Plasma Apolipoprotein E Levels and Adverse Clinical Outcomes After Ischemic Stroke

Abstract

Background

Apolipoprotein E (ApoE) is implicated in the development of cerebrovascular diseases, but its association with the prognosis of ischemic stroke remains unclear. We aimed to explore the associations between plasma ApoE levels and adverse clinical outcomes after ischemic stroke in a prognostic cohort study.

Method

We measured plasma ApoE levels among 5410 patients with ischemic stroke from the Minhang Stroke Cohort study. The primary outcome was the composite outcome of death and major disability (modified Rankin Scale score=3–6) at 3 months after stroke onset. Secondary outcomes included major disability, death, and the ordered 7‐level categorical score of the modified Rankin Scale.

Results

In the prognostic cohort study, the multivariable adjusted odds ratio associated with the highest quartile of plasma ApoE levels was 1.37 (95% CI=1.10–1.70; P _trend=0.003) for the primary outcome, 1.50 (95% CI=1.08–2.09; P _trend=0.019) for death, and 1.47 (95% CI=1.11–1.95; P _trend=0.005) for major disability. There was a worse shift in the distribution of modified Rankin Scale score at 3 months with higher quartiles of plasma ApoE levels among patients with ischemic stroke (P _trend=0.034). The multivariable‐adjusted spline regression model further showed positive linear associations of plasma ApoE levels with the primary outcome, death, and major disability (all P for linearity<0.05).

Conclusions

High plasma ApoE levels were independently associated with increased risk of adverse outcomes among patients with ischemic stroke, suggesting that plasma ApoE might be implicated in the prognosis of ischemic stroke.

Nonstandard Abbreviations and Acronyms

ApoE

apolipoprotein E

mRS

modified Rankin Scale

NIHSS

National Institutes of Health Stroke Scale

TOAST

Trial of ORG 10172 in Acute Stroke Treatment

Clinical Perspective.

What Is New?

• High plasma apolipoprotein E levels were independently associated with increased risk of adverse outcomes among patients with ischemic stroke, suggesting that plasma apolipoprotein E might be implicated in the prognosis of ischemic stroke.

What Are the Clinical Implications?

• Our findings reveal that patients with high plasma apolipoprotein E levels might be at high risk of adverse clinical outcomes and should receive early intervention to reduce the residual risk of poor prognosis of ischemic stroke.

• Our results suggest that plasma apolipoprotein E might be a promising therapeutic target for ischemic stroke.

Stroke is the third leading cause of death and the fourth most common cause of disability worldwide, ¹ and ischemic stroke accounts for approximately 87% of all strokes. ² Although the recent burden of ischemic stroke has been moderately reduced because of improved stroke treatment and care, ³ , ⁴ the substantial residual risk of adverse outcomes after ischemic stroke persists. ⁵ Given that the current guideline‐based interventions do not adequately account for all the pathways that lead to adverse outcomes, ⁵ there is an urgent need to identify novel biomarkers associated with the residual risk of adverse outcomes after ischemic stroke to better understand the pathogenesis and reveal the potential intervention targets for ischemic stroke.

Apolipoprotein E (ApoE), a soluble basic glycosylated secretory protein of the apolipoprotein superfamily primary synthesized in the liver and brain, is widely involved in lipid transport and metabolism. ⁶ , ⁷ Approximately half of plasma ApoE is associated with triglyceride‐rich lipoproteins, where ApoE serves as the main ligand for the low‐density lipoprotein receptor and the low‐density lipoprotein receptor related protein. ⁸ It has been reported that ApoE could induce neuroinflammation, oxidative stress, and mitochondrial dysfunction, ⁹ , ¹⁰ , ¹¹ while plasma ApoE was implicated in hypertriglyceridemia and metabolic syndrome. ¹² , ¹³ In addition, several epidemiological studies found that elevated plasma ApoE levels were associated with the risk of various cardiovascular diseases, including ischemic heart disease and stroke. ¹⁴ , ¹⁵ , ¹⁶ , ¹⁷ Notably, elevated ApoE levels were also demonstrated to be associated with high residual cardiovascular risk in patients with chronic coronary syndrome, and it could provide valuable prognostic information beyond the traditional prognostic factors. ¹⁸

However, to date, population‐based studies investigating the associations between plasma ApoE levels and adverse outcomes among patients with ischemic stroke are still lacking. Herein, we prospectively examined the associations between plasma ApoE levels and adverse outcomes after ischemic stroke in a large‐scale prognostic study based on the Minhang Stroke Cohort.

