12 January - 20 June 2016

Dietary fibre reduces brain inflammation during ageing

As the brain ages, some tissues become inflamed and it is this neuroinflammation which is typically associated with neurodegenerative diseases and eventually leads to memory loss and cognitive impairment in older individuals. Butyrate, a short-chain fatty acid, produced primarily by bacterial fermentation of fibre in the colon is attributed with anti-inflammatory properties in animal models and it has been hypothesised that its presence can lead to neurological benefits by reducing brain inflammation. A study by researchers in nutritional immunology at the University of Illinois, published in Frontiers in Immunology, has sought to investigate the decrease in neuroinflammation through dietary soluble fibre due to increased butyrate in the guts of aged mice.

As the brain ages, some tissues become inflamed and it is this neuroinflammation which is typically associated with neurodegenerative diseases and eventually leads to memory loss and cognitive impairment in older individuals.

Butyrate, a short-chain fatty acid, produced primarily by bacterial fermentation of fibre in the colon is attributed with anti-inflammatory properties in animal models and it has been hypothesised that its presence can lead to neurological benefits by reducing brain inflammation.  A study by researchers in nutritional immunology at the University of Illinois, published in Frontiers in Immunology, has sought to investigate the decrease in neuroinflammation through dietary soluble fibre due to increased butyrate in the guts of aged mice.

Research initially focused on the effects of butyrate on sickness-induced adult (3 to 6 months) and aged (22 to 25 months) male Balb/c mice. The mice were injected with either a control (saline) or sodium butyrate (NaB) (1.2 g/kg body weight) followed 2 hours later by saline or lipopolysaccharide (LPS) (0.33 mg/kg body weight) to induce neuroinflammation. Matt et al. found that the mice pre-treated with NaB had decreased gene expression of inflammatory markers, with the effects being more pronounced in the aged mice, confirming the anti-inflammatory affects attributed to butyrate. This lead to further investigation into whether dietary soluble fibre could promote changes in the gut microbiome to promote butyrate-producing bacteria to ultimately stimulate a reduction in neuroinflammation.

Adult and aged mice as previously described were fed either a low fibre (1% cellulose) or high fibre (5% inulin) diet for 4 weeks. Their gut microbiota composition and faecal samples were compared with equivalent mice fed a normal chow diet. At the start of the study, the microbiome composition in the aged mice showed a high presence of bacteria synonymous with frailty, Ruminococcus spp. and Rikenellaceae. After the 4-week period, this concentration was reduced in the aged mice fed the high fibre diet. Matt et al. found that the high fibre diet lead to an increased presence of blood butyrate in both age groups and it also lead to decreased inflammatory markers in the brains of the aged mice, these then having levels comparable levels to the adult mice on both diets. The opposite effects were also observed with the low fibre diet with an inflammatory marker increase exhibited in the brains of the aged mice fed the low fibre diet. Matt et al. suggest therefore that the high fibre diet has the potential to suppress neuroinflammation.

Highlighted within the study was the fact that the high fibre diet did not show the equivalent anti-inflammatory response as the mice injected with NaB before an immune challenge. The study however was unable compare the concentration of butyrate in circulation from both groups. It suggests that the route of administration could be responsible for this difference. According to the study, one aspect for future development would be the ability to determine the concentration of butyrate circulated to the brain from diet. Mechanisms by which NaB and dietary butyrate can suppress and/or prevent chronic neuroinflammation are also areas which need to be further explored.

Overall, the findings presented by Matt et al. provide supporting evidence that the neuroinflammation which comes with ageing can be altered by nutrients with anti-inflammatory attributes through dietary changes which could result in potentially delaying brain ageing either directly or indirectly.

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