Comparison of thrombin-catalyzed fibrin polymerization and factor XIIIa-catalyzed cross-linking of fibrin among three recombinant variant fibrinogens, gamma 275C, gamma 275H, and gamma 275A.

BACKGROUND AND OBJECTIVES: We have previously reported that recombinant gamma 275Cys fibrinogen exhibits a marked impairment of functions as well as aberrant fibrin clot and bundle structures, as compared with wild-type, gamma 275Arg, and plasma fibrinogen from a heterozygous proband. Since gamma Arg275His mutations have also been reported in 10 families, we synthesized recombinant gamma 275His fibrinogen and gamma 275Ala fibrinogen (as a control) and analyzed and compared them with gamma 275Cys and gamma 275Arg. METHODS: A variant gamma-chain expression plasmid was transfected into Chinese hamster ovary cells expressing normal human fibrinogen A alpha- and B beta-chains. After purification of the recombinant variant fibrinogens, we performed functional analyzes for thrombin-catalyzed fibrin polymerization and factor XIIIa (FXIIIa)-catalyzed gamma-gamma dimer formation from fibrin or fibrinogen and also ultrastructural analysis of fibrin clots and bundles. RESULTS: By comparison with both gamma 275His and gamma 275Ala fibrinogens, recombinant gamma 275Cys fibrinogen exhibited a more impaired gamma-gamma dimer formation from fibrin or fibrinogen, a more aberrant fibrin clot structure, and thicker fibers in fibrin bundles. In 1 : 1 mixtures of gamma 275Arg and gamma 275Cys fibrinogens or gamma 275Arg and gamma 275His fibrinogens, thrombin-catalyzed fibrin polymerization and both fibrin clot and fiber structures showed some compensation (as compared with gamma 275Cys or gamma 275His alone). CONCLUSION: These results strongly suggest that an amino acid substitution of gamma 275Arg alone disrupts D:D interactions in thrombin-catalyzed fibrin polymerization and the formation of fibrin bundles and fibrin clots. Moreover, the existence of a subsequent disulfide-linked Cys in gamma 275C fibrinogen augments the impairment caused by a His or Ala substitution.     

Role of ''B-b'' knob-hole interactions in fibrin binding to adsorbed fibrinogen

BACKGROUND: The formation of a fibrin clot is supported by multiple interactions, including those between polymerization knobs 'A' and 'B' exposed by thrombin cleavage and polymerization holes 'a' and 'b' present in fibrinogen and fibrin. Although structural studies have defined the 'A-a' and 'B-b' interactions in part, it has not been possible to measure the affinities of individual knob-hole interactions in the absence of the other interactions occurring in fibrin. OBJECTIVES: We designed experiments to determine the affinities of knob-hole interactions, either 'A-a' alone or 'A-a' and 'B-b' together. METHODS: We used surface plasmon resonance to measure binding between adsorbed fibrinogen and soluble fibrin fragments containing 'A' knobs, desA-NDSK, or both 'A' and 'B' knobs, desAB-NDSK. RESULTS: The desA- and desAB-NDSK fragments bound to fibrinogen with statistically similar K(d)'s of 5.8 +/- 1.1 microm and 3.7 +/- 0.7 microm (P = 0.14), respectively. This binding was specific, as we saw no significant binding of NDSK, which has no exposed knobs. Moreover, the synthetic 'A' knob peptide GPRP and synthetic 'B' knob peptides GHRP and AHRPY, inhibited the binding of desA- and/or desAB-NDSK. CONCLUSIONS: The peptide inhibition findings show both 'A-a' and 'B-b' interactions participate in desAB-NDSK binding to fibrinogen, indicating 'B-b' interactions can occur simultaneously with 'A-a'. Furthermore, 'A-a' interactions are much stronger than 'B-b' because the affinity of desA-NDSK was not markedly different from desAB-NDSK.     

