The Nutritional Biochemistry of Chromium(III) - Survival-training.info

Introduction: A history of chromium studies (1955–1995) 7Another attempt to identify “GTF” from Brewer’s yeast separated 11 apparentlyhomogeneous Cr-containing species from the yeast [23]. The species were amphoteric,anionic, and cationic. The four cationic species and one anionic species displayed someability to stimulate yeast fermentation. Further investigation [33], however, revealedthat all 11 species were artifacts formed between components of the growth media andchromic ions added to the media. The authors proposed that “GTF” could no longer beregarded as a chromium complex.Holdsworth, Neville, and coworkers have examined Brewer’s yeast extracts extensively[34–37]. They too have been able to distinguish between Cr-containing fractions(either cationic or anionic) and a fraction active in in vitro biological activity assaysusing rat adipocytes; rat hepatocytes from control rats, Cr-deficient rats, and rats onCr-deficient diets supplemented with chromium and yeast. They conclude that theenhanced response in the presence of insulin comes from gamma-aminobutyric acid inthe yeast extracts. No evidence was found that “GTF” aided the binding of insulin-toinsulinreceptor, such as by the formation of a ternary complex. The “GTF”-like activityfrom non-Cr-containing fractions using the adipocyte assay required the cells to be fromrats on a Torula yeast diet.Most recently, Hwang and coworkers [38] and also Simonoff et al. [39] showedthat the fractions of Brewer’s yeast that stimulate glucose oxidation by rat adipocytes inthe presence of insulin were distinct from the fractions containing chromium. The ratswere raised on a standard (i.e., Cradequate) diet.Biological activity assaysUntil this point in time, biological activity of a chromium-containing speciesreferred to the ability of the species to potentiate the action of insulin to stimulate in vitrothe metabolism of epididymal fat tissue from “chromium-deficient” rats. “Chromiumdeficient”rats in this definition means rats on the Torula yeast diet or another dietgiving rise to similar effects when rats are given glucose tolerance tests (which, asdiscussed earlier, have essentially no data supporting their actually being chromiumdeficient). The reproducibility and sensitivity of the assay for biological activity wasimproved in 1978 by Anderson and coworkers who showed that adipocytes isolatedfrom epididymal fat tissue of “Cr-deficient” rats could be utilized [40]. Replicate assaysat a series of insulin concentrations could now be readily performed, allowing fordetailed kinetics experiments. These assays showed that Brewer’s yeast extracts andthe synthetic Cr–nicotinate complexes described above potentiated the ability of insulinto stimulate glucose oxidation at a variety of insulin concentrations. The degree ofstimulation also depended on the chromium concentrations of either the extract orsynthetic complexes, leading to the conclusion that these compounds contain biologicallyactive forms of chromium. However, further analysis of these results has shown thatthe original interpretation is incorrect [41]. Addition of the chromium sources withoutadding insulin stimulated the metabolism of glucose; the stimulation due to insulin abovethis increased background was actually decreased. The chromium sources in fact madeinsulin less effective, consistent with components of the extracts binding to insulin (asdescribed above) and not allowing the complexed insulin to bind to its receptor. Analternative has been pointed out in that the isolated adipocytes may not have been washedsufficiently to remove traces of insulin [42]; however, extrapolation of the insulin dose