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Biomedical subjects

J F Gregory

Publications and source records attributed to J F Gregory.

At least 19 recordsLinked to original sources
PubMed1998

Kinetic model of folate metabolism in nonpregnant women consuming [2H2]folic acid: isotopic labeling of urinary folate and the catabolite para-acetamidobenzoylglutamate indicates slow, intake-dependent, turnover of folate pools.

In a 10-wk study of folate metabolism in nonpregnant women (21-27 y, n -6 per group), subjects were fed a diet containing approximately 68 nmol/d (30 microg/d) folate from food. The remainder of the ingested folate was provided as folic acid in apple juice (as nonlabeled during wk 1-2, as [2H2]folic acid during wk 3-10) to yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 microg/d). Isotopic enrichment of total urinary folate and the primary catabolite para-acetamidobenzoylglutamate (ApABG) was determined. Isotopic enrichment of ApABG served as an indicator of labeling of tissue folates. A kinetic model consisting of fast- and slow-turnover nonsaturable pools and a saturable slow-turnover pool, with provisions for urinary and fecal excretion, catabolism and enterohepatic circulation, yielded a close fit to the data. Mean residence times for total body folate were 212, 169 and 124 d for folate intakes of 454, 680, and 907 nmol/d, respectively. The model predicted that variation in folate intake over this range had little effect on the mass of the large saturable folate pool; however, the fast-turnover nonsaturable pools increased in proportion to folate intake, whereas the slow nonsaturable pool also tended to increase. This model will aid in evaluation of folate turnover and in predicting kinetic consequences of physiologic conditions associated with altered folate requirements.

Adult↗
PubMed1998

Urinary excretion of [2H4]folate by nonpregnant women following a single oral dose of [2H4]folic acid is a functional index of folate nutritional status.

In a 10-wk study with nonpregnant women (21-27 y, n = 5-6 per group), subjects were fed a diet containing approximately 68 nmol/d (30 microg/d) folate from food that was supplemented with folic acid in apple juice to yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 microg/d) to evaluate folate status and long-term in vivo kinetics. Reported here is an additional phase of this protocol conducted to determine the relationship between short-term urinary excretion after a single isotopically labeled dose and various measures of folate nutritional status. It was hypothesized that urinary excretion from a single [glutamate-2H4]folic acid ([2H4]folic acid) dose would increase in proportion to folate nutritional status due to saturable cellular uptake and retention processes along with saturation of renal reabsorption. Each subject was given 1.13 micromol (500 microg) of [2H4]folic acid orally on the morning of d 70 of the study, followed by a complete 24-h urine collection. Urine was analyzed to determine the isotopic enrichment of urinary folate by gas chromatography-mass spectrometry and the concentration of urinary folate by HPLC. Urinary excretion of [2H4]folate was greatest at the 907 nmol/d intake and was positively correlated with serum folate concentration but was not correlated with erythrocyte folate. Excretion of [2H4]folate tended to be greatest when plasma homocysteine concentrations were low (<8 micromol/L), although this relation was not significant. These results suggest that 24-h urinary excretion after a single oral dose of isotopically labeled folate is a functional indicator of folate nutritional status that complements other measures of folate nutriture.

Adult↗
PubMed1998

Folate catabolism in pregnant and nonpregnant women with controlled folate intakes.

