Apatite-collagen

Figure 10.4. Effect on apatite-collagen isotopic fractionation due to inhibition of amino acid production and preferred use of exogenous amino acids. Carnivore and herbivore, both based on C3 plants, have similar bulk isotopic composition of total edible tissues (T), leading to similar 5 C for apatite carbonate (AP). Collagen (CO) of carnivore is more enriched in Cthan that of herbivore, because of preferential utilization of amino acids derived from protein (P) of herbivore flesh in construction of carnivore s proteins. C ss = assimilated carbon.

The results of these experiments permit more detailed reconstruction of the isotopic composition of prehistoric human diets. The bulk diet value can be reconstructed from the apatite value minus 9.4%c, and that of dietary protein can be reconstructed from the apatite-collagen difference (5 C Specifically, a difference of 4.4%c occurs when the protein and bulk diet have the same value. A spacing of less than 4.4%o indicates that dietary protein is isotopically enriched relative to whole diet. If the spacing is greater than 4.4%c, then dietary protein is isotopically lighter than whole diet. 

Bone is a natural composite of apatite-collagen. So a composite of polymer matrix containing bioactive particulate filler is a natural choice for substituting cortical bone. Bone substitutes can be easily made by using hydroxyapatite (HA) particles as the bioactive component because of its close similarity with bone apatite and its excellent bioactivity. So a composite made of HA with polymer matrix provides... 

For bone tissue regeneration, three-dimensional porous biomimetic hydroxy-apatite/collagen composites crosslinked by mTGase were developed [23]. Again, the enzyme was used with the main purpose to increase the mechanical resistance of the organic matrix. The obtained composites supported adhesion, proliferation, viability and differentiation of MG63 osteoblast-like cells and human umbilical vein endothelial cells (Fig. 2). 

Y. Chen, A.F.T. Mak, M. Wang, J. Li, and M.S. Wong, PLLA scaffolds with biomimetic apatite coating and biomimetic apatite/collagen composite coating to enhance osteoblast-like cells attachment and activity. Surf Coat. Tech., 201 (3-4), 575-580, 2006. 

M. Otsuka, H. Nakagawa, K. Otsuka, A. Ito, and W. I. Higuchi, Drug release from a three-dimensionally perforated porous apatite/collagen composite cement. Bioceramics Development and Applications, 2, D110189,2012. 

M. Otsuka, Development of skeletal drug delivery system based on apatite/collagen composite cement, in B. Ben-Nissan, ed.. Advances in Calcium Phosphate Biomaterials, Springer Series in Biomaterials Science and Engineering, vol. 2, pp. 355-372,2014. 

M. Otsuka, and R. Hirano, Bone cell activity responsive drug release from biodegradable apatite/collagen nano-composite cements - In vitro dissolution medium responsive vitamin K2 release. Colloid. Surface. B Biointerfaces, 85 (2), 338-342, 2011. 

Doi, Y., Horiguchi, T., Moriwaki, Y., Kitago, H., Kajimoto, T. and Iwayama, Y. (1996) Formation of apatite-collagen complexes. Journal of Biomedical Materials Research, 31, 43-9. 

Li, X., Chang, J., 2008. Prqraration of bone-like apatite-collagen nanocomposites by a biomimetic process with phosphorylated coUagen. Journal of Biomedical Materials Research. Part A 85 (2), 293-300. Available at http //www.ncbi.nlm.nih.gov/pubmed/17688292 (accessed 10.10.14.). 

The 8 C values of the Preclassic humans at Cuello (Table 2.1) average -12.9 0.9%o (n = 28) in collagen, -9.8 1.0 in bone apatite (n = 16), and -8.7 2.3%o in tooth enamel apatite (n = 33) the S N values in collagen average 8.9 1.0%o (n = 23). The discrepancy in the number of specimens is due to the fact that more teeth were available than post-cranial material, while some of the specimens contained insufficient collagen to measure the nitrogen isotope ratios. Additional bone apatite analyses are in progress. 

Lee-Thorp, J.A., Sealy, J.C. and van der Merwe, N.J. 1989 Stable carbon isotope ratio differences between bone collagen and bone apatite, and their relationship to diet. Journal of Archaeological Science 16 585-599. 

Tykot, R.H., van der Merwe, N.J. and Hammond, N. 1996 Stable isotope analysis of bone collagen, bone apatite, and tooth enamel in the reconstruction of human diet. A case study from Cuello, Belize. In Orna, M.V., ed., Archaeological Chemistry Organic, Inorganic, and Biochemical Analysis. ACS Symposium Series 625, Washington, DC, American Chemical Society 355-365. 

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

One further difference between the tissues should be noted briefly—that of turnover—which holds implications for the nature of the isotopic signal recorded and its interpretation. Bone is constantly resorbed and reformed during life, i.e., it turns over , whereas enamel and dentine do not, although secondary dentine can be later accreted. Enamel and dentine form during a discrete period in the individual s life. This means that carbon isotope dietary signals in bone, for both collagen and apatite, reflect diet integrated over years, whereas those in enamel and dentine increments reflect diet at time of formation. 

Several authors, beginning with Kmeger and Sullivan (1984), have noted a smaller 8 C fractionation between collagen and apatite (A,p.co) in carnivores as compared to herbivores. These authors presented a model to accoimt for this, and the observation was confirmed in studies by Lee-Thorp and van der Merwe (1991) of populations of carnivores and herbivores that differed widely in their intake of C3- and C4-based foods. Here 1 shall show how this effect might be accounted for as a consequence of partial blocking of AA synthesis from lipids. 

Figure 10.2. Schematic diagram showing how restricted conversion of fatty acids to amino acids influences the fractionation between collagen and CO3 of bone apatite LI = lipid component, PR = protein, T = total isotopic composition AP = COj component of apatite, a) Herbivorous diet (Cj plants only) b) Carnivorous diet, assuming rj = 1 (no barrier to fatty acid conversion to AAs) c) Carnivorous diet, assuming ri < 1 note that carbonate-collagen fractionation is smaller.

On the other hand, the scrambled model of carbon sourcing does not seem to be applicable when we consider the metabolic fate of fatty acids. We find that there are partial barriers to the movement of FA-derived carbon atoms into the synthesis of proteins. This partial restriction leads us to expect a trophic level effect in the fractionation between collagen and bone apatite or respired CO2 of which apatitic carbonate is a sample. The magnitude of the fractionation depends on two separate fractionation factors which cannot be disentangled by analyses of bone samples alone. 

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