Studies on the Action of Bovine Serum Albumin on Aged Rat Liver Mitochondria

Cyclosporin A is unable to inhibit carboxyatractyloside-induced permeability transition in aged mitochondria

We studied the effect of mitochondrial ageing on membrane permeability transition. The results obtained indicate that aged mitochondria are neither able to retain Ca2+ nor to maintain a high transmembrane electric gradient. In addition, aged mitochondria undergo a large amplitude swelling. These dysfunctions were circumvented by the addition of cyclosporin A. Furthermore, it is shown that ageing-induced permeability transition causes oxidative damage on the matrix enzyme aconitase. The observed damage in aged mitochondria requires Ca2+ addition; therefore, it was not seen when Sr2+ replaced Ca2+. Two important findings in this work were the fact that despite of the presence of cyclosporin A, carboxyatractyloside was still able to induce permeability transition, and that ageing induced mitochondrial DNA disruption and release of cytochrome c. It is likely that the membrane's increased permeability is due to the effect of fatty acids, since bovine serum albumin makes mitochondria able to retain Ca2+. However, the possibility that the damage might be the result of oxidative stress cannot be discarded.

Evidence for involvement of nonesterified fatty acid-induced protonophoric uncoupling during mitochondrial dysfunction caused by hypoxia and reoxygenation

BACKGROUND

Proximal tubules subjected to hypoxia in vitro under conditions relevant to ischaemia in vivo develop an energetic deficit that is not corrected even after full reoxygenation. We have provided evidence that accumulation of nonesterified fatty acids (NEFA) is the primary reason for this energetic deficit. In this study, we have further investigated the mechanism for the NEFA-induced energetic deficit.

METHODS

Mitochondrial membrane potential (Deltapsi) was measured in digitonin-permeabilized, freshly isolated proximal tubules by safranin O uptake. Addition of the potassium/proton exchanger nigericin enables the determination of the mitochondrial proton motive force (Deltap) and the proton gradient (DeltapH). ATP was measured luminometrically and NEFA colorimetrically.

RESULTS

Tubule ATP content was depleted after hypoxia and recovered incompletely, even after full reoxygenation. Mitochondrial safranin O uptake was decreased in proximal tubules after hypoxia and reoxygenation (H/R). This decrease was attenuated by delipidated bovine serum albumin (dBSA) or citrate. Addition of nigericin increased safranin O uptake of mitochondria in normoxic proximal tubules, but not in proximal tubules after H/R. Addition of dBSA restored the effect of nigericin to increase mitochondrial safranin O uptake. Addition of the NEFA oleate had the same impact on mitochondrial safranin O uptake as subjecting proximal tubules to H/R.

CONCLUSION

The mechanism of the NEFA-induced energetic deficit in freshly isolated rat proximal tubules induced by H/R is characterized by impaired ATP production after full reoxygenation, impaired recovery of Deltapsi and Deltap, abrogation of DeltapH and sensitivity to citrate, consistent with involvement of the tricarboxylate carrier. The data support the concept that protonophoric uncoupling by NEFA movement on anion carriers plays a critical role in proximal tubule mitochochondrial dysfunction after H/R.

Accumulation of nonesterified fatty acids causes the sustained energetic deficit in kidney proximal tubules after hypoxia-reoxygenation

Kidney proximal tubules exhibit decreased ATP and reduced, but not absent, mitochondrial membrane potential (Deltapsi(m)) during reoxygenation after severe hypoxia. This energetic deficit, which plays a pivotal role in overall cellular recovery, cannot be explained by loss of mitochondrial membrane integrity, decreased electron transport, or compromised F1F0-ATPase and adenine nucleotide translocase activities. Addition of oleate to permeabilized tubules produced concentration-dependent decreases of Deltapsi(m) measured by safranin O uptake (threshold for oleate = 0.25 microM, 1.6 nmol/mg protein; maximal effect = 4 microM, 26 nmol/mg) that were reversed by delipidated BSA (dBSA). Cell nonesterified fatty acid (NEFA) levels increased from <1 to 17.4 nmol/mg protein during 60- min hypoxia and remained elevated at 7.6 nmol/mg after 60 min reoxygenation, at which time ATP had recovered to only 10% of control values. Safranin O uptake in reoxygenated tubules, which was decreased 85% after 60-min hypoxia, was normalized by dBSA, which improved ATP synthesis as well. dBSA also almost completely normalized Deltapsi(m) when the duration of hypoxia was increased to 120 min. In intact tubules, the protective substrate combination of alpha-ketoglutarate + malate (alpha-KG/MAL) increased ATP three- to fourfold, limited NEFA accumulation during hypoxia by 50%, and lowered NEFA during reoxygenation. Notably, dBSA also improved ATP recovery when added to intact tubules during reoxygenation and was additive to the effect of alpha-KG/MAL. We conclude that NEFA overload is the primary cause of energetic failure of reoxygenated proximal tubules and lowering NEFA substantially contributes to the benefit from supplementation with alpha-KG/MAL.

Atherogenesis and fibrinogen: historical perspective and current status

A review of 117 research publications describes a deficiency in fatty acid transport into intracellular oxidative energy metabolism which causes increased fibrinogen synthesis and turnover into fibrin. The increased production of fibrin, coupled with depressed activation of plasminogen, increases the fibrin/plasmin ratio causing thrombosis-induced atherogenesis. This discovery unifies the two schools of atherogenesis based on blood lipid or fibrin deposition theories.

On the nature of the mitochondrial proton leak

Respiring mitochondria have a significant passive permeability to protons; the mechanism of this proton leak is unknown. Several putative mechanisms were tested. Mitochondrial permeability to small sugars was unaffected by energization, suggesting that there is no significant dielectric breakdown at high membrane potential. Mitochondria are argued to have a proton permeability that is 6 to 8 orders of magnitude higher than the permeability to other cations, suggesting that the proton leak is probably not via a simple pore or membrane defect. 15-30% of the proton leak of freshly prepared mitochondria was extractable with bovine serum albumin and is probably due to fatty acids. Little if any of the proton leak appears to be due to cycling of ions other than protons, or to be associated with the functional activity of the proton pumps. The mitochondrial proton leak shares several properties with the proton permeability of pure phospholipid bilayers, suggesting that they share the same mechanism, although the leak through the bilayer in mitochondria may be modified by the presence of proteins.

Comparative studies on the influence of decapitation, ketamine and thiopental anesthesia on rat heart mitochondria

The influence of decapitation, ketamine and thiopental anesthesia on some properties of rat heart mitochondria was compared. Polarographic analysis were performed, oxygen consumption rates, respiratory control index, ADP : O ratio and oxidation of exogenous NADH were determined. Electronmicroscopic and gasometric examinations were also conducted. Mitochondrial fractions from hearts of decapitated rats oxidized at a generally faster rate and mitochondria from such hearts exhibited a significantly lower RCI value. These differences can be explained through the action of uncoupler(s) present in the decapitated group. A hypothesis linking decapitation with the uncoupling effect of fatty acids released intracellularly during catecholamine-stimulated lipolysis is discussed. No differences in the ADP : O ratio and electronmicroscopic details between the groups were found. Gasometric determinations in both anesthetized groups did not show any marked dysfunction of the respiratory system. It is concluded that decapitation leads to some changes in the functional integrity of rat heart mitochondria. Ketamine and thiopental anesthesia can be used with equal success for the isolation of mitochondria from the heart.