Altered metabolic profiles of valproic acid in a patient with Reye's syndrome

Influence of CYP2C9 polymorphism on metabolism of valproate and its hepatotoxin metabolite in Iranian patients

Sodium valproate (VPA) has 16 known metabolites in humans. The 2-ene-VPA has anti-convulsant efficacy and 4-ene-VPA is reported to contribute in VPA hepatotoxicity. The formation of 4-ene-VPA is catalyzed by cytochrome P450 2C9 (CYP2C9). CYP2C9 allele mutation is closely related to the attenuation of the enzymatic activity and 4-ene-VPA production. In the present work, VPA, 2-ene-VPA, and 4-ene-VPA in serum of patients receiving VPA were determined and the correlation between CYP2C9 polymorphism and 4-ene-VPA concentration was examined. Blood samplings in 68 patients were performed at two time-points (peak and trough) and one sample blood obtained from 50 healthy volunteers for genotype evaluation. Patients were divided into three groups (22 cases of monotherapy, 19 cases of enzyme inducer therapy, and 27 cases of polytherapy). There was a significant reduction in concentration of VPA and 4-ene-VPA between peak and trough time. In peak concentration, there was a significant correlation between 2-ene-VPA and VPA in all groups. The concentration of 4-ene-VPA in the enzyme inducer and polytherapy group was significantly higher than that of the monotherapy group. The allele frequencies of CYP2C9*1, CYP2C9*2, and CYP2C9*3 were 88.97%, 8.09%, and 2.94% in the patient group and 91%, 6%, and 3% in the normal group, respectively. There was no significant difference in allele frequency in two groups. Mutated alleles didn't have any significant effect on 4-ene-VPA production. No patient showed toxic level of 4-ene-VPA or saturation of ß-oxidation pathway. In conclusion, the role of CYP2C9*2 and CYP2C9*3 in attenuation of 4-ene-VPA formation cannot be confirmed.

Altered pharmacokinetics and metabolism of valproate after replacement of conventional valproate with the slow-release formulation in epileptic patients

Altered metabolism of valproate has been suggested as the mechanism of teratogenicity and hepatotoxicity of valproate. This study aimed at examining whether pharmacokinetics of a slow-release formulation of valproate affects valproate metabolism. Thirty-one epileptic patients were treated with fixed-doses of conventional valproate for at least 2 months. Thereafter, the drug was replaced with the same doses of slow-release formulation of valproate for 2 months. Blood samplings for determination of valproate and its metabolites by gas chromatography-mass spectrometry were performed at three time-points (just before morning dose and at 1 and 5 hr after morning dose) during both treatment phases. There was a significant difference (P < 0.005) in the mean serum concentration (+/- S.D.) of valproate after 1 hr between conventional valproate (63.1 +/- 27.9 microg/ml) and slow-release formulation of valproate (45.7 +/- 19.5 microg/ml). Mean serum concentrations (+/- S.D.) of 4-en and hydroxy metabolites after 5 hr were significantly reduced after replacement with slow-release formulation of valproate (4-en: 29.5 +/- 14.0-->23.0 +/- 15.3 ng/ml, 3-OH: 488.5 +/- 234.0-->419.6 +/- 171.1 ng/ml, 4-OH: 404.3 +/- 124.7-->342.8 +/- 147.6 ng/ml, 5-OH: 102.8 +/- 54.4-->81.0 +/- 43.6 ng/ml). The present study suggests that smaller diurnal fluctuations in valproate concentrations during treatment with slow-release formulation of valproate result in decreased formations of minor metabolites including 4-en, the most toxic metabolite.

Synthesis and intramitochondrial levels of valproyl-coenzyme A metabolites

A number of valproate adverse reactions are due to its interference with several metabolic pathways, including that of fatty acid oxidation. In order to resolve which mitochondrial enzymes of fatty acid oxidation are inhibited by which VPA intermediates we have developed methods to synthesize their CoA ester forms. This paper describes the synthesis of VPA acyl-CoA ester metabolites as well as data on the fate of VPA in rat liver mitochondria. Valproyl-CoA, Delta2-valproyl-CoA, and 3-OH-valproyl-CoA were obtained through chemical synthesis. 3-Keto-valproyl-CoA was prepared by a novel enzymatic procedure followed by a combination of solid-phase extraction and preparative HPLC purification. This approach proved to be efficient in obtaining all the beta-oxidation intermediates of valproyl-CoA. The synthetic standards were used for the determination of intramitochondrial concentrations of valproyl-CoA, Delta2-valproyl-CoA, 3-OH-valproyl-CoA, and 3-keto-valproyl-CoA by HPLC. These levels were determined after incubation of intact rat liver mitochondria with VPA under conditions of state 3 and state 4 respiration. The results show that valproyl-CoA and to a much lesser extent 3-keto-valproyl-CoA are the main metabolites of VPA in mitochondria. This information will be of great use in resolving the mechanisms involved in the inhibition of mitochondrial processes like fatty acid oxidation by VPA.

