Age-related accumulation of pentosidine in aggrecan and collagen from normal and degenerate human intervertebral discs

Abstract

During aging and degeneration, many changes occur in the structure and composition of human cartilaginous tissues, which include the accumulation of the AGE (advanced glycation end-product), pentosidine, in long-lived proteins. In the present study, we investigated the accumulation of pentosidine in constituents of the human IVD (intervertebral disc), i.e. collagen, aggrecan-derived PG (proteoglycan) (A1) and its fractions (A1D1-A1D6) in health and pathology. We found that, after maturity, pentosidine accumulates with age. Over the age range studied, a linear 6-fold increase was observed in pentosidine accumulation for A1 and collagen with respective rates of 0.12 and 0.66 nmol x (g of protein)(-1) x year(-1). Using previously reported protein turnover rate constants (k(T)) obtained from measurements of the D-isomer of aspartic residue in collagen and aggrecan of human IVD, we could calculate the pentosidine formation rate constants (k(F)) for these constituents [Sivan, Tsitron, Wachtel, Roughley, Sakkee, van der Ham, DeGroot, Roberts and Maroudas (2006) J. Biol. Chem. 281, 13009-13014; Tsitron (2006) MSc Thesis, Technion-Israel Institute of Technology, Haifa, Israel]. In spite of the comparable formation rate constants obtained for A1D1 and collagen [1.81+/-0.25 compared with 3.71+/-0.26 micromol of pentosidine x (mol of lysine)(-1) x year(-1) respectively], the higher pentosidine accumulation in collagen is consistent with its slower turnover (0.005 year(-1) compared with 0.134 year(-1) for A1D1). Pentosidine accumulation increased with decreasing buoyant density and decreasing turnover of the proteins from the most glycosaminoglycan-rich PG components (A1D1) to the least (A1D6), with respective k(F) values of 1.81+/-0.25 and 3.18+/-0.37 micromol of pentosidine.(mol of lysine)(-1) x year(-1). We concluded that protein turnover is an important determinant of pentosidine accumulation in aggrecan and collagen of human IVD, as was found for articular cartilage. Correlation of pentosidine accumulation with protein half-life in both normal and degenerate discs further supports this finding.

Molecular Basis of Intervertebral Disc Degeneration and Herniations: What Are the Important Translational Questions?

“…Higher levels of oxidized proteins and transcription factors activated by oxidative stresses have been found in older discs compared with young discs [64]. Other evidence of age-related oxidative damage in the disc is the presence of advanced glycalation endproducts, which are molecules produced by nonenzymatic glycosylation and oxidation of proteins and lipids [6,83]. The most common advanced glycalation endproducts in the disc are pentosidine and carboxymethyl-lysine.…”

Tissue engineering and the intervertebral disc: the challenges

“…However, disc biomechanical behaviour ultimately depends on the organisation and composition of the macromolecules which make up the tissue; full physiological responses to external loads may not thus be achieved in a tissueengineered disc until concentrations and network architecture of the various macromolecules reach those found in vivo. Matrix production and turnover is slow in normal and degenerate human discs with aggrecan half-lives being *12 and *8 years, respectively and that of collagen [90 years [105,106]. In animals, repair of the outer layers of the annulus is similarly slow [66].…”

“…Even though future developments in MRI might give more accurate information about the composition of the disc, because turnover of matrix is very slow [105,106], MRIs cannot give information on the current state of the cells. Indeed, even if most of the disc cells were dead, it might be several years before the composition of the tissue changed enough for it to be detected biochemically by MRI.…”

Aspartic Acid Racemization and Collagen Degradation Markers Reveal an Accumulation of Damage in Tendon Collagen That Is Enhanced with Aging

“…The most rapidly racemizing amino acid is aspartic acid (10), making it most suitable for aging biological tissues. Thus measurement of the ratio of D-aspartate (D-Asp) to L-aspartate can be used to calculate protein half-life (11)(12)(13)(14). Another marker widely accepted to give a good indication of protein age is the AGE pentosidine, which accumulates linearly with age in tissues with a low rate of matrix turnover, and also shows strong correlation with D-Asp measurements (15).…”