Blood donor screening: how to decrease the risk of transfusion-transmitted hepatitis B virus?

QUESTIONS UNDER STUDY

The risk of transfusion-transmitted HBV remains significant in Switzerland, where routine screening for hepatitis B virus (HBV) in blood donations relies solely on serological hepatitis B surface antigen (HBsAg) testing. This study was designed to determine the prevalence of anti-hepatitis B core (anti-HBc) and HBV nucleic acid testing (NAT) positive donations in two different Swiss donor populations, to help in deciding whether supplemental testing may bring additional safety to blood products.

METHODS

In a first population of donors, 18143 consecutive donations were screened initially for HBsAg, anti-HBc (with one EIA assay) and with HBV NAT in minipools of 24 donations. The screening repeatedly reactive anti-HBc donations were then "confirmed" with two supplemental anti-HBc assays, an anti-hepatitis B surface assay (anti-HBs) and with single donation HBV NAT. In a second population of donors, 4186 consecutive donations were screened initially with two different anti-HBc assays in addition to the mandatory HBsAg screening test. The screening repeatedly reactive donations with at least one anti-HBc assay were tested for anti-HBs.

RESULTS

In the first subset of 18143 donations, 17593 (97.0%) were negative for HBsAg, anti-HBc and HBV NAT in minipools. 549 (3.0%) were HBsAg and HBV NAT negative, but repeatedly reactive for anti-HBc. Of these 549 donations, 287 could not be "confirmed" with two additional anti-HBc assays and were negative with an anti-HBs assay, as well as with single donation HBV NAT. Only 211 (1.2% of the total screened donations) were "confirmed" positive with at least one of two supplemental anti-HBc assays. One repeatedly reactive HBsAg donation, from a first-time donor, was confirmed positive for HBsAg and anti-HBc, as well as with single donation HBV NAT. In the second subset of 4186 donations, 4014 (95.9%) were screened negative for HBsAg and for anti-HBc, tested with two independent anti-HBc assays. 172 donations (4.1%) were HBsAg negative but repeatedly reactive with at least one of the two anti-HBc assays. Of these 172 samples, 86 were reactive with the first anti-HBc assay only, 13 were reactive with the second anti-HBc assay only and 73 (1.7% of the total screened donations) were "confirmed" positive with both anti-HBc assays.

CONCLUSION

The prevalence of anti-HBc "confirmed" positive donations in the two Swiss blood donor populations studied was low (<2%) and we found only one HBV NAT positive (HBsAg positive) donation among more than 18000. Concerning blood product safety, an increase in the deferral rate of less than 2% of anti-HBc positive, potentially infectious donors, would in our opinion make routine anti-HBc testing of blood donations cost-effective. There is however still a need for more specific assays to avoid an unacceptably high deferral rate of "false" positive donors. In contrast, the introduction of HBV NAT in minipools gives minimal benefit due to the inadequate sensitivity of the assay. It remains to evaluate more extensively the value of individual donation NAT, alone or in addition to anti-HBc, as supplemental testing in the context of several Swiss blood donor populations.

Blood donor screening: how to decrease the risk of transfusion-transmitted hepatitis B virus?

QUESTIONS UNDER STUDY

The risk of transfusion-transmitted HBV remains significant in Switzerland, where routine screening for hepatitis B virus (HBV) in blood donations relies solely on serological hepatitis B surface antigen (HBsAg) testing. This study was designed to determine the prevalence of anti-hepatitis B core (anti-HBc) and HBV nucleic acid testing (NAT) positive donations in two different Swiss donor populations, to help in deciding whether supplemental testing may bring additional safety to blood products.

METHODS

In a first population of donors, 18143 consecutive donations were screened initially for HBsAg, anti-HBc (with one EIA assay) and with HBV NAT in minipools of 24 donations. The screening repeatedly reactive anti-HBc donations were then "confirmed" with two supplemental anti-HBc assays, an anti-hepatitis B surface assay (anti-HBs) and with single donation HBV NAT. In a second population of donors, 4186 consecutive donations were screened initially with two different anti-HBc assays in addition to the mandatory HBsAg screening test. The screening repeatedly reactive donations with at least one anti-HBc assay were tested for anti-HBs.

