Inhibitory Mechanism of A-type Oligomeric Proanthocyanidins from Abscising Litchi Fruits on Proinflammation Induced by Litchi Thaumatin-like Protein

Abstract

This study investigated the mechanism by which A-type oligomeric proanthocyanidins (A-OPC) from abscising litchi fruits inhibit proinflammation induced by litchi thaumatin-like protein (LcTLP). A-OPC were prepared by sequential ethanol extraction and purification by macroporous adsorption resin and preparative liquid chromatography. Structural analysis showed that A-OPC were mainly composed of proanthocyanidin A2, two A-type proanthocyanidin trimers and one A-type tetramer, with a purity of 88.69%. At 120 μg/mL concentration, A-OPC inhibited the secretion of nitric oxide (NO), interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) by 58.38%, 39.80% and 86.31% in RAW264.7 cells treated with LcTLP, respectively (P < 0.01). Western blot showed that 120 μg/mL A-OPC reduced the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and significantly decreased the phosphorylation levels of p65, inhibitor of NF-κB (IκBα), c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38. Therefore, A-OPC down-regulated the phosphorylation levels of downstream proteins in the nuclear transcription factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, thereby suppressing LcTLP-induced inflammatory response.

Keywords

• litchi fruit; a-type oligomeric proanthocyanidins; litchi thaumatin-like protein; anti-inflammatory mechanism