Deterioration of rat liver mitochondria under conditions of metabolite deprivation

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.

Quality control: from molecules to organelles

There is a vast body of literature on the quality control of protein folding and assembly into multisubunit complexes. Such control takes place everywhere in the cell. The correcting mechanisms involve cytosolic and organellar proteases; the result of such control is individual molecules with proper structure and individual complexes both with proper stoichiometry and proper structure. Obviously, the formation of organelles as such requires some additional criteria of correctness and some new mechanisms of their implementation. It is proposed in this article that the ability to carry out an integral (key) function may serve as a criterion of correct organelle assembly and that autophagy can be accepted as a mechanism eliminating the assembly mistakes.

Relation between accumulation of phospholipase A2 reaction products and Ca2+ release in isolated liver mitochondria

A Ca(2+)-dependent stimulation of mitochondrial phospholipase A2 is often assumed to play a role in mitochondrial Ca2+ release. We sought to clarify this relation by measuring Ca2+ transport and determining phospholipase A2 reaction products from the same sample of isolated, incubated rat liver mitochondria. When mitochondria had accumulated and spontaneously released again Ca2+, most probably by membrane permeability transition, there was no increase of phospholipase A2 reaction products. However, when the incubation was continued after Ca2+ release, significant increases of the content of lysophosphatidylcholine and unesterified fatty acids could be seen. Quinacrine, an inhibitor of phospholipase A2 activity, prevented Ca2+ release and p-hydroxymercuribenzoic acid, an inhibitor of lysophospholipid reesterification, induced a fast release of Ca2+ from isolated mitochondria. Such effects are usually taken as indirect evidence for a participation of phospholipase A2 in mitochondrial Ca2+ release, but analysis of the mitochondrial lipids revealed that no significant changes of the mass of phospholipase A2 reaction products had occurred. These experiments suggest that the accumulation of phospholipase A2 reaction products in mitochondria is the consequence rather than the cause of the membrane permeability transition. Exogenous phospholipase A2 products, lysophosphatidylcholine and arachidonic acid, induced mitochondrial Ca2+ release after a time lag, which decreased with aging of the mitochondrial preparation. The amount of lysophosphatidylcholine taken up by the mitochondria from the incubation medium during these experiments was measured and compared to the amount of lysophosphatidylcholine produced endogenously by mitochondrial phospholipase A2. From these data it appears likely that the amount of lysophosphatidylcholine generated in the mitochondria after the permeability transition is sufficient to sustain the permeable state. An accumulation of mitochondrially generated phospholipase A2 reaction products after the permeability transition could thus be a decisive factor for the limited reversibility of the membrane permeability transition.

Hypoxanthine, xanthine and uridine in body fluids, indicators of ATP depletion

Measurements of hyp, xan and urd in body fluids can provide evidence of energy, ATP, depletion in the body, in organs or in cells. Such information is clinically useful in the many diseases in which cellular energy supplies cannot be maintained like perinatal asphyxia, hydrocephalus and vascular insufficiency in brain, heart, limbs, kidneys or other organs. Similar HPLC methods using reversed-phase C18 columns and quantitation by UV absorption have been employed in a variety of centres to yield almost identical results. These have been assembled in this review to form a series of reference values. The current analytical problems are reviewed. Since concentrations of hyp and xan may alter independently situations are discussed in which separate measurements rather than their summed, total oxypurine concentrations are needed. The biochemistry and physiology underlying the use of such analyses is examined to guide sampling of the appropriate body fluid at a relevant time and to avoid oversimplified interpretation of results as well as unnecessary arguments. Specifically: (1) Intracellular concentrations of hyp and xan are inversely related to adenylate energy change and therefore to the energy currency of the cell ATP. Uridine in tissues is similarly 'controlled'. (2) There is extensive evidence that large increases in hyp, xan and urd in body fluids indicate ATP depletion. (3) Small changes in hyp probably reflect alterations of ATP turnover. (4) Xanthine arises mainly from guanine and can change independently of hyp. (5) Clinically useful information is obtainable from hyp and xan concentrations in CSF, amniotic fluid, urine and plasma. Extensive clinical correlations are reviewed. At present we are in a development phase for which HPLC is ideal but the most efficient way to perform and use such analyses in routine clinical practice remains to be established.

