Background Fever or inflammation state may enhance the Brugada syndrome (BrS) phenotype in some but not all patients. However, the underlying mechanism in human cardiomyocytes has not yet been clarified. This study was designed to investigate whether fever or inflammation effects are gene mutation dependent in BrS patients and to explore potential mechanisms underlying fever or inflammation effects.

Methods Human induced pluripotent stem cell (hiPSC) lines generated from fibroblasts of two BrS patients harboring variants in SCN10A (abbreviated as BrS1) and CACNB2 (abbreviated as BrS2), and one healthy donor (abbreviated as WT) and a site-corrected (using CRISPR/Cas9) hiPSC line of each BrS patient (abbreviated as isogenic1 and isogenic2) were used for differentiation into cardiomyocytes (hiPSC-CMs). Western blot, patch clamp and calcium transient analyses were carried out.

Results The hiPSC-CMs of BrS1 showed a significantly reduced peak sodium current (I_Na) and maximal velocity of depolarization (V_max) of action potential compared with isogenic1 or WT at baseline. hiPSC-CMs of BrS2 showed a significant reduction in L-type calcium channel currents (I_Ca-L), peak I_Na compared with the WT or the isogenic2 at baseline. Arrhythmia-like events were detected more frequently in hiPSC-CMs from both BrS patients. These data confirmed the BrS phenotype. When the temperature of hiPSC-CMs culture was increased from 37°C to 40°C for 24 hours, a significant decrease of I_Na and V_max was detected in hiPSC-CMs of BrS1 but not in BrS2. Increased arrhythmia-like events and interval variability as a sign of high arrhythmogenicity were recorded in hiPSC-CMs of BrS1 but not in BrS2 after increasing the temperature from 37°C to 40°C. At 40°C, the protein kinase A (PKA) level was reduced in hiPSC-CMs of BrS1. A PKA activator abolished the changes and a PKA inhibitor enhanced the BrS phenotype as well as the 40°C phenotype. Treating the BrS1 cells with lipopolysaccharide (LPS) showed a further reduction of peak I_Na and V_max, and increased arrhythmic events. Treating hiPSC-CMs of BrS2 with LPS reduced I_Ca-L and APD50, increased arrhythmic events and interval variability. ROS-Blocker abolished the LPS effects in the BrS1 and BrS2 hiPSC-CMs, while an interleukin-6 receptor blocker abolished the proarrhythmic effect of LPS only in BrS1 hiPSC-CMs but not in hiPSC-CMs of BrS2.

Conclusions Hyperthermia but not LPS display a gene variant-dependent impact on the BrS phenotype. The enhanced BrS phenotype at high temperature (40°C) may be related to reduced PKA activity in some BrS patients. LPS enhanced the BrS phenotype in hiPSC-CMs of both BrS1 and BrS2 and might be linked to increased ROS level or increased interleukin 6.