Can a continuous mineral foam explain the stiffening of aged bone tissue? A micromechanical approach to mineral fusion in musculoskeletal tissues.

UNLABELLED: Recent experimental data revealed a stiffening of aged cortical bone tissue, which could not be explained by common multiscale elastic material models. We explain this data by incorporating the role of mineral fusion via a new hierarchical modeling approach exploiting the asymptotic (periodic) homogenization (AH) technique for three-dimensional linear elastic composites. We quantify for the first time the stiffening that is obtained by considering a fused mineral structure in a softer matrix in comparison with a composite having non-fused cubic mineral inclusions. We integrate the AH approach in the Eshelby-based hierarchical mineralized turkey leg tendon model (Tiburtius et al 2014 Biomech. MODEL: Mechanobiol. 13 1003-23), which can be considered as a base for musculoskeletal mineralized tissue modeling. We model the finest scale compartments, i.e. the extrafibrillar space and the mineralized collagen fibril, by replacing the self-consistent scheme with our AH approach. This way, we perform a parametric analysis at increasing mineral volume fraction, by varying the amount of mineral that is fusing in the axial and transverse tissue directions in both compartments. Our effective stiffness results are in good agreement with those reported for aged human radius and support the argument that the axial stiffening in aged bone tissue is caused by the formation of a continuous mineral foam. Moreover, the proposed theoretical and computational approach supports the design of biomimetic materials which require an overall composite stiffening without increasing the amount of the reinforcing material.

HLA-B*38:55Q: a new alternatively expressed allele identified in a three-generation Italian family.

The new allelic variant HLA-B*38:55Q differs from the closest related B*38:01:01 by one nucleotide substitution at position 373 in exon 3 (TGC>CGC). This results in a difference of one amino acid at residue 101 of the HLA-B heavy chain, from a neutral-polar Cys to a basic-polar Arg, thus impairing disulphide bridge formation in the alpha-2 domain. This alteration of the secondary structure probably affects the maturation of the heavy chain and the level of surface expression, making the HLA-B*38:55Q undetectable by standard serological typing.

The role of the microvascular tortuosity in tumor transport phenomena.

The role of the microvascular network geometry in transport phenomena in solid tumors and its interplay with the leakage and pressure drop across the vessels is qualitatively and quantitatively discussed. Our starting point is a multiscale homogenization, suggested by the sharp length scale separation that exists between the characteristic vessels and the tumor tissue spatial scales, referred to as the microscale and the macroscale, respectively. The coupling between interstitial and capillary compartment is described by a double Darcy model on the macroscale, whereas the geometric information on the microvascular structure is encoded in the effective hydraulic conductivities, which are numerically computed by solving classical differential problems on the microscale representative cell. Then, microscale information is injected into the macroscopic model, which is analytically solved in a prototypical geometry and compared with previous experimentally validated, phenomenological models. In this way, we are able to capture the role of the standard blood flow determinants in the tumor, such as tumor radius, tissue hydraulic conductivity and vessels permeability, as well as influence of the vascular tortuosity on fluid convection. The results quantitatively confirm that transport of blood (and, as a consequence, of any advected anti-cancer drug) can be dramatically impaired by increasing the geometrical complexity of the microvasculature. Hence, our quantitative analysis supports the argument that geometric regularization of the capillary network improves blood transport and drug delivery in the tumor mass.

Helicobacter pylori and gastric epithelial cells: from gastritis to cancer.

