Cytochrome P450 induction prevent salsolinol- induced toxicity in SH-SY5Y cells

The aetiology and molecular mechanisms underlying the degeneration of dopaminergic neurons in Parkinson disease (PD) have long been the subject of intensive research, suggesting that certain endogenous and exogenous compounds may act as neurotoxins, thereby contributing to the onset of the disease. Among these, salsolinol, an isoquinoline synthesized in the central nervous system from acetaldehyde and dopamine, has been found in elevated concentrations, along with its derivatives, in the urine and cerebrospinal fluid of patients with idiopathic PD. These compounds induce significant inhibition of mitochondrial complex I, increase oxidative stress, and alter protein degradation mechanisms, suggesting a potential role in the pathogenesis and progression of PD. In the brain, cytochrome P450 (CYP) represents only 0.5–2% of the total amount present in the body. However, its uneven distribution, both in terms of quantity and specific isoenzymes across different brain regions, may play a crucial protective role in neurodegenerative processes by facilitating the elimination of neurotoxic substances. To investigate this hypothesis, the role of the main CYP isoforms in salsolinol-induced toxicity was studied using an in vitro model of SH-SY5Y human neuroblastoma cells differentiated into a dopaminergic phenotype. The first step was to corroborate the possibility of modulating CYP expression in differentiated SH-SY5Y cells. qRT-PCR analysis showed that expression of the CYP 1A1, 3A4, 2D6, and 2E1 isoforms was detectable in undifferentiated cells, with subsequent increases in CYP 2E1, 2D6 (also confirmed by Western Blot analysis), and 1A1 following differentiation. Two well-known CYP inducers, β-naphthoflavone (βNF) and ethanol (EtOH), were then used to further modulate CYP, and results showed additional increases in the 1A1, 2D6, and 2E1 isoforms with βNF, as well as 1A1 and 2D6 with EtOH. This suggests the potential of differentiated SH-SY5Y cells to investigate the role of CYPs in neuronal processes involved in the development of neurodegenerative diseases. The second step was to assess whether salsolinol-mediated toxicity could be reverted by CYP induction, possibly owing to an increased toxin metabolism. The findings indicated that βNF significantly restored cell viability compromised by salsolinol and reduced its apoptotic-mediated cell death, whereas EtOH appeared to be less effective. Given that βNF activates antioxidant enzymes via the NRF2 pathway, we investigated whether this mechanism underlies the observed protective effects. Experimental data revealed that the differentiation protocol maximized NRF2 nuclear translocation compared to undifferentiated cells, while treatment with βNF did not further enhance this translocation, suggesting that NRF2 activation is unlikely to contribute to the observed neuroprotection. Overall, the present findings suggest that CYP isoforms may contribute to salsolinol inactivation, possibly by accelerating its biotransformation into less toxic or more easily excretable metabolites, thereby limiting its intracellular accumulation and reducing cytotoxicity. These results highlight the potential role of CYP isoforms in cellular defence mechanisms against neurotoxin-induced toxicity and suggest that modulating their activity could be a promising strategy for neuroprotection.