Metabolic effects of valproate on dog renal cortical tubules

Evaluation of renal tubular function in children taking anti-epileptic treatment

AIM

To assess the effects of anti-epileptic drugs on renal tubular function.

METHODS

Urinary N-acetyl-beta-D-glucosaminidase activity was measured in 114 epileptic children (mean age 5.6 +/- 1.1 years) who were undergoing monotherapy with valproate (n = 46), carbamazepine (n = 34), lamotrigine (n = 13) and combined therapy with valproate+carbamazepine (n = 21).

RESULTS

The urinary N-acetyl-beta-D-glucosaminidase index of valproate (P < 0.01), carbamazepine (P < 0.05) and polytherapy group (P < 0.01) were significantly elevated when compared with that of the control group. No significant difference in N-acetyl-beta-D-glucosaminidase levels was found between the lamotrigine group and the control subjects. We found that the distribution of the N-acetyl-beta-D-glucosaminidase values of patients depended significantly on the length of therapy (P < 0.01). The level of urinary excretion of N-acetyl-beta-D-glucosaminidase was significantly higher in the patients who were taking long-term treatment (>10 years) with valproate, carbamazepine and combined therapy than those taking therapy shorter than 10 years (P < 0.01). The mean serum concentrations of valproate and carbamazepine were 68.7 +/- 17.44 microg/mL and 5.41 +/- 1.23 microg/mL, respectively. There was a significant correlation between the serum concentration of valproate and urinary N-acetyl-beta-D-glucosaminidase levels (r = 0.44, P < 0.01). There was also a significant correlation between the serum concentration of carbamazepine and N-acetyl-beta-D-glucosaminidase excretion (r = 0.52, P < 0.01).

CONCLUSION

The present study demonstrated that in patients treated with valproate and carbamazepine, an impairment of tubular function can be present, whereas lamotrigine does not cause any significant change.

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.

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.

Metabolic effects of 4-pentenoate on isolated dog kidney tubules

The effects of 4-pentenoate (0.01 to 10 mM) were studied on suspensions of cortical tubules and of thick ascending limbs (TAL) prepared from dog kidneys. When cortical tubules were incubated with 1 mM glutamine, 4-pentenoate accelerated glutamine uptake, ammoniagenesis, and the production of alpha-ketoglutarate, lactate and pyruvate, but decreased gluconeogenesis. With 5 mM glutamine, the marked accumulation of alpha-ketoglutarate reversed the net fluxes through the alanine and aspartate aminotransferases. When cortical tubules or TAL were incubated with lactate, its utilization and gluconeogenesis (in cortical tubules) were markedly decreased by 4-pentenoate. The mitochondrial NAD+/NADH ratio was markedly increased by 4-pentenoate in cortical tubules but not in TAL. The production of 14CO2 from 14C[1]-pyruvate or 14C-[1]-alpha-ketoglutarate was decreased by approximately 60% by 4-pentenoate in cortical tubules but not in TAL. In cortical tubules, these findings are best explained by depletion of mitochondrial free CoA, inhibition of pyruvate and alpha-ketoglutarate dehydrogenases and decreased mitochondrial NADH. By contrast, in TAL, accumulation of reducing equivalents probably resulted from the metabolism of 4-pentenoate itself.