Mitochondrial accumulation of a lipophilic cation conjugated to an ionisable group depends on membrane potential, pH gradient and pK(a): implications for the design of mitochondrial probes and therapies.

TitleMitochondrial accumulation of a lipophilic cation conjugated to an ionisable group depends on membrane potential, pH gradient and pK(a): implications for the design of mitochondrial probes and therapies.
Publication TypeJournal Article
Year of Publication2013
AuthorsFinichiu, PG, James, AM, Larsen, L, Smith, RAJ, Murphy, MP
JournalJ Bioenerg Biomembr
Volume45
Issue1-2
Pagination165-73
Date Published2013 Feb
ISSN1573-6881
KeywordsAnimals, Drug Design, Female, Membrane Potential, Mitochondrial, Mitochondria, Liver, Molecular Probes, Organoselenium Compounds, Proton-Motive Force, Rats, Rats, Wistar
Abstract

Mitochondria play key roles in a broad range of biomedical situations, consequently there is a need to direct bioactive compounds to mitochondria as both therapies and probes. A successful approach has been to target compounds to mitochondria by conjugation to lipophilic cations, such as triphenylphosphonium (TPP), which utilize the large mitochondrial membrane potential (Δψ(m), negative inside) to drive accumulation. This has proven effective both in vitro and in vivo for a range of bioactive compounds and probes. However so far only neutral appendages have been targeted to mitochondria in this way. Many bioactive functional moieties that we would like to send to mitochondria contain ionisable groups with pK (a) in the range that creates an assortment of charged species under physiological conditions. To see if such ionisable compounds can also be taken up by mitochondria, we determined the general requirements for the accumulation within mitochondria of a TPP cation conjugated to a carboxylic acid or an amine. Both were taken up by energised mitochondria in response to the protonmotive force. A lipophilic TPP cation attached to a carboxylic acid was accumulated to a greater extent than a simple TPP cation due to the interaction of the weakly acidic group with the pH gradient (ΔpH). In contrast, a lipophilic TPP cation attached to an amine was accumulated less than the simple cation due to exclusion of the weakly basic group by the ΔpH. From these data we derived a simple equation that describes the uptake of lipophilic cations containing ionisable groups as a function of Δψ(m), ΔpH and pK(a). These findings may facilitate the rational design of additional mitochondrial targeted probes and therapies.

DOI10.1007/s10863-012-9493-5
Alternate JournalJ. Bioenerg. Biomembr.
Citation Key10.1007/s10863-012-9493-5
PubMed ID23180142
Grant ListMC_U105663142 / / Medical Research Council / United Kingdom