SKIN PROTECTION 171
Crocus sativusflower extract restores circadian rhythm
Héléne Foliguet – Berkem, France
The Sun is known for its effects, often damaging, on the body but also on the cutaneous tissue. For this reason, photoprotection is one of the most important concerns of the cosmetic and personal care industry. Active ingredients suppliers aim to understand the mechanisms of skin’s self-defence, and to provide the best products to fight those external aggressions.
Sun’s effects on skin
Humans have always been submitted to the luminous environment which follows a day and night alternation. This variation of light is perceived by an internal clock, localised in the brain, which synchronises biological mechanisms with our environment. For example, skin cell proliferation is higher during the night, when the probability of DNA alterations by solar UV is minimal.1
Indeed, it has been extensively described that intense sun exposure negatively impacts the skin. Sunburn or ‘erythema’ is one of the first visible effects of UV exposure. It is an inflammatory reaction which induces a reddening of the skin. This phenomenon is a kind of alarm that indicates us to protect our skin by stopping the exposure. However, many invisible processes happen deeper in the different skin layers. The surface of the cutaneous tissue is modified (pleated,
Figure 2: Circadian clock genes expression study experimental procedure.
content due to the stimulation of matrix metalloproteinases (MMPs) and their inhibitor TIMP-1. At the molecular level, DNA damages appear, proteins are altered, notably because of the presence of free radicals that generates reactive chemical species. In the long term, these damaging effects lead to photoageing and cutaneous cancers.1
This is the
reason why we must protect our skin by avoiding too much exposure and by using cosmetics containing active ingredients which counteract those harmful UV effects.
A less known deleterious effect of intense sun exposure on cutaneous tissue is the alteration of skin circadian clock.
Figure 1: Schematic representation of the molecular mechanism regulating the circadian clock.
fragile, dry, hyper- or hypo- pigmented...) as well as its structure (loss of elasticity, thickness, wrinkles...). The epidermis is thinned, and the epidermal junction flattens out. In the dermis, very important changes in the structure and organisation of the extra cellular matrix (ECM) occur: accumulation of abnormal elastic fibres in the reticular dermis; disorganisation of the collagen network; decreased collagen
Chrono protector effect of Crocus sativusflower extract Chronobiology and circadian rhythms are more and more investigated and recently studied in skin biology. The central brain clock perceives light/dark alternation and synchronises peripherical clocks located in cells of others tissues such as skin.2
As a
result, cutaneous functions are naturally occurring under control of day/night cycle and exhibits a 24-hour rhythm. This rhythmic pattern is called circadian (circa: about, dies: day). For instance, sebum production is maximal at noon3
and skin has higher T0
Keratinocyte synchronization
Application of UVB stress (
20mj.cm-2
) 6h 10h 18h 24h
thickness during the day than at night in order to afford a better organism protection.4 Therefore, it is important to not deregulate this clock, to keep an optimal functionality of the skin at every time of the day. At the molecular level, the circadian clock consists of an autoregulatory feedback loop, inducing a 24-hour rhythm in the expression of several genes called clock-controlled genes (CCGs). These represent about 10% of the genome including genes involved in skin homeostasis, hydration or pigmentation and also genes specific to the circadian clock itself.2, 5, 6 The circadian clock involves many molecular actors (Fig 1). During the day, two proteins, CLOCK (CLOCK circadian regulator)
April 2019 PERSONAL CARE EUROPE
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