Sodium valproate and ornithine carbamyl transferase deficiency

Valproate-related hyperammonemic encephalopathy with generalized suppression EEG: a case report

BACKGROUND

Valproic acid (VPA) is a prevalent antiseizure medication (ASM) used to treat epilepsy. Valproate-related hyperammonemic encephalopathy (VHE) is a type of encephalopathy that can occur during neurocritical situations. In VHE, the electroencephalogram (EEG) displays diffuse slow waves or periodic waves, and there is no generalized suppression pattern.

CASE PRESENTATION

We present a case of a 29-year-old female with a history of epilepsy who was admitted for convulsive status epilepticus (CSE), which was controlled by intravenous VPA, as well as oral VPA and phenytoin. The patient did not experience further convulsions but instead developed impaired consciousness. Continuous EEG monitoring revealed a generalized suppression pattern, and the patient was unresponsive. The patient's blood ammonia level was significantly elevated at 386.8 μmol/L, indicating VHE. Additionally, the patient's serum VPA level was 58.37 μg/ml (normal range: 50-100 μg/ml). After stopping VPA and phenytoin and transitioning to oxcarbazepine for anti-seizure and symptomatic treatment, the patient's EEG gradually returned to normal, and her consciousness was fully restored.

DISCUSSION

VHE can cause the EEG to display a generalized suppression pattern. It is crucial to recognize this specific situation and not to infer a poor prognosis based on this EEG pattern.

Valproic acid-induced encephalopathy: A review of clinical features, risk factors, diagnosis, and treatment

Valproic acid (VPA), or sodium valproate, is a commonly used medication for seizure disorders, migraines, and mental illness. Although VPA is relatively safe, it still has several adverse effects; among these, VPA-induced encephalopathy is the most serious. Valproic acid-induced encephalopathy mainly manifests as acute or subacute encephalopathy and has been associated with hyperammonemia, L-carnitine deficiency, and urea cycle enzyme dysfunction. Delayed identification of VPA-induced encephalopathy could be potentially fatal. Here, we perform an extensive review of relevant literature pertaining to VPA-induced encephalopathy, including its epidemiology, clinical features, possible pathophysiology, risk factors, diagnosis, and treatment.

Valproate-induced hyperammonemic encephalopathy: an update on risk factors, clinical correlates and management

INTRODUCTION

Valproate (VPA)-induced hyperammonemic encephalopathy (VHE) is a serious drug-related adverse effect characterized by lethargy, vomiting, cognitive slowing, focal neurological deficits and decreased levels of consciousness ranging from drowsiness to coma.

METHODS

We present a case series (n=5) and also review previous cases of VHE (n=30) in psychiatric patients to provide an update on risk factors, clinical correlates and management of VHE.

RESULTS

To our knowledge, there are 30 (16 female, 14 male) previously reported VHE cases in psychiatric patients. Risk factors for VHE include VPA-drug interactions, mental retardation, carnitine deficiency and presence of urea cycle disorders. Length of VPA treatment, VPA dosage, serum VPA levels and serum ammonia levels do not appear to correlate with onset or severity of VHE.VPA discontinuation is the primary treatment of VHE, although, l-carnitine, lactulose and neomycin have been used adjunctively in some patients.

CONCLUSION

Clinicians should consider VHE in patients taking VPA who present with lethargy, gastrointestinal symptoms, confusion and decreased levels of drowsiness. VPA discontinuation is currently the mainstay of treatment for VHE, although more research is warranted to delineate the underlying risk factors for VHE and consolidate treatment modalities for this potentially life-threatening drug adverse effect.

Hyperammonemia in the ICU

Patients experiencing acute elevations of ammonia present to the ICU with encephalopathy, which may progress quickly to cerebral herniation. Patient survival requires immediate treatment of intracerebral hypertension and the reduction of ammonia levels. When hyperammonemia is not thought to be the result of liver failure, treatment for an occult disorder of metabolism must begin prior to the confirmation of an etiology. This article reviews ammonia metabolism, the effects of ammonia on the brain, the causes of hyperammonemia, and the diagnosis of inborn errors of metabolism in adult patients.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

Valproate-induced hyperammonaemic encephalopathy: review of 14 cases in the psychiatric setting

OBJECTIVES

To review signs and symptoms of valproate-induced hyperammonaemic encephalopathy without hepatotoxicity in the psychiatric setting, explore its mechanisms, and give recommendations for prevention and treatment.

