Low-Molecular Neurotrophin-3 Mimetics with Different Patterns of Postreceptor Signaling Activation Attenuate...

The accumulated evidence suggests that varying levels of tyrosine kinase receptor signaling pathway activity may regulate opiate-associated neuroadaptation of noradrenergic system. Neurotrophin-3 (NT-3) interacts with tropomyosin receptor kinases (TRKs), binding mainly to TRKC receptors, which are expressed within noradrenergic neurons in the blue spot (locus coeruleus, LC). Considering the difficulties in delivering full-length neurotrophins to the CNS after systemic administration, low-molecular mimetics of loop 4 in NT-3, hexamethylenediamide bis-(N-monosuccinyl-L-asparaginyl-L-asparagine) (GTS-301), and hexamethylenediamide bis-(N-γ-oxybutyryl-L-glutamyl-L-asparagine) (GTS-302), activating TRKC and TRKB receptors, were synthesized. The aim of the study is comparative examination of the effects of NT-3 dipeptide mimetics on the signs of morphine withdrawal in outbred white rats with opiate dependence, as well as investigation of activation of postreceptor signaling pathways by the mimetics. Dipeptides GTS-301 and GTS-302 after acute administration at doses of 0.1, 1.0, and 10.0 mg/kg (i.p., intraperitoneal) had a dose-dependent effect on the specific morphine withdrawal symptoms with the most effective dose being 1.0 mg/kg. Maximum decrease in the total index of morphine withdrawal syndrome for GTS-301 was 31.3% and for GTS-302 - 41.4%. Unlike GTS-301, GTS-302 weakened mechanical allodynia induced by morphine withdrawal, reducing tactile sensitivity. When studying activation of the postreceptor signaling pathways by the NT-3 mimetics in the HT-22 hippocampal cell culture, a different pattern of postreceptor signaling was shown: GTS-302 (10^-6 M), similar to NT-3, activates all three MAPK/ERK, PI3K/AKT/mTOR, and PLCγ1 pathways, while GTS-301 (10^-6 M) triggers only MAPK/ERK and PLCγ1 pathways. Thus, the identified features of attenuation of the morphine withdrawal syndrome in the rats under GTS-301 and GTS-302 effects could be associated with different activation pattern of the postreceptor pathways.