UDC 577.11:611.018.43 BIOCHEMICAL MARKERS OF BONE COLLAGEN TYPE I METABOLISM O. V. ZAITSEVA, S. G. SHANDRENKO, M. M. VELIKY Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv; e-mail: [email protected] T his review focuses on the analysis of diagnostic value of the major bone remodeling markers, in particular synthesis and degradation markers of collagen type I. These include carboxy- and aminoterminal telopeptide, carboxy- and aminoterminal propeptide of procollagen type I, hydroxyproline, hydroxylysine, pyridinoline and deoxypyridinoline. Their measurement allows evaluating the structural and functional conditions and also the rate of metabolic processes in the bone tissue. The advantages and disadvantages of determination of these markers in the condition of different bone diseases were examined. It is shown that determination of bone collagen type I metabolism markers is the most informative for assessment of bone resorption, formation and turnover. K e y w o r d s: collagen type I, the markers of collagen synthesis and degradation, bone. umerous bone diseases, such as osteopo- lytic activity of ALP depends on phosphate concen- rosis, osteomalacia, Paget’s disease, are tration and related to histocytological changes in the N associated with metabolism disorders and bone formation parameters [1, 3]. accompanied by substantial changes in biochemi- Three main ALP isoenzymes have been iden- cal markers of bone remodeling [1]. For diagnosing tified: placental, intestinal and isoenzyme specific and monitoring of bone diseases specific enzymes for bone (B-ALP), liver and kidneys. Bone and liver activities, mineral and organic components con- equally contribute to ALP circulation. The intestinal tent in blood are most commonly assessed. These mucosa makes it less. Methods that based on heat components enter the bloodstream in the process of stability, sensitivity to carbamide, peculiarities of their synthesis by osteoblasts and osteoclasts or their electrophoretic mobility, hydrocarbon composition formation in the osteoclasts as a result of mediated and immunochemical specificity are used for the bone resorption. Thus, changes in calcium, inorganic separate determination of individual isoenzymes. In phosphate, osteocalcin, 25-hydroxycholecalciferol particular, bone isoenzyme is thermolabile and B- (25OHD3) levels [2], alkaline and tartrate-resistant ALP activity is completely inhibited in response to acid phosphatase activities [1], collagen type I me- heat at 56 ºC for 10 min. Residual activity becomes tabolism products such as carboxy- and aminotermi- below 20% of initial activity after heating serum nal propeptides of procollagen type I, hydroxypro- sample that represents partial bone isoenzyme ac- line, hydroxylysine, pyridinoline, deoxypyridinoline tivity [4, 5]. in serum can reflect bone state. ALP activity elevation, mainly due to bone iso- Clinically the measurement of total alkaline enzyme, during extensive bone growth and in patho- phosphatase (ALP) activity and its bone isoen- logic conditions that is accompanied by abnormali- zyme are the most commonly used markers of bone ties in bone mineralization is observed. There are metabo lism disturbances. ALP is constitutively ex- osteoporosis, osteomalacia, vitamin D deficiency, pressed in osteoblasts (bone forming cells) which aluminium intoxication, hypophosphatemic rickets, catalyzes the phosphate ester hydrolysis during the hyperthyroidism, myocardial infarction, etc. This osteosynthesis and provides phosphate-ion transfer effect can also be associated with long-term use of onto organic components of bone pericellular ma- nonsteroidal anti-inflammatory drugs (allopurinol, trix. ALP is also involved in the process of phos- oral hypoglycemic agents) [3, 5]. phates elevation and their transportation to the site of Osteocalcin (bone Gla-protein) is a non-col- the hydroxyapatite crystals synthesis in bone. Cata- lagenous bone matrix protein which is prima rily ISSN 2409-4943. Ukr. Biochem. J., 2015, Vol. 87, N 1 21 огляди synthesized by mature osteoblasts, odontoblasts calcium-binding TRAP form. That is why it should and hypertrophic chondrocytes. Osteocalcin has be separated before measurement [4, 5, 8]. been found only in bones and in dentin. Three TRAP activity is elevated in patients with γ-carboxyglutamate residues in osteocalcin provide bone metastasis and other diseases accompanied by high Ca2+-ion binding affinity and stabilize the oste- extensive bone destruction, such as osteomalacia, ocalcin α-structure. This allows osteocalcin binding hyperthyroidism, Paget’s disease, long-term glu- with the hydroxyapatite. Theoretically, osteocalcin cocorticoid therapy. Like other resorption markers blood level reflects bone formation. However, owing