Tetrahexyldecyl Ascorbate (THDC) degrades rapidly under oxidative stress but can be stabilized by acetyl zingerone to enhance collagen production and antioxidant effects, International J Molecular Sciences, 22:8756, 2021
The topical delivery of Vitamin C (VC) holds longstanding challenges due to its poor stability and dermal penetration. Tetrahexyldecyl Ascorbate (THDC, VitaSynol® C), a lipid-soluble VC precursor esterified with branched chain fatty acid (2-hexyldecanoic acid), is reported to have an improved stability and ability to penetrate the lipophilic stratum corneum. This essentially makes THDC a pro-drug that facilitates delivery to the dermis where it may then undergo intracellular enzymatic conversion to release VC. As a result, THDC has garnered widespread interest and use within the cosmetics industry even though the molecule comprises only 15.5% VC, which means that in order to deliver 1% VC to skin at least 6.5% THDC would be required in a formulation assuming 100% conversion to VC.
Our study revealed that THDC, itself, is a poor antioxidant and undergoes rapid degradation when exposed to singlet oxygen, a well-recognized mediator of oxidative stress within skin. Interestingly, we observed that THDC degradation by singlet oxygen could be prevented by combining it with Synoxyl® AZ (Acetyl Zingerone, AZ) as a stabilizing antioxidant (non-sacrificing). Also, while THDC lacked ability to improve viability of HaCaT Keratinocytes exposed to oxidative stress (H2O2), combining THDC with AZ bestowed complete protection.
In gene expression studies using RHE (Reconstituted Human Epidermis, EpiDerm FT tissues, Mattek, Microarray), treatment with THDC as a standalone ingredient led to unexpected activation of type I interferon signaling, the unhealthy skin gene signature, as well as the pro-inflammatory STAT1-57 gene module, all of which were abrogated when THDC was combined with AZ. Activation of the type I interferon pathway plays important roles in antiviral defense responses, wounding and skin cancers, in addition to a broad spectrum of other skin diseases. To our knowledge, no prior studies have demonstrated detrimental pro-inflammatory effects for topically applied THDC as a standalone ingredient. In fact, there is not a single peer reviewed research article available on THDC as a standalone ingredient.
Synoxyl® AZ + VitaSynol® C: A Perfect Synergistic Mechanism
Intriguingly, the combination of THDC and AZ also increased expression of skin-friendly genes associated with phospholipid homeostasis and keratinocyte differentiation, along with repression of MMP1 and MMP7 expression, inhibition of MMP enzyme activity and increased production of collagen proteins by dermal fibroblasts.
These results support a synergistic mechanism by which AZ can stabilize THDC to facilitate and improve delivery of VC into the dermis and otherwise buffer against aberrant activation of genes associated with skin dysfunction and breakdown caused by THDC alone. This provides a step towards reaching the full potential of ascorbate as an active ingredient in topical preparations.
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