Elevation of intracellular Zn2+ level by nanomolar concentrations of triclocarban in rat thymocytes

Effects of multiwalled carbon nanotubes and triclocarban on several eukaryotic cell lines: elucidating cytotoxicity, endocrine disruption, and reactive oxygen species generation

To date, only a few reports about studies on toxic effects of carbon nanotubes (CNT) are available, and their results are often controversial. Three different cell lines (rainbow trout liver cells (RTL-W1), human adrenocortical carcinoma cells (T47Dluc), and human adrenocarcinoma cells (H295R)) were exposed to multiwalled carbon nanotubes, the antimicrobial agent triclocarban (TCC) as well as the mixture of both substances in a concentration range of 3.13 to 50 mg CNT/L, 31.25 to 500 μg TCC/L, and 3.13 to 50 mg CNT/L + 1% TCC (percentage relative to carbon nanotubes concentration), respectively. Triclocarban is a high-production volume chemical that is widely used as an antimicrobial compound and is known for its toxicity, hydrophobicity, endocrine disruption, bioaccumulation potential, and environmental persistence. Carbon nanotubes are known to interact with hydrophobic organic compounds. Therefore, triclocarban was selected as a model substance to examine mixture toxicity in this study. The influence of multiwalled carbon nanotubes and triclocarban on various toxicological endpoints was specified: neither cytotoxicity nor endocrine disruption could be observed after exposure of the three cell lines to carbon nanotubes, but the nanomaterial caused intracellular generation of reactive oxygen species in all cell types. For TCC on the other hand, cell vitality of 80% could be observed at a concentration of 2.1 mg/L for treated RTL-W1 cells. A decrease of luciferase activity in the ER Calux assay at a triclocarban concentration of 125 μg/L and higher was observed. This effect was less pronounced when multiwalled carbon nanotubes were present in the medium. Taken together, these results demonstrate that multiwalled carbon nanotubes induce the production of reactive oxygen species in RTL-W1, T47Dluc, and H295R cells, reveal no cytotoxicity, and reduce the bioavailability and toxicity of the biocide triclocarban.

Triclocarban-induced change in intracellular Ca²⁺ level in rat thymocytes: cytometric analysis with Fluo-3 under Zn²⁺-free conditions

Triclocarban (TCC) is an antimicrobial used in personal hygiene products. Recent health concerns arose after TCC was detected in the blood of human subjects who showered with soap containing TCC. In this study, the effect of TCC on intracellular Ca(2+) concentration in rat thymocytes was examined using Fluo-3, an indicator of intracellular Ca(2+). TCC at concentrations ranging from 0.1 μM to 3 μM increased intracellular Ca(2+) concentration biphasically: first by releasing Ca(2+) from intracellular Ca(2+) stores and then inducing Ca(2+) influx through store-operated Ca(2+) channels. The threshold TCC concentration to increase intracellular Ca(2+) concentration in this study was lower than the maximum TCC concentrations reported in human blood samples. Therefore, we anticipate that TCC at concentrations reported in human blood samples might disturb intracellular Ca(2+) signaling in human lymphocytes.

Nanomolar concentration of triclocarban increases the vulnerability of rat thymocytes to oxidative stress

It was recently reported that triclocarban was absorbed significantly from soap used during showering in human subjects and that its C(max) in their whole blood ranged from 23 nM to 530 nM. We revealed that a nanomolar concentration (300 nM) of triclocarban potentiated the cytotoxicity of 300 µM H(2)O(2) in rat thymocytes by using cytometric techniques with appropriate fluorescent probes. Although 300 nM triclocarban did not itself increase the population of dead cells (cell lethality), it facilitated the process of cell death induced by H(2)O(2), resulting in a further increase in the population of dead cells. Nanomolar concentrations (300 nM or higher) of triclocarban significantly decreased the cellular content of nonprotein thiol (glutathione), which has a protective role against oxidative stress. Triclocarban at 300 nM or higher increased the cell vulnerability to oxidative stress. The results may suggest that nanomolar concentration (300 nM or higher) of triclocarban affects some cellular functions although there is no evidence for adverse effects of triclocarban in humans at present.