An apple a day: pectin is an important source of formate in the rat.

Since formate plays an important role in one‐carbon metabolism we examined the potential role of pectin as a source of formate. Rats were fed purified, AIN 93‐based diets in which the source of fibre was either 5% pectin (PF rats) or 5% cellulose (CF rats). The intestinal formate content was much higher in the PF rats than in the CF rats, with ileum>caecum> large intestine. Formate was primarily found in intestinal contents rather than in tissue. The gut output and the hepatic uptake of methanol were significantly elevated in the PF rats, as was the hepatic uptake of formate. Both plasma formate and methanol were markedly higher in PF rats. Chow‐fed rats, treated with a mixture of antibiotics (vancomycin, gentamycin, rifampin) for 7 days, had markedly decreased formate levels and a complete suppression of intestinal formate output compared to chow‐fed rats without antibiotics. Hepatic uptake of formate continued in the antibiotic‐treated animals. There is a requirement for the intestinal microbiome in the maintenance of normal circulating formate levels. Pectins are polysaccharides, rich in galacturonic acid of which approximately 80% of the carboxyl groups are esterified with methanol. These methyl groups may be removed during digestion by means of a methylesterase. We suggest that methanol, so produced, can give rise to substantial quantities of formate which becomes available to rat tissues as a source of one‐carbon groups. These findings are also relevant to experiments with cobalamin‐deficient animals in which pectin is commonly used as a cobalamin‐binding agent. Support or Funding Information Supported by CIHR This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .