Cyclobutane pyrimidine dimers (CPDs) are ultraviolet radiation (UV)-induced carcinogenic DNA photoproducts that lead to UV signature mutations in melanoma. Previously, we discovered that, in addition to their incident formation (iCPDs), UV exposure induces melanin chemiexcitation (MeCh), where UV generates peroxynitrite (ONOO⁻), which oxidizes melanin into melanin-carbonyls (MCs) in their excited triplet state. Chronic MeCh and energy transfer by MCs to DNA generates CPDs for several hours after UV exposure ends (dark CPD, dCPDs). We hypothesized that MeCh and the resulting dCPDs can be inhibited using MeCh inhibitors, and MC and ONOO⁻ scavengers. Here, we investigated the efficacy of Acetyl Zingerone (AZ), a plant-based phenolic alkanone, and its chemical analogs in inhibiting iCPDs and dCPDs in skin fibroblasts, keratinocytes, and isogenic pigmented and albino melanocytes. While AZ and its methoxy analog, 3-(4-Methoxy-benzyl)-Pentane-2,4-dione (MBPD) completely inhibited the dCPDs, MBPD also inhibited ~50% of iCPDs. This suggests the inhibition of ~80% of total CPDs at any time point post UV exposure by MBPD, which is markedly significant. MBPD downregulated melanin synthesis, which is indispensable for dCPD generation, but this did not occur with AZ. Meanwhile, AZ and MBPD both upregulated the expression of nucleotide excision repair (NER) pathways genes including Xpa, Xpc, and Mitf. AZ and its analogs were non-toxic to the skin cells and did not act as photosensitizers. We propose that AZ and MBPD represent “next-generation skin care additives” that are safe and effective for use not only in sunscreens but also in other specialized clinical applications owing to their extremely high efficacy in blocking both iCPDs and dCPDs.

Background: Presynaptic G_i/o coupled GPCRs can act as negative feedback regulators of neurotransmitter release via Gβγ effector modulation through two mechanisms: decreased calcium influx and direct inhibition of membrane fusion by soluble N-ethylmaleimide—sensitive factor attachment protein (SNAP) receptor (SNARE). Previously, we discovered that truncation of the last three C-terminal amino acids of SNAP25 (SNAP25Δ3) prevents Gβγ-SNARE interaction, effectively removing the braking mechanism on neurotransmitter release. We have demonstrated enhanced metabolic protection in male SNAP25^Δ3/Δ3 mice housed at room temperature (22°C), including increased adipose tissue beiging and glucose uptake and enhanced insulin sensitivity, rendering them resistant to diet-induced obesity (DIO). When male SNAP25^Δ3/Δ3 mice were housed at thermoneutrality (30°C), all metabolic protection was abolished, suggesting sympathetic tone is important for the phenotypes.Methods: We housed male and female mice at either standard room temperature (21°C) or at thermoneutrality (30°C) and fed them a high fat diet (HFD) for 8 weeks. Glucose tolerance tests were performed before and after the 8 weeks of HFD along with body composition analyses. Organs were then dissected for mass analysis as well as immunohistochemistry. Additionally, we ovariectomized female mice to investigate the role of sex hormones in our phenotypes. Finally, we housed mice in Sable Promethion chambers at various environmental temperatures to investigate the effect of environmental temperature on basal metabolic rates.Results: We found SNAP25^Δ3/Δ3 female mice exhibited the same metabolic protection at RT (22°C) and displayed enhanced metabolic protection from DIO compared to standard chow just as males did. However, female SNAP25^Δ3/Δ3 mice display persistent metabolic protection even when housed at thermoneutrality. In this study, we investigate the mechanisms behind this sex dependent persistent phenotype. Thermoneutral set point did not differ between sexes nor genotype, suggesting that metabolic protection is not due to a difference in hypothalamic temperature regulation. Metabolic protection in SNAP25^Δ3/Δ3 persisted in ovariectomized mice despite increased weight gain compared to mice receiving sham operations.Conclusion: This study has identified that there is not a sex-dependent difference for thermoneutral set point in mice. Additionally, there is a sex hormone independent mechanism driving the persistent metabolic protection of female SNAP25^Δ3/Δ3 mice housed in thermoneutrality.