lactisole and trichlorosucrose

Capsaicin causes a burning or spicy sensation when this vanilloid compound comes in contact with trigeminal neurons of the tongue. This compound has low solubility in water, which presents difficulties in examining the psychophysical properties of capsaicin by standard aqueous chemosensory tests. This report describes a new approach that utilizes edible strips for delivering precise amounts of capsaicin to the human oral cavity for examining threshold and suprathreshold amounts of this irritant. When incorporated into pullulan-based edible strips, recognition thresholds for capsaicin occurred over a narrow range, with a mean value near 1 nmol. When incorporated into edible strips at suprathreshold amounts, capsaicin yielded robust intensity values that were readily measured in our subject population. Maximal capsaicin intensity was observed 20 s after strips dissolved on the tongue surface, and then decreased in intensity. Suprathreshold studies showed that complete blockage of nasal airflow diminished capsaicin perception in the oral cavity. Oral rinses with vanillin-linoleic acid emulsions decreased mean intensity values for capsaicin by approximately 75%, but only modestly affected recognition threshold values. Also, oral rinses with isointense amounts of aqueous sucrose and sucralose solutions decreased mean intensity values for capsaicin by approximately 50%. In addition, this decrease in capsaicin intensity following an oral rinse with sucrose was partially reversed by the sweet taste inhibitor lactisole. These results suggest that blockage of nasal airflow, vanillin, sucrose, and sucralose modulate capsaicin perception in the human oral cavity. The results further suggest a chemosensory link between receptor cells that detect sweet taste stimuli and trigeminal neurons that detect capsaicin.

Topics: Administration, Oral; Adult; Benzaldehydes; Benzene Derivatives; Capsaicin; Dose-Response Relationship, Drug; Female; Humans; Linoleic Acid; Male; Mouth; Mouthwashes; Recognition, Psychology; Sucrose; Taste; Taste Perception; Taste Threshold; Young Adult

Glucose activates the glucose-sensing receptor T1R3 and facilitates its own metabolism in pancreatic β-cells. An inhibitor of this receptor would be helpful in elucidating the physiological function of the glucose-sensing receptor. The present study was conducted to examine whether or not lactisole can be used as an inhibitor of the glucose-sensing receptor. In MIN6 cells, in a dose-dependent manner, lactisole inhibited insulin secretion induced by sweeteners, acesulfame-K, sucralose and glycyrrhizin. The IC50 was ∼4 mmol/l. Lactisole attenuated the elevation of cytoplasmic Ca2+ concentration ([Ca2+]c) evoked by sucralose and acesulfame-K but did not affect the elevation of intracellular cAMP concentration ([cAMP]c) induced by these sweeteners. Lactisole also inhibited the action of glucose in MIN6 cells. Thus, lactisole significantly reduced elevations of intracellular [NADH] and intracellular [ATP] induced by glucose, and also inhibited glucose-induced insulin secretion. To further examine the effect of lactisole on T1R3, we prepared HEK293 cells stably expressing mouse T1R3. In these cells, sucralose elevated both [Ca2+]c and [cAMP]c. Lactisole attenuated the sucralose-induced increase in [Ca2+]c but did not affect the elevation of [cAMP]c. Finally, lactisole inhibited insulin secretion induced by a high concentration of glucose in mouse islets. These results indicate that the mouse glucose-sensing receptor was inhibited by lactisole. Lactisole may be useful in assessing the role of the glucose-sensing receptor in mouse pancreatic β-cells.

Topics: Animals; Benzene Derivatives; Calcium; Cell Line; Cyclic AMP; Glucose; Glycyrrhizic Acid; HEK293 Cells; Humans; Insulin; Insulin Secretion; Insulin-Secreting Cells; Mice; Receptors, G-Protein-Coupled; Sucrose; Sweetening Agents; Thiazines

Sweet taste receptor regulates GLP-1 secretion in enteroendocrine L-cells. We investigated the signaling system activated by this receptor using Hutu-80 cells. We stimulated them with sucralose, saccharin, acesulfame K and glycyrrhizin. These sweeteners stimulated GLP-1 secretion, which was attenuated by lactisole. All these sweeteners elevated cytoplasmic cyclic AMP ([cAMP]c) whereas only sucralose and saccharin induced a monophasic increase in cytoplasmic Ca(2+) ([Ca(2+)]c). Removal of extracellular calcium or sodium and addition of a Gq/11 inhibitor greatly reduced the [Ca(2+)]c responses to two sweeteners. In contrast, acesulfame K induced rapid and sustained reduction of [Ca(2+)]c. In addition, glycyrrhizin first reduced [Ca(2+)]c which was followed by an elevation of [Ca(2+)]c. Reductions of [Ca(2+)]c induced by acesulfame K and glycyrrhizin were attenuated by a calmodulin inhibitor or by knockdown of the plasma membrane calcium pump. These results indicate that various sweet molecules act as biased agonists and evoke strikingly different patterns of intracellular signals.

Topics: Benzene Derivatives; Calcium; Calmodulin; Cell Line, Tumor; Cyclic AMP; Duodenum; Enzyme Inhibitors; Gene Expression Regulation; Glucagon-Like Peptide 1; Glycyrrhizic Acid; Guanine Nucleotide Exchange Factors; Humans; Plasma Membrane Calcium-Transporting ATPases; Receptors, G-Protein-Coupled; RNA, Small Interfering; Saccharin; Signal Transduction; Sucrose; Sweetening Agents; Thiazines