STUDIES ON ESSENTIAL FATTY ACID DEFICIENCY. EFFECT OF THE DEFICIENCY ON THE LIPIDS IN LIVER MITOCHONDRIA AND OXIDATIVE PHOSPHORYLATION

Oxidative phosphorylation in intact hepatocytes: quantitative characterization of the mechanisms of change in efficiency and cellular consequences

Two mechanisms may affect the yield of the oxidative phosphorylation pathway in isolated mitochondria: (i) a decrease in the intrinsic coupling of the proton pumps (H+/2e- or H+/ATP), and (ii) an increase in the inner membrane conductance (proton or cation leak). Hence three kinds of modifications can occur and each of them have been characterized in isolated rat liver mitochondria (see preceding chapter by Rigoulet et al.). In intact isolated hepatocytes, these modifications are linked to specific patterns of bioenergetic parameters, i.e. respiratory flux, mitochondrial redox potential, DY, and phosphate potential. (1) The increase in H+/ATP stoichiometry of the mitochondrial ATP synthase, as induced by almitrine [20], leads to a decrease in mitochondrial and cytosolic ATP/ADP ratios without any change in the protonmotive force nor in the respiratory rate or redox potential. (2) In comparison to carbohydrate, octanoate metabolism by beta-oxidation increases the proportion of electrons supplied at the second coupling site of the respiratory chain. This mimics a redox slipping. Octanoate addition results in an increased respiratory rate and mitochondrial NADH/NAD ratio while protonmotive force and phosphate potential are almost unaffected. The respiratory rate increase is associated with a decrease in the overall apparent thermodynamic driving force (2deltaE'o - ndeltap) which confirms the 'redox-slipping-like' effect. (3) An increase in proton conductance as induced by the protonophoric uncoupler 2,4-dinitrophenol (DNP) leads to a decrease, as expected, in the mitochondrial NADH/NAD and ATP/ ADP ratios and in deltapsi while respiratory rate is increased. Thus, each kind of modification (proton leak, respiratory chain redox slipping or increase in H+/ATP stoichiometry of ATPase) is related to a specific set of bioenergetic parameters in intact cells. Moreover, these patterns are in good agreement with the data found in isolated mitochondria. From this work, we conclude that quantitative analysis of four bioenergetic parameters (respiration rate, mitochondrial NADH/ NAD ratio, protonmotive force and mitochondrial phosphate potential) gives adequate tools to investigate the mechanism by which some alterations may affect the yield of the oxidative phosphorylation pathway in intact cells.

Quantitative analysis of some mechanisms affecting the yield of oxidative phosphorylation: dependence upon both fluxes and forces

The purpose of this work was to show how the quantitative definition of the different parameters involved in mitochondrial oxidative phosphorylation makes it possible to characterize the mechanisms by which the yield of ATP synthesis is affected. Three different factors have to be considered: (i) the size of the different forces involved (free energy of redox reactions and ATP synthesis, proton electrochemical difference); (ii) the physical properties of the inner mitochondrial membrane in terms of leaks (H+ and cations); and finally (iii) the properties of the different proton pumps involved in this system (kinetic properties, regulation, modification of intrinsic stoichiometry). The data presented different situations where one or more of these parameters are affected, leading to a different yield of oxidative phosphorylation. (1) By manipulating the actual flux through each of the respiratory chain units at constant protonmotive force in yeast mitochondria, we show that the ATP/O ratio decreases when the flux increases. Moreover, the highest efficiency was obtained when the respiratory rate was low and almost entirely controlled by the electron supply. (2) By using almitrine in different kinds of mitochondria, we show that this drug leads to a decrease in ATP synthesis efficiency by increasing the H+/ATP stoichiometry ofATP synthase (Rigoulet M et al. Biochim Biophys Acta 1018: 91-97, 1990). Since this enzyme is reversible, it was possible to test the effect of this drug on the reverse reaction of the enzyme i.e. extrusion of protons catalyzed by ATP hydrolysis. Hence, we are able to prove that, in this case, the decrease in efficiency of oxidative phosphorylation is due to a change in the mechanistic stoichiometry of this proton pump. To our knowledge, this is the first example of a modification in oxidative phosphorylation yield by a change in mechanistic stoichiometry of one of the proton pumps involved. (3) In a model of polyunsaturated fatty acid deficiency in rat, it was found that non-ohmic proton leak was increased, while ohmic leak was unchanged. Moreover, an increase in redox slipping was also involved, leading to a complex picture. However, the respective role of these two mechanisms may be deduced from their intrinsic properties. For each steady state condition, the quantitative effect of these two mechanisms in the decrease of oxidative phosphorylation efficiency depends on the values of different fluxes or forces involved. (4) Finally the comparison of the thermokinetic data in view of the three dimensional-structure of some pumps (X-ray diffraction) also gives some information concerning the putative mechanism of coupling (i.e. redox loop or proton pump) and their kinetic control versus regulation of mitochondrial oxidative phosphorylation.

