Ala Al Rajabi, MS
Ph.D. Candidate Friedman School of Nutrition Science and Policy
Tufts University, Boston, MA
2007–2008
Mentors: Dr. Booth & Dr. Ausman
Recent Work
Vitamin K is a fat soluble vitamin that is well known for its role in the coagulation process. New physiological functions have been attributed to vitamin K, including regulation of calcification in vessel walls and protection against oxidative stress. One form of vitamin K, MK-4, may have unique role in those novel functions of vitamin K. Even though MK-4 is present in low concentration in food supply, it is found in high concentrations in certain tissues. Mammals have the ability to convert phylloquinone, the major form of vitamin K in diet, into MK-4 and store the later in specific tissues. However, the mechanism and tissue location of biochemical reactions required to form MK-4 remain elusive. Measurement of one of the putative intermediates in this process, menadione, may provide insight into this formation. Sensitive assays for measurement of menadione are required for the study of this conversion process of phylloquinone into MK-4.
I have developed and validated a sensitive and reproducible high performance liquid chromatography (HPLC) method for the purpose of measuring urinary menadione. Archived urine samples from a 3-year, double-blind, randomized-controlled human phylloquinone supplementation study were analyzed for menadione. Menadione was measured in urine samples from both control and phylloquinone supplemented groups. Urinary menadione excretion was found to increase in response to phylloquinone supplementation, lending further support to the hypothesis that menadione is an intermediate metabolite in the conversion of phylloquinone to MK-4. I will evaluate the associations between the excretion of urinary menadione and measures of vitamin K status using archived samples for the phylloquinone supplementation study. I am also working on an animal study in which rats will be fed deuterium-labeled collard greens. The presence of deuterium labeled phylloquinone, MK-4 and menadione will be determined at different time points in urine, serum and certain tissues. Measuring labeled menadione and MK-4 will show that phylloquinone is converted in rats into MK-4 with menadione as an intermediate in the conversion process.