METHODS

Data Availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

Study Population

The Minhang Stroke Cohort study was a prognostic cohort study for ischemic stroke patients conducted in Shanghai, China. ¹⁹ As shown in Figure S1, from January 2018 to December 2022, a total of 7323 consecutive patients aged ≥18 years who had ischemic stroke confirmed by computed tomography scan or magnetic resonance imaging were recruited from the Department of Neurology at Minhang Hospital. After excluding those with time from onset to admission over 7 days (n=263) or cancer (n=168), a total of 6892 eligible patients were enrolled in the Minhang Stroke Cohort. In the present study, we further excluded 1094 participants (15.87%) who declined to provide blood samples because of privacy concerns or other reasons and 388 participants (5.63%) who were lost to follow‐up 3 months after ischemic stroke. Finally, a total of 5410 participants were included in the current study.

Ethics Approval and Consent to Participate

This study was approved by the Ethics Committee of Minhang Hospital (IRB:008‐01K). The patients or their immediate family members were fully informed about the purpose of the study and signed the informed consents, in accordance with the Declaration of Helsinki.

Data Collection

Baseline data on demographic characteristics, clinical features, medical history, and imaging data were collected at the time of admission using a standard questionnaire by trained investigators through face‐to‐face interviews. Stroke severity was evaluated using the National Institutes of Health Stroke Scale (NIHSS) by trained neurologists. ²⁰ Three blood pressure (BP) measurements were collected at admission when the patient was in the supine position using a standard mercury sphygmomanometer. Based on the TOAST (Trial of ORG 10172 in Acute Stroke Treatment) criteria, ischemic stroke were classified as large‐artery atherosclerosis, cardioembolism, small‐vessel occlusion, stroke of other determined etiology, and stroke of undetermined etiology according to the symptoms and imaging data of the patients. ²¹ Fasting plasma glucose, serum lipids, and other routine laboratory measurements were performed for all enrolled patients at Minhang Hospital.

Plasma ApoE Measurement

Fasting blood samples were collected after at least 8 hours of fasting within 24 hours of hospital admission. All plasma samples were separated and immediately frozen at −80°C until laboratory testing. Plasma ApoE levels at baseline were measured with the Cobas 8000 automatic analyzer (Roche Diagnostics, Indianapolis, Indiana). Laboratory technicians who performed these measurements were blind to the clinical characteristics and outcomes of the study participants. Intra‐assay and inter‐assay coefficients of variation for the plasma ApoE assay were less than 10% and 15%, respectively.

Outcome Assessment

Participants were followed up in person at 3 months after ischemic stroke by trained neurologists. The primary outcome was the composite outcome of death and major disability (modified Rankin Scale [mRS] score=3–6) at 3 months after ischemic stroke. The secondary outcomes included death (mRS score=6) and major disability (mRS score=3–5). We also included an ordered 7‐level categorical score of the mRS as a secondary outcome for neurological functional status, according to the recommendation from the European Stroke Organization Outcomes Working Group. ²² All study outcomes were reviewed and adjudicated by the outcome assessment committee that was blinded to participants' clinical characteristics.

