Treatment patterns of patients with worsening heart failure with reduced ejection fraction

AIMS

Patients with HFrEF and worsening HF events (WHFE) are at particularly high risk and urgently need disease-modifying therapy. CHART-HF assessed treatment patterns and reasons for medication decisions among HFrEF patients with and without WHFE.

METHODS AND RESULTS

CHART-HF collected retrospective electronic medical records of outpatients with HF and EF < 45% between 2017-2019 from a nationwide panel of 238 cardiologists (458 patients) and the Geisinger Health System (GHS) medical record (1000 patients). The index visit in the WHFE cohort was the first outpatient cardiologist visit ≤6 months following the WHFE, and in the reference cohort was the last visit in a calendar year without WHFE. Demographic characteristics were similar between patients with and without WHFE in both the nationwide panel and GHS. In the nationwide panel, the proportion of patients with versus without WHFE receiving ≥50% of guideline-recommended dose on index visit was 35% versus 40% for beta blocker, 74% versus 83% for ACEI/ARB/ARNI, and 48% versus 49% for MRA. The proportion of patients receiving ≥50% of guideline-recommended dose was lower in the GHS: 29% versus 34% for beta-blocker, 16% versus 31% for ACEI/ARB/ARNI, and 18% versus 22% for MRA. For patients with and without WHFE, triple therapy on index date was 42% and 44% of patients from the nationwide panel, and 14% and 17% in the GHS. Comparing end of index clinic visit with 12-month follow-up in the GHS, the proportion of patients on no GDMT increased from 14% to 28% in the WHFE cohort and from 14 to 21% in the non-WHFE group.

CONCLUSIONS

Major gaps in use of GDMT, particularly combination therapy, remain among US HFrEF patients. These gaps persist during longitudinal follow-up and are particularly large among patients with recent WHFE.

Accelerometer vs. other activity measures in heart failure with preserved ejection fraction: the VITALITY-HFpEF trial

AIMS

The relationship between accelerometry data and changes in Kansas City Cardiomyopathy Questionnaire-Physical Limitation Score (KCCQ-PLS) or 6 min walk test (6MWT) is not well understood.

METHODS AND RESULTS

VITALITY-HFpEF accelerometry substudy (n = 69) data were assessed at baseline and 24 weeks. Ordinal logistic regression models were used to assess the association between accelerometry activity and deterioration, improved, or unchanged KCCQ-PLS (≥8.33 and ≤ -4.17 points) and 6MWT (≥32 vs. ≤ -32 m). KCCQ-PLS score deteriorated in 16 patients, improved in 34, and was unchanged in 19. 6MWT deteriorated in 8 patients, improved in 21, and was unchanged in 19. Mean accelerometer wear was 21.4 (±2.1) h/day. Changes in hours active from baseline to 24 weeks were not significantly different among patients who exhibited deterioration, improvement, or no change in KCCQ-PLS [odds ratio (OR) 0.91, 95% confidence interval (CI) 0.71-1.18; P = 0.48] or 6MWT (OR 1.21, 95% CI 0.91-1.60; P = 0.18). Similar lack of association was observed for other accelerometry metrics and change in KCCQ and 6MWT. These findings were unaffected when KCCQ and 6MWT were examined as continuous variables.

CONCLUSIONS

Accelerometer-based activity measures did not correlate with subjective or objective standard measures of health status and functional capacity in heart failure with preserved ejection fraction. Further investigation of their relationships to clinical outcomes is required.

Vericiguat, a novel sGC stimulator: Mechanism of action, clinical, and translational science

Vericiguat, a novel soluble guanylate cyclase (sGC) stimulator, is approved for the treatment of heart failure (HF) with reduced ejection fraction (HFrEF). Decreased nitric oxide (NO) availability, sGC desensitization to NO, sGC deficiency, and reduced cyclic guanosine monophosphate (cGMP) signaling are potential contributing factors for HF disease progression. Vericiguat works via stimulation of sGC in the critical NO-sGC-cGMP pathway. Vericiguat is primarily metabolized by glucuronidation via uridine diphosphate-glucuronosyltransferase (UGT) isoforms UGT1A1 and UGT1A9. Urinary excretion and renal clearance of vericiguat are low. No intrinsic factor had a clinically relevant effect on vericiguat exposure. Vericiguat has low drug-drug interaction potential with no clinically relevant pharmacokinetic or pharmacodynamic interactions observed with warfarin, digoxin, aspirin, or sacubitril/valsartan. The global phase III study VICTORIA included patients with HFrEF who had a recent HF hospitalization or intravenous diuretic treatment for HF. Treatment with vericiguat on top of standard of care resulted in a 10% relative reduction in the primary composite outcome of death from cardiovascular causes or first hospitalization for HF. Vericiguat was well-tolerated with low incidence of symptomatic hypotension and syncope compared to placebo. Given its positive benefit-risk profile, vericiguat is an important option for high-risk patients with HFrEF who are already on guideline-directed medical therapy and had recent worsening of HF. Future efforts to develop additional effective therapies are needed to further reduce morbidity and mortality in patients with HF.

Evolution of NT-proBNP During Prerandomization Screening in VICTORIA: Implications for Clinical Outcomes and Efficacy of Vericiguat

BACKGROUND

Selecting high-risk patients with heart failure with potentially modifiable cardiovascular events is a priority. Our objective was to evaluate NT-proBNP (N-terminal pro-B-type natriuretic peptide) changes during a 30-day screening to establish (1) the frequency and direction of changes; (2) whether a relationship exists between changes in NT-proBNP and the primary composite outcome of cardiovascular death and heart failure hospitalization; and (3) whether changes in NT-proBNP relate to vericiguat's clinical benefit.

METHODS

VICTORIA (A Study of Vericiguat in Participants With Heart Failure With Reduced Ejection Fraction) randomized 5050 patients with heart failure with reduced ejection fraction and a recent worsening heart failure event. We studied 3821 patients who had NT-proBNP measured during screening and at randomization.

RESULTS

Sixteen hundred exhibited a >20% reduction, 1412 had ≤20% change, and 809 showed a >20% rise in NT-proBNP levels. As compared with the primary composite outcome of 28.4/100 patient-years (497 events; 31.1%) in patients with a >20% decline in NT-proBNP, those with >20% during screening had worse outcomes; 48.8/100 patient-years (359 events; 44.4%); adjusted hazard ratio, 1.61 (95% CI, 1.39-1.85). Those patients with a ≤20% change in NT-proBNP had intermediate outcomes; 39.2/100 patient-years (564 events; 39.9%); adjusted hazard ratio, 1.33 (95% CI, 1.17-1.51). No relationship existed between NT-proBNP changes during screening and vericiguat's effect on cardiovascular death and heart failure hospitalization.

CONCLUSIONS

Substantial differences occurred in the rates of cardiovascular death and heart failure hospitalization, especially in patients with a >20% change in NT-proBNP levels during screening interval. Sequential NT-proBNP levels add important prognostic information meriting consideration in future heart failure trials.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT02861534.

Relationship between baseline electrocardiographic measurements and outcomes in patients with high-risk heart failure: Insights from the VerICiguaT Global Study in Subjects with Heart Failure with Reduced Ejection Fraction (VICTORIA) trial

AIMS

Whether electrocardiographic (ECG) measurements predict mortality in chronic heart failure with reduced ejection fraction (HFrEF) is unknown.

METHODS AND RESULTS

We studied 4880 patients from the Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction (VICTORIA) trial with a baseline 12-lead ECG. Associations between ECG measurements and mortality were estimated as hazard ratios (HR) and adjusted for the Meta-Analysis Global Group in Chronic Heart Failure (MAGGIC) risk score, N-terminal pro-B-type natriuretic peptide, and index event. Select interactions between ECG measurements, patient characteristics and mortality were examined. Over a median of 10.8 months, there were 824 cardiovascular (CV) deaths (214 sudden) and 1005 all-cause deaths. Median age was 68 years (interquartile range [IQR] 60-76), 24% were women, median ejection fraction was 30% (IQR 23-35), 41% had New York Heart Association class III/IV, and median MAGGIC score was 24 (IQR 19-28). After multivariable adjustment, significant associations existed between heart rate (per 5 bpm: HR 1.02), QRS duration (per 10 ms: HR 1.02), absence of left ventricular hypertrophy (HR 0.64) and CV death, and similarly so with all-cause death (HR 1.02; HR 1.02; HR 0.61, respectively). Contiguous pathologic Q waves were significantly associated with sudden death (HR 1.46), and right ventricular hypertrophy with all-cause death (HR 1.44). The only sex-based interaction observed was for pathologic Q waves on CV (men: HR 1.05; women: HR 1.64, pinteraction  = 0.024) and all-cause death (men: HR 0.99; women: HR 1.57; pinteraction  = 0.010). Whereas sudden death doubled in females, it did not differ among males (male: HR 1.25, 95% confidence interval [CI] 0.87-1.79; female: HR 2.50, 95% CI 1.23-5.06; pinteraction  = 0.141).

