Studies have shown that aging results in chronic systemic inflammation, which can accelerate neuroinflammation in the brain. The exact mechanism is not clear, although the overproduction of the pro-inflammatory cytokine interleukin- 1 beta (Il-1) is known to play a role. As dietary intake is thought to affect this process, this study reviewed the effect of sodium butyrate (NaB), a short-chain fatty acid (SCFA) produced primarily by bacterial fermentation of fiber in the colon, on neuroinflammation.

A group of aged mice were injected with either a saline control or NaB at 1.2 g/kg body weight, as well as saline or LPS at 0.33 mg/kg body weight. At follow-up, the mice were euthanized for tissue analysis, microglial isolation, and RNA isolation. A second group was fed a diet with either a low or high soluble fiber content and underwent a similar post-mortem analysis.

In the first study, immune activation was noted in the microglia after LPS infusion, with increases in Il -1β，(P＝0.0005). When also infused with butyrate the Il-1β expression was attenuated (P＝0.0497). These findings were also true for the analysis at the hippocampus, and were more pronounced in the aged mice. In the diet study, cecum and colon analysis indicated severe inflammation associated with immune infiltration in aged animals on a low fiber diet. However, aged mice on a high fiber diet had a decrease in this inflammatory infiltrate. Histology scores supported these findings. Compared to the low fiber diet, the high fiber diet decreased gene expression in the microglia, including Il-1β，Il-1rn, Il-6, Nlrp3, Tlr4 and Tnf.

This animal study found that sodium butyrate can reduce inflammation and immune reactivity in the microglia of the brain, supporting a neuroprotective role of high soluble fiber.