Cytotoxicity of Biomaterials — Basic Mechanisms and In Vitro Test Methods: A Review

Biocompatibility is one of the main prerequisites for the clinical use of biomaterials. Central to the testing of biocompatibility is the estimation of cytotoxicity, which can be assessed in vitro by using a variety of different target primary cells or cell lines. The influence of toxic agents derived from biomaterials on cellular functions and cell viability can be characterised by reductions in cell adhesion, alterations in cellular morphology, reduced cellular proliferation, and cell death, demonstrated by an absence of metabolic activity, structural disintegration and cell lysis. A brief review of the basic mechanisms of cytotoxicity and the use of different in vitro methods for testing the cytotoxicity of biomaterials is presented.

Valorization of Brewer's spent grain to prebiotic oligosaccharide: Production, xylanase catalyzed hydrolysis, in-vitro evaluation with probiotic strains and in a batch human fecal fermentation model

Brewer's spent grain (BSG) accounts for around 85% of the solid by-products from beer production. BSG was first extracted to obtain water-soluble arabinoxylan (AX). Using subsequent alkali extraction (0.5 M KOH) it was possible to dissolve additional AX. In total, about 57% of the AX in BSG was extracted with the purity of 45-55%. After comparison of nine xylanases, Pentopan mono BG, a GH11 enzyme, was selected for hydrolysis of the extracts to oligosaccharides with minimal formation of monosaccharides. Growth of Bifidobacterium adolescentis (ATCC 15703) was promoted by the enzymatic hydrolysis to arabinoxylooligosaccharides, while Lactobacillus brevis (DSMZ 1264) utilized only unsubstituted xylooligosaccharides. Furthermore, utilization of the hydrolysates by human gut microbiota was also assessed in a batch human fecal fermentation model. Results revealed that the rates of fermentation of the BSG hydrolysates by human gut microbiota were similar to that of commercial prebiotic fructooligosaccharides, while inulin was fermented at a slower rate. In summary, a sustainable process to valorize BSG to functional food ingredients has been proposed.

Characterization of a family 43 β-xylosidase from the xylooligosaccharide utilizing putative probiotic Weissella sp. strain 92

In this work, we present the first XOS degrading glycoside hydrolase from Weissella, WXyn43, a two-domain enzyme from GH43. The gene was amplified from genomic DNA of the XOS utilizing Weissella strain 92, classified under the species-pair Weissella cibaria/W.confusa, and expressed in Escherichia coli. The enzyme is lacking a putative signal peptide and is, from a homology model, shown to be composed of an N-terminal 5-fold β-propeller catalytic domain and a C-terminal β-sandwich domain of unknown function. WXyn43 hydrolyzed short (1-4)-β-D-xylooligosaccharides, with similar kcat/KM for xylobiose (X2) and xylotriose (X3) and clearly lower efficiency in xylotetraose (X4) conversion. WXyn43 displays the highest reported kcat for conversion of X3 (900 s(-1) at 37 °C) and X4 (770 s(-1)), and kcat for hydrolysis of X2 (907 s(-1)) is comparable with or greater than the highest previously reported. The purified enzyme adopted a homotetrameric state in solution, while a truncated form with isolated N-terminal catalytic domain adopted a mixture of oligomeric states and lacked detectable activity. The homology model shows that residues from both domains are involved in monomer-monomer hydrogen bonds, while the bonds creating dimer-dimer interactions only involved residues from the N-terminal domain. Docking of X2 and X3 in the active site shows interactions corresponding to subsites -1 and +1, while presence of a third subsite is unclear, but interactions between a loop and the reducing-end xylose of X3 may be present.

Production of arabinoxylan-oligosaccharide mixtures of varying composition from rye bran by a combination of process conditions and type of xylanase

The aim was to study arabinoxylan-oligosaccharide production from rye bran using heat pretreatment and enzymatic hydrolysis. Due to the potential application in foods, the purity of arabinoxylan was also assessed. Rye bran was heat pretreated to improve xylanase-catalyzed hydrolysis of arabinoxylan into arabinoxylan-oligosaccharides. Enzymatic removal of starch and proteins before or after heat pretreatment increased the purity, although at lower yield. The most attractive process resulted in 62% (w/w) arabinoxylan content after ethanol precipitation. Using xylanases from two glycoside hydrolase families (RmXyn10A from GH10 and Pentopan Mono BG from GH11), different mixtures of unsubstituted and arabinose-substituted xylooligosaccharides were produced. GH10 gave a higher yield of short oligosaccharides (60%w/w) with xylobiose as the main product; xylobiose and xylotriose were the main products with GH11 (40%w/w). Thus, heat pretreatment combined with enzymatic hydrolysis can be used to produce arabinoxylan-oligosaccharides from rye bran that are potentially useful in functional foods.