Flux-force relationships in intact cells: a helpful tool for understanding the mechanism of oxidative phosphorylation alterations?

On isolated mitochondria, numerous studies of the relationships between fluxes and their associated forces have led to the description of some properties of the oxidative phosphorylation pathway. However whether such an approach can be applied to understanding the actual situation in intact living cells needs further consideration. In this study on isolated hepatocytes, we describe the dependence of the respiratory rate on the three thermodynamic forces linked to oxidative phosphorylation (i.e. the redox span over the respiratory chain, the electrical potential difference across the inner mitochondrial membrane and the free energy of ATP synthesis reaction). Even if this description is phenomenological and some objections may be raised regarding the relevance of such a bulk-phase force estimation, we present some results showing that the study of flux-force relationships in intact cells may be a helpful approach for understanding the mechanisms by which oxidative phosphorylation activity is changed.

Effect of polyunsaturated fatty acids deficiency on oxidative phosphorylation in rat liver mitochondria

Liver mitochondria isolated from controls or polyunsaturated fatty acid (PUFA) deficient rats were studied for oxidative phosphorylation. A PUFA-deficient diet led to a dramatic change in the fatty acid composition of mitochondrial lipid content, similar to that reported in the literature. Besides the changes in lipid composition, mitochondrial volume was enlarged (+45% in state 4 and two-fold in state 3). State 4 respiration was increased together with a decrease in protonmotive force. The non-ohmicity of the relationship between non-phosphorylating respiration and protonmotive force was more pronounced in the PUFA-deficient group. State 3 oxygen consumption as well as the rate of ATP synthesis showed no difference between the two groups, whereas the protonmotive force decreased substantially in mitochondria from PUFA-deficient animals. In contrast, ATP/O ratios were decreased in the PUFA-deficient group when determined at subsaturating ADP concentration. Taken together, these results are in agreement with both an increased non-ohmic proton leak and an increased redox slipping. The relative importance of these two effects on the overall efficiency of oxidative phosphorylation depends on both the rate of oxidative phosphorylation and the maintained protonmotive force. Hence, in isolated mitochondria the respective role of each effect may vary between state 4 and state 3.

Thermogenesis secondary to transdermal water loss causes growth retardation in essential fatty acid-deficient rats

Manifestations of essential fatty acid (EFA) deficiency in rats include growth retardation and increased transdermal water loss. The extra metabolic energy requirement could be caused by greater evaporative water loss from the skin surface. To test this hypothesis, 38 weanling rats were randomly assigned to one of two environments, control (CE) at 20 degrees C and 40% humidity or warm/humid (WHE) at 30 degrees C and 90% humidity. Half of the 20 CE rats were fed an EFA-adequate diet and the other 10 an EFA-deficient diet; the 18 WHE rats were also equally partitioned to the two diets. CE and WHE animals were independently group-fed to maintain equal energy intakes within each environment. Weight gain at 90 days was lower for CE EFA-deficient rats than for CE EFA-adequate rats (P < .0001). Growth rates in the WHE to 140 days did not differ. Mean weights at 90 days were as follows: CE EFA-adequate, 196 g; CE EFA-deficient, 148 g; WHE EFA-adequate, 148 g; WHE EFA-deficient, 135 g. In both CE and WHE animals, the triene/tetraene ratio of both serum and liver phospholipids (PL) was 100-fold greater for EFA-deficient versus EFA-adequate diets. PL fatty acids of liver in CE and WHE EFA-deficient rats contained 2.09 and 1.92 micrograms of 20:3 omega 9 per micrograms phosphorus (Pi), respectively, compared with 0.03 and 0.02 microgram 20:3 omega 9/micrograms Pi in CE and WHE EFA-adequate rats. These results indicate equivalent degrees of EFA deficiency in the two environments.(ABSTRACT TRUNCATED AT 250 WORDS)

Compositional changes of fatty acids in the 1(1")-and 2(2")-positions of cardiolipin from liver, heart, and kidney mitochondria of rats fed a low-fat diet