CONCLUSION

Routine ECG measurements provide additional prognostication of mortality in high-risk HFrEF patients, particularly in women with contiguous pathologic Q waves.

Age, Sex, and Outcomes in Heart Failure With Reduced EF: Insights From the VICTORIA Trial

BACKGROUND

Age and sex influence treatment and outcomes in patients with heart failure (HF).

OBJECTIVES

The authors examined the associations of age and sex with clinical characteristics, background therapies, outcomes, and response to vericiguat in this post hoc analysis of 5,050 VICTORIA (Vericiguat Global Study in Subjects With Heart Failure With Reduced Ejection Fraction) patients with HF and reduced ejection fraction; 1,568 (31%) were ≥75 years of age, of whom 445 (24%) were women.

METHODS

Clinical characteristics were compared across age (<65, 65 to <75, and ≥75 years) and sex. The treatment effect of vericiguat was estimated by age and sex on the primary composite outcome (time to first HF hospitalization or cardiovascular death) using Cox proportional hazards regression.

RESULTS

Compared with younger patients, those ≥75 years of age had more class III and IV symptoms, higher N-terminal pro-B-type natriuretic peptide levels, and worse kidney function but had the lowest use of triple therapy. No sex differences in triple therapy existed by age, but achieving target doses of triple therapy was less likely in older patients. Men ≥75 years of age were more than twice as likely to receive defibrillators and 65% more likely to undergo cardiac resynchronization than women. The primary composite outcome was nominally lower in women than men across all age groups. Vericiguat dosing did not differ between sexes in each age group, and its beneficial effect on the primary endpoint was not modified by age (continuous age, Pinteraction = 0.169; categorical age, Pinteraction = 0.189); and sex (3-way interaction; P = 0.847).

CONCLUSIONS

Although elderly women received less intense background HF therapy than men, their prognosis was nominally better. The benefit of vericiguat was independent of age and sex. (Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction [HFrEF] [MK-1242-001] [VICTORIA]; NCT02861534).

Nonclinical Cardiovascular Assessment of the Soluble Guanylate Cyclase Stimulator Vericiguat

Vericiguat and its metabolite M-1 were assessed for proarrhythmic risk in nonclinical in vitro and in vivo studies. In vitro manual voltage-clamp recordings at room temperature determined the effect of vericiguat on human Ether-a-go-go Related Gene (hERG) K+ channels. Effects of vericiguat and M-1 on hERG K+, Nav1.5, hCav1.2, hKvLQT1/1minK, and hKv4.3 channels were investigated via automated voltage-clamp recordings at ambient temperature. Effects of vericiguat and M-1 on hERG K+ and Nav1.5 channels at pathophysiological conditions were explored via manual voltage-clamp recordings at physiologic temperature. Single oral doses of vericiguat (0.6, 2.0, and 6.0 mg/kg) were assessed for in vivo proarrhythmic risk via administration to conscious telemetered dogs; electrocardiogram (ECG) and hemodynamic parameters were monitored. ECG recordings were included in 4- and 39-week dog toxicity studies. In manual voltage-clamp recordings, vericiguat inhibited hERG K+-mediated tail currents in a concentration-dependent manner (20% threshold inhibitory concentration ∼1.9 µM). In automated voltage-clamp recordings, neither vericiguat nor M-1 were associated with biologically relevant inhibition (>20%) of hNav1.5, hCav1.2, hKvLQT1, and hKv4.3. No clinically relevant observations were made for hNav1.5 and hKvLQT1 under simulated pathophysiological conditions. Vericiguat was associated with expected mode-of-action-related dose-dependent changes in systolic arterial blood pressure (up to -20%) and heart rate (up to +53%). At maximum vericiguat dose, corrected QT (QTc) interval changes from baseline varied slightly (-6 to +1%) depending on correction formula. Toxicity studies confirmed absence of significant QTc interval changes. There was no evidence of an increased proarrhythmic risk from nonclinical studies with vericiguat or M-1. SIGNIFICANCE STATEMENT: There was no evidence of an increased proarrhythmic risk from in vitro and in vivo nonclinical studies with vericiguat or M-1. The integrated risk assessment of these nonclinical data combined with existing clinical data demonstrate administration of vericiguat 10 mg once daily in patients with heart failure with reduced ejection fraction is not associated with a proarrhythmic risk.

Ejection Fraction, Biomarkers, and Outcomes and Impact of Vericiguat on Outcomes Across EF in VICTORIA

BACKGROUND

Vericiguat reduced the risk of cardiovascular death (CVD) or hospitalization for heart failure (HF) in patients with worsening HF and reduced left ventricular ejection fraction (LVEF).

OBJECTIVES

The authors assessed the association of LVEF with biomarker levels, risk of outcome, and whether the effect of vericiguat was homogeneous across LVEF in the VICTORIA (Vericiguat Global Study in Subjects with Heart Failure With Reduced Ejection Fraction) trial.

METHODS

Patients were grouped by LVEF tertiles (≤24%, 25%-33%, and >33%). Patient characteristics, clinical outcomes, and efficacy and safety of vericiguat were examined by tertile. Prespecified biomarkers including N-terminal pro-B-type natriuretic peptide, cardiac troponin T, growth differentiation factor 15, interleukin 6, high-sensitivity C-reactive protein, and cystatin C were examined.

RESULTS

The mean LVEF was 29% ± 8% (range: 5%-45%). A pattern of higher N-terminal pro-B-type natriuretic peptide, high-sensitivity C-reactive protein, and interleukin 6 was evident in patients in the lowest LVEF tertile vs the other tertiles. Patients with lower LVEF experienced higher rates of the composite outcome (41.7%, 36.3%, and 33.4% for LVEF ≤24, 25-33, and >33; P < 0.001). There was no significant treatment effect heterogeneity of vericiguat across LVEF groups (adjusted HR from lowest to highest tertiles: 0.79 [95% CI: 0.68-0.94]; 0.95 [95% CI: 0.82-1.11]; 0.94 [95% CI: 0.79-1.11]; P for interaction = 0.222), although the HR was numerically lower in the lowest tertile. There was also no heterogeneity of effect for CVD and HF hospitalization individually (P interaction for CVD = 0.964; HF hospitalization = 0.438). Discontinuation of treatment because of adverse events, symptomatic hypotension, or syncope was consistent across the range of LVEF.

CONCLUSIONS

Patients with lower LVEF had a distinctive biomarker profile and a higher risk for adverse clinical outcomes vs those with a higher LVEF. There was no significant interaction for the benefit of vericiguat across LVEF tertiles, although the largest signal for benefit in both the primary outcome and HF hospitalizations was noted in tertile 1 (LVEF ≤24%). (Vericiguat Global Study in Subjects with Heart Failure With Reduced Ejection Fraction [VICTORIA]; NCT02861534).

Assessment of Biomarkers of Myocardial injury, Inflammation, and Renal Function in Heart Failure With Reduced Ejection Fraction: The VICTORIA Biomarker Substudy

BACKGROUND

Circulating biomarkers may be useful in understanding prognosis and treatment efficacy in heart failure with reduced ejection fraction. In the VICTORIA (Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction) trial, vericiguat, a soluble guanylate cyclase stimulator, decreased the primary outcome of cardiovascular death or heart failure hospitalization in heart failure with reduced ejection fraction. We evaluated biomarkers of cardiac injury, inflammation, and renal function for associations with outcomes and vericiguat treatment effect.

METHODS AND RESULTS

High-sensitivity cardiac troponin T (hs-cTnT), growth differentiation factor-15 (GDF-15), interleukin-6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), and cystatin C were measured at baseline and 16 weeks. Associations of biomarkers with the primary outcome and its components were estimated. Interaction with study treatment was tested. Changes in biomarkers over time were examined by study treatment. One or more biomarkers were measured in 4652 (92%) of 5050 participants at baseline and 4063 (81%) at 16 weeks. After adjustment, higher values of hs-cTnT, growth differentiation factor-15, and interleukin-6 were associated with the primary outcome, independent of N-terminal pro-B-type natriuretic peptide. Higher hs-cTnT values were associated with a hazard ratio per log standard deviation of 1.21 (95% confidence interval 1.14-1.27). A treatment interaction with vericiguat was evident with hs-cTnT and cardiovascular death (P = .04), but not HF hospitalization (P = .38). All biomarkers except cystatin C decreased over 16 weeks and no relationship between treatment assignment and changes in biomarker levels was observed.

CONCLUSIONS

hs-cTnT, growth differentiation factor-15, and interleukin-6 levels were associated with risk of the primary outcome in VICTORIA (Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction). Uniquely, lower hs-cTnT was associated with a lower rate of cardiovascular death but not HF hospitalization after treatment with vericiguat.

Patient-Reported Frailty and Functional Status in Heart Failure With Preserved Ejection Fraction: Insights From VITALITY-HFpEF

BACKGROUND

The association between frailty and health status in patients with heart failure with preserved ejection fraction (HFpEF) is not well known.

