Induction of megamitochondria in the mouse liver by isonicotinic acid derivatives

Giant mitochondria in pancreatic acinar cells of alloxan-induced diabetic rats

This was a study of the microscopic, ultrastructural, immunohistochemical, and enzyme cytochemical features of giant eosinophilic granules encountered in pancreatic acinar cells of alloxan-induced diabetic rats. Seven male F344 rats with diabetes induced by a single i.v. dose of alloxan were sacrificed after twenty-five weeks of treatment. Histologically, the pancreatic acini were diffusely atrophied, and the islets showed marked atrophy or had disappeared, and giant eosinophilic granules and small vacuoles were observed in almost all acinar cells. The eosinophilic granules showed negative reactions for periodic acid-Schiff (PAS) and acid phosphatase, as well as fat stains such as Nile blue, Oil red O, and Sudan III. Ultrastructurally, the giant eosinophilic granules were huge structures surrounded by a double membrane containing many irregular cristae. A large amount of small lipid droplets was also apparent in the basal area of the acinar cells. Immunohistochemical analysis of prohibitin, a kind of protein located in the mitochondrial inner membrane, was partially positive in the marginal area of some giant eosinophilic granules, but negative for the central area. The enzyme activity for succinic dehydrogenase (SDH), one of the mitochondrial enzymes, showed a localizing pattern similar to that of prohibitin. These findings confirmed that the giant eosinophilic granules in the exocrine pancreas of alloxan-induced diabetic rats were giant mitochondria.

Megamitochondria formation - physiology and pathology

Mitochondria undergo structural changes simultaneously with their functional changes in both physiological and pathological conditions. These structural changes of mitochondria are classified into two categories: simple swelling and the formation of megamitochondria (MG). Data have been accumulated to indicate that free radicals play a crucial role in the mechanism of the MG formation induced by various experimental conditions which are apparently various. These include ethanol-, chloramphenicol- and hydrazine-induced MG formation. Involvement of free radicals in the mechanism of MG formation is showed by the fact that MG formation is successfully suppressed by free radical scavengers such as alpha-tocopherol, coenzyme Q(10), and 4-OH-TEMPO. Detailed mechanisms and pathophysiological meanings of MG formation still remain to be investigated. However, a body of evidence strongly suggests that enormous changes in physicochemical and biochemical properties of the mitochondrial membranes during MG formation take place and these changes are favorable for membrane fusion. A recent report showed that continous exposure of cells with MG to free radicals induces apoptosis, finding which suggests that MG formation is an adaptative process to unfavorable environments at the level of intracellular organelles. Mitochondria try to decrease intracellular reactive oxygen species (ROS) levels by decreasing the consume of oxygen via MG formation. If mitochondria succeed to suppress intracellular ROS levels, MG return to normal both structurally and functionally, and they restore the ability to actively synthesize ATP. If cells are additionally exposed to excess amounts of free radicals, MG become swollen, membrane potential of mitochondria (DeltaPsim) decreases, cytochrome c is released from mitochondria, leading to activation of caspases and apoptosis is induced.

Functional aspects of megamitochondria isolated from hydrazine- and ethanol-treated rat livers

