Rheumatoid arthritis: Scorpion venom compound may halt progression

The Indian red scorpion is one of the most dangerous scorpions in the world. Without treatment, a sting from this creature can kill a human in just 72 hours. But it's not all bad; a compound found in its venom could help to treat one of the most common and debilitating health conditions in the United States.

In a new study, researchers have revealed how iberiotoxin — one of several compounds in the deadly venom of the Indian red scorpion — stopped the progression of rheumatoid arthritis in rat models of the disease.

Study leader Dr. Christine Beeton, of the Baylor College of Medicine in Houston, TX, and her colleagues recently reported their findings in the Journal of Pharmacology and Experimental Therapeutics.

In rheumatoid arthritis, the immune system launches an attack on the joints — particularly those of the hands, wrists, and knees — causing pain and inflammation.

It is estimated that around 1.5 million people in the U.S. are living with rheumatoid arthritis, and the disease is around three times as common among women than men.

As Dr. Beeton notes, a specialized type of cell in the joints called fibroblast-like synoviocytes (FLS) play an important role in rheumatoid arthritis.

"As they grow and move from joint to joint," Dr. Beeton explains, "they secrete products that damage the joints and attract immune cells that cause inflammation and pain. As damage progresses, the joints become enlarged and are unable to move."

In a previous study of people with rheumatoid arthritis, Dr. Beeton and colleagues discovered a potassium channel on the membrane of FLS cells — called KCa1.1 — that is involved in the development of the disease.

The researchers speculated that blocking this potassium channel may be one way to halt the progression of rheumatoid arthritis. In their latest study, they found that the scorpion venom compound iberiotoxin could do just that.

Iberiotoxin halted rheumatoid arthritis

Iberiotoxin is found in the venom of the Indian red scorpion, or the Buthus tamulus. According to first study author Dr. Mark Tanner — who is also of the Baylor College of Medicine — iberiotoxin specifically targets the KCa1.1 channel on FLS, while avoiding other potassium channels.

For their new study, the researchers tested iberiotoxin on rat models of rheumatoid arthritis.

They discovered that the scorpion venom compound not only stopped rheumatoid arthritis progression in the rodents by blocking KCa1.1, but some rodents showed improvements in inflammation and joint mobility.

Importantly, iberiotoxin did not lead to any adverse side effects in the rats, while another potassium channel blocker called paxilline caused tremors and urinary incontinence.

"It was very exciting to see," explains Dr. Tanner, "that iberiotoxin is very specific for the potassium channel in FLS and that it did not seem to affect the channels in other types of cells, which might explain the lack of tremors and incontinence."

Based on these findings, Dr. Beeton and colleagues believe that iberiotoxin could open the door to an effective treatment for rheumatoid arthritis, though further studies are needed.

"Although these results are promising, much more research needs to be conducted before we can use scorpion venom components to treat rheumatoid arthritis. We think that this venom component, iberiotoxin, can become the basis for developing a new treatment for rheumatoid arthritis in the future."

Dr. Christine Beeton