Nano‐plastics disrupt systemic metabolism by remodeling the bile acid–microbiota axis and driving hepatic–intestinal dysfunction

The pervasiveness of microplastic pollution poses a growing health risk, yet its long-term metabolic consequences remain poorly defined. Here, we exposed mice to polyethylene terephthalate nanoparticle (NP) and combined histopathology, biochemistry, metabolomics, and metagenomics to resolve their interactions. NP ingestion induced a severe systemic phenotype characterized by weight loss, organ atrophy, dyslipidemia, and gut barrier collapse. Mechanistically, NPs disrupted bile acid (BA) homeostasis by hyperactivating hepatic synthesis pathways while suppressing microbial 7α-dehydroxylation. This accumulation of cytotoxic BAs drove hepatic lipogenesis and aggravated mucosal inflammation. Crucially, metagenomics uncovered significant gut microbiota dysbiosis, where the enrichment of bile salt hydrolase-encoding taxa and depletion of 7α-dehydroxylating clades reinforced this BA imbalance. Furthermore, the microbiota exhibited functional deterioration, shifting toward glycan degradation with a concurrent loss of antibiotic resistance genes, signaling reduced ecological resilience. These findings identify BA dysregulation and specific microbiota functional losses as primary drivers of NP-induced systemic metabolic collapse. To the Editor, Microplastic (MP) pollution has become globally pervasive, and nano-sized particles (≤1 μm) are now detected in food, water, and indoor air, rendering human exposure nearly unavoidable. Their small size enables them to cross epithelial barriers, circulate systemically, and accumulate in distal organs such as the liver, kidney, and brain [1, 2]. Yet regulatory limits remain undefined because the mechanistic basis of their chronic organismal and molecular toxicity is still poorly understood. MPs are known to induce oxidative stress, inflammation, apoptosis, genotoxicity, and disrupt mitochondrial, epigenetic, and endocrine pathways [3, 4]. However, most evidence centers on isolated organ injuries, leaving unclear how chronic exposure perturbs coordinated metabolic regulation. The gut–liver–kidney axis—critical for nutrient sensing and xenobiotic detoxification—is strongly shaped by gut microbiota, which govern lipid metabolism, bile acid (BA) transformation, redox balance, and immune homeostasis [2]. Microbial metabolites such as short-chain fatty acids (SCFAs) and secondary BAs act through farnesoid X receptor (FXR) and G protein-coupled receptor 5 (TGR5) to maintain metabolic stability, whereas dysbiosis drives metabolic disease [5]. Whether nanoplastics (NPs) dysregulate this inter-organ microbe–metabolism network remains unknown. To address these issues, we established a 2-month NPs exposure model and applied systems-level analyses to construct an integrated “NPs–gut–microbiota–metabolism” framework, revealing how persistent exposure reprograms BAs signaling, microbial ecology, and systemic metabolic homeostasis. Institute of Cancer Research (ICR) mice were fed 200 nm-NPs for long-term exposure risk assessment, followed by histopathological, biochemical, metabolomic, and metagenomic analyses (Supporting Information S1: Figure S1A). Behaviorally, exposed mice remained hyperactive during the day (Supporting Information S1: Figure S1B). Because NPs may cross the gut–vascular barrier and accumulate in the hypothalamus, disrupting neurotransmitter turnover in orexinergic and catecholaminergic nuclei [2], this arousal likely reflects central involvement. Mechanistically, NPs may increase dopamine/norepinephrine synthesis, limit their degradation, and enhance glutamatergic signaling, thereby activating cAMP–PKA pathways and ion-channel phosphorylation (HCN, Na⁺, Ca²⁺) to sustain neuronal firing [5]. Food intake