Rapid and extensive uptake and activation of hydrophobic triphenylphosphonium cations within cells

Abstract

Mitochondria-targeted molecules comprising the lipophilic TPP (triphenylphosphonium) cation covalently linked to a hydrophobic bioactive moiety are used to modify and probe mitochondria in cells and in vivo. However, it is unclear how hydrophobicity affects the rate and extent of their uptake into mitochondria within cells, making it difficult to interpret experiments because their intracellular concentration in different compartments is uncertain. To address this issue, we compared the uptake into both isolated mitochondria and mitochondria within cells of two hydrophobic TPP derivatives, [3H]MitoQ (mitoquinone) and [3H]DecylTPP, with the more hydrophilic TPP cation [3H]TPMP (methyltriphenylphosphonium). Uptake of MitoQ by mitochondria and cells was described by the Nernst equation and was approximately 5-fold greater than that for TPMP, as a result of its greater binding within the mitochondrial matrix. DecylTPP was also taken up extensively by cells, indicating that increased hydrophobicity enhanced uptake. Both MitoQ and DecylTPP were taken up very rapidly into cells, reaching a steady state within 15 min, compared with approximately 8 h for TPMP. This far faster uptake was the result of the increased rate of passage of hydrophobic TPP molecules through the plasma membrane. Within cells MitoQ was predominantly located within mitochondria, where it was rapidly reduced to the ubiquinol form, consistent with its protective effects in cells and in vivo being due to the ubiquinol antioxidant. The strong influence of hydrophobicity on TPP cation uptake into mitochondria within cells facilitates the rational design of mitochondria-targeted compounds to report on and modify mitochondrial function in vivo.

Polymer Functionalization of Isolated Mitochondria for Cellular Transplantation and Metabolic Phenotype Alteration

“…Cellular uptake of materials on the nano‐ and microscale is driven by charge, with positively charged materials undergoing higher rates of internalization due to attractive electrostatic interactions with the negatively charged cell membrane 23. Additionally, TPP is a hydrophobic cation,24 possessing a large lipophilic surface area that allows it to traverse phospholipid bilayers21 and promote efficient cellular uptake regardless of cell type through hydrophobic interactions with cell membrane components or via integration into cell membranes 25. Thus, the TPP associated with mitochondrial membranes may be coming into direct contact with cell membranes, resulting in increased cellular accumulation.…”

Molecular Strategies for Targeting Antioxidants to Mitochondria: Therapeutic Implications

“…Lipophilic cations. Lipophilic cations take advantage of mitochondrial DJ m to facilitate their selective targeting and accumulation within the mitochondrial matrix (273). This process can be expressed by the Nernst equation, by which the uptake of these molecules increases *10-fold for every *60 mV of membrane potential, leading to significant uptake within mitochondria in vivo (246,271) (Figs.…”

Mitochondria-Targeted Antioxidant MitoQ 10 Improves Endothelial Function and Attenuates Cardiac Hypertrophy

“…17,19 Lipophilic cations can easily move through phospholipid bilayers without requiring a specific uptake mechanism; therefore, the triphenylphosphonium cation concentrates MitoQ 10 several hundred-fold within the mitochondria, driven by the large mitochondrial membrane potential ( Figure 1). 1,17,19,20 Within mitochondria, MitoQ 10 is reduced by the respiratory chain to its active ubiquinol form, which is a particularly effective antioxidant that prevents lipid peroxidation and mitochondrial damage. 1,17,20 -26 MitoQ 10 is also orally bioavailable and has been shown to accumulate extensively in rat tissues after administration in the drinking water and to protect against tissue damage.…”

“…36 The aim of this study was to investigate the contribution of mitochondria-specific oxidative stress to the development of cardiovascular disease in the SHRSP using the novel mitochondria-targeted antioxidant MitoQ 10 . The effect of oral administration of MitoQ 10 was assessed in vivo and compared with the control compound decyltriphenylphosphonium (decylTPP), which is composed of the lipophilic triphenylphosphonium cation and aliphatic 10-carbon chain but lacks the ubiquinone moiety 20 and thereby enables us to control for any nonspecific effects attributed to the accumulation of lipophilic cations within mitochondria that are not attributed to the prevention of oxidative damage. It is anticipated that these studies will inform new therapeutic interventions in human essential hypertension.…”