A rapid method for the isolation of intact mitochondria from isolated rat liver cells

An Update on Isolation of Functional Mitochondria from Cells for Bioenergetics Studies

Mitochondria are the organelles where the most fundamental processes of energy transformation within the cell are located. They are also involved in several processes like apoptosis and autophagy, reactive oxygen species formation, and calcium signaling, which are crucial for proper cell functioning. In addition, mitochondrial genome hosts genes encoding important proteins incorporated in respiratory chain complexes and indispensable for the oxidative phosphorylation. Studying isolated mitochondria is, therefore, crucial for better understanding of cell physiology. The presented protocol describes a relatively simple and handy method for crude mitochondrial fraction isolation from different mammalian cell lines. It includes mechanical cells disruption (homogenization) and differential centrifugation. In addition, this chapter presents two basic ways to assess mitochondrial functionality: by measuring mitochondrial inner membrane potential and coupled respiration.

Fragrance chemicals lyral and lilial decrease viability of HaCat cells' by increasing free radical production and lowering intracellular ATP level: protection by antioxidants

We investigate in this study the biochemical effects on cells in culture of two commonly used fragrance chemicals: lyral and lilial. Whereas both chemicals exerted a significant effect on primary keratinocyte(s), HaCat cells, no effect was obtained with any of HepG2, Hek293, Caco2, NIH3T3, and MCF7 cells. Lyral and lilial: (a) decreased the viability of HaCat cells with a 50% cell death at 100 and 60 nM respectively; (b) decreased significantly in a dose dependant manner the intracellular ATP level following 12-h of treatment; (c) inhibited complexes I and II of electron transport chain in liver sub-mitochondrial particles; and (d) increased reactive oxygen species generation that was reversed by N-acetyl cysteine and trolox and the natural antioxidant lipoic acid, without influencing the level of free and/or oxidized glutathione. Lipoic acid protected HaCat cells against the decrease in viability induced by either compound. Dehydrogenation of lyral and lilial produce α,β-unsaturated aldehydes, that reacts with lipoic acid requiring proteins resulting in their inhibition. We propose lyral and lilial as toxic to mitochondria that have a direct effect on electron transport chain, increase ROS production, derange mitochondrial membrane potential, and decrease cellular ATP level, leading thus to cell death.

Linalool decreases HepG2 viability by inhibiting mitochondrial complexes I and II, increasing reactive oxygen species and decreasing ATP and GSH levels

Coriander is used as an appetizer, a common food seasoning in Mediterranean dishes, and a remedy for many ailments. In this study we tested the biochemical effect of its essential oil components, in particular linalool, its main component. The oil extract was prepared by hydro-distillation of coriander seeds. The various components were identified by gas chromatography coupled to mass spectroscopy. The effect of the various oil components on the viability of different cell lines (HepG2, Caco2, NIH3t3, MCF7 and Hek293) was examined using MTT assay. Linalool was the most potent and HepG2 cells the most sensitive. A 50% and 100% decrease in the viability of HepG2 was obtained at 0.4 microM and 2 microM linalool, respectively. Whereas none of the other components exerted a significant effect at concentrations lower than 50 microM, myrcene and nerolidol, the structural analogues of linalool, were more potent at 100 microM than the other components decreasing HepG2 viability to 26%. The biochemical effect of linalool on mitochondria isolated from HepG2 showed a concentration-dependent inhibition in complexes I and II activities of the respiratory chain, and a time-dependent decrease in ATP level. In addition, a time-dependent decrease in glutathione (GSH) level and in the reduction of nitroblue tetrazolium was obtained, indicating increase in reactive oxygen species (ROS) generation. Pretreatment with the antioxidants: N-acetyl cysteine (2mM), Trolox (100 microM) and different flavonoids (50 microM) was partially protective against the linalool-induced cell death; the most effective response was that of rutin and apigenin which restored 91% of HepG2 viability. We hereby report a decrease in cell viability of HepG2 cells by linalool and identify the mitochondria as one possible target for its site of action, inhibiting complexes I and II and decreasing ATP. In addition linalool increased ROS generation and decreased GSH level.