Functional analysis of recombinant Bβ15C and Bβ15A fibrinogens demonstrates that Bβ15G residue plays important roles in FPB release and in lateral aggregation of protofibrils

BACKGROUND AND OBJECTIVES: Analysis of dysfibrinogens has improved our understanding of molecular defects and their effects on the function of intact fibrinogen. To eliminate the influence of plasma heterozygous molecules, we synthesized and analyzed recombinant-variant fibrinogens. METHODS: We synthesized two recombinant-variant fibrinogens with a single amino acid substitution at the 15Gly residue in the Bbeta-chain: namely, Bbeta15Cys and Bbeta15Ala. RESULTS: Western blotting analysis of purified fibrinogen revealed the existence of a small amount of a dimeric form only for Bbeta15Cys fibrinogen. For Bbeta15Cys fibrinogen, functional analysis indicated (a) no thrombin-catalyzed fibrinopeptide B (FPB) release and (b) markedly impaired lateral aggregation in thrombin- and reptilase-catalyzed fibrin polymerizations. For Bbeta15Ala fibrinogen, such analysis indicated slight impairments of both thrombin-catalyzed FPB release and lateral aggregation in thrombin-catalyzed fibrin polymerization, but nearly normal lateral aggregation in reptilase-catalyzed fibrin polymerization. These impaired lateral aggregations were accompanied by thinner fibrin fiber diameters (determined by scanning electron microscopy of the corresponding fibrin clots). CONCLUSION: We conclude that a region adjacent to Bbeta15Gly plays important roles in lateral aggregation not only in desA fibrin polymerization, but also in desAB fibrin polymerization, and we speculate that the marked functional differences between Bbeta15A and Bbeta15C fibrinogens in FPB release and fibrin polymerization might not only be due to the presence of a substituted cysteine residue in Bbeta15C fibrinogen, but also to the existence of disulfide-bonded forms. Finally, our data indicate that the Bbeta15Gly residue plays important roles in FPB release and lateral aggregation of protofibrils.     

Polymorphisms of OATP-C (SLC21A6) and OAT3 (SLC22A8) genes: consequences for pravastatin pharmacokinetics

OBJECTIVE: Our objective was to quantitate the contribution of the genetic polymorphisms of the genes for 2 human organic anion transporters-organic anion transporting polypeptide C (OATP-C) and organic anion transporter 3 (OAT3)-to the pharmacokinetics of pravastatin. METHODS: Genetic polymorphisms were screened by polymerase chain reaction-single-strand conformation polymorphism analysis, after sequencing with deoxyribonucleic acid obtained from 120 healthy volunteers. To examine whether polymorphisms in these 2 genes of interest alter transport activity, we conducted a clinical study (n = 23) with pravastatin as a selective probe drug. RESULTS: Among 120 healthy individuals, 5 nonsynonymous variants and 1 nonsynonymous variant were observed in the OATP-C and OAT3 genes, respectively. The polymorphisms in the OAT3 gene did not appear to be associated with changes in renal and tubular secretory clearance. In contrast, the OATP-C variants were associated with differences in the disposition kinetics of pravastatin. Subjects with the OATP-C*15 allele (Asp130Ala174) had a reduced total and nonrenal clearance, as compared with those with the OATP-C*1b allele (Asp130Val174); nonrenal clearance values in *1b/*1b (n = 4), *1b/*15 (n = 9), and *15/*15 (n = 1) subjects were 2.01 +/- 0.42 L. kg(-1). h(-1), 1.11 +/- 0.34 L. kg(-1). h(-1), and 0.29 L. kg(-1). h(-1), respectively, and the difference between *1b/*1b and *1b/*15 subjects was significant (P <.05). CONCLUSION: Certain commonly occurring single-nucleotide polymorphisms in OATP-C, such as T521C (Val174Ala), are likely to be associated with altered pharmacokinetics of pravastatin. Large clinical studies are needed to confirm these observations.     

Identification of transthyretin variants by sequential proteomic and genomic analysis

