Phenytoin-induced bone loss and its prevention with alfacalcidol or calcitriol in growing rats

An insight into the implications of estrogen deficiency and transforming growth factor β in antiepileptic drugs-induced bone loss

There have been a number of reports that chronic antiepileptic drug (AEDs) therapy is associated with abnormal bone and calcium metabolism, osteoporosis/osteomalacia, and increased risk of fractures. Bony adverse effects of long term antiepileptic drug therapy have been reported for more than four decades but the exact molecular mechanism is still lacking. Several mechanisms have been proposed regarding AEDs induced bone loss; Hypovitaminosis D, hyperparathyroidism, estrogen deficiency, calcitonin deficiency. Transforming growth factor-β (TGF- β) is abundant in bone matrix and has been shown to regulate the activity of osteoblasts and osteoclasts in vitro. All isoforms of TGF- β are expressed in bone and intricately play role in bone homeostasis by modulating estrogen level. Ovariectomised animal have shown down regulation of TGF- β in bone that could also be a probable target of AEDs therapy associated bone loss. One of the widely accepted hypotheses regarding the conventional drugs induced bone loss is hypovitaminosis D which is by virtue of their microsomal enzyme inducing effect. However, despite of the lack of enzyme inducing effect of certain newer antiepileptic drugs, reduced bone mineral density with these drugs have also been reported. Thus an understanding of bone biology, pathophysiology of AEDs induced bone loss at molecular level can aid in the better management of bone loss in patients on chronic AEDs therapy. This review focuses mainly on certain new molecular targets of AEDs induced bone loss.

Effects of the Antiepileptic Drugs Phenytoin, Gabapentin, and Levetiracetam on Bone Strength, Bone Mass, and Bone Turnover in Rats

Long-term treatment with antiepileptic drugs (AEDs) is accompanied by reduced bone mass that is associated with an increased risk of bone fractures. Although phenytoin has been reported to adversely influence bone metabolism, little is known pertaining to more recent AEDs. The aim of this study was to evaluate the effects of gabapentin or levetiracetam on bone strength, bone mass, and bone turnover in rats. Male Sprague-Dawley rats were orally administered phenytoin (20 mg/kg), gabapentin (30 or 150 mg/kg), or levetiracetam (50 or 200 mg/kg) daily for 12 weeks. Bone histomorphometric analysis of the tibia was performed and femoral bone strength was evaluated using a three-point bending method. Bone mineral density (BMD) of the femur and tibia was measured using quantitative computed tomography. Administration of phenytoin significantly decreased bone strength and BMD, which was associated with enhanced bone resorption. In contrast, treatment with gabapentin (150 mg/kg) significantly decreased bone volume and increased trabecular separation, as shown by bone histomorphometric analysis. Moreover, the bone formation parameters, osteoid volume and mineralizing surface, decreased after gabapentin treatment, whereas the bone resorption parameters, osteoclast surface and number, increased. Levetiracetam treatment did not affect bone strength, bone mass, and bone turnover. Our data suggested that gabapentin induced the rarefaction of cancellous bone, which was associated with decreased bone formation and enhanced bone resorption, and may affect bone strength and BMD after chronic exposure. To prevent the risk of bone fractures, patients prescribed a long-term administration of gabapentin should be regularly monitored for changes in bone mass.

Effects of the antiepileptic drugs topiramate and lamotrigine on bone metabolism in rats