It is essential to analyze functions of megamitochondria (MG) to elucidate the mechanism of the formation of MG induced under various pathological conditions. The MG fraction obtained by a routine isolation procedure for normal mitochondria always consists of a mixed population of mitochondria enlarged to various degrees and also normal-sized ones. The purpose of the present study is to answer the question of whether or not data obtained from the MG fraction consisting of such a heterogeneous population of mitochondria with respect to their sizes really reflect functions of MG. In the present study mitochondria were obtained from the livers of rats treated with a 1% hydrazine diet for 8 days and those given 32% ethanol in drinking water for up to 2 months using various isolation procedures. Results obtained are summarized as follows: (i) mitochondria enlarged to various degrees and normal-sized ones are sometimes connected with each other by a narrow stalk in the hepatocyte of hydrazine-treated animals, and such connections are maintained to some extent when mitochondria are isolated; and (ii) mitochondria obtained from experimental animals by a routine isolation procedure for mitochondria ((700-7000)gR2"') and those obtained by alternative isolation procedure yielding the heavy ((500-2000)gR2"') and light ((2000-7000)gR2"') fractions show some functional similarities: decreases in the content of cytochrome a + a3; decreases in oxygen consumptions and phosphorylating abilities; decreases in monoamine oxidase and cytochrome c oxidase activities; lowered membrane potential of mitochondria; decreases in the rate of the generation of reactive oxygen species. These results may suggest that mitochondria enlarged to various degrees and normal-sized ones are functionally similar to each other and that the MG fraction obtained by a routine isolation procedure for normal mitochondria can be applied to the study of the function of MG.

Cycloheximide and 4-OH-TEMPO suppress chloramphenicol-induced apoptosis in RL-34 cells via the suppression of the formation of megamitochondria

Toxic effects of chloramphenicol, an antibiotic inhibitor of mitochondrial protein synthesis, on rat liver derived RL-34 cell line were completely blocked by a combined treatment with substances endowed with direct or indirect antioxidant properties. A stable, nitroxide free radical scavenger, 4-hydroxy-2,2,6, 6-tetramethylpiperidine-1-oxyl, and a protein synthesis inhibitor, cycloheximide, suppressed in a similar manner the following manifestations of the chloramphenicol cytotoxicity: (1) Oxidative stress state as evidenced by FACS analysis of cells loaded with carboxy-dichlorodihydrofluorescein diacetate and Mito Tracker CMTH2MRos; (2) megamitochondria formation detected by staining of mitochondria with MitoTracker CMXRos under a laser confocal microscopy and electron microscopy; (3) apoptotic changes of the cell detected by the phase contrast microscopy, DNA laddering analysis and cell cycle analysis. Since increases of ROS generation in chloramphenicol-treated cells were the first sign of the chloramphenicol toxicity, we assume that oxidative stress state is a mediator of above described alternations of RL-34 cells including MG formation. Pretreatment of cells with cycloheximide or 4-hydroxy-2,2, 6,6-tetramethylpiperidine-1-oxyl, which is known to be localized into mitochondria, inhibited the megamitochondria formation and succeeding apoptotic changes of the cell. Protective effects of cycloheximide, which enhances the expression of Bcl-2 protein, may further confirm our hypothesis that the megamitochondria formation is a cellular response to an increased ROS generation and raise a possibility that antiapoptotic action of the drug is exerted via the protection of the mitochondria functions.

Complete suppresion of ethanol-induced formation of megamitochondria by 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-OH-TEMPO)

An attempt has been made to suppress the ethanol-induced formation of megamitochondria (MG) in the rat liver by 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-OH-TEMPO), a free radical scavenger, and by allopurinol (AP), a xanthine oxidase inhibitor. Changes observed in the liver of animals given ethanol (EtOH) for 1 month were remarkable decreases both in the body weight gains during the course of the experiment and in the liver weight at the time of sacrifice compared to those of the control; remarkable increases in the level of thiobarbituric acid reactive substances and lipid soluble fluorophores both in microsomes and mitochondria; decreases in the content of cytochrome a+a3 and b and lowered phosphorylating ability of mitochondria; and formation of MG in the liver. A combined treatment of animals with EtOH plus 4-OH-TEMPO completely suppressed the formation of MG in the liver induced by EtOH and distinctly improved the changes caused by EtOH, as specified above, while AP partly suppressed the MG formation. Results described herein provide additional insight into chronic hepatotoxicity of EtOH besides that previously reported. A novelty of the present work is that we were able for the first time to demonstrate reversibility of EtOH-mediated ultrastructural changes of the liver by a simple administration of aminoxyl-type free radical scavenger, 4-OH-TEMPO. Our results suggest that free radicals may be involved in the mechanism of the formation of MG induced by EtOH.