METHODS

Medline search with keywords valproate, ammonia, hyperammonaemia, encephalopathy, and then cross-references to articles obtained through this search. Only cases with indication of valproate for psychiatric condition were included.

RESULTS

Fourteen cases published in the psychiatric setting are reviewed. Valproate-induced hyperammonaemic encephalopathy is a rare adverse event, occurring almost equally in men and women, with a large age range, and reported in two patients with mental retardation. Symptoms appeared either a few days after initiation of valproate therapy, or after several months or years. The main symptoms were fluctuations in consciousness and disorientation. Clinical severity was not related to blood ammonia levels. All patients recovered after valproate-induced hyperammonaemic encephalopathy diagnosis and treatment, usually involving discontinuation of valproate.

CONCLUSIONS

Valproate-induced hyperammonaemic encephalopathy is rare and usually reversible in patients without urea cycle disorders when valproate is discontinued. Therapy with carnitine is recommended. Special caution should be used in patients with mental retardation. Psychiatrists should suspect valproate-induced hyperammonaemic encephalopathy when consciousness deteriorates.

Acute Hyperammonemic Coma with Chronic Valproic Acid Therapy

OBJECTIVE

To report a case of dose-related hyperammonemic coma without liver failure in a patient receiving chronic valproate therapy.

CASE SUMMARY

A 56-year-old woman with poorly controlled epilepsy, receiving valproate at subtherapeutic levels for 6 years, developed a life-threatening hyperammonemic coma following a moderate dosage increase.

DISCUSSION

Hyperammonemic coma without associated liver failure is an extremely rare complication of valproate therapy, described primarily in patients with inborn errors of metabolism and occurring idiosyncratically during initial stages of therapy. In our case, family history was suggestive of an X-linked disorder, raising the possibility that our patient may have been an asymptomatic carrier of a urea cycle enzyme deficiency unmasked by valproate therapy. To our knowledge, as of October 24, 2005, only one prior case of hyperammonemic coma in the context of chronic valproate monotherapy has been described. Application of the Naranjo probability scale score suggests that a causal relationship between valproic acid and hyperammonemic coma was probable.

CONCLUSIONS

The widespread use of valproic acid emphasizes the need to maintain a high degree of suspicion with respect to this rare but potentially fatal adverse effect at all times, regardless of therapy duration.

Urea Cycle Disorders: Clinical Presentation Outside the Newborn Period

Although most commonly associated with infancy, the majority of individuals with urea cycle disorders (UCDs) present outside the neonatal period, frequently in childhood. Signs and symptoms are often vague, but recurrent; fulminant presentations associated with acute illness are also common. A disorder of urea cycle metabolism should be considered in children who have recurrent symptoms, especially neurologic abnormalities associated with periods of decompensation. Routine laboratory tests, including measurement of plasma ammonia concentrations, can indicate a potential UCD; however, specific metabolic testing and ultimately enzymatic or molecular confirmation are necessary to establish a diagnosis. Treatment with dietary protein restriction and medications may be challenging in children.

Urea cycle disorders

Most patients with urea cycle disorders who present as neonates, do so with deteriorating feeding, drowsiness and tachypnoea, following a short initial period when they appear well. The plasma ammonia should be measured at the same time as the septic screen in such patients. Ammonia levels above 200 micromol/l are usually caused by inherited metabolic diseases and it is essential to make a diagnosis for genetic counselling, even if the patients die. The aim of treatment is to lower the ammonia concentrations as fast as possible. Sodium benzoate, sodium phenylbutyrate and arginine can exploit alternative pathways for the elimination of nitrogen but haemodialysis or haemofiltration should be instituted if ammonia concentrations are >500 micromol/l or if they do not fall promptly. Long-term management involves drugs, dietary protein restriction and use of an emergency regimen during illness. Severe hyperammonaemia is usually associated with irreversible neurological damage, particularly if levels have been above 800 micromol/l for >24 hours, and the option of withdrawing treatment should be discussed with the family.

