Hypothermia Advocates Functional Mitochondria and Alleviates Oxidative Stress to Combat Acetaminophen-Induced Hepatotoxicity

Abstract

For years, moderate hypothermia (32 °C) has been proposed as an unorthodox therapy for liver injuries, with proven hepatoprotective potential. Yet, limited mechanistic understanding has largely denied its acceptance over conventional pharmaceuticals for hepatoprotection. Today, facing a high prevalence of acetaminophen-induced liver injury (AILI) which accounts for the highest incidence of acute liver failure, hypothermia was evaluated as a potential therapy to combat AILI. For which, transforming growth factor-α transgenic mouse hepatocytes (TAMH) were subjected to concomitant 5 mM acetaminophen toxicity and moderate hypothermic conditioning for 24 h. Thereafter, its impact on mitophagy, mitochondrial biogenesis, glutathione homeostasis and c-Jun N-terminal kinase (JNK) signaling pathways were investigated. In the presence of AILI, hypothermia displayed simultaneous mitophagy and mitochondrial biogenesis to conserve functional mitochondria. Furthermore, antioxidant response was apparent with higher glutathione recycling and repressed JNK activation. These effects were, however, unremarkable with hypothermia alone without liver injury. This may suggest an adaptive response of hypothermia only to the injured sites, rendering it favorable as a potential targeted therapy. In fact, its cytoprotective effects were displayed in other DILI of similar pathology as acetaminophen i.e., valproate- and diclofenac-induced liver injury and this further corroborates the mechanistic findings of hypothermic actions on AILI.

In vivo demonstration of a novel non-invasive model for inducing localized hypothermia to ameliorate hepatotoxicity

“…From our past study, moderate hypothermia was shown to render concomitant mitophagy and mitochondrial biogenesis vitro 2 . We thus inquired on their existence in a pulsed cooling animal model, to abate mitochondrial dysfunction in AILI.…”

“…Previous studies have characterized the effects of hypothermia on AILI in vitro 1 , 2 . With this established understanding, we hoped to translate the concept of hypothermic treatment into a clinically actionable therapy-one which achieved hepatoprotection with minimal invasiveness and adverse outcomes.…”

“…As a result, a four-hour empirical pulsed cooling could only manifests cold-mediated effects, independent of CSPs (Figs. 6 , 7 , 8 ), unlike conventional hypothermia which exhibits cold-mediated effects through both CSP-dependent and -independent pathways 1 , 2 . This therefore calls for a need in future study, to further optimize the pulsed cooling protocol to efficiently induce RBM3 proteins.…”

“…We have previously reported on the potential of using moderate hypothermia (32 °C) to ameliorate acetaminophen-induced liver injury (AILI) in vitro 1 and presented various mechanistic insights on the effect of hypothermia in AILI 2 . Notwithstanding its demonstrated efficacy, the conduct of systemic hypothermia in clinical settings drew skepticism as this could incur non-specific adverse effects such as a slowdown in overall metabolism 3 .…”

“…With this model of a novel, non-invasive pulsed cooling modality, we sought to validate its feasibility and efficacy for the amelioration of acute DILI through an in vivo mouse study. Acetaminophen (APAP) was used as the model toxicant in accordance with past studies of hypothermic conditioning in AILI in vitro 1 , 2 . Herein, the study first involved a pilot phase to evaluate the feasibility of attaining regional cooling close to the liver.…”