RESULTS

In the first subset of 18143 donations, 17593 (97.0%) were negative for HBsAg, anti-HBc and HBV NAT in minipools. 549 (3.0%) were HBsAg and HBV NAT negative, but repeatedly reactive for anti-HBc. Of these 549 donations, 287 could not be "confirmed" with two additional anti-HBc assays and were negative with an anti-HBs assay, as well as with single donation HBV NAT. Only 211 (1.2% of the total screened donations) were "confirmed" positive with at least one of two supplemental anti-HBc assays. One repeatedly reactive HBsAg donation, from a first-time donor, was confirmed positive for HBsAg and anti-HBc, as well as with single donation HBV NAT. In the second subset of 4186 donations, 4014 (95.9%) were screened negative for HBsAg and for anti-HBc, tested with two independent anti-HBc assays. 172 donations (4.1%) were HBsAg negative but repeatedly reactive with at least one of the two anti-HBc assays. Of these 172 samples, 86 were reactive with the first anti-HBc assay only, 13 were reactive with the second anti-HBc assay only and 73 (1.7% of the total screened donations) were "confirmed" positive with both anti-HBc assays.

CONCLUSION

The prevalence of anti-HBc "confirmed" positive donations in the two Swiss blood donor populations studied was low (<2%) and we found only one HBV NAT positive (HBsAg positive) donation among more than 18000. Concerning blood product safety, an increase in the deferral rate of less than 2% of anti-HBc positive, potentially infectious donors, would in our opinion make routine anti-HBc testing of blood donations cost-effective. There is however still a need for more specific assays to avoid an unacceptably high deferral rate of "false" positive donors. In contrast, the introduction of HBV NAT in minipools gives minimal benefit due to the inadequate sensitivity of the assay. It remains to evaluate more extensively the value of individual donation NAT, alone or in addition to anti-HBc, as supplemental testing in the context of several Swiss blood donor populations.

Developing scanning probe–based nanodevices—stepping out of the laboratory into the clinic

This report focuses on nanotools based on the scanning force microscope (SFM) for imaging, measuring, and manipulating biological matter at the sub-micron scale. Because pathophysiological processes often occur at the (sub-) cellular scale, the SFM has opened the exciting possibility to spot diseases at a stage before they become symptomatic and cause functional impairments in the affected part of the body. Such presymptomatic detection will be key to developing effective therapies to slow or halt disease progression.

Pulsatile dynamic stiffness of cartilage-like materials and use of agarose gels to validate mechanical methods and models

Stiffness is a fundamental indicator of the functional state of articular cartilage. Reported test modes include compressive incremental strain to determine the equilibrium modulus, and sinusoidal strain to determine the dynamic modulus and stress/strain loss angle. Here, initial development is described for a method recognizing that gait is pulsatile. Agarose gels have been used by others for validation or comparison of mechanical test methods and models for cartilage and proteoglycan aggregate. Accordingly, gels ranging from 0.5 to 20% agarose were prepared. Pulsatile stiffness in both indentation and unconfined compression were closely reproducible. Stiffness as a function of agarose concentration rose exponentially, as found using other methods. Indentation stiffness was higher than for unconfined compression and ranged from approximately 2.0 kPa for 0.5% gel to approximately 3,800 kPa for 20% gel. Pulsatile dynamic stiffness appears to be a useful method, although further development is needed. Agarose gel stiffness values obtained by other methods were reviewed for comparison. Unfortunately, reported values for a given agarose concentration ranged widely (e.g. fourfold) even when test methods were similar. Causes appear to include differences in molecular weight and gel preparation time-temperature regimens. Also, agarose is hygroscopic, leading to unintended variations in gel composition. Agarose gels are problematic materials for validation or comparison of cartilage mechanical test methods and models.