OBJECTIVES

The authors examined the association between: 1) patient-reported frailty, measured by the Fried frailty phenotype, Kansas City Cardiomyopathy Questionnaire physical limitation score (KCCQ-PLS), 6-minute walking distance (6MWD), and other baseline characteristics; 2) baseline frailty compared with KCCQ-PLS and 24-week 6MWD; 3) frailty and changes in KCCQ-PLS and 6MWD; and 4) vericiguat and frailty at 24 weeks.

METHODS

In a post hoc analysis, patients in the VITALITY-HFpEF (Patient-reported Outcomes in Vericiguat-treated Patients With HFpEF) trial were categorized as not frail (0 symptoms), prefrail (1-2 symptoms), and frail (≥3 symptoms) according to patient-reported number of frailty symptoms. Correlations and linear regression models were used to examine the association between frailty and other measures, and between frailty and KCCQ-PLS at baseline with 24-week 6MWD.

RESULTS

Among 739 patients, 27.3% were not frail, 37.6% were prefrail, and 35.0% were frail at baseline. Frail patients were older, more likely to be women, and less likely to be from Asia. Baseline KCCQ-PLS and 6MWD (mean ± SD) among not frail, prefrail, and frail patients was 68.2 ± 23.2, 61.7 ± 22.6, and 48.4 ± 23.8 and 328.5 ± 117.1 m, 310.8 ± 98.9 m, and 250.7 ± 104.3 m (P < 0.01 for both). After accounting for baseline 6MWD, frailty status at baseline, but not KCCQ-PLS, was significantly associated with 6MWD at 24 weeks. By 24 weeks, 47.5% of patients had no change in frailty, 45.5% had become less frail, and 7.0% had become more frail. Treatment with vericiguat did not alter frailty status at 24 weeks.

CONCLUSIONS

Patient-reported frailty is modestly correlated with both the KCCQ-PLS and 6MWD but offers prognostic insight into 6MWD at 24 weeks. (Patient-reported Outcomes in Vericiguat-treated Patients With HFpEF [VITALITY-HFpEF]; NCT03547583).

Soluble guanylate cyclase stimulators in patients with heart failure with reduced ejection fraction across the risk spectrum

Patients with heart failure with reduced ejection fraction (HFrEF) have a high residual risk of adverse outcomes, even when treated with optimal guideline-directed medical therapy and in a clinically stable state. Soluble guanylate cyclase (sGC) stimulators have the potential to lower this risk by modifying the nitric oxide-sGC-cyclic guanosine monophosphate cascade - a pathophysiological pathway that has been targeted with limited success in HFrEF previously. Vericiguat, an sGC stimulator, was shown to improve outcomes in patients with HFrEF in the VICTORIA (Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction) trial. However, this trial included patients with recently worsening disease. In this brief review, we discuss the rationale of evaluating sGC stimulators in lower-risk HFrEF patients. First, all key HFrEF medications have been evaluated in both higher- and lower-risk populations, and the treatment effect is not always consistent across the risk spectrum. Second, pre-clinical studies and post-hoc studies of the VICTORIA trial have suggested that sGC stimulators may have cardioprotective effects - these effects may be more apparent when the medication is initiated earlier in the disease process. Third, the effect of vericiguat on cardiovascular mortality remains uncertain and a trial with a longer follow-up in a lower-risk population may allow better assessment of its effect on cardiovascular mortality. Therefore, there is a pertinent need to investigate the effects of vericiguat in optimally treated, low-risk HFrEF patients (i.e. those without recently worsening heart failure).

Sequential Evaluation of NT-proBNP in Heart Failure: Insights Into Clinical Outcomes and Efficacy of Vericiguat

BACKGROUND

The effect of vericiguat on sequential N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels and influence of this relationship on clinical outcomes is unknown.

OBJECTIVES

This study assessed the relationship between changes in NT-proBNP and the primary outcome (cardiovascular death or heart failure hospitalization); evaluated the effect of vericiguat on changes in NT-proBNP; and explored the association between the efficacy of vericiguat and changes in NT-proBNP.

METHODS

NT-proBNP was measured at randomization and at 16, 32, 48, and 96 weeks in 4,805 of 5,050 patients. The association between NT-proBNP change at week 16 and the primary outcome was assessed. The relationship between changes in NT-proBNP and the primary outcome according to treatment group was assessed by using joint modeling and mediation analysis.

RESULTS

A significant and sustained decline in NT-proBNP levels was seen in both treatment groups. After week 16, NT-proBNP levels decreased more with vericiguat vs placebo (any reduction: odds ratio [OR]: 1.45 [95% CI: 1.28-1.65]; P < 0.001; ≥50% reduction: OR: 1.27 [95% CI: 1.10-1.47]; P = 0.001) and were less likely to increase (≥20% increase: OR: 0.68 [95% CI: 0.59-0.78]; P < 0.001; ≥50% increase: OR: 0.70 [95% CI: 0.59-0.82]; P < 0.001). The treatment effect related to serial NT-proBNP on the primary composite outcome was HR: 0.96 (95% CI: 0.95-0.99) at week 16, which increased to HR: 0.90 (95% CI: 0.85-0.96) at week 48; the average extent of mediation of the composite outcome related to NT-proBNP was 45%.

CONCLUSIONS

In patients with worsening HFrEF, vericiguat significantly decreased NT-proBNP levels compared with placebo. This change appeared associated with a modest relative improvement in the primary outcome of cardiovascular death or heart failure hospitalization. (Vericiguat Global Study in Subjects With Heart Failure With Reduced Ejection Fraction [VICTORIA]; NCT02861534).

Contemporary outpatient management of patients with worsening heart failure with reduced ejection fraction: Rationale and design of the CHART-HF study

BACKGROUND

Patients with heart failure with reduced ejection fraction (HFrEF) and worsening HF events (WHFE) represent a distinct subset of patients with a substantial comorbidity burden, greater potential for intolerance to medical therapy, and high risk of subsequent death, hospitalization and excessive healthcare costs. Although multiple therapies have been shown to be efficacious and safe in this high-risk population, there are limited real-world data regarding factors that impact clinical decision-making when initiating or modifying therapy. Likewise, prior analyses of US clinical practice support major gaps in medical therapy for HFrEF and few medication changes during longitudinal follow-up, yet granular data on reasons why clinicians do not initiate or up-titrate guideline-directed medication are lacking.

METHODS

We designed the CHART-HF study, an observational study of approximately 1,500 patients comparing patients with and without WHFE (WHFE defined as receipt of intravenous diuretics in the inpatient, outpatient, or emergency department setting) who had an index outpatient visit in the US between 2017 and 2019. Patient-level data on clinical characteristics, clinical outcomes, and therapy will be collected from 2 data sources: a single integrated health system, and a national panel of cardiologists. Furthermore, clinician-reported rationale for treatment decisions and the factors prioritized with selection and optimization of therapies in real-world practice will be obtained. To characterize elements of clinician decision-making not documented in the medical record, the panel of cardiologists will review records of patients seen under their care to explicitly note their primary reason for initiating, discontinuing, and titrating medications specific medications, as well as the reason for not making changes to each medication during the outpatient visit.

CONCLUSIONS

Results from CHART-HF have the potential to detail real-world US practice patterns regarding care of patients with HFrEF with versus without a recent WHFE, to examine clinician-reported reasons for use and non-use of guideline-directed medical therapy, and to characterize the magnitude and nature of clinical inertia toward evidence-based medication changes for HFrEF.

Population Pharmacokinetics of Vericiguat in Patients with Heart Failure with Reduced Ejection Fraction: An Integrated Analysis

Vericiguat, a novel stimulator of soluble guanylate cyclase (sGC), is indicated for the treatment of patients following a hospitalization for heart failure or need for outpatient IV diuretics, with symptomatic chronic heart failure and ejection fraction less than 45%. Pharmacokinetic (PK) data from the phase II trial SOCRATES-REDUCED (SOluble guanylate Cyclase stimulatoR in heArT failurE Study) and the phase III trial VICTORIA (Vericiguat Global Study in Patients with Heart Failure with Reduced Ejection Fraction) were used to characterize vericiguat PK. A total of 8,092 concentration records from 2,321 participants (362 from SOCRATES-REDUCED and 1,959 from VICTORIA) were utilized for the development of the population PK (PPK) model. The final PK model was a one-compartment model with first-order absorption and linear elimination. Baseline body weight and time-varying body weight were identified as statistically significant covariates affecting apparent clearance (CL/F) and volume of distribution (V_c ), respectively. Age, sex, race, bilirubin, estimated glomerular filtration rate (eGFR), and albumin did not affect vericiguat PK. Baseline disease-related factors, such as left ventricular ejection fraction, New York Heart Association (NYHA) class, and N-terminal pro B-type natriuretic peptide (NT-proBNP), also did not influence vericiguat PK. Since vericiguat is a titrated drug, the impact of vericiguat PK on the titration to and maintenance of the target dose in VICTORIA was assessed. The distribution of steady-state doses in VICTORIA was similar across CL/F quartiles, suggesting that the ability to reach and maintain dosing at the target 10 mg dose was not related to vericiguat exposure.

