Association between low selenoprotein P concentrations and anaemia in hospitalized heart failure patients

Abstract

Aims

Heart failure (HF) patients with anaemia tend to have a worse outcome, with increased hospitalization rates, decreased exercise tolerance, and higher mortality compared to those without anaemia. Limited research exists on the association between selenium deficiency and anaemia specifically in HF patients, despite previous findings of a correlation in different populations. The BIOSTAT‐CHF study demonstrated that higher selenium levels in HF patients were associated to a lower risk of anaemia and iron deficiency. This study investigates the relationship between selenoprotein P (SELENOP) concentrations, a major contributor and functional biomarker of selenium transport, and anaemia, Hb levels, and iron status in hospitalized HF patients.

Methods and results

SELENOP was analysed in 320 hospitalized HF subjects, with complete data available for 310 subjects. The relationships between continuous SELENOP concentrations and 1) Hb concentrations, 2) anaemia (Hb < 115 g/L (women), <130 g/L (men)), and 3) iron status (as measured by transferrin receptor 1 (TfR1) which increases in iron deficiency) were evaluated using multivariable logistic and linear regression models. Additionally, SELENOP concentrations in the lowest quartile were related to anaemia, haemoglobin, and iron state in multivariable logistic and linear models. The mean age of the study population was 75.0 ± 11.6 years, and 30% were women. Anaemia was present in 133 subjects (42.9%). SELENOP concentrations were positively correlated with haemoglobin concentrations (0.238; P < 0.001) and negatively with TfR1 concentrations (−0.238, P < 0.001). In multivariable regression models, higher SELENOP concentrations were associated with higher Hb concentrations (B = 3.23; P = 0.002) and lower TfR1 concentrations (B = −0.20; P < 0.001). Furthermore, SELENOP deficiency was associated with lower Hb concentrations (B = −7.64: P = 0.001), higher TfR1 concentrations (B = 0.31; P = 0.003), and higher odds of anaemia in HF patients (odds ratio 2.17; 95% confidence interval 1.23–3.82; P = 0.008).

Conclusions

In hospitalized heart failure patients, lower concentrations of SELENOP were associated with higher prevalence of anaemia.

Introduction

Heart failure (HF) is a prevalent and serious condition associated with significant morbidity and mortality. ¹ Anaemia is a common comorbidity observed in HF patients, with a prevalence ranging from 20% to 60%, and has been found to double the risk of death, as evidenced by a meta‐analysis of 33 studies involving over 150 000 patients. ² The presence of anaemia, particularly in combination with chronic kidney disease, further increases the risk of mortality. ³ However, it remains unclear whether anaemia is a mediator or simply a marker of HF severity. ⁴ Despite the lack of clear understanding regarding the aetiology of anaemia in HF, a substantial body of evidence indicates that renal dysfunction, concurrent with the activation of neurohormonal and proinflammatory cytokines in HF, contributes to the manifestation of anaemia of chronic disease. This form of anaemia is characterized by impaired iron utilization, inappropriate erythropoietin production, and suppressed bone marrow function. ⁵ Further, iron deficiency is highly prevalent in HF patients, affecting up to 50% of cases. ⁶ Also iron deficiency is associated with worse prognosis in HF patients. ⁶ , ⁷

Selenium is an essential micronutrient involved in various physiological processes, including antioxidant defence, thyroid hormone metabolism, and immune function. ⁸ Selenoprotein P (SELENOP) is a plasma protein that functions as a selenium transport protein, delivering selenium to target tissues and organs. ⁹ Higher SELENOP concentrations have been associated with higher Hb concentrations, ¹⁰ suggesting a positive influence on erythropoiesis. ¹¹ , ¹² Further, higher levels of selenium have been demonstrated to be associated with lower risk of the development of HF, ¹³ and low levels of selenium and SELENOP are associated with poorer prognosis in patients with existing HF. ¹⁴ , ¹⁵ Prior research has indicated a potential link between serum selenium deficiency and anaemia in certain populations, ¹⁶ , ¹⁷ , ¹⁸ and the study conducted by Bomer et al. ¹⁹ reveals associations between low selenium concentrations and anaemia in individuals with HF.