BACKGROUND: Transthyretin-associated hereditary amyloidosis (ATTR) is an inherited disease in which variants in the primary structure of transthyretin (TTR; prealbumin) lead to the extracellular polymerization of insoluble protein fibrils, causing organ failure and ultimately death when major organs are involved. We have developed an integrated approach to molecular diagnosis with initial analysis of intact plasma TTR by electrospray ionization mass spectrometry (MS) and referral of positive samples for DNA sequence analysis and real-time PCR to confirm the common Gly6Ser polymorphism. METHODS: Samples from 6 patients previously diagnosed with ATTR and from 25 controls with (n = 15) or without (n = 10) polyneuropathy were analyzed in a blinded fashion for the presence of variant TTR. TTR protein was extracted with an immunoaffinity resin from 20 microL of archived plasma samples. The purified TTR was reduced with tris(2-carboxyethyl)phosphine and analyzed by MS. The appearance of two peaks (or a single peak shifted in mass indicative of a homozygous variant), including the wild-type mass of 13,761 Da, was indicative of the presence of a variant, and the individual was referred for DNA sequence analysis. RESULTS: MS analysis of intact reduced TTR correctly identified each of six samples known to contain variant TTR. These results were corroborated by subsequent DNA sequence analysis. Additionally, all Gly6Ser polymorphisms were correctly called based on the +30 mass shift and an equal relative abundance of the +30 polymorphism relative to wild-type TTR. No false-positive results were seen. CONCLUSIONS: This referral method eliminates the necessity of sequencing most samples and allows screening for the familial forms of amyloidosis in a broad patient population in a timely fashion. This method correctly identified all previously known variants and also identified a novel variant, Val94Ala.     

Fibrinogens Kosai and Ogasa: Bβ15Gly→Cys (GGT→TGT) substitution associated with impairment of fibrinopeptide B release and lateral aggregation

Summary.  We found two heterozygous dysfibrinogenemias, designated fibrinogen Kosai and fibrinogen Ogasa. Kosai was associated with arteriosclerosis obliterans but Ogasa showed no bleeding or thrombotic tendencies. The plasma fibrinogen concentrations from the two propositi (Ogasa and Kosai) were much lower when determined by the thrombin-time method (0.94 and 1.06 g L⁻¹, respectively) than when determined by the immunological method (2.87 and 2.72 g L⁻¹, respectively). We performed DNA sequencing and functional analyses to clarify the relationship between the structural and functional abnormalities. Genetic analysis of PCR-amplified DNA from the propositi identified the heterozygous substitution Bβ15Gly→Cys ( G GT→ T GT). Western blotting analysis of purified fibrinogen revealed the existence of albumin–fibrinogen complexes. Functional analyses indicated that compared with the normal control, the propositi's fibrinogen released only half the normal amount of fibrinopeptide B and showed markedly impaired polymerization. In addition, the observation of thinner fibers in fibrin clots (by scanning electron microscopy) indicated markedly defective lateral aggregation in the variant fibrinogens. The impaired functions may be due to the substitution of Cys for Bβo15Gly plus the existence of some additional disulfide-bonded forms.     

Evidence that fibrinogen γ′ directly interferes with protofibril growth: implications for fibrin structure and clot stiffness

Summary. Background: Fibrinogen contains an alternatively spliced γ‐chain (γ′), which mainly exists as a heterodimer with the common γA‐chain (γA/γ′). Fibrinogen γ′ has been reported to inhibit thrombin and modulate fibrin structure, but the underlying mechanisms are unknown. Objective: We aimed to investigate the molecular mechanism underpinning the influence of γ′ on fibrin polymerization, structure and viscoelasticity. Methods: γA/γA and γA/γ′ fibrinogens were separated using anion exchange chromatography. Cross‐linking was controlled with purified FXIIIa and a synthetic inhibitor. Fibrin polymerization was analyzed by turbidity and gel‐point time was measured using a coagulometer. We used atomic force microscopy (AFM) to image protofibril formation while final clot structure was assessed by confocal and scanning electron microscopy. Clot viscoelasticity was measured using a magnetic microrheometer. Results: γA/γ′ fibrin formed shorter oligomers by AFM than γA/γA, which in addition gelled earlier. γA/γ′ clots displayed a non‐homogenous arrangement of thin fibers compared with the uniform arrangements of thick fibers for γA/γA clots. These differences in clot structure were not due to thrombin inhibition as demonstrated in clots made with reptilase. Non‐cross‐linked γA/γA fibrin was approximately 2.7 × stiffer than γA/γ′. Cross‐linking by FXIIIa increased the stiffness of both fibrin variants; however, the difference in stiffness increased to approximately 4.6 × (γA/γA vs. γA/γ′). Conclusions: Fibrinogen γ′ is associated with the formation of mechanically weaker, non‐uniform clots composed of thin fibers. This is caused by direct disruption of protofibril formation by γ′.     

