Multiple Functions for C1-INH - Increasing Importance of the Glyco of Glycoproteins

                   The function(s) of the  glycan moiety of glycoproteins has been a mystery for some time.   Considering that it takes a considerable amount of resources to place a glycan side chain on a protein, there should be a better reason that blocking an  epitope or enabling secretion from a cell.   There is an increasing body of work which addresses the biological function of the glycan moiety of glycoproteins.  Take, for example, the case of C1-inhibitor (C1-esterase inhibitor; C1- INH) which inhibits C1r and C1s in classical pathway of complement as well as plasma kallikrein and blood coagulation factor XIIa (1) .    C1-INH contains a large amount of carbohydrate (25-30% by mass) located in an approximate 100 amino acid extension amino terminal from the serpin domain (2); the amino terminal domain is not required for in vitro protease inhibition activity of C1-INH (3).   The deficiency  of C1-INH results in the clinical problem of hereditary angioedema (4) which is a sufficiently large clinical problem (1 in 50,000) that a therapeutic concentrate has been obtained from human plasma (5-7) and a recombinant product expressed in rabbit milk has been recently developed (8-10).   

                   As with other serpins, the biology of C1-INH is complex and there are likely other functions as important, if not more so, than protease inhibition (11).   I cite only several here in the interest of space.  Dorresteijn and coworkers (12) observed the anti-inflammatory action of CI-INH in the absence of complement activation while Thorgersen and coworkers (13) observed anti-inflammatory activity of C1 INH in the absence of protease inhibition.  Dorresteijn and coworkers (12) observed an increase in the anti-inflammatory cytokine IL-10 on the use of C1-INH (Cetor®, Sanquin, Netherlands)  in normal male volunteers challenged with E.Coli endotoxin.  The effect was not due to neutralization of LPS and these investigators suggest that C1-INH may have value in the treatment of the systemic inflammatory response in sepsis.    Thorgersen and colleagues (13) showed that both C1-INH and "inactive" C1-INH (C1-INH cleaved in the RCL domain with trypsin such that it is inactive inhibiting proteases) were effective in reducing the levels of inflammatory cytokines induced in vitro by E.coli endotoxin in porcine or human blood.   These studies and others (14-17) support the importance of C1-INH functions other than inhibition of proteases in the development of this protein as a therapeutic product.    It should be noted that many of these studies are in complex systems such that a role for protease inhibition cannot be excluded.

                   Therapeutic preparations of C1-INH are available from plasma and recombinant sources.  The recombinant form derived from rabbit milk has decreased glycosylation and decreased sialic acid content compared to the plasma protein (18).   Gesuete and coworkers (19) evaluated the use of a recombinant form of C1 INH in a murine model for stroke.  Recombinant C1 INH (intravenous) markedly reduced cerebral damage resulting from ischemia while the plasma-derived protein was far less effective.   It is suggested that difference in therapeutic effectiveness  is a reflection of the glycosylation patterns of the two proteins.   These investigators demonstrated binding of the recombinant protein to mannose-binding lectin resulting in inhibition of the complement lectin pathway.  

                   Both the plasma-derived  and recombinant forms of C1-INH are useful therapeutic products.   Expanded indications for either protein will required an understanding of the relationship between structure and function in the various glycan chains.  One interesting possibility is the use of the N-terminal domain as a free-standing therapeutic products with PEGylation to improve pharmacokinetics; PEGylation may also modulate function.    Glycoengineering (20,21)  of the oligosaccharide chains will likely prove useful considering the observed differences between the plasma-derived product and the recombinant product (19). 

                   The complexity of carbohydrate on  proteins is clearly demonstrated in a recent article by Zhuo and Bellis (22) on role of β-galactoside α2,6-sialyl transferase as a regulator of galactose-binding lectins (galactins) by adding α2,6-sialic acid residue to a terminal galactose residue.   Sialic acid is also an important ligand for sialic acid-binding  immunoglobulin like lectins (Siglecs)(23) and subject to control by sialidase activity (24) or by fucosylation (25).




1.  Career, F.M., The C1 inhibitor deficiency. A review, Eur.J.Clin.Chem.Clin.Biochem. 30,793-807, 1992.

2.  Wagnenaar-Bos, I.G., and Hack, C.E., Structure and function of C1-inhibitor, Immunol.Allergy Clin.North Am. 26, 615-632, 2006.

3.  Coutinho, M., Aulak, K.S., and Davis, A.E., III, Functional analysis of the serpin domain of C1 inhibitor, J.Immunol. 153, 3648-3654, 1994.

4.  Riedl, M., Gower, R.G., and Chrvala, C.A., Current medical management of hereditary angioedema: results from a large survey of US physicians, Ann.Allergy Asthma Immunol. 106, 316-322, 2011.