However, serum selenium is a composite marker encompassing several components, with liver‐derived SELENOP representing the major contributor and a functional biomarker of selenium transport. As SELENOP is directly responsible for selenium supply from liver to kidney, ²⁰ the purpose of this study was to investigate if SELENOP concentrations are associated with anaemia, haemoglobin (Hb) concentrations, and iron status (reflected by transferrin receptor 1 (TfR1)) in patients hospitalized for HF.

Methods

Study population

The ongoing HeARt and brain failure inVESTigation study (HARVEST‐Malmö) is being conducted in Malmö, Sweden, and focuses on patients who have been hospitalized for the diagnosis of HF. To be included in the HARVEST‐Malmö study, patients must have been admitted to the department of internal medicine or cardiology for the treatment of newly diagnosed or worsened chronic HF. A total of 324 consecutive patients who were hospitalized for HF between March 2014 and June 2018 participated in the study, undergoing clinical examinations and donating blood samples. Out of the 324 patients, 320 had their SELENOP concentrations successfully analysed and complete data on all co‐variates.

Clinical assessment

Upon hospitalization and subsequent admission to the clinical wards, all participants in the study underwent anthropometric measurements, and blood samples were collected after an overnight fast. Body mass index (BMI) was calculated using the weight in kilograms divided by the square of the height in meters. Blood pressure was measured using a validated automated BP monitor (Boso Medicus, Bosch and Sohn GmbH u. Co. KG, Jungingen, Germany) after a 10‐min rest period. The study adhered to the principles outlined in the Declaration of Helsinki and received ethical approval from the Ethical Review Board at Lund University, Sweden. Written informed consent was obtained from all participants.

Definitions

Anaemia was defined as Hb <115 g/L for women, and <130 g/L for men.

Laboratory analysis

At admission, fasting blood samples were obtained. For analyses of SELENOP, samples were collected in 4.5 mL EDTA tubes and centrifuged at 1950 g for 10 min. The plasma was then divided into 200 μL fractions in barcoded tubes (REMP, Brooks, Life Sciences, USA) and stored at −80°C until further analysis. SELENOP levels were measured using a validated ELISA immunoassay with monoclonal antibodies, following the methodology described elsewhere. ²¹ The plasma level of cystatin C was determined by an automated particle‐based immunoassay, using the Hitachi Modular P analysis system and reagents from DAKO (Dako A/S, Glostrup, Denmark), and plasma albumin was analysed using Atellica CH AlbP assay (Siemens) at the Department of Clinical Chemistry, Skåne University Hospital in Malmö, participating in a nationwide standardization and quality control program. Serum levels of high‐sensitivity C‐reactive protein (hsCRP) were analysed using BN II (Siemens Healthineers, Erlangen, Germany). Transferrin receptor 1 (TfR1) was assessed using a proximity extension assay (Olink, Uppsala, Sweden; www.olink.com).

Statistics

The variables were reported as means with standard deviation (SD) or medians with interquartile range (IQR) values. Variable distribution was checked prior to analyses by examining skewness and kurtosis. To compare subjects, Student's t‐tests were used for normally distributed continuous variables, Mann–Whitney U‐tests were used for continuous variables with skewed distribution, while chi‐square tests were employed for binary variables. Prior to analysis, SELENOP was standardized (z‐scored), while cystatin C, which exhibited a skewed distribution, underwent a natural logarithm transformation. In the initial step, unadjusted linear regression models were employed to examine associations between continuous levels of SELENOP and continuous values of Hb and TfR1. Subsequently, adjustments were made for clinical risk factors for anaemia: age and sex (Model 1), followed by the introduction of BMI, ln‐transformed cystatin C and TfR1 into the model (Model 2), except for analyses of associations between SELENOP and TfR1, which were adjusted for age, sex, BMI, and ln‐transformed Cystatin C. In the subsequent step, SELENOP was categorized into quartiles, and the quartile with the lowest SELENOP values (Q1) was then examined in relation to Hb and TfR1 using the same models as described above.