Use of hydrodynamic forces to engineer cartilaginous tissues resembling the non-uniform structure and function of meniscus

The aim of this study was to demonstrate that differences in the local composition of bi-zonal fibrocartilaginous tissues result in different local biomechanical properties in compression and tension. Bovine articular chondrocytes were loaded into hyaluronan-based meshes (HYAFF-11) and cultured for 4 weeks in mixed flask, a rotary Cell Culture System (RCCS), or statically. Resulting tissues were assessed histologically, immunohistochemically, by scanning electron microscopy and mechanically in different regions. Local mechanical analyses in compression and tension were performed by indentation-type scanning force microscopy and by tensile tests on punched out concentric rings, respectively. Tissues cultured in mixed flask or RCCS displayed an outer region positively stained for versican and type I collagen, and an inner region positively stained for glycosaminoglycans and types I and II collagen. The outer fibrocartilaginous capsule included bundles (up to 2 microm diameter) of collagen fibers and was stiffer in tension (up to 3.6-fold higher elastic modulus), whereas the inner region was stiffer in compression (up to 3.8-fold higher elastic modulus). Instead, molecule distribution and mechanical properties were similar in the outer and inner regions of statically grown tissues. In conclusion, exposure of articular chondrocyte-based constructs to hydrodynamic flow generated tissues with locally different composition and mechanical properties, resembling some aspects of the complex structure and function of the outer and inner zones of native meniscus.

Investigating native coronary artery endothelium in situ and in cell culture by scanning force microscopy

The purpose of our studies is to better understand the morphology and functioning of the arteries and their changes in pathogenesis. The most frequently used imaging techniques are intravascular ultrasound, magnetic resonance imaging, and optical coherence tomography. These methods do not image cell-level structural details and only provide biomechanical properties indirectly. We present a new protocol for imaging the endothelial surface and measuring elastic properties of vascular tissue by scanning force microscopy. Full-thickness sections of native pig coronary arteries were prepared. In addition, cultured human umbilical vein endothelial cells were studied as an in vitro model system and for comparison. We encountered a variety of difficulties mostly due to the softness of vascular tissue which required significant adaptations of standard equipment: (i) a new specimen holder designed to stably immobilize the coronary arteries; (ii) a phase-contrast microscope incorporated for assessing the status of the cultured endothelial cells and positioning the scanning force microscope (SFM) tip at a site of interest; and (iii) a continuous exchange of the culture medium at 37 degrees C to assure viability of the cells in the SFM over extended times. We were thus able to investigate both fresh arterial tissue and living endothelial cells in a near-physiological environment. We present initial SFM images of vascular tissue at a spatial resolution similar to scanning electron microscopy, but which also provide a closer view of the bona fide structure of native tissue. Novel morphological features such as distinct granular particles were observed. Moreover, we report initial measurements of vascular tissue surface stiffness, obtained by indentation-type SFM.

Dynamic elastic modulus of porcine articular cartilage determined at two different levels of tissue organization by indentation-type atomic force microscopy

Cartilage stiffness was measured ex vivo at the micrometer and nanometer scales to explore structure-mechanical property relationships at smaller scales than has been done previously. A method was developed to measure the dynamic elastic modulus, |E(*)|, in compression by indentation-type atomic force microscopy (IT AFM). Spherical indenter tips (radius = approximately 2.5 microm) and sharp pyramidal tips (radius = approximately 20 nm) were employed to probe micrometer-scale and nanometer-scale response, respectively. |E(*)| values were obtained at 3 Hz from 1024 unloading response curves recorded at a given location on subsurface cartilage from porcine femoral condyles. With the microsphere tips, the average modulus was approximately 2.6 MPa, in agreement with available millimeter-scale data, whereas with the sharp pyramidal tips, it was typically 100-fold lower. In contrast to cartilage, measurements made on agarose gels, a much more molecularly amorphous biomaterial, resulted in the same average modulus for both indentation tips. From results of AFM imaging of cartilage, the micrometer-scale spherical tips resolved no fine structure except some chondrocytes, whereas the nanometer-scale pyramidal tips resolved individual collagen fibers and their 67-nm axial repeat distance. These results suggest that the spherical AFM tip is large enough to measure the aggregate dynamic elastic modulus of cartilage, whereas the sharp AFM tip depicts the elastic properties of its fine structure. Additional measurements of cartilage stiffness following enzyme action revealed that elastase digestion of the collagen moiety lowered the modulus at the micrometer scale. In contrast, digestion of the proteoglycans moiety by cathepsin D had little effect on |E(*)| at the micrometer scale, but yielded a clear stiffening at the nanometer scale. Thus, cartilage compressive stiffness is different at the nanometer scale compared to the overall structural stiffness measured at the micrometer and larger scales because of the fine nanometer-scale structure, and enzyme-induced structural changes can affect this scale-dependent stiffness differently.

