Fourier Transform Infrared Spectroscopic Assessment of Changes in Composition of Proteoglycans and Collagen in Developing Human Fetal Tarsal Bones

The proteoglycan and collagen composition of cartilage is known to change during fetal and postnatal development. The current report represents the first attempt to semi-quantitatively determine the changes in the composition of developing human fetal cartilage. Human fetal talus bones were obtained from late 2^nd and 3^rd trimester specimen. Fetal bones are comprised of an intramembranous tissue commonly referred to as cartilage anlagen. During maturation the anlagen develops an ossific nucleus. Fourier Transform Infrared Spectroscopy (FT-IRS) and Fourier Transform Infrared Imaging Spectroscopy (FT-IRIS) were used to assess the changes in composition relating to tissues main constituents, collagen (COL) and proteoglycan (PG). FT-IRS was used to obtain average values of composition across the entire anterior-posterior length of each bone. Relative percent composition values of COL and PG were calculated by multivariate least-squares analysis of model compound spectral features associated with COL (Amide I spectral absorbance) and PG (C-O-C sugar absorbance). It was shown that PG/Amide I values decreases from 4.9 +/−3.4 to 2.9 +/−3.2 over development. These values were translated to a relative percent compositional drop of PG from 49.9% +/−16.2% to 36.4% +/−8.1%. FT-IRIS was used to observe the spatial changes in composition from the subchondral region to the articulating surfaces. Collagen was observed to be distributed away from the articulating surfaces with increase in development. Proteoglycans were observed to have uniform concentrations with a marked decrease in PG across developmental stages. A noticeable benchmark in development is the ossific nucleus which was absent in the 2^nd trimester. The findings of the current study demonstrate that cartilage anlage contains approximately triple the amount of proteoglycan in the 2^nd trimester as compared to that previously reported in hyaline articular cartilage. The proteoglycan decreases over development, resulting in double the proteoglycan in the 3^rd trimester as compared to previously reported adult values. No site-specific, macroscopic (FT-IRS), differences in PG content were found while microscopic assessment (FT-IRIS) observed heterogeneity with marked changes in PG content.