Associations between continuous concentrations of SELENOP and anaemia were explored using unadjusted logistic regression models, followed by adjustment according to Model 1, and subsequent adjustment according to Model 2. Further, the lowest quartile of SELENOP was analysed in relation to anaemia in unadjusted logistic regression, followed by adjustment according to Model 1 and Model 2. In the next step, plasma albumin was entered to the models for all analyses (Model 2a). Further, additional adjustment for ln‐tranformed hsCRP was carried out on top of Model 2 for analyses of SELENOP's associations with Hb, and for associations between the lowest SELENOP quartile and anaemia. All analyses were carried out in SPSS v.28 (IBM, Illinois, Chicago, USA).

Results

The characteristics of the study population are presented in Table 1 . Among the subjects, 133 (42.9%) were diagnosed with anaemia. Subjects with anaemia were older, more often male, with lower Hb, higher hsCRP, worse renal function, lower SELENOP levels and higher expression of TfR1. When subjects with SELENOP concentrations in the lowest quartile were compared to all other subjects, they presented with lower Hb, and higher hsCRP and TfR1. In multivariable linear regression analyses, each 1 SD increment in SELENOP concentrations was positively associated with Hb, and negatively associated with TfR1 concentrations (Table  2 ). SELENOP concentrations within the lowest quartile were associated with lower Hb concentrations, higher TfR1 concentrations (Table  2 ), and increased odds of anaemia (Table  3 ) in Model 2. In addition, SELENOP was positively correlated with Hb (Spearman's rho 0.235; P > 0.001), and negatively correlated with TfR1 (Spearman's rho −0.265; P < 0.001) and hsCRP (Spearman's rho −0.246; P > 0.001). Further, TfR1 was negatively correlated with Hb (Spearman's rho −0.229; P < 0.001). In order to account for potential malnutrition factors that may impact the concentrations of selenium and iron, the incorporation of albumin on top of Model 2 was implemented across all analyses (Model 2a), leading to consistent outcomes (Tables S1–S6). Each 1 SD increment in SELENOP‐concentrations remained positively associated with Hb concentrations when ln‐transformed hsCRP was entered upon Model 2 (β 2.89; P = 0.006). Similarly, the lowest quartile of SELENOP‐concentrations remained associated with anaemia when ln‐transformed hsCRP was entered upon Model 2 (OR 1.96; 95%CI 1.10–3.51; P = 0.024).

Table 1.

Characteristics of the study population

	Total	Subjects with anaemia	Subjects without anaemia	P	Q1	Q2–Q4	P
	n = 310	n = 133	n = 177		n = 79	n = 231
Age (years)	75.0 (±11.6)	77.9 (±9.4)	72.8 (±12.6)	<0.001	75.7 (±10.5)	74.8 (±12.0)	0.531
Sex (women; n (%))	93 (30.0)	23 (24.1)	61 (34.5)	0.048	29 (36.7)	64 (27.7)	0.132
BMI (kg/m2)	27.9 (±5.8)	27.5 (±5.0)	28.1 (±6.4)	0.347	27.6 (±6.2)	28.0 (±5.7)	0.613
Hb (g/L)	128 (±18)	113 (±12)	138 (±14)	<0.001	120 (±19)	131 (±17)	<0.001
Cystatin C (mg/L)	1.7 (1.3–2.1)	1.8 (1.5–2.4)	1.5 (1.2–1.9)	<0.001	1.7 (1.5–2.3)	1.7 (1.3–2.1)	0.028
Albumin (g/L)	33 (±4)	33 (±4)	34 (±3)	0.033	32 (±4)	34 (±3)	<0.001
SELENOP (mg/L)	3.1 (±1.1)	2.9 (±1.2)	3.2 (±1.0)	0.036	1.8 (±0.4)	3.6 (±0.9)	<0.001
TfR1 (AU)	5.8 (±0.8)	5.9 (±0.8)	5.7 (±0.8)	0.013	6.0 (±0.8)	5.7 (±0.8)	<0.001
hsCRP (mg/L)	10 (5–22)	12 (5–27)	9 (4–19)	0.003	16 (7–40)	9 (4–19)	<0.001
Anaemia (n (%))	133 (42.9)	‐	‐	‐	46 (58.2)	87 (37.7)	0.001

