Protective effects of myricetin and related flavonols against A2E and light mediated-cell death in bovine retinal primary cell culture

The present study was performed to investigate the effect of flavonols, namely myricetin and structurally related quercetin and kaempferol against A2E and blue light-induced photoreceptors death in primary retinal cell cultures. Primary retinal cell cultures were prepared from bovine retinas. Fourteen-day-old cultures were pretreated with different concentrations of myricetin, quercetin, kaempferol (1–40 μM) for 24 h, then treated with 30 μM of A2E or exposed to blue-actinic light for 20 h. Green nucleic acid stain assay was used to evaluate cell death. Photoreceptor and bipolar cells were immunolabeled with specific antibodies and were counted using automated microscope imaging and image-based cell counting software. Twenty hours exposure to blue light induced ∼75% death of photoreceptors in bovine retinal cell cultures. Myricetin protected 100% of photoreceptors against blue-light-mediated damage with an EC50 of 9 ± 0.7 μM. Quercetin resulted in a maximum of 15% protection against light damage, and kaempferol was inactive. A2E induced photoreceptor and bipolar cell death in a concentration-dependent manner with EC50 of 25 μM for photoreceptors and 31 μM for bipolar cells. Myricetin, quercetin and kaempferol protected against A2E-induced photoreceptors and bipolar cells death with EC50 values of 2 ± 0.3 μM, 2 ± 0.3 μM, 5 ± 0.09 μM and 0.8 ± 0.07 μM, 0.44 ± 0.06 μM, 1 ± 0.4 μM, respectively. Caspase-3 inhibitor (Z-DEVD-fmk) protected 42% photoreceptors and 57% bipolar cells from A2E toxicity. In contrast, this inhibitor had no effect against light-induced photoreceptor damage. Despite the poor activity of quercetin and the inactivity of kaempferol against blue light, myricetin, quercetin and kaempferol exhibited approximately 100% protection against A2E toxicity. This suggests that light- and A2E-induced cell deaths are mediated through different pathways. These results suggest that myricetin functions as potent and effective neuroprotective agent for photoreceptor cells against A2E and light damage.