Hair follicle protection from oxidative damage

An increased number of studies established the contribution of oxidative stress in hair loss and greying processes. Taking into consideration the importance of antioxidative prevention in the field of hair biology, we developed a biofunctional pea extract and tested its efficacy on human scalp skin explants containing HF. The outcomes on HF morphology, as well as the expression of the antioxidant enzyme catalase, were investigated after stress exposure. Our results obtained in an ex vivo model showed that HFs pretreated with the extract exhibited fewer signs of damage. This effect could be related to an increase in catalase expression in treated scalp biopsies. Moreover, the protective effect of the extract was also revealed by the reduction of stress-induced markers and the maintenance of the HF regeneration capacity marker. This study emphasises the importance of HF protection against oxidative stress, which can have damaging effects on hair structure, hair growth, and hair colour.

   Hair is an essential element of physical appearance, wellbeing, and attractiveness. Hair and scalp are constantly exposed to various environmental stresses, including UV irradiation as well as oxidative and chemical stresses. The effect of external stresses on the hair fibre is quite well documented. In particular, repeated sun exposure impairs the structure of the hair shaft keratin fibre, while UV radiation induces hair protein loss and colour changes.1 Moreover, with hair exposure to sun and bleaching treatments, a reduction of breaking strength was observed.2 Morphological and biochemical changes were mainly observed in UVB- and UVAirradiated hairs, respectively.3 However, few studies aim to investigate damage caused by UV radiation and oxidative stress on the hair follicle. It was recently shown that isolated hair follicle in culture demonstrated reduced hair shaft elongation and premature catagen entry upon exposure to repetitive UVB irradiation.4 Besides, oxidative DNA damage was observed in a hair follicle subjected to low UVB doses. Additionally, UVR reduced the melanin content of the hair follicle in culture. These observations strongly suggest that the hair follicle could be a direct target of UV radiation. Furthermore, oxidative stress appears to be implicated in hair greying. Indeed, accumulation of free radicals, which occurs with age-associated reduction of antioxidative enzymes, could affect tyrosinase, the rate-limiting enzyme of the melanogenesis pathway.5 Particularly, in the hair follicle, the accumulation of reactive oxidative species generates significant oxidative stress, which could impair the hair pigmentary unit.6 This results in greying hair (canities) with less and less melanin pigment produced in the hair follicle and subsequently transferred to the cells of the hair cortex. In the present study, we examined the effects of UV radiation and oxidative stress generated by H2O2 on human scalp skin grafts containing hair follicles. A biofunctional pea extract was applied before the stress, and the level of damage, was investigated by studying the hair follicle structure and the expression of specific stress markers. We observed an increase in catalase expression following application of the extract. This antioxidant enzyme, which converts hydrogen peroxide into water and oxygen, was shown to be defective in intrinsically and photo-aged skin7 as well as in grey hair follicle. The effect of pea extract application on scalp biopsies was accompanied by the maintenance of hair follicle morphology and a reduced level of stress markers, suggesting a protective effect delivered by this biofunctional compound.

Materials and methods