Autofluorescence of yeast Saccharomyces cerevisiae cells caused by glucose metabolism products and its methodological implications.

Autofluorescence is the natural fluorescence emitted by cellular compounds which have light emission properties. The main examples of these compounds, identified as an endogenous fluorophores, include aromatic amino acids, vitamins, coenzymes and electron acceptors. As many of them play a critical role in cell metabolism, changes in their content may provide important information on the physiological status of the cell. Nevertheless, the simultaneous occurrence of different endogenous fluorophores in cells makes it difficult to interpret the autofluorescence signal. Autofluorescence values may also be imposed on values obtained through exogenous fluorescent dyes. This study evaluates the origin and the methodological implications of autofluorescence observed in yeast cells. The results show that the level of autofluorescence may differ between yeast cells, which are a result of different concentrations of endogenous fluorophores, including tryptophan, pyridoxine and riboflavin. The study also shows an important influence of autofluorescence on the results obtained by methods based on external fluorescent dyes.

Macrocyclic triamine derived glucose analogues for 99m Tc(CO)3 labeling: synthesis and biological evaluation as potential tumor-imaging agents.

[99m Tc(CO)3 (H2 O)3 ]+ has attracted great attention among 99m Tc-labeling techniques, due to its ease of preparation, readily substituted water molecules of the precursor fac-[99m Tc(CO)3 (H2 O)3 ]+ by a variety of functional groups, small size and inertness. Bifunctional chelator based on a macrocyclic polyamine framework shows easy complexation with [99m Tc(CO)3 (H2 O)3 ]+ to produce stable complex. In this study, two novel 1, 5, 9-triazacyclododecane derivatives containing a glucose group (6 and 7) were successfully synthesized by reacting different glucose-azides with alkyne-[12]aneN3 via the so-called click chemistry and radiolabeled with [99m Tc(CO)3 (H2 O)3 ]+ to form 99m Tc(CO)3 -6 (C-1-substituted complex) and 99m Tc(CO)3 -7 (C-2-substituted complex) in high yields. The complexes were stable in vitro over 6 h when incubated in saline at room temperature and in mouse serum at 37 °C. The partition coefficient results showed that they were hydrophilic. The biodistribution studies in Kunming mice bearing S 180 tumor showed both complexes showed accumulation in the tumor. Between them, 99m Tc(CO)3 -7 had the advantages of much higher tumor uptake and tumor/muscle ratio. Compared with other reported 99m Tc-radiolabeled glucose derivatives, 99m Tc(CO)3 -7 also showed a higher tumor uptake and tumor/muscle ratio, suggesting it would be a potential candidate for further development as a tumor-imaging agent.