Key words
wound healing - split-thickness skin graft - burn wounds - Betulaceae -
Betula pendula
-
Betula pubescens
- betulin
Introduction
Betulin-0leogel (Episalvan) is a drug approved for the first time worldwide by the
EMA for the European Economic Area in 2016 (EU/1/15/1069/001) containing the triterpene-rich,
purified dry extract from the bark of Betula pendula and B. pubescens, or hybrids of both species, as active ingredient. In what follows, this new birch
bark extract will be referred to as “betulin” or “TE” for short, after the predominant
substance contained in it, constituting around 80%.
The indication is the treatment of superficial skin wounds (epidermis and upper dermis)
and II a-degree burn wounds to the skin in adults. So far, there has been no drug
approved in Europe with proven efficacy in accelerating wound closure of such wounds.
Betulin-oleogel opens up the area of application of wound healing for phytotherapy,
e.g. in plastic surgery, and especially in burn medicine.
The intention in what follows is to outline the development of this new drug.
The Starting Point: Two Inventions
The Starting Point: Two Inventions
The cork layer ([Fig. 1]) of white-barked, tree-forming birches contains about 20 – 22% betulin alongside
about 3 – 5% closely related pentacyclic triterpenes such as betulinic acid, lupeol,
erythrodiol, caffeoyl-betulin and oleanolic acid.
Fig. 1 The cork layer can be removed relatively easily from the cork skin of the birch bark.
This concentration of a closely related group of active substances with the lead substance
betulin in a relatively easily accessible plant tissue is extreme. Even more surprising,
however, is the fact that betulin was first described in 1788 [1], but was only processed for the first time into an herbal active pharmaceutical
ingredient with the innovation described here.
Two galenic properties of the refined, white, powdery dry extract that are important
for its therapeutic application were unexpectedly revealed:
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Betulin stabilises water-in-oil emulsions as a solid stabiliser and not as a surface-active
substance. It thereby has a multifunctional effect, in that microparticles stabilise
the interface between oil and water and at the same time form a gel network in the
oil [2].
-
Betulin gelatinises oils. The result is thixotropic gels whose solidity is higher
at body temperature than at room temperature. Thixotropic means they liquefy when
agitated, so they can be applied comfortably and solidify when at rest [3].
Both inventions are patented [4], [5]. The patents formed the basis for the foundation and financing of a pharmaceutical
company (Birken GmbH in 2000, renamed as Birken AG in 2011, and Amryt AG since 2017).
First of all, the dry extract was subjected to toxicological and pharmacological safety
testing with a view to drug development. Due to its excellent tolerability, we decided
to develop the betulin emulsion into a base for a new surfactant-free cosmetic and
to market this betulin-emulsion from 2004 (Imlan). Due to the continuous need for
production at increasing volumes, this approach led to a wealth of experience in the
extraction of the active ingredient and in product manufacturing, which was essential
for the development of the drug during the approval process. All quality assurance
procedures, the acceptable range of process parameters (design space), the function
and properties of the active substance and, last but not least, the pharmacological
impact analysis were able to be developed during this time. Physical, chemical and
pharmacological properties have been published by Laszczyk et al. [6].
Drug Development
The scientific interest in triterpenes such as betulin and its closest relatives has
risen dramatically worldwide since 1995, when Pisha wrote an article in the first
issue of Nature Medicine magazine about the discovery of betulinic acid counteracting
malignant melanoma [7].
The effects described range from antiviral to tumour-inhibiting and anti-inflammatory,
to anti-diabetic. Laszczyk summarises the tumour-inhibiting properties of relevant
triterpenes [8]. Cytotoxic effects of cyclodextrin-bonded triterpenes from birch bark are described
by Hertrampf et al. [9].
In addition to the drug to be applied, drug development requires an indication, which
is to be tested. Through the application of the betulin-emulsion, we obtained evidence
of efficacy in cases of actinic keratosis, which was also demonstrated in a small
mono-centric phase II study [10]. However, the results of a multi-centre phase II b study were too weak to brave
an expensive approval process.
