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A recent review performed at the centre for Immunobiology at the University of Glasgow has been looking at whether disruptions to the microbiome could be a causative factor in the development of rheumatoid arthritis (RA), an auto-immune condition which causes pain and swelling in the joints. The researchers reviewed a number of clinical studies, looking firstly at whether RA sufferers display an imbalance in gut flora or not. They then secondly, reviewed clinical trials that have attempted to manipulate the microbiome through the use of probiotics, to assess whether or not probiotics could be a useful treatment option for the condition.
The researchers reviewed numerous studies and found that alterations in the intestinal microbiota are generally associated with arthritis, however different studies implicate different species of bacteria in the disease process. Some suggest that high levels of Prevotella could be indicative of RA for example, whereas others found low levels of Bacteroides or Akkermansia to be prevalent in people with the condition.
One study by Shar et al1 detected increases in Prevotella and Leptotrichia species, with a reduction in Bacteroides species, in the stool samples from patients with recent onset of RA. However these findings are in direct conflict with findings from two independent studies, by Vaahtovuo et al2 and Liu et al3 which reported an increase in Lactobacillus salivarius and L. ruminis, with a decrease in Prevotella species.
All the studies reviewed did show changes to RA sufferers microbial communities, however a pattern is yet to be found as to which species could be having a causative effect on disease onset and progression.
Given that alterations to the intestinal microbiota have been found in patients with RA, it has been suggested that modifying the flora might be a valuable therapeutic strategy. Early trials using animal models showed some encouraging results, however these are yet to be replicated in human models.
Interestingly, some trials have shown improvements in pathology markers, such as markers of inflammation, however those improved plasma markers have not translated in to clinical, or symptomatic improvements. A study by Malin et al4 showed that juvenile patients treated with L. rhamnosus GG showed an increase in Immunoglobulin A (a marker of immunity), and a decrease in TNF (tumour necrosis factor), a marker of inflammation. Even despite these clinical improvements however, the patients being treated had no real improvement in their symptoms or pain levels, thus the probiotic intervention was deemed not to be of clinical benefit.
Trials of probiotics in arthritis have therefore yielded fairly disappointing results, and more in-depth research is certainly still needed. In particular it is felt that study participant ages should be taken in to account when the studies are designed, as our microbial populations change as we age which adds another degree of complexity to the trial results.
Having said that, we think it's fascinating to see the increasing plethora of seemingly unrelated health conditions being linked to gut bacteria, so will continue to watch this space with anticipation. We do know that auto-immune conditions are increasingly being linked to gut permeability or 'leaky gut'; scientists believe that the weakening of the mucosal barrier (which probiotics are thought to play a significant part in maintaining) is a pivotal factor in the development of auto-immune diseases. It may therefore make sense to support your gut health or those with auto-immune diseases. Head over to Probiotic Professionals to read more about how gut bacteria may affect auto-immunity in general, or read Kerry's blog post for more information about probiotics and the immune system.