Measurement of the urinary folate catabolites, para-aminobenzoylglutamate (pABG) and the more predominant acetylated form, acetamidobenzoylglutamate (apABG), has been used to assess folate requirements in both pregnant and nonpregnant women. Folate catabolite excretion has been reported to be significantly higher in pregnant women (second trimester) compared with nonpregnant controls. The primary goals of this study were to determine if pregnant women in a controlled metabolic study excreted higher quantities of urinary folate catabolites than nonpregnant controls and if catabolite excretion was influenced by folate intake. We evaluated the effect of gestation and folate intake on the urinary excretion of apABG and pABG in pregnant women (n = 12; wk 14-26 gestation) and nonpregnant controls (n = 12) assigned to consume folate levels approximating the current (400 microg/d) and previous (800 microg/d) RDA. Subjects were fed a controlled diet containing 120 microg folate/d and either 330 or 730 microg synthetic folic acid/d. In contrast to previously reported data, no differences in mean folate catabolite excretion were detected between pregnant and nonpregnant subjects. Catabolite excretion (pABG + apABG) decreased significantly relative to initial values in pregnant women consuming 450 microg folate/d (-40 +/- 20%; mean +/- SD) and final mean excretion was significantly lower in the pregnant women consuming 450 microg folate/d (86 +/- 32 nmol/d) compared with 850 microg folate/d (148 +/- 20 nmol/d). Data from this study indicate that second trimester pregnant women do not excrete more folate catabolites than nonpregnant controls and that consumption of 450 vs. 850 microg folate/d results in a significant reduction in the quantity of folate catabolites excreted.

Adult↗
PubMed1998

Nutritional Properties and significance of vitamin glycosides.

Glycosylated forms of pyridoxine, vitamin D, niacin, pantothenate, and riboflavin exist in nature, whereas glycosides of retinol and ascorbic acid are products of in vitro transglycosidation. Beta-Glucosides of pyridoxine (a) are prevalent in plant-derived foods, (b) contribute to human nutrition as partially available sources of vitamin B6, (c) undergo partial hydrolysis by a novel mammalian cytosolic beta-glucosidase, and (d) exert a weak antagonistic effect on the utilization of free pyridoxine. Niacin exists in grains as complexed forms with low bioavailability, whereas vitamin D glycosides are toxic components of certain calcinogenic plants of importance in animal health. Glycosides of pantothenate and riboflavin appear to be minor products of mammalian metabolism. Glycosylation of retinol or other hydrophobic alcohols may facilitate glycolipid turnover, whereas a stable ascorbyl glucoside may have nutritional applications. Glycosylation of vitamins exerts widely ranging chemical and biological effects, with great nutritional and metabolic significance.

Animals↗
PubMed1997

Cytosolic pyridoxine-beta-D-glucoside hydrolase from porcine jejunal mucosa. Purification, properties, and comparison with broad specificity beta-glucosidase.

During studies of the nutritional utilization of pyridoxine 5'-beta-D-glucoside, a major form of vitamin B6 in plants, we detected two cytosolic beta-glucosidases in jejunal mucosa. As expected, one was broad specificity beta-glucosidase that hydrolyzed aryl beta-D-glycosides but not pyridoxine beta-D-glucoside. We also found a previously unknown enzyme, designated pyridoxine-beta-D-glucoside hydrolase, that efficiently hydrolyzed pyridoxine beta-D-glucoside. These were separated and purified as follows: broad specificity beta-glucosidase 1460-fold and pyridoxine-beta-D-glucoside hydrolase 36,500-fold. Purified pyridoxine-beta-D-glucoside hydrolase did not hydrolyze any of the aryl glycosides tested but did hydrolyze cellobiose and lactose. Pyridoxine-beta-D-glucoside hydrolase exhibited a pH optimum of 5.5 and apparent molecular mass of 130 kDa by SDS-polyacrylamide gel electrophoresis and 160 kDa by nondenaturing gel filtration, in contrast to 60 kDa for native and denatured broad specificity beta-glucosidase. Glucono-delta-lactone was a strong inhibitor of both enzymes. Ionic and nonionic detergents were inhibitory for each enzyme. Conduritol B epoxide, a potent inhibitor of lysosomal acid beta-glucosidase, inhibited pyridoxine-beta-D-glucoside hydrolase but not broad specificity beta-glucosidase, but both were inhibited by the mechanism-based inhibitor 2-deoxy-2-fluoro-beta-D-glucosyl fluoride. Our findings indicate major differences between these two cytosolic beta-glucosidases. Studies addressing the role of vitamin B6 nutrition in regulating the activity and its consequences regarding pyridoxine glucoside bioavailability are in progress.

