A study by the Microbiome Research Group in collaboration with the Hepato-Bilio-Pancreatic Surgery (HBP) and Liver Transplantation Group, both at the Vall d'Hebron Institute of Research (VHIR), has investigated the relationship between the microbiome and the success of liver transplants. The results publish at Science Direct showed that people with more complications and a worse prognosis continue to have dysbiosis, a change in the bacterial microbiota, one year after the operation. In contrast, people with a more positive post-surgery evolution had achieved a healthy level of microbiota within a year, both in terms of diversity and a reduction in the number of pathogens. On the other hand, the increase in the quality and health of the microbiota was associated with an improvement in indicators of good liver function.

The relationship between liver function and gut flora has been demonstrated in several studies that have found a direct link between dysbiosis and the aggravation of chronic liver disease. One hypothesis for this relationship is that the altered microbiota leads to increased intestinal permeability. This allows potentially pathogenic micro-organisms to reach the circulatory system, i.e. bacteria that are harmless in the gut but can cause damage in other contexts, such as liver damage. It was also known that immediately after liver transplantation all patients experience a reduction in the diversity and health of the microbiota, but no clear relationship had ever been found between the microbiota and the severity of the patient who received a new liver. 

The trial analysed the microbiota of 17 patients at Vall d'Hebron University Hospital before and after the intervention and followed them up to one year later. The patients' partners were recruited as a control group, as this allowed control of variables such as diet and lifestyle. Samples were also collected from the donors.
As previously found, all patients experienced a worsening of their gut flora after the surgery and then a gradual recovery. However, there were significant differences depending on the severity of the patient's liver disease, with the most severe patients experiencing a much steeper decline and a much slower recovery. One year after the surgery, patients with a mild prognosis had gut health levels comparable to their control group, while patients with a severe prognosis continued to have dysbiosis, with an above-average number of pathogens in their microbiota. 

Positive relationship between gut health and indicators of good liver function

The research found a link between improved gut health and improved indicators of albumin and gamma-glutamyltranspeptidase, two of the main markers used to assess liver health. This strengthens the hypothesis of a link between a healthy microbiota and good liver function. Further research is needed to find out whether and to what extent the microbiota influences typical transplant complications such as rejection or infection. 

Another of the research team's hypotheses, which the results seem to confirm, is that antibiotic treatment, which is longer and more intense in patients with a more severe form of the disease, is one of the factors affecting the microbiota. Dr. Itxarone Bilbao, from the Hepato-bilio-pancreatic Surgery (HBP) and Liver Transplant group, explains that ‘the antibiotic treatment received by the patient prior to the operation must be taken into account when assessing or seeking to mitigate the effect on their microbiota. Therefore, the different medical professionals have to work in a transversal and coordinated way’.

Although further studies are needed to unravel some of the unknowns of this research, Dr Chaysavanh Manichanh, head of the Microbiome research group, explains that the work represents ‘a major step forward in understanding the evolution of the microbiota after liver transplantation and should be the foundation for further research aimed at improving the health and recovery of transplant patients’.