Exosome-Based Liquid Biopsy in Biliary Tract Cancer: Nanotechnology-Enabled Strategies and Future Perspectives.

Plastics are extensively utilized in medicine, agriculture, industry, and daily life due to their high yield, versatility, and low cost. However, the relentless growth in global plastic production has led to a corresponding surge in plastic waste (; ). Through physical, chemical, and biological degradation in the natural environment, plastic waste is broken down into increasingly smaller particles (). Microplastics (MPs), defined as plastic particles with diameters smaller than 5 mm, are widely distributed in freshwater, marine, and terrestrial ecosystems (; ). Because of their small size, MPs could be mistakenly ingested by many organisms, including marine zooplankton ( and ; ), zebra mussel (; ), whiteleg shrimp (; ), African catfish (; ), Nile Tilapia (; ), Japanese anchovy (; ), and human (; ). After ingestion, larger MPs tend to accumulate in the digestive tract and be excreted more quickly, whereas smaller ones can be transported through the digestive tract to the circulatory system and more likely to remain in the fish (). It has been reported that most MPs tend to be accumulated in and act on the intestinal tract, but a small proportion of MPs can be transferred to peripheral tissues and the circulatory system, crossing biological membranes and resulting in a significant ecological and societal issue worldwide (; ; ). For instance, aquatic organisms like fish, ingested MPs can accumulate in multiple internal organs, including the gut, gills, liver, and brain, subsequently inducing a spectrum of adverse effects such as gut microbiota dysbiosis, hypoactivity, molecular damage, growth inhibition, reproductive toxicity, neurotoxicity, and non-specific immunity response (; ; ; ; ). Globally, fish is gaining momentum as a result of its high protein level and low fat level. Consequently, there has been a growing emphasis on fish flesh quality and safety by consumers. Prior studies have indicated that MPs exposure adversely affects meat quality traits in chickens () and pigs () (; ). However, it remains unclear whether MPs can produce adverse effects on flesh quality, although it is indisputable that MPs have been accumulated in the fish body. Meat quality is governed by a multitude of factors, with muscle fiber properties playing a central role (). Consequently, any factor that alters muscle fiber properties may impact the final quality of meat. Research on pigs has demonstrated that MPs exposure reduces the density of type I muscle fibers and impairs angiogenesis within muscle tissue, thus potentially compromising meat quality development (). Consistently, the study performed by Wang et al., observed that MPs exposure decreased the average cross-sectional area (CSA) and diameter of muscle fibers in mice (), which are key determinants of meat yield and quality (). Given the established link between physical and biochemical characteristics of muscle fibers and meat quality, these terrestrial-animal studies provide a conceptual basis that MPs pollution may impair meat quality by disrupting muscle fiber properties. However, the specific impact of MPs on the fish flesh quality through muscle fiber characteristics has never been studied, and the underlying mechanisms remain to be determined. Acting as a second genome and a mediator of host-organ communication, the gut microbiota is implicated in the development of several chronic diseases, such as diabetes, obesity, autism, as well as schizophrenia (, ). Relevant studies have reported that ingestion of MPs could reshape the community structure of fish gut microbiota, and that gut microbiota homeostasis is closely linked to skeletal muscle metabolism and fiber phenotype (; , ). The hypothesis of the ‘gut–muscle axis’ has therefore been proposed by several authors (; ; ). Indeed, after fecal microbiota transplantation (FMT) from pigs, skeletal muscle characteristics could be transferred from pig donors to germ-free (GF) mice recipients (). Furthermore, the composition of muscle fiber types was regulated by the gut microbiota (). These evidences support the contention that the gut microbiota can influence muscle fiber characteristics. Studies conducted under both laboratory and natural conditions have demonstrated that the ingestion of MPs adversely alters the gut microbiota of aquatic animals (). Based on these findings, we hypothesize that MPs exposure perturbs the gut microbiota, and that these microbial changes may be associated with alterations in muscle fiber characteristics and impaired flesh quality in freshwater fish.