Cereal byproducts have prebiotic potential in mice fed a high-fat diet

Barley husks, rye bran, and a fiber residue from oat milk production were processed by heat pretreatment, various separation steps, and treatment with an endoxylanase in order to improve the prebiotic potential of these cereal byproducts. Metabolic functions were intended to improve along with improved microbial activity. The products obtained were included in a high-fat mouse diet so that all diets contained 5% dietary fiber. In addition, high-fat and low-fat controls as well as partially hydrolyzed guar gum were included in the study. The soluble fiber product obtained from rye bran caused a significant increase in the bifidobacteria (log copies of 16S rRNA genes; median (25-75 percentile): 6.38 (6.04-6.66) and 7.47 (7.30-7.74), respectively; p < 0.001) in parallel with a tendency of increased production of propionic acid and indications of improved metabolic function compared with high-fat fed control mice. The oat-derived product caused an increase in the pool of cecal propionic (from 0.62 ± 0.12 to 0.94 ± 0.08) and butyric acid (from 0.38 ± 0.04 to 0.60 ± 0.04) compared with the high-fat control, and it caused a significant increase in lactobacilli (log copies of 16S rRNA genes; median (25-75 percentile): 6.83 (6.65-7.53) and 8.04 (7.86-8.33), respectively; p < 0.01) in the cecal mucosa. However, no changes in measured metabolic parameters were observed by either oat or barley products.

Xylooligosaccharides from hardwood and cereal xylans produced by a thermostable xylanase as carbon sources for Lactobacillus brevis and Bifidobacterium adolescentis

To compare xylans from forestry with agricultural origins, hardwood xylan (birch) and cereal arabinoxylan (rye) were hydrolyzed using two variants of the xylanase RmXyn10A, full-length enzyme and catalytic module only, from Rhodothermus marinus . Cultivations of four selected bacterial species, using the xylooligosaccharide (XOS) containing hydrolysates as carbon source, showed selective growth of Lactobacillus brevis DSMZ 1264 and Bifidobacterium adolescentis ATCC 15703. Both strains were confirmed to utilize the XOS fraction (DP 2-5), whereas putative arabinoxylooligosaccharides from the rye arabinoxylan hydrolysate were utilized by only B. adolescentis. Escherichia coli did not grow, despite its capability to grow on the monosaccharides arabinose and xylose. It was also shown that Pediococcus parvulus strain 2.6 utilized neither xylose nor XOS for growth. In summary, RmXyn10A or its catalytic module proved suitable for high-temperature hydrolysis of hardwood xylan and cereal arabinoxylan, producing XOS that could qualify as prebiotics for use in functional food products.

Evidence for xylooligosaccharide utilization in Weissella strains isolated from Indian fermented foods and vegetables

Six strains isolated from fermented food were identified as Weissella species by 16S rDNA sequencing, clustering with the species pair W. confusa/W. cibaria. The strains were analysed for growth on glucose, xylose and xylooligosaccharides (XOS). All strains were xylose positive using the API CHL 50 test. Growth on XOS was observed for strains 85, 92, 145 and AV1, firstly by optical density measurements in microtitre plates and secondly in batch cultures also confirming concomitant decrease in pH. Analysis of XOS before and after growth established consumption in the DP2-DP5 range in the four XOS-fermenting strains. XOS were consumed simultaneously with glucose, while xylose was consumed after glucose depletion. Cell-associated β-xylosidase activity was detected in the XOS-fermenting strains. Analysis of genomic data suggests this activity to be linked with genes encoding glycoside hydrolases from family 3, 8 or 43. No endo-β-xylanase activity was detectable. Major end products were lactate and acetate. A higher ratio of acetic acid to lactic acid was obtained during growth on XOS compared with growth on glucose. This is the first report on utilization of XOS in Weissella, indicating an increased probiotic potential for XOS-utilizing strains from the species pair W. confusa/W. cibaria, but also showing that XOS utilization is strain dependent for these species.

