Introduction
ST-segment elevation myocardial infarction (STEMI)
is characterized by complete occlusion of a major coronary artery
and represents a severe clinical presentation of ischemic heart
disease. Global data indicate that ischemic heart disease affected
an estimated 254.28 million people and caused 8.99 million deaths
worldwide in 2021(1). Rapid
restoration of coronary blood flow is key in salvaging ischemic
myocardium and improving patient outcomes. Primary percutaneous
coronary intervention (PCI) has become the most established method
for treating STEMI and can effectively restore flow in the
infarct-related artery. However, the reperfusion process itself may
paradoxically induce further myocardial injury, known as
ischemia-reperfusion injury (IRI) (2). IRI markedly increases the final
infarct size and contributes to adverse left ventricular
remodeling, ultimately affecting long-term cardiac function and
increasing the risk of heart failure. The underlying mechanisms of
IRI are complex and multifactorial, involving oxidative stress,
inflammation, calcium overload and mitochondrial dysfunction.
Specifically, abrupt reperfusion induces a burst of reactive oxygen
species that damages cell lipids, proteins and DNA; inflammatory
cell activation and cytokine release further exacerbate endothelial
and myocardial injury; calcium overload promotes cardiomyocyte
hypercontracture and activation of calcium-dependent enzymes and
mitochondrial dysfunction impairs ATP production and triggers cell
death (2). Therefore, IRI has
become a challenging clinical issue with limited treatment options
currently available.
Iron metabolism serves a key role in maintaining
normal myocardial function. Iron is an important component of
hemoglobin and myoglobin, participating in the transport and
storage of oxygen and is also important for the energy metabolism
of cardiomyocytes (3).
Dysregulation of iron metabolism, particularly iron overload, has
been associated with the occurrence and development of a number of
cardiovascular diseases, including atherosclerosis, heart failure
and myocardial ischemia-reperfusion injury (3). Excess iron can catalyze the
production of reactive oxygen species (ROS) through the Fenton
reaction, resulting in oxidative stress and lipid peroxidation,
which damage cell membranes and organelles (4). Furthermore, iron overload may
activate inflammatory pathways, including NF-κB-mediated signaling
and downstream cytokine release, such as TNF-α and IL-6, thereby
exacerbating inflammatory responses and further injuring
cardiomyocytes (5). Ferritin,
hepcidin, heme and heme oxygenase-1 (HO-1) are key regulatory
factors of iron metabolism whose roles in cardiovascular diseases
have garnered increasing attention (3,5).
Ferritin is a notable intracellular iron-storage protein, and serum
ferritin is commonly used as a surrogate marker of body iron
stores, although it may also be influenced by inflammation and
tissue injury (3,5). Hepcidin is the key hormone in
regulating iron homeostasis, predominantly produced by the liver
and it inhibits iron absorption and release. Heme is the prosthetic
group of hemoglobin and myoglobin and exhibits pro-oxidative and
pro-inflammatory effects, whereas HO-1 is a protective enzyme with
antioxidant and anti-inflammatory properties that can degrade heme.
Given that iron overload, oxidative stress and inflammation are all
central to IRI pathology, it was hypothesized that disordered iron
metabolism may serve an important role in IRI following direct PCI
in patients with STEMI (5).
The present study aimed to investigate the dynamic
changes in iron metabolism indices (including ferritin, hepcidin,
heme and HO-1) in patients with STEMI following direct PCI and
analyze the association between these indices and IRI. The present
study aimed to expand the current understanding of the role of iron
metabolism in the development of IRI and discuss whether these iron
metabolism indices could serve as potential biomarkers and
therapeutic targets for IRI.
Materials and methods
Study population
From January to December 2024, patients diagnosed
with acute STEMI who underwent emergency PCI at Beijing Shijitan
Hospital (Beijing, China) were consecutively enrolled in the
present single-center, prospective, observational study. The
inclusion criteria ensured patients: i) Were aged ≥18 years; ii)
had STEMI determined by clinical presentation and
electrocardiography (ECG), consistent with the Fourth Universal
Definition of Myocardial Infarction (6); iii) were in a stable condition; iv)
demonstrated willingness to participate within the present study
with signed informed consent; and v) were in receipt of direct
primary PCI reperfusion therapy. The exclusion criteria
encompassed: i) Advanced malignancy; ii) severe hepatic or renal
failure; iii) active bleeding or marked hematological disorders;
iv) serious trauma, major surgery or a notable bleeding event
within the previous 3 months; v) immune system disorders or use of
corticosteroids or immunosuppressants; vi) pregnancy or lactation;
vii) or the inability to complete follow-up or related assessments
in the present study, for other reasons.
