Membrane permeability flavonoid effects

Similar to hydrophilic flavonoids, hydrophobic flavonoids can affect membrane permeability. Alterations in this biophysical property of liposome bilayers lead to the release of bulky molecules entrapped into the inner aqueous space. As mentioned in the previous section, a strong correlation was found between flavonoid retention to a hydrophobic matrix and their capacity to induce membrane leakage [Ollila et al., 2002]. Interestingly, hydrophilic flavonoids, such as (—)-epicatechin and related procyanidins (dimer to hex-amer) prevented Fe2 + -mediated liposome permeabilization, although in this case the beneficial effect could be related to both their antioxidant and metal chelating capacities and their membrane stabilizing properties [Verstraeten et al., 2004],... 

Santos, A.C. Uyemura, S.A. Lopes, J.L. Bazon, J.N. Mingatto, F.E. Cutti, C. Effect of naturally occurring flavonoids on lipid peroxidation and membrane permeability transition in mitochondria. Free Radical Biol. Med. 1998, 24, 1455-1461. 

By definition, the uncoupling effect of certain flavonoids should be independent of their inhibitory effects on mitochondrial respiration or FoFi-ATPase, suggesting an additional mode of action of flavonoids against mitochondrial function. A collapse of the transmembrane potential is likely under conditions in which the permeability barrier created by the mitochondrial inner membrane is compromised (as occurs in the presence of ionophores). Calcium, phosphate, oxidative stress, adenine nucleotide depletion, and membrane depolarization can induce such a nonspecific increase in the permeability of the inner membrane, in an event called the mitochondrial permeability transition (MPT) [30,34]. The MPT can be selectively inhibited by cyclosporin A and is believed to involve the assembly of a multiprotein complex to form a nonspecific pore that spans the inner and outer mitochondrial membranes. The latter assembly is referred to as the permeability transition pore complex (PTPC) (Fig. 1). Its exact composition is unknown, but appears to comprise cyclophilin D, ANT, the voltage-dependent anion channel (porin), and a benzodiazepinebinding site [10,30,34]. 

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