A stable isotope approach to measuring in vivo formate kinetics in vitamin-deficient rats
Formate, the simplest carboxylic acid, is an important intermediary metabolite at the crossroads of amino acid and one-carbon metabolism.
Recently our lab has shown that the levels of formate in the plasma are sensitive to deficiencies of in folate and B12. In addition, a mathematical model of one-carbon metabolism suggests that formate concentration may also be sensitive to riboflavin status.
Studies of formate production in vivo were carried out by infusing 13C-formate until an isotopic steady state is achieved. These samples were derivatized using pentafluorobenzylbromide (PFBBr) and analyzed by GCMS using 1,2-13C-acetate as internal standard. This allowed for simultaneous determination of plasma formate concentration and isotopic enrichment.
As expected, vitamin B12-deficient rats showed significantly elevated plasma formate concentrations and elevated plasma homocysteine (Hcy) compared to vitamin B12-replete control animals. Interestingly, the rate of formate production was also increased by approximately 30% in the B12-deficienct animals.
In the riboflavin-deficient animals no differences in plasma formate levels were detected when compared against control animals. However, we do observe an approximate 13% decrease in formate production rates in riboflavin-deficient animals.
These results will be discussed in terms of the important roles these vitamins play in the one-carbon metabolism pathway.