Plasma Levels Of C1 Inhibitor Research Articles

Restriction of C1-inhibitor activity in hereditary angioedema by dominant-negative effects of disease-associated SERPING1 gene variants

Patients with hereditary angioedema (HAE) experience recurrent, sometimes life-threatening, attacks of edema. It is a rare genetic disorder characterized by genetic and clinical heterogenicity. Most cases are caused by genetic variants in the SERPING1 gene leading to plasma deficiency of the encoded protein C1 inhibitor (C1INH). More than 500 different HAE-causing variants have been identified in the SERPING1 gene, but the disease mechanisms by which they result in pathologically low C1INH plasma levels remain largely unknown. The aim is to describe trans-inhibitory effects of full-length or near full-length C1INH encoded by 28 disease-associated SERPING1 variants. HeLa cells are transfected with expression constructs encoding the studied SERPING1 variants. Extensive and comparative studies of C1INH expression, secretion, functionality, and intracellular localisation are carried out. Our findings characterize functional properties of a subset of SERPING1 variants allowing the examined variants to be subdivided into five different clusters, each containing variants sharing specific molecular characteristics. For all variants, except two, we find that co-expression of mutant and normal C1INH negatively impacts the overall capacity to target proteases. Strikingly, for a subset of variants, intracellular formation of C1INH foci is detectable only in heterozygous configurations enabling simultaneous expression of normal and mutant C1INH. We provide a functional classification of SERPING1 gene variants suggesting that different SERPING1 variants drive the pathogenicity through different and in some cases overlapping molecular disease mechanisms. For a subset of gene variants, our data define some types of C1INH-HAE as serpinopathies driven by dominant-negative disease mechanisms.

Hereditary angioedema is associated with an increased risk of venous thromboembolism

Hereditary angioedema is associated with an increased risk of venous thromboembolism

Advances in Hereditary Angioedema: The Prevention of Angioedema Attacks With Subcutaneous C1-Inhibitor Replacement Therapy.

Hereditary angioedema (HAE) is a debilitating condition caused by a functional C1-inhibitor (C1-INH) deficiency and characterized clinically by episodes of subcutaneous or submucosal swelling. C1-INH replacement is highly effective for preventing HAE attacks and can improve health-related quality of life. Once available only for intravenous use, C1-INH is now available as a subcutaneous formulation for self-administration, shown to provide sustained plasma levels of C1-INH and reducing the monthly median HAE attack rate by 95% versus placebo in the phase 3 COMPACT study. Subcutaneously administered C1-INH satisfies multiple unmet needs in the management of patients with HAE.

SERPING1 exon 3 splicing variants using alternative acceptor splice sites

Mutations in the C1 inhibitor (C1INH) encoding gene, SERPING1, are associated with hereditary angioedema (HAE) which manifests as recurrent submucosal and subcutaneous edema episodes. The major C1INH function is the complement system inhibition, preventing its spontaneous activation. The presented study is focused on SERPING1 exon 3, an alternative and extraordinarily long exon (499 bp). Endogenous expression analysis performed in the HepG2, human liver, and human peripheral blood cells revealed several exon 3 splicing variants alongside exon inclusion: a highly prevalent exon skipping variant and less frequent +38 and -15 variants with alternative 3′ splice sites (ss) located 38 and 15 nucleotides downstream and upstream from the authentic 3′ ss, respectively. An exon skipping variant introducing a premature stop codon, represented nearly one third of all splicing variants and surprisingly appeared not to be degraded by NMD. The alternative -15 3′ ss was used to a small extent, although predicted to be extremely weak. Its use was shown to be independent of its strength and highly sensitive to any changes in the surrounding sequence. -15 3′ ss seems to be co-regulated with the authentic 3′ ss, whose use is dependent mainly on its strength and less on the presence of intronic regulatory motifs. Subtle SERPING1 exon 3 splicing regulation can contribute to overall C1INH plasma levels and HAE pathogenesis.

Dominant-negative SERPING1 variants cause intracellular retention of C1 inhibitor in hereditary angioedema.

Hereditary angioedema (HAE) is an autosomal dominant disease characterized by recurrent edema attacks associated with morbidity and mortality. HAE results from variations in the SERPING1 gene that encodes the C1 inhibitor (C1INH), a serine protease inhibitor (serpin). Reduced plasma levels of C1INH lead to enhanced activation of the contact system, triggering high levels of bradykinin and increased vascular permeability, but the cellular mechanisms leading to low C1INH levels (20%-30% of normal) in heterozygous HAE type I patients remain obscure. Here, we showed that C1INH encoded by a subset of HAE-causing SERPING1 alleles affected secretion of normal C1INH protein in a dominant-negative fashion by triggering formation of protein-protein interactions between normal and mutant C1INH, leading to the creation of larger intracellular C1INH aggregates that were trapped in the endoplasmic reticulum (ER). Notably, intracellular aggregation of C1INH and ER abnormality were observed in fibroblasts from a heterozygous carrier of a dominant-negative SERPING1 gene variant, but the condition was ameliorated by viral delivery of the SERPING1 gene. Collectively, our data link abnormal accumulation of serpins, a hallmark of serpinopathies, with dominant-negative disease mechanisms affecting C1INH plasma levels in HAE type I patients, and may pave the way for new treatments of HAE.

