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Small polystyrene microplastics interferes with the breakdown of milk proteins during static in vitro simulated human gastric digestion

ABSTRACT: Human ingestion of microplastics (MPs) is common and inevitable due to the widespread contamination of food items, but implications on the gastric digestion of food proteins are still unknown. In this study, the interaction between pepsin and polystyrene (PS) MPs was uncovered by investigating its effect on enzyme activity and conformation while in a simulated human gastric environment. The impact on food digestion was also determined by monitoring the kinetics of protein hydrolysis through static in vitro gastric digestion of cow’s milk contaminated with PS. The binding of pepsin to PS showed that surface chemistry of MPs dictates binding affinity. The key contributor to pepsin adsorption seems to be π−π interactions between the aromatic residues and the PS phenyl rings. During quick exposure (10 minutes) of pepsin to increasing concentrations (222, 2219, 22188 particles/mL) of 10 μm PS (PS10) and 100 μm PS (PS100), total enzymatic activities were not affected remarkably. However, upon prolonged exposure at 1 and 2 hours, preferential binding of pepsin to the small, low zeta-potential PS caused structural changes in the protein which led to a significant reduction of its activity. Digestion of cow’s milk mixed with PS10 resulted in transient accumulation of larger peptides (10-35 kDa) and reduced bioavailability of short peptides (2-9 kDa) in the gastric phase. This, however, was only observed at extremely high PS10 concentration (0.3 mg/mL or 5.46E+05 particles/mL). The digestion of milk peptides, bound preferentially over pepsin on the hard corona around PS10, was delayed up to 15 minutes in comparison to bulk protein digestion. Intact caseins, otherwise rapidly digested, remained bound to PS10 in hard corona for up to 15 minutes. This work presents valuable insights regarding the interaction of MPs, food proteins, and pepsin, and their dynamics during gastric digestion which provides new knowledge and understanding on the potential risks of MPs to human health.

INSTRUMENT(S): Orbitrap Exploris 240

ORGANISM(S): Bos Taurus (bovine)

SUBMITTER: Tamara Vasovic

LAB HEAD: Tanja Cirkovic Velickovic

PROVIDER: PXD041715 | Pride | 2024-03-19

REPOSITORIES: Pride

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Project description:Milk, renowned for its nutritional value, harbours bioactive compounds, including lactoferrin (Lf) [1], immunoglobulins, and functional proteins suggesting broader functionalities beyond nutrition. Lf, an iron glycoprotein, exhibits antimicrobial properties against bacteria, fungi, and viruses."In"this st"dy, Immune Powder (a functional dairy formulation) and Fractionated Milk Protein (FMP; a blend of bioactive proteins isolated from skim milk) containing Lf, zinc, and immunoglobulins produced by Ausnutria Australia Dairy Pty Ltd were evaluated for their broad spectrum pharmacological activity. In particular, the study aims to investigate the antibacterial (against pathogenic Escherichia coli), prebiotic (promoting Lactobacillus delbrueckii growth), anti-inflammatory (against RAW264.7 macrophages), and antiviral (against human coronavirus 229E, HCoV-229E cultured on MCR-5 cells) effects of the formulations. In addition, the impact of simulated gastric digestion on the efficacy of the formulations was explored. LCMS-based proteomics analysis was implemented to unveil cellular and molecular mechanisms underlying antiviral activity. The Immune Powder demonstrated antibacterial activity against E. coli (up to 99.74 ± 11.47% inhibition at 62.5 mg/mL), coupled with prebiotic action (10.84 ± 2.2 viability fold change at 125 mg/mL), albeit diminished post-digestion (p <0.01). The Immune Powder effectively mitigated inflammation by reducing NO production, with efficacy declining post-digestion (p < 0.0001). The potential antiviral activity of Immune Powder against HCoV-229E also shown an increase of 2.62 ± 0.42 in cell viability when treated at 500 µg/mL. Similarly, FMP exhibited antibacterial potency pre-digestion at high concentration (95.56 ± 1.23% inhibition at 125 mg/mL), and post-digestion at lower doses (61.82 ± 5.58% inhibition at 3906.25 µg/mL). FMP also shown enhanced prebiotic activity post-digestion (p < 0.0001), anti-inflammation pre-digestion, and significant antiviral activity against HCoV-229E (1.72 ± 0.52 cell viability fold change). The proteomics study suggested both formulas shared similar antiviral mechanism by inhibiting scavenger receptor binding and ECM interaction.

			Action	DRS
	OE0705.mgf	Mgf
	OE0705.raw	Raw
	OE0706.mgf	Mgf
	OE0706.raw	Raw
	OE0707.mgf	Mgf

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Small polystyrene microplastics interferes with the breakdown of milk proteins during static in vitro simulated human gastric digestion

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