ESJ Featured Article of the Month – February 2025

C-reactive protein expression in acute ischemic stroke blood clots: Implications for etiology

C-reactive protein (CRP) is a non-specific inflammatory marker, mainly used to detect infection, inflammation and to track response to treatment.¹ But CRP is also independently associated with vascular events and poor outcome after stroke.^2-4 CRP has been shown to be raised in across multiple stroke subtypes, including  large artery atherosclerosis (LAA) and cardioembolic stroke (CE), yet the impact of measuring CRP levels in stroke patients is as yet, uncertain.⁴

This month in European Stroke Journal, Liu and colleagues investigate whether CRP is a useful biomarker of stroke aetiology by examining and measuring CRP levels in clots retrieved during endovascular thrombectomy for ischaemic stroke.⁵

This study, by international collaborators contributing to the prospective Clotbase International Registry, analysed clots from 150 patients with acute ischaemic stroke, from hospitals in France, Spain, Serbia and Japan. The median age was 71-years old, cardiovascular risk factors were common. Two-thirds were treated with thrombolysis in addition to EVT, and over half of the strokes were severe, with an NIHSS score ≥15 at presentation. Although 82.7% had successful reperfusion (mTICI 2c or 3) after EVT, over half of this cohort had persistent disability (mRS ≥3) at 90-day follow-up. Importantly, no patients were excluded based on co-morbid inflammatory or infectious conditions, an important source of confounding to keep in mind.

The strokes were subtyped using the TOAST criteria, although the authors do not specify a minimum set of investigations to ensure accurate classification. The clots were retrieved during EVT, were fixed and analysed for CRP using  immunohistochemical and immunofluorescence staining.

Three categories of stroke subtype were studied: LAA, CE and cryptogenic stroke and there were 50 participants in each category. On histological examination, clots retrieved from strokes caused by LAA had a higher composition of red blood cells, while those caused by CE had higher level of white blood cels.

‘Red’ (composed mainly of red blood cells) and ‘white’ (composed predominantly of platelets and fibrin) have been previously described.⁶ ‘Red’ thrombi are associated with hyperdense MCA sign ⁷and with increased sensitivity to thrombolysis and thrombectomy.⁸ Prior studies correlating clot composition and stroke subtype have been small, but have also demonstrated  ‘red’ clots in strokes caused by LAA.^9,10 In 1,350 patients from the STRIP registry, strokes caused by LAA also had higher levels of RBCs, however RBC levels were only marginally better than chance to distinguish LAA strokes from CE strokes. ¹¹

In this study, Liu et al also analysed CRP level within the clots. They observed marked variation in CRP expression, with a skewed distribution. Other studies have described high intra-individual variability of CRP levels in vivo.¹² Consider also that extremely high levels of CRP could be driven by a systematic inflammatory response to cerebral ischaemia or infection.

The authors dichotomised CRP clot levels into low CRP (<1%) and high CRP (≥1%) CRP expression. When the authors compared CRP expression in the clot across the three stroke subtypes, LAA and cryptogenic stroke were more likely to have clots with <1% of CRP, while CE had the highest proportion of those with >1% CRP.  Fibrin levels were also higher in clots with higher CRP composition. (CRP and fibrin are biologically correlated. In vivo, CRP inhibits tissue plasminogen activator which cleaves plasminogen to form plasmin which in turn degrades fibrin. Therefore CRP promotes intravascular fibrin formation.¹)

There are a number of  limitations to this report: it is a modest sample size,  CRP-clot levels were not correlated with serum CRP levels, and information was lost when CRP as a continuous variable was dichotomised. We cannot draw definitive conclusions regarding CRP content in clots and stroke subtype from this observational data.

Nevertheless, this research is interesting and stimulates more questions.  Where does the CRP in the clot come from- is it a reflection of systemic inflammation or of localised vascular inflammation? Does it occur as a cause or as a consequence of the stroke? Does the time from stroke onset to clot retrieval influence the composition of the clot? Looking to the future, if this technique was applied in clinical practice, what added value could be gained from quantifying CRP in EVT-retrieved clots? Prognosis? Selection for intra-arterial thrombolytics? Clues to the underlying aetiology? Selection for targeted secondary prevention strategies? More research is needed to replicate these findings and for their translation to clinical practice.

C-reactive protein expression in acute ischemic stroke blood clots: Implications for etiology

Liu et al

Online first Feb 2025

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References

1. Fay WP. Linking inflammation and thrombosis: Role of C-reactive protein. World J Cardiol 2010; 2(11): 365-9.
2. den Hertog HM, van Rossum JA, van der Worp HB, et al. C-reactive protein in the very early phase of acute ischemic stroke: association with poor outcome and death. J Neurol 2009; 256(12): 2003-8.
3. McCabe JJ, Walsh C, Gorey S, et al. C-Reactive Protein, Interleukin-6, and Vascular Recurrence After Stroke: An Individual Participant Data Meta-Analysis. Stroke 2023; 54(5): 1289-99.
4. McCabe JJ, Walsh C, Gorey S, et al. C-Reactive Protein, Interleukin-6, and Vascular Recurrence According to Stroke Subtype: An Individual Participant Data Meta-Analysis. Neurology 2024; 102(2): e208016.
5. Liu W, Sahin C, Güner Sak N, et al. C-reactive protein expression in acute ischemic stroke blood clots: Implications for etiology. European Stroke Journal; 0(0): 23969873251315636.
6. Joundi RA, Menon BK. Thrombus Composition, Imaging, and Outcome Prediction in Acute Ischemic Stroke. Neurology 2021; 97(20 Suppl 2): S68-s78.
7. Liebeskind DS, Sanossian N, Yong WH, et al. CT and MRI early vessel signs reflect clot composition in acute stroke. Stroke 2011; 42(5): 1237-43.