Animals↗
PubMed1997

Kinetic modeling of folate metabolism through use of chronic administration of deuterium-labeled folic acid in men.

This study was conducted as an initial investigation of in vivo folate kinetics in healthy men (n = 4) and made use of a chronic-administration protocol with stable-isotope labeling. Subjects were given 0.453 mumol (200 micrograms) total folic acid in aqueous solution daily throughout the 18-wk study while they consumed self-selected folate-adequate diets. After a 2-wk pretrial period with unlabeled folic acid, subjects were given 0.227 mumol (100 micrograms) pteroyl-L-[2H4]glutamic acid/d ([2H4]folic acid) combined with 0.227 mumol nonlabeled folic acid or [2H2]pteroylhexaglutamic acid/d for the next 8 wk; then for the next 8 wk the [2H4]folic acid was withdrawn and the subjects received only nonlabeled folic acid. Little unmetabolized folic acid was excreted in urine. Isotopic enrichment of urinary folate during [2H4]folic acid administration and withdrawal was consistent with a kinetic model having a rapid turnover pool and a slow turnover pool. In contrast with previous two-pool models, provisions were made for folate turnover by urinary folate excretion (as measured here) and by fecal excretion and catabolic processes. The precision of modeling will be improved in future studies by measurement of enrichment of additional pools. However, this study shows clearly the slow turnover of the whole-body folate pool (< or = 1% per day) and the feasibility of further long-term kinetic analysis.

Adult↗
PubMed1997

Absorption of folate from fortified cereal-grain products and of supplemental folate consumed with or without food determined by using a dual-label stable-isotope protocol.

The absorption of folic acid in fortified white and whole-wheat bread, rice, or pasta or in solution was evaluated in human subjects with use of a single-dose, dual-label, stable-isotope protocol that did not involve prior loading of subjects with nonlabeled folate. In each of five sequential trials, 14 adults received a single oral dose of [13C5]folic acid in one of the four fortified cereal-grain products or in water concurrently with an intravenous injection of [2H2]folic acid. In two additional trials, subjects received oral [13C5]folic acid with or without a light breakfast meal. In all trials, urine was collected 24-36 h postdosing and the isotopic labeling of urinary folates determined. Isotope excretion ratios of urinary folates (% [13C5]folate dose/% [2H2]folate dose), which were used as criteria of absorption, indicated no significant differences among the various fortified foods and the control (P = 0.607). Because statistical power was sufficient to have detected a 50% difference from the control, these results suggest that [13C5]folic acid in these fortified cereal-grain foods was highly available. This study also suggests that fortification will contribute effectively to the folate status of the population. Consuming [13C5]folic acid after a light breakfast meal led to a small reduction in absorption relative to the control without food (P < 0.085). Between-subject variation in this protocol exceeded that observed in previous studies conducted using prior saturation of subjects with nonlabeled folic acid. We recommend that either prior saturation or multiple doses be used in future applications of this technique to improve precision.

Adult↗
PubMed1997

A dual-label stable-isotopic protocol is suitable for determination of folate bioavailability in humans: evaluation of urinary excretion and plasma folate kinetics of intravenous and oral doses of [13C5] and [2H2]folic acid.

