Racial and genetic determinants of plasma factor XIII activity

Low-dose intravenous tissue plasminogen activator for acute ischaemic stroke: an alternative or a new standard?

BACKGROUND

With the recent publication of a large clinical trial on the use of a lower dose of intravenous (IV) tissue plasminogen activator (tPA) for acute ischaemic stroke (AIS), the concept of using a different dose has been debated. We intend to review the literature on using a lower dose of IV tPA and gain a better understanding of the impact of different IV doses on the treatment of patients with AIS.

METHODS

A comprehensive literature search of the related topics in PubMed, EMBASE, Web of Science and MEDLINE was carried out. Key words used include low dose IV tPA, thrombolysis, Alteplace and tPA for AIS. Findings were tabulated according to the size of the cohort studied, outcome, adverse event and level of evidence. The results of all studies using lower doses were analysed for efficacy and adverse events.

RESULTS

From 1992 to 2016, there were 23 trials that included 10 950 patients published on the use of lower doses of IV tPA for AIS. Doses ranged from 0.5, 0.6, 0.75 to 0.85 mg/kg. Most were observational, retrospective and registry studies. One was a prospective open-label randomised controlled trial. 13 trials combined lower doses of IV tPA with a glycoprotein IIb/IIIa inhibitor or thrombectomy. Patients treated with lower doses of IV tPA showed a trend of lower rate of symptomatic intracranial haemorrhage and mortality at 3 months but slightly more disability.

CONCLUSIONS

Lower doses of IV tPA showed less haemorrhagic events but were not more effective compared with the standard dose. The optimal low dose of IV tPA remains unclear. Patients with AIS with a high risk of developing sypmtomatic intracranial haemorrhage might benefit from lower dose IV tPA, such as 0.6 mg/kg.

Blood coagulation factor XIII and factor XIII deficiency

Factor XIII (FXIII) is a multifunctional pro-γ-transglutaminase that, in addition to its well-known role in hemostasis, has a crucial role in angiogenesis, maintenance of pregnancy, wound healing, bone metabolism, and even cardio protection. FXIII deficiency (FXIIID) is a rare bleeding disorder (RBD) with an estimated incidence of one per two million that is accompanied by life-threatening bleeding such as umbilical cord bleeding, recurrent spontaneous miscarriage, and intracranial hemorrhage (ICH). Today, the disease is successfully managed by FXIII concentrate and recombinant FXIII for prophylaxis, management of minor and major bleeding, treatment of ICH, and successful delivery in women with recurrent pregnancy loss. Molecular analysis of patients with FXIIID revealed a wide spectrum of mutations, most frequently missense mutations in the FXIII-A subunit, with a few recurrent mutations observed worldwide. In vitro expression studies revealed that most of the missense mutations cause intracellular instability of the FXIII protein and, subsequently, FXIIID.

The Non-catalytic B Subunit of Coagulation Factor XIII Accelerates Fibrin Cross-linking

Covalent cross-linking of fibrin chains is required for stable blood clot formation, which is catalyzed by coagulation factor XIII (FXIII), a proenzyme of plasma transglutaminase consisting of catalytic A (FXIII-A) and non-catalytic B subunits (FXIII-B). Herein, we demonstrate that FXIII-B accelerates fibrin cross-linking. Depletion of FXIII-B from normal plasma supplemented with a physiological level of recombinant FXIII-A resulted in delayed fibrin cross-linking, reduced incorporation of FXIII-A into fibrin clots, and impaired activation peptide cleavage by thrombin; the addition of recombinant FXIII-B restored normal fibrin cross-linking, FXIII-A incorporation into fibrin clots, and activation peptide cleavage by thrombin. Immunoprecipitation with an anti-fibrinogen antibody revealed an interaction between the FXIII heterotetramer and fibrinogen mediated by FXIII-B and not FXIII-A. FXIII-B probably binds the γ-chain of fibrinogen with its D-domain, which is near the fibrin polymerization pockets, and dissociates from fibrin during or after cross-linking between γ-chains. Thus, FXIII-B plays important roles in the formation of a ternary complex between proenzyme FXIII, prosubstrate fibrinogen, and activator thrombin. Accordingly, congenital or acquired FXIII-B deficiency may result in increased bleeding tendency through impaired fibrin stabilization due to decreased FXIII-A activation by thrombin and secondary FXIII-A deficiency arising from enhanced circulatory clearance.

Polymorphism of transglutaminase 2: unusually low frequency of genomic variants with deficient functions

Transglutaminase 2 (TG2) is a multifunctional member of an enzyme family: it modifies glutamine residues by cross-linking proteins and incorporating primary amines into them, has protein disulphide isomerase and protein kinase activities, mediates trans-membrane signal transduction and interactions between cell surface proteins and the extracellular matrix. These unusual multiple roles encoded into one polypeptide chain suggest that genomic variations in the TGM2 gene should be limited. Indeed, the available information in databases shows that unlike in the case of most other transglutaminases there are no common single nucleotide polymorphisms in exons of human TGM2. We collected data on and produced some of the rare genetic variants of TGM2 by site directed mutagenesis and found that some were less stable than the most abundant (wild type) enzyme variant and the majority had deficient transamidating activity. Further studies are required to clarify the pathologic significance of these rare TGM2 alleles in the human population.

