Nano- and microparticles of gold inhibit autoimmune inflammation

While gold was once considered inert, gold implants have been found to release gold ions into the surrounding tissue. Danscher and Rasmussen provide an overview of the recent findings on the use of metallic gold particles to treat inflammation. They differentiate in size between (a) treatment with injected gold microparticles > 20 μm (and gold macro-implants [as used in gold implantation, with a size in the millimetre range]) on the one hand and (b) gold nanoparticles [size in the nanometre range] as used in other therapies on the other.* They summarise the current state of knowledge about effects and associated processes at the cellular level.

(a) Gold microparticles > 20 μm (and gold macro-implants [like in gold implantation]) are reported to remain where they were injected [or implanted]. Due to their size, macrophages [cells of the immune system] cannot “swallow” them. Instead, macrophages settle on the gold surface, oxidise gold atoms to gold ions Au+, secrete cyanide ions (CN)–, and dissolve the gold ions (Au+) creating dicyanoaurate ions [Au(CN)2]–. These migrate into the immediate vicinity (a few millimetres away) and are responsible for the anti-inflammatory effect of metallic gold. They have been traced there in macrophages, mast cells, fibroblasts, and fibres. The release of gold ions can continue for years, thus maintaining the anti-inflammatory effect.

It has been found that an unusually high amount of a special protein (“HMGB1”) is present in and around inflamed joints. This protein, in addition to functions within the cell, can, when released from the cell, stimulate the immune system and trigger inflammation. Gold ions (from aurothiomalate [gold compound for treating rheumatoid arthritis]) were found to inhibit the release of HMGB1 from the nucleus, thus reducing amounts outside the cell and lessening inflammation.

(b) Gold nanoparticles [not used in gold implantation], on the other hand, are spread throughout the body due to their small size. While there is a temporary and beneficial effect on autoimmune inflammation, possible side effects are indicated, fewer, but similar to those of gold-containing drugs.

* 1 mm (millimetre) = 1/1,000 metre, 1 μm (micrometre) = 1/1,000,000 metre, 1 nm (nanometre) = 1/1,000,000,000 metre.

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