Sex-related differences in patients presenting with heart failure-related cardiogenic shock

BACKGROUND

Heart failure-related cardiogenic shock (HF-CS) accounts for a significant proportion of all CS cases. Nevertheless, there is a lack of evidence on sex-related differences in HF-CS, especially regarding use of treatment and mortality risk in women vs. men. This study aimed to investigate potential differences in clinical presentation, use of treatments, and mortality between women and men with HF-CS.

METHODS

In this international observational study, patients with HF-CS (without acute myocardial infarction) from 16 tertiary-care centers in five countries were enrolled between 2010 and 2021. Logistic and Cox regression models were used to assess differences in clinical presentation, use of treatments, and 30-day mortality in women vs. men with HF-CS.

RESULTS

N = 1030 patients with HF-CS were analyzed, of whom 290 (28.2%) were women. Compared to men, women were more likely to be older, less likely to have a known history of heart failure or cardiovascular risk factors, and lower rates of highly depressed left ventricular ejection fraction and renal dysfunction. Nevertheless, CS severity as well as use of treatments were comparable, and female sex was not independently associated with 30-day mortality (53.0% vs. 50.8%; adjusted HR 0.94, 95% CI 0.75-1.19).

CONCLUSIONS

In this large HF-CS registry, sex disparities in risk factors and clinical presentation were observed. Despite these differences, the use of treatments was comparable, and both sexes exhibited similarly high mortality rates. Further research is necessary to evaluate if sex-tailored treatment, accounting for the differences in cardiovascular risk factors and clinical presentation, might improve outcomes in HF-CS.

Association between left ventricular ejection fraction, mortality and use of mechanical circulatory support in patients with non-ischaemic cardiogenic shock

BACKGROUND

Currently, use of mechanical circulatory support (MCS) in non-ischaemic cardiogenic shock (CS) is predominantly guided by shock-specific markers, and not by markers of cardiac function. We hypothesise that left ventricular ejection fraction (LVEF) can identify patients with a higher likelihood to benefit from MCS and thus help to optimise their expected benefit.

METHODS

Patients with non-ischaemic CS and available data on LVEF from 16 tertiary-care centres in five countries were analysed. Cox regression models were fitted to evaluate the association between LVEF and mortality, as well as the interaction between LVEF, MCS use and mortality.

RESULTS

N = 807 patients were analysed: mean age 63 [interquartile range (IQR) 51.5-72.0] years, 601 (74.5%) male, lactate 4.9 (IQR 2.6-8.5) mmol/l, LVEF 20 (IQR 15-30) %. Lower LVEF was more frequent amongst patients with more severe CS, and MCS was more likely used in patients with lower LVEF. There was no association between LVEF and 30-day mortality risk in the overall study cohort. However, there was a significant interaction between MCS use and LVEF, indicating a lower 30-day mortality risk with MCS use in patients with LVEF ≤ 20% (hazard ratio 0.72, 95% confidence interval 0.51-1.02 for LVEF ≤ 20% vs. hazard ratio 1.31, 95% confidence interval 0.85-2.01 for LVEF > 20%, interaction-p = 0.017).

CONCLUSION

This retrospective study may indicate a lower mortality risk with MCS use only in patients with severely reduced LVEF. This may propose the inclusion of LVEF as an adjunctive parameter for MCS decision-making in non-ischaemic CS, aiming to optimise the benefit-risk ratio.

Transitioning to Palliative Care in an Italian Cardiac Intensive Care Unit Network

BACKGROUND

Recent data indicate that end-of-life management for patients affected by acute decompensated heart failure in cardiac intensive care units is aggressive, with late or no engagement of palliative care teams.

OBJECTIVE

To assess current palliative care and end-of-life practices in a contemporary Italian multicenter registry of patients with cardiogenic shock due to acute decompensated heart failure.

METHODS

A survey-based approach was used to collect data on palliative care and end-of-life management practices. The AltShock-2 registry enrolled patients with cardiogenic shock from 12 participating centers. A subset of 153 patients with cardiogenic shock due to acute decompensated heart failure enrolled between March 2020 and March 2023 was analyzed, with a focus on early engagement of palliative care teams and deactivation of implantable cardioverter-defibrillators (ICDs).

RESULTS

"Do not resuscitate" orders were documented in patient records in only 5 of 12 centers (42%). Palliative care teams were engaged for 21 of 153 enrolled patients (13.7%). Among the 51 patients with ICDs, 6 of 17 patients who died (35%) had defibrillator deactivation. Of the 17 patients who died, 13 died in the hospital and 4 died within 6 months after discharge; 1 patient had ICD deactivation supported by palliative care services at home.

