Methylprednisolone induces activation of the contact system in a dose-dependent manner. An in vitro study

The effect of methylprednisolone sodium succinate (MP) on the contact system of plasma was studied in human citrated pool plasma. Contact activation was demonstrated by the presence of plasma kallikrein (KK) activity and activated Hageman factor (FXIIa) and/or KK in complex with C1 inhibitor (C1inh), detected by chromogenic peptide substrates or radioimmunoassays, using monoclonal antibodies directed to neodeterminants exposed on complexed C1inh, respectively. When plasma and different doses of MP were incubated for a period of 24 hours, the highest dose of MP (10 mg/ml) gave rapid and marked increases in KK activities and concentrations of C1inh complexes. MP at 5 mg/ml plasma also induced activation of the contact system, although this activation was less pronounced. Even the lower dose of MP (1 mg/ml), which is equivalent to doses used in humans, increased plasma concentrations of KK-C1inh complexes. In conclusion, this in vitro study shows that MP in a dose-dependent way activates the contact system of plasma.