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Introduction
Skin is in continuous contact with the external environment, and protects the human body from potentially hazardous environmental threats, including physical, chemical and biochemical factors (1). Furthermore, skin prevents the entry of bacteria, fungi and viruses into the body, and provides a protective barrier that prevents moisture loss (2). Skin aging comprises several intrinsic processes, which are predominately genetically determined, and extrinsic aging that is typically associated with sun exposure; however, other factors may be involved in extrinsic skin aging, including ultraviolet (UV) irradiation, excessive alcohol consumption and environmental pollution (1,2).
Chronic exposure of human skin to the sun is characterized by epidermal hyperplasia and changes in the biomechanical properties of the dermis (3). These lead to wrinkle formation that may be observed histologically, and the development of deep wrinkles, nodules, irregular hyperpigmentation, telangiectasia and skin that has a leathery, rough texture, all of which are clinically evident (3).
Repeated exposure to UV radiation ultimately causes premature skin aging, or photoaging, which is characterized by the formation of fine and coarse wrinkles, an increase in the thickness of the skin, dryness, laxity and pigmentation (4). Exposure of the skin to UV light initiates the generation of active oxygen species in the skin (5), and exposure of the skin to UVB radiation is associated with elevated risks of erythema, edema, hyperplasia, sunburn-cell formation, photoaging, immune system suppression and skin cancer (6).
The role of probiotics in the regulation of intestinal health has been widely investigated for over 100 years. Probiotics are used with increasing frequency to treat medical conditions such as allergic diseases and atopic dermatitis, and to prevent dental caries and respiratory infections (7). Human clinical trials have demonstrated that probiotic supplementation may relieve atopic dermatitis and dry skin (8). Several studies involving Lactobacillus acidophilus have demonstrated that probiotics are effective against atopic dermatitis (9,10). However, the anti-wrinkle effects of tyndalized L. acidophilus have not been investigated. Thus, the present study examined the effects of tyndalized L. acidophilus on hairless mice that had developed skin damage following skin exposure to UVB radiation.
Materials and methods
Materials
Tyndalized L. acidophilus, or ID-ACT3302, was obtained from Ildong Pharmaceutical Co., Ltd. (Seoul, South Korea). A total of 21 6-week-old HR-1 hairless male mice were purchased from...