Differential Effects of Crambescins and Crambescidin 816 in Voltage-Gated Sodium, Potassium and Calcium Channels in Neurons

Abstract

Crambescins and crambescidins are two families of guanidine alkaloids from the marine sponge Crambe crambe. Although very little information about their biological effect has been reported, it is known that crambescidin 816 (Cramb816) blocks calcium channels in a neuroblastoma X glioma cell line. Taking this into account, and the fact that ion channels are frequent targets for natural toxins, we examined the effect of Cramb816 and three compounds from the crambescin family, norcrambescin A2 (NcrambA2), crambescin A2 (CrambA2), and crambescin C1 (CrambC1), in the main voltage-dependent ion channels in neurons: sodium, potassium, and calcium channels. Electrophysiological recordings of voltage gated sodium, potassium, and calcium currents, in the presence of these guanidine alkaloids, were performed in cortical neurons from embryonic mice. Different effects were discovered: crambescins inhibited K(+) currents with the following potency: NcrambA2 > CrambC1 > CrambA2, while Cramb816 lacked an effect. Only CrambC1 and Cramb816 partially blocked Na(+) total current. However, Cramb816 partially blocked Ca(2+) , while NcrambA2 did not. Since the blocking effect of Cramb816 on calcium currents has not been previously reported in detail, we further pharmacologically isolated the two main fractions of HVA Ca(2+) channels in neurons and investigated the Cramb816 effect on them. Here, we revealed that Cav1 or L-type calcium channels are the main target for Cramb816. These two families of guanidine alkaloids clearly showed a structure-activity relationship with the crambescins acting on voltage-gated potassium channels, while Cramb816 blocks the voltage-gated calcium channel Cav1 with higher potency than nifedipine. The novel evidence that Cramb816 partially blocked CaV and NaV channels in neurons suggests that this compound might be involved in decreasing the neurotransmitter release and synaptic transmission in the central nervous system. The findings presented here provide the first detailed approach on the different effects of crambescin and crambescidin compounds in voltage-gated sodium, potassium, and calcium channels in neurons and thus provide a basis for future studies.

Synthetic Ciguatoxin CTX 3C Induces a Rapid Imbalance in Neuronal Excitability

“…Voltage-dependent sodium currents were elicited in cortical neurons by applying a series of 25 ms depolarizing pulses (voltage steps), in 5 mV increments, from a holding potential of −100 mV. 21 As shown in Figure 1A, the activation of sodium channels was shifted in the hyperpolarizing direction after bath application of CTC 3C. Despite the fact that 0.1 nM CTX 3C did not affect the activation of voltage gated sodium channels (data not shown), bath application of 1 and 5 nM CTX 3C shifted the activation threshold of sodium currents to more negative potentials, from −50.0 ± 4.7 mV (n = 5) under control conditions to −64.0 ± 3.6 mV (n = 5; p = 0.02) at 1 nM CTX 3C and −76.0 ± 2.9 mV (n = 5; p = 0.0008) at 5 nM CTX 3C ( Figure 1B).…”

“…Primary cortical neurons were obtained from embryonic day 16−18 Swiss mice as previously described. 21 Briefly, cerebral cortices were removed and dissociated by mild trypsinization, followed by mechanical trituration in a DNase solution (0.004% w/v) containing soybean trypsin inhibitor (0.05% w/ v). The cells were suspended in neurobasal medium supplemented with 1% B-27 (Invitrogen), 5 mm L-glutamine, and 1% penicillin/ streptomycin.…”

How Environmental Factors Affect the Production of Guanidine Alkaloids by the Mediterranean Sponge Crambe crambe

“…It is composed of two families of polycyclic guanidine alkaloids (PGA, Supplemental information Figure 1); the crambescins (one or two cycles) and crambescidins (five cycles) that both exhibit substantial biological activities [34,35,36,37,38,39]. From C. crambe , several crambescidins (named from their molecular weight i.e., 800, 816 and 830) have been isolated and characterized [36,40,41] together with three sub-families of crambescins A–C differing in the presence of a pyrrolidine ring (A), a spiroaminal (B) and a linear 3-hydroxypropyl chain (C) [37,40,42].…”

Syntheses of cyclic guanidine-containing natural products

“…Interestingly, crambescidin 816 ( 4 ) binds to the voltage-gated calcium ion channel selectively while crambescins ( 303 ) binds to the potassium ion channels preferentially. 370 The crambescidins ( 4's ) and batzelladines ( 301 ) also show anticancer, 371,372 antiviral, 363,373,374 antifungal, 375 and antimalarial 376 activities. Based on the observation that the “vessel” part of 4 exists in a dynamic equilibrium between the spiroaminal and the imine forms under high pH, Overman proposed that 4 binds to their protein targets covalently through its imine form.…”