Delta-12-Prostaglandin J2 (d12-PGJ2) is the ultimate metabolite of Prostaglandin D2 (PGD2). PGD2 is an unstable molecule and undergoes dehydration to form PGJ2 in aqueous solution, and is then converted to d12-PGJ2, in the presence of serum albumin or plasma. d12-PGJ2 forms a conjugate with the thiol of glutathione (GSH) and GSH suppresses the d12-PGJ2-induced HSP synthesis and subsequent inhibition of cell growth (HSPs are a set of proteins synthesized in response to heat shock or to other environmental stresses). d12-PGJ2 has been shown to stimulate alkaline phosphatase activity and calcification of human osteoblastic cells, the potency of the PGs being comparable to that of 1-a,25-dihydroxy vitamin D. d12-PGJ2 enhances the type-1 collagen synthesis in human osteoblasts during calcification. Thus, d12-PGJ2 modulates osteogenesis through induction of the syntheses of multiple proteins related to mineralization. Considering that PGD2 is a major arachidonate metabolite in bone marrow, d12-PGJ2, may be physiologically involved in the modulation of osteogenesis. d12-PGJ2 induces heme oxygenase, HO-l. Heme oxygenase is a key enzyme in heme catabolism, oxidatively clearing heme to yield biliverdin, iron and carbon monoxide. The biological function of this enzyme is the conversion of potentially toxic heme to bile and the recovery of the iron. Furthermore, carbon monoxide produced on the enzymatic degradation of heme has been suggested to function as a neural messenger. Two isozymes of heme oxygenase, HO-l and HO-2, have been identified. HO-2 is constitutively expressed, while HO-l is drastically induced in response to a variety of stresses, including heavy metals, heat shock and UV irradiation. (PMID: 8777585)Prostaglandins are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes), and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent, able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis, through receptor-mediated G-protein linked signalling pathways.