Preliminary study of the safety and efficacy of medium-chain triglycerides for use as an intraocular tamponading agent in minipigs

Pig Models in Retinal Research and Retinal Disease

The pig has been used as a large animal model in biomedical research for many years and its use continues to increase because induced mutations phenocopy several inherited human diseases. In addition, they are continuous breeders, can be propagated by artificial insemination, have large litter sizes (on the order of mice), and can be genetically manipulated using all of the techniques that are currently available in mice. The pioneering work of Petters and colleagues set the stage for the use of the pig as a model of inherited retinal disease. In the last 10 years, the pig has become a model of choice where specific disease-causing mutations that are not phenocopied in rodents need to be studied and therapeutic approaches explored. The pig is not only used for retinal eye disease but also for the study of the cornea and lens. This review attempts to show how broad the use of the pig has become and how it has contributed to the assessment of treatments for eye disease. In the last 10 years, there have been several reviews that included the use of the pig in biomedical research (see body of the review) that included information about retinal disease. None directly discuss the use of the pig as an animal model for retinal diseases, including inherited diseases, where a single genetic mutation has been identified or for multifactorial diseases such as glaucoma and diabetic retinopathy. Although the pig is used to explore diseases of the cornea and lens, this review focuses on how and why the pig, as a large animal model, is useful for research in neural retinal disease and its treatment.

Acute Oral Toxicity and Genotoxicity Test and Evaluation of Cinnamomum camphora Seed Kernel Oil

Cinnamomum camphora seed kernel oil (CCSKO) is one of the important natural medium chain triglycerides (MCT) resources, with more than 95.00% of medium chain fatty acids found in the world, and has various physiological effects. However, CCSKO has not been generally recognized as a safe oil or new food resource yet. The acute oral toxicity test and a standard battery of genotoxicity tests (mammalian erythrocyte micronucleus test, Ames test, and in vitro mammalian cell TK gene mutation test) of CCSKO as a new edible plant oil were used in the study. The results of the acute oral toxicity test showed that CCSKO was preliminary non-toxic, with an LD₅₀ value higher than 21.5 g/kg body weight. In the mammalian erythrocyte micronucleus test, there was no concentration-response relationship between the dose of CCSKO and micronucleus value in polychromatic erythrocytes compared to the negative control group. No genotoxicity was observed in the Ames test in the presence or absence of S9 at 5000 μg/mL. In vitro mammalian cell TK gene mutation test showed that CCSKO did not induce in vitro mammalian cell TK gene mutation in the presence or absence of S9 at 5000 μg/mL. These results indicated that CCSKO is a non-toxic natural medium-chain oil.

Injectable self-crosslinking hydrogels based on hyaluronic acid as vitreous substitutes

After vitrectomy, the ideal vitreous substitute should be implanted to maintain the normal function of the eye. However, the existing materials (such as silicone oil, air, perfluorocarbons, etc.) still have some shortcomings and cannot fully meet the clinical needs. In this study, thiolated hyaluronic acid (SH-HA) was prepared based on hyaluronic acid. The SH-HA hydrogel was formed by a simple transformation of the sulfhydryl group to the disulfide bond, which had high transparency, controllable swelling property, suitable mechanical strength, excellent biocompatibility and similar physical and chemical properties to natural vitreous. SH-HA hydrogel was filled into the eyes of experimental rabbits to replace their own vitreous after vitrectomy. During the 90 days follow-up period, SH-HA hydrogel showed excellent intraocular compatibility, maintained normal intraocular pressure (IOP), and no cataract, endophthalmitis, retinal detachment and other complications were observed. In general, SH-HA hydrogel has great potential as a vitreous substitute.

A Study on the Drug Concentration in Fellow Eyes After Unilateral Intravitreal Injection of Conbercept Into New Zealand Rabbit Eyes

Intravitreal injections of anti-vascular endothelial growth factor (VEGF) have become increasingly popular in the treatment of ocular diseases. However, few studies have determined the efficiency of unilateral intravitreal anti-VEGF injection in the fellow eye. Herein, we performed a study to investigate the drug concentration in fellow eyes and venous serum after unilateral intravitreal injection of conbercept into rabbit eyes. This is an experimental animal study. Thirty male New Zealand rabbits (60 eyes) were used. One eye of each rabbit was intravitreally injected with 0.5 mg of conbercept. Both eyes from six rabbits were enucleated on days 1, 3, 7, 14, and 30. Conbercept concentrations were measured in the serum, aqueous humor, and vitreous humor. We found conbercept was detected in the fellow eyes and serum of rabbits. Conbercept concentrations in the vitreous humor of the fellow eyes increased from 74.11 ng/ml on day 1 to 246.69 ng/ml on day 3 and then declined to 69.11 ng/ml after 30 days. The concentration in the aqueous humor peaked on day 1 with a concentration of 244.82 ng/ml and declined to 40.13 ng/ml after 30 days. The maximum conbercept concentrations in the aqueous humor and vitreous humor of fellow eyes were similar, which were 0.2 and 1.3% of those of the injected eye, respectively. A peak concentration of 102.49 ng/ml was achieved in the venous serum 1 day after intravitreal injection of conbercept, which was 0.08 and 0.5% of those of the maximum conbercept concentrations in the vitreous humor and aqueous humor of the injected eye, respectively, and 41.5 and 41.8% of the maximum conbercept concentrations in the vitreous humor and aqueous humor of the non-injected eye, respectively. In conclusion, after intravitreal injection of 0.5 mg of conbercept into rabbit eyes, very small amounts of conbercept were detected in the fellow non-injected eyes and venous serum.

Silicone oil in vitreoretinal surgery: indications, complications, new developments and alternative long-term tamponade agents

Silicone oil (SO) has been used as a long-term tamponade agent in the treatment of complicated vitreoretinal diseases for about half a century, during which time many advances in surgical techniques and technologies have been made. This review summarizes the chemical and physical properties of SO, its indications and complications, including particularly emulsification. The mechanisms and risk factors for emulsification are discussed, as well as novel strategies for its effective removal. Finally, the review focuses on new improved formulations of SO, including research into slow-release pharmacological agents within SO and provides an overview of alternatives to SO for the purpose of long-term tamponade that are being developed.

Vitreous substitutes: An overview of the properties, importance, and development

Vitreous or vitreous humor is a complex transparent gel that fills the space between the lens and retina of an eye and acts as a transparent medium that allows light to pass through it to reach the photoreceptor layer (retina) of the eye. The vitreous humor is removed in ocular surgery (vitrectomy) for pathologies like retinal detachment, macular hole, diabetes-related vitreous hemorrhage detachment, and ocular trauma. Since the vitreous is not actively regenerated or replenished, there is a need for a vitreous substitute to fill the vitreous cavity to provide a temporary or permanent tamponade to the retina following some vitreoretinal surgeries. An ideal vitreous substitute could probably be left inside the eye forever. The vitreous humor is transparent, biocompatible, viscoelastic and highly hydrophilic; polymeric hydrogels with these properties can be a potential candidate to be used as vitreous substitutes. To meet the tremendous demand for the vitreous substitute, many scientists all over the world have developed various kinds of vitreous substitutes or tamponade agent. Vitreous substitutes, whatsoever developed till date, are associated with several advantages and disadvantages, and there is no ideal vitreous substitute available till date. This review highlights the polymer-based vitreous substitutes developed so far, along with their advantages and limitations. The gas-based and oil-based substitutes have also been discussed but very briefly.