Reye's syndrome: patient serum alters mitochondrial function and morphology in vitro

Pretreatment with edaravone reduces lung mitochondrial damage in an infant rabbit ischemia-reperfusion model

PURPOSE

Free radical scavenger edaravone has been approved as a new drug for treatment of stroke patients. The purpose of this study was to examine whether pretreatment with edaravone could attenuate ischemia-reperfusion (IR)-induced lung damage in infant rabbits.

METHODS

New Zealand White rabbits (Experimental Animal Center, Nanjing Medical University, Nanjing, China) at age from 15 to 21 days were subjected to sham operation, IR, or edaravone plus IR. Ischemia/reperfusion was induced by clamping the right pulmonary hilum for 1 hour and then removal of the clamp for 4 hours. Edaravone (1 mg/kg, intravenous) was given 5 minutes before ischemia. Concentrations of reactive oxygen species-hydroxyl radical (ROS-HR) and malondialdehyde (MDA), and activities of glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) in the lung tissue were measured. Mitochondrial membrane potential, swelling rate, and ultrastructure of the lung were analyzed, and histologic condition of the lung was evaluated.

RESULTS

Edaravone pretreatment reduced markedly the productions of ROS-HR and MDA and increased the activities of GSH-PX and SOD. It attenuated both IR-induced decrease in mitochondrial membrane potential from 60% to 14% and IR-induced increase in mitochondrial swelling. As results, the mitochondrial and lung tissue damages were less, leading to an improved survival rate in IR rabbits pretreated with edaravone compared with IR rabbits without the treatment.

CONCLUSION

Edaravone pretreatment reduces the IR-induced lung mitochondrial damage in infant rabbits.

Effects on free radical generation by ligands of the peripheral benzodiazepine receptor in cultured neural cells

The effect of peripheral benzodiazepine receptor (PBR) ligands on free radical production was investigated in primary cultures of rat brain astrocytes and neurons as well as in BV-2 microglial cell lines using the fluorescent dye dichlorofluorescein-diacetate. Free radical production was measured at 2, 30, 60 and 120 min of treatment with the PBR ligands 1-(2-chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195), 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one (Ro5-4864) and protoporphyrin IX (PpIX) (all at 10 nm). In astrocytes, all ligands showed a significant increase in free radical production at 2 min. The increase was short-lived with PK11195, whereas with Ro5-4864 it persisted for at least 2 h. PpIX caused an increase at 2 and 30 min, but not at 2 h. Similar results were observed in microglial cells. In neurons, PK11195 and PpIX showed an increase in free radical production only at 2 min; Ro5-4864 had no effect. The central-type benzodiazepine receptor ligand, clonazepam, was ineffective in eliciting free radical production in all cell types. As the PBR may be a component of the mitochondrial permeability transition (MPT) pore, and free radical production may occur following induction of the MPT, we further investigated whether cyclosporin A (CsA), an inhibitor of the MPT, could prevent free radical formation by PBR ligands. CsA (1 micro m) completely blocked free radical production following treatment with PK11195 and Ro5-4864 in all cell types. CsA was also effective in blocking free radical production in astrocytes following PpIX treatment, but it failed to do so in neurons and microglia. Our results indicate that exposure of neural cells to PBR ligands generates free radicals, and that the MPT may be involved in this process.

Mitochondrial alterations induced by aspirin in rat hepatocytes expressing mitochondrially targeted green fluorescent protein (mtGFP)

Mitochondria in primary living hepatocytes were visualized in cells transfected with a chimeric plasmid encoding for the green fluorescent protein (GFP) of Aequorea victoria engineered to be specifically targeted to mitochondria, as described recently (Rizutto et al. (1995) Curr. Biol. 5, 635-642). The identification of the fluorescent organelles as authentic mitochondria was confirmed by double labeling with rhodamine 123. Acetylsalicylate treatment of hepatocytes induced in mitochondria typical morphological alterations closely analogous to the swelling promoted by acetylsalicylate in isolated mitochondria. Cyclosporin A, which in isolated mitochondria prevents the changes induced by acetylsalicylate, had no protective action but induced per se specific alterations in the morphology of mitochondria. Moreover, exposure of hepatocytes to cyclosporin A followed by acetylsalicylate caused the same mitochondrial changes induced by each of the two compounds separately. The structural alterations caused by acetylsalicylate were constantly associated with a decrease in mitochondrial urea synthesis and cell viability.

