Sources of hepatic glycogen synthesis following a milk-containing breakfast meal in healthy subjects

During feeding, dietary galactose is a potential source of hepatic glycogen synthesis; but its contribution has not been measured to date. In the presence of deuterated water ((2)H(2)O), uridine diphosphate (UDP)-glucose derived from galactose is not enriched, whereas the remainder derived from glucose-6-phosphate (G6P) is enriched in position 2 to the same level as body water, assuming complete G6P-fructose-6-phosphate (F6P) exchange. Hence, the difference between UDP-glucose position 2 and body water enrichments reflects the contribution of galactose to glycogen synthesis relative to all other sources. In study 1, G6P-F6P exchange in 6 healthy subjects was quantified by supplementing a milk-containing breakfast meal with 10 g of [U-(2)H(7)]glucose and quantifying the depletion of position 2 enrichment in urinary menthol glucuronide. In study 2, another 6 subjects ingested (2)H(2)O and acetaminophen followed by an identical breakfast meal with 10 g of [1-(13)C]glucose to resolve direct/indirect pathways and galactose contributions to glycogen synthesis. Metabolite enrichments were determined by (2)H and (13)C nuclear magnetic resonance. In study 1, G6P-F6P exchange approached completion; therefore, the difference between position 2 and body water enrichments in study 2 (0.20% ± 0.03% vs 0.27% ± 0.03%, P < .005) was attributed to galactose glycogenesis. Dietary galactose contributed 19% ± 3% to glycogen synthesis. Of the remainder, 58% ± 5% was derived from the direct pathway and 22% ± 4% via the indirect pathway. The contribution of galactose to hepatic glycogen synthesis was resolved from that of direct and indirect pathways using a combination of (2)H(2)O and [1-(13)C]glucose tracers.

Contribution of proteolytic and metabolic sources to hepatic glutamine by (2)H NMR analysis of urinary phenylacetylglutamine (2)H-enrichment from (2)H(2)O

Proteolytic and cataplerotic sources of hepatic glutamine were determined by (2)H NMR analysis of urinary phenylacetylglutamine (PAGN) (2)H-enrichments in eight healthy subjects after (2)H(2)O and phenylbutyric acid ingestion. Body water enrichment was 0.49+/-0.03%. PAGN was enriched to lower levels with significant differences between the various glutamine positions. PAGN position 2 enrichment=0.33+/-0.02%; 3R=0.27+/-0.02%; 3S=0.27+/-0.02% and position 4=0.17+/-0.01%. Position 3R,S enrichments are conditional with the net conversion of citrate to glutamate and are therefore markers of cataplerosis. From the ratio of positions 3R,S to body water enrichment, 55+/-3% of hepatic glutamine was derived from cataplerosis and 45+/-3% from proteolysis. In conclusion, enrichment of PAGN 3R,S hydrogens relative to that of body water reflects the contribution of cataplerotic and proteolytic sources to hepatic glutamine.

Hepatic UDP-glucose 13C isotopomers from [U-13C]glucose: a simple analysis by 13C NMR of urinary menthol glucuronide

Menthol glucuronide was isolated from the urine of a healthy 70-kg female subject following ingestion of 400 mg of peppermint oil and 6 g of 99% [U-(13)C]glucose. Glucuronide (13)C-excess enrichment levels were 4-6% and thus provided high signal-to-noise ratios (SNRs) for confident assignment of (13)C-(13)C spin-coupled multiplet components within each (13)C resonance by (13)C NMR. The [U-(13)C]glucuronide isotopomer derived via direct pathway conversion of [U-(13)C]glucose to [U-(13)C]UDP-glucose was resolved from [1,2,3-(13)C(3)]- and [1,2-(13)C(2)]glucuronide isotopomers derived via Cori cycle or indirect pathway metabolism of [U-(13)C]glucose. In a second study, a group of four overnight-fasted patients (63 +/- 10 kg) with severe heart failure were given peppermint oil and infused with [U-(13)C]glucose for 4 hr (14 mg/kg prime, 0.12 mg/kg/min constant infusion) resulting in a steady-state plasma [U-(13)C]glucose enrichment of 4.6% +/- 0.6%. Menthol glucuronide was harvested and glucuronide (13)C-isotopomers were analyzed by (13)C NMR. [U-(13)C]glucuronide enrichment was 0.6% +/- 0.1%, and the sum of [1,2,3-(13)C(3)] and [1,2-(13)C(2)]glucuronide enrichments was 0.9% +/- 0.2%. From these data, flux of plasma glucose to hepatic UDPG was estimated to be 15% +/- 4% that of endogenous glucose production (EGP), and the Cori cycle accounted for at least 32% +/- 10% of GP.

Noninvasive analysis of hepatic glycogen kinetics before and after breakfast with deuterated water and acetaminophen

The contributions of hepatic glycogenolysis to fasting glucose production and direct pathway to hepatic glycogen synthesis were quantified in eight type 1 diabetic patients and nine healthy control subjects by ingestion of (2)H(2)O and acetaminophen before breakfast followed by analysis of urinary water and acetaminophen glucuronide. After overnight fasting, enrichment of glucuronide position 5 relative to body water (G5/body water) was significantly higher in type 1 diabetic patients compared with control subjects, indicating a reduced contribution of glycogenolysis to glucose production (38 +/- 3 vs. 46 +/- 2%). Following breakfast, G5/body water was significantly higher in type 1 diabetic patients, indicating a smaller direct pathway contribution to glycogen synthesis (47 +/- 2 vs. 59 +/- 2%). Glucuronide hydrogen 2 enrichment (G2) was equivalent to body water during fasting (G2/body water 0.94 +/- 0.03 and 1.02 +/- 0.06 for control and type 1 diabetic subjects, respectively) but was significantly lower after breakfast (G2/body water 0.78 +/- 0.03 and 0.82 +/- 0.05 for control and type 1 diabetic subjects, respectively). The reduced postprandial G2 levels reflect incomplete glucose-6-phosphate-fructose-6-phosphate exchange or glycogen synthesis from dietary galactose. Unlike current measurements of human hepatic glycogen metabolism, the (2)H(2)O/acetaminophen assay does not require specialized on-site clinical equipment or personnel.