Functional evaluation of an inherited abnormal fibrinogen: fibrinogen “Baltimore”

The rate of clotting and the rate of development and degree of turbidity after addition of thrombin to plasma or purified fibrinogen from a patient with fibrinogen Baltimore was delayed when compared with normal, especially in the presence of low concentrations of thrombin. Optimal coagulation and development of translucent, rather than opaque, clots occurred at a lower pH with the abnormal fibrinogen than with normal. Development of turbidity during clotting of the abnormal plasma or fibrinogen was less than normal at each pH tested, but was maximal in both at approximately pH 6.4. The physical quality of clots formed from fibrinogen Baltimore was abnormal, as demonstrated by a decreased amplitude on thromboelastography. The morphologic appearance of fibrin strands formed from fibrinogen Baltimore by thrombin at pH 7.4 was abnormal when examined by phase contrast or electron microscopy, but those formed by thrombin at pH 6.4 or by thrombin and calcium chloride were similar to, though less compact, than normal fibrin. The periodicity of fibrin formed from fibrinogen Baltimore was similar to normal and was 231-233 A.A study of the release of the fibrinopeptides from the patient's fibrinogen and its chromatographic subfractions verified the existence of both a normally behaving and a defective form of fibrinogen in the patient's plasma. The defective form differed from normal in three functionally different ways: (a) the rate of release of fibrinopeptides A and AP was slower than normal; (b) no visible clot formation accompanied either partial or complete release of the fibrinopeptides from the defective form in 0.3 M NaCl at pH 7.4; and (c) the defective component possessed a high proportion of phosphorylated, relative to nonphosphorylated, fibrinopeptide A, while the coagulable component contained very little of the phosphorylated peptide (AP). The high phosphate content of the defective component did not appear to be the cause of the abnormality, but may be the result of an associated metabolic or genetic phenomenon.     

Fibrinogen degradation by hementin, a fibrinogenolytic anticoagulant from the salivary glands of the leech Haementeria ghilianii

The leech Haementeria ghilianii contains the anticoagulant hementin in its salivary glands, which renders ingested blood incoagulable. The loss of thrombin-coagulability of human fibrinogen, plasma, and blood was dependent on both dose and time, and it was attributable to direct proteolytic degradation of fibrinogen (Mr 340,000) by hementin. Using purified fibrinogen as the substrate, it was demonstrated that the enzyme cleaved with equal probability either through all three chains in the connector region between the D and E structural domains or in the COOH-terminal of the A alpha chain. The degradation pattern of fibrinogen in blood and purified counterpart was the same in respect to the types of degradation products formed and the rate of proteolysis. Three pairs of fibrinogen degradation products characterized by Mr were distinguished: 320,000 and 300,000, 225,000 and 200,000, 157,000 and 132,000. In each pair, the heavier product had the intact COOH-terminals of the A alpha, B beta, and gamma chains. Of special interest was the derivative of Mr 225,000 because it contained the intact A alpha, B beta, and gamma chains of the original fibrinogen. Hementin cleaved non-cross-linked and cross-linked fibrin clots; however, the rate of proteolysis was much slower than that of fibrinogen. Individual carboxymethylated chains of fibrinogen were not degraded by the enzyme. Hementin abolished coagulability of fibrinogen by a limited proteolysis that disassembled functionally bivalent polymerization sites. In addition, fibrin clot formation was inhibited by fibrinogen fragments generated by hementin. The enzyme appeared to have a unique and limited specificity for a few peptide bonds projected in the tertiary structure of the native fibrinogen molecule.     

