The non‐homogenous distribution and aggregation of carotenoids in the stratum corneum correlates with the organization of intercellular lipids in vivo

Abstract

The human stratum corneum (SC) contains an abundant amount of carotenoid antioxidants, quenching free radicals and thereby protecting the skin. For the precise measurements of the depth-dependent carotenoid concentration, confocal Raman microscopy is a suitable method. The quantitative concentration can be determined by the carotenoid-related peak intensity of a Gaussian function approached at ≈1524 cm −1 using non-linear regression. Results show that the carotenoid concentration is higher at the superficial layers of the SC then decreases to a minimum at 20% SC depth and increases again towards the bottom of the SC. In the present work, two carotenoid penetration pathways into the SC are postulated. The first pathway is from the stratum granulosum to the bottom of the SC, while in the second pathway, the carotenoids are delivered to the skin surface by sweat and/or sebum secretion and penetrate from outside. The carotenoids are aggregated at the superficial layers, which are shown by high correlation between the aggregation states of carotenoids and the lateral organization of lipids. At the 30%-40% SC depths, the ordered and dense lipid molecules intensify the lipid-carotenoid interactions and weaken the carotenoid-carotenoid interaction and thus exhibit the disaggregation of carotenoids. At 90%-100% SC depths, the carotenoid-lipid interaction is weakened and the carotenoids have a tendency to be aggregated. Thus, the molecular structural correlation of carotenoid and SC lipid might be reserved in the intercellular space of the SC and also serves as the skeleton of the intercellular lipids.

Melanin distribution from the dermal–epidermal junction to the stratum corneum: non-invasive in vivo assessment by fluorescence and Raman microspectroscopy

“…Figure 6 presents representative Raman spectra for different layers of the skin. The stratum corneum layer has been extensively studied in the literature and distribution of lipids, water, NMF, DNA, keratin and carotenoids have been described in detail 46,47,50,53,[60][61][62][63] . The maximum contribution from melanin was expectably found near the basal layer, where the characteristic twin peaks can be observed.…”

High‐energy visible light at ambient doses and intensities induces oxidative stress of skin—Protective effects of the antioxidant and Nrf2 inducer Licochalcone A in vitro and in vivo

“…ROS detoxification in skin is achieved by low molecular weight antioxidants, such as Vitamins C and E, and carotenoids like β‐carotene, as well as by enzymes and antioxidant proteins, many under the control of nuclear factor erythroid 2‐related factor 2 (Nrf2), the master regulator of cellular redox signaling and antioxidant defenses . Carotenoids are photoprotective, lipophilic plant‐derived pigments with highest concentration in the superficial stratum corneum (SC) and aggregation at skin surface . Carotenoids mainly exhibit absorbance maximum at wavelengths in the range of visible light and are rapidly degraded by blue light radiation in human skin ex vivo and in vivo, indicating ROS formation .…”

“…The SC carotenoid content remains completely preserved after treatment with the same sunscreen containing LicA. As epidermal carotenoids are concentrated in the superficial SC layers,22,23 protection from VIS-induced depletion can be achieved already by short-term application of the antioxidant LicA. β-Carotene degradation by VIS irradiation (400-800 nm, 24.6 J/cm 2 ) of human skin biopsies was reduced by 22% by pretreatment with a formulation containing 3%…”

“…20,21 Carotenoids are photoprotective, lipophilic plant-derived pigments with highest concentration in the superficial stratum corneum (SC) and aggregation at skin surface. 22,23 Carotenoids mainly exhibit absorbance maximum at wavelengths in the range of visible light 21 and are rapidly degraded by blue light radiation in human skin ex vivo 24 and in vivo, indicating ROS formation. 25 However, endogenous restoration takes up to 24 hours.…”

In Situ Monitoring of Lipid Phase State Make Target Lipid Mixtures Similar to Intercellular Lipid in the Stratum Corneum

“…It consists of corneocytes and intercellular lipids (ILs), which are analogous to a brick wall . The ratio of ILs is generally low in the SC, although it is a primary route for the percutaneous adsorption of active pharmaceutical and cosmeceutical ingredients, and interactions between ILs and the representative ingredients are crucial to the elucidation of the mechanisms of transdermal delivery . Human ILs primarily consist of ceramides (CER), free fatty acids, and cholesterol (CHOL) in equimolar ratio .…”