The biochemistry of Reye's syndrome

Reye Syndrome with Severe Hyperammonemia and a Good Neurological Outcome

Patient: Male, 4-year-old

Final Diagnosis: Reye syndrome

Symptoms: Hypoglycemia • disturbance of consciousness • diarrhoea • signs of respiratory infection • vomiting and nausea

Medication: —

Clinical Procedure: —

Specialty: Critical Care Medicine • Endocrinology and Metabolic • Pediatrics and Neonatology

Evaluation of a screening method by liquid chromatography-tandem mass spectrometry for estimating effect of drugs on the activation and β-oxidation of fatty acids in mitochondria

Objectives

Fatty acid metabolism is controlled not only by the acyl-coenzyme A (CoA) synthetases but by some enzymes in the β-oxidation cycle. Medium-chain and long-chain acyl-CoA esters are key metabolites in fatty acid metabolism. We have developed an enzymatic assay method for determining chain shortening of the acyl-CoAs via β-oxidation from palmitic and octanoic acids in liver mitochondria. We have evaluated the assay method for detecting whether drugs influence the activation or the β-oxidation of fatty acids.

Methods

Liver mitochondria were used for investigating the effect of drugs on fatty acid metabolism. The drugs selected were salicylic acid, diclofenac, valproic acid and paracetamol. Each acyl-CoA formed was analysed by liquid chromatography–tandem mass spectrometry.

Key findings

After less than 5 min of incubation, the levels of acyl-CoAs reflected the acyl-CoA synthetase activity, whereas after 60-min incubation they reflected the activity of some enzymes in the β-oxidation cycle. Salicylic acid, diclofenac and valproic acid inhibited the medium-chain acyl-CoA synthetases, whereas valproic acid only exhibited a weak inhibitory activity toward the β-oxidation of the medium-chain fatty acids. In the case of long-chain fatty acid metabolism, salicylic acid and diclofenac inhibited both the activation and β-oxidation, whereas valproic acid was a weak inhibitor for only the β-oxidation activity. Paracetamol showed hardly any influence on the metabolism of medium-chain and long-chain fatty acids.

Conclusions

These findings suggest that salicylic acid, diclofenac, valproic acid and paracetamol exert a different influence on fatty acid metabolism depending on the length of the acyl chain. This assay allows sensitive and selective analysis for predicting the pathways by which drugs exert a greater influence over fatty acid metabolism.

Effect of salicylic acid and diclofenac on the medium-chain and long-chain acyl-CoA formation in the liver and brain of mouse

Medium-chain and long-chain acyl-CoA esters are key metabolites in fatty acid metabolism. Effects of salicylic acid on the in vivo formation of acyl-CoAs in mouse liver and brain were investigated. Further, inhibition of the medium-chain and long-chain acyl-CoA synthetases by salicylic acid and diclofenac was determined in mouse liver and brain mitochondria. Acyl-CoA esters were analyzed by liquid chromatography-tandem mass spectrometry. The amounts of medium-chain acyl-CoAs (C(6), C(8) and C(10)) were less than long-chain acyl-CoAs (C(16:0), C(18:0), C(18:1) and C(20:4)) in both liver and brain. The administration of salicylic acid decreased the levels of both the medium-chain (C(6), C(8) and C(10)) and long-chain acyl-CoAs (C(16:0), C(18:0), C(18:1) and C(20:4)) in liver. In brain, however, only long-chain acyl-CoAs were decreased. The level of salicylyl-CoA detected in brain was about 12% of that in liver. Salicylic acid had a strong inhibitory activity (IC(50) = 0.1 mm) for the liver mitochondrial formation of hexanoyl-CoA from hexanoic acid, whereas diclofenac was weak (IC(50) = 4.4 mm). In contrast, diclofenac (IC(50) = 1.4 mm) inhibited the liver mitochondrial long-chain acyl-CoA synthetases more potently than salicylic acid (IC(50) = 25.5 mm). Similar inhibitory activities for the acyl-CoA synthetases were obtained in the case of the brain and liver mitochondria, except for the weak inhibition of brain medium-chain acyl-CoA synthetases by salicylic acid (IC(50) = 1.8 mm). These findings suggest that salicylic acid and diclofenac exhibit different mechanisms of inhibition of fatty acid metabolism depending on the length of the acyl chain and tissues, and they may contribute to the further understanding of the toxic effects associated with these drugs.

