Exposure of Polystyrene Micro- and Nanoplastics to Simulated Human Digestive Enzymatic Systems: Structural and Functional Implications

The current in vitro study explores the exposure of the emerging pollutants polystyrene micro- and nanoplastics (PS-MNPs) within the digestive system and their interaction with key digestive enzymes such as α-amylase, pepsin, and pancreatin. The present research aims to elucidate the potential health implications of digestive enzymes by PS-MNPs based on the previously estimated mean of ingested microplastics (MPs) (0.714 g/day). The study deepens our understanding of the environmental pollutants' impact on human health by examining the interactions between polystyrene (PS) microplastics (PS MPs, 37-50 μm approx.) and PS nanoplastics (PS NPs, 100 nm) with digestive enzymes. The study analyzes the effects of micro- and nanosized plastics on enzyme activity using multiple spectroscopic techniques, revealing the molecular mechanisms of enzyme inhibition and structural changes caused by PS NPs, more than those by PS MPs. The fluorescence emission spectra indicated a static quenching mechanism across all the digestive enzymes at <i>K</i> _q = 3.638, 4.615, and 1.855 (∼× 10¹⁸ M^-1·s^-1), predominantly affecting tyrosine (Tyr) and tryptophan (Trp) residues. Resonance light scattering (RLS) spectra confirmed the formation of enzyme-PS NPs complexes, leading to aggregation. Fourier transform infrared (FT-IR) and circular dichroism (CD) spectrometry results showed a decrease in protein content and structural alterations in the enzymes, potentially affecting their function. The half inhibitory concentration (IC₅₀) values of PS NPs for salivary α-amylase (180 μg/mL), pepsin (580 μg/mL), and pancreatic protease (314 μg/mL) indicate uncompetitive inhibition, and that of pancreatic α-amylase (592 μg/mL) indicates mixed reversible inhibition of digestive enzymes. The study highlights the potential health risks associated with PS NPs exposure and gives a broader understanding of the interplay between environmental plastic pollutants and human health.