Cytotoxicity and genotoxicity of phenazine in two human cell lines

Phenazine was recently identified as a drinking water disinfection byproduct (DBP), but little is known of its toxic effects. We examined in vitro cytotoxicity and genotoxicity of phenazine (1.9–123 μM) in HepG2 and T24 cell lines. Cytotoxicity was determined by an impedance-based real-time cell analysis instrument. The BrdU (5-bromo-2′-deoxyuridine) proliferation and MTT ((3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) viability assays were used to examine mechanisms of cytotoxicity. Genotoxicity was determined using the alkaline comet assay. Concentration-dependent cytotoxicity was observed in HepG2 cells, primarily due to an antiproliferative effect (BrdU 24 h IC₅₀: 11 μM; 48 h IC₅₀: 7.8 μM) observed as low as 1.9 μM. T24 cells experienced a minor antiproliferative effect (BrdU 24 h IC₅₀: 47 μM; 48 h IC₅₀: 17 μM). IC₅₀ values for HepG2 proliferation and viability were 54–77% lower compared to T24 cells. In both cell lines, IC₅₀ values for proliferation were 66–90% lower than those for viability. At phenazine concentrations producing equivalent cytotoxicity, HepG2 cells (1.9–30.8 μM) experienced no significant genotoxic effects, while T24 cells (7.7–123 μM) experienced significant genotoxicity at ⩾61.5 μM. While these effects were seen at phenazine concentrations above those found in disinfected water, the persistence of the antiproliferative effect and the differential toxicity in each cell line deserves further study.     

Prediction of skin sensitization potency of chemicals by human Cell Line Activation Test (h-CLAT) and an attempt at classifying skin sensitization potency

The human Cell Line Activation Test (h-CLAT), an in vitro skin sensitization test, is based on the augmentation of CD86 and CD54 expression in THP-1 cells following exposure to chemicals. The h-CLAT was found to be capable of determining the hazard of skin sensitization. In contrast, the local lymph node assay (LLNA), widely used as a stand-alone method in Europe and US, identifies the same hazard, but also classifies the potency by using the estimated concentration of SI = 3 (EC3). In this study, several values calculated from the h-CLAT data were evaluated for its correlation to the LLNA EC3 determination. A statistically significant correlation was observed between h-CLAT concentration providing a cell viability of 75% (CV75), h-CLAT estimated concentration of RFI = 150 for CD86 (EC150), and for CD54 (EC200) with LLNA’s EC3. From EC150 and EC200, a minimum induction threshold (MIT) was determined as the smaller of either EC150 or EC200. MIT showed a correlation with EC3 (R = 0.638). Also, MIT had an approximate 80% accuracy for sub-categories of the globally harmonized system (GHS) when a tentative threshold of 13 μg/mL was used. From these data, the h-CLAT values may be one of the useful tools to predict the allergic potency of chemicals.     

What are the differences between aerobic and anaerobic toxic effects of sulfonamides on Escherichia coli?

Bacteria in the environment face the threat of antibiotics. However, most studies investigating the toxicity and toxicity mechanisms of antibiotics have been conducted on microorganisms in aerobic conditions, while studies examining the anaerobic toxicity and toxicity mechanisms of antibiotics are still limited. In this study, we determined the aerobic and anaerobic toxicities of sulfonamides (SAs) on Escherichia coli. Next, a comparison of the aerobic and anaerobic toxicities indicated that the SAs could be divided into three groups: Group I: log(1/EC_50-anaerobic) > log(1/EC_50-aerobic) (EC_50-anaerobic/EC_50-aerobic, the median effective concentration under anaerobic/aerobic conditions), Group II: log(1/EC_50-anaerobic) ≈ log(1/EC_50-aerobic), and Group III: log(1/EC_50-anaerobic) < log(1/EC_50-aerobic). Furthermore, this division was not based on the reactive oxygen species (ROS) level or the interaction energy (E_binding) value, which represents the affinity between SAs and dihydropteroate synthase (dhps) but rather on the total binding energy. Furthermore, SAs with greatly similar structures were categorized into different groups. This deep insight into the difference between aerobic and anaerobic toxicities will benefit environmental science, and the results of this study will serve as a reference for the risk assessment of chemicals in the environment.     