CONCLUSIONS

Therapy-limiting practices, including ICD deactivation, are not routine in the Italian centers participating in this study. The results emphasize the importance of integrating palliative care as a simultaneous process with intensive care to address the unmet needs of these patients and their families.

Clinical presentation, shock severity and mortality in patients with de novo versus acute-on-chronic heart failure-related cardiogenic shock

AIMS

Heart failure-related cardiogenic shock (HF-CS) accounts for a significant proportion of CS cases. Whether patients with de novo HF and those with acute-on-chronic HF in CS differ in clinical characteristics and outcome remains unclear. The aim of this study was to evaluate differences in clinical presentation and mortality between patients with de novo and acute-on-chronic HF-CS.

METHODS AND RESULTS

In this international observational study, patients with HF-CS from 16 tertiary care centres in five countries were enrolled between 2010 and 2021. To investigate differences in clinical presentation and 30-day mortality, adjusted logistic/Cox regression models were fitted. Patients (n = 1030) with HF-CS were analysed, of whom 486 (47.2%) presented with de novo HF-CS and 544 (52.8%) with acute-on-chronic HF-CS. Traditional markers of CS severity (e.g. blood pressure, heart rate and lactate) as well as use of treatments were comparable between groups. However, patients with acute-on-chronic HF-CS were more likely to have a higher CS severity and also a higher mortality risk, after adjusting for relevant confounders (de novo HF 45.5%, acute-on-chronic HF 55.9%, adjusted hazard ratio 1.38, 95% confidence interval 1.10-1.72, p = 0.005).

CONCLUSION

In this large HF-CS cohort, acute-on-chronic HF-CS was associated with more severe CS and higher mortality risk compared to de novo HF-CS, although traditional markers of CS severity and use of treatments were comparable. These findings highlight the vast heterogeneity of patients with HF-CS, emphasize that HF chronicity is a relevant disease modifier in CS, and indicate that future clinical trials should account for this.

Ultrasound-Assisted, Catheter-Directed Thrombolysis for Acute Intermediate/High-Risk Pulmonary Embolism: Design of the Multicenter USAT IH-PE Registry and Preliminary Results

Catheter-based revascularization procedures were developed as an alternative to systemic thrombolysis for patients with intermediate-high- and high-risk pulmonary embolisms. USAT IH-PE is a retrospective and prospective multicenter registry of such patients treated with ultrasound-facilitated, catheter-directed thrombolysis, whose preliminary results are presented in this study. The primary endpoint was the incidence of pulmonary hypertension (PH) at follow-up. Secondary endpoints were short- and mid-term changes in the echocardiographic parameters of right ventricle (RV) function, in-hospital and all-cause mortality, and procedure-related bleeding events. Between March 2018 and July 2023, 102 patients were included. The majority were at intermediate-high-risk PE (86%), were mostly female (57%), and had a mean age of 63.7 ± 14.5 years, and 28.4% had active cancer. Echocardiographic follow-up was available for 70 patients, and in only one, the diagnosis of PH was confirmed by right heart catheterization, resulting in an incidence of 1.43% (CI 95%, 0.036-7.7). RV echocardiographic parameters improved both at 24 h and at follow-up. In-hospital mortality was 3.9% (CI 95%, 1.08-9.74), while all-cause mortality was 11% (CI 95%, 5.4-19.2). Only 12% had bleeding complications, of whom 4.9% were BARC ≥ 3. Preliminary results from the USAT IH-PE registry showed a low incidence of PH, improvement in RV function, and a safe profile.

Cardiogenic Shock Integrated PHenotyping for Event Reduction: A Pilot Metabolomics Analysis

Cardiogenic shock (CS) portends a dismal prognosis if hypoperfusion triggers uncontrolled inflammatory and metabolic derangements. We sought to investigate metabolomic profiles and temporal changes in IL6, Ang-2, and markers of glycocalyx perturbation from admission to discharge in eighteen patients with heart failure complicated by CS (HF-CS). Biological samples were collected from 18 consecutive HF-CS patients at admission (T0), 48 h after admission (T1), and at discharge (T2). ELISA analytical techniques and targeted metabolomics were performed Seven patients (44%) died at in-hospital follow-up. Among the survivors, IL-6 and kynurenine were significantly reduced at discharge compared to baseline. Conversely, the amino acids arginine, threonine, glycine, lysine, and asparagine; the biogenic amine putrescine; multiple sphingolipids; and glycerophospholipids were significantly increased. Patients with HF-CS have a metabolomic fingerprint that might allow for tailored treatment strategies for the patients' recovery or stabilization.

