Impact of Iron-Oxide Containing Formulations Against Visible Light-Induced Skin Pigmentation in Skin of Color Individuals

July 2020 | Volume 19 | Issue 7 | Original Article | 712 | Copyright © July 2020


Published online June 18, 2020

Hawasatu Dumbuya PhDa, Pearl E Grimes MDb, Stephen Lynch PhDa,b, Kalli Ji PhDa, Manisha Brahmachary PhDa, Qian Zheng Md PhDa, Charbel Bouez PhDa, Janet Wangari-Talbot PhDa

aL’Oréal Research and Innovation, Clark, NJ bVitiligo & Pigmentation Institute, Los Angeles, CA

mineral SPF 50+ sunscreen was included in the study to assess the efficacy of a UVA and UVB protection alone in blocking the mediated effects of visible light on the skin.

METHODS

Study Participants
The study was performed in accordance with Good Clinical Practices and the principles of the Declaration of Helsinki. The procedures used in this study were approved by IntegReview IRB (Austin, TX). Before any study procedure, the subjects received the necessary written and verbal information and signed an informed consent form. Eligibility was determined by physical examination and confirmation of all inclusion/exclusion criteria. Ten healthy women aged 18-50 years (mean age, 35 + 6 years) with Fitzpatrick skin phototype IV were included in this study. Subjects with planned UV exposure (sunlight or sunbeds) or who used laser or phototherapy to the back during the study; with a history of taking or planned on taking any photosensitizing, anti-inflammatory, immunosuppressive medications, or any medication known to cause abnormal responses to UV exposure; or having prior or current pathologies induced or aggravated by exposure to light, or having abnormal reactions to sunlight (eg, photosensitive dermatitis, skin cancers, solar urticaria), were excluded.

Study Design
The study was monocentric, randomized, and single-blinded. Following the screening visit, subjects were required to attend six evaluation visits as follows:

At baseline (day 0), five investigational zones of 2x2 cm were delineated on the middle section of each subject’s back: one negative control zone (unexposed and un-irradiated), one positive control zone (only irradiated), and three pre-treated and irradiated zones. The three test products were applied (2 mg/ cm²) according to randomization plan.

On day 0, fifteen minutes after product application, the four test zones, excluding the negative control zone, were exposed to a single dose of VIS at 144 J/cm², equivalent to one hour of exposure at midday in summertime. Product application and VIS exposure were similarly repeated on day 1, day 2, and day 3. Clinical grading for skin pigmentation, colorimetric measurements, and standardized photograph were performed before product application and VIS irradiation on day 0 to day 3, 24 hours post the last irradiation on day 4, and on day 14.

Test Materials
Test materials consisted of three currently marketed products: 1) Product A (mineral SPF 50+ sunscreen with ZnO and TiO2); 2) Product B (FeO and TiO2 formulation); and 3) Product C (FeO formulation). Figure 1A displays the concentrations of the metal oxides in each test products, and Figure 1B, their absorbance spectra within the UV and HEV range. Product B and C have wider absorption wavelength band extending in the HEV range, suggesting superior protection compared to Product A. All test products were applied in a randomized and single-blinded manner.

Solar Stimulator
An ORIEL solar simulator, model 94043A-SP01-1600W, was used (Stratford, CT, USA). Its artificial luminous source was composed of a 1600 Watts xenon arc Iamp, giving a continuous spectrum covering ultraviolet (280nm) to infrared (1720nm). The light source was fitted with an AM 1.5G filter to generate the standard solar spectrum.

The Schott WG 400nm filter was used to eliminate UVR, allowing only VIS and IR spectra to pass through. A Schott KG3/2mm filter was then used to output mostly VIS and some IR-A emission (400–900nm) as illustrated in Figure 1C. The resulting spectral output, which will be referred to as visible light*, contained no UVB, 0.01% UVA (320–400nm), 88.2% VIS (400–750nm), 10.7% HEV (400–450nm), and 9.8% IRA (750–900nm). For each test zone, light intensity was measured just prior to exposure in order to deliver an accurate dose of 144 J/cm², with an average fluence rate of 50 mW/cm2.

Pigmentation Assessments
The intensity of the induced skin pigmentation was visually assessed by expert grading using an internally validated scale, ranging 0 (no pigmentation) to 13 (pronounced brown pigmentation). The scale is based on the visual comparison of the pigmentation of the test zone with that of the surrounding unexposed control skin. Scoring was performed by the same clinical expert throughout the study.

The instrumental measurements of skin color were performed before the subject inclusion and during the study, with a Chromameter ® (Konica Minolta CR400), using the L*a*b* color system (CIE lab, 1976). The individual typology angle (ITA°) that defines skin fairness or darkness was calculated from L* and b* measurements, using the formula: ITA°= [arc Tangent (L* - 50)/b*)] 180 /π.

Skin color changes after irradiation were assessed by using the parameter ΔE = √ (ΔL² + Δa²+ Δb²), where ΔL is the difference between the L of exposed zone and the non-exposed zone. Similar calculations were performed for Δa and Δb.

Standardized photographs were taken using a Canon EOS Rebel T5 camera with standard cross polarized filters under the same source of artificial light.

Statistical Analysis
For pigmentation score, L* value, a* value, b* value, ITA°, and Delta E, a Gaussian linear mixed model was used to analyze the mean difference in change from baseline between treatment with baseline, treatment, time, treatment-time interaction as