TRAP activity is increased after oophorectomy or to post-translational metabolism one-third of osteo- the menopause [5]. calcin is presented in the intact protein form, one- Despite the fact that earlier discussed clinical third in the large N-terminal fragment form and one- markers are widely used in diagnostics, they are not third in the form of medium and small C-terminal universal for the bone conditions assessment. For an fragments. These immunoreactive osteocalcin frag- adequate diagnostics and monitoring of bone dis- ments are released into the blood and can charac- ease treatment efficacy special attention is paid to terize bone resorption process [6, 7]. the investigation of type I collagen fragments con- Osteocalcin is a valid bone remodeling marker tent in blood or urine as markers of bone formation in case of coupling between bone formation and re- and resorption. Because collagen is the major bone sorption. When remodeling process is disturbed, os- tissue protein and its amino acid composition differs teocalcin level is tightly related only to osteogenesis. from other proteins in connective tissues, biochemi- It occurs in conditions of long-term use of corticos- cal collagen metabolism markers are specific. These teroids, cancer-associated hypercalcemia, etc. It is markers allow characterizing the bone metabolic known that osteocalcin level is decreased in hypo- processes in normal and pathological conditions. thyroidism, hypoparathyroidism, and myelomatosis. It is well known that various diseases can lead to Osteocalcin in patients with acute lymphoblastic structural changes in collagen. E.g., bone collagen leukemia is decreased two times as compared with in patients with leukemia has different amino acid healthy children [7]. Serum osteocalcin elevation is composition, surface charge, content of covalently observed in primary hyperparathyroidism, hyper- bounded carbohydrate residues and polypeptide thyroidism, Paget’s disease, chronic kidney disease, chain length of molecule α-components compared postmenopausal osteoporosis [5]. However, osteocal- with normal collagen [9]. The substantial changes in cin is a widely used marker of bone formation but its collagen are specific not only for bone pathologies, short half-life in blood (~10 min) and fast excretion but also for other diseases. This makes collagen an through kidneys should be taked into account [5]. important subject for research. Five acid phosphatase (AP) isoenzymes have Numerous collagen molecule fragments been found. There are bone-, prostate-, platelets-, entering the bloodstream during the bone metabolic erythrocyte- and spleen-specific ones. Tartrate-re- lesion have been discovered. Some of them are well sistant acid phosphatase bone isoenzyme (TRAP) studied and widely used in clinical practice, while is produced only by osteoclasts. In this case TRAP the other are potentially important but require a is a specific marker of osteoclasts activity and bone more detailed research. Carboxy- and aminoterminal resorption. Methods for total AP determination and telopeptide, carboxy- and aminoterminal propeptide its isoenzymes activities have low specificity. Never- procollagen type I, pyridinoline, deoxypyridino- theless, inhibitive capability of TRAP by tartrate line, hydroxiproline and hydroxylisine are the main gives an opportunity to distinguish its activity from biochemical markers of collagen type I metabolism. activities of other phosphatases in particular eryth- The appropriateness of these markers determination rocyte- and prostate-specific isoenzymes. TRAP depends on the peculiarities of pathologies’ develop- activity measurement is also accompanied by elec- ment, difficulties of laboratory technique and in- trophoretic separation and immunoenzyme analy- formative capacity of obtained data. Therefore, this sis for accuracy improving. The use of TRAP as a review is focused on the analysis of the advantages marker of bone resorption is limited by its instability and disadvantages in clinical using of bone remode- in frozen serum and plasma samples, as well as by ling markers (resorption and formation) mainly of the presence of an enzyme inhibitor in blood. Addi- collagen type I metabolism markers in various bone tional difficulties are caused by the blood circulating pathologies. 22 ISSN 2409-4943. Ukr. Biochem. J., 2015, Vol. 87, N 1 o. v. zaitsevA, S. g. shandreNko, m. m. veliky C ollagen as a major structural helix is more elongated and less twisted. The amino element of bone acid composition of collagen is atypical for proteins. Bone tissue is one of the connective tissue Every third amino acid in the chain is glycine (its types. It performs important functions in the body, content is 33-35%). Collagen is also