An Endogenous Dopaminergic Neurotoxin, N‐Methyl‐(R)‐Salsolinol, Induces DNA Damage in Human Dopaminergic Neuroblastoma SH‐SY5Y Cells

Abstract

Recently, an endogenous neurotoxin, 1(R),2(N)‐dimethyl‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline [N‐methyl‐(R)‐salsolinol], was found to elicit parkinsonism in rats with selective depletion of dopamine neurons in the substantia nigra without necrotic tissue reaction. The mechanism of the cell death was examined by detection of DNA damage using a single‐cell gel electrophoresis (comet) assay in human dopaminergic neuroblastoma SH‐SY5Y cells. Only N‐methylsalsolinol was found to induce DNA damage, whereas other catechol isoquinolines, such as (R)‐salsolinol, (S)‐salsolinol, and 1,2‐dimethyl‐6,7‐dihydroxyisoquinolinium ion, did not. The (R)‐enantiomer of N‐methylsalsolinol damaged DNA much more profoundly than the (S)‐enantiomer. Cycloheximide protected the cells from DNA damage, suggesting that an apoptotic process may account for the DNA damage. Morphological changes indicating apoptotic cell death were also confirmed. Antioxidants and deprenyl reduced DNA damage, indicating that the damage was initiated by oxidative stress and that neuroprotection by deprenyl may be partially ascribed to its prevention of DNA damage. Apoptosis induced by neurotoxins may be a mechanism underlying the cell death of dopamine neurons in the substantia nigra of Parkinson's disease.

Catechol Tetrahydroisoquinolines Enhance a-Synuclein Aggregation and Specify the Neurotoxicity to Dopaminergic Neurons

“…And NM-Sal is considered to be a stronger neurotoxin than Sal and is capable of inhibiting mitochondrial functions and thus inducing apoptosis of dopaminergic cells [65,66]. And the (R)-enantiomer of NM-Sal can cause more severe DNA damage than the (S)-enantiomer [67]. So far, NM-Sal was expected to be the most toxic CTIQ.SH-SY5Y cells treated with NM-Sal exhibited significant apoptosis, while the cells treated with Sal or MPP + exhibited moderate apoptosis.…”

Influence of neurotoxins and oxidative stress on the onset and progression of Parkinson’s disease

“…Injected directly into the striatum, N-methyl-(R)-SAL elicited parkinsonian responses in rats, and depleted nigral DA stores without inducing necrosis [93], while in cell culture it caused oxidative damage to DNA leading to apoptosis [78]. Kawai et al [67] synthesized a novel TIQ species including a DA moiety which, when injected intraperitoneally into mice, induced parkinsonian symptoms; in synaptosomes, it exhibited a high affinity for the striatal DA transporter.…”

Review on apoptosis vs. necrosis of substantia nigrapars compacta in parkinson’s disease

“…In retinoic-acid differentiated human dopaminergic neuroblastoma SH-SY5Y cells, the endogenous neurotoxin N-methyl(R)salsolinol induced apoptosis (Maruyama et al, 1997a) by producing DNA damage (single-cell gel electrophoresis, comet assay) (Maruyama et al, 1997b). Caspase 3 activation was observed (Western blot analysis), while both DNA fragmentation and cell death were prevented by the caspase 3 inhibitor acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspartic aldehyde.…”