Carnitine, acylcarnitine and amino acid profiles analyzed by tandem mass spectrometry in a surfactant/virus mouse model of acute hepatic encephalopathy

Tandem mass spectrometry (MS/MS) was used to analyze multiple serum metabolites for the first time in a surfactant/virus mouse model of acute hepatic encephalopathy (AHE). AHE is characterized by acute liver failure that can lead to potentially lethal increases in intracranial pressure. We have reproduced AHE in young CD-1 mice exposed from postnatal day (P) 2-13 to the industrial surfactant, Toximul 3409F (Tox), and then infected intranasally on P14 with sublethal doses (LD(10-30)) of mouse-adapted human influenza B (Lee) virus (FluB). The sera analyzed by MS/MS were from mice exhibiting typical markers of Tox-mediated potentiation of viral illness, including reduced weights and blood glucose levels. Most metabolite abnormalities were not evident until five days after viral infection (P19), the time corresponding to the onset of weight loss and mortality. Values for fatty acylcarnitines and amino acids in the Tox+FluB-treated mice were either additive or supra-additive relative to the effects of either treatment alone. Amino acid profiles were consistent with those reported for human AHE. None of the treated mice exhibited signs of carnitine deficiency, and propionylcarnitine levels were normal. On P19, mice given combined Tox+FluB treatment had significant increases in levels of both medium- and long-chain acylcarnitines (C6:0-C12:0 and C14:0-C20:0, respectively), including their monounsaturated metabolites. Levels of medium-chain dicarboxylic and long-chain hydroxy-acylcarnitines were also elevated in the combined treatment group. The results of this study indicate a diffuse mitochondrial dysfunction in Tox+FluB-treated mice that results in a serum metabolite profile unique from those observed in classic inherited metabolic disorders.

Salicylate-induced kidney mitochondrial permeability transition is prevented by cyclosporin A

The effect of salicylate, the active metabolite of aspirin (acetyl salicylic acid) in the presence of Ca2+ and phosphate on mitochondrial permeability transition (MPT) was studied. MPT is often associated with opening of a Ca2+ -induced pore. The opening of this pore leads to swelling, loss of mitochondrial membrane potential and release of accumulated Ca2+. In freshly isolated rat kidney mitochondria, salicylate (400 microM) in the presence of 20 nmol Ca2+/mg protein and 0.1 mM phosphate induced swelling, loss of mitochondrial membrane potential and release of accumulated Ca2+. All these changes were eliminated when cyclosporin A (1 microM), (a pore inhibitory agent) was included in the incubation medium. Unlike salicylate, unhydrolyzed aspirin (400 microM) induced these changes slightly. We concluded that salicylate acts as an activator of Ca2+ and phosphate in promoting the opening of kidney inner mitochondrial membrane pore. As a result a great consideration should be given to its toxicological effect.

The mitochondrial permeability transition in cell death: a common mechanism in necrosis, apoptosis and autophagy

