Valproate-induced hyperammonemia of renal origin. Effects of valproate on glutamine transport in rat kidney mitochondria

Medicinal-Induced Behavior Disorders

Commonly used medications can have neuropsychiatric and behavioral effects that may be idiosyncratic or metabolic in nature, or a function of interactions with other drugs, toxicity, or withdrawal. This article explores an approach to the patient with central nervous system toxicity, depending on presentation of sedation versus agitation and accompanying physical signs and symptoms. The effects of antihypertensives, opioids, antibiotics, antiepileptic agents, steroids, Parkinson's disease medications, antipsychotics, medications for human immunodeficiency virus infection, cancer chemotherapeutics, and immunotherapies are discussed. A look at the prevalence of adverse reactions to medications and the errors underlying such occurrences is included.

Pharmacogenetics of antiepileptic drugs: A brief review

The goal of pharmacogenetic research is to assist clinicians in predicting patient response to medications when genetic variations are identified. The pharmacogenetic variation of antiepileptic drug response and side effects has yielded findings that have been included in drug labeling and guidelines. The goal of this review is to provide a brief overview of the pharmacogenetic research on antiepileptic drugs. It will focus on findings that have been included in drug labeling, guidelines, and candidate pharmacogenetic variation. Overall, several genes have been included in guidelines by national and international organizations; however, much work is needed to implement and evaluate their use in clinical settings.

Neurotoxicological effects of nicotine on the embryonic development of cerebellar cortex of chick embryo during various stages of incubation

Long-acting nicotine is known to exert pathological effects on almost all tissues including the cerebellar cortex. The present work was designed to elucidate the effect of nicotine on the development of cerebellar cortex of chick embryo during incubation period. The fertilized eggs of hen (Gallus gallus domesticus) were injected into the air space by a single dose of long acting nicotine (1.6 mg/kg/egg) at the 4th day of incubation. The embryos were taken out of the eggs on days 8, 12 and 16 of incubation. The cerebellum of the control and treated embryos at above ages were processed for histopathological examination. The TEM were examined at 16th day of incubation. The results of the present study revealed that, exposure to long-acting nicotine markedly influence the histogenesis of cerebellar cortex of chick embryo during the incubation period. At 8th day of incubation, nicotine delayed the differentiation of the cerebellar analge; especially the external granular layer (EGL) and inner cortical layer (ICL). Furthermore, at 12th day of incubation, the cerebellar foliation was irregular and the Purkinje cells not recognized. By 16th day of incubation, the cerebellar foliations were irregular with interrupted cerebellar cortex and irregular arrangement of Purkinje cells. Immunohistochemical analysis for antibody P53 protein revealed that the cerebellar cortex in all stages of nicotine treated groups possessed a moderate to weak reaction for P53 protein however; this reaction was markedly stronger in the cerebellar cortex of control groups. Moreover, the flow cytometric analysis confirmed that the percentage of apoptosis in control group was significantly higher compared with that of nicotine treated group. At the TEM level, the cerebellar Purkinje cells of 16th day of treated groups showed multiple subcellular alterations in compared with those of the corresponding control group. Such changes represented by appearing of vacuolated mitochondria, cisternal fragmentation of RER, irregular grooves of Golgi tubules. Also, multiple cytoplasmic vacuoles and aggregation of Nissl granules were recorded around pyknotic nucleus.

New insights on the mechanisms of valproate-induced hyperammonemia: inhibition of hepatic N-acetylglutamate synthase activity by valproyl-CoA

BACKGROUND & AIMS

Hyperammonemia is a frequent side-effect of valproic acid (VPA) therapy, which points to an imbalance between ammoniagenesis and ammonia disposal via the urea cycle. The impairment of this liver-specific metabolic pathway induced either by primary genetic defects or by secondary causes, namely associated with drugs administration, may result in accumulation of ammonia. To elucidate the mechanisms which underlie VPA-induced hyperammonemia, the aim of this study was to evaluate the effect of both VPA and its reactive intermediate, valproyl-CoA (VP-CoA), on the synthesis of N-acetylglutamate (NAG), a prime metabolite activator of the urea cycle.

METHODS

The amount of NAG in livers of rats treated with VPA was quantified by HPLC-MS/MS. The NAG synthase (NAGS) activity was evaluated in vitro in rat liver mitochondria, and the effect of both VPA and VP-CoA was characterized.

RESULTS

The present results clearly show that VP-CoA is a stronger inhibitor of NAGS activity in vitro than the parent drug VPA. The hepatic levels of NAG were significantly reduced in VPA-treated rats as compared with control tissues.

