Tuesday, September 22, 2009

Isotope-Reinforced Polyunsaturated Fatty Acids Protect Yeast Cells from Oxidative Stress

Dr. Catherine Clarke, a prominent lab head from UCLA, presented her findings on using the isotope-fortified PUFAs in yeast:

K. Hirano, V. V. Shmanai, B. N. Marbois, R. Molinari, S. Morvaridi, M. Shchepinov, C. F. Clarke
Department of Chemistry and Biochemistry University of California, Los Angeles 607 Charles E Young Dr E Los Angeles CA 90095-1569

Polyunsaturated fatty acids (PUFAs) are exquisitely sensitive to autoxidation damage. The autoxidation products include peroxyl and alky radicals, and small molecule aldehydes that form cross-links to other membrane components, or diffuse to other cellular sites and damage proteins and nucleic acids. Cells protect themselves from these autoxidation products by maintaining an arsenal of enzymes designed to keep reactive oxygen species in check, as well as a defensive system of small molecule antioxidants that terminate radical chain reactions. The enhanced vulnerability of PUFAs to such autoxidation stems from the labile nature of the bis-allylic hydrogen atoms. The facile abstraction of bis-allylic hydrogens from PUFAs is the hallmark chemistry responsible for initiation and propagation of autoxidation reactions. PUFAs synthesized to contain Deuterium atoms uniquely at the bis-allylic sites (termed isotope-reinforced PUFAs) would be expected to be more resistant to autoxidation reactions due to the isotope effect. This hypothesis was tested by making use of the coenzyme Q-deficient Saccharomyces cerevisiae model. The yeast coq mutants have defects in biosynthesis of coenzyme Q (CoQ, or ubiquinone). CoQ plays a well-known role in respiratory energy metabolism and also functions as a lipid soluble chain terminating antioxidant. Although yeast cannot synthesize PUFAs, they are able to incorporate exogenously supplied PUFAs into their membrane lipids. Yeast coq mutants incubated in the presence of linolenic acid (C18:3) exhibit profound loss of viability as ascertained by greater than 99% loss of colony formation at 4 hours. In contrast, the coq mutants treated with either the monounsaturated oleic acid (C18:1), or the isotope-reinforced linolenic acid (bis-allylic D4-C18:3) retain 80-90% viability, a value similar to wild-type or CoQ-replete yeast. These results indicate that isotope reinforced PUFAs are stabilized as compared to standard PUFAs, and the coq mutant yeast cells containing the D4-linolenic acid are protected against the toxic effects of lipid autoxidation products.

Presenting author: Clarke, Catherine
Keywords: Isotope Effect, Lipid Autoxidation, Coenzyme Q, Ubiquinone, Fatty Acid

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