Cellular binding and uptake of fluorescent glucose analogs 2-NBDG and 6-NBDG occurs independent of membrane glucose transporters

• Published in: Biochimie Vol. 190; pp. 1 - 11
• Main Authors: Hamilton, Kathryn E., Bouwer, Miranda F., Louters, Larry L., Looyenga, Brendan D.
• Format: Journal Article
• Language: English
• Published: France Elsevier B.V 01.11.2021
• Subjects: 2-NBDG; 4-Chloro-7-nitrobenzofurazan - analogs & derivatives; 4-Chloro-7-nitrobenzofurazan - metabolism; 4-Chloro-7-nitrobenzofurazan - pharmacokinetics; 6-NBDG; Animals; Biological Transport; Cell Line; Deoxyglucose - analogs & derivatives; Deoxyglucose - metabolism; Deoxyglucose - pharmacokinetics; Fibroblasts - metabolism; Fluorescent analog; Fluorescent Dyes - metabolism; Fluorescent Dyes - pharmacokinetics; Glucosamine - analogs & derivatives; Glucosamine - metabolism; Glucosamine - pharmacokinetics; Glucose - analogs & derivatives; Glucose - metabolism; Glucose Transport Proteins, Facilitative - antagonists & inhibitors; Glucose Transport Proteins, Facilitative - genetics; Glucose Transport Proteins, Facilitative - metabolism; Glucose Transporter Type 1 - antagonists & inhibitors; Glucose Transporter Type 1 - genetics; Glucose Transporter Type 1 - metabolism; Glucose uptake; Glut1; Humans; Mice; PBS; 2-NBDG; DMSO; GLUT; Fluorescent analog; 6-NBDG; siRNA; SLC2A; DMEM; MFI; Glucose uptake; rcf; Glut1; RPMI-1640; SGLT; (footnote): 2-DG; DPBS
• ISSN: 0300-9084; 1638-6183
• DOI: 10.1016/j.biochi.2021.06.017

The classical methods for determining glucose uptake rates in living cells involve the use of isotopically labeled 2-deoxy-d-glucose or 3-O-methyl-d-glucose, which enter cells via well-characterized membrane transporters of the SLC2A and SLC5A families, respectively. These classical methods, however, are increasingly being displaced by high-throughput assays that utilize fluorescent analogs of glucose. Among the most commonly used of these analogs are 2-NBDG and 6-NBDG, which contain a bulky 7-nitro-2,1,3-benzoxadiazol-4-yl-amino moiety in place of a hydroxy group on d-glucose. This fluorescent group significantly alters both the size and shape of these molecules compared to glucose, calling into question whether they actually enter cells by the same transport mechanisms. In this study, we took advantage of the well-defined glucose uptake mechanism of L929 murine fibroblasts, which rely exclusively on the Glut1/Slc2a1 membrane transporter. We demonstrate that neither pharmacologic inhibition of Glut1 nor genetic manipulation of its expression has a significant impact on the binding or uptake of 2-NBDG or 6-NBDG by L929 cells, though both approaches significantly impact [3H]-2-deoxyglucose uptake rates. Together these data indicate that 2-NBDG and 6-NBDG can bind and enter mammalian cells by transporter-independent mechanisms, which calls into question their utility as an accurate proxy for glucose transport. •Glucose uptake rates are a key metabolic parameter for cell growth.•Fluorescent glucose analogs are commonly used to monitor glucose uptake.•Murine L929 fibroblasts import glucose exclusively via the Glut1 transporter.•Multiple methods of Glut1 inhibition fail to block fluorescent analog uptake.•Fluorescent glucose analogs enter cells by transporter-independent mechanisms.