Experimental proliferative vitreoretinopathy in rabbits by delivery of bioactive proteins with gelatin microspheres

Biodegradable microspheres come into sight: A promising biomaterial for delivering drug to the posterior segment of the eyeball

Posterior segment disease acts as a major cause of irreversible visual impairments. Successful treatment of posterior segment disease requires the efficient delivery of therapeutic substances to the targeted lesion. However, the complex ocular architecture makes the bioavailability of topically applied drugs extremely low. Invasive delivery approaches like intravitreal injection may cause adverse complications. To enhance the efficiency, several biomedical engineering systems have been developed to increase the penetration efficiency and improve the bioavailability of drugs at the posterior segments. Advantageously, biodegradable microspheres are found to deliver the therapeutic agents in a controlled fashion. The microspheres prepared from novel biomaterials can realize the prolonged release at the posterior segment with minimum side effects. Moreover, it will be degraded automatically into products that are non-toxic to the human body without the necessity of secondary operation to remove the residual polymer matrix. Additionally, biodegradable microspheres have decent thermoplasticity, adjustable hydrophilicity, controlled crystallinity, and high tensile strength, which make them suitable for intraocular delivery. In this review, we introduce the latest advancements in microsphere production technology and elaborate on the biomaterials that are used to prepare microspheres. We discuss systematically the pharmacological characteristics of biodegradable microspheres and compare their potential advantages and limitations in the treatment of posterior segment diseases. These findings would enrich our knowledge of biodegradable microspheres and cast light into the discovery of effective biomaterials for ocular drug delivery.

Transition to Chronic Fibrosis in an Animal Model of Retinal Detachment With Features of Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is the most common cause of failure of surgically repaired rhegmatogenous retinal detachment (RRD). Chemically induced and cell injection PVR models do not fully simulate the clinical characteristics of PVR in the post-RRD context. There is an unmet need for translational models in which to study mechanisms and treatments specific to RRD-PVR.

Methods

RRD was induced in adult Dutch Belted rabbits. Posterior segments were fixed or processed for RNA sequencing at 6 hours and 2, 7, 14, and 35 days after induction. Histochemical staining and immunolabeling for glial fibrillary acidic protein, alpha smooth muscle actin, vascular endothelial growth factor receptor 2, CD68, and RPE 65 kDa protein were performed, and labeling intensity was scored. Single cell RNA sequencing was performed.

Results

Acute histopathological changes included intravitreal and intraretinal hemorrhage, leukocytic vitritis, chorioretinitis, and retinal rarefaction. Chronic lesions showed retinal atrophy, gliosis, fibrotic subretinal membranes, and epiretinal fibrovascular proliferation. Fibrillar collagen was present in the fibrocellular and fibrovascular membranes in chronic lesions. Moderate to strong labeling of glia and vasculature was detected in chronic lesions. At day 14, most cells profiled by single cell sequencing were identified as Mϋller glia and microglia, consistent with immunolabeling. Expression of several fibrillar collagen genes was upregulated in chronic lesions.

Conclusions

Histological and transcriptional features of this rabbit model simulate important features of human RRD-PVR, including the transition to chronic intraretinal and periretinal fibrosis. This animal model of RRD with features of PVR will enable further research on targeted treatment interventions.

Silibinin Prevents TGFβ-Induced EMT of RPE in Proliferative Vitreoretinopathy by Inhibiting Stat3 and Smad3 Phosphorylation

Purpose

The purpose of this study was to investigate the effects of silibinin on epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) and proliferative vitreoretinopathy (PVR) formation, as well as its underlying molecular mechanism.

Methods

Cellular morphological change and EMT molecular markers were evaluated by using phase contrast imaging, qPCR, and Western blot (WB) to investigate the impact of silibinin on the EMT of ARPE-19 cells. Scratch assay and transwell assay were used to study the effect of silibinin on cell migration. An intravitreally injected RPE-induced rat PVR model was used to assess the effect of silibinin on PVR in vivo. RNA-seq was applied to study the molecular mechanism of silibinin-mediated PVR prevention.

Results

Silibinin inhibited TGFβ1-induced EMT and migration of RPE in a dose-dependent manner in vitro. Moreover, silibinin prevented proliferative membrane formation in an intravitreal injected RPE-induced rat PVR model. In line with these findings, RNA-seq revealed a global suppression of TGFβ1-induced EMT and migration-related genes by silibinin in RPEs. Mechanistically, silibinin reduced TGFβ1-induced phosphorylation levels of Smad3 and Stat3, and Smad3 nuclear translocation in RPE.

