Clinical burden and predictors of non-cardiovascular mortality and morbidity in advanced heart failure

BACKGROUND

The changing demographic of heart failure (HF) increases the exposure to non-cardiovascular (non-CV) events. We investigated the distribution of non-CV mortality/morbidity and the characteristics associated with higher risk of non-CV events in patients with advanced HF.

METHODS

Patients from the HELP-HF registry were stratified according to the number of 2018 HFA-ESC criteria for advanced HF. Endpoints were non-CV mortality and non-CV hospitalization. Competing risk analyses were performed assessing the association between HFA-ESC criteria and study outcomes and the additional predictors of non-CV endpoints.

RESULTS

One thousand one hundred and forty-nine patients were included (median age 77 years-IQR 69-83). At 6, 12, 18 and 22 months, cumulative incidence of CV vs non-CV mortality was 13% vs 5%, 17% vs 8%, 20% vs 12%, 23% vs 12%, and of CV vs non-CV hospitalization was 26% vs 11%, 38% vs 17%, 45% vs 20%, 50% vs 21%. HFA-ESC criteria were associated with increasing adjusted risk of CV death, whereas no association was observed for CV hospitalization, non-CV death and non-CV hospitalization. Predictors of non-CV death were age, chronic obstructive pulmonary disease, dementia, preserved ejection fraction, >1 HF hospitalization and hemoglobin.

CONCLUSIONS

Patients with advanced HF are exposed to high, even though not predominant, burden of non-CV outcomes. HFA-ESC criteria aid to stratify the risk of CV death, but are not associated with lower competing risk of non-CV outcomes. Alternative factors can be useful to define the patients with advanced HF at risk of non-CV events in order to better select patients for treatments specifically reducing CV risk.

Characteristics and outcomes of patients with tricuspid regurgitation and advanced heart failure

AIMS

To evaluate the role of tricuspid regurgitation in advanced heart failure.

METHODS

The multicenter observational HELP-HF registry enrolled consecutive patients with heart failure and at least one 'I NEED HELP' criterion evaluated at four Italian centers between January 2020 and November 2021. Patients with no data on tricuspid regurgitation and/or receiving tricuspid valve intervention during follow-up were excluded. The population was stratified by no/mild tricuspid regurgitation vs. moderate tricuspid regurgitation vs. severe tricuspid regurgitation. Variables independently associated with tricuspid regurgitation, as well as the association between tricuspid regurgitation and clinical outcomes were investigated. The primary outcome was all-cause mortality.

RESULTS

Among the 1085 patients included in this study, 508 (46.8%) had no/mild tricuspid regurgitation, 373 (34.4%) had moderate tricuspid regurgitation and 204 (18.8%) had severe tricuspid regurgitation. History of atrial fibrillation, any prior valve surgery, high dose of furosemide, preserved left ventricular ejection fraction, moderate/severe mitral regurgitation and pulmonary hypertension were found to be independently associated with an increased likelihood of severe tricuspid regurgitation. Estimated rates of 1-year all-cause death were of 21.4, 24.5 and 37.1% in no/mild tricuspid regurgitation, moderate tricuspid regurgitation and severe tricuspid regurgitation, respectively (log-rank P  < 0.001). As compared with nonsevere tricuspid regurgitation, severe tricuspid regurgitation was independently associated with a higher risk of all-cause mortality (adjusted hazard ratio 1.38, 95% confidence interval 1.01-1.88, P  = 0.042), whereas moderate tricuspid regurgitation did not.

CONCLUSION

In a contemporary, real-world cohort of patients with advanced heart failure, several clinical and echocardiographic characteristics are associated with an increased likelihood of severe tricuspid regurgitation. Patients with severe tricuspid regurgitation have an increased risk of mortality.

Guideline-directed medical therapy in severe heart failure with reduced ejection fraction: An analysis from the HELP-HF registry

AIM

Persistent symptoms despite guideline-directed medical therapy (GDMT) and poor tolerance of GDMT are hallmarks of patients with advanced heart failure (HF) with reduced ejection fraction (HFrEF). However, real-world data on GDMT use, dose, and prognostic implications are lacking.