A total of 68 patients with STEMI who met the
aforementioned criteria and completed follow-up were ultimately
included. Based on whether IRI occurred after PCI, patients were
categorized into an IRI group and a non-IRI group. Clinical
characteristics and indicators were compared between the two
groups.
The present study conformed to the relevant ethical
principles for biomedical research involving human subjects
outlined in the Declaration of Helsinki. The present study protocol
was reviewed and approved by the Medical Ethics Committee of
Beijing Shijitan Hospital (Beijing, China; approval no.
IIT2024-040). All participants provided written informed consent
prior to participation in the present study.
Treatment protocol
All enrolled patients underwent primary PCI within
the standardized STEMI management pathway of Beijing Shijitan
Hospital, which aligned with contemporary guideline recommendations
(7). Before PCI, patients received
a loading dose of aspirin (300 mg) and an oral P2Y12 (adenosine
diphosphate) receptor inhibitor (300 mg clopidogrel or 180 mg
ticagrelor). Periprocedural anticoagulation was administered
(typically intravenous unfractionated heparin), with bivalirudin
used when clinically indicated. After PCI, dual antiplatelet
therapy was continued and guideline-directed secondary prevention
therapy was prescribed as appropriate, including high-intensity
statins, β-blockers, and angiotensin-converting enzyme inhibitors
or angiotensin receptor blockers. Additional medications (such as
nitrates, diuretics or mineralocorticoid receptor antagonists) were
used according to the clinical condition of the patient.
Definition and assessment of IRI
To the best of our knowledge, currently, there is no
fully standardized criterion for defining IRI. Therefore,
consistent with prior clinical evidence (8,9) and
guideline documents (6,7) using ECG ST-segment resolution and
angiographic perfusion abnormalities as surrogates of impaired
myocardial reperfusion/microvascular dysfunction after primary PCI,
IRI in the present study was assessed using ECG, angiographic and
biomarker indicators (6-9).
Specifically, within 2 h post-PCI, incomplete ST-segment resolution
(<50%) or new ST-segment elevation on the ECG, together with
either the occurrence of an angiographic ‘no-reflow’/‘slow-flow’
phenomenon during PCI or a markedly elevated peak cardiac troponin
level (>5-fold the 99th percentile upper reference limit), was
considered to be consistent with IRI (2,8-9).
Clinical assessment and laboratory
examination. Clinical data
Baseline data, including patient sex, age, major
cardiovascular risk factors (hypertension, diabetes mellitus,
smoking history and hyperlipidemia) and past cardiovascular
history, were collected. Preoperative venous blood samples (~10 ml
in total) were drawn to assess routine parameters such as complete
blood count, liver and renal function tests, lipid profiles,
fasting blood glucose and N-terminal pro-B-type natriuretic peptide
(NT-proBNP) levels.
Iron metabolism parameters. Fasting venous
blood samples (5 ml) were collected both pre-PCI (as soon as
possible after admission) and post-PCI (24±4 h after the
procedure). Samples were placed in anticoagulant or clot-activator
tubes and separated and stored according to the specific assay
requirements. Iron metabolism-related indicators included: i) Serum
ferritin, which was measured using the Human FE (Ferritin) ELISA
kit (cat. no. RXG60096; Quanzhou Ruixin Biotechnology Co., Ltd.)
and expressed in ng/ml; ii) hepcidin, determined by the Human
Hepcidin ELISA kit (cat. no. RX105169H; Quanzhou Ruixin
Biotechnology Co., Ltd.) and expressed in ng/ml; iii) heme (iron
protoporphyrin IX), which was measured by the Heme Microplate Assay
kit (cat. no. abs580148; Absin Bioscience Inc.) and expressed in
µmol/l; and iv) HO-1, which was also measured by the HO1 ELISA Kit
(cat. no. RX102881H; Quanzhou Ruixin Biotechnology Co., Ltd.) and
expressed in ng/ml. Samples were stored and transported in
accordance with the manufacturer's instructions. Each assay was
performed in duplicate, and the arithmetic mean of the duplicate
measurements was used for statistical analysis.
