Vitamin stable isotope

We have used stable Isotopes in several other zinc absorption studies. Sample analysis Is In progress from a study In which Zn was used to determine the effects of phtate and cellulose on zinc absorption In man. Studies were also conducted to determine zinc absorption from vegetarian diets, the effect of vitamin B-6 status on zinc absorption, and the effect of level of dietary zinc on zinc and copper absorption. 

Stable isotopes of retinal and (3-carotene have also been employed to assess liver vitamin A stores in healthy individuals, and the best measure of vitamin A status (Furr et ah, 1989). The relative ratio of circulating isotopically labeled retinol is later assessed to estimate liver levels (Wang et ak, 2000 Hickenbottom et ah, 2002b) and without this technique, a liver biopsy would be necessary to estimate liver levels. 

Replacement of Metabolic Losses An alternative approach to determining vitamin requirements is to measure the loss from the body pool in a steady state. This requires estimation of the total body pool, and measurement of the fractional rate of loss from that pool, generally using radioactive or stable isotope tracers. Three problems can arise in such studies. 

FIG. 2. Whole animal labeling kinetics with stable-isotope-labeled pyridoxine. Mice were placed on a vitamin B6-deficient diet and labeled with dideuterated pyridoxine. At intervals, urine samples were collected and the isotope abundance of excreted 4-pyridoxic acid was measured. After SO days, the animals have attained a plateau labeling. When analyzed as a biexponential process, the rate constant for the labeling of the slow pool is the same as that obtained by pulse labeling with radioactive pyridoxine. The symbols correspond to the data from four individuals in the study. 

Our interest in McArdle s disease and vitamin B6 metabolism is stimulated by consideration of the consequences of the loss of the major, slowly metabolizing pool of vitamin B6 in the body. It is conceivable that the whole body phosphorylase-derived pool acts as a buffer to compensate for day-to-day variation in vitamin B6 intake. It will therefore be important to assess the rate of degradation of phosphorylase in the human, and the stable isotope method we have developed is directly applicable to this problem. Analysis of the same kinetics in McArdle s patients will define the role of muscle phosphorylase in the compartmen-talization of vitamin B6. 

Beynon, R. J., leyland, D. M., Evershed, R. P., Edwards, R. H. T., and Cobum, S. P. (1996). Measurement of the turnover of glycogen phosphorylase by gas chromatography/mass spectrometry using stable isotope derivatives of pyridoxine (Vitamin B6). Biochem. J. 317, 613-619. 

Tumiund JR, Keys WR, Hudson CA, et al. 1991. A stable isotope study of zinc, copper, and iron absorption and retention by young women fed vitamin B6 deficient diets. Am J Clin Nutr 54(6) 1059-1064. 

The biosynthetic pathway of this alkaloid, starting with 5-aminolevu-linic acid, has been well studied by incorporation studies using radioisotope-labeled and H) and stable isotope-labeled ( C, and (D)) precursors [9-13]. The biosynthesis of vitamin Bj2 is reviewed [14],... 

A wide range of human studies has been conducted using enriched stable isotopes of nutrient minerals. Applications include the determination of the absorption and metabolism of iron, zinc, calcium, copper, selenium, and molybdenum. An example of the type of information that can be obtained is provided by a study of iron absorption from different weaning foods, and the effects of vitamin C on iron absorption. These measurements, conducted using enriched stable isotopes of Fe and Fe, demonstrated a doubling of iron absorption when a drink containing 50 mg of vitamin C was administered with the food. 

Rychlik, M. 2011. Stable isotope dilntion assays in vitamin analysis-A review of principles and applications. In Fortified Foods with Vitamins, edited by M. Rychlik, pp. 1-19. Wiley-VCH Verlag GmbH Co. KGaA. 

Intra- and interassay variability for aU analytes ranged from 0.4% to 7.9% and from 2.2% to 5.2%, respectively. Quantification was done by ratio response to the stable isotope-labeled internal standards. C4-Thiamine hydrochloride, 4, N2-riboflavin, and Hj-pyridoxal hydrochloride were added to the samples as internal standards for quantification. The standard addition method determined recovery rates for each vitamin (73.0-100.2%). The limit of quantitation for all vitamins was between 0.05 and 5 [ig/L depending on the vitamin. 

The present book is the second of two volumes that provide state of the art expert reviews of central topics in modern natural products chemistry and secondary metabolism. Using specific examples, the previous volume emphasized two revolutions in experimental techniques that completely transformed the field of natural products chemistry from what it was in the 1950s. These were the use of stable isotopes in conjunction with modern NMR and mass spectrometry, and more recently, the development of molecular biological techniques to identify, purify and manipulate the enzymes responsible for the intricate series of steps to complex natural compounds. The previous volume specifically covered the use of isotopes in biosynthetic research and the formation of enzyme cofactors, vitamin B12 and reduced polyketides. 

In 1948 chemists working for Glaxo in England and for Merck in the United States isolated a crystalline compound from liver that clinical tests proved to be the extrinsic factor. Because the factor proved to be a nutritional requirement, the Americans called it vitamin B12. Isolation of vitamin B12, the discovery that it contains cobalt, and the substitution of radioactive cobalt for the stable isotope made characterization of the intrinsic factor much easier, for it was no longer necessary to find a patient in relapse and then to exhaust his usefulness in one time-consuming test of a single preparation. ... 

Rychlik, M., and Roth-Maier, D., 2005. Pantothenic add quantification method comparison of a stable isotope dilution assay and a microbiological assay. International Journal for Vitamin and Nutrition Research. 75 218— 223. 

Rychlik, M., 2003. Simultaneous analysis of folic acid and pantothenic acid in foods enriched with vitamins by stable isotope dilution assays. Analytica Chimica Acta. 495 133-141. 

AJ Clifford, AD Jones, HC Furr. Stable isotope dilution mass spectrometry to assess vitamin A status. Methods Enzymol 189 94-104, 1990. 

G Fauler, HJ Leis, J Schalamon, W Muntean, H Gleispach. Method for the determination of vitamin Ki(20) in human plasma by stable isotope dilution/gas chromatography/mass spectrometry. J Mass Spectrom 31 655-660, 1996. 

MS/MS detection was shown to be a useful tool for the simultaneous determination of vitamins using stable isotope-labeled internal standards for their quantification in nutritional formulations [9]. Nevertheless, it is difficult to optimize the ionization and detection conditions, due to the different nature of the vitamins analyzed. Thus, frequently, compromise conditions have to be selected. Another critical factor for the multiple separation and detection of vitamins is the pH. In general, low pH values should be used, although the best conditions should be optimized in each... 

The relative bioavailability and bioactivity of the different forms and food sources of vitamin K need more research. Preliminary studies with deuterium-labeled broccoli suggest that the bioavailability of endogenous vitamin K can be studied in humans by intrinsic stable isotope-labeling procedures. 

A semi-quantitative determination can be made by comparison with a series of standards on the same layer, before or after carrying out a colour reaction. A flawless quantitative determination after elution has not so far been achieved as a result of the extreme instabflity of the vitamin A compounds, especially on active adsorbents. Success may perhaps be gained by conversion to the more stable anhydro-form and following then with TLC. The radioactive measurement of isotopes has been carried out frequently [68, 98]. 

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