Evaluation of Holotranscobalamin as an Indicator of Vitamin B12 Absorption
Condition: Disorder of Vitamin B12
Study type: Interventional

Summary: 
      Vitamin B12 is an essential nutrient that the body needs for cells to divide and function
      normally. Individuals may develop a deficiency of vitamin B12 by either limiting the amount
      in the diet or by decreased vitamin B12 intake into the body (absorption). Keeping adequate
      B12 blood levels is important for health. Vitamin B12 deficiency may increase one's risk for
      developing anemia and can even lead to neurological problems and paralysis if the deficiency
      is severe and lasts a long time. It is very important for doctors to have accurate tests to
      determine if people are absorbing vitamin B12 normally so that treatment can be started
      before severe clinical problems occur.

      The purpose of this research is to provide new information that may help scientists develop a
      better method to test for problems with absorbing vitamin B12. In this study, changes in the
      amounts of vitamin B12 bound to protein (transcobalamin) in the blood will be measured after
      doses of vitamin B12 are taken. If the amounts of this vitamin B12-protein complex (called
      holo-transcobalamin) change in response to taking a vitamin B12 supplement in normal
      individuals, it may be possible to use this information to develop a new sensitive test to
      identify individuals who have problems absorbing vitamin B12. This new vitamin B12 absorption
      test may be a better clinical test for vitamin B12 absorption than those now available for
      doctors to use.
    

Detailed description: 
      Part I Screening: Individuals who meet initial screening criteria will be scheduled to have
      fasting blood samples drawn in the General Clinical Research Center (GCRC). All participants
      will sign informed consent forms approved by the UF Institutional Review Board prior to the
      initiation of this part of the study. Subjects' heights and weights will be measured and
      subjects will be asked to complete a medical history questionnaire. Blood analyses will
      include serum B12, blood chemistry, and hematological indices. Females will be given a
      pregnancy test. Subjects eligible for Part II of the study (Intervention) will have serum B12
      concentrations that are ≥444 pmol/L; will be non-anemic; and will have normal general blood
      chemistry (all values within or near the normal range), and no history of chronic disease
      (e.g., pernicious anemia, cancer, diabetes, renal disease, hypertension, neurological
      abnormalities, gastrointestinal disorders). Any subject with deficient (<148 pmol/L) serum
      B12 concentration [18] will not be eligible for participation and will be instructed to see
      their personal physician for complete follow-up and treatment.

      Part II Intervention: Changes in B12 status assessment indicators in response to B12
      supplementation will be evaluated.

      Subjects will come to the GCRC the night before (Day 1) the intervention protocol. The next
      morning (Day 1) following an overnight fast, an indwelling catheter will be inserted from
      which repeated blood samples will be drawn throughout Day 1. A baseline fasting blood sample
      (#1) will be drawn. Subjects will then consume a light breakfast (including 1 piece of bread
      and 8 oz of orange juice) and will take a 9 ug dose of B12 (Dose 1). Thirty minutes after
      completion of the meal and consumption of the B12 supplement, a second blood sample (#2) will
      be drawn. Five subsequent hourly blood samples (# 3-7) will be drawn. After the 7th blood
      sample the subjects will consume one piece of bread and 8 ounces of orange juice and will
      take a second 9 ug dose of B12 (Dose 2) and have a blood sample (#8) drawn 30 minutes after
      consumption of the meal and the B12 dose. Five subsequent hourly blood samples (#9-13) will
      be drawn. The subjects will then consume one piece of bread and 8 ounces of orange juice and
      take a 9 ug dose of B12 (Dose 3). Another blood sample (#14) will be drawn 30 minutes after
      the meal and the B12 dose. One hour later, a final (Day 1) blood sample (#15) will be drawn
      followed by removal of the catheter. In addition to the bread and juice consumed with each
      B12 supplement, subjects will receive a mid-morning snack 2 hours after Dose 1 of the B12
      supplement, lunch 3.5 hrs after Dose 1 of the B12 supplement, dinner at 4 hours after Dose 2
      of the B12 supplement, and an evening snack at 3 hours after Dose 3. Low B12-containing foods
      will be provided in the GCRC. Water and non-caffeinated, non-caloric beverages will be
      allowed ad libitum.

      The subjects will remain in the GCRC overnight and a fasting blood sample (#16) will be drawn
      in the morning on Day 2. On Day 2 participants will be provided breakfast following the blood
      draw, after which they will be free to leave the GCRC. Subjects will be provided with
      take-away meals and snacks (lunch, dinner, snacks) consisting of low-B12 containing foods.

      Subjects will be instructed to return on the morning of Day 3 at which time they will have
      one am fasting blood sample (#17) drawn and will be provided with breakfast before they leave
      the GCRC. All overnight fasts will be from 10 pm the previous night. The following B12
      indicators will be measured at each blood draw (a) holo-TC; (b) total-TC; (c) holo-HC and
      total HC; (d) serum B12; and (e) plasma albumin. Additional B12 status indicators (e.g.
      homocysteine, methylmalonic acid, RBC B12) will be measured at select blood draw intervals. A
      baseline folate analysis will be done.
    

Intervention name(s): Vitamin B12
Intervention type(s): Dietary Supplement
Intervention description(s): After taking a fasting blood sample, all subjects were given a light breakfast plus 9 micrograms of vitamin B12. Two more doses of vitamin B12, 9 micrograms each, were administered 6 hours apart.
Intervention MeSH terms: Vitamin B 12; Hydroxocobalamin
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: Vitamin B12 absorption; Holo-transcobalamin