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Inhibition by epsilon-aminocaproic acid of the activation of the first component of the complement system
Insights
Epsilon-aminocaproic acid (EACA) selectively inhibits the intrinsic activation of complement component 1 (C1) in human serum without affecting other complement factors. This inhibition is reversible by dialysis, suggesting a role in C1 binding.
Area of Science:
- Immunology
- Biochemistry
Background:
- The complement system is a crucial part of innate immunity.
- Complement component 1 (C1) is the initial enzyme complex in the classical complement pathway.
Purpose of the Study:
- To investigate the influence of epsilon-aminocaproic acid (EACA) on C1 activity in human serum and as isolated molecules.
- To determine the mechanism of EACA's effect on C1 activation.
Main Methods:
- Hemolytic assays were used to assess C1 activity.
- Experiments were conducted using whole human serum and isolated C1 molecules.
- Dialysis was employed to investigate the reversibility of EACA's effects.
- Trypsin was used to probe C1 activation intermediates.
Main Results:
- EACA selectively inhibited C1 in whole human serum without affecting C4, C2, C3, and C9 levels.
- The inhibitory effect of EACA on C1 was reversible by dialysis.
- EACA inhibited the intrinsic activation of C1 but not already active C1.
- Trypsin could partially restore C1 activity in EACA-treated intermediates, suggesting an effect on C1 binding.
Conclusions:
- EACA acts as a selective inhibitor of C1 intrinsic activation.
- The reversibility by dialysis suggests EACA may interfere with C1 binding or conformational changes necessary for activation.
- Further studies are needed to fully elucidate the binding interactions affected by EACA.
Abstract:
The influence of EACA on C1 in whole human serum and on C1 and C (see article) as isolated molecules was assessed hemolytically. There was selective inhibition of C1 without effect on the levels of C4, C2, C3, and C9 in whole human serum that was reversed by dialysis. EACA was found to inhibit the intrinsic activation of C1 without inhibiting the already active molecule. This was confirmed by the capacity of trypsin to uncover C1 activity in cellular intermediates formed by C1 treated with EACA that did not evolve in the absence of this extrinsic activating mechanism. Inasmuch as the trypsin-dependent recovery of C1 was incomplete, an effect on binding cannot be excluded.