Acne vulgaris is a common skin disease that is characterized by papules, nodulocystic lesions, and inflammation of the pilosebaceous follicles. Acne vulgaris is mainly caused by
Pattern recognition receptors (PRRs) are the first line of defense against invading microbes as they recognize pathogen-associated molecular patterns and play an important role in the production of proinflammatory cytokines such as interleukin-1β (IL-1β) (Guo
Auranofin, a gold (Au)-containing acetylated carbohydrate complex, is used in the treatment of rheumatoid arthritis. It has been widely studied as a potential treatment for cutaneous staphylococcal infections (Thangamani
C57BL/6 mice were obtained from Raon Bio (Yongin, Korea). NLRP3-knockout mice (B6N.129-Nlrp3tm3Hhf/J) and caspase-1 knockout mice (B6N.129S2-Casp1tm1Flv/J) were obtained from the Jackson Laboratory (Bar Harbor, ME, USA). Mice were acclimated under specific pathogen-free conditions in an animal facility for at least one week before the experiments. They were housed in a room controlled for temperature (23 ± 3°C) and relative humidity (40–60%). The mice in each experiment were of similar age and weight and were randomly allocated into treatment groups. All experimental protocols followed the Institutional Animal Care and Use Committee (IACUC) of the Catholic University of Korea guidelines (Permission No. #2016-005).
Bone marrow cells were isolated from C57BL/6 mice and differentiated into macrophages in DMEM containing 10% (v/v) heat-inactivated fetal bovine serum (Thermo Fisher Scientiﬁc, Carlsbad, CA, USA) and 20% L929 conditioned medium for seven days (Lee
Purified LPS from
This was performed as described previously (Lee
IL-1β, IL-17, and TNF-α levels in culture media or ear homogenate supernatants were determined using a DuoSet ELISA kit (R&D Systems) according to the manufacturer’s instructions.
Ear tissue specimens were fixed in 4% buffered formalin, embedded in paraffin, and stained with hematoxylin and eosin (H&E) for the histological examination of inflammation as described previously (Yang
The enzymatic activity of caspase-1 in mouse ear homogenates (50 μg) was measured using a caspase-1 assay kit from Bio-vision (Milpitas, CA, USA) according to the manufacturer’s instructions. Fluorescence was recorded at 400 nm after excitation at 505 nm using a SpectraMaxM5 microplate reader (Molecular Devices, Sunnyvale, CA, USA).
MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide, methylthiazolyldiphenyl-tetrazolium bromide) was dissolved in PBS at 5 mg/mL. BMDMs were treated with and without auranofin and
The results are expressed as the mean ± standard error of the mean (SEM). One-way analysis of variance was performed followed by Duncan’s multiple range test to determine any significant differences between groups. SPSS 12.0 software (IBM Co., Chicago, IL, USA) was used. Statistical significance was considered when
To investigate whether auranofin inhibited activation of the NLRP3 inflammasome in macrophages, mouse bone marrow-derived macrophages were stimulated with NLRP3 inflammasome activators, ATP or nigericin, in the presence or absence of auranofin. Activation of the NLRP3 inflammasome involves two signals. The first signal is to induce pro-IL-1β expression by TLR agonist such as LPS. The second signal is triggered by the NLRP3 inflammasome agonists to form the inflammasome complex consisting of NLRP3, ASC, and pro-caspase-1 resulting in the activation of caspase-1 to cleave pro-IL-1β to mature form of IL-1β (Swanson
Next, we investigated whether auranofin could block
We examined whether IL-1β reduction by auranofin was related to cytotoxicity. Auranofin exhibited no cell toxicity to primary macrophages up to 1 μM treatment, at which concentration the suppression of NLRP3 was observed (Supplementary Fig. 1A). Even when macrophages were treated with auranofin together with
We examined whether auranofin suppressed acne-associated inflammation in a
Immunohistochemistry results showed that the levels of IL-1β and caspase-1 in ear tissues were enhanced by
Overall, our results demonstrate that topical application of auranofin on mouse ears alleviates inflammatory responses induced by
Our study demonstrates that topical application of auranofin is effective for preventing acne vulgaris induced by
Auranofin is used for the oral administration of rheumatoid arthritis. In addition, the potential application of auranofin for other diseases, including skin complications, has been extensively studied. Topical application of auranofin (1% or 2%) suppressed
In addition, repurposing auranofin for the treatment of neurodegenerative disorders such as Alzheimer and Parkinson’s disease has been investigated (Madeira
Auranofin is orally administered for rheumatoid arthritis. However, bioavailability with the oral administration route is not effective since the absorption rate is 20 to 30% and 50% of the absorbed auranofin is excreted in the urine (Blocka
Isotretinoin as a pro-drug for retinoic acid, exhibits a low affinity for retinoic acid receptors (RAR) and retinoid X receptors (RXR) while it is suggested that its intracellular metabolites may act as agonists of RAR and RXR (Layton, 2009). There is a report suggesting that the regulation of
Collectively, our results show the efficacy of auranofin in the inhibition of the NLRP3 inflammasome in cells and animals, leading to the improvement in inflammatory symptoms of acne vulgaris. Our study suggests that the repurposing of auranofin via dermal application to treat acne vulgaris could be beneficial.
This study was supported by the Research Fund, 2019 of The Catholic University of Korea, and grants from the National Research Foundation of Korea (NRF-2019R1A2C2085739, NRF-2017R1A4A1015036, and NRF-2020R1A4A2002894) funded by the Korean government (Ministry of Science, ICT and Future Planning) and Cooperative Research Program for Agriculture Science and Technology Development (Project no. PJ01199002) from Rural Development Administration, Republic of Korea.
Christos C. Zouboulis is the owner of an international patent on the immortalized human sebaceous gland SZ95 cell line (WO0046353).