Alberto Lazarowski

Genetic variants in C5 and poor response to eculizumab.

BACKGROUND Eculizumab is a humanized monoclonal antibody that targets complement protein C5 and inhibits terminal complement-mediated hemolysis associated with paroxysmal nocturnal hemoglobinuria (PNH). The molecular basis for the poor response to eculizumab in a small population of Japanese patients is unclear. METHODS We assessed the sequences of the gene encoding C5 in patients with PNH who had either a good or poor response to eculizumab. We also evaluated the functional properties of C5 as it was encoded in these patients. RESULTS Of 345 Japanese patients with PNH who received eculizumab, 11 patients had a poor response. All 11 had a single missense C5 heterozygous mutation, c.2654G → A, which predicts the polymorphism p.Arg885His. The prevalence of this mutation among the patients with PNH (3.2%) was similar to that among healthy Japanese persons (3.5%). This polymorphism was also identified in a Han Chinese population. A patient in Argentina of Asian ancestry who had a poor response had a very similar mutation, c.2653C → T, which predicts p.Arg885Cys. Nonmutant and mutant C5 both caused hemolysis in vitro, but only nonmutant C5 bound to and was blocked by eculizumab. In vitro hemolysis due to nonmutant and mutant C5 was completely blocked with the use of N19-8, a monoclonal antibody that binds to a different site on C5 than does eculizumab. CONCLUSIONS The functional capacity of C5 variants with mutations at Arg885, together with their failure to undergo blockade by eculizumab, account for the poor response to this agent in patients who carry these mutations. (Funded by Alexion Pharmaceuticals and the Ministry of Health, Labor, and Welfare of Japan.).

ABC Transporters during Epilepsy and Mechanisms Underlying Multidrug Resistance in Refractory Epilepsy

Summary:  It is estimated 20–25% of the epileptic patients fails to achieve good control with the different antiepileptic drugs (AEDs) treatments, developing refractory epilepsy (RE). Discovered first in cancer, the activity of P‐glycoprotein (P‐gp) and others ABC transporters as multidrug‐resistance‐associated proteins (MRPs) and breast cancer resistant protein (BCRP) are directly related with the refractoriness. We have observed the overexpression of these all transporters in the brain of patients with RE, and according with other authors, all these data suggests an active drug efflux from brain. Both constitutive and seizure induced brain P‐gp overexpression was also suggested. As confirmation of these clinical evidences, different models of experimental epilepsy have demonstrated P‐gp overexpression on blood brain barrier (BBB) and brain parenchyma cells, as astrocytes and neurons. In our model, early P‐pg detection in vessel‐related cells and later additional P‐gp detection in neurons, correlated with the gradual loss of protective effect of phenytoin. The progressive neuronal P‐gp expression, depending on intensity and time‐constancy of seizure‐injury, was in agreement with the development of “P‐gp‐positive seizure‐axis” proposed by Kwan & Brodie, who also showed that the development of RE directly correlated with the number and frequency of seizures before initiation of drug therapy. P‐gp expression in excretory organs suggests that P‐gp have a central role in drug elimination. Persistent low levels of AEDs in plasma and P‐gp brain overexpression in several RE pediatric patients were reported. We also observed in adult RE patients, an increased liver clearance of 99mTc‐hexakis‐2‐methoxyisobutylisonitrile (99mTc‐MIBI) (a P‐gp substrate), and the surgically treated cases showed P‐gp brain overexpression. These results suggest the systemic hyperactivity of P‐gp in RE patients, including brain P‐gp over‐expression should be suspected when persistent subtherapeutic levels of AEDs in plasma are detected. P‐gp neuronal expression described in both clinical and experimental reports indicates that additional mechanisms could be operative from seizure‐affected P‐gp‐positive neurons, due to AEDs targets are expressed at membrane level. An alternative mechanism was demonstrated in P‐gp‐expressed cells that exhibit lower membrane potential (Δψ0=−10 to –20) compared to normal physiological Δψ0 of –60 mV. Under this situation and irrespective to the P‐gp pharmacoresistant property or type of drug treatment selected, P‐gp‐expressed neurons could increase their sensitivity to new seizures perhaps as an epileptogenic mechanism. The understanding of properties of these ABC transporters can offer new tools for better selection of more effective preventive or therapeutic strategies and avoid the invasive surgical treatments for RE.

Tuberous sclerosis associated with MDR1 gene expression and drug-resistant epilepsy

Intractable seizures are the most common manifestation in severe cases of tuberous sclerosis. Multidrug resistance type 1 (MDR1) gene expression is directly linked to the resistance of tumor cells to chemotherapy as the major cause of treatment failure, but it has not been reported in tuberous sclerosis cells nor has the relationship between the MDR1 gene and antiepileptic drugs been described. A 4-month-old female is described with poorly controlled seizures secondary to tuberous sclerosis. The patient was treated with antiepileptic drugs, including phenytoin, phenobarbital, and lorazepam, without improvement of symptoms. Phenytoin blood levels were invariably subtherapeutic and ranged from 0.45 to 3.55 microg/mL, despite several consecutive intravenous loading doses. Surgical treatment with total resection of the brain lesions was performed as a last resort. Immunohistochemical analysis of the resected tissues revealed high levels of P-glycoprotein 170 expression, the product of the MDR1 gene. Both MDR1 gene expression and persistently low phenytoin levels likely share a common pathway liable to induce drug-resistant epilepsy.