Statistical Analysis

Baseline characteristics of the study participants were presented according to the quartiles of baseline plasma ApoE levels. Linear trends of baseline characteristics across plasma ApoE quartiles were tested using the generalized linear regression analysis for continuous variables, and the Cochran‐Armitage trend χ² test for categorical variables. Multivariable logistic regression analyses were used to calculate odds ratios (ORs) and 95% CIs of adverse outcomes after ischemic stroke for upper quartiles of plasma ApoE levels with the lowest quartile as a reference. Additionally, restricted cubic spline analyses were conducted to examine the potential linear or nonlinear relationships between plasma ApoE levels and adverse outcomes after ischemic stroke, with 4 knots defined at the 5th, 35th, 65th, and 95th percentiles of plasma ApoE levels. ²³ The effect estimates of plasma ApoE levels as a continuous variable were expressed as each SD increment when the association was linear, whereas fractional polynomial models were applied to model the curved relationship when nonlinearity was present. ²⁴ Potential covariates for adverse outcomes after ischemic stroke were selected based on our prior knowledge and baseline characteristics of the study participants. ²⁵ , ²⁶ The covariates included in the multivariable model were age, sex, current smoking, alcohol consumption, time from onset to hospitalization, systolic BP, NIHSS score at baseline, total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, fasting blood glucose, history of hypertension, history of diabetes, history of ischemic stroke, history of dementia, family history of stroke, use of antihypertensive medications before stroke onset, use of hypoglycemic agents before stroke onset, use of lipid‐lowering agents before stroke onset, ischemic stroke subtypes, intravenous thrombolysis, and mechanical thrombectomy. In addition, subgroup analyses were performed to evaluate the robustness of the associations between plasma ApoE levels and adverse outcomes after ischemic stroke. Interactions between plasma ApoE levels and subgroup variables on the primary outcome were tested in the multivariable model with interaction terms by the likelihood ratio test, adjusting for the aforementioned covariates. A 2‐tailed P < 0.05 was considered statistically significant. All statistical analyses were performed with SAS software version 9.4 (Cary, NC).

RESULTS

Baseline Characteristics

In the Minhang Stroke Cohort study (N=6892), patients included in the present analysis (N=5410) tended to have higher low‐density lipoprotein cholesterol; have lower systolic BP and NIHSS scores; have a higher prevalence of use of lipid‐lowering agents before stroke onset; have a lower prevalence of mechanical thrombectomy therapy; and have a longer time from onset to hospitalization than those excluded attributable to lacking blood samples or loss to follow‐up (N=1482) (Table S1).

Among the 5410 participants with ischemic stroke (3439 men and 1971 women) in the present study, the mean (SD) age was 70.0 (12.8) years, and the median plasma ApoE level was 43.00 mg/L (interquartile range, 34.00–54.00 mg/L; Table 1, Table S2, and Figure S2). Compared with participants with lower plasma ApoE levels, those with higher plasma ApoE levels were more likely to be women; had higher systolic BP, diastolic BP, baseline NIHSS score, total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, and fasting blood glucose; had a lower prevalence of history of ischemic stroke, and use of lipid‐lowering agents before stroke onset; had a higher prevalence of intravenous thrombolysis therapy; and had a shorter time from onset to hospitalization (Table 1).

Table 1.

Baseline Characteristics of the Study Participants According to the Quartiles of Plasma ApoE Levels