The effects of fetal energy depletion on amniotic fluid concentrations of amino acids, organic acids and related metabolites

Concentrations of amino and organic acids, phosphate, sulphate, gluconic acid and gluconolactone were measured in amniotic fluid samples which contained either normal or raised hypoxanthine concentrations. In this way, the effect of mild fetal ATP depletion could be determined. The effects of this mild asphyxia were to raise concentrations of phenylalanine, tyrosine, lysine, glycine, phosphate, sulphate, gluconic acid and glucono-1,5-lactone. However, concentrations of a variety of other metabolites were unchanged; thus no diagnostic confusion should arise with organic acidurias in mild asphyxia in contrast to the biochemical mimickry produced by severe asphyxia. Since clinically normal parturition can produce changes in amniotic fluid, urine from newborn or cord blood may not reflect the metabolic balance in utero.

Control of state 3 respiration in liver mitochondria from rats subjected to chronic ethanol consumption

Male Sprague-Dawley rats were pair-fed a liquid diet containing 36% of calories as ethanol for at least 31 days. Mitochondria were isolated from the livers and assayed for state 3, state 4 and uncoupled respiration at all three coupling sites. Assay conditions were established that maximized state 3 respiration with each substrate while maintaining a high respiratory control ratio. In mitochondria from ethanol-fed animals, state 3 respiratory rates were decreased at all three coupling sites. The decreased state 3 rate observed at site III was still significantly higher than the state 3 rates observed at site II in mitochondria from either ethanol-fed or control animals. Moreover, the maximal (FCCP-uncoupled) rates with succinate and alpha-ketoglutarate were the same in mitochondria from ethanol-fed and control animals, whereas with glutamate-malate as substrate it was lowered 23% by chronic ethanol consumption. To investigate the role of cytochrome oxidase in modulating the respiratory rate with site I and site II substrates, the effects of cyanide on state 3 and FCCP-uncoupled respiration were determined. When the mitochondria were uncoupled there was no decrease in the rate of succinate oxidation until the rates of ascorbate and succinate oxidation became equivalent. Conversely, parallel inhibition of ascorbate, succinate and glutamate-malate state 3 respiratory rates were observed at all concentrations (1-50 microM) of cyanide utilized. These observations suggest strongly that in coupled mitochondria ethanol-elicited decreases in cytochrome oxidase activity depress the state 3 respiratory rates with site I and II substrates.

Effect of oligomeric derivatives of prostaglandin B1 on oxidative phosphorylation and their Ca2+ ionophoretic activity

Dimers, trimers and tetramers of 15-dehydro-PGB1 and of 16,16'-dimethyl-15-dehydro-PGB1 have been synthesized and their effect on mitochondrial function evaluated. The trimers and tetramers, and to a lesser extent the dimers, of both series, protected isolated mitochondria from the loss of phosphorylating capacity during in vitro incubation. The monomers were inactive. The trimers and tetramers inhibited between 40 and 50% the F1F0-ATPase of submitochondrial particles. All of the oligomers, but not the monomers, had Ca2+ ionophoretic activity with isolated mitochondria. These activities are qualitatively similar to that reported for the oligomeric mixture of 15-dehydro-PGB1, termed PGBX.

A mathematical model to study short-term regulation of mitochondrial energy transduction

A mathematical model is presented which includes the following elementary process of mitochondrial energy transduction: hydrogen supply, proton translocation by the respiratory chain, proton-driven ATP synthesis by the F0F1-ATPase, passive back-flow of protons (leak) and carrier-mediated exchange of adenine nucleotides and phosphate. For these processes empirical rate laws are used. The model is applied to calculate time-dependent states of energy transduction in isolated rat liver mitochondria. From the general agreement of the computational results with experimental data (Ogawa, S. and Lee, T.M. (1984) J. Biol. Chem. 259, 10004-10011) the following conclusions can be drawn. (1) The length of the time interval during which mitochondria are able to maintain a relatively high and constant delta pH in the absence of oxygen (anaerobiosis) is limited by the availability of intramitochondrial ATP. (2) The overshoot kinetics of delta pH which appear when reoxigenating mitochondria after a preceeding anaerobiosis might be due to a lag phase kinetics of the F0F1-ATPase. (3) In phosphorylating mitochondria the homeostasis of delta pH is brought about by a high sensitivity of the respiration rate and the rate of the F0F1-ATPase as to changes of delta pH. (4) Analysis of the mean transient times shows that the rate of ATP synthesis in State 3 is controlled to almost the same extent by the hydrogen supply, the respiratory chain, the adenine nucleotide translocator and the proton leak.

