Ablation of Plasma Prekallikrein Decreases Low-Density Lipoprotein Cholesterol by Stabilizing Low-Density Lipoprotein Receptor and Protects Against Atherosclerosis.

BACKGROUND: High blood cholesterol accelerates the progression of atherosclerosis, which is an asymptomatic process lasting for decades. Rupture of atherosclerotic plaques induces thrombosis, which results in myocardial infarction or stroke. Lowering cholesterol levels is beneficial for preventing atherosclerotic cardiovascular disease. METHODS: Low-density lipoprotein (LDL) receptor (LDLR) was used as bait to identify its binding proteins in the plasma, and the coagulation factor prekallikrein (PK; encoded by the KLKB1 gene) was revealed. The correlation between serum PK protein content and lipid levels in young Chinese Han people was then analyzed. To investigate the effects of PK ablation on LDLR and lipid levels in vivo, we genetically deleted Klkb1 in hamsters and heterozygous Ldlr knockout mice and knocked down Klkb1 using adeno-associated virus-mediated shRNA in rats. The additive effect of PK and proprotein convertase subtilisin/kexin 9 inhibition also was evaluated. In addition, we applied the anti-PK neutralizing antibody that blocked the PK and LDLR interaction in mice. Mice lacking both PK and apolipoprotein e (Klkb1-/-Apoe-/-) were generated to assess the role of PK in atherosclerosis. RESULTS: PK directly bound LDLR and induced its lysosomal degradation. The serum PK concentrations positively correlated with LDL cholesterol levels in 198 young Chinese Han adults. Genetic depletion of Klkb1 increased hepatic LDLR and decreased circulating cholesterol in multiple rodent models. Inhibition of proprotein convertase subtilisin/kexin 9 with evolocumab further decreased plasma LDL cholesterol levels in Klkb1-deficient hamsters. The anti-PK neutralizing antibody could similarly lower plasma lipids through upregulating hepatic LDLR. Ablation of Klkb1 slowed the progression of atherosclerosis in mice on Apoe-deficient background. CONCLUSIONS: PK regulates circulating cholesterol levels through binding to LDLR and inducing its lysosomal degradation. Ablation of PK stabilizes LDLR, decreases LDL cholesterol, and prevents atherosclerotic plaque development. This study suggests that PK is a promising therapeutic target to treat atherosclerotic cardiovascular disease.

A Rare Cause of Isolated Prolonged Activated Partial Thromboplastin Time: An Overview of Prekallikrein Deficiency and the Contact System.

Prekallikrein (PK) deficiency, also known as Fletcher factor deficiency, is a very rare disorder inherited as an autosomal recessive trait. It is usually identified incidentally in asymptomatic patients with a prolonged activated partial thromboplastin time (aPTT). In this article, we present the case of a 52-year-old woman, with no prior personal or family history of thrombotic or hemorrhagic disorders, who was noted to have substantial protracted aPTT through the routine coagulation assessment before a kidney biopsy. The patient had an uneventful biopsy course after receiving fresh frozen plasma (FFP). Laboratory investigations performed before the biopsy indicated normal activity for factors VIII, IX, XI, XII, and von Willebrand factor (vWF) as well as negative lupus anticoagulant (LA) screen. The plasma PK assay revealed low activity at 15% consistent with mild PK deficiency. The deficit of PK is characterized by a severely prolonged aPTT and normal prothrombin time (PT) in the absence of bleeding tendency. PK plays a role in the contact-activated coagulation pathway and the inflammatory response. Thus, other differential diagnoses of isolated prolonged aPTT include intrinsic pathway factor deficiencies and nonspecific inhibitors such as LA. We concluded that the initial evaluation of a prolonged aPTT with normal PT should appraise the measurement of contact activation factors and factor inhibitors. PK deficiency should be considered in asymptomatic patients with isolated aPTT prolongation, which corrects on incubation, with normal levels of the contact activation factors and factor inhibitors.

c.451dupT in KLKB1 is common in Nigerians, confirming a higher prevalence of severe prekallikrein deficiency in Africans compared to Europeans.

