Aspects of Histopathological and Ultrastructural Retinal Changes in Chronic Exposure to Hydroxychloroquine

Background and Objective: Hydroxychloroquine sulfate (HCQ) is a lysosomotropic agent administered in systemic lupus erythematosus and rheumatoid arthritis that has fewer toxic effects than chloroquine. However, HCQ may still be responsible for retinal toxicity. In this study, we observed structural changes in the retinas of experimental rats after prolonged exposure to HCQ. Matherials and Methods: We investigated several aspects regarding retinal changes, at both the histopathological and ultrastructural levels. We used 96 male albino Wistar rats distributed into four equal groups (n = 24 per group): the first three groups were treated with different doses of HCQ (50, 100, and 200 mg/kg HCQ, injected intraperitoneally in a single dose daily), and the last group (the control group, n = 24) was treated with saline solution administered in the same way (0.4 mL of saline solution). The treated groups received HCQ daily for 4 months, and every month, six animals from each group were sacrificed to assess retinal changes. The eyes were examined via optical (OM) and electronic microscopy (EM). Statistical analysis was deployed, and results regarding retinal morpho-photometry were acquired. Results: We observed structural retinal changes in both high and low doses of HCQ; while high doses determined a significant thinning of the retina, lower doses caused retinal thickening. Morphological retinal changes upon exposure to HCQ are believed to be caused by accumulated HCQ in lysosomes found in retinal ganglion cells and in the inner nuclear and photoreceptor cell layers. Such changes were most evident in the group receiving HCQ intraperitoneally in doses of 100 mg/kg for a longer period (4 months). Conclusions: The present study highlights histopathological and ultrastructural retinal changes induced by chronic HCQ administration, which were strongly connected to the dosage and period of exposure.