Abstract
Background
Heart failure is currently one of the most important global health problems, which drastically decreases patients’ lifestyle, increases hospitalizations, mortality, and morbidity, much more than common cancers. Despite advances in heart failure treatment, new markers are constantly being investigated to improve outcomes. Interleukin-33 and its receptor suppression of tumorigenicity 2 system is a novel entity involved in the etiopathogenesis of heart failure. It has a cardioprotective role, retards fibrosis, apoptosis, and hypertrophy of the myocardium. Our study focused to assess the concentration of interleukin-33 in heart failure and its prognostic value.
Methodology
We recruited 26 (66.6%) heart failure patients and 13 (33.3%) controls based on echocardiography and clinical findings. All demographic profiles, clinical history, signs and symptoms, laboratory investigation reports, serum interleukin-33, treatment records, course in the hospital, and outcomes were recorded in the predesigned case record form, and the two groups were compared.
Results
The serum interleukin-33 (pg/mL) in the heart failure population was significantly lower as compared to the control group (458.7 ± 48 vs. 544.9 ± 45.9) (P < .001). Interleukin-33 at a level of 493 pg/mL had high diagnostic accuracy, with a sensitivity of 88.5% and a specificity of 100% in predicting heart failure.
Conclusion
The concentration of interleukin-33 being lower in heart failure emphasized its beneficial effect and its diagnostic accuracy in heart failure.
Keywords
Introduction
Heart failure is a complex clinical syndrome that comprises a battery of symptoms like shortness of breath, fatigue, and pedal edema, due to the structural or functional inadequacy of the heart to pump blood to meet tissue perfusion. 1 According to the Global Burden of Disease Study, the death rate due to heart failure (HF) is 272 per 1 lakh population. 2 When the heart first begins to fail as an effective pump, the body initiates several compensatory mechanisms aimed at maintaining adequate cardiac output and tissue perfusion. These include an increase in stroke volume through the Frank–Starling mechanism, activation of the sympathetic nervous system, and stimulation of the renin–angiotensin–aldosterone system (RAAS). Over time, these responses lead to cardiac remodeling, characterized by structural and functional changes in the myocardium. Additionally, mechanisms that elevate mean arterial pressure—such as vasoconstriction and fluid retention—are activated to preserve perfusion, although these compensations eventually contribute to the progression of HF. In the initial stages, these compensatory mechanisms try to improve the cardiac output, but gradually they worsen the HF with more stress on the myocardium, leading to a vicious cycle. So, our goal of treatment is not only the reduction of symptoms and the New York Heart Association (NYHA) grading of the person, but also to halt the compensatory mechanisms and thereby prevent further damage in the pathway of HF.
Despite vast major advances in medical science and treatment options, HF appears to be one of the important causes of mortality and morbidity (hospitalizations in patients older than 60 years). In search of new opportunities for treatment of HF, it is quite essential to investigate the novel pathogenesis and evolution of HF. Currently, there are a limited number of articles showing the effect of immunity in the pathogenesis of HF. The balance between pro-inflammatory and anti-inflammatory cytokines is disturbed in HF. 3 Interleukin-33 is a nuclear alarmin cytokine belonging to the interleukin-1 (IL-1) family. It is found in the endothelial and epithelial cells, fibroblasts, and stroma. It is released into the circulation due to cell injury or necrosis. Interleukin-33 from cardiac fibroblasts and endothelial cells contributes to tissue repair, angiogenesis, regulating immune response, and remodeling.4, 5
There is a significant association of interleukin-33 (IL-33) with the pathogenesis of HF. The aim of this study was to evaluate the association of IL-33 with the prognosis, and new modalities of treatment of HF are discussed.
Material and Methods
The Institutional Ethics Committee’s approval was obtained before the study was initiated. Heart failure was diagnosed on the basis of typical symptoms and signs, including shortness of breath, orthopnea, paroxysmal nocturnal dyspnea (PND), pedal edema, raised jugular venous pulse (JVP), and was confirmed by echocardiogram (ECHO) study. The sample size of 13 (control group) and 26 (test group) was calculated using the MEDCALC software. To achieve a power of 80% to detect a difference of 60 pg/mL in IL-33 levels between the groups, a standard deviation (SD) of 20 and 100, a significance level of 0.05, and an allocation ratio of 1:2 were considered for the two-sided two-sample t-test. The inclusion criteria for our study were that all patients included were hospitalized in our inpatient Department of Medicine and Cardiology wards with a diagnosis of HF and were screened for eligibility. Patients more than 18 years of age and of either sex who were willing to participate were included in the study after taking their written consent. The exclusion criteria were autoimmune disease, chronic or acute infection, recent use of immunosuppressants, myocardial infarction (MI) within 3 months, congenital heart disease, advanced liver cirrhosis, end-stage renal failure (chronic kidney disease (CKD) stage 5, estimated glomerular filtration rate (eGFR) <15 mL/min), from 2022 to December 2023.
