Vision evaluation by functional observational battery, operant behavior test, and light/dark box test in retinal dystrophic RCS rats versus normal rats

Animal models for the evaluation of retinal stem cell therapies

Retinal degeneration (RD) diseases leading to severe vision loss can affect photoreceptors (PRs) that are responsible for phototransduction, or retinal pigmented epithelium (RPE) providing support for PRs. Human pluripotent stem cell (hPSC)-based therapies are a potential approach for restoration of retinal structure in patients with currently incurable RD diseases. Currently, there are two targeted hPSC therapeutics: PR rescue and PR replacement. PR rescue involves the transplantation of RPE or other neural progenitors into the subretinal space to slow down or prevent further RD. RPE transplantation plays a critical role in preserving photoreceptors by providing trophic support and maintaining retinal integrity, particularly in diseases like age-related macular degeneration (AMD). Advances in RPE transplantation methods, such as polarized monolayer cultures and scaffold-based approaches, have shown promise in enhancing graft survival and integration. However, limitations include inconsistent integration, variable neurotrophic factor secretion, and immune rejection risks in non-autologous transplants. In PR replacement, stem cell-derived photoreceptor-like cells or photoreceptor progenitors (PRP) obtained are transplanted into the eye. While PRPs are commonly obtained from retinal organoids (ROs), alternative sources, such as early differentiation stages or direct differentiation protocols, are also utilized to enhance the efficiency and scalability of PRP generation. Challenges include achieving proper integration, forming outer segments, rosette formation, and avoiding immune rejection or tumorigenicity. Various animal models that simulate human RD diseases are being used for establishing surgical feasibility, graft survival and visual functional recovery but fail to replicate clinical immune challenges. Rodent models lack macula-like structures and have limited reliability in detecting subtle functional changes, while larger animal models pose ethical, logistical, and financial challenges. Immunocompromised models have been developed for minimizing xenograft issues. Visual functional testing for efficacy includes optokinetic testing (OKN), electroretinography (ERG), and electrophysiological recordings from the retina and brain. These tests often fail to capture the complexity of human visual recovery, highlighting the need for advanced models and improved functional testing techniques. This review aims to aggregate current knowledge about approaches to stem cell transplantation, requirements of animal models chosen for validating vision benefits of transplantation studies, advantages of using specific disease models and their limitations. While promising strides have been made, addressing these limitations remains essential for translating stem cell-based therapies into clinical success.

The pCREB/BDNF Pathway in the Hippocampus Is Involved in the Therapeutic Effect of Selective 5-HT Reuptake Inhibitors in Adult Male Rats Exposed to Blast Traumatic Brain Injury

BACKGROUND

Blast traumatic brain injury (bTBI) can result in depression-like behaviors in the acute and chronic phases. SSRIs have been shown to significantly alleviate depression-like behaviors in animal models of traumatic brain injury (TBI) by increasing serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) in the hippocampus. However, the therapeutic effects of SSRIs on depression caused by bTBI remain unclear.

OBJECTIVE

Therefore, this study was aimed at investigating the therapeutic effects of SSRIs on depression-like behaviors in bTBI models.

METHODS

We created a rat model to study mild TBI by subjecting rats to increased blast overpressures (BOP) and injecting fluoxetine and escitalopram SSRIs intraperitoneally for 28 days.

RESULTS

On day 14 post-BOP exposure, rats treated with SSRIs showed decreased depression-like behaviors. This finding was accompanied by higher 5-HT levels in the hippocampus and increased numbers of Nestin-positive cells in the dentate gyrus. Furthermore, rats treated with SSRIs exhibited increased pCREB and BDNF protein expression in the hippocampus on days 7, 14, and 28 after bTBI.

CONCLUSIONS

Overall, our findings indicate that SSRI-induced recovery from depression-like behaviors after mild bTBI is associated with the upregulation of 5-HT levels, pCREB and BDNF expression, and neurogenesis in the hippocampus.

Pre-clinical and cellular safety assessment of oral administered DHA rich microalgae oil from Schizochytrium sp. (Strain ATCC-20889): acute, sub-chronic and genotoxicity

