Heart transplant outcome linked to gut bacteria, study finds

Oct. 4 (UPI) -- Gut bacteria appears to play a key role in whether a body accepts a transplanted heart, according to a study.

Researchers at the University of Maryland School of Medicine studied the causal relationship between the presence of certain microbes and transplant outcome. The study was published published Thursday in the Journal of Clinical Investigation Insight.

"From our previous work we suspected that the microbiome might have an effect on how transplanted organs are accepted," Dr. Emmanuel Mongodin, an associate professor of microbiology and immunology at the UMSOM Institute for Genome Sciences, said in a press release. "This work clearly shows that there is a connection between these gut microbes and the body's response to the new organ. It's very exciting."

These findings can significantly change how researchers and doctors handle rejection and transplantation.

"Understanding the molecular mechanisms that govern the interplay between the microbiota - or specific bacterial species - and the host system will allow for the development of targeted strategies that should allow for improved prognostic or diagnostic tests in a clinical setting, or even for interventions targeting the microbiota that would promote an environment more favorable to transplant health," the authors wrote.

This is the first study to identify specific bacterial species that can affect whether a heart transplant is rejected, and how quickly it can happen.

The immune system is the link between the transplanted heart and the microbiome. Certain bacteria can trigger pro- or anti-inflammatory signals, which in turn affect how the immune system responds to the transplanted organ, the authors said.

Researchers and doctors haven't been able to improve the long-term organ rejection rate, the Maryland scientists noted.

The overall survival rate in the United States of heart transplants is about 88 percent after one year and about 75 percent after five years, according a 2014 report by the Organ Procurement and Transplantation Network and the Scientific Registry of Transplant Recipients.

Study co-author Jonathan S. Bromberg, who has transplanted hundreds of organs, knows first-hand the problem of rejection and knew many variables determine outcomes, such as quality of the donor organ and recipient factors, such as age, obesity, other organ system dysfunction.

But he want to find other factors and focused on microbiome.

"The more I looked, the more it seemed there might be something there," Bromberg, a professor of surgery, microbiology and immunology at UMSOM, said. "The immune system is deeply intertwined with our gut microbiome, and I wanted to explore this connection in more depth."

Studying mice, the two scientists found that by adjusting the microbiome, they could improve the outcome of the heart transplant.

For example, particular strains of bifidobacterium seem to have an anti-inflammatory and beneficial effect on transplant outcomes.

This process may be similar for other organs, such as kidneys.

Ultimately, they hope to mimic the effect with drugs.