Fibrinogen and fibrin structure and functions

Fibrinogen molecules are comprised of two sets of disulfide-bridged Aalpha-, Bbeta-, and gamma-chains. Each molecule contains two outer D domains connected to a central E domain by a coiled-coil segment. Fibrin is formed after thrombin cleavage of fibrinopeptide A (FPA) from fibrinogen Aalpha-chains, thus initiating fibrin polymerization. Double-stranded fibrils form through end-to-middle domain (D:E) associations, and concomitant lateral fibril associations and branching create a clot network. Fibrin assembly facilitates intermolecular antiparallel C-terminal alignment of gamma-chain pairs, which are then covalently 'cross-linked' by factor XIII ('plasma protransglutaminase') or XIIIa to form 'gamma-dimers'. In addition to its primary role of providing scaffolding for the intravascular thrombus and also accounting for important clot viscoelastic properties, fibrin(ogen) participates in other biologic functions involving unique binding sites, some of which become exposed as a consequence of fibrin formation. This review provides details about fibrinogen and fibrin structure, and correlates this information with biological functions that include: (i) suppression of plasma factor XIII-mediated cross-linking activity in blood by binding the factor XIII A2B2 complex. (ii) Non-substrate thrombin binding to fibrin, termed antithrombin I (AT-I), which down-regulates thrombin generation in clotting blood. (iii) Tissue-type plasminogen activator (tPA)-stimulated plasminogen activation by fibrin that results from formation of a ternary tPA-plasminogen-fibrin complex. Binding of inhibitors such as alpha2-antiplasmin, plasminogen activator inhibitor-2, lipoprotein(a), or histidine-rich glycoprotein, impairs plasminogen activation. (iv) Enhanced interactions with the extracellular matrix by binding of fibronectin to fibrin(ogen). (v) Molecular and cellular interactions of fibrin beta15-42. This sequence binds to heparin and mediates platelet and endothelial cell spreading, fibroblast proliferation, and capillary tube formation. Interactions between beta15-42 and vascular endothelial (VE)-cadherin, an endothelial cell receptor, also promote capillary tube formation and angiogenesis. These activities are enhanced by binding of growth factors like fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF), and cytokines like interleukin (IL)-1. (vi) Fibrinogen binding to the platelet alpha(IIb)beta3 receptor, which is important for incorporating platelets into a developing thrombus. (vii) Leukocyte binding to fibrin(ogen) via integrin alpha(M)beta2 (Mac-1), which is a high affinity receptor on stimulated monocytes and neutrophils.     

Common genetic variants associated with plasma fibrin D-dimer concentration in older European- and African-American adults

Summary.  Background and Objectives:  D-dimer is a hemostasis marker that reflects ongoing fibrin formation and degradation. There is significant inter-individual and inter-population variability in D-dimer concentration, but whether genetic factors underlie these differences is largely unknown. We hypothesized that common coagulation gene variants contribute to differences in circulating D-dimer concentration. Methods:  The setting was European-American (EA; n  =   1858) and African-American (AA; n  =   327) unrelated older adults from the Cardiovascular Health Study (CHS), in which we genotyped SNPs in 42 genes related to blood coagulation and fibrinolysis. Results:  Several fibrinogen gene polymorphisms, including the Thr312Ala Aα chain variant and the FGG-10034 C/T variant, were associated with ∼20% higher plasma D-dimer levels in EA (false discovery rate < 5% for covariate-adjusted model). There was also some evidence that a Pro41Leu variant of the PLAU gene encoding urinary plasminogen activator and non-coding polymorphism of the plasminogen activator inhibitor type 1 gene (SERPINE1) were associated with higher plasma D-dimer in EA. There were no significant associations between the studied coagulation or fibrinolysis gene SNPs and plasma D-dimer levels in the smaller AA sample. However, each standard deviation increase in European ancestry assessed by ancestry-informative gene markers was associated with ∼10% lower mean D-dimer levels in AA. Conclusions:  Together, common coagulation/fibrinolysis gene SNPs explained only ∼2% of the variance in plasma D-dimer levels in EA. These findings suggest that the association of D-dimer with risk of vascular outcomes may be mediated largely by environmental factors, other genes, and/or genetic interactions.     

Differential upregulation in DRG neurons of an α2δ-1 splice variant with a lower affinity for gabapentin after peripheral sensory nerve injury

The α₂δ-1 protein is an auxiliary subunit of voltage-gated calcium channels, critical for neurotransmitter release. It is upregulated in dorsal root ganglion (DRG) neurons following sensory nerve injury, and is also the therapeutic target of the gabapentinoid drugs, which are efficacious in both experimental and human neuropathic pain conditions. α₂δ-1 has 3 spliced regions: A, B, and C. A and C are cassette exons, whereas B is introduced via an alternative 3′ splice acceptor site. Here we have examined the presence of α₂δ-1 splice variants in DRG neurons, and have found that although the main α₂δ-1 splice variant in DRG is the same as that in brain (α₂δ-1 ΔA+B+C), there is also another α₂δ-1 splice variant (ΔA+BΔC), which is expressed in DRG neurons and is differentially upregulated compared to the main DRG splice variant α₂δ-1 ΔA+B+C following spinal nerve ligation. Furthermore, this differential upregulation occurs preferentially in a small nonmyelinated DRG neuron fraction, obtained by density gradient separation. The α₂δ-1 ΔA+BΔC splice variant supports Ca_V2 calcium currents with unaltered properties compared to α₂δ-1 ΔA+B+C, but shows a significantly reduced affinity for gabapentin. This variant could therefore play a role in determining the efficacy of gabapentin in neuropathic pain.     