Using confocal microscopy, onset of the mitochondrial permeability transition (MPT) in individual mitochondria within living cells can be visualized by the redistribution of the cytosolic fluorophore, calcein, into mitochondria. Simultaneously, mitochondria release membrane potential-indicating fluorophores like tetramethylrhodamine methylester. The MPT occurs in several forms of necrotic cell death, including oxidative stress, pH-dependent ischemia/reperfusion injury and Ca2+ ionophore toxicity. Cyclosporin A (CsA) and trifluoperazine block the MPT in these models and prevent cell killing, showing that the MPT is a causative factor in necrotic cell death. During oxidative injury induced by t-butylhydroperoxide, onset of the MPT is preceded by pyridine nucleotide oxidation, mitochondrial generation of reactive oxygen species, and an increase of mitochondrial free Ca2+, all changes that promote the MPT. During tissue ischemia, acidosis develops. Because of acidotic pH, anoxic cell death is substantially delayed. However, when pH is restored to normal after reperfusion (reoxygenation at pH 7.4), cell death occurs rapidly (pH paradox). This killing is caused by pH-dependent onset of the MPT, which is blocked by reperfusion at acidotic pH or with CsA. In isolated mitochondria, toxicants causing Reye's syndrome, such as salicylate and valproate, induce the MPT. Similarly, salicylate induces a CsA-sensitive MPT and killing of cultured hepatocytes. These in vitro findings suggest that the MPT is the pathophysiological mechanism underlying Reye's syndrome in vivo. Kroemer and coworkers proposed that the MPT is a critical event in the progression of apoptotic cell death. Using confocal microscopy, the MPT can be directly documented during tumor necrosis factor-alpha induced apoptosis in hepatocytes. CsA blocks this MPT and prevents apoptosis. The MPT does not occur uniformly during apoptosis. Initially, a small proportion of mitochondria undergo the MPT, which increases to nearly 100% over 1-3 h. A technique based on fluorescence resonance energy transfer can selectively reveal mitochondrial depolarization. After nutrient deprivation, a small fraction of mitochondria spontaneously depolarize and enter an acidic lysosomal compartment, suggesting that the MPT precedes the normal process of mitochondrial autophagy. A model is proposed in which onset of the MPT to increasing numbers of mitochondria within a cell leads progressively to autophagy, apoptosis and necrotic cell death.

Aspirin induces short-chain free fatty acid accumulation in rats

Aspirin is used for the prophylaxis of infarction. A low dose of aspirin is effective for the prophylaxis of myocardial infarction, whereas a higher dose is necessary for that of stroke. Salicylic acid, the in vivo metabolite of aspirin, inhibits the beta-oxidation of short-chain fatty acids. Accordingly, drinking water containing 400, 800, or 1200 mg/l aspirin was given to each of eight rats for 30 days to determine the serum short-chain fatty acid levels. Analysis of variance and a post-hoc Fisher's protected least significant differences test revealed significantly increased levels (P < 0.05) of monocarboxylic acids, n-hexanoate, n-octanoate, n-decanoate, n-dodecanoate, and dicarboxylic acids, adipate (C6,) and suberate (C8): 78.7 +/- 36.2, 61.1 +/- 30.6, 215 +/- 151, 47.5 +/- 24.0, 3.64 +/- 2.09 and 1.71 +/- 1.45 micromol/l in the 800 mg/l aspirin group compared to 23.8 +/- 12.3, 20.1 +/- 9.0, 24.3 +/- 12.1, 6.3 +/- 5.6, 0.56 +/- 0.50 and 0.44 +/- 0.25 micromol/l in the control group, respectively. These levels were also increased in the 400 or 1200 mg/l aspirin groups but less so. These findings may help us to understand the aspirin toxicity in Reye's syndrome.

Rapid method for the separation and detection of tissue short-chain coenzyme A esters by reversed-phase high-performance liquid chromatography

A simple and rapid method for the separation and identification of tissue levels of short chain coenzyme A (CoA) esters by a reversed-phase high-performance liquid chromatography with ultraviolet-visible adsorbance detection is described. Samples of liver, heart and kidney tissues were homogenised in 5% sulfosalicylic acid containing 50 microM of dithioerythritol in 1:9 w/v proportion. Following centrifugation, 20 microliters of the supernatant were directly injected onto a 3-micron ODS C18 column (100 x 4.6 mm I.D.). The separation of acetyl-CoA, malonyl-CoA, methylmalonyl-CoA, succinyl-CoA, propionyl-CoA and free CoASH was achieved in less than 20 min using gradient elution with sodium phosphate, sodium acetate and methanol at a constant flow-rate of 1.5 ml/min. The lowest detection limit was 3 pmol.

