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Biomedical subjects

K Mertens

Publications and source records attributed to K Mertens.

At least 19 recordsLinked to original sources
PubMed2006

The influence of line and laying period on the relationship between different eggshell and membrane strength parameters.

We investigated the correlations between different eggshell and membrane strength parameters and their changes over time. Eggshell and membrane characteristics were measured for 2 different lines of laying hens, Hisex Brown and Bovans Brown, from wk 33 up to wk 78. Several parameters were investigated: 2 parameters concerning total eggshell strength (static and dynamic stiffness), 1 structural parameter (i.e., eggshell thickness), 2 parameters describing the material characteristics of the shell [dynamic Young's modulus (EM) and nitrogen content], and 3 parameters to measure the membrane characteristics (attachment force breaking strength and nitrogen content). This study shows that the correlations among parameters change during the laying period and among lines. The EM of the eggshell increased during the laying period for the Hisex line. No difference was observed in case of the Bovans line. In general, a negative correlation was obtained between eggshell thickness and the EM. The correlation between static and dynamic stiffness increased during lay. Finally, the attachment force and breaking strength of the membranes declined during the laying period.

Animals↗
PubMed2006

Monitoring of eggshell breakage and eggshell strength in different production chains of consumption eggs.

We first tried to monitor the critical points for eggshell breakage in different logistic chains. Second, we examined whether there was a difference in eggshell strength among eggs produced in different housing systems. Finally, we developed a model to investigate the relation between eggshell strength and the likelihood of an egg cracking during handling and grading. Four logistic chains with different housing systems (battery cages, furnished cages, aviary, and free-range), all housing Bovans Goldline chickens in their mid-lay (45 wk), were compared. In every chain, a randomized set of 1,500 eggs was sampled, and the strength was defined. At every critical point in every logistic chain, the eggs were reexamined for breakage. The classic and furnished cage systems showed the highest percentage of breakage directly at point of lay (6.73 and 10.72%), whereas the other systems showed lower breakage (1.94% in the aviary and 1.99% in the free-range system). Further, in the logistic chain, grading and packing of the eggs generated the second highest percentage of breakage (from 1.50 to 2.65%). Breakage due to transportation ranged from 0.16 to 2.65%. There was a significant difference among the eggshell strength (shell stiffness and damping ratio) of eggs from chickens in different housing systems, showing eggs from chickens in the aviary system to be stronger than cage eggs (classic and furnished) and free-range eggs to be weaker than the other eggs. A significant correlation was found between eggshell strength and the likelihood of breakage in the production chains. In conclusion, it was first shown that, besides the laying, packing of the eggs is a critical point in the logistic chain of consumption eggs; second, the strength of the eggs in the different housing systems differed, and, finally, the eggshell stiffness and damping ratio of consumption eggs are an acceptable measure for rapid eggshell quality assessment and could provide a good predictive value for eggshell breakage in all types of table egg production chains.

Animal Husbandry↗
PubMed2006

Proteolytic cleavage of factor VIII heavy chain is required to expose the binding-site for low-density lipoprotein receptor-related protein within the A2 domain.

BACKGROUND: Low-density lipoprotein receptor-related protein (LRP) is an endocytic receptor that contributes to the clearance of coagulation factor (F) VIII from the circulation. Previously, we have demonstrated that region Glu(1811)-Lys(1818) within FVIII light chain constitutes an important binding region for this receptor. We have further found that FVIII light chain and intact FVIII are indistinguishable in their LRP-binding affinities. In apparent contrast to these observations, a second LRP-binding region has been identified within A2 domain region Arg(484)-Phe(509) of FVIII heavy chain. OBJECTIVE: In this study, we addressed the relative contribution of FVIII heavy chain in binding LRP. METHODS AND RESULTS: Surface plasmon resonance analysis unexpectedly showed that FVIII heavy chain poorly associated to the receptor. The binding to LRP was, however, markedly enhanced upon cleavage of the heavy chain by thrombin. The A2 domain, purified from thrombin-activated FVIII, also showed efficient binding to LRP. Competition studies employing a recombinant antibody fragment demonstrated that region Arg(484)-Phe(509) mediates the enhanced LRP binding after thrombin cleavage. CONCLUSIONS: We propose that LRP binding of non-activated FVIII is mediated via the FVIII light chain while in activated FVIII both the heavy and light chain contribute to LRP binding.

