Tauroursodeoxycholic acid prevents retinal degeneration in transgenic P23H rats

Purpose. To evaluate the preventive effect of tauroursodeoxycholic acid (TUDCA) on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP). Methods. P23H line-3 rats were injected with TUDCA once a week from postnatal day (P)21 to P120, in parallel with vehicle-administered controls. At P120, functional activity of the retina was evaluated by electroretinographic (ERG) recording. The effects of TUDCA on the number, morphology, integrity, and synaptic connectivity of retinal cells were characterized by immunofluorescence confocal microscopy. Results. The amplitude of ERG a- and b-waves was significantly higher in TUDCA-treated animals under both scotopic and photopic conditions than in control animals. In the central area of the retina, TUDCA-treated P23H rats showed threefold more photoreceptors than control animals. The number of TUNEL-positive cells was significantly smaller in TUDCA-treated rats, in which photoreceptor morphology was preserved. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in TUDCA-treated P23H rats. Furthermore, in TUDCA-treated rat retinas, the number of both rod bipolar and horizontal cell bodies, as well as the density of their synaptic terminals in the outer plexiform layer, was greater than in control rats. Conclusions. TUDCA treatment was capable of preserving cone and rod structure and function, together with their contacts with their postsynaptic neurons. The neuroprotective effects of TUDCA make this compound potentially useful for delaying retinal degeneration in RP.

Neuroprotective effects of the cannabinoid agonist HU210 on retinal degeneration

Cannabinoids have been demonstrated to exert neuroprotective effects on different types of neuronal insults. Here we have addressed the therapeutic potential of the synthetic cannabinoid HU210 on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model for autosomal dominant retinitis pigmentosa (RP). In P23H rats administered with HU210 (100 μg/kg, i.p.) from P24 to P90, ERG recordings showed an amelioration of vision loss, as compared to vehicle-administered animals. Under scotopic conditions, the maximum a-wave amplitudes recorded at P60 and P90 were higher in HU210-treated animals, as compared to the values obtained in untreated animals. The scotopic b-waves were significantly higher in treated animals than in untreated rats at P30, P60 and P90. This attenuation of visual deterioration correlated with a delay in photoreceptor degeneration and the preservation of retinal cytoarchitecture. HU210-treated animals had 40% more photoreceptors than untreated animals. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were also preserved in HU210-treated P23H rats. These results indicate that HU210 preserves cone and rod structure and function, together with their contacts with postsynaptic neurons, in P23H rats. These data suggest that cannabinoids are potentially useful to delay retinal degeneration in RP patients.

Microglia activation in a model of retinal degeneration and TUDCA neuroprotective effects

Background: Retinitis pigmentosa is a heterogeneous group of inherited neurodegenerative retinal disorders characterized by a progressive peripheral vision loss and night vision difficulties, subsequently leading to central vision impairment. Chronic microglia activation is associated with various neurodegenerative diseases including retinitis pigmentosa. The objective of this study was to quantify microglia activation in the retina of P23H rats, an animal model of retinitis pigmentosa, and to evaluate the therapeutic effects of TUDCA (tauroursodeoxycholic acid), which has been described as a neuroprotective compound. Methods: For this study, homozygous P23H line 3 and Sprague-Dawley (SD) rats were injected weekly with TUDCA (500 mg/kg, ip) or vehicle (saline) from 20 days to 4 months old. Vertical retinal sections and whole-mount retinas were immunostained for specific markers of microglial cells (anti-CD11b, anti-Iba1 and anti-MHC-II). Microglial cell morphology was analyzed and the number of retinal microglial was quantified. Results: Microglial cells in the SD rat retinas were arranged in regular mosaics homogenously distributed within the plexiform and ganglion cell layers. In the P23H rat retina, microglial cells increased in number in all layers compared with control SD rat retinas, preserving the regular mosaic distribution. In addition, a large number of amoeboid CD11b-positive cells were observed in the P23H rat retina, even in the subretinal space. Retinas of TUDCA-treated P23H animals exhibited lower microglial cell number in all layers and absence of microglial cells in the subretinal space. Conclusions: These results report novel TUDCA anti-inflammatory actions, with potential therapeutic implications for neurodegenerative diseases, including retinitis pigmentosa.

Corneal biomechanics: a review

Biomechanics is often defined as ‘mechanics applied to biology’. Due to the variety and complexity of the behaviour of biological structures and materials, biomechanics is better defined as the development, extension and application of mechanics for a better understanding of physiology and physiopathology and consequently for a better diagnosis and treatment of disease and injury. Different methods for the characterisation of corneal biomechanics are reviewed in detail, including those that are currently commercially available (Ocular Response Analyzer and CorVis ST). The clinical applicability of the parameters provided by these devices are discussed, especially in the fields of glaucoma, detection of ectatic disorders and orthokeratology. Likewise, other methods are also reviewed, such as Brillouin microscopy or dynamic optical coherence tomography and others with potential application to clinical practice but not validated for in vivo measurements, such as ultrasonic elastography. Advantages and disadvantages of all these techniques are described. Finally, the concept of biomechanical modelling is revised as well as the requirements for developing biomechanical models, with special emphasis on finite element modelling.