Clearance of human diamine oxidase via a cellular receptor

The human protein diamine oxidase (hDAO) is important for histamine inactivation. Histamine is a small substance, which contributes to symptoms during allergic reactions like nausea, headache, runny nose, and in more severe cases low blood pressure and fortunately rarely fatal hypersensitivity reactions. Medications blocking histamine are not powerful enough to prevent severe symptom development. Human DAO might be used as a new treatment option for histamine-mediated symptoms, but there are too many unknowns about DAO. We therefore produced hDAO in animal cells. When the protein was injected into animals it rapidly disappeared from the circulation. We found that DAO binds to sugar structures on the cell surface, so- called heparan sulfate proteoglycans (HSPGs) and is then taken up by cells. In addition, a specific docking protein, a so-called receptor, seems to be involved in the uptake. We could identify a potential receptor candidate. Furthermore, our experiments showed that DAO is not degraded but that it exits the cells by a mechanism called transcytosis. In this project we will investigate the interaction between DAO, the receptor candidate and HSPGs. Then we will identify the binding site for DAO on the receptor. Finally, we will investigate whether the receptor is responsible for the short half-life of DAO in the blood in rats and mice. This will be accomplished by blocking the binding of DAO by using animals that lack the receptor. The novel findings of this study will allow us to better understand, how the human body inactivates histamine. The generated knowledge will be essential for the development of recombinant hDAO as a treatment approach for human diseases with excess histamine. Successful completion of this project will move us closer to reach this important goal.