Gold nanoparticles could be used to build a new class of anti-arthritic drug that's more effective and has fewer side effects, scientists from the University of Wollongong in Australia have found.

Rheumatoid arthritis is an autoimmune disease that occurs when the immune system malfunctions and attacks a patient's joints, instead of invading pathogens.

Now new research has shown that tiny particles of gold can invade macrophages, a type of white blood cell, and potentially stop them from buliding up inflammation around the joints, without killing them.

Interestingly, this isn't the first time gold has been used to treat rheumatoid arthritis. For the past 80 years or so, scientists have been injecting patients with regular-sized gold compounds to reduce inflammation. But this tapered off in the 1990s because the gold was also causing a lot of side effects, such as kidney damage and skin rashes.

But by shrinking the gold into tiny nanoparticles - which are around 50 nanometres wide, or 1,000 times smaller than the width of a human hair - the University of Wollongong team was able to cause more gold to absorb into the immune cells, with far less toxicity. The results have been published in the Journal of Inorganic Biochemistry.

"We found that gold nanoparticles were taken up by more cells and in greater quantities than the traditional gold drugs, but without any toxicity which is often associated with negative side effects in clinical therapy," said lead research Lloyd James in a press release.

"Effectively, our study found gold nanoparticles didn't kill immune cells. While cell death is something that you look for, for example in cancer therapies, when it comes to rheumatoid arthritis, cell death can be associated with negative side effects."  

However, further investigation is now needed to work out exactly what the gold nanoparticles are doing in the macrophages, and why they're so much more effective than larger gold compounds.

"That's the million-dollar question," said James in the release. His team believes the benefit of the small particles may be that thousands of the nanoparticles can access the cells using their approach, compared to just a few traditional gold particles. They'll now be investigating whether this is the case, and also trying to work out exactly which size of gold nanoparticle is most effective against arthritis.

"It's very much a possibility that gold nanoparticles could become a potential treatment for rheumatoid arthritis," said James in the release, adding that the particles this size could also be taken orally, to make treatment easier. 

"I find that very interesting because gold was one of the early success stories for treating rheumatoid arthritis. And now it's coming full circle." 

Find out more about the research in the video below:

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