CONCLUSIONS

These data strongly suggest that the hyperammonemia observed in patients under VPA treatment may result from a direct inhibition of the NAGS activity by VP-CoA. The subsequent reduced availability of NAG will impair the flux through the urea cycle and compromise the major role of this pathway in ammonia detoxification.

Valproic Acid-induced hyperammonemia in the elderly: a review of the literature

Valproic acid and its derivatives are commonly used to treat many psychiatric conditions in the elderly. Hyperammonemia is a less common but important side effect of these drugs. The elderly patient appears highly vulnerable to this side effect of this group of medications. In this paper, we systematically review the published literature for hyperammonemia induced by valproic acid and its derivatives. We describe the three reported cases and review possible treatment strategies for this condition.

Different clinical manifestations of hyperammonemic encephalopathy

Valproate is an effective anticonvulsant. Although it is usually well tolerated, it has been associated with many neurological, hematopoietic, hepatic, and digestive system side effects. Among these side effects, hyperammonemia without clinical or laboratory evidence of hepatotoxicity is rare and is an important clinical consideration. The aim of this article was to evaluate the reasons for the unexpected symptoms observed in seven patients with epilepsy patients during valproate treatment. We evaluated seven adult patients with localization-related epilepsy who presented with different acute or subacute neurological symptoms related to valproate-induced hyperammonemic encephalopathy. Four of the seven patients had acute onset of confusion, decline in cognitive abilities, and ataxia. Two had subacute clinical symptoms, and the other patient had symptoms similar to those of acute toxicity. These unusual clinical symptoms and similar cases had not been reported in the literature before. Serum ammonia levels were elevated in all seven patients. After discontinuation of valproate, complete clinical improvement was observed within 5-10 days. On the basis of our work, we suggest that the ammonia levels of a patient who has new neurological symptoms and has been taking valproate must be checked. Clinicians should be aware that these clinical symptoms may be related to valproate-induced hyperammonemic encephalopathy. The symptoms have been observed to resolve dramatically after withdrawal of the drug.

Valproic Acid—Induced Hyperammonemia and Thrombocytopenia in an Elderly Woman

OBJECTIVE

To describe a case of oral valproic acid—induced hyperammonemia and thrombocytopenia in an elderly patient.

CASE SUMMARY

A 76-year-old white woman presented to the emergency department with generalized weakness, confusion, nausea, and vomiting. She was taking sodium divalproex 750 mg 3 times daily, with valproic acid concentration 144 mg/L. She was admitted to the medical ward. The dose of sodium divalproex was decreased and discontinued. During her hospital stay, the woman's ammonia level rose to 211 μg/dL despite a normal valproic acid concentration. She was confused, somnolent, and had decreased mobility. Her platelet count decreased from 133 to 86 × 103/mm 3 . Gabapentin was prescribed for seizure control. The patient's mental status, ammonia level, and platelet count returned to baseline following discontinuation of valproic acid.

DISCUSSION

It has been reported that valproic acid can interfere with the enzyme carbamoylphosphate synthetase, which is responsible for incorporating ammonia into the urea cycle. It has also been reported that valproic acid can increase the transport of glutamine across the mitochondrial membrane in the kidney, thereby increasing the production of ammonia. The etiology of valproic acid—induced thrombocytopenia has not been elucidated. Using the Naranjo probability scale, a probable relationship between hyperammonemia and valproic acid and a possible relationship between thrombocytopenia and valproic acid were determined.

CONCLUSIONS

Valproic acid can be associated with hyperammonemia and thrombocytopenia. Clinicians should be aware of changes in patients' cognitive and functional capacity, especially elderly patients on sodium divalproex.

Valproic acid toxicity: overview and management

Acute valproic acid intoxication is an increasing problem, accounting for more than 5000 calls to the American Association of Poison Control Centers in 2000. The purpose of this paper is to review the pharmacology and toxicology of valproic acid toxicity. Unlike earlier antiepileptic agents, valproic acid appears to function neither through sodium channel inhibition nor through direct gamma-aminobutyric acid agonism, but through an indirect increase in regional brain gamma-aminobutyric acid levels. Manifestations of acute valproic acid toxicity are myriad, and reflect both exaggerated therapeutic effect and impaired intermediary metabolism. Central nervous system depression is the most common finding noted in overdose, and may progress to coma and respiratory depression. Cerebral edema has also been observed. Although hepatotoxicity is rare in the acute overdose setting, pancreatitis and hyperammonemia have been reported. Metabolic and hematologic derangements have also been described. Management of acute valproic acid ingestion requires supportive care and close attention to the airway. The use of controversial adjunctive therapies, including extracorporeal drug elimination and L-carnitine supplementation, will be discussed.

