Mechanism of uptake and retention of 18F-MyoZone in cardiomyocytes: A novel PET myocardial perfusion imaging agent / 解放军医学杂志

ABSTRACT

Objective To investigate the mechanism of uptake and retention of a novel PET myocardial perfusion imaging agent 18F-MyoZone in cardiomyocytes. Methods 1) Mechanism of inhibition of mitochondrial respiratory chain enzyme activity With mitochondrial respiratory chain enzyme complex I (MC-I) activity assay kit, a sequence of 19F-MyoZone solution (start at 15 μmol/L, 3 times dilution, 12 points) was interacted with MC-I to detect the half inhibition rate (IC50) of 19F-MyoZone inhibiting mitochondrial respiratory chain activity. 2) Autoradiography experiment of 18F-MyoZone combining with MC-I Myocardial tissue sections of neonatal rat were hatched with normal saline and 4 known MC-I inhibitors [rotenone (4 μmol/L), 19F-Flurpiridaz (4 μmol/L), 19F-MyoZone (4 μmol/L) and pyridaben (4 μmol/L)], and then 18F-MyoZone was added to autoradiography for detecting whether 18F-MyoZone can specifically bind the cardiomyocytes MC-I; and then the myocardial tissue sections of rat were hatched for 30 min with different concentrations of rotenone or 19F-MyoZone solution (0, 20 μmol/L, 2 μmol/L and 200 nmol/L, 20 nmol/L), then the 18F-MyoZone was added and hatched for 30 min again, developing for 10 min with phosphor storage screen after cleaning the slice, and analyzing and calculating the inhibition rate of each inhibitor concentration. 3) Experiment of rotenone inhibitting the uptake of 18F-MyoZone by cardiomyocytes Neonate rats' primary cardiomyocytes were cultured for 15 min with different concentrations of 19F-MyoZone or equivalent rotenone (start at 10 μmol/L, 3 times dilution, 12 points), then 50 μl of 18F-MyoZone (about 17 kBq) was added and culturing for 30 min. The lysate was then collected, the radioactivity was counted and the IC50 of rotenone was calculated. 4) Outflow experiment of 18F-MyoZone from cardiomyocytes Cultured neonate rats' primary cardiomyocytes were interacted with 500 μl of 18F-MyoZone (about 37 kBq) for 30 min, then the cell supernatant and lysate were separated to do photon counts at the time points of 0, 10, 20, 30, 60, 90, 120 and 150 min. The ratio of cardiomyocyte outflow rate was then calculated. Results Enzyme activity studies showed that 19F-MyoZone may effectively inhibit the activity of MC-I(IC50=229.9 nmol/L) in a dose dependent manner. MyoZone could specifically bind to MC-I with binding sites in accordance with the inhibitors rotenone, pyridaben and 19F-Flurpiridaz. Experiment of rotenone inhibitting the uptake of 18F-MyoZone by cardiomyocytes showed that 18F-MyoZone could be absorbed by rat's cardiomyocytes, and with the increase of rotenone concentration, the radio uptake of cardiomyocytes decreased gradually with inhibitor IC50 as 7 nmol/L. Outflow experiment showed that rat's cardiomyocytes could uptake 18F-MyoZone and stably detain over time. The outflow rate increased gradually within 0-30 min, and then maintained constantly from 60 min to 150 min. The amount of retention was about 20% of the entire uptake. Conclusions 18F-MyoZone may specifically bind MC-I and detain for a long time in rat's cardiomyocytes. 18F-MyoZone is a valuable myocardial perfusion imaging agent with great research value.