Complement activation and plasma levels of C4b-binding protein in critical limb ischemia patients

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Abstract

Objective: Critical limb ischemia (CLI) is a peripheral arterial disease manifested by drastically diminished blood flow to the legs, pain at rest, nonhealing wounds, and gangrene caused by atherosclerosis. Significant tissue necrosis is associated with late stage CLI and the patients have a poor prognosis. Necrotic and apoptotic cells activate complement and bind complement inhibitor C4b-binding protein (C4BP). The major isoform of C4BP is composed of seven identical α-chains and one β-chain, here termed C4BPβ, whereas upon inflammation a normally less abundant isoform is upregulated that is exclusively composed of α-chains. Measuring the α-chains of C4BP includes both isoforms and is termed total C4BP (C4BPtot). The hypothesis of this study was that levels of complement activation and C4BP are predictive for the severity of the disease and that their measurement might be of clinical advantage. Methods: This was a prospective, single-center study of 259 consecutive patients with CLI admitted to a secondary referral center for vascular diseases. Interventions included evaluation of soluble terminal complement complexes (C5b-9), C4BPtot and C4BPβ, lipid levels, the inflammatory mediators tumor necrosis factor-α, interleukin-6, 8-iso-prostaglandin F2α, high-sensitivity C-reactive protein, neopterin, plasma homocysteine, and plasma endothelin-1 in plasma as well as resistance to activated protein C and ankle blood pressure. All data were compared with an age-matched population based control group of 219 currently healthy individuals. Results: The data are presented as mean ± SEM/median. CLI patients showed systemic complement activation (1.17 ± 0.06/1.13 AU/mL vs 0.69 ± 0.07/0.59 AU/mL in healthy controls, P < .0001), which was even higher in patients with gangrene (1.33 ± 0.11/1.28 AU/mL vs 1.1 ± 0.08/1.0 AU/mL, P = .0264), who also showed increased C4BP levels (421 ± 28.6/386 μg/mL vs 341 ± 10.8/318 μg/mL for C4BPtot, P = .0248; 374 ± 25.4/332 μg/mL vs 305 ± 9.5/285 μg/mL for C4BPβ, P = .0581). C4BP plasma levels were significantly elevated in CLI patients in comparison to healthy controls (351 ± 8.1/322 μg/mL vs 297 ± 8.0/288 μg/mL for C4BPtot, P = .0001; 314 ± 7.0/287 μg/mL vs 265 ± 7.0/263 μg/mL for C4BPβ, P = .0004) and correlated to levels of interleukin-6 (Ptot/β = .0048/.0019), high-sensitivity C-reactive protein (P < .0001), leukocyte (Ptot/β = .0086/.0043) and platelet count (P = .0001), LDL/HDL ratio (Ptot = .0151) and HDL (Ptot/β = .0047/.0177), but not to tumor necrosis factor-α. Conclusions: Increased complement activation and C4BP plasma levels are related to the degree of tissue necrosis and disease severity of critical limb ischemia. This knowledge in combination with the found correlations to other biomarkers is useful for understanding the pathophysiology of the disease. © 2009 Society for Vascular Surgery.

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Martin, M., Gottsäter, A., Nilsson, P. M., Mollnes, T. E., Lindblad, B., & Blom, A. M. (2009). Complement activation and plasma levels of C4b-binding protein in critical limb ischemia patients. Journal of Vascular Surgery, 50(1), 100–106. https://doi.org/10.1016/j.jvs.2008.12.033

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