The content of adenosine polyphosphates in fatty livers

Intramitochondrial crystalline inclusions in nonalcoholic steatohepatitis

Mitochondrial dysfunction is an important element in the pathogenesis of nonalcoholic steatohepatitis (NASH). Intramitochondrial crystals (IMCs) are a well-documented morphological abnormality seen on transmission electron microscopy in this disease. It has been suggested that IMCs consist of phospholipids, but their exact composition remain uncertain many years after their discovery. Micellar phase transitions of phospholipid bilayers is a well-known but little-studied phenomenon in living systems. Its presence in the mitochondria of NASH would offer significant insight into the disease with possible therapeutic implications. We postulated that intramitochondrial disturbances in NASH are sufficient to produce such transitions and that their detection in fresh biopsies would therefore be a dynamic process. To test this, we performed a blinded, prospective analysis of fresh liver biopsy samples immediately fixed under different conditions. Quantitative transmission electron microscopy morphometry, performed by systematically counting total mitochondria and IMCs within areas of uniform dimension, showed a stepwise decline in IMCs with cooler fixation temperature in each subject studied. Randomization testing (Monte Carlo resampling) confirmed that the detection of IMCs was strongly dependent on fixation temperature (P < 0.0001).

CONCLUSION

These results indicate that the intramitochondrial crystals characteristic of NASH are highly dynamic and unstable structures. The findings offer the strongest support yet for their origin in micellar phase transitions. We speculate that such transitions result from microenvironmental changes within the mitochondria and carry therapeutic implications, especially in regard to dietary manipulations of mitochondrial lipid composition.

The effects of 48 weeks of rosiglitazone on hepatocyte mitochondria in human nonalcoholic steatohepatitis

Rosiglitazone, a thiazolidinedione peroxisome proliferator-activated receptor gamma ligand, reduces disease activity in nonalcoholic steatohepatitis (NASH), a disease associated with hepatocyte mitochondrial crystalline inclusions that are not seen in animal models of NASH. In human and animal studies of adipose tissue, thiazolidinediones may induce mitochondrial biogenesis and associated morphological changes. To determine if rosiglitazone alters the hepatocyte mitochondrial morphology in human NASH, we prospectively and systematically examined liver biopsies from human subjects with NASH before and after 48 weeks of rosiglitazone by transmission electron microscopy. Twenty patients (body mass index = 34 +/- 7) were studied. Four coded sections from each of 20 pretherapy biopsies and each of 20 posttherapy biopsies were examined by transmission electron microscopy. The total hepatocyte mitochondria and crystal-containing mitochondria were counted, and semiquantitative scoring was performed for macrosteatosis, microsteatosis, dilated endoplasmic reticulum, apoptosis, Mallory bodies, and hepatocyte enlargement. The total mitochondria count was unchanged after therapy, but there was a significant increase in crystal-containing mitochondria from 4.0% (95% confidence interval = 1.8-8.8) to 7.2% (95% confidence interval = 3.9-12.6; odds ratio = 1.80; P = 0.04) after the treatment with rosiglitazone. Macrosteatosis (P < 0.001) and Mallory bodies (P = 0.05) significantly decreased, but no change was evident in microsteatosis, cellular enlargement, dilated endoplasmic reticulum, or apoptosis.

CONCLUSION

Rosiglitazone therapy of NASH is associated with increased crystalline inclusions in hepatocyte mitochondria. Whether these are adaptive or pathological remains unknown, and further studies are warranted to assess hepatic mitochondrial function during thiazolidinedione therapy for NASH.

Mitochondria in nonalcoholic fatty liver disease

Nonalcoholic fatty liver (NAFL) is associated with fundamental issues of fat metabolism and insulin resistance. These abnormalities have been linked to impairment of ATP homeostasis, and a growing body of literature has reported mitochondrial abnormalities in various forms of hepatic steatosis. The changes are evident as structural abnormalities, including greatly increased size and the development of crystalline inclusions, and are usually regarded as pathologic, reflecting either a protective or degenerative response to injury. Although the relationships between structural changes,decreased mitochondrial function, and disease states are becoming clearer, the molecular basis for the perturbations is not well understood. Oxidative damage is the most likely causative process and may result in alterations of mitochondrial DNA (mtDNA), stimulated apoptotic pathways, and increased propensity for necrosis.Overall mitochondrial health likely depends on multiple factors including the integrity of the mtDNA, the composition of cellular lipids, lipoprotein trafficking, the balance of pro- and antioxidant factors, and the metabolic demands placed on the liver. Mitochondrial dysfunction may play a role in numerous clinical conditions associated with NAFL, such as hepatocellular carcinoma, lipodystrophy,age-related insulin resistance, gut dysmotility, cryptogenic cirrhosis, a mild form of gaze palsy, and possibly other more severe neurodegenerative diseases. The prominent role of mitochondrial dysfunction in NAFL provides a new and exciting paradigm in which to view this disorder, its complications, and potential dietary and pharmacologic intervention.

