Effect of Hepatic Impairment on the Pharmacokinetics and Pharmacodynamics of Cilofexor, a Selective Nonsteroidal Farnesoid X Receptor Agonist.

Cilofexor is a nonsteroidal farnesoid X receptor agonist in clinical development for treatment of nonalcoholic steatohepatitis. This work characterized the pharmacokinetics, pharmacodynamics, safety, and tolerability of cilofexor in participants with normal hepatic function or hepatic impairment (HI). Participants with stable mild, moderate, or severe HI (Child-Pugh [CP] A, B, or C, respectively, [n = 10/group]) and healthy matched controls with normal hepatic function received a single oral dose of cilofexor (30 mg for CP-A or B; 10 mg for CP-C) with a standardized meal. Overall, 56 participants received cilofexor and completed the study. Cilofexor area under the plasma concentration-time curve was 76%, 2.5-fold, and 6.3-fold higher in participants with mild, moderate, or severe HI, respectively, relative to the area under the plasma concentration-time curve in matched participants with normal hepatic function. Cilofexor unbound fraction was 38%, 2-fold, and 3.16-fold higher in participants with mild, moderate, and severe HI, respectively, relative to participants with normal hepatic function. Moderate correlations were identified between cilofexor exposure and CP score or laboratory tests components of CP score. Serum 7α-hydroxy-4-cholesten-3-one and plasma fibroblast growth factor 19 were similar in participants with mild, moderate, or severe HI and participants with normal hepatic function. Cilofexor was generally well tolerated; all cilofexor-related adverse events were mild in severity. Cilofexor can be administered to patients with mild HI without dose adjustment. Caution and dose modification are warranted when administering cilofexor to patients with moderate or severe HI.

Phase 1 first-in-human study of dalutrafusp alfa, an anti-CD73-TGF-ß-trap bifunctional antibody, in patients with advanced solid tumors.

BACKGROUND: Cluster of differentiation (CD)73-adenosine and transforming growth factor (TGF)-ß pathways are involved in abrogated antitumor immune responses and can lead to protumor conditions. This Phase 1 study (NCT03954704) evaluated the safety, pharmacokinetics, pharmacodynamics, and efficacy of dalutrafusp alfa (also known as GS-1423 and AGEN1423), a bifunctional, humanized, aglycosylated immunoglobulin G1 kappa antibody that selectively inhibits CD73-adenosine production and neutralizes active TGF-ß signaling in patients with advanced solid tumors. METHODS: Dose escalation started with an accelerated titration followed by a 3+3 design. Patients received dalutrafusp alfa (0.3, 1, 3, 10, 20, 30, or 45 mg/kg) intravenously every 2 weeks (Q2W) up to 1 year or until progressive disease (PD) or unacceptable toxicity. RESULTS: In total, 21/22 patients received at least one dose of dalutrafusp alfa. The median number of dalutrafusp alfa doses administered was 3 (range 1-14). All patients had at least one adverse event (AE), most commonly fatigue (47.6%), nausea (33.3%), diarrhea (28.6%), and vomiting (28.6%). Nine (42.9%) patients had a Grade 3 or 4 AE; two had Grade 5 AEs of pulmonary embolism and PD, both unrelated to dalutrafusp alfa. Target-mediated drug disposition appears to be saturated at dalutrafusp alfa doses above 20 mg/kg. Complete CD73 target occupancy on B cells and CD8+ T cells was observed, and TGF-ß 1/2/3 levels were undetectable at dalutrafusp alfa doses of 20 mg/kg and higher. Free soluble (s)CD73 levels and sCD73 activity increased with dalutrafusp alfa treatment. Seventeen patients reached the first response assessment, with complete response, partial response, stable disease, and PD in 0, 1 (4.8%), 7 (33.3%), and 9 (42.9%) patients, respectively. CONCLUSIONS: Dalutrafusp alfa doses up to 45 mg/kg Q2W were well tolerated in patients with advanced solid tumors. Additional evaluation of dalutrafusp alfa could further elucidate the clinical utility of targeting CD73-adenosine and TGF-ß pathways in oncology.

Sofosbuvir-velpatasvir-voxilaprevir in adolescents 12 to 17 years old with HCV infection.

