Archives of Biochemistry and Biophysics 454 (2006) 114–122 www.elsevier.com/locate/yabbi 0003-9861/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.abb.2006.08.008 Avicins, natural anticancer saponins, permeabilize mitochondrial membranes  Victor V. Lemeshko a,¤ , Valsala Haridas b , Jairo C. Quijano Pérez a , Jordan U. Gutterman b,¤ a Escuela de Física, Facultad de Ciencias, Universidad Nacional de Colombia, sede Medellín, AA3840 Medellín, Colombia b Department of Molecular Therapeutics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA Received 8 July 2006, and in revised form 5 August 2006 Available online 23 August 2006 Abstract Avicins are a class of natural saponins with selective pro-apoptotic activity in cancer cells. In this work, we studied the inXuence of avicins on metabolic state of rat liver mitochondria. Avicin-treated mitochondria underwent a signiWcant decrease in oxygen consump- tion rate that was completely restored by addition of exogenous cytochrome c. On the other hand, avicins increased the rotenone-insensi- tive oxidation of external NADH in the presence of exogenous cytochrome c, long before high amplitude swelling of mitochondria was observed. The increase in external NADH oxidation was cyclosporin A-insensitive. Avicin G signiWcantly accelerated hydroperoxide- induced oxidation of mitochondrial endogenous NAD(P)H, the drop of the inner membrane potential and the high amplitude swelling of mitochondria. The obtained data might explain selective induction of apoptosis in tumor cells by avicins. Based on other studies showing that tumor cells generate hydroperoxides with a very high rate, avicins could provide a new strategy of anticancer therapy by sensitizing cells with high levels of reactive oxygen species to apoptosis.  2006 Elsevier Inc. All rights reserved. Keywords: Mitochondria; Outer mitochondrial membrane; NADPH; Cytochrome c; Avicin; Hydroperoxides; Cancer; Apoptosis Avicins represent a new class of plant stress metabolites that exhibit selective pro-apoptotic [1–4] and cytotoxic activity [5] in tumor cells, as well as anti-inXammatory [6,7] and antioxidant properties [8–10]. Our previous Wnding that avicins induce apoptosis in Jurkat cells by a direct per- turbation of mitochondria [1], prompted us to study their eVects on the oxidative phosphorylation system of rat liver mitochondria. Most common eVects of anti-tumor drugs, by which they target mitochondrial structure and functions, are revealed in direct permeabilization of the outer mitochondrial mem- brane (OMM 1 ) to cytochrome c, or in oxidative stress and mitochondrial swelling. The rupture or direct permeabiliza- tion of the OMM results in release of cytochrome c and other pro-apoptotic factors from mitochondria, as well as in disturbance of oxidative phosphorylation system [11,12]. Allosteric interactions of various factors with the voltage- dependent anion channel that increase the probability of its closure under some physiological and pathological condi- tions, have been also considered as a possible way to induce tumor cells death [13,14]. Thus, mitochondria play a central role in cancer survival and are one of the main targets for developing anticancer drugs [11–15].  Financial support for this work was provided by the: Clayton Founda- tion for Research; Biomedical Research Foundation; Abraham J. and Phyllis Katz Foundation; Colciencias (Colombia) Grant #2213-05-16851. * Corresponding authors. E-mail addresses: vvasilie@unal.edu.co (V.V. Lemeshko), jgutterm @mdanderson.org (J.U. Gutterman). 1 Abbreviations used: OMM, outer membrane of mitochondria; IMM, inner membrane of mitochondria; ROS, reactive oxygen species; TMPD,N,N,N',N'-tetramethyl-p-phenylenediamine; FCCP, carbonyl-cya- nide-p-triXuoromethoxy phenylhydrazone; DNP, 2,4-dinitrophenol; tBH, tert-butylhydroperoxide.