Isotope methods, determination bioavailability

JF Gregory, PR Trumbo, LB Bailey, JP Toth, TG Baumgartner, JJ Cerda. Bioavailability of pyridox-ine-5 -/S-D-glucoside determined in humans by stable-isotopic methods. J Nutr 121 177-186, 1991. 

Strong JM, Dutcher JS, Lee W-K, Atkinson AJ Jr. Absolute bioavailability in man of N-acetylprocainamide determined by a novel stable isotope method. Clin Pharmacol Ther 1975 18 613-22. 

Whole-body isotope retention experiments were performed (via the method described above in the Smith experiment and with confirmed corrections for isotope decay rates), using extrinsically labeled ferric chloride hexahydrate and Ca from CCM (i.e., [ FeJFeCla and [" Ca] CaCl2) to determine the bioavailability of these minerals at an Fe Ca ratio of 1 167 mol/mol. CCM solubility was also assessed via a filtration method. 

Element uptake from soil and transfer into the edible parts of plants have been addressed in several other studies. Soil-to-plant transfer factors in fruit and vegetables grown in various agricultural conditions have been determined for, for example, Pt [100], T1 [101], and various other metal contaminants [102], In a study on stable isotopes of fission product elements (Ce, Cs, Sr), an in vitro enzy-molysis method has been applied to investigate the solubilization of the analytes from fodder in a simulated ruminant digestion [103], The effect of inhibitors of fission product solubility was also considered and essential elements were determined simultaneously to evaluate potential nutrition problems for the animals from the use of such inhibitors. Selective leaching of individual classes of metal complexes with different ligands and sequential enzymolysis have been recently applied to estimate the potential bioavailability to humans of Cd and Pb in cocoa powder and related products [104]. 

The ability to conduct bioavailability studies on foods labeled intrinsically with stable isotopes is particularly important as this type of labeling is the gold standard for metabolic studies, i.e., intrinsic label should mimic the behavior of endogenous nutrients most closely. However, the mass spectrometric measurement of the metabolism of intrinsically stable isotope labeled materials is far more challenging than measuring extrinsically labeled nutrients. Low levels of isotope incorporation must be determined in small samples and it is only quite recently that modern LC-MS and LC-MS/MS methods, as demonstrated by the folate studies described above, have begun to rise to this challenge. 

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