Helicobacter pylori is a spiral, gram-negative rod-shaped pathogen that attaches to gastric epithelial cells in the human stomach and is a causative agent of chronic active gastritis, peptic ulcer and neoplasia. H. pylori is one of the most common pathogens afflicting humans and is the major environmental factor in the development of gastric cancer increasing from 4 to 6 folds the risk of its development. Several specific virulence factors are implicated in the mechanism of H. pylori infection like the bacterial motility; the secretion of large amounts of urease; specific adhesins for the interaction between H. pylori and the gastric surface epithelium; the traslocation into gastric ephitelial cells of the cytotoxin-associated gene A (CagA), the vacuolating cytotoxin A (VacA) and the heat shock protein HspB. Adherence of H. pylori to the gastric epithelium and secretion of interleukins are believed to be an important step in the induction of active inflammation of the mucosal layer. Several studies have demonstrated that H. pylori infection induces gastric epithelial cell proliferation activating ERK and MAPK pathways and increase of mitosis and mutations. Therefore, H. pylori infection seems to increase apoptosis, implying increased gastric epithelial cell turnover. Recently, it has been shown that H. pylori-induced apoptosis in gastric epithelial cells is mediated via the CD95-receptor/ ligand system but that TRAIL also plays an important role in this regulation.

Apoptosis and human placenta: expression of proteins belonging to different apoptotic pathways during pregnancy.

Apoptosis occurs during normal development and it is important for the right balance between the loss of old, non-functional cells and the formation of new cells in different organs and tissues. Apoptosis is triggered by different cell-type-specific signals which involve several pathways, such as mitochondrial and receptor-mediated pathways, resulting in caspase cascade activation. Several studies have suggested that apoptosis plays an important role in the normal development, remodelling and aging of the placenta. Moreover, it has been demonstrated that apoptosis increases as pregnancy progresses suggesting that it is a normal physiological phenomenon throughout gestation. In the last years, it has been hypothesized that the process known as syncytial fusion is directly or indirectly related to apoptotic events. In particular, it has been suggested that cytotrophoblast cells early express most important apoptotic proteins that translocate in the syncytiotrophoblast with the fusion. This suggests that apoptosis has a central role in the villous trophoblast turnover. Recently, another important involvement of apoptotic processes in human placenta has been demonstrated. In particular, the apoptosis, mainly through Fas-FasL or TRAIL-R-TRAIL signalling, may be a defence mechanism against rejection of the fetal allograft by maternal immune system. The whole data suggest that regulation of apoptotic events is important to allow a correct development, differentiation and function of the placenta throughout pregnancy and that an unbalance of this process leads to severe pathologies such as pre-eclampsia and intrauterine growth retardation. Therefore, due to its extensive proliferation and invasive properties, the placenta mimics a malignant tumor and represents an interesting model to evaluate those processes leading to carcinogenesis.

C-MYB, serum P-53M, genetic instability, labeling index and endoscopic findings in patients with adenoma or colorectal cancer.

Structural alterations of c-myb proto-oncogenes and serum p53 mutant level, Mitomycin C-induced chromosomal aberrations and sister chromatid exchanges and proliferative activity of mucosa (H3-thymidine -labeling index LI) are often determined to obtain more information about the diagnosis and prognosis of neoplastic and preneoplastic lesions of the colon. The aim of this study was to evaluate the endoscopic findings of a 5 year follow-up in three groups of subjects (normal, adenoma or cancer patients) and to correlate these findings with the biological alterations in the same subjects between 1990 and 1993. We analyzed 200 subjects (118 Male and 82 Female), 78 normal subjects (group A), 60 patients with adenoma (group B) and 62 with carcinoma (group C). Data regarding endoscopic lesions was collected from June 1998 to December 2000 after a 5 year follow-up and correlated with the biological alterations in the same subjects between 1990--1993. We obtained endoscopic findings from 23/137 subjects (16.8%), 6/137 (4.4%) died from other causes and 108/137 (78.8 %) were negative for lesions. The percentage of disease after 5 years is not statistically different among the three groups (groups A, B and C). There was no statistically significant association between values of the labeling index, structural alterations of c-myb, p-53-M serum levels and chromosomal aberrations and endoscopic findings in the 5 year follow-up. We conclude that the biological markers considered are not able to stratify patients in terms of risk of progression to malignant disease.