Can gut bacteria aid recovery from spinal cord injury?
A new paper in the Journal of Experimental Medicine suggests that they might.
It seems like every week there is a new study showing that the gut flora influences our health in new and unexpected ways. Every time I read the titles of these papers I am equal parts excited and sceptical.
This paper is no exception. The authors nicely show that spinal cord injury (SCI) in mice induces drastic changes in the gut microbiota and causes bacterial translocation across the epithelium. This in turn leads to inflammation which prevents recovery from SCI. They then show that administering probiotics post injury improved recovery by preventing bacterial translocation and reversing the dysbiosis.
This is intriguing work. The slight worry I have is not with the study itself but with the implications for probiotic use in general. As with many probiotic studies the key to seeing an effect is the amount of bacteria that are administered. Here the authors use 5 billion bacteria per day for 35 days for 1 mouse. Considering one bottle of Actimel contains 10 billion bacteria, adult humans would have to drink litres of the stuff every single day to get the same effect. The point is that to change the gut microbiota with probiotics, you have to put a lot of them in.
Medical grade probiotics are much different. The author resuspended 5 billion bacteria in 100 microlitres of water which is far more manageable as a treatment.
That shouldn't detract from this study which presents important and very interesting results. Is it time to start prescribing litres of probiotics to spinal cord injury patients just yet? I think more work needs to be done but this paper is a step in that direction and I look forward to seeing the follow up work.
The trillions of microbes that exist in the gastrointestinal tract have emerged as pivotal regulators of mammalian development and physiology. Disruption of this gut microbiome, a process known as dysbiosis, causes or exacerbates various diseases, but whether gut dysbiosis affects recovery of neurological function or lesion pathology after traumatic spinal cord injury (SCI) is unknown. Data in this study show that SCI increases intestinal permeability and bacterial translocation from the gut. These changes are associated with immune cell activation in gut-associated lymphoid tissues (GALTs) and significant changes in the composition of both major and minor gut bacterial taxa. Postinjury changes in gut microbiota persist for at least one month and predict the magnitude of locomotor impairment. Experimental induction of gut dysbiosis in naive mice before SCI (e.g., via oral delivery of broad-spectrum antibiotics) exacerbates neurological impairment and spinal cord pathology after SCI. Conversely, feeding SCI mice commercial probiotics (VSL#3) enriched with lactic acid–producing bacteria triggers a protective immune response in GALTs and confers neuroprotection with improved locomotor recovery. Our data reveal a previously unknown role for the gut microbiota in influencing recovery of neurological function and neuropathology after SCI.
Gut dysbiosis impairs recovery after spinal cord injury
Kristina A. Kigerl, Jodie C.E. Hall, Lingling Wang, Xiaokui Mo, Zhongtang Yu, Phillip G. Popovich