Constantin Koulbanis

Circadian dosing time dependency in the forearm skin penetration of methyl and hexyl nicotinate

The forearm skin penetration of hydrophilic methyl nicotinate (MN) and lipophilic hexyl nicotinate (HN) was assessed around the clock. The sixteen healthy women (median age: 22 years, weight: 57 kg and height: 162 cm) who volunteered for the study were synchronized with a diurnal activity from 07.00h (+/- 1h) to 23.00h (+/- 1h.30min) and a nocturnal rest before and during the 48h sojourn in air-conditioned rooms (26 degrees C +/- 0.5 degrees C). Both HN (0.5% ethanol solution) and MN (5% ethanol solution) have a vasodilative effect on dermal vessels. The lag time (LT) between the delivery of a fixed volume (10 microliters) of the agent at the skin surface and the beginning of the vasodilatation, detected with a laser-Doppler method, was used to quantify the penetration kinetics. Tests were performed every 4h, at fixed clock hours, over a span of a 40h. Two types of tests were done with each of the agents: fixed site (one site only) and shifted sites (10 different places). Both cosinor and ANOVA have been used for statistical analyses. The shortest LT (fastest penetration) was located around 04.00h. The longest LT (slowest penetration) occurred during the day with a single peak around 13.00h in three of the situations, or two peaks (HN with fixed site). A rather large rhythm amplitude (peak-to-trough difference larger than 50% of the 24h mean LT) was validated.

DAY-NIGHT DIFFERENCES IN EFFECTS OF COSMETIC TREATMENTS ON FACIAL SKIN. EFFECTS ON FACIAL SKIN APPEARANCE

Two groups of 24 healthy caucasian women, similar with regard to age classes (from 19 to 55) as well as fair and dark complexion of skin and hair, volunteered to use during a 14-day span a conventional facial cream (active placebo: AP) and thereafter, during a 21-day span Noctosome (Noctos). The latter is a new generation of liposome made with non-ionic lipids leading to microspheres which include glycopeptides in the aqueous compartment of the vesicle, alpha-tocopherol ester in the membrane-like structure and sphingo-ceramides at the surface of the microspheres. The aim of the study was to test the beneficial effects of Noctos (vsAP) with respectively morning (7-9-hr) and evening (21-23-hr) applications as facial ointments. Observed differences were validated using several statistical tests: ANOVA, cosinor, etc. Subjects were socially synchronized with a diurnal activity from 7 hr to 23 hr and a nocturnal rest. Each day, at fixed clock hours (7, 10, 20 and 23 hr), each subject used visual analogue scales to self-rate a set of variables characterizing facial aspects. Brilliance of complexion and texture of skin exhibited a circadian rhythm (peak time at 10 hr), both with AP and Noctos. The latter produces a beneficial effect with regard to reference values (AP). The evening application of Noctos is more efficient than the morning one. However, the magnitude of this beneficial effect is related both to age (greater for the age class 25-35 years than for younger and older subjects) and to skin complexion (greater for fair than dark complexioned subjects). Major beneficial effects of Noctos in the evening hours are related neither to fatigue nor to mood of the women since the respective circadian rhythms of these variables appear to vary independently from those of facial skin characteristics.

Optimization of external oil phase systems by differential thermal analysis

Abstract The stability of emulsions is, in most cases, linked to the homogeneity and fineness of dispersed particles. For external oil phase systems, surfusion temperature and disperse-phase water-particle crystallization kinetics are particle-size dependent, according to a statistical probability function, f 1 = 1/ N 1 ʃ D 0 d N where N 1 is the number of particles, and D is the diameter. DTA, Investigation of emulsion size distribution by surfusion thermograms, and dispersed phase crystallization kinetics (observed during freeze-thaw cycles with isotherm plateau), can be helpful in the choice of surfactant, coupling agents and raw materials and can provide an approach for estimation of the stability of w/o emulsions. This method has also been applied to technological procedure optimization and quality control of end products. Retained optimization criteria are, in decreasing order of importance, a very low polydispersity and a particle-size distribution as near Gaussian distribution as possible. Surfusion temperature, which varies from one system to another (−10 to −47°C), must remain stable with time or after the ageing process.