Characterising the post-antifungal effects of micafungin against Candida albicans,Candida glabrata,Candida parapsilosis and Candida krusei isolates

In this study, we measured time–kills and post-antifungal effects (PAFEs) for micafungin against Candida albicans (n = 4), Candida glabrata (n = 3), Candida parapsilosis (n = 3) and Candida krusei (n = 2) isolates and further characterised the PAFEs. Minimum inhibitory concentrations (MICs) were 0.5–1.0 mg/L against C. parapsilosis and 0.008–0.125 mg/L against the other species. Micafungin caused kills >1 log at 1 × MIC, 4 × MIC (range 1.19–3.10 log) and 16 × MIC (2.27–3.68 log), achieving fungicidal levels (≥3 log) against nine isolates. One-hour drug exposure during PAFE experiments resulted in kills of 0.73–2.88 log and 1.72–3.55 log at 4× and 16× MIC, respectively, achieving fungicidal levels against five isolates. Isolates of each species collected 8 h after a 1-h exposure to micafungin (4× and 16× MIC) were hypersusceptible to sodium dodecyl sulphate (SDS) and Calcofluor White. Cells tested during the PAFE period demonstrated cell wall disturbances as evident on electron micrographs as well as significant reductions in adherence to epithelial cells. Phagocytosis by J774 macrophages was significantly enhanced for three PAFE isolates tested. Micafungin is fungicidal and exerts PAFEs that kill diverse Candida spp., disturb cell walls of viable organisms, reduce adherence and enhance susceptibility to phagocytosis.     

Profiling of the toxicity mechanisms of coated and uncoated silver nanoparticles to yeast Saccharomyces cerevisiae BY4741 using a set of its 9 single-gene deletion mutants defective in oxidative stress response,cell wall or membrane integrity and endocytosis

The widespread use of nanosilver in various antibacterial, antifungal, and antiviral products warrants the studies of the toxicity pathways of nanosilver-enabled materials toward microbes and viruses. We profiled the toxicity mechanisms of uncoated, casein-coated, and polyvinylpyrrolidone-coated silver nanoparticles (AgNPs) using Saccharomyces cerevisiae wild-type (wt) and its 9 single-gene deletion mutants defective in oxidative stress (OS) defense, cell wall/membrane integrity, and endocytosis. The 48-h growth inhibition assay in organic-rich growth medium and 24-h cell viability assay in deionized (DI) water were applied whereas AgNO₃, H₂O_2, and SDS served as positive controls. Both coated AgNPs (primary size 8–12 nm) were significantly more toxic than the uncoated (~ 85 nm) AgNPs. All studied AgNPs were ~ 30 times more toxic if exposed to yeast cells in DI water than in the rich growth medium: the IC₅₀ based on nominal concentration of AgNPs in the growth inhibition test ranged from 77 to 576 mg Ag/L and in the cell viability test from 2.7 to 18.7 mg Ag/L, respectively. Confocal microscopy showed that wt but not endocytosis mutant (end3Δ) internalized AgNPs. Comparison of toxicity patterns of wt and mutant strains defective in OS defense and membrane integrity revealed that the toxicity of the studied AgNPs to S. cerevisiae was not caused by the OS or cell wall/membrane permeabilization.     

Boar spermatozoa as a biosensor for detecting toxic substances in indoor dust and aerosols

The presence, quantity and origins of potentially toxic airborne substances were searched in moisture damaged indoor environments, where building related ill health symptoms were suspected and reference sites with no health complaints. Boar spermatozoa were used as the toxicity sensor. Indoor aerosols and dusts were collected from kindergartens, schools, offices and residences (n = 25) by electrostatic filtering, vacuuming, wiping from elevated surfaces and from the interior of personal computers. Toxicity was measured from the ethanol or methanol extracts of the dusts and aerosols. EC₅₀ was expressed as the lowest concentration of the airborne substance that inhibited motility of >50% of the exposed sperm cells compared to vehicle control, within 30 min, 1 day or 3–4 days of exposure. Remarkably toxic aerosols (EC₅₀ ⩽6 μg ml⁻¹) were found from 11 sites, all of these were sites with known or suspected for building related ill health. Toxic microbial cultures were obtained from subsamples of the toxic aerosols/dusts. From these cereulide, amylosin, valinomycin and a novel indoor toxin, stephacidin B were identified and toxicities measured. Airborn dispersal of valinomycin from Streptomyces griseus cultures was evaluated using a flow-through chamber. Significant amounts of valinomycin (LC–MS assay) and toxicity (boar sperm motility assay) were carried by air and were after 14 days mainly recovered from the interior surfaces of the flow chamber.     

