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Lily Dasso, Nicholas Maxwell Pfahler, Indre Bielskus, Michael Giovingo, Paul A Knepper; C-reactive protein potentiates platelet activation. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1222. doi: https://doi.org/.
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C-reactive protein (CRP) is an acute-phase serum protein and systemic marker of inflammation associated with an increased risk for age-related macular degeneration (AMD), particularly in patients with complement factor H (CFH) gene polymorphisms. Some evidence suggests that AMD is associated with systemic microvascular abnormalities consistent with platelet dysfunction, although the mechanism remains unclear. This study tested the hypothesis that CRP plays a role in the potentiation of thrombin-induced platelet activation.
Whole blood was obtained by venipuncture from control subjects (n=3) after informed consent. Platelets were isolated by centrifugation and challenged with 1 (normal level), 5 (mildly elevated level), or 10 (increased level in AMD or systemic infection) μg/ml monomeric CRP (mCRP), lipopolysaccharide (LPS; positive control), or 0.01 U/ml thrombin alone or in combination. CRP or LPS was added concurrently or 1 hour before challenge with thrombin for 5 minutes at 37°C. Conjugated antibodies were used to detect platelets (anti-CD41) and activated platelets (anti-PAC-1; activated GPIIb/IIIa) by flow cytometry. Two-sided Student’s t-test was used for statistical analysis.
mCRP at 1, 5, or 10 µg/mL had minimal effect on platelet activation alone or when added concurrently with thrombin. Platelets incubated with mCRP for 1 hour and then challenged with thrombin, however, exhibited significantly increased levels of activation: thrombin alone at 0.01 U/mL resulted in 54.0±4.7% activated platelets while thrombin plus mCRP at 1, 5, and 10 µg/mL resulted in 70.6±5.4% (p=0.04 compared to thrombin alone), 81.5±7.3 (p=0.007), and 86.6±7.7% (p=0.008) activated platelets, respectively. LPS at 1, 5, and 10 µg/mL resulted in 71.5±4.3% (p=0.04), 77.2±4.5% (p=0.008), and 81.3±5.4% (p=0.002) activated platelets, respectively.
CRP potentiates thrombin-induced platelet activation in vitro in a manner similar to that of LPS, suggesting the involvement of innate immune receptor toll-like receptor 4. Increased levels of CRP in AMD may therefore correspond with increased levels of platelet activation and dysfunction. Because CRP is regulated in part by CFH to dampen its proinflammatory response, CFH polymorphisms further the risk of CRP-induced inflammation and platelet dysfunction. CRP-induced platelet dysfunction may play a role in systemic vascular abnormalities observed in ocular degenerative diseases such as AMD.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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