Distinct C-terminus of the B subunit of factor XIII in a population-associated major phenotype: the first case of complete allele-specific alternative splicing products in the coagulation and fibrinolytic systems

OBJECTIVES

The purpose of this study was to elucidate the molecular bases of the heterogeneity of the B subunit of coagulation factor XIII (FXIII-B), classified by isoelectric focusing into its three population-associated major phenotypes.

METHODS AND RESULTS

By genetic sequencing and polymerase chain reaction (PCR)-restriction fragment length polymorphism analyses, a C-to-G change was identified in intron K for the Asian-associated major phenotype FXIII-B*3. A transcript containing the novel exon XII' was detected by reverse transcription PCR using hepatocyte cell lines with this allele. The exclusive existence of a novel C-terminal peptide in a homozygote of FXIII-B*3 was also detected by matrix-assisted laser-desorption ionization time of flight mass spectrometry. The FXIII-B*3 isoform had a C-terminus 15 residues longer than the other isoforms, containing two additional basic amino acids and one extra acidic amino acid. Accordingly, the C-to-G nucleotide substitution created an efficient splice acceptor AG dinucleotide, which resulted in allele-specific alternative splicing in intron K. When compared with FXIII-B*1, the third major phenotype, FXIII-B*2, had an A-to-G change in exon III, converting His95 to Arg, and a rare phenotype, FXIII-B*4, had an A-to-T change in exon VII, converting Glu368 to Val.

CONCLUSIONS

We found an extremely rare event of complete allele-specific alternative splicing for FXIII-B. The FXIII-B*3 isoform had a distinct C-terminal peptide, while the FXIII-B*2 and FXIII-B*4 isoforms had His95 to Arg and Glu368 to Val substitutions, respectively, which led to differential isoelectric points of these isoforms. Such variations in the amino acid sequence of FXIII-B may have profound effects on its structure-function relationship, plasma FXIII levels, and disease susceptibility.

Natural selection and the molecular basis of electrophoretic variation at the coagulation F13B locus

Electrophoretic analysis of protein variation at the coagulation F13B locus has previously revealed three alleles, with alleles 1, 2, and 3 each being at high frequency in European, African, and Asian populations, respectively. To determine if this unusual pattern of interpopulation differentiation reflects local natural selection or neutral genetic drift, we re-sequenced 4.6 kb of the gene, encompassing all exons, splice junctions, and 1.4 kb of the promoter, in African, European, and Asian samples. These analyses revealed three major lineages, which correspond to the common protein alleles and differ from each other at a non-synonymous substitution in exon 3 and a novel splice acceptor in intron K. There is previous evidence that these lineages are not functionally equivalent; we therefore carried out case-control analyses and confirmed that variability at F13B modulates susceptibility and/or survivorship in coronary artery disease (P<0.05) and type II diabetes within the coronary artery disease cohort (P<0.01). Tajima's D and Fu and Li's tests did not indicate significant departures from neutral expectations. However, publicly available data from SeattleSNPs and HapMap do indicate highly unusual levels of population differentiation (P=0.003) and an excess of allele-specific, extended haplotype homozygosity within the African population (P=0.0125). Possible causes of this putative signal of selection include hematophagous organisms, infection by pathogens that cause disseminated intravascular coagulation, and metabolic or dietary factors.

Insulin resistance syndrome (metabolic syndrome) and obesity in Asian Indians: evidence and implications

OBJECTIVES

This review describes prevalence, determinants, and possible pathophysiologic mechanisms and suggests management and research directions for insulin resistance syndrome (metabolic syndrome) in Asian Indians.

METHOD

We reviewed the topic using the terms Asian Indians, Asians, South Asians, and Indians coupled with the terms insulin resistance, hyperinsulinemia, metabolic syndrome, and obesity from the databases Pubmed (National Library of Medicine, Bethesda, MD, USA) and Current Contents (Institute for Scientific Information, Thomson Scientific, Philadelphia, PA, USA) and from non-indexed publications of the medical research and governmental institutions in India.

RESULTS

Asian Indians have a high prevalence of insulin resistance syndrome that may underlie their greater than normal tendency to develop diabetes mellitus and early atherosclerosis. Important reasons could be their excess body fat and adverse body fat patterning including abdominal adiposity even when the body mass index is within the currently defined normal limits. Some of these features have been reported at birth and childhood. Whether Asian Indians also have tendency to develop insulin resistance de novo, independent of total or regional adiposity, needs further investigation. Underlying genetic tendency or early-life adverse events may contribute to such a phenotype, but lifestyle factors alone or modulated by inherited factors appear to play an important role because obesity and dyslipidemia become worse with urbanization and migration. Systemic stress may contribute to insulin resistance syndrome in the intra-country and inter-country migrant Asian Indians.

