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Biomedical subjects

J F Gregory

Publications and source records attributed to J F Gregory.

At least 37 records · Page 2Linked to original sources
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folic acid or [2H2]pteroylhexaglutamic acid/d for the next 8 wk; then for the next 8 wk the [2H4]folic acid was withdrawn and the subjects received only nonlabeled folic acid.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↗
PubMed1995

Folic acid absorption in women with a history of pregnancy with neural tube defect.

Folic acid absorption was compared in nonpregnant women with a history of pregnancy with a neural tube defect (cases)(n = 10) with that of control women (n = 10) with a normal pregnancy history. [2H4]folic acid was administered in an oral dose (400 micrograms) to fasting case and control subjects after a 30-d saturation protocol involving daily ingestion of two 1-mg folic acid supplements. Serum and red blood cell folate concentrations were not different for case and control subjects before or during the saturation protocol (P > 0.05). The percentage (x +/- SD) of the oral dose of [2H4]folic acid excreted in 24-h urine collections postdose was not different (P > 0.05) for case compared with control subjects (9.05 +/- 2.25% and 11.10 +/- 3.41%, respectively). These data suggest that the absorption of folic acid routinely consumed in supplements and fortified food products is not impaired in women with a history of a pregnancy with a neural tube defect. Further case-controlled studies are needed to compare the absorption of the predominant dietary form of the vitamin.

Administration, Oral↗
PubMed1995

Zinc status is not adversely affected by folic acid supplementation and zinc intake does not impair folate utilization in human subjects.

Changes in zinc status in response to folic acid supplementation and the effect of zinc intake on folate utilization were evaluated in 12 men (20-34 y old) consuming a diet containing 3.5 or 14.5 mg zinc/d for two 25-d intervals. Deuterium-labeled folic acid (800 micrograms/d) or a placebo was administered orally during each phase. No differences in plasma zinc, erythrocyte zinc, urinary zinc, erythrocyte metallothionein or serum alkaline phosphatase, due to supplemental folic acid, were detected at either level of zinc intake. Differences in the response to folic acid supplementation, due to the level of zinc intake, were not detected for serum, erythrocyte or urinary (labeled and unlabeled) folate. Within the constraints of this short-term folic acid supplementation study, adverse effects on zinc status were not observed and our data suggest that folic acid utilization was not influenced by level of zinc intake.

Administration, Oral↗
PubMed1995

Controlled dietary folate affects folate status in nonpregnant women.

In a study designed to estimate the requirement for dietary folate in nonpregnant women, 17 women (21-27 y) consumed 200, 300, or 400 micrograms/d of total folate for 70 d which was provided by low folate conventional foods (30 micrograms) plus supplemental folic acid. Group means for initial serum and erythrocyte folate and plasma homocysteine concentrations were not significantly different. Serum and erythrocyte folate decreased relative to the initial value in the 200 micrograms/d group (43.4 +/- 12.1%, 13.6 +/- 16.6%, respectively; mean +/- SD), in contrast to an increase in the 400 micrograms/d group (16.8 +/- 52.0%, 10.2 +/- 18.5%, respectively). The final serum folate in the 200 and 300 micrograms/d groups (6.4 +/- 0.8 nmol/L, 7.3 +/- 1.1 nmol/L, respectively) was significantly lower than that of the 400 micrograms/d group (14.3 +/- 2.0 nmol/L), with evidence in the 200 micrograms/d and 300 micrograms/d groups of low ( < 6.8 nmol/L) serum folate concentrations. Differences in final erythrocyte folate did not reach statistical significance, although low values ( < 362 nmol/L) were frequent in subjects with 200 micrograms/d intake. In the 200 micrograms/d group, plasma homocysteine was negatively correlated with serum and erythrocyte folate, and final mean plasma homocysteine (12.6 +/- 1.7 mumol/L) was significantly higher than that of the 300 or 400 micrograms/d groups. Elevated plasma homocysteine levels ( > 16 mumol/L) were observed in the 200 micrograms/d group only.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Pyridoxine and pyridoxine-5'-beta-D-glucoside exert different effects on tissue B-6 vitamers but similar effects on beta-glucosidase activity in rats.

Pyridoxine glucoside is a partially available form of vitamin B-6 present in plant-derived foods. In this set of three studies, rats were fed diets containing different concentrations of either pyridoxine or pyridoxine glucoside in the presence or absence of a fixed concentration of pyridoxine for 2 wk. The distribution of B-6 vitamers and beta-glucosidase activity in tissues was examined to determine the metabolic effects of chronic consumption of pyridoxine glucoside. Rats fed pyridoxine glucoside either with or without pyridoxine exhibited a significant increase in the amount of hepatic pyridoxine 5'-phosphate (not detected in rats fed pyridoxine alone), whereas hepatic pyridoxal 5'-phosphate was decreased with increasing dietary pyridoxine glucoside. The activity of cytosolic beta-glucosidases in small intestine and kidney was affected by the dietary concentration of both pyridoxine and pyridoxine glucoside. Enzymatic activity capable of hydrolyzing pyridoxine glucoside was found in mucosal and intraluminal fractions of small intestine and in the kidney. Other tissues examined, including liver, spleen and stomach, did not hydrolyze pyridoxine glucoside in detectable quantities. These findings indicate that microbial and mucosal enzymes can participate in the intestinal hydrolysis of pyridoxine glucoside and that the kidney may contribute to postabsorptive hydrolysis. These findings further support the observations that dietary pyridoxine glucoside influences vitamin B-6 metabolism.

