Molecular Quantity Variations in Human-Mandibular-Bone Osteoid

Abstract

Osteoid is a layer of new-formed bone that is deposited on the bone border during the process of new bone formation. This deposition process is crucial for bone tissue, and flaws in it can lead to bone diseases. Certain bone diseases, i.e. medication related osteonecrosis, are overexpressed in mandibular bone. Because mandibular bone presents different properties than other bone types, the data concerning osteoid formation in other bones are inapplicable for human-mandibular bone. Previously, the molecular distribution of other bone types has been presented using Fourier-transform infrared (FTIR) spectroscopy. However, the spatial distribution of molecular components of healthy-human-mandibular-bone osteoid in relation to histologic landmarks has not been previously presented and needs to be studied in order to understand diseases that occur human-mandibular bone. This study presents for the first time the variation in molecular distribution inside healthy-human-mandibular-bone osteoid by juxtaposing FTIR data with its corresponding histologic image obtained by autofluorescence imaging of its same bone section. During new bone formation, bone-forming cells produce an osteoid constituted primarily of type I collagen. It was observed that in mandibular bone, the collagen type I increases from the osteoblast line with the distance from the osteoblasts, indicating progressive accumulation of collagen during osteoid formation. Only later inside the collagen matrix, the osteoid starts to mineralize. When the mineralization starts, the collagen accumulation diminishes whereas the collagen maturation still continues. This chemical-apposition process in healthy mandibular bone will be used in future as a reference to understand different pathologic conditions that occur in human-mandibular bone.

Keywords: Bone FTIR; Bone autofluorescence; Bone modeling and remodeling; Collagen; Matrix mineralization.

Fig. 1

Schematic image (a) and autofluorescence image (b) of osteonal-bone osteoid and new bone with alignment of osteoblasts (Ob) adjacent to the border of osteoid, osteoid (O) consisting of a growth zone (GZ, light blue feature) and mineralizing front (MFr, bright yellow-white feature) and mineralized cortex (Ct) represented in a blue color in autofluorescence image (b) and in purple in schematic image (a)

Fig. 2

FTIR-absorption spectra of bone tissues, representative of variation spectra in all osteons of all biopsies, inside osteoid and new bone as a function of the distance from osteoblast line to deep cortex. a Autofluorescence image of an osteon with a color bar (from violet to dark red) indicating the anatomic locations of tissues observed in autofluorescence image, possessing the corresponding colored-FTIR spectrum presented in (b) and (c) (Ob osteoblasts, GZ growth zone, MFr mineralizing front, Ct near, middle and deep cortex)

Fig. 3

Variations in organic absorption bands and indexes representative of all osteon of all biopsies. a Variation of collagen-subband intensity (at 1338 cm⁻¹), Pyr (at 1660 cm⁻¹), deH-DHLNL (1690 cm⁻¹) and DPD (1680 cm⁻¹) intensity, and magnitudes of indexes: XLR (1660/1690) and Pyr/DPD (1660/1680) according to the anatomic distance from the osteoblasts. b Two-dimensional distribution of collagen-subband intensity (at 1338 cm⁻¹) represented by FTIR equilevel lines juxtaposed on the corresponding autofluorescence color image. The equilevel lines represent the magnitude of absorption in FTIR, i.e. the amount of collagen content at each location

Fig. 4

Variations in inorganic absorption bands and indexes. a Variation of the phosphate absorption obtained by integrating area from 950 to 970 cm⁻¹ (phosphate ${\nu }_1$ ${\text{PO}}_4^{3-}$), of the subband at 871 cm⁻¹ represents B-type carbonate’s absorption, and of the subband at 880 cm⁻¹ represents A-type carbonate’s absorption and variations in magnitude of inorganic indexes: APS: 1130/1096, XST (1030/1020), CM (1030/1110) and MM according to the anatomic distance from the osteoblasts (Ob). b Two-dimensional distribution of phosphate-subband intensity represented by FTIR equilevel lines juxtaposed on the corresponding autofluorescence color image. The equilevel lines represent the magnitude of absorption in FTIR, i.e. the amount of phosphate content

Fig. 5

Collagen (at 1338 cm⁻¹) and phosphate (at 960 cm⁻¹) absorption-front lines represented in red and black respectively over the autofluorescence image of different osteons of different biopsies