Characteristics†	Plasma ApoE levels, mg/L				P trend
	<34.00	34.00–42.99	43.00–53.99	≥54.00
No. of subjects	1317 (24.34)	1339 (24.75)	1368 (25.29)	1386 (25.62)
Demographics
Age, y	70.37±12.38	69.71±12.67	69.85±12.79	70.12±13.11	0.705
Men	1013 (76.92)	889 (66.39)	841 (61.48)	696 (50.22)	<0.001
Current cigarette smoking	275 (20.88)	297 (22.18)	291 (21.27)	258 (18.61)	0.112
Current alcohol drinking	122 (9.26)	117 (8.74)	168 (12.28)	127 (9.16)	0.384
Medical history
History of hypertension	868 (65.91)	861 (64.30)	893 (65.28)	932 (67.24)	0.377
History of diabetes	453 (34.40)	372 (27.78)	392 (28.65)	444 (32.03)	0.295
History of ischemic stroke	289 (21.94)	229 (17.10)	205 (14.99)	192 (13.85)	<0.001
History of dementia	20 (1.52)	16 (1.19)	20 (1.46)	12 (0.87)	0.210
Family history of stroke	12 (0.91)	15 (1.12)	27 (1.97)	14 (1.01)	0.412
Medication history
Use of antihypertensive medications	697 (52.92)	692 (51.68)	687 (50.22)	721 (52.02)	0.503
Use of hypoglycemic agents	395 (29.99)	328 (24.50)	321 (23.46)	360 (25.97)	0.016
Use of lipid‐lowering agents	377 (28.63)	306 (22.85)	291 (21.27)	270 (19.48)	<0.001
Clinical features
Time from onset to hospitalization, h	8.80 (2.50–29.05)	8.45 (2.42–28.90)	8.06 (2.24–27.67)	6.95 (2.03–25.00)	0.001
Systolic BP, mm Hg	140.55±19.90	142.59±19.89	143.84±21.02	145.20±20.52	<0.001
Diastolic BP, mm Hg	80.88±10.92	81.74±11.23	81.68±11.49	82.59±11.70	<0.001
Baseline NIHSS score	2.00 (1.00–5.00)	3.00 (1.00–5.00)	3.00 (1.00–5.50)	3.00 (1.00–6.00)	<0.001
Total cholesterol, mmol/L	3.47 (2.95–3.99)	4.07 (3.54–4.58)	4.37 (3.82–4.96)	4.91 (4.25–5.64)	<0.001
Triglyceride, mmol/L	1.08 (0.86–1.39)	1.28 (1.00–1.64)	1.47 (1.13–1.93)	1.97 (1.36–2.88)	<0.001
Low‐density lipoprotein cholesterol, mmol/L	2.28 (1.74–2.78)	2.75 (2.23–3.28)	3.00 (2.40–3.59)	3.14 (2.48–3.91)	<0.001
High‐density lipoprotein cholesterol, mmol/L	1.01 (0.87–1.19)	1.06 (0.91–1.25)	1.09 (0.91–1.29)	1.05 (0.87–1.31)	<0.001
Fasting blood glucose, mmol/L	5.50 (4.90–6.90)	5.50 (4.90–6.80)	5.60 (4.90–7.20)	6.00 (5.10–8.10)	<0.001
Ischemic stroke subtype*
Large‐artery atherosclerosis	805 (61.12)	826 (61.69)	803 (58.70)	821 (59.24)	0.146
Cardioembolism	183 (13.90)	150 (11.20)	184 (13.45)	175 (12.63)	0.713
Small‐vessel occlusion	302 (22.93)	334 (24.94)	343 (25.07)	353 (25.47)	0.142
Stroke of other determined etiology	4 (0.30)	4 (0.30)	10 (0.73)	3 (0.22)	0.839
Stroke of undetermined etiology	23 (1.75)	25 (1.87)	28 (2.05)	34 (2.45)	0.179
Endovascular treatment
Intravenous thrombolysis	114 (8.66)	99 (7.39)	128 (9.36)	169 (12.19)	<0.001
Mechanical thrombectomy	47 (3.57)	45 (3.36)	45 (3.29)	36 (2.60)	0.161

ApoE indicates apolipoprotein E; BP, blood pressure; and NIHSS, National Institute of Health Stroke Scale.

^*Ischemic stroke subtypes were classified based on the TOAST (Trial of ORG 10172 in Acute Stroke Treatment) criteria.

^† Continuous variables are expressed as mean ± SD or as median (interquartile range). Categorical variables are expressed as frequency (%).

Plasma ApoE Levels and Adverse Clinical Outcomes

During a 3‐month follow‐up period, a total of 1834 (33.90%) developed the primary outcome (563 deaths and 1271 major disabilities) 3 months after ischemic stroke (Table 2). After adjusting for age, sex, baseline NIHSS score, and other important prognostic factors, the ORs (95% CIs) associated with the highest quartile of plasma ApoE levels were 1.37 (95% CI=1.10–1.70; P _trend=0.003) for the primary outcome, 1.50 (95% CI=1.08–2.09; P _trend=0.019) for death, and 1.47 (95% CI=1.11–1.95; P _trend=0.005) for major disability. In addition, multivariable ordinal logistic regression analyses showed a significantly worse shift in the distribution of mRS score at 3 months with higher quartiles of plasma ApoE levels in participants after ischemic stroke (P _trend=0.034; Figure 1).

Table 2.

