Polystyrene Microplastics Disrupt the Gut-Brain Axis via Activating Brain TLR4 and Impair Hippocampal Synapses through the TLR4/MyD88/NF-κB Pathway.

PS-MPs exhibit size-dependent bioaccumulation with enhanced barrier penetration at submicron scales.

• Bioaccumulation followed the pattern: 500 nm > 1 μm ≫ 5 μm
• Smaller particles (500 nm) demonstrated superior biodistribution compared to larger sizes
• 5 μm particles showed markedly inferior barrier penetration compared to submicron and 1 μm particles
• Enhanced penetration at submicron scales suggests a size threshold effect for barrier crossing

1 μm PS-MPs demonstrated maximum neuroinflammation despite inferior biodistribution compared to 500 nm particles.

• This was described as 'paradoxical' by the authors — 500 nm particles accumulated more but 1 μm particles caused greater neuroinflammation
• This dissociation between biodistribution and neuroinflammatory response suggests particle size influences biological reactivity independently of accumulation levels
• Both 500 nm and 1 μm sizes were classified as 'latent neurodegeneration risk factors'
• 5 μm particles were not highlighted as a major neuroinflammatory concern

PS-MPs induce gut dysbiosis-mediated barrier disruption that elevates circulating LPS levels.

• Both 500 nm and 1 μm PS-MPs induced gut dysbiosis
• Gut dysbiosis led to intestinal barrier disruption
• Barrier disruption allowed LPS (lipopolysaccharide) to translocate into circulation
• Elevated circulatory LPS subsequently translocated across a compromised blood-brain barrier (BBB)

PS-MPs activate the TLR4/MyD88/NF-κB signaling pathway in the brain, leading to pro-inflammatory cytokine surges.

• LPS translocation across the BBB triggers excessive activation of the TLR4/MyD88/NF-κB pathway
• Pathway activation was described as 'excessive'
• This activation induced 'a surge in pro-inflammatory cytokines'
• Brain TLR4 activation was identified as a key mechanistic node in the gut-brain axis disruption

PS-MPs ultimately cause synaptic lesions in the hippocampal region.

• Synaptic damage was localized to the hippocampal region
• The synaptic lesions were downstream consequences of the TLR4/MyD88/NF-κB pathway activation and cytokine surge
• Hippocampal synaptic damage is a hallmark of neurodegenerative processes
• The findings implicate PS-MPs (≤1 μm) as risk factors for neurodegeneration

PS-MPs disrupt the gut-brain axis through a mechanistic cascade involving intestinal dysbiosis, BBB compromise, and central neuroinflammation.

• The study identified a linked pathway: PS-MP exposure → gut dysbiosis → intestinal barrier disruption → elevated circulating LPS → BBB compromise → TLR4 brain activation → NF-κB signaling → pro-inflammatory cytokines → hippocampal synaptic lesions
• The mechanism connects peripheral gut effects to central nervous system damage via the gut-brain axis
• Both intestinal and central nervous system (CNS) damage were documented
• The study calls for 'urgent assessment of chronic exposure consequences' for smaller PS-MPs (≤1 μm)