declined while water intake increased (Supporting Information S1: Figure S1C), and reduced nutrient availability combined with elevated expenditure led to weight loss after Week 5 (Supporting Information S1: Figure S1D). Colon shortening and reduced mass (–21.28%, –30.30%; Figure S1E) suggest chronic inflammation and epithelial atrophy that impair absorption and enteroendocrine signaling [2], further suppressing appetite. Liver and kidney mass also decreased (–27.46%, –38.24%; Supporting Information S1: Figure S1E), indicating catabolic remodeling. Serum biochemistry revealed systemic metabolic disruption: plasma glucose (+1.48-fold), triglyceride (TG) (+4.17-fold), total cholesterol (TC) (+1.79-fold), pyruvate (PYR) (+1.23-fold), and total bile acids (TBA) (+1.92-fold) increased (Supporting Information S1: Figure S1F), consistent with impaired hepatic lipid metabolism and perturbed FXR–SHP signaling [5]. Arginase (ARG) activity rose (+2.76-fold), diverting arginine from nitric oxide synthase, reducing nitric oxide, worsening insulin sensitivity and microvascular control, and aggravating hyperglycemia and renal concentrating defects [6]. Targeted metabolomics showed broad re-routing of energy flow: flavin adenine dinucleotide (FAD), guanosine monophosphate (GMP), guanosine triphosphate (GTP), and nicotinamide adenine dinucleotide phosphate (NADP) declined, while adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), nicotinamide adenine dinucleotide (NADH), cyclic adenosine monophosphate (cAMP), phosphoenolpyruvate (PEP), and pyruvate increased (Supporting Information S1: Figure S1G), indicating constrained mitochondrial oxidative phosphorylation—especially complex II—with compensatory glycolysis and gluconeogenesis [7]. Elevated ATP/ADP/AMP indicates accelerated substrate-level phosphorylation; increased PEP and GDP with reduced GTP suggests PCK1-driven gluconeogenesis. NADP depletion marks heightened oxidative stress with NADPH diverted to antioxidant defense, while 2-oxoacid accumulation indicates a pyruvate dehydrogenase (PDH) redox block [8]. Reduced GMP and elevated cyclic guanosine monophosphate (cGMP) suggest guanylate reallocation to second-messenger signaling, amplifying natriuretic and G protein coupled receptor (GPCR) pathways that intersect water–salt balance and BAs signaling [5, 9]. NPs provoked pronounced hepatic–renal remodeling. AB-PAS staining showed hepatocyte shrinkage, reduced lipid vacuoles, cytoplasmic loosening, fatty degeneration with eosinophilic bodies, lymphocytic infiltration, and congestion relative to orderly controls (Figure 1A). Hepatic TC and TG increased (2.18-fold, 2.08-fold), paralleled by renal TC and TG accumulation (TC +41.35%; TG +100.9%) (Figure 1B–E). Hepatic and renal TC/TG correlated positively (Supporting Information S1: Figure S2), and blood TC and TG also rose (Supporting Information S1: Figure S1F), indicating impaired hepatic lipid handling as a central driver of systemic dyslipidemia. The coordinated repression of Chrebp, Gk, and Pkm suggests a glucose-insensitive, low-glycolytic hepatic state, while the induction of Fas, Gpat, Dgat1, and Dgat2 drives de novo lipogenesis and triglyceride packaging [10]. Coupled with down-regulated Pparα and Cpt1α, this profile reflects a shift toward lipid storage with compromised mitochondrial fatty-acid oxidation (Figure 1F). Elevated serum TBAs and ARGs (Supporting Information S1: Figure S1F) indicate hepatocellular stress, disrupted nitrogen–lipid coupling, and perturbed FXR–SHP and SREBP1c feedback, linking TBA imbalance to cholesterol overload [5]. Inflammation mirrored metabolic injury. NF-κB p65, NLRP3, IL-1β, and IL-6 rose 1.14–4.09-fold in liver and kidney (Figure 1G), with renal Caspase-3 elevation (Figure 1H). Renal NF-κB/NLRP3/IL-6 correlated with hepatic Dgat1/Dgat2/Gpat (Supporting Information S1: Figure S2), highlighting inflammation-driven inter-organ coupling. Mechanistically, NF-κB inhibits Pparα-dependent β-oxidation, while inflammasome IL-1β suppresses Pparα/Cpt1α and activates SREBP1c, diverting acetyl-CoA to DGAT-mediated TG storage [3, 8]. BA dysregulation further enhances lipid accumulation via FXR–SHP and SREBP1c crosstalk [5]. In epididymal adipose tissue, Acl, Dgat1/2, and Gpa were downregulated (–44.43% to –66.56%) except Acc (Figure 1I), indicating systemic suppression of peripheral lipogenesis and lipid redistribution toward hepatic storage. Thus, NPs drive hepatic–renal lipid remodeling through inflammation–metabolism coupling, where NF-κB/NLRP3 activation limits FAO, enhances lipogenesis, and reinforces DGAT-dependent TG esterification (Figure 1J). NPs also accumulated along the intestinal epithelium (Figure S3A,B). AB-PAS staining revealed goblet-cell depletion, discontinuous mucus, shortened villi, and epithelial disorganization with lymphocytic infiltration and vacuolar degeneration (Supporting Information S1: Figure S3C). Oxidative balance deteriorated: reactive oxygen species (ROS) (+1.36-fold), malondialdehyde (MDA) (+1.42-fold), and NO (+1.35-fold) increased, while superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), myeloperoxidase (MPO), and GSH-Px decreased and oxidized glutathione (GSSG) rose (Supporting Information S1: Figure S3D), indicating impaired detoxification of O₂−/H₂O₂ and hydroperoxides and enhanced ONOO−-mediated protein/lipid damage [8, 11]. Muc1 and Retnlb rose, whereas Muc2, Muc3, Klf4, and Meprin-β declined (Supporting Information S1: Figure S3E). Barrier-gene responses were segment-specific: ileal ZO-1, CLDN2, OCLN, and SLC15A1 increased, while the colon displayed broad downregulation and ALP1 loss (Supporting Information S1: Figure S3F). This likely reflects Nrf2-mediated ileal reinforcement versus colonic NF-κB/NLRP3-driven collapse under higher microbial and oxidative burden [3, 5]. Inflammation reinforced dysfunction: NF-κB p65, NLRP3, IL-1β, IL-6, and TNF-α were strongly increased in colon and moderately in ileum (Supporting Information S1: Figure S3F). Correlation analysis (Supporting Information S1: Figure S3G) supports a coherent mechanism: NPs suppress antioxidants, elevate ROS and NO, impair mucus secretion, disrupt junctions, and amplify NF-κB/NLRP3 remodeling, forming a self-reinforcing cycle of oxidative imbalance, mucus loss, barrier collapse, and cytokine-driven inflammation [5]. NPs reshaped the BA pool, enriching primary conjugated BAs, including 7-ketoLCA, taurodeoxycholic acid (TDCA), allocholic acid (ACA), tauro-α-muricholic acid (T-α-MCA), glycoursodeoxycholic acid (GUDCA), taurohyocholic acid (THCA), taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA), glycocholic acid (GCA), α-muricholic acid (α-MCA), ursodeoxycholic acid (β-UDCA), 6,7-diketolithocholic acid (6,7-diketoLCA), and cholic acid (CA). Conversely, NPs depleted unconjugated and secondary BAs, such as tauro-β-muricholic acid (T-β-MCA), chenodeoxycholic acid (CDCA), β-muricholic acid (β-MCA), deoxycholic acid (DCA), lithocholic acid (LCA), and LCA-3S (Figure 2). Potential drivers include (i) adsorption or sequestration of cholesterol and BA intermediates, (ii) interference with hepatic CYP7A1/CYP27A1 caused by oxidative and mitochondrial stress, and (iii) disruption of microbial deconjugation and 7α-dehydroxylation [12]. Hepatically, elevated CA/TCA/GCA indicate hyperactivation of the classical CYP7A1–CYP8B1 pathway, diverting cholesterol toward CA/TCA rather than CDCA-derived species (Figure 2A). Reduced CDCA/β-MCA suggests suppression of the alternative CYP27A1–CYP7B1 arm, consistent with mitochondrial and oxidative inhibition of CYP27A1 [5, 13]. The sharp reduction of DCA/LCA reflects loss