The European Society of Cardiology (ESC) guidelines for the calculation of ejection fraction (EF) by Simpson’s rule were used. Other parameters like left ventricular systolic dysfunction (LVSD), left ventricular diastolic dysfunction (LVDD), left atrial (LA) enlargement/size, and right ventricular systolic pressure (RVSP) were also measured. A comprehensive 2D ECHO was done to rule out any valvular abnormalities, echocardiographic regional wall motion abnormalities (RWMA), and other myocardial and pericardial disorders. All demographic profiles, clinical history, signs and symptoms, laboratory investigation reports, treatment records, course in the hospital, and outcome were recorded in the predesigned case record form. Serum IL-33 was estimated by sandwich enzyme-linked immunosorbent assay (ELISA) (Cat. No.: CK-bio-12126, Shanghai Coon Koon Biotech Co., Ltd., Shanghai, China).
This research being self-funded, the following measures were taken to minimize potential conflicts of interest and maintain scientific integrity. The funding source was fully disclosed to ensure transparency. The study adhered to all institutional ethical guidelines, and standardized and validated instruments were employed to reduce measurement bias. Methodological procedures—including sampling, data collection, and analytical techniques—were predefined prior to data collection to prevent any outcome-driven adjustments. Data triangulation strategies (from the cardiology ECHO lab, biochemistry lab, medical records department, and general medicine outpatient department (OPD)) were used to enhance credibility and integrity. The samples stored for the serum IL-33 assay were blinded to the researcher in the lab to avoid bias.
Results
In this study, 39 subjects who satisfied the inclusion and exclusion criteria were recruited. They were further grouped into two: (A) HF patients (N = 26) and (B) healthy subjects not having HF (N = 13). The most common age in Group A and Group B was 61-70 (N = 8, 30.8%) and 41-50 years (N = 5, 38.5%), respectively (Table 1). The median interquartile range (IQR) of age (years) in Group A was 55 (45.5-65.75). The median (IQR) of age (years) in Group B was 49 (42-62). The age (years) in Group A ranged from 23 to 75. The age (years) in Group B ranged from 36 to 67 (Table 2). The males and females in Group A were 18 (69.2%) and 8 (30.8%), and in Group B were 6 (46.2%) and 7 (53.8%), respectively (Figure 1).
Distribution of Patients Based on Age.
Comparison of Age of Subjects and Serum Levels of Interleukin-33 (IL-33) in the Two Groups.
Gender Distribution in the Two Study Groups. Group A: Heart Failure Patients. Group B: Healthy Controls.
There was no difference between the two groups in terms of gender distribution (P = .163, not shown in the figure). The variable IL-33 was not normally distributed in the two subgroups. Thus, the Wilcoxon–Mann–Whitney U test used showed a significant difference between the two groups in terms of IL-33 (W = 20.000, P = <.001), with the median IL-33 being highest in the B group (Table 2). The Strength of Association (Point-Biserial Correlation) = 0.66 (Large Effect Size). The LVSD, LVDD, and LA size were significantly higher in the cases as compared to the controls (P < .001 for all three). Though the RVSP was higher in the cases, it was not statistically significant. There was a significant difference between the two groups in terms of EF (%) (W = 0.000, P = <.001), with the median EF (%) being highest in the B group (Table 3).
Echocardiography Findings Compared in the Two Groups.
The area under the receiver operating characteristic curve (AUROC) for IL-33 predicting Group A versus Group B was 0.941 (95% CI: 0.862-1), thus showed excellent diagnostic potential. It was statistically significant (P = <.001) (Figure 2).
Receiver Operating Characteristic (ROC) Curve Analysis Showing Diagnostic Performance of Interleukin-33 (IL-33) in Predicting Group A Versus Group B (n = 39).
At a cutoff of IL-33 ≤493 pg/mL, it predicted Group A with a sensitivity of 88% and a specificity of 100% (Figure 2 and Table 4). In Table 5, Fisher’s exact test was used to explore the association between “Group” and “Outcome,” as more than 20% of the total number of cells had an expected count of less than 5. There was a significant difference between the various groups in terms of the distribution of outcome (χ2 = 8.946, P = .010). A larger percentage of the population in Group B belonged to the “recovery group,” whereas in Group A, a larger percentage of the population had “prolonged hospitalization” as an outcome. Participants in Group A had a larger proportion of the outcome: death.
Description and Comparison of Variables for the Diagnostic Efficacy of Interleukin-33 (IL-33).
Role of Interleukin-33 (IL-33) in Assessing Prognosis in Heart Failure Patients.
Discussion
Our study demonstrated a statistically significant difference in serum IL-33 levels between the two groups, suggesting a potential role of this cytokine in the pathophysiology and progression of HF. The mean (SD) IL-33 concentration in Group A was 458.77 (48.39) pg/mL, whereas in Group B, it was 544.92 (45.90) pg/mL (P < .001). These findings are consistent with earlier reports by Kakkar and Lee 6 and Sun et al., 7 which also highlighted elevated IL-33 concentrations in patients with HF.
