Partners and International Organizations
(English)
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CNRS.IGBMC, Strasbourg (D), Eberhard-Karls-Universität Tübingen (D), INSERM, Paris (F), Université Catholique de Louvain (B)
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Abstract
(English)
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By the end of this reporting time period, we successfully developed a cellular assay for Friedreich Ataxia. This assay is based on the utilization of BSO, an irreversible inhibitor of g-glutamyl-cysteine synthase. The inhibition of this rate limiting enzyme of the glutathione (GSH) de novo synthesis produces within hours a cellular glutathione depletion. After 12-48 hours exposure to BSO, FRDA fibroblasts die, whereas fibroblasts from control donors appear almost unaffected. This discriminating effect can be observed over a large range of BSO concentrations, and was found in all FRDA cell lines tested so far.
We have found that Idebenone, an antioxidant molecule that was shown to ameliorate cardiomyopathy in patients, can rescue this cell death phenotype with an EC50 in the submicromolar range. Various idebenone analogues were tested and the results showed, that a certain lipophilicity is essential for activity. Several lipophilic antioxidants demonstrated activity in this assay, but others, reported to be very powerfull were inactive. These data indicate that we have established a disease-relevant cell assay in which idebenone, currently the only drug used for the treatment of FRDA patients, also displays activity. Moreover, several, but not all, antioxidants were active in this assay.
We also found that the BSO-mediated cell death can be rescued by very low selenium concentrations, indicating that FRDA cells, in contrast to fibroblasts from unaffected donors, appear starved for selenium. The reason for this effect is not known yet.
With the observation that FRDA cells might have an impaired glutathione metabolism, we reasoned that they might suffer from impaired glutathione peroxidase (GPX) activity. We found that basal levels of GPX are similar in both cell types, however, upon selenium supplementation, only in FRDA cells GPX activity is increased, again indicating a need for selenium which is an integral part of the GPX active site.
We then verified whether small molecule GPX mimetics could be active in this cell system. Consistent with the previous observations, we found that all GPX mimetics tested so far displayed activity in this cellular assay, indicating thereby that GPX mimetics could be of therapeutic interest for FRDA.
The results of our studies are currently prepared for patent protection and publication.
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