Polylactic acid microplastics as metabolic disruptors: Linking gut dysbiosis to systemic toxicity by disrupting microbiota-host co-metabolism

The increasing application of polylactic acid (PLA) in consumer products leads to the widespread environmental distribution of its micro- and nano-plastics (PLA-MNPs). These particles pose potential health risks following environmental exposure, yet the mechanisms underlying their systemic toxicity remain inadequately defined. This review synthesizes current evidence demonstrating that PLA-MNPs accumulate in the intestine, compromising the gut barrier and inducing dysbiosis of the gut microbiota. We also explore the hypothetical role of disrupted gut microbiota-host co-metabolism - particularly involving aromatic amino acid pathways such as tryptophan metabolism - as a potential mechanism linking PLA-MNPs exposure to intestinal inflammation and injury, while acknowledging the current lack of direct experimental evidence for PLA-MNPs-specific effects on these pathways. By integrating literature on the gut-liver axis, we further elucidate how intestinal injury propagates to systemic metabolic disturbances. This overview aims to provide a structured synthesis of existing findings, identify key knowledge gaps, and suggest targeted approaches for future mechanistic and exposure-informed risk assessment of PLA-MNPs.