Valproate-induced hyperammonemic encephalopathy

Valproic acid (VPA) is an effective anticonvulsant useful in many types of epilepsy and, although it is usually well tolerated, it has been associated with many neurological and systemic side effects. Among these, one of the most important is VPA-induced hyperammonemic encephalopathy (VHE): its typical signs are acute onset of impaired consciousness, focal neurologic symptoms, and increased seizure frequency. The pathogenesis of VHE is still unclear, but it has been suggested that hyperammonemia can produce encephalopathy via inhibition of glutamate uptake by astrocytes which may lead to potential neuronal injury and perhaps cerebral edema. Glutamine production is increased, whereas its release is inhibited in astrocytes exposed to ammonia. The elevated glutamine increases intracellular osmolarity, promoting an influx of water with resultant astrocytic swelling. This swelling could compromise astrocyte energy metabolism and result in cerebral edema with increased intracranial pressure. Moreover, VHE seems to be more frequently in patients with carnitine deficiency or with congenital urea cycle enzymatic defects.

Ultrastructure of Purkinje cell perikarya and their dendritic processes in the rat cerebellar cortex in experimental encephalopathy induced by chronic application of valproate

Long-term intragastric administration of the antiepileptic drug sodium valproate (Vuprol Polfa) to rats for 1, 3, 6, 9 and 12 months, once daily at the effective dose of 200 mg/kg body weight showed morphological evidence of encephalopathy, manifested by numerous nonspecific changes within Purkinje cell perikarya and their dendritic processes. The first ultrastructural abnormalities appeared after 3 months. They became more severe in animals with longer survival and were most pronounced after 12 months. The changes were maintained both 1 and 3 months after drug withdrawal. Mitochondria of Purkinje cell perikarya were most severely affected. Damage to mitochondria was accompanied by disintegration and fragmentation of granular endoplasmic reticulum, dilation of channels and cisterns of Golgi apparatus, enlargement of smooth endoplasmic reticulum elements including submembranous cisterns, and accumulation of profuse lipofuscin deposits. Frequently, Purkinje cells appeared as dark ischemic neurones, with focally damaged cellular membrane and features of disintegration. Swollen Bergmann's astrocytes were seen among damaged Purkinje cells or at the site of their loss. The general pattern of submicroscopic alterations of Purkinje cell perikarya suggested severe disorders in several intercellular biochemical extents, including inhibition of oxidative phosphorylation and abnormal protein synthesis, both of which could lead to lethal damage. Ultrastructural abnormalities within dendrites were characterized by damage to elements of smooth endoplasmic reticulum, which was considerably enlarged, with formation of large vacuolar structures situated deep in the dendroplasm. Mitochondrial lesions and alterations in cytoskeletal elements--disintegration of microtubules or even their complete loss--were also observed. The general pattern of abnormalities within the organelles and cytoskeletal elements of dendritic processes in Purkinje cells in the VPA chronic experimental model imply that there are disturbances in detoxication processes. Furthermore these changes were irreversible, as they were maintained after drug withdrawal.

Renal tubular function in patients receiving anticonvulsant therapy: a long-term study

PURPOSE

The goal of the study was to evaluate the tubular renal function in children and adolescents who are undergoing monotherapy with sodium valproate (VPA), carbamazepine (CBZ), and phenobarbital (PB).

METHODS

The urinary excretion of N-acetyl-beta-glucosaminidase (NAG), beta-galactosidase (beta-Gal), alanine-amino-peptidase (AAP), and alpha1-microglobulin (alpha1M) was measured in 58 epileptic patients (29 girls and 29 boys), aged 12.6 +/- 3.9 years, who were subdivided into three groups according to their therapy. Fifty healthy sex-and age-matched children served as controls. The measurements were taken before the beginning of therapy and after 6 months, 1 year, and 2 years of therapy.

RESULTS

Before the beginning of therapy, there were no significant differences in NAG, beta-Gal, AAP, and alpha1M values between the control group and the three groups of epileptic children. After 6 months of therapy, patients treated with VPA and CBZ showed a significant increase in the urinary excretion of NAG and beta-Gal compared with baseline data and control values. After 1 and 2 years, these patients showed a persistence of the changes found after 6 months of therapy. In patients treated with PB, we did not find any significant variation in NAG, beta-Gal, AAP, and alpha1M urinary excretion.

CONCLUSIONS

Our study demonstrates that in patients treated with VPA and CBZ, an impairment of tubular function can be present, whereas PB does not cause any significant change.

