Oral ellagic acid attenuated LPS-induced neuroinflammation in rat brain: MEK1 interaction and M2 microglial polarization

Abstract

Ellagic acid, the marker component of peels of Punica granatum L., is known traditionally to treat traumatic hemorrhage. In this study, the cellular mechanism underlying ellagic acid-induced anti-inflammation was investigated using lipopolysaccharides (LPSs) as a neuroinflammation inducer. Our in vitro data showed that LPS (1 μg/mL) consistently phosphorylated ERK and induced neuroinflammation, such as elevation in tumor necrosis factor-α (TNF-α) and nitric oxide production in treated BV-2 cells. Incubation of ellagic acid significantly inhibited LPS-induced ERK phosphorylation and subsequent neuroinflammation in treated BV-2 cells. Furthermore, our in vivo study of neuroinflammation employed an intranigral infusion of LPS that resulted in a time-dependent elevation in phosphorylated ERK levels in the infused substantia nigra (SN). Oral administration of ellagic acid (100 mg/kg) significantly attenuated LPS-induced ERK phosphorylation. A four-day treatment of ellagic acid did not alter LPS-induced ED-1 elevation but ameliorated LPS-induced reduction in CD206 and arginase-1 (two biomarkers of M2 microglia). A seven-day treatment of ellagic acid abolished LPS-induced increases in heme-oxygenase-1, cyclo-oxygenase 2, and α-synuclein trimer levels (a pathological hallmark) in the infused SN. At the same time, ellagic acid attenuated LPS-induced increases in active caspase 3 and receptor-interacting protein kinase-3 levels (respective biomarkers of apoptosis and necroptosis) as well as reduction in tyrosine hydroxylase–positive cells in the infused SN. In silico analysis showed that ellagic acid binds to the catalytic site of MEK1. Our data suggest that ellagic acid is capable of inhibiting MEK1–ERK signaling and then attenuated LPS-induced neuroinflammation, protein aggregation, and programmed cell deaths. Moreover, M2 microglial polarization is suggested as a novel antineuroinflammatory mechanism in the ellagic acid–induced neuroprotection.