Pentosan Polysulfate Sodium Causes Diminished Function and Subtle Morphological Changes in Retina and RPE of Mice

**Background:** Pentosan polysulfate sodium (PPS) is an FDA-approved oral treatment for interstitial cystitis, but recent reports have linked long-term use to a distinctive maculopathy suggestive of primary RPE injury. The authors aimed to determine whether PPS exposure causes retinal or RPE damage in mice, potentially providing a model for the human condition.

**Methods:** Adult 129S2/SvPasCrl mice (10 per group, 5 males and 5 females) were fed PPS-supplemented chow at escalating doses (504 mg/kg/d for 4 months, 1 g/kg/d for 3 months, then 2 g/kg/d for 7 months) or standard chow. Retinal function was assessed monthly via scotopic electroretinography (ERG) with flash intensities from 0.001 to 10.000 cd·s/m². After 14 months, eyes were processed for histology: one eye for sagittal paraffin sections (H&E staining) and the contralateral for RPE flatmounts immunostained for ZO-1 and alpha-catenin. RPE cell morphology was analyzed using CellProfiler, and retinal layer thicknesses were measured in 100-µm-wide segments.

**Key Results:** After 10 months of PPS treatment, scotopic c-wave amplitudes were significantly reduced (untreated: 145 ± 7.24 µV vs. treated: 112 ± 5.97 µV; P = 0.0229). At 11 months, a-wave (untreated: −184 ± 11.0 µV vs. treated: −142 ± 6.63 µV; P = 0.0069) and b-wave (untreated: 568 ± 30.5 µV vs. treated: 441 ± 16.1 µV; P = 0.0032) amplitudes were also diminished. Over the entire study, PPS had a significant main effect on all wave amplitudes (a-waves: F(1,81)=20.35, P<0.0001; b-waves: F(1,81)=25.19, P<0.0001; c-waves: F(1,81)=3.01, P<0.0001). RPE flatmounts showed increased mean cell area (treated: 278.60 ± 6.03 µm² vs. untreated: 245.10 ± 2.05 µm²; P=0.0002), increased eccentricity (treated: 0.72740 ± 0.00292 vs. untreated: 0.71170 ± 0.00256; P=0.0016), decreased solidity (treated: 0.84620 ± 0.00301 vs. untreated: 0.86160 ± 0.00138; P=0.0005), and decreased extent (treated: 0.60000 ± 0.00395 vs. untreated: 0.62350 ± 0.00156; P=0.0001). Intracellular alpha-catenin immunostaining was increased in treated animals (treated: 45.2 ± 1.52 vs. untreated: 38.5 ± 2.31; P=0.0310). These RPE changes were more pronounced in central regions. Histology revealed reduced outer segment thickness in the inferior retina (at 750 µm inferior to optic nerve head: untreated: 14.2 ± 0.677 µm vs. treated: 11.5 ± 0.458 µm; P=0.0471), with main drug effects on outer segment (F(1,131)=8.681; P=0.0038), inner segment (F(1,128)=4.248; P=0.0413), and outer plexiform layer thickness (F(1,127)=4.159; P=0.0435). No significant cell loss was observed. Sex differences were noted in some RPE measures, with females showing greater effects in cell area and alpha-catenin signal.

**Clinical Implications:** This study provides direct experimental evidence that PPS causes progressive RPE and photoreceptor dysfunction in mice, mirroring the human maculopathy. The early involvement of the c-wave suggests primary RPE injury, followed by photoreceptor and bipolar cell dysfunction. The RPE morphological changes (polymegathism, eccentricity, alpha-catenin translocation) are consistent with cellular stress. Although the mouse model lacks a macula and uses higher doses than human therapy, it supports a causal relationship and offers a platform for mechanistic studies and potential therapeutic interventions. The findings underscore the need for ophthalmologic monitoring in patients on long-term PPS therapy.