Hepatoprotection by curcumin and sulforaphane against tBHP-induced oxidative damage

Background and aim: Antioxidants have recently been of keen therapeutic interest, due to the causative role of oxidative stress in induction and progression of liver, pancreatic and neurodegenerative diseases. Most plant-derived antioxidants are key components of vegetables and spices which are part of daily meals. Curcumin (from Asian spice turmeric) and sulforaphane (abundant in cruciferous vegetables such as broccoli), are reported to have antioxidant potential [1, 2] and were assessed in the current study for their cytoprotective activity in HepG2 liver cells.

Methods: Radical scavenging activities of curcumin and sulforaphane were investigated against 2,2-diphenyl-1-picrylhydrazyl (DPPH). Using HepG2 liver cells, cytoprotection against tert-butyl hydroperoxide (tBHP)-induced cytotoxicity was evaluated in 5h co-exposure and 20h pre-exposure protocols with phytochemicals. Cell viability was determined in Neutral Red assay. Quercetin served as a positive phyto-antioxidant standard [3]. All phytochemicals were dissolved in DMSO to final solution of 10 mg/ml.

Results and Discussion: Radical scavenging activity of quercetin was stronger than curcumin, but not significantly more potent in 5h co-exposure with tBHP. Sulforaphane was not cytoprotective in 5h protocol, this it lacked antiradical activity. Unlike quercetin, both phytochemicals were cytotoxic at high concentrations (Table 1).

Tab. 1: Comparing antioxidant potencies of phytochemicals. – HepG2 liver cells were incubated with increasing concentrations of quercetin, curcumin and sulforaphane in the absence/presence of tBHP in direct (5hr co-exposure) and indirect (20hr pre-exposure with phyto-antioxidant). DMSO used as negative control. Mean EC₅₀ and Emax (with 95% confidence intervals) were determined. Values are mean EC₅₀ [± CI], n = at least 4 independent assays.

Phytochemical	DPPH		5hr Co-exposure		20hr Pre-exposure		Toxicity
	EC50 (MM)	Emax ± SEM	EC50 (MM)	Emax ± SEM	EC50 (MM)	Emax ± SEM
Quercetin	201.3 [183.6, 219.0]	103.0 ± 0.44	15.4 [8.5, 22.3]	98.83 ± 1.2	51.0 [16.3, 85.7	97.24 ± 1.9	No toxicity (> 330.9µM)
Curcumin	364.8 [259.2, 70.4]*	106.4 ± 6.6	46.3 [35.9, 56.7]	92 2 ± 5.2	14.3 [5.5, 23.1]*	93.5 ± 2.8	Toxicity (> 135.7µM)
Sulforaphane	No effect (> 1805.3µM)	No effect (> 1805.3µM)	No effect (> 564.1µM)	No effect (> 564.1µM)	59.9 [36.9, 82.8]	55.8 ± 6.6*	Toxicity (> 141.1µM)
*P < 0.05 when compared to quercetin – Mann-Whitney test.

Conclusion: Sulforaphane, curcumin and quercetin could protect HepG2 cells via indirectly inducing intrinsic cytoprotective mechanisms during 20h pre-exposure protocol. Sulforophane does not act as a free radical scavenger, whilst curcumin and quercetin have antiradical properties, acting as direct and indirect antioxidants. The cytoprotective activities of quercetin, curcumin and sulforaphane suggest that these may be strong therapeutic phyto-antioxidants in preventing oxidative damage.

Keywords: Curcumin, Antioxidant, Quercetin, Sulforaphane, HepG2

References:

[1] Zhao, S. G., Li, Q., 2011. Curcumin Attenuates Insulin Resistance in Hepatocytes by Inducing Nrf2 Nuclear Translocation. Hepato-Gastroenterology, 58, 2106 – 2111.

[2] Guerrero-Beltrán, C. E., Calderón-Oliver, M., 2012. Protective effect of sulforaphane against oxidative stress: recent advances. Experimental and toxicologic pathology: official journal of the Gesellschaft fur Toxikologische Pathologie, 64, 503 – 8.

[3] Adomako-Bonsu, A. G., Fry, J., 2013. Protection against oxidative stress by rosmarinic acid and its major metabolites in hepatic cells. Planta Med, 79, PJ3.