Reduced bone growth in rats treated with anticonvulsant drugs: a type II pseudohypoparathyroidism?

Adverse effects of valproate on bone: defining a model to investigate the pathophysiology

PURPOSE

Bone disease and fractures are common with chronic antiepileptic drug (AED) therapy, but the underlying mechanisms are poorly understood. This study aimed to characterize adverse bone effects of valproate and to identify mouse strains either resistant or sensitive to these effects.

METHODS

Seven mouse strains (n = 40/strain; 10/diet) were screened for the effect of chronic (8 weeks) valproate treatment (0, 2, 4, and 6 g/kg food) on total bone mineral content (BMC, by dual energy x-ray absorptiometry). In a confirmatory study the effect of valproate (0 or 4 g/kg food) over 16 weeks was assessed in five of the mouse strains (n = 60/strain; 30/diet) identified in the screening phase as either sensitive or resistant. Ex vivo volumetric bone measures and structural changes were assessed using peripheral quantitative computed tomography (pQCT) and histomorphometry.

RESULTS

Chronic valproate treatment reproducibly affected bone in C3H/HeJ mice, with a 9.1% (p < 0.01) reduction in total BMC and a 10.7% (p < 0.01) reduction in trabecular volumetric density, indicating a sensitive strain to AED-induced bone loss. Histomorphometry was consistent, revealing reductions in trabecular volume (19.6%, p < 0.05) and number (14.3%, p < 0.04), and a 19.9% (p < 0.05) increase in trabecular separation. In contrast the A/J mice were reproducibly resistant to the bone effects.

CONCLUSION

Mouse strains sensitive and resistant to the adverse bone effects of chronic valproate treatment were identified. The strain-specific effects suggest a role of genetic factors in the pathogenesis of AED-induced bone disease. This novel model provides a new, powerful tool to investigate the pathophysiology and therapy of AED-associated bone disease.

Levetiracetam, Phenytoin, and Valproate Act Differently on Rat Bone Mass, Structure, and Metabolism

PURPOSE

Long-term treatment with antiepileptic drugs (AEDs) is associated with increased risk of fractures. Phenytoin (PHT) and valproate (VPA) have both been suggested to influence bone health, whereas levetiracetam (LEV) is scarcely studied. The present study compares the effect of these AEDs on bone mass, biomechanical strength, and bone turnover in rats.

METHODS

Female rats received PHT (50 mg/kg), VPA (300 mg/kg), or LEV (50 and 150 mg/kg) for 90 days. Dissected femurs were analyzed using dual energy x-ray absorptiometry (DXA), three-point cantilever bending, and histomorphological evaluation. Serum levels of biochemical bone turnover markers were monitored using immunoassay quantification.

RESULTS

PHT and VPA reduced bone mineral density (BMD) and content (BMC) in one or more bone compartments, whereas LEV did not. VPA induced increased bone turnover, whereas modest changes were observed for PHT. Interestingly, low-dose LEV was associated with reduced biomechanical strength of the femoral neck (mainly trabecular bone). In addition, low-dose LEV treatment resulted in significantly reduced levels of serum osteocalcin, a marker of bone formation. Histomorphological analyses indicated increased retention of cartilage remnants at the growth plate metaphysis of rats treated with low-dose LEV vs. controls.

CONCLUSIONS

PHT, VPA, and LEV exert differential effects on bone mass and strength, suggesting different mechanisms of action. The weakening effect of low-dose LEV on the femoral neck, despite a constant BMD, suggests a primary effect on bone quality. These findings warrant further human studies of possible adverse effects of LEV on bone development and growth, particularly in children and adolescents.

Effects of valproic acid on longitudinal bone growth

Valproic acid is widely used in the treatment of children with epilepsy. Evidence indicates that valproic acid has teratogenic effects on the skeletal system. In addition, the use of valproic acid in children has been associated with short stature. Thus, we hypothesized that valproic acid could also affect bone growth after skeletal morphogenesis is completed. To test this hypothesis, we cultured fetal rat metatarsal bones in the presence of valproic acid. Valproic acid markedly suppressed metatarsal longitudinal growth. To determine the underlying mechanisms, we studied cell proliferation and hypertrophy in the growth plate, the site where bone growth takes place. At the end of the culture period, valproic acid-treated bones exhibited narrow growth plate proliferative and hypertrophic zones and an expanded ossification center. In addition, valproic acid suppressed chondrocyte proliferation in the metatarsal rudiments. Our results suggest that valproic acid suppresses longitudinal bone growth by inhibiting cartilage formation and accelerating ossification of the growth plate. These findings warrant a prospective study on the effects of valproic acid on growth in children treated with valproic acid.

Multiple idiopathic external root resorption. A case report

An unusual case of multiple idiopathic external apical root resorption affecting all four quadrants, in a patient with a history of narcotic intravenous drug addiction and liver disease, is reported. The literature relating to a systemic etiology for external root resorption is briefly reviewed.

Effects of carbamazepine on serum electrolytes in affectively ill patients

The effects on serum electrolytes of carbamazepine, an acute and prophylactic treatment for manic-depressive illness, were assessed in subjects with primary affective disorder. Carbamazepine caused statistically significant, but clinically insubstantial, reductions in serum sodium and calcium, but not in the other electrolytes measured. Decreases in serum sodium and calcium were not related to carbamazepine dose, blood levels, or the degree of clinical improvement. The theoretical implications of these findings are discussed.