9 New and novel fillers

highlighting elastin and soft tissue augmentation, platelet-rich plasma and a combination of carboxymethyl cellulose (CMC), and polyethylene oxide (PEO)

Anthony S. Weiss, Greg J. Goodman, Philippa Lowe, Nicholas J. Lowe

Summary and Key Features

• Dermal elastin confers on tissue the ability to stretch and recoil and is important in cutaneous support

• Elastin may be a useful tissue filler and attempts to regenerate elastin are currently underway using recombinant tropoelastin

• Hyaluronic acid may be used as the crosslinking agent for tropoelastin and is being trialled in this form as a cutaneous filling agent

• Platelet rich plasma is a platelet rich concentrate in a small volume of plasma

• Platelets are a rich source of at least 7 growth factors including transforming vasoactive and epithelial factors

• Simplified methods have allowed harvesting of platelets and separation from other blood cells without lysing of the platelets

• Platelet rich plasma may have roles both in topical wound healing and in injected approaches as an augmentation and tissue regenerative agent.

• Platelet rich plasma has been shown to induce neocollagenesis, neovascularization and neolipogenesis after injection

• A novel filler comprising carboxymethyl cellulose and polyetheleneoxide (Laresse) has been used as a tissue filler

• Laresse has been compared favourably to Restylane in a short term study

• Laresse has been injected into upper lips, nasolabial and melomental folds in a small cohort of patients with few adverse reactions

Introduction

The rise and fall of new tissue fillers is a perennial event. The rise of hyaluronic acid (HA) as the main filler of choice over the last decade has been fueled by its twin strengths of reliability and relative safety. However, HAs are not perfect and the lure of a filler that may provide greater longevity, more economy, and even greater safety fosters the search for the perfect material.

In this chapter we will look at some novel and emerging technologies and materials that are aiming to produce for our patients the optimal safe experience we all desire for them. Elastagen^® is a novel material based on tropoelastin, the building block of the extremely long-lived elastin fiber and cross-linked in a novel way to allow adjustment to occur if required. Laresse^® is a mixture of two innocuous carbohydrates and represents a novel route for researchers to take. It was not marketed after initial studies but is included because of its novelty and possible direction for future product development. The third product to be showcased is certainly a work in progress. The injection of autologous blood or blood products has a rich but somewhat checkered past. Platelet-enriched autologous transfer is a technique that has recently been simplified in an attempt at resurrecting the injection of application of blood products to enhance appearance and skin health.

Elastin and soft tissue augmentation

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.

Pearl 1

Elastin is concentrated in the dermis and is required for skin elasticity.

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.

Pearl 2

Tropoelastin is needed to make elastin, but its expression drops after early childhood and damaged elastic fibers give an aged and wrinkled appearance.

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.