ORs and 95% CIs of Clinical Outcomes at 3 Months After Ischemic Stroke According to the Quartiles of Plasma ApoE Levels at Baseline

	Plasma ApoE levels, mg/L					Each SD (0.16) increment of log‐ApoE
	<34.00	34.00–42.99	43.00–53.99	≥54.00	P trend
Primary outcome: death or major disability (mRS score=3–6)
No. of cases (%)	427 (32.42)	423 (31.59)	467 (34.14)	517 (37.30)		1834 (33.90)
Unadjusted OR	1.00	1.04 (0.88–1.22)	1.12 (0.96–1.32)	1.29 (1.10–1.51)	0.003	1.08 (1.02–1.14)
Multiple‐adjusted OR*	1.00	1.02 (0.85–1.22)	1.13 (0.94–1.37)	1.37 (1.10–1.70)	0.003	1.17 (1.07–1.28)
Secondary outcomes
Death (mRS score=6)
No. of cases (%)	119 (9.04)	127 (9.48)	142 (10.38)	175 (12.63)		563 (10.41)
Unadjusted OR	1.00	0.95 (0.73–1.23)	1.11 (0.86–1.42)	1.38 (1.08–1.76)	0.002	1.13 (1.04–1.23)
Multiple‐adjusted OR*	1.00	1.14 (0.86–1.53)	1.20 (0.90–1.62)	1.50 (1.08–2.09)	0.019	1.17 (1.02–1.33)
Major disability (mRS score = 3–5)
No. of cases (%)	308 (23.39)	296 (22.11)	325 (23.76)	342 (24.68)		1271 (23.49)
Unadjusted OR	1.00	1.08 (0.90–1.29)	1.10 (0.92–1.31)	1.15 (0.97–1.38)	0.278	1.03 (0.97–1.10)
Multiple‐adjusted OR*	1.00	1.08 (0.87–1.34)	1.26 (1.00–1.58)	1.47 (1.11–1.95)	0.005	1.20 (1.07–1.35)
Modified Rankin scale score
Unadjusted OR†	1.00	1.00 (0.87–1.14)	1.04 (0.91–1.19)	1.15 (1.01–1.31)	0.029	1.05 (1.00–1.10)
Multiple‐adjusted OR* , †	1.00	1.06 (0.92–1.22)	1.09 (0.94–1.26)	1.21 (1.02–1.44)	0.034	1.10 (1.03–1.18)

ApoE indicates apolipoprotein E; log‐ApoE, log‐transformed plasma apolipoprotein E levels; mRS score, modified Rankin scale score; and ORs, odds ratios.

^*Adjusted for age, sex, current smoking, alcohol consumption, time from onset to hospitalization, systolic blood pressure, National Institute of Health Stroke Scale score at baseline, total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, fasting blood glucose, history of hypertension, history of diabetes, history of ischemic stroke, history of dementia, family history of stroke, use of antihypertensive medications before stroke onset, use of hypoglycemic agents before stroke onset, use of lipid‐lowering agents before stroke onset, ischemic stroke subtypes, intravenous thrombolysis, and mechanical thrombectomy.

^† Odds of a 1‐unit higher modified Rankin scale score.

Figure 1. Distribution of modified Rankin Scale score at 3 months according to the quartiles of plasma apolipoprotein E (ApoE) levels at baseline among patients with ischemic stroke.

Multivariable‐adjusted ordinal logistic regression analyses showed that the odds ratio associated with the highest vs the lowest quartile of plasma ApoE was 1.21 (95% CIs: 1.02–1.44; P _trend=0.034) for mRS score at 3 months after ischemic stroke. The mRS score for each quartile of plasma ApoE levels is expressed as frequency (%). Dashed lines show differences in the distribution of mRS score across the quartiles of plasma ApoE levels. mRS indicates modified Rankin Scale.

