Finite element analyses of human vertebral bodies embedded in polymethylmethalcrylate or loaded via the hyperelastic intervertebral disc models provide equivalent predictions of experimental strength

Quantitative computer tomography (QCT)-based finite element (FE) models of vertebral body provide better prediction of vertebral strength than dual energy X-ray absorptiometry. However, most models were validated against compression of vertebral bodies with endplates embedded in polymethylmethalcrylate (PMMA). Yet, loading being as important as bone density, the absence of intervertebral disc (IVD) affects the strength. Accordingly, the aim was to assess the strength predictions of the classic FE models (vertebral body embedded) against the in vitro and in silico strengths of vertebral bodies loaded via IVDs. High resolution peripheral QCT (HR-pQCT) were performed on 13 segments (T11/T12/L1). T11 and L1 were augmented with PMMA and the samples were tested under a 4° wedge compression until failure of T12. Specimen-specific model was generated for each T12 from the HR-pQCT data. Two FE sets were created: FE-PMMA refers to the classical vertebral body embedded model under axial compression; FE-IVD to their loading via hyperelastic IVD model under the wedge compression as conducted experimentally. Results showed that FE-PMMA models overestimated the experimental strength and their strength prediction was satisfactory considering the different experimental set-up. On the other hand, the FE-IVD models did not prove significantly better (Exp/FE-PMMA: R²=0.68; Exp/FE-IVD: R²=0.71, p=0.84). In conclusion, FE-PMMA correlates well with in vitro strength of human vertebral bodies loaded via real IVDs and FE-IVD with hyperelastic IVDs do not significantly improve this correlation. Therefore, it seems not worth adding the IVDs to vertebral body models until fully validated patient-specific IVD models become available.     

Impact of Geese on the Limnology of Lakes and Ponds from Bylot Island (Nunavut,Canada)

Arctic freshwater ecosystems are important habitats for northern wildlife. Arctic climate impact studies suggest that global change could result in major modifications and perturbations of lakes, ponds and wildlife. Most studies focus either on freshwater ecosystems or on animal populations, but few have investigated the links that exist between them. Animal populations have the potential to alter the nutrient inputs in lakes and ponds via faeces. The present study is the first to reveal the impact of an expanding Greater Snow Goose (Chen caerulescens atlantica) population on the limnology of arctic lakes and ponds. A survey of 27 freshwater ecosystems was performed on Bylot Island (Nunavut, Canada) in order to identify patterns in limnological conditions. Using a multivariate statistical approach, our study shows that the presence of birds in the catchment of lakes and ponds has an impact on their nutrient status. Concentrations of major ions that were related to the distance from the sea were the main environmental variable explaining the limnological differences observed among lakes and ponds. Nutrient variables that were mostly related to the presence of Snow Geese played a secondary but significant role. N and P concentrations were different among impacted and non‐impacted sites, underlining the impact of animal populations on northern freshwater ecosystems. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Increased protein glycation in fructosamine 3-kinase-deficient mice

Amines, including those present on proteins, spontaneously react with glucose to form fructosamines in a reaction known as glycation. In the present paper, we have explored, through a targeted gene inactivation approach, the role of FN3K (fructosamine 3-kinase), an intracellular enzyme that phosphorylates free and protein-bound fructose-epsilon-lysines and which is potentially involved in protein repair. Fn3k-/- mice looked healthy and had normal blood glucose and serum fructosamine levels. However, their level of haemoglobin-bound fructosamines was approx. 2.5-fold higher than that of control (Fn3k+/+) or Fn3k+/- mice. Other intracellular proteins were also significantly more glycated in Fn3k-/- mice in erythrocytes (1.8-2.2-fold) and in brain, kidney, liver and skeletal muscle (1.2-1.8-fold), indicating that FN3K removes fructosamines from intracellular proteins in vivo. The urinary excretion of free fructose-epsilon-lysine was 10-20-fold higher in fed mice compared with mice starved for 36 h, and did not differ between fed Fn3k+/+ and Fn3k-/- mice, indicating that food is the main source of urinary fructose-epsilon-lysine in these mice and that FN3K does not participate in the metabolism of food-derived fructose-epsilon-lysine. However, in starved animals, the urinary excretion of fructose-epsilon-lysine was 2.5-fold higher in Fn3k-/- mice compared with Fn3k+/+ or Fn3k+/- mice. Furthermore, a marked increase (5-13-fold) was observed in the concentration of free fructose-epsilon-lysine in tissues of fed Fn3k-/- mice compared with control mice, indicating that FN3K participates in the metabolism of endogenously produced fructose-epsilon-lysine. Taken together, these data indicate that FN3K serves as a protein repair enzyme and also in the metabolism of endogenously produced free fructose-epsilon-lysine.     

