Thrombolytic efficacy of recombinant human microplasmin in a canine model of copper coil-induced coronary artery thrombosis

2022 Update of the Consensus on the Rational Use of Antithrombotics and Thrombolytics in Veterinary Critical Care (CURATIVE) Domain 6: Defining rational use of thrombolytics

OBJECTIVES

To systematically review available evidence and establish guidelines related to the use of thrombolytics for the management of small animals with suspected or confirmed thrombosis.

DESIGN

PICO (Population, Intervention, Control, and Outcome) questions were formulated, and worksheets completed as part of a standardized and systematic literature evaluation. The population of interest included dogs and cats (considered separately) and arterial and venous thrombosis. The interventions assessed were the use of thrombolytics, compared to no thrombolytics, with or without anticoagulants or antiplatelet agents. Specific protocols for recombinant tissue plasminogen activator were also evaluated. Outcomes assessed included efficacy and safety. Relevant articles were categorized according to level of evidence, quality, and as to whether they supported, were neutral to, or opposed the PICO questions. Conclusions from the PICO worksheets were used to draft guidelines, which were subsequently refined via Delphi surveys undertaken by the Consensus on the Rational Use of Antithrombotics and Thrombolytics in Veterinary Critical Care (CURATIVE) working group.

RESULTS

Fourteen PICO questions were developed, generating 14 guidelines. The majority of the literature addressing the PICO questions in dogs is experimental studies (level of evidence 3), thus providing insufficient evidence to determine if thrombolysis improves patient-centered outcomes. In cats, literature was more limited and often neutral to the PICO questions, precluding strong evidence-based recommendations for thrombolytic use. Rather, for both species, suggestions are made regarding considerations for when thrombolytic drugs may be considered, the combination of thrombolytics with anticoagulant or antiplatelet drugs, and the choice of thrombolytic agent.

CONCLUSIONS

Substantial additional research is needed to address the role of thrombolytics for the treatment of arterial and venous thrombosis in dogs and cats. Clinical trials with patient-centered outcomes will be most valuable for addressing knowledge gaps in the field.

Assessment of E. coli Expression System for Overexpression of Active Recombinant Ocriplasmin

Purpose: Ocriplasmin (Jetrea TM) is a FDA approved recombinant enzyme utilized in the treatment of vitreomacular adhesion (VMA). This is a recombinant C-terminal fragment of human plasmin produced using yeast Pichia pastoris. Since ocriplasmin does not contain any Oor N-glycosylation or some other post-translational modifications, bacterial expression systems such as Escherichia coli could be considered as an economical host for recombinant expression. In the present study, we aimed to evaluate the efficiency of E. coli expression system for highlevel expression of recombinant ocriplasmin.

Methods: The gene coding for ocriplasmin was cloned and expressed in E. coli BL21. The bacterial cells were cultured on large scale and the expressed recombinant protein was purified using Ni-NTA chromatography. Refolding of denatured ocriplasmin to active enzyme was carried out by the stepwise removal of denaturant. The identity of recombinant ocriplasmin was confirmed using western blotting and ELISA assays. The presence of the active ocriplasmin was monitored by the hydrolytic activity assay against the chromogenic substrate S-2403.

Results: The final yield of E. coli BL21-produced ocriplasmin was approximately 1 mg/mL which was greater than that of P. pastoris. Using western blotting and ELISA assay, the identity of recombinant ocriplasmin was confirmed. The hydrolysis of chromogenic substrate S-2403 verified the functional activity of E. coli produced ocriplasmin.

Conclusion: The results of this study indicated that E. coli could be used for high level expression of ocriplasmin. Although the recombinant protein was expressed as inclusion body, the stepwise refolding leads to the biologically active proteins.

Phase I trial on robot assisted retinal vein cannulation with ocriplasmin infusion for central retinal vein occlusion

PURPOSE

To evaluate the safety and feasibility of robot-assisted retinal vein cannulation with Ocriplasmin infusion for central retinal vein occlusion.

METHODS

Prospective phase I trial including four patients suffering from central retinal vein occlusion (CRVO). Diagnosis was confirmed by preoperative fluo-angiography and followed by a standard three-port pars plana vitrectomy. Afterwards, a custom-built microneedle was inserted into a branch retinal vein with robotic assistance and infusion of Ocriplasmin started. Primary outcomes were the occurrence of intra-operative complications and success of cannulation. Secondary outcomes were change in visual acuity, central macular thickness (CMT) and venous filling times (VFT) during fluo-angiography two weeks after the intervention.

RESULTS

Cannulation with infusion of ocriplasmin was successful in all four eyes with a mean total infusion time of 355 ± 204 seconds (range 120-600 seconds). Best corrected visual acuity (BCVA) remained counting fingers (CF) in case 3 and 4, increased in case 1 from CF to 0.9LogMAR and decreased in case 2 from 0.4 to 1.3 LogMAR. CMT and VFT both showed a trend towards significant decrease comparing preoperative measurements with two weeks postintervention (1061 ± 541 μm versus 477 ± 376 μm, p = 0.068) and 24 ll 4 seconds versus 15 ± 1 seconds, p = 0.068, respectively). In one eye a needle tip broke and could be removed with an endoforceps. There were no other intervention-related complications.

CONCLUSION

Robot-assisted retinal vein cannulation is feasible and safe. Local intravenous infusion with Ocriplasmin led to an improved retinal circulation.

Robot-assisted retinal vein cannulation in an in vivo porcine retinal vein occlusion model

PURPOSE

To evaluate the feasibility of robot-assisted retinal vein cannulation for retinal vein occlusion.

METHODS

Prospective experimental study performed in in vivo porcine eyes. A standard three port pars plana vitrectomy was followed by laser-induced branch retinal vein occlusion. Consequently, a retinal vein cannulation with the help of a surgical robot and a microneedle was performed. Complete success was defined as a stable intravenous position of the needle tip confirmed by blood washout for at least 3 min. Secondary outcomes were the occurrence of intra-operative complications and technical failures.

RESULTS

Cannulation was successful in 15 of 18 eyes with a complete success rate (duration of infusion of more than 3 min) of 73% after exclusion of two eyes from analysis due to failure in establishing a blood clot. There were no technical failures regarding the robotic device. The intravessel injections of ocriplasmin in two of two eyes led to a clot dissolution. In a subset of five eyes, a second cannulation attempt at the border of the optic disc resulted in a stable intravessel position and infusion during 362 (±138) seconds.

CONCLUSION

Robot-assisted retinal vein cannulation with prolonged infusion time is technically feasible. Human experiments are required to analyse the clinical benefit of this new therapy.