Rapid and extensive uptake and activation of hydrophobic triphenylphosphonium cations within cells
Résumé
Mitochondria-targeted molecules comprising the lipophilic triphenylphosphonium (TPP) cation covalently linked to a hydrophobic bioactive moiety are increasingly 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 concentrations in different compartments are uncertain. To address this issue, we compared the uptake into isolated mitochondria, and mitochondria within cells, of two hydrophobic TPP derivatives, [3H]-MitoQ and [3H]-DecylTPP, with the more hydrophilic TPP cation [3H]-TPMP. Uptake of MitoQ by mitochondria and cells was described by the Nernst equation and was ~5-fold greater than that for TPMP, due to 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, coming to a steady state within 15 min, compared to ~8 h for TPMP. This far faster uptake was due to the increased rate of passage of hydrophobic TPP molecules through the plasma membrane. Within cells MitoQ was predominantly present within mitochondria where it was rapidly reduced to the ubiquinol, consistent with its protective effects in cells and in vivo being due to the active ubiquinol antioxidant. The strong influence of hydrophobicity on the rate and extent of TPP cation uptake into mitochondria within cells facilitates the rational design of mitochondria-targeted compounds to report on and modify mitochondrial function in vivo.
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