Reye's and Reye-like syndromes, drug-related diseases? (causative agents, etiology, pathogenesis, and therapeutic approaches)

In the literature the separation between RS and RLS is confusing and makes it difficult to plan an appropriate preventive action or to develop new therapeutic approaches. We suggest that the generalized damage and encephalopathy seen in both RS and RLS may be due to a wide variety of causative agents that contribute to a common derangement, principally involving mitochondrial oxidative pathway. Fasting status and infections increase the catabolism and the subsequent flux of metabolites from peripheral tissues to the liver (FA and amino acids); cytokines (TNF, IL-1, and IL-6), in particular, mediate this effect during infection and experimental endotoxemia. Some drugs and other toxic compounds induce functional and morphological liver mitochondrial derangement. Oxidative metabolism is impaired, with subsequent stimulation of alternative pathways of oxidation, following production of unusual toxic acyl CoAs and dicarboxylic acids. Toxic compounds accumulate in the liver, deranging its functions and causing energy depletion, and are also released in the circulation from which they reach other tissues, including the brain. Neurons and astrocytes in the brain may be affected differently: Neurons suffer from the lack of energy and the effect of toxic compounds arriving from the bloodstream, and astrocytes may be directly affected by the beta-oxidation derangement. Very important may be genetic predisposition, which, by making the patient more sensitive to a particular causative agent, may facilitate the onset of RS and RLS. The therapeutic approach is, presently, mainly symptomatic, directed as it is to counteracting each alteration shown, depending by the clinical gravity. Other pharmacological approaches are only studied experimentally, like carnitine supplementation and PGE2 administration, or theoretically envisaged, like monoclonal antibody therapy directed at LPS or at pro-inflammatory cytokines or treatment with interferon-alpha.

Inhibition of beta-oxidation by 3-mercaptopropionic acid produces features of Reye's syndrome in perfused rat liver

BACKGROUND/AIMS

The cause of Reye's syndrome has not been completely defined. The rate of ketogenesis in the liver is a key determinant of, and reciprocally related to, triglyceride secretion. In the present study, 3-mercaptopropionic acid (MPA), a known inhibitor of mitochondrial long-chain acyl coenzyme A (CoA) dehydrogenase, was used to investigate the relationship between ketone body production, triglyceride secretion, and triglyceride accumulation in perfused rat liver.

METHODS

Livers from fasted rats were perfused 225 minutes with or without MPA in the presence of [1-14C]oleic acid. Morphology was studied by light and electron microscopy.

RESULTS

Inhibition of fatty acid oxidation by the liver with MPA resulted in a decrease in ketone body production. Treatment with MPA caused an accumulation of small-droplet triglycerides in liver, whereas the net secretion of triglyceride ceased after an initial period of increased secretion with continued decreased ketogenesis. At the end of the perfusion period, mitochondria in the MPA group appeared to be damaged.

CONCLUSIONS

The rates of both ketogenesis and triglyceride secretion by the liver appear to be the major determinants of hepatic triglyceride content. In addition, the MPA-mediated biochemical and morphological findings are quite similar to those of Reye's syndrome.

Effect of carboxylic acid xenobiotics and their metabolites on the activity of carnitine acyltransferases

Salicylyl-CoA and benzoyl-CoA were good inhibitors of carnitine acetyltransferase (CAT), competing with acetyl-CoA with Ki values of 7.5 and 22 microM respectively in the forward direction and with CoA in the reverse reaction with similar Ki values. They were also competitive inhibitors of carnitine octanoyltransferase (Ki = 261 and 295 microM respectively), but were only weakly inhibitory to carnitine palmitoyltransferase. Inhibition of energy production by salicylate may result from the inhibition of CAT by salicylyl-CoA.