Human plasma-derived C1 esterase inhibitor for on-demand or prophylaxis treatment of patients with hereditary angioedema: intravenous and subcutaneous formulations

ABSTRACTIntroduction: Hereditary angioedema with C1 inhibitor (C1-INH) deficiency (C1-INH-HAE) is a rare disease in which patients have debilitating, unpredictable swelling attacks. Treatment approaches include prophylaxis therapies to prevent future attacks and on-demand therapies that reduce the duration and severity of an attack.Areas covered: This review summarizes the characteristics and efficacy and safety profiles of two formulations of human plasma-derived C1-INH concentrates, intravenous BERINERT® for on-demand treatment of attacks and subcutaneous HAEGARDA® for routine prophylaxis of attacks.Expert opinion: Intravenous C1-INH concentrates have long been used in the treatment of patients with C1-INH-HAE, and the recent approval of the subcutaneous formulation is a major advancement in prophylaxis therapy. Subcutaneous administration provides more stable and sustained trough C1-INH levels compared with intravenous administration. Pharmacokinetic modeling revealed a close relationship between trough functional C1-INH activity levels and the patient’s risk of experiencing an angioedema attack. The approved dose of subcutaneous C1-INH (60 IU/kg) provides clinically relevant and protective plasma levels of C1-INH throughout the dosing interval. The pharmacokinetic profile of the intravenous formulation consists of a rapid increase and high peak plasma levels of C1-INH, making intravenous administration well suited for the on-demand treatment of acute attacks.

Pharmacokinetic analysis of human plasma–derived pasteurized C1‐inhibitor concentrate in adults and children with hereditary angioedema: a prospective study

Hereditary angioedema (HAE) is a rare and potentially life-threatening disease presenting with acute edema of subcutaneous tissues and/or mucous membranes. Patients with HAE have abnormally low or dysfunctional C1-inhibitor (C1-INH). Preventing the progression of acute attacks is the main goal of C1-INH replacement therapy; knowledge of the C1-INH concentrate half-life is of crucial importance. This pharmacokinetic study was conducted to investigate the pharmacokinetics of pasteurized human plasma-derived C1-INH concentrate (pC1-INH). This was a prospective, single-center study of six children and 34 adults with an established diagnosis of HAE. On-demand treatment with pC1-INH was administered to all children, whereas adults received either pC1-INH on-demand treatment or individual replacement therapy (IRT). Functional C1-INH plasma levels were fitted to a single-compartment model with nonlinear regression, and the area under the curve was standardized to a dose equivalent of 15 U/kg body weight of pC1-INH concentrate. The median half-life of functional C1-INH plasma levels in pediatric patients receiving on-demand therapy was 32.9 hours (mean, 31.5 hr). In adults, the median half-lives of functional C1-INH plasma levels after on-demand therapy were 39.1 hours (mean, 47.8 hr) and 30.9 hours (mean 33.3 hr) for patients on IRT. The median times to achieve maximum plasma activity after administration were 0.6 hour for children, 1.0 hour for adults receiving on-demand treatment, and 0.5 hour for adults on IRT. pC1-INH concentrate has a long median terminal elimination half-life and rapidly reaches maximum plasma concentrations. This rapid onset of clinical efficacy is essential in patients suffering from HAE.

Increased expression of C1-inhibitor mRNA in patients with hereditary angioedema treated with Danazol

The attenuated androgen Danazol can partially reverse the biochemical defect and prevent angioedema in patients with inherited C1-inhibitor (C1-INH) deficiency (hereditary angioedema, HAE). Though its clinical effectiveness is independent from significant increase of C1-INH plasma levels, its mechanism of action remains unknown. Since angioedema is a local phenomenon, it could be controlled by restoring tissue levels of C1-INH. We measured the expression of C1-INH mRNA in peripheral blood mononuclear cells (PBMCs) of 13 patients with HAE type 1 (seven untreated and asymptomatic, and six on Danazol at the minimal effective dose) and of eight normal controls. mRNA levels were quantitated by computerized optical densitometry of reverse transcriptase-PCR products, normalized for the amount of glyceraldehyde-3-phosphate-dehydrogenase and expressed as percent of normal pooled RNAs. Each determination represented the mean of three separate experiments. Measurement of C1-INH mRNA in two patients before and after 1 month of Danazol 400 mg per day demonstrated a post-treatment increase of 15 and 21%, respectively. When HAE patients and controls were analyzed as groups, C1-INH mRNA levels of patients untreated and asymptomatic (median 73%, range 65–78) were significantly lower ( P=0.001) compared to controls (median 101%, range 87–121) and to patients on Danazol (median 91%, range 82–96); the difference among the last two groups was not statistically significant. Our data demonstrate that minimal effective doses of Danazol increase the expression of C1-INH mRNA in PBMC of HAE patients even in the absence of a significant increase of C1-INH plasma levels.

