Gyrate atrophy of the choroid and retina is a chorioretinal degeneration caused by hyperornithinemia and a deficiency of
ornithine-delta-
aminotransferase (OAT). We recently showed that
ornithine exhibits cytotoxicity to human
retinal pigment epithelial (RPE) cell lines treated with the OAT inhibitor,
5-fluoromethylornithine (5-FMOrn), and suggested that this system may be an in vitro model of
gyrate atrophy. In the present study, in order to apply this system to primary cultured RPE cells, we freshly prepared RPE cells from bovine eyes and studied the effect of
ornithine on cell damage. Two phenotypes, epithelioid and fusiform, which coexisted in the primary culture and epithelioid phenotype cells, but not fusiform ones, were severely damaged and partially detached from the substrate by 10 m m
ornithine and 0.5 m m 5-FMOrn. Neither
ornithine nor 5-FMOrn alone exhibited such cytotoxicity to both phenotypes of RPE cells.
Proline significantly prevented the
ornithine-induced cytotoxicity. Epithelioid and fusiform phenotypes isolated from the primary culture showed different distribution of actin filaments. A combination of
ornithine and 5-FMOrn time-dependently inhibited [(3)H]
thymidine incorporation in the epithelioid, but not fusiform, cells.
Proline prevented the inhibition of [(3)H]
thymidine incorporation by
ornithine in 5-FMOrn-treated epithelioid cells. Furthermore, l -azetidine-2-carboxylic
acid, a
collagen synthesis inhibitor, reduced [(3)H]
thymidine incorporation in epithelioid, but not fusiform, cells, which was reversed by
proline. These results demonstrate that the epithelioid phenotype of bovine RPE cells becomes susceptible to
ornithine following inactivation of OAT. The phenotypic cells and its prevention by
proline may provide insight into biochemical triggers that induce
gyrate atrophy.