Long-term treatment with antiepileptic drugs (AED) is associated with an elevated risk of bone fracture due to decreased bone mineral density (BMD). Phenytoin has been shown to affect bone metabolism adversely, whereas newly developed AEDs have not been studied. This study evaluated the effects of topiramate and lamotrigine on bone metabolism in rats. Five-week-old male Sprague-Dawley rats were treated orally with phenytoin (20 mg/kg), topiramate (5 or 20 mg/kg), or lamotrigine (2 or 10 mg/kg) daily for 12 weeks. Phenytoin reduced bone strength, measured by maximum load to failure of the femoral mid-diaphysis, along with reduced femur total BMD. Serum tartrate-resistant acid phosphatase-5b levels significantly increased after phenytoin treatment, while serum osteocalcin levels decreased after topiramate 20 mg/kg treatment. Furthermore, osteoblast surface and bone mineralizing surface were significantly lowered by topiramate. Lamotrigine treatment did not affect bone strength, BMD, or bone turnover. We demonstrated that phenytoin treatment significantly increased bone resorption and lowered BMD and bone strength. Since lamotrigine did not affect bone metabolism, it can be concluded that lamotrigine is safety medicine for bone health. Topiramate was associated with decreased bone formation, which may affect bone strength and BMD with chronic use. Thus, patients taking topiramate should be monitored for changes in BMD to avoid risk of fracture.

Side-Effects of Convulsive Seizures and Anti-Seizure Therapy on Bone in a Rat Model of Epilepsy

The severe sole effects of seizures on the cortical part of bone were reported in our previous study. However, the side effects of anti-epileptic drug therapy on bones has not been differentiated from the effects of the convulsive seizures, yet. This study provides the first report on differentiation of the effects of seizures and carbamazepine (a widely used antiepileptic drug) therapy on bones; 50 mg/kg/day drug was given to genetically induced absence epileptic rats for five weeks. Distinct bone regions including cortical, trabecular, and growth plate in each of tibia, femur, and spine tissues were studied using Fourier transform infrared (FT-IR) imaging and Vickers microhardness test. Blood levels of vitamin D and bone turnover biomarkers were also measured. According to the FT-IR imaging results, both seizure and carbamazepine-treated groups, more dominantly the drug-treated group, had lower mineral content with altered collagen crosslinks and higher crystallinity, implying reduced bone strength. Lower microhardness values also supported lower mechanical strength in bones. The most affected bone tissue and region from seizures and treatment was found as the spine and cortical, respectively. While there was a reduction in vitamin D and calcium levels in both seizure and carbamazepin-treated groups, significantly elevated PTH and bone turnover biomarkers were only seen in the drug-treated group.

Activation of lysosomal cathepsins in pregnant bovine leukocytes

In ruminants, interferon-tau (IFNT)-mediated expression of interferon-stimulated genes in peripheral blood leukocytes (PBLs) can indicate pregnancy. Recently, type 1 IFN-mediated activation of lysosomes and lysosomal cathepsins (CTSs) was observed in immune cells. This study investigated the status of lysosomal CTSs and lysosomes in PBLs collected from pregnant (P) and non-pregnant (NP) dairy cows, and conducted in vitro IFNT stimulation of NP blood leukocytes. Blood samples were collected 0, 7, 14 and 18 days post-artificial insemination, and the peripheral blood mononuclear cells (PBMCs) and polymorphonuclear granulocytes (PMNs) separated. The fluorescent activity of CTSB and CTSK in PMNs significantly increased with the progress of pregnancy, especially on day 18. In vitro supplementation of IFNT significantly increased the activities of CTSB and CTSK in NP PBMCs and PMNs. CTSB expression was significantly higher in PBMCs and PMNs collected from P day-18 cows than from NP cows, whereas there was no difference in CTSK expression. IFNT increased CTSB expression but did not affect CTSK expression. Immunodetection showed an increase of CTSB in P day-18 PBMCs and PMNs. In vitro stimulation of IFNT increased CTSB in NP PBMCs and PMNs. Lysosomal acidification showed a significant increase in P day-18 PBMCs and PMNs. IFNT also stimulated lysosomal acidification. Expressions of lysosome-associated membrane protein (LAMP) 1 and LAMP2 were significantly higher in P day-18 PBMCs and PMNs. The results suggest that pregnancy-specific activation of lysosomal functions by CTS activation in blood leukocytes is highly associated with IFNT during maternal and fetal recognition of pregnancy.

