N‐acetyl‐l‐tryptophan, but not N‐acetyl‐d‐tryptophan, rescues neuronal cell death in models of amyotrophic lateral sclerosis

Abstract Amyotrophic lateral sclerosis ( ALS ) is a neurodegenerative disease characterized by progressive motor neuron loss. Evidence suggests that mitochondrial dysfunction, apoptosis, oxidative stress, inflammation, glutamate excitotoxicity, and proteasomal dysfunction are all responsible for ALS pathogenesis. N‐acetyl‐tryptophan has been identified as an inhibitor of mitochondrial cytochrome c release and therefore is a potential neuroprotective agent. By quantifying cell death, we demonstrate that N‐acetyl‐ l ‐tryptophan (L‐ NAT ) and N‐acetyl‐ DL ‐tryptophan are neuroprotective in NSC ‐34 motor neuron‐like cells and/or primary motor neurons, while their isomer N‐acetyl‐ d ‐tryptophan has no protective effect. These findings are consistent with energy minimization and molecular modeling analysis, confirming that L‐ NAT generates the most stable complex with the neurokinin‐1 receptor ( NK ‐1R). L‐ NAT inhibits the secretion of Substance P and IL ‐1β (Enzyme‐Linked Immunosorbent Assay and/or dot blots) and mitochondrial dysfunction by effectively inhibiting the release of cytochrome c/Smac/ AIF from mitochondria into the cytoplasm and activation of apoptotic pathways, including the activation of caspase‐1, ‐9, and ‐3, as well as proteasomal dysfunction through restoring chymotrypsin‐like, trypsin‐like, and caspase‐like proteasome activity. These data provide insight into the molecular mechanisms by which L‐ NAT offers neuroprotection in models of ALS and suggest its potential as a novel therapeutic strategy for ALS . image We demonstrate that L‐NAT (N‐acetyl‐ l ‐tryptophan), but not D‐NAT, rescues NSC‐34 cells and primary motor neurons from cell death. L‐NAT inhibits the secretion of Substance P and IL‐1β, and caspase‐1 activation, the release of cytochrome c/Smac/AIF, and the activation of caspase ‐9, and ‐3, as well as proteasomal dysfunction. The data suggest the potential of L‐NAT as a novel therapeutic strategy for amyotrophic lateral sclerosis (ALS). AIF, apoptosis‐inducing factor.