ECVAM’s ongoing activities in the area of acute oral toxicity

The 7th Amendment of the Cosmetics Directive (2003/15/EC) set up timelines for banning animal testing and marketing of cosmetic products and their ingredients tested on animals. For most of the human health effects, including acute toxicity, the deadline for these bans was in March 2009. Moreover, the new Regulation EC 1907/2006 on Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) provided a strong impetus towards the application of alternative approaches to reduce the number of animals used for toxicological testing. Therefore, the European Centre for the Validation of Alternative Methods (ECVAM) is currently putting considerable effort into developing and validating alternative methods in the field of acute toxicity. The main activities in this area include: (1) the Integrated Project ACuteTox, funded by the European Commission’s 6th Framework Programme in 2005 with the aim to develop and pre-validate a testing strategy to fully replace acute oral toxicity testing in vivo; (2) a follow-up validation study to assess the predictive capacity of the validated BALB/3T3 Neutral Red Uptake cytotoxicity assay to discriminate between toxic/hazardous (LD₅₀ < 2000 mg/kg) substances and substances not classified for acute toxicity (LD₅₀ > 2000 mg/kg); (3) an approach to identify compounds with LD₅₀ > 2000 mg/kg using information from 28-days repeated dose toxicity studies.     

Oxidative stress contributes to silica nanoparticle-induced cytotoxicity in human embryonic kidney cells

In order to elucidate the nanoparticle-induced cytotoxicity and its mechanism, the effects of 20 and 50 nm silica nanoparticles on cultured human embryonic kidney (HEK293) cells were investigated. Cell viability, mitochondrial function, cell morphology, reactive oxygen species (ROS), glutathione (GSH), thiobarbituric acid reactive substance (TBARS), cell cycle and apoptosis were assessed under control and silica exposed conditions. Exposure to 20 or 50 nm SiO₂ nanoparticles at dosage levels between 20 and 100 μg/ml decreased cell viability in a dose-dependent manner. Median lethal dose (LD₅₀) of 24 h exposure was 80.2 ± 6.4 and 140.3 ± 8.6 μg/ml for 20 and 50 nm SiO₂ nanoparticles, respectively. Morphological examination revealed cell shrinkage and nuclear condensation after SiO₂ nanoparticle exposure. Increase in intracellular ROS level and reduction in GSH content were also observed in SiO₂ nanoparticle-exposed HEK293 cells. Increase in the amount of TBARS suggested an elevated level of lipid peroxidation. Flow cytometric analysis showed that SiO₂ nanoparticles can cause G2/M phase arrest and apoptotic sub-G1 population increase in a dose-dependent manner. In summary, exposure to SiO₂ nanoparticles resulted in a dose-dependent cytotoxicity in cultured HEK293 cells that was associated with increased oxidative stress.     

Inhibition of sphingosine kinase-2 ablates androgen resistant prostate cancer proliferation and survival

BackgroundEndogenous sphingolipid signaling has been shown to play an important role in prostate cancer endocrine resistance.MethodsThe novel SphK2 inhibitor, ABC294640, was used to explore SphK signaling in androgen resistant prostate cancer cell death signaling.ResultsIt dose-dependently decreased PC-3 and LNCaP cell viability, IC₅₀ of 28 ± 6.1 μM (p < 0.05) and 25 ± 4.0 μM (p < 0.05), respectively. ABC294640 was more potent in long-term clonogenic survival assays; IC₅₀ of 14 ± 0.4 μM (p < 0.05) in PC-3 cells and 12 ± 0.9 μM (p < 0.05) in LNCaP cells. Intrinsic apoptotic assays failed to demonstrate increased caspase-9 activity. Ki-67 staining demonstrated decreased proliferation by 50 ± 8.4% (p < 0.01) in PC-3 cells.ConclusionsSphK2 inhibition decreases androgen resistant prostate cancer viability, survival, and proliferation independently of the intrinsic apoptotic pathway. Findings are in contrast to recent observations of ABC29460 acting dependently on the intrinsic pathway in other endocrine resistant cancer cell lines.     

