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J. Cosmet. Sci., 75.2, 128–145 (March/April 2024)
*Address all correspondence to Danielle Guimarães Almeida Diniz, danielle_diniz@ufg.br
Improved Photostability and Skin Retention of Avobenzone
Encapsulated in Compatible Nanostructured Lipid Carriers
ISABELLY PAULA SOUSA, AMANDA CECÍLIA TEODORO LANDIM, BÁRBARA
CRISTINA CAMPOS RIBEIRO, EMILIO RAMOS CINTRA, LORENA MAIONE SILVA,
THAIS LEITE NASCIMENTO, ELIANA MARTINS LIMA, LUÍS ANTÔNIO DANTAS
SILVA AND DANIELLE GUIMARÃES ALMEIDA DINIZ
Laboratory of Pharmaceutical Technology and Drug Delivery Systems, Federal University of Goias, Brazil
(I.P.S., A.C.T.L., B.C.C.R., E.R.C., L.M.S., T.L.N., E.M.L., L.A.D.S., D.G.A.D.)
State University of Goias, Brazil (L.M.S.)
Accepted for publication February 28, 2024.
Synopsis
Avobenzone (AVB) is an organic filter acting in the UVA spectrum. To exert its photoprotective effect, AVB
must be protected from UV radiation since it can suffer photoisomerization and incur adverse effects, such
as endocrine and metabolic disruption. Nanostructured carriers are an interesting strategy for protecting
the molecule and reducing skin permeation. This study aimed to improve AVB photostability and skin
retention through encapsulation in nanostructured lipid carriers. Our results showed that nanoencapsulation
in carnauba wax-nanostructured lipid carriers prepared with compatible lipid excipients proved to be an
efficient strategy in preventing AVB photo-instability. The formulation showed improved skin retention,
could be further investigated as a carrier to overcome AVB limitations as a long-wave UVA filter, and may
contribute to improving the efficiency and safety of this active cosmetic ingredient.
INTRODUCTION
Nonmelanoma skin cancer is the most common human malignancy worldwide, with
increasing yearly incidence rates.1 Even with this high incidence, the disease has low
mortality and a high probability of remission. Some important risk factors are related
to the disease, such as genetic predisposition, skin phenotypes, and prolonged exposure
to UV radiation without proper use of UV protection.2,3 There is a growing need for
more effective topical sunscreens to prevent the harmful effects of UV radiation on
human skin.4 While most sunscreens provide excellent protection against UVB radiation,
adequate protection against UVA radiation is becoming increasingly necessary.5 Studies
highlight the significant role played by UVA radiation in sunlight-induced skin damage
and changes, such as immunosuppression, DNA mutations, lipid and protein oxidative
damage, increased epidermal ferritin expression, skin photoaging, and decreased skin

129 ImprovedPROVED AVB PhotostabilityOTOSTABILITY UsingING NLCs
hydration and elasticity.6–8. Through the generation of singlet oxygen, UVA radiation can
induce the expression of matrix metalloproteinases that destroy connective tissue.9 In this
context, the availability of sunscreens with broader protection is an increasing consumer
concern. Although most available commercial formulations have a variety of UVB filters,
the number of UVB filters that are also effective UVA absorbers are rare, and they often
present poor performance or are not photostable.
In 2019, the American Regulatory Agency Food and Drug Administration published
regulations for products containing sunscreens, providing for their classification regarding
the safety of filters that are marketed in the USA, classifying them as totally safe, unsafe,
and requiring additional research.10 Among those that require further research is butyl
methoxydibenzoylmethane, also known as avobenzone (AVB).10 AVB is a chemical UV
filter associated with UVA protection. It is presented as a mixture of two tautomeric forms:
enol and keto.11 Chemical equilibrium between the two isoforms favors the enol form
in almost all media due to its ability to form hydrogen bonds. The enol form absorbs in
the UVA spectrum and is responsible for the UVA protection effect. Under irradiation,
the enol form in solution photoisomerizes to the keto form, causing a large decrease in
absorption. The keto form mainly absorbs in the UVC spectrum region, losing its UVA
protective effect.11,12
Photostabilization is critical to the development of sunscreen formulations. Studies have
shown that the use of nanotechnology in photoprotective formulations can improve the
photo stability of some filters.13,14 Formulations of lipid nanoparticles containing AVB have
been evaluated for their ability to absorb UV radiation and their UVA protection factor
after irradiation.14 Type, physical properties, and chemical nature of lipid-based excipients
may influence the physicochemical properties and stability of the lipid carriers,15,16 as well
as their interaction with biological systems.17,18 Therefore, the screening of the excipients
has been described to ensure the development of safe, stable, and efficient lipid-based
formulations.19,20 In this study, we used thermogravimetry (TG/DTG), differential thermal
analysis (DTA), and Fourier-transform infrared spectroscopy (FTIR) techniques to evaluate
the interaction between AVB and lipid excipients and to select the most suitable components
for a rational nanostructured lipid carrier (NLC) design.
In the development of photoprotective formulations minimal skin permeation is required,
since the exposure to many organic sunscreens has been associated with several adverse
effects, such as endocrine21 and metabolic disruption.22,23 Besides the safety concern, the
search for sunscreens that are stable, and thus maintain the photoprotective ability of the
formulation, mobilizes the investigation of new applications, methods, and technologies
applied to photoprotective formulations. In this work, we designed a NLC formulation
encapsulating AVB, and evaluated its photostability against UV radiation and its ability to
reduce the cutaneous penetration of AVB, favoring its retention on the skin surface.
MATERIALS
Avobenzone was purchased from Symrise AG (Holzminden, Germany). Avobenzone
standard was purchased from Sigma-Aldrich (Missouri, USA). Beeswax, carnauba wax,
isopropyl myristate, sorbitan monoleate (Span 80) and trioleate sorbitan (Span 85) were of
cosmetic grade and purchased from Sigma-Aldrich (Missouri, USA). Oleic acid of cosmetic
grade was acquired from Labsynth Products Laboratories (Diadema, Brazil), Polysorbate 20