Gene- and variant-specific efficacy of serum/glucocorticoid-regulated kinase 1 inhibition in long QT syndrome types 1 and 2.

AIMS Current long QT syndrome (LQTS) therapy, largely based on beta-blockade, does not prevent arrhythmias in all patients; therefore, novel therapies are warranted. Pharmacological inhibition of the serum/glucocorticoid-regulated kinase 1 (SGK1-Inh) has been shown to shorten action potential duration (APD) in LQTS type 3. We aimed to investigate whether SGK1-Inh could similarly shorten APD in LQTS types 1 and 2. METHODS AND RESULTS Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and hiPSC-cardiac cell sheets (CCS) were obtained from LQT1 and LQT2 patients; CMs were isolated from transgenic LQT1, LQT2, and wild-type (WT) rabbits. Serum/glucocorticoid-regulated kinase 1 inhibition effects (300 nM-10 µM) on field potential durations (FPD) were investigated in hiPSC-CMs with multielectrode arrays; optical mapping was performed in LQT2 CCS. Whole-cell and perforated patch clamp recordings were performed in isolated LQT1, LQT2, and WT rabbit CMs to investigate SGK1-Inh (3 µM) effects on APD. In all LQT2 models across different species (hiPSC-CMs, hiPSC-CCS, and rabbit CMs) and independent of the disease-causing variant (KCNH2-p.A561V/p.A614V/p.G628S/IVS9-28A/G), SGK1-Inh dose-dependently shortened FPD/APD at 0.3-10 µM (by 20-32%/25-30%/44-45%). Importantly, in LQT2 rabbit CMs, 3 µM SGK1-Inh normalized APD to its WT value. A significant FPD shortening was observed in KCNQ1-p.R594Q hiPSC-CMs at 1/3/10 µM (by 19/26/35%) and in KCNQ1-p.A341V hiPSC-CMs at 10 µM (by 29%). No SGK1-Inh-induced FPD/APD shortening effect was observed in LQT1 KCNQ1-p.A341V hiPSC-CMs or KCNQ1-p.Y315S rabbit CMs at 0.3-3 µM. CONCLUSION A robust SGK1-Inh-induced APD shortening was observed across different LQT2 models, species, and genetic variants but less consistently in LQT1 models. This suggests a genotype- and variant-specific beneficial effect of this novel therapeutic approach in LQTS

Bacterial modulation of visceral sensation: mediators and mechanisms

The potential role of the intestinal microbiota in modulating visceral pain has received increasing attention during recent years. This has led to the identification of signaling pathways that have been implicated in communication between gut bacteria and peripheral pain pathways. In addition to the well-characterised impact of the microbiota on the immune system, which in turn affects nociceptor excitability, bacteria can modulate visceral afferent pathways by effects on enterocytes, enteroendocrine cells and the neurons themselves. Proteases produced by bacteria, or by host cells in response to bacteria, can increase or decrease the excitability of nociceptive dorsal root ganglion (DRG) neurons depending on the receptor activated. Short chain fatty acids generated by colonic bacteria are involved in gut-brain communication, and intracolonic short chain fatty acids have pro-nociceptive effects in rodents but may be anti-nociceptive in humans. Gut bacteria modulate the synthesis and release of enteroendocrine cell mediators including serotonin and glucagon-like peptide-1, which activate extrinsic afferent neurons. Deciphering the complex interactions between visceral afferent neurons and the gut microbiota may lead to the development of improved probiotic therapies for visceral pain

Deoxycholic acid activates colonic afferent nerves via 5-HT3 receptor dependent and independent mechanisms

Increased bile acids in the colon can evoke increased epithelial secretion resulting in diarrhea, but little is known about whether colonic bile acids contribute to abdominal pain. This study aimed to investigate the mechanisms underlying activation of colonic extrinsic afferent nerves and their neuronal cell bodies by a major secondary bile acid, deoxycholic acid (DCA). All experiments were performed on male C57BL/6 mice. Afferent sensitivity was evaluated using in vitro extracellular recordings from mesenteric nerves in the proximal colon (innervated by vagal and spinal afferents) and distal colon (spinal afferents only). Neuronal excitability of cultured dorsal root ganglion (DRG) and nodose ganglion (NG) neurons was examined with perforated patch clamp. Colonic 5-HT release was assessed using ELISA, and 5-HT immunoreactive enterochromaffin (EC) cells were quantified. Intraluminal DCA increased afferent nerve firing rate concentration dependently in both proximal and distal colon. This DCA-elicited increase was significantly inhibited by a 5-HT3 antagonist in the proximal colon but not in the distal colon, which may be in part due to lower 5-HT immunoreactive EC cell density and lower 5-HT levels in the distal colon following DCA stimulation. DCA increased the excitability of DRG neurons, whereas it decreased the excitability of NG neurons. DCA potentiated mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. Together, this study suggests that DCA can excite colonic afferents via direct and indirect mechanisms but the predominant mechanism may differ between vagal and spinal afferents. Furthermore, DCA increased mechanosensitivity of high-threshold spinal afferents and may be a mechanism of visceral hypersensitivity.NEW & NOTEWORTHY Deoxycholic acid (DCA) directly excites spinal afferents and, to a lesser extent, indirectly via mucosal 5-HT release. DCA potentiates mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. DCA increases vagal afferent firing in proximal colon via 5-HT release but directly inhibits the excitability of their cell bodies.Peer reviewedFinal Accepted Versio