Vericiguat and Health-Related Quality of Life in Patients With Heart Failure With Reduced Ejection Fraction: Insights From the VICTORIA Trial

BACKGROUND

We examined the effects of vericiguat compared with placebo in patients with heart failure with reduced ejection fraction enrolled in VICTORIA (Vericiguat Global Study in Patients With Heart Failure With Reduced Ejection Fraction) on health status outcomes measured by the Kansas City Cardiomyopathy Questionnaire (KCCQ) and evaluated whether clinical outcomes varied by baseline KCCQ score.

METHODS

KCCQ was completed at baseline and 4, 16, and 32 weeks. We assessed treatment effect on KCCQ using a mixed-effects model adjusting for baseline KCCQ and stratification variables. Cox proportional-hazards modeling was performed to evaluate the effect of vericiguat on clinical outcomes by tertiles of baseline KCCQ clinical summary score (CSS), total symptom score (TSS), and overall summary score (OSS).

RESULTS

Of 5050 patients, 4664, 4741, and 4470 had KCCQ CSS (median [25th to 75th], 65.6 [45.8-81.8]), TSS (68.8 [47.9-85.4]), and OSS (59.9 [42.0-77.1]) at baseline; 94%, 88%, and 82% had data at 4, 16, and 32 weeks. At 16 weeks, CSS improved by a median of 6.3 in both arms; no significant differences in improvement were seen for TSS and OSS between the 2 groups (P=0.69, 0.97, and 0.13 for CSS, TSS, and OSS). Trends were similar at 4 and 32 weeks. Vericiguat versus placebo reduced cardiovascular death or heart failure hospitalization risk similarly across tertiles of baseline KCCQ CSS, TSS, and OSS (interaction P=0.13, 0.21, and 0.65).

CONCLUSIONS

Vericiguat did not significantly improve KCCQ scores compared with placebo. Vericiguat reduced the risk of cardiovascular death or heart failure hospitalization across the range of baseline health status.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT02861534.

Defining Changes in Physical Limitation from the Patient Perspective: Insights from the VITALITY-HFpEF Randomized Trial

BACKGROUND

Clinically important thresholds in patient-reported outcomes measures like the Kansas City Cardiomyopathy Questionnaire (KCCQ) have not been defined for patients with heart failure and preserved ejection fraction (HFpEF). The aim of this study was to estimate meaningful thresholds for improvement or worsening in the KCCQ-Physical Limitation Score (PLS) in patients with HFpEF.

METHODS

In this pre-specified analysis from VITALITY-HFpEF, anchor- and distribution-based approaches were used to estimate thresholds for improvement or worsening in the KCCQ-PLS using Patient Global Impression of Change (PGIC) as an anchor. The KCCQ-PLS contains 6 elements, with each increment in response resulting in a change of 4.17 points when converted to a 0-100 scale. The mean change in KCCQ-PLS from baseline to week 12 was calculated for each PGIC group to estimate a meaningful within-patient change.

RESULTS

Of 789 patients enrolled, 698 had complete KCCQ-PLS and PGIC data at week 12. The mean (±SD) changes in KCCQ-PLS corresponding to PGIC changes of "a little better," "better," and "much better" were 5.7±18.6, 11.6±19.3, and 18.4±25.3 points, respectively. The scores of patients who responded "a little better" (n=177) overlapped substantially with those who reported "no change" (n=193; mean change 2.8±18.9). The mean change in KCCQ-PLS for patients responding "a little worse" (n=32) was -2.6±18.0 points. The threshold for meaningful within-patient change in KCCQ-PLS based on distribution-based analyses was 12.3 points. Using area-under-curve (AUC) analyses of KCCQ-PLS, the sensitivity and specificity of a 4.17-point change were 0.61 and 0.57, for an 8.33-point change they were 0.49 and 0.64, and for a 12.5-point change were 0.44 and 0.72 for being at least a little better on the PGIC (AUC=0.54).

CONCLUSION

In the VITALITY-HFpEF trial, a change in KCCQ-PLS of ≥8.33 points (corresponding to an improvement in ≥2 response categories of KCCQ-PLS) may represent the minimal clinically important difference for improvement and a change of ≤ -4.17 points (corresponding to a worsening in ≥1 response category of KCCQ-PLS) may suggest deterioration in patients with HFpEF.

Vericiguat in Patients with Coronary Artery Disease and Heart Failure with Reduced Ejection Fraction

AIMS

Coronary artery disease (CAD) portends worse outcomes in heart failure (HF). We aimed to characterize patients with CAD and worsening HF with reduced ejection fraction (HFrEF) and evaluate post hoc whether vericiguat's treatment effect varied according to CAD.

METHODS AND RESULTS

Cox proportional hazards were generated for the primary endpoint of cardiovascular death or HF hospitalization (CVD/HFH). CAD was defined as previous myocardial infarction, percutaneous coronary intervention, or coronary artery bypass grafting. Of 5048 patients in VICTORIA with available data on CAD status, 2704 had CAD and were older, were more frequently male, diabetic, and had a lower glomerular filtration rate than those without CAD (all p <0.0001). Use of implantable cardioverter defibrillators and cardiac resynchronization therapy (CRT) was higher in patients with versus without CAD (33.5 vs. 21.1%; p <0.0001 and 16.3 vs. 12.8%; p = 0.0006). The primary endpoint of CVD/HFH was higher in those with versus without CAD (40.6 vs. 30.1/100 patient-years; adjusted hazard ratio [HR] 1.23; p <0.001) as was all-cause mortality (17.9% vs. 12.7%; adjusted HR 1.32; p <0.001). The primary outcome of CVD/HFH associated with vericiguat in patients with or without CAD was 38.8 vs. 27.6 per 100 patient-years and for placebo was 42.6 vs. 32.7 per 100 patient-years (interaction p = 0.78).

CONCLUSION

In this post hoc study, CAD was associated with more CVD and HFH in patients with HFrEF and worsening HF. Vericiguat was beneficial and safe regardless of concomitant CAD. This article is protected by copyright. All rights reserved.

Invention of MK-8262, a Cholesteryl Ester Transfer Protein (CETP) Inhibitor Backup to Anacetrapib with Best-in-Class Properties

Cholesteryl ester transfer protein (CETP) represents one of the key regulators of the homeostasis of lipid particles, including high-density lipoprotein (HDL) and low-density lipoprotein (LDL) particles. Epidemiological evidence correlates increased HDL and decreased LDL to coronary heart disease (CHD) risk reduction. This relationship is consistent with a clinical outcomes trial of a CETP inhibitor (anacetrapib) combined with standard of care (statin), which led to a 9% additional risk reduction compared to standard of care alone. We discuss here the discovery of MK-8262, a CETP inhibitor with the potential for being the best-in-class molecule. Novel in vitro and in vivo paradigms were integrated to drug discovery to guide optimization informed by a critical understanding of key clinical adverse effect profiles. We present preclinical and clinical evidence of MK-8262 safety and efficacy by means of HDL increase and LDL reduction as biomarkers for reduced CHD risk.

Effect of Vericiguat vs Placebo on Quality of Life in Patients With Heart Failure and Preserved Ejection Fraction: The VITALITY-HFpEF Randomized Clinical Trial

IMPORTANCE

Patients with heart failure and preserved ejection fraction (HFpEF) are at high risk of mortality, hospitalizations, and reduced functional capacity and quality of life.

OBJECTIVE

To assess the efficacy of the oral soluble guanylate cyclase stimulator vericiguat on the physical limitation score (PLS) of the Kansas City Cardiomyopathy Questionnaire (KCCQ).

DESIGN, SETTING, AND PARTICIPANTS

Phase 2b randomized, double-blind, placebo-controlled, multicenter trial of 789 patients with chronic HFpEF and left ventricular ejection fraction 45% or higher with New York Heart Association class II-III symptoms, within 6 months of a recent decompensation (HF hospitalization or intravenous diuretics for HF without hospitalization), and with elevated natriuretic peptides, enrolled at 167 sites in 21 countries from June 15, 2018, through March 27, 2019; follow-up was completed on November 4, 2019.

INTERVENTIONS

Patients were randomized to receive vericiguat, up-titrated to 15-mg (n = 264) or 10-mg (n = 263) daily oral dosages, compared with placebo (n = 262) and randomized 1:1:1.

MAIN OUTCOMES AND MEASURES

The primary outcome was change in the KCCQ PLS (range, 0-100; higher values indicate better functioning) after 24 weeks of treatment. The secondary outcome was 6-minute walking distance from baseline to 24 weeks.