Diagnostic tests and biomarker
measurements. Echocardiography
Transthoracic echocardiography was performed within
24 h of admission to measure left ventricular ejection fraction
(LVEF) and cardiac structural parameters.
ECG. Routine 12-lead ECGs were conducted upon
admission, 2 h post-PCI, 24 h post-PCI and during any clinical
events such as chest pain or arrhythmias.
Cardiac enzymology. Venous blood samples were
collected every 4 h preoperatively and postoperatively until peak
levels were reached and began to decline. Subsequent sampling
intervals and duration were determined based on the condition of
the patient. Serum cardiac troponin I (cTnI) was quantitatively
measured using the Access hsTnI high-sensitivity cardiac troponin I
chemiluminescent immunoassay kit (cat. no. B52699; Immunotech SAS)
on a Beckman Coulter Access immunoassay system in the clinical
laboratory of Beijing Shijitan Hospital. The maximum cTnI value
recorded during the present study period for each patient was
designated as the peak cTnI and used for subsequent statistical
analysis.
Statistical analysis
Statistical analyses were performed using SPSS
(version 27; IBM Corp.). Normality of continuous variables was
assessed using the Shapiro-Wilk test and homogeneity of variances
was evaluated using Levene's test. Continuous variables are
presented as the mean ± SD when normally distributed and as the
median and interquartile range (IQR) when non-normally distributed.
Between-group comparisons (IRI vs. non-IRI) were conducted using
the independent-samples Student's t-test when data were normally
distributed with equal variances, while Welch's Student's t-test
was used for normally distributed data with unequal variances and
the Mann-Whitney U test was applied for non-normally distributed
variables. Categorical variables are expressed as n (%) and were
compared using the χ2 or Fisher's exact test, as
appropriate. Comparisons between two time points within the same
participants (pre-PCI vs. post-PCI) were performed using the paired
Student's t-test or the Wilcoxon signed-rank test, as appropriate.
For analyses of changes over time, the change value
(Δ=post-PCI-pre-PCI) was calculated for each participant and
compared between groups using the independent-sample Student's
t-test. Welch's t-test or Mann-Whitney U test, as appropriate. Heme
and ferritin were presented as median with IQR at all time points
for consistent reporting. All tests were two-tailed and P<0.05
was considered to indicate a statistically significant
difference.
Results
Demographic characteristics
A total of 68 patients with STEMI who underwent
primary PCI were enrolled in the present study. There were 57 male
(83.8%) and 11 female patients (16.2%). The average age of the
patients was 63.0 years. Regarding past medical history,
hypertension and hyperlipidemia were the most common comorbidities
in this cohort, with 49 (72.1%) and 41 (60.3%) patients,
respectively. A total of 27 patients (39.7%) had a history of
smoking, and 19 patients (27.9%) had diabetes. Among them, 30
patients developed IRI, accounting for 44.1% (Table I).
 | Table IBaseline characteristics of patients
with and without reperfusion injury following acute myocardial
infarction. |
Table I
Baseline characteristics of patients
with and without reperfusion injury following acute myocardial
infarction.
