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Fibrinolytic agents including plasmin and plasminogen activators improve outcomes in acute ischemic stroke and thrombosis by recanalizing occluded vessels. In the decades since their introduction into clinical practice, several limitations of have been identified in terms of both efficacy and bleeding risk associated with these agents. Engineered nanoparticles and microparticles address some of these limitations by improving circulation time, reducing inhibition and degradation in circulation, accelerating recanalization, improving targeting to thrombotic occlusions, and reducing off-target effects; however, many particle-based approaches have only been used in preclinical studies to date. This review covers four advances in coupling fibrinolytic agents with engineered particles: (a) modifications of plasminogen activators with macromolecules, (b) encapsulation of plasminogen activators and plasmin in polymer and liposomal particles, (c) triggered release of encapsulated fibrinolytic agents and mechanical disruption of clots with ultrasound, and (d) enhancing targeting with magnetic particles and magnetic fields. Technical challenges for the translation of these approaches to the clinic are discussed.

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Purpose: The purpose of this study was to evaluate the dispersion of intravitreally injected solutions and investigate the influence of varying injection techniques. Methods: This was a prospective study using enucleated porcine eyes and ultra-high-resolution computed tomography (UHRCT) scanning to visualize iomeprol intravitreal dispersion. Sixty eyes were divided over 12 different groups according to the injection procedure: fast (2 seconds) or slow (10 seconds) injection speed and needle tip location (6- and 12-mm needle shaft insertion or premacular tip placement verified by indirect ophthalmoscopy). For each of these combinations, eyes were either injected with the combination of V20I (which is an analogue of ocriplasmin) and iomeprol or iomeprol alone. Distance to the macula and volume measurements were performed at 1, 2, 3, and 5 hours after injection. Results: The measured contrast bolus volume increases slowly over time to an average of 0.70 (P = 0.03), 1.04 (P = 0.006), and 0.79 (P = 0.0001) cm3 5 hours after the injection for the 6-mm needle shaft insertion, 12-mm needle shaft insertion, and premacular needle tip placement, respectively. The distance to the macular marker was significantly lower for premacular needle tip placement injections compared with 6- and 12-mm needle shaft insertion depths. Conclusions: Ultra-high-resolution computed tomography with three-dimensional reconstruction offers the possibility to study the dispersion of intravitreally injected solutions in a noninvasive manner. Intravitreal premacular solution delivery is possible with an indirect ophthalmoscope-guided injection technique and significantly reduces the time to reach the posterior pole in respect to 6- and 12-mm needle insertion depths. The speed of injection does not influence dispersion significantly.

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PURPOSE: To characterize the levels of active ocriplasmin over a period of ascending time points (range, 5 minutes to 7 days) from intravitreal injection of a 125-µg dose to sampling. METHODS: During this 7-week controlled, open-label, phase 2 study, a single intravitreal (125 µg) dose of ocriplasmin was injected into the midvitreous of one eye of each of 34 patients prior to their scheduled primary pars plana vitrectomy. Patients were allocated to vitreous sampling at the beginning of the surgery, which occurred 5 to 30 minutes, 31 to 60 minutes, 2 to 4 hours, 24 ± 2 hours, or 7 ± 1 days after ocriplasmin injection, or to the control group, who received no ocriplasmin injection. RESULTS: With increasing time from ocriplasmin injection to vitreous sampling, mean active ocriplasmin concentration decreased. While at 5 to 30 minutes postinjection, mean active ocriplasmin concentration was 11,597.7 ng/mL, within 31 to 60 minutes from injection the mean active ocriplasmin concentration had reduced to 8108.7 ng/mL; and by 24 hours after injection, half of the patients (2/4) had active ocriplasmin concentrations below the lower limit of quantification (LLQ; <272.4 ng/mL), as did all samples from the day 7 and control groups. No ocular serious adverse events (SAEs) were reported in patients who received ocriplasmin, while three ocular SAEs occurred in the study eye of one patient in the control group (1/38; 2.6%). CONCLUSIONS: Active ocriplasmin concentrations in vitreous samples decreased with increasing time from injection to sample, with enzyme levels in all of the patients in the day 7 group being comparable to those in the control group. (ClinicalTrials.gov number, NCT01159665.).