The lack of toxicity data for DHA-rich oil from Schizochytrium sp. (Strain ATCC-20889) leads to its exclusion from the Qualified Presumption of Safety list. Therefore, present study addresses toxicity evaluation of DHA-rich microalgae oil using ex-vivo (cytotoxicity assay) and in-vivo methods (acute (OECD 423 guidelines), sub-chronic (OECD 452 guidelines), and genotoxicity assay). The ex-vivo results showed >90% cell viability of Caco-2 cells after 48 h of treatment (200 µg/mL of DHA). Additionally, the in-vivo acute toxicity study found that microalgae oil was nontoxic and classified under category 5 molecule according to OECD 423 guidelines with a highest degree of safety at 2000 mg/kg b.w. The in-vivo sub-chronic study revealed no significant mortality and changes in feed intake, body weight, haematological, biochemical, neurological, and urine parameters after repeated 180-days administration of DHA-rich microalgae oil at 250 mg/kg, 500 mg/kg, and 1000 mg/kg. Moreover, histopathology evaluation, comet assay, chromosomal aberration, and micronuclei assay also confirmed the nontoxic behavior of DHA-rich oil. Thus, the results from the ex-vivo and in-vivo studies indicate that DHA-rich oil from Schizochytrium sp. (Strain ATCC-20889) is safe for use as a novel food, and can be included in infants, adults, pregnant women, and children formula.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Photoelectric Dye, NK-5962, as a Potential Drug for Preventing Retinal Neurons from Apoptosis: Pharmacokinetic Studies Based on Review of the Evidence

NK-5962 is a key component of photoelectric dye-based retinal prosthesis (OUReP). In testing the safety and efficacy, NK-5962 was safe in all tests for the biological evaluation of medical devices (ISO 10993) and effective in preventing retinal cells from death even under dark conditions. The long-term implantation of the photoelectric dye-coupled polyethylene film in the subretinal space of hereditary retinal dystrophic (RCS) rats prevented neurons from apoptosis in the adjacent retinal tissue. The intravitreous injection of NK-5962 in the eyes of RCS rats, indeed, reduced the number of apoptotic cells in the retinal outer nuclear layer irrespective of light or dark conditions. In this study, we reviewed the in vitro and in vivo evidence of neuroprotective effect of NK-5962 and designed pharmacokinetic experiments. The in vitro IC₅₀ of 1.7 μM, based on the protective effect on retinal cells in culture, could explain the in vivo EC₅₀ of 3 μM that is calculated from concentrations of intravitreous injection to prevent retinal neurons from apoptosis. Pharmacokinetics of NK-5962 showed that intravenous administration, but not oral administration, led to the effective concentration in the eye of rats. NK-5962 would be a candidate drug for delaying the deterioration of retinal dystrophy, such as retinitis pigmentosa.

Modelling the visual response to an OUReP retinal prosthesis with photoelectric dye coupled to polyethylene film

Objective.Retinal prostheses have been developed to restore vision in blind patients suffering from diseases like retinitis pigmentosa.Approach.A new type of retinal prosthesis called the Okayama University-type retinal prosthesis (OUReP) was developed by chemically coupling photoelectric dyes to a polyethylene film surface. The prosthesis works by passively generating an electric potential when stimulated by light. However, the neurophysiological mechanism of how OUReP stimulates the degenerated retina is unknown.Main results.Here, we explore how the OUReP affects retinal tissues using a finite element model to solve for the potential inside the tissue and an active Hodgkin-Huxley model based on rat vision to predict the corresponding retinal bipolar response.Significance.We show that the OUReP is likely capable of eliciting responses in retinal bipolar cells necessary to generate vision under most ambient conditions.

Development of highly durable retinal prosthesis using photoelectric dyes coupled to polyethylene film and quantitative in vitro evaluation of its durability

Retinal prostheses have been developed to restore vision in blind patients suffering from such diseases as retinitis pigmentosa. In our previous studies, we developed a retinal prosthesis called dye-coupled film by chemical coupling of photoelectric dyes, which absorb light and then generate electrical potential, with a polyethylene film surface. The dye-coupled film is nontoxic, and we recovered the vision of a monkey with macular degeneration. The amount of dye on the dye-coupled film, however, decreased to one-third after five months in the monkey's eye. The photoelectric dye consists of a cation with photoresponsivity and a bromide ion (Br^-). Therefore, an anion-exchange reaction could be applied to the dye-coupled film to improve its durability. In this study, the anion-exchange reaction was conducted using bis(trifluoromethanesulfonyl)imide ion (TFSI^-), which has lower nucleophilicity than Br^-. First, the long-term durability was examined without using animal subjects and in a short period. Subsequently, an elemental analysis was performed to confirm the exchange between Br^-and TFSI^-, and chemical properties, such as photoresponsivity and durability, before and after the anion exchange, were evaluated. It was quantitatively confirmed that the long-term durability of dye-coupled films can be evaluated in an in vitro environment and in a short period of one-thirtieth by utilizing a saline solution at 60°C, compared with an in vivo environment. In addition, the durability of the dye-coupled film with TFSI^-was improved to 270%-320% compared with that of the dye-coupled film with Br^-.