An antibody panel for immunohistochemical analysis of the retina in Davidson's-fixed, paraffin-embedded eyes of rats

Therapeutic effect of the mesenchymal stem cells on vigabatrin-induced retinopathy in adult male albino rat

Vigabatrin (VGB) is an effective antiepileptic drug used mainly to treat infantile spasms and refractory complex partial seizures. However, using VGB was restricted as it was known to cause retinal toxicity that appears as a severe peripheral visual field defect. Accordingly, this study was conducted to examine the histopathological and biochemical effects of VGB on the retina in adult male albino rats and assess the possible therapeutic role of mesenchymal stem cells (MSCs) against this potential toxicity. The rats were divided into three groups (control group, VGB group, and VGB/MSCs group), one week after 65 days of VGB treatment ±MSCs. The right eyeballs were prepared for histological and immunohistochemical examination, whereas the left eyeballs were prepared for real-time polymerase chain reaction analysis. Our results demonstrated that MSCs ameliorated retinal pathological changes and downregulated the expression of glial fibrillary acidic protein, vascular endothelial growth factor, and synaptophysin after VGB administration suggesting MSCs function and vascular modulating effect. Moreover, MSCs regulate retinal tissue gene expression of BAX, Bcl-2, BDNF, NGF, synapsin, interleukin (IL)-6, IL-1β, and occludin suggesting MSCs antiapoptotic and immunomodulating effect. In conclusion, MSCs administration could be a suitable therapeutic line to ameliorate VGB-induced retinopathy.

Neonatal and Juvenile Ocular Development in Göttingen Minipigs and Domestic Pigs: A Histomorphological and Immunohistochemical Study

Pigs are considered one of the relevant animal models for ocular research as they share several histological and anatomical similarities with the human eye. With the increasing interest in juvenile animal models, this study aimed to describe the postnatal development of ocular structures in 16 Göttingen minipigs and 25 F2 domestic pigs, between birth and 6 months of age, using histopathology and immunohistochemistry against Ki-67, caspase-3, calbindin, glial fibrillary acidic protein, rhodopsin, and synaptophysin. All ocular structures in both pig breeds were incompletely developed at birth and for variable periods postnatally. Noteworthy histological features of immaturity included vascularization in the corneal stroma in neonatal Göttingen minipigs, increased cellularity in different substructures, remnants of the hyaloid vasculature, short and poorly ramified ciliary body processes, and a poorly developed cone inner segment. Increased cellular proliferation, highlighted by abundant Ki-67 immunolabeling, was observed in almost all developing structures of the pig eye for variable periods postnatally. Apoptosis, highlighted with caspase-3 immunolabeling, was observed in the retinal inner nuclear layer at birth and in the regressing hyaloid vasculature remnants. Immunohistochemistry against rhodopsin, synaptophysin, and calbindin demonstrated the short size of the developing photoreceptors and the immature cone inner segment morphology. Calbindin labeling revealed significant differences in the amount of positively labeled cone nuclei between the retinal area centralis and the non-area centralis regions. The elongation of Müller cell processes in the developing retina was shown with glial fibrillary acidic protein. In both pig breeds, the eyes reached histomorphological and immunohistochemical maturity at 6 months of age.

Improved immunohistochemical detection of phosphorylated mitogen-activated protein kinases in the injured rat optic nerve head

The activity of mitogen-activated protein kinases (MAPKs) is largely controlled by addition or removal of phosphate groups, which are carried out by kinase or phosphatase enzymes, respectively. Determining the phosphorylation status of MAPK isoenzymes, therefore, aids elucidation of the physiological and pathological roles of this enzyme. In practical terms, however, end-point procurement of appropriate experimental tissues produces conditions where MAPK phosphorylation status can rapidly alter, thus giving rise to aberrant data. We therefore attempted to instigate a means of stabilising end-point MAPK phosphorylation levels when procuring tissues for analysis. We employed a well-described rat model of ocular hypertension in which MAPK isoenzyme activation occurs in the optic nerve head (ONH), but can vary according to the level of resultant tissue pathology. Animals were appropriately treated and after 3 days were perfused in the presence or absence of a cocktail of phosphatase inhibitors (PIs), immediately prior to tissue fixation, in order to prevent dephosphorylation of phosphorylated MAPKs. Immunohistochemical labelling for phosphorylated MAPKs in untreated ONH sections was unaffected by the presence of PIs in the perfusate. MAPK activation was detected by immunohistochemistry in the treated ONH, but findings varied considerably, particularly in animals with less extensive tissue damage. The presence of PIs in the perfusate, however, significantly reduced this variation and enabled consistent changes to be detected, particularly in the animals with less extensive tissue damage. Thus, the addition of PIs to the perfusate is suggested when studying MAPK activation by immunohistochemistry, especially in the ONH.