Experimental work by Díez 8 demonstrated that mechanical strain on cardiomyocytes upregulates transcription of the two interleukin-1 receptor-like isoforms, the transmembrane (ST2L) and the soluble (sST2) receptors. Interleukin-33 serves as the functional ligand for ST2L and exerts cardioprotective effects by antagonizing angiotensin II- and phenylephrine-induced activation of the nuclear factor kappa B (NF-κB) pathway, thereby reducing myocardial hypertrophy. In contrast, sST2 acts as a circulating decoy receptor that neutralizes IL-33, diminishing its beneficial effects and promoting adverse cardiac remodeling.8, 9
Kunes et al. 10 and Sanada et al. 11 observed a transient rise in IL-33 and sST2 following coronary artery ligation-induced myocardial ischemia in animal models. Moreover, sST2 levels correlated positively with creatine kinase and negatively with the EF, linking this pathway to myocardial stress. 12 Wang et al. 13 reported that increased sST2 concentrations predict prolonged hospital stay and poorer prognosis in patients with acute HF. Similarly, Dudek et al. 14 and Bai et al. 15 found that the combined assessment of sST2 and NT-proBNP enhanced the prediction of adverse cardiovascular events.
Interleukin-33 is mainly produced by cardiac fibroblasts in response to mechanical stress and plays an important role in limiting hypertrophy and fibrosis. In vivo administration of IL-33 in murine models reduced myocardial fibrosis and apoptosis after transverse aortic constriction by inhibiting the NF-κB and caspase-3 pathways. 16 However, excess production of sST2 by the ventricular myocardium sequesters circulating IL-33, thereby reducing its protective effects and explaining the negative prognostic association of sST2 with HF outcomes. 8
Segiet et al. 3 further suggested that IL-33 functions both extracellularly as a cytokine through the ST2L receptor complex and intracellularly by regulating gene transcription within the nucleus. Garcia-Pena et al. 16 reported that IL-33 activates both innate and adaptive immune responses, modulating inflammation depending on the disease context. In their study of myxomatous mitral valve disease, IL-33 levels correlated with markers of inflammation and extracellular matrix remodeling. 16
Zhang et al. 17 found that although IL-33 concentrations were elevated in advanced systolic HF, its bioactivity was reduced because of increased circulating sST2. These findings underscore the complex, dual nature of the IL-33/ST2 axis, which can exhibit both protective and deleterious effects depending on the relative concentrations of its soluble and membrane-bound forms.
The diagnostic performance of IL-33 in our study was encouraging, with a sensitivity of 88% and a specificity of 100% at a cutoff value of 493 pg/mL. Patients with lower IL-33 levels (Group A) had poorer outcomes, including prolonged hospitalization and higher mortality. This aligns with the PRIDE study by Januzzi et al. 18 and the findings of Mueller et al., 19 both of which showed that elevated sST2 levels predict adverse cardiac outcomes in patients with acute HF. Gungor et al. 20 also demonstrated that IL-33 levels correlate with CKD stages and cardiac outcomes; however, our study excluded CKD patients by design.
Among the currently approved biomarkers, sST2 ELISA (threshold >35 ng/mL) has been cleared by the US Food and Drug Administration (FDA) as a prognostic tool in HF.21, 22 In contrast, IL-33 alone is not yet approved for clinical use because of its involvement in various inflammatory and autoimmune disorders.
Preclinical studies are exploring IL-33 modulation as a therapeutic target. 23 For instance, anti-IL-33 antibodies (etokimab) have shown benefit in asthma and atopic dermatitis,24-26 but trials targeting the IL-33/ST2 pathway in HF remain in early stages.
The limitations of our study did not assess standard biochemical markers of HF, such as NT-proBNP and sST2, which could have allowed a direct comparison of predictive values. The cross-sectional design, small sample size, and single tertiary care center also restricted the causal inference. Nevertheless, the significant association between IL-33 levels and clinical outcomes highlights its potential as an adjunct biomarker in HF assessment.
Conclusion
The role of the IL-33/ST2 system in preventing cardiac remodeling is gaining attention recently due to its potential therapeutic role. We found that the concentration of IL-33 was much lesser in the HF population compared to healthy subjects, which emphasized the beneficial effect of the IL-33 system. These results could help in the designing of randomized controlled trials (RCTs), which will aid in assessing IL-33 as a diagnostic and prognostic marker in HF. Understanding of the pathogenesis of HF will also support in developing of molecules targeting the IL-33/ST2 system and newer treatment strategies in the management of HF.
Footnotes
Acknowledgment
The authors are grateful to their institution and patients for their cooperation and support provided in carrying out the research.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest regarding the research, authorship, and/or publication of this article.
Ethical Approval
Ethical approval was obtained from the Institutional Ethics Committee.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Patient Consent
Written informed consent was obtained from the participants for the conduct of the study.
