Reduction of thiazine dyes by bovine pulmonary arterial endothelial cells in culture

Abstract

The uptake of methylene blue (MB), and toluidine blue O (TBO) by bovine pulmonary arterial endothelial cells grown on microcarrier beads was detected as a decrease in the concentration of dye in the medium after these thiazine dyes were added to the medium surrounding the cells. Because the reduced forms of these dyes are much more lipophilic than the oxidized forms, we considered the possibility that reduction of the dyes at the cell surface might have preceded the uptake by the cells. Therefore, we studied the ability of the cells to reduce a toluidine blue O-polyacrylamide polymer (TBOP), which was too large to enter the cells in either the oxidized or reduced form. The TBO moieties of the polymer were reduced by the cells, indicating that the dyes did not have to enter the cells to be reduced and that reduction can occur at, or near, the cell surface. The rate of TBOP reduction was about the same as the rate of uptake of the monomeric dyes, indicating that the cell surface reduction mechanism had a sufficient capacity to account for the monomer uptake by the cells. We also found that ferricyanide ion, which also did not permeate the cells, was reduced by the cells and that external ferricyanide inhibited the monomeric MB uptake. Thus the results with ferricyanide were also consistent with the concept that the monomeric thiazine dyes are reduced at the cell surface before the more lipophilic reduced forms are taken up by the endothelial cells.

Behavioral, Physiological and Biochemical Hormetic Responses to the Autoxidizable Dye Methylene Blue

“…In its oxidized form, MB is blue in color and readily reduced by many living cells [14]. In order for MB to enter the cytosol, it is reduced at the exofacial cell surface into its colorless lipophilic form, leuko MB (MBH 2 ) [15]. Once inside the cell, this reduced MBH 2 can be re-oxidized to MB, which is trapped in the cell [16].…”

Encapsulation of methylene blue in polyacrylamide nanoparticle platforms protects its photodynamic effectiveness

“…However, the clinical use of MB has been hampered by its propensity for rapid chemical alteration when systemically applied: MB in the biological environment is usually converted by accepting electrons from NADH/NADPH, and unfortunately, the formed colorless leukomethylene blue (LMB) has negligible photodynamic activity [11][12][13]. Recent studies suggested the presence of a transmembrane thiazine dye reductase at the cell surface as the initial factor for MB reduction [14][15][16]. Once within the cells, MB also can be reduced via NADH/NADPH dehydrogenases.…”

Quantifying mitochondrial and plasma membrane potentials in intact pulmonary arterial endothelial cells based on extracellular disposition of rhodamine dyes

“…In such cases, inhibitors are used to provide discriminating data relevant to these processes, and kinetic modeling is used to interpret such data and obtain values for kinetic parameters descriptive of the individual processes involved. Using this overall strategy, we have studied the impact of pulmonary endothelial cells on a variety of redox-active and other substances (4,12,13,38,40,41). The studies have revealed the wide range of pulmonary endothelial redox enzymes and other processes capable of influencing the metabolism, redox status, and disposition of compounds carried in the blood.…”