Optimization of fixative solution for retinal morphology: a comparison with Davidson's fixative and other fixation solutions

PURPOSE

Numerous fixative solutions are available but many are not amenable to the histomorphological preservation of retinae. The investigators specifically focused on retinal histological studies, which rather than 4% formaldehyde (FA), often use Davidson's fixative. However the latter has its limitations. The purpose of this study was to produce a new fixative which maintains retinae closer to the in vivo conditions.

STUDY DESIGN

Experimental design.

METHODS

Four fixative formulations (4% paraformaldehyde, Davidson's fixative, modified Davidson's fixative and an in-house fixative - TB-Fix) were tested on retinae and the outcomes on histomorphology and immunohistochemical staining for selected antigenic markers was compared.

RESULTS

TB-Fix markedly improved morphological detail following hematoxylin and eosin staining, most importantly eliminating the spongiform appearance in the plexiform layer and the swelling of somata (including Müller cells), when compared to FA, Davidson's fixative and its modified version. Retinal samples fixed with TB-Fix or FA showed comparable results in immunohistological staining for neurons and glia in the retina. Importantly, while the whole eye fixed with FA collapsed in shape and induced artificial retinal detachment, the eye fixed with TB-Fix avoided deformation and detachment. Furthermore, we found that TB-Fix also prevented detachment from the culture plate when used to fix HEK293 cells, which are known to detach from the plate easily.

CONCLUSION

It was demonstrated that TB-Fix provides an overall improvement in the preservation of retinal morphology and chemical composition.

Expression and activation of mitogen-activated protein kinases in the optic nerve head in a rat model of ocular hypertension

BACKGROUND

Glaucoma is a leading cause of irreversible blindness manifesting as an age-related, progressive optic neuropathy with associated retinal ganglion cell (RGC) loss. Mitogen-activated protein kinases (MAPKs: p42/44 MAPK, SAPK/JNK, p38 MAPK) are activated in various retinal disease models and likely contribute to the mechanisms of RGC death. Although MAPKs play roles in the development of retinal pathology, their action in the optic nerve head (ONH), where the initial insult to RGC axons likely resides in glaucoma, remains unexplored.

METHODS

An experimental paradigm representing glaucoma was established by induction of chronic ocular hypertension (OHT) via laser-induced coagulation of the trabecular meshwork in Sprague-Dawley rats. MAPKs were subsequently investigated over the following days for expression and activity alterations, using RT-PCR, immunohistochemistry and Western immunoblot.

RESULTS

p42/44 MAPK expression was unaltered after intraocular pressure (IOP) elevation, but there was a significant activation of this enzyme in ONH astrocytes after 6-24 h. Activated SAPK/JNK isoforms were present throughout healthy RGC axons but after IOP elevation or optic nerve crush, they both accumulated at the ONH, likely due to RGC axon transport disruption, and were subject to additional activation. p38 MAPK was expressed by a population of microglia which were significantly more populous following IOP elevation. However it was only significantly activated in microglia after 3 days, and then only in the ONH and optic nerve; in the retina it was solely activated in RGC perikarya.

CONCLUSIONS

In conclusion, each of the MAPKs showed a specific spatio-temporal expression and activation pattern in the retina, ONH and optic nerve as a result of IOP elevation. These findings likely reflect the roles of the individual enzymes, and the cells in which they reside, in the developing pathology following IOP elevation. These data have implications for understanding the mechanisms of ocular pathology in diseases such as glaucoma.

