Comprehensive investigation into the preventive and therapeutic efficacy and underlying mechanisms of phycocyanin in diabetic retinopathy in rats

To investigate the protective effects of phycocyanin (PC) on diabetic retinopathy (DR) in a rat model and explore its underlying mechanisms. Male Sprague-Dawley rats aged 6-8 weeks were used to establish a diabetes model through a high-fat and high-sugar diet followed by intraperitoneal injection of streptozotocin. The rats were randomly divided into the normal, model, and PC groups (n=9). The PC group received a daily oral gavage of 35 mg/kg PC, while the normal and model groups received an equal amount of drinking water. The animals were sacrificed at 8, 12, and 16 weeks after intervention to collect samples. General conditions, body weight, blood glucose levels, retinal morphology, expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and vascular endothelial growth factor (VEGF) proteins, and levels of interleukin-6 (IL-6) and tumor-necrosis factor-alpha (TNF-α) in serum were assessed. PC significantly improved the symptoms and signs of diabetic rats; alleviated polydipsia, polyphagia, polyuria, and weight loss; and reduced the incidence of diabetic cataracts. After intervention, the rats in the PC group showed significant improvements in body weight and fasting blood glucose levels compared with the model group (P<0.01). Hematoxylin-eosin staining of retinal sections revealed that PC inhibited retinal damage, mitigated the reduction of cell numbers in the inner and outer nuclear layers, and significantly restored retinal thickness at week 16 (P<0.01). Immunohistochemical staining showed that PC significantly reduced the overexpression of NF-κB and VEGF in the retina (P<0.05). Enzyme-linked immunosorbent assay results indicated that PC significantly decreased the serum levels of IL-6 and TNF-α (P<0.01). PC exerts protective effects against DR by mitigating inflammatory responses and modulating the expression of NF-κB and VEGF, suggesting its potential as a therapeutic agent for DR.