METHODS AND RESULTS

We included 699 consecutive patients with HFrEF and at least one 'I NEED HELP' marker for advanced HF enrolled in a multicentre registry. Beta-blockers (BB) were administered to 574 (82%) patients, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers or angiotensin receptor-neprilysin inhibitors (ACEi/ARB/ARNI) were administered to 381 (55%) patients and 416 (60%) received mineralocorticoid receptor antagonists (MRA). Overall, ≥50% of target doses were reached in 41%, 22%, and 56% of the patients on BB, ACEi/ARB/ARNI and MRA, respectively. Hypotension, bradycardia, kidney dysfunction and hyperkalaemia were the main causes of underprescription and/or underdosing, but up to a half of the patients did not receive target doses for unknown causes (51%, 41%, and 55% for BB, ACEi/ARB/ARNI and MRA, respectively). The proportions of patients receiving BB and ACEi/ARB/ARNI were lower among those fulfilling the 2018 HFA-ESC criteria for advanced HF. Treatment with BB and ACEi/ARB/ARNI were associated with a lower risk of death or HF hospitalizations (adjusted hazard ratio [HR] 0.63, 95% confidence interval [CI] 0.48-0.84, and HR 0.74, 95% CI 0.58-0.95, respectively).

CONCLUSIONS

In a large, real-world, contemporary cohort of patients with severe HFrEF, with at least one marker for advanced HF, prescription and uptitration of GDMT remained limited. A significant proportion of patients were undertreated due to unknown reasons suggesting a potential role of clinical inertia either by the prescribing healthcare professional or by the patient. Treatment with BB and ACEi/ARB/ARNI was associated with lower mortality/morbidity.

Role of ejection fraction in patients at risk for advanced heart failure: insights from the HELP-HF registry

AIMS

Patients with heart failure (HF) with reduced ejection fraction (EF) (HFrEF), mildly reduced EF (HFmrEF), and preserved EF (HFpEF) may all progress to advanced HF, but the impact of EF in the advanced setting is not well established. Our aim was to assess the prognostic impact of EF in patients with at least one 'I NEED HELP' marker for advanced HF.

METHODS AND RESULTS

Patients with HF and at least one high-risk 'I NEED HELP' criterion from four centres were included in this analysis. Outcomes were assessed in patients with HFrEF (EF ≤ 40%), HFmrEF (EF 41-49%), and HFpEF (EF ≥ 50%) and with EF analysed as a continuous variable. The prognostic impact of medical therapy for HF in patients with EF < 50% and EF > 50% was also evaluated. All-cause death was the primary endpoint, and cardiovascular death was a secondary endpoint. Among 1149 patients enrolled [mean age 75.1 ± 11.5 years, 67.3% males, 67.6% hospitalized, median follow-up 260 days (inter-quartile range 105-390 days)], HFrEF, HFmrEF, and HFpEF were observed in 699 (60.8%), 122 (10.6%), and 328 (28.6%) patients, and 1 year mortality was 28.3%, 26.2%, and 20.1, respectively (log-rank P = 0.036). As compared with HFrEF patients, HFpEF patients had a lower risk of all-cause death [adjusted hazard ratio (HRadj ) 0.67, 95% confidence interval (CI) 0.48-0.94, P = 0.022], whereas no difference was noted for HFmrEF patients. After multivariable adjustment, a lower risk of all-cause death (HRadj for 5% increase 0.94, 95% CI 0.89-0.99, P = 0.017) and cardiovascular death (HRadj for 5% increase 0.94, 95% CI 0.88-1.00, P = 0.049) was observed at higher EF values. Beta-blockers and renin-angiotensin system inhibitors or sacubitril/valsartan were associated with lower mortality in both EF < 50% and EF ≥ 50% groups.

CONCLUSIONS

Among patients with HF and at least one 'I NEED HELP' marker for advanced HF, left ventricular EF is still of prognostic value.

Clinical and prognostic implications of heart failure hospitalization in patients with advanced heart failure

BACKGROUND

Hospitalization is associated with poor outcomes in patients with heart failure, but its prognostic role in advanced heart failure is still unsettled. We evaluated the prognostic role of heart failure hospitalization in patients with advanced heart failure.

