Effect of human milk folate binding protein on folate intestinal transport.
The present study examined the effect of human milk folate binding protein (FBP) on the intestinal transport of 5-methyltetrahydrofolate (5-CH3H4PteGlu). This was performed by examining the transport of radiolabeled 5-CH3H4PteGlu bound to FBP using everted sacs of rat intestine. In the jejunum at pH 6, transport of 27 nM bound 5-CH3H4PteGlu was linear with time for 30 min of incubation. Transport of 13 nM bound 5-CH3H4PteGlu was higher in the jejunum than in the ileum at both pH 6 (2.1 +/- 0.3 and 0.36 +/- 0.03 pmol/g wet wt/25 min, respectively) and pH 8 (1.9 +/- 0.3 and 0.32 +/- 0.02 pmol/g wet wt/25 min, respectively). In the jejunum, transport of 13 nM bound 5-CH3H4PteGlu at pH 6 was less than transport of an equimolar concentration of free 5-CH3H4PteGlu (2.1 +/- 0.3 and 5.1 +/- 0.5 pmol/g wet wt/25 min, respectively) but was similar at pH 8 (1.9 +/- 0.3 and 2.47 +/- 0.3 pmol/g wet wt/25 min, respectively). In the ileum transport of bound and free 5-CH3H4PteGlu was similar at pH 6 (0.36 +/- 0.03) and 0.41 +/- 0.06 pmol/g wet wt/25 min, respectively) and pH 8 (0.32 +/- 0.02 and 0.43 +/- 0.1 pmol/g wet wt/25 min, respectively). The transport process of bound 5-CH3H4PteGlu in the jejunum was energy, temperature, and Na+ dependent, but not pH dependent, and was competitively inhibited by sulfasalazine. Ninety-two percent of the transport substrate that appeared in the serosal compartment following incubation with bound 5-CH3H4PteGlu was found to be free (unbound) 5-CH3H4PteGlu. These results show that human milk FBP decreases the rate of transport of 5-CH3H4PteGlu in the jejunum and suggest that FBP-bound 5-CH3H4PteGlu may utilize the same transport system as free 5-CH3H4PteGlu. The results also suggest a role for human milk FBP in regulating the nutritional bioavailability of folate.
D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007583:Jejunum / Q000378:metabolism; D007700:Kinetics; D008727:Methotrexate / Q000494:pharmacology; D008894:Milk Proteins / Q000378:metabolism*; D008895:Milk, Human / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface; D012964:Sodium / Q000502:physiology; D012460:Sulfasalazine / Q000494:pharmacology; D013696:Temperature
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D008894:Milk Proteins; D011956:Receptors, Cell Surface; D012460:Sulfasalazine; D005492:Folic Acid; D012964:Sodium; D008727:Methotrexate