Clinical and Mechanistic Review of Amiodarone-Associated Optic Neuropathy

Figures

• 

  Figure 1. (a) The percentage of viable RPE cells decreases from 100% to approximately 40% as amiodarone (AM) concentration increases from 0 μM to 100 μM. (b) The percentage of RPE cells undergoing apoptosis increases from 0% to approximately 63% as AM concentration increases from 0 μM to 100 μM [37].

• 

  Figure 2. (a) The percentage of viable RPE cells decreases dramatically with the introduction of 50 μM AM, but this decline is attenuated by increasing the concentration of administered IGF-1 from 1 ng/mL to 300 ng/mL. (b) The percentage of apoptotic RPE cells significantly increases with the addition of 50 μM AM. The effect of AM on apoptosis is attenuated by addition of IGF-1 over a concentration range of 1 ng/mL to 300 ng/mL [37].

• 

  Figure 3. (a) The percentage of viable RPE cells decreases in response to AM exposure and is protected by IGF-1. Inhibiting the PI3K/Akt pathway by LY294002 causes a reduction in IGF-1 efficacy, while inhibiting MAPK by PD98059 or PD160316 has no effect on maintaining RPE cell viability by IGF-1 in the presence of AM. PI3K/Akt is the pathway by which IGF-1 protects RPE cells from AM toxicity. (b) Caspase 3/7 activity in RPE cells approximately doubles in the presence of AM compared to control, and IGF-1 attenuates this increase. Inhibiting the PI3K/Akt pathway by LY294002 diminishes apoptotic protection from IGF-1, while inhibiting MAPK by PD98059 or PD160316 has no effect on the ability of IGF-1 to reduce caspase 3/7 activity in the presence of AM [37].

• 

  Figure 4. A proposed mechanism of IGF-1 mediated attenuation of amiodarone toxicity in the RPE. Amiodarone inhibits the activity of Akt and decreases mitochondrial membrane potential stability (∆ψm). This membrane instability in turn results in increased ROS production, MDA lipid peroxidation, and caspase 3/7 driven apoptosis. IGF-1 stimulates the activity of Akt, thereby reducing oxidative and proapoptotic mechanisms of cell death from amiodarone [37].

• 

  Figure 5. Amiodarone (AM) decreases cell viability and increases apoptosis in a concentration-dependent manner. (a) RGCs were treated with amiodarone and measured for cell viability using an MTT assay at 24 h. (b) Cellular apoptosis was determined using Hoechst 33342 staining at 24 h. The data are expressed as the mean ± SEM of results obtained from five independent experiments. * p < 0.05, ** p < 0.01 [40].

• 

  Figure 6. IGF-1 pretreatment preserves RGC viability in the presence of AM. RGC cells received varying concentrations of IGF-1 and then exposed to 3 μM AM for 24 h. Cell viability was determined via the MTT assay. Results show the mean ± SEM of five independent experiments. * p < 0.05 compared with control, # p < 0.05 compared with amiodarone, ## p < 0.01 compared with amiodarone [40].

• 

  Figure 7. LY294002, a PI3K inhibitor, inhibited the protective effect of IGF-1 against amiodarone-induced apoptosis of RGC cells. The ERK pathway inhibitor PD98059 and p38 MAPK inhibitor PD160316 had no effect. RGC cells were pretreated with either LY294002, PD98059, or PD160316 and then treated with IGF-1 and amiodarone for 24 h. Cell viability was determined by the MTT assay. Data are expressed as a percentage of the corresponding control value which was normalized as 100%. Results show the mean ± SEM and represent assays from five independent experiments [40].

• 

  Figure 8. Amiodarone increases nuclear translocation of FoxO3a in RGCs, leading to increased apoptosis. IGF-1 significantly attenuates this process in amiodarone-treated RGCs. Fluorescence microscopy was utilized to identify cytosolic or nuclear localization of FoxO3a, and the nuclear translocation ration was calculated as the percentage of RGCs with nuclear predominance of FoxO3a compared to all cells that could be classified as either nuclear or cytosol predominant [40].

• 

  Figure 9. A proposed mechanism of IGF-1 and amiodarone in the RGC. Amiodarone decreases Akt phosphorylation of FoxO3a, leading to nuclear translocation of FoxO3a and increased caspase mediated apoptosis. IGF-1 antagonizes amiodarone by stimulating Akt phosphorylation of FoxO3a, leading to increased cytosolic localization and improved RGC survival [40].