Copper-adenine complex, a compound, with multi-biochemical targets and potential anti-cancer effect

A series of adenine-copper complexes (1-6) with various ligands (Cl(-), SCN(-), BF(4)(-) and acac [acetylacetonate ion]) have been synthesized and characterized by elemental analysis, infrared spectroscopy and thermal analysis. Among the six complexes only complex (1), Cu(2)(adenine)(4)Cl(4).2EtOH (abbreviated as Cu-Ad), demonstrated some toxic effect on different cell lines. In vitro investigations of the biological effect of Cu-Ad complex have shown that it: (1) binds genomic DNA; (2) decreases significantly, the viability of cells in culture in a concentration (15-125 microM)-dependant manner; an estimated IC(50) of: 45 microM with HepG2; 73 microM with C2C12; 103 microM with NIH3T3; and 108 microM with MCF7. Cu-Ad had no effect on A549 cells; (3) inhibits Taq polymerase-catalyzed reaction; (4) inhibits the binding of the transcription factor GATA-5 to labeled DNA probes; (5) inhibits mitochondrial NADH-UQ-reductase with an estimated IC(50) of 2.8 nmol, but had no effect on succinate dehydrogenase activity; (6) increases reactive oxygen species (60%) at 45 microM Cu-Ad; and (7) decreases ATP (80%) at 50 microM Cu-Ad. The new compound Cu(2)(adenine)(4)Cl(4).2EtOH (Cu-Ad), belongs to a class of copper-adenylate complexes that target many biochemical sites and with potential anti-cancer activity.

Determination of the intracellular protein thiol distribution of hepatocytes using monobromobimane derivatisation of intact cells and isolated subcellular fractions

The derivatisation of intact rat hepatocytes with monobromobimane resulted in rapid labelling of accessible protein thiols in several subcellular fractions. The derivatisation procedure did not cause acute cytotoxicity, nor did it alter the buoyant densities of the fractions or their gross protein compositions. Quantitation of the fluorescence irreversibly associated with the fractions demonstrated considerable intracellular heterogeneity in this pool of thiols. Values were highest in cytosol (ca. 90 nmol/mg protein), intermediate in microsomes (ca. 65 nmol/mg protein) and mitochondria (ca. 45 nmol/mg protein) and lowest in a crude fraction containing both nuclei and plasma membrane (ca. 35 nmol/mg protein). Similar values were obtained from microsomes and cytosol derivatised after fractionation but there were significant increases of ca. 100% in corresponding values from isolated mitochondria and the nuclear/plasma membrane fraction. These results are discussed in terms of the dynamic fluxes in monobromobimane protein thiols during fractionation and the applicability of this noninvasive method to studies of the mechanism(s) of toxicity of reactive xenobiotics and the role(s) of protein thiols in normal cellular function.

Stimulation by D-glucose of mitochondrial respiration

D-glucose increases O2 uptake by cerebellum mitochondria. This effect is abolished by D-glucose-6-phosphate and D-mannoheptulose. It is proposed that the phosphorylation of D-glucose as catalyzed by bound hexokinase directly affects mitochondrial respiration.

Rhodamine 123 inhibits import of rat liver mitochondrial transhydrogenase

Rhodamine 123, a laser dye, has been demonstrated to inhibit import of the precursor to pyridine dinucleotide transhydrogenase into mitochondria in rat liver cells. When rat hepatocytes were labeled with 35[S] methionine in the presence of 0.4 mM rhodamine 123, the precursor to transhydrogenase was found to have a half-life in the cytoplasm of 15 minutes as opposed to a half-life of 1-2 minutes when cells were radiolabeled in the absence of the dye. To clarify the mechanism of import inhibition, studies were initiated to assess the effect of rhodamine 123 on mitochondrial respiration. Upon addition of the dye to a mitochondrial suspension, respiration was initially enhanced, then inhibited. The inability of FCCP, a classical uncoupler, to enhance respiration during the inhibitory phase suggests that rhodamine 123 is primarily inhibiting respiration through the electron transport system rather than through the ATPase. These results suggest that rhodamine 123 may inhibit import of the transhydrogenase precursor into mitochondria by disrupting components in the mitochondrial membrane necessary for efficient import.

Import and processing of cytochrome b-c1 complex subunits in isolated hepatoma ascites cells. Inhibition by Rhodamine 6G

