With its two square meters of surface, the skin is the largest organ of the human body. The external skin layer or epidermis is a dynamic system of continuous proliferation and differentiation. The most important function besides its many other tasks such as temperature regulation, sensory organ, protection against harmful substances and mechanical impacts, is to act as hydration barrier which impedes the dehydration and maintains the osmotic balance of the inner tissues. All these functions are carried out by the stratum corneum which is the outermost of the five epidermis layers. In contact with the environment, horny cells are constantly worn away, and appropriately keratinizing keratinocytes are reproduced in the stratum basale. This regenerative process normally takes about 20 days and is increasing in the course of life, whereby particularly the water binding capacity of the horny layer is decreasing. The skin loses its elasticity, becomes dry and cracked and barrier damages begin to appear. The result is that the skin starts to be sensitive to damaging environmental influences, penetration of microorganisms, toxins and allergens. The formation of epidermal lipids is reduced in quantity as well as in composition. The consequences are an increased permeability of the horny layer and a loss of hygroscopic substances and water. Water is of vital importance for the function of the skin. Water is a transport medium and essential for the various physiological functions in the different skin layers. The skin enzymes can only maintain their specific functions in a sufficiently hydrated skin. In this context, the adequate pH level is a prerequisite for appropriate enzyme activities. The transport of water across cell membranes is a fundamental process of life. Age-related variations from the normal condition due to environmental wear and tear, light damages, intrinsic and extrinsic skin aging cause disorders of the protective function of the skin surface. These disorders tend to result in skin diseases like atopic dermatitis, psoriasis, rosacea, acne, dry and sensitive skin or premature skin aging. The epidermal water content regulates the elasticity and tonicity of the skin. Water is bound in the hydrophobic milieu of the stratum corneum by the natural moisturizing factor substances (NMF) such as glycerin, urea, amino acids and peptides. Vital for the protective function of the skin barrier is the specific lipid composition. Enzymes modify the lipids in the different skin layers. Essential prerequisites for sufficient enzyme activity are water and an acidic pH value. The intact stratum corneum is an insuperable barrier for hydrophilic substances. Numerous pharmaceutical and instrument-based methods have been developed to transport substances through the protective barrier. Electric current, ultrasound and light energy induce oscillations of the viscous lipid bilayer and thus modify the consistency as well as permeability of the membrane. Appropriate vehicles for the transport across the protective barrier are liposomes and nanoparticles whose shells consist of skin-physiological phospholipids. Hydrophilic substances are encapsulated in liposomes and lipophilic substances in nanoparticles. With skin contact the shell combines with the lipids of the stratum corneum and transports the content of liposomes and nanoparticles into the deeper layers of the skin. Aquaporins Every living organism has to control the water inflow and drain in order to maintain function, structure and size of the cells. This process is regulated by specific proteins called "aquaporins". Aquaporins (AQP) are water channels that can be controlled from the outside in order to regulate the water inflow and drain from the cells. The fact, that the water can be exchanged via cell membranes has been known for quite some time. After the discovery of the lipid bilayer in plasma membranes in the late 1920ies, a simple diffusion of water across the cell membranes has been assumed. In the 1970ies, Arthur Solomon, Robert Macey and Alan Finkelstein have postulated the existence of specific water channels, based on biophysical models. Only in the early 1990ies, the team around Peter Agre managed to identify the water channel they were looking for. They called the protein aquaporin-1 (AQP1). In 2003, he was awarded the Nobel Prize for Chemistry for his research work in the field of aquaporins. Up to the present day, a whole series of aquaporins has been identified in the human body, in animals, plants and bacteria. References: [Agre P. et al: Aquaporin water channels - from atomic structure to clinical medicine. J. Physiol. (2002) 542, 3-16. Agre P et al: Aquaporin water channels: molecular mechanisms for human diseases. FEBS Lett (2003) 555, 72-78. Burghardt, B: Distribution of aquaporin water channels AQP1 and AQP5 in the ductal system of the human pancreas. GUT (2003) 52, 1008-1016] Aquaporins are integral membrane proteins All currently known aquaporins show a similar structure and amino acid sequence. The AQP1 consists of a chain of 268 amino acids which forms six helices that cross the membrane (integral membrane protein). Located at the end of the helix is a characteristic structure consisting of three amino acids (asparagine-proline-alanine) which essentially contributes to the selectivity of the water channel. The narrowest part of the channel is in the center part (0.3nm) both the openings show a diameter of 2nm. 12 different aquaporins have been found in mammalians. The water conductance per channel and per second amounts to 3 x 109 water molecules. This means that a membrane of the size of 10 x 10 cm2 with embedded aquaporins is able to filter one liter of water in about 7 seconds. Reference: [Farage MA. Textbook of Aging Skin, Springer-Verlag Berlin Heidelberg 2010] Aquaporins are highly selective. Because of the narrow center, all particles larger than water molecules cannot pass through the channel. The excellent efficacy of aquaporins is based on the fact that they pass the water molecules individually and in a controlled way through the channel where they intermittently loosen the hydrogen bonds. Positively charged amino acid residues in the inner channel impede the flow of cations which are smaller than water molecules. The water balance of cells is controlled by the osmotic pressure. There is a significant difference between diffusion and permeability via channels. Diffusion is