Acanthoscurria gomesiana spider-derived synthetic mygalin in the dorsal raphe nucleus modulates acute and chronic pain

Mygalin, a diacylspermidine that is naturally found in the hemolymph of the spider Acanthoscurria gomesiana, is of interest for development as a potential analgesic. Previous studies have shown that acylpolyamines modulate glutamatergic receptors with the potential to alter pain pathways. This study aimed to evaluate the effects of mygalin on acute and chronic pain in rodents. For evaluation of acute pain, Wistar rats were subjected to tail-flick and hot-plate nociceptive tests. For the evaluation of chronic neuropathic pain, a partial ligation of the sciatic nerve was performed and, 21 days later, animals were examined in hot-plate, tail-flick, acetone, and von Frey tests. Either Mygalin or vehicle was microinjected in the dorsal raphe nucleus (DRN) before the tests. Another group was pretreated with selective antagonists of glutamate receptors (LY 235959, MK-801, CNQX, and NBQX). Mygalin decreases nociceptive thresholds on both acute and chronic neuropathic pain models in all the tests performed. The lowest dose of mygalin yielded the most effective nociception, showing an increase of 63% of the nociceptive threshold of animals with neuropathic chronic pain. In conclusion, mygalin microinjection in the DRN results in antinociceptive effect in models of neuropathic pain, suggesting that acylpolyamines and their derivatives, such as this diacylspermidine, could be pursued for the treatment of neuropathic pain and development of selective analgesics.

Antagonism of NMDA receptors by butanesulfonyl-homospermine guanidine and neuroprotective effects in in vitro and in vivo

The polyamine derivative BsHSPMG (butanesulfonyl-homospermine with guanidine group) was found to inhibit macroscopic currents strongly at heteromeric N-methyl-D-aspartate (NMDA) receptors (NR1/NR2A and NR1/NR2B) and Ca(2+)-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (homomeric glutamate receptor 1) receptors expressed in Xenopus laevis oocytes on voltage-clamp recording. The IC(50) values of BsHSPMG for NR1/NR2A, NR1/NR2B, NR1/NR2C, and NR1/NR2D receptors were 0.016, 0.021, 5.4, and 9.0 μM, respectively. BsHSPMG inhibited the activity of NR1/NR2A and NR1/NR2B receptors more strongly and did it for those of NR1/NR2C and NR1/NR2D receptors more weakly than a therapeutic drug of Alzheimer's disease, memantine. The inhibition by BsHSPMG was voltage-dependent, since it was prominent at -100 mV compared to that at -20 mV. Mutations including NR1 N616Q, E621Q, N650A, L655A, T807C, NR2B W559L, M562S, W607L, N616Q, and V620E, among others, reduced the inhibition by BsHSPMG, suggesting that BsHSPMG penetrates the channel pore of NMDA receptors deeply. The toxicity of BsHSPMG in neuroblastoma SH-SY5Y cells was much weaker than that of memantine. The effect of BsHSPMG was measured on the focal cerebral ischemia induced by occlusion (1 h) of the middle cerebral artery in mice. BsHSPMG applied before or after occlusion greatly reduced the volume of infarct in mice. These findings demonstrate that BsHSPMG penetrates the NMDA channel pore and exhibits neuroprotective effects against excitatory toxicity in mice.