BACKGROUND AND AIMS: Sofosbuvir-velpatasvir-voxilaprevir is a pangenotypic regimen for chronic HCV infection. In the USA and Europe, sofosbuvir-velpatasvir-voxilaprevir once daily for 12 weeks is indicated for adults who previously received an HCV NS5A inhibitor. In Europe, sofosbuvir-velpatasvir-voxilaprevir is also indicated in the absence of prior HCV direct-acting antiviral (DAA) therapy as an 8-week or 12-week regimen. In an open-label study, we evaluated the safety, efficacy, and pharmacokinetics of sofosbuvir-velpatasvir-voxilaprevir in adolescents 12 to 17 years with chronic HCV of any genotype. METHODS: In this Phase 2, multicenter study, sofosbuvir-velpatasvir-voxilaprevir 400/100/100 mg daily was administered to adolescents for 8 weeks if DAA-naïve or for 12 weeks for cirrhosis or prior DAA failure. The key efficacy endpoint was sustained virologic response 12 weeks after therapy (SVR12). Intensive pharmacokinetic sampling was done in 14 patients at week 2 or 4, and samples for population pharmacokinetics were collected in all patients. RESULTS: All patients (n = 21) were naïve to HCV DAAs, and none had cirrhosis. HCV genotype 3a infection was most common, occurring in 43% of patients. Overall, 100% of patients (21 of 21) reached SVR12. The most common adverse events were abdominal pain and headache (24% each) and nausea (19%); no adverse events led to discontinuation. The only serious adverse event, hypotension, was considered related to study drug and resolved the same day without interruption of treatment. Sofosbuvir-velpatasvir-voxilaprevir exposures were similar to those observed in adults. CONCLUSIONS: The pangenotypic regimen of sofosbuvir-velpatasvir-voxilaprevir is highly efficacious and well-tolerated in treating chronic HCV infection in adolescents.

Semi-Mechanistic PK/PD Modeling and Simulation of Irreversible BTK Inhibition to Support Dose Selection of Tirabrutinib in Subjects with RA.

Tirabrutinib is an irreversible, small-molecule Bruton's tyrosine kinase (BTK) inhibitor, which was approved in Japan (VELEXBRU) to treat B-cell malignancies and is in clinical development for inflammatory diseases. As an application of model-informed drug development, a semimechanistic pharmacokinetic/pharmacodynamic (PK/PD) model for irreversible BTK inhibition of tirabrutinib was developed to support dose selection in clinical development, based on clinical PK and BTK occupancy data from two phase I studies with a wide range of PK exposures in healthy volunteers and in subjects with rheumatoid arthritis. The developed model adequately described and predicted the PK and PD data. Overall, the model-based simulation supported a total daily dose of at least 40 mg, either q.d. or b.i.d., with adequate BTK occupancy (> 90%) for further development in inflammatory diseases. Following the PK/PD modeling and simulation, the relationship between model-predicted BTK occupancy and preliminary clinical efficacy data was also explored and a positive trend was identified between the increasing time above adequate BTK occupancy and better efficacy in treatment for RA by linear regression.

Evaluation of the potential drug interactions mediated through P-gp, OCT2, and MATE1/2K with filgotinib in healthy subjects.

Filgotinib, a preferential Janus Kinase-1 inhibitor, is approved in Europe and Japan for treatment of rheumatoid arthritis and is being developed for treatment of other chronic inflammatory diseases. Three drug-drug interactions studies were conducted in healthy subjects to evaluate the effect of P-glycoprotein (P-gp) modulation (study 1: P-gp inhibition by itraconazole and study 2: P-gp induction by rifampin) on filgotinib pharmacokinetics and the potential of filgotinib to impact exposure of metformin, an organic cation transporter (OCT) 2 and multidrug and toxin extrusion (MATE) 1/2K substrate (study 3). Co-administration of filgotinib with itraconazole increased filgotinib exposure (maximum concentration [Cmax ] by 64% and area under the curve to infinity [AUCinf ] by 45%) but had no effect on the exposure of GS-829845, filgotinib's primary metabolite. Rifampin moderately reduced exposures of filgotinib and GS-829845 (Cmax by 26% and AUCinf by 27% for filgotinib; Cmax by 19% and AUCinf by 38% for GS-829845). The data confirmed that filgotinib is a P-gp substrate. However, the magnitude of change in filgotinib/GS-829845 exposure by P-gp modulators is not deemed to be clinically relevant based on filgotinib exposure-response analyses in subjects with rheumatoid arthritis. Filgotinib did not alter metformin exposures, indicating that filgotinib and GS-829845 do not inhibit OCT2 and MATE1/2K at the clinical doses. Filgotinib was generally well-tolerated when administered alone or with the co-administered drugs in the studies. Results from these studies were the basis to enable the use of P-gp modulators and substrates of OCT2, MATE1, and MATE2K with filgotinib without the need for dose modifications in the current approved rheumatoid arthritis population.