a low capacity process in both directions via cell membranes. With these specific water channels, the water can pass almost unobstructed in direction of the osmotic gradient. The channel works bidirectional which means that the water can flow through the channel in both directions. While it is impossible to block the diffusion, there is a potential that mercury compounds jam the aquaporins though. On the other hand, specific substances like glyceryl glucoside, caffeine and theophylline but also osmotic stress from the outside can stimulate the formation of aquaporins. Aquaporins have also been found in the lipid membrane of the skin. The inner lipid layer of the stratum corneum is hydrophobic. Hence, the conductance of water molecules there is rather low. In order to have water flow into the deeper skin layers, free water must either be passed via specific channels or bonded to hydrophilic substances and then transported along the desmosomes bridges into the epidermis. The water content of the epidermis is controlled by the substances of the natural moisturizing factor (NMF). In case of barrier damages the transepidermal water loss (TEWL) is increased, a fact that leads to dry and sensitive skin. Appropriate dermatocosmetic products can improve the hydration of the epidermis if they use the water transport ways of the aquaporins. The protein family of the aquaporins is divided into so-called simple aquaporins and aquaglyceroporins. Simple aquaporins are pure water channels. Aquaglyceroporins additionally transport tiny organic molecules like glycerin and urea. It is assumed that aquaporin-3 plays a specific role in the skin. Hara et al. could prove that a faulty aquaporin-3 leads to a damaged water and glycerin transport into the epidermis. Hence, hydration and elasticity of the skin are reduced and the repair of barrier damages is slowed down. Reference: [Hara M et al. Glycerol replacement corrects defective skin hydration, elasticity and barrier function in aquaporin-3 deficient mice. Prog Natl Acad Sci USA (2003) 100, 7360-7365] Aquaglyceroporins are rather important transport channels for the moisturizing substances of the skin and should therefore be called "corneoporins". The aquaporin-3 of the skin does not only transport water into the deeper skin layers but also glycerin and urea. This leads to an improved hydration of the skin with enhanced receptivity for glycerin and water from cosmetic or dermatological products. Radiofrequency therapy The radiofrequency therapy employs diathermy (diathermy is the Greek word for heat penetration), which is a process to generate heat in the body by means of high frequency current. For this purpose, electrodes are attached to the skin and then connected with a high frequency source. One electrode serves as a transmitter and the counter electrode is the receiver antenna. The radio waves induce eddy currents in the tissue which in turn lead to heat generation. The physical process of warming is based on the increased inner energy of the tissue. The cause for the temperature rise is a stimulated motion of the water dipoles in the tissue. Warming also improves the permeation of lipophilic molecules through the skin barrier. The intensity of the heat generated in the different tissues depends on the specific tissue composition and the permittivity (the term originates from the Latin word for "let pass") for electric fields. The heating fluidizes the viscous lipid membrane of the skin and shrinks the collagen and elastin fibers so that a smoothing of wrinkles can be observed. Due to the gentle heating and stimulation of fibroblasts in the dermis, the formation of collagen and elastin fibers is induced. Mono- bi- and tripolar radiofrequency devices are used for dermatocosmetic treatments. On the part of the manufacturers, bi- and tripolar devices are reported to show better treatment results because the temperature rise is not that stressful for the patient. From the physical point of view, however, this statement has to be contradicted. In bipolar devices, active electrode and antenna electrode are placed next to each other in the handpiece. The high frequency field spreads between the two electrodes. In tripolar devices, two active electrodes are connected against a neutral electrode. Both bi and tripolar electrode arrays create the electromagnetic field between the active and the neutral electrode in a horizontal level which means in this context that it is parallel to the stratum corneum. The electric field strengths do not extend in a vertical way through the barrier but rather cause shearing forces and destabilizing eddy currents in the stratum corneum. In contrast, the active electrode of monopolar devices is integrated in the handpiece and the neutral electrode is attached to the body of the patient. The high frequency field lines spread out vertically to the skin surface and transport energy through the barrier. Aquaporation improves the elasticity and hydration of the skin The aquaporation treatment is used to penetrate appropriate dermatocosmetic products via barrier into the deeper layers of the epidermis. The transport of active agents via membrane is accelerated with the help of high frequency currents. A scientific study shows that barrier damages have been repaired and the moisture content of the skin has been improved. The additional application of radio waves could transport even more moisture into the skin and smoothen out the wrinkles. This effect proved to be sustainable and could still be intensified with a series of several treatments. It is assumed that radio waves increase the water transport capacity of aquaporins by conformation changes of the protein structures in the channel. The eddy currents of the radio waves will not only cause a separation of the water molecules by weakening the hydrogen bridges in the narrow channel but also a heat-induced change of the spatial structure of the protein structures. This considerably increases the water flow via aquaporins through the lipid membrane in the epidermis. The following test series has been run in order to examine the hypothesis that integrating appropriate products with the help of electromagnetic fields shows better hydration results than a simple application of the product. 1. After measuring the skin hydration with a corneometer®, a mixture of liposomal NMF and hyaluronic acid was applied on the inside of the test person's forearm.
