Hepatotoxic Effect of Sodium Valproate Therapy in Epileptic Children

 

N. Sangeetha and U.S. Mahadeva Rao*

PG Department of Biochemistry. SRM College of Arts and Science, Chennai-603 203.India.

 

ABSTRACT:

Background: Epilepsy is more common in children than in adults. Valproate (VPA) is a widely used drug in the treatment of epilepsy and, compared to other anticonvulsant drugs, is considered safe. However, more serious adverse reactions can occur such as hepatotoxicity and pancreatitis.

 

Aim: The present study was aimed to evaluate whether children with epilepsy undergoing valproate therapy has been associated with hepatotoxicity. So, a comparative study was done in epileptic children before and after treatment with VPA.

 

Methods: Serum levels of hepatic marker enzymes, protein and bilirubin profile and prothrombin time in plasma were estimated.

 

Results: Significant increase (p<0.05) of hepatic marker enzymes was observed in the epileptic children after VPA treatment. There was a significant decrease (p<0.05) in the levels of protein, albumin and globulin in post treated children. The levels of bilirubin showed no significant (p<0.05) changes but the prothrombin time was observed to be increased significantly (p<0.05).

 

Discussion: The increase in hepatic marker enzymes may reflect enzyme induction and the decrease in protein level showed increase binding of VPA to albumin. Increase in prothrombin time might be synthetic function of liver. The secretory function of liver not affected from the values of bilirubin.

 

Conclusion: The above results suggest that valproate treatment in epileptic children is associated with mild hepatotoxicity.

 

KEYWORDS: sodium valproate, hepatic marker enzymes, hepatotoxicity, epilepsy, antiepileptic drug.

 

INTRODUCTION:

Most of the pediatric epilepsies occur as primary generalized seizures, for which a single antiepileptic drug, sodium valproate is mostly preferred in children1. Valproic acid (VPA) is a broad-spectrum antiepileptic drug that is now used commonly for several other neurological and psychiatric indications. VPA is usually well tolerated, but serious complications, including hepatotoxicity and hyperammonemic encephalopathy, may occur. These complications may also arise following acute VPA overdose, the incidence of which is increasing. Intoxication usually only results in mild central nervous system depression, but serious toxicity and death have been reported2. During the past decade over 100 cases of fatal hepatotoxicity have been reported3-5. The risk of liver failure is much higher in children under 2 years of age. Hepatotoxicity has greatest concern with VPA therapy6-8. In children, very little of a VPA dose is excreted unchanged in urine, the drug is cleared almost entirely by xenobiotic metabolism.

 

The mitochondrial β-oxidation of VPA leads to the generation of 2-ene VPA, 3-hydroxy VPA and 3-keto VPA7,9,10. These metabolites of VPA inhibit mitochondrial function by a dual effect on both oxidation and respiratory chain enzymes. Free fattyacids cannot be metabolized and the lack of aerobic respiration results in the accumulation of lactate and reactive oxygen species. The presence of reactive oxygen species may further disrupt mitochondrial DNA.

 

Thus the pathogenesis of VPA hepatotoxicity is unclear but may relate to the accumulation of a toxic metabolite of VPA which impairs fattyacid oxidation11. Jeavons PM12 have reported VPA hepatotoxicity appears to be an idiosyncratic reaction and is most likely to appear within 6 months from the start of therapy. Thus it is reasonable to obtain baseline liver function studies prior to the initiation of valproate for the first two to three months of the therapy. In this present study, we have compared the hepatotoxic effect of valproate in epileptic children before and after treatment by estimating the levels of serum hepatic marker enzymes, proteins and bilirubin profile and prothrombin time in plasma.

 

MATERIALS AND METHODS:

Sample collection: The study population consisted of 25 epileptic children of both sexes aged between 0-12 years and 25 normal age-matched individuals as normal group. Detailed information of the study was given to the parents and blood samples were collected from the children with their parent’s consent. Only those patients who had a confirmed diagnosis of epilepsy were used for our study. The samples were collected through proper channel from the Department of Pediatric Neurology, Stanley Medical College and Hospital, Chennai, India. After collecting the samples from epileptic children, they were administered with sodium valproate (15mg/kg/day) orally and follow up study was conducted for two months interval of time.