Ca2+ responses to interleukin 1 and tumor necrosis factor in cultured human skin fibroblasts. Possible implications for Reye syndrome

Elevated concentrations of cytokines were found in the plasma of patients acutely ill with Reye syndrome (RS) but not in control subjects or recovered RS patients. To determine whether this disorder involves a genetically determined abnormal response to cytokines, the effects of tumor necrosis factor (TNF) and IL-1 on intracellular free Ca2+ were compared in cultured skin fibroblasts from control subjects and patients with RS. IL-1 and TNF caused rapid, transient, and concentration-dependent increases in cytosolic free Ca2+. The peak cytosolic free Ca2+ was greater and occurred at higher concentrations of IL-1 and TNF in patient cells than in cells from age-matched controls. In control cells, the Ca2+ transient diminished sharply with increasing amounts of IL-1 or TNF above the maximum stimulatory concentration. In contrast, in patient fibroblast this bell-shaped curve of concentration dependency was much less apparent. Bradykinin-stimulated Ca2+ transients were similar in the two groups and did not exhibit the bell-shaped concentration dependency. Thus, plasma cytokine levels are elevated in RS patients and the Ca2+ response to cytokines is increased in cells derived from these patients. We propose that the increased response reflects a genetic defect in cytokine receptor-modulated signal transduction.

Non-icteric fulminant hepatitis and Reye's syndrome: comparison of laboratory data

Twenty-eight patients with suspected Reye's syndrome (RS) were seen in our Department from 1974 through 1987. Liver biopsy confirmed the diagnoses of RS and non-icteric fulminant hepatitis (NIFH) in 7 and 5 cases, respectively. NIFH was the most common RS mimicker. Total bilirubin, LDH and serum ammonia levels showed no significant differences between RS and NIFH. However, the levels of serum GOT and GPT were significantly higher in the NIFH group. Serum and urinary carnitine levels were measured in both groups, but the results were inconclusive. Amino acid analysis in one RS and two NIFH patients showed no significant differences in the ratio of branched chain to aromatic amino acids. However, one RS patient showed a high level of lysine. Histological findings in the liver of two NIFH patients showed minor mitochondrial swelling and microvesicular fat, but the major finding was hepatic necrosis. Our experience indicates that NIFH and RS cannot be differentiated by routine laboratory tests. Liver biopsy is essential for the accurate diagnosis of RS.

Animal model of margosa oil ingestion with Reye-like syndrome. Pathogenesis of microvesicular fatty liver

The aetiology and pathogenesis of Reye's syndrome (RS) are incompletely understood. A number of environmental toxins and biological agents, including viruses, have been postulated to cause RS, either acting alone or synergistically. Most investigations have suggested that the primary insult is in the liver mitochondria, leading to a complex biochemical catastrophe, with death from encephalopathy. Margosa oil (MO), a long-chain fatty acid compound, has been shown to cause a Reye-like syndrome with death from hepatoencephalopathy, in children in Malaysia and India. The present time-course study performed in MO-administered mice showed the development of hepatic lesions with many features of RS. MO acts rapidly, within 30 min, on the nuclei of hepatocytes inducing mitoses and binucleated cells. This is followed by mitochondrial injury, with swelling, rarefaction of matrix, loss of dense bodies, pleomorphism, and loss of ribosomes starting at 60 min. There is loss of liver glycogen, and proliferation and hypertrophy of the endoplasmic reticulum (ER), followed by the presence of lipid droplets in the hyaloplasm, and globules within dilated cisterns of the ER. Additional fatty acids from lipolysis of body adipocytes, and fat globules from intestinal MO ingestion further aggravate the liver fatty change. There is evidence of fat globule ingestion by endocytosis into hepatocytes at the level of the sinusoids. The development of microvesicular liver steatosis and glycogen depletion due to involvement of liver cell organelles occur rapidly as in RS.