Acetylsalicylate (ASA)-induced mitochondrial dysfunction and its potentiation by Ca2+

Although it has been suggested that acetylsalicylate (ASA)-induced mitochondrial dysfunction plays an important role in the pathogenesis of Reye's syndrome, administration of ASA alone does not cause this syndrome in therapeutic doses. We noted, however, that Ca2+ plays important roles in the regulation of cellular functions. ASA at concentrations of 250 microM or less, which had little effect on succinate-linked respiration, impaired Ca2+ accumulation in liver mitochondria by causing an increase in Ca2+ release. ASA plus Ca2+, which in concentrations of 150 microM or less alone had little effect on mitochondrial respiration, inhibited state 3 respiration and dinitrophenol-induced uncoupling of respiration. In addition, ASA plus Ca2+ increased state 4 respiration and ATPase activity. These results indicate that ASA plus Ca2+ impaired mitochondrial ATP synthesis, and suggest that ASA and ASA-induced Ca2+ increases in cytosol form a vicious circle of effects. Furthermore, oral administration of ASA (150 mg/kg for 5 days running) to rats did not affect mitochondrial structure or liver function, but resulted in aberrations of mitochondrial respiration. These results suggest that even therapeutic doses of ASA may induce alteration in mitochondrial function.

Mechanisms by which mitochondria transport calcium

It has been firmly established that the rapid uptake of Ca2+ by mitochondria from a wide range of sources is mediated by a uniporter which permits transport of the ion down its electrochemical gradient. Several mechanisms of Ca2+ efflux from mitochondria have also been extensively discussed in the literature. Energized mitochondria must expend a significant amount of energy to transport Ca2+ against its electrochemical gradient from the matrix space to the external space. Two separate mechanisms have been found to mediate this outward transport: a Ca2+/nNa+ exchanger and a Na(+)-independent efflux mechanism. These efflux mechanisms are considered from the perspective of available energy. In addition, a reversible Ca2(+)-induced increase in inner membrane permeability can also occur. The induction of this permeability transition is characterized by swelling of the mitochondria, leakiness to small ions such as K+, Mg2+, and Ca2+, and loss of the mitochondrial membrane potential. It has been suggested that the permeability transition and its reversal may also function as a mitochondrial Ca2+ efflux mechanism under some conditions. The characteristics of each of these mechanisms are discussed, as well as their possible physiological functions.

Salicylates and proton transport through lipid bilayer membranes: a model for salicylate-induced uncoupling and swelling in mitochondria

Mechanisms of proton transport were investigated in phospholipid bilayer membranes exposed to salicylates and benzoates. Membranes were formed from diphytanoyl phosphatidylcholine in decane plus chlorodecane (50% vol/vol). Proton and anion conductances (GH and GA) were calculated from the total conductances and the H+ or A diffusion potentials produced by transmembrane H+ or A gradients. At low pH salicylate caused a GH which was proportional to the square of the total weak acid concentration, and GH was maximum when pH = pK. At neutral to alkaline pH salicylate caused a GA which was proportional to the first power of the salicylate concentration, and GA was independent of pH. Both GH and GA were inhibited by phloretin. The results suggest that salicylate acts as an HA2-type proton carrier at low pH and as a lipid-soluble anion at neutral pH. Salicylate has been implicated as a causal factor in Reye's syndrome, as well as in aspirin poisoning, and salicylate has been reported to increase the proton conductance of inner mitochondrial membranes. The present results suggest that in mitochondria salicylate increases passive proton uptake by a combination of HA influx (driven by the concentration gradient) and A efflux (driven by the voltage and concentration gradients). Model calculations suggest that over the range of therapeutic to toxic concentrations, salicylate causes net H+ influx sufficient to explain the reported "loose coupling," uncoupling and swelling of mitochondria. The relative ineffectiveness of aspirin and benzoate can be explained by their low A permeabilities, whereas the ineffectiveness of 2,6-dihydroxybenzoate can be explained by its low pK.