Differences between cardiogenic shock related to acute decompensated heart failure and acute myocardial infarction

AIMS

The present analysis from the multicentre prospective Altshock-2 registry aims to better define clinical features, in-hospital course, and management of cardiogenic shock complicating acutely decompensated heart failure (ADHF-CS) as compared with that complicating acute myocardial infarction (AMI-CS).

METHODS AND RESULTS

All patients with AMI-CS or ADHF-CS enrolled in the Altshock-2 registry between March 2020 and February 2022 were selected. The primary objective was the characterization of ADHF-CS patients as compared with AMI-CS. In-hospital length of stay and mortality were secondary endpoints. One-hundred-ninety of the 238 CS patients enrolled in the aforementioned period were considered for the present analysis: 101 AMI-CS (80% ST-elevated myocardial infarction and 20% non-ST-elevated myocardial infarction) and 89 ADHF-CS. As compared with AMI-CS, ADHF-CS patients were younger [63 (IQR 59-76) vs. 67 (IQR 54-73) years, P = 0.01], but presented with higher creatinine [1.6 (IQR 1.0-2.6) vs. 1.2 (IQR 1.0-1.4) mg/dL, P < 0.001], bilirubin [1.3 (IQR 0.9-2.3) vs. 0.6 (IQR 0.4-1.1) mg/dL, P = 0.01], and central venous pressure values [14 mmHg (IQR 8-12) vs. 10 mmHg (IQR 7-14),P = 0.01]. Norepinephrine was the most common catecholamine used in AMI-CS (79.3%), whereas epinephrine was used more commonly in ADHF-CS (65.5%); 75.8% vs. 46.6% received a temporary mechanical support in AMI-CS and ADHF-CS, respectively (P < 0.001). Length of hospital stay was longer in the latter [28 (IQR 13-48) vs. 17 (IQR 9-29) days, P = 0.001]. Heart replacement therapies were more frequently used in the ADHF-CS group (heart transplantation 13.5% vs. 0% and left ventricular assist device 11% vs. 2%, P < 0.01 and 0.01, respectively). In-hospital mortality was 41.1% (38.6% AMI-CS vs. 43.8% ADHF-CS, P = 0.5).

CONCLUSIONS

ADHF-CS is characterized by a higher prevalence of end-organ and biventricular dysfunction at presentation, a longer hospital length of stay, and higher need of heart replacement therapies when compared with AMI-CS. In-hospital mortality was similar between the two aetiologies. Our data warrant development of new management protocols focused on CS aetiology.

Use of mechanical circulatory support in patients with non-ischaemic cardiogenic shock

AIMS

Despite its high incidence and mortality risk, there is no evidence-based treatment for non-ischaemic cardiogenic shock (CS). The aim of this study was to evaluate the use of mechanical circulatory support (MCS) for non-ischaemic CS treatment.

METHODS AND RESULTS

In this multicentre, international, retrospective study, data from 890 patients with non-ischaemic CS, defined as CS due to severe de-novo or acute-on-chronic heart failure with no need for urgent revascularization, treated with or without active MCS, were collected. The association between active MCS use and the primary endpoint of 30-day mortality was assessed in a 1:1 propensity-matched cohort. MCS was used in 386 (43%) patients. Patients treated with MCS presented with more severe CS (37% vs. 23% deteriorating CS, 30% vs. 25% in extremis CS) and had a lower left ventricular ejection fraction at baseline (21% vs. 25%). After matching, 267 patients treated with MCS were compared with 267 patients treated without MCS. In the matched cohort, MCS use was associated with a lower 30-day mortality (hazard ratio 0.76, 95% confidence interval 0.59-0.97). This finding was consistent through all tested subgroups except when CS severity was considered, indicating risk reduction especially in patients with deteriorating CS. However, complications occurred more frequently in patients with MCS; e.g. severe bleeding (16.5% vs. 6.4%) and access-site related ischaemia (6.7% vs. 0%).

CONCLUSION

In patients with non-ischaemic CS, MCS use was associated with lower 30-day mortality as compared to medical therapy only, but also with more complications. Randomized trials are needed to validate these findings.

