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Mitochondrial effects of triarylmethane dyes
A J Kowaltowski1, J Turin, G L Indig
1Departamento de Patologia Clínica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, SP, Brazil.
Abstract:
The mitochondrial effects of submicromolar concentrations of six triarylmethane dyes, with potential applications in antioncotic photodynamic therapy, were studied. All dyes promoted an inhibition of glutamate or succinate-supported respiration in uncoupled mitochondria, in a manner stimulated photodynamically. No inhibition of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) supported respiration was observed, indicating that these dyes do not affect mitochondrial complex IV. When mitochondria were energized with TMPD in the absence of an uncoupler, treatment with victoria blue R, B, or BO, promoted a dissipation of mitochondrial membrane potential and increase of respiratory rates, compatible with mitochondrial uncoupling. This effect was observed even in the dark, and was not prevented by EGTA, Mg2+ or cyclosporin A, suggesting that it is promoted by a direct effect of the dye on inner mitochondrial membrane permeability to protons. Indeed, victoria blue R, B, and BO promoted swelling of valinomycin-treated mitochondria incubated in a hyposmotic K+-acetate-based medium, confirming that these dyes act as classic protonophores such as FCCP. On the other hand, ethyl violet, crystal violet, and malachite green promoted a dissipation of mitochondrial membrane potential, accompanied by mitochondrial swelling, which was prevented by EGTA, Mg2+, and cyclosporin A, demonstrating that these drugs induce mitochondrial permeability transition. This mitochondrial permeabilization was followed by respiratory inhibition, attributable to cytochrome c release, and was caused by the oxidation of NAD(P)H promoted by these drugs.
Insights
Triarylmethane dyes impact mitochondrial respiration and membrane potential. Some dyes act as protonophores, while others induce permeability transition, affecting cell viability.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Triarylmethane dyes are investigated for antioncotic photodynamic therapy.
- Mitochondria are key targets for cancer treatment due to their role in cellular energy and apoptosis.
Purpose of the Study:
- To investigate the mitochondrial effects of six triarylmethane dyes at submicromolar concentrations.
- To differentiate the mechanisms by which these dyes affect mitochondrial function, specifically respiration and membrane potential.
Main Methods:
- Studied the effects of dyes on glutamate, succinate, and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) supported mitochondrial respiration.
- Assessed mitochondrial membrane potential dissipation and swelling in isolated mitochondria.
- Investigated the role of calcium (EGTA, Mg2+) and mitochondrial permeability transition pore (cyclosporin A) in dye-induced effects.
Main Results:
- All six dyes inhibited glutamate or succinate-supported respiration, with photodynamic enhancement.
- Victoria blue dyes (R, B, BO) acted as protonophores, uncoupling mitochondria by increasing proton permeability.
- Ethyl violet, crystal violet, and malachite green induced mitochondrial permeability transition, leading to respiratory inhibition via cytochrome c release, driven by NAD(P)H oxidation.
Conclusions:
- Triarylmethane dyes exhibit distinct mechanisms of mitochondrial toxicity.
- Victoria blue dyes function as protonophores, while other dyes trigger the mitochondrial permeability transition.
- These findings are crucial for understanding the therapeutic potential and side effects of these dyes in antioncotic photodynamic therapy.