Valproate metabolism during valproate-associated hepatotoxicity in a surviving adult patient

The plasma profiles of valproate (VPA), its beta-oxidation metabolites E-2-en-VPA and 3-oxo-VPA and its terminal desaturation metabolite 4-en-VPA, have been measured in a patient receiving NaVPA 1000 mg twice per day from early in the course of serious hepatotoxicity and for 2 weeks after the drug was stopped. Concurrent profiles of liver, renal and haematological function parameters were available. Relative to concurrent plasma VPA concentrations, E-2-en-VPA concentrations were not different to those of the VPA-treated epileptic population at any stage of the illness, whereas 3-oxo-VPA concentrations relative to concurrent VPA concentrations were abnormally high early in the toxicity, abnormally low at its peak (3-5 days later), and comfortably within normal limits for the treated epileptic population late in the recovery phase (9-13 days from the onset). When measurable, plasma 4-en-VPA concentrations were not elevated. The elimination half-life of VPA during the recovery phase was 100 h, which is some 6-12 times greater than values reported for this parameter in normal patients. These data clearly define, in this patient, a link between idiosyncratic VPA-associated hepatotoxicity at its onset and peak and the later stages of VPA beta-oxidation. Whether the beta-oxidation abnormalities are causative or a consequence of an as yet undefined defect is unknown. In this patient, 4-en-VPA was unlikely to have been involved in the pathogenesis of the toxicity.

On-column gas chromatographic-mass spectrometric assay for metabolic profiling of valproate in brain tissue and serum

A sensitive capillary gas chromatographic-mass spectrometric method for the determination of valproic acid and at least twelve of its metabolites in serum based on tert-butyldimethylsilyl (tBDMS) derivatives is described. Low detection limits are achieved by using a direct on-column injection technique. The addition of dry pyridine during the derivatization step now leads to uniform formation of 3-keto-VPA di-tBDMS derivatives and thereby avoids the necessity of a deuterated internal standard. A novel extraction procedure for metabolic profiling of valproate in brain tissue samples is presented. Using this method, (Z)-2-en-VPA was determined in rat brain tissue for the first time.

Sensitive capillary gas chromatographic-mass spectrometric method for the therapeutic drug monitoring of valproic acid and seven of its metabolites in human serum. Application of the assay for a group of pediatric epileptics

A sensitive capillary gas chromatographic-mass spectrometric method for the determination of valproic acid and 7 of its metabolites is described. It is based on the selected-ion monitoring of the tert.-butyldimethylsilyl derivatives using N-(tert.-butyldimethylsilyl)-N-methyl-trifluoracetamid (MTBSTFA) as the derivatization reagent. The limits of detection for valproic acid and its metabolites are in the low ng/ml-range, except for the 4-hydroxy metabolite with a limit of detection of 100 ng/ml. The method has been tested against an established GC method for valproic acid. The assay has been used for therapeutic drug monitoring in epileptic pediatric patients. The concentrations of the omega- and omega 1-oxidation metabolites in a group of patients receiving additional antiepileptic drugs were found to be significantly enhanced compared to the levels found in a monotherapy group.

Valproate (VPA) metabolites in various clinical conditions of probable VPA-associated hepatotoxicity