Cranial neural crest cells contribute to connective tissue in cranial muscles in the anuran amphibian, Bombina orientalis

The contribution of cranial neural crest cells to the development and patterning of cranial muscles in amphibians was investigated in the phylogenetically basal and morphologically generalized frog, Bombina orientalis. Experimental methods included fluorescent marking of premigratory cranial neural crest and extirpation of individual migratory streams. Neural crest cells contributed to the connective tissue component, but not the myofibers, of many larval muscles within the first two branchial arches (mandibular and hyoid), and complex changes in muscle patterning followed neural crest extirpation. Connective tissue components of individual muscles of either arch originate from the particular crest migratory stream that is associated with that arch, and this relationship is maintained regardless of the segmental identity-or embryonic derivation-of associated skeletal components. These developmental relations define a pattern of segmentation in the head of larval anurans that is similar to that previously described in the domestic chicken, the only vertebrate that has been thoroughly investigated in this respect. The fundamental role of the neural crest in patterning skeleton and musculature may represent a primitive feature of cranial development in vertebrates. Moreover, the corresponding developmental processes and cell fates appear to be conserved even when major evolutionary innovations-such as the novel cartilages and muscles of anuran larvae-result in major differences in cranial form.

Cranial neural crest cell migration in the Australian lungfish, Neoceratodus forsteri

A crucial role for the cranial neural crest in head development has been established for both actinopterygian fishes and tetrapods. It has been claimed, however, that the neural crest is unimportant for head development in the Australian lungfish (Neoceratodus forsteri), a member of the group (Dipnoi) which is commonly considered to be the living sister group of the tetrapods. In the present study, we used scanning electron microscopy to study cranial neural crest development in the Australian lungfish. Our results, contrary to those of Kemp, show that cranial neural crest cells do emerge and migrate in the Australian lungfish in the same way as in other vertebrates, forming mandibular, hyoid, and branchial streams. The major difference is in the timing of the onset of cranial neural crest migration. It is delayed in the Australian lungfish in comparison with their living sister group the Lissamphibia. Furthermore, the delay in timing between the emergence of the hyoid and branchial crest streams is very long, indicating a steeper anterior-posterior gradient than in amphibians. We are now extending our work on lungfish head development to include experimental studies (ablation of selected streams of neural crest cells) and fate mapping (using fluoresent tracer dyes such as Dil) to document the normal fate as well as the role in head patterning of the cranial neural crest in the Australian lungfish.

PDGFB regulates the development of the labyrinthine layer of the mouse fetal placenta

PDGFB is a growth factor which is vital for the completion of normal prenatal development. In this study, we report the phenotypic analysis of placentas from mouse conceptuses that lack a functional PDGFB or PDGFRbeta gene. Placentas of both types of mutant exhibit changes in the labyrinthine layer, including dilated embryonic blood vessels and reduced numbers of both pericytes and trophoblasts. These changes are seen from embryonic day (E) 13.5, which coincides with the upregulation of PDGFB mRNA levels in normal placentas. By E17, modifications in shape, size, and number of the fetal blood vessels in the mutant placentas cause an abnormal ratio of the surface areas between the fetal and the maternal blood vessels in the labyrinthine layer. Our data suggest that PDGFB acts locally to contribute to the development of the labyrinthine layer of the fetal placenta and the formation of a proper nutrient-waste exchange system during fetal development. We point out that the roles of PDGFB/Rbeta signaling in the placenta may be analogous to those in the developing kidney, by controlling pericytes in the labyrinthine layer and mesangial cells in the kidney.

Neurotrophin-7: a novel member of the neurotrophin family from the zebrafish

A novel member of the neurotrophin family, zebrafish neurotrophin-7 (zNT-7), was isolated from the zebrafish Danio rerio. The amino acid sequence of zNT-7 is more closely related to that of fish nerve growth factor (NGF) and neurotrophin-6 (NT-6) than to that of any other neurotrophin. zNT-7 is, however, equally related to fish NGF and NT-6 (65% and 63% amino acid sequence identity, respectively) indicating that it represents a distinct neurotrophin sequence. zNT-7 contains a 15 amino acid residue insertion in a beta-turn region in the middle of the mature protein. Recombinant zNT-7 was able to bind to the human p75 neurotrophin receptor and to induce tyrosine phosphorylation of the rat TrkA receptor tyrosine kinase, albeit less efficiently than rat NGF. zNT-7 did not interact with rat TrkB or TrkC, indicating a similar receptor specificity as NGF. We propose that a diversification of the NGF subfamily in the neurotrophin evolutionary tree occurred during the evolution of teleost fishes which resulted in the appearance of several additional members, such as zNT-7 and NT-6, structurally and functionally related to NGF.

Characterization of human neutrophils adherent to organic polymers

The adherence of human neutrophils to surfaces from organic polymers (Pellethane, two types of polyvinyl chloride (PVC), polypropylene and polyethylene) is associated to a different extent with O2- formation. No comparable differences were observed for the liberation of the granular enzyme elastase. Only cells attached to Pellethane responded strongly after a second stimulation by opsonized zymosan, N-formyl-methionyl-leucyl-phenylalanine (FMLP) and aggregated IgG. The expression of related antigens on adherent cells was measured by a cell-ELISA (enzyme-linked immunosorbent assay). Cells adherent to five various untreated organic polymers show no differences of their Fc gamma- and C3bi-receptors. A considerable increase of all investigated cellular antigens was observed for neutrophils adherent to films precoated with autologous plasma. The adherence rates and the viability for cells adherent to different materials were similar and may not account for the observed differences in O2- production during the primary adherence reaction and a further secondary stimulation.