Role of free radicals in the mechanism of the hydrazine-induced formation of megamitochondria

The effect of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl(4-OH-TEMPO), a scavenger for free radicals, and 4-hydroxypyrazolo [3,4-d(pyrimidine)allopurinol], a xanthine oxidase inhibitor, on the hydrazine-induced changes of mitochondrial ultrastructure and those in the antioxidant system of the liver were investigated using rats as experimental animals. Animals were placed on a powdered diet containing 0.5% hydrazine for 7 d in the presence and absence of a combined treatment with 4-OH-TEMPO or allopurinol. Results obtained were as follows. 4-OH-TEMPO completely prevented the hydrazine-induced formation of megamitochondria in the liver, while it was partly prevented by allopurinol. The following changes observed in hydrazine-treated animals were improved almost completely by 4-OH-TEMPO:decreases in the body weight and liver weight; lowered rates of ADP-stimulated respiration and coupling efficiency of hepatic mitochondria; remarkable elevation of the level of lipid peroxidation. Improving effects of allopurinol were incomplete. The present results suggest that free radicals may play a key role in the mechanism of the hydrazine-induced formation of megamitochondria and that a part of free radicals generated during the hydrazine intoxication is ascribed to the degradation of purine nucleotides via xanthine oxidase. A general mechanism of the megamitochondria formation induced in various pathological conditions besides the case of hydrazine are discussed.

Suppression of the formation of megamitochondria by scavengers for free radicals

In the present study we have attempted to suppress the formation of megamitochondria by scavengers for free radicals since conditions for the formation of megamitochondria are often intimately related to the generation of free radicals. We employed three different experimental conditions to induce megamitochondria in the liver: ethanol, hydrazine and chloramphenicol (CP). Scavengers for free radicals tested were: alpha-tocopherol, coenzyme Q10(CoQ10) and 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl(4-OH-TEMPO). Allopurinol (AP), a xanthine oxidase inhibitor, was also tested. Results obtained were as follows. (1) Changes observed in the liver of animals treated with ethanol, hydrazine or CP were: formation of megamitochondria; decreases in the body weight and the weight of the liver; remarkable increases in the level of lipid peroxidation; increases in the activity of xanthine oxidase. (2) 4-OH-TEMPO was most effective in improving these changes. A mechanism of the formation of megamitochondria is proposed stressing the role of free radicals in the mechanism.

Suppression of the hydrazine-induced formation of megamitochondria in the rat liver by coenzyme Q10

The effects of coenzyme Q10 (CoQ10) on the hydrazine-induced changes in the structure of mitochondria and those in antioxidant systems of the liver were investigated using rats as experimental animals. Animals were placed on a powdered diet containing 1.0% hydrazine for 7-8 days in the presence or absence of the combined treatment with CoQ10. Results obtained were as follows: (a) treatment of animals with CoQ10 prevented the hydrazine-induced formation of megamitochondria in the liver; (b) changes observed in the liver of the hydrazine-treated animals in comparison to the control were increases in the contents of alpha-tocopherol and CoQ analogs, increases in the levels of lipid peroxidation, decreases in the level of reduced glutathione with increases in that of oxidized glutathione, and increases in the ratio of unsaturated to saturated fatty acids in phospholipid domains of mitochondrial membranes; and (c) administration of CoQ10 to hydrazine-treated animals suppressed enhanced lipid peroxidation and improved lowered adenosine diphosphate/O ratios of mitochondria. The present data suggest that CoQ10 suppresses the hydrazine-induced formation of megamitochondria by scavenging free radicals generated from hydrazine and its metabolites.

