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 alpha-chains and one beta-chain, here termed C4BP(beta), whereas upon inflammation a normally less abundant isoform is upregulated that is exclusively composed of alpha-chains. Measuring the alpha-chains of C4BP includes both isoforms and is termed total C4BP (C4BP(tot)). 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), C4BP(tot) and C4BP(beta), lipid levels, the inflammatory mediators tumor necrosis factor-alpha, interleukin-6, 8-iso-prostaglandin F(2alpha), 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 microg/mL vs 341 +/- 10.8/318 microg/mL for C4BP(tot), P = .0248; 374 +/- 25.4/332 microg/mL vs 305 +/- 9.5/285 microg/mL for C4BP(beta), P = .0581). C4BP plasma levels were significantly elevated in CLI patients in comparison to healthy controls (351 +/- 8.1/322 microg/mL vs 297 +/- 8.0/288 microg/mL for C4BP(tot), P = .0001; 314 +/- 7.0/287 microg/mL vs 265 +/- 7.0/263 microg/mL for C4BP(beta), P = .0004) and correlated to levels of interleukin-6 (P(tot/beta) = .0048/.0019), high-sensitivity C-reactive protein (P < .0001), leukocyte (P(tot/beta) = .0086/.0043) and platelet count (P = .0001), LDL/HDL ratio (P(tot) = .0151) and HDL (P(tot/beta) = .0047/.0177), but not to tumor necrosis factor-alpha.
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.