Valproate-induced liver failure in one of two siblings with Alpers disease

Alpers disease is a neurodegenerative disorder of childhood characterized by early developmental delay, intractable seizures, and death in childhood. Neuropathologic changes are most severe in the gray matter and consist of diffuse neuronal loss, spongiform changes, and astrocytosis. We report 2 siblings with Alpers disease who were discordant for exposure to valproate (VPA). Both had developmental delay, and a progressive seizure disorder beginning at 5 years of age. The proband died at age 8 years of complications of ongoing seizures, including epilepsia partialis continua, with only minimal liver abnormalities. Her younger brother was treated with VPA for new-onset seizures and developed fulminant liver failure 6 months later, which led to his death at 5 years of age. Neuropathologic abnormalities of both siblings were consistent with Alpers disease. These observations support classification of Alpers disease and Alpers disease with liver cirrhosis as a single disease. They also confirm previous reports indicating that VPA may accelerate fulminant liver failure in Alpers disease. We recommend that a diagnosis of Alpers disease be considered in children with unexplained early developmental delay, cerebellar signs, or partial seizures, especially epilepsia partialis continua. When Alpers disease is strongly suspected, use of VPA should be avoided.

Biochemical basis of sodium valproate hepatotoxicity and renal tubular disorder: time dependence of peroxidative injury

Mice fed with sodium valproate for 7, 14 and 21 days were evaluated for hepatotoxicity and renal tubular disorder. The drug was administered as an aqueous solution with an increasing concentration up to five days gradually reaching up to 0.71% w/v, which persisted throughout the study period. Mice fed with sodium valproate for 7, 14 and 21 days showed, marked hepatic injury and renal tubular disorder, evidenced by increased levels of malondialdehyde as a measure of lipid peroxidation. Administration of sodium valproate affected the glutathione contents both in liver and kidney tissue at all the three time points. However, this reduction in glutathione concentration was more pronounced in kidney when compared to control group. These results support the hypothesis that lipid peroxidation mediates the effect of sodium valproate on liver and kidney. Furthermore, the valproate induced toxicity is time related and the increase in lipid peroxide levels and depletion of glutathione occur time dependent even if the dose is clinically appropriate.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

Carbamoylphosphate synthetase deficiency in an adult: deterioration due to administration of valproic acid

A 24-year-old patient had symptoms of lethargy, convulsions and hyperammonaemia during valproic acid therapy. Cessation of valproic acid treatment brought about an improvement both of the symptoms and of the hyperammonaemia. However, enzymatic analysis after the cessation of valproic acid therapy revealed a complete absence of carbamoylphosphate synthetase (CPS) activity in liver biopsy. A unique polypeptide band, corresponding to the control CPS protein in molecular weight ('CPS-like' protein), was found in normal amounts in the patient's liver on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. This CPS-like protein seemed to be more labile than the control, because the polypeptide band became faint after freeze-thawing. Intravenous administration of L-alanine resulted in a significant increase of serum urea and a transient increase of blood ammonia concentrations. These results strongly suggest that the patient has a labile CPS protein with no activity in vitro but some activity in vivo. We consider that valproic acid may have disrupted some metabolic adaptation by reducing N-acetylglutamate in the liver, which in combination with CPS deficiency induced severe hyperammonaemia.

Carbamyl phosphate synthetase-1 deficiency discovered after valproic acid-induced coma

Valproic acid induced coma is presented in an adult patient without a history of metabolic disease. Liver biopsy revealed a reduction in activity of carbamyl phosphate synthetase-I, an enzyme obligated for transformation of ammonia to urea in the urea cycle. After recovery CT scan follow-up showed marked cerebral atrophy which did not exist prior to the state of coma. Risk factors are discussed.

Valproate hepatotoxicity syndrome: hypotheses of pathogenesis

Therapeutic use of the anticonvulsant valproate (VPA) has been associated with a rare, but severe and often fatal hepatotoxicity. Cases usually present with lethargy, anorexia, and vomiting with rapid progression to coma. Liver histopathology is characterized by steatosis with and without necrosis. In some instances only necrosis was present. Several hypotheses of pathogenesis have been postulated. These deal mainly with biochemical systems that are known to be affected by VPA, or with the possible idiosyncratic production of toxic VPA metabolites, especially delta 4-VPA. At present, no hypothesis entirely explains the diverse characteristics of the disorder.