Studies on urea synthesis in the liver of rats treated chronically with ethanol using perfused livers, isolated hepatocytes, and mitochondria

Changes in urea synthesis in the liver of rats treated with 32% ethanol in the drinking water for up to 6 months were studied using perfused livers, isolated hepatocytes, and mitochondria. Results obtained from ethanol-treated rats are summarized as follows: (1) the mitochondria of the hepatocytes of rats treated with ethanol for 2 months or longer became enlarged to various degrees, (2) the levels of ammonia in the serum remained within a normal range, while those in liver tissue were elevated compared with the control, (3) urea synthesis from ammonia in perfused livers was decreased markedly, while that from citrulline remained in the normal range, (4) the activities of carbamyl phosphate synthetase (CPS; EC 2.7.2.5) and ornithine transcarbamylase (OTC; EC 2.1.3.3) in mitochondria were unchanged compared with those of the control, and (5) the levels of ATP in liver tissue and the ability of mitochondria to synthesize ATP were decreased markedly compared with the control. Both the level of ATP in the hepatocytes and the synthesis of urea from ammonia by perfused livers of rats treated with ethanol were resistant to externally added ethanol, while those of control animals were severely affected. These results suggest that the intracellular level of ATP is intimately related to urea synthesis in both control and ethanol-treated animals, and lowered levels of ATP may be a key factor in the suppression of urea synthesis in ethanol-treated animals.

Liver giant mitochondria revisited

AIMS

To examine the correlation between the severity of alcohol induced liver damage and the presence of intracytoplasmic red bodies (defined as periodic acid-Schiff diastase negative, globular, hyaline cytoplasmic inclusions larger in size than the hepatocyte nucleolus). To investigate the incidence of intracytoplasmic red bodies (ICRBs) in non-alcoholic liver disease.

METHODS

Liver biopsy specimens from 53 patients with alcoholic liver disease and 50 patients with a variety of nonalcohol related liver diseases were examined by light microscopy for the presence of ICRBs. For the 53 patients with alcoholic liver disease an assessment of recent alcohol consumption was made indirectly from measurements of red cell volume (MCV) and plasma gamma-glutamyl transferase (GGT). In addition, 10 liver biopsies with alcohol induced changes and ICRBs were examined by electron microscopy for the presence of mitochondrial aberrations including enlargement.

RESULTS

ICRBs were detected in 18 of the 53 liver biopsy specimens showing alcohol induced changes, and were more abundant in those showing more advanced changes. Those patients whose liver specimens contained ICRBs were found to have a significantly higher mean plasma GGT activity and mean MCV than those individuals whose liver biopsy specimens did not contain ICRBs. Two of the 50 liver biopsy specimens showing non-alcohol induced changes contained ICRBs. Giant mitochondria were not detected by electron microscopy, but this may reflect sampling.

CONCLUSIONS

The results of this study indicate that ICRBs are definitely associated with alcoholic liver disease and are more likely to be found in liver biopsy specimens showing more advanced alcohol induced damage, and when recent alcohol consumption has been high.

Effects of alkyl alcohols and related chemicals on rat liver structure and function. II. Some biochemical properties of ethanol-, propanol- and butanol-treated rat liver mitochondria

Functional changes of mitochondria in the liver obtained from rats given 32% ethanol, 32% propanol and 6.9% butanol in drinking water for up to 3 months were investigated. Animals were also fed a liquid diet containing ethanol for comparison. Results obtained were as follows: 1) Animals given ethanol in drinking water consumed twice as much ethanol daily as those fed a liquid diet containing ethanol, while ultrastructural changes of hepatic mitochondria were essentially the same between the former and the latter animals: the co-existence of megamitochondria and small mitochondria with poorly developed cristae. 2) Effects of alkyl alcohols tested on the respiratory rates and coupling efficiency of mitochondria were variable, depending on the kind of alkyl alcohols, the duration of experiments and oxidizable substrates used. 3) There was essentially no difference between the heavy and the light mitochondrial fractions obtained from alkyl alcohol-treated rat livers in terms of respiratory rates and coupling efficiencies. 4) Decreases in the content of cytochrome aa3 and the activity of activity of cytochrome oxidase, and increases in MEOS activity were most distinct in ethanol-treated rat livers. A possible role of chronic relative oxygen deficiency inside the hepatocyte caused by the metabolization of alkyl alcohols is discussed in order to interpret such peculiar ultrastructural changes of mitochondria.

