Q&A Report: In Vivo Modeling of Immune-mediated Optic Neuropathies

Oliver W. Gramlich, PhD
Research Assistant Professor
Ophthalmology and Visual Sciences
The University of Iowa

We think this is because of the timing when we recorded the VEP, which was 21 days after injection of the disease-specific antibodies. We probably would see a more pronounced delay in latency after a longer time.

We used a nonspecific antibody, 2B4, as a comparator and found a certain degree of visual impairment 4 days after injection. However, recovery was much faster with a higher magnitude when compared to injection of disease-specific antibodies. More recent OCT data show significant thinning in animals having received disease specific antibody injections when compared to 2B4.

We did not test 8-18-C5. Some preliminary tissue array experiments show binding of the human MOG serum derived antibodies to rodent tissue. However, confirmatory experiments are still pending.

Long Evans rats are complement-competent animals of which changes in visual function and structure (visual acuity, OCT, and electrophysiology) can be measured. In addition, the animal’s size is ideal for performing surgeries to access the optic nerve.

We used Advaita’s iPathwayGuide software for our RNA-seq analysis to identify potentially targetable pathways which includes literature database searches. One hit as a potential modulator of ABCA1 was gentisic acid.

50mg/kg once per week.

The optimal dosage of gentisic acid was determined based on preliminary in vitro and in vivo experiments and based on literature research.

Gentisic acid treatment has potentially pleiotropic effects that affect cholesterol synthesis in the retina and cause increased myelin debris clearance after demyelinating events. Furthermore, it has been reported that Gentisic acid directly interferes with inflammatory pathways and most likely acts as a Cyclooxygenase inhibitor.

We did not conduct a pharmacokinetic profiling; however, the literature indicates that gentisic acid is able to pass the Blood-Brain/Retina barrier.

In terms of drug testing related to vision, Yes! OCT, VEP and visual acuity readouts have been used as secondary readouts in clinical studies for testing of new MS drugs. Implementation of these visual systems biomarkers in preclinical settings significantly increases the scientific rigor due to their highly translational value. However, other confirmatory outcome measurements should also be considered.

Our RT-PCR results indicate that PLP and MYRF expression is significantly increased in gentisic acid-treated brain organoids. Thus, it is conceivable that we have enhanced myelination.

Generally speaking, the flash VEP signal highly depends on the retinal input, whereas the pattern VEP signal recapitulates the electrical activity of the visual pathway, driven by foveal vision. The reason why changes in the pattern VEP in our experiments are so small may be because rodents don’t have a fovea and significant changes in latency may only be evident after massive demyelinating events.

Luxol Fast Blue combined with standard H&E.

There is some evidence in the current literature that high cholesterol levels in combination with hypertension may increase the risk for optic neuropathies.