Of a cohort of 470 epileptic patients in whom valproate (VPA) serum metabolites had been measured, 170 subjects without symptoms or signs of hepatic side effects were chosen as a reference group to establish the usual metabolic pattern. A wide interindividual variation of VPA metabolite concentrations was noted. Infants receiving VPA monotherapy and comedication with other antiepileptic drugs (AEDs) showed lower concentrations of the potential hepatotoxin 4-ene-VPA than did older children. In 11 patients with early symptoms and signs of possible fatal VPA-associated hepatotoxicity, the following spectrum of benign clinical conditions was observed: unusually severe side effect during initiation of VPA therapy (1 patient), high VPA dosage (2 patients), reversible impairment of coagulation with bleeding manifestations in association with a slight increase in transaminase levels (1 child), and reversible liver dysfunction associated with febrile illness (7 patients). Reversible or irreversible fulminant liver failure had occurred in 5 children. Three of the 4 children with a fatal outcome had massive lactic acidosis. In all patients with probable VPA-associated hepatotoxicity, some aspects of VPA metabolism differed distinctly from that of the reference group, but the inter-individual profile of metabolites varied considerably, even in the subgroup of 4 children who died. Impairment of VPA beta-oxidation and increase of metabolites of alternative metabolic pathways (omega- and omega 1-hydroxylation, dehydrogenation reactions) were the most frequent findings. Increased values of 2-n-propyl-4-pentenoic acid metabolite of VPA (4-ene-VPA), could be detected only in 1 of the 5 patients with fulminant liver failure and in one other child with a slight hepatic dysfunction, indicating that this VPA metabolite is not the decisive hepatotoxin or indicator of hepatotoxicity. Because we cannot distinguish between benign and life-threatening hepatic adverse reactions on the basis of VPA metabolites, all identified changes are considered secondary to an as-yet-unknown primary metabolic event. The most toxic compound could be VPA itself, which may unmask an inborn or an acquired metabolic defect in the processing of fatty acids.

Investigation of metabolic disorders resembling Reye's syndrome

Ten per cent of patients initially reported with Reye's syndrome in the British Isles (1981-91) were subsequently found to have an underlying inherited metabolic disorder (IMD). There was also evidence to suggest that other cases may not have been recognised. The range of metabolic disorders that mimic Reye's syndrome is wide and specialist, often complex, investigations are required to make a specific diagnosis. Those patients presenting with Reye's syndrome-like illness but also with one or more clinical features suggestive of an IMD require particular attention and detailed investigation. Recommendations for specimen collection and investigation are presented.

Differentiation between valproate-induced anticonvulsant effect, teratogenicity and hepatotoxicity. Aspects of species variation, pharmacokinetics, metabolism and implications of structural specificity for the development of alternative antiepileptic agents such as delta 2-valproate

Valproate is metabolized into a large number of compounds via various metabolic routes. Metabolic profiles depend on species and age. Hepatotoxicity may be correlated with abnormal metabolism, especially in young age. Teratogenicity is associated with specific structural requirements: a free carboxyl atom connected to a carbon atom which also carries a hydrogen, and two carbon chains. This provides a clue for the development of alternative antiepileptic agents.

Abnormal metabolism of carnitine and valproate in a case of acute encephalopathy during chronic valproate therapy

We analyzed the urinary metabolic profiles of valproate (VPA) and carnitine metabolism in an epileptic patient who died of acute encephalopathy during VPA therapy. On admission, the serum free carnitine level was greatly decreased and gas chromatographic mass spectrometric analysis of organic acids in urine showed a complete lack of beta-oxidation metabolites of VPA, while omega-oxidation was markedly increased. After administration of L-carnitine, the levels of acylcarnitine in both serum and urine, and of serum free carnitine increased, and the metabolites of beta-oxidation appeared in urine, while there was no improvement in the liver and renal functions. This is not a typical case of VPA-induced hepatotoxicity and the main cause of the disease is not clear. But the results show that the mitochondrial beta-oxidation of VPA was greatly disturbed in this patient, which may be related to the carnitine deficiency induced by the chronic VPA-therapy.

Associations between risk factors for valproate hepatotoxicity and altered valproate metabolism

The effects of three risk factors for valproate (VPA) hepatotoxicity (i.e., young age, polypharmacy, and high VPA serum level) on the metabolism of VPA to its monounsaturated metabolites [2-en-VPA (2-en), 3-en-VPA (3-en) and 4-en-VPA (4-en)] were investigated in 106 patients treated with VPA (56 cases of monotherapy and 50 cases of polytherapy). In the monotherapy group, there was a significant negative correlation between age and 4-en/VPA ratio. In the same group, the 4-en/VPA ratio showed a significant positive correlation with serum VPA level, while 3-en/VPA and 2-en/VPA ratios showed significant negative correlations. In patients greater than 10 years, the 4-en/VPA ratio was significantly higher, while the 2-en/VPA ratio was significantly lower in the polytherapy group than in the monotherapy group. Our results indicate that all three risk factors clearly increase the metabolic conversion of VPA to 4-en, the most toxic VPA metabolite, and that polytherapy and high VPA serum level result in the inhibited beta-oxidative metabolism of VPA to 2-en. These altered VPA metabolic profiles are strikingly similar to the abnormal VPA metabolism previously reported in cases with fatal hepatic failure. Although VPA-induced fatal hepatotoxicity has been regarded as an idiosyncratic reaction, it is possible that these three factors enhance susceptibility to VPA hepatotoxicity by altering the metabolism of VPA.

