Organic matter degradation and redistribution of sediment associated contaminants by benthic invertebrate activities

The fate of sediment associated compounds is the combined result of chemical properties and biological activities. Yet, studies simultaneously addressing the effects of biota on the redistribution and bioaccumulation of contaminants are scarce. Our aim was therefore to assess the effect of benthic invertebrate activities on organic matter degradation and the redistribution of metals and Polycyclic Aromatic Hydrocarbons (PAHs) in contaminated sediment. To this end, we introduced egg ropes of the non-biting midge Chironomus riparius into wastewater treatment plant sludge and allowed these to either develop until fourth instar larvae or to fully complete their life cycle into terrestrial flying adults. Chironomid larvae enhanced sludge degradation, resulting in increased metal concentrations in the sludge and in a flux of metals into the overlying water. Moreover, they hampered PAH degradation in the sludge. Contaminant transport from aquatic to terrestrial ecosystems with emerging invertebrates as a vector is widely acknowledged, but here we showed that biomanipulation prevailed over bioaccumulation, since due to chironomid activity, the flux of metals from the sludge into the overlying water was larger than into chironomid biomass. It is therefore concluded that contaminant-macroinvertebrate interactions are bilateral relationships driven by the interplay between macroinvertebrate traits and contaminant properties

Transepidermal water loss of NHS, FTMs and CC-FTMs.

<p>TEWL was measured over 900 second time period and plotted as mean values +SEM. Data is obtained from three independent experiments and three NHS samples.</p

Dynamics of inter-heavy chain interactions in human IgG subclasses studied by kinetic Fab arm exchange

Background: Fab arm exchange requires weak interactions between CH3 domains, such as in human IgG4. Results: CH3-CH3 interactions differ >1,000,000-fold between human subclasses and allotypes due to variations Lys/Asn-392, Val/Met-397, and Lys/Arg-409. Conclusion: For IgG2 and IgG3, but not IgG1, hinge disulfide bonds are essential to prevent half-molecule dissociation. Significance: Subclass/allotype variation in the CH3 domain can alter antibody stability and functionality. Interdomain interactions between the CH3 domains of antibody heavy chains are the first step in antibody assembly and are of prime importance for maintaining the native structure of IgG. For human IgG4 it was shown that CH3-CH3 interactions are weak, resulting in the potential for half-molecule exchange (Fab arm exchange). Here we systematically investigated non-covalent interchain interactions for CH3 domains in the other human subclasses, including polymorphisms (allotypes), using real-time monitoring of Fab arm exchange with a FRET-based kinetic assay. We identified structural variation between human IgG subclasses and allotypes at three amino acid positions (Lys/Asn-392, Val/Met-397, Lys/Arg-409) to alter the strength of inter-domain interactions by >6 orders of magnitude. Each substitution affected the interactions independent from the other substitutions in terms of affinity, but the enthalpic and entropic contributions were non-additive, suggesting a complex interplay. Allotypic variation in IgG3 resulted in widely different CH3 interaction strengths that were even weaker for IgG3 than for IgG4 in the case of allotype G3m(c3c5*/6,24*), whereas G3m(s*/15*) was equally stable to IgG1. These interactions are sufficiently strong to maintain the structural integrity of IgG1 during its normal life span; for IgG2 and IgG3 the inter-heavy chain disulfide bonds are essential to prevent half-molecule dissociation, whereas the labile hinge disulfide bonds favor half-molecule exchange in vivo for IgG

Improved epidermal barrier formation in human skin models by chitosan modulated dermal matrices

<div><p>Full thickness human skin models (FTMs) contain an epidermal and a dermal equivalent. The latter is composed of a collagen dermal matrix which harbours fibroblasts. Current epidermal barrier properties of FTMs do not fully resemble that of native human skin (NHS), which makes these human skin models less suitable for barrier related studies. To further enhance the resemblance of NHS for epidermal morphogenesis and barrier formation, we modulated the collagen dermal matrix with the biocompatible polymer chitosan. Herein, we report that these collagen-chitosan FTMs (CC-FTMs) possess a well-organized epidermis and maintain both the early and late differentiation programs as in FTMs. Distinctively, the epidermal cell activation is reduced in CC-FTMs to levels observed in NHS. Dermal-epidermal interactions are functional in both FTM types, based on the formation of the basement membrane. Evaluation of the barrier structure by the organization of the extracellular lipid matrix of the stratum corneum revealed an elongated repeat distance of the long periodicity phase. The ceramide composition exhibited a higher resemblance of the NHS, based on the carbon chain-length distribution and subclass profile. The inside-out barrier functionality indicated by the transepidermal water loss is significantly improved in the CC-FTMs. The expression of epidermal barrier lipid processing enzymes is marginally affected, although more restricted to a single granular layer. The novel CC-FTM resembles the NHS more closely, which makes them a promising tool for epidermal barrier related studies.</p></div

Expression of lipid processing enzymes in NHS, FTM and CC-FTM.

<p>Tissue sections of NHS, FTMs and CC-FTMs are analysed by immunofluorescence for the expression of lipid processing enzymes GBA, aSMase, CER-S3 and ELOVL1. Representative images show the localization (red) of GBA, aSMase and CER-S3 in the stratum granulosum, while the expression of ELOVL1 is more diffuse throughout the epidermis. Nuclei are stained blue using DAPI, the yellow dotted line indicates the dermal-epidermal junction. Scale bar represents 100μm.</p

Ceramide subclass profile in FTMs and CC-FTMs.

<p>Box and whisker plot of CER subclasses with indicated benchmark values of NHS. Significant differences in relative abundance are indicated, which are the reduction in NS and AS and an increase of NdS, NP and NH in SC of CC-FTMs compared to FTMs. Whiskers indicate the 95% confidence interval. Data is obtained from four independent experiments.</p