Protective effect of riluzole on MPTP-induced depletion of dopamine and its metabolite content in mice

Effect of ciprofloxacin and grapefruit juice on oral pharmacokinetics of riluzole in Wistar rats

Objectives

The objective of this study was to explore potential drug–drug/food interactions of ciprofloxacin and grapefruit juice, known hepatic cytochrome P450 (CYP) 1A2 inhibitors, on single-dose oral pharmacokinetics of riluzole, a substrate of CYP 1A2 enzymes.

Methods

Pharmacokinetic parameters of riluzole were determined in Wistar rats after single-dose co-administration with ciprofloxacin and grapefruit juice. In-vitro metabolic inhibition studies using rat and human liver microsomes and intestinal absorption studies of riluzole in a rat everted gut-sac model were conducted to elucidate the mechanism of interaction. A validated HPLC method was employed to quantify riluzole in the samples obtained in various studies.

Key findings

Co-administration of ciprofloxacin with riluzole caused significant increase in systemic exposure of riluzole (area under the curve, maximum plasma concentration and mean residence time were found to increase). Co-administration of grapefruit juice with riluzole did not cause any significant difference in the pharmacokinetic parameters of riluzole. In-vitro metabolism studies demonstrated significant inhibition of riluzole metabolism when it was co-incubated with ciprofloxacin or grapefruit juice. No significant change was observed in apparent permeability of riluzole.

Conclusions

Co-administration of ciprofloxacin with riluzole increases the systemic levels of riluzole and thereby the oral pharmacokinetic properties of riluzole while co-administration of grapefruit juice with riluzole has no significant effect.

Group III and subtype 4 metabotropic glutamate receptor agonists: discovery and pathophysiological applications in Parkinson's disease

Restoring the balance between excitatory and inhibitory circuits in the basal ganglia, following the loss of dopaminergic (DA) neurons of the substantia nigra pars compacta, represents a major challenge to treat patients affected by Parkinson's disease (PD). The imbalanced situation in favor of excitation in the disease state may also accelerate excitotoxic processes, thereby representing a potential target for neuroprotective therapies. Reducing the excitatory action of glutamate, the major excitatory neurotransmitter in the basal ganglia, should lead to symptomatic improvement for PD patients and may promote the survival of DA neurons. Recent studies have focused on the modulatory action of metabotropic glutamate (mGlu) receptors on neurodegenerative diseases including PD. Group III mGlu receptors, including subtypes 4, 7 and 8, are largely expressed in the basal ganglia. Recent studies highlight the use of selective mGlu4 receptor positive allosteric modulators (PAMs) for the treatment of PD. Here we review the effects of newly-designed group-III orthosteric agonists on neuroprotection, neurorestoration and reduction of l-DOPA induced dyskinesia in animal models of PD. The combination of orthosteric mGlu4 receptor selective agonists with PAMs may open new avenues for the symptomatic treatment of PD. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Riluzole suppresses experimental autoimmune encephalomyelitis: implications for the treatment of multiple sclerosis

Recent studies suggest that glutamate neurotoxicity is involved in the pathogenesis of multiple sclerosis (MS), and that treatment with glutamate receptor (AMPA/kainate) antagonists inhibits experimental autoimmune encephalomyelitis (EAE), the conventional model of MS. Therefore, we examined whether riluzole, an inhibitor of glutamate transmission, affects the pathogenesis and clinical features of MS-like disease in myelin oligodendrocyte glycoprotein (MOG)-induced EAE in mice. Here we report that riluzole (10 mg/kgx2/day, i.p.), administered before and even after the appearance of clinical symptoms, dramatically reduced the clinical severity of MOG-induced EAE, while all the MOG-immunized control mice developed significant clinical manifestations. Moreover, the riluzole-treated mice demonstrated only mild focal inflammation, and less demyelination, compared to MOG-treated mice, using histological methods. Furthermore, riluzole markedly reduced axonal disruption, as assessed by Bielshowesky's silver staining and by antibodies against non-phosphorylated neurofilaments (SMI-32). No difference was detected in the immune system potency, as T-cell proliferative responses to MOG were similar in both groups. In conclusion, our study demonstrates, for the first time, that riluzole can reduce inflammation, demyelination and axonal damage in the CNS and attenuate the clinical severity of MOG-induced EAE. These results suggest that riluzole, a drug used in amyotrophic lateral sclerosis (ALS), might be beneficial for the treatment of MS.

Therapeutic effect of neuronal nitric oxide synthase inhibitor (7-nitroindazole) against MPTP neurotoxicity in mice

Effects of neuronal nitric oxide synthase (nNOS) inhibitor (7-nitroindazole), nonselective NOS inhibitor (N(G)-nitro-L-arginine methyl ester; L-NAME), and monoamine oxidase inhibitor (pargyline) were studied on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. The mice received four intraperitoneal injections of MPTP at 1-h intervals. A significant depletion in dopamine and DOPAC concentration was observed in the striatum from 1 day after MPTP treatment. The pretreatment of 7-nitroindazole and pargyline, but not L-NAME, dose-dependently protected against MPTP-induced depletion in dopamine content 3 days after MPTP treatment. Our histochemical study also showed that 7-nitroindazole and pargyline can prevent a marked decrease in the nigral cells and a marked increase in astrocytes in striatum 7 days after MPTP treatment. The protective effect of 7-nitroindazole against MPTP-induced dopamine and DOPAC depletion in the striatum was not attenuated by intraperitoneal pretreatment with L-arginine. Furthermore, the posttreatment of 7-nitroindazole or pargyline protected against MPTP-induced depletion of dopamine content. These results demonstrate that the protective mechanism by which 7-nitroindazole counteracts MPTP neurotoxicity in mice may be due not only to inhibition of nNOS, but also to MAO-B inhibition. Furthermore, our study suggests that the posttreatment of 7-nitroindazole and pargyline can prevent a significant decrease in dopamine levels in the striatum of MPTP-treated mice. These findings have important implications for the therapeutic time window and choice of nNOS or MAO inhibitors in patients with Parkinson's disease.