SEA0400

SEA0400 is a potent and selective inhibitor of Na+-Ca2+ exchanger (NCX) with IC50 values of 5 to 33 nM in cultured neurons, microglia and astrocytes [1].
The Na+-Ca2+ exchanger is an anti-porter that pumps Ca2+ out of the cells and keeps the low concentration of Ca2+ inside cells through exchanging the Na+ and Ca2+. In the reperfusion injury, the reverse mode NCX is activated, inducing the paradoxical Ca2+ influx and subsequently causing the generation of free radicals, leucotriene and thromboxane. Many existed drugs target NCX treated for reperfusion injury are reported of lacking selectivity or cell- permeability while SEA0400 is reported to be the most selective and potent NCX inhibitor [1].
SEA0400 was screened out of a chemical library designed for inhibition of NCX in cultured astrocytes and isolated cardiac sarcolemmal vesicles. It showed potent inhibitory effects on Na+-dependent Ca2+ uptake in cultured microglia, astrocytes and neurons with IC50 values of 8.3, 5 and 33 nM, respectively. The activity of SEA0400 was more than 100-fold higher than that of KB-R7943. SEA0400 was also proved to be selective against NCX over other ion fluxes since it displayed no significant effect on SOCE even at the concentration up to 3 μM. Besides that, SEA0400 had no effect on a serious of similar ion channels or ion transporters such as Ca2+-ATPase, Na+, K+-ATPase and K+ channel. Moreover, SEA0400 was found to suppress the Ca2+ influx-induced apoptosis in astrocytes [1].
In a rat model of cerebral ischemia, injection of SEA0400 at dose of 3 mg/kg resulted in decreased infarct volume in both striatum and cerebral cortex. In a rabbit model of Langendorff-perfused 1-month myocardial infarction, SEA0400 administration inhibited the pacing-induced ventricular premature beats and displayed proarrhythmic activity through enhancing spatially discordant alternans (SDA) and steepening Action potential duration (APD) restitution [1 and 2].
References:
[1] Matsuda T, Arakawa N, Takuma K, et al. SEA0400, a novel and selective inhibitor of the Na+-Ca2+ exchanger, attenuates reperfusion injury in the in vitro and in vivo cerebral ischemic models. Journal of Pharmacology and Experimental Therapeutics, 2001, 298(1): 249-256.
[2] CHOU C C, CHANG P O C, WEN M S, et al. Effects of SEA0400 on Arrhythmogenicity in a Langendorff-Perfused 1-Month Myocardial Infarction Rabbit Model Pacing and Clinical Electrophysiology, 2013, 36(5): 596-606.

Block of Na(+)/Ca(2+) exchanger by SEA0400 in human right atrial preparations from patients in sinus rhythm and in atrial fibrillation.[Pubmed:27373849]

Eur J Pharmacol. 2016 Oct 5;788:286-293.

The Na(+)/Ca(2+) exchanger (NCX) plays a major role in myocardial Ca(2+) homoeostasis, but is also considered to contribute to the electrical instability and contractile dysfunction in chronic atrial fibrillation (AF). Here we have investigated the effects of the selective NCX blocker SEA0400 in human right atrial cardiomyocytes from patients in sinus rhythm (SR) and AF in order to obtain electrophysiological evidence for putative antiarrhythmic activity of this new class of drugs. Action potentials were measured in right atrial trabeculae using conventional microelectrodes. Human myocytes were enzymatically isolated. Rat atrial and ventricular cardiomyocytes were used for comparison. Using perforated-patch, NCX was measured as Ni(2+)-sensitive current during ramp pulses. In ruptured-patch experiments, NCX current was activated by changing the extracellular Ca(2+) concentration from 0 to 1mM in Na(+)-free bath solution (100mM Na(+) intracellular, "Hilgemann protocol"). Although SEA0400 was effective in rat cardiomyocytes, 10microM did not influence action potentials and contractility, neither in SR nor AF. SEA0400 (10muM) also failed to affect human atrial NCX current measured with perforated patch. With the "Hilgemann protocol" SEA0400 concentration-dependently suppressed human atrial NCX current, and its amplitude was larger in AF than in SR cardiomyocytes. Our results confirm higher NCX activity in AF than SR. SEA0400 fails to block Ni(2+)-sensitive current in human atrial cells unless unphysiological conditions are used. We speculate that block of NCX with SEA0400 depends on intracellular Na(+) concentration.

The Na+/Ca2+ exchange inhibitor SEA0400 limits intracellular Ca2+ accumulation and improves recovery of ventricular function when added to cardioplegia.[Pubmed:24401610]

J Cardiothorac Surg. 2014 Jan 8;9:11.