METHODS

The multicenter HELP-HF registry enrolled consecutive patients with heart failure and at least one high-risk 'I NEED HELP' marker. Characteristics and outcomes were compared between patients who were hospitalized for decompensated heart failure (inpatients) or not (outpatients) at the time of enrolment. The primary endpoint was the composite of all-cause mortality or first heart failure hospitalization.

RESULTS

Among the 1149 patients included [mean age 75.1 ± 11.5 years, 67.3% men, median left ventricular ejection fraction (LVEF) 35% (IQR 25-50%)], 777 (67.6%) were inpatients at the time of enrolment. As compared with outpatients, inpatients had lower LVEF, higher natriuretic peptides and a worse clinical profile. The 1-year rate of the primary endpoint was 50.9% in inpatients versus 36.8% in outpatients [crude hazard ratio 1.70, 95% confidence interval (CI) 1.39-2.07, P < 0.001]. At multivariable analysis, inpatient status was independently associated with a higher risk of the primary endpoint (adjusted hazard ratio 1.54, 95% CI 1.23-1.93, P < 0.001). Among inpatients, the independent predictors of the primary endpoint were older age, lower SBP, heart failure association criteria for advanced heart failure and glomerular filtration rate 30 ml/min/1.73 m2 or less.

CONCLUSION

Hospitalization for heart failure in patients with at least one high-risk 'I NEED HELP' marker is associated with an extremely poor prognosis supporting the need for specific interventions, such as mechanical circulatory support or heart transplantation.

Implantable-cardioverter-defibrillator after ST-elevation myocardial infarction: when and how frequently is it implanted and what is the rate of appropriate interventions? Insight from Trieste registry

BACKGROUND

There are limited data on implantable-cardioverter-defibrillator (ICD) implantation after ST-elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (pPCI). Therefore, we evaluated when and how frequently an ICD is implanted after pPCI, the rate of appropriate ICD interventions, and predictors of ICD implantation.

METHODS

We analyzed STEMI patients treated with pPCI at the University Hospital of Trieste, Italy, between January 2010 and December 2019. We cross-matched patients' data with those present in the Trieste ICD registry.

RESULTS

Among 1805 consecutive patients treated with pPCI, 3.6% underwent ICD implantation during a median follow-up of 6.7 [interquartile range (IQR) 4.3-9.2] years. At 12 months, the mean number of ICD implantations was 2.3/100 patients [95% confidence interval (95% CI) 1.7-3.1] and remained stable over time (at 24 months: 2.5/100 patients, 95% CI 2.0-3.5 and at 36 months: 2.6/100 patients, 95% CI 2.3-3.8); 83.1% of ICDs were implanted for primary prevention, and more than half (55%) were implanted in patients with ejection fraction more than 35% at the moment of STEMI discharge. The rate of appropriate ICD interventions was 16.9% at a median follow-up of 5.7 years (IQR 3.3-8.3 years) after ICD implantation. At 12 months, the mean number of appropriate ICD interventions was 5/100 patients and 7/100 patients after 24 months. In patients with ejection fraction more than 35% at STEMI discharge (median ejection fraction 43%; IQR 40-48), independent predictors of ICD implantation were male sex, anterior STEMI and troponin peak more than 100 000 ng/dl.

CONCLUSION

The rate of ICD implantations after pPCI is low; however, the rate of appropriate ICD interventions is high. A relevant subgroup of patients received ICD implantations at follow-up despite a nonsevere ejection fraction at discharge after STEMI. Among these patients, those with high troponin release deserve strict follow-up and full optimal medical treatment.

Detailed Assessment of the "I Need Help" Criteria in Patients With Heart Failure: Insights From the HELP-HF Registry

BACKGROUND

The "I Need Help" markers have been proposed to identify patients with advanced heart failure (HF). We evaluated the prognostic impact of these markers on clinical outcomes in a real-world, contemporary, multicenter HF population.

METHODS

We included consecutive patients with HF and at least 1 high-risk "I Need Help" marker from 4 centers. The impact of the cumulative number of "I Need Help" criteria and that of each individual "I Need Help" criterion was evaluated. The primary end point was the composite of all-cause mortality or first HF hospitalization.

