Glatiramer acetate persists at the injection site and draining lymph nodes via electrostatically-induced aggregation

Glatiramer acetate (GA) is widely prescribed for the treatment of relapsing-remitting multiple sclerosis, however, the mechanism of action is still not fully understood. We investigated the structural properties of GA and examined alterations to the drug upon injection into the subcutaneous space. First, a variety of biophysical characterization techniques were employed to characterize GA in solution. GA was found to exist as alpha helices in solution with a hydrodynamic radius of ~3 nm in size. To simulate GA behavior at the site of injection, GA was injected into a solution of 1.5 MDa hyaluronic acid (HA). Visible aggregates were observed immediately upon injection and subsequent testing indicated aggregation was driven by electrostatic interactions between the positively-charged GA and negatively-charged HA. In vivo testing confirmed GA formed spherical particles in the nano- to micrometer size range, suggesting this mechanism contributes to persistence at the injection site and in draining lymph nodes. The aggregates were found to associate with glycosaminoglycans, suggesting an electrostatic mechanism of induced aggregation like the simulated injection. These novel observations may help explain the complex immunomodulatory mechanisms of GA and adverse injection site reactions seen in patients. [Display omitted] •Glatiramer Acetate (GA) can form secondary structure in solution: α-helices and β-sheets.•Mean size of GA is determined to be around 3 nm, and pI of around 9.75.•GA forms micron sized aggregates in the presence of hyaluronic acid.•GA forms spherical, micron sized aggregates in vivo at the site of injection.•GA can localize at the injection site and travel towards the draining lymph nodes.