2. The same active agents were permeated through the skin of the other arm with a radio frequency device for 20 minutes. The treatment with radio waves allowed transporting noticeably more moisture into the skin than the mere application of the moisturizing products. Specific products that contain substances of the natural moisturizing factor (NMF) in a liposomal formulation and hyaluronic acid have been developed for the aquaporation method [KOKO GmbH & Co. KG, Leichlingen]. The liposomes are used as a vehicle to transport hydrophilic substances through the lipid membranes of the epidermis. The liposome shell consists of a phospholipid bilayer that fuses with the identically structured lipid layer of the stratum corneum after skin contact and thus transports the liposome content into the deeper layers of the skin. The aquaporation method uses two different ways to transport water, glycerin, urea and further hydrophilic substances via lipid membrane: Via liposomal pathway Via aquaporins.
Hyaluronic acid acts on the skin like a water soaked sponge which is squeezed by radio waves. With the warming of the lipid bilayer the barrier is fluidized and thus becomes more permeable to lipophilic substances. The phospholipids of the liposome shells reinforce the lipid membrane and provide essential linoleic acid for the formation of ceramide 1 and 4, which interlock the two lipid layers via long fatty acid chains. The RF heat stimulus prompts the formation of aquaporins in the skin. The radio waves induce eddy currents of the water dipoles, loosen the existing hydrogen bridges and thus initiate the water flow via aquaporin channels into the deeper skin layers. Heat generation additionally modifies the array of the protein structures in the aquaporin channels which broadens the channel. The result is a considerably increased flow of water. This way, large amounts of water arrive in the deeper skin layers. Hence aquaporation sustainably increases the water content and elasticity of the skin. Aquaporation treatment sequence Before each treatment the moisture and sebum content of the skin is measured. After cleansing with a mixture of cleansing gel and cleansing milk (1:1) the following active agent concentrates [KOKO GmbH & Co.KG, Leichlingen] are applied on the facial skin with a brush: The radio frequency device [radioSURG® 2200, Fa. Meyer-Haake GmbH, Wehrheim] is used to create an electromagnetic field and radio waves are evenly applied on the respective area with a RF cone electrode. For treatments of the facial, neck or décolleté areas, the neutral electrode is placed underneath the shoulder of the patient. Thus the field lines are aligned vertically to the stratum corneum. Attention should be paid to the fact, that the neutral electrode is entirely covered by the patient. Direct skin contact is not required as the electrode serves as an antenna. The radioSURG® 2200 is set to MONO CUT (no coagulation rate) and then adjusted to 18-20 Watt. The electrode is gently pressed onto the respective skin area in order to avoid gaps between electrode and skin. Only then the device is turned on via foot or hand switch while the electrode is applied in circling movements over the specific skin area. It is recommended to do a tolerance test before each treatment. If the skin turns lightly red around the décolleté, the setting is perfect for the more sensitive areas of the skin. Cooling gels or traditional ultrasound gels should not be used as the perfume and preserving components contained may have an allergenic and sensitizing effect on the skin which could be intensified by the radio waves. The study comprised 6 treatments at weekly intervals. For the home treatment the test persons were handed out a DMS® membrane cream mixed with liposomal NMF, hyaluronic acid and D-panthenol. It was advised to apply the skin care cream mornings and evenings on the facial skin and gently massage it into the skin. The aquaporation method combined with appropriate dermatocosmetic active agents improves the hydration and elasticity of the skin, repairs barrier damages and stops the premature skin aging process which could not be achieved so far with traditional cosmetic products and moisturizers alone. Dr. Hans-Ulrich Jabs
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Aquaporins as integral structural proteins in the lipid membrane. [de Groot, B et al: Water Permeation Across Biological Membranes: Mechanism and Dynamics of Aquaporin-1 and GlpF, Science (2001), 294, 2353-2357] X-ray structural analysis of Aquaporin-1 with a resolution of 0,115 nm. [Fischer G. et al: Crystal Structure of a Yeast Aquaporin at 1.15 Å Reveals a Novel Gating Mechanism. PLoS Biol. (2009) 7 (9), e 10001300
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