Vitamin K Supplementation Study in Healthy Volunteers (Aim 2B)

Description

The investigators will study the effect of vitamin K supplementation on two biomarkers of hepatic vitamin K concentration in groups with defined CYP4F23 genotype. Specifically, the investigators will test for an association between our novel biomarkers of long-term (plasma Factor II proteoforms) and short-term (urinary K-Acid catabolites) hepatic vitamin K concentration and CYP4F23 following a 10-day period of vitamin K supplementation in healthy volunteers.

The investigators will recruit, by posted advertisements at UWMC, male and female healthy volunteers. A two-step selection process will be employed. Subjects will self-select by responding to flyers, and contact the research coordinator. The research coordinator will screen them for eligibility over the phone and if eligible, make an appointment for the first study visit. For the first phase, the Research Coordinator will collect a buccal swab of DNA from ~ 200 eligible candidates; the DNA will be tested for absence or presence of the CYP4F23 variant allele. The PI and Research Coordinator will review the genotyping results and then select 14 individuals with a homozygous CYP4F23 genotype and a demographically matched group of 14 with a homozygous CYP4F2*1 genotype at the diagnostic locus for the supplementation phase of the study. The study coordinator will then contact these subjects by phone for Phase II participation.

Procedures - Phase I, Buccal Swab Collection for DNA Isolation.

Demographic Questionnaire: Self-reported heritage, age, and sex will be collected through a brief demographic questionnaire.

Buccal Swab: We will collect cheek cells with a cotton swab and isolate DNA and test for the CYP4F21 and CYP4F23 alleles.

Genotyping: CYP4F2 genotype will be determined by a validated TaqMan assay (ABI/ThermoFisher Scientific), using commercially available DNA hybridization probes to test for the absence or presence of the CYP4F23 allele. Subjects who are homozygous for the CYP4F21 and CYP4F2*3 alleles will be eligible for Phase II.

Procedures - Phase II, Vitamin K Supplementation.

Vitamin K Supplementation: Research participants selected for the supplementation study based on CYP4F2 genotype will be given 1-mg/day phylloquinone (Vitacost; Natures Life K-1 Phylloquinone) for 10 consecutive days. Each dose will be taken in the morning (~ 8 am), with one half pint of 2% milk to facilitate absorption.

Sample Collection: For the supplementation study, a venous blood sample (10 mL EDTA tube) and a spot urine sample will be collected after an overnight fast from d1 through d5 and on d8 and d10 of Vitamin K supplementation for 10 days. Plasma will be isolated and both samples will be stored at -70C until analysis. Women of child-bearing potential will have a urine pregnancy test of d1 and if positive, will be withdrawn from the study, and all samples and data will be destroyed.

Measurement of Plasma Factor II Proteoforms: Plasma concentration of the 11 individual proteoforms of Factor II will be measured byLC-MS/MS. This data will be used to calculate three metrics of long-term vitamin K status, unFII, ucFII:iFII and inFII:aFII. These represent different mathematical measures of the degree of Factor II undercarboxylation. Prospective analysis of plasma vitamin K1, PIVKA II and ucOC is not planned, but will be held in reserve should the need for that data arise.

Measurement of Urinary K-Acid I and II: Quantitation of K-Acid I and II, and creatinine (Cr) in spot urine samples will be performed, using a validated LC-MS/MS assay that the investigators have recently developed. The total and individual urinary K-Acid/Cr ratio will be computed.

Statistical Analysis Plan: The investigators will conduct an unpaired t-test to compare the mean response to vitamin K supplementation in the two CYP4F2 genotype groups. Response is defined as the area under the vitamin K status value x time curve, corrected for baseline, for the 10-day intervention period. A secondary metric will be the absolute peak change in the vitamin K status ratio. Both short (urinary K-Acid/Cr ratio) and long-term (ucFII:iFII and inFII:aFII) biomarkers will tested separately. Based on pilot data, a sample size of 14 in each genotype group will provide a power of at least 80% to detect a significant effect at the significance 0.05 level, when there is a two-fold difference in the response to supplementation.

Details