Biochemical relationships between Reye's and Reye's-like metabolic and toxicological syndromes

Reye's syndrome is a hepatic encephalopathy with fatty infiltration of the liver and is due to mitochondrial dysfunction. Knowledge of the mechanisms causing Reye's syndrome has been gained from the study of Reye's syndrome-like diseases, including inborn errors of mitochondrial energy production, viral disease and toxicological injury. Entry of fatty acids into mitochondria or beta-oxidation itself may be impaired. Toxins such as hypoglycin, pentanoate, valproate, salicylate, and their metabolites inhibit beta-oxidation pathways and can produce Reye's syndrome-like presentations. Biochemical manifestations of the diverse causes of Reye's syndrome-like disorders are similar and include: hypoglycaemia due to impaired gluconeogenesis, accumulation of fatty acids, fatty acyl CoAs, and acyl carnitines with depletion of free CoA and carnitine. Accumulated products may further injure mitochondria and exacerbate impaired beta-oxidation, uncouple oxidative phosphorylation or increase mitochondrial permeability. Mitochondrial swelling and steatosis of hepatic cells are the histological result. With the advances of biochemical techniques for the study of organic acid excretion patterns, serum fatty acid patterns and identification of enzymatic deficiencies in cells from patients with Reye's syndrome-like presentations, it is clear that Reye's syndrome is, in part, a collection of various inborn errors and toxicological states. Circumstances such as viral disease, prolonged fasting and drugs may precipitate clinical expression of these deficiencies as Reye's syndrome. As work progresses, further causes of Reye's syndrome will be identified.

Inhibition of mitochondrial phospholipase A2 by mono- and dilysocardiolipin

Phospholipase A2 extracted from the acetone powder of previously frozen rat liver mitochondria is strongly inhibited compared to the activity manifest before acetone powder preparation. Activity is substantially recovered upon partial purification of the enzyme by gel filtration chromatography. Inhibitor activity elutes in the void volume from the column and is obtained in the chloroform layer when void volume fractions are subjected to a Folch extraction. Structural studies support the inhibitor being monolysocardiolipin. Under the assay conditions employed, 1 molecule of the inhibitor per 5000 substrate molecules or 40 nM on a nominal concentration basis is I50 for the mitochondrial enzyme. The agent is similarly effective against pancreatic and snake venom phospholipases A2. Monolysocardiolipin and dilysocardiolipin prepared enzymatically from bovine heart cardiolipin are less potent than the material arising from rat liver cardiolipin by factors of 10- and 30-fold, respectively, yet are still highly potent compared to the other known inhibitors of this enzyme. Differences in acyl group composition, in the degree of acyl group oxidation, or in structural isomerism between the sn-1 and sn-2 positions of the lyso compounds may account for the difference in potency between the materials derived from rat liver and bovine heart.

Application of trace metal analysis to basic problems in neurobiology studies of patients with Reye's syndrome

Reye's syndrome (Rs) is an acute illness in children manifested by encephalopathy and fatty degeneration of the liver. The syndrome may be secondary to injury of mitochondria following a toxic insult in a susceptible individual with a viral illness. Since the response to infection often involves a change in trace metals, we investigated the metal status of patients with Rs. Decreased levels of serum and liver selenium (Se) and copper (Cu) were demonstrated via PIXE analysis, in addition to an increase in serum iron (Fe) and zinc (Zn). In a subsequent study using a rat animal model of Rs, the hepatotoxin 4-pentenoic acid (4-PA) produced similar changes in serum and liver trace metals. Serum and liver Se levels were also significantly depleted in rats exposed to another toxin, valproic acid (VPA). Aspirin, known to complex metals, may also be associated with Rs. Rats chronically exposed to aspirin had decreased serum Se, Fe, and Zn compared to controls. Selenium was also decreased in liver, as was Cu. Atomic absorption spectrophotometric analysis of serum and liver Cu for mice exposed to aspirin and influenza A virus were also studied. In liver, Cu was significantly decreased in mice on Cu-deficient diets but, not in control mice exposed to virus, or aspirin and virus. For the Se-deficient animals, liver Cu was not different from controls, but there was an increase in tissue Cu for Se-sufficient mice exposed to virus and aspirin; Cu levels were decreased in sera of this latter group. Serum Cu was increased in Cu-sufficient mice exposed to virus and aspirin. The above data are of biologic and toxicologic interest because of metalloenzyme localization in the mitochondrial matrix, the cellular compartment showing the greatest degree of pathologic change in Rs. In particular, Se-dependent gluthathione peroxidase is a major deterent of peroxidative damage of lipid membranes. The accumulated evidence suggests that alteration of trace metals, e.g., decrease in Se, may promote peroxidation of mitochondrial membranes in patients with Rs.