Hepatic metabolic alterations in rats treated with low-dose endotoxin and aspirin: an animal model of Reye's syndrome

The administration of a sublethal dose of endotoxin (LPS) followed one hour later by a low dose of aspirin (LPS + ASA) to fasted rats leads to biochemical perturbations similar to Reye's syndrome. In this study hepatic energy metabolism was assessed in freeze-clamped liver samples (12 hours posttreatment) obtained from (250 to 300 g Sprague-Dawley) rats. The administration of aspirin alone to fasted rats did not significantly alter the hepatic levels of adenine nucleotides, total ketones, or acyl-CoA thioesters as compared to controls. In contrast, in both LPS and LPS + ASA samples, there were declines in ATP/ADP ratio (P less than .005), total ketones (P less than .001) and acetyl CoA (P less than .005) compared to their respective controls. A striking alteration in acyl-CoA thioesters was observed in LPS + ASA-treated animals. Unlike control, aspirin, or LPS-treated animals, LPS + ASA-treated animals accumulated relatively large amounts of unusual CoA esters, including propionyl-CoA, (iso)butyryl-CoA, beta-methylcrotonyl-CoA, and isovaleryl-CoA, metabolites of the branch chain amino acid and odd-chain fatty acid oxidation pathways. The acyl-CoA profile is similar to that obtained in patients with Reye's syndrome. Like human patients with Reye's syndrome, these rats showed hyperammonemia, compromised fatty acid oxidation, and accumulation of branched chain amino acid oxidation metabolites. Accumulation of these intermediates with LPS + ASA is a possible mechanism for the potentiation of Reye's syndrome by aspirin. These findings provide biochemical evidence that sublethal doses of LPS + ASA administered to fasted rats produces an animal model of Reye's syndrome.

Relationship between unusual hepatic acyl coenzyme A profiles and the pathogenesis of Reye syndrome

This study examines the relationship between impaired fatty acid oxidation and the pathogenesis of Reye syndrome. We present a hypothesis proposing that many clinical signs of this childhood disease are caused by accumulation of unusual acyl CoA esters, precursors to deacylated metabolites found in the patients' blood and urine. A new method was developed to measure acyl CoA compounds in small human liver biopsy samples, offering several advantages over previous techniques. A major finding was an accumulation in Reye syndrome patients of short- and medium-chain acyl CoA intermediates of fatty acid and branched-chain amino acid oxidation. These metabolites included octanoyl, isovaleryl, butyryl, isobutyryl, propionyl, and methylmalonyl CoA esters. The findings were explained in a model of hepatic fatty acid oxidation involving three interrelated pathways: mitochondrial beta-oxidation, peroxisomal beta-oxidation, and omega-oxidation in the endoplasmic reticulum. The results suggest that pathogenesis in Reye syndrome stems from generalized mitochondrial damage resulting in accumulation of acyl CoA esters. High levels of these compounds lead to inhibition of mitochondrial pathways for ureogenesis, gluconeogenesis, and fatty acid oxidation. The inhibited pathways, in turn, could cause the hyperammonemia, hypoglycemia, and hypoketonemia observed in patients. The model also explains underlying biochemical differences between patients with Reye syndrome and medium-chain acyl CoA dehydrogenase deficiency, another disorder of fatty acid metabolism. Acetyl CoA levels, in the latter disease, were dramatically decreased, compared with both human controls and Reye syndrome patients.

The biochemical basis of mitochondrial diseases

Dysfunctioning of human mitochondria is found in a rapidly increasing number of patients. The mitochondrial system for energy transduction is very vulnerable to damage by genetic and environmental factors. A primary mitochondrial disease is caused by a genetic defect in a mitochondrial enzyme or translocator. More than 60 mitochondrial enzyme deficiencies have been reported. Secondary mitochondrial defects are caused by lack of compounds to enable a proper mitochondrial function or by inhibition of that function. This may result from malnutrition, circulatory or hormonal disturbances, viral infection, poisoning, or an extramitochondrial error of metabolism. Once mitochondrial ATP synthesis decreases, secondary mitochondrial lesions may be generated further, due to changes in synthesis and degradation of mitochondrial phospholipids and proteins, to mitochondrial antibody formation following massive degradation, to accumulation of toxic products as excess acyl-CoA, to the depletion of Krebs cycle intermediates, and to the increase of free radical formation and lipid peroxidation.