| Variable | Total (n=68) | No reperfusion injury
(n=38) | Reperfusion injury
(n=30) | P-value |
|---|
| Sex (women), n
(%) | 11 (16.2) | 5 (13.2) | 6(20) | 0.930 |
| Age, years (mean ±
SD) | 63.0±12.6 | 65.7±11.9 | 59.4±12.7 | 0.229 |
| Diabetes, n (%) | 19 (27.9) | 8 (21.1) | 11 (36.7) | 0.409 |
| Smoking, n (%) | 27 (39.7) | 11 (28.9) | 16 (53.3) | 0.188 |
| Hyperlipidemia, n
(%) | 41 (60.3) | 25 (65.8) | 16 (53.3) | 0.244 |
| Hypertension, n
(%) | 49 (72.1) | 27 (71.1) | 22 (73.3) | 0.943 |
| PtoB time, h (%) | | | | 0.893 |
|
<3 | 8 (11.8) | 5 (13.2) | 3 (10.0) | |
|
3-5 | 44 (64.7) | 25 (65.8) | 19 (63.3) | |
|
6-12 | 16 (23.5) | 8 (21.0) | 8 (26.7) | |
| Culprit vessel (LAD),
n (%) | 38 (55.9) | 16 (42.1) | 22 (73.3) | 0.326 |
| Infarction location
(anterior wall), n (%) | 38 (55.9) | 16 (42.1) | 22 (73.3) | 0.135 |
| Proximal lesion, n
(%) | 33 (48.5) | 19 (50.0) | 14 (46.7) | 0.821 |
| NT-proBNP, pg/ml | 137.4
(27.6-480.7) | 58.6
(13.5-155.3) | 480.7
(197.3-512.4) | 0.026 |
| hsCRP, mg/l | 2.0 (1.1-2.9) | 1.5 (0.6-2.2) | 2.1 (2.0-2.9) | 0.340 |
| Peak cTnI, ng/l | 37,932.7
(5,654.1-79,109.0) | 12,504.0
(4,723.0-43,861.9) | 49,155.7
(14,641.0-102,639.0) | 0.106 |
| Creatinine, µmol/l
(mean ± SD) | 76.6±16.4 | 77.4±17.7 | 75.8±14.5 | 0.825 |
| Left ventricular
ejection fraction, % | 58.0 (53.0-61.0) | 59.0 (53.0-63.0) | 56.0 (49.0-59.0) | 0.277 |
| Hemoglobin, g/l | 144.0
(137.0-157.0) | 141.0
(137.0-145.0) | 153.0
(132.0-158.0) | 0.298 |
| Blood glucose,
mmol/l | 8.9 (7.8-10.5) | 8.5 (8.0-9.1) | 9.7 (7.8-10.9) | 0.325 |
| Neutrophil count,
x109 cells/l (mean ± SD) | 6.0±1.6 | 5.5±1.4 | 6.7±1.6 | 0.053 |
| Serum iron, µmol/l
(mean ± SD) | 13.0±5.6 | 9.8±6.3 | 13.5±7.1 | 0.199 |
Clinical characteristics of patients
with STEMI and IRI
Based on the presence or absence of IRI, the 68
enrolled patients with STEMI who received primary PCI were divided
into an IRI group (n=30) and a non-IRI group (n=38). Compared with
the non-IRI group, the IRI group appeared to be younger (59.4±12.7
vs. 65.7±11.9 years) and there was no statistically significant
difference in the sex ratio. Common cardiovascular risk factors
(hypertension, diabetes, smoking and hyperlipidemia) also showed no
statistically significant differences between the two groups. With
regard to culprit vessels, the IRI group exhibited a higher
proportion of left anterior descending artery involvement (73.3 vs.
42.1%), but the difference was not statistically significant.
Regarding peak TnI levels, the median in the IRI group was higher
(49,155.7 vs. 12,504.0 ng/l), although the difference was not
statistically significant. Notably, the IRI group had a
significantly higher NT-proBNP level upon admission compared with
the non-IRI group (480.7 vs. 58.6 pg/ml), suggesting a greater
cardiac burden. Differences in high-sensitivity CRP, LVEF and serum
creatinine were not statistically significant between the two
groups. The neutrophil count in the IRI group
(6.7±1.6x109 cells/l) was higher compared with that in
the non-IRI group (5.6±1.4x109 cells/l), approaching
statistical significance, indicating that more active inflammatory
responses may exist in the IRI group. Serum iron levels in the IRI
and non-IRI groups were 13.5 and 9.8 µmol/l, respectively, with no
significance observed. Overall, there were no major differences in
sex, age or risk factors among patients with IRI and without IRI,
however the IRI group exhibited higher NT-proBNP levels and
neutrophil count (Table I).
Changes in iron metabolism indices
(ferritin, hepcidin, heme and HO-1) in patients with STEMI after
primary PCI
Results showed that ferritin was significantly
increased after PCI in patients with STEMI. The median ferritin
levels before PCI were 61.2 (29.2-84.7) ng/ml and rose to 85.1
(64.2-124.1) ng/ml post-PCI. The median hepcidin level before PCI
was 27.6 ng/ml and after PCI remained at 27.6 ng/ml, with no
significant change. The median heme level before PCI was 8.9 µmol/l
and rose to 14.8 µmol/l post-PCI but this was not significant. For
HO-1, the median value increased from 13.1 ng/ml pre-PCI to 17.7
ng/ml post-PCI, also without statistical significance, but
displaying an increasing tendency (Table II).