On continuous analyses, restricted cubic spline analyses revealed significant linear associations of plasma ApoE levels with the risk of the primary outcome (P for linearity<0.001), death (P for linearity=0.012), and major disability (P for linearity=0.001; Figure 2). Considering that the distribution of plasma ApoE levels exhibited pronounced right skewness (skewness coefficient=3.02) but approximated normality following log transformation (skewness coefficient=0.24; Figure S2), we further explored each SD increment of log‐transformed plasma ApoE levels in the multivariable logistic regression model. Each SD difference in log‐transformed plasma ApoE levels was associated with a 17% (95% CI=7%–28%) higher risk of the primary outcome, a 17% (95% CI=2%–33%) higher risk of death, and a 20% (95% CI=7%–35%) higher risk of major disability (Table 2).

Figure 2. Association of plasma apolipoprotein E (ApoE) levels with clinical outcomes 3 months after ischemic stroke.

Adjusted odds ratios (ORs) and 95% CIs derived from restricted cubic spline regression, with knots placed at the 5th, 35th, 65th, and 95th percentiles of plasma ApoE levels. The reference point is the midpoint of the lowest quartile of plasma ApoE levels (29.00 mg/L). ORs were adjusted for age, sex, current smoking, alcohol consumption, time from onset to hospitalization, systolic blood pressure, National Institute of Health Stroke Scale score at baseline, serum total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, fasting blood glucose, history of hypertension, history of diabetes, history of ischemic stroke, history of dementia, family history of stroke, use of antihypertensive medications before stroke onset, use of hypoglycemic agents before stroke onset, use of lipid‐lowering agents before stroke onset, ischemic stroke subtypes, intravenous thrombolysis, and mechanical thrombectomy. A, The primary outcome (modified Rankin Scale [mRS] score=3–6); B, death (mRS score=6); C, major disability (mRS score=3–5).

Subgroup Analyses

In the subgroup analyses stratified by age, sex, current smoking, alcohol drinking, history of dementia, time from onset to hospitalization, systolic BP, and NIHSS score at baseline, we found that high plasma ApoE levels were associated with an increased risk of the primary outcome in most categories (Table 3). There was no interaction between plasma ApoE levels and these subgroup variables in the risk of the primary outcome (all P for interaction >0.05).

Table 3.

Subgroup Analyses of the Association Between Plasma ApoE Levels and the Primary Outcome Among Patients With Ischemic Stroke

	Plasma ApoE levels, mg/L					Each SD (0.16) increment of log‐ApoE	P interaction
	<34.00	34.00–42.99	43.00–53.99	≥54.00	P trend
Age, y							0.868
<65	1.00	1.26 (0.86–1.85)	1.13 (0.75–1.69)	1.12 (0.70–1.80)	0.771	1.04 (0.86–1.27)
≥65	1.00	0.96 (0.78–1.17)	1.16 (0.94–1.44)	1.47 (1.15–1.87)	<0.001	1.22 (1.10–1.34)
Sex							0.420
Men	1.00	1.05 (0.84–1.30)	1.08 (0.86–1.37)	1.13 (0.85–1.51)	0.361	1.09 (0.97–1.21)
Women	1.00	1.00 (0.71–1.40)	1.19 (0.85–1.66)	1.73 (1.20–2.49)	<0.001	1.31 (1.13–1.51)
Current cigarette smoking							0.222
Yes	1.00	1.54 (0.98–2.41)	1.49 (0.93–2.41)	1.82 (1.03–3.23)	0.057	1.28 (1.01–1.60)
No	1.00	0.94 (0.77–1.15)	1.05 (0.86–1.30)	1.29 (1.01–1.63)	0.030	1.14 (1.04–1.26)
Current alcohol drinking							0.273
Yes	1.00	1.39 (0.71–2.70)	1.06 (0.54–2.09)	1.55 (0.67–3.60)	0.510	1.30 (0.92–1.84)
No	1.00	1.00 (0.83–1.21)	1.13 (0.92–1.37)	1.35 (1.08–1.69)	0.007	1.15 (1.05–1.26)
History of dementia							0.591
Yes	1.00	1.10 (0.87–1.39)	1.15 (0.89–1.48)	1.46 (1.08–1.97)	0.019	1.18 (1.04–1.33)
No	1.00	0.94 (0.70–1.25)	1.13 (0.84–1.50)	1.27 (0.92–1.76)	0.080	1.15 (1.01–1.31)
Time from onset to hospitalization, h							0.452
<24	1.00	0.96 (0.77–1.19)	1.15 (0.91–1.44)	1.25 (0.97–1.62)	0.041	1.13 (1.02–1.26)
≥24	1.00	1.19 (0.86–1.66)	1.15 (0.81–1.64)	1.84 (1.20–2.81)	0.016	1.27 (1.08–1.50)
Systolic BP, mm Hg							0.872
<160	1.00	1.02 (0.83–1.25)	1.09 (0.88–1.35)	1.34 (1.04–1.72)	0.027	1.13 (1.02–1.25)
160–180	1.00	0.99 (0.61–1.60)	1.17 (0.71–1.92)	1.40 (0.81–2.44)	0.186	1.32 (1.04–1.67)
≥180	1.00	1.01 (0.46–2.26)	1.34 (0.59–3.02)	1.48 (0.61–3.64)	0.281	1.22 (0.85–1.73)
Baseline NIHSS score							0.398
<4	1.00	1.10 (0.87–1.40)	1.14 (0.89–1.47)	1.45 (1.08–1.96)	0.022	1.17 (1.04–1.32)
≥4	1.00	0.99 (0.75–1.32)	1.22 (0.92–1.62)	1.42 (1.03–1.96)	0.013	1.19 (1.05–1.35)