Intermittent hypoxia during sleep induces reactive gliosis and limited neuronal death in rats: implications for sleep apnea.

J. Neurochem. (2010) 112, 854–869.

Multidrug resistance proteins in tuberous sclerosis and refractory epilepsy.

Tuberous sclerosis is an autosomal dominant syndrome characterized by seizures that are refractory to medication in severely affected individuals. The mechanism involved in drug resistance in tuberous sclerosis is unknown. The proteins MDR-1 (multidrug resistance) and MRP-1 (multidrug resistance-associated protein-1) are linked to chemotherapy resistance in tumor cells. However, the relationship between refractoriness to antiepileptic drugs and MDR-1 or MRP-1 brain expression has been poorly studied. We have previously described a case of tuberous sclerosis with refractory epilepsy that expressed multidrug resistance gene (MDR-1) in tuber cells from epileptogenic brain lesion. In this retrospective study, we describe the expression of MDR-1 and MRP-1 in the epileptogenic cortical tubers of three pediatric patients with tuberous sclerosis and refractory epilepsy surgically treated. Monoclonal antibodies for MDR-1 and MRP-1 proteins were used for immunohistochemistry. In epileptogenic cortical tuber brain specimens, MDR-1 and MRP-1 proteins were strongly immunoreactive in abnormal balloon cells, dysplastic neurons, astrocytes, microglial cells, and some blood-brain vessels. A more extensive MDR-1 immunoreactivity was observed. These data suggest that refractory epilepsy phenotype in tuberous sclerosis can be associated with the expression of both multidrug resistance MDR-1 and MRP-1 transporters in epileptogenic cortical tubers.

Neuronal and Glial Expression of the Multidrug Resistance Gene Product in an Experimental Epilepsy Model

Abstract1. Failure of anticonvulsive drugs to prevent seizures is a common complication of epilepsy treatment known as drug-refractory epilepsy but their causes are not well understood. It is hypothesized that the multidrug resistance P-glycoprotein (Pgp-170), the product of the MDR-1 gene that is normally expressed in several excretory tissues including the blood brain barrier, may be participating in the refractory epilepsy.2. Using two monoclonal antibodies against Pgp-170, we investigated the expression and cellular distribution of this protein in the rat brain during experimentally induced epilepsy. Repeated seizures were induced in male Wistar rats by daily administration of 3-mercaptopropionic acid (MP) 45 mg/kg i.p. for either 4 days (MP-4) or 7 days (MP-7). Control rats received an equivalent volume of vehicle. One day after the last injection, rats were sacrificed and brains were processed for immunohistochemistry for Pgp-170. As it was previously described, Pgp-170 immunostaining was observed in some brain capillary endothelial cells of animals from control group.3. Increased Pgp-170 immunoreactivity was detected in MP-treated animals. Besides the Pgp-170 expressed in blood vessels, neuronal, and glial immunostaining was detected in hippocampus, striatum, and cerebral cortex of MP-treated rats. Pgp-170 immunolabeled neurons and glial cells were observed in a nonhomogeneous distribution. MP-4 animals presented a very prominent Pgp-170 immunostaining in the capillary endothelium, surrounding astrocytes and some neighboring neurons while MP-7 group showed increased neuronal labeling.4. Our results demonstrate a selective increase in Pgp-170 immunoreactivity in the brain capillary endothelial cells, astrocytes, and neurons during repetitive MP-induced seizures.5. The role for this Pgp-170 overexpression in endothelium and astrocytes as a clearance mechanism in the refractory epilepsy, and the consequences of neuronal Pgp-170 expression remain to be disclosed.

Nimodipine restores the altered hippocampal phenytoin pharmacokinetics in a refractory epileptic model

The present work was undertaken to examine the central pharmacokinetics of phenytoin (PHT) in an experimental model of epilepsy, induced by administration of 3-mercaptopropionic acid (MP), and possible participation of P-glycoprotein in this model of epilepsy. Repeated seizures were induced in male Wistar rats by injection of 3-MP (45 mg kg(-1), i.p.) during 10 days. Control rats (C) were injected with saline solution. In order to monitor extracellular PHT levels, either a shunt microdialysis probe or a concentric probe was inserted into carotid artery or hippocampus, respectively. All animals were administered with PHT (30 mg kg(-1), i.v.) 30 min after intraperitoneal administration of vehicle (V) or nimodipine (NIMO, 2 mg kg(-1)). No differences were found in PHT plasma levels comparing all experimental groups. In pre-treated rats with V, hippocampal PHT concentrations were lower in MP (maximal concentration, C(max): 2.7+/-0.3 microg ml(-1), p<0.05 versus C rats) than in C animals (C(max): 5.3+/-0.9 microg ml(-1)). Control rats pre-treated with NIMO showed similar results (C(max): 4.5+/-0.8 microg ml(-1)) than those pre-treated with V. NIMO pre-treatment of MP rats showed higher PHT concentrations (C(max): 6.8+/-1.0 microg ml(-1), p<0.05) when compared with V pre-treated MP group. Our results indicate that central pharmacokinetics of PHT is altered in MP epileptic rats. The effect of NIMO on hippocampal concentrations of PHT suggests that P-glycoprotein has a role in reduced central bioavailability of PHT in our epileptic refractory model.