Human placental mitochondrial respiration and its regulation by adenine nucleotides

Respiratory parameters were studied in mitochondria from human placenta. Respiratory control and ADP/O ratios were low in this preparation. The adenine nucleotide content of placental mitochondria was found to be only one quarter of that found for adult uterine muscle tissue mitochondria prepared in the same way. Loading placental mitochondria with adenine nucleotides by incubation in the presence of ATP produced increased respiratory control ratios but no improvement in ADP/O ratios. Our evidence is consistent with the developmental changes shown to occur in rat liver, in which an increased concentration of adenine nucleotides is responsible for changes in respiratory parameters.

Alloxan effects on mitochondria: study of oxygen consumption, fluxes of Mg2+, Ca2+, K+ and adenine nucleotides, membrane potential and volume change in vitro

Isolated mouse liver mitochondria incubated with alloxan showed stimulated resting (state 4) respiration with succinate, and inhibited resting respiration with pyridine-linked substrates, whereas active (state 3) respiration was decreased with both kinds of substrates. The effects were dependent on the concentration of alloxan, on the energy state, and on transport of inorganic phosphate and uptake of Ca2+. Using succinate as substrate, the effects of alloxan on endogenous Mg2+, K+ and adenine nucleotides, uptake of K+, accumulated Ca2+, membrane potential and volume were studied in liver mitochondria, and in addition efflux of endogenous K+ and accumulated Ca2+ were investigated in mouse islet mitochondria. High concentrations of alloxan (greater than or equal to 3 mmol/l) induced efflux of endogenous Mg2+, K+ and adenine nucleotides, efflux of accumulated Ca2+, inhibition of uptake of K+, loss of membrane potential, and swelling. Low concentrations of alloxan (less than 3 mmol/l) had similar effects only in the presence of added Ca2+ and inorganic phosphate. The influence of potentially protective agents was studied mainly with regard to alloxan induced swelling. Complete or partial protection was offered by antimycin A, malonate, La3+, Ni2+, ruthenium red, mersalyl and N-ethylmaleimide, suggesting requirement for energized transport of Ca2+ and uptake of inorganic phosphate. The start of the respiratory changes, decrease of membrane potential and loss of Mg2+ preceded the release of accumulated Ca2+, which occurred in parallel with efflux of K+ and swelling. The loss of Ca2+ in association with swelling agrees with data previously obtained using qualitative and quantitative electron microscopy and X-ray microanalysis of islet beta cells from alloxan-treated mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical and metabolic viability of a placental perfusion system in vitro under oxygenated and anoxic conditions

In vitro dual circuit perfusion of the placenta with well-oxygenated medium results in the continuous and stable consumption of oxygen and glucose over a 2-h perfusion period. This is reflected in a stable production of lactate and an energy charge which is higher at the end of the perfusion period than that seen in fresh placental tissue immediately after vaginal delivery. Anoxic perfusion causes an increase in glucose consumption which is more than twofold higher than that seen in the oxygenated perfusion, resulting finally in placental uptake of glucose not only from the maternal but also from the fetal circulation. Lactate production is increased during the anoxic perfusion, while the final tissue energy charge value lies between the values observed for fresh tissue and for the oxygenated perfusion. The shift to anaerobic metabolism shown by placental tissue in anoxic conditions enables continued functioning of the tissue over the 2-h perfusion period but it appears that under anoxic conditions the tissue may incur an energy debt not observed in oxygenated perfusions.

Respiratory activities of subsarcolemmal and intermyofibrillar mitochondrial populations isolated from denervated and control rat soleus muscles

Ultraturrax and Nagarse released populations of mitochondria isolated from control and day 21 denervated rat soleus muscle were characterized with respect to their oxidative phosphorylation, ADP translocase and ATPase activities. Both Ultraturrax and Nagarse released mitochondrial populations displayed lower capacities for oxidative phosphorylation; lower ADP translocase activities and higher Mg2+ stimulated ATPase activities than their corresponding controls. For both the denervated and control states, the Nagarse-released mitochondrial populations displayed significantly higher respiratory activities than the Ultraturrax released fractions. The significance of these findings is discussed with regard to the process of mitochondrial respiratory control. In addition the role of mitochondrial dysfunction in denervation muscular atrophy is assessed.