Nonalcoholic steatohepatitis: summary of an AASLD Single Topic Conference

Fatty liver disease that develops in the absence of alcohol abuse is recognized increasingly as a major health burden. This report summarizes the presentations and discussions at a Single Topic Conference held September 20-22, 2002, and sponsored by the American Association for the Study of Liver Diseases. The conference focused on fatty liver disorders. Estimates based on imaging and autopsy studies suggest that about 20% to 30% of adults in the United States and other Western countries have excess fat accumulation in the liver. About 10% of these individuals, or fully 2% to 3% of adults, are estimated to meet current diagnostic criteria for nonalcoholic steatohepatitis (NASH). Sustained liver injury leads to progressive fibrosis and cirrhosis in a fraction, possibly up to one third, of those with NASH, and NASH may be a cause of cryptogenic cirrhosis. NASH is now a significant health issue for obese children as well, leading to cirrhosis in some. The diagnostic criteria for NASH continue to evolve and rely on the histologic findings of steatosis, hepatocellular injury (ballooning, Mallory bodies), and the pattern of fibrosis. Generally recognized indications for biopsy include establishing the diagnosis and staging of the injury, but strict guidelines do not exist. Liver enzymes are insensitive and cannot be used reliably to confirm the diagnosis or stage the extent of fibrosis. Older age, obesity, and diabetes are predictive of fibrosis. The pathogenesis of NASH is multifactorial. Insulin resistance may be an important factor in the accumulation of hepatocellular fat, whereas excess intracellular fatty acids, oxidant stress, adenosine triphosphate (ATP) depletion, and mitochondrial dysfunction may be important causes of hepatocellular injury in the steatotic liver. Efforts are underway to refine the role of insulin resistance in NASH and determine whether improving insulin sensitivity pharmacologically is an effective treatment. An altered lifestyle may be a more effective means of improving insulin sensitivity. The research agenda for the future includes establishing the role of insulin resistance and abnormal lipoprotein metabolism in NASH, determining the pathogenesis of cellular injury, defining predisposing genetic abnormalities, identifying better noninvasive predictors of disease, and defining effective therapy.

Protein synthesis by hepatic mitochondria isolated from carbon tetrachloride-exposed rats

Hepatic mitochondria isolated from rats 40 h after dosage with 1.1 ml/kg CCl4 are uncoupled and display structural damage. Mitochondrial function returns during hepatic recovery. Because the products of mitochondrial protein synthesis are essential to mitochondrial structure and function, the effects of CCl4 on the rate of mitochondrial protein synthesis, and on the products, was studied using mitochondria from CCl4-exposed rats during the early, maximum development and resolution stages of CCl4-induced mitochondrial damage. Rates of mitochondrial protein synthesis (incorporation of [35S]methionine) were elevated 300% over that of mitochondria from non-exposed rats 17 h after exposure; depressed by 50% at 40 h and above control at 113 h. When the radiolabeled products of incorporation were separated and examined by autoradiography, a novel, low-molecular-weight band, of approx. 9700, was apparent 40 h after CCl4 exposure. A band of similar molecular weight appeared when control mitochondria were incubated without an exogenous supply of ATP. Mitochondria from exposed rats which displayed rates of protein synthesis greater than control consistently had a relative increase in a band that corresponded in size to that of cytochrome oxidase subunit I. It was concluded that the loss of mitochondrial function induced by CCl4 could not be attributed to inhibition of mitochondrial protein synthesis, and that the mitochondria may not always synthesize protein in constant proportions.

