Intrinsic labeling

The in vitro procedure was tested in "critical" experiments designed to make direct comparisons of in vivo and in vitro estimates of exchangeability and potential bioavailability and to test the use of in vitro exchangeability values in in vivo experiments. (8). Three foods which were expected to show different levels of calcium solubility and exchangeability, collards, soybeans and spinach, were intrinsically labeled with 45Ca in nutrient solution culture. They were used together with 47 Ca as an extrinsic label in both in vitro and in vivo experiments. 

Janghorbani et al. (58) fed isonitrogenous diets to 10 subjects for 12 days. Both an intrinsic label (chicken) and extrinsic labels were used. Zinc absorptions from an all-chicken diet and from a 50% chicken-50% soy isolate diet were equivalent. Solomons et al. (59) fed 5 or 10 subjects diets in which milk, soy isolate, and beef (or mixtures of these) were protein sources for the milk and/or soy diets, absorptions were similar "fractional" absorptions from beef bologna may have been higher than from soy bologna (Table IV). 

Expt. 1—CaCOs tablets versus Ca citrate malate (CCM) tablets intrinsically labeled CCM molar ratio 6 2 3... 

All oral Ca test loads (250 mg) intrinsically labeled with Ca tracer and consumed as tablets or in juice... 

Solid preparations intrinsically labeled prior to precipitation [i.e., CaC03, Ca oxalate (CaC204), TCP, HA, and CCM], spinach and kale grown hydroponically and labeled via a nutrient solution during growth... 

Oral gavage with various Ca fortification salts of different solubilities that were intrinsically labeled with " Ca... 

Andon (2003) compared five different CCM formulations covering a threefold range of Ca citrate malate molar ratios from 154 previous studies in humans. Intrinsically labeled tablets or juices comprising 250 mg Ca as CCM were tested in adolescents and groups of women 20 to 30-years and 40 to 77-years old. A comparison of mean values for age groups, molar ratios, and vehicles revealed no differences. Comparison with reported values in the literature, after adjustment to equalize Ca doses and indexing versus a standard (i.e., milk = 100), revealed Ca absorption from CCM consistently exceeded absorption from other sources including milk, various dairy products, fortified foods, and Ca supplements. 

While considerable efforts have been spent in the past few years in the field of solid supports for combinatorial chemistry [73], most of them were devoted to modified polystyrenic beads with different sizes, loadings or swelling properties [74], or carrying different functionalities or linkers for library synthesis [75], or to solid supports different from resin beads (pins [76], cellulose [77], soluble supports [78], and so on). Few reports dealt with labelled solid supports prepared by chemical reactions (see the previous paragraphs) and significant efforts in the field of material sciences to obtain intrinsically labeled, nonchemically encoded, easily readable, combinatorial solid supports have not been reported. 

The versatility of the SPR technique has been shown by a vast amount of publications in the past decades the method has matured into a well-accepted analytical tool for the characterization of interfaces and thin films as well as for the sensitive detection of interfacial biomolecular interaction. With a significant input from engineering, SPR has reached a decent signal-to-noise level with a lower limit for a reliable signal detection corresponding to an effective layer of about 0.3 A [6], which is sufficient for most thin film studies. However, the intrinsic label-free characteristic of SPR detection technique still imposes limitation on further sensitivity improvement, especially if the analysis involves small molecules. 

In vitro tests using other procedures (19) were carried out in our laboratory (Ketelsen et al., manuscript in prep.) to study the dialyzability of zinc from slurries of defatted soy flours over a range of pH s. Either 2inc was added to soy slurries as zinc carbonate (extrinsic label) or the zinc was intrinsically labeled in soybeans grown hydroponically. Results from these studies (data not shown) indicated that the extrinsic and intrinsic zinc pools do not completely mix. The results showed that the pH of the soy suspensions affected the quantity of zinc that was bound in complexes of molecular weight in excess of 12,000. Also, intrinsic zinc was more likely to be bound to high molecular weight complexes than extrinsic zinc, especially for slurries at pH 3. 

Intrinsic Labeling of Edible Plants th Stable Isotopes... 

Intrinsic labeling is time consuming and specialized. Extrinsic labeling whereby a mineral isotope is mixed with a food prior to consumption is an appealing alternative to intrinsic labeling. The extrinsic labeling approach assumes that the extrinsic label... 

Radioisotope techniques have allowed precise measurement of dietary iron absorption. Initial studies utilized test meals of individual food which had been intrinsically labeled with radios active iron prior to harvesting (1,2). Utilization of these single food meals allowed a rank order to be established among the tested foods. Subjects could serve as their own controls when an identical reference dose was given to each subject. 

House WA, Welch RM. 1989. Bioavailability of and interactions between zinc and selenium in rats fed wheat grain intrinsically labeled with 65Zn and 75Se. J Nutr 119(6) 916-921. 

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