Study of Vesicular Monoamine Transporter 2 in Myopic Retina Using [ 18 F]FP-(+)-DTBZ.

PURPOSE: To investigate the relationship between expression level of vesicular monoamine transporter 2 (VMAT2) and myopia, as well as the feasibility of noninvasive myopia diagnosis through imaging VMAT2 in retina by using [18 F]fluoropropyl-(+)-dihydrotetrabenazine ([18 F]FP-(+)-DTBZ).

PROCEDURES: The right eyes of ten guinea pigs were deprived of vision to establish form-deprived (FD) myopia and the left eyes were untreated as the self-control eyes. The location and expression level of VMAT2 in the eyes were detected by micro-positron emission tomography (PET)/X-ray computed tomography (CT) imaging through using [18 F]FP-(+)-DTBZ. Immunofluorescence staining and Western blot were used to confirm the location and expression level of VMAT2 in the eyes. The concentrations of dopamine (DA) and its metabolites including 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were also investigated by high-performance liquid chromatography.

RESULTS: The right eyes deprived of vision were obviously myopic (- 3.17 ± 1.33 D) after procedure, while the left eyes were hyperopic (4.60 ± 0.83 D, P < 0.0001). The main expressions of VMAT2 in the eyes were located in retina. VMAT2 was significantly reduced in the myopic retina compared to the normal one from PET/CT results (P = 0.0008), which could also be verified by Western blots (P = 0.029). The concentrations of DA, DOPAC, and HVA in the FD eyes were all significantly less than those in the control eyes (P = 0.024, P = 0.018, P = 0.008). As a role of storing and releasing DA in vesicles, VMAT2 was demonstrated positively correlating with the amounts of DA (P = 0.030), DOPAC (P = 0.038), and HVA (P = 0.025) through Pearson's correlation coefficient test.

CONCLUSIONS: We demonstrate that [18 F]FP-(+)-DTBZ can be used to noninvasively image VMAT2 in retina. The expression level of VMAT2 in retina may act as a new biomarker for myopia diagnosis. The decreasing of VMAT2 expression level may play an important role in the development of myopia through correspondingly reducing the amount of DA in retina.