Activation of AMPK/Nrf2 signalling by Manuka honey protects human dermal fibroblasts against oxidative damage by improving antioxidant response and mitochondrial function promoting wound healing

Highlights

• Manuka honey protects against oxidative stress, improving mitochondrial functionality.

• Manuka honey activates AMPK/Nrf2/ARE pathway, enhancing antioxidant defence.

• Manuka honey promotes the healing of wounds.

Abstract

Excessive amounts of free radicals are deleterious for cells, resulting in cell damage, affecting the wound healing process and causing premature ageing or even neoplastic transformation. Here the capacity of Manuka honey (MH) to protect against oxidative damage and improve the process of skin wound healing was investigated. Up to 16 compounds were identified in MH, with leptosin derivatives and methyl syringate as the major ones. MH protected against apoptosis, intracellular ROS production, and lipid and protein oxidative damage. MH also protected mitochondrial functionality, promoted cell proliferation and activated the AMPK/Nrf2/ARE signalling pathway, as well as the expression of the antioxidant enzymes such as SOD and CAT. Here we describe for the first time that one of the possible mechanisms by which MH exhibits its ability to promote wound healing could be due to its capacity to improve the antioxidant response by activating AMPK phosphorylation and the ARE response.

Introduction

Manuka honey (MH) derived from the Leptospermum scoparium tree has been described to have additional therapeutic advantages in wound health over other honeys, thanks to its high antibacterial capacity (Alvarez-Suarez, Gasparrini, Forbes-Hernández, Mazzoni, & Giampieri, 2014). In addition to the antibacterial capacity of honey, other mechanisms have been associated with their ability to heal wounds, like those related to their physical properties (Molan, 2011). These properties, such as its pH of around 3.2–4.4, favours the topical acidification of wounds and promotes healing by increasing the release of oxygen from haemoglobin (Molan & Rhodes, 2015). Moreover, this pH is less favourable for protease activity, favouring the reduction of the destruction of the matrix needed for tissue repair. Other mechanisms that promote wound healing are related to the immunostimulatory, anti-inflammatory and debriding action of honey (Molan & Rhodes, 2015). MH is also a natural source of a group of polyphenol compounds (Alvarez-Suarez et al, 2014, Chan et al, 2013), which besides their anti-bacterial capacity may synergistically contribute to the healing of wounds.

Clinical reports have demonstrated the capacity of MH in healing chronic wounds in humans and animals. There are many reports of single case studies where MH resulted in healing previously non-healing wounds (Biglari et al, 2012, Bischofberger et al, 2015, Bischofberger et al, 2016, Sell et al, 2012). In fact, MH has been used for treating problematic wounds, like leg ulceration (Gethin & Cowman, 2005); however, the relationship between its healing properties and wound repair mechanism is still unexplored. The purpose of this study was to investigate the potential effects of MH as a potential therapeutic agent against oxidative damage in human skin fibroblasts, which can play an important role in the process of skin wound healing. Special emphasis was made on the possible molecular pathways involved in improving the cellular redox and metabolic state by studying the activation of AMPK/Nrf2 signalling as mainly responsible for the antioxidant response as well as the cascade related to antioxidant defences and mitochondrial functionality.