Methylphenidate triggers retinal oxidative stress and mitochondrial dysfunction under physiological conditions but has beneficial effects in inflammatory settings

Abstract

Methylphenidate (MPH) is widely used as the first-line pharmacological treatment for attention-deficit/hyperactivity disorder (ADHD). However, its misuse as a cognitive enhancer has been increasing worldwide. Despite the scientific advances in understanding the effects of MPH on the brain, its impact on the retina, which shares the same embryonic origin with the brain, remains poorly understood. In the present study, primary retinal neural cell cultures were exposed to MPH (0.1-1 mM) alone or to MPH after an inflammatory stimulus (lipopolysaccharide; LPS, 1 μg/ml). Additionally, male Wistar Kyoto rats (WKY, control rats) and Spontaneously Hypertensive rats (SHR, ADHD model) were orally treated with MPH (1.5 mg/kg/day, P28-57). MPH (0.1 mM) preserved retinal cell viability but induced oxidative stress through NOX2 and PI3K/AKT/DRP1 signaling activation and mitochondrial dysfunction. This was evidenced by a decrease in the mitochondria number, increased fragmentation, impaired membrane potential, reduced oxygen consumption rate, and shifted metabolism towards a glycolytic metabolic profile. Under an inflammatory environment, MPH enhanced antioxidant defenses, decreased oxidative stress and intracellular calcium levels, and improved mitochondrial structure and function. These contrasting effects were corroborated in animal studies, where MPH treatment reduced oxidative stress and improved mitochondrial function in the ADHD model, despite having detrimental effects in control rats. Our findings uncover a novel mechanism through which MPH affects retinal cells via NOX2/PI3K/AKT/DRP1 signaling and mitochondrial alterations. Moreover, MPH demonstrates a context-dependent effect, yielding detrimental outcomes under physiological conditions but beneficial effects in inflammatory settings. These results provide new insights into both MPH's therapeutic potential and misuse-associated risks.

Keywords: Attention-deficit/hyperactivity disorder; Inflammation; Methylphenidate; Mitochondrial (dys)Function; Oxidative stress; Retina.