Inhibitory effect of valproate on weak organic acid uptake in rat renal proximal tubules

The effects of an antiepileptic drug, valproic acid (VPA), on transport mechanisms involved in renal excretion of anionic xenobiotics were investigated on rat renal proximal tubules in vitro. It was found that VPA (0.1-1 mM) dose dependently inhibited the baseline uptake of a marker organic anion, fluorescein, in the tubules. The inhibition could not be exclusively accounted for by competition between VPA and fluorescein. Taking into account a proposed relationship between the weak organic anion uptake and ammoniagenesis, the influence of VPA (0.5 mM) on the effects of glutamine and glutamate (both at 5 mM) on fluorescein uptake and ammonia production were examined. Glutamine stimulated ammonia production by the tubules, with the glutamine-induced ammoniagenesis being further augmented by VPA, while glutamate failed to affect the basal ammoniagenesis. Both glutamine (5 mM) and glutamate (5 mM) slightly inhibited fluorescein uptake, with the inhibitory effects not modified by VPA. Thus, there was no coincidence in the effects of VPA on organic anion uptake and renal ammoniagenesis. At the same time, the inhibitory effect of VPA (0.5 mM) on fluorescein uptake was largely overcome by addition of pyruvate (5 mM) to the incubation medium. In addition, VPA strongly inhibited glucose production from pyruvate. A known modulator of pyruvate metabolism, dichloroacetic acid (DCA, 1 mM), also inhibited fluorescein uptake, although its inhibitory effect was less pronounced than that of VPA. Both inhibitors failed to alter the tissue content of alpha-ketoglutarate or lactate but did slightly augment the pyruvate level. The inhibitory effects of VPA and DCA on the baseline fluorescein uptake were not additive, suggesting their similar intracellular targeting. It is assumed that the inhibitory effect of VPA on baseline fluorescein uptake in rat renal proximal tubules in vitro may be associated with its action on pyruvate metabolism.

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.

Urinary N-acetyl-beta-glucosaminidase and guanidinoacetic acid levels in epileptic patients treated with anti-epileptic drugs

We investigated potential renal functional impairment induced by chronic use of anti-epileptic drugs (AEDs) in 79 epileptic children. They were divided into five groups: valproic acid (VPA) monotherapy where the serum concentration (SC) of VPA was no less than 60 micrograms/ml (VPA [SC > or = 60]) (15 cases), VPA monotherapy where the SC VPA was less than 60 micrograms/ml (VPA [SC < 60]) (29 cases), phenobarbital monotherapy (PB) (7 cases), carbamazepine monotherapy (CBZ) (16 cases), and polytherapy containing VPA (12 cases). Urinalysis (proteinuria and hematuria) and serum creatinine were normal except for two cases of proteinuria and two cases of hematuria. The level of urinary excretion of N-acetyl-beta-glucosaminidase (u-NAG) was high in 29% of all patients, and 47% of VPA (SC > or = 60), 38% of CBZ, 25% of polytherapy, and 24% of VPA (SC < 60) groups. There was a significant positive correlation between serum concentration of VPA and u-NAG/urinary creatinine (u-Cr). The level of guanidinoacetic acid (u-GAA) excreted in the urine was normal except in one patient. U-NAG/u-Cr may be a more sensitive marker than u-GAA/u-Cr for renal functional impairment in AED therapy.

Valproate increases glutaminase and decreases glutamine synthetase activities in primary cultures of rat brain astrocytes

It has been proposed that hyperammonemia may be associated with valproate therapy. As astrocytes are the primary site of ammonia detoxification in brain, the effects of valproate on glutamate and glutamine metabolism in astrocytes were studied. It is well established that, because of compartmentation of glutamine synthetase, astrocytes are the site of synthesis of glutamine from glutamate and ammonia. The reverse reaction is catalyzed by the ubiquitous enzyme glutaminase, which is present in both neurons and astrocytes. In astrocytes exposed to 1.2 mM valproate, glutaminase activity increased 80% by day 2 and remained elevated at day 4; glutamine synthetase activity was decreased 30%. Direct addition of valproate to assay tubes with enzyme extracts from untreated astrocytes had significant effects only at concentrations of 10 and 20 mM. When astrocytes were exposed for 4 days to 0.3, 0.6, or 1.2 mM valproate and subsequently incubated with L-[U-14C]glutamate, label incorporation into [14C]glutamine was decreased by 11, 25, and 48%, respectively, and is consistent with a reduction in glutamine synthetase activity. Label incorporation from L-[U-14C]glutamate into [14C]aspartate also decreased with increasing concentrations of valproate. Following a 4-day exposure to 0.6 mM valproate, the glutamine levels increased 40% and the glutamate levels 100%. These effects were not directly proportional to valproate concentration, because exposure to 1.2 mM valproate resulted in a 15% decrease in glutamine levels and a 25% increase in glutamate levels compared with control cultures. Intracellular aspartate was inversely proportional to all concentrations of extracellular valproate, decreasing 60% with exposure to 1.2 mM valproate.(ABSTRACT TRUNCATED AT 250 WORDS)