Multiple mechanisms of action: the pharmacological profile of budipine

Effects of amantadine and budipine on antidepressant drug-evoked changes in extracellular dopamine in the frontal cortex of freely moving rats

NMDA receptors play a role in the aetiology of depression with non-competitive NMDA receptor antagonists such as amantadine showing synergy with conventional antidepressants. To advance a neurochemical rational for these findings, we have studied the effects of administration of amantadine and budipine with the antidepressants reboxetine (REB), paroxetine (PAROX) and clomipramine (CLOM) on extracellular DA in rats using microdialysis. Acutely, amantadine (40 mg/kg) or budipine (10 mg/kg) did not significantly alter extracellular DA. REB (10 mg/kg), PAROX (10 mg/kg) both increased cortical DA while CLOM (10 mg/kg) produced a decrease. When amantadine or budipine was administered 30 min before the antidepressants, DA increases were markedly greater than following the antidepressants alone. Chronically drug effects were studied at 4, 7, 14 and 21 days. Amantadine and budipine did not significantly alter extracellular DA at any time. The three antidepressants elicited a gradual increase in DA which became significant after 7 days and tended to plateau thereafter. When amantadine (20 mg/kg) or budipine (5 mg/kg) was co-administered with the three antidepressants, two differences were seen compared with the antidepressants alone. Firstly, the time required for significant increases in cortical DA was reduced with elevated levels now being observed by 4 days. Secondly, the increase in extracellular DA was greater in these rats throughout the experiment. If increased extracellular DA represents a step in the mechanism of action of antidepressants, these data suggest that combined treatment with clinically tolerated NMDA antagonists such as amantadine could reduce the delay in therapeutic onset of antidepressants and possibly enhance their efficacy.

Effects of amantadine and budipine on antidepressant drug-evoked changes in extracellular 5-HT in the frontal cortex of freely moving rats

1. Evidence has recently suggested that NMDA receptors may play a role in the aetiology and possible treatment of depression and that weak noncompetitive NMDA receptor antagonists such as amantadine can synergize with conventional antidepressants in a model of the illness. 2. To try to obtain a neurochemical rationale for these findings, we have studied the effects of acute and chronic administration of amantadine or the related drug budipine on cortical release of 5-hydroxytryptamine (5-HT) following the antidepressants reboxitine (REB), paroxetine (PAROX) and clomipramine (CLOM) in freely moving rats by using microdialysis. 3. Acute administration of amantadine (40 mg kg(-1)), budipine (10 mg kg(-1)), REB (10 mg kg(-1)), PAROX (10 mg kg(-1)) or CLOM (10 mg kg(-1)) all failed to significantly alter extracellular 5-HT in the cortex. However, when either amantadine or budipine was administered 30 min prior to any of the three antidepressants, a significant rise in 5-HT was observed. 4. For chronic studies, the effects of the drugs were studied at 4, 7, 14 and 21 days. Amantadine and budipine did not significantly alter extracellular 5-HT at any time point. The three antidepressant drugs all elicited a gradual increase in 5-HT, which became significant after 14 days and tended to plateau thereafter. When either amantadine (20 mg kg(-1)) or budipine (5 mg kg(-1)) was coadministered with any of the three antidepressants, two differences were seen compared with the effects of the antidepressants alone. Firstly, the time required for significant increases in cortical 5-HT was reduced with elevated levels now being observed by 7 days. Secondly, the absolute magnitude of the increase in extracellular 5-HT was markedly greater in these rats from day 7 until the end of the experiment. 5. If, as is widely considered, an increase in extracellular 5-HT represents a critical step in the mechanism of action of antidepressants, these data suggest that combined treatment with clinically tolerated NMDA antagonists such as amantadine could reduce the delay in therapeutic onset of antidepressants as well as possibly enhance their efficacy.