C1 inhibitor infusion modifies platelet activity in hereditary angioedema patients.

C1 inhibitor (C1-INH) is an alpha2-globulin that blocks esterolytic activity of the first component of the classic complement cascade. The alpha-granules of normal human platelets also contain C1-INH, which is expressed on the platelet surface during platelet secretion in healthy patients, but it is clearly reduced in patients with hereditary angioedema (HAE). To evaluate the effects of in vivo C1-INH concentrate infusion on platelet responsiveness and coagulation system activity in patients with HAE. Assessment of the platelet activity and plasma levels of C1-INH, activated factor XII (XIIa), and prothrombin fragment F1.2 (F1.2) before and after infusion of 15 U/kg of C1-INH concentrate. In 6 patients (4 men and 2 women), HAE was diagnosed according to the accepted clinical and laboratory criteria. Platelet aggregation (final concentrations: adenosine diphosphate, 0.5, 1.25, and 2.5 microM; collagen, 5 microg/mL), C1-INH antigen (radial immunodiffusion), C1-INH activity (chromogenic substrates), and XIIa and F1.2 (enzyme-linked immunosorbent assay). After C1-INH infusion, we observed a prompt increase of C1-INH level and a slow return toward its plasma preinfusion values within 4 to 7 days, a significant decrease of both adenosine diphosphate- and collagen-induced platelet aggregation versus preinfusion values (maximum after 1-2 days; P <.001), and a rapid decrease of high basal values of XIIa and F1.2 in 30 and 120 minutes, respectively. These data show a role of C1-INH in the control of platelet activity and that its deficiency increases platelet aggregability and plasma levels of XIIa and F1.2 in patients with HAE.

Regulation of C1 Inhibitor Synthesis

The primary biologic roles of C1 inhibitor (C1-INH) are the regulation of activation of the classical complement pathway and of the contact system of kinin formation. Heterozygosity for deficiency or dysfunction of C1-INH results in hereditary angioedema (HAE). This deficiency results in loss of homeostasis with unregulated complement and contact system activation. Due to the consequent C1-INH consumption, plasma levels of C1-INH in patients with HAE are decreased below 50% of normal. In addition, diminished synthesis contributes to the lowered levels in some patients. The hepatocyte is the primary source of C1-INH, although a number of other cell types, including peripheral blood monocytes, microglial cells, fibroblasts, endothelial cells, the placenta, and megakaryocytes also synthesize and secrete the protein both in vivo and in vitro. Interferon-γ and α (IFN), colony stimulating factor-1, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) all induce C1-INH synthesis in a variety of cell types. The IFN-response elements in the 5'-flanking region and in the first intron have been partially characterized, as have several of the promoter elements that direct basal transcription of the gene. However, although androgen therapy, in vivo, results in an increase in C1-INH plasma levels, a direct effect of androgens on C1-INH synthesis has not been convincingly demonstrated. Although the C1-INH gene contains a potential glucocorticoid/androgen response element, this element does not appear to respond to androgen. Continued analysis of the transcriptional regulation of the C1-INH gene may lead to new approaches to therapy of HAE.

Clusters of intragenic Alu repeats predispose the human C1 inhibitor locus to deleterious rearrangements.

Frequent alterations in the structure of the complement component C1 inhibitor gene have been found in patients affected by the common variant of hereditary angioedema, characterized by low plasma levels of C1 inhibitor. This control protein limits the enzymic activity of the first component of complement and of other plasma serine proteases. Sequence comparisons of a 4.6-kilobase-long segment of the normal gene and the corresponding gene segments isolated from two patients carrying family-specific DNA deletions point to unusually long clusters of tandem repeats of the Alu sequence family as a source of genetic instability in this locus. Unequal crossovers, in a variety of registers, among Alu sequences of the clusters result in deletions of variable length that encompass exon 4. In a third family, exon 4 was instead found to be duplicated along with the same tracts of flanking introns lost in one of the deletions. In addition to undergoing Alu-mediated partial deletions and duplications, the gene is also a target for more recent retroposition events. Gross alterations in the C1 inhibitor gene account for about 20% of the hereditary angioedema chromosomes and consequently make this gene a prime example of the mutagenic liability of Alu repeats.