Peroxidation of cardiolipin

As a rule, oxygen radical overproduction in mitochondria is accompanied by peroxidation of mitochondrial lipids, glutathione depletion, and an increase in other parameters of oxidative stress. Thus, the enhancement of superoxide production in bovine heart submitochondrial particles by antimycin resulted in a decrease in the activity of cytochrome c oxidase through the peroxidation of cardiolipin [45]. Iron overload also induced lipid peroxidation and a decrease in mitochondrial membrane potential in rat liver mitochondria [46]. Sensi et al. [47] demonstrated that zinc influx induced mitochondrial superoxide production in postsynaptic neurons. 

In this chapter, we describe a molecular interaction between cytochrome c and cardiolipin which prevents peroxidation of the lipid, implying that cardiolipin may play an important role in determination of the fate of the cell. In other words, a peroxidation of cardiolipin may well allow cytochrome c to discharge from the mitochondrial inner membrane into the cytosoUc space during apoptotic ceU death. 

Exposure of cardiolipin to oxygen gas resulted in a substantial loss of the lipid and most of the degradation products were hydroperoxide derivatives. Even though we have not done the comparative experiment, our experience tells us that cardiolipin is more sensitive to oxidative stress than free linoleic acid or trilinolein. Taking into account that mitochondria is the site where reactive oxygen species are often produced, we propose that peroxidation of cardiolipin may easily take place once the intracellular oxidative stress occurs. 

Hence, in the present chapter, we addressed the important questionas to how cytochrome c is released from mitochondrial inner membrane by apoptotic signals independently of A Fm dissipation. We have proposed that peroxidation of cardiolipin may result in a discharge of cytochrome c due to a weakening of the interaction between the lipid and the protein. 

Nomura, K., Imai, H., Koumura, T., Kobayashi, T., andNakagawa, Y., 2000, Mitochondrial phosphohpid hydroperoxide glutathione peroxidase inhibits the release of cytochrome c from mitochondria by suppressing the peroxidation of cardiolipin in hypoglycaemia-induced apoptosis. Biochem. J., 351 183-193 Nunez, G., Benedict, M., Hu, Y., and Inohara, N., 1998, Caspases the proteases of the apoptotic pathway. Oncogene, 17 157-168... 

During the process of cell death, cytochrome c is released from mitochondria into the cytosol where it assists to activate the caspases, a family of killer caspases that trigger cell death, hi this chapter evidence that transmission of cell death signals into the release of cytochrome c involves phospholipids at several stages will be presented. Thus, phospholipids target proapoptotic proteins to mitochondria, enable these or other proteins to form channels or pores and to break the mitochondrial permeability barrier. Finally, peroxidation or increased levels of disrupt the ability of cardiolipin to interact with cytochrome c, initiating a sequence of events that ultimately lead to cell death. 

Table 2. Peroxidized molecular species of cardiolipin from bovine heart mitochondria (from...

In addition, there is experimental evidence showing that mitochondrial cardiolipin content markedly decreases following ischemia and reperfusion injury due to cardiolipin peroxidation (Soussi et al., 1990) and that a decrease in the mitochondrial phospholipid cardiolipin occurred in aged rat hearts (Pepe, 2000). These decreases may he attrihutahle to the hydroperoxide-formation of cardiolipin after exposure to intense or repeated oxidative stress during disease state or normal aging, respectively. 

Figure 5. Effect of degree of cardiolipin peroxidation on the signal in inohMi NMR sp troscopy of cytochrome c (Shidoji et al., 1999). A half-width of die wniidd signal at 34.2 ppm w e plotted.

Our proposed mechanism is outlined in Figure 6, with a tentative assumption that once the acyl chains of cardiolipin are peroxidized, their hydrophobicity will diminish and a resulting conformational change cannot be accommodated within the cavity between the heme plane and the iimer surface of cytochrome c. 

Fragmentation (Sgi) of the vicinal peroxides yields 4-H(P)NE and hydroper-oxy epoxides in a reaction that is similar to the mechanism of styrene/oxygen co-polymerization and subsequent degradation to benzaldehyde and formaldehyde [57,65,66], An equivalent cross-chain mechanism is likely to contribute to the formation of 4-H(P)NE during autoxidation of cardiolipin [67]. 

As described earlier, superoxide is a well-proven participant in apoptosis, and its role is tightly connected with the release of cytochrome c. It has been proposed that a switch from the normal four-electron reduction of dioxygen through mitochondrial respiratory chain to the one-electron reduction of dioxygen to superoxide can be an initial event in apoptosis development. This proposal was supported by experimental data. Thus, Petrosillo et al. [104] have shown that mitochondrial-produced oxygen radicals induced the dissociation of cytochrome c from bovine heart submitochondrial particles supposedly via cardiolipin peroxidation. Similarly, it has been found [105] that superoxide elicited rapid cytochrome c release in permeabilized HepG2 cells. In contrast, it was also suggested [106] that it is the release of cytochrome c that inhibits mitochondrial respiration and stimulates superoxide production. 

In this chapter, we have postulated that cardiolipin may participate in determination of cell fate by allowing cytochrome c release from mitochondrial inner membrane through its peroxidative damage during apoptotic ceU death. And anti-oxidant mitochondrial enzyme, PHGPx may protect cardiolipin from its peroxidation as well as apoptotic cell death. 

Biochem. Biophys. Res. Commutt. 230 58-63 Shidoji, Y., Hayashi, K., Komura, S., Ohishi, N., andYagi, K., 1999, Loss of molecular interaction between cytochrome c and cardiolipin due to lipid peroxidation. Biochem. Biophys. Res. Commun. 264 343-347... 

It should not be assumed that hydroxy fatty acids are biologically inactive. Hydroxy fatty acids are chemotactic and vasoactive. Such fatty acids could perturb phospholipids in membranes. For instance, cardiolipin containing hydroxy-linoleic acid does not support the electron transport coupled to ATP production of the mitochondrion. 5-Hydroxy de-canoic acid is a well-known inhibitor of the K -ATP channel. Isoprostanes, trihydroxy oxidation products of arachi-donic acid, are vasoconstrictors (76). 13-Hydroxy linoleic acid (13-HODE) is a lipoxygenase-derived metabolite that influences the thromboresistant properties of endothelial cells in culture (77). However, there is some doubt about the tme nature of these hydroxy-fatty acids generated by the cells, as there are several GSH- and NADPH-dependent pathways that can immediately reduce hydroperoxy- to hydroxy-fatty acids. Furthermore, the reduction step of the analytical method would have converted the hydroperoxy- to a hydroxy-group. Nevertheless, much work remains to be done to determine the relative contribution of hydroperoxy- and hydroxy- to the biological effects of fried fat, and in particular their role in endothelial dysfunction and activation of factor VII. There have been earlier suggestions that a diet rich in lipid peroxidation products may lead to atherosclerosis and CHD (34,78). 

---