Flares of systemic lupus erythematosus (SLE), particularly those involving severe kidney disease, were associated with growth spikes of the gut bacteria Ruminococcus blautia gnavus in a small, 4-year observational study that also demonstrated an underlying, inherent instability in the gut microbiome of patients with SLE.
Dr Gregg J. Silverman
Of 16 patients with SLE studied during the provision of routine care and monitoring, 5 had R. gnavus blooms that were “strikingly concordant with periods of raised disease activity,” Gregg J. Silverman, MD, of NYU Grossman School of Medicine, New York, and coinvestigators reported in Annals of the Rheumatic Diseases.
Four of the five patients with flare-associated R. gnavus blooms had lupus nephritis (LN); the other had a flare involving inflammation in multiple joints. The four patients with concurrent LN and spikes in R. gnavus also represented almost half of patients who had LN disease flares (four of nine) during the study period. The nine patients in the study with renal involvement, and the four with concurrent R. gnavus spikes and flares, represented different races and ethnicities.
The findings build upon research published by the NYU group several years ago showing that patients with SLE had more R. gnavus in the gut than similar patients without the disease, and that flares closely tracked major increases in R. gnavus growth. Evidence of R. gnavus expansions in patients with SLE now comes from several cohorts in the United States as well as cohorts in Europe and China, the researchers noted in their new paper.
An underlying, unstable microbiome
The new study at NYU took a “deeper dive” than previous research, looking at individuals over a longer period of time, Dr. Silverman, the study’s senior investigator and associate director of rheumatology at NYU Langone Health, said in an interview. Blood and a total of 44 stool samples from the 16 patients were analyzed, as were a total of 72 stool samples from 22 healthy control volunteers.
Importantly, he said, the gut microbiome in patients with SLE was found to be inherently unstable over time, compared with the microbiota communities of the controls. “There was an instability, a shifting dynamic composition of the microbiome [in patients with lupus]. … Healthy individuals had more of a balance, with small changes over time” and a stable, low abundance of R. gnavus, Dr. Silverman said.
Transient expansions of several pathogenic species occurred in some of the patients with lupus (and not in controls), but blooms of R. gnavus were the most common. The researchers said in their paper that they “speculate that susceptibility for specific clinical features during R. gnavus blooms reflect in part differences in genetic susceptibility of the patient.”
Patients on cytotoxic agents or antibiotics were excluded from the study, but the study was not designed to disentangle the potential influence of diet or prior antibiotic exposure, they noted. Larger studies are needed that are better controlled and that include more frequent assessments, Dr. Silverman added.
A sure association and probable cause
“There seems to be a special connection [of R. gnavus] to lupus nephritis, which is an important, major subset of disease,” said Martin Kriegel, MD, PhD, chief or rheumatology and clinical immunology at the University of Munster (Germany). Dr. Kriegel also researches the gut microbiome in lupus and was asked to comment on the new findings from NYU.
Dr Martin Kriegel
The “difficult question is, is the bug driving the flare [as the NYU paper proposes], or is it the lupus nephritis that leads to overgrowth?” he said, noting that it “is well known that kidney disease, whether from lupus or other causes, creates disturbances in the microbiome.”
It’s “likely the case” that the pathobiome – with R. gnavus being an important pathobiont – helps to drive flares, he said. The new research shows only an association, but studies done in mice – including prior research by Dr. Silverman – support a mechanistic link, said Dr. Kriegel, also adjunct associate professor of immunobiology and of medicine at Yale University, New Haven, Conn.
Investigators in the microbiome space are moving toward more strain-level analysis – “not only measuring what organisms are there, but culturing them and sequencing them,” Dr. Kriegel noted, and the new study does just this.
The R. gnavus strains isolated during lupus flares were distinguishable from strains found in healthy people – and from strains found by other researchers in patients with inflammatory bowel disease – by their common expression of a novel type of cell membrane–associated lipoglycan. The lipoglycans were recognized by specific serum IgG2 antibodies that were detected concurrently with R. gnavus blooms and lupus flares, Dr. Silverman and his colleagues reported.
Dr. Silverman and Dr. Kriegel both study the paradigm of a gut-barrier breach, whereby pathogenic bacteria cause intestinal permeability, allowing bacterial leakages that trigger inflammation and immune responses. “We think that in lupus and other rheumatic diseases like rheumatoid arthritis, a leaky gut barrier is an important mechanism, even though these patients don’t have gastrointestinal symptoms,” said Dr. Kriegel, who has studied the role of another potentially pathogenic bacteria, Enterococcus gallinarum, in SLE.
Strengthening the gut barrier may be a plausible, general approach to reducing the severity of diseases like SLE and RA until more personalized approaches targeting individuals’ microbiome are developed, he noted.
Future treatments involving antibacterial agents, probiotics or dietary regimens that prevent imbalances in the gut microbiome would be “benign,” compared with currently utilized immunosuppressive medications, Dr. Silverman said.
The NYU study was funded in part by grants from the National Institutes of Health and the Lupus Research Alliance. Dr. Silverman disclosed that NYU has filed a patent application for an antibody test to detect serum antibodies to the lipoglycan made by some strains of R. gnavus. Dr. Kriegel disclosed that he holds a patent at Yale related to the Enterococcus bacteria he studies, and that he consults for Roche, Enterome, and Eligo Biosciences.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.