Abstract
Objectives
Pregnancy is a metabolically active life stage. Formate plays a major role in one-carbon metabolism, a biosynthetic pathway critical for cellular growth and function. Because formate can be synthesized from amino acid precursors serine, glycine, tryptophan and methionine, it suggests that urinary formate concentration may be low in response to low protein intakes. Additionally, sulfate is the excretory endpoint for the breakdown of indispensable, sulfur containing amino acids methionine and cysteine. Our objectives were to determine if urinary excretion of formate/sulfate can be utilized as non-invasive biomarkers in pregnancy, when protein intakes range from deficient to adequate.
Methods
Urinary samples (n = 81) from pregnant women (11–20- and 30–38-weeks’ gestation) were collected when consuming graded protein intakes (0.2–2.56 g/kg/d) and were analyzed for sulfate and formate concentrations. For sulfate, spectrophotometric absorbance was measured and compared to a standard curve, and formate was analyzed using an enzymatic assay. Concentrations of the catabolites were normalized using creatinine concentrations and plotted against protein intakes. Regression models were used to examine potential relationships. Sulfate excretion was also compared to the estimated total sulfur amino acid intake (TSAA, methionine + cysteine).
Results
With increasing protein intakes, formate excretion remained constant. Urinary sulfate concentrations increased in response to increasing protein. A bi-phase linear regression model revealed there was an observable breakpoint in increased sulfate excretion in early gestation at 33–36 mg/kg/d of estimated TSAA intake, and at 30–39 mg/kg/d for late gestation.
Conclusions
There was no observable relationship to suggest urinary formate could be used as a biomarker for protein/amino acid status during pregnancy. Urinary sulfate concentrations may be a viable indicator for measuring total sulfur amino acid (methionine, cysteine) status. Further studies on TSAA requirements in pregnancy using more state-of-the-art stable isotope techniques are needed to confirm these findings from non-invasive urinary biomarkers.
Funding Sources
Canadian Institutes of Health Research.
Changes in cecum microbial community in response to total sulfur amino acid (TSAA: DL-methionine) in antibiotic-free and supplemented poultry birds