Conclusions

Silibinin inhibits the EMT of RPE cells in vitro and prevents the formation of PVR membranes in vivo. Mechanistically, silibinin inhibits Smad3 phosphorylation and suppresses Smad3 nuclear translocation through the inhibition of Stat3 phosphorylation. These findings suggest that silibinin may serve as a potential treatment for PVR.

Current Trends in Gelatin-Based Drug Delivery Systems

Gelatin is a highly versatile natural polymer, which is widely used in healthcare-related sectors due to its advantageous properties, such as biocompatibility, biodegradability, low-cost, and the availability of exposed chemical groups. In the biomedical field, gelatin is used also as a biomaterial for the development of drug delivery systems (DDSs) due to its applicability to several synthesis techniques. In this review, after a brief overview of its chemical and physical properties, the focus is placed on the commonly used techniques for the development of gelatin-based micro- or nano-sized DDSs. We highlight the potential of gelatin as a carrier of many types of bioactive compounds and its ability to tune and control select drugs' release kinetics. The desolvation, nanoprecipitation, coacervation, emulsion, electrospray, and spray drying techniques are described from a methodological and mechanistic point of view, with a careful analysis of the effects of the main variable parameters on the DDSs' properties. Lastly, the outcomes of preclinical and clinical studies involving gelatin-based DDSs are thoroughly discussed.

Changes in the vitreous body after experimental vitreous hemorrhage in rabbit: An interdisciplinary study

PURPOSE

To explore the changes in vitreous body after vitreous hemorrhage and assess its prognosis from the perspective of vitreoretinal interface.

METHODS

The experiment was performed on 32 New Zealand rabbits (64 eyes), weighing 2500-3000 g for 4 months and unlimited gender, which was injected with 0.2 mL of autologous blood into the center of vitreous cavity-the study group (right eyes), and the control one was treated in the same manner with equal volumes of saline. The rabbits were randomly and equally divided into the following four batches according to the days of observation: Days 3, 7, 14, and 30 after injection. IOP and severity grading were evaluated before rabbits' execution and eyeballs were enucleated. The anterior segment was separated to flow out the vitreous body naturally to detect the liquefaction degree and viscosity. Then, chemical composition of electrolytes, PCT and bFGF were determined by colorimetry and enzyme-linked immunosorbent assay (ELISA). Finally, the incidence of posterior vitreous detachment (PVD) was observed after vitreous sampled. The studies were double-blind.

RESULTS

After injection, the extent of vitreous opacity and coagulum size decreased over time. Both the degree of liquefaction and the length of tow differed significantly between two groups at different time points (all p < 0.001). The liquefaction degree in the study group rose obviously from the Day 14, which the viscosity declined significantly on the initial time. Biochemical markers fluctuated temporarily, except for basic fibroblast growth factor (bFGF), which continued to rise and was correlated with the liquefaction degree (r = 0.658, p < 0.001). Besides, the incidence of PVD increased from the 14th day (p < 0.05), and it was highly positively correlated with the number of macrophages (r = 0.934; p < 0.001).

CONCLUSION

After vitreous hemorrhage, the changes of the vitreous body are relatively minor earlier (2-4 weeks), but irreversible later. Specifically, the degree of liquefaction increases with a decrease in viscosity, and the chemotaxis of macrophages and bFGF induce incomplete PVD.

Yes-associated protein is essential for proliferative vitreoretinopathy development via the epithelial-mesenchymal transition in retinal pigment epithelial fibrosis

This study was aim to investigate whether the progression of proliferative vitreoretinopathy (PVR) depended on the activation of Yes‐associated protein (YAP) and the subsequent epithelial‐mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cell. The effect of YAP activation on retinal fibrosis in a PVR mouse model and in human ARPE‐19 cells in vitro was studied. After treated with transforming growth factor‐β2(TGF‐β2), the expressions of fibrogenic molecules, YAP activation and the TGF‐β2‐Smad signalling pathway in ARPE‐19 cells were detected by Western blot and immunocytochemical analyses. The effect of YAP on change in fibrosis and EMT was tested by knockdown experiment using verteporfin (YAP inhibitor). YAP was upregulated in the PVR mouse model and during TGF‐β2–induced RPE cell EMT. In an in vivo study, verteporfin attenuated PVR progression in a mouse model. Additionally, YAP knockdown retained phenotype of RPE cells and ameliorated TGF‐β2–induced migration, gel contraction and EMT in vitro. YAP knockdown inhibited the TGF‐β2–induced upregulation of connective tissue growth factor (CTGF), smooth muscle actin (SMA‐α) and fibronectin. YAP was essential for the TGF‐β2–induced nuclear translocation and phosphorylation of Smad2/3. Our work provides direct evidence that YAP is an essential regulator of EMT and profibrotic responses in PVR and indicates that YAP inhibition could be a potential target in PVR therapeutic intervention.

