BC01 Daily photoprotection with an antioxidant-enriched sunscreen preserves mitochondrial DNA integrity in facial skin in vivo : a randomized, double-blind, vehicle-controlled trial

Abstract

Mitochondrial DNA (mtDNA) damage is a sensitive biomarker of photo-oxidative stress and has been widely studied in vitro. Human sunscreen studies have traditionally relied on indirect nuclear DNA endpoints measured in urine or invasive skin biopsies. However, the application of mtDNA damage as a primary, noninvasive in vivo outcome measure in cosmetic photoprotection trials has not been established. Objective biomarkers capable of quantifying real-world skin ageing prevention are needed in aesthetic dermatology. We aimed to evaluate, for the first time in vivo, whether daily use of an antioxidant-enriched sunscreen preserves mtDNA integrity compared with vehicle, and to assess its utility for detecting individual-level cosmetic photoprotection responses using noninvasive sampling. Adults completed a randomized, double-blind, vehicle-controlled 12-week trial. Cheek swabs were collected at baseline and week 12 and analysed using blinded quantitative polymerase chain reaction. mtDNA damage was expressed as ΔCt, where higher values indicate greater damage. The primary outcome was change in ΔCt. Responders were defined as having ΔCt < 0. Between-group comparisons using nonparametric testing were conducted. Commercial product supply and laboratory processing were provided by industry partners and declared. Thirty-seven participants provided valid paired samples (active n = 19, vehicle n = 18). Mean ΔCt change favoured the active formulation (−0.48 vs. +0.35; between-group difference −0.83; 95% confidence interval −1.71 to 0.05; P = 0.06). Responder rates were higher with active treatment (74% vs. 39%; P = 0.05). Among habitual sunscreen users, mtDNA integrity improved with active treatment (median ΔCt −0.67; P = 0.04) and worsened with vehicle (median ΔCt +0.58; P = 0.03). Responder rates in this subgroup were 75% vs. 25% (P = 0.03). mtDNA demonstrated clear sensitivity to individual-level in vivo change. This study provides novel in vivo evidence that an antioxidant-­enriched sunscreen can reduce mtDNA damage in human facial skin using a noninvasive sampling method. mtDNA integrity represents a novel, practical biomarker for evaluating cosmetic photoprotection and skin ageing prevention under real-world conditions.