Introduction

Elastin confers on tissue the ability to stretch and recoil and plays a critical role in supporting and maintaining healthy tissue. In the skin, most elastin is located in the dermis. Generally, the more mature, thicker elastin fibers are found deeper in the dermis, where they function as an interpenetrating elastin network.

The building blocks of elastin therapy

The protein tropoelastin is the fundamental building component of all elastin. The production of tropoelastin mainly occurs before birth and in the first few years of life when the elastin required for the body to develop is produced. In adults, the low level of elastin production may mean that damage cannot be efficiently repaired and the skin gradually loses its elasticity.

The primary transcript from the single ELN gene is spliced to give different forms of the tropoelastin protein that either lack or contain various exons, which in turn give rise to forms of tropoelastin that may vary slightly in their protein sequence. The implications of this splicing are not clear, although some exons remain while others are occasionally spliced out. For example, exon 26A is unique to humans and appears to be spliced out in healthy elastic skin tissue but may be present under conditions of elastin damage, such as following UV exposure or extreme temperature treatments, as reported by Schmelzer et al. Therefore some forms of the tropoelastin protein may be associated with healthy elastic tissues and other forms with injury or disease.

As a key step in making elastin, many tropoelastin molecules associate and are then cross-linked, or connected, to form insoluble elastin. The process of elastic fiber formation is also known to include a number of other molecules. Microfibrils, of which fibrillin-1 is the major component, are structures present in the extracellular matrix and are thought to anchor elastic fiber formation. Cross-linking tropoelastin spherules are introduced to the microfibrils by the molecules fibulin-5 and possibly fibulin-4 and accrete on pre-existing elastin. Chapman et al found that fibulin-2 may work cooperatively with fibulin-5 to assist in elastic fiber formation. Emilin-1 may also regulate oxytalan fiber formation but, in a study by Nakatomi et al, did not appear to directly regulate elastin expression or deposition. The cross-linking of tropoelastin is carried out by lysyl oxidases – a family of five enzymes (LOX and LOXL, LOXL 2–4) that are likely to redundantly contribute to the cross-linking process. Maki et al found that LOX knockout mice show a reduction in elastin cross-linking. In addition, in studies by Noblesse et al, both LOX and LOXL were detected by immunohistochemistry in the dermis and epidermis of normal human foreskin and dermal equivalents with expression levels shown to decrease with age.

The raisons d’être of elastin regeneration and injecting elastin products

Damaged elastic fibers are responsible for an aged and wrinkled appearance (Fig. 9.1). Given the importance of elastin to the skin and its loss in the aging process, it is not surprising that various attempts have been made to maintain or replenish elastin levels. Treatments aiming to repair or regenerate elastin in elastic tissues should consider all the molecules implicated in elastin fiber formation. However, as elastin fibers develop, they ultimately consist of over 90% elastin and so the integration of sufficient tropoelastin into elastin fibers is clearly the major target. Effective treatment approaches are restricted owing to the obvious physical challenge of transferring materials and / or treatments across the epidermis and into the dermis, resulting in a preference for small molecules and physical treatments. Tretinoin or all-trans retinoic acid is a small molecule utilized for many years in topical formulations to increase elastin production through increased tropoelastin and fibrillin expression and secretion. Molecules such as aldosterone and mineralocorticoid receptor antagonists may impact on elastin fiber deposition in skin. Soy and rice (USPTO 19469891) extracts may also increase elastin formation, as can a combination of zinc and copper. More recently, a dill extract has also been shown by Cenizo et al to have the potential to promote elastin formation by promoting LOXL synthesis and secretion into the dermis.

Figure 9.1 Wrinkled skin due to loss of elastic fibers in a patient aged 12 years. Example of a male with acquired cutis laxa. Six months after presenting with an inflammatory condition, the patient developed generalized cutis laxa with marked sagging and wrinkling of the skin.

Courtesy of Hu Q, Reymond JL, Pinel N, et al 2006 Inflammatory destruction of elastic fibers in acquired cutis laxa is associated with missense alleles in the elastin and fibulin-5 genes. Journal of Investigative Dermatology 126(2):283-290.

However, the major challenge to overcome is the very low level of expression of tropoelastin in adult skin, as such treatments are likely to have only incremental benefits on the density of skin elastin, as reported by Sephel et al.

A new approach to treat aged and damaged skin using elastin is currently in clinical development in Australia by Elastagen Pty Ltd. The approach is unique to skin augmentation treatments in that it is based on a recombinant human tropoelastin protein, which is identical to the one naturally occurring in healthy human skin. As seen in early clinical studies, this high degree of similarity to the natural elastin protein promises a significantly higher level of tissue compatibility than achieved with animal-derived products or synthetic polymer materials (Fig. 9.2). The treatment process, trademarked as elastatherapy^®, also benefits from a new formulation chemistry that enables the tropoelastin protein to be cross-linked with a low-concentration HA component. There is no requirement for the toxic cross-linking agents often used in other products and the use of hyaluronidase to correct poor treatment outcomes is still an option – a significant advantage over alternative dermal filler materials. Elastin treatments benefit from the cell-supporting properties of elastin and the potential to stimulate skin cells, leading to the formation of new collagen at the treatment site. This latter property coupled with the product’s smooth, cohesive structure may present significant advantages over particulate products, which target collagen regeneration but carry a significant risk of lumps and nodules. The product range also includes the potential to bulk the skin with a long-lasting, highly biocompatible elastin material and the unique prospect of restoring elastin to improve the skin’s physical properties and suppleness.

Figure 9.2 Hematoxylin and eosin staining of upper arm dermis following biopsy 7 days after implantation. Note the irregular bands of the brightly eosinophilic fibrous elastin deposit amongst the dermal collagen in the reticular dermis.

Courtesy of Dr Robert Daniels, Elastagen Pty Ltd.

Ongoing clinical development will help identify the unique potential of what will be the first recombinant human elastin product as an aesthetic skin treatment.

Introduction

Platelet-rich plasma (PRP) is an autologous concentration of human platelets in a small volume of plasma. Multiple alternative terms to PRP are used in the literature including autologous platelet gel, plasma-rich growth factors, and autologous platelet concentrate. The use of growth factors permeates many fields of medicine and surgery, including facial rejuvenation and plastic surgery, maxillofacial surgery, dentistry and oral surgery, tissue engineering and research and development, cardiovascular surgery, orthopedic surgery and sports medicine, gastroenterology, and urology.

Concentrated platelets are a rich source of seven fundamental protein growth factors actively secreted by platelets during the initiation of wound healing. Human growth factors have been investigated extensively and clinical applications of individual growth factors such as keratinocyte growth factor and platelet-derived growth factors are used for the treatment of oral mucositis and non-healing diabetic wounds, respectively, as reported by Scalafan.