Original Paper Cerebrovasc Dis 2014;38:324–327 DOI: 10.1159/000368218
Received: June 27, 2014 Accepted: September 8, 2014 Published online: November 21, 2014
Lipoprotein Phospholipase A2 Mass and Activity Are Not Associated with the Diagnosis of Acute Brain Ischemia Waimei Tai Madelleine Garcia Michael Mlynash Stephanie Kemp Gregory W. Albers Jean-Marc Olivot Stanford Stroke Center, Stanford University, Palo Alto, Calif., USA
Abstract Background: Elevated lipoprotein-associated phospholipase A2 (Lp-PLA2) levels are associated with both coronary artery and cerebrovascular diseases. The clinical diagnosis of neurovascular events, specifically transient ischemic attack can be challenging, although there is disagreement among vascular trained neurologists regarding this. Currently, there is no single accurate biomarker for the diagnosis of acute brain ischemia. Aim: We studied the relationship between Lp-PLA2 mass and activity levels and the diagnosis of acute brain ischemia in the acute phase among patients evaluated in the emergency department following transient focal neurological symptoms. Methods: Patients evaluated in our academic center for transient neurological symptoms of possible ischemic mechanism were enrolled with informed consent. Lp-PLA2 mass and activity levels were performed by DiaDexus, Inc. Results: 100 patients were enrolled: 58 were ischemic (30 stroke, 28 TIA), 10 were unknown, and 28 were non-ischemic. Blood samples were collected after a median delay of 23 h (IQR: 17, 36) after symptom onset. The median levels of Lp-PLA2 activity level for ischemic (stroke and TIA) versus non-ischemic events were 186.5 nmol/ml/min (IQR = 153, 216.3) and 169 nmol/ml/min (IQR = 137, 212.5), respectively. The median levels of Lp-PLA2 mass level for ischemic
© 2014 S. Karger AG, Basel 1015–9770/14/0385–0324$39.50/0 E-Mail [email protected] www.karger.com/ced
versus non-ischemic events were 202 ng/ml (IQR = 171.6, 226.1) and 192 ng/ml (167.8, 230). The differences in median Lp-PLA2 mass and activity levels were not statistically significant in the ischemic versus non-ischemic patients. Vessel imaging revealed a symptomatic stenosis in 14 patients (10 intracranial and 4 cervical). The median Lp-PLA2 mass and activity levels among patients with a symptomatic stenosis were not significantly higher than the levels measured in TIA/stroke patients without stenosis. Conclusion: The results of our study do not support the early measurement of LpPLA2 mass or activity levels for confirming an ischemic etiology in patients experiencing minor or transient focal neuro© 2014 S. Karger AG, Basel logical events.
Introduction
In clinical practice, the diagnosis of a TIA or minor stroke is sometimes challenging [1]. Multimodal brain MRI may help the physician to confirm an ischemic etiology for transient neurological symptoms in about 50% of the patients [2]. Evaluations using a panel of serum biomarkers hold some promise [3], but no single serum biological marker has demonstrated sufficient accuracy to be proposed for the diagnosis of acute brain ischemia [4]. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is produced by monocytes (and macrophages in tissue) and it Waimei Tai 300 Pasteur Dr., MC 5778 Stanford, CA 94305–5778 (USA) E-Mail wtai @ stanford.edu
Downloaded by: University of Tokyo 157.82.153.40 - 5/16/2015 7:51:17 PM
Key Words Lipoprotein phospholipase A2 · Stroke
Methods Patients with an acute onset of transient or minor neurological symptoms within 48 h of symptom onset, with a suspected ischemic mechanism were prospectively enrolled at a single academic center from April 2011–December 2012. The Institutional Review Board approved the study protocol and informed consent was obtained from all subjects. Per protocol, patients underwent a standard evaluation with MRI brain including diffusion-weighted imaging (DWI), MR, or CT-angiogram of the head and neck, laboratory studies and vascular neurology evaluation. At the end of the diagnostic evaluations, 2 vascular neurologists (WT, JMO) adjudicated the clinical neurologic syndrome as TIA, ischemic stroke, unknown, or other. TIA was defined as patients with a transient neurologic deficit of presumed ischemic origin, without evidence of DWI changes on imaging. Stroke (IS) was defined as patients with a transient or fixed neurologic deficit of ischemic origin lasting >24 h. TIA and stroke were categorized as definite ischemic events. Per protocol, systematic vessel imaging was performed on all patients. Symptomatic vessel stenosis was defined as a 50% or more stenosis of the vascular territory most likely to be responsible for the patient’s symptoms. Patients whose history, physical exam, or other diagnos-
Lp-PLA2 Not Correlated with Acute Brain Ischemia
tic tests that suggested a non-ischemic etiology were categorized as non-ischemic. Patients whose symptoms did not fit with ischemic or non-ischemic diagnosis were classified as unknown. Patients with a discharge diagnosis of unknown or definite ischemic event (TIA/ Stroke) were categorized as those who possibly had a ischemic event. Lp-PLA2 mass and activity levels were measured with commercially available assays at diaDexus, Inc. Statistical analysis was performed on SPSS version 20 for Windows. Tukey’s hinges definition was used to estimate the interquartile range (IQR). MannWhitney U test was used to evaluate for significance in non-parametric analysis. Baseline characteristics were compared using ANOVA and Fisher’s Exact tests.
