PINP is a trimeric peptide consisting of two type 1 procollagen-α1 chains and a procollagen-α2 chain which are bonded non-covalently.
PINP has very low circadian and biological variation, is not affected by food intake, and is very stable in serum after venepuncture.
Systemic lupus erythematosus (SLE) is characterized by high-titer serological autoantibodies, including antibodies that bind to double-stranded DNA (dsDNA). The origin, specificity, and pathogenicity of anti-dsDNA antibodies have been studied from a wider perspective. These autoantibodies have been suggested to contribute to multiple end-organ injuries, especially to lupus nephritis, in patients with SLE.
Anti-citrullinated peptide (or anti-CCP) antibodies are an essential immunological marker in the diagnosis of rheumatoid arthritis (RA) and are among the poor prognosis factors.
Several markers for CD with a progressive diagnostic accuracy have been identified over the years, but only three of them, i.e. anti-tissue transglutaminase (anti-tTG), anti-endomysial (EmA) and anti-deamidated gliadin antibodies (DGP) are currently assessed in the daily clinical practice.
Basement membranes form an anatomic barrier that contains connective tissue. They are composed of type IV collagen, laminin and proteoglycans. Anti-basement membrane antibodies bind to the non-collagen site of the α 3 chain of type IV collagen. A group of renal diseases, pulmonary diseases and perhaps others affecting different organs have long been associated with the presence of antibodies directed against glomerular basement membrane (GBM), alveolar basement membrane and tubular basement membrane.
Among the Coeliac Disease markers that have been identified over the years, only three are currently used in clinical practice, i.e., anti-tissue transglutaminase (atTG) IgA, anti-endomysial (EmA) IgA, and anti-deamidated gliadin (DGP) antibodies IgA and IgG.
Bone-specific alkaline phosphatase (BAP) is synthesized by the osteoblasts and is presumed to be involved in the calcification of bone matrix, though its precise role in the formation process is unknown. In the serum of most healthy individuals, bone and liver isoenzymes of the tissue non-specific AP gene predominate in approximately equal proportions. ALP isoenzymes mainly exist in bones, liver, intestine, placenta, mammary glands and kidneys.
CTX is a degradation product of the type I collagen. The latter is a triple helix made up of two α1-chains and one α2-chain. The chains have a helical section thanks to the repetition, in their primary structure, of three amino acids: Gly-X-Y in which Y is often a proline or a hydroxyproline increasing the molecule stability while X can be either a proline or lysine. Triple helix structures are stabilized by covalent links. These covalent links are called cross-links. CTX is thus a degradatoion product of type 1 collagen, containing a cross-lap.
Osteocalcin, which is a major γ-carboxyglutamic acid (Gla) protein, is the most abundant non-collagenous protein in bone. Pre-pro-osteocalcin is initially synthesized. Carboxylated osteocalcin (Gla osteocalcin) exhibits high affinity to Ca2+ and adopts an α-helical conformation by binding to Ca2+, whereas uncarboxylated osteocalcin (Glu osteocalcin) has no affinity to Ca2+. Based on the relationship between the appearance of osteocalcin and mineralization, in addition to its unique hydroxyapatite-binding properties, Gla osteocalcin has also been implicated in mineralization. Gla osteocalcin was reported to inhibit hydroxyapatite growth in mineralization. Previous studies also demonstrated that it functions as a chemoattractant of osteoclast precursors.
Acid phosphatase is a ubiquitous lysosomal enzyme. Bone acid phosphatase is resistant to l(+)-tartrate. Tartrate-resistant acid phosphatase (TRAP) is a group of enzymes synthesized mainly in bone spleen and lungs. Other acid phosphatases are present in many other tissues (e.g., prostate, erythrocytes, macrophages, and platelets). The fraction of TRAP that is most specific of the osteoclasts is the subform b of the isoenzyme 5 (TRACP5b).