Endoperoxidation, hyperprostaglandinemia, and hyperlipidemia in a case of erythrophagocytic lymphohistiocytosis. Reversal with VP-16 and indomethacin

Clinicopathologic and histopathologic evidence of both endoperoxidation with hyperprostaglandinemia and hyperlipidemia in a 5-week-old infant with a hemophagocytic syndrome is reported. Institution of histiocytolytic (VP-16) and cyclo-oxygenase inhibitor (indomethacin) therapies returned the prostaglandin levels and lipid profile to a nearly normal state coincidental with clinical recovery. It appears that by reducing the cell mass of histiocytes and controlling the over-production of prostaglandins, some types of hemophagocytic syndrome can be reversed.

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.

Hepatic lipid abnormalities in a chemical/viral mouse model for Reye's syndrome

We have examined hepatic lipid profiles in a mouse model for Reye's Syndrome (RS) in which young animals are exposed to nontoxic doses of an industrial pesticide emulsifier and subsequently are infected with sublethal doses of mouse-adapted human Influenza B (Lee) virus (FluB). The purpose of this study was to determine whether liver lipid content was altered in the mice, the time course of any changes, and whether lipid changes were consistent with liver pathology. Neonatal mice exposed dermally to the emulsifier, Toximul MP8 (Tox), had significantly elevated levels of hepatic cholesterol, with otherwise normal lipid composition. Subsequent inoculation of the mice with FluB significantly increased mortality rate. The combined Tox + FluB treatment had several significant effects on liver lipids, including a transient increase in phospholipid (PL) content, a reduction in neutral glycerides and persistently high cholesterol levels. Abnormalities in fatty acid profiles included an apparent elevation in medium chain fatty acids and increased ratios of PL arachidonic to docosahexaenoic acids. Histologically, there was no evidence of fat accumulation in the liver; however, hepatic mitochondria had severe structural abnormalities characteristic of RS. These studies demonstrate that chemical-dependent enhancement of viral virulence is associated with significant alterations of hepatic lipids. We believe that these abnormalities are related to mitochondrial structural damage in RS despite the absence of hepatic steatosis.

Reye's syndrome: current concepts

Despite greater than 23 years of study, an incomplete understanding of the etiology, epidemiology and pathogenesis of Reye's syndrome persists. Better understanding of the disease has been hampered by the lack of a good animal model on which hypotheses of its pathogenesis could be tested. Human studies indicate that a primary mitochondrial injury may lead to complex metabolic disturbances that produce the observed pathophysiology. Specific directions regarding avenues for future research should pursue two lines: a good animal model still needs to be developed in which the biochemical and morphologic alterations identified in Reye's syndrome are duplicated. This model should include an antecedent viral illness but may not require aspirin exposure as an essential ingredient. With the identification of a satisfactory model, specific questions about the roles of environmental toxins or medications may be answered. Study of noncomatose cases of Reye's syndrome should continue. The specific emphasis should be to delineate what factors (NH3, free fatty acids and dicarboxylic acids) may be implicated in the pathogenesis of the CNS disease with the hopes of devising strategies for more effective treatment of encephalopathy and its attendant morbidity and mortality.

Serum lipid abnormalities in a chemical/viral mouse model for Reye's syndrome

Neonatal mice given nontoxic dermal applications of an industrial surfactant, Toximul MP8 (Tox), and subsequently infected with sublethal doses of mouse-adapted human Influenza B (Lee) virus (FluB) develop many of the biochemical features of Reye's Syndrome (RS). To determine whether these also include abnormal circulating lipid, we examined serum lipid profiles in the mouse model throughout the treatment course using Iatroscan-TH10. Following 10 days of exposure to surfactant, serum phospholipid and cholesterol levels were significantly reduced relative to control animals. These reductions were transient; however, four days following virus administration, significant differences in serum lipid were again evident. These abnormalities coincided and correlated with increased animal mortality. Animals that received combined Tox + virus treatment had significant decreases in serum total lipids relative to control animals, a reflection of a reduction in all lipid classes, including phospholipid, cholesterol, neutral glycerides (triglycerides plus diglycerides) and free fatty acids. Phospholipid (specifically phosphatidylcholine and lysophosphatidylcholine) and free fatty acid levels in the Tox + virus group were also significantly lower than those in animals that received virus alone. This study has demonstrated that suckling mice given chemical/viral treatment have the serum hypopanlipidemia but not the freefattyacidemia that are characteristic of RS.