Filgotinib as induction and maintenance therapy for ulcerative colitis (SELECTION): a phase 2b/3 double-blind, randomised, placebo-controlled trial.

BACKGROUND: The global prevalence of ulcerative colitis is increasing, and induction and maintenance of remission is a crucial therapeutic goal. We assessed the efficacy and safety of filgotinib, a once-daily, oral Janus kinase 1 preferential inhibitor, for treatment of ulcerative colitis. METHODS: This phase 2b/3, double-blind, randomised, placebo-controlled trial including two induction studies and one maintenance study was done in 341 study centres in 40 countries. Eligible patients were aged 18-75 years with moderately to severely active ulcerative colitis for at least 6 months before enrolment (induction study A: inadequate clinical response, loss of response to or intolerance to corticosteroids or immunosuppressants, naive to tumour necrosis factor [TNF] antagonists and vedolizumab [biologic-naive]; induction study B: inadequate clinical response, loss of response to or intolerance to any TNF antagonist or vedolizumab, no TNF antagonist or vedolizumab use within 8 weeks before screening [biologic-experienced]). Patients were randomly assigned 2:2:1 to receive oral filgotinib 200 mg, filgotinib 100 mg, or placebo once per day for 11 weeks. Patients who had either clinical remission or a Mayo Clinic Score response at week 10 in either induction study entered the maintenance study. Patients who received induction filgotinib were rerandomised 2:1 to continue their induction filgotinib regimen or to placebo. Patients who received induction placebo continued receiving placebo. The primary endpoint was clinical remission by Mayo endoscopic, rectal bleeding, and stool frequency subscores at weeks 10 and 58. For the induction studies, efficacy was assessed in all randomised patients who received at least one dose of study drug or placebo within that study. For the maintenance study, efficacy was assessed in all patients randomised to any filgotinib treatment group in the induction studies who received at least one dose of study drug or placebo in the maintenance study. Patients who received placebo throughout the induction and maintenance study were not included in the full analysis set for the maintenance study. Safety was assessed in all patients who received at least one dose of the study drug or placebo within each study. This trial is registered with ClinicalTrials.gov, NCT02914522. FINDINGS: Between Nov 14, 2016, and March 31, 2020, we screened 2040 patients for eligibility. 659 patients enrolled in induction study A were randomly assigned to receive filgotinib 100 mg (n=277), filgotinib 200 mg (n=245), or placebo (n=137). 689 patients enrolled into induction study B were randomly assigned to receive filgotinib 100 mg (n=285), filgotinib 200 mg (n=262), or placebo (n=142). 34 patients in induction study A and 54 patients in induction study B discontinued the study drug before week 10. After efficacy assessment at week 10, 664 patients entered the maintenance study (391 from induction study A, 273 from induction study B). 93 patients continued to receive placebo. 270 patients who had received filgotinib 100 mg in the induction study were randomly assigned to receive filgotinib 100 mg (n=179) or placebo (n=91). 301 patients who had received filgotinib 200 mg in the induction study were randomly assigned to receive filgotinib 200 mg (n=202) or placebo (n=99). 263 patients discontinued treatment in the maintenance study. At week 10, a greater proportion of patients given filgotinib 200 mg had clinical remission than those given placebo (induction study A 26·1% vs 15·3%, difference 10·8%; 95% CI 2·1-19·5, p=0·0157; induction study B 11·5% vs 4·2%, 7·2%; 1·6-12·8, p=0·0103). At week 58, 37·2% of patients given filgotinib 200 mg had clinical remission versus 11·2% in the respective placebo group (difference 26·0%, 95% CI 16·0-35·9; p<0·0001). Clinical remission was not significantly different between filgotinib 100 mg and placebo at week 10, but was significant by week 58 (23·8% vs 13·5%, 10·4%; 0·0-20·7, p=0·0420). The incidence of serious adverse events and adverse events of interest was similar between treatment groups. In the induction studies, serious adverse events occurred in 28 (5·0%) of 562 patients given filgotinib 100 mg, 22 (4·3%) of 507 patients given filgotinib 200 mg, and 13 (4·7%) of 279 patients given placebo. In the maintenance study, serious adverse events were reported in eight (4·5%) of 179 patients given filgotinib 100 mg, seven (7·7%) of 91 patients in the respective placebo group, nine (4·5%) of 202 patients in the filgotinib 200 mg group, and no patients in the respective placebo group. No deaths were reported during either induction study. Two patients died during the maintenance study; neither was related to treatment. INTERPRETATION: Filgotinib 200 mg was well tolerated, and efficacious in inducing and maintaining clinical remission compared with placebo in patients with moderately to severely active ulcerative colitis. FUNDING: Gilead Sciences.

