Methylene Blue Delays Cellular Senescence and Enhances Key Mitochondrial Biochemical Pathways

Abstract

Methylene blue (MB) has been used clinically for about a century to treat numerous ailments. We show that MB and other diaminophenothia‐zines extend the life span of human IMR90 fibroblasts in tissue culture by >20 population doubling (PDLs). MB delays senescence at nM levels in IMR90 by enhancing mitochondrial function. MB increases mitochon‐drial complex IV by 30%, enhances cellular oxygen consumption by 37–70%, increases heme synthesis, and reverses premature senescence caused by H 2 O 2 or cadmium. MB also induces phase‐2 antioxidant enzymes in hepG2 cells. Flavin‐dependent enzymes are known to use NAD(P)H to reduce MB to leucomethyl‐ene blue (MBH 2 ), whereas cytochrome c reoxidizes MBH 2 to MB. Experiments on lysates from rat liver mitochondria suggest the ratio MB/cytochrome c is important for the protective actions of MB. We propose that the cellular senescence delay caused by MB is due to cycling between MB and MBH 2 in mitochondria, which may partly explain the increase in specific mito‐chondrial activities. Cycling of MB between oxidized and reduced forms may block oxidant production by mitochondria. Mitochondrial dysfunction and oxidative stress are thought to be key aberrations that lead to cellular senescence and aging. MB may be useful to delay mitochondrial dysfunction with aging and the decrease in complex IV in Alzheimer disease.—At‐amna H., Nguyen, A., Schultz, C., Boyle, K., Newberry, J., Kato, H., Ames B. N. Methylene blue delays cellular senescence and enhances key mitochondrial biochemical pathways. FASEB J . 22, 703–712 (2008)