Phase II
The breakthrough came in 2010 with a phase II study on accelerating wound closure
at split-thickness-skin graft donor sites. The new study design [11] made use of an intra-individual comparison of betulin-oleogel in combination with
a non-adhesive, siliconised wound dressing versus the same wound dressing without
any medication on a wound split into halves. A blind, independent evaluation was performed
by 2 external experts on macro images of the wound. Every time the dressing was changed,
re-epithelialisation was compared for both halves of the wound – unblinded, by the
attending physicians (percentage estimate) and blinded, by the independent experts,
on the basis of the photos, whereby the more strongly closed half was scored with
a 1, and the other with a 0, and where no decision could be made, both halves were
rated 0. A score was established for each wound healing process. For details see Table
3 in [12].
To adjust the number of patients, an interim evaluation was planned after 20 evaluable
processes. The result was surprisingly clear: out of 24 wounds, 20 were re-epithelialised
faster with Episalvan, 2 with the wound dressing alone, and for 2, no decision could
be reached. The result was highly significant (p < 0.0001) and the study was completed.
A typical course of progress is shown in Fig. 3 in [12].
The results were published in more detail in Skin Pharmacology and Physiology [12], as were investigations into the validity of the study design, in the journal Trials
[13].
Consultation with the authorities for phase III
The task was now to carefully prepare the substantiating studies of phase III. Is
one even permitted to carry out a human study still with such a clear result? Scientific
consultations at the Federal Institute for Drugs and Medical Devices and the European
Medicines Agency resulted to important advices.
Therefore, three phase III trials were conducted in a total of 48 hospitals in 13
countries, from Valencia in Spain to Pori in Finland, from Birmingham in England to
Varna in Romania and Athens in Greece, with 280 patients. In addition to 2 studies
at the split-thickness-skin graft donor site, similar to in Phase II, 60 patients
with 2nd-degree burns were treated in the third study. A representative course of
progress at a burn wound is shown in Fig. 1 in [14].
All three studies demonstrate faster wound closure with the use of betulin-oleogel,
to a highly significant degree: by 1 – 2 days when determined by blind evaluation
of photographs, and by 1.8 – 2.5 days in open evaluation by the physician. What is
impressive, and clearly relieves pain for the patient, is the rapid abatement of redness
under betulin-oleogel. Even more important, however, is the long-term result. The
wounds were re-examined after 3 months (Fig. 9 in [15]) and after one year.
In those patients where a difference could still be observed, as assessment was made
as to whether the healed skin was more similar to healthy skin in texture, redness
and pigmentation when treated with betulin-oleogel or with the wound dressing alone.
The results are: texture (27.5% vs. 7.1% after 3 months [p < 0.001], 13.5% vs. 2.7%
after 12 months [p = 0.002]), redness (28.0% vs. 10.4% after 3 months [p < 0.001],
12.8% vs. 4.1% after 12 months [p = 0.015]), and, in particular, pigmentation (36.8%
vs. 10.4% after 3 months [p < 0.001], 23.6% vs. 8.9% after 12 months [p = 0.002]).
Where a difference in the scarring pattern could still be seen, the half treated with
betulin-oleogel resembled the healthy skin significantly more frequently than did
the re-epithelialised skin with the wound dressing alone. The results for the split-skin
studies are published in detail in the journal Burns [14].
Benefits for the patient and the approval process
In general, accelerated wound healing has advantages for patients: reduced pain, lower
risk of infection and fewer complications such as hypertrophic scarring. In general,
the faster a wound closes, the better the cosmetic result. The new skin more closely
resembles the uninjured skin. As already mentioned, this was impressively demonstrated
in the phase III programme.
After careful evaluation of the study results and compilation of the approval dossiers
on quality, harmlessness and clinical efficacy, the company applied to the EMA in
October 2014 for central European approval as a drug with a new active ingredient.