Ledipasvir-Sofosbuvir for 12 Weeks in Children 3 to <6 Years Old With Chronic Hepatitis C.

For children under 12 years of age who have chronic hepatitis C virus (HCV) infection, there are currently no approved treatments with direct-acting antiviral agents. We therefore evaluated the safety and efficacy of ledipasvir-sofosbuvir in HCV-infected children aged 3 to <6 years. In an open-label study, patients 3 to <6 years old chronically infected with HCV genotype 1 (n = 33) or 4 (n = 1) received weight-based doses of combined ledipasvir-sofosbuvir as granules (33.75 mg/150 mg for weights <17 kg or 45 mg/200 mg for weights ≥17 kg) for 12 weeks. The primary endpoint was sustained virological response 12 weeks after treatment (SVR12). For the first 14 patients, intensive pharmacokinetic sampling was done on day 10 of treatment. All patients had been infected through perinatal transmission and were treatment naïve. No patients had known cirrhosis. Ten patients (29%) weighed <17 kg. SVR12 was achieved in 97% of patients (33 of 34); the patient who did not achieve SVR12 was 3 years old and discontinued treatment after 5 days because of an adverse event "abnormal drug taste." The most common adverse events were vomiting (24% of patients), cough (21%), and pyrexia (21%). No patients experienced a serious adverse event. Intensive pharmacokinetic analysis of 13 patients for whom data were evaluable confirmed that the doses selected were appropriate. Conclusion: Ledipasvir-sofosbuvir was well tolerated and highly effective in children 3 to <6 years old with chronic HCV infection.

Sofosbuvir and Ribavirin Therapy for Children Aged 3 to <12 Years With Hepatitis C Virus Genotype 2 or 3 Infection.

Currently, the only approved hepatitis C virus (HCV) treatment for children aged <12 years is pegylated interferon plus ribavirin. In an open-label study, we evaluated the safety and efficacy of sofosbuvir plus ribavirin for 12 weeks in children aged 3 to <12 years chronically infected with genotype 2 or for 24 weeks in patients with genotype 3. Patients aged 3 to <6 years weighing <17 kg received sofosbuvir 150 mg, and patients aged 3 to <6 years weighing ≥17 kg and all patients aged 6 to <12 years received sofosbuvir 200 mg once daily. Intensive pharmacokinetic sampling conducted in each age group confirmed the appropriateness of sofosbuvir doses. For all patients, ribavirin dosing was determined by baseline weight (up to 1,400 mg/day, two divided doses). The primary efficacy endpoint was sustained virologic response 12 weeks after therapy (SVR12). Fifty-four patients were enrolled (41 aged 6 to <12 years and 13 aged 3 to <6 years). Most were treatment naïve (98%) and infected perinatally (94%). All but one patient achieved SVR12 (53/54, 98%; 95% confidence interval, 90%-100%). The patient who did not achieve SVR12 was a 4-year-old who discontinued treatment after 3 days because of "abnormal drug taste." The most commonly reported adverse events in patients aged 6 to <12 years were vomiting (32%) and headache (29%), and those in patients aged 3 to <6 years were vomiting (46%) and diarrhea (39%). One 3-year-old patient had a serious adverse event of accidental ribavirin overdose requiring hospitalization for monitoring; this patient completed treatment and achieved SVR12. Conclusion: Sofosbuvir plus ribavirin was well tolerated and highly effective in children aged 3 to <12 years with chronic HCV genotype 2 or 3 infection.