Cytotoxicity and apoptosis induction on RTG-2 cells of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209)

Recently, the environmental residues of polybrominated diphenyl ethers (PBDEs) have markedly increased. In particular, the levels of certain PBDE congeners in fish have raised concern regarding potential risks associated with dietary PBDEs exposures. However, little is known regarding PBDE-mediated cell injury in relevant in vitro fish cell models. In this study, the cytotoxic effects of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209) on RTG-2 cells were investigated. RTG-2 cells were incubated with different concentrations of BDE-47 and BDE-209 (1–100 μM) for 72 h, and a set of bioassays were conducted to measure: cell viability (evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and neutral red (NR) uptake), lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation and cell apoptosis. The results showed that BDE-47 and BDE-209 inhibited the cells viability, increased LDH leakage, and induced cell apoptosis in time and concentration-dependent manner. All significant effects were observed at concentrations of 12.5 μM and above for BDE-47 and 25 μM and above for BDE-209 (P < 0.05). At the concentration of 100 μM BDE-47 and BDE-209, the cell viability of the exposed cells dropped to about 40% and 50% of the control, and the apoptotic rates were 52.6% and 34.6%, respectively. After 12 h exposure, a concentration-dependent increases of BDE-47 and BDE-209 (12.5–100 μM) in ROS formation were observed. Collectively, the results of cell viability, LDH leakage, cell apoptosis and ROS formation demonstrated that the toxic mechanism of PBDEs on RTG-2 might be mediated by oxidative stress.     

The potential effects of efavirenz on Oreochromis mossambicus after acute exposure

Antiretroviral drugs (ARVs) are hazardous therapeutic pharmaceuticals present in South African surface water. Efavirenz is an ARV commonly used in human immunodeficiency virus (HIV) treatment in South Africa. Although little is known about the toxic effects of efavirenz on fish health, threats of toxicity to the aquatic environment have been reported. Oreochromis mossambicus were exposed under controlled conditions to environmentally-relevant efavirenz concentrations (10.3 ng/l) as measured in rivers that flow into the Nandoni Dam in the Vhembe District, South Africa. Acute (96 h) exposures were conducted using efavirenz concentrations of 10.3 ng/l and 20.6 ng/l. The overall health of exposed fish was determined using a histology-based fish health assessment index. Necropsies and haematology were conducted and somatic indices calculated after which the liver, kidney, heart, gills and gonads were microscopically quantitatively assessed. Results indicated that fish exposed to 20.6 ng/l efavirenz had significantly (p < 0.02) higher liver indices than the control fish, indicating increased liver damage including steatosis and frank necrosis. Fish exposed to 20.6 ng/l efavirenz presented with significantly (p < 0.02) higher total fish indices, representative of declined overall health compared to control fish. It was concluded that the exposure of O. mossambicus to efavirenz resulted in liver damage and overall decline in fish health. These novel findings may indicate a health risk for O. mossambicus and other biota exposed to efavirenz in aquatic ecosystems. Thus, ARV’s in water sources of South Africa pose a definite threat to wildlife and ultimately human health.     

In vitro cytotoxicity of hydrothermally synthesized ZnO nanoparticles on human periodontal ligament fibroblast and mouse dermal fibroblast cells

The use of metal oxide nanoparticles (NPs) in industrial applications has been expanding, as a consequence, risk of human exposure increases. In this study, the potential toxic effects of zinc oxide (ZnO) NPs on human periodontal ligament fibroblast cells (hPDLFs) and on mouse dermal fibroblast cells (mDFs) were evaluated in vitro. We synthesized ZnO NPs (particle size; 7–8 nm) by the hydrothermal method. Characterization assays were performed with atomic force microscopy, Braun–Emmet–Teller analysis, and dynamic light scattering. The hPDLFs and mDFs were incubated with the NPs with concentrations of 0.1, 1, 10, 50 and 100 μg/mL for 6, 24 and 48 h. Under the control and NP-exposed conditions, we have made different types of measurements for cell viability and morphology, membrane leakage and intracellular reactive oxygen species generation. Also, we monitored cell responses to ZnO NPs using an impedance measurement system in real-time. While the morphological changes were visualized using scanning electron microscopy, the subcellular localization of NPs was investigated by transmission electron microscopy. Results indicated that ZnO NPs have significant toxic effects on both of the primary fibroblastic cells at concentrations of ∼50–100 μg/mL. The cytotoxicity of ZnO NPs on fibroblasts depended on concentration and duration of exposure.     

