Tuesday, October 4, 2011

Oxidative stress induced cancers: Is the trivalent chromium really oxidized hexavalent chromium? (2 of x)

Note: It has been publicized that the Depuy hip contains the less toxic trivalent chromium (aka Chromium 3.) There are quite a number of studies which I have uncovered that suggest  the trivalent chromium may be an oxidized hexavalent chromium (aka, chromium 6) which is known to have greater carcinogenic properties than the chromium 3. I have also learned that much of the underlying molecular damage my be due to its intracellular reduction to the even more highly reactive and short lived Chromium 3 and Chromium 5. I hope that someone at some point can clarify the chromium 3 vs 6 issues.


Chem Biol Interact. 2010 Nov 5;188(2):276-88. Epub 2010 Apr 27.

Chromium genotoxicity: A double-edged sword.

Source

Department of Pharmacology and Physiology, The George Washington University Medical Center, Washington, DC 20037, United States.

Abstract

Certain forms of hexavalent chromium [Cr(VI)] are known respiratory carcinogens that induce a broad spectrum of DNA damage. Cr(VI)-carcinogenesis may be initiated or promoted through several mechanistic processes including, the intracellular metabolic reduction of Cr(VI) producing chromium species capable of interacting with DNA to yield genotoxic and mutagenic effects, Cr(VI)-induced inflammatory/immunological responses, and alteration of survival signaling pathways. Cr(VI) enters the cell through non-specific anion channels, and is metabolically reduced by agents including ascorbate, glutathione, and cysteine to Cr(V), Cr(IV), and Cr(III).

Cr(III) has a weak membrane permeability capacity and is unable to cross the cell membrane, thereby trapping it within the cell where it can bind to DNA and produce genetic damage leading to genomic instability. Structural genetic lesions produced by the intracellular reduction of Cr(VI) include DNA adducts, DNA-strand breaks, DNA-protein crosslinks, oxidized bases, abasic sites, and DNA inter- and intrastrand crosslinks. The damage induced by Cr(VI) can lead to dysfunctional DNA replication and transcription, aberrant cell cycle checkpoints, dysregulated DNA repair mechanisms, microsatelite instability, inflammatory responses, and the disruption of key regulatory gene networks responsible for the balance of cell survival and cell death, which may all play an important role in Cr(VI) carcinogenesis. Several lines of evidence have indicated that neoplastic progression is a result of consecutive genetic/epigenetic changes that provide cellular survival advantages, and ultimately lead to the conversion of normal human cells to malignant cancer cells. This review is based on studies that provide a glimpse into Cr(VI) carcinogenicity via mechanisms including Cr(VI)-induced death-resistance, the involvement of DNA repair mechanisms in survival after chromium exposure, and the activation of survival signaling cascades in response to Cr(VI) genotoxicity.

[from Connie:  I thought this was a terrific explanation of what goes on with the reduction of chromium 6 to chromium 3.  Now why is it so difficult to get responses from anyone confirming or denying that Chromium 3 in the Depuy hip, or other hips for that matter, is in fact oxidized from Chromium 6?  If the long terms systemic DNA damage is likely to occur during the oxidation, it is really important that someone take a look at this issue. Key bibliography that must be reviewed.]

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