Binding Sites↗
PubMed2005

Dirt detection on brown eggs by means of color computer vision.

In the last 20 yr, different methods for detecting defects in eggs were developed. Until now, no satisfying technique existed to sort and quantify dirt on eggshells. The work presented here focuses on the design of an off-line computer vision system to differentiate and quantify the presence of different dirt stains on brown eggs: dark (feces), white (uric acid), blood, and yolk stains. A system that provides uniform light exposure around the egg was designed. In this uniform light, pictures of dirty and clean eggs were taken, stored, and analyzed. The classification was based on a few standard logical operators, allowing for a quick implementation in an online set-up. In an experiment, 100 clean and 100 dirty eggs were used to validate the classification algorithm. The designed vision system showed an accuracy of 99% for the detection of dirt stains. Two percent of the clean eggs had a light-colored eggshell and were subsequently mistaken for showing large white stains. The accuracy of differentiation of the different kinds of dirt stains was 91%. Of the eggs with dark stains, 10.81% were mistaken for having bloodstains, and 33.33% of eggs with bloodstains were mistaken for having dark stains. The developed system is possibly a first step toward an on line dirt evaluation technique for brown eggs.

Animals↗
PubMed2005

Effects of turning duration during incubation on embryo growth, utilization of albumen, and stress regulation.

Eggs from Cobb broiler breeders were incubated for 18 d. Eggs were not turned (T0) or were turned until 9 (T9), 12 (T12), 15 (T15), or 18 (T18) d. First, the effects of turning on embryo and albumen weights were studied. Samples of eggs were opened at d 9, 12, 15, and 18 for embryo and albumen weighing. The results show that embryos from unturned eggs had lower weights and higher remaining albumen weights than those from turned eggs. At d 18, albumen utilization was completed in the T12, T15, and T18 groups only. Also, further turning until d 15 and 18 increased embryo weights. The responsiveness of the embryo after adrenocorticotropic hormone (ACTH) injection was studied to test stress control in embryos. Blood samples were collected from embryos at 60 and 150 min after injection at d 12, 15, and 18 and were analyzed for corticosterone concentrations. The results showed that basal corticosterone levels increased with embryo age. At 60 min after ACTH injection, corticosterone levels were lower at d 12 than at d 15 and 18. At 150 min after ACTH injection, corticosterone levels followed different trends according to incubation stage and turning duration. The highest basal corticosterone levels were obtained with the T15 group at d 15 and 18. Also at d 18, corticosterone levels in the T15 group were the highest at 150 min after ACTH injection. We concluded that egg turning was required during incubation until d 12, at least, and should not be stopped until after d 15.

Agriculture↗
PubMed2005

An automatic monitoring of the hatching process based on the noise of the hatching chicks.

In this manuscript, a new tool is presented for automatic monitoring of the hatching process of eggs without opening the incubator doors. The amount of energy in the noise produced by the hatchlings was registered by means of a microphone and a personal computer for signal treatment. Evidence is shown that it is possible to detect exactly when the first chicks are hatched, the mean hatching time, and the finish of hatch. The information generated by this tool can be used by the hatchery manager to make the decision to end the incubation at the right moment, resulting in a higher number of first quality chicks without the risk of a reduced hatchability due to too early termination of the incubation process. The presented research also shows evidence that there is already a circadian rhythm in the newborn hatchling even when no external stimulus is present.

Animal Husbandry↗
PubMed2005

Does activated protein C-resistant factor V contribute to thrombin generation in hemophilic plasma?