Animals↗
PubMed1995

Pyridoxine-5'-beta-D-glucoside influences the short-term metabolic utilization of pyridoxine in rats.

This study was conducted to characterize the initial time course of the apparent competitive effect of pyridoxine-5'-beta-D-glucoside against co-ingested pyridoxine. Two groups of rats were administered a single oral dose of 100 nmol of [14C]pyridoxine along with either 0 or 20 nmol of unlabeled pyridoxine-5'-beta-D-glucoside. At 6, 12, 24 and 48 h post-dose, the distribution of labeled vitamin B-6 metabolites in blood, tissues and urine was determined. Urinary [14C]4-pyridoxic acid comprised a significantly greater percentage of excreted 14C in the control group, with the greatest difference at 12 h post-dose. Pyridoxine-5'-beta-D-glucoside (10-15 nmol) was excreted mainly in unchanged form within 6 h. Rats that received pyridoxine-5'-beta-D-glucoside retained less 14C in liver, with a maximal difference between groups at 6-12 h post-dose. The relative concentrations of hepatic [14C]pyridoxal 5'-phosphate and [14C]pyridoxamine 5'-phosphate in the treatment group were greater than in the control group at approximately 12 h post-dose. At 48 h post-dose, there was no difference in the distribution of any vitamin B-6 metabolite except pyridoxal 5'-phosphate in the two groups. These results confirm that a small, nutritionally relevant dose of pyridoxine-5'-beta-D-glucoside influences the utilization of pyridoxine and indicate that this is a short-term, transient effect.

Animals↗
PubMed1994

Mice, hamsters and guinea pigs differ in efficiency of pyridoxine-5'-beta-D-glucoside utilization.

Mice, hamsters and guinea pigs were studied to assess species variation in utilization of pyridoxine-5'-D-glucoside (PN-glucoside), a form of vitamin B-6 found in plants. Animals fed vitamin B-6-deficient or marginally supplemented diets [1 mg pyridoxine (PN)/kg] were given an oral dose of [3H]PN-glucoside plus [14C]PN. Urinary and fecal isotopic excretion was measured over 24 h and the distribution of B-6 vitamins in liver determined at the end of the 24-h period. Intestinal absorption was nearly complete, as very little (< 6%) of each isotope was excreted in the feces. In mice, hamsters and guinea pigs, 31.3, 31.5 and 9.5%, respectively, of urinary 3H was present as intact PN-glucoside. Incorporation into liver was reflected by 3H/14C ratios of hepatic vitamin B-6 as follows: mice, 0.39; hamsters, 0.73; guinea pigs, 1.49 (means for both diets). The intake of dietary vitamin B-6 had little effect on [3H]PN-glucoside metabolism. Guinea pigs displayed greater utilization of PN-glucoside than did mice, hamsters or rats (seen previously), although they may not be the best animal model for the study of PN-glucoside metabolism. Because the bioavailability of PN-glucoside in humans has been estimated to be 58% relative to PN, mice or hamsters, rather than guinea pigs or rats, would be better species for quantitative studies of PN-glucoside bioavailability and associated enzymatic processes.

Animals↗
PubMed1993

Pyridoxine-5'-beta-D-glucoside competitively inhibits uptake of vitamin B-6 into isolated rat liver cells.

Uptake of pyridoxine-5'-beta-D-glucoside by freshly isolated rat liver cells was studied at a concentration (0.5 mumol/L) approximating the physiological range of vitamin B-6 by using a membrane filtration method. Unlabeled pyridoxine glucoside was found to competitively inhibit the uptake of [4'-3H]pyridoxine but have no detectable effect on the uptake of D-[1-3H]glucose by hepatocytes. The uptake of [3H]pyridoxine glucoside by isolated rat liver cells was very similar to the uptake of [3H]pyridoxine with Kt = 13.8 mumol/L (6.3 mumol/L for pyridoxine) and Vmax = 82 pmol/(10(6) cells.min) [28 pmol/(10(6) cells.min for pyridoxine)]. The results of this study indicate that pyridoxine glucoside uses the same transport system as does pyridoxine. Upon entry to the cell, pyridoxine glucoside undergoes hydrolysis to release pyridoxine, which is the rate-limiting step in metabolism of this beta-glucoside.

Animals↗