RESULTS

Among 789 randomized patients, the mean age was 72.7 (SD, 9.4) years; 385 (49%) were female; mean EF was 56%; and median N-terminal pro-brain natriuretic peptide level was 1403 pg/mL; 761 (96.5%) completed the trial. The baseline and 24-week KCCQ PLS means for the 15-mg/d vericiguat, 10-mg/d vericiguat, and placebo groups were 60.0 and 68.3, 57.3 and 69.0, and 59.0 and 67.1, respectively, and the least-squares mean changes were 5.5, 6.4, and 6.9, respectively. The least-squares mean difference in scores between the 15-mg/d vericiguat and placebo groups was -1.5 (95% CI, -5.5 to 2.5; P = .47) and between the 10-mg/d vericiguat and placebo groups was -0.5 (95% CI, -4.6 to 3.5; P = .80). The baseline and 24-week 6-minute walking distance mean scores in the 15-mg/d vericiguat, 10-mg/d vericiguat, and placebo groups were 295.0 m and 311.8m , 292.1 m and 318.3 m, and 295.8 m and 311.4 m, and the least-squares mean changes were 5.0 m, 8.7 m, and 10.5 m, respectively. The least-squares mean difference between the 15-mg/d vericiguat and placebo groups was -5.5 m (95% CI, -19.7 m to 8.8 m; P = .45) and between the 10-mg/d vericiguat and placebo groups was -1.8 m (95% CI, -16.2 m to 12.6 m; P = .81), respectively. The proportions of patients who experienced symptomatic hypotension were 6.4% in the 15-mg/d vericiguat group, 4.2% in the 10-mg/d vericiguat group, and 3.4% in the placebo group; those with syncope were 1.5%, 0.8%, and 0.4%, respectively.

CONCLUSIONS AND RELEVANCE

Among patients with HFpEF and recent decompensation, 24-week treatment with vericiguat at either 15-mg/d or 10-mg/d dosages compared with placebo did not improve the physical limitation score of the KCCQ.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03547583.

Bayesian Meta-analysis of Safety Outcomes Using Blinded Clinical Trial Data

BACKGROUND

During the development of an investigational new drug, identifying potential safety risks is imperative. Early detection, as well as federal regulations, requires safety monitoring procedures during clinical trials while the data are still blinded.

METHOD

We introduce a Bayesian meta-analytic approach for detecting a potential elevated safety risk conferred by an investigational treatment, as compared to control, using blinded data from multiple trials.

RESULTS

Simulation studies of our approach demonstrate good operating characteristics when some relevant prior information is available. The utility of our procedure is demonstrated on data from a real clinical trial program with informative results based on blinded data compared with unblinded data.

CONCLUSION

At any time during the drug development program, our approach provides easily interpretable posterior probability statements about the risk ratio for the safety event(s) of interest.

Impact of drug distribution into adipose on tissue function: The cholesteryl ester transfer protein (CETP) inhibitor anacetrapib as a test case

Anacetrapib is an inhibitor of cholesteryl ester transfer protein (CETP) previously under development as a lipid-modifying agent that reduces LDL-cholesterol and increases HDL-cholesterol in hypercholesterolemic patients. Anacetrapib demonstrates a long terminal half-life and accumulates in adipose tissue, which contributes to a long residence time of anacetrapib. Given our previous report that anacetrapib distributes into the lipid droplet of adipose tissue, we sought to understand whether anacetrapib affected adipose function, using a diet-induced obese (DIO) mouse model. Following 20 weeks of treatment with anacetrapib (100 mg/kg/day), levels of the drug increased to approximately 0.6 mmol/L in white adipose tissue. This level of anacetrapib was not associated with any impairment in adipose functionality as evidenced by a lack of any reduction in biomarkers of adipose functionality (plasma adiponectin, leptin, insulin; adipose adiponectin, leptin mRNA). In DIO wild-type (WT) mice treated with anacetrapib for 2 weeks and then subjected to 30% food restriction during washout to induce weight loss (18%) and fat mass loss (7%), levels of anacetrapib in adipose and plasma were not different between food restricted and ad lib-fed mice. These data indicate that despite deposition and long-term residence of ~0.6 mmol/L levels of anacetrapib in adipose tissue, adipose tissue function appears to be unaffected in mice. In addition, these data also indicate that even with severe caloric restriction and acute loss of fat mass, anacetrapib does not appear to be mobilized from the fat depot, thereby solidifying the role of adipose as a long-term storage site of anacetrapib.

Impact of ADCY9 Genotype on Response to Anacetrapib

BACKGROUND

Exploratory analyses of previous randomized trials generated a hypothesis that the clinical response to cholesteryl ester transfer protein (CETP) inhibitor therapy differs by ADCY9 genotype, prompting the ongoing dal-GenE trial in individuals with a particular genetic profile. The randomized placebo-controlled REVEAL trial (Randomized Evaluation of the Effects of Anacetrapib through Lipid-Modification) demonstrated the clinical efficacy of the CETP inhibitor anacetrapib among patients with preexisting atherosclerotic vascular disease. In the present study, we examined the impact of ADCY9 genotype on response to anacetrapib in the REVEAL trial.

METHODS

Individuals with stable atherosclerotic vascular disease who were treated with intensive atorvastatin therapy received either anacetrapib 100 mg daily or matching placebo. Cox proportional hazards models, adjusted for the first 5 principal components of ancestry, were used to estimate the effects of allocation to anacetrapib on major vascular events (a composite of coronary death, myocardial infarction, coronary revascularization, or presumed ischemic stroke) and the interaction with ADCY9 rs1967309 genotype.

RESULTS

Among 19 210 genotyped individuals of European ancestry, 2504 (13.0%) had a first major vascular event during 4 years median follow-up: 1216 (12.6%) among anacetrapib-allocated participants and 1288 (13.4%) among placebo-allocated participants. Proportional reductions in the risk of major vascular events with anacetrapib did not differ significantly by ADCY9 genotype: hazard ratio (HR) = 0.92 (95% CI, 0.81-1.05) for GG; HR = 0.94 (95% CI, 0.84-1.06) for AG; and HR = 0.93 (95% CI, 0.76-1.13) for AA genotype carriers, respectively; genotypic P for interaction = 0.96. Furthermore, there were no associations between ADCY9 genotype and the proportional reductions in the separate components of major vascular events or meaningful differences in lipid response to anacetrapib.

CONCLUSIONS

The REVEAL trial is the single largest study to date evaluating the ADCY9 pharmacogenetic interaction. It provides no support for the hypothesis that ADCY9 genotype is materially relevant to the clinical effects of the CETP inhibitor anacetrapib. The ongoing dal-GenE study will provide direct evidence as to whether there is any specific pharmacogenetic interaction with dalcetrapib.

CLINICAL TRIAL REGISTRATION

URL: https://www.

CLINICALTRIALS

gov. Unique identifier: NCT01252953. URL: http://www.isrctn.com. Unique identifier: ISRCTN48678192. URL: https://www.clinicaltrialsregister.eu. Unique identifier: 2010-023467-18.

HDL-cholesterol levels and risk of age-related macular degeneration: a multiethnic genetic study using Mendelian randomization

Background

Dyslipidemia, particularly high-density lipoprotein cholesterol (HDL-C), has recently been implicated in the pathogenesis of age-related macular degeneration (AMD), the leading cause of vision loss. However, epidemiological studies have yielded conflicting results.

Methods

We investigated the causal role of plasma lipid levels in AMD in multiethnic populations comprising 16 144 advanced AMD cases and 17 832 controls of European descent, together with 2219 cases and 5275 controls of Asian descent, using Mendelian randomization in three models. Model 1 is a conventional meta-analysis which does not account for pleiotropy of instrumental variable (IV) effects. Model 2 is a univariate, inverse variance weighted regression analysis that accounts for potential unbalanced pleiotropy using MR-Egger method. Finally, Model 3 is a multivariate regression analysis that addresses pleiotropy by MR-Egger method and by adjusting for effects on other lipid traits.

Results

A 1 standard deviation (SD) higher HDL-cholesterol level was associated with an odds ratio (OR) for AMD of 1.17 (95% confidence interval: 1.07–1.29) in Europeans (P = 6.88 × 10^–4) and of 1.58 (1.24–2.00) in Asians (P = 2.92 × 10^–4) in Model 3. The corresponding OR estimates were 1.30 (1.09–1.55) in Europeans (P = 3.18 × 10^–3) and 1.42 (1.11—1.80) in Asians (P = 4.42 × 10^–3) in Model 1, and 1.21 (1.11–1.31) in Europeans (P = 3.12 × 10^–5) and 1.51 (1.20–1.91) in Asians (P = 7.61 × 10^–4) in Model 2. Conversely, neither LDL-C (Europeans: OR = 0.96, P = 0.272; Asians: OR = 1.02, P = 0.874; Model 3) nor triglyceride levels (Europeans: OR = 0.91, P = 0.102; Asians: OR = 1.06, P = 0.613) were associated with AMD. We also assessed the association between lipid levels and polypoidal choroidal vasculopathy (PCV) in Asians, a subtype of AMD, and found a similar trend for association of PCV with HDL-C levels.