Results
One hundred consecutive patients were enrolled. Discharge diagnoses were TIA [n = 28, median ABCD2 = 4 (IQR: 2, 5)], minor IS [n = 30, median NIHSS = 1 (IQR: 1, 2)], unknown (10) and non-ischemic (32) (table 1). Nonischemic diagnoses included: migraine (5), vertigo (2), seizure (3), or other (22). Blood samples were collected after a median delay of 23 h (IQR: 17, 36) after symptom onset. The median Lp-PLA2 mass levels measured after a non-ischemic event (192 ng/ml, IQR: 168, 230) were not different than the levels measured after a possible (200 ng/ml, IQR: 171, 222) or a definite (202 ng/ml, IQR: 172, 226) ischemic event , (p = 0.21 and p = 0.68). The median Lp-PLA2 activity levels measured after a possible (185 nmol/ml/min, IQR: 152, 216) or a definite (186 nmol/ml/ min, IQR: 153, 216) ischemic event were not different than the levels observed after a non-ischemic event (169 nmol/ml/min, IQR: 137, 213), were not different (p = 0.21 for both comparisons) (fig. 1 and 2). Vessel imaging revealed a symptomatic stenosis in 14 patients (10 intracranial and 4 cervical). The median LpPLA2 mass and activity levels among patients with a symptomatic stenosis were not significantly higher than the level measured in TIA/stroke patients without stenosis.
Discussion
The results of this small prospective cohort study did not support the hypothesis raised by the results observed with the same biological assays in a small retrospective dataset and the conclusion of the study published 2 decades ago by Satoh et al. [11]. To elucidate this discrepancy of results observed between our 2 cohorts, we performed a direct comparison of these 2 cohorts (Tai and Olivot, unpublished data, 2012). This comparison revealed unusually low Lp-PLA2 activity levels in the conCerebrovasc Dis 2014;38:324–327 DOI: 10.1159/000368218
325
Downloaded by: University of Tokyo 157.82.153.40 - 5/16/2015 7:51:17 PM
participates in the metabolism of oxidized LDL. The metabolites generated are involved in promoting vascular specific inflammation and the progression of atherogenesis [5]. Elevated Lp-PLA2 levels have been associated with the prevalence of cervical and brain vessel disease among stroke patients [5–7]. In addition, increased Lp-PLA2 levels have been associated with an increased risk of vascular events and the diagnosis of symptomatic vessel stenosis among TIA patients [8, 9]. In 2009, Elkind et al., demonstrated in a subset of the prospective North Manhattan Study, that the levels of Lp-PLA2 mass decreased after the occurrence of an acute cardiac/cerebral ischemic event [10]. Satoh et al. measured higher Lp-PLA2 activity (also known as Platelet Activating Factor Acetyl Hydrolase) after an acute brain infarction in a case-control study [11]. They hypothesized that the hyperactivity of platelets in the acute ischemic stroke increases the generation of the platelet activating factor, and in turn, upregulates its metabolizing enzyme, Lp-PLA2 [11]. Previously, we had found in a small retrospective cohort of patients who experienced acute ischemic events that Lp-PLA2 activity levels increased but Lp-PLA2 mass levels remained constant [12]. These results suggested that Lp-PLA2 could be a possible biomarker of acute brain ischemia. We therefore reinvestigated the relationship between Lp-PLA2 levels and the diagnosis of a transient/minor cerebral ischemic event, in a prospective cohort of consecutive patients evaluated for the acute onset of transient or minor neurological symptoms of presumed ischemic mechanism.
