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

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

Co-ingestion of aspirin and acetaminophen promoting fulminant liver failure: A critical review of Reye syndrome in the current perspective at the dawn of the 21st century

In the paediatric population, there is some evidence of possible interaction, synergism, and co-toxicity of aspirin and acetaminophen. The toxicity of salicylates such as aspirin in this population is well known and documented, specifically in the form of Reye syndrome. The possible toxic synergism with aspirin and acetaminophen, however, is not previously described; though case reports suggest such co-toxicities with low levels of aspirin and other compounds can exist. In vitro studies into mechanistic processes of salicylate toxicity propose that there is a bi-directional link and potentiation with glutathione (GSH) depletion and salicylate toxicity. Data may suggest a plausible explanation for salicylate and acetaminophen toxic synergism. Further studies investigating this potential toxic synergism are warranted. Given the lack of awareness in the clinical community about potential toxic synergism between these relatively common medications, caution is advised in the co-administration of these drugs, particularly in communities using natural or alternative therapy.

Quantification of metabolites for assessing human exposure to soapberry toxins hypoglycin A and methylenecyclopropylglycine

Ingestion of soapberry fruit toxins hypoglycin A and methylenecyclopropylglycine has been linked to public health challenges worldwide. In 1976, over 100 years after Jamaican vomiting sickness (JVS) was first reported, the cause of JVS was linked to the ingestion of the toxin hypoglycin A produced by ackee fruit. A structural analogue of hypoglycin A, methylenecyclopropylglycine (MCPG), was implicated as the cause of an acute encephalitis syndrome (AES). Much of the evidence linking hypoglycin A and MCPG to these diseases has been largely circumstantial due to the lack of an analytical method for specific metabolites. This study presents an analytical approach to identify and quantify specific urine metabolites for exposure to hypoglycin A and MCPG. The metabolites are excreted in urine as glycine adducts methylenecyclopropylacetyl-glycine (MCPA-Gly) and methylenecyclopropylformyl-glycine (MCPF-Gly). These metabolites were processed by isotope dilution, separated by reverse-phase liquid chromatography, and monitored by electrospray ionization tandem mass spectrometry. The analytical response ratio was linearly proportional to the concentration of MCPF-Gly and MCPA-Gly in urine from 0.10 to 20 μg/mL with a correlation coefficient of r > 0.99. The assay demonstrated accuracy ≥80% and precision ≤20% RSD across the calibration range. This method has been applied to assess exposure to hypoglycin A and MCPG as part of a larger public health initiative and was used to provide the first reported identification of MCPF-Gly and MCPA-Gly in human urine.

Reye's or Reye's-like syndrome in western lowland gorilla (Gorilla gorilla gorilla)

BACKGROUND

A 15-year-old western lowland gorilla (Gorilla gorilla gorilla) died shortly after transfer to the North Carolina Zoo.

METHODS

Complete blood count, serum biochemical analysis, and necropsy were performed.

RESULTS

Combination of compatible clinical signs, biochemical and histopathological findings fulfilled all of the CDC definition criteria of Reye's or a Reye's like syndrome.

CONCLUSIONS

This report describes a case of Reye's syndrome or Reye's-like syndrome in a non-human primate.

Signal transduction pathways involved in drug-induced liver injury

Hepatocyte death following drug intake is the critical event in the clinical manifestation of drug-induced liver injury (DILI). Traditionally, hepatocyte death caused by drugs had been attributed to overwhelming oxidative stress and mitochondria dysfunction caused by reactive metabolites formed during drug metabolism. However, recent studies have also shown that signal transduction pathways activated/inhibited during oxidative stress play a key role in DILI. In acetaminophen (APAP)-induced liver injury, hepatocyte death requires the sustained activation of c-Jun kinase (JNK), a kinase important in mediating apoptotic and necrotic death. Inhibition of JNK using chemical inhibitors or knocking down JNK can prevent hepatocyte death even in the presence of extensive glutathione (GSH) depletion, covalent binding, and oxidative stress. Once activated, JNK translocates to mitochondria, to induce mitochondria permeability transition and trigger hepatocyte death. Mitochondria are central targets where prodeath kinases such as JNK, prosurvival death proteins such as bcl-xl, and oxidative damage converge to determine hepatocyte survival. The importance of mitochondria in DILI is also observed in the Mn-SOD heterozygous (+/-) model, where mice with less mitochondrial Mn-SOD are sensitized to liver injury caused by certain drugs. An extensive body of research is accumulating suggesting a central role of mitochondria in DILI. Drugs can also cause redox changes that inhibit important prosurvival pathways such as NF-kappaB. The inhibition of NF-kappaB by subtoxic doses of APAP sensitizes hepatocyte to the cytotoxic actions of tumor necrosis factor (TNF). Many drugs will induce liver injury if simultaneously treated with LPS, which promotes inflammation and cytokine release. Drugs may be sensitizing hepatocytes to the cytotoxic effects of cytokines such as TNF, or vice versa. Overall many signaling pathways are important in regulating DILI, and represent potential therapeutic targets to reduce liver injury caused by drugs.