Fatal hepatocerebral syndrome in siblings discordant for exposure to valproate

Occurrence of a progressive encephalopathy with seizures in siblings was associated with hepatic pathology. One of these patients was exposed to valproate (VPA) and developed hepatic necrosis, confirmed at autopsy. The other had not been exposed to VPA, and her hepatic lesions at autopsy were less severe. The liver pathology in both was within the range described in previous cases of liver disease attributed to VPA. These facts and the otherwise similar course of their disease suggests that in these patients, and probably in other cases of fatal liver failure attributed to VPA, the drug actually either had no effect or acted only to increase the severity of the preexisting hepatic component of the hepatocerebral disorder.

Changes in urea cycle-related metabolites in the mouse after combined administration of valproic acid and an amino acid load

Increased blood ammonia was induced in fasting mice by ip administration of 200 mg/kg Na-valproate followed 1 h later by 13 and 4 mmol/kg alanine and ornithine, respectively. When valproate was not used blood or liver ammonia was not increased, but increases were observed in liver glutamate (5-fold), glutamine (2-fold), aspartate (5-fold), acetylglutamate (15-fold), citrulline (35-fold), argininosuccinate (11-fold), arginine (11-fold), and urea (3-fold). The level of carbamoyl phosphate (less than 2 nmol/g) was, by far, the lowest of all urea cycle intermediates. The large increase in citrulline indicates that argininosuccinate synthesis was limiting, and that the increase in acetylglutamate induced a considerable activation of carbamoyl phosphate synthetase, which agrees with theoretical expectations, irrespective of the actual KD value for acetylglutamate. Pretreatment with valproate resulted in lower hepatic levels of glutamate, glutamine, aspartate, acetyl-CoA, and acetylglutamate. At the level found of acetylglutamate the activation of carbamoyl phosphate synthetase would be expected to be similar to that without valproate. Indeed, the levels of citrulline were similar with or without valproate. Argininosuccinate, arginine, and urea levels exhibited little if any change. Although the model used may not replicate exactly the situation in patients, from our results it appears that changes in citrullinogenesis or in other steps of the urea cycle do not account for the increase in blood ammonia induced by valproate, and it is proposed that valproate may alter glutamine metabolism.

Fatal liver failure in 16 children with valproate therapy

The data of 16 children who died while receiving valproate (VPA) therapy in West Germany were analyzed. Five were normally developed, 5 were receiving VPA-monotherapy, and only 2 patients were aged less than 3 years. The first clinical symptoms of impending hepatotoxicity usually included nausea, vomiting, and apathy; pathologic laboratory tests reflected liver failure. Liver histology revealed microvesicular steatosis, cell necrosis, and bile duct proliferation of varying degree. An abnormal metabolite, 4-ene-VPA, was detected in all examined patients (six of six) and persisted after drug withdrawal. The pathogenesis of fatal liver failure during VPA treatment remains unknown. World-wide, approximately 100 fatalities have been reported in relation to VPA treatment. More than 90% were aged less than 20 years, 95% developed their first symptoms within the first 6 months of treatment, and 16 were treated with VPA alone. Since it is difficult precisely to define a group at risk for fatalities with VPA, careful clinical and laboratory monitoring with a special focus on vomiting and apathy, liver enzymes, and coagulation tests seem mandatory during the first 6 months after introduction of VPA. Taking into account the considerable number of fatalities during VPA treatment, the indication for its use requires careful reevaluation.

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.

Secondary carnitine deficiency in hyperammonemic attacks of ornithine transcarbamylase deficiency

Carnitine status was evaluated in 12 patients with hyperammonemic attacks caused by a deficiency in ornithine transcarbamylase. We found decreased free carnitine and increased acylcarnitine levels in the serum, a decreased free carnitine content and an elevated acyl/free carnitine ratio in the liver, and increased excretion of free and acylcarnitine in the urine. Analyses of urinary acylcarnitine using the secondary ion mass spectrometry technique revealed increased amounts of acetylcarnitine and dicarboxylic acid derivatives. These data suggest that the patients had a secondary carnitine deficiency, possibly an aggravating factor in urea cycle dysfunction. After oral administration of L-carnitine (50 to 100 mg/kg/d) in two patients, hyperammonemic episodes were less frequent. Blood ammonia levels decreased significantly, accompanied by an increase in serum free carnitine levels.