Control of adenine nucleotide metabolism in hepatic mitochondria from rats with ethanol-induced fatty liver

Male rats developed fatty liver after being fed on an ethanol-containing diet for 31 days. Liver mitochondria from these animals catalysed ATP synthesis at a slower rate when compared with mitochondria from pair-fed control rats (control mitochondria), and demonstrated lowered respiratory control with succinate as substrate, owing to a decrease in the State-3 respiratory rate. Respiration in the presence of uncoupler was comparable in mitochondria from both groups of rats. Translocation of both ATP and ADP was decreased in mitochondria from ethanol-fed rats, with ADP uptake being lowered more dramatically by ethanol feeding. Parameters influencing adenine nucleotide translocation were investigated in mitochondria from ethanol-fed rats. Experiments performed suggested that lowered adenine nucleotide translocation in these mitochondria is not the result of inhibition of the translocase by either long-chain acyl-CoA derivatives or unesterified fatty acids. Analysis of endogenous adenine nucleotides in these mitochondria revealed lowered ATP concentrations, but no decrease in total adenine nucleotides. In experiments where the endogenous ATP in these mitochondria was shifted to higher concentrations by incubation with oxidizable substrates or defatted bovine serum albumin, the rate of ADP translocation was increased, with a linear correlation being observed between endogenous ATP concentrations and the rate of ADP translocation. The depressed ATP concentration in mitochondria from ethanol-fed rats suggests that the ATP synthetase complex is replenishing endogenous ATP at a slower rate. The lowered ATPase activity of the ATP synthetase observed in submitochondrial particles from ethanol-fed animals suggests a decrease in the function of the synthetase complex. A decrease in the rate of ATP synthesis in mitochondria from ethanol-fed rats is sufficient to explain the decreased ADP translocation and State-3 respiration.

Effect of dietary ethanol and cholesterol on metabolic functions of hepatic mitochondria and microsomes from the monkey, Macaca nemestrina

Monkeys (Macaca nemestrina) were divided into four groups, and each group was fed a particular diet. The variables in the diets were as follows: diet A, 0.3 mg cholesterol/kcal nutrient; diet B, 1.0 mg cholesterol/kcal nutrient; diet C, 0.3 mg cholesterol/kcal nutrient, ethanol (36% of calories); diet D, 1.0 mg cholesterol/kcal nutrient, ethanol (36% of calories). Monkeys on the diets containing ethanol developed fatty liver. Mitochondria from ethanol-fed animals demonstrated significant decreases in uncoupler-stimulated, state 3, and state 4 succinate oxidation activity; respiratory control ratio; and ATP content. Liver microsomes isolated from the ethanol-fed groups demonstrated increased ethanol oxidizing activity with either NADPH or H2O2 as cosubstrate. Aniline hydroxylase and aminopyrine-N-demethylase activities were also elevated in ethanol-fed animals. The alterations in these functional properties were related primarily to ethanol in the diets. Cholesterol, while being less of a perturbant than ethanol, did elicit a significant decrease in cytochrome oxidase activity of mitochondria and a small but statistically significant increase in microsomal-associated ethanol oxidation activity. It appeared to potentiate the effect of ethanol in lowering mitochondrial respiratory control and ATP concentrations.

Control of adenine nucleotide translocation in liver mitochondria from ethanol-fed rats

Male rats developed fatty liver after being fed an ethanol-containing diet for 31 days. Liver mitochondria from these animals (ethanol mitochondria) catalyzed ATP synthesis at a slower rate than did mitochondria from pair-fed control rats (control mitochondria). Furthermore, ATP translocation was decreased in ethanol mitochondria and parameters influencing such were investigated. Several experiments indicated that ADP uptake into ethanol mitochondria is not decreased due to inhibition of the adenine nucleotide translocase by either long chain acyl CoA derivatives or unesterified fatty acids. Analyses of endogenous adenine nucleotides in ethanol mitochondria revealed lower ATP concentrations, but no decrease in total adenine nucleotides. In experiments where endogenous ATP was shifted to higher concentrations by incubation with BSA, the rate of ADP translocation was increased, with a linear correlation being observed between endogenous ATP concentrations and the rate of ADP translocation. The depressed ATP concentration in ethanol mitochondria suggests that the ATP synthetase complex is replenishing endogenous ATP at a slower rate. A decrease in the rate of ATP synthesis in ethanol mitochondria is sufficient to explain the decreased ADP translocation.