Nateglinide

Oral drug absorption involves drug permeation across the apical and basolateral membranes of enterocytes. Although transporters mediating the influx of anionic drugs in the apical membranes have been identified, transporters responsible for efflux in the basolateral membranes remain unclear. Monocarboxylate transporter 6 (MCT6/SLC16A5) has been reported to localize to the apical and basolateral membranes of human enterocytes and to transport organic anions such as bumetanide and nateglinide in the Xenopus oocyte expression system; however, its transport functions have not been elucidated in detail. In this study, we characterized the function of MCT6 expressed in HEK293T cells and explored fluorescent probes to more easily evaluate MCT6 function. The results illustrated that MCT6 interacts with CD147 to localize at the plasma membrane. When the uptake of various fluorescein derivatives was examined in NaCl-free uptake buffer (pH 5.5), the uptake of 5-carboxyfluorescein (5-CF) was significantly greater in MCT6 and CD147-expressing cells. MCT6-mediated 5-CF uptake was saturable with a K_m of 1.07 mM and inhibited by several substrates/inhibitors of organic anion transporters and extracellular Cl ion with an IC₅₀ of 53.7 mM. These results suggest that MCT6 is a chloride-sensitive organic anion transporter that can be characterized using 5-CF as a fluorescent probe.

A rapid and simple method to measure oral hypoglycemic agents is essential in the evaluation of a patient with spontaneous hypoglycemia. As a result, a robust high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the qualitative detection of first-generation sulfonylureas (e.g., chlorpropamide, tolazamide, and tolbutamide), second-generation sulfonylureas (e.g., glimepiride, glipizide, and glyburide), meglitinides (e.g., repaglinide, nateglinide), and thiazolidinediones (e.g., rosiglitazone and pioglitazone). HPLC involved a C8 column and MS/MS was used in electrospray ionization (ESI) positive mode. Identification of all compounds was made using various multiple-reaction monitoring (MRMs). Isotopic labeled chlorpropamide-d4, glimepiride-d5, glyburide-d11, nateglinide-d5, repaglinide-ethyl-d5, rosiglitazone-d3, and zomepirac were used as the internal standards. The cutoffs for each drug were as follows: chlorpropamide 100 ng/mL, tolazamide 50 ng/mL, tolbutamide 20 ng/mL, glimepiride 20 ng/mL, glipizide 5 ng/mL, glyburide 5 ng/mL, repaglinide 5 ng/mL, rosiglitazone 20 ng/mL, pioglitazone 20 ng/mL, and nateglinide 5 ng/mL.