Mitochondrial control of apoptosis through modulation of cardiolipin oxidation in hepatocellular carcinoma: A novel link between oxidative stress and cancer.

Altered redox status in cancer cells has been linked to lipid peroxidation induced by reactive oxygen species (ROS) and subsequent formation of reactive lipid electrophiles, especially 4-hydroxy-nonenal (4-HNE). Emerging evidence suggests that cancer cells manipulate redox status to acquire anti-apoptotic phenotype but the underlying mechanisms are poorly understood. Cardiolipin (CL), a mitochondria-specific inner membrane phospholipid, is critical for maintaining mitochondrial function. Paradoxically, liver tissues contain tetralinoleoyl cardiolipin (TLCL) as the major CL in mitochondria yet emerging evidence suggests that ROS generated in mitochondria may lead to CL peroxidation and activation of intrinsic apoptosis. It remains unclear how CL oxidation leads to apoptosis and its relevance to the pathogenesis of hepatocellular carcinoma (HCC). We employed a mass spectrometry-based lipidomic approach to profile lipids in human tissues of HCC and found that CL was gradually decreased in tumor comparing to peripheral non-cancerous tissues, accompanied by a concomitant decrease of oxidized CL and its oxidation product, 4-HNE. Incubation of liver cancer cells with TLCL significantly restored apoptotic sensitivity accompanied by an increase of CL and its oxidation products when treated with staurosporine (STS) or Sorafenib (the standard treatment for late stage HCC patients). Our studies uncovered a novel mechanism by which cancer cells adopt to evade apoptosis, highlighting the importance of mitochondrial control of apoptosis through modulation of CL oxidation and subsequent 4-HNE formation in HCC. Thus manipulation of mitochondrial CL oxidation and lipid electrophile formation may have potential therapeutic value for diseases linked to oxidative stress and mitochondrial dysfunctions.