350
300
300
Lp-PLA2 mass level (ng/ml)
Lp-PLA2 activity level (nmol/ml/min)
350
250 –
200
–
150
–
–
100 50 0
TIA
Ischemic stroke
Unknown
Fig. 1. Lp-PLA2 activity level by patient type.
n = 10
n = 32
250 200
–
–
–
150
–
100 50 0
Non-ischemic
n = 30
n = 28
TIA
Ischemic stroke
Unknown
Non-ischemic
Fig. 2. Lp-PLA2 mass level by patient type.
Table 1. Characteristics of study population (n = 100)
Characteristic
Non-ischemic (32)
TIA (28)
Stroke (30)
Unknown (10)
p value
Age (mean ± SD) Female, n (%) CAD, n (%) Diabetes, n (%) Hypertension, n (%) Dyslipidemia, n (%) Smoker, n (%) Atrial fibrillation, n (%) h/o TIA or stroke, n (%) Symptomatic Stenosis, n (%)
63±15 15 (47) 0 (0) 4 (13) 17 (53) 17 (53) 1 (3) 3 (9) 11 (34) 0 (0)
68±12 8 (29) 2 (7) 8 (29) 19 (68) 15 (54) 2 (7) 5 (18) 8 (29) 7 (25)
68±15 12 (40) 3 (10) 6 (20) 21 (70) 16 (53) 4 (13) 7 (23) 15 (50) 7 (23)
64±12 3 (30) 0 (0) 1 (10) 4 (40) 6 (60) 0 (0) 2 (20) 4 (40) 0 (0)
0.40 0.51 0.30 0.43 0.25 1.0 0.44 0.50 0.39
Received: June 27, 2014 Accepted: September 8, 2014 Published online: November 21, 2014
Lipoprotein Phospholipase A2 Mass and Activity Are Not Associated with the Diagnosis of Acute Brain Ischemia Waimei Tai Madelleine Garcia Michael Mlynash Stephanie Kemp Gregory W. Albers Jean-Marc Olivot Stanford Stroke Center, Stanford University, Palo Alto, Calif., USA
Abstract Background: Elevated lipoprotein-associated phospholipase A2 (Lp-PLA2) levels are associated with both coronary artery and cerebrovascular diseases. The clinical diagnosis of neurovascular events, specifically transient ischemic attack can be challenging, although there is disagreement among vascular trained neurologists regarding this. Currently, there is no single accurate biomarker for the diagnosis of acute brain ischemia. Aim: We studied the relationship between Lp-PLA2 mass and activity levels and the diagnosis of acute brain ischemia in the acute phase among patients evaluated in the emergency department following transient focal neurological symptoms. Methods: Patients evaluated in our academic center for transient neurological symptoms of possible ischemic mechanism were enrolled with informed consent. Lp-PLA2 mass and activity levels were performed by DiaDexus, Inc. Results: 100 patients were enrolled: 58 were ischemic (30 stroke, 28 TIA), 10 were unknown, and 28 were non-ischemic. Blood samples were collected after a median delay of 23 h (IQR: 17, 36) after symptom onset. The median levels of Lp-PLA2 activity level for ischemic (stroke and TIA) versus non-ischemic events were 186.5 nmol/ml/min (IQR = 153, 216.3) and 169 nmol/ml/min (IQR = 137, 212.5), respectively. The median levels of Lp-PLA2 mass level for ischemic
© 2014 S. Karger AG, Basel 1015–9770/14/0385–0324$39.50/0 E-Mail [email protected] www.karger.com/ced
versus non-ischemic events were 202 ng/ml (IQR = 171.6, 226.1) and 192 ng/ml (167.8, 230). The differences in median Lp-PLA2 mass and activity levels were not statistically significant in the ischemic versus non-ischemic patients. Vessel imaging revealed a symptomatic stenosis in 14 patients (10 intracranial and 4 cervical). The median Lp-PLA2 mass and activity levels among patients with a symptomatic stenosis were not significantly higher than the levels measured in TIA/stroke patients without stenosis. Conclusion: The results of our study do not support the early measurement of LpPLA2 mass or activity levels for confirming an ischemic etiology in patients experiencing minor or transient focal neuro© 2014 S. Karger AG, Basel logical events.
