The scientists, headed by Peter van Lent of the University Hospital in Nijmegen, said that using the polymer to coat lipid particles (liposomes) that encase the active drug improves the inflammation-dampening effects of the treatment and also reduces cartilage destruction.
The rationale is that the liposomal coating will extend the time that the active drug circulates in the body, and make it more likely that the steroid reaches the sites of inflammation.
In animal models, the corticosteroid prednisone, bound within liposomes and coated with polyethylene glycol (PEG), gave much longer-lasting anti-inflammatory effect that uncoated prednisone.
The scientists created mice with the characteristics of rheumatoid arthritis by injecting them with type II collagen, stimulating an immune response against their own cartilage. A few days after symptoms appeared, the mice received injections with either liposomal or free prednisone, and the researchers looked at the level of joint damage and inflammation over the following week.
The results indicated that inflammation was starting to re-occur by the end of the week with a single dose of liposomal prednisone. But repeated injections of free prednisone were needed to maintain an anti-inflammatory effect. And by the end of the study, the level of joint damage was significantly reduced compared to mice treated with free prednisone.
A second experiment, using liposomes containing a marker compound (colloidal gold), indicated that the liposomes were accumulating in the synovial fluid in inflamed joints, but were not found in unaffected joints. And this supports the idea that the coated drug will be preferentially delivered to where it is needed.
The report can be found in the April issue of Annals of the Rheumatic Diseases, published by the European League Against Rheumatism (EULAR).