Predictive Performance of Physiologically-Based Pharmacokinetic Models in Predicting Drug-Drug Interactions Involving Enzyme Modulation.

BACKGROUND: Physiologically-based pharmacokinetic (PBPK) modeling in predicting metabolic drug-drug interactions (mDDIs) is routinely used in drug development. Currently, the US FDA endorses the use of PBPK to potentially support dosing recommendations for investigational drugs as enzyme substrates of mDDIs, and to inform a lack of mDDIs for investigational drugs as enzyme modulators. METHODS: We systematically evaluated the performance of PBPK modeling in predicting mDDIs published in the literature. Models developed to assess both investigational drugs as enzyme substrates (Groups 1 and 2, as being inhibited and induced, respectively) or enzyme modulators (Groups 3 and 4, as inhibitors and inducers, respectively) were evaluated. Predicted ratios of the area under the curve (AUCRs) and/or maximum plasma concentration (CmaxRs) with and without comedication were compared with the observed ratios. RESULTS: For Groups 1, 2, 3, and 4, 62, 50, 44, and 43% of model-predicted AUCRs, respectively, were within a predefined threshold of 1.25-fold of observed values (0.8-1.25x). When the threshold was widened to twofold, the values increased to 100, 80, 81, and 86% (0.5-2.0x). For Groups 3 and 4, prediction for mDDI liability (the existence or lack of mDDIs) using PBPK appears to be satisfactory. CONCLUSION: Our analysis supports the FDA's current recommendations on the use of PBPK to predict mDDIs.

Small-Conductance Calcium-Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells.

BACKGROUND: Purkinje cells (PCs) are important in cardiac arrhythmogenesis. Whether small-conductance calcium-activated potassium (SK) channels are present in PCs remains unclear. We tested the hypotheses that subtype 2 SK (SK2) channel proteins and apamin-sensitive SK currents are abundantly present in PCs. METHODS AND RESULTS: We studied 25 normal rabbit ventricles, including 13 patch-clamp studies, 4 for Western blotting, and 8 for immunohistochemical staining. Transmembrane action potentials were recorded in current-clamp mode using the perforated-patch technique. For PCs, the apamin (100 nmol/L) significantly prolonged action potential duration measured to 80% repolarization by an average of 10.4 ms (95% CI, 0.11-20.72) (n=9, P=0.047). Voltage-clamp study showed that apamin-sensitive SK current density was significantly larger in PCs compared with ventricular myocytes at potentials ≥0 mV. Western blotting of SK2 expression showed that the SK2 protein expression in the midmyocardium was 58% (P=0.028) and the epicardium was 50% (P=0.018) of that in the pseudotendons. Immunostaining of SK2 protein showed that PCs stained stronger than ventricular myocytes. Confocal microscope study showed SK2 protein was distributed to the periphery of the PCs. CONCLUSIONS: SK2 proteins are more abundantly present in the PCs than in the ventricular myocytes of normal rabbit ventricles. Apamin-sensitive SK current is important in ventricular repolarization of normal PCs.

The Effect of Uremic Solutes on the Organic Cation Transporter 2.

