Larval Exposure to Polychlorinated Biphenyl-126 Led to a Long-Lasting Decrease in Immune Function in Postmetamorphic Juvenile Northern Leopard Frogs, Lithobates pipiens

Insight into the mechanism of melatonin in attenuating PCB126-induced liver injury: Resistance to ROS-dependent NETs formation to alleviate inflammation and lipid metabolism dysfunction

3,3',4',4',5-Polychlorinated biphenyls (PCB126) is classified as a persistent organic environmental pollutant that can cause liver damage by producing excessive reactive oxygen species (ROS). ROS also can stimulate neutrophil extracellular traps (NETs) formation, which cause damage to organism if NETs are produced in excess. Melatonin is generally considered to possess strong antioxidant and anti-inflammation prosperities, but it is unclear whether it can alleviate PCB126-induced injury. To explore whether PCB126-induced liver injury is related to the formation of NETs and whether melatonin has a potent protective effect, we established PCB126 exposure/ PCB126 and melatonin co-treatment mouse models by gavage. To further clarify the specific mechanism, we also cultured neutrophils and AML12 cells to replicate in vivo model. Here, we found PCB126 exposure resulted in an elevation in the activities of MDA, LPO, PCO, and 8-OHdG, and a reduction in the activities of CAT, GSH-PX and SOD. We found that PCB126 exposure led to an elevation in the expression levels of chemokines (CCL2, CCL3, CCL4, CXCL12, and CXCL8) and marker factors for NETs formation (MPO, NE, NOX2, PKCα, and PKCζ) in the PCB126 group. IF, SYTOX staining, and SEM results also revealed that PCB126 could stimulate NETs formation. In addition, results of a co-culture system of PBNs and AML12 cells revealed that the expression levels of inflammatory cytokines (IL-1β, IL-6, and TNF-α) significantly decreased and the expression levels of metabolism factors (Fas, Acc, and Srebp) slightly decreased for scavenging NETs, indicating NETs formation aggravated PCB126-induced hepatic damages. Noteworthy, treatment with melatonin reversed these results. In summary, our findings revealed that melatonin alleviated hepatic damage aggravated by PCB126-induced ROS-dependent NETs formation through suppressing excessive ROS production. This finding not only enriches toxicological mechanism of PCB126, but more importantly extends biological effects of melatonin and its potential application values.

Toxicity assessment of polyethylene microplastics in combination with a mix of emerging pollutants on Physalaemus cuvieri tadpoles

Studies in recent years have shown that aquatic pollution by microplastics (MPs) can be considered to pose additional stress to amphibian populations. However, our knowledge of how MPs affect amphibians is very rudimentary, and even more limited is our understanding of their effects in combination with other emerging pollutants. Thus, we aimed to evaluate the possible toxicity of polyethylene MPs (PE-MPs) (alone or in combination with a mix of pollutants) on the health of Physalaemus cuvieri tadpoles. After 30 days of exposure, multiple biomarkers were measured, including morphological, biometric, and developmental indices, behavioral parameters, mutagenicity, cytotoxicity, antioxidant and cholinesterase responses, as well as the uptake and accumulation of PE-MPs in animals. Based on the results, there was no significant change in any of the parameters measured in tadpoles exposed to treatments, but induced stress was observed in tadpoles exposed to PE-MPs combined with the mixture of pollutants, reflecting significant changes in physiological and biochemical responses. Through principal component analysis (PCA) and integrated biomarker response (IBR) assessment, effects induced by pollutants in each test group were distinguished, confirming that the exposure of P. cuvieri tadpoles to the PE-MPs in combination with a mix of emerging pollutants induces an enhanced stress response, although the uptake and accumulation of PE-MPs in these animals was reduced. Thus, our study provides new insight into the danger to amphibians of MPs coexisting with other pollutants in aquatic environments.