Hepatotoxicity of sodium valproate in ornithine transcarbamylase-deficient mice

Susceptibility to sodium valproate (SV) hepatotoxicity was investigated in male sparse-fur mutant (spf/Y) mice with X-linked ornithine transcarbamylase (OTC) deficiency, as compared to normals (+/Y). SV was given in drinking water, in increasing concentrations of 0, 0.05, 0.15 and 0.25%. Actual SV intake was similar in both groups. There were no significant changes in orotate excretion, but alpha-amino nitrogen increased progressively with SV intake in both groups. Valproate-treated animals also had a significant increase in hepatic carbamyl phosphate synthetase-I (CPS-I) activity. OTC-deficient spf/Y mice showed 33% mortality and morbidity at 0.05-0.15% valproate, while normal mice remained non-symptomatic. spf/Y Mice also showed a higher incidence of hepatocellular necrosis, microvesicular steatosis and polymorphic infiltration. Centrilobular necrosis was seen only in symptomatic OTC-deficient mice, indicating an idiosyncratic hepatotoxic response which may be different from the dose-related effects seen in all SV-treated mice. Electron microscopy of liver sections from severely affected spf/Y mice showed marked abnormalities of mitochondria, which appeared swollen or rounded. The rough endoplasmic reticulum was dilated and filled with a flocculent material. It is postulated that the idiosyncratic response in OTC-deficient mice may be caused by an interaction between a metabolic aberration of mitochondria and toxic metabolites of valproate.

The effects of valproate on intermediary metabolism in isolated rat hepatocytes and intact rats

Valproate is a valuable anticonvulsant which is associated with hepatotoxicity in some patients. In concentrations in the range found in man during valproate therapy (0.1-1.0 mM), it inhibited pyruvate and palmitate oxidation, urea synthesis and gluconeogenesis by 30-50% in isolated rat hepatocytes. Valproate (100 mg/kg body weight) is also hypoglycaemic and hypoketonaemic in fasted rats. All these inhibitions can be explained in terms of the accumulation of valproyl-CoA and its further metabolites in the matrix of hepatic mitochondria. Although these inhibitions are only partial, and normally well tolerated, they could significantly impair liver function when there is an additional insult, such as may occur with multiple drug therapy or if there is already an inborn error of metabolism. Such an association with inborn errors may explain the higher incidence of valproate-associated toxicity in children. It may be of more value to measure blood urea and ammonia concentrations routinely shortly after starting valproate therapy than to do conventional liver function tests.

Valproate-induced hepatic injury: analyses of 23 fatal cases

Analyses of 23 fatal instances of hepatic injury in patients taking valproic acid reveals that all but three were less than 20 years old, and all but four had been taking the drugs for more than 1 month. Convulsions, facial edema, lassitude, and vomiting were prominent clinical features. Hypoglycemia was recorded in six patients. Rash and eosinophilia were not seen. Values for transaminases were modestly elevated in most patients. Most levels of SGOT were below 500 IU, and SGPT levels were below 200 IU. Livers showed microvesicular steatosis in most patients, usually accompanies by necrosis. Four patients had cirrhosis. Overt valproic acid-induced hepatic injury appears to be rare and hence, by definition, idiosyncratic. That it may be an idiosyncratic exaggeration of a much more frequent phenomenon is suggested by the higher incidence of seemingly trivial injury. The idiosyncrasy appears to be metabolic rather than immunologic, and the available information leads to the plausible hypothesis that a metabolite is responsible for the microvesicular steatosis seen in most fatal cases. The steatosis resembles that of Reye's syndrome and Jamaican vomiting sickness, and there is reason to believe that the metabolite responsible for the steatosis resembles the agent responsible for Jamaican vomiting sickness. A different metabolite is presumably responsible for the necrosis seen in many of the cases.