Hepatic steatosis is associated with mitochondrial oxidative alterations. This study aimed to characterize in a choline-deficient model of rat fatty liver whether this oxidative imbalance is related to an impairment of the capacity of ATP synthesis both under fed conditions and after starvation, which may sensitize mitochondria to oxidative injury. Mitochondria were isolated from normal and fatty livers of fed or 18-hour fasted rats. Oxidative injury was evaluated by measuring the mitochondrial content of thiobarbituric reactive substances, protein carbonyls, glutathione, and protein sulfhydryls. The mitochondrial F 0 F 1 -ATP synthase content, tissue ATP concentration, and liver histology were also determined. Compared with normal liver, under fed conditions, fatty livers showed a greater mitochondrial content of oxidized lipids and proteins together with a low concentration of sulfhydryls and glutathione. The mitochondrial catalytic ␤-F 1 subunit of the F 0 F 1 -ATP synthase was about 35% lower in fatty livers. Hepatic ATP was also significantly reduced in fatty liver. Starvation exacerbated mitochondrial oxidative injury in both groups but to a greater extent in fatty livers. In the steatotic group, fasting induced a significant decrease of the ATP levels, which was accompanied by a 70% fall of the catalytic ␤-F 1 subunit. These data indicate that the mitochondrial oxidative alterations in fatty livers are associated with an important reduction of the F 0 F 1 -ATP synthase. These changes, which are greatly exacerbated after starvation, may account for the reduced synthesis of the hepatic ATP observed in the presence of fatty infiltration. (HEPATOLOGY 2001;33:808-815.)Hepatic steatosis without concomitant inflammation or fibrosis, is usually considered a benign condition. However, fatty degeneration increases the sensitivity of the liver to several types of injury, such as those due to ischemia-reperfusion 1 or drug toxicity. 2 Fatty infiltration is associated with a number of intracellular disorders, which can be either a cause or a consequence of lipid accumulation. 3 Among them, mitochondrial abnormalities related to an increased generation of reactive oxygen species have been described in human steatosis of various etiology (alcoholic 4 and nonalcoholic steatohepatitis, 5 iron, 6 or copper 7 overload) and in several experimental models of fatty liver, including alcohol administration 8 and drug toxicity. 2,9 Mitochondrial oxidative injury has been also described in conditions of chronic administration of commonly used drugs, such as valproate 10 or amiodarone, 11 the hepatic metabolites of which are known to interfere with mitochondrial respiration and fatty acid metabolism, thus producing fatty degeneration.Oxidative metabolism in mitochondria represent the main source of energy for the cells. Alterations of specific mitochondrial functions may, therefore, lead to an impaired production of ATP and a reduced uptake of substrates for mitochondrial metabolism 12 and eventually limit resistance and survival o...

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Mitochondrial bioenergetic impairment has been found in the organelles isolated from rat liver during the prereplicative phase of liver regeneration. To gain insight into the mechanism underlying this impairment, we investigated mitochondrial ultrastructure and membrane permeability properties in the course of liver regeneration after partial hepatectomy, with special interest to the role played by Ca 2+ in this process. The results show that during the first day after partial hepatectomy, significant changes in the ultrastructure of mitochondria in situ occur. Mitochondrial swelling and release from mitochondria of both glutamate dehydrogenase and aspartate aminotransferase isoenzymes with an increase in the mitochondrial Ca 2+ content were also observed. Cyclosporin-A proved to be able to prevent the changes in mitochondrial membrane permeability properties. At 24 h after partial hepatectomy, despite alteration in mitochondrial membrane permeability properties, no release of cytochrome c was found. The ultrastructure of mitochondria, the membrane permeability properties and the Ca 2+ content returned to normal values during the replicative phase of liver regeneration. These results suggest that, during the prereplicative phase of liver regeneration, the changes in mitochondrial ultrastructure observed in liver specimens were correlated with Ca 2+ -induced permeability transition in mitochondria.Keywords: liver regeneration; mitochondria ultrastructure; membrane permeability; calcium; cyclosporin-A.Seventy percent partial hepatectomy (PH) induces cell proliferation until the original mass of the liver is restored [1]. The tissue regeneration process consists of two phases: the prereplicative phase, the duration of which depends on the age of the animal [2,3] as well as on hormones and dietary manipulation [2,4] and the replicative phase, during which a sharp increase in DNA synthesis occurs with active mitosis [2]. In the light of early changes in ATP concentration found in liver after PH, before activation of cell proliferation [5,6], mitochondria were investigated as they are directly involved in the process of liver regeneration [4,[7][8][9][10][11][12][13][14][15][16]. Many mitochondrial functions, including oxidative phosphorylation [11][12][13] and generation of reactive oxygen species [14,15], were investigated in some detail in the prereplicative phase of liver regeneration. In isolated mitochondria, a decrease in the respiratory control index [12], ATP synthesis, probably due to a decrease in the ATPsynthase complex content [14], and glutathione content[13] as well as an increase in malondialdehyde production [14] and oxidant production [15] were found. This suggests the occurrence in the prereplicative phase of liver regeneration of a transient mitochondrial oxidative stress in which mitochondria can also release proteins from the matrix [16]. Despite this, mitochondria recover their functions in the replicative phase of liver regeneration [12,[14][15][16].In this paper, we investigated whether and ho...

Proton conduction in submitochondrial particles with various degrees of resolution of the H '--ATPase has been studied.Proton conduction was analyzed by following the kinetics of the anaerobic decay of protons taken up by submitochondrial particles during respiratory pulses.1. In EDTA submitochondrial particles proton release exhibited biphasic kinetics; both phases were depressed by collapsing aerobic A$.2. The slow phase of proton diffusion was inhibited by oligomycin and N,N'-dicyclohexylcarbodiimide as well as by FI ligands like adenylyl5'-imidophosphate and alkyl cations. Inhibition of proton conduction by F1 ligands exhibited a sigmoidal titration curve and was synergistic with inhibition by oligomycin. Removal of the ATPase inhibitor markedly enhanced the kinetic constant of the slow proton diffusion process.3. The initial rapid phase of proton diffusion was inhibited by N,N'-dicyclohexylcarbodiimide and oligomycin but was unaffected by FI ligands.4. When the FI moiety was removed from the particles, proton conduction became monophasic and was not any more inhibited by F1 ligands.5. It is concluded that the H'-ATPase contributes to both phases of proton conduction and that energy-linked cooperative interaction of the F1 with the FO moiety controls proton conductivity.Evidence is also provided for involvement of negatively charged groups in hydrophobic environments of the FI moiety in proton translocation by the H+-ATPase.The HA-ATPase of mitochondria consists of two moieties (see for review [l -61). The ATPase proper, or the F1 moiety [l -3,5], and a proteolipid complex, the FO moiety, which is thought to function as an oligomycin-sensitive and a N,N'-dicyclohexylcarbodiimidesensitive proton conductor [4,7,8].In the intact H+-ATPase complex, normally arranged in the membrane, downhill proton diffusion through the FO moiety has to be strictly coupled to ATP synthesis, otherwise uncoupling of oxidative phosphorylation occurs.In loosely coupled submitochondrial particles [9], where displacement of the F1 moiety might have occurred [lo], or in particles from which the F1 moiety and a protein component of the H+-ATPase known as oligomycin-sensitivity-conferral protein [l 11, have been removed [12], a proton leakage occurs, which