Folate and homocysteine phenotypes: Comparative findings using research and clinical laboratory data.
OBJECTIVE
A low folate/high homocysteine phenotype is associated with several pathologies, including spina bifida and cardiovascular disease. Folate and total homocysteine (tHcy) measurements are used clinically to assess risk and the need for folic acid supplementation and in research to investigate the metabolic basis of disease. Red blood cell (RBC) folate, the best indicator of long-term folate status, is usually measured as "total" folate. However, different folate derivatives support distinct biochemical functions, suggesting a need to develop more precise methods. This study was designed to evaluate a method based on stable isotope dilution liquid chromatography-multiple reaction monitoring/mass spectrometry (LC-MRM/MS).


METHODS
We used LC-MRM/MS to quantify the RBC folate derivatives 5-methyltetrahydrofolate (5-CH(3)-THF), tetrahydrofolate (THF), and 5,10-methenyltetrahydrofolate (5,10-methenylTHF) in pre-menopausal women. The concentration of each folate derivative was assessed for utility in predicting tHcy levels, and compared to folate and tHcy measurements derived by routine clinical laboratory methods.


RESULTS
LC-MRM/MS was qualitatively and quantitatively superior to routine clinical laboratory methods for determining folate and tHcy concentrations. RBC 5-CH(3)-THF had a reciprocal relationship with tHcy (p=0.0003), whereas RBC THF and RBC 5,10-methenylTHF had direct relationships (p=0.01, 0.04 respectively). In combination, these three variables accounted for 42% of the variation in tHcy.


CONCLUSIONS
Robust methods for measuring RBC 5-CH(3)-THF would improve the utility of folate/homocysteine phenotyping in patient management. The use of LC-MRM/MS would allow studies of hyperhomocysteinemia and diseases associated with a low folate/high homocysteine phenotype to be performed with less measurement error and greater statistical power to generate data with the potential to elucidate the etiologic mechanisms of complex diseases and traits.
Mitchell
Laura E
LE
Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, USA.
Morales
Megan
M
Khartulyari
Stefanie
S
Huang
Yuehua
Y
Murphy
Kristen
K
Mei
Minghua
M
Von Feldt
Joan M
JM
Blair
Ian A
IA
Whitehead
Alexander S
AS
D000328:Adult; D002853:Chromatography, Liquid / Q000379:methods* / Q000592:standards; D004912:Erythrocytes / Q000737:chemistry; D005260:Female; D005492:Folic Acid / Q000097:blood* / Q000737:chemistry; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods* / Q000592:standards; D008875:Middle Aged; D010641:Phenotype; D011247:Pregnancy; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
D006710:Homocysteine; D005492:Folic Acid