Expression and inflammatory regulation of haptoglobin gene in adipocytes.

Haptoglobin (HP) is the major hemoglobin binding protein which is synthesized mainly in the liver. It functions to prevent iron loss and kidney damage in human and other mammals. Recently, HP has been shown to possess antioxidant and angiogenic properties. As one of the major acute phase reactants, HP's levels in plasma increase significantly during inflammation, infection and malignancy. In this study, high levels of HP mRNA were found to be transcribed by adipocytes in addition to liver cells in mice. After inflammation had been induced in vivo, expression of the haptoglobin gene rose six-fold in adipose tissue, an increase compatible with that observed in the normal mouse liver. The expression of HP by adipocytes presents new directions in which HP's role as an antioxidant or as an angiogenic factor can be investigated.