Kokumi substances, enhancers of basic tastes, induce responses in calcium-sensing receptor expressing taste cells.

Recently, we reported that calcium-sensing receptor (CaSR) is a receptor for kokumi substances, which enhance the intensities of salty, sweet and umami tastes. Furthermore, we found that several γ-glutamyl peptides, which are CaSR agonists, are kokumi substances. In this study, we elucidated the receptor cells for kokumi substances, and their physiological properties. For this purpose, we used Calcium Green-1 loaded mouse taste cells in lingual tissue slices and confocal microscopy. Kokumi substances, applied focally around taste pores, induced an increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in a subset of taste cells. These responses were inhibited by pretreatment with the CaSR inhibitor, NPS2143. However, the kokumi substance-induced responses did not require extracellular Ca(2+). CaSR-expressing taste cells are a different subset of cells from the T1R3-expressing umami or sweet taste receptor cells. These observations indicate that CaSR-expressing taste cells are the primary detectors of kokumi substances, and that they are an independent population from the influenced basic taste receptor cells, at least in the case of sweet and umami.

Nateglinide stimulates glucagon-like peptide-1 release by human intestinal L cells via a K(ATP) channel-independent mechanism.

A reduced incretin effect is one of the well-known characteristics of patients with type 2 diabetes, and impaired release of glucagon-like peptide-1 (GLP-1) has been reported to be at least partly involved. In this study, we investigated the effect of nateglinide on GLP-1 release in vivo and in vitro. The GLP-1 level in the portal blood at 20 min after oral administration of nateglinide to Wistar rats was about twice that in vehicle-treated rats. To clarify whether this effect of nateglinide was related to direct stimulation of intestinal cells, in vitro studies were performed using human intestinal L cells (NCI-H716). Nateglinide stimulated GLP-1 release in a concentration-dependent manner from 500 µM, along with transient elevation of the intracellular calcium level. However, diazoxide, nitrendipine, and dantrolene did not block this effect of nateglinide. In addition, the major metabolite of nateglinide, tolbutamide, and mitiglinide, all of which augment insulin secretion by the pancreatic islets, had no effect on GLP-1 release by this cell line. On the other hand, capsazepine significantly inhibited the promotion of GLP-1 release by nateglinide in a concentration-dependent manner. These findings indicate that nateglinide directly stimulates GLP-1 release by intestinal L cells in a K(ATP) channel-independent manner. A novel target of nateglinide may be involved in increasing intracellular calcium to stimulate GLP-1 release, e.g., the transient receptor potential channels. Taken together, the present findings indicate that promotion of GLP-1 release from intestinal L cells may be another important mechanism by which nateglinide restores early-phase insulin secretion and regulates postprandial glucose metabolism.

Chitosan-interferon-ß gene complex powder for inhalation treatment of lung metastasis in mice.

We prepared gene powders with chitosan as a non-viral vector and mannitol as a dry powder carrier to compare their gene expression and therapeutic efficacy to intravenous or intratracheal gene solutions using mice burdened with pulmonary metastasis prepared by injecting CT26 cells. The expression of a luciferase expression plasmid driven by the cytomegalovirus promoter (pCMV-Luc) and plasmid DNA encoding farnesylated enhanced green fluorescent protein (pEGFP-F) suggested that the genes expressed in both normal and tumorous tissues and the intratracheal powder resulted in higher expression than the intravenous or intratracheal solution. The intravenous and intratracheal solutions and the intratracheal powder of pCMV-Muß encoding murine interferon-ß were administered the day after the inoculation of mice with CT26 cells. Lung weight and the number of pulmonary nodules at day 21 were significantly suppressed by the three formulations at a dose of 10 µg (N/P = 5). Reducing the dose to 1 µg resulted in a loss of effect by the intravenous solution; however, the intratracheal formulations, especially the powder, were still effective. The intratracheal powder of pCMV-Muß at a dose of 1 µg administered on day 1 significantly extended mean survival time compared to the untreated control. These findings showed that therapeutic gene powders are promising for gene therapy to treat lung cancer or metastasis.