社区呼吸道感染肺炎链球菌对头孢妥仑的耐药机制研究

目的研究头孢妥仑敏感性降低肺炎链球菌的耐药机制。方法收集2009年1月至2010年1月来自全国各地10所教学医院的37株头孢妥仑最低抑菌浓度(MIC)≥1 mg/L的社区呼吸道感染肺炎链球菌作为研究组,并取6株头孢妥仑MIC≤0.5 mg/L的社区呼吸道感染肺炎链球菌作为对照组。采用微量肉汤稀释法测定菌株对11种抗菌药物的MIC。采用多重PCR法对所有菌株进行血清分型。采用PCR法扩增43株菌的pbp2b、pbp1a、pbp2x和murM基因。用限制性内切酶进行pbp2b、pbp1a、pbp2x的指纹图谱分析。根据酶切试验分型结果,同一型的菌株挑选1～5个PCR产物送测序,测序结果与肺炎链球菌标准菌株R6比较以分析耐药菌株的青霉素结合蛋白(PBP)保守基序,特别是SXXK盒、SXN盒、KT(S)G盒的突变情况。结果根据药敏试验结果将菌株分为3组:3株对青霉素敏感、头孢妥仑MIC值≤0.5 mg/L作为C1组;3株对青霉素中介、头孢妥仑MIC值≤0.5 mg/L作为C2组;37株对青霉素中介,头孢妥仑MIC为1～4 mg/L的为R组。R组的肺炎链球菌对左氧氟沙星、莫西沙星和万古霉素均敏感,对头孢呋辛、头孢克洛、阿奇霉素和克拉霉素均耐药,仅有8.2%和5.4%的菌株分别对阿莫西林-克拉维酸和头孢曲松敏感。37株R组菌株血清学分型结果35株为19F型,1株为14型,1株为19A型。C1组菌的PBP氨基酸保守基序与野生株R6相比无突变。C2组菌PBP氨基酸保守基序与R6株相比在PBP2B、PBP2X和PBP1A中均发生3点突变。R组菌株PBP氨基酸保守基序与R6株相比则在C2组突变的基础上增加了2～3个活性位点的突变。结论 PBP2B、PBP1A和PBP2X的突变与肺炎链球菌的头孢妥仑耐药性密切相关,特别是PBP2B的Ala618→Gly,PBP2X的Met339→Phe和Tyr595→Phe可能与头孢妥仑MIC升高相关。     

Regulation of fibrinolysis by C‐terminal lysines operates through plasminogen and plasmin but not tissue‐type plasminogen activator

Summary. Background: Binding of tissue‐type plasminogen (Pgn) activator (t‐PA) and Pgn to fibrin regulates plasmin generation, but there is no consistent, quantitative understanding of the individual contribution of t‐PA finger and kringle 2 domains to the regulation of fibrinolysis. Kringle domains bind to lysines in fibrin, and this interaction can be studied by competition with lysine analogs and removal of C‐terminal lysines by carboxypeptidase B (CPB). Methods: High‐throughput, precise clot lysis assays incorporating the lysine analog tranexamic acid (TA) or CPB and genetically engineered variants of t‐PA were performed. In particular, wild‐type (WT) t‐PA (F‐G‐K1‐K2‐P) and a domain‐switched variant K1K1t‐PA (F‐G‐K1‐K1‐P) that lacks kringle 2 but retains normal t‐PA structure were compared to probe the importance of fibrin lysine binding by t‐PA kringle 2. Results: WT t‐PA showed higher rates of fibrinolysis than K1K1t‐PA, but the inhibitory effects of TA or CPB were very similar for WT t‐PA and the variant t‐PA (< 10% difference). Urokinase plasminogen activator (u‐PA)‐catalyzed fibrinolysis was also inhibited by TA, even though Pgn activation could be stimulated. Fibrin treated with factor XIIIa (FXIIIa) generates crosslinked degradation products, but these did not affect the results obtained with WT t‐PA and K1K1t‐PA. Conclusions: t‐PA kringle 2 has a minor role in the initial interaction of t‐PA and fibrin, but stimulation of fibrinolysis by C‐terminal lysines (or inhibition by carboxypeptidases or TA) operates through Pgn and plasmin binding, not through t‐PA. This is also true when fibrin is crosslinked by treatment with FXIIIa.     

