E. Gineyts et al., Racemization and isomerization of type I collagen C-telopeptides in human bone and soft tissues: assessment of tissue turnover, BIOCHEM J, 345, 2000, pp. 481-485
Urinary excretion of the type I collagen C-telopeptide (CTx) has been shown
to be a sensitive index of the rate of bone resorption, The human type I c
ollagen sequence A(1209)HDGGR(1214) Of CTX can undergo racemization of the
aspartic acid residue Asp(1211) and isomerization of the bond between this
residue and Gly(1212) These spontaneous non-enzymic chemical reactions take
s place in vivo in bone, and the degree of racemization and isomerization o
f CTx molecules may be an index of the biological age and the remodelling o
f bone. The aim of the present study was to investigate the degree of racem
ization and isomerization of type I collagen in human connective soft tissu
es, in order to estimate the rate of collagen turnover in adult tissues and
compare it with that of bone. We also performed a systematic evaluation of
the pyridinium cross-link content in adult human tissues. Using antibodies
raised against the different CTx forms, we found that bone and dermis are
the tissues that show most racemization and isomerization. The type I colla
gen of arteries, lung, intestine, kidney, skeletal muscle and heart shows s
ignificantly less racemization and isomerization than that of bone, suggest
ing that these soft tissues have a faster turnover than bone. We also found
that pyridinoline and, to a lesser degree, deoxypyridinoline are distribut
ed throughout the different tissues investigated. Because bone type I colla
gen is characterized by a high degree of both racemization/isomerization an
d deoxypyridinoline crosslinking, the concomitant assessment of these two p
osttranslational modifications is likely to result in a highly specific mar
ker of bone resorption.