Neurite Outgrowth Inhibitor (NogoA) Is Upregulated in White Matter Lesions of Complex Cortical Malformations.

Complex cortical malformations (CCMs), such as hemimegalencephaly and polymicrogyria, are associated with drug-resistant epilepsy and developmental impairment. They share certain neuropathological characteristics including mammalian target of rapamycin (mTOR) activation and an atypical number of white matter neurons. To get a better understanding of the pathobiology of the lesion architecture, we investigated the role of neurite outgrowth inhibitor A (NogoA), a known regulator of neuronal migration. Epilepsy surgery specimens from 16 CCM patients were analyzed and compared with sections of focal cortical dysplasia IIB (FCD IIB, n = 22), tuberous sclerosis complex (TSC, n = 8) as well as healthy controls (n = 15). Immunohistochemistry was used to characterize NogoA, myelination, and mTOR signaling. Digital slides were evaluated automatically with ImageJ. NogoA staining showed a significantly higher expression within the white matter of CCM and FCD IIB, whereas cortical tubers presented levels similar to controls. Further analysis of possible associations of NogoA with other factors revealed a positive correlation with mTOR and seizure frequency. To identify the main expressing NogoA cell type, double staining revealed dysmorphic neuronal white matter cells. Increased NogoA expression is associated with profound inhibition of neuritic sprouting and therefore contributes to a decrease in neuronal network complexity in CCM patients.

Impaired oligodendroglial turnover is associated with myelin pathology in focal cortical dysplasia and tuberous sclerosis complex.

Conventional antiepileptic drugs suppress the excessive firing of neurons during seizures. In drug-resistant patients, treatment failure indicates an alternative important epileptogenic trigger. Two epilepsy-associated pathologies show myelin deficiencies in seizure-related brain regions: Focal Cortical Dysplasia IIB (FCD) and cortical tubers in Tuberous Sclerosis Complex (TSC). Studies uncovering white matter-pathology mechanisms are therefore urgently needed to gain more insight into epileptogenesis, the propensity to maintain seizures, and their associated comorbidities such as cognitive defects. We analyzed epilepsy surgery specimens of FCD IIB (n = 22), TSC (n = 8), and other malformations of cortical development MCD (n = 12), and compared them to autopsy and biopsy cases (n = 15). The entire lesional pathology was assessed using digital immunohistochemistry, immunofluorescence and western blotting for oligodendroglial lineage, myelin and mTOR markers, and findings were correlated to clinical parameters. White matter pathology with depleted myelin and oligodendroglia were found in 50% of FCD IIB and 62% of TSC cases. Other MCDs had either a normal content or even showed reactive oligodendrolial hyperplasia. Furthermore, myelin deficiency was associated with increased mTOR expression and the lower amount of oligodendroglia was linked with their precursor cells (PDGFRa). The relative duration of epilepsy (normalized to age) also correlated positively to mTOR activation and negatively to myelination. Decreased content of oligodendroglia and missing precursor cells indicated insufficient oligodendroglial development, probably mediated by mTOR, which may ultimately lead to severe myelin loss. In terms of disease management, an early and targeted treatment could restore normal myelin development and, therefore, alter seizure threshold and improve cognitive outcome.

Sildenafil is not a useful modulator of ABCB1 and ABCG2 mediated drug resistance in vivo.

AIM: Recently, sildenafil was reported to be an inhibitor of P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) in vitro. We have now investigated the in vivo potency of sildenafil. METHODS: By using wild-type and Abcb1; Abcg2 knockout mice we have investigated the effect of sildenafil on the brain penetration of two substrate drugs (docetaxel and topotecan). Next we have investigated if sildenafil was able to improve the efficacy of doxorubicin against P-glycoprotein expressing CT26 colon cancer cells in syngeneic Balb/c mice. RESULTS: Sildenafil administered orally at a dose of 50mg/kg did not improve the brain penetration of docetaxel and topotecan, although the plasma level of sildenafil was already much higher than can be achieved in humans. On the other hand, sildenafil increased the plasma levels of the cytotoxic drugs, but not by inhibition of Abcb1 or Abcg2, since this effect was also seen in Abcb1;Abcg2 knockout mice. The brain penetration of sildenafil was more than 20-fold higher in Abcb1;Abcg2 mice versus wild-type mice, indicating that sildenafil is a good substrate of the two transporters. Sildenafil was also not able to improve the efficacy of doxorubicin against subcutaneous CT26 tumours. The doxorubicin level in tumour tissue did increase, but so did the concentration of doxorubicin in plasma and heart. CONCLUSION: These results demonstrate that the potency and specificity of sildenafil as an inhibitor of ABCB1 and ABCG2 is not sufficient to warrant further clinical testing of this agent in combination with anticancer drugs.