Impact of ciguatoxins on human cardiac and neuronal physiology

Ciguatera (CG) is a syndrome induced by Ciguatoxins (CTXs), natural phycotoxins among the most harmful we know. They are produced by benthic dinoflagellates of the Gambierdiscus and Fukuyoa. CG is the result of food poisoning caused by the consumption of contaminated fish meat along the food chain, from herbivorous fish to higher carnivorous fish. It is the most common non-bacterial seafood poisoning in the world with an increasing 50,000 to 100,000 new cases per year although only 2 to 10% of them are actually reported. CG is manifested by multiple undefined symptoms (gastrointestinal, cardiovascular, neurosensory, skin and inflammatory) in the form of polymorphic syndrome. CTXs are known to modify the cellular membrane permeability. Several fundamental studies have highlighted a common action of CTXs by modulating the ion channels (Na+, K+, Ca2+) essential to excitable cells such as cardiomyocytes (CM) and neurons (NR). Our main objective is to understand and characterize the impact of CTXs on human cardiac and neuronal physiology. We hypothesized that CTXs can affect the intracellular calcium handling and therefore the cardiac excitation-contraction coupling (ECC) and neuronal functional and molecular properties. We differentiated human induced pluripotent stem cell-derived ventricular-like cardiomyocytes (hiPSC-CMs) and neurons (hiPSC-NRs), we used 2 types of purified CTXs (CTX1B and CTX3C) and 2 types of hiPSC healthy control (HC). We investigated the effects of CTXs on cytosolic calcium, cells morphology and CM contractile properties. To determine if CTXs modulate the RyR2 channel activity, we performed single-channel measurements using the planar lipid bilayer technique. We observed that CTXs lead to intracellular calcium leaks and increase in cardiac and neuronal basal calcium level. They cause increased activity of the RyR2 channels as reflected by higher opening frequency Fo (Fo of 244 ± 112 events/s for HC vs. 2279 ± 836 events/s for HC + CTX1B, P < 0.01). Exposure of CTXs also cause reduced contractions of the hiPSC-derived cardiac sheets and cardiac hypertrophy as evidenced by an increase in cell area (1997 ± 119 μm2 for HC vs. 2852 ± 475 μm2 for HC + CTX1B, P < 0.01). Our preliminary data suggest that CTXs lead to RyR2 aberrant kinetic properties. CTXs also induce reduced beat rate and hiPSC-CM hypertrophy.