| Table IIChanges in iron metabolism markers
before and after primary percutaneous coronary intervention in
patients with ST-segment elevation myocardial infarction. |
Table II
Changes in iron metabolism markers
before and after primary percutaneous coronary intervention in
patients with ST-segment elevation myocardial infarction.
| Variable | Total (n=68) | Pre-operative
(n=68) | Post-operative
(n=68) | P-value |
|---|
| Ferritin,
ng/ml | 68.8
(55.5-114.8) | 61.2
(29.2-84.7) | 85.1
(64.2-124.1) | 0.020 |
| Hepcidin,
ng/ml | 27.6
(20.5-30.9) | 27.6
(20.5-29.0) | 27.6
(21.3-32.0) | 0.425 |
| Heme, µmol/l | 12.6 (7.9,
19.7) | 8.9 (6.8,
17.5) | 14.8 (9.8,
20.1) | 0.124 |
| HO-1, ng/ml | 16.1 (2.0,
32.7) | 13.1 (2.0,
32.7) | 17.7
(2.2-28.9) | 0.544 |
Characteristics of serum ferritin and
hepcidin changes in patients with STEMI and IRI
After primary PCI, iron metabolism indices in
patients with STEMI exhibited certain changes. In the IRI group,
pre-PCI serum ferritin was lower compared with that in the non-IRI
group [median, 57.2 (15.0-67.6) vs. 72.1 (37.9, 101.6) ng/ml],
whereas post-PCI ferritin levels were 89.1 (62.4-124.3) and 75.6
(65.0-116.5) ng/ml in the IRI and non-IRI groups, respectively;
neither difference was statistically significant. However, the
median change in ferritin in the IRI group was an increase of 51.1
ng/ml, significantly higher than the decrease of 6.9 ng/ml in the
non-IRI group. Meanwhile, the mean pre-PCI hepcidin levels in the
IRI and non-IRI groups were 20.6 and 27.1 ng/ml, respectively and
the mean post-PCI levels were 27.0 and 27.1 ng/ml, respectively,
with no statistically significant differences between groups at
either time point. Notwithstanding the lack of a statistically
significant baseline difference, post-PCI hepcidin values tended to
converge; the mean increase in hepcidin was 7.7 ng/ml in the IRI
group, significantly greater compared with the 1.1 ng/ml increase
observed in the non-IRI group (Table
III).
| Table IIIPre- and post-operative levels of
ferritin and hepcidin in patients undergoing primary percutaneous
coronary intervention for ST-segment elevation myocardial
infarction, stratified by reperfusion injury. |
Table III
Pre- and post-operative levels of
ferritin and hepcidin in patients undergoing primary percutaneous
coronary intervention for ST-segment elevation myocardial
infarction, stratified by reperfusion injury.
| A, Ferritin |
|---|
| Variable | Total (n=68) | Reperfusion injury
(n=30) | No reperfusion
injury (n=38) | P-value |
|---|
| Pre-operative,
ng/ml | 61.2
(29.2-84.7) | 57.2
(15.0-67.6) | 72.1
(37.9-101.6) | 0.112 |
| Post-operative,
ng/ml | 85.1
(64.2-124.1) | 89.1
(62.4-124.3) | 75.6
(65.0-116.5) | 0.780 |
| Change, ng/ml | 34.8
(-10.9-63.9) | 51.1
(37.4-64.9) | -6.9
(-20.5-33.1) | 0.016 |
| B, Hepcidin |
| Variable | Total (n=68) | Reperfusion injury
(n=30) | No reperfusion
injury (n=38) | P-value |
| Pre-operative,
ng/ml (mean ± SD) | 23.9±9.1 | 20.6±11.1 | 27.1±4.7 | 0.094 |
| Post-operative,
ng/ml (mean ± SD) | 27.0±9.2 | 27.0±10.5 | 27.1±8.0 | 0.974 |
| Change, ng/ml (mean
± SD) | 4.1±6.5 | 7.7±6.7 | 1.1±4.4 | 0.016 |
Characteristics of serum heme and HO-1
changes in patients with STEMI and IRI
Pre-PCI median heme levels in the IRI and non-IRI
groups were 10.4 and 8.9 µmol/l, respectively, while the post-PCI
median levels were 13.0 and 17.4 µmol/l, respectively. There was no
statistically significant difference between the groups. The median
heme changes for the IRI and non-IRI groups was an increase of 0.4
and 5.1 µmol/l, respectively, with no statistically significant
difference. For HO-1, the IRI and non-IRI groups had pre-PCI median
levels of 13.1 and 18.7 ng/ml, respectively and post-PCI levels of
15.2 and 24.7 ng/ml, respectively, with no statistically
significant differences between the groups. The median HO-1 changes
in the two groups showed an increase of 0.1 and 1.2 ng/ml,
respectively, without a statistically significant difference
observed (Table IV).
