Preparation of pegylated lumbrokinase and an evaluation of its thrombolytic activity both in vitro and in vivo

Lumbrokinase(LK)is a group of serine proteases with strong fibrinolytic and thrombolytic activities.In clinical practice,LK can only be administered orally because of its antigenicity,iinmunogenicity and potential to produce anaphylactic reactions after injection.However,many useful drugs such as interferon,insulin,erythropoietin and interleukin have been modified with polyethylene glycol(PEG)to prepare injectable formulations.In this study,LK was modified with methoxy PEG succinimidyl carbonate(mPEG-SC)with molecular weights of 5000,10,000 and 20,000 and the pegylatcd products were isolated and purified using the Akta protein purification system.The extent of pegylation was detennined by HPLC.Fibrinolytic activities of pegylatcd and unmodified LK were measured both in vitro against urokinase on fibrin plates and in vivo using a mouse carageenan black tail model.Optimal pegylation was obtainal using mPEG-SC_(5000) in a buffer pH 8.0 with a reaction time of 5 h,reaction temperature of 0℃ and LK:mPEG-SC molar ratio of 1:25.The results show that mPEG modified LK has strong fibrinolytic and thrombolytic activities both in vitro and in vivo.It is suggested that the pegylatcd LK is a promising injectable thrombolytic agent for the treatment of thrombotic diseases in clinical practice.