Impact of pyridoxine (B6) deficiency on serine kinetics in the pig

Abstract

The water‐soluble vitamin B6 serves a cofactor for serine hydroxymethyltransferase (SHMT), an enzyme critical to cellular one carbon flow. The current experiment was designed to test the alternate hypothesis that B6 deficiency in an animal model will reduce SHMT activity and serine flux, as measured by stable isotopic dilution protocols. Pigs (commercial genotype; initial wt = 4.7 kg; n=6/treatment) were offered a basal semi‐purified diet (20.5% casein; 3474 kcal ME/kg) containing either 0 (B6−) or 3 (B6+) mg/kg pyridoxine·HCl for a 3 week feeding period, using a pair‐feeding design. At the end of the depletion period, a 6 hr primed (90 μmole/kg)‐constant (90 μmole/kg/h) infusion of L‐[2,3,3‐2H3] serine was administered via indwelling jugular vein catheter. Blood samples (femoral vein catheter) were collected at −60, 0, 60, 120, 180, 240, 300 and 360 min. Tissues were harvested at termination and samples processed for plasma serine m+3 enrichment (GC‐MS), plasma pyridoxal‐5‐phosphate (PLP; radioimmunoassay), and liver SHMT activity. Different superscripts indicate significant differences (P<0.05) by ANOVA F‐test.The current data allow us to accept the alternate hypothesis of a reduction in SHMT activity induced by dietary pyridoxine deficiency, with a concomitant reduction in serine flux. This reduction in serine flux may have implications for overall one‐carbon metabolism, including pathways linked to folate and sulfur amino acid metabolism. Support: Natural Sciences and Engineering Research Council of Canada (NSERC)