Liver Health: a role for probiotics?

The liver is an essential organ involved in more than 300 vital functions, the main ones being the absorption, storage and transformation of nutrients, the detoxification of toxic substances and the production of bile acids. But did you know that there is a crosstalk between the gut and the liver?

This bidirectional communication has been highlighted in the past decade and is more and more recognized and researched, allowing to understand the important role of the microbiome in the maintenance of liver health [Tripathi, 2018].

 The Gut-Liver axis

There is a bidirectional communication between the gut and the liver. These two organs communicate via the biliary tract and the portal vein. Liver products influence the gut microbiota composition, but the gut microbiota also has an impact on liver health.

The liver produces primary bile acids which are then excreted in the intestine through the gall bladder, which contribute to the absorption of fat from food intake and are also important in the preservation of microbial homeostasis. When bile acids reach the colon, the gut microbiota can transform a portion of bile acids from the liver into secondary bile acids. An impaired gut microbiota can shift the balance between primary and secondary bile acids, which in turn can alter liver signaling and cholesterol metabolism.

Intestinal permeability is also an important component in the maintenance of liver health. The gut barrier is composed of specific cells called enterocytes, that are tightly bound together to maintain the intestine’s impermeability. However, some external components like diet (alcohol intake or a fatty diet) stress, intense physical activity or changes in the gut microbiota can alter the gut barrier function, letting opportunistic microorganisms or microbial compounds enter the portal vein, a vein which is directly connected to the liver. These microbial compounds and opportunistic microorganisms, after reaching the liver, can then modify the normal gut-liver interactions and set the stage for abnormal metabolism and liver cell health. Therefore, it is important to maintain this barrier which is key to maintain the health of the liver, along with many other organs.

The gut microbiota has also an impact on several metabolic cycles that can have impacts on liver health:

• Choline is an essential nutrient found in food that is important for the maintenance of liver metabolism. Appropriate use by a normal gut microbiome can lead to healthy fat levels in the liver, supporting long term health of the host.
• Butyrate is a short-chain fatty acid produced by gut bacteria which facilitates maintenance of the gut barrier. Healthy butyrate levels produced by a healthy gut microbiota, leads to a strong gut barrier function, maintaining normal interactions between the gut and the liver.

How can probiotic help in the maintenance of liver health?

Probiotics, through their various modes of action can participate in the maintenance of liver health. First, probiotics can help maintain gut barrier integrity for normal gut-liver interactions. By competing with opportunistic microorganisms, producing antimicrobial products, and binding to epithelial cells, probiotics have been demonstrated to participate in the maintenance of gut barrier integrity. Probiotics can also support the maintenance of a healthy microflora to maintain proper choline, bile acids and short-chain fatty acids metabolism for a healthy liver. By maintaining a healthy gut microflora, probiotics can help maintain a proper choline metabolism, which assists in the excretion of VLDL in the liver and allows a normal triglyceride (main constituent of fat) metabolism. By maintaining a healthy gut microflora, probiotics can help in the maintenance of bile acid metabolism, which will allow the normal cycling of cholesterol metabolism. Finally, a healthy gut microbiota allows the normal production of butyrate by intestinal bacteria which helps in the maintenance of gut barrier integrity.

Probiotics for other uses than food and dietary supplements also showed promising results in the management of liver disease, such as Alcoholic Liver Disease (ALD) and Non-Alcoholic Fatty Liver Diseases (NAFLD). The intake of probiotic has been demonstrated to modify the gut microflora and ameliorate liver parameters among ALD patients [Han, 2015 ; Suk 2017]. Clinical studies in children with NAFLD taking medical probiotics that are not food or dietary supplements also showed improvement in liver parameters and symptoms of NAFLD, as well as improvement in total body fat and BMI [Yang, 2012; Cakir, 2017].