Growth factors are highly specialised proteins or hormones that are transmitted from cell to cell as so-called signal transmitters. This way, they transport information that triggers cellular replication, production or proliferation.
How does growth factor work?
Skin growth factors There are different growth factors in the skin. The best known is the epidermal growth factor (EGF for short), which is responsible for cell proliferation and the activation of stem cells in the skin. The important role of the EGF becomes clear in a wound. The more EGF available, the faster the wound healing and the less scar tissue. As signal peptides, the growth factors TGF-alpha (transforming growth factor) and TGF-beta stimulate both cell growth and differentiation. The FGF (Fibroblast Growth Factor) stimulates the formation of fibroblasts, which in turn form essential components of the dermis such as collagen, elastin or hyaluronic acid. Therefore, the FGF plays a major role in anti-aging therapy. In the course of life, the quality of the skin decreases due to extrinsic and intrinsic factors. Various processes in the skin such as the dermal synthesis of collagen, elastin or hyaluronic acid slow down. In addition, external influences such as cigarette smoke, fine dust or the sun's rays induce matrix metalloproteinases, which lead to the breakdown of dermal components. In addition, there is evidence of a decline in growth factors, which can also be accelerated by external influences. It has been scientifically proven that UV radiation leads to a reduction in TGF-beta. Since TGF-beta is the main regulator of type I procollagen synthesis, collagen production is impaired. It is therefore not surprising that growth factors are of great interest to the cosmetics industry as an anti-aging ingredient. Promising active ingredients They are considered to be promising active ingredients, although the study situation is still very poor. The effect of topically applied growth factors on the skin was first investigated in medicine in the context of wound healing. Advances in understanding the role of growth factors in this area have in turn sparked interest in the possible role of these molecules in the repair and remodelling of skin structures. It is assumed that the cosmetic mechanism of action of EGF lies in an accelerated cell turnover with a faster regeneration process. In a placebo-controlled study from 2013, a product containing a plant-based so-called human-like EGF (hEGF) was applied twice a day to 30 women aged between 30 and 65 for eight weeks. After completing the examinations, a significant improvement in skin density and skin thickness could be evaluated. Further studies have confirmed the positive effect of hEGF on skin quality. Furthermore, the positive effect of TGF-beta as a cosmetic active ingredient has already been investigated. In a study in 2006, a product with TGF-beta and other growth factors was examined with a vitamin C preparation over three months in 20 subjects with signs of skin aging. Although there was an improvement in the skin parameters with both test products, the product with the TGF-beta was superior to the vitamin C preparation. Histological examinations were also able to demonstrate an improvement in signs of skin aging, particularly in so-called UV-induced photoaging. In 2016, scientists from Poland published a study on recombinant FGF (rFGF). They were able to demonstrate a stimulating effect of rFGF on fibroblasts and keratinocytes and, in addition, to evaluate an improvement in skin aging symptoms such as wrinkle depth and wrinkle volume on test persons. In addition to the human growth factors described, which are often obtained from bacteria, plant growth factors are increasingly being used in cosmetics. These include kinetin, a growth factor from green-leaved plants. It is a stable antioxidant that has shown positive effects on cell aging in initial studies in cell cultures.
A question of molecular size
A major problem in cosmetic applications is the molecular size of the growth factors. Growth factors are hydrophilic molecules that are larger than 15,000 daltons. In principle, however, active ingredients with a molecular size greater than 500 have difficulty penetrating the skin barrier. However, the current results of growth factor research indicate a clinical benefit. Therefore, different penetration routes are discussed.
First, growth factors are believed to be absorbed through the sweat glands and hair follicles and then interact with keratinocytes, which then release chemical signals to fibroblasts.
Second, aging skin is drier and has a reduced barrier capacity, making it more susceptible to penetration by larger molecules. In addition, recent studies show that the topical application of vaccines has an immunological effect, possibly due to the penetration of a small number of proteins through healthy skin.
A similar phenomenon could occur when growth factors are applied to the skin as there is paracrine communication between keratinocytes and fibroblasts. A keratinocyte-induced production of growth factors by the fibroblasts can occur, which in turn stimulates the proliferation of keratinocytes.
Finally, the entry of small amounts of topically applied growth factors could result in the production of other growth factors (e.g., TGF-alpha and TGF-beta) by the fibroblasts. Both TGF-alpha and TGF-beta have a paracrine effect consisting of the activation and proliferation of dermal fibroblasts that cause remodelling and regeneration of the extracellular matrix.
Apparative cosmetics
Induction of growth factors can also be achieved with the help of apparatus-based cosmetics. It is known that in percutaneous collagen induction therapy with needles longer than one millimetre, the TGF-beta signalling cascade is activated with collagen synthesis and a skin-regenerating effect. Due to the paracrine communication between keratinocytes and fibroblasts, a similar effect, albeit in a weaker form, can already be expected with cosmetic micro-needling, in which the needles penetrate up to 0.5 millimetres into the skin. Microneedling is also suitable for the transepidermal application of active ingredients. Therefore, from a cosmetic point of view, a micro-needling treatment with growth factors is particularly suitable.
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