A prospective registry to get insights into profile, management and outcome of cardiogenic shock patients

Background

Cardiogenic shock (CS) is the most severe form of acute heart failure, characterized by life-threatening end-organ hypoperfusion resulting from a low cardiac output state. Data on epidemiology of CS has been mostly drawn from registries focusing on acute myocardial infarction (AMI). However, recent evidence in a contemporary cohort in North America has shown that more than two thirds of all CS cases were related to causes other than AMI and that these patients had outcomes at least as poor as patients with AMICS.

Purpose

To provide data on profile, management, outcome, and evolution over time of CS patients admitted to ICCU/ICU and to compare them between patients with AMICS and acute decompensated heart failure (ADHF-CS).

Methods

The Altshock-2 Registry is a multicenter national prospective data collection, part of the Italian Altshock-2 program. Recruitment started on 2 March 2020 with 11 Italian Centers contributing to patients' enrolment. A total of 238 patients were hospitalized with confirmed diagnosis of CS between March 2020 and February 2022 in a multicenter national initiative. The mean age of this patient population was 64 years (interquartile range [IQR] 54–74) and 76% were male. Ninety-seven patients (41%) were admitted for AMICS, whereas 84 patients (35.3%) had ADHF-CS; 57 patients (24%) had other causes. As compared to AMICS patients, those admitted for ADHF-CS were younger, but with a higher burden of comorbidities (renal, liver, thyroid disease, atrial fibrillation, anemia), pre-existing decreased ejection fraction and a higher number of chronic drugs. Patients with ADHF-CS had a prevalent cardio-metabolic phenotype upon admission with prevalent congestion. Mechanical ventilation was more commonly used in patients with AMICS, compared to ADHF-CS, along with an increased inotropic score. Conversely, sodium nitroprusside was used in about sixty percent of patients with ADHF-CS. Sixty percent of the included population received a temporary mechanical circulatory support (MCS) device, which was intra-aortic balloon pump (IABP) in the eighty percent of the supported patients. Pulmonary artery catheter was used for monitoring only in the 18% of the included patients whereas an extensive echocardiographic approach was applied. Twenty-one patients (25%) underwent heart replacement therapy in the ADHF-CS patients versus 2 (2%) in the AMICS. Thirty-day mortality occurred in 32 patients (33%) in the AMICS group versus 23 (27%) in the ADHF-CS group (p=0.41).

Conclusions

Different diagnostic approaches and uses of mechanical circulatory support devises and inotropes are implemented in transatlantic settings. Uniform definitions and more homogenous protocols tailored on CS etiologies and clinical and biochemical phenotypes are needed in prospective initiatives in order to effectively compared results and outcome.

Funding Acknowledgement

Type of funding sources: None.

Left Ventricular Unloading in Acute on Chronic Heart Failure: From Statements to Clinical Practice

Cardiogenic shock remains a deadly complication of acute on chronic decompensated heart failure (ADHF-CS). Despite its increasing prevalence, it is incompletely understood and therefore often misdiagnosed in the early phase. Precise diagnosis of the underlying cause of CS is fundamental for undertaking the correct therapeutic strategy. Temporary mechanical circulatory support (tMCS) is the mainstay of management: identifying and selecting optimal patients through understanding of the hemodynamics and a prompt profiling and timing, is key for success. A recent statement from the American Heart Association provided pragmatic suggestions on tMCS device selection, escalation, and weaning strategies. However, several areas of uncertainty still remain in clinical practice. Accordingly, we present an overview of the main pitfalls that can occur during patients’ management with tMCS through a clinical case. This case illustrates the strict interdependency between left ventricular unloading and right ventricular dysfunction in the case of low filling pressures. Moreover, it further illustrates the pivotal role of stepwise escalation of therapy in a patient with an ADHF-CS and its peculiarities as compared to other forms of acute heart failure.

Effect of landiolol in patients with tachyarrhythmias and acute decompensated heart failure (ADHF): a case series

Tachycardia and rapid tachyarrhythmias are common in acute clinical settings and may hasten the deterioration of haemodynamics in patients with acute decompensated heart failure (ADHF), treated with inotropes. The concomitant use of a short‐acting β1‐selective beta‐blocker, such as landiolol, could rapidly and safely restore an adequate heart rate without any negative inotropic effect. We present a case series of five patients with left ventricular dysfunction, admitted to our Intensive Cardiac Care Unit with ADHF deteriorated to cardiogenic shock, treated with a combination of landiolol and inotropes. Landiolol was effective in terms of rate control and haemodynamics optimization, enabling de‐escalation of catecholamine dosing in all patients. The infusion was always well tolerated without hypotension. In conclusion, a continuous infusion of a low dose of landiolol (3–16 mcg/kg/min) to manage tachycardia and ventricular or supraventricular tachyarrhythmias in haemodynamically unstable patients may be considered.