Atomic force microscopy reveals defects within mica supported lipid bilayers induced by the amyloidogenic human amylin peptide

To date, over 20 peptides or proteins have been identified that can form amyloid fibrils in the body and are thought to cause disease. The mechanism by which amyloid peptides cause the cytotoxicity observed and disease is not understood. However, one of the major hypotheses is that amyloid peptides cause membrane perturbation. Hence, we have studied the interaction between lipid bilayers and the 37 amino acid residue polypeptide amylin, which is the primary constituent of the pancreatic amyloid associated with type 2 diabetes. Using a dye release assay we confirmed that the amyloidogenic human amylin peptide causes membrane disruption; however, time-lapse atomic force microscopy revealed that this did not occur by the formation of defined pores. On the contrary, the peptide induced the formation of small defects spreading over the lipid surface. We also found that rat amylin, which has 84% identity with human amylin but cannot form amyloid fibrils, could also induce similar lesions to supported lipid bilayers. The effect, however, for rat amylin but not human amylin, was inhibited under high ionic conditions. These data provide an alternative theory to pore formation, and how amyloid peptides may cause membrane disruption and possibly cytotoxicity.

Unusual wetting dynamics of aqueous surfactant solutions on polymer surfaces

Static and dynamic contact angles of aqueous solutions of three surfactants--anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C(12)E(5))--were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid-vapor interface. Obviously, another process involving adsorption at the expanding solid-liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.

Trägerübergreifende Aspekte der Begutachtung nach dem SGB IX

A project group of the Medical Advisory Board of the German Federal Rehabilitation Council (BAR) developed fundamental joint principles on experts' opinions according to the social law code no. IX (SGB IX). The principles aim at medical experts working in different social organisations and statutory health care insurance. It was intended to create a "sociomedical language" which should be used as jointly as possible by experts in rehabilitation and social medicine and which is based on the ICF (International Classification of Functioning, Disability and Health, WHO 2001). Its stringent application will increase the utility of medical expertise across different institutions. The authors recommend to evaluate whether this model could provide a tool in the communication and cooperation between different sectors of the health system. Part I describes the theoretical model, Part II its application to a virtual individual case history.

[Aspects of expertising which are jointly valid for German sociomedicine and statutory health care]

A project group of the Medical Advisory Board of the German Federal Rehabilitation Council (BAR) developed fundamental joint principles on experts' opinions according to the social law code no. IX (SGB IX). The principles aim at medical experts working in different social organisations and statutory health care insurances. It was intended to create a "sociomedical language" which should be used as jointly as possible by experts in rehabilitation and social medicine and which is based on the ICF (International Classification of Functioning, Disability and Health, WHO 2001). Its stringent application will increase the utility of medical expertise across different institutions. The authors recommend to evaluate whether this model could provide a tool in the communication and cooperation between different sectors of the health system. Part I describes the theoretical model, Part II its application to a virtual individual case history.

Hepatitis C virus-polymerase chain reaction minipool testing: 3 years in the largest Swiss blood transfusion service

BACKGROUND AND OBJECTIVES

Hepatitis C virus-polymerase chain reaction (HCV-PCR) minipool testing can improve the safety of labile blood products owing to a reduction in the diagnostic preseroconversion window period. In Switzerland, HCV-PCR minipool testing for the release of labile blood components became mandatory in September 1999. In the largest Swiss blood transfusion centre, HCV-PCR minipool testing began in January 1999. This report analyses the performance of the test during a 3-year period: 1 January 1999 to 31 December 2001.

