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Uptake of a fluorescent L-glucose derivative 2-NBDLG into three-dimensionally accumulating insulinoma cells in a phloretin-sensitive manner.

Human cell (2015-11-11)
Ayako Sasaki, Katsuhiro Nagatomo, Koki Ono, Toshihiro Yamamoto, Yuji Otsuka, Tadashi Teshima, Katsuya Yamada
ABSTRACT

Of two stereoisomers of glucose, only D- and not L-glucose is abundantly found in nature, being utilized as an essential fuel by most organisms. The uptake of D-glucose into mammalian cells occurs through glucose transporters such as GLUTs, and this process has been effectively monitored by a fluorescent D-glucose derivative 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG) at the single cell level. However, since fluorescence is an arbitrary measure, we have developed a fluorescent analog of L-glucose 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-L-glucose (2-NBDLG), as a negative control substrate for more accurately identifying the stereoselectivity of the uptake. Interestingly, a small portion of mouse insulinoma cells MIN6 abundantly took up 2-NBDLG at a late culture stage (≳ 10 days in vitro, DIV) when multi-cellular spheroids exhibiting heterogeneous nuclei were formed, whereas no such uptake was detected at an early culture stage (≲ 6 DIV). The 2-NBDLG uptake was persistently observed in the presence of a GLUT inhibitor cytochalasin B. Neither D- nor L-glucose in 50 mM abolished the uptake. No significant inhibition was detected by inactivating sodium/glucose cotransporters (SGLTs) with Na(+)-free condition. To our surprise, the 2-NBDLG uptake was totally inhibited by phloretin, a broad spectrum inhibitor against transporters/channels including GLUTs and aquaporins. From these, a question might be raised if non-GLUT/non-SGLT pathways participate in the 2-NBDLG uptake into spheroid-forming MIN6 insulinoma. It might also be worthwhile investigating whether 2-NBDLG can be used as a functional probe for detecting cancer, since the nuclear heterogeneity is among critical features of malignancy.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Dulbecco′s Modified Eagle′s Medium - high glucose, With 4500 mg/L glucose and L-glutamine, without sodium bicarbonate, powder, suitable for cell culture
Sigma-Aldrich
Poly-L-lysine hydrobromide, mol wt 70,000-150,000, lyophilized powder, γ-irradiated, BioXtra, suitable for cell culture
Sigma-Aldrich
2-Deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose, ≥97% (HPLC)
Sigma-Aldrich
1,2-Dilinoleoyl-3-palmitoyl-rac-glycerol, ≥95% (TLC), liquid