Placebo-controlled Assessment of the Effect of a Food Supplement on Skin Protection After Exposure to UV Radiation

Langerhans cells (LC), the dendritic cells (DC) from epidermis, constitute the first line of immune defense against environmental attacks. Under steady state conditions, LC turnover is very low. The LCs reside in the epidermis in an immature state and can be distinguished from other epidermal cells by their surface expression of HLA-DR, CD1a and langerin. Upon stimulation by inflammatory mediators LCs are activated and acquire CCR7 expression, the chemokine receptor for CCL21 that mediates their migration to lymph nodes. Moreover, activated LCs display a mature phenotype characterized by increased expression of co-stimulatory molecules and acquisition of maturation markers that facilitate their interaction with T-cells and aid in the elicitation of the immune response.

It has long been known that, in addition to being carcinogenic via DNA damage and mutations, solar UV radiation induces local and systemic immune suppression which represents a major risk for skin cancer induction and progression in sun-exposed areas. The process is mostly related to direct LC damage through induction of apoptosis and impairment of antigen-presenting function. Moreover, UV radiation elicits an inflammatory response and subsequent recruitment of immune cells, including CD36+ monocytic cells. These cells colonize the epidermis in the days following UV exposure and are the major source of immunosuppressive cytokines such as IL-10. All these mechanisms ultimately lead to impaired cell-mediated reactions and establishment of immune tolerance.

Nutritional intervention, particularly with dietary antioxidants and vitamins, has been proposed to protect against UV-induced skin damage and to a certain extent skin cancer occurrence. In recent years, there has been an increasing interest for probiotics, defined as live microorganisms which, when consumed in adequate amounts, confer a health benefit upon the host. Particular focus has been on species of lactic acid bacteria including Lactobacilli and Bifidobacteria that are part of the natural human intestinal microbiota. Indeed, it is well documented that the endogenous intestinal microbiota plays a crucial role in immune maturation, gut integrity and defense against pathogens. Recently, it has been shown that some probiotic bacteria possess the ability to modulate the immune system at both the local and systemic levels and thereby improve immune defense mechanisms and/or down-regulate immune disorders such as intestinal inflammations or allergies.

The Probiotic used as the dietary supplement, was isolated from healthy adult microbiota and was shown to have a strong anti-pathogenic activity against a wide range of entero-pathogens. Furthermore, a pre-clinical study demonstrated that it can maintain the epidermal LC density.

Here, we analyzed, in a randomized double blind, placebo controlled, clinical trial, whether this dietary supplement could also modulate the cutaneous immune homeostasis after solar-simulated UV exposure in humans.For this purpose, we analyzed whether this dietary supplement could interfere with LC allostimulatory function and activation/maturation phenotypic status of skin DC, after solar-simulated UV irradiation.