Stable isotopic protocols for the study of folate absorption were conducted to determine the following: (1) the equivalence of the [13C5] and [2H2] forms of folic acid, and (2) the merits of short-term plasma kinetics from injected and oral doses vs. urinary excretion of [13C5] and [2H2]folates. Another objective was to evaluate the merits of protocols not involving "saturation" of subjects with nonlabeled folate. Oral administration of [13C5] and [2H2]folic acid ( approximately 500 nmol each) to adult subjects (n = 4) yielded an equivalent 24-h urinary excretion of approximately 2% of each dose (molar ratio of urinary [13C5]/[2H2]folates = 0.96 +/- 0.055; mean +/- SEM). Expression of urinary excretion as a ratio of [13C5]/[2H2]folates yielded less within-group variability than seen for absolute excretion of each form of labeled folate. In the second study, subjects received 226 nmol of [2H2]folic acid intravenously and 1010 nmol of [13C5]folic acid orally. Isotopic enrichment of plasma [2H2]folates rose rapidly and returned to near basal values by approximately 2 h postdose. In contrast, enrichment of plasma [13C5]folates was detected until 4 h after dose, whereas enrichment values were far lower than seen with [2H2]folate. Adjusting for the difference in dose, the molar response of plasma area under the curve for isotopic enrichment was 15- to 20-fold greater for injected folates. In view of this very limited short-term plasma response even with a relatively large oral dose, presumably due to hepatic first-pass uptake, these findings suggest that plasma kinetics would be of limited usefulness in assessing the relative bioavailability of nutritionally relevant oral doses of labeled folate.

Administration, Oral↗
PubMed1997

Folate status response to controlled folate intake in pregnant women.

A metabolic study (84-d) was conducted to investigate the folate status response of pregnant subjects (n = 12) during their second trimester and nonpregnant controls (n = 12) to folate intakes approximating the current (400 microg/d) and former (800 microg/d) recommended dietary allowance (RDA). The overall goal of the study was to provide metabolic data to assist in the interpretation of the current RDA for folate. Subjects were fed a controlled diet containing 120 +/- 15 microg/d (mean +/- SD) folate and either 330 or 730 microg/d synthetic folic acid. Outcome variables between and within supplementation groups were compared at steady state. Serum folate was higher (P </= 0.05) in pregnant women consuming 850 compared with 450 microg/d (44.6 +/- 13.4, 26.3 +/- 11.3 nmol/L, respectively, mean +/- SD). No differences (P > 0.05) were detected in serum folate between pregnant and nonpregnant women within the same supplementation group. Urinary 5-methyl-tetrahydrofolate excretion was greater (P </= 0.05) in pregnant women consuming 850 compared with 450 microg/d (198.0 +/- 100.4, 9.5 +/- 3.2 nmol/d, respectively). No differences (P > 0.05) in 5-methyl-tetrahydrofolate excretion were detected between pregnant and nonpregnant women within supplementation groups. Differences (P </= 0.05) were not detected in red cell folate between pregnant women consuming either 450 or 850 microg/d (1452.5 +/- 251.8, 1733.5 +/- 208.5 nmol/L, respectively) or between pregnant and nonpregnant women consuming 450 microg/d. Our data suggest that 450 microg/d (dietary folate + synthetic folic acid) is sufficient to maintain folate status in pregnant women. This level of intake equates to approximately 600 microg/d dietary equivalents, assuming 50 and 75% availability of dietary folate and synthetic folic acid consumed with meals, respectively.

Adolescent↗
PubMed1997

Pyridoxine-5'-beta--glucoside exhibits incomplete bioavailability as a source of vitamin B-6 and partially inhibits the utilization of co-ingested pyridoxine in humans.

This research was conducted to investigate 1) the bioavailability of pyridoxine-5'-beta-D-glucoside (PN-glucoside) relative to that of pyridoxine (PN) in human subjects, and 2) the competitive effect of PN-glucoside on the metabolism of co-ingested PN. To evaluate PN-glucoside bioavailability, the subjects were administered a single oral dose of either deuterium-labeled ([2H2]) PN (Trial 1) or [2H2] PN-glucoside (Trial 2), and the urinary excretion rates of labeled 4-pyridoxic acid (4PA) were measured. The [2H2]4PA derived from [2H2] PN or [2H2]PN-glucoside was excreted mainly in the first 8 h after the dose. Excretion of [2H2]4PA during the 48-h postdose period indicated that the bioavailability of PN-glucoside was approximately 50% relative to PN, which is consistent with our previous report of 58% bioavailability determined using a different protocol and fewer subjects. To assess the effects of PN-glucoside on PN utilization, the subjects were administered different ratios of nonlabeled PN-glucoside with [2H2]PN in Trials 3 and 4. Comparing Trial 1 with Trials 3 and 4, the quantity of nonlabeled PN-glucoside, as a fraction of total vitamin B-6 administered, ranged from 0 to 40% (on the basis of pyridoxine equivalents), with a constant dose of [2H2]PN in each. In these trials, the rate but not the total extent of the excretion of [2H2]4PA derived from [2H2]PN was inversely related to the proportion of co-ingested nonlabeled PN-glucoside. Thus, antagonistic effects of PN-glucoside on PN metabolism do occur in humans, although the effect is less pronounced than that seen previously in rats. Such interactive effects must be considered in evaluating the net bioavailability of dietary forms of vitamin B-6.

