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Arsenic is a well-known potent toxicant affecting people by causing various human diseases. Long-term exposure to arsenic has strong adverse health effects on liver and kidney disorders, and various forms of cancer. Contrarily, curcumin and D-pinitol are bioactive dietary compounds that have antioxidant properties. Both are used to treat a broad variety of human diseases. Thus, we hypothesized that both may have synergistic effects against arsenic-induced toxicity in PC12 cells. Cells were pretreated with curcumin (1, 2.5, 5 and 10 μM), D-pinitol (1, 2.5, 5 and 10 μM) alone or in combination, then exposed to sodium arsenite (10 μM). The final concentration of curcumin 2.5 μM and D-pinitol 5 μM was selected for combination treatment based on their highest protection at lowest concentration against arsenic toxicity. Results demonstrated that pretreatment of curcumin and D-pinitol and their combined treatment with arsenic rescued PC12 cells. Western blot analysis results showed that pretreatment of curcumin and D-pinitol and their combined treatment with arsenic significantly inhibited arsenic-induced cell death through up-regulation of pro-survival proteins and down-regulation of cell death-related proteins, although these protein expressions were negatively regulated by arsenic. Furthermore, the effect of combined treatment with curcumin and D-pinitol was stronger than individual treatment., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Arsenic is a recognized highly toxic contaminant, responsible for numerous human diseases and affecting many millions of people in different parts of the world. Contrarily, curcumin is a natural dietary polyphenolic compound and the main active ingredient in turmeric. Recently it has drawn great attention due to its diverse biological activities, strong antioxidant properties and therapeutic potential against many human ailments. In this study, we aimed to explore the protective effects and the regulatory role of curcumin on arsenic-induced toxicity and gain insights into biomolecular mechanism/s. Arsenic (10 μM) treatment in PC12 cells for 24 h induced cytotoxicity by decreasing cell viability and intracellular glutathione level and increasing lactate dehydrogenase activity and DNA fragmentation. In addition, arsenic caused apoptotic cell death in PC12 cells, which were confirmed from flow cytometry results. Moreover, arsenic (10 μM) treatment significantly down-regulated the inhibition factors of autophagy/apoptosis; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap protein expressions, up-regulated the enhanced factors of autophagy/apoptosis; ULK, LC3, p53, Bax, cytochrome c, caspase 9, cleaved caspase 3 proteins and eventually caused autophagic and apoptotic cell death. However, curcumin (2.5 μM) pretreatment with arsenic (10 μM) effectively saves PC12 cells against arsenic-induced cytotoxicity through increasing cell viability, intracellular GSH level and boosting the antioxidant defense system, and limiting the LDH activity and DNA damage. Furthermore, pretreatment of curcumin with arsenic expressively alleviated arsenic-induced toxicity and cell death by reversing the expressions of proteins; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap, ULK, LC3, p53, Bax, cytochrome c, caspase 9 and cleaved caspase 3. Our findings indicated that curcumin showed antioxidant properties through the Nrf2 antioxidant signaling pathway and alleviates arsenic-triggered toxicity in PC12 cells by regulating autophagy/apoptosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)