Lacking the 'protective label' of diabetes: Phenytoin-induced distal symmetrical peripheral neuropathy. A clinical case report

This report documents an unusual case of distal symmetrical peripheral neuropathy (DSPN) in an otherwise healthy patient without diabetes mellitus (DM) presenting to a podiatric wound care clinic. The development of gas gangrene coupled with Charcot neuroarthropathic changes ultimately resulted in a potentially life-saving transmetatarsal (TMT) amputation. Causation of, or at least a contributor to, the DSPN was likely phenytoin usage for epileptic seizures. Long-term use of phenytoin can lead to axonal shrinkage and random clusters of nerve demyelination [1]. Clinical standards for DM-induced DSPN indicate that annual comprehensive neurological assessment to detect nerve function deterioration is warranted [2]. This can aid in identifying patients at high risk of diabetic foot ulceration. However, oftentimes, patients exhibiting medication-induced neuropathy are not assessed to determine severity of the neuropathy nor are they educated about ulcer prevention in the same manner as patients with DM. This report advocates for a standardized threshold of diagnostic and preventative investigation for neuropathy of all aetiologies; diabetic, traumatic, viral, medication-induced and idiopathic.

Potential effects of valproate and oxcarbazepine on growth velocity and bone metabolism in epileptic children- a medical center experience

Background

Children with longstanding use of antiepileptic drugs (AEDs) are susceptible to developing low bone mineral density and an increased fracture risk. However, the literature regarding the effects of AEDs on growth in epileptic children is limited. The aim of this study was to investigate the potential effects of valproate (VPA) and/or oxcarbazepine (OXC) therapy on growth velocity and bone metabolism.

Methods

Seventy-three ambulatory children (40 boys and 33 girls) with epilepsy, aged between 1 and 18 years (mean age 9.8 ± 4.1 years), were evaluated for growth velocity before and for 1 year after VPA and/or OXC treatment. The bone resorption marker serum tartrate-resistant acid phosphatase 5b (TRAcP5b) and the bone formation marker serum bone-specific alkaline phosphatase (BAP) were measured post-AEDs therapy for 1 year.

Results

The difference in growth velocity (ΔHt) and body weight change (ΔWt) between pre- and post-AEDs treatment were -1.0 ± 2.8 cm/year (P < 0.05) and 0.1 ± 3.9 kg/year (P = 0.84), respectively. The study population had serum TRAcP5b-SDS of -1.6 ± 1.2 and BAP-SDS of 1.7 ± 3.7 compared with sex- and age-matched healthy children. Significant correlation between serum TRAcP 5b and BAP activities was noted (r = 0.60, p < 0.001). There was a positive correlation between growth velocity and serum TRAcP 5b activity after AED treatment (r = 0.42, p < 0.01). No correlation was found between ΔHt, ΔWt, serum TRAcP 5b, BAP activity and types of AEDs.

Conclusion

Growth velocity was significantly decreased in epileptic children after 1 year of VPA and/or OXC treatment. The effect of VPA and/or OXC therapy on dysregulation of bone metabolism might play a crucial role in physical growth.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-016-0597-7) contains supplementary material, which is available to authorized users.

The problem of osteoporosis in epileptic patients taking antiepileptic drugs

INTRODUCTION

Epilepsy is a common neurological disorder associated with recurrent seizures. Therapy with antiepileptic drugs (AEDs) helps achieve seizure remission in approximately 70% of epileptic patients. Treatment with AEDs is frequently lifelong and there are reports suggesting its negative influence on bone health. This is especially important in terms of general occurrence of osteoporosis, affecting over 50 million people worldwide.

AREAS COVERED

This study refers to two main groups of AEDs: hepatic enzyme inducers (carbamazepine, oxcarbazepine, phenobarbital, phenytoin, primidone and topiramate) and non-inducers (clobazam, clonazepam, ethosuximide, gabapentin, lacosamide, lamotrigine, levetiracetam, pregabalin, tiagabine, valproate, vigabatrin and zonisamide). Some reports indicate that enzyme inducers may exert a more negative influence on bone mineral density (BMD) compared to non-inducers. Bone problems may appear in both sexes during AED therapy, although women are additionally burdened with postmenopausal osteoporosis. Supplementation of vitamin D and calcium in patients on AEDs is recommended.

