Expression and characterization of recombinant human micro-plasminogen

The evolution of recombinant thrombolytics: Current status and future directions

Cardiovascular disorders are on the rise worldwide due to alcohol abuse, obesity, hypertension, raised blood lipids, diabetes and age-related risks. The use of classical antiplatelet and anticoagulant therapies combined with surgical intervention helped to clear blood clots during the inceptive years. However, the discovery of streptokinase and urokinase ushered the way of using these enzymes as thrombolytic agents to degrade the fibrin network with an issue of systemic hemorrhage. The development of second generation plasminogen activators like anistreplase and tissue plasminogen activator partially controlled this problem. The third generation molecules, majorly t-PA variants, showed desirable properties of improved stability, safety and efficacy with enhanced fibrin specificity. Plasmin variants are produced as direct fibrinolytic agents as a futuristic approach with targeted delivery of these drugs using liposome technlogy. The novel molecules from microbial, plant and animal origin present the future of direct thrombolytics due to their safety and ease of administration.

High-level expression, purification, and enzymatic characterization of truncated human plasminogen (Lys531-Asn791) in the methylotrophic yeast Pichia pastoris

Background

Plasmin is a serine protease that plays a critical role in fibrinolysis, which is a process that prevents blood clots from growing and becoming problematic. Recombinant human microplasminogen (rhμPlg) is a derivative of plasmin that solely consists of the catalytic domain of human plasmin and lacks the five kringle domains found in the native protein. Developing an industrial production method that provides high yields of this protein with high purity, quality, and potency is critical for preclinical research.

Results

The human microplasminogen gene was cloned into the pPIC9K vector, and the recombinant plasmid was transformed into Pichia pastoris strain GS115. The concentration of plasmin reached 510.1 mg/L of culture medium. Under fermentation conditions, the yield of rhμPlg was 1.0 g/L. We purified rhμPlg to 96 % purity by gel-filtration and cation-exchange chromatography. The specific activity of rhμPlg reached 23.6 U/mg. The K_m of substrate hydrolysis by recombinant human microplasmin was comparable to that of human plasmin, while rhμPlm had higher k_cat/Km values than plasmin. The high purity and activity of the rhμPlg obtained here will likely prove to be a valuable tool for studies of its application in thrombotic diseases and vitreoretinopathies.

Conclusions

Reliable rhμPlg production (for use in therapeutic applications) is feasible using genetically modified P. pastoris as a host strain. The successful expression of rhμPlg in P. pastoris lays a solid foundation for its downstream application.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0179-z) contains supplementary material, which is available to authorized users.

Binding of tissue-type plasminogen activator to the glucose-regulated protein 78 (GRP78) modulates plasminogen activation and promotes human neuroblastoma cell proliferation in vitro

The glucose-regulated protein 78 (GRP78) is a plasminogen (Pg) receptor on the cell surface. In this study, we demonstrate that GRP78 also binds the tissue-type plasminogen activator (t-PA), which results in a decrease in K(m) and an increase in the V(max) for both its amidolytic activity and activation of its substrate, Pg. This results in accelerated Pg activation when GRP78, t-PA, and Pg are bound together. The increase in t-PA activity is the result of a mechanism involving a t-PA lysine-dependent binding site in the GRP78 amino acid sequence (98)LIGRTWNDPSVQQDIKFL(115). We found that GRP78 is expressed on the surface of neuroblastoma SK-N-SH cells where it is co-localized with the voltage-dependent anion channel (VDAC), which is also a t-PA-binding protein in these cells. We demonstrate that both Pg and t-PA serve as a bridge between GRP78 and VDAC bringing them together to facilitate Pg activation. t-PA induces SK-N-SH cell proliferation via binding to GRP78 on the cell surface. Furthermore, Pg binding to the COOH-terminal region of GRP78 stimulates cell proliferation via its microplasminogen domain. This study confirms previous findings from our laboratory showing that GRP78 acts as a growth factor-like receptor and that its association with t-PA, Pg, and VDAC on the cell surface may be part of a system controlling cell growth.

Differential vitreous dye diffusion following microplasmin or plasmin pre-treatment

PURPOSE

Plasmin and microplasmin are related enzymes that differ mainly in size. The differential effect of plasmin and microplasmin on vitreous structure, protein degradation, and dye diffusion through porcine vitreous was evaluated.

METHODS

The enzymatic effect was examined using a number of approaches on fresh porcine eyes: (1) structural integrity of vitreous after a 2-hr incubation using the electron microscope (EM); (2) effect on soluble proteins within the vitreous using gel electrophoresis after incubation at various time points over a 24-hr period; (3) fluorescein dye diffusion within the vitreous cavity measured over a 1-hr period following a 2-hr incubation. The chosen enzymatic activities for plasmin 0.5 IU and microplasmin 125 microg were within the clinical range, and were chosen for equipotence. A saline control was also used in all experiments.

RESULTS

Significant structural changes were seen with both microplasmin and plasmin when examined by EM. Gel electrophoresis showed that microplasmin and plasmin digested the same proteins, mainly molecular weights above 50 kDa. The enzymatic effect was noticeable earlier in microplasmin-treated eyes and was more significant by the end of the incubation period. Differential fluorescein diffusion rates were seen between normal saline, plasmin, and microplasmin within the vitreous cavity. The greatest diffusion rate was seen with microplasmin and was statistically significantly higher than plasmin.

CONCLUSION

Microplasmin and plasmin have a similar enzymatic effect on vitreous. However, an equipotent amount of microplasmin appears to have a more extended effect on vitreous gel. This may, in part, be related to its smaller size allowing it to diffuse more readily through the vitreous matrix.

Direct fibrinolytic agents: biochemical attributes, preclinical foundation and clinical potential

Direct fibrinolytics are proteolytic enzymes that degrade fibrin without requiring an intermediate step of plasminogen activation. This review summarizes the current information available for five such agents, namely, plasmin (the prototypical form), three derivatives of plasmin (mini-plasmin, micro-plasmin, and delta-plasmin), and alfimeprase, a recombinant variant of a snake venom alpha-fibrinogenase, fibrolase. Biochemical attributes of molecular size, fibrin binding and inhibitor neutralization are compared. Preclinical investigations that assess the potential for thrombolytic efficacy in vitro and in animal models of vascular occlusion and for hemostatic safety in animal models of bleeding are detailed. Clinical potential has been assessed in patients with peripheral arterial and graft occlusion, acute ischemic stroke, and access catheter and hemodialysis shunt occlusions. The direct fibrinolytic agents have impressive biochemical and preclinical foundations for ultimate clinical application. However, clinical trial results for micro-plasmin and alfimeprase have not measured up to their anticipated benefit. Plasmin has thus far shown encouraging hemostatic safety, but efficacy data await completion of clinical trials. Whether direct fibrinolytics will provide clinical superiority in major thrombotic disorders over currently utilized indirect fibrinolytics such as tissue plasminogen activator remains to be determined.