Toxicity Assessment of Nano-ZnO Exposure on the Human Intestinal Microbiome, Metabolic Functions, and Resistome Using an In Vitro Colon Simulator

Nano-ZnO, as a commonly used nanomaterial,
has been found in drinking
water, food, and medicine; therefore, it poses potential health risks
via the digestion system. However, little is known about the toxicity
of nano-ZnO on the human intestinal microbiome, which plays critical
roles in human health. This study comprehensively investigated the
impact of nano-ZnO on the human gut microbiome, metabolic functions,
and resistome using an in vitro colon simulator. Nano-ZnO induced
concentration-dependent decreases in the production of short-chain
fatty acids (SCFAs). Metagenomic analysis revealed that nano-ZnO not
only led to dose-dependent shifts in the composition and diversity
of the gut microbiota but also changed the key functional pathways
of the gut microbiome. Although the diversity of the gut microbiota
basically recovered after stopping exposure to nano-ZnO, SCFAs still
showed a concentration-dependent decrease. Furthermore, although a
medium concentration of nano-ZnO (2.5 mg/L) reduced the abundance
of many antibiotic resistance genes (ARGs) by inhibiting the growth
of related host bacteria, a low concentration of nano-ZnO (0.1 mg/L)
greatly enriched the abundance of tetracycline resistance genes. Our
findings provide evidence that nano-ZnO can impact the diversity,
metabolism, and functional pathways of the human gut microbiome, as
well as the gut resistome, highlighting the potential health effects
of nanoparticles.