Cells can dissolve gold in nano size

Gold is one of our most noble metals and has since ancient times had a special value because of its persistence - "gold never rusts". Researchers at Karolinska Institutet now show that this is a truth with modification. Nano-sized gold particles can be dissolved by cells.

Nanoparticles are very small and have a size of 1-100 nanometers (billions of meters). Such particles are increasingly used in society and researchers therefore study whether they can pose risks to people and the environment. Nano gold has many applications, such as improved x-ray and other imaging techniques, in diagnostics and treatment of cancer. It is also important to study what happens to nano gold in the body. Metallic gold is considered to solely be dissolved by specific chemicals such as a mixture of strong acids (king’s water) or cyanide. New research from Karolinska Institutet, published in the journal "ACS Applied Biomaterials", now shows that this is not true for nano gold.

We wanted to test the hypothesis that particles that are not considered capable of dissolving in the body actually can do so, especially when they are in nano size. Therefore, we tested gold, which is one of the most durable materials available, says research leader Hanna Karlsson, associate professor at the Institute of Environmental Medicine.

The researchers have developed a new method for testing the hypothesis. The method is based on the fact that macrophages (special immune cells that take care of bacteria and particles in the body) are cultured together with nano gold for a week. Then the cells are destroyed and dissolved gold can be separated. The amount of gold dissolved is analyzed by metal analysis (ICP-MS). Two different sizes of nano-gold were tested, 5 and 50 nanometers.

We found that both sizes of nano gold could be dissolved by cells. What was exceptional was that the smallest particles were dissolved to a relatively high degree (14%) if we simultaneously simulated inflammation in the cells, Hanna Karlsson explains.

The researchers mimicked inflammation by treating the macrophages with LPS, a substance found on the surface of bacteria that the immune system can recognize, whereby an immune response can start. Exactly what reactions that cause gold to dissolve are not clear, but reactive oxygen molecules probably play a role. The researchers are now continuing to study this in more detail.

It is still too early to determine the importance of the dissolution of gold nano to gold ions, for example if it can cause adverse effects or, on the contrary, be useful for treating diseases. Gold salts have long been used to treat for example rheumatism, and possibly dissolution of gold ions from nanoparticles in connection with inflammation may in the future prove to be a new successful treatment.

Publication

Macrophage-Assisted Dissolution of Gold Nanoparticles
Carlander U, Midande K, Hedberg Y, Johanson G, Bottai M, Karlsson HL
Applied Bio Materials, American Chemical Society, 2019

Contact

Hanna Karlsson, docent
Insitute of Environmental Medicine
Karolinska Institutet
Tel: 08-52487576
E-post: Hanna.L.Karlsson@ki.se
Webb: https://ki.se/people/hkarlss