Conclusions

Our study shows that high levels of plasma HDL-C are causally associated with an increased risk for advanced AMD in European and Asian populations, implying that strategies reducing HDL-C levels may be useful to prevent and treat AMD.

Comprehensive healthcare resource use among newly diagnosed congestive heart failure

BACKGROUND

Congestive heart failure (CHF) is among the most common causes of hospital admissions and readmissions in the Western world. However, the burden of ambulatory care has not been as well investigated. The objective of this study was to assess the relative burden and direct medical costs of CHF including inpatient and outpatient care.

METHODS

We used longitudinal clinical data from a two-million member health organization in Israel (Maccabi Healthcare Services) to identify adults with newly diagnosed CHF between January 2006 and December 2012, either in the in- or outpatient setting. Adults without CHF were age- and sex-matched to CHF patients and healthcare utilization and all modes of healthcare costs were compared among them, excluding those in their last year of life.

RESULTS

The burden posed by 6592 CHF patients was significantly (p < 0.001) larger than that of 32,960 matched controls. CHF patients had significantly higher rates of baseline comorbidity and healthcare utilization compared to non-CHF controls. This was evident in all categories of healthcare services and expenses, including in- and outpatient visits, laboratory expenses, medication costs, among younger and older, men and women. Among those who incurred any healthcare costs, younger (45-64y) and older (65 + y) subjects with CHF were observed to have about 3.25 (95% CI: 2.96-3.56) and 2.08 (95% CI: 1.99-2.17) times the healthcare costs, respectively, compared to subjects without CHF after adjusting for patient characteristics.

CONCLUSION

CHF is associated with an overall two- to three-fold higher cost of healthcare services depending on patient age, accounting for over half of all healthcare costs incurred by elderly CHF patients, and more than two-thirds of all costs among younger CHF patients. Observations of the large burden posed on one of the youngest societies in the developed world are profound, implicative of great opportunities to control the costs of CHF. Further research to understand how resource use impacts health outcomes and quality of care is warranted.

A randomized, open-label, dose-response study of losartan in hypertensive children

BACKGROUND AND OBJECTIVES

Once-daily losartan reduces BP in a dose-dependent manner and is well tolerated in hypertensive children aged 6-16 years. This study assessed the dose-response relationship, safety, and tolerability of losartan in hypertensive children aged 6 months to 6 years.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a 12-week, randomized, open-label, dose-ranging study, with a 2-year extension. Patients were randomized to losartan at the following dosages: 0.1 mg/kg per day (low), 0.3 mg/kg per day (medium), or 0.7 mg/kg per day (high). Losartan was titrated to the next dose level (to a 1.4 mg/kg per day maximum dosage, not exceeding 100 mg/d, which was not one of the three original doses offered at randomization) at weeks 3, 6, and 9 for patients who did not attain their goal BP and were not taking the highest dose. Dose response was evaluated by analyzing the slope of change in sitting systolic BP (SBP; primary end point) and diastolic BP (DBP; secondary end point) after 3 weeks compared with baseline. Adverse events (AEs) were recorded throughout.

RESULTS

Of the 101 patients randomized, 99 were included in the analysis (low dose, n=32; medium dose, n=34; and high dose, n=33). Mean sitting BP decreased from baseline in the low-, medium-, and high-dose groups by 7.3, 7.6, and 6.7 mmHg, respectively, for SBP and 8.2, 5.1, and 6.7 mmHg, respectively, for DBP after 3 weeks. No dose-response relationship was established by the slope analysis on SBP (P=0.75) or DBP (P=0.64). The BP-lowering effect was observed throughout the 2-year extension. The incidence of AEs was low and comparable between groups.

CONCLUSIONS

Hypertensive children aged 6 months to 6 years treated with losartan 0.1-0.7 mg/kg per day had clinically significant decreases from baseline in SBP and DBP, yet no dose-response relationship was evident. Losartan, at a dosage up to 1.4 mg/kg per day, was well tolerated.

Role of SREBP-1 in the development of parasympathetic dysfunction in the hearts of type 1 diabetic Akita mice

RATIONALE

Diabetic autonomic neuropathy (DAN), a major complication of diabetes mellitus, is characterized, in part, by impaired cardiac parasympathetic responsiveness. Parasympathetic stimulation of the heart involves activation of an acetylcholine-gated K+ current, I(KAch), via a (GIRK1)2/(GIRK4)2 K+ channel. Sterol regulatory element binding protein-1 (SREBP-1) is a lipid-sensitive transcription factor.

OBJECTIVE

We describe a unique SREBP-1-dependent mechanism for insulin regulation of cardiac parasympathetic response in a mouse model for DAN.

METHODS AND RESULTS

Using implantable EKG transmitters, we demonstrated that compared with wild-type, Ins2(Akita) type I diabetic mice demonstrated a decrease in the negative chronotropic response to carbamylcholine characterized by a 2.4-fold decrease in the duration of bradycardia, a 52+/-8% decrease in atrial expression of GIRK1 (P<0.01), and a 31.3+/-2.1% decrease in SREBP-1 (P<0.05). Whole-cell patch-clamp studies of atrial myocytes from Akita mice exhibited a markedly decreased carbamylcholine stimulation of I(KAch) with a peak value of -181+/-31 pA/pF compared with -451+/-62 pA/pF (P<0.01) in cells from wild-type mice. Western blot analysis of extracts of Akita mice demonstrated that insulin treatment increased the expression of GIRK1, SREBP-1, and I(KAch) activity in atrial myocytes from these mice to levels in wild-type mice. Insulin treatment of cultured atrial myocytes stimulated GIRK1 expression 2.68+/-0.12-fold (P<0.01), which was reversed by overexpression of dominant negative SREBP-1. Finally, adenoviral expression of SREBP-1 in Akita atrial myocytes reversed the impaired I(KAch) to levels in cells from wild-type mice.

CONCLUSIONS

These results support a unique molecular mechanism for insulin regulation of GIRK1 expression and parasympathetic response via SREBP-1, which might play a role in the pathogenesis of DAN in response to insulin deficiency in the diabetic heart.

Preventing voltage-dependent gating of anthrax toxin channels using engineered disulfides

The channel-forming component of anthrax toxin, (PA(63))(7), is a heptameric water-soluble protein at neutral pH, but under acidic conditions it spontaneously inserts into lipid bilayers to form a 14-stranded beta-barrel ion-conducting channel. This channel plays a vital role in anthrax pathogenesis because it serves as a conduit for the membrane translocation of the two enzymatic components of anthrax toxin, lethal factor and edema factor. Anthrax channels open and close in response to changes in transmembrane voltage, a property shared by several other pore-forming toxins. We have discovered an unexpected phenomenon in cysteine-substituted channels that provides a window into this gating process: their normal voltage-dependent gating can be abolished by reaction with methanethiosulfonate (MTS) reagents or exposure to oxidizing conditions. Remarkably, this perturbation is seen with cysteines substituted at sites all along the approximately 100 A length of the channel's beta-barrel. In contrast, reaction with N-ethylmaleimide, a thiol-reactive compound that does not form a mixed disulfide, does not affect gating at any of the sites tested. These findings, coupled with our biochemical detection of dimers, have led us to conclude that MTS reagents are catalyzing the formation of intersubunit disulfide bonds that lock channels in a conducting state, and that voltage gating requires a conformational change that involves the entire beta-barrel.

Parasympathetic response in chick myocytes and mouse heart is controlled by SREBP

Parasympathetic stimulation of the heart, which provides protection from arrhythmias and sudden death, involves activation of the G protein-coupled inward rectifying K+ channel GIRK1/4 and results in an acetylcholine-sensitive K+ current, I KACh. We describe a unique relationship between lipid homeostasis, the lipid-sensitive transcription factor SREBP-1, regulation of the cardiac parasympathetic response, and the development of ventricular arrhythmia. In embryonic chick atrial myocytes, lipid lowering by culture in lipoprotein-depleted serum increased SREBP-1 levels, GIRK1 expression, and I KACh activation. Regulation of the GIRK1 promoter by SREBP-1 and lipid lowering was dependent on interaction with 2 tandem sterol response elements and an upstream E-box motif. Expression of dominant negative SREBP-1 (DN-SREBP-1) reversed the effect of lipid lowering on I KACh and GIRK1. In SREBP-1 knockout mice, both the response of the heart to parasympathetic stimulation and the expression of GIRK1 were reduced compared with WT. I KACh, attenuated in atrial myocytes from SREBP-1 knockout mice, was stimulated by SREBP-1 expression. Following myocardial infarction, SREBP-1 knockout mice were twice as likely as WT mice to develop ventricular tachycardia in response to programmed ventricular stimulation. These results demonstrate a relationship between lipid metabolism and parasympathetic response that may play a role in arrhythmogenesis.