Neuronal mdr-1 gene expression after experimental focal hypoxia: A new obstacle for neuroprotection?

Neuronal damage after stroke-associated brain hypoxia is a leading cause of long-term disability and death. The refractoriness to therapeutic strategies for neuroprotection after 3 h post brain ischemia is poorly understood. P-glycoprotein (P-gp), the multidrug resistance gene (MDR-1) product is normally expressed at blood-brain-barrier. P-gp neuronal expression has been demonstrated in refractory epilepsy and after brain ischemia. In this report we investigated the hypoxia-induced neuronal P-gp expression after local injection of CoCl(2) (1-200 mM) in the fronto-parietal cortex of male adult rats (Bregma -1.30 mm) by stereotaxic surgery. P-gp immunostaining of brain slides was analyzed using specific monoclonal antibodies and double immunolabeling was done with specific astrocytic and neuronal markers. Five days after injection of 1 mM CoCl(2), P-gp expression surrounding the lesion site was observed in neurons, astrocytic end-foot on capillary blood vessels and endothelial cells on blood vessels. Higher CoCl(2) doses (200 mM) resulted in additional P-gp immunostaining of the entire astrocytic and neuronal cytoplasm. Electron microscopy (EM) studies showed alterations in neurons as early as 6 h after the CoCl(2) injection. P-gp expression in hypoxic neurons and astrocytic end-foot could potentially impair of drugs access to the brain parenchyma thus suggesting the presence of two P-gp-based pumping systems (one in astrocytes and other in the hypoxic neurons) that are able to behave as a previously unnoticed obstacle for pharmacological strategies of neuroprotection.

Neuronal MDR-1 gene expression and persistent low levels of anticonvulsants in a child with refractory epilepsy.

It is estimated that 20–25% of epileptic patients fail to achieve good control with antiepileptic drug (AED) treatment; thus, refractory epilepsy (RE) has been described in patients who have adequate therapeutic levels of AEDs without control of seizures. Multidrug resistance genes have been reported to be highly expressed in brain of patients with RE. Persistent low plasma levels of AEDs and high brain expression of the multidrug resistance product P-glycoprotein (P-gp) have been previously communicated in a case report of RE secondary to tuberous sclerosis. Here, the authors report a case of an 8-year-old boy diagnosed with partial RE with focal seizures who was admitted to hospital for a severe episode of subintrant crisis. The patient received polytherapy with carbamazepine (CBZ), phenytoin (PHT), and valproic acid (VA); however, habitual doses of these AEDs failed to control the patients symptoms. AED blood levels were monitored for 25 consecutive days and showed low values in 8/25 (33%) for CBZ, 10/25 (40%) for PHT, and 25/25 (100%) for VA of samples studied. Because the patient developed focal status epilepticus, surgical treatment by callosotomy was done, resulting in a significant improvement in epileptic symptoms. The immunostaining of brain specimens showed significantly increased expression of P-gp not only in vascular endothelial cells and related astrocytes but also in neurons. Overexpression of P-gp in the brain does not explain the low blood levels of AEDs described in these cases. Different mechanisms such as drug–drug interactions and drug transporters can be involved in the results observed. The P-gp overexpression and/or its pharmacologic induction should be considered as a potential mechanism responsible for drug resistance to epilepsy treatment and highly suspected in patients with persistent subtherapeutic AEDs plasma levels.

Potential role of multidrug resistant proteins in refractory epilepsy and antiepileptic drugs interactions

Abstract Epilepsy is a common neurological disorder. About one-third of epilepsy patients have a multidrug resistance (MDR) phenotype and develop refractory epilepsy (RE). Changes in the properties of the antiepileptic drugs (AEDs) targets resulting in reduced drug sensitivity, can’t explain the MDR phenotype. This particular refractoriness is now attributed to overexpression of multidrug transporters in brain, leading to impaired access of AEDs to CNS targets, and it was documented in both human as well as in experimental models of RE. Single nucleotide polymorphism (SNP) identified in the MDR1-ABCB1gene (C3435T/CC-genotype) is associated with increased intestinal expression of P-glycoprotein (P-gp) that affects levels of AEDs in plasma. The functional studies of P-gp using P-gp inhibitors could show the still unclear clinical impact of ABCB1 polymorphisms on AEDs resistance. Some drug-drug interactions previously believed to be cytochrome P450 (CYP) mediated are now also considered to be due to the modulation of multidrug-transporters. Because in certain cases pharmacoresistance can be overcome by add-on therapy, co-administered P-gp inhibitors could contribute to the effectiveness of AEDs treatment in RE. And in this regard, perhaps we can postulate to P-gp as a new clinical therapeutic target in multidrug-refractory epilepsy.