Ketone body 3-hydroxybutyrate mimics calorie restriction via the Nrf2 activator, fumarate, in the retina

Calorie restriction (CR) being the most robust dietary intervention provides various health benefits. D-3-hydroxybutyrate (3HB), a major physiological ketone, has been proposed as an important endogenous molecule for CR. To investigate the role of 3HB in CR, we investigated potential shared mechanisms underlying increased retinal 3HB induced by CR and exogenously applied 3HB without CR to protect against ischemic retinal degeneration. The repeated elevation of retinal 3HB, with or without CR, suppressed retinal degeneration. Metabolomic analysis showed that the antioxidant pentose phosphate pathway and its limiting enzyme, glucose-6-phosphate dehydrogenase (G6PD), were concomitantly preserved. Importantly, the upregulation of nuclear factor erythroid 2 p45-related factor 2 (Nrf2), a regulator of G6PD, and elevation of the tricarboxylic acid cycle's Nrf2 activator, fumarate, were also shared. Together, our findings suggest that CR provides retinal antioxidative defense by 3HB through the antioxidant Nrf2 pathway via modification of a tricarboxylic acid cycle intermediate during 3HB metabolism.

Advanced Clinical Imaging and Tissue-based Biomarkers of the Eye for Toxicology Studies in Minipigs

There is increased interest to use minipigs in ocular toxicology studies due to their anatomical similarities with human eyes and as a substitute for nonhuman primates. This requires adaptation of enhanced optical coherence tomography (OCT) techniques and of ocular relevant immunohistochemistry (IHC) or in situ hybridization (ISH) markers to porcine eyes. In this study, OCT and OCT angiography (AngioOCT) were performed on adult Göttingen minipigs. To increase structural information on retinal and choroidal vasculature, OCT data were speckle denoized and choroidal blood vessels were segmented with threshold filtering. In addition, we established a set of IHC and ISH markers on Davidson's fixed paraffin-embedded minipig eyes: neurofilament-160, neuronal nuclei, calretinin, protein kinase C-α, vimentin, glial fibrillary acidic protein, glutamine synthetase, ionized calcium-binding adaptor molecule-1, rhodopsin, synaptophysin, postsynaptic density protein-95, retinal pigment epithelium (RPE)-specific protein-65, von Willebrand factor, α-smooth muscle actin, desmin, and Ki-67, thus enabling visualization of retinal neuronal and glial cells, photoreceptors, synapses, RPE, blood vessels, myocytes, macrophages, or cell proliferation. Using ISH, transcripts of vascular endothelial growth factor A, angiopoietin-2, and endothelial tyrosine kinase were visualized. This article describes for the first time in minipig eyes speckle noise-free OCT, AngioOCT, and a set of IHC/ISH markers on Davidson's fixed paraffin-embedded tissues and helps to establish the minipig for ocular toxicology and pharmacology studies.

Fixation strategies for retinal immunohistochemistry

Immunohistochemical and ex vivo anatomical studies have provided many glimpses of the variety, distribution, and signaling components of vertebrate retinal neurons. The beauty of numerous images published to date, and the qualitative and quantitative information they provide, indicate that these approaches are fundamentally useful. However, obtaining these images entailed tissue handling and exposure to chemical solutions that differ from normal extracellular fluid in composition, temperature, and osmolarity. Because the differences are large enough to alter intercellular and intracellular signaling in neurons, and because retinae are susceptible to crush, shear, and fray, it is natural to wonder if immunohistochemical and anatomical methods disturb or damage the cells they are designed to examine. Tissue fixation is typically incorporated to guard against this damage and is therefore critically important to the quality and significance of the harvested data. Here, we describe mechanisms of fixation; advantages and disadvantages of using formaldehyde and glutaraldehyde as fixatives during immunohistochemistry; and modifications of widely used protocols that have recently been found to improve cell shape preservation and immunostaining patterns, especially in proximal retinal neurons.

Hydrophobically-modified poly(vinyl pyrrolidone) as a physically-associative, shear-responsive ophthalmic hydrogel

