Combined topical rapamycin and melatonin improve biomarkers of aging/senescence in aged human scalp skin ex vivo

Summary: Abstract Body: Given the multifactorial nature of human skin aging, we tested whether the combined topical application of two agents with well-known, but quite distinct anti-aging effects improves core biomarkers of skin aging/senescence aged human scalp skin: the endogenous indoleamine neurohormone, melatonin (MT), which inhibits human eyelid skin aging ex vivo, and the immunosuppressive mTOR inhibitor, rapamycin (RPM), which can stimulate repigmentation in gray/white human hair follicles, after addition to the culture medium. Topical MT application circumvents rapid MT metabolism by the liver, while topical RPM reduces the risk of systemic immunosuppression. Combined MT (1 mM) and RPM (2uM) was applied every other day topically to aged, organ-cultured, full-thickness human scalp skin from 5 healthy male donors (age range: 42-63y-o) for 6 days in a PEG/isopropanol vehicle. Quantitative immunohistomorphometry revealed that topical MT+RPM significantly decreased p16INK4, mTORC1 activity (reduced S6 phosphorylation), and MMP1 protein expression in the basal and granular layers of the epidermis compared to vehicle-treated skin. Instead, MT+RPM significantly increased the epidermal protein expression of SIRT-1, PGC1a, and Lamin B1. Instead, no changes were seen in VEGF-A, and MTCO1 protein expression in the epidermis and fibrillin-1, and collagen 1&3 in the dermis of MT+RPM skin compared to control. Our study provides proof-of-principle that the combined topical application of two established, well-tolerated, anti-aging actives, MT and RPM, unfolds potent, interindividually reproducible anti-ageing/-senescence properties in aged male scalp epidermis ex vivo. This encourages subsequent in vivo testing of this senotherapeutic combination in skin aging trials. Tatiana Gomez-Gomez¹, Kinga Linowiecka^{2, 3}, Mara A. Hartoyo¹, Daniela H. Buchbinder¹, Mounika Vattigunta¹, Alexa Paulaitis¹, Divya E. Varughese¹, Sofia M. Perez¹, Kazi Taheruzzaman¹, Ramtin Kassir⁴, Jeremy Cheret^{1, 3}, Ralf Paus^{1, 3} 1. Dermatology, University of Miami Miller School of Medicine, Miami, FL, United States. 2. Human Biology, Uniwersytet Mikolaja Kopernika w Toruniu, Torun, Kuyavian-Pomeranian Voivodeship, Poland. 3. CUTANEON-Skin&Hair Innovations GmbH, Hamburg&Berlin, Germany. 4. Kassir Plastic Surgery, New York City, NY, United States. Stem Cell Biology, Tissue Regeneration and Wound Healing