Giant mitochondria in acute lymphocytic leukemia

Giant mitochondria were observed in 2 cases among 28 cases of ALL by electron microscopy. The cristae of the giant mitochondria in the leukemic cells were irregularly arranged, decreased in number, and formed concentric circles. Several morphological abnormalities were also observed in the normal mitochondria. Morphometric analysis of the mitochondria in the 2 patients disclosed that the sizes of mitochondria were well distributed from small to large and thus, the mitochondria could not be divided into different populations. Also, there were no clear differences in the distribution of shape between normal and giant mitochondria. These results suggest that the giant mitochondria were derived from normal mitochondria. Since they were observed before the initial treatment, they did not developed as a result of drug action.

Changes in physicochemical properties of mitochondrial membranes during the formation process of megamitochondria induced by hydrazine

Changes in some biochemical and physico-chemical properties of rat liver mitochondrial membranes during the formation process of megamitochondria induced by hydrazine were analyzed. Hepatic mitochondria obtained from rats placed on a 1% hydrazine diet for 3 days became slightly enlarged and sometimes elongated, while they became gigantic after 7 days of hydrazine intoxication. Changes were observed in mitochondria from rats treated with hydrazine for 3 days. Total amounts of phospholipids extracted from mitochondria and submitochondrial fractions were increased. Among phospholipid species, relative amounts of acidic phospholipids were increased. Contents of Ca2+ in mitochondria were increased. Differential scanning calorimetric analysis of mitochondria, especially that of the outer membrane fraction, showed that the thermotropic lipid phase transition temperatures were elevated accompanying the broadening of thermograms and the increase in transition enthalpy. Contents of water in mitochondria were increased significantly with the ratio of freezable water to unfreezable water unchanged. Among the changes observed was that the total amount of phospholipids (except for that of the outer membrane fraction) and the contents of water and Ca2+ nearly returned to normal in megamitochondria after 7 days of hydrazine intoxication. Relative amounts of phospholipids and thermotropic lipid phase transition temperatures of megamitochondria did not return to normal levels and yet changes were smaller than those obtained from 3 days of hydrazine intoxication. The fluidity of mitochondrial membranes was not affected by hydrazine treatment. These data would suggest that hydrazine-induced megamitochondrial formation is not due simply to the swelling of mitochondria, but might be due to the fusion of adjacent mitochondria by Ca2+-acidic phospholipid interactions, and once megamitochondria are formed the mitochondrial membranes are stabilized.

Mechanism of hepatic megamitochondria formation by ammonia derivatives. Correlation between structure of chemicals and their ability to induce the formation of megamitochondria

Correlation between the chemical structure and the ability to induce hepatic megamitochondria formation was studied by feeding mice and rats diets containing a wide spectrum of ammonia derivatives. Ammonia derivatives with electron-releasing groups, such as hydrazine, phenylhydrazine, hydroxylamine and aniline were effective in inducing megamitochondria. Ammonia derivatives with electron-withdrawing groups, such as formamide, sulfamic acid, acetamide were ineffective in inducing megamitochondria. Inducibility of ammonia derivatives with electron-releasing groups plus electron-withdrawing groups for the megamitochondria formation was dependent upon nucleophilicity of the chemical: 2,4-dinitrophenylhydrazine induced megamitochondria, while acetanilide did not induce megamitochondria. The megamitochondria formation induced by ammonia derivatives was a reversible process. Freeze-fracture studies on megamitochondria indicated that megamitochondria were formed by the fusion of adjacent mitochondria. Phosphorylating capacity of megamitochondria (hydrazine-induced megamitochondria, for example) were normal despite morphological changes. These data might suggest that the nucleophilicity of chemicals plays a key role in the induction of hepatic megamitochondria. These data might also suggest that the phenomenon is an adaptive process to changes of intracellular milieu.

