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Dermatology
Skincare is one of the most profitable product categories today. Consumers’ demand for skin-friendly products has stimulated the development of natural-ingredient-based cosmeceutical preparations over synthetic chemicals. Thus, natural polysaccharides have gained much attention since the promising potent efficacy in wound healing, moisturizing, antiaging, and whitening. The challenge is to raise awareness of polysaccharides with excellent bioactivities from natural sources and consequently incorporate them in novel and safer cosmetics.
- natural polysaccharides
- skin health
- cosmetics
1. Introduction
The skin is the largest organ of the human body and is also the first line of defense from the external environment [1]. Due to its extensive area, it is easily exposed to and even damaged by a range of external factors such as ultraviolet radiation, which may lead to wounds, dehydration, skin aging, melanin deposition, microbial invasion, and skin barrier abnormalities [2]. Hence, different strategies to treat skin problems or promote skin health have been used, such as the use of skin care products or some physical therapies [3]. Among various treatments, natural skin care compounds are considered more skin-friendly from the perspective of consumers, so natural reagents are readily accepted and the demand for natural skin care products is increased [4].
Naturally occurring polysaccharides can be obtained from plants, algae, and fungi through a series of steps of extraction, isolation, and purification [5]. They display distinct structural features, including their molecular weight, monosaccharide composition, glycosidic linkages, three-dimensional conformations, charge properties, and types and numbers of groups, which contribute to their functional properties and determine their extensive applications [6]. The application of some functional polysaccharides in cosmetics is based on their functionalities in the formulation technology, such as thickener, film former, conditioner, emulsifier, and gelling agent, which generally rely on their physicochemical properties [4]. On the other hand, bioactive polysaccharides are role by the ability of water retention, water absorption, anti-oxidant, anti-inflammation, anti-collagenase, anti-elastase, anti-melanogenic, or anti-tyrosinase [7]. Recently, the use of low-cost natural polysaccharides for skin applications has been gaining more attention because of their promising potent efficacy in wound healing, moisturizing, antiaging, and whitening, which in most cases depends not only on their physicochemical properties but also biological activities [7]. However, reliable natural reagents are still in short supply as many problems need to be solved before they can be converted into products, such as the instability of natural ingredients, low efficacy, and biosafety concerns [8,9].
2. Skin Health Promoting Effects
2.1. Wound Healing
Wound healing is a complex dynamic process that is classically divided into four sequential and orchestrated stages of hemostasis, inflammation, proliferation, and tissue remodeling [3]. Repair refers to the body’s attempt to restore normal structure and function after injury, and its success mainly depends on the degree of injuries, necrotic tissue, tissue regeneration capacity, and foreign body infection [10,11]. In recent decades, various strategies have been developed to improve healing and to limit scar formation by modulating wound healing processes, especially using natural polysaccharides as wound healing agents regarding their biodegradable, biocompatibility, and low toxicity characteristics compared with synthetic polymers [12].
In addition to facilitating skin wound healing, their high film-forming ability and beneficial barrier properties contribute to their potential to be developed as an ideal biodegradable film to promote wound healing efficiency by providing a wound physiological environment [16,17]. Moreover, poly (vinyl alcohol) (PVA) is a non-toxic vinyl polymer with good chemical stability, biocompatibility, film-forming properties, and hydrophobicity, which is often used as a crosslinking agent to reinforce the functional properties of polysaccharide films [18].
2.2. Moisturizing
Moisturizing is a critical part of skin care and has a positive effect on enhancing skin barrier function, metabolism, and appearance. From an aesthetic point of view, dryness of the skin can lead to some undesirable experiences that can undermine a person’s confidence, such as painful, itchy, tingles, stings, and uncomfortable sensory feelings, or redness, dry white patches, crackers, and even fissures appearance, or the uneven and rough tactile feelings [4]. Additionally, if this skin condition persists for a long time, the skin will lose elasticity and wrinkles will gradually appear [4]. Thus, moisturizing products formulated with humectants or occlusive ingredients are used to retain the content of water in stratum corneum (SC) or suppress transepidermal water loss (TEWL) [7].
Although natural polysaccharides exhibit strong bioactivity, most studies demonstrated that the moisturizing effect of polysaccharides could be significantly improved through chemical structure modification [24,25]. Polysaccharides with a higher molecular weight are more likely to form a net-like structure to prevent water loss, resulting in better moisturizing retention properties [24]. Functional groups of polysaccharides, including pyruvate groups, glyoxylate groups, uronic acid groups, and sulfate groups, are potential factors for moisturizing retention [24].
2.3. Anti-Aging
Skin aging can be divided into endogenous and exogenous processes. The endogenous aging process is associated with reduced antioxidant status and cell proliferation capacity. Senescent cells express genes that produce inflammatory cytokines, growth factors, and degradative enzymes [7]. Exposure to nicotine or air pollution, sunlight through ultraviolet (UV) radiation, diet, and medication can be the main exogenous factors [26]. Both intrinsic and extrinsic aging can lead to the weakening of the skin’s structural integrity and loss of physiological functions [27], which is manifested in the decrease of elasticity, appearance of wrinkles, dryness, changes in the thickness of the epidermis, dermal-epidermal junction, and dermis [28].
Reactive oxygen species (ROS) are continuously produced as a by-product of mitochondrial aerobic metabolism and have been proven to play a beneficial role in maintaining the body or cell health when present in a small amount [29]. However, excessive ROS in the body can induce and accelerate the intrinsic aging process, especially in skin that is usually present in areas that are not exposed to sunlight. In addition, the occurrence of photoaging relates to the production of ROS as well. Repeated exposure to solar UV can cause an increase in ROS, damage the cell structure and function, and mediate inflammatory responses [30,31]. Consequently, excessive ROS can activate numerous signaling pathways, leading to decreased skin collagen production, stimulate the production of senescence-associated secretory phenotype (SASP), and promote synthesis and activation of matrix metalloproteinases (MMPs), which ultimately accelerate the aging process of skin [32] (Figure 1).
Figure 1. The schematic diagram of UV irradiation-induced skin aging and polysaccharides acting for skin protection.
2.4. Whitening
Melanin, the dominant pigment responsible for skin color, derives from tyrosine through a series of oxidative reactions in melanosomes. The first period of melanogenesis is called the Raper-Mason pathway, which depends on tyrosinase (TYR), the rate-limiting enzyme [37]. Moreover, some proteins are involved in the maturation of melanosomes, like tyrosinase-related proteins (TRP1 and TRP2) [38]. After that, melanosomes are transported to nearby keratinocytes and deposited around the nucleus, where they work and eventually degrade [8]. Thus, the whole process of melanogenesis includes melanin synthesis, transport, and degradation.
Melanin synthesis is the most studied area in the regulation of melanogenesis rather than the transport and degradation [39]. First and foremost, according to the melanogenesis pathway, the expression and activation of tyrosinase have the most direct impact on the synthesis of melanin. Secondly, oxidative stress triggered by ROS is another crucial factor in stimulating melanin synthesis [40]. Besides, the Microphthalmia-associated transcription factor (MITF) is a critical transcription factor that can increase the expression of TYR, TRP1, and TRP2. Several signaling pathways can modulate MITF, such as the cAMP/PKA/CREB signaling pathway [41], and the MAPFs signaling pathway [42].
This entry is adapted from the peer-reviewed paper 10.3390/polysaccharides3040048
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