J. Dessolin et al. / European Journal of Pharmacology 447 (2002) 155–161
161
had a comparable inhibiting activity (Fig. 4). However, it is
Acknowledgements
clear that TEMPOL–TPP and JD-29 did not exhibit any
increase in their antiapoptotic activity against sodium selen-
ite as a result of their covalent coupling to TPP + .
We thank D.R. Green and N.J. Waterhouse for the gift of
the 2H18 HeLa cell clone. This study was supported by
grants to F.I. from the INSERM, the Association pour la
Recherche sur le Cancer, the Foundation pour la Recherche
´
Medicale, and Region Aquitaine. J.D. is recipient of a
postdoctoral fellowship of the Ecole Polytechnique.
4. Discussion
Since staurosporine treatment somehow mimics the pro-
tein kinase inhibition induced by growth factor withdrawal,
the first series of results suggests that free radicals are not
involved in staurosporine-induced apoptosis, this can be
taken to indicate that antioxidants (targeted or not) do not
inhibit physiological apoptosis. On the other hand, sodium
selenite treatment increases the cellular concentration of
superoxide and promotes ‘‘accidental’’ apoptosis by mito-
chondrial oxidative damage (Shen et al., 2001). Our results
indicate that there is no significant difference between the
targeted and untargeted compounds against apoptosis
induced by selenite. Several suggestions can be made to
account for this observation: (i) the coupling to TPP + was
inefficient at driving the mitochondrial accumulation of the
drugs, and/or (ii) the coupling to TPP + impaired the free
radical scavenging activity of the compounds, and/or (iii)
the oxidative stress generated by selenite and its primary
effector targets are located outside mitochondria, and are
thus out of reach of drugs accumulated in the mitochondrial
matrix compartment. While these diverse hypotheses are
currently being investigated, it must be noted that the
possibility that the covalent coupling to TPP + was ineffi-
cient at driving the mitochondrial accumulation of the drugs
has a precedent. Indeed, it was observed that, in spite of a
very good membrane solubility, fullerenes coupled to TPP +
failed to get accumulated by mitochondria (Coulter et al.,
2000). Thus, TPP + is probably not universal in conferring
possible mitochondrial targeting. In addition, it is likely that
sodium selenite treatment is not correctly mimicking endog-
enous mitochondrial oxidative stresses like those taking
place during neurodegenerative disorders, and thus that the
targeted drugs need to be evaluated in a more relevant
context in which the oxidative damage originates from
mitochondria.
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