Effect of Gambierol and Its Tetracyclic and Heptacyclic Analogues in Cultured Cerebellar Neurons: A Structure–Activity Relationships Study

Abstract

The polycyclic ether class of marine natural products has attracted the attention of researchers due to their complex and large chemical structures and diverse biological activities. Gambierol is a marine polycyclic ether toxin, first isolated along with ciguatoxin congeners from the dinoflagellate Gambierdiscus toxicus. The parent compound gambierol and the analogues evaluated in this work share the main crucial elements for biological activity, previously described to be the C28=C29 double bond within the H ring and the unsaturated side chain [Fuwa, H., Kainuma, N., Tachibana, K., Tsukano, C., Satake, M., and Sasaki, M. (2004) Diverted total synthesis and biological evaluation of gambierol analogues: Elucidation of crucial structural elements for potent toxicity. Chem. Eur. J. 10, 4894-4909]. With the aim to gain a deeper understanding of the cellular mechanisms involved in the biological activity of these compounds, we compared its activity in primary cultured neurons. The three compounds inhibited voltage-gated potassium channels (Kv) in a concentration-dependent manner and with similar potency, caused a small inhibition of voltage-gated sodium channels (Nav), and evoked cytosolic calcium oscillations. Moreover, the three compounds elicited a "loss of function" effect on Kv channels at concentrations of 0.1 nM. Additionally, both the tetracyclic and the heptacyclic derivatives of gambierol elicited synchronous calcium oscillations similar to those previously described for gambierol in cultured cerebellar neurons. Neither gambierol nor its tetracyclic derivative elicited cell toxicity, while the heptacyclic analogue caused a time-dependent decrease in cell viability. Neither the tetracyclic nor the heptacyclic analogues of gambierol exhibited lethality in mice after ip injection of 50 or 80 μg/kg of each compound. Altogether, the results presented in this work support an identical mechanism of action for gambierol and its tetracyclic and heptacyclic analogues and indicate a "loss of function" effect on potassium channels even after administration of the three compounds at subnanomolar concentrations. In addition, because gambierol is known to stabilize the closed state of Kv3 channels, the results presented in this paper may have implications for understanding of channel functions and for future development of therapies against ciguatera poisoning and potassium channel-related diseases.

Gambierol Inhibition of Voltage-Gated Potassium Channels Augments Spontaneous Ca2+Oscillations in Cerebrocortical Neurons

“…10, gambierol has been demonstrated to be both a low-efficacy partial agonist of VGSCs (Inoue et al, 2003;LePage et al, 2007;Cao et al, 2008) and a high-affinity K v channel blocker (Ghiaroni et al, 2005;Cuypers et al, 2008;Kopljar et al, 2009;Pérez et al, 2012). Here we demonstrate that gambierol augments spontaneous Ca 21 oscillation frequency in cerebrocortical neurons.…”

“…Gambierol has been demonstrated to act as either a low-efficacy partial agonist at VGSCs or a high-affinity K v channel inhibitor (Inoue et al, 2003;Ghiaroni et al, 2005;Cuypers et al, 2008;Kopljar et al, 2009;Cagide et al, 2011;Pérez et al, 2012). Either activation of VGSCs or inhibition of K v channels can alter Ca 21 dynamics in neurons (Wang and Gruenstein, 1997;Cao et al, 2011).…”

Ciguatoxin and Ciguatera

“…In addition to profound effects on Na + conductance, ciguatoxins also inhibit neuronal potassium channels (Hidalgo et al 2002;Birinyi-Strachan et al 2005b;Schlumberger et al 2010;Perez et al 2011Perez et al , 2012. In dorsal root ganglion neurons, inhibition of the I K(DR) and the I KA currents in particular leads to prolonged action potential and afterhyperpolarization (AHP) duration and contributes to the increased neuronal excitability, altered membrane potential, and spontaneous action potential firing induced by P-CTX-1 (Birinyi- Strachan et al 2005b).…”

Potassium currents inhibition by gambierol analogs prevents human T lymphocyte activation

“…The same study described that the structural elements of gambierol indispensable for exhibiting potent toxicity are the c28=c29 double bond within the H-ring and the unsaturated side chain attached to the H-ring. In this context, we have recently evaluated the structureactivity relationship of gambierol and its heptacyclic and tetracyclic derivatives, showing that the truncated analogs of gambierol have similar potency to the parent natural product inhibiting voltage-dependent potassium channels and ameliorating Alzheimer's disease pathology in mice-cultured neurons Perez et al 2012).…”

“…Furthermore, we have recently demonstrated that gambierol and its tetracyclic and heptacyclic derivatives have similar potency to inhibit Kv channels in cortical neurons and in cerebellar granule cells Perez et al 2012) from mice, being able to ameliorate Alzheimer's disease pathology in vitro . Since the inhibitory effect of gambierol in mammalian Kv1.3 channels has been previously reported (cuypers et al 2008), in this work, we aimed at clarifying the effect of the two truncated analogs of gambierol in human cells employing purified T lymphocytes from healthy donors as the experimental model.…”