potentially offering early insight into possible links between the disease and gut germs.
The findings by an Italian team don’t confirm any connection between bacteria in the digestive system and diabetes. Still, “this study is probably the best example to date in the literature of inflammatory events happening in the gut that are correlated with type 1 diabetes,” said Aleksandar Kostic, PhD, of the department of microbiology and immunobiology at Harvard Medical School, Boston, who conducts similar research.
At issue: What role, if any, does the gut play in the development of type 1 diabetes (T1D)? Scientists already believe that the gut microbiome directly affects metabolism and the development of type 2 diabetes, according to Dr. Kostic. But T1D is an autoimmune disease, not a metabolic one, he said, “and the mechanisms are very different. For type 1, we don’t know a whole lot. We’re in the very early days.”
Still, “there’s a theory that inflammatory stimulus in the gut that is somehow partially responsible for causing T1D. The idea is that the microbiome is less diverse, which means that it loses its integrity in some way and loses the ability to crowd out inflammatory organisms,” he said in an interview.
For the new study, researchers led by scientists at Milan’s IRCCS San Raffaele Scientific Institute measured inflammation and the microbiome in the duodenal mucosa of 19 patients with T1D, 19 with celiac disease, and 16 healthy controls. They reported their findings online Jan. 19 (J Clin Endocrinol Metab. 2017. doi: 10.1210/jc.2016-3222).
The researchers found a unique inflammation profile through an analysis of gene expression in the patients with T1D. They called it a “peculiar signature” that’s notable for increased numbers of infiltration from the monocyte/macrophage lineage.
“In T1D patients, we didn’t observe any correlation between gene expression and [hemoglobin A1c] level, duration of diabetes, presence of secondary complications or the reason that led to endoscopy, indicating that gene expression was not influenced by these variables,” the researchers write.
They also found a “specific microbiota composition” featuring a reduction in the role of Proteobacteria and an increase in Firmicutes; this was unique to the T1D patients. Bacteroidetes “showed a trend to reduction” in both T1D and celiac patients compared to the controls.
“The expression of genes specific for T1D inflammation was associated with the abundance of specific bacteria in duodenum,” the researchers added.
Elena Barengolts, MD, of the division of endocrinology, diabetes, and metabolism at the University of Illinois, Chicago, who’s familiar with the study, said it appears to be valid. However, the methods used have limited powers to define specific types of bacteria, making it difficult to know if the germs in question are “bad” or “good,” she said in an interview.
For his part, Dr. Kostic said the findings are “really neat” and consistent with previous findings regarding the role of the gut microbiome and T1D. He pointed to a study he led that found less-diverse microbiomes in the guts of Finnish infants with T1D (Cell Host Microbe. 2015 Feb 11;17[2]:260-73).
As a result, the gut microbiome is “functionally capable of doing fewer things, and the community gets overrun by certain pathogens,” he said. “We saw that a lot of organisms were capable of promoting inflammation in the gut.”
Dr. Kostic, Dr. Barengolts, and the study authors report no relevant disclosures.