Role of the Guanidinium Groups in Ligand–Receptor Binding of Arginine-Containing Short Peptides to the Slow Sodium Channel: Quantitative Approach to Drug Design of Peptide Analgesics

Abstract

Several arginine-containing short peptides have been shown by the patch-clamp method to effectively modulate the NaV1.8 channel activation gating system, which makes them promising candidates for the role of a novel analgesic medicinal substance. As demonstrated by the organotypic tissue culture method, all active and inactive peptides studied do not trigger the downstream signaling cascades controlling neurite outgrowth and should not be expected to evoke adverse side effects on the tissue level upon their medicinal administration. The conformational analysis of Ac-RAR-NH2, Ac-RER-NH2, Ac-RAAR-NH2, Ac-REAR-NH2, Ac-RERR-NH2, Ac-REAAR-NH2, Ac-PRERRA-NH2, and Ac-PRARRA-NH2 has made it possible to find the structural parameter, the value of which is correlated with the target physiological effect of arginine-containing short peptides. The distances between the positively charged guanidinium groups of the arginine side chains involved in intermolecular ligand–receptor ion–ion bonds between the attacking peptide molecules and the NaV1.8 channel molecule should fall within a certain range, the lower threshold of which is estimated to be around 9 Å. The distance values have been calculated to be below 9 Å in the inactive peptide molecules, except for Ac-RER-NH2, and in the range of 9–12 Å in the active peptide molecules.

Role of the Rhamnosyl Residue of Ouabain in the Activation of the Na,K-ATPase Signaling Function

“…In our opinion, the opioid crisis could be overcome only by using safe substances of endogenous nature. As an example, a number of short peptides were demonstrated at very low concentrations to modulate the Na V 1.8 channel activation gating system in nociceptors [19,20]. According to our data, another potentially very effective substance is EO, the Ca 2+ chelate complex of ouabain, which is also capable of modulating the Na V 1.8 channels via activation of the NKA signaling function (Kd = 1 nM) [13,21].…”

“…The total number of rats utilized to register the data presented herein was 42. The compositions of the extracellular and intracellular solutions used when studying the Na V 1.8 currents were described earlier [11,19,30]. The whole-cell recording configuration of the patchclamp method [31] was implemented using the hardware-software setup that comprised the patch-clamp L/M-EPC 7 amplifier, the digital-analog and analog-digital converters.…”

“…According to the Almers theory, Z eff can be easily evaluated from the tangent of the slope of the asymptote passing through the very first points of the L(E) function due to the application of Boltzmann distribution. This approach is described in more detail elsewhere [5,6,11,19,21].…”

“…Four stable conformations were detected for both OUA and OBG, differing by the conformation of the ring A (the chair or the twist) and orientation of the lactone ring E, which is allowed to rotate freely with respect to the steroid core. For OBG-Ca, six conformations and two possible modes of cation chelation were identified: Ca 2+ can be chelated either by four (O 1 , O 3 , O 5 , O 19 ) or by three (O 1 , O 11 , O 19 ) oxygen atoms. The respective chelation modes were designated further as OBG-Ca 4 and OBG-Ca 3 .…”

“…For OBG-Ca, six conformations and two possible modes of cation chelation were identified: Ca 2+ can be chelated either by four (O 1 , O 3 , O 5 , O 19 ) or by three (O 1 , O 11 , O 19 ) oxygen atoms. The respective chelation modes were designated further as OBG-Ca4 and OBG-Ca3.…”