RESULTS

Among 1149 patients enrolled, the majority had 2 (30.9%) or 3 (22.6%) "I Need Help" criteria. A higher cumulative number of "I Need Help" criteria was independently associated with a higher risk of the primary end point (adjusted hazard ratio for each criterion increase, 1.19 [95% CI, 1.11-1.27]; P<0.001), and patients with >5 criteria had the worst prognosis. Need of inotropes, persistently high New York Heart Association classes III and IV or natriuretic peptides, end-organ dysfunction, >1 HF hospitalization in the last year, persisting fluid overload or escalating diuretics, and low blood pressure were the individual criteria independently associated with a higher risk of the primary end point.

CONCLUSIONS

In our HF population, a higher number of "I Need Help" criteria was associated with a worse prognosis. The individual criteria with an independent impact on mortality or HF hospitalization were need of inotropes, New York Heart Association class or natriuretic peptides, end-organ dysfunction, multiple HF hospitalizations, persisting edema or escalating diuretics, and low blood pressure.

Ischemic Etiology in Advanced Heart Failure: Insight from the HELP-HF Registry

In patients with advanced heart failure (HF), defined according to the presence of at least one I-NEED-HELP criterium, the updated 2018 Heart Failure Association of the European Society of Cardiology (HFA-ESC) criteria for advanced HF identify a subgroup of patients with HF with worse prognosis, but whether ischemic etiology has a relevant prognostic impact in this very high-risk cohort is unknown. Patients from the HELP-HF registry were stratified according to ischemic etiology and presence of advanced HF based on 2018 HFA-ESC criteria. The primary end point was a composite of all-cause death and HF hospitalization at 1 year. Secondary end points were all-cause death, HF hospitalization, and cardiovascular death at 1 year. Ischemic etiology was a leading cause of HF, in both patients with advanced and nonadvanced HF (46.1% and 42.4%, respectively, p = 0.337). The risk of the primary end point (hazard ratio [HR] 1.31, 95% confidence interval [CI] 1.09 to 1.58) and all-cause mortality (HR 1.37, 95% CI 1.06 to 1.76) was increased in ischemic as compared with nonischemic patients. The risk of the primary end point was consistently higher in ischemic patients in both patients with advanced and nonadvanced HF (advanced HF, HR 1.50 95% CI 1.04 to 2.16; nonadvanced HF, HR 1.25 95% CI 1.01 to 1.56, pinteraction = 0.333), driven by an increased risk of mortality, mainly because of cardiovascular causes. In conclusion, ischemic etiology is the most common cause of HF in patients with at least one I-NEED-HELP marker and with or without advanced HF as defined by the 2018 HFA-ESC definition. In both patients with advanced and not-advanced HF, ischemic etiology carried an increased risk of worse prognosis.

Association of Tricuspid Regurgitation With Outcome in Acute Heart Failure

BACKGROUND

Tricuspid regurgitation (TR) is common in chronic heart failure (HF) and is associated with negative prognosis. However, evidence on prognostic implications of TR in acute HF is lacking. We sought to investigate the association between TR and mortality and the interaction with pulmonary hypertension (PH) in patients admitted for acute HF.

METHODS

We enrolled 1176 consecutive patients with a primary diagnosis of acute HF and with available noninvasive estimation of TR and pulmonary arterial systolic pressure.

RESULTS

Moderate-severe TR was present in 352 patients (29.9%) and was associated with older age and more comorbidities. The prevalence of PH (ie, pulmonary arterial systolic pressure >40 mm Hg), right ventricular dysfunction, and mitral regurgitation was higher in moderate-severe TR. At 1 year, 184 (15.6%) patients died. Moderate-severe TR was associated with higher 1-year mortality risk after adjustment for other echocardiographic parameters (pulmonary arterial systolic pressure, left ventricle ejection fraction, right ventricular dysfunction, mitral regurgitation, left and right atrial indexed volumes; hazard ratio, 1.718; P=0.009), and the association with outcome was maintained when clinical variables (eg, natriuretic peptides, serum creatinine and urea, systolic blood pressure, atrial fibrillation) were added to the multivariable model (hazard ratio, 1.761; P=0.024). The association between moderate-severe TR and outcome was consistent in patients with versus without PH, with versus without right ventricular dysfunction, and with versus without left ventricle ejection fraction <50%. Patients with coexistent moderate-severe TR and PH had 3-fold higher 1-year mortality risk compared with patients with no TR or PH (hazard ratio, 3.024; P<0.001).

