Gut Microbiome Has Potential to Counter Gout

Efforts to combat hyperuricemia may find help from gut microbes, according to Dylan Dodd, MD, PhD, who spoke at the annual research symposium of the Gout, Hyperuricemia, and Crystal-Associated Disease Network.

Dodd is an assistant professor of pathology and microbiology and immunology at Stanford University, Palo Alto, California, where he studies novel metabolic pathways in microbes. “The idea is that we can leverage these novel pathways that microbes have as therapeutics to promote human health, and in particular for this meeting today, we’re focused on hyperuricemia and how microbes that break down purines may actually have a role as urate-lowering therapies,” Dodd said during his presentation.

Specifically, he highlighted the fact that some microbes found in the gut break down purines as a food source, producing both energy and molecular building blocks for their own use. Dietary purines, left intact, can otherwise be absorbed and metabolized by the body to produce urate.

Nucleic acids like DNA and RNA in the diet are first broken down by enzymes produced in the pancreas, resulting in purine nucleosides, which in turn are believed to be the source of purines absorbed in the small intestine and eventually into circulation, according to Dodd. “I really view urate in the intestine as being in equilibrium between being secreted into the lumen but also being reabsorbed, and specifically, as it pertains to microbes in the gut. If the microbes degrade the urate, then it will limit its reabsorption, and that could increase net excretion,” Dodd said.

There is evidence that some strains of Lactobacillus species, which are the most important group in the human gut, can metabolize purine nucleosides, he said. In recent years, researchers have screened for Lactobacillus species capable of metabolizing purine nucleosides. The research shows some strain-to-strain variation, but most are proprietary, making it impossible to conduct follow-up research. A small number of human trials have suggested efficacy, but they have generally been conducted in few patients with mixed results. “Overall, I think it’s promising that these lactobacilli probiotics could potentially be used as urate-lowering therapies,” Dodd said.

Aside from direct metabolism of purines, Dodd’s group has identified an additional pathway that some microbes can use to break down urate into short-chain fatty acids. His group cultured various purine nucleosides with various bacterial strains, including two Lactobacillus strains, under anaerobic conditions. The Lactobacillus strains did not degrade urate, but some bacterial species did. The group also found that Lactobacillus could convert nucleosides, including those derived from purines, into the smaller nucleobase compounds, but they did not consume the resultant purines. Some other types of bacteria consumed all purines “voraciously,” according to Dodd, and his team is working to identify the bacterial genetic pathways that drive the metabolic pathways. 

Such studies may open up various therapeutic pathways, he said. One is to employ Lactobacillus probiotics to convert purine nucleosides to their nucleobases, which could reduce absorption in the small intestine. Other bacteria could potentially be used to convert urate produced by paracellular reabsorption to short-chain fatty acids, which have potential benefits through their anti-inflammatory properties. Finally, probiotics could be engineered to degrade urate produced in the intestine. 

Dodd noted that probiotics would have the advantage of high patient acceptance and are generally regarded as safe. Some existing products might have purine-degrading capabilities but haven’t been tested, he said. However, there is strain-to-strain variation and the probiotic formulas would likely need to be optimized to reduce nucleobases. On the other hand, bacteria that degrade urate are likely safe since they have been found in the guts of healthy individuals. However, there are still potential safety concerns, and it is unknown if they could withstand the harsh conditions of the upper gastrointestinal tract or if they would remain active even in the presence of oxygen found in the small intestine, he said. 

During the Q&A period after his talk, Dodd was asked whether fructose consumption could suppress the function of anaerobic bacteria that naturally degrade purine. “When people talk about fructose-induced hyperuricemia, they talk about the ATP degradation in fructose metabolism in the liver or small intestine, [but] they never talk about this potential pathway in the gut,” the questioner said.

Dodd responded that his group found that some carbohydrates suppress urate degradation in some bacterial strains. “It’s certainly a possible mechanism that increased fructose intake could suppress microbial urate degradation in the gut, and that could contribute to hyperuricemia, but obviously more studies need to be done,” he said.

Another audience member wondered if antibiotic use could be tied to gout risk and whether serum urate levels might rise after antibiotic use. “Do you have any data on serum urate before and after antibiotic use, where you might expect to see changes which might support your hypothesis?” she asked. Dodd said that the group had done a retrospective analysis of data from Stanford’s medical records and did not find a change in serum urate after antibiotic exposure. However, a controlled feeding study of healthy individuals who later received antibiotics showed a large increase in urate levels, but the study did not include plasma samples. “It’s a really good question, and we hope to be able to follow that up,” he said.

Dodd disclosed no relevant financial relationships.