Administration, Oral↗
PubMed1996

Bioavailability for humans of deuterium-labeled monoglutamyl and polyglutamyl folates is affected by selected foods.

Dietary folate exists mainly as polyglutamyl forms that require deconjugation by Zn-dependent pteroylpolyglutamate hydrolase prior to intestinal absorption. Because deconjugation by pteroylpolyglutamate hydrolase is an essential step in the absorption of dietary polyglutamyl folates, factors influencing the deconjugation process may affect folate bioavailability. This study was conducted to evaluate in vivo the bioavailability of [2H4]folic acid (d4-PteGlu1) and [2H2]-pteroylhexaglutamate (d2-PteGlu6) administered in solution in water or citrate buffer or added to selected foods using a single-dose, dual-label protocol. In each of six trials, healthy men (n = 7) were given a single oral dose of d2-PteGlu6 and d4-PteGlu1 (677 nmol of each form) blended into orange juice, tomatoes, lima beans, 52 mmol/L citrate (pH 4.1), or water as the control. Urine was collected for 48 h and the isotopic labeling of urinary folates used as criteria of the relative bioavailability of administered PteGlu1 and PteGlu6. Urinary excretion of d4-folates and d2-folates derived from the respective oral doses did not differ from the control in any treatment within the statistical power of this protocol. High relative bioavailability of the polyglutamyl folate was reflected by ratios of urinary d2/d4 folates of approximately 1.0 for control, tomato, lima bean and citrate buffer trials, whereas the ratio of urinary d2/d4 folates when subjects consumed orange juice was approximately 33% less than the control ratio (P < 0.05). These findings suggest that the bioavailability of polyglutamyl folates in orange juice would be partially incomplete. However, this would be compensated by the high total folate concentration of orange juice. The relation of these findings to endogenous dietary folates requires further investigation.

Administration, Oral↗
PubMed1996

Enzymatic deconjugation of erythrocyte polyglutamyl folates during preparation for folate assay: investigation with reversed-phase liquid chromatography.

Erythrocyte (RBC) folates occur mainly as 5-methyltetrahydrofolate polyglutamates. Determination of RBC folate concentration requires an initial deconjugation of these polyglutamates. In this study, existing HPLC methods were adapted to investigate the rate and extent of this deconjugation process. The action of endogenous plasma pteroyl-polyglutamate hydrolase activity was strongly affected by the conditions of sample preparation, with pH of the incubation mixture more critical to effective deconjugation than incubation time. Dilution of whole blood with 10 g/L ascorbic acid yielded fast hydrolysis of long-chain polyglutamates, and total conversion to 5-methyltetrahydrofolate monoglutamate occurred after 90 min of incubation at 37 degrees C. In contrast, dilution of whole blood with 10 g/L sodium ascorbate, with up to 90 min of incubation at 37 degrees C, yielded a mixture of polyglutamates of 5-methyltetrahydrofolate (glun = 1-8). As documented by direct HPLC analysis and in concurrent assays with Lactobacillus casei, acidification provided by ascorbic acid can have dramatic effects on the measurement of RBC folates.

Ascorbic Acid↗