[Analysis of T-cell subpopulations and expression patterns of lymphocytic activation markers in patients in the early phase following kidney transplantation using laser flow cytometry]

In 10 patients after kidney transplantation the T cell subpopulations (CD4, CD8) and the number of activated lymphocytes (IL-2R and transferrin receptor+, 4F2+, HLA-DR+, CD3+) in the peripheral blood were determined. In 9 out of 9 cases with rejection a clear immune activation could observed. In patients with CMV-associated rejection crisis the CD4/CD8 ratio was significantly higher compared with patients with rejection crisis but without CMV infection. In all patients with CMV infection (n = 5) an increase of activated lymphocytes was observed. In a clinical-immunological monitoring the dynamics of the CD4/CD8 ratio, the expression of activation marker (especially CD3+, HLA-DR+ and 4F2+) and the absolute number of lymphocyte subpopulations should included.

The influence of interferon-gamma and various phagocytic stimuli on the expression of MHC-class II antigens on human monocytes--relation to the generation of reactive oxygen intermediates

Human monocytes show a dose-dependent decrease of the MHC-class II antigen expression (HLA-DR and HLA-DQ) after addition of zymosan or Staphylococcus aureus Cowan I particles. Interferon-gamma did not prevent this process. The expression of MHC-class I antigens was not affected. The dose-response and kinetic curves showed individual differences. An association between the capacity to form reactive oxygen intermediates and the downregulation of MHC-class II antigen expression was observed. In addition, after digestion of the phagocytosed particles interferon-gamma could restore the MHC-class II antigen expression on the cultured monocytes. The possible biological significance of these interactions between interferon-gamma and phagocytosis for the function of monocytes/macrophages in the local inflammatory process is discussed.

The influence of phagocytic stimuli on the expression of HLA-DR antigens; role of reactive oxygen intermediates

Human peripheral blood mononuclear cells show after one day of culture with opsonized zymosan a decreased expression of HLA-DR (but not HLA-A, B, C) antigens, which can be prevented by the scavenger of reactive oxygen intermediates beta-carotene, or superoxide dismutase or indomethacin. Mononuclear cells of a patient with a heterozygous form of chronic granulomatous disease show no alterations in HLA-DR antigen expression after culture with opsonized zymosan. Possible roles of reactive oxygen intermediates or prostaglandins in the modulation of HLA-DR antigens are discussed.

Histamine and immune reactions. 3. Inhibition of early events of human lymphocyte activation by histamine

Histamine inhibits the chemiluminescence response of human lymphocytes to Concanavalin A by interfering with early triggering events. The inhibition seems to be mediated via H2 receptors, acts immediately, and is reversible by washing. A longer incubation in a histamine-containing medium induces a refractory state of the cells. The inhibitory effect described here is compared with the inhibitory action of histamine in the lymphocyte transformation test.

Circulating immune complexes after cadaver kidney transplantation

351 sera from 27 human recipients of renal allografts and 21 healthy blood donors were assayed for circulating immune complexes by the Clq solid-phase radioimmune assay. Increased Clq-binding activity (Clq-BA) was detected in pretransplant sera from 5 patients with chronic pyelonephritis (PN) and 3 patients with chronic glomerulonephritis (GN). A significant decrease of Clq-BA immediately after transplantation could not be found. 6 weeks after transplantation only 2 patients of the PN group showed increased Clq-BA. Serial studies in 17 patients with rejection crises did not show any correlation between the level of serum Clq-BA and the occurrence of rejections. Furthermore, no correlation could be found between the occurrence of complement-dependent lymphocytotoxic antibodies measured by the 51Cr release technique and the level of serum Clq-BA. In contrast, our results show that the probability of graftectomy or graft failure is significantly higher, at least in the early phase after transplantation, when the serum Clq-BA is lowered for several weeks.

[Radioimmunological detection of soluble immune complexes in serum (author's transl)]

Immune complexes could be measured in sera with the use of plastfixed Clq and 125J-labeled anti-Ig-antibody. The sensitivity of the system is 0.1 microgram aggregated human IgG, the working range is between 0.1 and 10 micrograms per 0.5 ml. In 58% of the sera from patients with systemic lupus erythematosus was found an increase in the immune complex content.