BACKGROUND: The Na+/Ca2+ exchange inhibitor SEA0400 prevents myocardial injury in models of global ischemia and reperfusion. We therefore evaluated its potential as a cardioplegia additive. METHODS: Isolated rat cardiomyocytes were exposed to hypoxia (45 min) followed by reperfusion. During hypoxia, cells were protected using cardioplegia with (n=25) or without (n=24) SEA0400 (1 muM), or were not protected with cardioplegia (hypoxic control, n=8). Intracellular Ca2+ levels were measured using Ca2+ sensitive dye (fura-2 AM). Isolated rat hearts were arrested using cardioplegia with (n=7) or without (n=6) SEA0400 (1 muM) then reperfused after 45 min of ischemia. Left ventricular (LV) function, troponin release, and mitochondrial morphology were evaluated. RESULTS: Cardiomyocytes exposed to hypoxia without cardioplegia had poor survival (13%). Survival was significantly improved when cells were protected with cardioplegia containing SEA0400 (68%, p=0.009); cardioplegia without SEA0400 was associated with intermediate survival (42%). Cardiomyocytes exposed to hypoxia alone had a rapid increase in intracellular Ca2+ (305 +/- 123 nM after 20 minutes of ischemia). Increases in intracellular Ca2+ were reduced in cells arrested with cardioplegia without SEA0400; however cardioplegia containing SEA0400 was associated with the lowest intracellular Ca2+ levels (110 +/- 17 vs. 156 +/- 42 nM after 45 minutes of ischemia, p=0.004). Hearts arrested with cardioplegia containing SEA0400 had better recovery of LV work compared to cardioplegia without SEA0400 (23140 +/- 2264 vs. 7750 +/- 929 mmHg.mul, p=0.0001). Troponin release during reperfusion was lower (0.6 +/- 0.2 vs. 2.4 +/- 0.5 ng/mL, p=0.0026), and there were more intact (41 +/- 3 vs. 22 +/- 5%, p<0.005), and fewer disrupted mitochondria (24 +/- 2 vs. 33 +/- 3%, p<0.05) in the SEA0400 group. CONCLUSIONS: SEA0400 added to cardioplegia limits accumulation of intracellular Ca2+ during ischemic arrest in isolated cardiomyocytes and prevents myocardial injury and improves recovery of LV function in isolated hearts.

Effects of renal Na+/Ca2+ exchanger 1 inhibitor (SEA0400) treatment on electrolytes, renal function and hemodynamics in rats.[Pubmed:25410661]

Clin Exp Nephrol. 2015 Aug;19(4):585-90.

BACKGROUND: Na(+)/Ca(2+) exchanger 1 (NCX1) controls intracellular Ca(2+) concentration in various cell types. In the kidney, NCX1 is expressed mainly in the distal tubular basolateral membrane as well as in vascular smooth muscle. Tubular NCX1 is involved in Ca(2+) reabsorption, and NCX1 in renal arterioles may control intraglomerular pressure. However, the functions of renal NCX1 have not been studied in vivo. Therefore, this study examined the effects of renal NCX1 blockade on water and solute metabolism, renal function and blood pressure in rats. METHODS: Wistar-Kyoto rats were uninephrectomized, and an osmotic mini pump was implanted to infuse the remnant kidney cortex with a specific NCX1 inhibitor, SEA0400 (SEA), or vehicle for 7 days. RESULTS: Serum Ca(2+) concentration and urinary Ca(2+) excretion were similar between the vehicle- and SEA-treated groups. However, serum phosphate was significantly decreased by 8 % in the SEA group, with similar urinary phosphate excretion between the two groups. Systolic blood pressure was higher in the SEA group (117 +/- 3 vs. 126 +/- 1 mmHg, n = 9-11), with a 1.6-fold increase in plasma aldosterone concentration. However, SEA significantly reduced urinary protein excretion and the glomerular sectional area by 16 and 8 %, respectively. Similar experiment in spontaneously hypertensive rats produced different results. CONCLUSION: Renal SEA treatment reduced serum phosphate concentration, urinary protein and glomerular size with higher systemic blood pressure compared to control Wistar-Kyoto rats. Further study on renal NCX1 may be beneficial in delineating the pathophysiology of glomerular pressure control and calcium/phosphate regulations.

Effects of SEA0400 on arrhythmogenicity in a Langendorff-perfused 1-month myocardial infarction rabbit model.[Pubmed:23380010]

Pacing Clin Electrophysiol. 2013 May;36(5):596-606.

BACKGROUND: The effects of SEA0400, a Na(+) /Ca(2+) exchanger (NCX) blocker, on dynamic factors and arrhythmogenic alternans in 1-month myocardial infarction (MI) hearts remain unknown. METHODS: Simultaneous voltage and intracellular Ca(2+) (Cai ) optical mapping was performed in 12 rabbit hearts with MI for 1 month and six normal rabbit hearts as control. Western-blot studies were performed in both groups in an additional six hearts for each. Action potential duration (APD) restitution was constructed and arrhythmogenic alternans was induced by dynamic pacing. SEA0400 (0.03, 3 muM) was administered after baseline studies. RESULTS: SEA0400 suppressed pacing-induced ventricular premature beats in a concentration-dependent manner. SEA0400 at 0.03 muM steepened APD restitution slopes and enhanced spatially discordant alternans (SDA), which became insignificant at 3 muM. The VF inducibility was seven of nine at baseline, nine of nine at 0.03 muM SEA0400, and five of nine at 3 muM SEA0400 (P = NS). Significant upregulation of NCX in the remote but not periinfarct zone and less degree downregulation of DHP1alpha in the remote versus periinfarct zone may play a role in enhancing SDA induction by SEA0400 in 1-month MI hearts. CONCLUSIONS: In 1-month MI hearts, SEA0400 suppresses pacing-induced ventricular premature beats, but also is proarrhythmic by steepening APD restitution and enhancing SDA via NCX inhibition. Heterogeneous upregulation of NCX and downregulation of DHP1alpha may contribute to SDA augmentation by SEA0400 in this model. The insignificant effect of SEA0400 on VF inducibility suggests that suppression of both reentry and triggered activity is required to suppress VF induction in this model.

SEA0400 is a novel and selective inhibitor of the Na+-Ca2+ exchanger (NCX), inhibiting Na+-dependent Ca2+ uptake in cultured neurons, astrocytes, and microglia with IC50s of from 5 to 33 nM.

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