Abstract
Photoageing and skin cancer are major causes of morbidity and are a high cost to society. Interest in the development of photoprotective agents for inclusion in topical cosmetic and sunscreen products is profound. Recently, amino acids with a sulfinic group, notably hypotaurine, have been included as ingredients in cosmetic preparations. However, the mechanism of action of hypotaurine as a possible anti-aging agent is unknown, despite its use as a free radical scavenger. To address this issue, we investigated hypotaurine uptake in a human keratinocyte model and examined its effect on UVR-induced cytotoxicity. Hypotaurine was taken up by keratinocytes in a time- and concentration-dependent manner, with levels remaining significantly above baseline 48h after washout. A cytoprotective effect of pre-incubation with 2.5-5mMhypotaurine was shown as indicated by increased cell viability when keratinocytes were irradiated with UVA at 5 or 10 Jcm-2 , with the level of hypotaurine also significantly reduced. These findings indicate a potential cytoprotective effect of hypotaurine against the deleterious effects of UVA irradiation. This provides support for further studies to evaluate the potential photoprotective benefits of hypotaurine supplementation of topical cosmetic and sunscreen products.
Highlights
Photoageing and skin cancer are consequences of cumulative cutaneous exposure to ultraviolet radiation (UVR) and are increasingly major causes of morbidity, placing huge burdens on society and health service provision and having important economic impact [1,2,3]
The intracellular hypotaurine concentration was determined by HPLC analysis (Fig. 1a), which shows that hypotaurine levels were significantly increased in cells from 0.21 Æ 0.2 nmol mgÀ1 protein in untreated cells to 9.87 Æ 0.8 nmol mgÀ1 protein (*P < 0.05)
We investigated whether the presence of Propargylglycine cystathionine c-lyase inhibitor (PPG) affected hypotaurine uptake and cell viability, where HaCaT cells pre-treated with PPG are capable of reducing hypotaurine levels [31]
Summary
Photoageing and skin cancer are consequences of cumulative cutaneous exposure to ultraviolet radiation (UVR) and are increasingly major causes of morbidity, placing huge burdens on society and health service provision and having important economic impact [1,2,3]. In addition to the harmful effects of UVR on skin, induction of several protective mechanisms is initiated, including production of enzymatic and non-enzymatic antioxidants that interact with reactive oxygen species (ROS) to minimize oxidative damage [4]. Considerable efforts have been made to prevent or limit oxidative stress-induced harmful effects of UVR on human skin, notably through supplementation with antioxidants, which are increasingly included in topical anti-aging, photoprotective and cosmetic products [8,9]. Hypotaurine is a sulfur amino acid, characterized by the presence of a sulfinic group rather than a carboxyl group, which can be oxidized to taurine [11,12] through a non-enzymatic reaction upon interaction with ROS such as hydroxyl radical [13]. Hypotaurine has been shown to have a protective effect against oxidative stress-induced damage in rat placental trophoblasts [16] as well as in human skin fibroblast models of cigarette smoke-induced oxidation [17]
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