In this study we assessed the role of factor V (FV) inactivation in hemophilic plasma with particular reference to the activated protein C (APC)-resistant variants FV-R506Q (FV Leiden) and FV-R306T (FV Cambridge). Purified recombinant full-length FV carrying these single substitutions and FV-R306T/R506Q were used in thrombin generation experiments. Plasma was first immunodepleted of FV, and subsequently of factors VIII, IX, or combinations thereof. Thrombin generation was initiated by low concentrations of recombinant tissue factor. Recombinant soluble thrombomodulin (TM) was used to trigger the APC system. Surprisingly, TM concentrations that reduced thrombin generation in normal plasma by no more than 50% virtually abolished thrombin formation in plasma deficient in the factor VIII/IX complex. This was already apparent at TM levels as low as 0.1 nmol L(-1). By varying the concentrations of purified (activated) protein C to plasma that was additionally depleted of protein C, we confirmed that impaired thrombin generation indeed was the result of the action of APC. In contrast, this did not occur when FV-depleted plasma had been reconstituted with FV-R306T/R506Q. Addition of FV-R306T or FV-R506Q partially reduced prothrombin activation, demonstrating the involvement of both APC cleavage sites. FV inactivation also occurred on the surface of human microvascular endothelial cells. Apparently, these cells express sufficient TM to down-regulate thrombin production via the APC pathway. We further conclude that in hemophilic plasma this pathway can induce a secondary defect because of premature FV inactivation. It therefore seems conceivable that APC-resistant FV has the potential of alleviating hemophilic bleeding.

Activated Protein C Resistance↗
PubMed2005

The B domain of coagulation factor VIII interacts with the asialoglycoprotein receptor.

BACKGROUND: Coagulation factor VIII (FVIII) is a heavily glycosylated heterodimeric plasma protein that consists of a heavy (domains A1-A2-B) and light chain (domains A3-C1-C2). It has been well established that the clearance of FVIII from the circulation involves mechanisms that are sensitive to the low-density lipoprotein receptor (LDLR) family antagonist receptor-associated protein (RAP), including LDLR-related protein. Because FVIII clearance in the presence of a bolus injection of RAP still occurs fairly efficient, also RAP-independent mechanisms are likely to be involved. OBJECTIVES: In the present study, we investigated the interaction of FVIII with the endocytic lectin asialoglycoprotein receptor (ASGPR) and the physiological relevance thereof. METHODS AND RESULTS: Surface plasmon resonance studies demonstrated that FVIII dose-dependently bound to ASGPR with high affinity (Kd approximately 2 nM). FVIII subunits were different in that only the heavy chain displayed high-affinity binding to ASGPR. Studies employing a FVIII variant that lacks the B domain revealed that FVIII-ASGPR complex assembly is driven by structure elements within the B domain of the heavy chain. The FVIII heavy chain-ASGPR interaction required calcium ions and was inhibited by soluble D-galactose. Furthermore, deglycosylation of the FVIII heavy chain by endoglycosidase F completely abrogated the interaction with ASGPR. In clearance experiments in mice, the FVIII mean residence time was prolonged by the ASGPR-antagonist asialo-orosomucoid (ASOR). CONCLUSIONS: We conclude that asparagine-linked oligosaccharide structures of the FVIII B domain recognize the carbohydrate recognition domains of ASGPR and that an ASOR-sensitive mechanism, most likely ASGPR, contributes to the catabolism of coagulation FVIII in vivo.

Animals↗
PubMed2005

Molecular models of the procoagulant factor VIIIa-factor IXa complex.

BACKGROUND: Formation of the intrinsic tenase complex is an essential event in the procoagulant reactions that lead to clot formation. The tenase complex is formed when the activated serine protease, Factor IXa (FIXa), and its cofactor Factor VIIIa (FVIIIa) assemble on a phospholipid surface to proteolytically convert the zymogen Factor X (FX) into its active form FXa. The physiological relevance of the tenase complex is evident in hemophilia A or B patients who present with bleeding disorders. OBJECTIVES: The purpose of this study was to establish three-dimensional (3D) models of the FVIIIa-FIXa complex. METHODS: First, we built two new theoretical models of FVIIIa via homology modeling, inter-domain docking and loop simulation algorithms as well as a model for FIXa. This was followed by pseudo-Brownian protein-protein docking in internal coordinates with the ICM (Internal Coordinates Mechanics) program between the two FVIIIa and the FIXa structures. RESULTS: Ten representative models of this complex are presented based on agreements with known experimental data and according to structural criteria. CONCLUSIONS: These novel 3D models will help guide future site directed mutagenesis aimed at improving the functionality of FVIIIa and/or FIXa and will contribute to a better understanding of the role of this macromolecular complex in the blood coagulation cascade.