Chronic kidney disease (CKD) is characterized by the accumulation of uremic solutes; however, little is known about how these solutes affect drug absorption and disposition. The goal of this study is to evaluate the effect of uremic solutes on the organic cation transporter, OCT2, which plays a key role in the renal secretion of many basic drugs. As a second goal, we reviewed the literature to determine whether there was evidence for the effect of CKD on the renal secretion of basic drugs. We first screened 72 uremic solutes as inhibitors of [14C]-labeled metformin uptake by OCT2. Seven were identified as inhibitors and 3 of them were determined to be clinically relevant. Of the 7 solutes, dimethylamine, malondialdehyde, trimethylamine, homocysteine, indoxyl-ß-d-glucuronide, and glutathione disulfide were novel OCT2 inhibitors. For 6 drugs that are known OCT2 substrates, both secretory clearance and glomerular filtration rate declined in parallel with progression of CKD from stage 2 to 4, suggesting that selective effects of uremic solutes on net tubular secretion of organic cations do not occur. Further clinical studies are warranted with a broader range of OCT2 substrates to determine whether CKD may differentially affect tubular secretion of drugs especially in patients with advanced CKD.

Identification and Quantitative Assessment of Uremic Solutes as Inhibitors of Renal Organic Anion Transporters, OAT1 and OAT3.

One of the characteristics of chronic kidney disease (CKD) is the accumulation of uremic solutes in the plasma. Less is known about the effects of uremic solutes on transporters that may play critical roles in pharmacokinetics. We evaluated the effect of 72 uremic solutes on organic anion transporter 1 and 3 (OAT1 and OAT3) using a fluorescent probe substrate, 6-carboxyfluorescein. A total of 12 and 13 solutes were identified as inhibitors of OAT1 and OAT3, respectively. Several of them inhibited OAT1 or OAT3 at clinically relevant concentrations and reduced the transport of other OAT1/3 substrates in vitro. Review of clinical studies showed that the active secretion of most drugs that are known substrates of OAT1/3 deteriorated faster than the renal filtration in CKD. Collectively, these data suggest that through inhibition of OAT1 and OAT3, uremic solutes contribute to the decline in renal drug clearance in patients with CKD.

Small conductance calcium-activated potassium current and the mechanism of atrial arrhythmia in mice with dysfunctional melanocyte-like cells.

BACKGROUND: The melanin synthesis enzyme dopachrome tautomerase (Dct) regulates intracellular Ca(2+) in melanocytes. Homozygous Dct knockout (Dct(-/-)) adult mice are vulnerable to atrial arrhythmias (AA). OBJECTIVE: The purpose of this study was to determine whether apamin-sensitive small conductance Ca(2+)-activated K(+) (SK) currents are upregulated in Dct(-/-) mice and contribute to AA. METHODS: Optical mapping was used to study the membrane potential of the right atrium in Langendorff perfused Dct(-/-) (n = 9) and Dct(+/-) (n = 9) mice. RESULTS: Apamin prolonged action potential duration (APD) by 18.8 ms (95% confidence interval [CI] 13.4-24.1 ms) in Dct(-/-) mice and by 11.5 ms (95% CI 5.4-17.6 ms) in Dct(+/-) mice at a pacing cycle length of 150 ms (P = .047). The pacing cycle length threshold to induce APD alternans was 48 ms (95% CI 34-62 ms) for Dct(-/-) mice and 21 ms (95% CI 12-29 ms) for Dct(+/-) mice (P = .002) at baseline, and it was 35 ms (95% CI 21-49 ms) for Dct(-/-) mice and 22 ms (95% CI 11-32 ms) for Dct(+/-) mice (P = .025) after apamin administration. Apamin prolonged post-burst pacing APD by 8.9 ms (95% CI 3.9-14.0 ms) in Dct(-/-) mice and by 1.5 ms (95% CI 0.7-2.3 ms) in Dct(+/-) mice (P = .005). Immunoblot and quantitative polymerase chain reaction analyses showed that protein and transcripts levels of SK1 and SK3 were increased in the right atrium of Dct(-/-) mice. AA inducibility (89% vs 11%; P = .003) and duration (281 seconds vs 66 seconds; P = .008) were greater in Dct(-/-) mice than in Dct(+/-) mice at baseline, but not different (22% vs 11%; P = 1.00) after apamin administration. Five of 8 (63%) induced atrial fibrillation episodes in Dct(-/-) mice had focal drivers. CONCLUSION: Apamin-sensitive SK current upregulation in Dct(-/-) mice plays an important role in the mechanism of AA.