Introduction
In clinical practice, the diagnosis of a TIA or minor stroke is sometimes challenging [1]. Multimodal brain MRI may help the physician to confirm an ischemic etiology for transient neurological symptoms in about 50% of the patients [2]. Evaluations using a panel of serum biomarkers hold some promise [3], but no single serum biological marker has demonstrated sufficient accuracy to be proposed for the diagnosis of acute brain ischemia [4]. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is produced by monocytes (and macrophages in tissue) and it Waimei Tai 300 Pasteur Dr., MC 5778 Stanford, CA 94305–5778 (USA) E-Mail wtai @ stanford.edu
Downloaded by: University of Tokyo 157.82.153.40 - 5/16/2015 7:51:17 PM
Key Words Lipoprotein phospholipase A2 · Stroke
Methods Patients with an acute onset of transient or minor neurological symptoms within 48 h of symptom onset, with a suspected ischemic mechanism were prospectively enrolled at a single academic center from April 2011–December 2012. The Institutional Review Board approved the study protocol and informed consent was obtained from all subjects. Per protocol, patients underwent a standard evaluation with MRI brain including diffusion-weighted imaging (DWI), MR, or CT-angiogram of the head and neck, laboratory studies and vascular neurology evaluation. At the end of the diagnostic evaluations, 2 vascular neurologists (WT, JMO) adjudicated the clinical neurologic syndrome as TIA, ischemic stroke, unknown, or other. TIA was defined as patients with a transient neurologic deficit of presumed ischemic origin, without evidence of DWI changes on imaging. Stroke (IS) was defined as patients with a transient or fixed neurologic deficit of ischemic origin lasting >24 h. TIA and stroke were categorized as definite ischemic events. Per protocol, systematic vessel imaging was performed on all patients. Symptomatic vessel stenosis was defined as a 50% or more stenosis of the vascular territory most likely to be responsible for the patient’s symptoms. Patients whose history, physical exam, or other diagnos-
Lp-PLA2 Not Correlated with Acute Brain Ischemia
tic tests that suggested a non-ischemic etiology were categorized as non-ischemic. Patients whose symptoms did not fit with ischemic or non-ischemic diagnosis were classified as unknown. Patients with a discharge diagnosis of unknown or definite ischemic event (TIA/ Stroke) were categorized as those who possibly had a ischemic event. Lp-PLA2 mass and activity levels were measured with commercially available assays at diaDexus, Inc. Statistical analysis was performed on SPSS version 20 for Windows. Tukey’s hinges definition was used to estimate the interquartile range (IQR). MannWhitney U test was used to evaluate for significance in non-parametric analysis. Baseline characteristics were compared using ANOVA and Fisher’s Exact tests.
Results
One hundred consecutive patients were enrolled. Discharge diagnoses were TIA [n = 28, median ABCD2 = 4 (IQR: 2, 5)], minor IS [n = 30, median NIHSS = 1 (IQR: 1, 2)], unknown (10) and non-ischemic (32) (table 1). Nonischemic diagnoses included: migraine (5), vertigo (2), seizure (3), or other (22). Blood samples were collected after a median delay of 23 h (IQR: 17, 36) after symptom onset. The median Lp-PLA2 mass levels measured after a non-ischemic event (192 ng/ml, IQR: 168, 230) were not different than the levels measured after a possible (200 ng/ml, IQR: 171, 222) or a definite (202 ng/ml, IQR: 172, 226) ischemic event , (p = 0.21 and p = 0.68). The median Lp-PLA2 activity levels measured after a possible (185 nmol/ml/min, IQR: 152, 216) or a definite (186 nmol/ml/ min, IQR: 153, 216) ischemic event were not different than the levels observed after a non-ischemic event (169 nmol/ml/min, IQR: 137, 213), were not different (p = 0.21 for both comparisons) (fig. 1 and 2). Vessel imaging revealed a symptomatic stenosis in 14 patients (10 intracranial and 4 cervical). The median LpPLA2 mass and activity levels among patients with a symptomatic stenosis were not significantly higher than the level measured in TIA/stroke patients without stenosis.