In November 2015, the Committee for Medicinal Products for Human Use issued a unanimously
positive vote, and so, in January 2016, approval was granted for 28 European countries.
In April 2016, the company was acquired by a stock-listed new founded company (now
Amryt-Pharma), which is seeking further approval for Europe and the USA for the indication
epidermolysis bullosa [16].
Orphan Drug Designation for the Indication Epidermolysis Bullosa
Orphan Drug Designation for the Indication Epidermolysis Bullosa
Both the EMA, in 2011, and the FDA, in 2014, issued an orphan drug designation for
the active ingredient betulin for the indication epidermolysis bullosa. In this rare
disease, which is also known as butterfly disease, the skin lacks certain anchor proteins
due to hereditary factors, with the result that even slight mechanical stress results
in detachment of the skin, with open wounds or blisters. Case reports and a phase
II study on the acceleration of re-epithelialisation revealed birch bark extract to
be beneficial for wound healing [17]. Verification by means of a substantiating phase III study was initiated in April
2017. An interim efficacy analysis at the end of 2018 recommended that the trial should
continue with an increase of 48 patients to a total of 230. Results are expected in
H2 2019 [16].
Mode of Action: Acceleration in All 3 Phases of Wound Healing
Mode of Action: Acceleration in All 3 Phases of Wound Healing
As already mentioned above, studies on the pharmacological effect of betulins were
carried out during the development years, from 2006 to 2013. In collaboration with
the research groups of Professor Schempp and Professor Merfort in Freiburg, as well
as Professor Brandner in Hamburg, important evidence of the effect of betulins and
the dry extract (TE) was obtained for the different phases of wound healing.
Wound healing takes place in three stages: the process begins with the inflammatory
phase, in which mediators are released to attract macrophages, phagocytes and granulocytes
into the wound in order to clean the wound. In the second phase, the inflammation
is resolved, and the skin cells multiply and migrate in order to close the wound.
The third and final phase is the longest lasting. The skin cells differentiate, mature
and remodel the wound.
Temporary stimulation of the inflammatory phase
Inflammation mediators such as COX-2, IL-6 and IL-8 are temporarily up-regulated by
TE thanks to its stabilisation of their mRNA (half-life increases by a factor of 3.5).
Possible and investigated pathways for this process are p38 MAPK and HuR [18].
Skin cells migrate faster
TE influences the cell migration of primary human keratinocytes via the induction
of IL-6 and STAT3. Stabilisation of IL-6 mRNA by TE leads to up-regulation of the
transcription factor STAT3. In the scratch assay, it was possible to demonstrate faster
closure of a split under the influence of TE (Fig. 9 in [18]).
Another effect on keratinocytes is the increased formation of lamellipodia, filopodia
and stress fibres. Keratinocytes exhibit these phenomena when stimulated to migrate
until they come into contact with neighbouring cells again (Fig. 10 in [18]). Clinically, this manifests in accelerated re-epithelialisation.
Accelerated maturation of the barrier
For the final stage of wound healing, it was possible to show that TE stimulates keratinocyte
differentiation markers to bring about maturation of the barrier. In the early differentiation
phase, involucrin and keratin 10 are increasingly expressed, and in the late phase,
transglutaminase. In the end, the terminal differentiation – the apoptosis-like transition
of keratinocytes to corneocytes – is specifically triggered by TE. Proof was able
to be furnished ex vivo through apoptosis staining (Fig. 8 in [19]).
Accelerated Wound Healing by Means of Episalvan is a Rational Phytotherapy
Accelerated Wound Healing by Means of Episalvan is a Rational Phytotherapy
With proof of the mode of action as outlined above, accelerated wound healing by means
of betulin-oleogel (Episalvan) is a rational phytotherapy. It has been shown that
chemically and physico-chemically analysed plant extracts can be subjected to a precise
biological impact analysis. However, it was helpful for this analysis that the therapeutic
effect of faster re-epithelialisation had already been discovered in the phase II
clinical observation test. As a result, the impact analysis was able to be much more
effective and targeted.
