[Nanoparticles as drug delivery systems in ophthalmology]. / Nanopartikel als Drug-Delivery-Systeme für die Ophthalmologie.

Nanoparticles are perfectly suited as drug delivery systems due to their size and the diversity of materials used. They are able to penetrate biological barriers, can directly deliver drugs to the target site and provide a sustained release profile. Having long been established in oncology, in the last decade research has started to take a closer look at the potential of nanoparticles for ocular drug delivery. Obstacles, such as poor delivery of drugs via eye drops and the side effects of invasive methods, such as placing implants as drug depots could be overcome. Among the most relevant investigated structures are polymeric nanoparticles, micelles, liposomes, solid lipid nanoparticles, dendrimers and cyclodextrins. Besides the composition of the nanoparticle itself, its efficacy and stability can be optimized through coatings; however, long-term stability, standardization of production and toxicity remain the major challenges. The preclinical and partly clinical results obtained so far will hopefully give impulse to the idea of applying nanoparticles for optimized ocular drug delivery in the near future.

Establishment of a retinal hypoxia organ culture model.

Hypoxia plays an important role in several retinal diseases, especially in central retinal artery occlusion (CRAO). Although CRAO has been known for over a hundred years, no cure or sufficient treatment is available. Potential therapies are being evaluated in several in vivo models or primary cultures. However, in vivo models or primary cultures are very time-consuming, expensive, and furthermore several therapies or agents cannot be tested. Therefore, we aimed to develop a standardized organotypic ex vivo retinal hypoxia model. A chamber was developed in which rat retinal explants were incubated for different hypoxia durations. Afterwards, the retinas were adjusted to normal air and incubated for 24, 48 or 72 h under standard conditions. To analyze the retinal explants, and in particular the retinal ganglion cells (RGC) immunohistology, western blot and optical coherence tomography (OCT) measurements were performed. To compare our model to a standardized degeneration model, additional retinal explants were treated with 0.5 and 1 mM glutamate. Depending on hypoxia duration and incubation time, the amount of RGCs decreased and accordingly, the amount of TUNEL-positive RGCs increased. Furthermore, ß-III-tubulin expression and retinal thickness significantly decreased with longer-lasting hypoxia. The reduction of RGCs induced by 75 min of hypoxia was comparable to the one of 1 mM glutamate treatment after 24 h (20.27% versus 19.69%) and 48 h (13.41% versus 14.41%) of incubation. We successfully established a cheap, standardized, easy-to-use organotypic culture model for retinal hypoxia. We selected 75 min of hypoxia for further studies, as approximately 50% of the RGC died compared to the control group after 48 h.

Degenerative effects of cobalt-chloride treatment on neurons and microglia in a porcine retina organ culture model.

In order to understand the pathological processes of retinal diseases, experimental models are necessary. Cobalt, as part of the vitamin B12 complex, is important for neuronal integrity. However, it is known that high quantities of cobalt induce cytotoxic mechanisms via hypoxia mimicry. Therefore, we tested the degenerative effect of cobalt chloride (CoCl2) on neurons and microglia in a porcine retina organ culture model. Organotypic cultures of porcine retinas were cultured and treated with different concentrations of CoCl2 (0, 100, 300 and 500 µM) for 48 h. After four and eight days, CoCl2 induced a strong degeneration of the porcine retina, starting at 300 µM. A loss of retinal ganglion cells (RGCs, Brn-3a), amacrine cells (calretinin) and bipolar cells (PKCα) was observed. Additionally, a high expression of hypoxia induced factor-1a (HIF-1a) and heat shock protein 70 (HSP70) was noted at both points in time. Also, the Caspase 3 protein was activated and P21 expression was induced. However, only at day four, the Bax/Bcl-2 ratio was increased. The effect of CoCl2 was not restricted to neurons. CoCl2 concentrations reduced the microglia amount (Iba1) and activity (Iba1 + Fcγ-Receptor) at both points in time. These damaging effects on microglia were surprising, since CoCl2 causes hypoxia and a pro-inflammatory environment. However, high concentrations of CoCl2 also seem to be toxic to these cells. Similar degenerative mechanisms as in comparison to retinal ischemia animal models were observed. In summary, an effective and reproducible hypoxia-mimicking organotypic model for retinal degeneration was established, which is easy to handle and ready for drug studies.