BB-14

Peptidomimetics hold a great promise as therapeutic agents for neurodegenerative disorders. We previously described a Nerve Growth Factor (NGF)-like peptide, now named BB14, which was found to act as a strong TrkA agonist and to be effective in the sciatic nerve injury model of neuropathic pain. In this report we present the effects of BB14 in reducing reactive astrocytosis and reverting neuroplastic changes of the glutamate/GABAergic circuitry in the lumbar spinal cord following spared nerve injury (SNI) of the sciatic nerve. Immunohistochemical analysis of spinal cord sections revealed that SNI was associated with increased microglial (Iba1) and astrocytic (GFAP) responses, indicative of reactive gliosis. These changes were paralleled by (i) decreased glial aminoacid transporters (GLT1 and GlyT1) and increased levels of (ii) neuronal glutamate transporter EAAC1, (iii) neuronal vesicular GABA transporter (vGAT) and (iv) the GABAergic neuron marker GAD65/67. A remarkable increase of the Glutamate/GABA ratio and the reduction of glutathione (GSH) levels were also indicative of modifications of glial function in neuroprotection. All these molecular changes were found to be linked to an alteration of endogenous NGF metabolism, as demonstrated by decreased levels of mature NGF, increase of proNGF and increased activity of NGF-degrading methallo-proteinases (MMPs). Biochemical alterations and SNI-related neuropathic behavior, characterized by allodynia and hyperalgesia, were reversed by 7-days i.t. administration of the NGF-like peptide BB14, as well as by increasing endogenous NGF levels by i.t. infusion of GM6001, a MMPs inhibitor. All together, while confirming the correlation between reactive astrogliosis and perturbation of synaptic circuitry in the SNI model of peripheral nerve injury, these data strongly support the beneficial effect of BB14 in reducing reactive astrogliosis and restoring synaptic homeostasis under pathological conditions linked to alteration of NGF availability and signaling, thereby suggesting a potential role of BB14 as a therapeutic agent.

Endothelial cells were isolated from rat brain microvessels and grown in vitro. They expressed a high density of [125I‐Tyr4]bombesin receptors (Bmax= 0.9 pmol/mg protein) with an apparent Kd value of 10nM. The pharmacological profile of inhibition of the specific [125I‐Tyr4]bombesin binding [bombesin = neuromedin B > gastrin releasing peptide (GRP)] was consistent with the presence of a neuromedin‐B‐preferring receptor. Addition of bombesin, neuromedin B and GRP increased the activity of phospholipase C as measured by the production of total inositol phosphates and from intracellular Ca2+ measurements. They increase 86Rb4 uptake by the Na+, K+, 2C1− cotransporter and by a charybdotoxin‐sensitive, Ca2+‐activated K+ channel and 22Na+ uptake by the Na+/H+ exchanger. The pharmacological profiles of activation of phospholipase C., Na+, K+, 2C1 cotransport and Na+/H+ exchange by bombesin‐like peptide were consistent with an involvement of the neuromedin‐B‐preferring receptor characterized in binding experiments. It is suggested that one of the actions of neuromedin B in brain vessels could be to control K+ secretion by the blood/brain barrier.