| Table IVPre- and post-operative levels of
heme and HO-1 in patients undergoing primary percutaneous coronary
intervention for ST-segment elevation myocardial infarction. |
Table IV
Pre- and post-operative levels of
heme and HO-1 in patients undergoing primary percutaneous coronary
intervention for ST-segment elevation myocardial infarction.
| A, Heme |
|---|
| Variable | Total (n=68) | Reperfusion injury
(n=30) | Non-reperfusion
injury (n=38) | P-value |
|---|
| Pre-operative,
µmol/l | 8.9 (6.8,
17.5) | 10.4 (7.2,
17.5) | 8.9 (5.0,
16.4) | 0.544 |
| Post-operative,
µmol/l | 14.8 (9.8,
20.1) | 13.0 (10.4,
23.2) | 17.4 (9.8,
19.6) | 0.975 |
| Change, µmol/l | 4.3 (-4.2,
6.3) | 0.4 (-4.7,
4.6) | 5.1 (-2.3,
6.9) | 0.307 |
| B, HO-1 |
| Variable | Total (n=68) | Reperfusion injury
(n=30) | Non-reperfusion
injury (n=38) | P-value |
| Pre-operative,
ng/ml | 13.1
(2.0-32.7) | 13.1
(1.5-29.1) | 18.7
(2.9-33.8) | 0.314 |
| Post-operative,
ng/ml | 17.7
(2.2-28.9) | 15.2
(2.0-25.1) | 24.7
(3.2-35.9) | 0.289 |
| Change, ng/ml | 1.1 (-0.1-1.7) | 0.1 (-3.8-1.7) | 1.2 (0.2-2.0) | 0.230 |
Discussion
The present study aimed to investigate the changes
in iron metabolism indices (ferritin, hepcidin, heme and HO-1) in
patients with STEMI after primary PCI, grouping them by the
presence or absence of IRI. The findings revealed that post-PCI
ferritin was significantly increased compared with pre-PCI levels
among patients with STEMI. The ferritin elevation in patients with
IRI was significantly greater compared with that in the non-IRI
group. Likewise, the change in hepcidin in patients with IRI was
also higher compared with the non-IRI group. Although no
statistically significant difference was observed between groups,
both heme and HO-1 levels tended to increase after primary PCI and,
compared with patients without IRI.
IRI is a complex and multifactorial
pathophysiological process in patients with STEMI undergoing
primary PCI. The reported incidence of IRI ranges from 11-48%
(2). In the present study, the
incidence of IRI was 44.1%. The occurrence of IRI is associated
with multiple factors, including ischemic duration, ischemic
severity, reperfusion strategy and the baseline disease status of
the patient. In the present study, the IRI group exhibited a
significantly higher NT-proBNP level upon admission compared with
the non-IRI group (P=0.026), suggesting a heavier cardiac burden,
consistent with previous findings that elevated NT-proBNP is
associated with the extent of myocardial damage and the severity of
IRI (10). Furthermore, although
it did not reach statistical significance (P=0.053), the IRI group
had a higher granulocyte count, suggesting inflammation may serve a
role in the development of IRI (11).
The present findings demonstrated that, despite the
lack of statistically significant baseline differences, the IRI
group of patients with STEMI experiencing IRI after PCI displayed a
significantly greater ferritin elevation (P=0.016) compared with
the non-IRI group. These findings indicate an association between
dysregulated iron metabolism and IRI; however, given the
observational design, causality cannot be inferred and residual
confounding cannot be excluded. Ferritin is the major iron-storage
protein, and its elevated level generally reflects increased iron
content in the body or disordered iron metabolism (12). During IRI, myocardial cell damage
and necrosis lead to the release of intracellular iron to the
circulation, raising ferritin levels (13). Furthermore, ROS produced during IRI
can promote the release and degradation of ferritin, further
exacerbating iron overload (14).
