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

Introduction: A history of chromium studies (1955–1995) 3removal of intravenously injected glucose to the approximately 4% rate of control rats.Brewer’s yeast and acid-hydrolyzed porcine kidney powder were identified as naturalsources of “GTF”, and the active (i.e., effective in reversing the inability to handle theglucose load) ingredient could be concentrated from these materials by physical andchemical means [4]. When given by stomach tube (500–1000 g/kg body mass), theintact materials and the concentrates could restore proper glucose metabolism in rats onthe Torula yeast-based diet. Although the separation means to isolate “GTF” were notdescribed in detail, “GTF” was found to be water-soluble, extractable with phenol andisobutanol, and absorbable on charcoal and ion-exchange resins.From the benefit of over 40 years of hindsight, these studies are deeplyflawed despite the success of similar studies in identifying other dietary requirements.Unfortunately, for example, the Cr content of the diet was not reported (although theexperimental procedures at the time would not have likely produced the correct value).Additionally, the rats were maintained in wire-mess cages, possibly with stainless steelcomponents, allowing the rats to obtain chromium by chewing on these components.Consequently, the actual Cr intake of the rats in these studies is impossible to gauge,putting into great question the suggestion that the rats were Cr deficient. The use of thelarge amounts of the metal ions is also of concern; as will be discussed in Chapter 9,large doses of chromium may have pharmacological effects, which may or may not berelated to any nutritional requirements. These doses are probably about 10 3 times thetypical daily content of a rat’s diet. Questions about data handling and the significanceof the effect observed from the chromium treatment have also been raised (vide infra).Considerable confusion in terminology in terms of the use of GTF has arisen.Studies over the last nearly 50 years have more often than not failed to distinguish thedifference among the inorganic ion Cr 3+ , Cr(III) complexes, and the biologically activeform of chromium (i.e., the naturally occurring biomolecule(s) which has an inherentfunction when containing bound Cr(III) if such exists), each called GTF. As originallyproposed in 1957, GTF is a substance that is involved in maintaining normal glucose,prevents and cures impairment of glucose removal when given in the diet or by stomachtube, and results in impairment of intravenous glucose tolerance when it is deficient inthe diet [3]. If one assumes that chromium is related to GTF and follows this definition,then GTF can only be the chromic ion, Cr 3+ . In publications soon after 1959, Mertzand Schwarz equated GTF and trivalent chromium [5, 6]. However, thereafter “GTF”takes on a different usage. As chromium must presumably interact with some organicbiomolecule(s) to manifest an effect(s) in mammals, attempts were subsequently madeto identify this (these) species. Unfortunately, the products of such attempts have alsobeen termed as “GTF”. To distinguish between organic Cr(III) complexes termed “GTF”and Cr 3+ being referred to as GTF, “GTF” when used to indicate an organic Cr(III)ligand complex will be enclosed in quotation marks.Research just prior to and in the 1960s was consistent with these early results.Continuing studies using rats fed a variety of diets found that rats on some dietsin addition to the Torula yeast-based diet apparently possessed low glucose removalrates; the glucose removal rates could be improved by addition of “GTF” concentrates.The concentrates were prepared from dried Brewer’s yeast, an enzymatic digest ofBrewer’s yeast, and dried defatted porcine kidney powder [7]. However, the methods ofpreparation of these materials were not described; while the amounts of the concentrates