Carnosic Acid Prevents
6‑Hydroxydopamine-Induced
Cell Death in SH-SY5Y Cells via Mediation of Glutathione Synthesis
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Abstract
Understanding the neuroprotective effects of the rosemary
phenolic
diterpene carnosic acid (CA) has attracted increasing attention. We
explored the mechanism by which CA modulates the neurotoxic effects
of 6-hydroxydopamine (6-OHDA) in SH-SY5Y cells. Cells were pretreated
with CA for 12 h followed by treatment with 100 μM 6-OHDA for
12 or 24 h. Cell viability determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolim
bromide (MTT) assay indicated that 0.1 to 1 μM CA dose-dependently
attenuated the cell death induced by 6-OHDA, whereas the effect of
3–5 μM CA was weaker. CA at 1 μM suppressed the
6-OHDA-induced nuclear condensation, reactive oxygen species generation,
and cleavage of caspase 3 and PARP. Immunoblots showed that the phosphorylation
of c-Jun NH<sub>2</sub>-terminal kinase (JNK) and p38 by 6-OHDA was
reduced in the presence of CA. Incubation of cells with CA resulted
in significant increases in the total glutathione (GSH) level and
the protein expression of the γ-glutamylcysteine ligase catalytic
subunit and modifier subunit. l-Buthionine-sulfoximine, an
inhibitor of GSH synthesis, attenuated the effect of CA on cell death
and apoptosis. Treatment with CA also led to an increase in nuclear
factor erythroid-2 related factor 2 (Nrf2) activation, antioxidant
response element (ARE)-luciferase reporter activity, and DNA binding
to the ARE. Silencing of Nrf2 expression alleviated the reversal of
p38 and JNK1/2 activation by CA. These results suggest that the attenuation
of 6-OHDA-induced apoptosis by CA is associated with the Nrf2-driven
synthesis of GSH, which in turn down-regulates the JNK and p38 signaling
pathways. The CA compound may be a promising candidate for neuroprotection
in Parkinson’s disease