Increased urinary excretion of beta-hydroxyisovaleric acid in ketotic and non-ketotic type II diabetes mellitus

To evaluate the catabolism of leucine in diabetes mellitus, the urinary excretion of beta-hydroxyisovaleric acid, a by-product of leucine catabolism, in 21 nonproteinuric type II diabetic patients with and without ketosis and 21 control subjects was measured using gas chromatography-mass spectrometry. Urinary beta-hydroxyisovaleric acid and serum leucine concentrations were higher in the 9 ketotic diabetic patients than in the 12 nonketotic diabetic patients (p less than 0.005, p less than 0.01, respectively) or in the control subjects (p less than 0.01, p less than 0.01, respectively). The serum leucine concentrations in the nonketotic diabetic patients and control subjects did not differ significantly (p greater than 0.05), but urinary beta-hydroxyisovaleric acid concentrations were significantly greater in the former (p less than 0.01). These data suggest that in type II diabetic patients the catabolism of leucine is accelerated even in the absence of ketosis and that the urinary beta-hydroxyisovaleric acid concentration is a useful marker of short-term metabolic control in these patients.

Markedly increased omega-oxidation of valproate in fulminant hepatic failure

Using gas chromatography-mass spectrometry, we showed that the urinary metabolite profile of valproate (VPA) in a subject receiving VPA and phenobarbital (PB) who died of fulminant hepatic failure was quite different from those of reported patients with Reye's syndrome or fatal hepatic failure. Only 2-n-propylglutarate, the end product of omega-oxidation of VPA, was excreted in markedly increased amounts, while other VPA metabolites were undetectable. Although the primary cause of fulminant hepatitis and the mechanism of enhanced VPA metabolism by the hepatic P-450 system in this patient are not clear, our findings suggest that P-450-mediated reactions become the predominant metabolic pathway of VPA in a stage of fulminant hepatic failure.

Profiles in altered metabolism. IV--Induction of acute dicarboxylic aciduria following 2-octynoic acid administration to the rat

Rats given 2-octynoic acid by intraperitoneal injection excrete elevated amounts of medium-chain dicarboxylic acids and other acidic metabolites usually associated with human medium-chain acyl-CoA dehydrogenase deficiency. Onset of this organic acid profile is immediate and lasts for approximately 24 h. The induced acidosis in this animal model closely, acutely and transiently resembles the human disorder. The 2-octynoate load is also extensively omega- and psi-oxidized, and evidence is presented for the enzymic hydration of 2-octynoate to 3-ketooctanoic acid.

Clinical pharmacokinetics of valproic acid--1988

Sodium valproate (valproic acid) has been widely used in the last decade and is now considered a relatively safe and effective anticonvulsant agent. Recently, several investigators have proposed its use in the treatment of anxiety, alcoholism and mood disorders, although these indications require further clinical studies. Valproic acid is available in different oral formulations such as solutions, tablets, enteric-coated capsules and slow-release preparations. For most of these formulations bio-availability approaches 100%, while the absorption half-life varies from less than 30 minutes to 3 or 4 hours depending on the type of preparation used. Once absorbed, valproic acid is largely bound to plasma proteins and has a relatively small volume of distribution (0.1 to 0.4 L/kg). Its concentration in CSF is approximately one-tenth that in plasma and is directly correlated with the concentration found in tears. At therapeutic doses, valproic acid half-life varies from 10 to 20 hours in adults, while it is significantly shorter (6 to 9 hours) in children. Valproic acid undergoes extensive liver metabolism. Numerous metabolites have been positively identified and there is reasonable evidence that several of them contribute to its pharmacological and toxic actions. In fact, several valproic acid metabolites have anti-convulsant properties, while many of the side effects it may cause (e.g. those related to hyperammonaemia or liver damage) are most often observed in patients previously treated with phenobarbitone. This could indicate that induction of liver enzymes is responsible for the formation of toxic valproic acid metabolites.

Abnormal 13C-fatty acid breath tests in patients treated with valproic acid

Breath tests using fatty acids labeled with a stable isotope (carbon 13) were carried out on epileptic patients treated with valproic acid in order to detect abnormal fatty acid metabolism. The patients were given 13C-octanoic acid or 13C-palmitic acid orally, and expired air was collected at appropriate intervals for the analysis of 13CO2 content by a mass spectrometer. Eight patients were tested in the palmitic acid breath test and nine patients in the octanoic acid breath test. Controls for these tests were patients treated with antiepileptic drugs other than valproic acid and unmedicated cerebral palsy patients. In the valproic acid-treated group, 13C recovery was reduced by 56% in seven hours on the 13C-palmitic acid breath test, while the octanoic acid breath test showed a 52% reduction in one hour. This suppression of fatty acid oxidation was significantly correlated with dose of valproic acid in both tests. No influence of other drugs was detected, and the effect of administered carnitine was not conclusive. This study demonstrates the usefulness of 13C-labeled fatty acid breath tests in clinical practice.