 

Experimental groups: To investigate the VPA monotherapy in normal, pre- and post- treated epileptic children, their samples were categorized into three groups respectively as Group I- Normal; Group II- Before treatment; Group III- After treatment.

 

Chemicals: The chemicals and reagent kits used for the estimations were purchased from Sigma Chemical, Loba Chemie, Qualigens, Fischer, SDS and they were of analytical grade.

 

Biochemical Parameters: Venous blood was collected and divided into two parts: one part was allowed to clot at room temperature and centrifuged at 5000rpm for 10min and the serum was collected and aliquots of this serum was kept frozen at -70°C until they were used to assay Aspartate transaminase, AST13, Alanine transaminase, ALT13, Alkaline phosphatase, ALP14, Lactate dehydrogenase, LDH15, γ-glutamyl transferase, γ-GT16, Bilirubin17, Total protein and A/G ratio18. The second part of the blood samples were collected in a tube containing sodium citrate, centrifuged and the separated plasma was kept frozen at -70°C in aliquots that were later used for assays to determine prothrombin time19,20.

 

Statistical Analysis:

Descriptive Statistics were calculated for all the outcome variables and expressed as mean±s.d. The results were analyzed statistically by Student’s t-test. Differences were considered statistically significant when p<0.05.

 

RESULTS:

Effect of VPA on Hepatic marker enzymes:

Table 1 depicts the activity of pathophysiological enzymes in serum of normal, pre- and post- treated patients which shown to be increased significantly (p<0.05) in group III.

 

Effect of VPA on Protein profile:

GroupII children exhibited unaltered levels of protein profile compared to group I. Incontrast, group III showed significantly (p<0.05) lower levels to that of normal and before treated abnormal is portraited in Table 2.

 

Effect of VPA on Bilirubin and Prothrombin time:

No significant difference was observed in bilirubin profile between all the groups in this study. But in group II children when compared to group I, the level of prothrombin time significantly (p<0.05) increased which has been depicted in Table3.

 

 

Table 1: Serum Hepatic marker enzymes profile in normal and Pre- and Post- treated epileptic children

GROUPS

AST(IU/L)

ALT(IU/L)

ALP(IU/L)

LDH(IU/L)

γ-GT(IU/L)

Normal

9.8±0.9a,*

12.5±2.12a,ns

180.75±12.15a,ε

114±15.3a,*

7.5±0.5a,ε

Before treatment

7.44±0.32b,*

12.12±2.05b,*

189.85±15.2b,*

135±20.25b,*

7±0.9b,*

After treatment

15.2±1.24c,*

24.78±3.2c,*

251.64±35.85c,*

156±18c,*

9±0.85c,*

Values were expressed as mean±s.d. *p<0.001, εp<0.05 by Student’s T-test, ns-not significant.

(a - Group II Vs Group I; b - Group III Vs Group II; c - Group III Vs Group I)

 

Table 2: Serum Protein profile in normal and epilepsy with before and after treatment.

GROUPS

TOTAL PROTEIN (g/dl)

ALBUMIN (g/dl)

GLOBULIN (g/dl)

A/G ratio

Normal

7.2±0.7a,ns

4.3±0.38a,ns

2.9±0.29a,ns

1.4±0.09a,ns

Before treatment

7.3±0.8b,*

4.5±0.5b,*

2.8±0.2b,δ

1.6±0.15b,*

After treatment

6.5±0.6c,*

3.8±0.3c,*

2.7±0.2c,$

1.41±0.12c,ns

Values were expressed as mean±s.d.*p<0.001, $p<0.002, δp<0.10 by Student’s T-test, ns-not significant.

(a - Group II Vs Group I; b - Group III Vs Group II; c - Group III Vs Group I)

Table 3: Serum bilirubin and plasma prothrombin time estimation in normal and in pre- and post- treated epileptic children

GROUPS

Total Bilirubin (mg/dl)

Direct Bilirubin (mg/dl)

Indirect Bilirubin (mg/dl)

Prothrombin time (sec)

Normal

0.6±0.04a,ns

0.4±0.02a,*

0.2±0.01a,ns

14.5±1.12a,ns

Before treatment

0.7±0.08e

0.5±0.05e

0.2±0.01e

14.9±1.16d

After treatment

0.7±0.06a

0.5±0.04a

0.2±0.03e

15.8±1.37c

Values were expressed as mean±s.d. *p<0.001, $p<0.002, δp<0.10 by Student’s T-test, ns-not significant.

