An HMG-I protein from human endothelial cells apparently is secreted and impairs activation of Hageman factor (factor XII).

A highly purified protein from lysates of human umbilical vein endothelial cells (HUVECs) inhibited the activation of factor XII [Hageman factor (HF)] and removed factor XIIa from an activating surface, thus impairing HF-dependent coagulation and kinin-releasing activities. Two tryptic peptides from this protein had 100% identity with amino acids 31-44 and 89-101 of a nonhistone DNA-binding protein known as high-mobility group protein (HMG-I). In specific antibody experiments, the clot-inhibiting property in purified lysate protein from HUVECs was associated with HMG-I. The molecular weight of the protein that inhibited clotting was consistent with that predicted for HMG-I. Protein that inhibited contact activation and had antigenic properties of HMG-I and HUVEC lysate protein also was found in conditioned media from unchallenged cultured HUVECs. After HUVECs were incubated with 14C lysine, conditioned media contained immunoprecipitable radiolabeled protein with the same molecular weight as that recovered from cell lysates, suggesting that this high-mobility group protein (HMG-I) may be secreted. Purified factor XII antigens were displaced from a glass surface by HMG-I from lysates in proportion to the amount of HMG-I protein that was added. This HMG-I probably inhibits factor XII functions because its high positive charge favors competitive binding to an activating substance.

Molecular defects in hereditary angioneurotic edema.

Thirty-eight previously unreported, unrelated patients with hereditary angioneurotic edema were studied, and each was found to have a single mutation in the C1 inhibitor gene. On the basis of serine protease inhibitor crystal structure, these and published mutations affect critical domains in the reactive center loop, alpha-helices A, B, C, E, and F, and beta-sheets A and C. Almost all mutations, other than in the reactive center loop, occur at residues that are highly conserved among serine protease inhibitors, and the others are likely to interfere with molecular movement. These mutations begin to identify residues critical for molecular function of the C1 inhibitor molecule.

Antibody to C1-inhibitor in a patient receiving C1-inhibitor infusions for treatment of hereditary angioneurotic edema with systemic lupus erythematosus reacts with a normal allotype of residue 458 of C1-inhibitor.

Patients with hereditary C4 deficiency are likely to have severe lupus erythematosus. A patient with hereditary angioneurotic edema (HANE) and systemic lupus erythematosus (SLE) had a chronic deficiency in C4 because the hereditary deficiency in C1-inhibitor allowed the C1 in her serum to become activated and then inactivate C4. An attempt was made to repair the C4 deficiency as well as the deficiency in C1-inhibitor by giving infusions of human C1-inhibitor in the hope of inducing remissions of both HANE and SLE. During treatment, antibody to C1-inhibitor developed in the patient; this cleared when the infusions were stopped. During subsequent treatment with danazol alone, measurable C1-inhibitor developed in the patient's serum, but levels of C4 were never significantly increased. Antibody to normal C1-inhibitor was not expected to develop in the patient because she is heterozygous for this autosomal dominant trait. A normal allotype (VAL or MET 458), which would have been in the preparation used but which the patient does not synthesize because she can produce only one allotype (MET 458), appears to have been immunogenic. The antibody isolated from the patient's serum reacted with C1-inhibitor from a normal individual known to be homozygous for 458-VAL but not with one from a homozygote for MET-458.

An autoantibody to C1-inhibitor recognizes the reactive center of the inhibitor.

An autoantibody to C1-inhibitor produced a clinical disorder resembling that of patients with hereditary angioneurotic edema. The antibody could not interact with C1-inhibitor after exposure to synthetic peptides representing the primary structure of the reactive center region of the protein. Therefore the antibody recognized this domain of the inhibitor, and it probably impaired the function of C1-inhibitor by altering its conformational properties.

A cluster of mutations within a short triplet repeat in the C1 inhibitor gene.

Mutations in the C1 inhibitor gene that result in low functional levels of C1 inhibitor protein cause hereditary angioneurotic edema. This disease is characterized by episodic edema leading to considerable morbidity and death. Among 60 unreported kindred with the disease, four patients were discovered to have mutations clustered within a 12-bp segment of exon 5 from nucleotide 8449 to nucleotide 8460. This short segment of DNA contains three direct repeats of the triplet CAA and is immediately preceded by a similar adenosine-rich sequence (CAAGAACAC). These triplet repeats make this region susceptible to mutation by a slipped mispairing mechanism. There are two other short triplet repeat elements in the coding region for this gene, but they have not become mutated in any kindred examined. This suggests that the apparent enhanced mutation rate in this region of exon 5 may be influenced by DNA structural characteristics.

Contiguous deletion and duplication mutations resulting in type 1 hereditary angioneurotic edema.

Mutations that cause low antigenic and functional levels of C1 inhibitor protein result in type 1 hereditary angioneurotic edema. This disease is characterized by episodic edema leading to considerable morbidity and sometimes death. We present here two novel mutations in the reactive center coding region. One mutation is a deletion of an imperfect palindrome encompassing nucleotides 1395-1428 and the other is a direct duplication of nucleotides 1414-1433. These mutations do not depend on improper pairing of direct repeats, but may form as a consequence of a peculiar consensus sequence or an alternative secondary structure.

