Cathelicidins act as a primary defense against bacteria and other pathogens in the case of inflammation. They are able to kill bacteria and fungi, inhibit and destroy bacterial biofilms, and possess antiviral and antiparasitics properties. They can also play a role in angiogenesis, wound healing, and the regulation of apoptosis. Cathelicidins are able to directly and selectively destroy membranes of various microbes and cancer cells, but they do not attack normal cells.

Cathepsin K is a unique and potent collagenase primarily expressed in osteoclasts. Inhibition of this enzyme abrogates bone resorption, highlighting the potential clinical benefit of targeting cathepsin K activity.

Chemokines are a family of small and secreted proteins that play pleiotropic roles in inflammation-related pathological diseases including cancer. Among the identified 50 human chemokines, chemokine (C-C motif) ligand 2 (CCL2) is of particular importance in cancer development since it serves as one of the key mediators of interactions between tumor and host cells.

Chemokine (C-C motif) ligand 15 (CCL15) is a small cytokine belonging to the CC chemokine family that is also known as leukotactin-1, MIP5 and HCC-2. CCL15 is expressed i liver, small intestine, colon, and in certain leukocytes and macrophages of the lung. It is chemotactic for neutrophils, monocytes, and lymphocytes and elicits its effects by binding to cell surface chemokine receptors like CCR1 and CCR3.

Chemokine (C-C motif) ligand 18 (CCL18) is a small cytokine belonging to the CC chemokine family. The receptor for CCL18 has been identified in humans only recently, which will help scientists understand the molecule's role in the body.

CCL18 is produced and secreted mainly by innate immune system, and has effects mainly on the adaptive immune system.

Non-enzymatic chitinase-3 like-protein-1 (CHI3L1) belongs to glycoside hydrolase family 18. It binds to chitin, heparin, and hyaluronic acid, and is regulated by extracellular matrix changes, cytokines, growth factors, drugs, and stress. CHI3L1 is synthesized and secreted by a multitude of cells including macrophages, neutrophils, synoviocytes, chondrocytes, fibroblast-like cells, smooth muscle cells, and tumor cells. It plays a major role in tissue injury, inflammation, tissue repair, and remodeling responses.

The circulatory level of CAF may represent an early indicator of NMJ dismantling and muscle fiber denervation, which signals the onset of sarcopenia.

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.

Cartilage tissue mainly consists of type II collagen which forms the fibrillar structure of the extracellular matrix. Type II collagen is constituted by the association of three identical α1 chains in a triple helix except at the two ends, in the N- and C-telopeptides. Proteolytic cleavage of type II collagen involves several proteases including matrix-metalloproteases (MMPs) and cathepsins (Cats) which are synthesized by the chondrocytes and synovial cells in response to cytokines and growth factors. CTXII is a product of degradation coming from Type II collagen. It is composed of a crosslap.

Dickkopf-1 (DKK1) is a soluble inhibitor of Wnt/β-catenin signaling that is required for embryonic head formation in vertebrate development. DKK1 regulates Wnt signaling pathway by binding to lipoprotein-related protein-5/6 (LRP5/6) and Kremen proteins and induces LRP endocytosis, which prevents the formation of Wnt-Frizzled-LRP5/6 receptor complexes. This allows entry of β-catenin into the nucleus where it interacts with members of T cell factor (TCF) family, which regulate Wnt target genes that are essential for embryonic development and tumorigenesis.

Erythropoietin (Epo) controls a variety of signal transduction pathways during oxidative stress. The main function of Epo and its receptor (EpoR) is the stimulation of erythropoiesis.

Fibroblast growth factor 21 (FGF21) is a hormone that regulates important metabolic pathways. FGF21 is expressed in several metabolically active organs and interacts with different tissues. Striated muscles have been found to be an important source of FGF21.