MATERIALS AND METHODS

EDTA-blood was collected in either standard tubes or plasma preparation (PPT) tubes from 10 blood transfusion services in Switzerland and then sent to the Blood Transfusion Service SRC Berne. Up to 48 donor samples were pooled overnight using Tecan Genesis RSP 200/8 pipettors. Viral RNA was extracted by using the Qiagen QIAamp 96 viral RNA BioRobot kit on a BioRobot 9604. For PCR amplification and detection of HCV or internal control (IC) sequences, the Roche Cobas Amplicor v2.0 test kit was used. Data management, pool resolution and identification of positive samples were performed using the PMS Software from Tecan.

RESULTS

In the 3-year period from 1 January 1999 to 31 December 2001, 839056 blood donor samples were tested in minipools of up to 48 samples. Thirty-five HCV-PCR-positive donations were identified. Thirty-four samples had antibodies against HCV and were therefore also detected by screening for antibody to HCV (anti-HCV). In October 2001, one seronegative (but PCR-positive) donor was detected.

CONCLUSIONS

HCV-PCR minipool testing was successfully introduced in the largest Swiss blood transfusion service. It was shown that the release of HCV-PCR minipool results can be accomplished concurrently with the results of serological analysis. The challenge with a seronegative, but PCR-positive, donor demonstrates that the minipool testing strategy adds additional safety to blood products.

Mutation of conserved active-site threonine residues in creatine kinase affects autophosphorylation and enzyme kinetics

Muscle-type creatine kinase (MM-CK) is a member of an isoenzyme family with key functions in cellular energetics. It has become a matter of debate whether the enzyme is autophosphorylated, as reported earlier [Hemmer, Furter-Graves, Frank, Wallimann and Furter (1995) Biochim. Biophys. Acta 1251, 81-90], or exclusively nucleotidylated. In the present paper, we demonstrate unambiguously that CK is indeed autophosphorylated. However, this autophosphorylation is not solely responsible for the observed microheterogeneity of MM-CK on two-dimensional isoelectric focusing gels. Using phosphoamino-acid analysis of (32)P-labelled CK isoforms, phosphothreonine (P-Thr) residues were identified as the only product of autophosphorylation for all CK isoenzymes. The phosphorylated residues in chicken MM-CK were allocated to a region in the vicinity of the active site, where five putative phosphorylation sites were identified. Site-directed threonine-valine-replacement mutants reveal that autophosphorylation is not specific for one particular residue but occurs at all examined threonine residues. The enzyme kinetic parameters indicate that the autophosphorylation of CK exerts a modulatory effect on substrate binding and the equilibrium constant, rather than on the catalytic mechanism itself.

Localization of uroplakin Ia, the urothelial receptor for bacterial adhesin FimH, on the six inner domains of the 16 nm urothelial plaque particle

The binding of uropathogenic Escherichia coli to the urothelial surface is a critical initial event for establishing urinary tract infection, because it prevents the bacteria from being removed by micturition and it triggers bacterial invasion as well as host cell defense. This binding is mediated by the FimH adhesin located at the tip of the bacterial type 1-fimbrium and its urothelial receptor, uroplakin Ia (UPIa). To localize the UPIa receptor on the 16 nm particles that form two-dimensional crystals of asymmetric unit membrane (AUM) covering >90 % of the apical urothelial surface, we constructed a 15 A resolution 3-D model of the mouse 16 nm AUM particle by negative staining and electron crystallography. Similar to previous lower-resolution models of bovine and pig AUM particles, the mouse 16 nm AUM particle consists of six inner and six outer domains that are interconnected to form a twisted ribbon-like structure. Treatment of urothelial plaques with 0.02-0.1 % (v/v) Triton X-100 allowed the stain to penetrate into the membrane, revealing parts of the uroplakin transmembrane moiety with an overall diameter of 14 nm, which was much bigger than the 11 nm value determined earlier by quick-freeze deep-etch. Atomic force microscopy of native, unfixed mouse and bovine urothelial plaques confirmed the overall structure of the luminal 16 nm AUM particle that was raised by 6.5 nm above the luminal membrane surface and, in addition, revealed a circular, 0.5 nm high, cytoplasmic protrusion of approximately 14 nm diameter. Finally, a difference map calculated from the mouse urothelial plaque images collected in the presence and absence of recombinant bacterial FimH/FimC complex revealed the selective binding of FimH to the six inner domains of the 16 nm AUM particle. These results indicate that the 16 nm AUM particle is anchored by a approximately 14 nm diameter transmembrane stalk, and suggest that bacterial binding to UPIa that resides within the six inner domains of the 16 nm AUM particle may preferentially trigger transmembrane signaling involved in bacterial invasion and host cell defense.

