Neuroprotective effects of curcumin on endothelin-1 mediated cell death in hippocampal neurons

Abstract

Objectives: Alzheimer's disease is a progressive neurodegenerative disease characterized by loss of hippocampal neurons leading to memory deficits and cognitive decline. Studies suggest that levels of the vasoactive peptide endothelin-1 (ET-1) are increased in the brain tissue of Alzheimer's patients. Curcumin, the main ingredient of the spice turmeric, has been shown to have anti-inflammatory, anti-cancer, and neuroprotective effects. However, the mechanisms underlying some of these beneficial effects are not completely understood. The objective of this study was to determine if curcumin could protect hippocampal neurons from ET-1 mediated cell death and examine the involvement of c-Jun in this pathway.

Methods: Primary hippocampal neurons from rat pups were isolated using a previously published protocol. Viability of the cells was measured by the live/dead assay. Immunoblot and immunohistochemical analyses were performed to analyze c-Jun levels in hippocampal neurons treated with either ET-1 or a combination of ET-1 and curcumin. Apoptotic changes were evaluated by immunoblot detection of cleaved caspase-3, cleaved fodrin, and a caspase 3/7 activation assay.

Results: ET-1 treatment produced a 2-fold increase in the levels of c-Jun as determined by an immunoblot analysis in hippocampal neurons. Co-treatment with curcumin significantly attenuated the ET-1 mediated increase in c-Jun levels. ET-1 caused increased neuronal cell death of hippocampal neurons indicated by elevation of cleaved caspase-3, cleaved fodrin and an increased activity of caspases 3 and 7 which was attenuated by co-treatment with curcumin. Blockade of JNK, an upstream effector of c-Jun by specific inhibitor SP600125 did not fully protect from ET-1 mediated activation of pro-apoptotic enzymes in primary hippocampal cells.

Discussion: Our data suggests that one mechanism by which curcumin protects against ET-1-mediated cell death is through blocking an increase in c-Jun levels. Other possible mechanisms include decreasing pro-apoptotic signaling activated by ET-1 in primary hippocampal neurons.

Keywords:

• Neuroprotection
• Endothelin
• Curcumin
• Alzheimer's disease
• Primary hippocampal neurons

Acknowledgements

The authors thank Dr Thomas Yorio for several insightful discussions and useful comments on various aspects of this project.

Disclaimer statements

Contributors D.L.S. performed experiments, analyzed data, prepared figures, and wrote the manuscript. V.R.K. performed experiments and analyzed data. D.Z.E. provided brains of the animals for the research and edited manuscript. R.R.K. designed experiments, analyzed data, and wrote manuscript.

Conflicts of interest There are no conflicts-of-interest.

Ethics approval Studies performed conformed to the guidelines issued in the Declaration of Helsinki, and all animal-related procedures were approved by the Institutional Animal Care and Use Committee (IACUC) at the UNT Health Science Center.

Additional information

Funding

The work was partially supported by a grant from the National Eye Institute (1R01EY019952) to RRK.