Ixeris dentata-induced regulation of amylase synthesis and secretion in glucose-treated human salivary gland cells

The endoplasmic reticulum (ER) is an organelle which controls synthesis of secretory and membrane proteins. Alterations in protein folding capacity, leading to ER stress, can be observed in patients with diabetes and related diseases such as xerostomia. The objectives of this study were to investigate the effects of Ixeris dentata (IXD) extract, which has been used for diabetes treatment, and compounds purified from IXD, 8-epidesacylcynaropicrin-3-O-beta-glucopyranoside (ID-57D), on amylase synthesis and secretion in human salivary gland (HSG) cells exposed to a high concentration of glucose. A high concentration of glucose in the experimental medium of cultured cells can model diabetes in vitro. IXD extracts and ID-57D increased oxidative folding-associated protein expression, including p-IRE-1α, PDI and ERO-1α, with the enhanced oxidative folding pattern seen in HSG cells transiently exposed to a high concentration of glucose. Moreover, the treatments reduced the ER stress response, such as the expression of GRP78, maintaining amylase synthesis and secretion in chronically glucose-exposed HSG cells. This study suggests the potential therapeutic value of IXD extract for the treatment of diabetes or its complications such as xerostomia.