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Beyond C. difficile: The future of fecal microbial transplantation



– Two leading figures in microbiome research took time during the annual Digestive Disease Week to share their perspective with members of the press. Identifying key research presented at the meeting and painting a broader picture of trends and challenges in research on the interplay with the microbiota with gut health, Colleen Kelly, MD, of Brown University, Providence, R.I., cochair and principal investigator, AGA FMT Registry Steering Committee, led off the round table with a discussion of human research on fecal microbial transplantation (FMT) and obesity.

Purna Kashyap, MBBS, of the Mayo Clinic, Rochester, Minn., member, AGA Center for Gut Microbiome Research and Education Scientific Advisory Board, delved into the potential for donor microbiota transplant to address small bowel disorders, such as small intestinal bacterial overgrowth, and provided commentary regarding the potential – and limitations – of using FMT in functional bowel disorders such as irritable bowel syndrome (IBS).


Dr. Kelly noted that two abstracts at the conference presented data about FMT in obesity. The first study was presented by Jessica Allegretti, MD, a gastroenterologist at Brigham and Women’s Hospital, Boston; the second study was presented by Elaine Yu, MD, an endocrinologist at Massachusetts General Hospital, Boston.

The two studies shared some similarities, but had some differences, said Dr. Kelly. “They both used lean donor encapsulated FMT ... and they both were placebo controlled, using placebo capsules.” The first study looked at metabolically healthy obese patients, while the second study included patients with mild to moderate insulin resistance.

Dr. Allegretti’s work looked at the effect that FMT from lean donors had on levels of a satiety peptide, glucagonlike peptide–1 (GLP-1), while also looking at changes in weight and microbiota, as well as safety. Patients received an initial 30-capsule dose as well as two later doses of 12 capsules each. The 22-patient study, in which individuals were randomized 1:1 to FMT or placebo capsules, didn’t show statistically significant changes in GLP-1 levels or body mass index with FMT over the 12-week study period. “But they were able to show engraftment, which I think is an important thing that you do wonder about – over this period of time, the bacteria that came from the lean donor actually engrafted into the recipient and affected the diversity. The recipient became more similar to the donor,” said Dr. Kelly.

There were some clues among the findings that engraftment was effecting metabolic change in the recipient, she said, including differences in bile acid conversion among gut bacteria; also, lower levels of the primary bile acid taurocholic acid in recipients after FMT. “So it was a negative study in what she was looking for, but an example of these smaller studies kind of pushing the field along.”

In discussing the study presented by Dr. Yu that examined lean donor FMT in individuals with insulin resistance, Dr. Kelly said, “It was actually pretty sophisticated.” By using hyperinsulinemic euglycemic clamping, the investigators were able to measure insulin sensitivity based on glucose load. In this study of 24 individuals randomized 1:1 to receive FMT or placebo capsules, recipients received weekly doses over a period of 6 weeks. Here again, though Dr. Yu and colleagues again found engraftment, “they did not find the big changes in metabolic parameters that they hoped that they would,” said Dr. Kelly.

These two studies furthered previous work completed in the Netherlands examining lean donor FMT for individuals with metabolic syndrome. “Those [studies] did show both engraftment and some changes in insulin resistance,” but they were also small studies, noted Dr. Kelly. Dr. Kashyap pointed out that the earlier studies had shown in a subgroup analysis that response to FMT was limited to those patients who lacked microbial diversity pretransplant.

This makes some mechanistic sense when thinking about FMT’s greatest success to date: Treating Clostridioides difficile infection, a condition whose very hallmark is dysbiosis characterized by monospecies gut domination, noted Dr. Kashyap.

Added Dr. Kelly, “I think everyone’s hoping there’s going to be this pill that’s going to make us skinny, but I don’t think we’re going to find that with FMT and obesity. I do think these studies are important, because there’s so much animal data already, and we’re kind of like, ‘How much more can you do in mice?’ ” By translating this preclinical work into humans, the mechanisms of obesity and the role of the microbiome can be better understood.


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