Advances in the application of biochemical tests to diseases of the liver and biliary tract: their role in diagnosis, prognosis, and the elucidation of pathogenetic mechanisms

Despite the biochemical complexity of the liver, few laboratory tests provide discriminatory diagnostic information in patients with hepatobiliary disease. Recent efforts have concentrated upon tests which assess the function of the liver, the severity of the disease state, and underlying pathological processes. Bile Acids: The emergence of facile technology and widespread application has brought the realization that these assays are not as sensitive in detecting liver disease as previously believed, although the cholate/chenate ratio may be useful in distinguishing cholestasis from chronic liver disease. The presence of unusual bile acids in serum or urine may be helpful in some cases. Drug Metabolism: A number of tests provide good evidence about liver function, hepatic blood flow and portal shunting, but the aminopyrine breath tests is the most useful, giving prognostic information in acetaminophen overdose and alcoholic liver disease. The antipyrine half-life identifies surgical cases at risk from poor hepatic function. Proteins and Immunochemical Tests: Interest has developed in plasma proteins such as prealbumin and retinol-binding protein to monitor hepatic protein synthetic function. Secretory IgA is more elevated in biliary tract disease, unlike the native protein which is increased principally in cirrhosis. Type III procollagen can be measured in serum, and correlates with the activity of collagen synthesis and the degree of fibrosis in biopsy samples. Reye's Syndrome: Biochemical tests play an essential role in diagnosis of this recently discovered disease. These will be presented and discussed.

Carnitine status in Reye and Reye-like syndromes

Fourteen children with the following Reye and Reye-like syndromes were studied to determine each patient's carnitine status: valproate-induced Reye-like attack, ornithine transcarbamylase deficiency, systemic carnitine deficiency, methylmalonic acidemia, and propionic acidemia. Reduced free carnitine and increased serum and urine acylcarnitine levels were found in all patients except for 2 with Reye syndrome, in whom serum creatinine levels were mildly elevated and serum free carnitine levels were not reduced. The renal free carnitine reabsorption rate was reduced in all cases. The free carnitine content of autopsied liver samples were reduced in 2 Reye syndrome patients, 2 OTC deficiency patients, and in a single systemic carnitine deficiency patient. The observed secondary free carnitine deficiency may be a factor in the pathogenesis of Reye and Reye-like syndromes.

Reye's syndrome: mitochondrial swelling and Ca2+ release induced by Reye's plasma, allantoin, and salicylate

The effects of Reye's plasma, allantoin, and salicylates on mitochondrial structure and Ca2+ transport have been investigated. Measurements of Ca2+ transport showed that when 20-30 microM Ca2+ was added to isolated rat liver mitochondria preincubated with one of these agents, Ca2+ uptake was followed by its spontaneous release into the medium. This was accompanied by large-amplitude swelling; the onset preceded the Ca2+ release. No further Ca2+ release was induced by uncoupler or the Ca2+ ionophore, A23187. The mitochondria continued to swell even after all of the Ca2+ had been released. The time between the addition of Ca2+ and the onset of swelling (or Ca2+ release) depended on the concentration of the agent added and the preincubation time; the extent of swelling did not. These effects were prevented, but not reversed, by ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid, ruthenium red, rotenone, or adenine nucleotides. The massive swelling and membrane disruption were confirmed by electron microscopy of the treated vs untreated mitochondria. Similar results concerning swelling and Ca2+ release were also seen with Ca2+ alone, but the time scale was much longer (i.e., greater than 3-4 min), indicating that these agents act by potentiating Ca2+-induced alterations in mitochondrial structure, as suggested by our earlier work (T.Y. Segalman and C.P. Lee (1982) Arch. Biochem. Biophys. 214, 522-530; M.E. Martens and C.P. Lee (1984) Biochem. Pharmacol. 33, 2869-2876). Our data show, therefore, that allantoin, salicylates, and the "toxic" agent in Reye's plasma severely limit the ability of isolated rat liver mitochondria to maintain their structural integrity under conditions of limited Ca2+ loading.

Effect of Reye's syndrome serum on isolated chinchilla liver mitochondria

A general impairment of liver mitochondrial enzymes is central to Reye's syndrome (RS). The respiration of isolated liver mitochondria was measured after the addition of concentrated normal serum or RS serum derived from 12 patients. RS serum stimulates oxygen consumption in isolated rat liver mitochondria. This effect is due to the oxidation of uric acid by peroxisomes contaminating the preparation and a stimulation of mitochondrial respiration (1.05 +/- 0.14 nmol of O2/min X mg of protein; control 0.30 +/- 0.08 nmol O2/min X mg). The stimulation of respiration occurs in the presence of all respiratory substrates, is dependent on the amount of serum added, and represents an uncoupling of oxidative phosphorylation. RS serum reduces ATP formation by 15-76%. The uncoupling effect correlates with the amount of free fatty acid in the serum sample and resembles the effect induced by the addition of a dicarboxylic fatty acid. Dicarboxylic fatty acids, especially long-chain dicarboxylic acids, impair ATP formation. Dicarboxylic acids were found in the serum of all RS patients and comprised as much as 54% of the total serum free fatty acids. 90% of the serum dicarboxylic acids were of 16-18 carbon lengths. The amount of dicarboxylic acids in the RS serum corresponded directly with the reduction in ATP formation by the RS serum. This demonstrates that dicarboxylic acids occur in RS and may be important in the general impairment of mitochondrial function in RS and other disorders where they are present.