Values are means ± standard deviations, medians (interquartile range (25–75)) or n (%) in the entire population, in subjects with and without anaemia, and within quartile 1 (Q1) compared to quartiles 2–4 (Q2–Q4) of SELENOP concentrations.

AU, arbitrary unit, expressed in normalized protein expression corresponding to a doubling in concentration; Hb, haemoglobin; hsCRP, high‐sensitivity C‐reactive protein; SELENOP, selenoprotein P; TfR1, transferrin receptor 1.

Table 2.

Associations between SELENOP and haemoglobin and transferrin receptor 1 levels

	Hb		TfR1
	B	P	B	P
Continuous SELENOP levels
Unadjusted
SELENOP	4.37	<0.001	−0.23	<0.001
Model 1
SELENOP	4.10	<0.001	−0.21	<0.001
Age	−0.43	<0.001	0.00	0.954
Sex	−0.91	0.679	0.31	0.002
Model 2
SELENOP	3.23	0.002	−0.20	<0.001
Age	−0.36	<0.001	0.00	0.311
Sex	−0.53	0.814	0.34	0.001
BMI	−0.05	0.762	0.01	0.190
Cystatin C	−6.50	0.046	0.47	0.001
TfR1	−3.07	0.015	‐	‐
Lowest quartile of SELENOP
Unadjusted
Q1	−9.87	<0.001	0.38	<0.001
Model 1
Q1	−9.36	<0.001	0.35	0.001
Age	−0.43	<0.001	0.00	0.963
Sex	−1.43	0.511	0.35	0.001
Model 2
Q1	−7.64	0.001	0.31	0.003
Age	−0.37	<0.001	0.00	0.309
Sex	−0.76	0.735	0.37	0.000
BMI	−0.06	0.724	0.01	0.196
Cystatin C	−6.05	0.064	0.48	0.001
TfR1	−3.35	0.007	‐	‐

Values are unstandardized beta coefficients (B).

Hb, haemoglobin; Q1, SELENOP‐levels within the lowest quartile; SELENOP, selenoprotein P; TfR1, transferrin receptor 1.

Table 3.

Associations between SELENOP and anaemia

	Anaemia
	OR (95% CI)	P
Continuous SELENOP levels
Unadjusted
SELENOP	0.80 (0.63–1.01)	0.060
Model 1
SELENOP	0.76 (0.60–0.97)	0.028
Age	1.05 (1.03–1.07)	<0.001
Sex	0.43 (0.25–0.74)	0.002
Model 2
SELENOP	0.84 (0.65–1.08)	0.172
Age	1.04 (1.01–1.06)	0.007
Sex	0.43 (0.24–0.77)	0.005
BMI	1.00 (0.95–1.04)	0.892
Cystatin C	3.43 (1.50–7.83)	0.003
TfR1	1.40 (1.01–1.93)	0.042
Lowest quartile of SELENOP levels
Unadjusted
Q1	2.31 (1.37–3.88)	0.002
Model 1
Q1	2.59 (1.50–4.48)	0.001
Age	1.05 (1.03–1.08)	<0.001
Sex	0.42 (0.24–0.73)	0.002
Model 2
Q1	2.17 (1.23–3.82)	0.008
Age	1.04 (1.01–1.07)	0.005
Sex	0.42 (0.23–0.75)	0.003
BMI	1.00 (0.95–1.05)	0.965
Cystatin C	3.24 (1.40–7.47)	0.006
TfR1	1.37 (1.00–1.89)	0.053

Q1 means SELENOP‐levels within the lowest quartile. Values are odds ratios (OR) with 95% confidence intervals (95% CI).