Hybrid origins of cultivated potatoes

Solanum section Petota is taxonomically difficult, partly because of interspecific hybridization at both the diploid and polyploid levels. The taxonomy of cultivated potatoes is particularly controversial. Using DNA sequence data of the waxy gene, we here infer relationships among the four species of cultivated potatoes accepted in the latest taxonomic treatment (S. ajanhuiri, S. curtilobum, S. juzepczukii and S. tuberosum, the latter divided into the Andigenum and Chilotanum Cultivar Groups). The data support prior ideas of hybrid origins of S. ajanhuiri from the S. tuberosum Andigenum Group (2x = S. stenotomum) × S. megistacrolobum; S. juzepczukii from the S. tuberosum Andigenum Group (2x = S. stenotomum) × S. acaule; and S. curtilobum from the S. tuberosum Andigenum Group (4x = S. tuberosum subsp. andigenum) × S. juzepczukii. For the tetraploid cultivar-groups of S. tuberosum, hybrid origins are suggested entirely within much more closely related species, except for two of three examined accessions of the S. tuberosum Chilotanum Group that appear to have hybridized with the wild species S. maglia. Hybrid origins of the crop/weed species S. sucrense are more difficult to support and S. vernei is not supported as a wild species progenitor of the S. tuberosum Andigenum Group.     

Calcium pathway through a mineralizing epithelium in the crustacean Orchestia in pre-molt: Ultrastructural cytochemistry and X-ray microanalysis

During the pre-exuvial period of the terrestrial crustacean Orchestia, the calcium of the old cuticle is almost entirely reabsorbed and stored as calcareous concretions in the lumen of the midgut posterior caeca. The elaboration of these concretions is due to transport by the caecal epithelium. With ultrastructural cytochemistry controlled by X-ray microanalysis, it can be demonstrated that the main sites of ionized or ionizable calcium are the apical microvilli and an extracellular (lateral and basal) network of channels. Direct precipitating cytochemical methods, using potassium pyroantimonate or pyrophosphate, potassium oxalate or oxalic acid, sodium fluoride, sodium tungstate, and indirect substitution methods, using lead acetate or nitrate and cobalt nitrate were comparatively used. The results are interpreted in favour of the hypothesis of an extracellular transport pathway for calcium through the lateral smooth septate junctions, in conjunction with a more classical apical transport through the microvilli.     

Fructosamine 3-kinase and other enzymes involved in protein deglycation

FN3K is a recently identified enzyme that phosphorylates both low-molecular-weight and protein-bound fructosamines. Fructosamine 3-phosphates are unstable, breaking down spontaneously to 3-deoxyglucosone, inorganic phosphate and the amino compound that originally reacted with glucose. FN3K is therefore a ‘deglycating’ enzyme. Evidence has been provided for the fact that this enzyme indeed removes a significant proportion of the fructosamine residues that form on hemoglobin in erythrocytes. Recent results obtained with FN3K-deficient mice confirm that FN3K acts as a protein deglycating enzyme in tissues.Unlike FN3K, FN3K-RP does not act on fructosamines, but it does phosphorylate ketoamines with a D configuration in C3 (ribulosamines, erythrulosamines and, with a lower affinity, psicosamines). The ketoamine 3-phosphates that are formed by FN3K-RP are also unstable and their spontaneous decomposition leads to the regeneration of a free amino group, indicating that FN3K-RP is also a protein repair enzyme. This role has been confirmed in human erythrocytes, which are rich in FN3K-RP. Remarkably, the single FN3K–FN3K-RP homologue that is present in fishes, plants and bacteria appears to be also a ribulosamine/erythrulosamine 3-kinase, indicating that the repair of ribulosamines or erythrulosamines may be more important than the removal of fructosamines.Ribulosamines and erythrulosamines most likely arise through a reaction of proteins with ribose 5-phosphate and erythrose 4-phosphate, two extremely potent glycating agents. The ribulosamine 5-phosphates and erythrulosamine 4-phosphates that are formed in this way must be dephosphorylated by a phosphatase that still needs to be identified. Glucose 6-phosphate is also a potent glycating agent, and a phosphatase acting best on protein-bound fructosamine 6-phosphates has recently been identified.In conclusion, protein deglycation appears to involve a whole set of enzymes. A key question for future investigations is why it is important to rid proteins of their sugar adducts rather than replace them with newly synthesized macromolecules.