CONCLUSIONS

In patients hospitalized for acute HF, the severity of TR is associated with 1-year survival, regardless of the presence of PH. The coexistence of moderate-severe TR and estimated PH was associated with a further increase in mortality risk. Our data must be interpreted in the context of potential underestimation of pulmonary arterial systolic pressure in patients with severe TR.

480 ICD AFTER STEMI: WHEN AND HOW FREQUENTLY IS IMPLANTED AND WHICH IS THE RATE OF APPROPRIATE INTERVENTIONS

Background

there are limited data of implantable-cardioverter-defibrillator (ICD) implantation after STEMI treated with primary percutaneous coronary intervention (pPCI). This study sought to evaluate when and how frequently is ICD implanted after STEMI, the rate of appropriate ICD-interventions, and the independent predictors of ICD implantation.

Methods

We analyzed STEMI patients treated with pPCI at the University Hospital of Trieste, Italy, between January 2010 and December 2019. We cross-matched patients data with those present in the Trieste ICD registry.

Results

1805 consecutive patients treated with pPCI were analyzed. During a median follow-up of 6.7 (IQR 4.3-9.2) years, the probability of ICD implantation at 12 months was 2.3% (95%CI: 1.7-3.1) and it remained stable overtime (at 24 months: 2.5%, 95%CI 2.0-3.5 and at 36 months: 2.6%, 95%CI 2.3-3.8). Mean time before ICD implantation was 35.5 months (95%CI: 34.8-36) . 83.1% of implanted ICD were for primary prevention, and more than half (55%) were implanted in patients with ejection fraction (EF)&gt;35% at the moment of STEMI discharge. During a median follow-up of 5.7 (IQR 3.3-8.3) years after ICD implantation, the probability of appropriate ICD intervention was 9% and 11% after 12 and 24 months respectively. In patients with EF&gt;35% at STEMI discharge (median EF 43%; IQR 40-48), predictors of ICD implantation were male sex, anterior STEMI and troponin peak &gt;100.000 ng/dl.

Conclusions

The rate of ICD implantation after pPCI is low, however the rate of appropriate ICD interventions is high. A relevant subgroup of patients received ICD implantation at follow-up despite a non-severe EF at discharge after STEMI. Among these patients those with high troponin release deserve strict follow-up and full optimal medical treatment.

[Italian Society of Cardiology-Italian Society of Nephrology Consensus document: The cardio-renal interaction in the prevention and treatment of cardiovascular diseases - Part II: From preventive strategies to treatment of patients with cardio-renal damage]

Chronic kidney disease and cardiovascular disease are strictly connected each other with a bidirectional interaction. Thus, the prevention of cardio-renal damage, as its appropriate treatment, are essential steps for a correct management of long-term patients' prognosis. Several preventive and therapeutic strategies, pharmacological and not, are now available for cardio-renal damage prevention and treatment, and for the management of its complications. The second part of this consensus document focuses on the management and treatment of cardio-renal damage, directing the attention on the correct use of drugs that may slow renal disease progression, on the application of preventive strategies in case of invasive cardiac procedures with the use of contrast agents, and on the accurate use of cardiological drugs in patients with chronic kidney disease.

[Italian Society of Cardiology-Italian Society of Nephrology Consensus document: The cardio-renal interaction in the prevention and treatment of cardiovascular diseases - Part I: From cardiovascular risk factors to the mechanisms of cardio-renal syndrome]

Chronic kidney disease (CKD) and cardiovascular (CV) disease are highly prevalent conditions in the general population and are strictly connected to each other with a bidirectional interaction. In patients affected by CKD, the leading cause of morbidity and mortality is represented by CV disease, since CKD promotes the atherosclerotic process increasing inflammation, and modifying lipid and bone mineral metabolism. On the other side, a strict relationship exists between CKD and CV risk factors, which are prevalent in nephropathic patients and impose a stringent assessment of the risk of CV events in this population together with an optimized pharmacological approach, complicated by the coexistence of the two pathological conditions. The first part of this consensus document focuses on the mechanisms of cardio-renal damage and on the impact, as well as the management, of the main CV risk factors in the context of CKD.