Valproate-associated hepatotoxicity and its biochemical mechanisms

Intake of the anticonvulsant drug valproic acid, or its sodium salt, has been associated with occasional instances of severe and sometimes fatal hepatotoxicity. Probably at least 80 cases have occurred worldwide. The syndrome affects perhaps 1 in 10,000 persons taking the drug, and usually develops in the early weeks or months of therapy. Most instances have involved children, usually those receiving more than 1 anticonvulsant. Multiple cases have occurred in 2 families. The typical presentation is of worsening epilepsy, increasing depression of consciousness, and progressive clinical and biochemical evidence of liver failure. The liver has sometimes shown hepatocyte necrosis, and on other occasions widespread microvesicular steatosis, while cholestatic changes have also occurred. The appearances are interpreted as consistent with a drug toxicity reaction. During the hepatotoxicity increased amounts of unsaturated metabolites of valproate, notably 4-en-valproate, have been found in blood and urine. In 4 cases there has been evidence of impaired beta-oxidation of valproate with, in 1 case, accumulation of isomers of valproate glucuronide caused by intramolecular rearrangement of the conjugate. There are molecular structural similarities between 4-en-valproate and 2 known hepatotoxins (4-en-pentanoate and methylenecyclopropylacetic acid, the latter being responsible for hypoglycin poisoning). There are also clinical and histopathological similarities between valproate hepatotoxicity and both hypoglycin poisoning and certain spontaneous disorders of isoleucine metabolism (one pathway of valproate metabolism is analogous to oxidative degradation of isoleucine). Unsaturated metabolites of valproate, in particular 4-en-valproate, may contribute to the hepatotoxicity of the drug. However, since the hepatotoxicity appears to involve an element of idiosyncrasy, the primary defect in some cases may be an inherited or acquired deficiency in the drug's beta-oxidation. This defect may divert valproate metabolism towards omega-oxidation, with increased formation of the toxin 4-en-valproate, but may also allow increased formation of a toxic metabolite derived from isoleucine, since beta-oxidation of isoleucine derivatives will also be impaired.

Identification and quantification of octanoyl glucuronide in the urine of children who ingested medium-chain triglycerides

In addition to the previously described metabolites, octanoyl glucuronide was identified in the urine of four children who received medium-chain triglycerides. Octanoyl glucuronide in the urine of a child after ingestion of medium-chain triglycerides (C8:C10, 3:1) was quantitated as octanoic acid after glucuronidase treatment by means of gas chromatography/mass spectrometry. The urinary excretion increased rapidly to a maximum 1-2 h after ingestion, and decreased thereafter. During 0-3 h, 6.11 mumol of octanoyl glucuronide was excreted, which comprised 0.034% octanoic acid administered as glyceride, and 0.07% octanoic acid was postulated to be excreted as glucuronide within 24 h. Neither decanoyl glucuronide nor hexanoyl glucuronide was detected. Glucuronidation of branched medium-chain fatty acids, whose beta-oxidation is hindered, has been described previously. The present findings show that even straight-chain fatty acids undergo glucuronidation, although to a lesser extent, in addition to omega-oxidation and beta-oxidation.

Serum and urinary carnitine and organic acids in Reye syndrome and Reye-like syndrome

Free and acyl-carnitine in serum and urine, and urinary organic acids were measured in 6 patients with Reye syndrome and Reye-like syndrome. The free and total carnitine concentrations were significantly reduced in serum during the acute phases of the diseases. Thus, the ratio of acylcarnitine to free carnitine was significantly increased. Urinary excretion of acylcarnitine was greatly increased, and the acylcarnitine to total carnitine ratio was therefore greater than in controls. The urinary organic acids comprised large amounts of lactic acid, dicarboxylic acids and ketone bodies. It is suggested that carnitine deficiency is induced as more carnitine is consumed to buffer the increased amount of toxic acyl-CoA compounds metabolized from free fatty acids and the many organic acids. These results indicate that administration of L-carnitine should generally be considered in patients with Reye syndrome and Reye-like syndrome.