Induction of megamitochondria in the rat liver by N-propyl alcohol and N-butyl alcohol

Propyl alcohol and butyl alcohol had similar effects to ethyl alcohol on ultrastructure of liver mitochondria. Rats were given 32% ethyl alcohol, 32% n-propyl alcohol, and 6.9% n-butyl alcohol in drinking water for up to three months. After one month, mitochondria in hepatocytes obtained from the experimental animals became elongated, constricted or cup-shaped with scanty cristae. After two months, mitochondria in some hepatocytes became gigantic. In extreme cases, the megamitochondria exceeded 10 micron in diameter. Coupling efficiencies of hepatic mitochondria obtained from alcohol-fed animals were well preserved despite their drastic morphologic changes.

Giant mitochondria in the alcoholic liver diseases--their identification, frequency and pathologic significance

Three types of giant mitochondria have been described in hepatocytes, and we have investigated their ultrastructural features and occurrence in alcoholic liver disease. Type I mitochondria are spherical, with a paucity of cristae. Type II are elongated and have long crystalline insertions. Type III are relatively smaller and often bizarre in shape, containing multiple crystalline insertions. We defined megamitochondria as spheroidal giant mitochondria with a diameter roughly more than one third of the hepatocyte nucleus and visible under light microscopy. Type I was the most common form of megamitochondria in livers with ALD. Megamitochondria were present in livers of 58 (27.8%) of 209 consecutive patients with alcoholic liver disease, compared with 1 (0.7%) of a series of 145 patients with non-alcoholic liver disease. The frequency and occurrence of megamitochondria varied in different types and/or stages of alcoholic liver disease. In particular, livers with alcoholic foamy degeneration had significantly increased frequency and numbers of megamitochondria compared to other patterns of alcoholic liver disease. The ultrastructural studies showed that hepatocytes containing Type I mitochondria frequently had other damaged organelles and extensive focal cytoplasmic degradation. Enzyme histochemistry showed the foamy hepatocytes containing Type I had markedly decreased staining for glucose-6-phosphatase and slightly decreased staining for succinic dehydrogenase activities, while the hepatocytes with Type II or III had normal staining. In general, Type I giant mitochondria seem more characteristic to alcoholic liver disease, or conditions that produce similar hepatic morphology. It is particularly seen in alcoholic foamy degeneration and may be part of decompensation of the hepatocytes, while Types II and III occurred in hepatocytes of both alcoholic and non-alcoholic patients and had preserved function.

Induction of megamitochondria in the mouse and rat livers by hydrazine

The correlation between structures of chemicals and their inducibility for megamitochondrial formation was investigated. Since the chemical structure universal to the inducers of megamitochondria previously reported (cuprizone and isonicotinic acid derivatives) is the carbazoyl group (-CONHNH2), semicarbazide (NH2NHCONH2) was tested first. Then, hydrazine (NH2NH2) was tested, replacing the carbazoyl group of semicarbazide by an amino group (-NH2). The present study demonstrates that (1) megamitochondria were induced in mouse and rat hepatocytes by feeding the animals with a diet containing semicarbazide or hydrazine, suggesting that the carbazoyl group was not essential for megamitochondrial formation; (2) hydrazine-induced megamitochondrial formation was a reversible process. Coupling efficiencies and activities of ATPase and cytochrome oxidase of megamitochondria induced by hydrazine were slightly decreased, while the activity of monoamine oxidase was moderately decreased. Freeze-fracture electron microscopy revealed particle-free regions in the outer membranes of megamitochondria fixed with glutaraldehyde at 22 degrees C; the regions disappeared at 25 degrees C, indicating that the temperature of the liquid crystalline to gel state lipid phase transition in the megamitochondrial outer membrane was elevated. It is speculated that chemical structure of inducer of megamitochondria could be simplified to NH2-G (G, substituting group).