Abstract
We have previously discovered that heated honey but not unheated honey could induce the secretion of granulocyte-colony stimulating factor (G-CSF) in the MCE301 intestinal epithelial cells. The objective of this study was to identify compounds in honey that could contribute to this activity. We bought several kinds of commercial honey samples derived from different flowers, as well as corn syrup samples, in the markets of China and Japan, and heated them at 180 °C for 30 min. MCE301 cells were treated with the medium containing the samples, and G-CSF levels in the medium were measured by ELISA. By comparing their activities and sugar contents, we discovered that isomaltose was primarily implicated. The optimum heating conditions for isomaltose were at 180 °C for 60 min or at 200 °C for 15-30 min, and these time- and temperature-dependencies were similar to those of honey in our previous study. When heated isomaltose was partitioned by dialysis, the active ingredients were transferred into a high-molecular-weight fraction. By size-exclusion HPLC analysis, the average molecular weight of heated isomaltose was 790 kDa. When heated isomaltose was hydrolyzed by acids, glucose was subsequently produced. Maltose, sucrose, turanose, and trehalose did not exhibited any activity when heated at 180 °C for 60 min, indicating that the glucose groups with α(1 → 6)-binding in the isomaltose molecule play important roles in its activity when oxidatively polymerized by heat. The stimulating activity of heated isomaltose was inhibited by toll-like receptor 4 (TLR4) inhibitor, suggesting that heated isomaltose activates TLR4 to induce G-CSF. Since G-CSF is clinically used for cancer patients to accelerate their recovery from neutropenia following chemotherapy or accompanied with aplastic anemia, these findings indicate that honey which contains high level of isomaltose could improve immunosuppressive conditions when honey is heated, and that heated isomaltose might be of potential therapeutic use in patients with compromised immunity caused by chemotherapeutic agents.