Penetrating cation/fatty acid anion pair as a mitochondria-targeted protonophore

Abstract

A unique phenomenon of mitochondria-targeted protonophores is described.ItconsistsinatransmembraneH þ -conductingfattyacidcycling mediated by penetrating cations such as 10-(6'-plastoquinonyl) decyltriphenylphosphonium (SkQ1) or dodecyltriphenylphosphonium (C 12 TPP). The phenomenon has been modeled by molecular dynamics and directly proved by experiments on bilayer planar phospholipid membrane, liposomes, isolated mitochondria, and yeast cells. In bilayer planar phospholipid membrane, the concerted action of penetrating cations and fatty acids is found to result in conversion of a pH gradient (ΔpH) to a membrane potential (Δψ) of the Nernstian value (about 60 mV Δψ at ΔpH ¼ 1). A hydrophobic cation with localized charge (cetyltrimethylammonium) failed to substitute for hydrophobic cations with delocalized charge. In isolated mitochondria, SkQ1 and C 12 TPP, but not cetyltrimethylammonium, potentiatedfattyacid-induced(i)uncouplingofrespirationandphosphorylation, and (ii) inhibition of H 2 O 2 formation. In intact yeast cells, C 12 TPP stimulated respiration regardless of the extracellular pH value, whereas a nontargeted protonophorous uncoupler (trifluoromethoxycarbonylcyanidephenylhydrazone)stimulatedrespiration at pH 5 but not at pH 3. Hydrophobic penetrating cations might be promising to treat obesity, senescence, and some kinds of cancer that require mitochondrial hyperpolarization.mild uncoupling | membrane | Mitochondria-targeted uncoupler | penetrating ion | antioxidant S ome decrease in mitochondrial membrane potential (Δψ) in the resting state may be favorable in treating obesity and hypothyroidism as well as in preventing senescence and certain types of cancer [for reviews, see refs. 1, 2]. In the first two cases, Δψ lowering stimulates respiratory metabolism. As to senescence and cancer, such an effect seems to be related to a decrease in production of reactive oxygen species (ROS) in mitochondria. ROS, in turn, were assumed to mediate senescence and some steps of cancerogenesis (2, 3). As was shown in our group (4), there is a very steep dependence of mitochondrial ROS formation on Δψ. Small (10-15%) lowering of Δψ resulted in ten-fold decrease in the ROS production rate (4). In isolated mitochondria, this can be achieved by adding a low concentration of a protonophorous uncoupler (4-6). This approach, called "mild uncoupling" (4, 6), was recently used by Padalko (7) and by Kowaltowski and coworkers (8) to prolong the lifespan of Drosophila and mice, respectively. However, long-term treatment of animals with uncouplers results in toxic side effects (9).In this paper, we put forward an alternative approach based on the use of synthetic cations that easily penetrate through biological membranes. Penetrating ions were suggested by our group to reveal electric potential difference across mitochondrial membrane (9, 10). In tetraphenylphosphonium (TPP), a typical representative of such ions, the positive charge is strongly displaced over four phenyl residues. As a result, water dipoles cannot be held by t...

Derivatives of Rhodamine 19 as Mild Mitochondria-targeted Cationic Uncouplers

“…However, the existence of ⌬ on the inner mitochondrial membrane being negative inside makes cationic compounds capable of being accumulated inside mitochondria, which should increase their efficiency. It has been shown that SkQR1 accumulates effectively in mitochondria (experiments on isolated mitochondria, mammalian cell cultures, yeast cells, and intact organisms (7,53,54).…”

“…The force field parameters for C 12 -TPP were taken from Ref. 7, and parameters for SkQR1 were developed using those for sulforhodamine (36). All molecular dynamics calculations were performed at the supercomputer SKIF "Chebyshev" in the Computation Center, Moscow State University.…”

“…Another conjugate of triphenylphosphonium, with butylated hydroxytoluene, exhibited protonophorous activity within a wide range of concentrations because of its interaction with adenine nucleotide translocase (17). It has recently been shown that mitochondria-targeted antioxidants (SkQ1 and 10-(6Ј-ubiquinonyl) decyltriphenylphosphonium) as well as SkQ1 lacking quinone (dodecyltriphenylphosphonium) exhibit protonophorous action when added together with free fatty acids (7). Because a certain amount of free fatty acids is usually present in living cells, SkQ1 may be considered as a mitochondriatargeted protonophore.…”

Fluorescent Nitrones for the Study of ROS Formation with Subcellular Resolution

“…The positive charge is not localized but spread over the aromatic rings, thus allowing for membrane permeation due to the already negative potential of cells with respect to their outside and even more so of mitochondria, the only human organelle with a negative potential with respect to the cytoplasm. Once inside, they are trapped by the opposite potential outside (Severin et al, 2010 The fluorescence half-life of 1 in mitochondria was studied under a variety of conditions. Data are summarized in Table I together with those from the coumaryl derivative 2.…”

Mitochondrial Metabolism and Insulin Action

“…Due to the current obesity epidemic, and illicit sales via the internet, it is alarming to see that DNP has made a comeback as a weight loss agent, with predictable lethal results [235,236]. Thus, while mitochondrial uncoupling with DNP does not appears to be a safe weight-loss therapy, other more recently described uncoupling agents may potentially have a safer profile for use in humans [237][238][239]. An additional approach may to be to upregulate physiological uncoupling in brown adipose tissue, via sympathomimetic agents or agonists for thyroid hormone or bile acid receptors.…”