Protective effects and possible mechanisms of ergothioneine and hispidin against methylglyoxal-induced injuries in rat pheochromocytoma cells

Diabetic encephalopathy (DE) is often a complication in patients with Alzheimer's disease due to high blood sugar induced by diabetic mellitus. Ergothioneine (EGT) and hispidin (HIP) are antioxidants present in Phellinus linteus. Methylglyoxal (MGO), a toxic precursor of advanced glycated end products (AGEs), is responsible for protein glycation. We investigated whether a combination EGT and HIP (EGT + HIP) protects against MGO-induced neuronal cell damage. Rat pheochromocytoma (PC12) cells were preincubated with EGT (2 μM), HIP (2 μM), or EGT + HIP, then challenged with MGO under high-glucose condition (30 μM MGO + 30 mM glucose; GLU + MGO) for 24-96 h. GLU + MGO markedly increased protein carbonyls and reactive oxygen species in PC12 cells; both of these levels were strongly reduced by EGT or HIP with effects comparable to those of 100 nM aminoguanidine (an AGE inhibitor) but stronger than those of 10 μM epalrestat (an aldose reductase inhibitor). GLU + MGO significantly increased the levels of AGE and AGE receptor (RAGE) protein expression of nuclear factor kappa-B (NF-κB) in the cytosol, but treatment with EGT, HIP, or EGT + HIP significantly attenuated these levels. These results suggest that EGT and HIP protect against hyperglycemic damage in PC12 cells by inhibiting the NF-κB transcription pathway through antioxidant activities.