Inactivation Of C5a Research Articles

Deficiency of Either Carboxypeptidase B2 or Carboxypeptidase N Exacerbated Disease Activity in a Mouse Model of Hemolytic Uremic Syndrome

Two different basic carboxypeptidases circulate in blood - carboxypeptidase N (CPN) and proCPB2. CPN is constitutively active, while proCPB2 is a zymogen, (also termed thrombin activatable fibrinolysis inhibitor, TAFI), and is activated by the endothelial thrombin/thrombomodulin complex to CPB2. Their kinetics of substrate cleavage are distinct but both can efficiently inactivate the complement anaphylatoxins, C3a and C5a. Hemolytic uremic syndrome (HUS) is caused by Shiga toxin (stx) producing strains of E. coli and is characterized by the triad of hemolysis, thrombocytopenia and uremia. We hypothesized that in a mouse model of HUS, Cpb2-/- and Cpn-/- mice would have prolonged C5a anaphylatoxin activity thus causing disease exacerbation.HUS was induced by stx2 and LPS administration in WT, Cpn-/- and Cpb2-/- mice. In Cpb2-/- mice, median time to death was earlier (60 hours, n=15) than in WT mice (96 hours: n=42, p<0.0001), and had greater kidney and liver damage shown by increases in ALT, AST, BUN and creatinine levels at 48 hours (creatinine Cpb2-/-: 1.01 mg/dL, WT: 0.25 mg/dL; Cpb2-/- control: 0.20 mg/dL and WT control: 0.19 mg/dL; Cpb2-/- p<0.0001 vs. all other groups, n>9). An increase in hemolysis was demonstrated by reduced RBC count and hemoglobin level plus an increase in total bilirubin and LDH. Profound thrombocytopenia (Cpb2-/-: 121,000/μL vs. WT: 217,000/μL; p=ns) developed in both genotypes (control Cpb2-/-: 1,001,000/μL vs. control WT: 1,141,000/μL; p=ns but vs. either Cpb2-/- or WT with HUS, p<0.0001) and thus the HUS clinical triad was present. Histology showed tubular epithelial necrosis in the kidney ante-mortem. Administration of either toxin separately caused milder disease without the characteristics of HUS and with no observed mortality. Induction of the disease depended on co-administration of both toxins. Treatment with anti-murine C5 antibody (0.75 mg every 24 hours from 3 hours before disease initiation) improved survival of both WT and Cpb2-/- mice with a median survival time of 168 hours for both genotypes (n=11, p=0.003 and <0.0001 respectively) and normalized the outcomes between the genotypes.Cpn-/- mice also died sooner (median time to survival 81.5 hours, n=28) than WT mice (96 hours, n=42, p=0.0002). The median survival time between Cpb2-/- and Cpn-/- mice was also significantly different (60 vs. 81.5 hours, p=0.0083). This is a first direct comparison of the role of CPN vs. CPB2 in regulating C5a activity in a disease relevant mouse model. Our study suggests that both CPB2 and CPN protect against HUS by inactivation of C5a with CPB2 having a greater effect than CPN. When Cpb2+/-/Cpn+/- mice are crossed, all expected genotypes are recovered in the expected Mendelian ratios including double deficient Cpb2-/-/Cpn-/- mice. Thus absence of both plasma basic carboxypeptidases is not essential for murine life. We are currently evaluating the Cpb2-/-/Cpn-/- mice in our HUS model. DisclosuresNo relevant conflicts of interest to declare.

Inactivation of human anaphylatoxin C5a and C5a des-Arg through cleavage by the plasminogen activator activity of a human fibrosarcoma cell line.

The HT-1080 human fibrosarcoma cell line exhibited a plasminogen-dependent ability to inactivate recombinant anaphylatoxin C5a or zymosan-activated serum. The inactivation was obtained at physiological levels of both plasminogen (2 microM) and C5a (1-5 nM). Inactivated C5a and zymosan-activated serum were no longer able to induce chemotaxis and degranulation of neutrophils. Inactivation of C5a paralleled the emergence of plasmin activity, assayed by cleavage of the synthetic substrate H-D-valyl-L-leucyl-L-lysine-p-nitroanilide (S-2251). Both C5a inactivation and S-2251 cleavage were inhibited by the plasmin inhibitor alpha 2-antiplasmin, the urokinase inhibitor amiloride, and by anti-urokinase antibodies. In a cell-free system, inactivation of C5a was shown to depend on the simultaneous presence of urokinase and plasminogen and was inhibited by alpha 2-antiplasmin and by anti-urokinase antibodies. SDS-polyacrylamide electrophoresis demonstrated the cleavage of C5a by the plasminogen activation system and inhibition of the cleavage by amiloride. Amino acid sequencing of the band corresponding to the C5a degradation product revealed that C5a was cleaved at positions Lys14-His15 and Arg40-Ile41; cleavage at position Arg40-Ile41 seemed to be responsible for the loss of activity. Since neoplastic cells extensively produce and exhibit plasminogen activator activity, the present observations suggest that plasminogen activation may, by inactivation of C5a, reduce the anti-tumor immune response and support the immunological escape phenomenon of tumors.

A Functional Differentiation of Human Neutrophil Granules: Generation of C5a by a Specific (Secondary) Granule Product and Inactivation of C5a by Azurophil (Primary) Granule Products

Abstract During phagocytosis of latex particles human neutrophils not only release a serum activator that generates the chemotactic C5 fragment, C5a, by complement activation, but these cells also release a product that destroys the chemotactic activity of C5a. These separate neutrophil products, however, are released sequentially by neutrophils during phagocytosis with the serum activator appearing more rapidly in incubation media. Chemotactic activity is generated optimally in serum by post-phagocytic media at pH 7.2 to 7.4, whereas C5a inactivation occurs both at neutral pH and at a more acid pH, 6.2 to 6.4. Studies in which the azurophil (primary) granules and specific (secondary) granules are separated from neutrophil lysates by sucrose density centrifugation show that the serum activator is contained in specific granules whereas C5a inactivators are restricted to the azurophil granules. Gel filtration chromatography of lysates of purified granule preparations indicates that the serum activator contained in specific granules is a large molecule (m.w. greater than 150,000), and that there are at least two C5a inactivators associated with the azurophil granules, with estimated m.w.'s of 65,000 and 30,000. Isoelectric focusing of azurophil granule lysates also indicates at least two separate C5a inactivators. It is evident that mediators contained in the specific and azurophil neutrophil granules may have functionally opposing roles once released by the cells. These mediators, which effect the generation or inactivation of C5a, have different pH optima of activity and distinct kinetics of release from neutrophils and together may contribute to the self-limited amplification and localization of acute inflammatory responses.