1. INTRODUCTION
The human body has different ways for protecting itself against
potential injuries and infections, by means of the skin characteristics
acting as an effective barrier. The physiological process of tissue
repair at an injured site is the wound healing, which represents a
complex integrated system of biological and molecular processes, such as
cell migration, proliferation, extracellular matrix deposition and
remodelling.[1] Under normal conditions, the healing process cascade
is initiated by an inflammatory phase yielding to granulation tissue
accumulation and scar remodelling after epithelial wound closure has
been accomplished.[2] A normal wound healing process is constituted
by various phases: coagulation (hemostasis), inflammation, cellular
migration and proliferation, protein synthesis and wound contraction
(fibroplasia), and scar formation (remodelling). Among these phases,
three are the most important for a successful wound healing:
fibroplasia, angiogenesis and re-epithelialisation. A delay in the
development of these mechanisms leads to failure or prolong wound
healing process with a crucial part attributable to the wound
neovascularisation.[3,4] However, any change or pathological problem
(for example ischemia, diabetes mellitus and so on) may result in the
formation of chronic wounds difficult to heal, due to the failure of the
normal wound healing process.[3,5] Another very important objective
of the wound treatment is the inhibition of all the pathogenic organisms
able to cause serious infection, by accelerating the healing process
with reducing cicatrices and pain to the patients of all ages.[5] In
fact, any delay during the tissue repair process could be defined as
chronic injury and can have a highly detrimental impact on human health
being more subjected to pathogens. Rapid closure of dermatological
wounds is of vital importance in preventing infection and reducing
post-treatment side-effects.[6] So, shortening the chronic wound
healing process is a prime challenge in modern dermatology.[7]
Several different topical and systemic agents, together with the
antimicrobial ones have been developed for improving the cure of
surgical and traumatic wounds. However, these functional topical
biomaterials might delay re-epithelialisation and might result a risk
for oversensitivity and resistance.[4] Hence, some alternative wound
treatment methods have been searched for and, in this regard, the use of
nanotechnology could be useful as a prominent scientific discipline in
the technological revolution of this millennium.[8]
Nanobiotechnology-based therapies in the field of wound healing are
considered to be a promising area with new benefits based on the
utilization of bionanomaterials in promoting wound healing, including
antibacterial, antiinflammatory, regulating extracellular matrix
production, promoting stem cell proliferation and differentiation, and
enhancing growth factors.[9] Researches using gold nanoparticles
(AuNPs) of different sizes and morphologies have been proposed in
biomedical applications for skin injury therapy with great
potential.[6] AuNPs have received great attention due to their low
toxicity to animal and microorganism cells compared to other metal
nanoparticles,[10] promoting their use as drug delivery systems,
markers, and photothermal agents, as well as radiotherapy enhancers as
well.[6] Recent studies have established new prospects for
developing properly functionalized AuNPs for wound healing, acting as
triggers to activate proliferation and migration of wound
cells.[7,11,12] The AuNPs use should exhibit benefits including
enhanced mechanical stability and resistance against enzymatic
degradation when incorporated into tissue scaffolds, in presence of
antibodies, growth factors, and peptides, rendering them promising
candidates for skin tissue engineering applications.[8]
Chemical methods, in which reduction or co-precipitation processes take
place for the generation of nanoparticles, have been investigated since
ancient times. However, the main drawbacks of these synthetic routes are
the use of harsh chemical conditions of work, organic solvents and the
production of toxic by-products during the synthesis and/or
functionalization of the nanoparticles. For this purpose, many studies
are focused on finding alternative therapeutic approaches by adopting
biocompatible, safer and greener methods employing plant extracts for
the fast and economical synthesis of biogenic nanogold.[13-15] Green
synthesized AuNPs can also exhibit anticancer and antimicrobial
activity,[16] antioxidant moisture retention, skin lightening
properties,[17] and sunscreen ability, enlarging their
applicability.[18,19] As reported by Gonnelli et al. ,[20]
synthetic routes relying on green chemistry show other advantages for
large scale production adopting mild conditions of work.[20] For
green synthesized AuNPs, additional assembling steps are not necessary
since the AuNPs properties are ascribed to main components present on
their surface and used to induce their formation. Thus, considering
these factors, the snail secretion (SS) from Helix Aspersa ,
currently revolutionizing the world of cosmetics and human skin care,
has been used in this work for synthesizing AuNPs (AuNPs-SS), conferring
them interesting properties. Indeed, the SS protein content plays a key
role in cell regeneration and growth, preventing the effect of the
inflammatory disease.[21,22] The SS main compounds are used as
reducing agents enabling the AuNPs synthesis via reduction of Au(III),
from a HAuCl4 solution, to Au(0), while forming an
organic layer around the AuNPs. AuNPs-SS are thus synthetized by using a
single step reaction, avoiding the use of additional and toxic agents.
The nanoconfined main components of the SS on the AuNPs surface could be
an interesting way for improving the whole process, combining the
properties of gold and SS. For example, Conte et al .[23]
reported that the pharmacokinetics of snail components do not permit
their optimal absorption, so the combined use of AuNPs, well-known
antibacterial agents, and SS could be a functional ingredient in the
treatment of acne and in biotechnology, or used as a preservative in
cosmetic products formulation. Considering the overall literature
published,[21,22,24-27] although interesting information can be
found on the SS use, the presence of fragmentary and not detailed
investigations suggests that this research field has not been
extensively explored yet. In a time when cosmetic dermatology and beauty
care are increasingly influential,[28,29] we intend to discuss the
biogenic formation of AuNPs-SS by characterizing them and by applying as
accelerating wound healing and anti-inflammatory agents in biomedicine.
More specifically, we tested the effect of AuNPs-SS on improving wound
healing in human keratinocytes. Furthermore, considering that gold has
been used historically in the treatment of painful inflammatory
conditions, such as rheumatoid arthritis, and snail slime has been
proved to clear up skin inflammation, we evaluated the potential
anti-inflammatory properties of AuNPs-SS in Murine Macrophages.
2. EXPERIMENTAL SECTION