Hb, haemoglobin; SELENOP, selenoprotein P; TfR1, transferrin receptor 1.

^*Adjusted for age, sex, renal function (cystatin C) and TfR1.

^† Adjusted for age, sex, and renal function (cystatin C).

Discussion

The findings of the HARVEST‐Malmö study provide valuable insights into the relationship between selenium deficiency and anaemia in patients hospitalized for HF. The study demonstrates that lower levels of SELENOP, a functional biomarker of selenium status and selenium transport, are associated with lower Hb levels and higher TfR1 levels indicative of poorer iron status, ²² and a higher prevalence of anaemia in HF patients. These results are consistent with previous research findings and highlight the potential relevance of SELENOP for the observed interrelationsship. ¹⁹

TfR1 is a protein involved in cellular iron uptake. ²³ Soluble TfR1 levels exhibit a reduction in conditions characterized by decreased erythropoietic activity, while an increase is observed when erythropoiesis is stimulated by haemolysis or ineffective erythropoiesis. ²⁴ Further, iron status impacts soluble TfR levels, which are significantly elevated in cases of iron deficiency anaemia but remain within the normal range in the context of anaemia associated with inflammation. ²³ The association between SELENOP‐concentrations and Hb‐concentrations, as well as the association between lowest SELENOP‐concentrations and anaemia, remained significant upon adjustment for hsCRP, suggesting that this association is not directly controlled by inflammation. The negative correlation between SELENOP and TfR1 suggests that higher SELENOP levels are associated with better iron status.

The mechanisms underlying the interplay between SELENOP, iron, and anaemia are not yet fully understood. However, selenium‐containing enzymes, such as glutathione peroxidases, protect cells from oxidative stress and maintain redox balance, ⁹ which is crucial for normal erythropoiesis. ¹² In recent years, studies have linked selenium deficiency to anaemia associated with chronic inflammatory diseases and aging. ¹⁸ , ²⁵ , ²⁶ Further, in a transgenic mouse model where the tRNA[Ser]Sec (Trsp) gene, which controls selenoprotein synthesis was deleted by conditional inactivation in erythroid cell precursors via Mx1‐inducible Cre‐recombinase, Kawatani et al. demonstrated the primary role of selenoproteins in regulation of erythropoiesis. ²⁷ These selenoprotein knockout mice exhibited anaemia accompanied by notable pathological indicators of impaired erythropoiesis, including reduced haematocrit, diminished serum Hb levels, and elevated mean corpuscular volume. Furthermore, histological examination revealed the presence of immature and damaged erythrocytes in both the peripheral circulation and bone marrow of the transgenic selenoprotein knockout mice. Importantly, an upregulation of genes associated with oxidative stress was observed. These findings provide evidence supporting the important role of selenoproteins in maintaining redox homeostasis within erythroid cells. Therefore, adequate selenium levels, facilitated by SELENOP‐mediated selenium transport, may contribute to optimal red blood cell production. Additionally, selenium is involved in the metabolism of thyroid hormones, ⁸ which play a role in erythropoiesis. Selenium is required for the synthesis and activation of thyroid hormones, which in turn regulate the production of erythropoietin, a hormone responsible for stimulating red blood cell production. Thus, the relationship between SELENOP, selenium, and iron metabolism may involve complex interactions with the thyroid hormone axis. Further, both selenium and iron are essential nutrients that rely on sufficient dietary intake for optimal levels within the body. The two minerals co‐exist in many animal‐derived food items, and in particular vegans and vegetarians are at increased risk of deficiency for both iron and selenium. ²⁸ Consequently, restricted dietary habits can contribute to deficiencies in both micronutrients if not counteracted for by learned food pattern choices or personalized supplementation. We carried out adjustment for albumin as a marker of malnutrition yielding unchanged results. However, albumin's role in nutritional evaluation has faced criticism owing to its lack of specificity and extended half‐life, which spans roughly 20 days. ²⁹

