Rod bipolar cell dysfunction in mice treated with cyclophosphamide and doxorubicin

Abstract

Purpose : Chemotherapy-related neurotoxicity (CRNT) poses a major public health challenge to cancer survivors. The retina, being an outpost of the brain, may be sensitive to pathophysiological mechanisms of CRNT. Preliminary clinical studies, including those from our lab, support this hypothesis. Here, we aimed to develop a pre-clinical animal of CRNT to begin exploring underlying pathophysiological mechanisms and supporting translational research.

Methods : 10-week old female C57BL/6J mice were treated with four weekly intravenous injections of either chemotherapy (CTX+ group; n=7) or 0.9% physiologic saline (CTX- group; n=5). CTX+ mice received cyclophosphamide (50 mg/kg) and doxorubicin (2 mg/kg). Retinal structure and function was assessed prior to and following treatment. Optical coherence tomography (OCT) was used to measure combined retinal nerve fiber layer, ganglion cell layer, and inner plexiform layer thickness in both eyes; thickness measurements were performed by two separate expert graders, and measurement disagreement was resolved by a third expert grader. Electroretinography (ERG) was used to measure photoreceptor (a-wave) and bipolar cell (b-wave) function; left eye ERG was recorded under scotopic conditions with a single 5ms white flash stimulus presented at a flash intensity range from -3.6 to 2.1 log cd/m² across 10 uniform steps. ERG analyses were performed using custom MATLAB scripts. Independent-sample t-tests were used to assess between-group changes in OCT and ERG parameters.

Results : OCT measurements from 14 CTX+ eyes and 10 CTX- eyes revealed significant retinal thinning (7.46 um) in CTX+ relative to CTX- mice (t(10)=3.68, p=.0043). Reproducible ERG waveforms were obtained from 6 CTX+ mice and 5 CTX- mice. Both groups showed no change in a-wave amplitude. CTX+ mice showed reduced b-wave amplitudes post-treatment at lower stimulus intensities (<-1.78 log cd/m²) relative to CTX- mice (t(9)=2.22, p=.054).

Conclusions : Our preliminary results demonstrate chemotherapy-related changes in retinal structure and function. Reduced b-wave amplitudes at lower stimulus intensities are suggestive of rod bipolar cell dysfunction in CTX+ mice. Further work is needed to uncover the pathophysiological mechanisms of these findings and their relationship with CRNT.

This is a 2020 ARVO Annual Meeting abstract.