Phloretin reduced the secretion of IL‐8 in retinal pigment epithelial cells suffering from mitochondrial dysfunction via activation of nuclear factor erythroid 2 related factor 2 (NFE2L2/Nrf2)

Abstract Purpose Phloretin is a natural polyphenol that is present e.g. in apple and pear trees. Previous research has demonstrated that phloretin has anti‐inflammatory properties. Inflammation and mitochondrial dysfunction play key roles in the development of age‐related macular degeneration, the most common cause of vision loss amongst the elderly in the developed countries. Here, we assessed the effects of phloretin in a model of mitochondrial damage‐induced inflammation in retinal pigment epithelial (RPE) cells. Methods ARPE‐19 cells were exposed to 25 µM antimycin A for 24 hr to induce mitochondrial dysfunction. Cells were pretreated with 100 µM phloretin for 1 hour and cell viability as well as the release of pro‐inflammatory interleukines (IL)‐6, IL‐8 and the vascular endothelial growth factor (VEGF) was studied. The effect of either high glucose or glucose‐free culture medium was assessed. ELISA measurements of phosphorylated mitogen‐activated protein kinases (MAPK), p38, JNK, and extracellular signal‐regulated protein kinase (ERK1/2) as well as of the cAMP response element binding protein (CREB) were determined alongside the DNA binding efficiency of nuclear factor kB (NF‐kB) subunit p65 and of NFE2L2. Effects on ERK1/2 phosphorylation and NFE2L2 DNA binding were confirmed using the MAPK kinase 1/2 (MEK1/2) inhibitor PD98059, the NFE2L2 activator sulforaphane, and specific NFE2L2 siRNA. Results Phloretin significantly reduced the levels of IL‐6, IL‐8, and VEGF in the presence and the absence of antimycin A, without affecting cellular viability. Higher levels or absence of glucose had no effect on the anti‐inflammatory activities of phloretin. Pathway analysis showed that phloretin‐activated ERK1/2 phosphorylation but this was not related to its anti‐inflammatory effects as preventing ERK1/2 phosphorylation using PD98059 decreased inflammation even further. Instead, siRNA experiments revealed that NFE2L2 was involved in phloretin’s ameliorating effect on IL‐8 secretion. Conclusions Phloretin is a strong anti‐inflammatory agent that is well‐tolerated by RPE cells suffering from mitochondrial dysfunction.