Sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a signaling sphingolipid. It is also referred to as a bioactive lipid mediator. Sphingolipids at large form a class of lipids characterized by a particular aliphatic aminoalcohol, which is sphingosine.

Production
Sphingosine can be released from ceramides, a process catalyzed by the enzyme ceramidase. Phosphorylation of sphingosine is catalyzed by sphingosine kinase, an enzyme ubiquitously found in the cytosol and endoplasmatic reticulum of various types of cells. S1P can be dephosphorylated to sphingosine by sphingosine phosphatases and can be irreversibly degraded by an enzyme, Sphingosine phosphate lyase.

Function
S1P is a blood borne lipid mediator, in particular in association with lipoproteins such as high density lipoprotein (HDL). It is less abundant in tissue fluids. This is referred to as the S1P gradient, which seems to have biological significance in immune cell trafficking.

Originally thought as an intracellular second messenger, it was discovered to be an extracellular ligand for G protein-coupled receptor S1PR1 in 1998. It is now known that S1P receptors are members of the Lysophospholipid receptor family. There are five described to date. Most of the biological effects of S1P are mediated by signaling through the cell surface receptors.

Although S1P is of importance in the entire human body, it is a major regulator of vascular and immune systems. In addition, it might be relevant in the skin. In the vascular system, S1P regulates angiogenesis, vascular stability, and permeability. In the immune system, it is now recognized as a major regulator of trafficking of T- and B-cells. S1P interaction with its receptor S1PR1 is needed for the egress of immune cells from the lymphoid organs (such as thymus and lymph nodes) into the lymphatic vessels. Inhibition of S1P receptors was shown to be critical for immunomodulation.

Clinical significance
The levels of S1P ( in a range of 5-40 µmol/L ) are 5 to 10 times up-regulated in ovarian cancer patients ascites. S1P at this physiological concentration stimulates migration and invasion of epithelial ovarian cancer cells but inhibits migration of normal ovarian surface epithelial cells. Most (more than 90%) ovarian cancers are arised from the epithelium of the ovary. Therefore, extracellular S1P could have an important role in cancer progression by promoting migration of epithelial ovarian cancer cells.

The drug fingolimod (FTY720), which antagonizes the S1P receptor, prevents autoimmune lymphocytes from moving from the lymphoid organs into the central nervous system. It has been shown in phase III clinical trials to reduce relapses and improve other outcomes in multiple sclerosis.

In addition, S1P modulates the proliferation of skin cells. This in particular applies to keratinocytes while fibroblasts are not addressed in this way, apart from cell growth and differentiation While S1P suppresses epidermal proliferation as the glucocorticoids do, it differs from them in so far, as proliferation of dermal fibroblasts is not reduced. In fact, S1P even activates fibroblast-derived extracellular matrix protein production. Due to the hyperproliferative action against epidermal cells, S1P has been considered as an active pharmaceutical ingredient for hyperproliferative skin diseases, in particular, psoriasis vulgaris and acne vulgaris.

Although S1P is active at very low concentrations, bioavailability of the compound in human skin is a concern. Therefore, a topical formulation based on specific drug carriers has been considered inevitable.