Differential actions of nerve growth factor receptors TrkA and p75NTR in a rat model of epileptogenesis

Kindling, an experimental model of epileptogenesis, and activation-induced synaptic reorganization are modulated by nerve growth factor (NGF), but whether NGF acts via its high-affinity receptor TrkA and/or the common neurotrophin receptor p75NTR is unknown. We previously demonstrated, and confirmed in this study, that inhibition of NGF binding to both TrkA and p75NTR inhibited kindling and decreased kindling-induced mossy fiber sprouting. We now report specific inhibition of TrkA.NGF binding, but not p75NTR.NGF binding, retarded perforant path kindling progression. However, mossy fiber sprouting was inhibited by either selective TrkA.NGF or p75NTR.NGF antagonists. Our results suggest that TrkA, but not p75NTR, plays a role in kindling, while both receptors modulate kindling-induced mossy fiber sprouting. This implicates different mechanisms of neurotrophin action on kindling (mediated by TrkA) and neuronal sprouting (mediated by both TrkA and p75NTR) and suggests that sprouting involves kindling-independent neurotrophin action via p75NTR.

Sargachromenol, a novel nerve growth factor-potentiating substance isolated from Sargassum macrocarpum, promotes neurite outgrowth and survival via distinct signaling pathways in PC12D cells

We previously found that the methanol extract of a marine brown alga, Sargassum macrocarpum showed marked nerve growth factor (NGF)-dependent neurite outgrowth promoting activity to PC12D cells. The active substance purified was elucidated to be sargachromenol. The median effective dose (ED50) was 9 microM against PC12D cells in the presence of 10 ng/ml NGF, although it showed no neurotrophic effect on its own. Pretreatment of cells with protein kinase A (PKA) inhibitor or U0126 substantially suppressed the sargachromenol-enhanced neurite outgrowth from PC12D cells, suggesting that the activation of cyclic AMP-mediated protein kinase and mitogen-activated protein (MAP) kinase 1/2 was apparently required for the action of sargachromenol. On the other hand, sargachromenol significantly promoted the survival of neuronal PC12D cells at 0-50 ng/ml NGF in serum-free medium. Neither PKA inhibitor nor U0126 could inhibit the survival supporting effect of sargachromenol, whereas wortmannin significantly blocked the sargachromenol-induced survival supporting effect on neuronal PC12D cells, suggesting that sargachromenol rescued neuronal PC12D cells by activating phosphatidylinositol-3 kinase. These results demonstrate that sargachromenol promotes neuronal differentiation of PC12D cells and supports the survival of neuronal PC12D cells via two distinct signaling pathways.

Syntheses and activities of new C10 beta-turn peptidomimetics

A program to identify small molecules that mimic or disrupt protein-protein interactions led us to design the peptidomimetics 1-3. Solid-phase syntheses of 1-3 were developed. The purities of the crude materials isolated from the resin tend to be highest for the S- and N-compounds 2 and 3 and better than in the corresponding syntheses of peptidomimetics A. The particular dipeptide units incorporated were chosen to correspond with the turn regions of the neurotrophins (e.g., nerve growth factor [NGF] and the neurotrophin factor-3 [NT-3]). Preliminary studies were performed to access the binding of these analogues to Trk receptors and their ability to induce cell survival (just as NGF and NT-3 do). Several active compounds were identified. However, poor water solubilities of some of the other compounds preclude reliable testing. Consequently, solid-phase modifications to the synthetic procedures were investigated to provide access to the derivatives 12-14 in which the aromatic nitro group is replaced by amine, guanidine, or sulfonamide functionalities. The latter are more acceptable pharmacophores than nitro groups and also tend to increase the water solubilities of the peptidomimetics.

Cerebrolysin therapy in Rett syndrome: clinical and EEG mapping study

Based on the suggestion that nerve growth factor plays a core role in the brain maturation process, which is altered in Rett syndrome, we investigate the influence of Cerebrolysin--the brain-derived peptidergic drug - on motor and higher cortical functions in Rett syndrome girls. The open pilot study was performed on nine Rett syndrome girls (aged from 2 years and 2 months to 7 years and 6 months) at stage 3 of the illness, and included both clinical and quantitative EEG evaluations before and after Cerebrolysin treatment. After Cerebrolysin treatment, increases in the behavioral activity, attention level, motor functions, and non-verbal social communication have been shown in Rett syndrome patients. EEG parameters after Cerebrolysin treatment also changed towards normal values, indicating an improvement of the brain functional state. EEG changes included: decrease of theta activity over all cortical regions, increase of beta activity in the frequency band 13-15 Hz, and some restoration of the occipital alpha rhythm (in the narrow 8-9 Hz band). The data obtained suggested possible perspectives of Cerebrolysin in complex therapy of Rett syndrome.