Activated Blood Coagulation Factor X (FXa) Contributes to the Development of Traumatic PVR Through Promoting RPE Epithelial-Mesenchymal Transition

Purpose

Uncontrolled coagulation reactions contribute to pathological fibroproliferation in several organs, and yet their role in proliferative vitreoretinopathy (PVR) remains to be elucidated. In this study, we evaluated the profibrotic effects of FXa in RPE cells and in a mouse model of PVR.

Methods

FXa levels in the eyes of traumatic PVR patients and rabbit models of mechanical ocular trauma was measured by ELISA and immunohistochemistry. FXa-induced RPE EMT was assessed by examining cell proliferation, migration, tight junction changes, and expression of fibrotic markers. For in vivo study, FXa was injected into dispase-injured eyes, then intraocular fibrosis was evaluated by histological analysis and Western blotting. The therapeutic effect of FXa inhibitor was also examined in PVR mouse models.

Results

Vitreous FXa were higher in patients with traumatic PVR compared to patients with macular hole. Moreover, expressions of FXa and PAR1 were found in the epiretinal membranes from traumatic PVR patients. Vitreous FXa were markedly increased after mechanical ocular trauma in rabbits. In vitro, FXa stimulated RPE EMT characterized as ZO-1 disruption, compromised cell polarity, and increased fibronectin expressions. Co-injection of FXa and dispase in mice induced more severely damaged retinal structures, and increased α-SMA expressions than FXa or dispase treatment alone. Oral FXa or thrombin inhibitors significantly blocked intraocular fibrosis in PVR mouse models. FXa promoted phospho-activation of p38 in ARPE19 cells, which was dependent on PAR1. Moreover, TGF-βR inhibitor also significantly alleviated FXa-induced intraocular fibrosis in mice.

Conclusions

FXa promotes intraocular fibrosis in mice via mechanisms involving RPE activation.

Progress of gelatin-based microspheres (GMSs) as delivery vehicles of drug and cell

Gelatin has various attractive features as biomedical materials, for instance, biocompatibility, low immunogenicity, biodegradability, and ease of manipulation. In recent years, various gelatin-based microspheres (GMSs) have been fabricated with innovative technologies to serve as sustained delivery vehicles of drugs and genetic materials as well as beneficial bacteria. Moreover, GMSs have exhibited promising potentials to act as both cell carriers and 3D scaffold components in tissue engineering and regenerative medicine, which not only exhibit excellent injectability but also could be integrated into a macroscale construct with the laden cells. Herein, we aim to thoroughly summarize the recent progress in the preparations and biomedical applications of GMSs and then to point out the research direction in future. First, various methods for the fabrication of GMSs will be described. Second, the recent use of GMSs in tumor embolization and in the delivery of cells, drugs, and genetic material as well as bacteria will be presented. Finally, several key factors that may enhance the improvement of GMSs were suggested as delivery vehicles.

Gelatin Matrices for Growth Factor Sequestration

Gelatin is used in a broad range of tissue engineering applications because of its bioactivity, mild processing conditions, and ease of modification, which have increased interest in its use as a growth factor delivery vehicle. Traditional methods to control growth factor sequestration and delivery have relied on controlling hydrogel mesh size via chemical crosslinking with corollary changes to the physical properties of the hydrogel. To decouple growth factor release from scaffold properties, affinity sequestration modalities have been developed to preserve the bioactivity of the growth factor through interactions with the modified gelatin. This review provides a summary of these mechanisms, highlights current gelatin growth factor delivery systems, and addresses the future perspective of gelatin matrices for growth factor delivery in tissue engineering.

Porous Silk Fibroin Microspheres Sustainably Releasing Bioactive Basic Fibroblast Growth Factor

Basic fibroblast growth factor (bFGF) plays a significant role in stimulating cell proliferation. It remains a challenge in the field of biomaterials to develop a carrier with the capacity of continuously releasing bioactive bFGF. In this study, porous bFGF-loaded silk fibroin (SF) microspheres, with inside-out channels, were fabricated by high-voltage electrostatic differentiation, and followed by lyophilization. The embedded bFGF exhibited a slow release mode for over 13 days without suffering burst release. SEM observations showed that incubated L929 cells could fully spread and produce collagen-like fibrous matrix on the surface of SF microspheres. CLSM observations and the results of cell viability assay indicated that bFGF-loaded microspheres could significantly promote cell proliferation during five to nine days of culture, compared to bFGF-unloaded microspheres. This reveals that the bFGF released from SF microspheres retained obvious bioactivity to stimulate cell growth. Such microspheres sustainably releasing bioactive bFGF might be applied to massive cell culture and tissue engineering as a matrix directly, or after being combined with three-dimensional scaffolds.