Predicting survival in patients with acute decompensated heart failure complicated by cardiogenic shock

Background

Acute decompensated heart failure (ADHF) complicated by cardiogenic shock (CS) has unique pathophysiological background requiring specific patient stratification, management and therapeutic targets. Accordingly, the aim of this study was to derive a simple stratification tool to predict survival in patients with ADHF complicated by CS.

Methods and results

Using logistic regression, univariable testing was performed to identify the variables potentially associated with 28-day mortality. We propose a new logistic model (ALC-Shock score) based on three easy parameters (age, serum creatinine and serum lactate at the ICU admission) as a powerful predictor of survival or successful bridge to heart replacement therapy at 28-day follow-up in this specific population. A multivariable analysis (logistic model) was performed to evaluate the association between selected variables and outcome (overall death at 28-day follow up). The score was then validated in a different cohort of 93 ADHF-CS patients and compared to a previous developed score (the Cardshock score).Overall, 28-day mortality was 34%. The ALC-shock score showed better discrimination (Area Under the Curve-AUC- 0.82; 95% CI 0.73-0.91) as compared to the Cardshock score (AUC 0.67; 95% CI 0.55-0.79) (p = 0.009) to predict 28-days overall mortality. In the validation cohort the AUC for the ALC-shock score was 0.66.

Conclusions

A simple score including age, lactates and creatinine on admission could be considered to predict short-term mortality in CS-ADHF patients in order to drive towards a treatment intensification.

Withdrawal of active treatments in terminally ill heart failure patients

INTRODUCTION

Heart failure (HF) constitutes a growing public health problem in aging societies: when pharmacological therapies fail, HF can be sustained intensively if patients are eligible for either orthotopic heart transplantation (OHT) or mechanical ventricular assistance, otherwise additional treatments could be inappropriate. In December 2017 Italian Legislator brought in the provisions regarding the end-of-life choices, including indications for withdrawing and withholding life-sustaining therapies. The aim of our study was to provide an overview of the daily practice of our center with regard to terminally ill HF patients.

METHODS AND RESULTS

In April 2019 the 7 intensivist cardiologists and 21 nurses of a tertiary ICCU were asked in, to complete a questionnaire relating to a hypothetical terminally ill HF patient for whom the decision to withdraw active treatment had been made. To assess current practice, we also identified patients who died in the previous 12 months. Out of 29 deceased patients, 18 were identified as terminally ill HF, with no indications for therapy upgrading. We observed a striking disparity between belief and practice.

CONCLUSIONS

Our survey showed that the care of terminally ill HF patients in our ICCU was characterized by aggressive use of medical therapy and invasive technology. The wide disparity between belief and practice could be in part a consequence of lack of professional training, with regard to law, ethics and communication techniques.

Phase dependent encapsulation and release profile of ZIF-based biocomposites

Biocomposites composed of Zeolitic Imidazolate Frameworks (ZIFs) are generating significant interest due to their facile synthesis, and capacity to protect proteins from harsh environments. Here we systematically varied the composition (i.e. relative amounts of ligand (2-methylimidazole), metal precursor (Zn(OAc)2·2H2O), and protein) and post synthetic treatments (i.e. washes with water or water/ethanol) to prepare a series of protein@ZIF biocomposites. These data were used to construct two ternary phase diagrams that showed the synthesis conditions employed gave rise to five different phases including, for the first time, biocomposites based on ZIF-CO3-1. We examined the influence of the different phases on two properties relevant to drug delivery applications: encapsulation efficiency and release profile. The encapsulation efficiencies of bovine serum albumin and insulin were phase dependent and ranged from 75% to 100%. In addition, release profiles showed that 100% protein release varied between 40 and 300 minutes depending on the phase. This study provides a detailed compositional map for the targeted preparation of ZIF-based biocomposites of specific phases and a tool for the straightforward analysis of the crystalline phases of ZIF based materials (web application named "ZIF phase analysis"). These data will facilitate the progress of ZIF bio-composites in the fields of biomedicine and biotechnology.