Effect of AMP on acute carbon-tetrachloride hepatotoxicity

The effect of carbon-tetrachloride poisoning and the protection caused by AMP were studied. A single dose of CCl4 has resulted in a rapid development of a fatty liver, a considerable increase in serum enzymes, glutamic oxalacetic and pyruvic transaminases as well as serum-alkaline phosphatase. Total serum protein showed a tendency to decrease accompanied by a decrease in A/G ratio. Administration of adenosine-5-monophosphate prevented the increase in serum-alkaline phosphatase and increased the A/G ratio. There was, however, a slight but significant decrease in serum GOT and GPT within the 24-hrs. period of study, but it remained still higher than that of the control. AMP lowered liver fat without complete protection against the development of fatty liver.

Metabolic intermediates, enzymes and lysosomal activity in aortas of spontaneously hypertensive rats

Metabolic intermediate levels, glycolytic and Krebs cycle enzyme activities and lysosomal acid hydrolase activities were measured in aortas of spontaneously hypertensive (SHR) versus normotensive (WKY) rats. In the hypertensive aortas the level of lactate, the ratio of lactate to glucose and of lactate to malate was higher in the SHR than WKY aortas. In the hypertensive aortas the obvious shift of metabolism toward higher rate of glycolysis was associated with decreased activity of malate dehydrogenase and espically of lipoamide dehydrogenase. The latter is an essential compoenent of the alpha-ketoglutarate and pyruvate dehydrogenase enzyme complexes and it appears that these complexes are among the sites of arterialmetavolism which are primarily altered by the elevated blood pressure, resulting in increased production of lactate. The activity of the marker lysosomal enzyme N-acetyl-beta-glucosaminidase was unequivocally elevated in the hypertensive aortas. The activity of beta-glucuronidase exhibited incogruous differences between the SHR and WKY aortas and the activity of aortic acid phosphatase did not differ in the two rat strains. The results are discussed in relation to arterial injury, permeability, and atherogenesis.

Effect of ethanol ingestion on choline phosphotransferase and phosphatidyl ethanolamine methyltransferase activities in liver microsomes

The effect of ethanol ingestion on choline phosphotransferase and phosphatidyl ethanolamine methyltransferase activities, the two enzymes involved in phosphatidyl choline biosynthesis in liver microsomes, has been investigated. Female rats were fed a 5% ethanol-liquid diet containing amino acids, minerals, vitamins, with and without choline, for 2, 6 and 10 weeks. Control animals were pair-fed the same isocaloric diet with 5% sucrose with and without choline. Ethanol administration with or without dietary choline stimulated significantly (P less than 0.001) the specific activities of phosphatidyl ethanolamine methyltransferase in liver microsomes in the animals fed 5% ethanol for 2, 6, and 10 weeks, when compared to those control animals pair-fed the isocaloric diet with or without choline. Ethanol administration with or without dietary choline for 2 weeks stimulated significantly (P less than 0.02) the specific activities of choline phosphotransferase. The specific activities of phosphatidyl ethanolamine methyltransferase continued to increase in the liver microsomes from the animals in which dietary choline was omitted for 2, 6, and 10 weeks in the sucrose controls and alcohol-fed animals. Ethanol administration stimulates significantly (P less than 0.001) the phosphatidyl ethanolamine methyltransferase specific activities in liver microsomes of animals fed the liquid diet with dietary omission of choline and methionine for 2 weeks.

Effect of "drugs for liver disease" on hepatotoxic action of carbon tetrachloride. I. Changes of lysosomal enzyme levels and effect of protoporphyrin on the levels

In order to clarify the action of drugs for liver disease, the effect of protoporphyrin (PP) on CCl4-induced liver injury was studied. Attention was given to the levels of lysosomal enzymes, some components of the liver, and inhibition of enzymes and lysis of lysosomal membranes by lipid peroxides. Administration of PP to CCl4-poisoned rats was found to prevent the decrease in lysosomal lipolytic enzyme level in the liver, but not in other enzyme levels tested. The inhibition of lipolytic enzyme by CCl4 administered may be partially involved in lipid accumulation in the liver. A dose of PP administered to CCl4-poisoned rats for 8 days depressed the neutral lipid content in the liver nearly to the control value. Methyl linoleate hydroperoxide (hydroperoxide) at a lower concentration of 10(-6)% inhibited the lipolytic enzyme acitivity by 30% and in concentrations ranging from 10(-4) to 10(-3)% inhibited beta-glucuronidase activity. Addition of PP to the medium containing 10(-6) to 10(-5)% hydroperoxide and alpha-tocopherol reduced the enzyme inhibition further than in the absence of PP. The hydroperoxide in concentrations varying from 10(-6) to 10(-3)% caused a partial lysis of liver lysosomal membranes, but addition of PP slightly reduced the damage by the hydroperoxide in concentration lower than 10(-5)%.