The potential of hydrophobically-modified poly(vinyl pyrrolidone) as a shear-responsive, self-associative hydrogel for ophthalmic applications is demonstrated. Hydrophobic modification was achieved via random copolymerization of N-vinylpyrrolidone with N-vinylformamide, the latter of which can be hydrolyzed to expose a desired degree of reactive amine groups permitting grafting of alkyl chlorides of varying alkyl chain lengths. The resulting materials formed highly shear-responsive physical hydrogels, exhibiting tunable shear thinning over 4-5 decades of viscosity from infinite shear to zero shear conditions that facilitates lubrication upon blinking and/or facile injection or drop-based delivery to the anterior or posterior segments of the eye. Viscosity changes due to self-association over time can also be tuned by changing the length of the hydrophobe, with C18-grafted materials exhibiting prolonged thickening over several weeks to form extremely stiff hydrogels and shorter grafts equilibrating significantly faster but forming weaker gels. The hydrogels remained transparent even at very high polymer concentrations (20 wt%) and are demonstrated to facilitate controlled release of a model drug (doxorubicin). The polymers exhibit minimal cytotoxicity in vitro to human corneal epithelial cells and retinal pigment epithelial cells, particularly when lower molecular weight backbone polymers were used. In vivo assessments in rabbits indicated no significant conjunctival edema or redness, secretion, corneal opacity, or iris involvement upon anterior application. Following intravitreal injection in rat eyes, no opacification of the lens, cornea or vitreous, nor any morphological or functional change to the posterior segment was observed. Examination of wholemount tissues and histology demonstrated no adverse effect from the injection or deposition of material. As such, these shear-thinning materials offer potential for drug delivery in both the anterior and posterior segments or as a vitreal replacement that can be easily administered or removed.

Localization of a wide-ranging panel of antigens in the rat retina by immunohistochemistry: comparison of Davidson's solution and formalin as fixatives

The preferred fixative for whole eyes is Davidson's solution, which provides optimal tissue preservation while avoiding retinal detachment. Hitherto, the compatibility of Davidson's solution with immunohistochemistry has been largely untested. The goal of the present study was to compare the immunolabeling patterns of a wide-ranging panel of commercially available, previously validated antibodies in formalin- and Davidson's-fixed retinas. Immunohistochemistry was performed in normal pigmented rat eyes and, to facilitate localization of inducible proteins, eyes injected with the bacterial toxin lipopolysaccharide or subjected to laser-induced photoreceptor damage. Specificity of labeling was judged by the morphology and distribution of immunopositive cells, by the absence of signal in appropriate controls, and by comparison with expected staining patterns. Retinas fixed in formalin displayed only adequate morphological integrity but were highly compatible with all 39 antibodies evaluated. Retinas fixed in Davidson's solution displayed morphological integrity superior to those fixed in formalin. Generally, the cellular and subcellular patterns and intensities of immunoreactivities obtained with each fixative were identical; however, Davidson's fixative was less compatible with certain antibodies, such as the neurotransmitter γ-aminobutyric acid, the microglial marker iba1, the macroglial stress protein nestin, and the small heat shock proteins Hsp27 and αB-crystallin, shortfalls that somewhat temper enthusiasm concerning its use.

Evaluation of a convenient method of assessing rodent visual function in safety pharmacology studies: effects of sodium iodate on visual acuity and retinal morphology in albino and pigmented rats and mice

INTRODUCTION

We have evaluated the ability of a semi-automated, optomotor reflex method to assess drug-induced visual dysfunction, in albino and pigmented rats and mice.

METHODS

Male Han Wistar (HW) and Long Evans (LE) rats and mice (CD-1 and C57BL/6) were tested in a chamber formed by 4 computer monitors displaying a rotating vertical grating, to elicit head-tracking movements. The highest visible grating frequency was taken as the threshold of visual acuity, in cycles per degree (c/d). Animals received an intravenous infusion of either sodium iodate (50mg/kg) or 0.9% w/v NaCl (aq). They were tested 2h later, then re-tested daily for a further 3 days. The time course of the effect was assessed in HW rats over a 6-week period, including electron microscopy, and immunohistochemical analysis of markers of injury and repair in the retina.

RESULTS

Baseline visual acuities for HW and LE rats were 0.355 ± 0.007 and 0.530 ± 0.004 c/d, respectively, and 0.296 ± 0.003 c/d and 0.370 ± 0.001 c/d for CD-1 and C57BL/6 mice, respectively (n=10 for each). In HW rats there was a dramatic loss of visual acuity 2h after administration of sodium iodate (0.021 ± 0.021 c/d; P<0.001). Less dramatic decreases in visual acuity were seen in LE rats and in the two mouse strains. In HW rats, visual acuity was restored after 4 weeks. This paralleled the histopathological recovery of the peripheral retina, whereas the central retina did not recover.

DISCUSSION

The method proved to be very convenient, and the stability of visual acuity in vehicle control rats over a 6-week period also demonstrated its suitability for inclusion in long-term toxicity studies. Both albino and pigmented mice and rats are suitable for assessment of retinotoxicity using this method, but albino rats are the most sensitive to sodium iodate.