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Discriminating microplastics from lipid artifacts in the human brain: refined digestion and multi-analytical strategies to overcome matrix effect challenges in neuro-toxicology
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Scientists trying to detect microplastics in human brain tissue have run into a tricky problem: the brain's natural fats can clump together in ways that look just like plastic particles under lab instruments, leading to false alarms. This study developed a more reliable cleanup method, using a specific combination of chemicals, that strips away these fat clumps without destroying or distorting real plastic particles, giving researchers a more trustworthy way to measure how much plastic actually builds up in our brains. This matters because as concerns grow about microplastics' health effects, we need accurate detection methods before we can draw real conclusions about the risks.
The detection of micro- and nanoplastics (MNPs) in the human brain is a critical frontier in neurotoxicology, yet analysis is severely hindered by the brain’s complex, lipid-rich matrix. Recent concerns regarding “false positive” signals from endogenous fats necessitate the development of rigorous, validatable pretreatment protocols. This study optimized pretreatment procedures for post-mortem human dorsal thalamus samples. We compared oxidative (H₂O₂), alkaline-oxidative (NaOH/H₂O₂), and acidic microwave-assisted (HNO₃) digestion. MNP presence and polymer integrity were cross-validated using a multi-analytical suite: Laser Direct Infrared (LDIR) imaging, Optical Photothermal Infrared (O-PTIR) spectroscopy, SEM-EDS, and MALDI-TOF MS. Lipid removal efficiency was quantitatively assessed via GC-MS. Standard oxidative or alkaline digestions were found insufficient, as they promote the formation of insoluble zinc and calcium lipid salts (soaps) that mimic polymer spectra. A critical methodological advancement was achieved by incorporating an ethanol-assisted solvent stage and a 5% acetic acid filter rinse. This dual-action approach significantly facilitated the removal of recalcitrant fatty compounds (e.g., C16:0) and dissociated lipid-metal complexes. While acidic microwave digestion provided rapid matrix destruction and high filtration rates, it caused unacceptable degradation of synthetic polymers (e.g., PS, PET), as confirmed by MALDI-TOF signals in the filtrates. The optimal protocol for maintaining polymer integrity while ensuring a clean matrix was identified as a two-step process: (1) 0.05 M NaOH/30% H₂O₂ (1:2.5, v/v) at 50 °C, followed by (2) ethanol (1:1, v/v) addition and a 5% acetic acid rinse. This study provides a refined analytical framework for neurotoxicological research, ensuring that the reported biodistribution of environmental contaminants in the central nervous system is free from endogenous organic interference. Not applicable.
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