Retinol binding protein and prealbumin in Reye's syndrome

Retinol binding protein (RBP) and prealbumin (PA) were analyzed in 29 serum samples from 8 patients with stages II and III Reye's Syndrome (RS), and from 10 healthy fasting children. All RS patients had at least one abnormally low RBP and PA value. A return toward normal was evident within 2-3 days in serial samples. The nadir RBP and PA values in RS (means of 9 and 107 mg/L) were significantly different (p less than 0.001) from those of the controls (RBP mean of 40 and PA of 157 mg/L). A significant correlation was found between RBP and PA serum values in RS (r = 0.7, p less than 0.001); the high admission NH4+ values tended to associate with low RBP levels; however, the correlation was not very high (r = -0.4, p less than 0.01). The presence of an abnormal vitamin A transport system at an early stage of RS raises the possibility of additional abnormalities in vitamin A metabolism in these patients. The findings of reduced serum levels of complement, clotting factors, fibronectin, and now RBP and PA, suggest a marked short-term impairment of hepatic synthesis of proteins and/or their release in RS.

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.

Reye syndrome

Reye syndrome has emerged as the quintessential example of an acute metabolic encephalopathy with an annual incidence ranging from 0.3 to 6.0 cases per 100,000 children. The general management has become standardized, and the mortality has declined to approximately 10 per cent. The role of aspirin in the etiopathogenesis remains controversial.

Reye's syndrome: salicylates and mitochondrial functions

The effects of aspirin (acetylsalicylate, ASA) and related compounds in the presence of Ca2+ on the oxidative metabolism of isolated rat liver mitochondria were studied. Intact mitochondrial preparations preincubated with ASA + Ca2+ exhibited a transient stimulation of the state 4 respiratory rate with NAD+-linked substrates, followed by an inhibition which could not be released by the addition of ADP or uncoupler. Maximum respiratory rates were achieved by subsequent addition of NAD+ or succinate. The Ca2+-transport inhibitors ruthenium red and ethylene glycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) prevented these effects. Five brands of commercial aspirin were tested and were as effective as purified ASA. Tylenol (acetaminophen) could reproduce these effects only at much higher (greater than or equal to 10-fold) concentrations. Other salicyl derivatives showed results qualitatively similar to ASA, with potencies in the order: acid much much greater than ASA much greater than alcohol greater than or equal to catechol greater than amide, salicylate being approximately 10-fold more potent than ASA. The magnitude of the effect seen depended on the Ca2+ (endogenous + exogenous) and salicylate concentrations/mg mitochondrial protein, and on the length of the preincubation. Added inorganic phosphate was also required. That salicylate + Ca2+ induces an increase in the permeability of the mitochondrial inner membrane was demonstrated by the observation that 90% of the intramitochondrial NAD(P)+ was released into the surrounding medium upon preincubation of intact mitochondria with these agents. Salicylate + Ca2+ had virtually no effect on respiration with succinate (+ rotenone) as substrate at salicylate concentrations which markedly affected NAD+-linked substrate oxidation. The presence of rotenone in the preincubation mixture prevented the damaging effects of salicylate + Ca2+ on the mitochondrial membrane, suggesting that the redox state of intramitochondrial pyridine nucleotides can modulate these effects. The results reported here are similar to those reported previously by our laboratory for the effects of Reye's plasma and allantoin + Ca2+, and indicate that, like these agents, salicylate and salicyl compounds can potentiate the Ca2+-induced damage to the mitochondrial inner membrane and may be another factor responsible for Reye's syndrome.

Adult Reye's syndrome

Images