Where is the Initial Site of Biotransformation of Folates in Humans?

Study Overview
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Brief Summary
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The aim of this study is to test the assumption that, in humans, folic acid, a dietary supplement is biotransformed (reduced and methylated) to the natural circulating plasma folate 6S-5Methyltetrahydrofolic acid (5-MTHF) in the intestinal mucosa.

Detailed Description
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Current thinking, based mainly on rodent studies, is that physiological doses of folic acid (pteroylmonoglutamic acid), like dietary vitamin folates, are biotransformed in the intestinal mucosa and transferred to the portal vein as the natural circulating plasma folate, 5-methyltetrahydrofolic acid (5-MTHF), before entering the liver and the wider systemic blood supply. Study design:Open labelled study that samples portal and peripheral veins for labelled folate concentrations following oral ingestion with physiological doses of dietary supplements stable-isotope-labelled folic acid, or, the reduced folate, 5-formyltetrahydrofolic acid (5-FormylTHF). The study was performed in subjects with a Transjugular Intrahepatic Porto Systemic Shunt (TIPSS) in situ at the time of a routine annual patency check to allow blood samples to be taken from the portal vein. The aim of this study is to test the assumption that, in humans, folic acid is biotransformed (reduced and methylated) to 5-MTHF in the intestinal mucosa.

Official Title
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Folic Acid Handling by the Human Gut: Implications for Food Fortification and Supplementation

Conditions
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Healthy

Intervention / Treatment
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* Dietary Supplement: 13C5-folic acid or 13C5-6S-5-FormylTHF


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Stable, synthetic liver function without recent evidence of decompensation (defined as liver function inadequacy or active complications of portal hypertension) Abstinent from alcohol Free from malignant disease Normal gut permeability (as assessed by the lactulose/mannitol test) Patent TIPSS on their last surveillance Exclusion Criteria: Taking Vitamin B supplements Taking Folic Acid supplementation Unable to provide informed consent
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: 13C5-folic acid or 13C5-6S-5-FormylTHF<br>Physiological 500 nmol (220 µg folic acid equivalent) dose of dietary supplement 13C5-folic acid or 13C5-6S-5-FormylTHF given to subjects with in situ transjugular intrahepatic portosystemic stent at the time of routine venography patency check followed by regular portal venous sampling for 85 minutes at pre determined intervals and then physiological 500 nmol dose of 13C-6S-5-FormylTHF or 13C5-folic acid respectively at the next annual routine venography patency check followed by portal venous sampling for 85 minutes | Dietary Supplement: 13C5-folic acid or 13C5-6S-5-FormylTHF<br>* Subjects with an insitu transjugular intrahepatic porto systemic stent shunt assigned to receive either a physiological 500 nmol (220 µg folic acid equivalent) dose of 13C5-folic acid or 13C5-6S-5-FormylTHF at the time of routine shunt venography to check patency followed by portal venous sampling at pre defined time points for 85 minutes and then given 13C5-6S-5-FormylTHF ator 13C5-folic acid at their next annual venography patency check with portal venous sampling at pre defined time points for 85 minutes<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The percentage of folate in un-modified and modified form in the portal vein for each of the different oral folate dosing formulations |  | 85 minutes |