Effect of microplasmin on the clearance of vitreous haemorrhage from an experimental model in rabbits.

PURPOSE: Microplasmin is known to alter the structure of the vitreous gel. The current experiments were designed to assess its ability to enhance clearance of an experimentally induced vitreous haemorrhage, and to compare it to ovine hyaluronidase. METHODS: Twenty-five rabbits were used for this experiment, divided into five groups; groups 1-3 are microplasmin-treated eyes with 25, 75 and 125 µg, respectively. Group 4 treated with 55 IU of hyaluronidase, while group 5 was treated with normal saline (control). Eyes were injected in the mid-vitreous with 0.05 ml of autologous blood obtained from the marginal ear vein. One week later, all the groups were injected with the test solution injected in mid-vitreous as stated above. Clearance of the vitreous haemorrhage was assessed weekly indirect ophthalmoscopy for 8 weeks. RESULTS: Microplasmin-treated eyes showed a significant clearance of the vitreous haemorrhage in a dose-dependent fashion, where group 3 (125 µg) had the highest clearance rate in comparison with control eyes. Hyaluronidase-treated eyes showed a similar clearance rate as group 3. In addition, group 3 showed a complete posterior vitreous detachment, which did not develop in hyaluronidase-treated eyes. CONCLUSION: Microplasmin may be a useful agent to accelerate the clearance of vitreous haemorrhage.

The vitreous, the retinal interface in ocular health and disease.

The vitreous is a complex structure whose composition and appearance change with age. Anomalous adhesions between the posterior vitreous face and the retinal surface are the cause of numerous vitreoretinal complications, while the presence of an intact posterior hyaloid provides a scaffold for vascular growth and anteroposterior traction. This review summarizes what is known about the biochemistry of the vitreous, the process of posterior vitreous detachment (PVD) development, and the available clinical approaches to examining the vitreous and its interface. A pooled analysis of studies looking at the presence of a complete, partial or absent PVD in a number of macular and retinal diseases allows us to establish odds ratios for these various states. From this emerge both protective and disease-associated states in conditions such as proliferative diabetic retinopathy, macular edema, and age-related macular degeneration. With the emergence of pharmacological means to separate the posterior hyaloid, a better understanding of the possible role of the vitreous in tractional syndromes is required.

Characterization of a stabilized form of microplasmin for the induction of posterior vitreous detachment.

PURPOSE: To investigate the stability and safety of a diluted acidified form of microplasmin and its ability to induce a posterior vitreous detachment (PVD) following intravitreal injection in post-mortem porcine eyes. METHODS: Microplasmin diluted in normal saline (NS) and balanced salt solution (BSS+) was assayed for residual activity by hydrolysis of the chromogenic substrate Glu-Phe-Lys-pNA. Residual activity on vitreous was determined by injecting aliquots of microplasmin reconstituted in balanced salt solution (BSS+) or normal saline (NS) kept at room temperature (RT) for up to 1 hr, then injected in aliquots of porcine vitreous and incubated for 2 hr at 37°C. The breakdown products were submitted to SDS Page electrophoresis and compared to determine the level of enzymatic activity. Pig eyes were incubated with graded concentrations of microplasmin 0.625, 1.25, or 2.50 mg/mL reconstituted in BBS+ or NS. Morphologic alterations and the ability to induce a PVD was assessed by light and electron microscopy. RESULTS: Microplasmin's enzymatic activity in an in vitro assay in BSS+ was 70% of its baseline value after 30 min, and about 50% after 60 min at RT. The corresponding effect on degradation of vitreous gel was 60 and 40% baseline at 30 and 60 min. There was no loss of activity in the microplasmin diluted in normal saline over this time period. Dilution of acidified microplasmin in normal saline did not lead to structural changes within the retina. A dose dependent PVD was observed in eyes treated with microplasmin diluted in NS. CONCLUSIONS: Acidified (stabilized) microplasmin has the same intraocular activity profile as microplasmin at a neutral pH. Better retention of activity at room temperature makes it a better candidate for use in clinical practice.

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.