CONCLUSIONS

High prevalences of excess body fat, adverse body fat patterning, hypertriglyceridemia, and insulin resistance beginning at a young age have been consistently recorded in Asian Indians irrespective of their geographic locations. These data suggest that primary prevention strategies should be initiated early in this ethnic group.

Increased risk for postoperative hemorrhage after intracranial surgery in patients with decreased factor XIII activity: implications of a prospective study

BACKGROUND AND PURPOSE

The functional integrity of the hemostatic system is a prerequisite for the safe performance of neurosurgical procedures. To monitor the individual coagulation capacity of each patient, standard tests are effective to detect deficiencies involving the generation of fibrin. However, fibrin clot strength depends primarily on coagulation factor XIII, which cross-links fibrin monomers and enhances clot resistance against fibrinolysis. Therefore, factor XIII is functionally involved in both the hemostatic and fibrinolytic systems. The objective of this prospective study was to determine the incidence and clinical relevance of perioperative decreased factor XIII with respect to standard coagulation parameters and the occurrence of postoperative hematoma.

METHODS

In 876 patients, 910 neurosurgical procedures were performed. Prothrombin time (PT), partial thromboplastin time (PTT), platelet count, fibrinogen, and factor XIII were tested in each patient preoperatively and postoperatively.

RESULTS

Postoperative intracranial hematoma (defined as requiring surgical evacuation) occurred after 39 (4.3%) of 910 surgical procedures. Patients with postoperative hematoma had significantly lower factor XIII and fibrinogen levels preoperatively and postoperatively than patients without hematoma. In patients with postoperative hematoma, PT and platelets differed significantly only postoperatively, whereas PTT was different neither preoperatively nor postoperatively. Of the 39 patients with a postoperative hematoma, 13 (33.3%) had a postoperative factor XIII <60% compared with 61 (7%) of 867 patients without hematoma (P<0.01, Fisher's exact test). The relative risk of developing a postoperative hematoma is therefore increased 6.4-fold in patients with postoperative factor XIII <60%. The risk is increased 12-fold in patients who additionally have postoperative decreased fibrinogen levels (<1.5 g/L) and 9-fold in patients with platelet count <150x10(9)/L and factor XIII <60%.

CONCLUSIONS

This is the first prospective study that demonstrates the association of decreased perioperative factor XIII with an increased risk of postoperative hematoma in neurosurgical patients. The risk is further increased in those patients with low factor XIII and additional abnormalities of fibrinogen, PT, platelets, and PTT. Factor XIII testing and specific replacement, as accepted for other clotting factors, may reduce the risk of postoperative hematoma.

Factor XIIIA Val34Leu polymorphism does not predict risk of coronary heart disease: The Atherosclerosis Risk in Communities (ARIC) Study

Factor XIII catalyzes the cross-linking of fibrin. Cross-sectional studies have suggested that a common polymorphism site at residue 34 of the A subunit of factor XIII (FXIIIA) with a substitution of Leu for Val (FXIIIA Val34Leu) was associated with reduced coronary heart disease (CHD). This association has not been examined in prospective studies. Healthy subjects (n=15 792) were recruited from 4 US communities into the Atherosclerosis Risk in Communities (ARIC) study from 1987 to 1989. They were followed, and incident CHD events were identified and verified. For the present study, we included 423 patients with CHD as cases and 479 noncases. FXIIIA Val34Leu polymorphism was determined by the single-strand conformational polymorphism method. There were no significant differences in the genotype frequencies between cases and noncases. The genotypes showed little association with known CHD risk factors. A weighted proportional hazards regression analysis adjusting for other risk factors confirmed no association of the genotypes with risk of CHD. This prospective study did not provide evidence of a reduced CHD risk for the FXIIIA 34Leu allele.

Coagulation factor XIII polymorphisms and the risk of myocardial infarction and ischaemic stroke in young women

The inconsistent findings among association studies that have examined the relationship between factor XIIIA Val34Leu and thrombosis may be owing to (1) population differences in the prevalence of other risk factors that modify the association with Val34Leu, or (2) linkage disequilibrium with other functional factor XIIIA polymorphisms. We therefore performed genotyping for factor XIIIA Val34Leu, Tyr204Phe and Pro564Leu in a population-based study of myocardial infarction (MI) and ischaemic stroke among white women <45-years of age and 345 demographically similar controls, and examined potential interactions with other risk factors. The presence of the factor XIIIA Leu34 allele was associated with a slight decreased risk of MI [odds ratio (OR) = 0.80] that was most pronounced among women with traditional cardiovascular risk factors. Paradoxically, women carrying two copies of the Leu34 allele had a nearly fourfold increased risk of ischaemic stroke relative to the Val34/Val34 genotype. Heterozygosity for factor XIIIA Phe204 was associated with a milder increased risk of ischaemic stroke, and analysis of a kindred with congenital dysfibrinogenaemia suggested that co-inheritance of the factor XIIIA Phe204 allele may increase susceptibility to ischaemic stroke. Our results suggest that the factor XIIIA Val34Leu variant may be associated with a decreased risk of MI among young women with other risk factors. The relationship of factor XIIIA polymorphisms to cerebrovascular disease requires further study.