Free iron can catalyze ROS production through the Fenton reaction,
resulting in lipid peroxidation, protein oxidation and DNA damage,
aggravating myocardial damage and apoptosis (15). Simultaneously, iron overload may
activate inflammatory cascades and promote the release of
inflammatory cytokines, such as TNF-α, IL-1β and IL-6, further
worsening the inflammatory injury of IRI (16). Hepcidin is a key hormone regulating
iron metabolism, functioning mainly by inhibiting iron absorption
and release. The present study showed that the magnitude of change
in hepcidin in patients with IRI was also significantly higher
compared with that in patients without IRI (P=0.016), potentially
being associated with inflammatory response, as inflammation can
elevate the synthesis and release of hepcidin, promoting
intracellular iron retention and exacerbating iron overload and
oxidative stress injury (17).
The present study demonstrated that heme levels
exhibited an upward trend post-PCI in patients with STEMI both in
the IRI and non-IRI groups. However, the difference between the
groups was not statistically significant. Notably, although there
were no statistically significant differences in heme levels
between the two groups before PCI (P=0.544) and after PCI
(P=0.975), the heme levels in the IRI group were higher compared
with those in the non-IRI group. This trend suggests that heme may
serve a role in the pathophysiological mechanisms of IRI. One
possible explanation is that patients in the IRI group had higher
baseline heme levels, reflecting an inherent susceptibility to
oxidative stress and inflammation, which are primary drivers of
IRI. This may predispose these patients to greater myocardial
injury upon reperfusion. Heme is a component of hemoglobin and
myoglobin, serving a key role in oxygen transport and storage.
During IRI, myocardial cell damage and hemolysis can lead to the
release of heme into the bloodstream (18). Free heme possesses pro-oxidant and
pro-inflammatory properties, exacerbating tissue damage caused by
IRI (19). It can catalyze the
production of ROS through Fenton reactions, leading to lipid
peroxidation, protein oxidation and DNA damage (20). Additionally, heme can activate
inflammatory cascades, including TLR4-mediated signaling and
downstream NF-κB activation, thereby promoting the release of
inflammatory cytokines such as TNF-α, IL-1β and IL-6, thereby
further intensifying the inflammatory response and tissue injury
(16,19). Furthermore, it should be noted that
the magnitude of heme level changes in the IRI group was smaller
compared with the non-IRI group (a median increase of 0.4 µmol/l in
the IRI group vs. a median increase of 5.1 µmol/l in the non-IRI
group; P=0.307), although this difference did not reach statistical
significance. This may suggest an impaired capacity for clearance
or metabolism of free heme in patients with IRI. Reduced clearance
efficiency could lead to sustained elevated heme levels in these
patients, thereby exacerbating oxidative damage. However, the role
of heme is not entirely detrimental. Previous studies have
indicated that lower concentrations of heme may induce the
expression of HO-1, exerting antioxidant and anti-inflammatory
protective effects (21,22). Therefore, the role of heme in IRI
may be dualistic, with its ultimate effect depending on its
concentration, duration of action and the physiological state of
the organism.
HO-1 is a protective enzyme with antioxidant and
anti-inflammatory properties that catalyzes the degradation of heme
into biliverdin, carbon monoxide and free iron (21). In the present study, HO-1 levels
exhibited an upward trend post-PCI in both the IRI and non-IRI
groups of patients with STEMI, although the difference between the
groups was not statistically significant. Upregulation of HO-1 may
represent an endogenous protective mechanism of the body attempting
to counteract the oxidative stress and inflammatory responses
induced by IRI (22). The
protective effects of HO-1 are primarily mediated through its
degradation products biliverdin, carbon monoxide and bilirubin.
Biliverdin and bilirubin are effective antioxidants that can
scavenge ROS and inhibit lipid peroxidation (23). Carbon monoxide exerts
anti-inflammatory, anti-apoptotic and vasodilatory effects
(24). However, the modest
increase in HO-1 observed in the present study suggests that this
protective mechanism may be insufficient to fully offset the damage
caused by IRI. This insufficiency could be due to inadequate
induction of HO-1 during the IRI process or the inhibition of HO-1
activity.