Discussion
The results of this small prospective cohort study did not support the hypothesis raised by the results observed with the same biological assays in a small retrospective dataset and the conclusion of the study published 2 decades ago by Satoh et al. [11]. To elucidate this discrepancy of results observed between our 2 cohorts, we performed a direct comparison of these 2 cohorts (Tai and Olivot, unpublished data, 2012). This comparison revealed unusually low Lp-PLA2 activity levels in the conCerebrovasc Dis 2014;38:324–327 DOI: 10.1159/000368218
325
Downloaded by: University of Tokyo 157.82.153.40 - 5/16/2015 7:51:17 PM
participates in the metabolism of oxidized LDL. The metabolites generated are involved in promoting vascular specific inflammation and the progression of atherogenesis [5]. Elevated Lp-PLA2 levels have been associated with the prevalence of cervical and brain vessel disease among stroke patients [5–7]. In addition, increased Lp-PLA2 levels have been associated with an increased risk of vascular events and the diagnosis of symptomatic vessel stenosis among TIA patients [8, 9]. In 2009, Elkind et al., demonstrated in a subset of the prospective North Manhattan Study, that the levels of Lp-PLA2 mass decreased after the occurrence of an acute cardiac/cerebral ischemic event [10]. Satoh et al. measured higher Lp-PLA2 activity (also known as Platelet Activating Factor Acetyl Hydrolase) after an acute brain infarction in a case-control study [11]. They hypothesized that the hyperactivity of platelets in the acute ischemic stroke increases the generation of the platelet activating factor, and in turn, upregulates its metabolizing enzyme, Lp-PLA2 [11]. Previously, we had found in a small retrospective cohort of patients who experienced acute ischemic events that Lp-PLA2 activity levels increased but Lp-PLA2 mass levels remained constant [12]. These results suggested that Lp-PLA2 could be a possible biomarker of acute brain ischemia. We therefore reinvestigated the relationship between Lp-PLA2 levels and the diagnosis of a transient/minor cerebral ischemic event, in a prospective cohort of consecutive patients evaluated for the acute onset of transient or minor neurological symptoms of presumed ischemic mechanism.
350
300
300
Lp-PLA2 mass level (ng/ml)
Lp-PLA2 activity level (nmol/ml/min)
350
250 –
200
–
150
–
–
100 50 0
TIA
Ischemic stroke
Unknown
Fig. 1. Lp-PLA2 activity level by patient type.
n = 10
n = 32
250 200
–
–
–
150
–
100 50 0
Non-ischemic
n = 30
n = 28
TIA
Ischemic stroke
Unknown
Non-ischemic
Fig. 2. Lp-PLA2 mass level by patient type.
Table 1. Characteristics of study population (n = 100)
Characteristic
Non-ischemic (32)
TIA (28)
Stroke (30)
Unknown (10)
p value
Age (mean ± SD) Female, n (%) CAD, n (%) Diabetes, n (%) Hypertension, n (%) Dyslipidemia, n (%) Smoker, n (%) Atrial fibrillation, n (%) h/o TIA or stroke, n (%) Symptomatic Stenosis, n (%)
63±15 15 (47) 0 (0) 4 (13) 17 (53) 17 (53) 1 (3) 3 (9) 11 (34) 0 (0)
68±12 8 (29) 2 (7) 8 (29) 19 (68) 15 (54) 2 (7) 5 (18) 8 (29) 7 (25)
68±15 12 (40) 3 (10) 6 (20) 21 (70) 16 (53) 4 (13) 7 (23) 15 (50) 7 (23)
64±12 3 (30) 0 (0) 1 (10) 4 (40) 6 (60) 0 (0) 2 (20) 4 (40) 0 (0)
0.40 0.51 0.30 0.43 0.25 1.0 0.44 0.50 0.39