Cardiolipins from liver, heart and kidney mitochondria of rats fed a fat-free diet for 66 days have been analyzed for their fatty acid composition and positional distribution. The main effect was a dramatic decrease of linoleic acid which was counterbalanced by increases in the levels of palmitoleic, oleic and cis-vaccenic acids. Linoleic acid remains asymmetrically distributed between positions 1(1") and 2(2") with a positive selectivity for positions 1(1"). Its decrease is considerably faster in positions 2(2") than in positions 1(1"), which would suggest different rates of fatty acid turnover. Fat deficiency induces the appearance of 18:2(n-7) and a significant increase of 20:3(n-6) (dihomo-gamma-linolenic acid) in liver and kidney cardiolipins. In contrast, 20:3(n-6) level remains unchanged in other mitochondrial phospholipids. 18:2(n-7) and 20:3(n-6) are almost evenly distributed between both pairs of positions. Both acids have a common structural feature, that is double bonds in positions 8 and 11. 20:3(n-9) accumulates in large amounts in other mitochondrial phospholipids, but not in cardiolipins. Although surprising, 20:3(n-6) has thus to be considered as a specific marker of deficiency for cardiolipins when it is esterified to positions 1(1"). Taking into account various analytical data, it would appear that positions 1(1") of cardiolipins can only incorporate unsaturated fatty acids containing at least one cis double bond in position 8 or 9, with no other double bond between these positions and the carboxylic group.

Non-shivering thermogenesis and brown adipose tissue activity in essential fatty acid deficient rats

The effects of essential fatty acid (EFA) deficiency on energetic metabolism and interscapular brown adipose tissue (BAT) activity were examined in the cold acclimated rat. Weanling male Long-Evans rats were fed on a low fat semipurified diet (control diet, 2% sunflower oil; EFA deficient diet, 2% hydrogenated coconut oil) for 9 weeks. They were exposed at 5 degrees C for the last 5 weeks. In EFA deficient rats, compared to controls, growth retardation reached 22% at sacrifice. Caloric intake being the same in the two groups, it follows that food efficiency was decreased by 40%. Resting metabolism in relation to body surface area was 25% increased. Calorigenic effect of norepinephrine (NE) in vivo (test of non-shivering thermogenesis) underwent a marked decrease of 34%. BAT weight was 21% decreased but total and mitochondrial protein content showed no variation. A 26% increase in purine nucleotide binding per BAT (taken as an index of thermogenic activity) was observed, suggesting that the enhancement in resting metabolism observed was mainly due to increased BAT thermogenesis. However, BAT mitochondria respiratory studies which are more direct functional tests showed a marked impairment of maximal O2 consumption of about 30% with palmitoyl-carnitine or acetyl-carnitine (both in presence of malate) or with alpha-glycerophosphate as substrate. It is likely that this impaired maximal BAT oxidative capacity may explain the impaired NE calorigenic effect in vivo. A possible increase in mitochondrial basal permeability is also discussed.

Relation between membrane phospholipid composition, fluidity and function in mitochondria of rat brown adipose tissue. Effect of thermal adaptation and essential fatty acid deficiency

Male weanling rats were maintained either at 28 degrees C (thermoneutrality) or at 5 degrees C (cold adaptation). During 9 weeks they were fed either a 2% hydrogenated coconut oil diet deficient in essential fatty acids or a diet containing 2% sunflower oil. The respective incidences of cold adaptation and of EFA deficiency on lipid composition of mitochondrial membranes from brown adipose tissue (BAT) were investigated. Using 1,6 diphenylhexatriene (DPH) as a probe, the parameters of membrane fluidity were estimated by steady-state fluorescence polarization measurements (rs) and by time-resolved fluorescence anisotropy decay (order parameter S). Cold acclimation induced a decrease of phosphatidylcholine to phosphatidylethanolamine (PC/PE ratio), an increase of the total fatty acid unsaturation index (T.U.). EFA deficiency had the same effect as cold on the PC/PE ratio, but decreased T.U. Cold adaptation induced a larger decrease of S than of rs, whereas EFA deficiency only increased rs and did not modify S. In liposomes prepared from mitochondrial lipids, rs values were smaller than in whole mitochondria. Both in cold-adapted and in EFA-deficient rats the variations of rs were correlated with lipid unsaturation. Comparison between BAT thermogenic activity, assessed by GDP binding and proportions of PE and PC showed a high correlation suggesting a change in the membrane occurring with the increase of mitochondrial activity that could be related to phospholipid composition rather than to membrane fluidity.