Cervical vagal nerve stimulation activates the stellate ganglion in ambulatory dogs.

BACKGROUND AND OBJECTIVES: Recent studies showed that, in addition to parasympathetic nerves, cervical vagal nerves contained significant sympathetic nerves. We hypothesized that cervical vagal nerve stimulation (VNS) may capture the sympathetic nerves within the vagal nerve and activate the stellate ganglion. MATERIALS AND METHODS: We recorded left stellate ganglion nerve activity (SGNA), left thoracic vagal nerve activity (VNA), and subcutaneous electrocardiogram in seven dogs during left cervical VNS with 30 seconds on-time and 30 seconds off time. We then compared the SGNA between VNS on and off times. RESULTS: Cervical VNS at moderate (0.75 mA) output induced large SGNA, elevated heart rate (HR), and reduced HR variability, suggesting sympathetic activation. Further increase of the VNS output to >1.5 mA increased SGNA but did not significantly increase the HR, suggesting simultaneous sympathetic and parasympathetic activation. The differences of integrated SGNA and integrated VNA between VNS on and off times (ΔSGNA) increased progressively from 5.2 mV-s {95% confidence interval (CI): 1.25-9.06, p=0.018, n=7} at 1.0 mA to 13.7 mV-s (CI: 5.97-21.43, p=0.005, n=7) at 1.5 mA. The difference in HR (ΔHR, bpm) between on and off times was 5.8 bpm (CI: 0.28-11.29, p=0.042, n=7) at 1.0 mA and 5.3 bpm (CI 1.92 to 12.61, p=0.122, n=7) at 1.5 mA. CONCLUSION: Intermittent cervical VNS may selectively capture the sympathetic components of the vagal nerve and excite the stellate ganglion at moderate output. Increasing the output may result in simultaneously sympathetic and parasympathetic capture.

Pathogenesis of arrhythmias in a model of CKD.

Patients with CKD have an increased risk of cardiovascular mortality from arrhythmias and sudden cardiac death. We used a rat model of CKD (Cy/+) to study potential mechanisms of increased ventricular arrhythmias. Rats with CKD showed normal ejection fraction but hypertrophic myocardium. Premature ventricular complexes occurred more frequently in CKD rats than normal rats (42% versus 11%, P=0.18). By optical mapping techniques, action potential duration (APD) at 80% of repolarization was longer in CKD rats (78±4ms) than normal rats (63±3 ms, P<0.05) at a 200-ms pacing cycle length. Calcium transient (CaT) duration was comparable. Pacing cycle length thresholds to induce CaT alternans or APD alternans were longer in CKD rats than normal rats (100±7 versus 80±3 ms and 93±6 versus 76±4 ms for CaT and APD alternans, respectively, P<0.05), suggesting increased vulnerability to ventricular arrhythmia. Ventricular fibrillation was induced in 9 of 12 CKD rats and 2 of 9 normal rats (P<0.05); early afterdepolarization occurred in two CKD rats but not normal rats. The mRNA levels of TGF-ß, microRNA-21, and sodium calcium-exchanger type 1 were upregulated, whereas the levels of microRNA-29, L-type calcium channel, sarco/endoplasmic reticulum calcium-ATPase type 2a, Kv1.4, and Kv4.3 were downregulated in CKD rats. Cardiac fibrosis was mild and not different between groups. We conclude that cardiac ion channel and calcium handling are abnormal in CKD rats, leading to increased vulnerability to early afterdepolarization, triggered activity, and ventricular arrhythmias.

Utilizing multiple in silico analyses to identify putative causal SCN5A variants in Brugada syndrome.

Brugada syndrome (BrS) is an inheritable sudden cardiac death disease mainly caused by SCN5A mutations. Traditional approaches can be costly and time-consuming if all candidate variants need to be validated through in vitro studies. Therefore, we developed a new approach by combining multiple in silico analyses to predict functional and structural changes of candidate SCN5A variants in BrS before conducting in vitro studies. Five SCN5A non-synonymous variants (1651G>A, 1776C>G, 1673A>G, 3269C>T and 3578G>A) were identified in 14 BrS patients using direct DNA sequencing. Several bioinformatics algorithms were applied and predicted that 1651G>A (A551T) and 1776C>G (N592K) were high-risk SCN5A variants (odds ratio 59.59 and 23.93). The results were validated by Mass spectrometry and in vitro electrophysiological assays. We concluded that integrating sequence-based information and secondary protein structures elements may help select highly potential variants in BrS before conducting time-consuming electrophysiological studies and two novel SCN5A mutations were validated.