Algorithms↗
PubMed2005

Proteolytic cleavage of protein S during the hemostatic response.

BACKGROUND: Protein S is a vitamin K-dependent protein with anticoagulant properties. It contains a so-called thrombin-sensitive region (TSR), which is susceptible to cleavage by coagulation factor Xa (FXa) and thrombin. Upon cleavage, the anticoagulant activity of protein S is abolished. OBJECTIVE: The aim of the present study was to determine whether protein S is cleaved within the TSR during activation of the coagulation system under near physiological conditions. RESULTS: In a reconstituted coagulation system containing apart from protein S only procoagulant constituents and synthetic phospholipid vesicles, protein S was cleaved at Arg60 by the FXa generated (3 mol min(-1) mol(-1) enzyme). FXa-catalyzed cleavage of protein S, however, was inhibited by factor Va and prothrombin by more than 70%. During clotting of recalcified citrated plasma in the presence of a synthetic lipid membrane, no FXa-catalyzed proteolysis of protein S was observed. Substituting platelets for phospholipid vesicles resulted both in the reconstituted system and in plasma in cleavage of the TSR. Cleavage was at Arg60 and was observed upon platelet activation, irrespective of the presence of FXa (13 pmol min(-1) 10(-8) platelets). No cleavage by thrombin was observed in either the reconstituted coagulation system or clotting plasma. CONCLUSION: These findings suggest that in vivo the anticoagulant activity of protein S is not down-regulated by FXa or thrombin during activation of coagulation. Our results rather suggest a role for a platelet protease in down-regulating the anticoagulant activity of protein S during the hemostatic response.

Binding Sites↗
PubMed2004

A one-year survey of candidemia in Belgium in 2002.

A total of 211 episodes of bloodstream yeast infections in 207 patients, hospitalized in 28 Belgian hospitals participating in a National Surveillance Program, were evaluated. A total of 81% of the patients were more than 50 years of age. Candida albicans was the cause of infections in 55% of patients, 22% were due to C. glabrata and 13% to C. parapsilosis. The most common predisposing factors were antibacterial therapy (42%), residence in an intensive care unit (32.9%) and presence of an intravascular catheter (29.7%). Most patients had more than one predisposing factor. Fluconazole alone or in association with another antifungal agent was the treatment of choice for 89.7% of the cases. In vitro susceptibility testing of the isolates revealed that 99% were susceptible to amphotericin B, 95% to 5-fluorocytosine, 82% to fluconazole and 69% to itraconazole. Resistance to azoles was more common among C. glabrata isolates in the elderly. We conclude that the frequency of C. albicans infection is decreasing in Belgium and this is associated with the emergence of other species, most notably, C. glabrata.

Adolescent↗
PubMed2004

New approach of testing the effect of heat stress on eggshell quality: mechanical and material properties of eggshell and membrane.

1. The effect of high temperature on eggshell quality was investigated by measuring the mechanical and material properties of shell and membranes. 2. Heat exposure resulted in a decrease in zootechnical performance and eggshell thickness, increase in egg breakage, and unchanged egg shape index. 3. The static stiffness (Kstat), dynamic stiffness (Kdyn) and modulus of elasticity of the eggshell were not significantly affected by high temperature. Membrane prolongation increased significantly while membrane attachment strength and breakage strength tended to decrease and increase, respectively. The relationships between these variables were changed by high temperature. 4. Neither Kstat nor Kdyn could give a reasonable explanation for the changed eggshell quality induced by heat stress. The decreased eggshell thickness and changed properties of shell membrane may be responsible, at least partially, for the decreased shell quality of eggs from heat-stressed hens.

Animals↗
PubMed2004

Changing albumen-membrane adhesive forces during early embryonic development.