Hereditary angioneurotic oedema: characterization of plasma kinin and vascular permeability-enhancing activities.

The mediator(s) responsible for localized enhanced vascular permeability that characterizes an exacerbation of hereditary angioneurotic oedema (HAE) is thought to be a product of either contact or complement system activation. In contrast to normal individuals, plasma from these patients generates both kinin and vascular permeability-enhancing activity following incubation at 37 degrees C. Depletion of C1 inhibitor in both normal and C2-deficient plasma, but not in contact factor-deficient plasmas, resulted in generation of these activities. The kinin activity from incubated HAE plasma was susceptible to kininase inactivation and was blocked by a Bk2 receptor antagonist. Furthermore, this activity was isolated from HAE plasma; amino acid sequence analysis proved it to be bradykinin. Similarly, the vasopermeability-enhancing activity from ethanol-fractionated or boiled HAE plasma, collected during either attack or remission, co-eluted with bradykinin on reverse-phase high performance liquid chromatography (HPLC). These studies conclusively demonstrate that bradykinin is the major kinin and mediator of enhanced vascular permeability generated during incubation of HAE plasma. The role of other bioactive products, such as the C2 kinin, at local sites of oedema formation remains to be further defined.

Chymotrypsin inhibitory activity of normal C1-inhibitor and a P1 Arg to His mutant: evidence for the presence of overlapping reactive centers.

C1-inhibitor is a serine proteinase inhibitor that is active against C1s, C1r, kallikrein, and factor XII. Recently, it has been shown that it also has inhibitory activity against chymotrypsin. We have investigated this activity of normal human C1-inhibitor, normal rabbit C1-inhibitor, and P1 Arg to His mutant human C1-inhibitors and find that all are able to inhibit chymotrypsin and form stable sodium dodecyl sulfate-resistant complexes. The Kass values show that the P1 His mutant is a slightly better inhibitor of chymotrypsin than normal human C1-inhibitor (3.4 x 10(4) compared with 7.3 x 10(3)). The carboxy-terminal peptide of normal human C1-inhibitor, derived from the dissociated protease-inhibitor complex, shows cleavage between the P2 and P1 residues. Therefore, as with alpha 2-antiplasmin, C1-inhibitor possesses two overlapping P1 residues, one for chymotrypsin and the other for Arg-specific proteinases. In contrast, with the P1 His mutant, the peptide generated from the dissociation of its complex with chymotrypsin demonstrated cleavage between the P1 and P'1 residues. Therefore, unlike alpha 2-antiplasmin, chymotrypsin utilizes the P2 residue as its reactive site in normal C1-inhibitor but utilizes the P1 residue as its reactive site in the P1 His mutant protein. This suggests that the reactive center loop allows a degree of induced fit and therefore must be relatively flexible.

Endothelial cells produce a substance that inhibits contact activation of coagulation by blocking the activation of Hageman factor.

Human umbilical vein endothelial cells (HUVECs) produce a property that impairs the generation of coagulant and amidolytic activity initiated when normal human plasma is exposed to glass. This inhibitory property blocks the adsorption of Hageman factor (factor XII) to glass, thereby preventing the activation of Hageman factor, but does not impair the coagulant or amidolytic activity of already activated Hageman factor (factor XIIa). This property in HUVEC lysates could be neutralized by a purified preparation of Hageman factor but not by purified prekallikrein or high molecular mass kininogen. A partially purified inhibitory fraction from cell lysates exhibited a single homogeneous band in SDS/PAGE of approximately 22.5 kDa. Inhibitory activity was also found in concentrates of conditioned media from HUVECs, which also impaired the binding of Hageman factor to a surface; it may not be identical with that found in cell lysates.

A modification of an affinity procedure for purification of human C1- inhibitor that provides a homogeneous stable preparation.

Human C1- inhibitor can be rapidly purified by the affinity chromatography procedure described by Pilatte and his associates (1989), but the inhibitor so purified breaks down during storage or is in a cleaved form when initially purified. By adding an ion-exchange chromatography procedure after the affinity chromatography, a stable, single species of C1- inhibitor molecules is obtained. It is likely that serine proteinases in trace amounts, which may be complexed with some of the C1- inhibitor, are removed during the ion-exchange procedure. This procedure provides a highly purified and useful preparation of C1- inhibitor.

Angioneurotic edema with acquired C1- inhibitor deficiency and autoantibody to C1- inhibitor: response to plasmapheresis and cytotoxic therapy.