Evaluation of the poly(ADP‐ribose) polymerase‐1 gene variants in Alzheimer's disease

Amyloid peptide is thought to play a critical role in neuronal death in Alzheimer's disease (AD), most likely through oxidative stress. Free radical‐related injury leads to DNA breaks, which subsequently activates the repair enzyme poly(ADP‐ribose) polymerase‐1 (PARP‐1). In this study, the relationship between genetic variants situated at the PARP‐1 gene and AD development was investigated. We performed a case and control study from a Taiwanese population enrolled 120 AD patients and 111 healthy controls by using a polymerase chain reaction restriction fragment length polymorphism approach for two PARP‐1 exonic polymorphisms, 414C/T (rs1805404) and 2456T/C (rs1136410), corresponding to protein residues at positions 81Asp/Asp and762Val/Ala. There were no significant differences in allele or genotype frequencies for either PARP‐1 gene variant between the case and control groups; however, upon analysis of the haplotype distribution, four haplotypes (Hts) were identified. We found that the distributions of Ht3‐TT and Ht4‐CC were significantly associated with an increased risk of AD (P<0.0001), whereas the Ht1‐TC haplotype showed a protective effect for cases compared with the control group (P<0.05). These results reveal that the PARP‐1 gene is highly associated with AD susceptibility and might contribute to a critical mechanism that mediates cell survival or death as a response to cytotoxic stress. J. Clin. Lab. Anal. 24:182–186, 2010. © 2010 Wiley‐Liss, Inc.     

Genetic polymorphisms of cytochrome P450 among patients with Balkan endemic nephropathy (BEN)

OBJECTIVES: The concept of multifactorial etiology of BEN anticipates that a combination of polymorphic gene variants and various environmental factors causes an increased risk for the disease. CYP enzymes play a key role in the metabolic activation of environmental chemicals and toxins. CYP3A enzymes are particularly relevant for xenobiotic metabolism because of their broad substrate specificity and abundant expression in the human liver, intestine, and kidney. Previous phenotyping analysis on CYP2D6 enzyme activity in BEN patients proposed a modifying effect of CYP2D6 gene variants on BEN risk, but it was not approved with molecular-genetic methods. The aim of the current case-control study was to compare the frequency of CYP2D6 and CYP3A5 polymorphisms, as well as one CYP3A4 promoter variant in BEN patients and controls in order to investigate a possible association between individual genetic variations in these genes and susceptibility to BEN. DESIGN AND METHODS: Ninety-six nonrelated Bulgarian BEN patients from endemic villages in the Vratza district and 112 healthy Bulgarians from nonendemic areas (controls) were genotyped. Identification of alleles was done by allele-specific PCR or by rapid-cycle amplification on the LightCycler, followed by sequence-specific detection. RESULTS: The UM, PM, and EM + IM genotype frequencies of CYP2D6 did not differ significantly between the two groups (P > 0.05). The CYP3A4*1B allele was only found in the heterozygous form, with allelic frequencies of 5.21% in the patients and 2.23% in the healthy individuals (P = 0.11). The CYP3A5*1 allele was more prevalent in BEN patients with a frequency of 9.38% compared to 5.36% in the controls and was associated with a higher risk for BEN (OR 2.41, 95% CI 1.09-5.33) (P = 0.02). CONCLUSIONS: Our results demonstrate that the CYP3A5*1 allele, previously reported as a marker for CYP3A5 expression in human kidney, is associated with increased risk for BEN, while CYP3A4*1B and CYP2D6 genotypes do not significantly modify the risk for the disease.     