Using acoustic resonance analysis, it is possible to detect embryonic development. In fertile eggs, the resonant frequency suddenly decreases after about 100 h of incubation. Previous research has shown that this decrease coincides with changing mechanical properties of the albumen near the shell, caused by the formation of subembryonic fluid (SEF). In the present experiment, the adhesive forces between the shell, the membranes, and the albumen were measured before and after the decrease in the resonant frequency. The adhesive forces between shell and outer membrane and between the 2 membranes remained constant, whereas the adhesive force between the inner membrane and the albumen, indirectly measured by a Kjeldahl analysis, increased significantly. Whether the decrease in resonant frequency is caused by the increase of adhesive force between albumen and inner membrane or by the changed properties of the membranes (both of which are altered by dehydration of the albumen) is still open for discussion.

Adhesiveness↗
PubMed2001

Functional mapping of anti-factor IX inhibitors developed in patients with severe hemophilia B.

Development of inhibitory antibodies is a serious complication of treatment with repeated factor IX infusions in a minority of patients with hemophilia B. Such antibodies detected in 8 patients have been characterized. Typing studies revealed that patients' immune response toward factor IX is highly heterogeneous and involves immunoglobulin G (IgG) antibodies, preferentially IgG1 and IgG4. The preservation of the sequence and the 3-dimensional orientation of the amino acids constituting one epitope are highly important for the assembly of an antibody-antigen complex. To localize the epitopes on the factor IX molecule, an original approach was designed using a set of factor X chimeras carrying regions of factor IX. Results showed that some patients' antibodies were directed against both the domain containing the gamma-carboxy glutamic acid residues (Gla domain) and the protease domain of factor IX. In contrast, no binding was observed to the epidermal growth factor-like domains or to the activation peptide. Functional characterization showed that the purified IgG from patients' serum inhibited the factor VIIIa-dependent activation of factor X. Moreover, patients' IgG directed against the Gla domain inhibited the binding of factor IX to phospholipids as well as the binding of factor VIII light chain to factor IXa. These data demonstrate that inhibitors appearing in patients with severe hemophilia B display specificity against restricted functional domains of factor IX.

Antibody Specificity↗
PubMed2001

Multiple VH genes are used to assemble human antibodies directed toward the A3-C1 domains of factor VIII.

A well-known complication of factor VIII replacement therapy in patients with hemophilia A is the development of inhibitory antibodies. Several studies have demonstrated the presence of a binding site for factor VIII inhibitors in the A3 domain. Six different human monoclonal single-chain variable domain antibody fragments (scFv) directed toward the A3-C1 domains of factor VIII have been isolated, using phage display technology. Sequence analysis revealed that the V(H) domains of 2 scFv were encoded by germline gene segments from the V(H)1 gene family and 4 by germline gene segments belonging to the V(H)3 gene family. Epitope mapping of the scFv was performed, using a series of hybrid factor VIII/factor V light chain fragments. This analysis revealed that 5 of 6 scFv were directed against a region encompassing amino acid sequence Q1778-D1840 in the A3 domain, a previously identified binding site for factor VIII inhibitors. Only 2 of 5 scFv directed against amino acid sequence Q1778-D1840 inhibited the procoagulant activity of factor VIII. Our results define the properties of human antibodies directed against region Q1778-D1840 in the A3 domain. Binding of one, noninhibitory scFv was independent of the region Q1778-D1840, suggesting the presence of an additional binding site for anti-factor VIII antibodies in the A3-C1 domains of factor VIII.

Amino Acid Sequence↗
PubMed2001

The future of plasma derivatives.

In the early 1980s, the advent of recombinant DNA technology provided the perspective of an unlimited supply of recombinant plasma proteins. However, the cost of mammalian cell expression, downstream processing, and the development time of biotechnological pharmaceuticals have generally been underestimated. Despite the initial optimism that plasma derivatives would soon become obsolete, no more than three plasma proteins have been licensed for therapeutic use since that time. The current situation favours a reappraisal of plasma derivatives, which nowadays can meet safety standards similar to those of recombinant products. In terms of cost, human blood has the further advantage over biotechnological sources in that it allows the production of multiple pharmaceutical proteins from one single material. This provides a favourable starting point for exploring the therapeutic potential of the numerous plasma proteins that have remained unused so far.

Animals↗