Comparative hepatoprotective effects of tocotrienol analogs against drug-induced liver injury

Cheau Yih Tan ^a, Tzuen Yih Saw ^b, Chee Wai Fong ^b, Han Kiat Ho ^a,*
^a Department of Pharmacy, National University of Singapore, Block S4, 18 Science Drive 4, Singapore 117543, Singapore
^b Davos Life Science, 3 Biopolis Drive, #04-19, Synapse, Singapore 138623, Singapore

Redox Biology 4 (2015) 308–320
http://dx.doi.org/10.1016/j.redox.2015.01.013
2213-2317/& 2015 The Authors. Published by Elsevier B.V.
Available online 20 January 2015

Abstract:

Oxidative stress plays a major part in the pathogenesis of drug-induced liver injury. Yet, overcoming it with other xenobiotics impose additional risks. In this study, we consider the use of natural-occurring and puriﬁed Vitamin E analogs as hepatoprotective agents. Vitamin E is well-known for its intrinsic antioxidant property even though the differential effect of speciﬁc analogs of tocopherol (TP) and tocotrienol (T3) is still not ascertained. This study investigates the protective effect of T3 analogs (α-, δ-, γ􀀁) in comparison with α-TP followed by assessing the underlying mechanisms of the cytoprotective T3 analog(s) in two xenobiotics-induced liver injury models using (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H2O2). Both α-TP and α-T3 exerted cytoprotective effects while only lower con-centration of γ-T3 was effective in inhibiting both toxicants induced injury. α-TP/α-T3 protected hepatocytes from APAP and H2O2-induced liver injury through arresting free radicals and inhibiting oxidative stress (inhibition of reactive oxygen species, lipid peroxidation and mitochondrial permeability transition). There was also demonstrable inhibition of the apoptotic pathway (inhibition of caspse-3 activity and overexpression of Bcl-XL), accompanied with an induction of liver regeneration (PCNA and NF-kB). The cellular uptake of α-T3 was higher than α-TP at the same treatment dosage after 24 h. Overall, α-T3 seems to be a more potent hepatoprotective analog among the tocotrienols and α-TP at the same in vitro treatment dosage. In summary, these results suggest that α-TP/α-T3 elicit hepatoprotective effects against toxicants-induced damage mainly through activation of antioxidant responses at an early stage to prevent the exacerbation of injury.

Keywords:

Tocotrienol, Tocopherol, Antioxidant, Drug-induced liver injury