The results of the present study indicate that there
were differences in the magnitude of changes in heme and HO-1
levels post-PCI between the IRI and non-IRI groups of patients with
STEMI, although these differences did not reach statistical
significance. In the IRI group, the median change in heme was an
increase of 0.4 µmol/l, whereas in the non-IRI group it was an
increase of 5.1 µmol/l (P>0.05). For HO-1, the median change in
the IRI group was an increase of 0.1 ng/ml, compared with an
increase of 1.2 ng/ml in the non-IRI group (P=0.230). These
findings suggest that, although both groups exhibited trends of
increased heme and upregulated HO-1 post-PCI, the increases in heme
and HO-1 were smaller in the IRI group. However, because these
between-group differences were not significant, any mechanistic
interpretation should be made with caution.
Based on the observed associations between changes
in iron metabolism parameters and IRI, therapeutic strategies
targeting iron handling and downstream oxidative/inflammatory
pathways (such as iron chelation, antioxidant therapy or HO-1
modulation) merit further investigation. Notably, the present
observational study did not establish causality or therapeutic
efficacy; therefore, these strategies should be evaluated in
adequately powered randomized clinical trials and mechanistic
studies before clinical application. Iron chelators can mitigate
oxidative stress damage by binding free iron ions, thereby
inhibiting Fenton reactions and reducing the generation of ROS
(25). In addition, iron chelators
can decrease iron-mediated inflammatory responses, further
protecting myocardial cells. Another potential therapeutic target
is antioxidants, which can directly scavenge ROS, inhibit lipid
peroxidation and protein oxidation, thereby alleviating oxidative
stress damage (26). Furthermore,
a number of antioxidants can enhance endogenous protective
mechanisms by upregulating HO-1 expression. The direct use of HO-1
inducers or HO-1 gene therapy may also serve as potential
therapeutic strategies (18);
however, further research is needed to verify their safety and
efficacy.
The present study exhibits a number of limitations
that should be considered when interpreting the results. First, the
sample size was relatively small, which may have resulted in
insufficient statistical power, especially in subgroup analyses
such as comparisons between the IRI and non-IRI groups. Second, the
single-center design may have limited the generalizability of the
findings. Third, as an observational study, multivariable
adjustment was not performed; therefore, residual confounding
cannot be excluded, and the observed associations should be
interpreted as simple associations rather than evidence of
causality. Given the sample size and event number, more complex
multivariable models may increase the risk of overfitting. Future
larger multicenter prospective studies with multivariable analyses
and mechanistic investigations are warranted.
In conclusion, following primary PCI in patients
with STEMI, the levels of ferritin and hepcidin increased, with
more pronounced post-PCI rises in patients with IRI. Heme and HO-1
showed upward trends without statistically significant inter-group
differences. Overall, these findings support an association between
altered iron/heme metabolism and the occurrence of IRI, suggesting
that serial ferritin and hepcidin assessment may be explored as
candidate biomarkers for early risk stratification, while
iron-related pathways merit further investigation as potential
therapeutic targets. However, given the single-center observational
design, the limited sample size and the lack of multivariable
adjustment, the results of the present study should be interpreted
cautiously and require further determination in larger multicenter
cohorts with multivariable analyses.
Acknowledgements
Not applicable.
Funding
Funding: The present study was supported by the Scientific
Research Cultivation Program for Health Development of Haidian,
Beijing (grant no. HP2024-03-506004).
Availability of data and materials
The data generated in the present study may be
requested from the corresponding author.
Authors' contributions
ZW conceived and designed the present study,
analyzed data and wrote the manuscript. ZW, YZ, KZ and XH
contributed to data acquisition. JP interpreted data and revised
the manuscript. ZW and YZ confirm the authenticity of all the raw
data. All authors read and approved the final version of the
manuscript.
Ethics approval and consent to
participate
The present study was approved by the Ethics
Committee of Beijing Shijitan Hospital, Capital Medical University
(Beijing, China; approval no. IIT2024-040). All procedures
conformed to the Declaration of Helsinki. Written informed consent
was obtained from all the participants before enrolment.
Patient consent for publication
The participants provided written consent for the
publication of their anonymized data.
Competing interests
The authors declare that they have no competing
interests.
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