Monday, July 25, 2011

Review of the Cell biology surrounding metal on metal hips (7 of x in a series)

The material for this series of posts  are sourced through the the following journal article:

Acta Orthop. 2008 Dec;79(6):734-47.
Metal-on-metal hip resurfacing arthroplasty: a review of periprosthetic biological reactions.
Mabilleau G, Kwon YM, Pandit H, Murray DW, Sabokbar A.

Metal ions  in cells (metal transport)

1. Microparticles of  Cobalt (Co) and  Chromium (Cr) can be phaogcytosed* by cells

*phagocytsis- is the cellular process of engulfing solid particles by the cell membrane.  It is a major mechanism used to remove pathogens and cell debris

2.  The metal particles are exposed to a series of oxidative mechanisms designed to destroy a foreign body which leads to to the generation of metal ions and free radicals.

3.  It is still unclear as to how the metal ions can be released from the lysosome*.

*lysosome-cellular organelles that contain acidic enzymes to break down waste materials and cellular debris.

4.  It has been suggested that nanoparticles may be taken into the cells by a well-characterized pathway used by cells to absorb nutrients.

5.  Corrosion is the main degradation process of metals.

6.  Metals become  protected against corrosion by the formation of an oxide layer at the surface however, under certain conditions, the oxide layer can be removed, allowing the surface of the metal to come into direct contact with the corrosive compounds of the biological fluids.

7.  Metal ions may also enter cells directly by different pathways such as using an ion transporter or by using specific metal ion binding proteins.

8.  Cr ions cross the cell membrane.

9.  Within the cell, Cr6 undergoes rapid metabolic reduction via acid and other chemicals.

10.  Although Cr3 is known to exist, it is unclear how it can cross the cell membrane.

[ have blogged extensively on the confusion surrounding Chromium 6 (the toxic form of Chromium) and Chromium 3, (purportedly the non toxic form of Chromium found in the Depuy hip.)    As mentioned previously, Chromium seems to have the ability to oxidize from 3 to 6 and vice versa. Thus far, reported cases of this oxidation have occurred only under specific industrial conditions however that is not what this document seems to suggest. see next post on this subject.]

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