Constraints on voltage sensor movement in the shaker K+ channel

In nerve and muscle cells, the voltage-gated opening and closing of cation-selective ion channels is accompanied by the translocation of 12-14 elementary charges across the membrane's electric field. Although most of these charges are carried by residues in the S4 helix of the gating module of these channels, the precise nature of their physical movement is currently the topic of spirited debate. Broadly speaking, two classes of models have emerged: those that suggest that small-scale motions can account for the extensive charge displacement, and those that invoke a much larger physical movement. In the most recent incarnation of the latter type of model, which is based on structural and functional data from the archaebacterial K(+) channel KvAP, a "voltage-sensor paddle" comprising a helix-turn-helix of S3-S4 translocates approximately 20 A through the bilayer during the gating cycle (Jiang, Y., A. Lee, J. Chen, V. Ruta, M. Cadene, B.T. Chait, and R. MacKinnon. 2003. Nature. 423:33-41; Jiang, Y., V. Ruta, J. Chen, A. Lee, and R. MacKinnon. 2003. Nature. 423:42-48.; Ruta, V., J. Chen, and R. MacKinnon. 2005. Cell. 123:463-475). We used two methods to test for analogous motions in the Shaker K(+) channel, each examining the aqueous exposure of residues near S3. In the first, we employed a pore-blocking maleimide reagent (Blaustein, R.O., P.A. Cole, C. Williams, and C. Miller. 2000. Nat. Struct. Biol. 7:309-311) to probe for state-dependent changes in the chemical reactivity of substituted cysteines; in the second, we tested the state-dependent accessibility of a tethered biotin to external streptavidin (Qiu, X.Q., K.S. Jakes, A. Finkelstein, and S.L. Slatin. 1994. J. Biol. Chem. 269:7483-7488; Slatin, S.L., X.Q. Qiu, K.S. Jakes, and A. Finkelstein. 1994. Nature. 371:158-161). In both types of experiments, residues predicted to lie near the top of S3 did not exhibit any change in aqueous exposure during the gating cycle. This lack of state dependence argues against large-scale movements, either axially or radially, of Shaker's S3-S4 voltage-sensor paddle.

Sizing the protein translocation pathway of colicin Ia channels

The bacterial toxin colicin Ia forms voltage-gated channels in planar lipid bilayers. The toxin consists of three domains, with the carboxy-terminal domain (C-domain) responsible for channel formation. The C-domain contributes four membrane-spanning segments and a 68-residue translocated segment to the open channel, whereas the upstream domains and the amino-terminal end of the C-domain stay on the cis side of the membrane. The isolated C-domain, lacking the two upstream domains, also forms channels; however, the amino terminus and one of the normally membrane-spanning segments can move across the membrane. (This can be observed as a drop in single-channel conductance.) In longer carboxy-terminal fragments of colicin Ia that include </=169 residues upstream from the C-domain, the entire upstream region is translocated. Presumably, a portion of the C-domain creates a pathway for the polar upstream region to move through the membrane. To determine the size of this translocation pathway, we have attached "molecular stoppers," small disulfide-bonded polypeptides, to the amino terminus of the C-domain, and determined whether they could be translocated. We have found that the translocation rate is strongly voltage dependent, and that at voltages >/=90 mV, even a 26-A stopper is translocated. Upon reduction of their disulfide bonds, all of the stoppers are easily translocated, indicating that it is the folded structure, rather than some aspect of the primary sequence, that slows translocation of the stoppers. Thus, the pathway for translocation is >/=26 A in diameter, or can stretch to this value. This is large enough for an alpha-helical hairpin to fit through.

Kinetics of tethering quaternary ammonium compounds to K(+) channels

Polymeric maleimido-quaternary ammonium (QA) compounds have been shown to function as molecular tape measures when covalently tethered to external cysteine residues of a Shaker K(+) channel (Blaustein R.O., P.A. Cole, C. Williams, and C. Miller. 2000. Nat. Struct. Biol. 7:309-311). For sufficiently long compounds, the cysteine-maleimide tethering reaction creates a high concentration, at the channel's pore, of a TEA-like moiety that irreversibly blocks current. This paper investigates a striking feature of the maleimide-cysteine tethering kinetics. Strong blockers-those that induce substantial levels (>80%) of irreversible inhibition of current-react with channel cysteines much more rapidly than weak blockers and, when delivered to channels with four cysteine targets, react with multiexponential kinetics. This behavior is shown to arise from the ability of a strong blocker to concentrate its maleimide end near a channel's cysteine target by exploiting the reversible pore-blocking affinity of its QA headgroup.

The diphtheria toxin channel-forming T-domain translocates its own NH2-terminal region and the catalytic domain across planar phospholipid bilayers

The T-domain of diphtheria toxin, which extends from residue 202 to 378, causes the translocation of the catalytic A fragment (residues 1-201) across endosomal membranes and also forms ion-conducting channels in planar phospholipid bilayers. The carboxy-terminal 57-amino acid segment (residues 322-378) in the T-domain is all that is required to form these channels, but its ability to do so is greatly augmented by the portion of the T-domain upstream from this. Here we show that in association with channel formation by the T-domain, its hydrophilic 63-amino acid NH2-terminal region (residues 202-264) as well as the entire catalytic A fragment (residues 1-201) cross the lipid bilayer. The phenomenon that enabled us to demonstrate this was the rapid closure of channels at cis negative voltages when a histidine tag was placed at various positions in the NH2-terminal region of the T-domain or in the A fragment; the inhibition of this effect by trans nickel established that the histidine tag was present on the trans side of the membrane. Thus, all of the machinery necessary to translocate the A fragment across membranes is built into the 114 residues at the carboxy-terminal end of the T-domain (residues 265-378), without the requirement of any proteins in the plasma membrane (e.g., toxin receptor) or of any other cellular components.

Tethered blockers as molecular 'tape measures' for a voltage-gated K+ channel

The propagation of electrical signals in excitable cells is orchestrated by a molecular family of voltage-dependent ion channel proteins. These K+, Na+, and Ca++ channels are all composed of four identical or similar units, each containing six transmembrane segments (S1-S6) in a roughly four-fold symmetric structure. The S5-S6 sequences fold into a central pore unit, which is surrounded by a voltage-gating module composed of S1-S4. The recent structure of KcsA, a two-transmembrane bacterial K+ channel, illuminates the physical character of the pore unit, but little is known about the arrangement of the surrounding S1-S4 sequences. To locate regions of this gating module in space, we synthesized a series of compounds of varying length that function as molecular 'tape measures': quaternary ammonium (QA) pore blockers that can be tethered to specific test residues. We show that in a Shaker K+ channel, the extracellular ends of S1 and S3 are approximately 30 ¿ from the tetraethylammonium (TEA) blocking site at the external opening of the pore. A portion of the S3-S4 loop is, at 17-18 ¿, considerably closer.

Topography of diphtheria Toxin's T domain in the open channel state

When diphtheria toxin encounters a low pH environment, the channel-forming T domain undergoes a poorly understood conformational change that allows for both its own membrane insertion and the translocation of the toxin's catalytic domain across the membrane. From the crystallographic structure of the water-soluble form of diphtheria toxin, a "double dagger" model was proposed in which two transmembrane helical hairpins, TH5-7 and TH8-9, anchor the T domain in the membrane. In this paper, we report the topography of the T domain in the open channel state. This topography was derived from experiments in which either a hexahistidine (H6) tag or biotin moiety was attached at residues that were mutated to cysteines. From the sign of the voltage gating induced by the H6 tag and the accessibility of the biotinylated residues to streptavidin added to the cis or trans side of the membrane, we determined which segments of the T domain are on the cis or trans side of the membrane and, consequently, which segments span the membrane. We find that there are three membrane-spanning segments. Two of them are in the channel-forming piece of the T domain, near its carboxy terminal end, and correspond to one of the proposed "daggers," TH8-9. The other membrane-spanning segment roughly corresponds to only TH5 of the TH5-7 dagger, with the rest of that region lying on or near the cis surface. We also find that, in association with channel formation, the amino terminal third of the T domain, a hydrophilic stretch of approximately 70 residues, is translocated across the membrane to the trans side.

Voltage-dependent block of anthrax toxin channels in planar phospholipid bilayer membranes by symmetric tetraalkylammonium ions. Single-channel analysis

Previous studies have shown that symmetric tetraalkylammonium ions affect, in a voltage-dependent manner, the conductance of membranes containing many channels formed by the PA65 fragment of anthrax toxin. In this paper we analyze this phenomenon at the single-channel level for tetrabutylammonium ion (Bu4N+). We find that Bu4N+ induces a flickery block of the PA65 channel when present on either side of the membrane, and this block is relieved by large positive voltages on the blocking-ion side. At high frequencies (greater than 2 kHz) we have resolved individual blocking events and measured the dwell times in the blocked and unblocked states. These dwell times have single-exponential distributions, with time constants tau b and tau u that are voltage dependent, consistent with the two-barrier, single-well potential energy diagram that we postulated in our previous paper. The fraction of time the channel spends unblocked [tau u/(tau u + tau b)] as a function of voltage is identical to the normalized conductance-voltage relation determined from macroscopic measurements of blocking, thus demonstrating that these single channels mirror the behavior seen with many (greater than 10,000) channels in the membrane. In going from large negative to large positive voltages (-100 to +160 mV) on the cis (PA65-containing) side of the membrane, one sees the mean blocked time (tau b) increase to a maximum at +60 mV and then steadily decline for voltages greater than +60 mV, thereby clearly demonstrating that Bu4N+ is driven through the channel by positive voltages on the blocking-ion side. In other words, the channel is permeable to Bu4N+. An interesting finding that emerges from analysis of the voltage dependence of mean blocked and unblocked times is that the blocking rate, with Bu4N+ present on the cis side of the membrane, plateaus at large positive cis voltages to a voltage-independent value consistent with the rate of Bu4N+ entry into the blocking site being diffusion limited.

