New anticonvulsant candidates prevent P-glycoprotein (P-gp) overexpression in a pharmacoresistant seizure model in mice.

Despite the approval of a considerable number of last generation antiepileptic drugs (AEDs) (only in the last decade, six drugs have gained Food and Drug Administration approval), the global figures of seizure control have seemingly not improved, and available AED can still be regarded as symptomatic treatments. Fresh thinking in AEDs drug discovery, including the development of drugs with novel mechanisms of action, is required to achieve truly innovative antiepileptic medications. The transporter hypothesis proposes that inadequate penetration of AEDs across the blood-brain barrier, caused by increased expression of efflux transporters such as P-glycoprotein (P-gp), contributes to drug-resistant epilepsy. Neuroinflammation due to high levels of glutamate has been identified as one of the causes of P-gp upregulation, and several studies in animal models of epilepsy suggest that antiinflammatory drugs might prevent P-gp overexpression and, thus, avoid the development of refractory epilepsy. We have applied ligand-based in silico screening to select compounds that exert dual anticonvulsant and antiinflammatory effects. Five of the hits were tested in animal models of seizure, with protective effects. Later, two of them (sebacic acid (SA) and gamma-decanolactone) were submitted to the recently described MP23 model of drug-resistant seizures. All in all, SA displayed the best profile, showing activity in the maximal electroshock seizure (MES) and pentylenetetrazol (PTZ) seizure models, and reversing resistance to phenytoin (PHT) and decreasing the P-gp upregulation in the MP23 model. Furthermore, pretreatment with SA in the pilocarpine status epilepticus (SE) model resulted in decreased histamine release in comparison with nontreated animals. This is the first report of the use of the MP23 model to screen for novel anticonvulsant compounds that may avoid the development of P-gp-related drug resistance.

Protective effects of progesterone administration on axonal pathology in mice with experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE), an induced model of Multiple Sclerosis presents spinal cord demyelination, axonal pathology and neuronal dysfunction. Previous work has shown that progesterone attenuated the clinical severity, demyelination and neuronal dysfunction of EAE mice (Garay et al., J. Steroid Biochem. Mol. Biol., 2008). Here we studied if progesterone also prevented axonal damage, a main cause of neurological disability. To this end, some axonal parameters were compared in EAE mice pretreated with progesterone a week before immunization with MOG(40-54) and in a group of steroid-free EAE mice. On day 16th after EAE induction, we determined in both groups and in control mice: a) axonal density in semithin sections of the spinal cord ventral funiculus; b) appearance of amyloid precursor protein (APP) immunopositive spheroids as an index of damaged axons; c) levels of the growth associated protein GAP43 mRNA and immunopositive cell bodies, as an index of aberrant axonal sprouting. Steroid-naive EAE mice showed decreased axonal density, shrunken axons, abundance of irregular vesicular structures, degenerating APP+ axons, increased expression of GAP43 mRNA and immunoreactive protein in motoneurons. Instead, EAE mice receiving progesterone treatment showed increased axonal counts, high proportion of small diameter axons, reduced APP+ profiles, and decreased GAP43 expression. In conclusion, progesterone enhanced axonal density, decreased axonal damage and prevented GAP43 hyperexpression in the spinal cord of EAE mice. Thus, progesterone also exerts protective effects on the axonal pathology developing in EAE mice.