Pentachlorophenol intoxication: report of a fatal case, with comments on the clinical course and pathologic anatomy

A case of a 33-yr-old man who died following occupational exposure to pentachlorophenol is presented. Postmortem examination revealed cerebral edema and fatty degeneration of the viscera. Review of the literature indicates that the clinical syndrome of poisoning with the compound results from mitochondrial toxicity with derangement of aerobic metabolism.

Inhibition of oxidative phosphorylation in hepatic and cerebral mitochondria of sodium valproate-treated rats

Rats were treated with intraperitoneal injections of sodium valproate (VPA), either acutely, one injection VPA 200 mg/kg, or chronically, VPA 600 mg/kg/day for 5 days, and the oxygen consumption, MO2, of isolated hepatic and cerebral mitochondria measured. For hepatic mitochondria, Stade IV MO2 decreased by more than 20%, and Stage III MO2 by more than 50%, in the presence of succinate or glutamate-malate substrates. A decoupling agent intensified this inhibition. With cerebral mitochondria, the effects were similar but weaker, for pyruvate-malate or glutamate-malate substrates. These findings suggest that VPA, a short-chain fatty acid, may affect the properties of the internal mitochondrial membrane, although an action on substrate carriers, or on indispensable mitochondrial metabolites, is not excluded. Inhibition of oxidative phosphorylation cannot, however, alone account for hepatotoxicities seen in VPA-treated subjects. These are rare, whereas inhibition of mitochondrial respiration by VPA is consistently observed.

Salicylate and mitochondrial injury in Reye's syndrome

Electron microscopic and spectrophotometric studies showed that salicylate causes gross swelling of mitochondria in isotonic salt solutions. In overall morphology the salicylate-treated mitochondria resembled those from patients with Reye's syndrome. Salicylate analogs such as m-hydroxybenzoate, p-hydroxybenzoate, and benzoate did not exert this effect. The mitochondria deformed by salicylate tended to return to their original condensed form on removal of the drug.

Masking by enzyme inhibitor of raised serum glutamate dehydrogenase activity in Reye's syndrome

Serum glutamate dehydrogenase (GDH) activity was greatly raised (up to 830 times the upper limit of normal) in 16 patients with Reye's syndrome. The serum activity was masked by an inhibitor, and the rises were observed only after dialysis or sample dilution. Serum GDH values from 38 paediatric patients, including 10 with hyperammonaemia due to other causes, showed no such rise after dialysis. Only 1 of 13 adult patients with liver disease had high GDH activity, but this level was not increased after dialysis. Serum ornithine carbamyl transferase activity was also raised in patients with Reye's syndrome, but levels were not increased after dialysis. The ratio of dialysed/undialysed GDH activity clearly distinguished all Reye's patients from controls. The inhibition of a mitochondrial enzyme which regulates ammonia metabolism may contribute to the hyperammonaemia of Reye's syndrome. Serum GDH levels before and after dialysis would seem to be a useful diagnostic aid in Reye's disease.

Abnormalities of the complement system in Reye syndrome

Sixteen patients with Reye syndrome had diminished concentration of serum complement proteins and/or hemolytic activity in the earliest blood sample. All 12 studied with hemolytic methods had significantly reduced C1 activity; total hemolytic complement activity was reduced in only three. Low Cl activity was accompanied by equivalent reduction of Cls in 11 of 12 patients; Clq was less than normal in only two of 12. Decreased levels of at least one other classical pathway complement hemolytic activity or protein concentration were found in 13 patients, whereas factor B or the alternate complement pathway was normal or elevated in the ten patients studied. The consistent reduction of Cls protein concentration in Reye syndrome suggests that early metabolic abnormalities regularly affect the production or catabolism of this protein. Although normal serum Clq concentration in the majority of these patients does not support an immune pathogenesis, decreased Clq, C4, and C2 in three patients does suggest that immune mechanisms may be responsible for the serum complement abnormalities in this latter group of patients.