Assessment of Ocriplasmin Effects on the Vitreoretinal Compartment in Porcine and Human Model Systems

Topical Drug Delivery to the Posterior Segment of the Eye

Topical drug delivery to the posterior segment of the eye is a very complex challenge. However, topical delivery is highly desired, to achieve an easy-to-use treatment option for retinal diseases. In this review, we focus on the drug characteristics that are relevant to succeed in this challenge. An overview on the ocular barriers that need to be overcome and some relevant animal models to study ocular pharmacokinetics are given. Furthermore, a summary of substances that were able to reach the posterior segment after eye drop application is provided, as well as an outline of investigated delivery systems to improve ocular drug delivery. Some promising results of substances delivered to the retina suggest that topical treatment of retinal diseases might be possible in the future, which warrants further research.

Importance of the pig as a human biomedical model

[Figure: see text].

Xentry-Gap19 inhibits Connexin43 hemichannel opening especially during hypoxic injury

Hypoxic injury results in cell death, tissue damage and activation of inflammatory pathways. This is mediated by pathological Connexin43 (Cx43) hemichannel (HC) opening resulting in osmotic and ionic imbalances as well as cytokine production perpetuating the inflammatory environment. Gap19 is an intracellularly acting Cx43 mimetic peptide that blocks HC opening and thus promotes cell survival. However, native Gap19, which must enter the cell in order to function, exhibits low cell permeability. In this study, Gap19 was conjugated to the cell-penetrating peptide, Xentry, to investigate if cellular uptake could be improved while maintaining peptide function. Cellular uptake of Xentry-Gap19 (XG19) was much greater than that of native Gap19 even under normal cell culture conditions. Peptide function was maintained post uptake as shown by reduced ethidium homodimer influx and ATP release due to Cx43 HC block. While XG19 blocked pathologic HC opening though, normal gap junction communication required for cell repair and survival mechanisms was not affected as shown in a dye scrape-load assay. Under hypoxic conditions, increased expression of Syndecan-4, a plasma membrane proteoglycan targeted by Xentry, enabled even greater XG19 uptake leading to higher inhibition of ATP release and greater cell survival. This suggests that XG19, which is targeted specifically to hypoxic cells, can efficiently and safely block Cx43 HC and could therefore be a novel treatment for hypoxic and inflammatory diseases.

Enzymatic vitreolysis using reengineered Vibrio mimicus-derived collagenase

PURPOSE

Collagen is a key player contributing to vitreoelasticity and vitreoretinal adhesions. Molecular reorganization causes spontaneous weakening of these adhesions with age, resulting in the separation of the posterior hyaloid membrane (PHM) from the retina in what is called complete posterior vitreous detachment (PVD). Incomplete separation of the posterior hyaloid or tight adherence or both can lead to retinal detachment, vitreomacular traction syndrome, or epiretinal membrane formation, which requires surgical intervention. Pharmacological vitrectomy has the potential of avoiding surgical vitrectomy; it is also useful as an adjunct during retinal surgery to induce PVD. Previously studied enzymatic reagents, such as collagenase derived from Clostridium histolyticum, are nonspecific and potentially toxic. We studied a novel collagenase from Vibrio mimicus (VMC) which remains active (VMA), even after deletion of 51 C-terminal amino acids. To limit the activity of VMA to the vitreous cavity, a fusion construct (inhibitor of hyaluronic acid-VMA [iHA-VMA]) was made in which a 12-mer peptide (iHA, which binds to HA) was fused to the N-terminus of VMA. The construct was evaluated in the context of PVD.

METHODS

VMA and iHA-VMA were expressed in Escherichia coli, purified, and characterized with gelatin zymography, collagen degradation assay, fluorescamine-based assay, and cell-based assays. Two sets of experiments were performed in New Zealand albino rabbits. Group A (n = 10) received iHA-VMA, while group B (n = 5) received the equivalent dose of VMA. In both groups, saline was injected as a control in the contralateral eyes. Animals were monitored with indirect ophthalmoscopy, optical coherence tomography (OCT), and B-scan ultrasonography. Retinal toxicity was assessed with hematoxylin and eosin (H&E) staining of retinal tissue.

RESULTS

The activity of iHA-VMA and VMA was comparable and 65-fold lower than that of C. histolyticum collagenase Type IV. In the iHA-VMA group, all the rabbits (n = 10) developed PVD, with complete PVD seen in six animals. No statistically significant histomorphological changes were seen. In the VMA group, four of the five rabbits developed complete PVD; however, retinal morphological changes were seen in two animals.

CONCLUSIONS

iHA-VMA displays targeted action confined to the vitreous and shows potential for safe pharmacologic vitreolysis.

