Indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme in the kynurenine pathway (KP) of tryptophan catabolism, was recently established as one of the potential players involved in the pathogenesis of Alzheimer's disease (AD). Coptisine is a main pharmacological active constituent of the traditional Chinese medicinal prescription Oren-gedoku-to (OGT) which has therapeutic potential for the treatment of AD. Our recent studies have demonstrated that OGT significantly inhibited recombinant human IDO activity, which shed light on the possible mechanism of OGT's action on AD. Here, we characterized the effects of coptisine in an AD mouse model on the basis of its IDO inhibitory ability. Coptisine was found to be an efficient uncompetitive IDO inhibitor with a Ki value of 5.8 μM and an IC50 value of 6.3 μM. In AβPP/PS1 transgenic mice, oral administration of coptisine inhibited IDO in the blood and decreased the activation of microglia and astrocytes, consequently prevented neuron loss, reduced amyloid plaque formation, and ameliorated impaired cognition. Neuronal pheochromocytoma (PC12) cells induced with amyloid-β peptide 1-42 and interferon-γ showed reduction of cell viability and enhancement of IDO activity, while coptisine treatment increased cell viability based on its reversal effect on the enhanced activity of IDO. In conclusion, our present findings provide further evidence supporting the critical links between IDO, KP, and AD, and demonstrate coptisine, a novel IDO inhibitor, as a potential new class of drugs for AD treatment.

BackgroundmiR-126 plays an important role in the proliferation, invasion, migration, and chemotherapeutics resistance in cancer. Epigallocatechin-3-gallate (EGCG), as the major polyphenolic constituent present in green tea, is a promising anticancer agent. However, the role of miR-126 in EGCG anticancer remains unclear. Here, we investigated the effects of miR-126 and EGCG on cell viability, apoptosis, cell cycle distribution of osteosarcoma cells and the sensitization of miR-126 on osteosarcoma cells to EGCG.MethodsThe cell viability, apoptosis and cycle distribution were analyzed using MTT assay and flow cytometry.ResultsOur results showed that EGCG (0.025, 0.05, 0.1, 0.2 g/L) suppresses proliferation of osteosarcoma MG63 and U2OS cells in a concentration-dependent and time-dependent manner and the inhibitory effects of 0.05 g/L EGCG on U2OS cells were roughly equivalent to 20 μM cisplatin (DDP); miR-126 could promote apoptosis and inhibit proliferation in U2OS cells but without significant effects on cell cycle G1 phase arrest; EGCG suppressed proliferation of U2OS cells through induction of cell cycle G1 arrest and apoptotic death; overexpression of miR-126 enhanced the inhibitory effects of EGCG on proliferation in U2OS cells via promotion of apoptosis.ConclusionsOur results demonstrate that enhanced expression of miR-126 increased the sensitivity of osteosarcoma cells to EGCG through induction of apoptosis.

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