EXPERT OPINION

Apart from enzyme inducers, valproate (an even enzyme inhibitor) may also negatively affect BMD. However, the untoward effects of AEDs may depend upon their doses and duration of treatment. Although the problem of supplementation of vitamin D and calcium in epileptic patients on AEDs is controversial, there are recommendations to do so.

Effects of carbamazepine on serum parathormone, 25- hydroxyvitamin D, bone specific alkaline phosphatase, C-telopeptide, and osteocalcin levels in healthy rats

It is still not completely clear whether carbamazepine causes alterations in vitamin D status and in bone metabolism. The objective of this study was to investigate the effects of carbamazepine on serum levels of 25-hydroxyvitamin D and on biomarkers of bone formation and resorption in healthy rats. Levels of calcium, 25- hydroxyvitamin D, parathormone, C-telopeptide, bone specific alkaline phosphatase and osteocalcin were measured in 3 groups of rats consisting of controls (n=10), isotonic saline solution group (n=10) and carbamazepine group (n=10). Mean calcium levels were found to be significantly lower in healthy controls in comparison to isotonic saline solution and carbamazepine groups (10.0±0.24, 10.81±0.16, 10.93±0.22 mg/dL, respectively, p<0.05). Mean levels of 25- hydroxyvitamin D, were found to be significantly higher in control group compared to isotonic saline solution group (25- hydroxyvitamin D; 25.91±1.12, 19.99±0.99 ng/mL, respectively, p<0.01). Mean levels of parathormone and osteocalcin were found to be significantly higher in control group compared to isotonic saline solution group and carbamazepine group. Parathormone levels were measured as 3.46±0.83, 1.08±0.08, 0.94±0.02 pg/mL, respectively (p<0.01). Osteocalcine levels were measured as 1.66±0.001, 1.32±0.002, 1.32±0.001 ng/mL, respectively (p<0.001). A significant difference in terms of mean serum bone specific alkaline phosphatase and C-telopeptide levels among groups was not observed. The main outcome of this prospective study in healthy rats showed no change in biochemical parameters of bone turnover during treatment with carbamazepine.

Pharmacological and biochemical analysis of interactions between N-acetylcysteine and some antiepileptic drugs on experimental seizures in mice

PURPOSE

In view of a putative role of oxidative stress in the pathophysiology of seizures, this study addressed the interactions between N-acetylcysteine (NAC), a potent antioxidant and two antiepileptic drugs sodium valproate (SVP) and phenytoin (PHT) on experimental seizures in mice.

METHODS

The interaction was studied at three fixed ratio combinations (i.e., 1:1, 1:3, and 3:1) in the mouse maximal electroshock (MES) test using isobolographic analysis. Markers of oxidative stress (reduced glutathione [GSH] and malondialdehyde [MDA]) were estimated in the cortex of mice pretreated with either of these drugs alone or their 3:1 ratio combinations at the experimentally determined ED(50) values (ED(50 exp) values). The grip strength and spontaneous alternation behavior (SAB) were also assessed. In addition, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and calcium levels were estimated.

RESULTS

We found an anticonvulsant action of NAC in the MES test. Further, the ED(50 exp) values for the combinations of PHT and NAC did not differ from the theoretically calculated ED(50) values indicating additive effects. In case of SVP and NAC, however, the ED(50 exp) values were lower than the theoretically calculated ED(50) values. The interaction of SVP with NAC at the fixed ratios of 1:3 and 3:1 was found to be synergistic. No significant changes were observed in the grip strength, SAB, cortical GSH and MDA levels, serum AST, ALT, ALP, or calcium levels.

CONCLUSION

Our results thus hold promise for the use of NAC as an adjunct to PHT and SVP therapy.

Vitamin D analogs

Vitamin D has gone through a renaissance with the association of vitamin D deficiency with a wide array of common diseases including breast, colorectal and prostate cancers, cardio-vascular disease, autoimmune conditions and infections. Vitamin D analogs constitute a valuable group of compounds which can be used to regulate gene expression in functions as varied as calcium and phosphate homeostasis, as well as cell growth regulation and cell differentiation of a wide spectrum of cell types. This review will discuss the full range of vitamin D compounds currently available, some of their possible uses, and potential mechanisms of action.

