The in vitro osteoclastic degradation of nacre.

Osteoclast activity was studied on nacre, the mother of pearl (MOP) in order to assess the plasticity of bone resorbing cells and their capacity to adapt to a biomineralized material with a different organic and mineral composition from that of its natural substrate, bone. Pure MOP, a natural biomineralized CaCO(3) material, was obtained from Pinctada oyster shell. When implanted in the living system, nacre has proven to be a sustainable bone grafting material although a limited surface degradation process. Osteoclast stem cells and mature osteoclasts were cultured on MOP substrate and osteoclast precursor cells were shown to differentiate into osteoclasts capable of resorbing nacre substrate. However, analysis of the organization of the cytoskeleton showed that both a sealing zone and a podosome structure were observed on the nacre substrate. Moreover, MOP resorption efficiency was consistently found to be lower than that of bone and appeared to be a limited process.

Identification of calconectin, a calcium-binding protein specifically expressed by the mantle of Pinctada margaritifera.

Nacre or mother-of-pearl in the shell of Pinctada margaritifera is composed of 95-99% calcium carbonate and 1-5% organic matrix. In this study, we developed an original technique to characterize the genes differentially expressed in nacre-forming cells (NFC) by combining suppression subtractive hybridization (SSH), to establish a cDNA subtractive library, with rapid amplification of cDNA ends (RACE)-PCR. Seventy-two specific cDNA sequences have been obtained so far. These include a protein containing two EF-hand Ca2+-binding domains which was completely sequenced after amplification by RACE-PCR. Its specific expression as well as the specificity of the SSH method was confirmed by semi-quantitative RT-PCR on NFC and mantle cells.

Aroma analysis of fresh and preserved onions and leek by dual solid-phase microextraction-liquid extraction and gas chromatography-mass spectrometry.

The lachrymatory factor (thiopropanal-S-oxide) was directly analysed on fresh onion (Allium cepa) juice by solid-phase microextraction (polyacrylate fibre) using a fast routine GC-MS method on a 10 m x 0.32 mm I.D. (4 microm thick polydimethylsiloxane film) column with splitless mode injection. The identification and quantification of thiosulphinates and zwiebelanes were obtained on the same juice extracted by diethyl ether after 80 min maceration using the same GC-MS method. Selected ion recording enhanced the differentiation possibilities and the detection limits. This dual method was used to evaluate flavour differences between onion and shallot varieties as it provides accurate profiles of all initially formed compounds. Moreover, this method allowed us to compare qualitatively and quantitatively transformed products: frozen, freeze-dried powders and sterilised products. Excepting the lachrymatory factor, frozen onion compounds were similar compared to those of fresh onion sample. Conversely, the other transformed samples have lost most of the initially formed compounds and produced mainly di- and trisulphides corresponding to the degradation of thiosulphinates and zwiebelanes. These dramatic changes can explain the very different flavours of these manufactured products compared to fresh material.