Mineralization of collagen

Bradt JH, Mertig M, Teresiak A, Pompe W (1999) Biomimetic mineralization of collagen by combined fibril assembly and calcium phosphate formation. Chem Mater 11(10) 2694—2701... 

Figure 9.8 outlines how matrix vesicles increase and decrease the concentration of pyrophosphate. NTP-PPi hydrolase synthesizes pyrophosphate from stromal fluid nucleotides, mostly ATP (ATP —> AMP + PPi). Many cells secrete ATP into the extracellular fluid and it passes into the blood plasma where it affects a variety of cells independently of its function in intracellular energy metabolism. In mice, a nonfunctional ANK protein or a deletion of NTP-PPi hydrolase decreases the extracellular pyrophosphate concentration and the phenotype exhibits extensive mineralization. Thus, the hydrolysis of pyrophosphate appears to be a major function of alkaline phosphatase (TNAP) after the calcium phosphate precipitate has raptured the matrix vesicles. Rapid mineralization of collagen and the rest of the osteoid matrix ensue without a need to transport any more Ca2+ or Pi to the region. 

Phosphorylation initiates crystallization like serine-phosphorylated collagen, but the mineralization alters enamel matrix structure (nanospheres formation and degradation), unlike the mineralization of collagen matrix. 

Vandeputte, K.A., Urist, M.R., 1965. Experimental mineralization of collagen sponge and decalcified bone. Clin. Orthop. Relat. Res. 40, 48-56. 

Mechanism of Mineralization of Collagen-Based Connective Tissues... 

There are approximately 200 other proteins present in bone, though most of them are present only in trace amounts (Delmas et al., 1984 Linde et al., 1980, as cited in van Klinken, 1991). The second most common bone protein, osteocalcin, comprises 1-2 weight % of total fresh bone. Osteocalcin bonds with both the bone mineral fraction and bone collagen, but it seems to be unstable in solutions. Due to its small molecular size and strong mineral stabilization, osteocalcin can survive up to 50.000 years (C.l. Smith et al., 2005), and it may offer an alternative to the use of collagen in paleoenvironmental stable isotope research. However, osteocalcin s role and importance in this field of study has yet to be defined (Collins et al., 2002). 

Bone is an extremely dense connective tissue that, in various shapes, constitutes the skeleton. Although it is one of the hardest structures in the body, bone maintains a degree of elasticity owing to its structure and composition. It possesses a hierarchical structure and, as most of the tissues, is nanostructured in fact, it is a nanoscaled composite of collagen (organic extracellular matrix) and hydroxycarbonate apatite, (HCA, bone mineral). This nanostructure is in intimate contact with the bone cells (several microns in size), which result (at the macroscopic level) in the bone tissue. Figure 12.2 shows the bone hierarchical ordering from the bone to the crystalline structure of HCA. 

Biosynthesis and degradation of glycosaminoglycans biosynthesis of collagen, mineralization and demineralization of bone. Fatty acid synthesis and triglyceride storage in adipocytes promoted by insulin and triglyceride hydrolysis and fatty acid release stimulated by glucagon and adrenaline (epinephrine). 

Wu JJ and Eyre DR (1988) Fine powdering exposes the mineral-protected collagen of bone to protease digestion. Calcif Tissue Int 42, 243-247. 

Yamauchi M and Katz EP (1993) The post-translational chemistry and molecular packing of mineralizing tendon collagens. Connect Tissue Res 29, 81-98. 

Renal effects have been observed in both male and female rats in a chronic-duration oral study. Male Fischer 344 rats exposed to 1,4-dichlorobenzene at 150 and 300 mg/kg/day for 2 years exhibited nephropathy, epithelial hyperplasia of the renal pelvis, mineralization of the collecting tubules in the renal medulla, and focal hyperplasia of the tubular epithelium. Each of these effects was associated with hyalin droplet formation. There were also increased incidences of nephropathy in female Fischer 344 rats dosed with 1,4-dichlorobenzene at 300 and 600 mg/kg/day. Histopathologically, the nephropathy was characterized by degeneration and regeneration of the tubular epithelium, tubular dilatation with attenuation and atrophy of the epithelium, granular casts in the tubules of the outer stripe of the medulla, thickening of the basement membranes, and minimal accumulation of interstitial collagen (NTP 1987). 

Cement, dentin, and enamel are bone-like substances. The high proportion of inorganic matter they contain (about 97% in the dental enamel) gives them their characteristic hardness. The organic components of cement, dentin, and enamel mainly consist of collagens and proteoglycans their most important mineral component is apatite, as in bone (see above). 

In contrast to soft biologies, whose mechanical properties primarily depend upon the orientation of collagen fibers, the mechanical properties of mineralized tissues, or hard biologies, are more complicated. Factors such as density, mineral content, fat content, water content, and sample preservation and preparation play important roles in mechanical property determination. Specimen orientation also plays a key role, since most hard biologies such as bone are composite structures. For the most part, we will concentrate on the average properties of these materials and will relate these values to those of important, man-made replacement materials. 

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