Doxorubicin-induced cardiotoxicity: direct correlation of cardiac fibroblast and H9c2 cell survival and aconitase activity with heat shock protein 27

Reactive oxygen species-independent apoptosis in doxorubicin-treated H9c2 cardiomyocytes: role for heme oxygenase-1 down-modulation

Increased oxidative stress and apoptosis have been implicated in the cardiotoxicity that limits the clinical use of doxorubicin (DOX) as an anti-tumoral drug, but the mechanism of DOX-mediated apoptosis remains unclear. We examined the interplay between oxidative stress and cell death in cardiac-derived H9c2 myocytes exposed to DOX doses in the range of the plasma levels found in patients undergoing chemotherapy. A low DOX concentration (0.25 microM) induced apoptosis, whereas the cells treated with the high dose of 2 microM also showed necrosis. The production of reactive oxygen species (ROS) and induction of oxidative stress markers was increased in the cells treated with 2 microM DOX but not in those treated with the low dose. Surprisingly, heme oxygenase (HO-1) expression was down-modulated in the cells exposed to 0.25 microM DOX, and its Bach 1 transcriptional repressor was induced. In line with the role of HO-1 as an anti-apoptotic protein, inhibiting HO-1 activity with SnPPIX was sufficient to induce apoptosis and increased DOX-mediated apoptosis, whereas hemin-induced HO-1 activation prevented DOX-mediated apoptotic cell death. In brief, our findings do not support the hypothesis that oxidative stress plays a role in the apoptotic cell death occurring in cardiomyocytes exposed to low concentrations of DOX, but suggest that DOX may facilitate the apoptosis of cardiomyocytes by inhibiting the anti-apoptotic HO-1.

Deferiprone targets aconitase: implication for Friedreich's ataxia treatment

Background

Friedreich ataxia is a neurological disease originating from an iron-sulfur cluster enzyme deficiency due to impaired iron handling in the mitochondrion, aconitase being particularly affected. As a mean to counteract disease progression, it has been suggested to chelate free mitochondrial iron. Recent years have witnessed a renewed interest in this strategy because of availability of deferiprone, a chelator preferentially targeting mitochondrial iron.

Method

Control and Friedreich's ataxia patient cultured skin fibroblasts, frataxin-depleted neuroblastoma-derived cells (SK-N-AS) were studied for their response to iron chelation, with a particular attention paid to iron-sensitive aconitase activity.

Results

We found that a direct consequence of chelating mitochondrial free iron in various cell systems is a concentration and time dependent loss of aconitase activity. Impairing aconitase activity was shown to precede decreased cell proliferation.

Conclusion

We conclude that, if chelating excessive mitochondrial iron may be beneficial at some stage of the disease, great attention should be paid to not fully deplete mitochondrial iron store in order to avoid undesirable consequences.

HSP27 regulates p53 transcriptional activity in doxorubicin-treated fibroblasts and cardiac H9c2 cells: p21 upregulation and G2/M phase cell cycle arrest

Treatment of cancer patients with anthracyclin-based chemotherapeutic drugs induces congestive heart failure by a mechanism involving p53. However, it is not known how p53 aggravates doxorubicin (Dox)-induced toxicity in the heart. On the basis of in vitro acute toxicity assay using heat shock factor-1 (HSF-1) wild-type (HSF-1(+/+)) and HSF-1-knockout (HSF-1(-/-)) mouse embryonic fibroblasts and neonatal rat cardiomyocyte-derived H9c2 cells, we demonstrate a novel mechanism whereby heat shock protein 27 (HSP27) regulates transcriptional activity of p53 in Dox-treated cells. Inhibition of p53 by pifithrin-alpha (PFT-alpha) provided different levels of protection from Dox that correlate with HSP27 levels in these cells. In HSF-1(+/+) cells, PFT-alpha attenuated Dox-induced toxicity. However, in HSF-1(-/-) cells (which express a very low level of HSP27 compared with HSF-1(+/+) cells), there was no such attenuation, indicating an important role of HSP27 in p53-dependent cell death. On the other hand, immunoprecipitation of p53 was found to coimmunoprecipitate HSP27 and vice versa (confirmed by Western blotting and matrix-assisted laser desorption/ionization time of flight), demonstrating HSP27 binding to p53 in Dox-treated cells. Moreover, upregulation of p21 was observed in HSF-1(+/+) and H9c2 cells, indicating that HSP27 binding transactivates p53 and enhances transcription of p21 in response to Dox treatment. Further analysis with flow cytometry showed that increased expression of p21 results in G(2)/M phase cell cycle arrest in Dox-treated cells. Overall, HSP27 binding to p53 attenuated the cellular toxicity by upregulating p21 and prevented cell death.