The import and processing of cytochrome c1 and the iron sulfur protein of the cytochrome b-c1 complex were studied in Zajdela hepatoma ascites cells. Both peptides were synthesized as larger percursor molecules which were approximately 2-3 kDa and 5-6 kDa larger than the mature forms of apocytochrome c1 and apo-iron sulfur protein, respectively. Comparison of these precursors to those reported for functionally homologous peptides in yeast and Neurospora indicate significant size changes have occurred in mammals. Rhodamine 6G, a specific vital stain for mitochondria, is a potent inhibitor of precursor processing in isolated hepatoma cells. Both precursor to cytochrome c1 and precursor to FeS accumulate in the soluble and particulate fractions obtained by digitonin treatment of tumor cells treated with Rhodamine 6G. Appearance of the mature peptides was abolished. The precursors are unstable, however, and disappear from the cytosolic and membrane fractions during a 10 min chase. Comparison of the effects of Rhodamine 6G and carbonylcyanide m-chlorophenylhydrazone on precursor processing shows that: (a) Rhodamine 6G is a more effective inhibitor of processing, (b) it has less of an inhibitory effect on cellular protein synthesis, and (c) it inhibits processing under conditions in which it appears to have little influence on coupled respiration in whole cells. The data suggest that the most likely mode of action of Rhodamine 6G is on the matrix processing step.

Subcellular distribution of lead in cultured rat hepatocytes

A clear understanding of the sequence and molecular mechanism of the events involved in lead toxicity is hampered by a lack of information about lead compartmentation within the cell. As part of a continuing effort to identify the mechanism by which lead affects cellular functions, we examined the subcellular distribution of 210Pb in cultured hepatocytes. The cells were isolated, labeled, homogenized in sucrose-N-[(2-hydroxyethyl)piperazine]-N'-2-ethanesulfonic acid buffer, and fractionated into mitochondrial, microsomal, and cytosolic components by differential centrifugation. Complete fractionation of the cells revealed that 71% of the cellular 210Pb was associated with the mitochondria, 5% with the microsomes, and 24% with the cytosol. A modified, rapid fractionation procedure indicated that 45% of the cellular lead was associated with both the mitochondria and the cytosol and 10% with the microsomes. When the cells were separated into total particulates and cytosol with a single centrifugation, 22% of the 210Pb was associated with the soluble fraction. The process of homogenization and fractionation of the isolated hepatocytes altered the intracellular distribution of 210Pb. This experimental approach to studying the localization of lead may be compromised by the redistribution of 210Pb during the extensive centrifugations and resuspensions required for subcellular fractionation and suggests that the subcellular distribution patterns of 210Pb obtained by the fractionation of cells reflects the distribution of lead in the homogenate rather than the distribution of 210Pb in the intact cell.

Immunochemical analysis of the membrane proteins of rat liver and Zajdela hepatoma mitochondria

The contents of mitochondrial inner membrane protein complexes were compared in normal liver and in Zajdela hepatoma mitochondria by the immunotransfer technique. Antibodies against core proteins 1 and 2, cytochrome c1, the iron-sulfur protein of Complex III, subunits I and II of cytochrome oxidase, and the alpha and beta subunits of the F1-ATPase were used. In addition, antibodies against a primary dehydrogenase, beta-hydroxybutyrate dehydrogenase, as well as the outer membrane pore protein were used. The results indicate that the components of the cytochrome chain and porin are greatly enriched in hepatoma mitochondria compared to normal rat liver mitochondria. This enrichment was also reflected in the rates of respiration in tumor mitochondria using a variety of substrates. Enrichment of porin may partially account for increased hexokinase binding to tumor mitochondria. In contrast to the respiratory chain components, the F1-ATPase and F0 (measured by DCCD binding) were not increased in tumor mitochondria. Thus, Zajdela hepatoma mitochondria components are nonstoichiometric, being enriched in oxidative capacity but relatively deficient in ATP synthesizing capacity. Finally, beta-hydroxybutyrate dehydrogenase, which is often decreased in hepatoma mitochondria, was shown here by immunological methods to be decreased by only 40%, whereas enzyme activity was less than 5% of that in normal rat liver.

Regulation of biosynthesis of the rat liver inner mitochondrial membrane by thyroid hormone

Regulation of mitochondrial protein synthesis by thyroid hormone has been studied in isolated rat hepatocytes and liver mitochondria. Small doses (5 micrograms/100 g body wt) of triiodothyronine (T3) injected into hypothyroid rats increased both state 3 and 4 respiration by approximately 100%, while the ADP:O ratio remained constant. This suggests that T3 increases the numbers of functional respiratory chain units. T3 also induces mitochondrial protein synthesis by 50-100%. Analysis of the mitochondrial translation products show that all of the products were induced. No differential translation of the peptides involved in the respiratory chain was found. Regulation of the cytoplasmically made inner membrane peptides was also investigated in isolated hepatocytes. The majority of these peptides were not influenced by T3, in contrast to the finding with mitochondrial translation products. Those found to be regulated by T3 belong to two subsets, which were either induced or repressed by hormone. Thus, T3 stimulated a general increase in the synthesis of mitochondrially translated inner membrane peptides, but regulates selectively those inner membrane peptides translated on cytoplasmic ribosomes. The findings suggest that hormone regulation of the respiratory chain is exerted through a few selective proteins, perhaps those which require subunits made from both nuclear and mitochondrial genes.

