Table 4.

Impacts of microplastics on the development of intestinal diseases and associated molecular mechanisms

Disease type	Biological effect	Mechanism	Reference
Gut dysbiosis	Human colonic microbiota changed Reduced Staphylococcus sp, Bifidobacterium spp., Clostridium spp., Enterobacteriaceae spp.	Colonic microbiota adherence to microplastics leads to biofilms formation	Tamargo et al. (2022b)
Gut dysbiosis	Colonic microbiota changes, inflammation	Enrichment of Chlamydia, Firmicutes, and Proteobacteria	Souza-Silva et al. (2022)
Gut barrier dysfunction and dysbiosis	Induction of gut barrier dysfunction and microbiota dysbiosis	Reduced intestinal mucus secretion Increased intestinal permeability Decreased expression messenger ribonucleic acid levels of colonic mucus secretion-related genes Modulation of gut microbiota composition	Chen et al. (2022b)
Gut inflammation	Transcriptional changes in the colon Inflammatory responses	Interaction between microplastics and the lumen side of the colonic epithelium Activating innate lymphoid cells, which could migrate to joint tissues and induce inflammation, worsens arthritis	Rawle et al. (2022)
Gut inflammation	Induced inflammation Increased nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), interleukin-6, tumour necrosis factor-α, interleukin-1β protein levels	Decreased thickness of mid-colon mucosa, muscle, flat luminal surface, and crypt layer Increased nucleotide-binding domain, leucine-rich–containing family, pyrin domain–containing-3 (NLRP3). Apoptosis-associated speck-like, cleaved caspase-1 increases nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB ad p-IκB α) protein expression	Choi et al. (2021b)
Inflammatory bowel disease	Modulating the disease process in the induction of inflammatory bowel disease	Microplastic exposure is involved in disease progression Inflammatory bowel disease may enhance the retention of microplastics	Yan et al. (2022b)
Non-specific	Microplastics interact with lipid droplets and lipases, hence, reducing lipid digestion	Microplastics decreased the bioavailability of lipid droplets via the formation of large lipid-microplastics heteroaggregates Microplastics adsorbed lipase and changed the secondary structure of the enzyme	Tan et al. (2020)
Non-specific	Worsens Helicobacter pylori infection Inducing inflammation	Increased gastric organ index, myeloperoxidase, tumour necrosis factor-α and interleukin-6 Increased bacterial colonisation, improved microplastic entry into tissues, and promoted gastric injury and inflammation Microplastics act as stable habitats for bacteria	Tong et al. (2022)

Microplastic ingestion could cause gut dysbiosis by changing the colonic microbiota, inducing inflammation, causing gut barrier dysfunction, aggravating or inducing inflammatory bowel disease, affecting lipid digestion, and may worsening Helicobacter pylori infection.