Vitamin E and hepatotoxic agents. 1. Carbon tetrachloride and lipid peroxidation in the rat

1. It has been suggested that carbon tetrachloride damages rat liver by accelerating processes of lipid peroxidation at subcellular sites and that the protective action of vitamin E is due to its functioning as an antioxidant in vivo. Direct evidence for these mechanisms in vivo has been sought and is critically examined.

2. The increased production of malondialdehyde by rat liver microsomal fractions during incubation with CCl4 was shown to be a function of the vitamin E status of the rat and of an in vitro reaction, which could not be correlated with the hepatotoxic action of CCI4.

3. Evidence for the production of lipid peroxides by CCl4 in the livers of vitamin E-deficient and vitamin E-supplemented rats was sought (I) by measurement of ultraviolet spectral changes ('diene' formation) and (2) by direct micro-iodimetric determination of the peroxide. No differences in peroxide content were found between CC14-treated and control rats, nor were the spectrophotometric changes in the ultraviolet region related to the presence of vitamin E.

4. The effect of CCI4 (2.0 ml/kg orally) on ATP levels in rat liver was studied at intervals from 3 to 68 h. The primary lesion leading to necrosis and fat accumulation after CCl4 treatment occurred many hours before the eventual slight decline in ATP. Although the levels of ATP were somewhat higher in vitamin E-deficient rats, vitamin E did not prevent the slight decline in ATP that took place. Since ATP is known to be highly sensitive to peroxidation, the results suggest that lipid peroxidation is not the primary event in CCl4 poisoning.

5. The effect of CC14on the metabolism of [14C]D-α-tocopherol in the rat was studied. A single intraperitoneal dose of CCl4 (2.0 m/kg) did not increase the destruction of α-tocopherol in the liver or carcass after 24 h. Three smaller daily doses of CC14 (0.25 ml/kg) also did not increase α-tocopherol catabolism; on the contrary, significantly more α-tocopherol was found in the livers of rats treated with CCI4. These results suggest that CCl4 does not increase lipid peroxidation in vivo.

The mode of inhibition by calcium of cell-membrane adenosine-triphosphatase activity

1. The mechanism of the inhibition of Na(+)-plus-K(+)-activated adenosine triphosphatase by calcium was investigated with an enzyme preparation from rabbit kidney cortex and with membranes of human erythrocytes. 2. CaATP, rather than ionic Ca(2+), acts as a competitive inhibitor, competing with MgATP in the Na(+)-plus-K(+)-activated adenosine-triphosphatase reaction. 3. There appears to be no competition between calcium and Na(+) for the activation of adenosine triphosphatase. 4. The inhibition of Na(+)-plus-K(+)-activated adenosine triphosphatase of cell membranes by low concentrations of CaATP and the consequent need of intact cells to keep the cytoplasmic concentration of calcium low relative to that of magnesium suggests a raison d'être for the mitochondrial calcium pump.

Liver parenchymal cell injury. 3. The nature of calcium--associated electron-opaque masses in rat liver mitochondria following poisoning with carbon tetrachloride

Accumulation of calcium in the mitochondria of rat liver parenchymal cells at 16 and 24 hours after poisoning with carbon tetrachloride is associated with an increase in amount of liver inorganic phosphate, the persistence of mitochondrial adenosine triphosphatase activity, and the formation of electron-opaque intramitochondrial masses in cells with increased calcium contents. These masses, which form within the mitochondrial matrix adjacent to internal mitochondrial membranes, resemble those observed in isolated mitochondria which accumulate calcium and inorganic phosphate; are present in a locus similar to that of electron opacities which result from electron-histochemical determination of mitochondrial ATPase activity; and differ in both appearance and position from matrix granules of normal mitochondria. After poisoning, normal matrix granules disappear from mitochondria prior to their accumulation of calcium. As calcium-associated electron-opaque intramitochondrial masses increase in size, mitochondria degenerate in appearance. At the same time, cytoplasmic membrane systems of mid-zonal and centrilobular cells are disrupted by degranulation of the rough endoplasmic reticulum and the formation of labyrinthine tubular aggregates. The increase in amount of inorganic phosphate in rat liver following poisoning is balanced by a decreased amount of phosphoprotein. These chemical events do not appear to be related, however, as the inorganic phosphate accumulated is derived from serum inorganic phosphate.