Effects of the radiocontrast agent iodixanol on endothelial cell morphology and function

Iodinated radiocontrast media (RCM) are usually well tolerated, but their large and increasing use renders their toxicity a relevant problem, especially in high risk patients. The aim of the study was to investigate the possible toxic or activating effects of iodixanol on endothelial cells (EC) and the putative in vitro protective action of N-acetylcysteine and rosuvastatin. Morphology, oxidative status, redistribution of heat-shock protein 60 and secretion of proinflammatory products were studied in cultured human EC through confocal microscopy, immunofluorescence and immuno-enzymatic methods. EC reacted to iodixanol with shrinking and bulging, increase in intracellular oxidation and translocation of Heat Shock Protein 60 to the cell membrane. The secretion of proinflammatory products was strongly stimulated by sequential incubation of EC with iodixanol and TNFα (p < 0.00001 for all tested molecules, namely TNFα, IL-8, sVCAM-1, MCP-1, and IL-6). N-acetylcysteine prevented morphologic and oxidative derangements, and significantly reduced proinflammatory product secretion (P range < 0.0001 to < 0.00001 for TNFα, VCAM-1, MCP-1, and IL-6); rosuvastatin inhibited morphology and oxidative modifications only. Our data help clarifying the mechanisms of early and late toxicity of RCM and support the use of anti-oxidant and anti-inflammatory agents for optimization of radiological procedures in high risk patients.     

Maturin acetate from Psacalium peltatum (Kunth) Cass. (Asteraceae) induces immunostimulatory effects in vitro and in vivo

Maturin acetate (MA) is one of main constituents in Psacalium peltatum. The cytotoxic effects of MA on tumorigenic cells were evaluated using the MTT assay. The in vitro immunostimulatory effects of maturin acetate (MA) were evaluated on the viability of murine splenocytes and macrophages, and human peripheral blood mononuclear cells (PBMC). The effects of MA on the production of nitrous oxide, pinocytosis and lysosomal enzyme activity were assayed in murine macrophages RAW 264.7. The effects of MA on the NK cell activity were also assayed. The in vivo immunostimulatory activities of MA were evaluated on BALB/c mice immunosuppressed with cyclophosphamide (CY). MA lacks cytotoxic activity against human cancer cells (IC₅₀ > 200 μM). In the absence of LPS, MA 10 μM or higher stimulated significantly (P ? 0.05), compared to untreated cells (-LPS), the viability of murine macrophages and splenocytes. In the absence of LPS, MA 10 μM or higher stimulated significantly (P ? 0.05), compared to untreated cells (-LPS), the lysosomal enzyme activity and pinocytosis. In immunosuppressed mice, MA increases significantly (P ? 0.05), compared to CY-treated mice, the production of IL-2 and IL-15 and IFN-γ. In conclusion, MA exerts immunostimulatory activities in vitro and in vivo.     

Evaluating the validity and applicable domain of the toxic load model: Impact of concentration vs. time profile on inhalation lethality of hydrogen cyanide

The ten Berge model (or “toxic load” model) is often used to estimate the acute toxicity for varying combinations of inhaled concentration and duration. Expressed as Cⁿ × t = toxic load (TL), TLs are assumed constant for various combinations of concentration (C) and time (t). Experimental data in a recent acute inhalation study of rats exposed to time-varying concentrations of hydrogen cyanide (HCN) supported the validity of the toxic load model except under very brief, discontinuous, high concentration exposures. In the present investigation, experiments were conducted to extend the evaluation of the applicable domain of the model for acute lethality of HCN in the rat (cumulative exposure range of 2900–11,000 ppm min). The lethality of HCN over very short (<5 min) durations of high concentrations did not conform to the toxic load model. A value of n = 1.57 was determined for uninterrupted exposures ⩾5 min. For 30-min exposures, the presence or absence of a gap between two exposure pulses of different concentrations, the relative duration, relative height, and the ordering of the pulses (low then high, vs. high then low) did not appear to have a meaningful impact on the toxic load required for median lethality.     