ApoE indicates apolipoprotein E; BP, blood pressure; and NIHSS, National Institute of Health Stroke Scale.

Model adjusted for age, sex, current smoking, alcohol consumption, time from onset to hospitalization, systolic blood pressure, National Institute of Health Stroke Scale score at baseline, total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, fasting blood glucose, history of hypertension, history of diabetes, history of ischemic stroke, history of dementia, family history of stroke, use of antihypertensive medications before stroke onset, use of hypoglycemic agents before stroke onset, use of lipid‐lowering agents before stroke onset, ischemic stroke subtypes, intravenous thrombolysis, and mechanical thrombectomy.

DISCUSSION

In this large‐scale prospective study with 5410 patients with ischemic stroke, we found that high plasma ApoE levels at baseline were associated with increased risk of adverse outcomes at 3 months after ischemic stroke, and there were linear dose–response relationships between them. These associations were independent of established prognostic factors for ischemic stroke, and subgroup analyses further confirmed these findings. These findings indicate that plasma ApoE levels are implicated in the prognosis of ischemic stroke and may be a valuable prognostic biomarker for ischemic stroke.

Lipid homeostasis is crucial for proper cellular and systemic functions. ²⁷ Given its central role in lipoprotein metabolism, ApoE has gained increasing focus as a potential regulator implicated in the pathogenesis of cardiovascular disease. ²⁸ For example, in an analysis based on the 941 patients with coronary heart disease and 975 controls, high plasma triglyceride‐carrying ApoE levels were associated with an increased risk of coronary heart disease. ¹⁴ Similarly, a cohort study with 91 695 individuals from the general population also suggested a positive association between plasma ApoE levels and the risk of ischemic heart disease. ¹⁵ Another cohort study conducted in Netherlandish population found that elevated plasma ApoE levels were associated with a high risk of stroke. ¹⁷ Recently, Fukase et al. analyzed the data of 1109 consecutive patients with chronic coronary syndrome and revealed that ApoE level was a strong predictor of residual cardiovascular risk, ¹⁸ but no such evidence was available for patients with ischemic stroke.

To our knowledge, prior to this research, there was no report investigating the association between plasma ApoE levels and adverse clinical outcomes after ischemic stroke. Our study is a prospective study based on the Minhang Stroke Cohort with a large sample size and sufficient statistical power. Standardized protocols and rigid quality control procedures were used for data collection and outcome assessment. Moreover, comprehensive information about important prognostic factors of ischemic stroke was collected and controlled in multivariable models to ensure the independence of the associations observed. Thus, the methods used in this study were appropriate and rigorous, and our study could provide a valid appraisal for the prognostic significance of plasma ApoE levels among ischemic stroke patients. In the present study, we found that elevated plasma ApoE levels at baseline were significantly associated with increased risks of death or major disability at 3 months after ischemic stroke, independent of stroke severity, ischemic stroke subtypes, and conventional lipid measures. Additionally, the APOE gene has been well recognized as playing a critical role in Alzheimer's and related dementias. ²⁹ , ³⁰ Given the non‐negligible association between dementia (eg, Alzheimer's disease) and functional disability after ischemic stroke, ³¹ , ³² we adjusted for history of dementia in the multivariable models and performed further subgroup analyses stratified by history of dementia to eliminate the confounding effects. We found that the significant association of plasma ApoE levels with the primary outcome was independent of history of dementia, and there was no modified effect of history of dementia on the association between plasma ApoE levels and the prognosis of ischemic stroke, suggesting that plasma ApoE level had additional prognostic value when dementia was considered.