Essentials Prekallikrein (PK) deficiency is a recessive trait with isolated aPTT prolongation. KLKB1 c.451dupT is common in Nigerians (7/600 alleles) and absent in a European group (0/600). To date, all genotyped PK-deficient patients of African ancestry were homozygous for 451dupT. Diagnostics of isolated aPTT prolongation in African descendants should include PK testing. ABSTRACT: Background Severe prekallikrein deficiency (PK deficiency) is an autosomal-recessive condition thought to be very rare. Recently we reported that the previously unnoticed variant c.451dupT, p.Ser151Phefs*34 in KLKB1, which is listed in databases aggregating genome data, causes PK deficiency and is common in Africans according to gnomAD (allele frequency 1.43%). Patients/Methods The most common African (c.451dupT) and European (c.1643G>A, p.Cys548Tyr) PK deficiency causing KLKB1 variants were analyzed in two population-based collectives of 300 Nigerian and 300 German subjects. Genome databases were evaluated for variant frequencies and ethnicity of the subjects. The geographic origin of PK-deficient cases due to 451dupT was assessed. Results Two of five patients with PK deficiency caused by homozygous 451dupT were African, one African American, one from Oman, and one of unknown origin. The frequency of 451dupT was 1.17% in the Nigerian collective (7/600 alleles); none had Cys548Tyr. Subjects with 451dupT were found among different Nigerian ethnicities. Both variants were absent in the European collective. Database research was compatible with these findings, even though mainly data of African Americans (451dupT: 1.12%-1.78%) was accessible. A relevant number of non-American Africans are included only in the 1000Genomes collective: 451dupT frequency was 1.29% in native Africans and 1.56% in African Caribbeans. Conclusions This study underlines the higher prevalence of PK deficiency among people with African descent compared to Europeans. In order to avoid delay of necessary surgical procedures in patients of African origin, diagnostic algorithms for isolated, unexplained, activated partial thromboplastin time prolongation in these subjects should include PK deficiency screening.

Role of Factor XIa and Plasma Kallikrein in Arterial and Venous Thrombosis.

Cardiovascular disease, including stroke, myocardial infarction, and venous thromboembolism, is one of the leading causes of morbidity and mortality worldwide. Excessive coagulation may cause vascular occlusion in arteries and veins eventually leading to thrombotic diseases. Studies in recent years suggest that coagulation factors are involved in these pathological mechanisms. Factors XIa (FXIa), XIIa (FXIIa), and plasma kallikrein (PKa) of the contact system of coagulation appear to contribute to thrombosis while playing a limited role in hemostasis. Contact activation is initiated upon autoactivation of FXII on negatively charged surfaces. FXIIa activates plasma prekallikrein (PK) to PKa, which in turn activates FXII and initiates the kallikrein-kinin pathway. FXI is also activated by FXIIa, leading to activation of FIX and finally to thrombin formation, which in turn activates FXI in an amplification loop. Animal studies have shown that arterial and venous thrombosis can be reduced by the inhibition of FXI(a) or PKa. Furthermore, data from human studies suggest that these enzymes may be valuable targets to reduce thrombosis risk. In this review, we discuss the structure and function of FXI(a) and PK(a), their involvement in the development of venous and arterial thrombosis in animal models and human studies, and current therapeutic strategies.

Severe plasma prekallikrein deficiency: Clinical characteristics, novel KLKB1 mutations, and estimated prevalence.

BACKGROUND: Severe plasma prekallikrein (PK) deficiency is an autosomal-recessive defect characterized by isolated activated partial thromboplastin time prolongation. To date, no comprehensive methodologically firm analysis has investigated the diagnostic, clinical, and genetic characteristics of PK deficiency, and its prevalence remains unknown. PATIENTS/METHODS: We described new families with PK deficiency, retrieved clinical and laboratory information of cases systematically searched in the (gray) literature, and collected blood of these cases for complementary analyses. The Genome Aggregation Database (gnomAD) and the population-based Gutenberg Health Study served to study the prevalence of mutations and relevant genetic variants. RESULTS: We assembled a cohort of 111 cases from 89 families and performed new genetic analyses in eight families (three unpublished). We identified new KLKB1 mutations, excluded the pathogenicity of some of the previously described ones, and estimated a prevalence of severe PK deficiency of 1/155 668 overall and 1/4725 among Africans. One individual reported with PK deficiency had, in fact, congenital kininogen deficiency associated with decreased PK activity. One quarter of individuals had factor XII clotting activity below the reference range. Four major bleeding events were described in 96 individuals, of which 3 were provoked, for a prevalence of 4% and an annualized rate of 0.1%. The prevalence of cardiovascular events was 15% (6% <40 years; 21% 40-65 years; 33% >65 years) for an annualized rate of 0.4%. CONCLUSIONS: We characterized the genetic background of severe PK deficiency, critically appraised mutations, and provided prevalence estimates. Our data on laboratory characteristics and clinical course of severe PK deficiency may have clinical implications.

Long-term safety outcomes of prekallikrein (Fletcher factor) deficiency: A systematic literature review of case reports.

