Oral halloysite nanotubes-induced subacute toxicity in the large intestine of mice and recovery

Natural halloysite nanotubes (HNTs) with a hollow lumen have been widely applied in many fields, such as traditional Chinese medicines, drug carriers, cosmetics, feed additives, antibacterials and water purification. However their toxicity in the gastrointestinal tract is still unclear. The aim of this study is to evaluate subacute oral toxicity of HNTs in the large intestines of mice and their recovery from it. Oral HNTs at low dose (5 mg/kg) for 30 days had no obvious adverse effect on the large intestine. Oral HNTs at high dose (50 mg/kg) for 30 days induced Al and Si accumulation and oxidative stress in the large intestine as indicated by the significant decreases in GSH-Px and SOD activities and the significant increase in MDA level in the large intestine, which caused significant increases in COX-2 and iNOS levels and inflammatory response and iNOS-mediated damages in the large intestine. Oral HNTs-induced changes at high dose described above were not observed after a 30 days recovery period, suggesting that oral HNTs-induced subacute toxicity in the large intestine was reversible.