Submitted to: Cancer Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/8/2004
Publication Date: 11/8/2004
Citation: Kellner, C., Zunino, S.J. 2004. Nitric oxide is synthesized in acute leukemia cells after exposure to phenolic antioxidants and initially protects against mitochondrial membrane depolarization. Cancer Letters. Nov 8;215(1):43-52. Interpretive Summary: Curcumin, found in the spice turmeric, carnosol, found in the herb rosemary, and the flavone quercetin, found in many fruits and vegetables are phenolic antioxidants and display anti-cancer properties. Cells derived from patients diagnosed with different types of leukemia were used to study how these antioxidants kill cancer cells by disrupting the energy state of the mitochondria, the organelle responsible for generation of energy for the cell. After exposure of the leukemia cells to the antioxidants, an increase in the free radical nitric oxide was observed within four hours post-treatment. Inhibition of nitric oxide synthetase, the enzyme that synthesizes nitric oxide, induced an increase in the damage to the mitochondria, resulting in a loss of normal electrical and chemical membrane potential that normally drive energy production. These results suggest that nitric oxide may be synthesized as a protective mechanism for the leukemia cells in response to an environmental insult, such as treatment with the antioxidants. The data also suggests that nitric oxide synthetase may be a chemotherapeutic target and inhibition of the enzyme activity may make these leukemia cells more sensitive to killing by these phenolic compounds.
Technical Abstract: We investigated the early events involved in loss of mitochondrial membrane potential leading to apoptosis in cells derived from patients with acute lymphocytic leukemia after exposure to phenolic antioxidants. Using the nitric oxide binding dye diaminofluorescein-FM diacetate, we found that intracellular nitric oxide (NO) levels increased significantly within four hours after exposure to the antioxidants curcumin, carnosol, and quercetin. Inhibition of nitric oxide synthetase (NOS) activity with mercaptoethylguanidine increased the percentage of leukemia cells with depolarized mitochondria membranes after antioxidant treatment. These data suggest that NO production in the leukemia-derived cells may be a protective response to maintain mitochondrial membrane potential@after antioxidant exposure and inhibition of NOS increases the disruption of mitochondrial homeostasis induced by the antioxidants.