Date Published: May 3, 2017
Publisher: Public Library of Science
Author(s): Srithar Gunaseelan, Agilan Balupillai, Kanimozhi Govindasamy, Karthikeyan Ramasamy, Ganesan Muthusamy, Mohana Shanmugam, Radhiga Thangaiyan, Beaulah Mary Robert, Rajendra Prasad Nagarajan, Veeramani kandan Ponniresan, Pierson Rathinaraj, Andrzej T. Slominski.
Ultraviolet-B radiation (285–320 nm) elicits a number of cellular signaling elements. We investigated the preventive effect of linalool, a natural monoterpene, against UVB-induced oxidative imbalance, activation of mitogen-activated protein kinase (MAPK) and nuclear factor kappa-B (NF-κB) signaling in HDFa cells. We observed that linalool treatment (30 μM) prevented acute UVB-irradiation (20 mJ/cm2) mediated loss of activities of antioxidant enzymes in HDFa cells. The comet assay results illustrate that linalool significantly prevents UVB-mediated 8-deoxy guanosine formation (oxidative DNA damage) rather than UVB-induced cyclobutane pyrimidine (CPD) formation. This might be due to its ability to prevent UVB-induced ROS formation and to restore the oxidative imbalance of cells. This has been reflected in UVB-induced overexpression of MAPK and NF-κB signaling. We observed that linalool inhibited UVB-induced phosphorylation of ERK1, JNK and p38 proteins of MAPK family. Linalool inhibited UVB-induced activation of NF-κB/p65 by activating IκBa. We further observed that UVB-induced expression of TNF-α, IL6, IL-10, MMP-2 and MMP-9 was modulated by linalool treatment in HDFa cells. Thus, linalool protects the human skin cells from the oxidative damages of UVB radiation and modulates MAPK and NF-κB signaling in HDFa cells. The present findings substantiate that linalool may act as a photoprotective agent against UVB-induced skin damages.
The skin is the largest organ of the body and serves as the barrier between the environment and internal cellular milieu which determines its critical function in the preservation of body homeostasis, and eventually organism survival . As skin is continuously exposed to numerous biotic and abiotic factors, it has been evolved with protective mechanisms in order to cope up local and global aggressive environment . For example, skin possesses strong antioxidant systems which maintain redox homeostasis against oxidative threat in the cellular milieu . Further, recently Solmonski described the role of neuroendocrine systems such as melatonin/serotonin in the maintenance of cellular homeostasis in the skin against various environmental stresses . Ultraviolet radiation (UVR) is the prominent environmental agent which continually affects cellular homeostasis in the human skin . Solmonski et al. (2014) reported significant alterations in the neuroendocrine system after UVB exposure correlated with carcinogeneic events in the skin cells . In addition, UVB stimulates cortisol production in the human skin keratinocytes and melanocytes which are predictable implications in local cancerogenesis . It has also been well reported that ultraviolet -B (UVB; 285–320 nm) alters skin homeostasis through oxidative imbalance and induces several adverse effects such as erythema, edema, inflammation, photoaging and skin cancer .
Exposure of UVB radiation induces intracellular oxidative stress and elicits several cellular signaling. In this study, we evaluated the role of linalool against oxidative stress activated protein kinases in single UVB-exposed human skin cells. Several studies have been reported that various antioxidant agents could protect UVB-induced cell toxicity or cell damage . Linalool is one of the most abundant naturally existing monoterpene in many plant aromatic species and it is a potent antioxidant in nature. In this study, we tested (20–50 μM) concentration of linalool against UVB induced cytotoxicity in HDFa cells. We found that 30 μM of linalool pretreatment significantly prevented UVB-induced cytotoxicity in HDFa cells (Fig 1A). We observed that lower concentration of linalool (20 μM) was insufficient to protect UVB toxicity and the maximum concentrations of linalool (40–50 μM) exhibits adverse results due to cytotoxic nature of linalool at physiologically higher concentrations and hence we chosen 30 μM linalool as optimum protective dose against UVB experiments.
In this study, linalool exhibits significant antioxidant potential in the in vitro free radical scavenging system which has been reflected in its preventive effect against low-dose UVB-induced ROS generation and subsequent antioxidant enzyme depletion. Further, linalool prevents UVB-mediated oxidative DNA damage and ineffective against UVB-induced CPDs formation. This indicates its ability to prevent UVB-induced ROS formation and to maintain redox homeostasis in the cell. As linalool prevents UVB induced ROS mediated damages it contributes for the prevention of UVB-induced activation of MAPKs mediated inflammatory reactions (Fig 9). This has been noticed in UVB-induced overexpression of MAPK and NF-κB signaling. Further, it prevents UVB-mediated translocation of NF-κB from the cytosol to the nucleus. Moreover, linalool protects skin cells from UVB-induced photoaging responses through modulating expression of inflammatory cytokines and MMPs. Thus, linalool prevents oxidative stress activated protein kinases in single low-dose UVB-exposed human skin cells. Blockade of the oxidative stress signaling elements may offer an effective approach to prevent skin damage resulting from acute solar radiation.