Variations in energization parameters and proton conductance induced by cold adaptation and essential fatty acid deficiency in mitochondria of brown adipose tissue in the rat

Male weanling Long-Evans rats were fed on a low-fat semipurified diet (control diet, 2% sunflower oil; essential fatty acid (EFA) deficient diet, 2% hydrogenated coconut oil) for 9 weeks. In order to modulate need for non-shivering thermogenesis, groups of rats on each diet were exposed at 28 degrees C (thermoneutrality) and at 5 degrees C (cold acclimation) for the last 5 weeks. In brown adipose tissue (BAT) mitochondria, several parameters of mitochondrial energization, protonmotive force (delta p) and its components delta pH and membrane potential, delta psi, were investigated. Simultaneous measurement of oxygen consumption and delta psi (the main component of delta p) was performed by varying alpha-glycerophosphate concentration and the force/flux relationship of the mitochondria was established by comparison of proton conductance, CmH+, over the whole range of protonmotive force. delta p. In the absence of GDP, at 28 degrees C, EFA deficiency induced a marked increase in CmH+. Cold acclimation led to comparable enhanced CmH+ in control and EFA-deficient mitochondria. In the presence of GDP which binds and inhibits the BAT 32 kDa uncoupling protein, CmH+ was the same in 28 degrees C and 5 degrees C control mitochondria, but EFA deficiency led to an enhanced GDP independent CmH+ at 28 degrees C and to a lesser extent at 5 degrees C. These results are discussed with reference to substantial changes in mitochondrial lipid composition induced by the deficiency.

Essential fatty acid-deficient rats. I. Growth and testes development

Partially hydrogenated oils as the sole dietary fat enhances the development of essential fatty acid (EFA) deficiency in young rats. Partially hydrogenated herring oil (HHO) caused total impairment of the spermatogenic tissue after five weeks of experiment, while partially hydrogenated arachis oil (HAO) caused severe degeneration of this tissue in 15 weeks. A fat‐free diet caused degeneration in 26 weeks. In the dietary fats, the total content oftrans acids, calculated as elaidic acid, was 47% and 23% in HAO and HHO, respectively. Further, varying amounts of different positional isomeric fatty acids were also present in the partially hydrogenated oils. Besides the specific tissue changes, poor growth, poor feed efficiency and skin signs characteristic of EFA deficiency were noticed. On the other hand, partially hydrogenated soybean oil (HSO) as the sole dietary fat kept the animals normal in all respects. this oil still contained 32% linoleic acid; the total content oftrans acids amounted to 11%, calculated as elaidic acid.

Effect of ethanol on rat liver. 4. The influence of vitamins, electrolytes and amino acids on the structure and function of mitochondria from rats receiving ethanol

1. Feeding rats with a 15% ethanol solution for several weeks caused structural and functional changes in their liver mitochondria, although their intake of solid food was about the same as that of the controls.

2. Attempts were made to counteract these effects of ethanol by increasing the intake of amino acids, vitamins, lipotropic compounds and electrolytes beyond that which is adequate when water is the drinking fluid.

3. An increased intake of nicotinic acid, together with aqueous ethanol, caused a further enlargement of the mitochondria above that obtained with ethanol solution alone. the diluted matrix observed with the ethanol and nicotinic acid treatment suggested that water imbibition by the mitochondria caused this further enlargement.

4. In rats receiving ethanol fortified with magnesium sulphate and lipotropic compounds (choline, methionine) there was a further increase in mitochondrial size, as compared with those receiving ethanol alone. The matrix was, however, of the same density as in the mitochondria from the rats receiving ethanol alone. the oxidation rate of pyruvate and succinate was unchanged, but α-glycerophosphate and β-hydroxybutyrate were oxidized at a higher rate than in mitochondria from rats drinking ethanol or water.

5. When the ethanol solution was supplemented with amino acids (casein hydrolysate), vitamins and electrolytes, the mitochondrial enlargement after 120 days of treatment was less than with ethanol alone and was completely absent after 300 days. the oxidation rate of pyruvate and succinate was, however, not fully restored to normal.

Lysosomes and essential fatty acid deficiency

The hydrolytic activity usually associated with lysosomes increased in the homogenates and subcellular fractions of rat liver as a result of essential fatty acid (EFA) deficiency. The proportion of the total (tissue homogenate) activity found in each subcellular fraction, however, was unchanged by EFA deficiency.Lysosomes isolated from normal and EFA-deficient rat livers differed significantly in their stability to thermal and osmotic variations. This suggested that lysosomal membranes, like other membranes, were altered by EFA deficiency.In spite of increased tissue-bound hydrolytic activity and altered lysosomal membranes, hydrolytic activity of the serum was not markedly changed in EFA deficiency. These minor changes in hydrolytic activity and in lysosomal membrane stability seemed insufficient to explain the general lesions of EFA deficiency.