Fig 2: Effect of IP-DHA on light-induced degeneration over time.a Full-field ERG responses of Abca4-/- mice 3 months after a single IP-DHA injection. ERG scotopic responses were recorded, and a-wave amplitudes were plotted as a function of light intensity. IP-DHA (25 mg/kg)-treated mice exposed to light showed an a-wave amplitude similar to that of DA control mice, whereas BSA-treated and untreated (NI) mice exposed to light did not recover amplitudes. The data are presented as the mean ± SEM from n = 5–6 mice. b a-wave amplitudes recorded at 2-log cd.s.m-2 did not change in each treatment over the 3-month period. The data are presented as the mean ± SEM from n = 5 mice. One-way ANOVA with Bonferroni’s multiple comparison posttest: ###p < 0.001, NI vs. DA; ***p < 0.001, IP-DHA25 mg/kg vs. BSA; IP-DHA vs. DA, nonsignificant.

Fig 3: Susceptibility of retinae from Abca4-/- mice to acute light-induced degeneration.a Representative hematoxylin/eosin/saffron (HES)-stained retinal sections from Abca4-/- mice after dark adaptation (DA) or bright light exposure (LE) for 1 or 2 h followed by darkness for 5 days. ONL outer nuclear layer, INL inner nuclear layer, GCL ganglion cell layer. b Quantification of photoreceptor loss measured as a ratio of outer and inner nuclear layer thickness (ONL/INL) under the conditions stated in a. The INL thickness did not change significantly with light exposure and was used as the internal reference. Light exposure for 2 h significantly decreased ONL thickness compared to the DA control condition and 1-h light exposure. The data are presented as a scatterplot, and red bars indicate the mean ± SEM from n = 30 ratios, ***p < 0.001 one-way ANOVA with Bonferroni’s posttest.

Fig 4: Comparative protective effects of IP-DHA, DHA ethyl ester, and EMX on light-induced retinal degeneration.a Dark-adapted (DA) 8–9-week-old Abca4-/- mice were treated by oral gavage with emixustat (EMX, 40 mg/kg, 24 h), IP-DHA (40 and 150 mg/kg, 6 h), or DHA ethyl ester (Et-ODHA 150 mg/kg, 6 h), pupils were dilated, and mice were exposed to light for 2 h. The mice were returned to the dark for 5 days before full-field ERG recordings. The a-wave amplitudes were recorded at 2-log cd.s/m2 light intensity for each treatment and statistically compared to the amplitude of mice treated with the vehicle (soybean oil). Data are expressed as the mean ± SEM. Three asterisk, one-way ANOVA with Bonferroni’s multicomparison test: p < 0.001, DA (n = 12), 40 mg/kg EMX (n = 11), 150 mg/kg IP-DHA (n = 11), 40 mg/kg IP-DHA (n = 3), 150 mg/kg Et-ODHA (n = 6) vs. soybean oil (oil, n = 18); ns nonsignificant. b Chemical structures of IP-DHA, EMX, and Et-ODHA.

Fig 5: Histological analysis of retinae after light-induced acute retinal degeneration.a HES staining of retinal sections from Abca4-/- mice that were dark-adapted (DA) or injected with BSA (BSA) or 25 mg/kg IP-DHA (IP-DHA 25) before light exposure. b IP-DHA treatment prevented the thinning of the outer nuclear layer (ONL), which contains photoreceptors, in untreated or BSA-treated mice. The data are presented as scatterplots, and horizontal bars indicate the mean ± SEM from n = 6 mice. One-way ANOVA with Bonferroni’s test: ###p < 0.001 vs. DA; ***p < 0.001 vs IP-DHA.