L-Histidine decarboxylase protein and activity in rat brain microvascular endothelial cells

Objective and Design: L-Histidine decarboxylase (HDC) is the primary enzyme regulating histamine biosynthesis. This study was carried out to examine whether the cultured rat brain microvascular endothelial cells (BMEC), which constitute the blood-brain barrier (BBB), have the ability to form histamine, and whether HDC mRNA is expressed in rat BMEC. Material: Male, 3-week-old Wistar rats were used. For in vitro studies, rat BMEC were isolated from rat brains, and subculture cells were grown on collagen-coated culture flask and slide. Methods: HDC assay, immunofluorescence analysis and expression of HDC mRNA by RT-PCR were performed in rat BMEC. Results: The HDC activity of the BMEC was estimated to be 0.14 ± 0.05 p mol/min/mg protein. This activity was completely inhibited by (S)-α-fluoromethylhistidine, a specific inhibitor of HDC. Using a polyclonal anti HDC antibody and immunofluorescence microscopy, we confirmed the presence of HDC protein in rat BMEC. RT-PCR also showed the expression of HDC mRNA in rat BMEC. Conclusions: L-Histidine uptaken by rat BMEC was shown to be converted to histamine, suggesting that HDC plays an important role in BBB.