Metabolic, idiosyncratic toxicity of drugs: overview of the hepatic toxicity induced by the anxiolytic, panadiplon

Preclinical drug safety evaluation studies, typically conducted in two or more animal species, reveal and define dose-dependent toxicities and undesirable effects related to pharmacological mechanism of action. Idiosyncratic toxic responses are often not detected during this phase in development due to their relative rarity in incidence and differences in species sensitivity. This paper reviews and discusses the metabolic idiosyncratic toxicity and species differences observed for the experimental non-benzodiazepine anxiolytic, panadiplon. This compound produced evidence of hepatic toxicity in Phase 1 clinical trial volunteers that was not predicted by rat, dog or monkey preclinical studies. However, subsequent studies in Dutch-belted rabbits revealed a hepatic toxic syndrome consistent with a Reye's Syndrome-like idiosyncratic response. Investigations into the mechanism of toxicity using rabbits and cultured hepatocytes from several species, including human, provided a sketch of the complex pathway required to produce hepatic injury. This pathway includes drug metabolism to a carboxylic acid metabolite (cyclopropane carboxylic acid), inhibition of mitochondrial fatty acid beta-oxidation, and effects on intermediary metabolism including depletion of glycogen and disruption of glucose homeostasis. We also provide evidence suggesting that the carboxylic acid metabolite decreases the availability of liver CoA and carnitine secondary to the formation of unusual acyl derivatives. Hepatic toxicity could be ameliorated by administration of carnitine, and to a lesser extent by pantothenate. These hepatocellular pathway defects, though not directly resulting in cell death, rendered hepatocytes sensitive to secondary stress, which subsequently produced apoptosis and hepatocellular necrosis. Not all rabbits showed evidence of hepatic toxicity, suggesting that individual or species differences in any step along this pathway may account for idiosyncratic responses. These differences may be roughly applied to other metabolic idiosyncratic hepatotoxic responses and include variations in drug metabolism, effects on mitochondrial function, nutritional status, and health or underlying disease.

Disruption of mitochondrial activities in rabbit and human hepatocytes by a quinoxalinone anxiolytic and its carboxylic acid metabolite

The quinoxalinone anxiolytic, panadiplon, was dropped from clinical development due to unexpected hepatic toxicity in human volunteers. Subsequent experimental studies in rabbits demonstrated a hepatic toxicity that resembled Reye's syndrome. In the present studies, we examined the effects of panadiplon and a metabolite, cyclopropane carboxylic acid (CPCA) on hepatic mitochondrial activities in vitro and ex vivo. Acute inhibition of beta-oidation of [14C]palmitate was observed in rabbit and human hepatocyte suspensions incubated with 100 microM panadiplon. Panadiplon (30 microM) also reduced mitochondrial uptake of rhodamine 123 (R123) in cultured rabbit and human, but not rat hepatocytes, following 18 h exposure. CPCA also impaired beta-oxidation and R123 uptake in rabbit and human hepatocytes. R123 uptake and beta-oxidation in cells from some donors was not impaired by either agent, and cell death was not observed in any experiment. Hepatocytes isolated from panadiplon-treated rabbits had reduced palmitate beta-oxidation rates and inhibited mitochondrial R123 uptake; R123 uptake remained inhibited until 48-72 h in culture. Rabbit mitochondrial respiration experiments revealed a slightly lower ratio of ATP formed/oxygen consumed in panadiplon-treated animals: direct exposure of normal rabbit liver mitochondria to panadiplon did not have this effect. Hepatocytes isolated from panadiplon-treated rabbits showed reduced respiratory control ratios and lower oxygen consumption compared to controls. Our results indicate that panadiplon induces a mitochondrial dysfunction in the liver, and suggest that this dysfunction may be attributed to the carboxylic acid metabolite.

