Original articleThymoquinone prevents endoplasmic reticulum stress and mitochondria-induced apoptosis in a rat model of partial hepatic warm ischemia reperfusion
Graphical abstract
Introduction
Hepatic ischemia reperfusion (I/R) is one of the major concerns after liver surgery and transplantation. In the past few decades, different works have explored the molecular pathways involved in liver I/R injury. The pathophysiological mechanisms of I/R-induced damage are multifactorial and a lot of experimental data indicate that reactive oxygen species (ROS) accumulated in the injured tissues are the hallmark of all subsequent lesions [1]. ROS can cause lipid peroxidation, protein oxidation and DNA damage which can lead to organelles malfunction and further cellular disorders.
Oxygen and glucose deprivations induce abnormalities in protein-folding processes and accumulation of unfolded/misfolded proteins into endoplasmic reticulum (ER). This protein misfolding in the ER lumen can initiate ROS production. In addition, ROS could exacerbate protein misfolding in the ER lumen by oxidizing amino acids in folding proteins or modifying chaperone [2]. This situation activates the unfolded protein response (UPR) to resolve this protein-folding defect and so to restore ER homeostasis [3], [4]. However, an excessive and continuous ER stress can activate pro-apoptotic factors, including C/EBP-homologous protein (CHOP) and caspase-12, conducting to cell dysfunction and even cell death [5]. Several studies were interested in developing strategies that limit or avoid the consequences of ER stress in I/R process [6]. Among these strategies, pharmacological pretreatment has been of great interest [7], [8].
Mitochondria produce cellular energy needed for normal cellular function through oxidative phosphorylation [9]. Oxygen deprivation during ischemia triggers events that alter mitochondrial electron transport chain complexes resulting in further oxidative stress increase and mitochondrial bioenergetic decline [10], [11]. Moreover, mitochondrial membrane permeability can be affected by Ca2+-accumulation in the mitochondrial matrix during the ischemic period [12]. A continuous damage in mitochondria leads cell to undergo apoptosis. Therefore, remedial strategies targeting ER and mitochondria stress are fundamental to reduce the harmful effects of I/R.
Thymoquinone (TQ) (2-isopropyl-5-methylbenzo-1, 4-quinone), is the main active compound of the volatile oil isolated from the Nigella sativa seeds [13]. TQ was reported to possess strong antioxidant properties [14], [15], [16] and to scavenge ROS [17]. Also, TQ was shown to have anti-inflammatory action [18]. Previous research demonstrated that TQ pretreatment protects from warm I/R injury in a variety of tissues and organs [19], [20], [21], [22], [23]. Although its antioxidant and anti-inflammatory properties has been reported in a number of studies, its effect on ER stress has not been studied yet. Cellular mechanisms involved in TQ protection against I/R injury are still unclear and need more experiments to be clarified. Hence, the present study, by using a partial warm hepatic ischemia rat model, investigates TQ effects on ER stress, mitochondrial damage and apoptosis.
Section snippets
Animals
Male Wistar albino rats weighing between 200 and 230 g were used in this study. Rats were housed in an air-conditioned room with 12 h light and dark cycles, and a constant temperature (22 ± 2 °C). They had free access to food and water. All procedures were carried out in accordance with the European Union Regulations (Directive 2010/63/EU) for animal experiments.
Surgical procedure
Rats were anaesthetized with an intra-peritoneal (ip) injection of pentobarbital (5%), and then they were subjected to surgery as described
Thymoquinone attenuates warm I/R liver injury
The first part of this work allowed us to determine the effective dose of TQ able to protect rat livers against I/R lesions. As it is shown in Fig. 1, I/R induced liver injury as evidenced by a significant increase in AST and ALT activities when compared to Sham group. We noticed that TQ at 30 and 40 mg/kg significantly decreased the AST activity, whereas for ALT activity, we recorded a significant decrease with 20 and 30 mg/kg of TQ. Moreover, rat treatment with the vehicle alone (ethanol and
Discussion
Recently, there has been a growing interest in using natural phytochemical compounds as alternative treatments in several conditions including I/R injury. This is due to their relatively low toxicity. In our work, we have chosen to study the effect of TQ, the active compound of Nigella sativa seeds.
It is well known that I/R injury is a multifactorial process including energy depletion, oxidative stress, apoptosis and inflammation. In contrast to other phytochemicals which have generally one
Conclusion
In conclusion, we have demonstrated the protective effect of TQ in liver I/R injury. We have also demonstrated for the first time the effects of thymoquinone in reducing ER stress. We think that the future research should be directed to strengthen the protective effect of TQ by using a cocktail of phytochemicals which have proven their efficacy and low toxicity such as fucoïdan and curcumin… Such cocktail could target all the factors implicated in the physiopathology of I/R injury and could be
Conflicts of interest
The authors declare that they have no competing interests.
Acknowledgements
This work was supported by grants from the Tunisian Ministry of Higher Education and Scientific Research (UR12ES11).
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