Influence of age and physical exercise on sirtuin activity in humans

Sirtuins are NAD+-dependent lysine deacetylases. Sirtuins acquired worldwide attention because of their ability to increase yeast, flies, worms and mice lifespan. Recently, this assumption has been challenged. However, their beneficial role on the quality of ageing is widely accepted. In this work we aimed to study how and if sirtuins expression and activity levels varies in function of age and, in the case of young subjects, of exercise. Fifteen blood donors of different ages and fifteen athletes of the Italian rowing male team were enrolled and peripheral blood mononuclear cells (PBMCs) isolated from blood samples. Our results show that sirtuins deacetylases activity measured in PBMCs increases from 18 to 40 years of age and then decreases during the following 20 years. Moreover, physical exercise in professional athletes can upregulate sirtuin activity. Thus, for the first time in humans, we demonstrate that sirtuin activity is a function of age and can be altered through physical exercise.

Efficacy of oleuropein against UVB irradiation: preliminary evaluation

Oleuropein, a phenolic compound derived from olive leaves and oil, is known to possess several biological properties, many of which may be attributed to its antioxidant and free radical-scavenging activities. Nevertheless, up to now, the cosmetic activity of this molecule has not been extensively investigated. The aim of this work was to evaluate the cosmetic properties of oleuropein against UVB-induced erythema. To this end, an emulsion and an emulgel containing oleuropein were prepared, applied and evaluated on healthy volunteers who had undergone UVB irradiation to investigate its protective and/or lenitive activity. Protective effect was assayed by application of topical preparations before irradiation and lenitive effect was evaluated after erythema induction. Vitamin E was used as the reference compound. Our study was carried out by using noninvasive techniques to assess specific skin parameters: barrier function, skin colour and microcirculation. Results clearly showed that oleuropein formulations highlighted lenitive efficacy by reducing erythema, transepidermal water loss and blood flow of about 22%, 35% and 30% respectively. The study allowed us to point out the lenitive property of oleuropein, opening the way to further trials to deepen our specific knowledge about this natural molecule, which could be used in association with other active ingredients in cosmetics to repair UV damages.

[Evaluation of the bactericidal activity of a disinfectant containing sodium hypochlorite (Amiclor)]

We evaluated the stability and the bactericidal activity of a disinfectant containing sodium hypochlorite (Amiclor), which associates the buffer effect of the system sodium carbonate/sodium tetraborate to the stabilizing action of sodium chloride. The stability was determined evaluating the trend of the active chlorine title in various conservation conditions and comparing it with a product having only sodium chloride as stabilizing component. The bactericidal activity, instead, was evaluated by suspension and surface tests against Escherichia coli (ATCC 10536) and in relation to several variables, as product concentration, contact time, presence of interfering substances and water hardness. From the obtained data it is possible to affirm that Amiclor owns a greater stability as regards the traditional products stabilized only with sodium chloride. The activity tests have pointed out that the practical conditions affect the choice of the combination "product concentration/contact time" necessary to obtain an effective bactericidal activity. The activity of Amiclor is conditioned by the presence of proteins in the mixture or on the surface of reaction. This influence is not very clear in clean conditions while it considerably increases in dirty conditions. A decrease of bactericidal activity was observed when the product was diluted in hard water, mainly for contact times of 5 minutes or low product concentrations.

Calcium ions and 1-palmitoyl carnitine reduce erythrocyte electrophoretic mobility: test of a surface charge hypothesis

In ventricular muscle, 1-palmitoyl carnitine (1-PC) acted like calcium ions to shift the voltage-dependent inactivation of excitatory ion currents to less negative potentials. We proposed that 1-PC affected ion current kinetics by reducing surface negative charge. This hypothesis was tested in cell electrophoresis experiments where the electrophoretic mobility (EPM) of erythrocytes was measured in the absence and presence of test ligands. Calcium (0.18 to 3.6 mM) or 1-PC (10(-7) to 10(-6) M) reduced erythrocyte EPM in a concentration-dependent manner; the maximum reduction of EPM by either ligand was approximately 40%. In the presence of calcium, 1-PC produced a smaller decrement of EPM as expected from an occlusive interaction. Treatment of erythrocytes to remove sialic acids not only predictably reduced EPM but also diminished the ability of 1-PC and calcium to do so. These results indicate that the surface negative charge of sialic acid carboxyl groups is an important determinant both of erythrocyte EPM and of erythrocyte interaction with either 1-PC or calcium. The findings are consistent with the surface charge hypothesis for 1-PC action. We propose that 1-PC is not a neutral molecule at the cell surface but is able to neutralize surface negative charge by electrostatic interaction between the sialic acid carboxyl groups and the 1-PC quaternary ammonium moiety on the one hand and between the 1-PC carboxyl group and counterions near the membrane surface.