GASTROENTEROLOGY 1996;110:991 – 998 Folate Synthesized by Bacteria in the Human Upper Small Intestine Is Assimilated by the Host ERMALINDA CAMILO,* JOSEPH ZIMMERMAN, ‡ JOEL B. MASON, § BARBARA GOLNER, x ROBERT RUSSELL, x JACOB SELHUB, § and IRWIN H. ROSENBERG § *University Hospital de Santa Maria, Servico de Medicina 2, Lisbon, Portugal; ‡ Gastroenterology Unit, Hadassah Medical School, Jerusalem, Israel; and § Vitamin Bioavailability and x Gastrointestinal Nutrition Laboratories, Jean Mayer U. S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, Massachusetts Background & Aims: Some intestinal flora are known tinal microflora can be used by the host animal. In hu- to synthesize folate. The aim of this study was to deter- mans, fecal folate concentrations have been observed to mine whether folate synthesized by small intestinal be considerably higher than what would be expected flora is assimilated by the human host. Methods: Sub- based on dietary intake, providing indirect evidence of jects with atrophic gastritis and healthy volunteers in vivo folate biosynthesis by the intestinal microflora. 15 were studied before and after omeprazole administra- In addition, elevated serum concentrations of folate in tion. A double-lumen perfusion tube was placed in the individuals with atrophic gastritis, a condition associated duodenum. 3 H-labeled P-aminobenzoic acid, a precur- with a modest bacterial overgrowth of the upper small sor substrate for bacterial folate synthesis, was per- intestine, have been ascribed to bacterial synthesis of fused. Downstream intestinal aspirates and a 48-hour the vitamin. 9 However, there are no human studies that urine collection were obtained. Results: Atrophic gastri- directly show in vivo synthesis of folate or that examine tis and omeprazole administration were associated the fate of this bacterially synthesized folate. In the pres- with increases in duodenal pH and in small intestinal flora. Bacterially synthesized folates were isolated from ent study, tracer quantities of tritiated PABA ( 3 [H]- the intestinal aspirates. Tritiated 5-methyltetrahydrofo- PABA) were introduced into the duodenum of human late, a major metabolite of folate, was isolated from subjects who had a modest bacterial overgrowth as a the urine of omeprazole-treated subjects in greater result of either atrophic gastritis or the use of omepra- quantities than from drug-free subjects (P õ 0.01); zole. 16 The latter subjects were also studied while not the quantity of tritiated 5-methyltetrahydrofolate in the undergoing omeprazole therapy. The radiolabeled folates urine of the subjects with atrophic gastritis was simi- synthesized by intestinal microflora from the tritiated larly elevated. Conclusions: (1) Mild bacterial over- PABA provided the means to follow the fate of these growth caused by atrophic gastritis and administration folates. of omeprazole are associated with de novo folate syn- thesis in the lumen of the small intestine; (2) the hu- Materials and Methods man host absorbs and uses some of these folates; and Subjects (3) the contribution to folate nutriture from this source remains unclear. Eight healthy male volunteers were selected for the study. Two subjects had atrophic gastritis and 6 did not. The latter are called normal subjects in the study. The presence of H atrophic gastritis was defined as a serum pepsinogen I/pepsino- umans cannot synthesize the vitamin folate. In- stead, they rely on exogenous sources of the vitamin gen II ratio of õ2.0 17 and was confirmed by findings of subnor- to maintain adequate folate status. The only source of mal acid secretion in a pentagastrin stimulation test (peak acid folate known with certainty to contribute to human folate output, õ2 mmol/h; maximal acid output, õ1 mmol/h). 18 nutriture is the folates present in the diet. The subjects with atrophic gastritis were 71 and 75 years old; mean / SD age of the normal subjects was 27.5 / 4.2 years. Many bacterial species, 1–11 including some present in Both subjects with atrophic gastritis were male; 3 of the nor- the human gastrointestinal tract, have been shown to be mal subjects were male and 3 female. All subjects were well capable of synthesizing folate by a process that involves condensation of P-aminobenzoic acid (PABA) with dihy- Abbreviations used in this paper: HPLC, high-performance liquid dropterin pyrophosphate. 12 This synthetic pathway is not chromatography; PABA, P-aminobenzoic acid. present in eukaryotes. In animals, there is indirect 10,11,13  1996 by the American Gastroenterological Association 0016-5085/96/$3.00 and direct 14 evidence that folate synthesized by the intes- / 5e0b$$0020 03-06-96 17:09:22 gasas WBS-Gastro