Efecto de los nanoplásticos en la fisiología tiroidea de células de mamífero

Despite international efforts that aim to reduce the impact of plastic, the production of these materials is not only expected to maintain the high trends of the last decades, but also to increase considerably in the near future. As a result, a great amount of plastic debris will join the already existing waste in landfills and the natural world. Big plastics are eventually broken down and become smaller fragments, microplastics (1 m - 5 mm) and nanoplastics (1 - 1000 nm), which spread all over the biosphere, from remote lakes in Patagonia to the snow that blankets the Alps. In turn, these small plastics are able to reach humans and all the other living beings on Earth, mainly through trophic transfer in the food chain and suspended in the air that we breathe, potentially causing harms which remain largely unknown. Due to their importance for normal development and other physiological processes, the thyroid gland and the hormones produced by it constitute targets of interest for the assay of the impact of microplastics and nanoplastics on human health. With that in mind, the following study aimed to quantify the internalization of polystyrene plastics (300 and 3000 nm) into rat follicular thyroid cells (PCCL3) via real-time image acquisition over a 72-hour incubation time. Furthermore, the effects of 30 nm and 300 nm nanoplastics on the expression levels of thyroid-related genes in PCCL3 cells were evaluated by quantitative polymerase chain reaction. Lastly, cells overexpressing the thyroid hormone transporter MCT8 were exposed to 300 nm and the transport of T3 was assayed. The results showed that nanoplastics entered the cells in a size and concentration-dependent manner. The 300 nm particles were more readily taken up by the cells than the 3000 nm ones. The expression of genes related to thyroid hormone synthesis and secretion was reduced when cells where exposed to 30 nm nanoplastics, while the opposite effect was true for the bigger plastics, showing an augmented expression. In terms of MCT8 function, 300 nm nanoplastics didn’t appear to cause inhibition of thyroid hormone transport across the cell membrane by that protein. This study provides new insights into the interaction and effects of differently-sized polystyrene nanoplastics (30, 300 and 3000 nm) on a follicular thyroid cell experimental model and on the MCT8 transporter.