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PURPOSE: Ocriplasmin contains the active moiety of plasmin enzyme. At a physiologic pH, ocriplasmin is highly proteolytic and autolytic, limiting its duration of activity. Specific inhibitors of plasmin are present in the vitreous under normal and disease conditions and could affect its activity. Each may contribute to its mode of action. METHODS: Degradation characteristics were determined in porcine, human vitreous, and PBS under reducing conditions with different incubation periods between 0 and 24 hours on SDS-PAGE Tris-glycine gels. Residual activity was determined by spectrophotometry of p-nitroaniline release through hydrolysis of L-pyroglutamyl-L-phenylalanyl-L-lysine-p-nitroaniline hydrochloride. The presence of endogenous inactivators of ocriplasmin in human vitreous was determined in a series of vitreous samples using an ELISA specific for alpha(2)-antiplasmin, antithrombin, and antitrypsin. RESULTS: Degradation productions from autolysis are similar between vitreous and PBS with a significant prolongation of the effect in vitreous. Both follow a nonlinear pattern over time. The degradation corresponds best to a second-order kinetic process. The resulting rate constants were 207 ± 60 M(-1) s(-1) in PBS, 81 ± 15 M(-1) s(-1) in porcine vitreous, and 195 M(-1) s(-1) in human vitreous natural inhibitors were identified in samples of donor vitreous. Amounts differed significantly between samples, which may help explain the observed variability in human subjects. CONCLUSIONS: Ocriplasmin is autolytic in vitreous. Biologic activity extends to several days following injection. The exact duration will vary based on the presence and concentration of serine protease inhibitors.

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BACKGROUND AND PURPOSE: Microplasmin is a recombinant truncated form of human plasmin. It has demonstrated efficacy in experimental animal models of stroke and tolerability in healthy volunteers. We tested the tolerability of microplasmin in patients with acute ischemic stroke. METHODS: In a multicenter, double-blind, randomized, placebo-controlled Phase II trial, 40 patients with ischemic stroke were treated with either placebo or active drug between 3 and 12 hours after symptom onset in a dose-finding design. Ten patients received placebo, 6 patients received a total dose of 2 mg/kg, 12 patients received a total dose of 3 mg/kg, and 12 patients received a total dose of 4 mg/kg. We studied the pharmacodynamics of microplasmin and its effect on the clinical and hemodynamic parameters of the patients. MRI was used as a surrogate marker and matrix metalloproteinases serum concentrations were used as markers of neurovascular integrity. The study was underpowered to detect clinical efficacy. RESULTS: Microplasmin induced reversible effects on markers of systemic thrombolysis and neutralized alpha(2)-antiplasmin by up to 80%. It was well tolerated with one of 30 treated patients developing a fatal symptomatic intracerebral hemorrhage. No significant effect on reperfusion rate or on clinical outcome was observed. Matrix metalloproteinase-2 levels were reduced in microplasmin-treated patients. CONCLUSIONS: Microplasmin was well tolerated and achieved neutralization of alpha(2)-antiplasmin. Further studies are warranted to determine whether microplasmin is an effective therapeutic agent for ischemic stroke.

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The use of plasmin for pharmacologic vitreolysis and the creation of a posterior vitreous detachment offers several potential advantages over surgery. The nonclinical pharmacokinetics and safety of human-derived plasmin was evaluated following single or multiple intravitreal injections to rabbits and minipigs. Single intravitreal injections of plasmin at 45-900 microg resulted in a no adverse effect level (NOAEL) of 45 microg in both species; effects at higher doses included chemosis, mucopurulent discharge, mononuclear cell infiltrates in the iris-ciliary body, and reversible changes in electroretinogram waveforms and parameters. No retinal histopathology abnormalities were observed. Following 4 weekly intravitreal injections at 4-423 microg, a NOAEL of 4 microg was identified. Effects at the higher doses included myosis, iritis, iridolenticular synechiae, and changes in electroretinogram waveforms and parameters that were generally not reversible in the present investigation. Vitreal plasmin concentrations were highest at 30 min after dosing and decreased rapidly; measurable concentrations remained, in some animals, at 24 h. Intravitreal plasmin exposure increased in a less-than-dose-proportional manner and tended to be lower in minipigs than in rabbits. The current findings demonstrate acceptable nonclinical safety and pharmacokinetics of intravitreal human plasmin in rabbits and minipigs and support the clinical development of plasmin for ocular diseases.

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The amidolytic activity of plasmin (Pln) that spontaneously adsorbs from solutions to modified-graphite (GR) and glassy carbon (GL) surfaces was studied in the 10-45 degrees C temperature range in the presence of a chromogenic substrate. Surfaces were modified with a coating of fibrinogen, either electrochemically oxidized or not. The effect of an additional modification via deposition of Langmuir-Blodgett films of behenic acid (BA-LB) onto the former surfaces, thus leading to either hydrophobic or hydrophilic surfaces according to the number of deposed layers, was examined. In all cases results showed the occurrence of a first order transition which strongly and transiently increases the surface activity of Pln. At BA-LB surfaces, the most prominent change compared with other coatings was a significant enhancement of the critical temperature Tc that characterizes the beginning of the transition. When fibrinogen was present in the solution, the transition was no longer observable up to 37 degrees C as shown by the linear kinetics exhibited by surfaces bearing oxidized fibrinogen.