A patient with severe acquired angioneurotic edema had essentially no C1- inhibitor activity in his serum and nearly died of cardiopulmonary arrest during an acute episode of facial, oral, and pharyngeal edema. This patient had an antibody directed against C1- inhibitor and C1- inhibitor-anti-C1- inhibitor complexes in his serum. The antibody required a normal residue (Arg) in the reactive center of the inhibitor for its optimal interaction with the inhibitor. Plasmapheresis with 5% human serum albumin replacement relieved him of his antibody load and the edema; additional treatment with pulsed cyclophosphamide has provided a sustained remission. The 5% albumin solution that was used contained functional C1- inhibitor; other lots that were tested contained only traces or none. No underlying disease has yet been identified. During this acute episode of edema, the C1- inhibitor in the patient's plasma was a 92 kd component, and on recovery, a 105 kd component reappeared. C1- inhibitor isolated from the patient's plasma, which was obtained before pheresis, was mainly in lower molecular weight forms (56 kd and 45 kd). The antibody in the patient's serum appeared to render C1- inhibitor susceptible to proteolysis, for when purified antibody was added to normal serum, a cleaved form of C1- inhibitor was generated.

Interactions of C1(-)-inhibitors from normal persons and patients with type II hereditary angioneurotic edema with purified activated Hageman factor (factor XIIa).

Activated high molecular weight Hageman factor (75 Kd) and Hageman factor carboxy-terminal fragments both formed complexes with purified C1(-)-inhibitor, but the Hageman factor fragments appeared to have a higher affinity for the C1(-)-inhibitor than activated Hageman factor. Therefore, the clot-promoting activity of activated Hageman factor might be relatively unimpaired if Hageman factor fragments are also present. Normal C1(-)-inhibitor was cleaved by Hageman factor fragments. Clot-promoting activity was not generated in Hageman factor by exposure to Hageman factor fragments, nor was Hageman factor cleaved by Hageman factor fragments. When Hageman factor was cleaved by streptokinase-activated plasminogen, a 40 Kd fragment was released. In contrast to their interactions with other proteinases, which are blocked by normal C1(-)-inhibitor, Type II C1(-)-inhibitors from plasmas of affected members of eight different kindred with this form of hereditary angioneurotic edema all inhibited the specific coagulant activity of activated Hageman factor to some degree. They did not all form complexes with activated Hageman factor that were stable during sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Danazol.

Danazol is a synthetic attenuated androgen that can interfere with normal interactions between the pituitary-hypothalamic axis and the gonads. These effects are mediated by complex mechanisms, including those in which danazol can compete with natural steroids in binding to androgen receptors or to sex hormone-binding globulin, possibly displacing natural steroids from this protein, and in binding to reactive sites of enzymes required for synthesis of natural steroids, thereby depressing synthesis. Because of danazol's impairment of the pituitary-hypothalamic interactions with gonads, it is an effective therapeutic agent for treatment of endometriosis and cystic disease of the breast. It is effective in the treatment of hereditary angioneurotic edema, but the mechanism of this therapeutic success is unclear. Danazol has been used, without universal success, in the treatment of other gynecologic and certain hematologic disorders.

CpG mutations in the reactive site of human C1 inhibitor.

C1 inhibitor plays an important role in the regulation of vascular permeability through its ability to inactivate enzymes which release polypeptide kinins. Dysfunctional C1 inhibitor molecules are present in the plasma of affected members of the Da and Ri hereditary angioneurotic edema kindreds. We constructed genomic libraries from Da and Ri patient DNAs which had been cleaved with BclI to generate a fragment containing 21 kilobases of the C1 inhibitor locus. C1 inhibitor gene-containing recombinants originating from mutant Da and Ri alleles were differentiated from those derived from normal alleles by linkage analysis using the intragenic HgiAI restriction fragment length polymorphism. Nucleotide sequencing of the complete protein-coding regions of the mutant alleles identified two different mutations in a CpG dinucleotide corresponding to the first two bases of arginine codon 444. These single base mutations changed the identity of the functionally critical P1 reactive site residue from arginine to cysteine (Da) or histidine (Ri). The additional cysteine residue in C1 inhibitor Da suggests how it is covalently bound to albumin in plasma. The presence of CpG dinucleotides in the codons specifying the P1 arginines of C1 inhibitor and antithrombin III explains the high incidence of histidine and cysteine substitutions observed among dysfunctional mutants of these serine protease inhibitors.

Angioedema induced by a peptide derived from complement component C2.

Synthetic peptides that correspond to the COOH-terminal portion of C2b enhance vascular permeability in human and guinea pig skin. In human studies, 1 nmol of the most active peptide of 25-amino acid residues produced substantial local edema. A pentapeptide and a heptapeptide corresponding to the COOH-terminal sequence of C2b each induced contraction of estrous rat uterus in the micromole range; a peptide of 25 amino acids from this region induced a like contraction of rat uterus at a concentration 20-fold lower than the smaller peptides. The vascular permeability of guinea pig skin was enhanced by doses of these synthetic peptides in a similar fashion as that observed for the concentration of rat uterus. The induction of localized edema by intradermal injection in both the guinea pig and the human proceeds in the presence of antihistaminic drugs, suggesting that there is a histamine-independent component to the observed increase in vascular permeability. Cleavage of C2 with the enzymic subcomponent of C1, C1s, yields only C2a and C2b, and no small peptides, whereas cleavage of C2 with C1s and plasmin yields a set of small peptides. These plasmin-cleaved peptides are derived from the COOH terminus of C2b, and they induce the contraction of estrous rat uterus.