Microplastics (PP, PE, PS, and PVC) Induce Structural and Functional Changes in Digestive Enzymes: Insights from Spectroscopic Approaches

Abstract Exposure to microplastics (MPs) poses evolving health risks due to their interactions with biological systems; however, their mechanistic effects on digestive enzymes remain incompletely understood. This study employed in vitro structural and functional analyses, utilizing spectroscopic and enzyme inhibition assays, to investigate the impact of various simulated secondary postconsumer microplastics (PC-MPs) at a single concentration (714 μg/mL/day) on digestive enzymes, including α-amylase, pepsin, and pancreatin. Structural analysis was performed in a simulated digestive fluid system, examining fluorescence and circular dichroism (CD) spectra, including fluorophore quantum yield, quenching percentage, amino acid residue changes, aggregation and complex formation, and the percentage of protein secondary structural content. Functional analysis was conducted using enzyme activity inhibition assays. Comparative spectroscopic findings highlighted marked conformational changes and functional disruptions in digestive enzymes. Fluorescence and CD spectra, along with secondary structure analysis, revealed a consistent loss of emission from (Tyr and Trp) amino acid residues and α-helices and β-sheets, indicating potential destabilization. From the observation, it is evident that PP-MPs have a pronounced impact on α-amylase and pepsin, whereas PE-MPs affect the pancreatic enzyme mixtures. On the other hand, functional analysis revealed that PP-MPs strongly inhibited the activities of salivary α-amylase, pepsin, and pancreatic α-amylase, whereas PS-MPs inhibited pancreatic protease. In the present study, the PP-MPs had a substantial effect on salivary α-amylase and pepsin. In the case of PE- and PS-MPs, distinct differences were observed with pancreatin enzyme, possibly due to the mixture of enzymes contained. This study reveals that PC-MPs disrupt the structure of digestive enzymes and impair their activity, raising concerns about digestive health.