Action mechanism as a cause of chronic constipation of inhaled and intravenously injected polystyrene nanoplastics in ICR mice.

The inhalation effects of airborne nanoplastics (NPs) on the gastrointestinal (GI) tract are rarely investigated, with most studies focusing only on the lungs and other organs. This study examined the changes in the key constipation phenotypes, mucin secretion, water and ion balance, and enteric nervous system (ENS) function in ICR mice after inhalation of polystyrene (PS)-NPs with 500 nm size for two weeks to determine if inhaled NPs can cause constipation. Significant constipation phenotypes, including the weight, water contents and morphology of stools, GI motility, intestinal length, histopathological structure of the colon, and concentration of GI hormone, were detected in NPs-inhaled ICR mice compared to a Vehicle-treated group. In addition, NPs-induced defecation delay was accompanied by a decrease in mucin secretion, suppressed transcription of mucin-related genes, and abnormal regulation of the colonic fluid transport system, including water and ions. NPs-inhaled mice showed a decrease in the neuronal cell density and dysfunction of excitatory neurons and inhibitory neurons in the ENS of the colon. Moreover, similar phenotypes for constipation were verified in ICR mice injected intravenously with NPs. Therefore, these results provide the first scientific evidence that inhalation and intravenous injection of PS-NPs can be considered as one of novel causes of constipation.