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The kinetic and fibrinolytic properties of a reversibly acylated stoichiometric complex between human plasmin and recombinant staphylokinase (plasmin-STAR complex) were evaluated. The acylation rate constant of plasmin-STAR by p-amidinophenyl-p'-anisate-HCl was 52 M-1 s-1 and its deacylation rate constant 1.2 x 10(-4) s-1 (t1/2 of 95 min) which are respectively 50-fold and around 3-fold lower than for the plasmin-streptokinase complex. The acylated complex was stable as evidenced by binding to lysine-Sepharose. However, following an initial short lag phase, the acylated plasmin-STAR complex activated plasminogen at a similar rate as the unblocked complex, whereas the acylated plasmin-streptokinase complex did not activate plasminogen. These findings indicate that STAR, unlike streptokinase, dissociates from its acylated complex with plasmin in the presence of excess plasminogen. In agreement with this hypothesis, the time course of the lysis of a 125I-fibrin labeled plasma clot submerged in citrated human plasma, is similar for acylated plasmin-STAR, unblocked plasmin-STAR and free STAR (50% clot lysis in 2 h requires 12 nM of each agent). The plasma clearances of STAR-related antigen following bolus injection in hamsters were 1.0 to 1.5 ml/min for acylated plasmin-STAR, unblocked plasmin-STAR and free STAR, as a result of short initial half-lives of 2.0 to 2.5 min. The dissociation of the anisoylated plasmin-STAR complex and its consequent rapid clearance suggest that it has no apparent advantages as compared to free STAR for clinical thrombolysis.

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A hybrid plasminogen activator consisting of the "A" chain of plasmin linked to the "B" chain of rt-PA was inhibited in vitro in human and guinea pig plasmas 4 to 5-fold more rapidly than its parent activator, two-chain t-PA. Using zymographic and autoradiographic techniques together with the use of immunodepleted plasma the major inhibitor was identified as alpha-2-antiplasmin. The pharmacokinetic profile of the hybrid in guinea pigs was determined by two different methods: disappearance of fibrinolytic activity and removal of radiolabelled hybrid from the circulation. Fibrinolytic activity was cleared rapidly via inhibitory mechanisms, whilst radiolabelled material was cleared considerably more slowly due to the formation of hybrid-inhibitor complexes. When the active site of the hybrid was reversibly acylated inhibitory mechanisms were evaded and a prolonged pharmacokinetic profile of activity was observed.

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We studied the pharmacokinetics of single doses of intravenous immunoglobulin (IVIG) of 1000, 750 and 500 mg/kg administered to 21 neonates with birth weights from 750 to 1500 g. No adverse effects were detected. Mean pharmacokinetic values for the large, intermediate and small dose groups, respectively, were: elimination half-life, 19.6, 28.7 and 22.1 days; clearance, 5.2, 5.6 and 3.7 ml/kg/day; volume of distribution, 151, 255 and 130 ml/kg. Mean peak IgG concentrations in serum were 1826, 1476 and 1257 mg/dl for the large, intermediate and small dose groups, respectively. Mean IgG on post-infusion Days 1 to 28 were similar for the intermediate and small dose groups but were higher in the larger dose group. Both large and intermediate doses achieved larger increases in IgG over preinfusion values (delta IgG) than the small dose. The differences in delta IgG between the large and intermediate doses were less notable. The wide variability observed indicates that individualization of intravenous immunoglobulin dosage will be required in these patients.

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A plasmin generation method to determine tissue plasminogen activator (t-PA) activity in plasma is described. A protein solution of homogenized fibrin was used as a stimulator in the presence of plasminogen and the plasmin generated was measured by the release of para-Nitroanilide (p-NA) from the chromogenic substrate S-2251. Plasmin generation by 5 iu/mL t-PA in the presence of 1 CU/mL of plasminogen and 850 micrograms/mL of fibrin solution reaches a peak at about 5 h incubation whilst in plasma, plasmin generation peaks after about 16 h incubation. The highest t-PA activity in plasma was determined using an assay involving 18 h incubation. In the 21 subjects studied by this method the t-PA activity at rest ranged from 0.34 to 0.92 iu/mL with a mean of 0.57 +/- 0.15 iu/mL of plasma whilst in the post-occlusion state the activity ranged from 1.12 to 18.0 iu/mL, with a mean of 5.25 +/- 4.49 iu/mL of plasma. We also found that subjects who developed petechiae during occlusion had significantly higher t-PA activity both at pre- and post-occlusion when compared with those who did not develop petechiae. The t-PA activity of acid-treated plasma stored at -70 degrees C showed no significant changes in activity after 12 weeks of storage when compared with the t-PA activity of the same plasma tested prior to storage.

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