Hydroxychloroquine attenuates cigarette smoke induced autophagic signaling in the mouse ovary

We previously demonstrated that Cigarette Smoke (CS) induces autophagy in the ovary. Therefore we aimed to determine if chloroquine (CQ) could inhibit CS-induced autophagy in the ovary. Eight week old mice were implanted with CQ pellets; 0, 25, and 50 mg CQ/kg. Half of the animals in each group were exposed to room air and the other half were exposed to CS twice daily for 8 weeks. Ovaries were harvested for electron microscopy, gene and protein expression analysis. There was a significant increase in the production of autophagosomes in granulosa cells of mice exposed to CS (p = 0.0297). However 25 and 50 mg/kg CQ treatment significantly decreased the CS-induced autophagosomes (p = 0.0505; p = 0.0065) and attenuated the effects of CS on LC3B and BECN1 expression. In summary, this suggests that CQ attenuates CS-induced autophagy in the ovary and that ovarian protection from toxic insult is potentially feasible.     

Toxic effects induced by mycotoxin fumonisin B1 on equine spermatozoa: Assessment of viability,sperm chromatin structure stability,ROS production and motility

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium species that exerts its toxic effect through interference with the sphingolipid pathway by inhibiting ceramide synthase. A FB1-dependent sperm toxicity was reported in boars. No information on FB1-related reproductive toxicity in stallions, the most sensitive animal species, has been reported. The aim of the present study was to assess the in vitro toxicity of FB1 on fresh and frozen-thawed equine spermatozoa by analyzing sperm viability, chromatin stability (SCSA) and reactive oxygen species (ROS) production by flow cytometry and sperm motility by CASA system. Fumonisin B1 did not affect viability of fresh spermatozoa after 2 h exposure up to 25 μM. Damage on sperm chromatin structure was observed only in one frozen sample after exposure up to 2.5 × 10⁻⁵ μM FB1 without associated increase of ROS. Increase of ROS, at FB1 levels up to 2.5 × 10⁻⁴ μM, was found on another frozen-thawed sperm sample, may be as a consequence of seminal plasma removal. At 7.5 and 15 μM, FB1 induced reduction of total and progressive motility.     

Endogenous cannabinoids in post-mortem brains of Cloninger type 1 and 2 alcoholics

The endogenous cannabinoid (EC) system has been recently implicated in several neuropsychiatric disorders. This study analyzed post-mortem brain regions of Cloninger type 1 (n = 9) and 2 (n = 8) alcoholics and non-alcoholic controls (n = 10) for ECs by quantitative liquid chromatography with triple quadrupole mass spectrometric detection. A significant difference was found in anandamide (AEA) levels in nucleus accumbens (NAcc) between the three groups (p = 0.047). AEA levels were significantly lower when compared to controls in both perigenual anterior cingulate (p = 0.017) and frontal cortices (p = 0.018) of type 1 alcoholics. Similar trends were observed for dihomo-γ-linolenoyl ethanolamide and docosahexaenoyl ethanolamide, but not for 2-arachidonoylglycerol, palmitoyl ethanolamide, or oleoyl ethanolamide. Although preliminary, and from diagnostic groups with a relatively small number of subjects and substantially different mean ages for each group, these results suggest that the EC system may be hyperactive in type 2 alcoholics and hypoactive in type 1 alcoholics.     

The effects of jaspamide on human cardiomyocyte function and cardiac ion channel activity

Jaspamide (jasplakinolide; NSC-613009) is a cyclodepsipeptide that has antitumor activity. A narrow margin of safety was observed between doses required for efficacy in mouse tumor models and doses that caused severe acute toxicity in rats and dogs. We explored the hypothesis that the observed toxicity was due to cardiotoxicity. Jaspamide was tested in a patch clamp assay to determine its effect on selected cardiac ion channels. Jaspamide (10 μM) inhibited Kv1.5 activity by 98.5%. Jaspamide also inhibited other channels including Cav1.2, Cav3.2, and HCN2; however, the Kv11.1 (hERG) channel was minimally affected. Using spontaneously contracting human cardiomyocytes derived from induced pluripotent stem cells, effects on cardiomyocyte contraction and viability were also examined. Jaspamide (30 nM to 30 μM) decreased cardiomyocyte cell indices and beat amplitude, putative measurements of cell viability and cardiac contractility, respectively. Concentration-dependent increases in rhythmic beating rate were noted at ?6 h of treatment, followed by dose-dependent decreases after 6 and 72 h exposure. The toxic effects of jaspamide were compared with that of the known cardiotoxicant mitoxantrone, and confirmed by multiparameter fluorescence imaging analysis. These results support the hypothesis that the toxicity observed in rats and dogs is due to toxic effects of jaspamide on cardiomyocytes.