The effect of carnitine supplementation in valproate-induced hyperammonaemia

The aim of the study was to investigate the effect of carnitine supplementation of valproic acid (VPA) treated patients presenting with increased plasma ammonia concentrations. Plasma ammonia concentrations were recorded in 69 children and young adults on VPA monotherapy (25.6 +/- 9.2 mg VPA/kg per day; mean plasma VPA concentration 68.8 +/- 27.6 mg/l). Their mean plasma ammonia concentration was 80.2 +/- 32.1 micrograms/dl (median 73.1 microgram/dl). A total of 24 patients (35.3%) presenting with ammonia concentrations > 80 microgram/dl were considered hyperammonaemic. Of these, 15/24 (22.1%) showed ammonia concentrations > 100 microgram/dl, even up to 194 micrograms/dl. In 48/69 patients, plasma carnitine concentrations could be determined. The plasma total carnitine (TC) concentrations were rather low (26.9 +/- 8.8 mumol/1) compared to normal values obtained in our laboratory (40.9 +/- 7.2 mumol/1). The percentage of free carnitine was considered decreased (< 75% TC) in 13/48 samples (27%). Fourteen hyperammonaemic patients and one with a plasma ammonia level of 60 micrograms/dl agreed to be supplemented with L-carnitine (1 g/m2 per day divided into two equal doses). Their plasma ammonia and carnitine concentrations were re-evaluated after a mean of 9.1 +/- 4.0 days (median 9.0 days) and in 9 patients again after a mean of 79.6 +/- 30.1 days (median 75 days) of L-carnitine supplementation. Plasma ammonia concentrations decreased in all 15 patients. The decrease was 25.4 +/- 11.2% (median 28.3%) after a mean of 9.1 +/- 4.0 days and amounted to 46.0 +/- 17.2% (median 48%) after 79.6 +/- 30.1 days. L-Carnitine supplementation led to an increase in plasma free carnitine of 11.6 +/- 13.0% (median 15.6%) and to a further increase of 11.1 +/- 8.4% (median 11.5%) when re-evaluated a second time. The plasma ammonia concentrations were significantly correlated with the percentage of free plasma carnitine (r = -0.67; p < 0.0001). The results show that carnitine supplementation is a means of normalizing elevated plasma ammonia concentrations. However, we cannot conclude from our results whether this lowers the risk of developing a VPA-induced Reye's-like syndrome.

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.

Hypoglycaemia: principles of diagnosis and treatment in children

The diagnostic approach to children with suspected hypoglycaemia is facilitated by the fact that two clinically distinct groups exist with little overlap: 1. Hypoglycaemias characterized by a fuel deficit only. 2. Hypoglycaemias in which the fuel deficit is overshadowed by symptoms of intoxication. This differentiation is used when taking the medical history, performing the physical examination, and planning the laboratory investigations. The latter may encompass tolerance tests, a fasting test or the use of a non-radioactive glucose isotope. Protocols for such tests are given.

Beta-oxidation of [1-14C]palmitic acid by mouse astrocytes in primary culture: effects of agents implicated in the encephalopathy of Reye's syndrome

beta-Oxidation of [1-14C]palmitic acid was examined in homogenates of astrocytes cultured from neonatal mouse brain. Under optimal reaction conditions (< or = 50 micrograms protein, 10 min at 37 degrees C), oxidation increased as a function of palmitate concentration (15 microM to 2 mM) and reached a maximum rate of 1.98 +/- 0.29 nmol/min/mg protein (mean +/- SEM) at 0.2 mM substrate. Eadie-Hofstee analysis of data from four experiments yielded apparent values for Vmax of 1.87 nmol/min/mg protein, and for Km, 35-40 microM. There were no dramatic changes in the oxidation rate in cells between 10 and 36 days in culture. During the 10-min assays, less than 0.05% of the radioactivity was converted to 14CO2 by the astrocytes; water-soluble products accounted for 1-2% of the total substrate added. Studies with KCN indicated that 60-70% of the total activity occurred in the mitochondria. We have been studying the structural and functional changes associated with the cerebral encephalopathy of Reye's syndrome (RS). Three-week-old astrocytes exposed to serum from RS children for the final 7 days of culture exhibited minor mitochondrial pleomorphism and had increased numbers of other intracellular organelles. Examination of the effects of agents implicated in RS indicated that oxidation of [1-14C]palmitate was not altered by Na+ salicylate (1-3 mM), but was inhibited by the industrial surfactant, Toximul MP-8 (> or = 10 micrograms/ml), 4-pentenoic acid (> or = 0.1 microM), or with 4 days' exposure to ammonia (10 nM). The latter treatment also resulted in an increase in protein synthesis, cell volume, and malondialdehyde formation. These results suggest that some of the "toxins" implicated in RS inhibit fatty-acid oxidation in the astrocytes and produce other lipid-related abnormalities that could be related to encephalopathy.