Background: Hereditary prekallikrein (Fletcher factor) deficiency is a rare condition characterized by a prolonged activated partial thromboplastin time. Inhibitors of plasma kallikrein have recently been approved for prophylaxis of hereditary angioedema and are under investigation for use in other indications. Objective: We attempted to conservatively assess the impact of long-term inhibition of this pathway by reviewing reported comorbidities in patients with hereditary prekallikrein deficiency. Methods: We searched several medical literature databases for publications that reported data from patients with hereditary prekallikrein deficiency (<10% of normal and/or shortening of activated partial thromboplastin time on increased incubation time). Data reporting of cardiovascular, bleeding, and autoimmune-related diseases were extracted. Results: Of 1966 publications screened, 45 publications (which represented 53 patients with prekallikrein deficiency) were included. Among 53 identified patients with prekallikrein deficiency, 25 were explicitly defined as asymptomatic, with no comorbidities mentioned in another three cases. Another 16 of the 53 patients were described as having undergone surgery or dental extractions with no complications. Cardiovascular comorbidities were reported in 19 patients, mainly hypertension (9 patients) and cerebrovascular ischemia or stroke (5 patients). Excessive bleeding episodes after surgery were reported in four patients. Autoimmune-related diseases were reported for three patients (two with Graves disease and one with systemic lupus erythematosus). Conclusion: This review identified patients with hereditary prekallikrein deficiency who reported a spectrum of health outcomes from asymptomatic to infrequent reports of cardiovascular, bleeding, and autoimmune comorbidities. The majority of the reports did not indicate any association between prekallikrein deficiency and comorbidities; however, additional observation is required to confirm the long-term safety of plasma kallikrein inhibition.

Prolonged activated partial thromboplastin time due to plasma prekallikrein deficiency: a case study and literature review on its clinical significance.

: Activated partial thromboplastin time is a test assessing the intrinsic and common pathways of the coagulation cascade. We presented an asymptomatic case with isolated activated partial thromboplastin time prolongation. After excluding coagulation factor deficiency and lupus anticoagulant, the patient was diagnosed with plasma prekallikrein (PPK) deficiency. We reviewed the literature regarding effects of PPK deficiency which could have both antithrombotic and prothrombotic effects. At the moment, research supports that PPK deficiency in healthy adults rarely causes bleeding as it is not a major contributor of hemastasis; whereas in adults with multiple comorbidities or with predominant systemic inflammation, effects of PPK deficiency remain debatable. Further research is needed to clarify impacts of PPK deficiency in clinical settings.

Cardiovascular diseases in congenital prekallikrein deficiency: comparison with other chance-associated morbidities.

: To compare the prevalence of cardiovascular diseases with other chance-associated morbidities in patients with congenital prekallikrein deficiency. Patients with prekallikrein deficiency were gathered from two time unlimited PubMed searches and from personal files. Inclusion criteria were prekallikrein level less than 15% of normal; correction of aPTT on long incubation times; prolonged aPTT corrected by normal plasma or serum; normal prothrombin time and normal FXII and FXI. Acquired forms were excluded. Out of 106 patients, we have found that 45 patients had at least one chance-associated defect or morbidity at the time of the diagnosis of the clotting defect. Twenty-nine of these 45 patients had cardiovascular disorders. Other comorbidities were found in a much smaller proportion. Congenital prekallikrein deficiency is frequently associated with cardiovascular conditions, namely hypertension, coronary disease, ischemic stroke, venous thrombosis. The significance of these findings is critically discussed as association between two diseases does not necessarily indicate the existence of a causative relation between the two. However, the findings presented here clearly indicate the possibility that such a relation might indeed exist.

A structure-function analysis in patients with prekallikrein deficiency.

OBJECTIVE: To investigate the structure-function relation in prekallikrein (PK) deficiency. PK is one of the proteins of the contact phase of blood coagulation which at the present time is the object of a revival of interest. METHODS: All patients with PK deficiency who had been investigated by molecular biology techniques are the object of the present investigation. Details of patients were obtained from personal files and a time-unlimited PubMed search. Only cases with a molecular-biology-based diagnosis were included. RESULTS: Twelve families were included. The total number of missense mutation was 10, together with 3 stop codons and 2 insertions. These mutations involved mainly exons 11 and 14. There were eight proved homozygotes and three compound heterozygotes. In one instance, homozygosity was probable but not proved. In nine cases, the defect was Type I, whereas it was Type II in the remaining three. No bleeding manifestations were present in 11 of the 12 probands. One proband had epistaxis, but she had hypertension. Altogether, four patients had hypertension and one of them had also two myocardial infarctions. CONCLUSIONS: Despite the paucity of cases, it was established that the majority of mutations involved the catalytic domain. It is auspicable that future reports of patients with this disorder should include molecular studies. This would certainly contribute to the understanding of the contact phase of blood coagulation.

Prekallikrein deficiency in a 15-year-old boy with Ménière's disease: a case report.

Congenital prekallikrein deficiency is a rare disorder in which there is an in vitro clotting defect despite absence of bleeding or thrombotic tendency. In this report, a 15-year-old boy with an unexpected markedly prolonged activated partial thrombin time, a normal prothrombin time, and without personal nor familial history of bleeding or thrombosis is presented. Laboratory investigation revealed a severe prekallikrein deficiency. This case highlights the importance of following a diagnostic algorithm to establish the correct diagnosis. Moreover, by selecting appropriate laboratory tests, unnecessary and repeatedly testing can be avoided.