(a - Group II Vs Group I; b - Group III Vs Group II; c - Group III Vs Group I)

 

 

DISCUSSION:

Our study showed a highly significant increase (p<0.05)  in the level of serum AST in valproate treated epileptic children. The increase in serum transaminase often without associated symptoms, are frequent within the first two months of administration of sodium valproate8. Valproic acid inhibit mitochondrial metabolism of long chain fattyacid. The increased amount of unsaturated metabolites of valproate mainly 4-en-valproate have been found in blood and urine21. The mitochondrial β-oxidation of 4-en-VPA also gives 2, 4-diene VPA22 which binds to a protein responsible for the mitochondrial β-oxidation of fatty acids lead to inhibition of mitochondrial long chain fattyacid oxidation, reduction in energy supply and fat deposition in the liver.

 

The levels of serum ALP and γ-GT in valproate treated children were found to be higher. It was also reported about the increased level of serum γ-GT activity in valproate treated children23, 24.

 

The transient elevation of enzymes and hepatotoxicity has caused the greatest concern with VPA therapy8. Valproate associated hepatotoxicity is due to the structural, clinical and histopathological similarities between 4-en-valproate and 2 known hepatotoxins, 4-en-pentanoate and methylene cyclopropyl acetic acid, later being responsible for hypoglycin poisoning21. Specific alterations were observed in acrylcarnitine subspecies, unequivocally associated with VPA treatment in children with epilepsy. This might point to impaired intermediary metabolism that is responsible for VPA induced hepatotoxicity25. The level of LDH was also increased in epileptic children after treatment with VPA in comparison to normal. Thus the elevated levels of hepatic marker enzymes in valproate treated children might be due to impaired metabolic activity of liver.

 

Our study further showed that the lower level of total protein in valproate treated children in comparison to epileptic children. This is due to high affinity of valproic acid towards protein which may be one of the methods of its detoxification. It was also suggested that the decreased level of serum protein in valproate treated epileptic children who indicates an impaired liver synthetic function in asymptomatic children treated with VPA monotherapy26,27. The major metabolic pathway of VPA is glucuronidation of the carboxylic acid in liver21. The other minor pathways are β-oxidation and ω-hydroxylation at aliphatic hydrocarbon side chains26.

 

Many workers have reported plasma albumin has high binding capacity towards valproic acid. The decreased level of albumin found in epileptic children under VPA monotherapy might be due to affinity of albumin towards valproic acid. The VPA binding protein is mainly albumin28,29. We observed a low level of albumin in valproate treated children in comparison to normal. The binding of VPA to the albumin is inhibited by many drugs30. Valproic acid is highly bound to plasma protein significantly alter or inhibits hepatic drug metabolism and displace other highly bound drug from their plasma protein binding sites31. The level of albumin and A/G ratio were found to be reduced in epileptic children under VPA monotherapy.

 

There were no significant changes in the levels of total bilirubin, direct and indirect bilirubin in epileptic children before and after treatment with VPA. But the previous study revealed that an elevated level of bilirubin was reported which might be due to abnormal liver function32. Inside the hepatocytes, bilirubin is conjugated with glucuronic acid. Thus it undergoes effective conjugation by the microsomal enzyme uridine-di-phosphate glucuronyl transferase. This shows that VPA administration to epileptic children did not affect the secretory function of liver.

 

Prothrombin time was found to be high in VPA treated children when compared to normal. This elevated level may be due to decreased synthetic function of liver. The bleeding time was significantly longer in patients taking VPA compared with control33, 34. It might be due to deficiency of vitamin K or clotting factors indicating the synthetic function of liver.

 

CONCLUSION:

Thus the present study hypothesised that the epileptic children taking VPA monotherapy have the risk of hepatic damage due to its toxic metabolites which effect proliferation of enzymes into blood stream. It is generally advisable for epileptic children to undergo clinical or biochemical investigation during the administration of valproate.

 

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Received on 10.07.2011

Accepted on 13.08.2011        

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Research Journal of Pharmaceutical Dosage Forms and Technology. 3(4): July-Aug. 2011, 135-138