early toxic manifestations of anthracycline antibiotics may be on the transport of nutrients such as amino acids, glucose, and adenine.