Identification and partial purification of a heart mitochondrial membrane proteinase

Membrane-bound proteinase activity was demonstrated by a solid-phase assay system in both beef heart and rat liver mitochondria. The activity was sensitive to SH reagents and assorted proteinase inhibitors. Although stimulated by nonionic detergents, it became labile when solubilized by detergents. The proteinase activity from heart mitochondria copurified with the ADP:ATP translocator protein. Gel electrophoresis of this preparation revealed the translocator polypeptide as well as a number of minor components. In solubilized mitochondria the ADP:ATP translocator polypeptide slowly disappeared upon standing at 0 degrees C as revealed by polyacrylamide gel electrophoresis under denaturing conditions. The loss of this polypeptide was prevented by addition of proteinase inhibitors as well as the translocator affinity ligand, carboxyatractylate. These observations confirm the presence of an integral membrane proteinase in mitochondria and suggest a structural and enzymatic interaction between the proteinase and the ADP:ATP translocator.

The short term hormonal control of cytoplasmic protein phosphorylation in hepatocytes from fed rats

Exposure of 32P-prelabelled isolated hepatocytes to vasopressin affected the phosphorylation of nine of the 26 phosphoproteins resolved by sodium dodecyl sulphate gel electrophoresis. Glucagon (2 nM) or cyclic AMP elicited significant changes in the phosphorylation of only four phosphoproteins. A very high concentration of glucagon (1000 nM) affected additional phosphoproteins. Insulin alone significantly increased the phosphorylation of a single protein. Vasopressin, A23187, glucagon and cyclic AMP all induced the dephosphorylation of a single phosphoprotein of mol. wt 20,000. The significance of these results with respect to the short-term control of hepatic metabolism is discussed.

Rapid preparation of metabolically active mitochondria from control and hormone-treated rat liver cells

A method is described for the rapid isolation of mitochondria from liver cells. The method involves the breakage of hepatocytes by brief sonication followed by Percoll density gradient centrifugation. Mitochondria obtained using this method are well coupled, slightly contaminated by other organelles or membrane fractions and compare favourably with mitochondria isolated from whole liver by conventional techniques.

Synthesis of cytochrome oxidase in isolated rat hepatocytes

1. The synthesis of cytochrome oxidase was studied in isolated rat hepatocytes labeled in vitro. Labeled whole cells, isolated mitochondria, microsomes and the post microsomal supernatant were treated with antisera to rat liver holo-cytochrome oxidase, and the subunits were adsorbed onto Sepharose-protein A. 2. Seven peptides, corresponding to subunits of rat liver cytochrome oxidase, were immunoabsorbed from mitochondria isolated from cells labeled in the absence of inhibitors. Two peptides, corresponding to subunits I (45 500 daltons) and II (26 000 daltons), were labeled in mitochondria isolated from cycloheximide-treated cells. Labeling of these peptides was inhibited by chloramphenicol. Peptides I and II correspond to the two most heavily labeled mitochondrial translation products found in submitochondrial particles. Possible explanations for the lack of labeling of a third mitochondrially translated subunit are discussed. Labeling of the five smallest peptides was inhibited by cyclohexamide but not by chloramphenicol. 3. Peptide I appears in the holoenzyme later than the other six peptides after a pulse-chase. It is not labeled in the immunoabsorbed cytochrome oxidase after a 30 min pulse with [35S]-methionine, but appears after a 3 h chase with unlabeled methionine. Labeling of the other subunits showed no further increase after the chase.

The effects of tri-iodothyronine on the synthesis of mitochondrial proteins in isolated rat hepatocytes

The effects of tri-iodothyronine on mitochondrial protein synthesis have been studied in in vitro labeled, isolated rat hepatocytes. Hepatocytes were isolated from hypothyroid rats or from hypothyroid rats 24 h after injecting a single, low dose of hormone (20-30 microgram/180-230 g body weight). Tri-iodothyronine increased translation on mitochondrial ribosomes by 2-3-fold, but, under our conditions, appears to have little or not effect on the general synthesis of cytoplasmically-translated mitochondrial proteins. Electrophoretic and fluorographic analysis indicated that tri-iodothyronine stimultes labeling of the four major mitochondrially-translated peptides. The hormone appears to act by inducing a general increase in translation/transcription of mitochondrially-synthesized peptides.