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.

Establishment of rat model of drug-induced gingival overgrowth induced by continuous administration of phenytoin

It is well-known that the anticonvulsant drug, phenytoin (PHT), induces gingival overgrowth as a side effect. The mechanism of PHT-induced gingival overgrowth, however, is not well understood. One reason for this is the lack of an adequate animal model for the PHT-induced gingival overgrowth. The purpose of this study was to establish a rat model of the drug-induced gingival overgrowth. Fourteen-day-old rats were randomly divided into 3 groups (5 rats/group). The control rats received only the vehicle. The rats in the experimental group were injected with 50 mg/kg per day (group L) and 100 mg/kg per day (group H) of PHT. They received a subcutaneous injection of vehicle or PHT twice a day for 42 days. A charge-coupled device (CCD) laser displacement sensor was used for measurement of the severity of gingival overgrowth of the mandibles. There was no significant difference in the growth of rats between the PHT-injected and the control groups. The CCD laser displacement sensor can measure minute changes in the gingival overgrowth in rats, and a significant extension of the buccal gingiva was observed in groups L and H. Using the CCD sensor, it is possible to quantify the change in the gingiva under precise control of the PHT dose.

Antiepileptic drugs and reduced bone mineral density

There is a growing interest in recognizing the association between antiepileptic drugs and reduced bone mineral density. Although the literature regarding this association has been available for more than three decades, the management of this complication remains unclear. We review the relevant literature regarding antiepileptic drugs and reduction in bone mineral density with the aim of developing some guidelines for practical management of this problem. This review focuses on the mechanism of antiepileptic drug-induced bone loss, its recognition, and its management.

Effects of menatetrenone on the bone and serum levels of vitamin K2 (menaquinone derivatives) in osteopenia induced by phenytoin in growing rats

OBJECTIVE

We investigated the effects of phenytoin, an antiepileptic drug, and vitamin K2 (menatetrenone) on bone mineral density and the changes in the levels of menaquinone derivatives (MK-1 approximately MK-14) in the sera and femurs of growing male rats.

METHODS

Levels of menaquinone derivatives were measured with high-performance liquid chromatography with an electrochemical detector.

RESULTS

Bone mineral density values decreased significantly in all parts of the femoral bones measured (diaphysis and metaphysis) in the phenytoin-treated group. When the serum and bone levels of menatetrenone and MK-6 decreased due to phenytoin administration, we observed bone loss in rats. Conversely, when bone loss was prevented by the combined administration of phenytoin and menatetrenone, serum and bone levels of menatetrenone and MK-6 increased to the levels of vehicle-treated rats.

CONCLUSIONS

Long-term phenytoin exposure may inhibit bone formation concomitantly with insufficient vitamin K, which, at least in part, contributes to bone loss in rats.

Effects of chronic administration of zonisamide, an antiepileptic drug, on bone mineral density and their prevention with alfacalcidol in growing rats

We investigated the effects of chronic administration of zonisamide, an antiepileptic agent, on bone metabolism in growing rats. Administration of zonisamide at a dose of 80 mg/kg per day, s.c. for 5 weeks significantly decreased bone mineral density (BMD) at the tibial metaphysis and the diaphysis. The percent rate of decrease in BMD at the tibial metaphysis and the tibial diaphysis was 9.2% and 5.0%, respectively. There was no significant difference between these groups in the growth of the rats. Treatment with zonisamide at a dose of 80 mg/kg increased serum pyridinoline level, a marker of bone resorption, while it does not affect the serum intact osteocalcin level, a marker of bone formation. Combined administration of alfacalcidol, an active vitamin D(3) metabolite, at a dose of 0.1 microg/kg per day with zonisamide prevented a decrease in BMD and showed an increase of serum pyridinoline levels. These results suggest that zonisamide may cause bone loss by accelerating bone resorption rather than inhibiting bone formation. Moreover, the bone loss induced by zonisamide could be prevented by combining zonisamide with alfacalcidol.