of microbial 7α-dehydroxylase activity. Thus, cholesterol is funneled toward CA/TCA while conversion to hydrophobic FXR/TGR5-active secondary BAs is blocked [14]. Altered BAs flux activates SREBP1c and weakens FXR–SHP feedback, promoting hepatic lipogenesis. Reduced CDCA/LCA diminishes FXR/TGR5 signaling that normally suppresses CYP7A1, restrains inflammation, and supports β-oxidation [13]. This aligns with the observed transcriptional reprogramming: Fas and Gpat induction drives fatty acid synthesis; and Pparα/Cpt1α downregulation suppresses β-oxidation (Figure 1F). DGAT1 upregulation further channels acetyl-CoA into triglyceride esterification [6], culminating in hepatic TG accumulation. Intestinal consequences are similarly profound. Loss of CDCA, DCA, and LCA—secondary BAs with epithelial-protective and anti-inflammatory activities—coincides with goblet cell depletion, reduced Muc2 expression, and weakened mucus continuity. Enrichment of cytotoxic hydrophobic BAs (CA, 7-ketoLCA, TDCA) intensifies epithelial injury and oxidative stress, elevating ROS/MDA and reducing SOD, CAT, GSH-Px, and MPO while increasing NO (Figure 2B and Supporting Information S1: S3D). Redox injury destabilizes tight junctions, producing compensatory upregulation in the ileum but collapse in the colon. BAs-driven oxidative stress activates NF-κB p65 and NLRP3 in the colon, increasing IL-1β, IL-6, and TNF-α (Figure 1G). These cytokines further suppress hepatic Pparα/Cpt1α and reinforce DGAT-mediated TG storage, integrating BA dysregulation with inflammation and lipid overload [15, 16]. Reduced LCA/CDCA also weakens FXR/TGR5-dependent anti-inflammatory signaling, locking the system into a pro-inflammatory, lipogenic state [14, 17]. Although our multi-dimensional data strongly support a major role of BAs remodeling in mediating hepatic–intestinal metabolic injury, causality remains to be validated. Future studies using BA sequestration, FXR/TGR5 modulation, or microbiota-directed interventions are crucial to disentangle BA imbalance from direct toxicity. Metagenomic profiling revealed that NP exposure fundamentally restructured the gut ecosystem across bacterial, fungal, and viral domains. Bacterial communities exhibited a marked decline in α-diversity (Supporting Information S1: Figure S4) and a shift toward deterministic assembly (Supporting Information S1: Figure S5A,B). Specifically, taxa abundance was significantly altered: carbohydrate-fermenting genera such as Prevotella and Bacteroides were enriched, whereas SCFA-producing and 7α-dehydroxylation-associated lineages like Ruminococcus_sp.1xD2123 and Lachnoclostridium_sp. An138 were depleted (Supporting Information S1: Figures S6A, 7). LEfSe analyses identified shifts in Prevotella, Bacteroides, and Alistipes (Supporting Information S1: Figure S8A and Supporting Information S1: Table S1). This bacterial contraction strongly correlated with elevated oxidative stress markers (e.g., SOD, GSH, MDA, ROS) (Supporting Information S1: Figure S9), reflecting a redox imbalance tied to the loss of beneficial microbes. Conversely, the fungal and viral biospheres expanded. Fungal populations showed increased diversity (Supporting Information S1: Figure S10) and dispersal (Supporting Information S1: Figure S5C,D), with enriched families like Aspergillaceae and Glomeraceae linking to sterol metabolism and ROS production (Supporting Information S1: Figures S6B, 11). LEfSe analyses revealed significant abundance shifts in genera including Puccinia, Lobosporangium, Erysiphe, and Trichoderma (Supporting Information S1: Figure S8B and Supporting Information S1: Table S1). These fungal shifts negatively correlated with mucosal barrier integrity markers (e.g., Muc1/2/3, Klf4, Meprin-b, Retnlb) (Supporting Information S1: Figure S9), suggesting that fungal overgrowth