Diffusion limitation in the block by symmetric tetraalkylammonium ions of anthrax toxin channels in planar phospholipid bilayer membranes

Current flow through the channel formed in planar phospholipid bilayer membranes by the PA65 fragment of anthrax toxin is blocked, in a voltage-dependent manner, by tetraalkylammonium ions (at micromolar concentrations), which bind to a blocking site within the channel lumen. We have presented evidence that diffusion plays a significant role in the kinetics of blocking by tetrabutylammonium ion (Bu4N+) from the cis (toxin-containing) side of the membrane (Blaustein, R. O., E. J. A. Lea, and A. Finkelstein. 1990. J. Gen. Physiol. 96:921-942); in this paper we examine the implications and consequences of diffusion control for binding kinetics. As expected for a diffusion-affected reaction, both the entry rate constant (kcis1) of Bu4N+ from the cis solution to the blocking site and the exit rate constant (kcis-1) of Bu4N+ from the blocking site to the cis solution are reduced if the viscosity of that medium is increased by the addition of dextran. In conformity with both thermodynamics and kinetic arguments, however, the voltage-dependent equilibrium binding constant, Keq (= kcis-1/kcis1), is not altered by the dextran-induced viscosity increase of the cis solution. The entry rate constants (kcis1) for tetrapentylammonium (Pe4N+), tetrahexylammonium (Hx4N+), and tetraheptylammonium (Hp4N+) are also diffusion controlled, and all of them, including that for Bu4N+, attain a voltage-independent plateau value at large positive cis voltages consistent with diffusion limitation. Although the plateau value of kcis1 for Hx4N+ is only a factor of 3 less than that for Bu4N+, the plateau value for Hp4N+ is a factor of 35 less. This precipitous fall in value indicates, from diffusion-limitation theory, that the diameter of the channel entrance facing the cis solution is not much larger than the diameter of Hp4N+, i.e., approximately 12 A.

Voltage-dependent block of anthrax toxin channels in planar phospholipid bilayer membranes by symmetric tetraalkylammonium ions. Effects on macroscopic conductance

In a recent paper (Blaustein, R. O., T. M. Koehler, R. J. Collier, and A. Finkelstein, 1989. Proc. Natl. Acad. Sci. USA. 86:2209-2213) we described the general channel-forming properties of the PA65 fragment of anthrax toxin in planar phospholipid bilayer membranes. In the present paper we extend our previous studies of the permeability properties of this channel, using a series of symmetric tetraalkylammonium (TAA) ions. Our main finding is that at micromolar concentrations on either the cis (toxin-containing) or trans side of a membrane containing many (greater than 1,000) channels, these ions, ranging in size from tetramethylammonium to tetrahexylammonium, induce a voltage-dependent reduction of membrane conductance. (We attribute a similar voltage-dependent reduction of membrane conductance by millimolar concentrations of HEPES to a cationic form of this buffer present at micromolar concentrations.) In going from large negative to large positive voltages (on the TAA side) one sees that the conductance first decreases from its value in the absence of TAA, reaches a minimum, and then rises back at larger positive voltages toward the level in the absence of TAA. Our interpretation of this behavior is that these symmetric TAA ions block the cation-selective PA65 channel in a voltage-dependent manner. We postulate that there is a single site within the channel to which TAA ions can bind and thereby block the passage of the major current-carrying ion (potassium). A blocking ion is driven into the site by modest positive voltages, but is driven off the site and through the channel by larger positive voltages, thus explaining the relief of block. (In the accompanying paper [Blaustein, R. O., E. J. A. Lea, and A. Finkelstein. 1990. J. Gen. Physiol. 96:921-942] we confirm this interpretation of the data by analysis at the single-channel level.) This means that these blocking ions can pass through the channel; the permeability to tetrahexylammonium, the largest ion studied, implies that the narrowest part of the channel has a diameter of at least 11 A.

Anthrax toxin: channel-forming activity of protective antigen in planar phospholipid bilayers

The three separate proteins that make up anthrax toxin--protective antigen (PA), edema factor (EF), and lethal factor (LF)--act in binary combinations to produce two distinct reactions in experimental animals: edema (PA + EF) and death (PA + LF). PA is believed to interact with a membrane receptor, and after proteolytic processing, to mediate endocytosis and subsequent translocation of EF or LF into the cytosol. PA can be separated, after mild trypsinolysis, into two fragments, PA65 (65 kDa) and PA20 (20 kDa). We demonstrate that trypsin-cleaved PA is capable of forming cation-selective channels in planar phospholipid bilayer membranes and that this activity is confined to the PA65 fragment; PA20, LF, and EF are devoid of channel-forming activity. These PA65 channels exhibit pH-dependent and voltage-dependent activity--a property reminiscent of the channels formed by the two-chain proteins diphtheria, tetanus, and botulinum toxins.

A hydroxide ion carrier in planar phospholipid bilayer membranes: (C6F5)2Hg (dipentafluorophenylmercury)

Although a number of molecules are known to function as current-carrying proton carriers across lipid bilayer membranes, no such hydroxide ion carriers have been found to date. We report that (C6F5)2Hg, which can function as a chloride ion carrier, can also carry a hydroxide ion. In 100 mM Na2SO4 solutions, membranes treated with (C6F5)2Hg are almost ideally selective for H+/OH- between pH 6.0 and 9.5. Membrane conductance varies linearly with [OH-] over this pH range and with the square of the (C6F5)2Hg concentration. The presumed current-carrying species is the dimer [(C6F5)2Hg]2OH-, which, along with the neutral molecule (C6F5)2Hg, shuttles back and forth within the bilayer. In 0.2 M NaCl at pH 9.5, the OH- and Cl- conductances are approximately equal. Thus, the carrier displays an approximately 10(4)-fold preference for OH- over Cl-.

The N-terminal half of the heavy chain of botulinum type A neurotoxin forms channels in planar phospholipid bilayers

The heavy chain of botulinum type A neurotoxin forms channels in planar phospholipid bilayer membranes. Channel activity is confined to the N-terminal half of this chain; the C-terminal half is inactive. Channel activity is stimulated by low pH (4.5-5.5) on the cis side (the side to which protein is added), neutral pH on the opposite (trans) side, and cis positive voltages. These findings are strikingly similar to those previously reported for analogous fragments of diphtheria and tetanus toxins.

[3H]mazindol binding associated with neuronal dopamine and norepinephrine uptake sites

[3H]Mazindol labels neuronal dopamine uptake sites in corpus striatum membranes (KD = 18 nM) and neuronal norepinephrine uptake sites in cerebral cortex and submaxillary/sublingual gland membranes (KD = 4 nM). The potencies of various inhibitors of biogenic amine uptake in reducing [3H]mazindol binding in striatal membranes correlate with their potencies for inhibition of neuronal [3H]dopamine accumulation, whereas their potencies in reducing [3H]mazindol binding to cortical and salivary gland membranes correlate with their potencies for inhibition of neuronal [3H]norepinephrine accumulation. Similar to the dopamine and norepinephrine uptake systems, [3H]mazindol binding in all three tissues is dependent upon sodium (with potassium, lithium, rubidium, and Tris being ineffective substitutes) and chloride (with sulfate and phosphate being ineffective substitutes). In membranes of the cerebral cortex and salivary gland, half-maximal stimulation is observed at 50-80 mM NaCl, whereas in membranes of the corpus striatum half-maximal stimulation occurs at 240 mM NaCl. In striatal membranes NaCl increases the affinity of [3H]mazindol binding with no effect on the maximal number of sites. The enhancement of affinity is due to a selective slowing of the dissociation of the ligand from its binding site. The association of [3H]mazindol binding sites with neuronal dopamine uptake sites in the corpus striatum is further supported by the reduction of [3H]mazindol binding sites in striatal membranes following destruction of dopaminergic neurons by 6-hydroxydopamine. Similarly, the association of [3H]mazindol binding sites with neuronal norepinephrine uptake sites in cerebral cortex is supported by the reduction of [3H]mazindol binding to cortical membranes following destruction of noradrenergic neurons by N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine.