Gut-Liver Axis: Review on How Microplastics Can Cause Toxicity Through an Interaction Between the Gut, Microbial Community, and Liver
Microplastics can cause liver damage when consumed by terrestrial and aquatic organisms. This review proposes a novel mechanism to help explain the toxic effects following ingestion, which involves the gut, microbial community, and liver through the gut-liver axis.
What are microplastics?
Plastic fragments, fibers, films, and spheres that are between 0.1 µm and 5 mm in size are commonly described as microplastics. Natural processes, such as mechanical wear, biodegradation, and ultraviolet radiation break down plastics into microplastics, which can cause harm to organisms in terrestrial and aquatic environments through consumption. Microplastics may be harmful to organisms when consumed due to a blockage that can form in the gut, preventing the consumption of food, as well as from the plastic itself breaking down to cause toxicity from compounds that comprise it. Additionally, microplastics can serve as vectors for other contaminants, binding to the plastic and increasing toxic responses once taken in by the organism, which can be passed up the food chain.
The accumulation of microplastics in plants and animals can increase the potential of uptake in humans. As such, microplastics have been shown to be present in lungs, placenta, gonads, brain, blood, liver, and the gut. Once in the body, microplastics can cause oxidative stress, neurotoxicity, metabolic dysregulation, and an energy imbalance. Recent research has suggested that the microbiota living in the gut is impacted, leading to immune function responses, inflammation, and impaired digestion. However, there remains a lack of understanding of how microplastics may target certain tissues once in the body, with potential links involving the gut-liver axis, or the relationship between a dysbiosis of the bacterial community in the gut to liver damage.
Review focus
To better understand the interplay between the gut, liver, and the bacterial community that is in the gut, also known as the microbiome, and the influence that microplastics have on causing toxicity through the gut-liver axis, an integrated perspective was conducted to better conceptualize what is occurring and the mechanisms in which these effects are caused. This review includes studies conducted in mice, fish, chickens, and humans to understand the targets of microplastics across terrestrial and aquatic organisms, alike, to characterize the way in which microplastics are most likely causing toxicity once consumed. The information gathered from this review is two-fold, as it serves to identify the effects and associated mechanisms of microplastics, acting through the gut-liver axis, inducing toxicity through the liver and an imbalance in the microbial community comprising the intestine. Additionally, a new perspective is gained in the understanding of how microplastics can impact human health.
Relationship between the gut and liver axis
Recent studies have identified direct effects of microplastics to toxicity on the intestinal barrier, intestinal microbiome, and liver, although the interaction, or cross-talk, that can occur between these organs and bacteria has been viewed as targeted effects, opposed to the involvement of all acting in tandem. Microplastics enter into the gut, damaging the intestine, which then allows bacteria and metabolites to enter the blood stream to the liver through a weakened intestinal barrier. Once in the liver, this can induce damage through inflammation, oxidative stress, and altered metabolism.
More to be understood about influence of microplastics to organism health
Although the toxic effects of microplastics have been identified and suggested to act through the gut-liver axis, there remains some subsequent analyses that could be conducted to more fully characterize the mechanisms by which toxicity is seen. These may include a closer look into gut microbial structure changes and link to liver disease, as well as if metabolites, such as fatty acids and bile acids, can influence liver injury. Additionally, areas of interest to better target the treatment of liver disease is to gain a better insight if enhancing gut microbial health through the use of probiotics could help reduce liver-induced injury when exposed to microplastics.
Microplastics can cause liver damage when consumed by terrestrial and aquatic organisms. This review proposes a novel mechanism to help explain the toxic effects following ingestion, which involves the gut, microbial community, and liver through the gut-liver axis.
What are microplastics?
Plastic fragments, fibers, films, and spheres that are between 0.1 µm and 5 mm in size are commonly described as microplastics. Natural processes, such as mechanical wear, biodegradation, and ultraviolet radiation break down plastics into microplastics, which can cause harm to organisms in terrestrial and aquatic environments through consumption. Microplastics may be harmful to organisms when consumed due to a blockage that can form in the gut, preventing the consumption of food, as well as from the plastic itself breaking down to cause toxicity from compounds that comprise it. Additionally, microplastics can serve as vectors for other contaminants, binding to the plastic and increasing toxic responses once taken in by the organism, which can be passed up the food chain.
The accumulation of microplastics in plants and animals can increase the potential of uptake in humans. As such, microplastics have been shown to be present in lungs, placenta, gonads, brain, blood, liver, and the gut. Once in the body, microplastics can cause oxidative stress, neurotoxicity, metabolic dysregulation, and an energy imbalance. Recent research has suggested that the microbiota living in the gut is impacted, leading to immune function responses, inflammation, and impaired digestion. However, there remains a lack of understanding of how microplastics may target certain tissues once in the body, with potential links involving the gut-liver axis, or the relationship between a dysbiosis of the bacterial community in the gut to liver damage.
Review focus
To better understand the interplay between the gut, liver, and the bacterial community that is in the gut, also known as the microbiome, and the influence that microplastics have on causing toxicity through the gut-liver axis, an integrated perspective was conducted to better conceptualize what is occurring and the mechanisms in which these effects are caused. This review includes studies conducted in mice, fish, chickens, and humans to understand the targets of microplastics across terrestrial and aquatic organisms, alike, to characterize the way in which microplastics are most likely causing toxicity once consumed. The information gathered from this review is two-fold, as it serves to identify the effects and associated mechanisms of microplastics, acting through the gut-liver axis, inducing toxicity through the liver and an imbalance in the microbial community comprising the intestine. Additionally, a new perspective is gained in the understanding of how microplastics can impact human health.
Relationship between the gut and liver axis
Recent studies have identified direct effects of microplastics to toxicity on the intestinal barrier, intestinal microbiome, and liver, although the interaction, or cross-talk, that can occur between these organs and bacteria has been viewed as targeted effects, opposed to the involvement of all acting in tandem. Microplastics enter into the gut, damaging the intestine, which then allows bacteria and metabolites to enter the blood stream to the liver through a weakened intestinal barrier. Once in the liver, this can induce damage through inflammation, oxidative stress, and altered metabolism.
More to be understood about influence of microplastics to organism health
Although the toxic effects of microplastics have been identified and suggested to act through the gut-liver axis, there remains some subsequent analyses that could be conducted to more fully characterize the mechanisms by which toxicity is seen. These may include a closer look into gut microbial structure changes and link to liver disease, as well as if metabolites, such as fatty acids and bile acids, can influence liver injury. Additionally, areas of interest to better target the treatment of liver disease is to gain a better insight if enhancing gut microbial health through the use of probiotics could help reduce liver-induced injury when exposed to microplastics.