Visualization of nitric oxide in living cells by a copper-based fluorescent probe

Nitric oxide (NO) serves as a messenger for cellular signaling. To visualize NO in living cells, we synthesized a turn-on fluorescent probe for use in combination with microscopy. Unlike existing fluorescent sensors, the construct--a Cu(II) complex of a fluorescein modified with an appended metal-chelating ligand (FL)--directly and immediately images NO rather than a derivative reactive nitrogen species. Using spectroscopic and mass spectrometric methods, we established that the mechanism of the reaction responsible for the NO-induced fluorescence involves reduction of the complex to Cu(I) with release of the nitrosated ligand, which occurs irreversibly. We detected NO produced by both constitutive and inducible NO synthases (cNOS and iNOS, respectively) in live neurons and macrophages in a concentration- and time-dependent manner by using the Cu(II)-based imaging agent. Both the sensitivity to nanomolar concentrations of NO and the spatiotemporal information provided by this complex demonstrate its value for numerous biological applications.

Comparison of dyes for cataract surgery. Part 1: cytotoxicity to corneal endothelial cells in a rabbit model

PURPOSE

To investigate the corneal endothelial cytotoxicity of dyes for capsule staining in cataract surgery.

SETTING

Department of Ophthalmology and Institute of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.

METHODS

Cultured corneal endothelial cells of New Zealand white rabbits were exposed for 1 minute to 1 of the following dyes (various concentrations): indocyanine green (ICG), methylene blue (MB), gentian violet (GV), trypan blue (TB), and fluorescein sodium (FS). The degree of cell damage was determined by in vitro staining with TB and comparison with results in a control group. The effect of longer exposure (up to 10 minutes) to ICG 0.25% was also investigated. Structural changes in corneal endothelial cells after dye exposure were evaluated by light microscopy and transmission electron microscopy (TEM).

RESULTS

Indocyanine green 0.25%, MB 0.20%, GV 0.01%, TB 0.40%, and FS 10% did not induce significant damage to corneal endothelial cells. Significant cytotoxicity was observed with the following or higher dye concentrations: ICG 0.50%, MB 0.50%, and GV 0.10%. Exposure to ICG 0.25% for 1 to 10 minutes showed a trend toward cytotoxicity after 10 minutes. On TEM, corneal endothelial cells that had been exposed to ICG 0.50% showed remarkable organelle swelling and disruption, electron-dense granules, and cell lysis.

CONCLUSION

One minute of exposure to ICG 0.25%, MB 0.20%, GV 0.01%, TB 0.40%, and FS 10% appeared to be safe as determined by no cytotoxic effects on rabbit corneal endothelial cells in culture.

Coumarin/fluorescein-fused fluorescent dyes for rapidly monitoring mitochondrial pH changes in living cells

On base of the good optical properties of coumarin and fluorescein, we designed and synthesized two coumarin/fluorescein-fused fluorescent dyes (CF dyes), which enlarged the emission wavelength and increased the Stokes shift of fluorescein moiety. The corresponding optical properties of CF dyes were investigated in detail. CF dyes could easily introduce other groups to design different functional molecules. CF dyes also exhibited rapid and sensitive responses to pH values in the range of 4.0-7.4 through the characterization of absorption and fluorescence spectra in buffer solution. More importantly, CF ethyl ester dye (CFE dye) not only showed good cell membrane permeability and low cytotoxicity, but also had the ability to rapidly monitor mitochondrial pH changes in living cells.

Visible light induced photodegradation and phototoxicity of phloxine B and uranine

OBJECTIVE

To determine the visible light-induced photodegradation kinetics of two xanthene photosensitizers, phloxine B and uranine, in solution and on the surface of silica TLC plates, and to examine the phototoxicity of residues of degradation, which could provide valuable safety data on the two photosensitizers and other xanthene chemicals when applied in the environment.

METHODS

UV-Vis absorption during photodegradation was monitored with a Unico 2102 spectrophotometer. Organic content of samples was measured with a Shimadzu TOC 4100. Phototoxicity tests were carried out using Saccharomyces cerevisiae with the methods modified from Daniels.

RESULTS

When phloxine B and uranine degraded in solution, their apparent rate constant k was 0.0019 and 0.0027 min(-1), respectively. The total organic carbon (TOC) content decreased by approximately 50% during the 8 h irradiation period, which led to a gradual decrease in phototoxicity of the residues. The photodegradation of photosensitizers on the surface of silica TLC plates was much faster than that in the solution. The apparent rate constant k and the half life of phloxine B were 0.0073 min(-1) and 95 min, respectively.

CONCLUSION

Visible light can rapidly induce photodegradation of phloxine B and uranine. The phototoxicity of residues is also decreased. The environmental risk of applications of phloxine B and uranine is minimal.

Toxicity of organic fluorophores used in molecular imaging: literature review

Fluorophores are potentially useful for in vivo cancer diagnosis. Using relatively inexpensive and portable equipment, optical imaging with fluorophores permits real-time detection of cancer. However, fluorophores can be toxic and must be investigated before they can be administered safely to patients. A review of published literature on the toxicity of 19 widely used fluorophores was conducted by searching 26 comprehensive biomedical and chemical literature databases and analyzing the retrieved material. These fluorophores included Alexa Fluor 488 and 514, BODIPY FL, BODIPY R6G, Cy 5.5, Cy 7, cypate, fluorescein, indocyanine green, Oregon green, 8-phenyl BODIPY, rhodamine 110, rhodamine 6G, rhodamine X, rhodol, TAMRA, Texas red, and Tokyo green. Information regarding cytotoxicity, tissue toxicity, in vivo toxicity, and mutagenicity was included. Considerable toxicity-related information was available for the Food and Drug Administration (FDA)-approved compounds indocyanine green and fluorescein, but published information on many of the non-FDA-approved fluorophores was limited. The information located was encouraging because the amounts of fluorophore used in molecular imaging probes are typically much lower than the toxic doses described in the literature. Ultimately, the most effective and appropriate probes for use in patients will be determined by their fluorescent characteristics and the safety of the conjugates.