A new way of isolating calcium phosphate crystals will greatly benefit research into the diagnosis and treatment of arthritis, say scientists from Ireland.

Patients with conditions such as arthritis and pseudogout often have calcium phosphate crystals in the fluid of their joints. Isolating and detecting these crystals is no easy matter, making it difficult to understand the role they play in the diseases. 

Now Gillian McMahon from Dublin City University and colleagues have solved the problem, using superparamagnetic beads that have bisphosphonate groups attached. When the beads are mixed into a sample of joint fluid, the bisphosphonate groups selectively bind to the calcium phosphate. The beads, and the bound crystals, are then easily removed using a magnet. The researchers say their method is less time consuming, with higher sensitivity, than previous techniques.

'We are starting now to examine the crystals present in a bank of patient samples, with a view to diagnosing the type of arthritis the patient has,' says McMahon. 'In particular osteoarthritis is of interest, as it is not known whether the crystals are a cause or an effect in this disease.'  To answer this question, the group will carry out a range of studies including monitoring samples from the same patients over an extended period of time.

'This is an original, intriguing approach that deserves continued study', enthuses Ralph Schumacher, an expert in osteoarthritis and related diseases from the University of Pennsylvania, Philadelphia, US. He adds that further development of the method is necessary to make it capable of quantitating the isolated crystals. 'If there are eventual treatments to decrease crystals you need to be able to quantitate change,' he explains.

McMahon agrees that quantitation is important for studying the progression of crystal deposition over time, and diagnosing the severity of disease. The group are working on combining their isolation method with techniques such as spectrophotometry, which will allow quantitative analysis.

Danièle Gibney