Pyridinoline and deoxypyridinoline in the urine

The stability of the collagen matrix is ​​provided by intermolecular irreversible bonds formed between some amino acids entering the polypeptide chain of collagen. Due to the presence of the pyridine ring, the cross bonds are called pyridinoline( Pid) and deoxypyridinoline( Dpid).Pyridine linkages are present only in extracellular collagen fibrils and are characteristic of a differentiated matrix of strong types of connective tissue - bone, cartilage, dentin. They are not included in the collagen of the skin, soft tissues, so their study is more specific for assessing bone resorption.

Pyridine cross links are specific components of mature collagen. They consist of 2 N- and 2 C-propeptides( telopeptides) of type I collagen. Bone tissue is the main source of Pid of body fluids. This type of connection is also present in the cartilaginous tissue, tendons. Taking into account the more active metabolism of bone tissue than in other types of connective tissue, it is believed that the PID in the urine basically reflects the destructive processes of a physiological or pathological nature in the bones. The reference values ​​of PID and DID in urine are presented in Table.[Titz N., 1997].

Table Reference values ​​for the concentration of PID and DYPID in urine

Table Reference values ​​for the concentration of PID and DYPID in urine

Dipid is found practically exclu- sively in collagen of bone tissue, in which the ratio PID / DID corresponds to 4: 1, this ratio persists in urine,the share of Dpidum accounts for 20-22% of the total excretion level of pyridine bonds. With diseases of joints of different genesis, the ratio of PID / DID in the urine increases, in contrast to diseases that occur with the destruction of bone tissue.

For the study, Pid and Dipid recommend the study of the second morning portion of urine( from 7 to 11 hours).

The study of PID and DID in urine is shown not only to monitor the activity of resorptive processes in bone tissue, but also to evaluate the effectiveness of the treatment. Treatment is considered effective if excretion of Pid and especially Dipida decreases by 25% within 3-6 months of therapy.

The content of PID and DID in urine increases significantly with primary hyperparathyroidism and normalizes after surgical removal of parathyroid gland adenoma;the excretion of hydroxyproline during this period remains somewhat elevated.

During menopause, the content of PID and DID in urine increases by 50-100% and decreases to normal values ​​after administration of estrogens. In patients with osteoporosis of the spine, the concentration of pyridine cross links in the urine, especially Diph, correlates with the rate of bone exchange.

With hypercalcemia in patients with malignant tumors, the excretion of Pid and Dpidum with urine increases by an average of 2-3 times, and under the influence of bisphosphonate therapy, the level of pyridine bonds decreases to a lesser extent and more slowly than calcium excretion.