Our findings have important clinical implications for better understanding the pathogenesis of ischemic stroke and further improving the risk stratification of adverse outcomes after ischemic stroke. From our study, ischemic stroke patients with high plasma ApoE levels might be at high risk of adverse clinical outcomes and should receive early intervention to reduce the residual risk of poor prognosis of ischemic stroke. Several studies found that plasma ApoE levels were decreased in patients with dyslipidemia who received atorvastatin treatment. ³³ , ³⁴ Therefore, further clinical trials are warranted to explore whether statins would improve the prognosis of ischemic stroke with high plasma ApoE levels.

Although the biological mechanisms underlying the observed associations between plasma ApoE levels and ischemic stroke prognosis remained unclear, several potential pathophysiological processes might explain these findings. First, elevated plasma ApoE levels are associated with increased atherogenic lipids and lipoproteins, ²⁸ , ³⁵ thus leading to high risk of metabolic syndrome and atherosclerosis. ¹² , ¹³ , ³⁶ Second, several studies have indicated that ApoE is implicated in the process of the proliferation and differentiation of smooth muscle cells, which can induce thickening and narrowing of blood vessel walls. ³⁷ , ³⁸ Third, the clinical outcomes after ischemic stroke are affected by post‐ischemic inflammation, ³⁹ while ApoE is suggested to be involved in immunity and inflammatory responses, thereby driving neuroinflammation and oxidative stress. ⁹ , ¹⁰ Finally, ApoE may exert its adverse effects by inducing mitochondrial dysfunction and influencing the permeability of the blood–brain barrier. ¹¹ , ⁴⁰ Further studies are needed to explore the precise mechanisms underlying the associations between higher plasma ApoE levels and the worse prognosis of ischemic stroke.

Our study had several limitations that should be considered. First, although most baseline characteristics were similar, some differences existed between included and excluded patients, including low‐density lipoprotein cholesterol, systolic BP, and NIHSS score. Therefore, selection bias might be present. Second, plasma ApoE levels were only measured once at admission, so we were unable to investigate the associations between dynamic variations in plasma ApoE levels and the prognosis of ischemic stroke. Third, we only followed up participants at 3 months after ischemic stroke, so we could not assess the association of plasma ApoE levels at baseline with the long‐term prognosis of ischemic stroke. Fourth, during the follow‐up, we only collected death status, and the detailed reason for death was not collected. Further studies are needed to investigate this. Fifth, we only collected baseline data and conducted follow‐up for outcomes, without obtaining information on interim events between stroke onset/ApoE measurement and outcome assessment. Further studies are needed to investigate this. Finally, all patients in the current study are Chinese, so the generalizability of our findings to other populations is limited. Further prospective studies conducted among different populations are needed to replicate our findings.

CONCLUSIONS

High plasma ApoE levels were independently associated with increased risk of adverse clinical outcomes among ischemic stroke patients, suggesting that plasma ApoE might be implicated in the prognosis of ischemic stroke. Further studies from various populations are needed to validate our findings.

Sources of Funding

This study was supported by the National Natural Science Foundation of China (grant: 81973157 and 82173646), Public Health Discipline Construction project of Shanghai Minhang District Health Commission (grant: MGWXK2023‐04), and DCMST.NHC Clinical Research Project (grant: WKZX2023CZ0201).

Disclosures

None.

Supporting information

STROBE checklist

Tables S1–S2

Figures S1–S2