Simple measurement of gluconeogenesis by direct2H NMR analysis of menthol glucuronide enrichment from2H2O

The contribution of gluconeogenesis to fasting glucose production was determined by a simple measurement of urinary menthol glucuronide (MG) 2H enrichment from 2H2O. Following ingestion of 2H2O (0.5% body water) during an overnight fast and a pharmacological dose (400 mg) of a commercial peppermint oil preparation the next morning, 364 micromol MG was quantitatively recovered from a 2-h urine collection by ether extraction and a 125 micromol portion was directly analyzed by 2H NMR. The glucuronide 2H-signals were fully resolved and their relative intensities matched those of the monoacetone glucose derivative. The pharmacokinetics and yields of urinary MG after ingestion of 400 mg peppermint oil as either gelatin or enteric-coated capsules 1 h before breakfast were quantified in five healthy subjects. Gelatin capsules yielded 197 +/- 81 micromol of MG from the initial 2-h urine collection while enteric-coated capsules gave 238 +/- 84 micromol MG from the 2- to 4-h urine collection.

NMR study of the complexation of D-gulonic acid with tungsten(VI) and molybdenum(VI)

By using multinuclear (1H, 13C, 17O, 95Mo, 183W) magnetic resonance spectroscopy (1D and 2D), D-gulonic acid is found to form ten and seven complexes, respectively, with tungsten(VI) and molybdenum(VI), in aqueous solution, depending on pH and metal-ligand molar ratios. Two isomeric 1:2 (metal-ligand) complexes involving the carboxylate and the adjacent OH group are present in the pH range 2-9. At intermediate and high pH, molybdate forms a 2:1 tetradentate complex involving the four secondary hydroxyl groups, whereas tungstate forms one 2:1 terdentate species. At low and intermediate pH values, three 2:1 complexes are found for both metals, involving the carboxylate group and three secondary hydroxyl groups, as well as a 5:2 species involving the carboxylate group and all the secondary hydroxyl groups; the concentration of this species increases in time mainly at the expense of 2:1 and 1:2 complexes. Tungstate can also form two additional species, probably a 5:2 species involving the carboxylate group and all the hydroxyl groups, and a 2:1 pentadentate species involving the carboxylate group and all the secondary hydroxyl groups. In alkaline solutions, tungstate is able to form an additional 2:1 pentadentate complex involving all the hydroxyl groups.

Complexes of vanadium(V) with α-hydroxycarboxylic acids studied by 1H, 13C, and 51V nuclear magnetic resonance spectroscopy

A proton, carbon-13, and vanadium-51 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and relative stability of the complexes that form when vanadate(V) solutions are mixed with each one of the following organic α-hydroxyacids in the pH range ~2.5 – ~7: glycolic, lactic, chloro-3- and phenyl-3-lactic, mandelic, glyceric, and malic acids. The predominant complexes have 1:1 composition (almost certainly in a polymeric structure) in contrast with the 1:2 (metal:ligand) stoichiometry of the corresponding Mo(VI) and W(VI) complexes.

Piroxicam-induced photosensitivity

During the last 3 years, 9 patients with a photosensitive eruption related to piroxicam therapy were seen. In all but one, it occurred within 4 days of first exposure to the drug. 7 patients required systemic corticosteroids, and 2 hospitalization. Clinical, histological and provocation studies were not conclusive in classifying the eruption as photoallergic or phototoxic. Experimental studies including photohaemolysis, Bacillus subtilis culture and nuclear magnetic resonance showed: (i) in irradiated piroxicam solutions, there was more haemolysis; (ii) in irradiated Petri dishes, piroxicam solutions showed greater inhibition of growth of B. subtilis; (iii) Piroxicam's NMR spectrum is not modified after irradiation. The results provide evidence of piroxicam phototoxic potential.

Complexes of W(VI) and Mo(VI) with glycolic, lactic, chloro- and phenyl-lactic, mandelic, and glyceric acids studied by 1H and 13C nuclear magnetic resonance spectroscopy

A proton and carbon-13 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and stability of the complexes that form when sodium tungstate or sodium molybdate is mixed with each one of the following α-hydroxyacids in aqueous solution at pH values in the range 3–8: glycolic, lactic, chloro-3- andphenyl-3-lactic, mandelic, and glyceric acids. The predominant complexes have 1:2 composition and pK of formation of the order of −5 to −16.

Complexes of tungsten(VI) with thiomalic acid studied by 1H and 13C nuclear magnetic resonance spectroscopy

Proton and carbon-13 nmr evidence is presented on the number, stoichiometry, geometry, and stability of the complexes which form when sodium tungstate and (D,L)-thiomalic acid are mixed in aqueous solution at pH values in the range 2–7. In particular, three (or four) complexes are detected having a 1:2 composition (metal–ligand), as well as a less stable complex which seems to be a 1:1 species. Preliminary data are also given on the exchange of bound ligand in these complexes.