Nevertheless, the exact mechanisms by which SELENOP influences iron metabolism and the development of anaemia require further investigation. Understanding these mechanisms may contribute to the development of targeted interventions to improve iron and selenium status and mitigate anaemia in various clinical conditions, including HF.

Strengths and limitations

Study strengths include the broad inclusion criteria that helped to ensure a representative sample of HF patients. Secondly, we adjusted our analyses for TfR1, which is less affected by inflammation compared to markers such as ferritin. Thus, TfR1 is considered an appealing marker in HF, which is characterized by a low‐grade inflammatory state. All the samples were analysed blinded to the clinical condition, reducing risk of analytical bias. Study limitations include that our data were collected at a single university hospital, which restricts the generalizability of the findings to other populations of HF patients. We did not have data on dietary intake, which might be an important confounder, as dietary intake affects both iron and selenium (and thus SELENOP) concentrations. Additionally, the participants in HARVEST‐Malmö predominantly consisted of individuals of Swedish descent, which limits the applicability of the conclusions to other ethnicities. Lastly, as a cross‐sectional study, it is not possible to establish causality based on the findings.

Conclusion

Here, we highlight the association between low concentrations of SELENOP and Hb, anaemia and higher levels of TfR1 in patients hospitalized for HF. The results suggest that selenium deficiency, as indicated by lower SELENOP concentrations, may contribute to the development of anaemia and poorer iron status in HF patients. Further research is warranted to elucidate the underlying mechanisms.

Conflict of interest

AB is employed by Sphingotec GmbH, the company that provided the Selenoprotein P assays used in this study. LS hold shares of selenOmed GmbH, a company involved in Se status assessment. The other authors have nothing to declare.

Funding

Dr Magnusson was supported by grants from the Medical Faculty of Lund University Skane University Hospital, the Crafoord Foundation, the Region Skane, the Research Funds of Region Skåne and the Swedish Heart and Lung Foundation [2021‐0354], the Swedish Research Council [2022‐00973] and the Wallenberg Center for Molecular Medicine, Lund University, all Swedish. Dr. Schomburg was supported by Deutsche Forschungsgemeinschaft (DFG), FOR‐2558 “TraceAge” (Scho 849/6‐2) and CRC/TR 296 ‘LocoTact’ (#P17). The funding organizations had no role in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; or the preparation or approval of the manuscript.

Supporting information

Table S1. Associations between each 1 SD increment in SELENOP and haemoglobin with additional adjustment for nutrition status as assessed by albumin.

Table S2. Associations between each 1 SD increment in SELENOP and TfR1 with additional adjustment for nutrition status as assessed by albumin.

Table S3. Associations between the lowest quartile of SELENOP levels and haemoglobin with additional adjustment for nutrition status as assessed by albumin.

Table S4. Associations between the lowest quartile of SELENOP levels and TfR1 with additional adjustment for nutrition status as assessed by albumin.

Table S5. Associations between each 1 SD increment of SELENOP levels and anaemia with additional adjustment for nutrition status as assessed by albumin.

Table S6. Associations between the lowest quartile of SELENOP levels and anaemia with additional adjustment for nutrition status as assessed by albumin.

Jujić, A. , Molvin, J. , Holm Isholth, H. , Dieden, A. , Korduner, J. , Zaghi, A. , Nezami, Z. , Bergmann, A. , Schomburg, L. , and Magnusson, M. (2024) Association between low selenoprotein P concentrations and anaemia in hospitalized heart failure patients. ESC Heart Failure, 11: 877–882. 10.1002/ehf2.14651.