[Retinal detachment after intravitreal ocriplasmin injection]

After an uneventful intravitreal injection (IVI) of Ocriplasmin in a patient with reduced visual acuity due to vitreomacular traction (VMT) and a small macular hole, retinal detachment occurred within a few days after the operation. Although retinal detachment is known as a risk factor of IVI this case is noteworthy: an excessive reaction occurred in the region of the vitreous body, which resulted in the development of severe traction on the retina leading to a posterior vitreous body detachment, retinal holes and complete retinal detachment. This possible complication should be discussed in the preoperative patient informed consent and the reason for this excessive reaction should be the subject of further investigations.

A Method to Prepare a Bioprobe for Regulatory Science of the Drug Delivery System to the Brain: An Angulin Binder to Modulate Tricellular Tight Junction-Seal

Epithelium acts as a barrier separating the interior and exterior of the body, and the epithelial and endothelial cells form tight junctions (TJs) by sealing the paracellular space. The blood-brain barrier (BBB) endothelial cells have well-developed TJs and express specific polarized transport systems to tightly control paracellular movements of solutes, ions, and water. Thus, more than 98% of small-molecular-weight drugs cannot pass the BBB. The tricellular TJ (tTJ) is a structure at contacts of three cells. Angulin-1, also known as lipolysis-stimulated lipoprotein receptor (LSR), is one of angulin family and is abundantly expressed in brain endothelial cells, which plays an important role in barrier function of the BBB. The C-terminal domain of a receptor-binding component of Clostridium perfringens iota-toxin (Ib421-664), also named as angubindin-1, binds to its receptors angulin-1 and angulin-3. This angubindin-1 modulates the tTJ barrier and is able to deliver a 16-mer gapmer antisense oligonucleotide (5.3 kDa) without adverse effects. Thus, angulin binders, such as angubindin-1, are useful tools for studying the safety assessment of tTJ-targeted drug delivery and BBB permeability modulation. Here, we provide a protocol for the expression and purification of recombinant angubindin-1 protein as angulin binders, an analysis method for angubindin-1 binding affinity, and a procedure for assessing the effect of modulating tight junction integrity.

[Microstructural retinal changes after pharmacological vitreolysis with ocriplasmin-an SD-OCT supported analysis]

PURPOSE

Ocriplasmin (Jetrea®) is a therapeutic option for patients with focal vitreomacular traction (VMT) with or without small full thickness macular holes (FTMH) < 400 µm. Retinal alterations after injection with ocriplasmin have been described. The purpose of this essay was to determine Ocriplasmin-associated side-effects and changes in the retinal microstructure.

METHODS

We included 70 patients with ocriplasmin treatment in our study. On all patients SD-OCT (spectral-domain optical coherence tomography) scans were performed prior to injection with Ocriplasmin. If present, adverse events were registered. The OCT scans were then evaluated taking the following into account: macular hole (MH) size, macular edema, subretinal fluid (SRF), changes in the ellipsoid zone (EZ) and the external limiting membrane (ELM).

RESULTS

Twenty of the 70 examined patients showed a preoperative FTMH. One week after ocriplasmin IVI (intravitreal injection) 8 of the 20 FTMHs were already closed. Overall 12 patients showed a FTMH closure and 4 patients developed a FTMH after ocriplasmin IVI. Twelve of the 24 MH (macular hole) patients still required an operative closure of the FTMH. We noticed a resolution of the VMT on 51 patients. Three patients developed a retinal detachment. Furthermore, after ocriplasmin IVI we detected changes in the EZ and ELM on 8 patients.

CONCLUSIONS

Ocriplasmin is a substantial minimal invasive option in the therapy of VMT with or without small FTMH. Nevertheless, there seem to be some specific ocriplasmin-associated risks, although usually transient. Severe complications like retinal detachment are rare but exist. Therefore, every indication of ocriplasmin should be considered carefully.

Pharmacotherapy for Choroidal Neovascularization Due to Uncommon Causes

BACKGROUND

Choroidal neovascularization (CNV) in adults is most commonly associated with neovascular age-related macular degeneration (AMD) and pathologic myopia. Though less common, CNV can also develop from other conditions such as uveitis, central serous chorioretinopathy, angioid streaks, intraocular tumors, hereditary chorioretinal dystrophies, or can be idiopathic in origin. If left untreated, CNV may cause visual loss because of exudation of intraretinal or subretinal fluid, retinal or subretinal hemorrhage, or fibrosis involving the macula. It is well known that one of the main drivers of angiogenesis in CNV development is vascular endothelial growth factor (VEGF) and therefore inhibitors of VEGF might be an effective treatment for CNV.

METHODS

The goal of this review is to provide an overview and summary in the use of pharmacotherapy especially anti-VEGF therapy, in the treatment of CNV due to uncommon causes.

RESULTS

Results from uncontrolled case series and controlled clinical trials have reported good efficacy and safety in using anti-VEGF agents including bevacizumab, ranibizumab, aflibercept and ziv-aflibercept in the treatment of CNV due to uncommon causes. Anti-VEGF has also been used in combination with verteporfin PDT and anti-inflammatory agents for treating CNV of various causes.

CONCLUSION

Pharmacotherapy with anti-VEGF agents is an effective treatment option for CNV due to uncommon etiologies.