5.  Keating, G.M., Human C1-esterase inhibitor concentrate (Berinert®), BioDrugs 23, 399-306, 2009.

6.  Wouters, D., Wagenaar-Bos, I., van Ham, H., and Zeerleder, S., C1 inhibitor: just a serine protease inhibitor? New and old considerations on therapeutic applications of C1 inhibitor, Expert Opin.Biol.Ther. 8, 1225-1240, 2008.

7.  Hofstra, J.J., Kleine Budde, I., van Twuyver, E., et al., Treatment of hereditary angioedema with nanofilitered C1-esterase inhibitor concentrate (Cetor®): Multi-center phase II and III studies to assess pharmacokinetics, clinical efficacy and safety, Clin.Immunol. 142, 280-290, 2012.

8.  Choi, F., Soeters, M.R., Farkas, H., et al., Recombinant human C1-inhibitor in the treatment of acute angioedema attacks, Transfusion 47, 1028-1032, 2007.

9. Varga, L. and Farkas, H., rhC1INH: a new drug for the treatment of attacks in hereditary angioedema caused by C1-inhibitor deficiency, Expert Rev.Clin.Immunol. 7, 143-153, 2011.

10.  Zuraw, B., Cicardi, M., Levy, R.J., et al., Recombinant human C1-inhibitor for the treatment of acute angioedema attacks in patients with hereditary angioedema, J.Allergy Clin.Immunol. 126, 821-827, 2010.

11. Davis, A.E.., III., Lu, F., and Mejia, P., C1 inhibitor, a multi-functional serine protease inhibitor, Thromb.Haemost. 104, 886-893, 2010.

12.  Dorresteijn, M.J., Visser, T., Cox, L.A., et al., C1-esterase inhibitor attenuates the inflammatory response during human endotoxemia, Crit.Care.Med. 38, 2139-2145, 2010.

13.  Thorgersen, E.B ., Ludviksen, J.K., Lambris, J.D., et al., Anti-inflammatory effects of C1-inhibitor in porcine and human whole blood are independent of its protease inhibition activity, Innate Immun. 16, 254-264, 2010.

14.  Cheng, Z.-D., Liu, M.-Y., Chen, G., et al., Anti-vascular permeability of the cleaved reactive center loop within the carboxyl-terminal domain of C1 inhibitor, Mol.Immunol. 45, 1743-1751, 2008.

15.  Liu, D., Gu, X., Scafidi, J., and Davies, A.E., III, N-Linked glycosylation is required for C1 inhibitor-mediated protection from endotoxin shock in mice, Infect.Immun. 72, 1946-1955, 2004.

16.  Cai, S., Dole, V.S., Bergmeier, W., et al., A direct role for C1 inibitor in regulation of leukocyte adhesion, J.Immunol. 174, 6462-6466, 2005.

17.  Cai, S. and Davis, A.E.,III, Complement regulatory protein C1 inhibitor binds to selectins and interferes with endothelial-leukocyte adhesion, J.Immunol. 171, 4785-4791, 2003.

18.  Koles, K., van Berkel, P.H.C., Pieper, F.R., et al., N- and O-glycans of recombinant human C1-inhibitor expressed in the milk of transgenic rabbits, Glycobiology 14, 51-64, 2004.

19.  Gesuete, R., Storini, C., Fantin, A., et al., Recombinant C1 inhibitor in brain ischemia injury, Ann.Neurol. 66, 332-342, 2009.

20. Solá, R.J.  and Griebenow, K., Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy,  BioDrugs 24, 9-21, 2010.

21.  Carter, P.J., Introduction to current and future protein therapeutics: a protein engineering perspective, Exp.Cell Res. 317, 1261-1269, 2011.

22.  Zhuo, Y. and Bellis, S.L., Emerging role of α2,6-sialic acid as a negative regulator of galactin binding and function, J.Biol.Chem. 286, 5935-5941, 2011.

23. Magesh, S., Ando, H., Tsubata, T., et al., High-affinity ligands of siglec receptors and their therapeutic potentials, Curr.Med.Chem. 18, 3537-3550, 2011, 2011.

24.  Kawasaki, Y., Ito, A., Withers, D.A., et al., Ganglioside Dsgb5, preferred ligand for Siglec-7, inhibits NK cell cytotoxicity against renal cell carcinoma cells, Glycobiology 20, 1373-1379, 2010.

25.  Levander, L., Gunnarsson, P., Grenegård, M., et al., Effects of α1-acid glycoprotein fucosylation on its Ca2+ mobilizing capacity in neutrophils, Scand.J.Immunol. 69, 412-420, 2009.