Acute oxidative stress induced by ischemia-reperfusion or inflammation causes serious damage to tissues, and persistent oxidative stress is accepted as one of the causes of many common diseases including cancer. We show here that hydrogen (H(2)) has potential as an antioxidant in preventive and therapeutic applications. We induced acute oxidative stress in cultured cells by three independent methods. H(2) selectively reduced the hydroxyl radical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H(2) did not react with other ROS, which possess physiological roles. We used an acute rat model in which oxidative stress damage was induced in the brain by focal ischemia and reperfusion. The inhalation of H(2) gas markedly suppressed brain injury by buffering the effects of oxidative stress. Thus H(2) can be used as an effective antioxidant therapy; owing to its ability to rapidly diffuse across membranes, it can reach and react with cytotoxic ROS and thus protect against oxidative damage.

The role of mitochondrial dysfunction in cancer has been a subject of great interest and much ongoing investigation. Although most cancer cells harbor somatic mutations in mitochondrial DNA (mtDNA), the question of whether such mutations contribute to the promotion of carcinomas remains unsolved. Here we used trans-mitochondrial hybrids (cybrids) containing a common HeLa nucleus and mtDNA of interest to compare the role of mtDNA against the common nuclear background. We constructed cybrids with or without a homoplasmic pathogenic point mutation at nucleotide position 8,993 or 9,176 in the mtDNA ATP synthase subunit 6 gene (MTATP6) derived from patients with mitochondrial encephalomyopathy. When the cybrids were transplanted into nude mice, the MTATP6 mutations conferred an advantage in the early stage of tumor growth. The mutant cybrids also increased faster than wild type in culture. To complement the mtDNA mutations, we transfected a wild-type nuclear version of MTATP, whose codons were converted to the universal genetic codes containing a mitochondrial target sequence, into the nucleus of cybrids carrying mutant MTATP6. The restoration of MTATP slowed down the growth of tumor in transplantation. Conversely, expression of a mutant nuclear version of MTATP6 in the wild-type cybrids declined respiration and accelerated the tumor growth. These findings showed that the advantage in tumor growth depended upon the MTATP6 function but was not due to secondary nuclear mutations caused by the mutant mitochondria. Because apoptosis occurred less frequently in the mutant versus wild-type cybrids in cultures and tumors, the pathogenic mtDNA mutations seem to promote tumors by preventing apoptosis. (Cancer Res 2005; 65(5): 1655-63)

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Protection of cells from necrosis would be important for many medical applications. Here, we show protein transduction domain (PTD)-FNK therapeutics based on protein transduction to prevent necrosis and acute hepatic injury with zonal death induced by carbon tetrachloride (CCl 4 ). PTD-FNK is a fusion protein comprising the HIV/Tat PTD and FNK, a gain-offunction mutant of anti-apoptotic Bcl-x L . PTD-FNK protected hepatoma HepG2 from necrotic death induced by CCl 4 , and additionally, increased the apoptotic population among cells treated with CCl 4 . A concomitant treatment with a pancaspase inhibitor Z-VAD-FMK (N-benzyloxycarbonyl-Val-AlaAsp-fluoromethylketone), which alone could not prevent the necrosis, protected these cells from the apoptosis. When preinjected intraperitoneally, PTD-FNK markedly reduced zonal liver necrosis caused by CCl 4 . Moreover, injection of PTD-FNK accompanied by Z-VAD-FMK suppressed necrotic injury even after CCl 4 administration. These results suggest that PTD-FNK has great potential for clinical applications to prevent cell death, whether from apoptosis or necrosis, and organ failure.

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