Vacuolar morphology and cell cycle distribution are modified by leucine limitation in auxotrophic Saccharomyces cerevisiae

Yeast vacuoles are highly dynamic and flexible organelles. In a previous paper, we have shown that subtle, often unrecognised amino acid limitations lead to much lower final cell densities in cultures of different commonly used auxotrophic Saccharomyces cerevisiae strains (Cakar et al., Biotechnol. Lett. 21 (1999) 611). Here, we demonstrate for two of these strains, CEN.PK 113.6B and CBS7752, that such subtle leucine limitations also affect the number and morphology of vacuoles, and that these changes are correlated with the cell cycle in batch cultures in a similar way as is known from synchronized cultures. Morphological aspects were studied by electron microscopy, using advanced high pressure freezing/freeze-substitution techniques for sample preparation that so far have been barely successful in yeast. Cells of leucine-limited cultures had single, large vacuoles with a hexagonal tonoplast pattern and were partially arrested in G1 phase. To relieve leucine-limitation, additional leucine was supplied extracellularly via the medium or intracellularly via enhanced leucine biosynthesis due to plasmid-based expression of a leucine marker gene. Such cultures reached more than two-fold higher final optical densities in stationary phase. Cells in later growth phase were characterized by fragmented vacuoles lacking any tonoplast pattern and by a smaller proportion of cells in G1 phase. These drastic effects of subtle leucine limitation on cell physiology, vacuolar morphology and cell cycle distribution present a note of caution for morphological and cell cycle studies in yeast.

Coupling of creatine kinase to glycolytic enzymes at the sarcomeric I-band of skeletal muscle: a biochemical study in situ

The specific interaction of muscle type creatine-kinase (MM-CK) with the myofibrillar M-line was demonstrated by exchanging endogenous MM-CK with an excess of fluorescently labeled MM-CK in situ, using chemically skinned skeletal muscle fibers and confocal microscopy. No binding of labeled MM-CK was noticed at the I-band of skinned fibers, where the enzyme is additionally located in vivo, as shown earlier by immunofluorescence staining of cryosections of intact muscle. However, when rhodamine-labeled MM-CK was diffused into skinned fibers that had been preincubated with phosphofructokinase (PFK), a glycolytic enzyme known to bind to actin, a striking in vivo-like interaction of Rh-MM-CK with the I-band was found, presumably mediated by binding of Rh-MM-CK to the glycolytic enzyme. Aldolase, another actin-binding glycolytic enzyme was also able to bind Rh-MM-CK to the I-band, but formation of the complex occurred preferably at long sarcomere length (> 3.0 microm). Neither pyruvate kinase, although known for its binding to actin, nor phosphoglycerate kinase (PGK), not directly interacting with the I-band itself, did mediate I-band targeting of MM-CK. Anchoring of MM-CK to the I-band via PFK, but not so via aldolase, was strongly pH-dependent and occurred below pH 7.0. Labeling performed at different sarcomere length indicated that the PFK/MM-CK complex bound to thin filaments of the I-band, but not within the actomyosin overlap zones. The physiological consequences of the structural interaction of MM-CK with PFK at the I-band is discussed with respect to functional coupling of MM-CK to glycolysis, metabolic regulation and channeling in multi-enzyme complexes. The in situ binding assay with skinned skeletal muscle fibers described here represents a useful method for further studies of specific protein-protein interactions in a structurally intact contractile system under various precisely controlled conditions.