MARINE INGREDIENTS
homeostasis including aquaporins (AQPs), glycerol, natural moisturising factors (NMFs), lipids and tight junctions, as well as osmolytes. ■ AQPs are water-permeable protein channels that allow movement of water across cell membranes having an important role in keratinocyte migration and cell volume regulation.5 ■ NMFs are free amino acids and their derivatives that act as humectants reducing the drive for water loss by absorbing water molecules in order to maintain optimal cellular hydration. Along with molecules such as hyaluronic acid and glycerol aid skin barrier function and provide skin elasticity.6
External
factors such as harsh cleansing routines and UVR exposure and internal factor like aged skin reduce NMFs content on skin via enzymatic breakdown of proteins.7 ■ Lipid composition and organization in the stratum corneum is essential for an effective water permeable skin barrier regulating diffusion levels and prevents excessive TEWL (trans epidermal water loss).8 ■ Tight junctions are cell-cell junctions that have been shown to form a paracellular barrier for solutes and water between epidermal cells by maintaining the electrochemical gradient and allowing only selective passage of ions and solutes.9 ■ When osmotic disruption occurs due to a physiological stressor these mechanisms aim to restore the cell to a homeostatic state via either accumulation or release of naturally occurring compounds called osmolytes.10 The cytoplasm of all organisms from
bacteria to humans can contain high concentrations (10 to 100 mM) of organic osmolytes. In animal cells, these can be grouped into three classes: (1) polyols (glycerol, sorbitol and myo-inositol); (2) amino acid derivatives (taurine, alanine, glutamate and proline); and (3) methylamines (betaine, trimethylamine N-oxide (TMAO) and glycerophosphorylcholine. In humans the role of organic osmolytes has not been widely examined in many tissues apart from renal cells.
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Figure 1: Organic osmolytes of epilithic holobiont interchanged by microalgae and its microbiota
Organic osmolytes strategy on skin repair
The main role of organic osmolytes is osmoprotection for cells by counteracting the effects of altered osmolarity in the surrounding microenvironment and to ensure vital cell function is not compromised.4 Organic osmolytes respond to physiological stressors by adapting the synthesis, accumulation, and release into and out of cells. The main functions of osmolytes (Figure 2) are listed below. ■ Cell volume regulation to maintain water homeostasis. These regulatory mechanisms exist to restore altered cell volume and these work through the accumulation or release of organic osmolytes. Upon cell shrinkage due to hyperosmolarity, the cells mechanism is employed to ensure an influx of water via the
uptake of ions and an accumulation of organic osmolytes occurs through the respective transporters in order to restore cell volume.11 ■ The protein stabilisation via shifting the hydrophobic properties of the protein backbone and provide one mechanism of protection. Therefore, as skin is the outermost barrier to the external environment, age- related disruption of osmolyte strategy could impact, not only the appearance of the skin, but also susceptibility of the human system to external challenge or disease.12 ■ Organic osmolytes, have been shown to play a role in antioxidant mechanisms. When cells are exposed to physiological stressors, e.g. UVR, this can lead to accumulation of oxidative stress which is an imbalance of reactive oxygen species (ROS) in biological systems. Accumulation of ROS can lead to protein perturbation and lipid degradation, therefore, the antioxidant properties of organic osmolytes can counteract the effects of oxidative stress.13
Osmoregulation affected by skin ageing process Recent ageing research has directed the focus not only on age-related illnesses, but also healthy ageing. Skin ageing is associated with deterioration of tissue structure and function that leads to physical changes to the appearance of the skin such as wrinkles, loss of elasticity, dryness and hyperpigmentation. Osmoregulation of human epidermal
Figure 2: Model of organic osmolytes skin function and protection. Osmolytes (red stars) skin protection: 1. Restore cell volume; 2. Protein stabilisation; 3. Antioxidant protection
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keratinocytes is disrupted with natural skin aged and photoageing. Therefore, this impacts skin hydration and impairs the ability of the skin to repair in response to physiological stress. Skin ageing specifically affects osmolyte transport mechanisms. Then it can cause the skin to become dehydrated and more
September 2022 PERSONAL CARE
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