Characterization of V36C,a Novel Amino Acid Substitution Conferring Hepatitis C Virus (HCV) Resistance to Telaprevir,a Potent Peptidomimetic Inhibitor of HCV Protease

We characterized a novel substitution conferring moderate resistance to telaprevir, a peptidomimetic inhibitor of hepatitis C virus protease. V36C conferred a 4.0-fold increase in the telaprevir 50% inhibitory concentration in an enzyme assay and a 9.5-fold increase in the replicon model. The replication capacity of a replicon harboring V36C was close to that of the wild-type protease. This case emphasizes the complexity of hepatitis C virus resistance to protease inhibitors.Advances in virology have led to the development of novel therapeutics specifically targeting hepatitis C virus (HCV) (4). Telaprevir (VX-950; Vertex Pharmaceuticals Incorporated, Cambridge, MA) is a novel, highly selective, potent peptidomimetic inhibitor of the HCV nonstructural protein 3/4A (NS3/4A) protease (1, 3) which has reached phase III clinical development in combination with pegylated alpha interferon (IFN-α) and ribavirin. Amino acid substitutions conferring telaprevir resistance have been reported at positions Val 36, Thr 54, Arg 155, and Ala 156 of the NS3 protease (2, 5). In patients treated with telaprevir and pegylated IFN-α with and without ribavirin, breakthroughs during treatment and relapses after treatment are characterized by the recurrence of telaprevir-resistant HCV variant replication (1).Here, we characterized a novel, so far unknown, telaprevir resistance substitution at position Val 36 in a 38-year-old treatment-naïve woman with chronic hepatitis C due to HCV genotype 1b infection. The patient was enrolled in PROVE2, a phase II randomized clinical trial assessing the efficacy and safety of telaprevir in combination with pegylated IFN-α2a with or without ribavirin (1). The patient was treated with telaprevir at 750 mg/8 h, pegylated IFN-α2a at 180 μg/week, and ribavirin at 1.0 g/day. HCV RNA became undetectable (<10 IU/ml) on therapy, but after 43 days of treatment, the patient withdrew consent and stopped therapy. She continued to be followed up after treatment withdrawal.Figure ​Figure11 shows the kinetics of HCV RNA levels in the patient during the 43 days of therapy. HCV RNA was detected 8 weeks after treatment withdrawal, and HCV RNA levels returned to nearly baseline levels. Twenty to 24 full-length NS3 protease clones were sequenced at each HCV RNA-positive time point. The patient was infected with a wild-type, telaprevir sensitive viral population at the baseline (Fig. ​(Fig.1).1). At the time of posttreatment relapse, the HCV variants all bore a Val-to-Cys substitution at position 36 (V36C). The V36C substitution remained dominant throughout posttreatment follow-up, up to day 512 after the start of therapy (Fig. ​(Fig.1).1). This substitution was associated with a Leu-to-Phe substitution at position 14 of the protease (L14F). L14F is present in approximately 6% of all HCV sequences and 8.5% of HCV subtype 1b sequences available in the European HCV database (http://euhcvdb.ibcp.fr/euHCVdb/). Based on molecular modeling, it is predicted to be located at more than 20 Å of the telaprevir binding site and is therefore unlikely to alter telaprevir-NS3 protease interaction.Open in a separate windowFIG. 1.(Top) HCV RNA kinetics in a patient who selected a V36C amino acid substitution on triple therapy with pegylated IFN-α2a, ribavirin, and telaprevir. The HCV RNA levels are expressed in log₁₀ IU/ml. LLD, lower limit of detection. The circled dots represent the four time points at which quasispecies sequence analysis was performed. (Bottom) Dynamics of NS3 quasispecies populations after treatment withdrawal relative to the baseline.The V36C substitution was further characterized and compared to other substitutions at NS3 protease position 36 observed in dominant populations in the PROVE2 trial (Table ​(Table1).1). The methods are described in the supplemental material. As shown in Table ​Table1,1, the V36C substitution conferred a 4.0-fold increase in the telaprevir 50% inhibitory concentration (IC₅₀) in our NS3/4A protease enzyme assay. This moderate increase in the IC₅₀ was on the same order as that conferred by V36M and slightly greater than that conferred by V36L. The K_m and V_max values of the NS3 protease-catalyzed enzymatic reaction were on the same order for the V36C variant and the other V36 variants and close to that of the wild-type protease (Table ​(Table11).

TABLE 1.

V36 substitutions observed in patients included in the PROVE2 clinical trial