Apamin induces early afterdepolarizations and torsades de pointes ventricular arrhythmia from failing rabbit ventricles exhibiting secondary rises in intracellular calcium.

BACKGROUND: A secondary rise of intracellular Ca(2+) (Cai) and an upregulation of apamin-sensitive K(+) current (I(KAS)) are characteristic findings of failing ventricular myocytes. We hypothesize that apamin, a specific I(KAS) blocker, may induce torsades de pointes (TdP) ventricular arrhythmia from failing ventricles exhibiting secondary rises of Cai. OBJECTIVE: To test the hypothesis that small conductance Ca(2+) activated IKAS maintains repolarization reserve and prevents ventricular arrhythmia in a rabbit model of heart failure (HF). METHODS: We performed Langendorff perfusion and optical mapping studies in 7 hearts with pacing-induced HF and in 5 normal control rabbit hearts. Atrioventricular block was created by cryoablation to allow pacing at slow rates. RESULTS: The left ventricular ejection fraction reduced from 69.1% [95% confidence interval 62.3%-76.0%] before pacing to 30.4% [26.8%-34.0%] (N = 7; P < .001) after pacing. The corrected QT interval in failing ventricles was 337 [313-360] ms at baseline and 410 [381-439] ms after applying 100 nmol/L of apamin (P = .01). Apamin induced early afterdepolarizations (EADs) in 6 ventricles, premature ventricular beats (PVBs) in 7 ventricles, and polymorphic ventricular tachycardia consistent with TdP in 4 ventricles. The earliest activation site of EADs and PVBs always occurred at the site with long action potential duration and large amplitude of the secondary rises of Ca(i). Apamin induced secondary rises of Ca(i) in 1 nonfailing ventricle, but no EAD or TdP were observed. CONCLUSIONS: In HF ventricles, apamin induces EADs, PVBs, and TdP from areas with secondary rises of Ca(i). I(KAS) is important in maintaining repolarization reserve and preventing TdP in HF ventricles.

Apamin-sensitive calcium-activated potassium currents in rabbit ventricles with chronic myocardial infarction.

INTRODUCTION: The apamin-sensitive small-conductance calcium-activated potassium current (IKAS ) is increased in heart failure. It is unknown if myocardial infarction (MI) is also associated with an increase of IKAS . METHODS AND RESULTS: We performed Langendorff perfusion and optical mapping in 6 normal hearts and 10 hearts with chronic (5 weeks) MI. An additional 6 normal and 10 MI hearts were used for patch clamp studies. The infarct size was 25% (95% confidence interval, 20-31) and the left ventricular ejection fraction was 50 (46-54). The rabbits did not have symptoms of heart failure. The action potential duration measured to 80% repolarization (APD80 ) in the peri-infarct zone (PZ) was 150 (142-159) milliseconds, significantly (P = 0.01) shorter than that in the normal ventricles (167 [158-177] milliseconds. The intracellular Ca transient duration was also shorter in the PZ (148 [139-157] milliseconds) than that in normal ventricles (168 [157-180] milliseconds; P = 0.017). Apamin prolonged the APD80 in PZ by 9.8 (5.5-14.1)%, which is greater than that in normal ventricles (2.8 [1.3-4.3]%, P = 0.006). Significant shortening of APD80 was observed at the cessation of rapid pacing in MI but not in normal ventricles. Apamin prevented postpacing APD80 shortening. Patch clamp studies showed that IKAS was significantly higher in the PZ cells (2.51 [1.55-3.47] pA/pF, N = 17) than in the normal cells (1.08 [0.36-1.80] pA/pF, N = 15, P = 0.019). CONCLUSION: We conclude that IKAS is increased in MI ventricles and contributes significantly to ventricular repolarization especially during tachycardia.