Prognostic impact of the updated 2018 HFA-ESC definition of advanced heart failure: results from the HELP-HF registry

AIMS

The Heart Failure Association of the European Society of Cardiology (HFA-ESC) proposed a definition of advanced heart failure (HF) that has not been validated, yet. We assessed its prognostic impact in a consecutive series of patients with high-risk HF.

METHODS AND RESULTS

The HELP-HF registry enrolled consecutive patients with HF and at least one high-risk 'I NEED HELP' marker, evaluated at four Italian centres between 1^st January 2020 and 30^th November 2021. Patients meeting the HFA-ESC advanced HF definition were compared to patients not meeting this definition. The primary endpoint was the composite of all-cause mortality or first HF hospitalization. Out of 4753 patients with HF screened, 1149 (24.3%) patients with at least one high-risk 'I NEED HELP' marker were included (mean age 75.1 ± 11.5 years, 67.3% male, median left ventricular ejection fraction [LVEF] 35% [interquartile range 25%-50%]). Among them, 193 (16.8%) patients met the HFA-ESC advanced HF definition. As compared to others, these patients were younger, had lower LVEF, higher natriuretic peptides and a worse clinical profile. The 1-year rate of the primary endpoint was 69.3% in patients with advanced HF according to the HFA-ESC definition versus 41.8% in the others (hazard ratio [HR] 2.23, 95% confidence interval [CI] 1.82-2.74, p < 0.001). The prognostic impact of the HFA-ESC advanced HF definition was confirmed after multivariable adjustment for relevant covariates (adjusted HR 1.98, 95% CI 1.57-2.50, p < 0.001).

CONCLUSIONS

The HFA-ESC advanced HF definition had a strong prognostic impact in a contemporary, real-world, multicentre high-risk cohort of patients with HF.

Mitochondrial F(0) F(1) -ATP synthase is a molecular target of 3-iodothyronamine, an endogenous metabolite of thyroid hormone

BACKGROUND AND PURPOSE

3-iodothyronamine (T1AM) is a metabolite of thyroid hormone acting as a signalling molecule via non-genomic effectors and can reach intracellular targets. Because of the importance of mitochondrial F(0) F(1) -ATP synthase as a drug target, here we evaluated interactions of T1AM with this enzyme.

EXPERIMENTAL APPROACH

Kinetic analyses were performed on F(0) F(1) -ATP synthase in sub-mitochondrial particles and soluble F(1) -ATPase. Activity assays and immunodetection of the inhibitor protein IF(1) were used and combined with molecular docking analyses. Effects of T1AM on H9c2 cardiomyocytes were measured by in situ respirometric analysis.

KEY RESULTS

T1AM was a non-competitive inhibitor of F(0) F(1) -ATP synthase whose binding was mutually exclusive with that of the inhibitors IF(1) and aurovertin B. Both kinetic and docking analyses were consistent with two different binding sites for T1AM. At low nanomolar concentrations, T1AM bound to a high-affinity region most likely located within the IF(1) binding site, causing IF(1) release. At higher concentrations, T1AM bound to a low affinity-region probably located within the aurovertin binding cavity and inhibited enzyme activity. Low nanomolar concentrations of T1AM increased ADP-stimulated mitochondrial respiration in cardiomyocytes, indicating activation of F(0) F(1) -ATP synthase consistent with displacement of endogenous IF(1,) , reinforcing the in vitro results.

CONCLUSIONS AND IMPLICATIONS

Effects of T1AM on F(0) F(1) -ATP synthase were twofold: IF(1) displacement and enzyme inhibition. By targeting F(0) F(1) -ATP synthase within mitochondria, T1AM might affect cell bioenergetics with a positive effect on mitochondrial energy production at low, endogenous, concentrations. T1AM putative binding locations overlapping with IF(1) and aurovertin binding sites are described.