exacerbates goblet cell dysfunction. Similarly, viral diversity increased with higher stochasticity (Supporting Information S1: Figure S12). Gammaretrovirus, Betaretrovirus, and T7virus were enriched (Supporting Information S1: Figures S6C, 8C). Phylogenetically identified taxa, including Mouse mammary tumor virus and Microbacterium phage Lyell, were mapped to families (e.g., Retroviridae, Siphoviridae) strongly correlated with NF-κB/NLRP3 signaling and epithelial junction markers (e.g., SI, SLC15A1) (Supporting Information S1: Figures S9, 13). This indicates a viral mechanism driving NF-κB activation, barrier disruption, and enhanced phage-mediated gene transfer that exacerbates BA dysmetabolism [18]. Overall, enriched Prevotella/Bacteroides supply BSHs that deconjugate TCA/TCDCA, whereas loss of Ruminococcus/Lachnoclostridium reduces 7α-dehydroxylation and impairs CA/CDCA conversion to DCA/LCA [16]. Fungal expansion (e.g., Aspergillaceae, Glomeraceae) elevates ROS and competes for cholesterol substrates, while retroviridae amplification disrupts tight junctions and BAs transporters (taurocholic acid co-transport polypeptide, apical membrane sodium-dependent bile salt transporter protein) [5, 14, 18]. NPs-induced multi-kingdom dysbiosis drives BAs remodeling, hepatic lipogenesis, intestinal barrier failure, and systemic inflammation. Gene ontology (GO) analysis highlighted a strategic pivot toward defense responses and GPCR signaling (Supporting Information S1: Figure S14 and Supporting Information S1: Table S2), indicating intensified immunometabolic crosstalk where microbial metabolites (e.g., SCFAs, BAs) act as ligands to modulate enterohepatic circulation [5]. CAZy analysis further revealed a profound enzymatic restructuring from anabolic glycosylation to catabolic degradation: glycoside hydrolases (GHs) expanded to dominate the landscape (>40%) (Table S3), while glycosyltransferases (GTs) significantly declined (Supporting Information S1: Figure S15A,B). Parallel increases in CEs (11.4% → 12.2%) and PLs (1.2% → 1.8%), contrasted with a decline in AAs (1.6% → 1.1%) (Supporting Information S1: Figure S15C,D), reinforce a metabolic shift prioritizing aggressive polysaccharide cleavage over mucin-related glycosylation. Specifically, the upregulation of GH1, GH81, and GH119—primarily mapped to Muribaculaceae bacterium Isolate-105 and Firmicutes bacterium ASF500—accelerates saccharide hydrolysis (Supporting Information S1: Figure S15E). This functional shift increases monosaccharide availability, which fuels hepatic glycolytic-lipogenic flux and drives triglyceride accumulation via Chrebp and DGAT1 [19]. Conversely, the suppression of GT8 and GT10 from mucin-degrading specialists like Akkermansia muciniphila and Prevotella sp. impairs mucin O-glycosylation, directly compromising epithelial defense [4]. Furthermore, despite a general CBM expansion, the specific loss of butyrate-associated modules (CBM11, CBM71) deprives colonocytes of energy and weakens NF-κB suppression, thereby amplifying intestinal inflammation (Supporting Information S1: Figure S15F). Modest CE and PL increases (Anaerotruncus) further enhanced deacetylation and glycan cleavage, destabilizing microbial niches. Concurrently, ARG profiling exhibited a distinct “contraction-retention” pattern (Supporting Information S1: Figure S15G–I). While broad-spectrum resistance genes (vanI, tetW, pp-flo) significantly decreased (Supporting Information S1: Figure S15J and Supporting Information S1: Table S4), the multidrug efflux pump adeF was upregulated (Supporting Information S1: Figure S15K), indicating a survival strategy focused on retaining stress-adaptive capacity. Mechanistically, this functional collapse establishes a pathogenic feed-forward loop. 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