Sensitive Fluorescence Probe with Long Analytical Wavelengths for γ-Glutamyl Transpeptidase Detection in Human Serum and Living Cells

A new sensitive fluorescent probe with long analytical wavelengths for gamma-glutamyl transpeptidase (GGT) assay has been developed by incorporating the gamma-glutamyl group as a recognition unit into the fluorophore of cresyl violet (CV). The detection mechanism is based on the GGT-catalyzed cleavage of the gamma-glutamyl group, followed by the release of CV, which leads to a distinct color change from light yellow to pink and a large fluorescence enhancement at 615 nm (lambda(ex) = 585 nm). Under the optimized conditions, the fluorescence intensity of the probe is directly proportional to the activity of GGT in the range of 1-50 U/L with a detection limit of 5.6 mU/L. By virtue of its high sensitivity and long analytical wavelengths, the probe has been used to directly determine GGT in human serum samples from both healthy people and liver cancer patients, and the obtained results accord well with those acquired by commercial GGT fluorometric assay kit. The probe has also been employed to image endogenous GGT in living cells. Notably, with our probe the expression level of GGT in HepG2 cells under the action of sodium butyrate (an anticancer drug) was studied by fluorescence confocal microscopy, revealing that sodium butyrate can induce the upregulation of GGT in HepG2 cells in a dose- and time-dependent manner. This behavior of sodium butyrate has further been confirmed by lysate assay and inhibitor experiment. The proposed probe is rather simple and may find a wide use in the determination of GGT in clinical and biological samples.