Is semicarbazide-sensitive amine oxidase in blood plasma partly derived from the skeleton?

Semicarbazide-sensitive amine oxidases (SSAOs) are widely expressed copper-containing enzymes. One enzyme of this family have high specific activity towards benzylamine and is present in human blood plasma. This enzyme is altered in several diseases, for instance in diabetes. Presently it is unclear where the plasma SSAO is synthesized. Previous autoradiographic studies have suggested that SSAO may be expressed in bone tissue. In the current study we have analyzed levels of SSAO in serum from cases with 'skeletal disease', i.e. patients with severe skeletal metastases of prostate cancer and subjects having recent fractures. Interestingly, subjects with metastases showed significantly elevated levels of SSAO in serum compared to individuals having prostate cancer without skeletal metastases. It is speculated that, at least in part, SSAO in the blood stream may be derived from bone tissue.