Neuromodulatory effects of N-acetyl-L-leucine in a human induced neuronal cell culture system

N-acetyl-L-leucine (NALL), an acetylated derivative of the amino acid leucine, has been shown to reduce neuronal cell death and neuroinflammation in murine models. Its beneficial effects in patients with the lysosomal storage disease Niemann-Pick Type C have led to recent FDA and EMA approval. However, neuroprotective effects of NALL remain to be further elucidated. In this study, we investigate and characterize the neuroprotective effects of NALL. To this end, we used human induced primary neurons (hiPNs), which were generated from induced pluripotent stem cells derived from reprogrammed renal proximal tubule epithelial cells obtained from either healthy controls (HC) or individuals with relapsing-remitting multiple sclerosis (MS). We demonstrated that NALL exhibits neuroprotective properties in MS- and HC-derived hiPNs subjected to acute damage induced by the microtubule-destabilizing agent nocodazole determined by neurite length. This effect can be blocked by inhibition of transporter-specific NALL uptake. HiPNs from MS donors treated with NALL expressed higher levels of glutamate cysteine ligase (GCL), the ratelimiting enzyme in glutathione synthesis. MS-specific cells are more susceptible to stress induced by the protein kinase inhibitor staurosporine, whereas in HC-specific cells only, NALL is able to modulate this stress induction. In summary, we demonstrate differential responses to induced stress in MS- and HC-specific neurons and the capacity of NALL to modulate neurite outgrowth and stress mechanisms in this cell culture system. NALL may represent an interesting additive treatment for MS or other diseases associated with oxidative stress and neurodegeneration if further substantiated.