The nucleotide-independent Fe(III)-binding site is located on β subunit of the mitochondrial F1-ATPase

Upon separation of a crude preparation of beta subunit ("beta fraction") from mitochondrial F(1)-ATPase containing one equivalent of Fe(III) in the nucleotide-independent site (1Fe(III)-loaded MF(1)), Fe(III) is almost completely recovered. CD spectra show that "beta fraction" maintains the structural changes induced by Fe(III) in the whole enzyme. In accordance, EPR reveals that the Fe(III) site geometry is conserved in "beta fraction." Moreover, the EPR spectra of 1Fe(III)-loaded MF(1) and its "beta fraction" undergo similar changes of the line-shape upon Pi binding at the catalytic site, indicating that the Pi and Fe(III) are proximal on beta. Highly purified beta in nucleotide-free form binds 1mol of Fe(III)/mol of protein. MF(1) "freezed" by inhibitors with two beta in closed conformation and one beta in open or half-closed conformation binds 1mol of Fe(III)/mol of enzyme. Therefore, the Fe(III) site location in the unique beta subunit not adopting the closed conformation is proposed.

Effects of Fe(III) binding to the nucleotide-independent site of F1-ATPase: enzyme thermostability and response to activating anions

Mitochondrial F1-ATPase was induced in different conformations by binding of specific ligands, such as nucleotides. Then, Fourier transform infrared spectroscopy (FT-IR) and kinetic analyses were run to evaluate the structural and functional effects of Fe(III) binding to the nucleotide-independent site. Binding of one equivalent of Fe(III) induced a localised stabilising effect on the F1-ATPase structure destabilised by a high concentration of NaCl, through rearrangements of the ionic network essential for the maintenance of enzyme tertiary and/or quaternary structure. Concomitantly, a lower response of ATPase activity to activating anions was observed. Both FT-IR and kinetic data were in accordance with the hypothesis of the Fe(III) site location near one of the catalytic sites, i.e. at the alpha/beta subunit interface.

Fe(III) binding to Bacillus PS3 F(1)ATPase, alphabeta subcomplexes and isolated alpha- and beta-subunits

Isolated alpha- and beta-subunits of Thermophilic Bacillus PS3 F(1)ATPase (TF(1)) bind about 1 Fe(III) equivalent. Upon reassembling in the symmetric alpha(3)beta(3) hexamer, Fe(III) binding capacity decreases, as this complex binds about three Fe(III) equivalents. In accordance, when the hexamer is dissociated in the alpha(1)beta(1) heterodimer, each heterodimer binds about one Fe(III) equivalent. On the contrary, native TF(1) exhibits a single Fe(III) site. CD spectra in far UV indicate that upon Fe(III) binding both the whole complex and the isolated beta-subunit undergo structural modifications accompanied by decrease of alpha-helix content, while alpha-subunit doesn't. As in alpha(3)beta(3) and in the whole enzyme the number of bound Fe(III) equivalents is consistent with the number of beta-subunits in the "empty" conformation, it is inferred that the single Fe(III) site in TF(1) is probably located in beta(E).

Effect of inhibitor binding to beta subunits of F1ATPase on enzyme thermostability: a kinetic and FT-IR spectroscopic analysis

FT-IR analysis shows that treatment of F1ATPase with the inhibitors DCCD and Nbf-Cl, in the presence of saturating concentrations of ADP and AMP-PNP and in the absence of Mg2+, does not modify the secondary structure of the enzyme, but significantly modifies its compactness and thermal stability, although to different extents. Nbf-Cl causes a significant increase in stabilisation, in addition to that induced by nucleotides, while DCCD is less effective in this regard. Determination by HPLC of the exchange rate, in the absence of Mg2+, of tightly bound nucleotides of F1ATPase treated with the two inhibitors shows that DCCD does not significantly affect the exchange rate of ADP with AMP-PNP and vice versa in catalytic and non-catalytic tight sites, while Nbf-Cl selectively reduces the enzyme's capacity to exchange ADP bound in the tight catalytic site. It is suggested that the effects of DCCD, unlike those of Nbf-Cl, are closely related to the presence or absence of Mg2+.