The anti-Parkinson drug budipine is exported actively out of the brain by P-glycoprotein in mice

P-glycoprotein, a product of the ABCB1 gene, is a plasma membrane transporter that exports certain drugs as well as endogenous substances against a concentration gradient in the intestines, kidney and testes. It also constitutes an important part of the blood-brain barrier, where it exports its substrates out of the brain back into the circulation. To investigate whether the uptake of the anti-Parkinson drug budipine into the brain is mediated by P-glycoprotein, abcb1ab(-/-) double knock-out mice and wild-type control mice received budipine continuously over 11 days via implanted osmotic infusion pumps at the rate of 30ug over 24h. Concentrations of the drug in plasma, brain, and organs were measured with HPLC. Budipine concentrations in the abcb1ab knock-out animals were 3.1 times higher than in control mice. This study confirms the important role P-gp plays at the blood-brain barrier and shows that budipine is a substrate of P-gp.

Synergism between Topiramate and Budipine in Refractory Status Epilepticus in the Rat

PURPOSE

To evaluate the antiepileptic and neuroprotective properties of topiramate (TPM) alone and with coadministration of the N-methyl-D-aspartate (NMDA)-receptor antagonist budipine in a rat model of refractory status epilepticus.

METHODS

Male Sprague-Dawley rats had electrodes implanted into the perforant path and dentate granule cell layer of the hippocampus under halothane anesthesia. Approximately 1 week after surgery, the perforant path of each animal was electrically stimulated for 2 h to induce self-sustaining status epilepticus. Successfully stimulated rats were given intraperitoneally vehicle (n = 6), TPM (20-320 mg/kg; n = 28), budipine (10 mg/kg; n = 5), or budipine (10 mg/kg) and TPM (80 mg/kg; n = 6) 10 min after the end of the stimulation and monitored behaviorally and electroencephalographically for a further 3 h. The animals were killed 14 days later, and histopathology was assessed.

RESULTS

Neither budipine alone nor TPM at any dose terminated status epilepticus. Despite this, TPM resulted in various degrees of neuroprotection at doses between 40 and 320 mg/kg. Coadministration of budipine with TPM terminated the status epilepticus in all rats. This combination also significantly improved the behavioral profile and prevented status-induced cell death compared with control.

CONCLUSIONS

Budipine and TPM are an effective drug combination in stopping self-sustained status epilepticus, and TPM alone was neuroprotective, despite the continuation of seizure activity.

Recent developments in the pharmacological treatment of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder associated with the loss of dopaminergic neurons in the substantia nigra. The decline of dopamine leads to motor dysfunctions manifested as tremor, rigidity and bradykinesia. The pharmacological treatment of choice for the past 30 years has primarily been the dopamine precursor levodopa. Although it is the most effective treatment available, it is clear that other drugs are needed in order to sustain a therapeutic benefit and to alleviate fluctuations in mobility (i.e., motor fluctuations). Furthermore, there is some evidence that levodopa may hasten the occurrence of motor fluctuations and involuntary movements called dyskinesias. Hence, many clinicians delay the use of levodopa and employ the use of other symptomatic treatments including monoamine oxidase type B (MAO-B) inhibitors and dopamine agonists as first-line therapy in de novo patients. Regardless of treatment, the disease continues to progress as there is still no obvious means of altering disease progression (i.e., no neuroprotective therapy), to restore loss of dopamine (i.e., no restorative therapy) or prevent the disease (i.e. preventative therapy). With disease progression, polypharmacy is common and often employs a combination of antiparkinsonian agents. There have been some key advances in treatment with the advent of MAO-B inhibitors, dopamine agonists and catechol-O-methyltransferase inhibitors; however, the arsenal of drug treatment remains limited. As the mechanism of PD is further elucidated, novel drug treatments will continue to emerge in the areas of preventative, restorative or symptomatic therapy. Despite the purpose of treatment, the ideal pharmacological drug for PD will include the presence of a safe side-effect profile, a simple dosing schedule, the ability to provide symptomatic relief and the potential to alter disease progression. The purpose of this article is to examine upcoming antiparkinsonian drugs in clinical trials based on their pharmacology, safety and efficacy.