Comparison of triclosan and triclocarban in triggering immunotoxicity in larval zebrafish

Abstract:

As two efficient broad-spectrum sterilizing agents, triclosan (TCS) and triclocarban (TCC) are widely used, especially during the COVID-19 pandemic. The health risks caused by secondary pollution of TCS and TCC have aroused wide concern. Because of the similar mother nucleus structure and high lipophilicity, it remains unknown about the differences in the effect and mechanism of the toxicity (especially immunotoxicity) between TCS and TCC in organisms in the environment. In this study, we used zebrafish as a model to compare the immunotoxicity and mechanisms between the two pollutants at the same exposure concentration (0.6 µmol/L). The results showed that both TCS and TCC led to a hatching rate below 60% at the time point of 72 hours post fertilization (hpf) and the mortality rates of 40% and 50% at 120 hpf in larval zebrafish, respectively. The zebrafish exposed to TCS and TCC displayed malformations, such as shortened body, swimming sac closure, pericardial edema, yolk cyst deposition, and absorption disorder. Moreover, the developmental abnormalities caused by TCC were significantly severer than those caused by TCS. TCS exposure increased the proliferation rate of innate immune cells to 20% and decreased the number of mature T cells by 35%, while TCC exposure inhibited the differentiation of both innate immune cells and T cells, with the inhibition rates of 25% and 60%, respectively. The results of real-time quantitative PCR (RT-qPCR) and ELISA showed that TCS and TCC exposure up-regulated the expression levels of il-1β, il-6, and tnf-α, while il-10 and IgM exhibited opposite expression patterns. Additionally, both compounds slightly decreased C3 expression. The Pearson correlation analysis showed that the developmental toxicity induced by TCS and TCC had positive and negative correlations with the differentiation of immune cells, respectively. However, the toxicity induced by either TCS or TCC was positively correlated with the expression of pro-inflammatory cytokines. GO function and KEGG pathway enrichment analyses demonstrated that the target molecules of TCS and TCC were enriched in different signaling pathways, and the key network hub genes and the enriched regulatory pathways differed between TCS and TCC. The findings provide compelling evidence that TCS and TCC adopt different mechanisms in triggering immunotoxicity and offer a theoretical reference for the recognition, warning, and management of TCS and TCC-induced health risks.