Appropriate Technologies to Accompany Sunscreens in the Battle Against Ultraviolet, Superoxide, and Singlet Oxygen.

The interaction of ultraviolet radiation with biological matter results in direct damage such as pyrimidine dimers in DNA. It also results in indirect damage provoked by the production of reactive oxygen species (ROS) catalyzed by photosensitizers. Photosensitizers can be endogenous (e.g., tryptophan) or exogenous (e.g., TiO2 and other photostable UVA sunscreens). Direct damage triggers an inflammatory response and the oxidative and proteolytic bursts that characterize its onset. The inflammatory reaction multiplies the effects of one single photon. Indirect damage, such as the peroxidative cascade in membrane lipids, can extend to thousands of molecular modifications per absorbed photon. Sunscreens should therefore be formulated in the presence of appropriate antioxidants. Superoxide and singlet oxygen are the main ROS that need to be tackled: this review describes some of the molecular, biochemical, cellular, and clinical consequences of exposure to UV radiation as well as some results associated with scavengers and quenchers of superoxide and singlet oxygen, as well as with inhibitors of singlet oxygen production.

UV protection afforded by gel-trapped TiO2 particles.

We have developed a technology to incorporate micronized titanium dioxide (TiO(2)), together with antioxidants, in particles of a UV-visible transparent polymer gel. These particles are coated with silica to avoid clustering and the size of the micronized TiO(2) reduces the back scattering of white light. gel-trapped TiO(2) minimizes the oxidative stress exerted by UV radiation, increases the photo-stability of some accompanying ingredients, such as avobenzone. The size of the particles is in the micrometre range. This favors their permanence on the top of the stratum corneum. Gel-trapped TiO(2)-based sunscreens provide a larger SPF and two-fold larger UVA protection than equal-composition sunscreens that contain larger amounts of untrapped TiO(2).

Modification of skin discoloration by a topical treatment containing an extract of Dianella ensifolia: a potent antioxidant.

Skin hyperpigmentation, and the reactions that precipitate it, have been linked to free radicals by the fact that free radical scavengers or antioxidants can slow that hyperpigmentation. We have screened several hundred plant extracts for antioxidants and discovered one that is both a strong antioxidant and can reduce skin hyperpigmentation. Extracts of Dianella ensifolia contain 1-(2,4-dihydrophenyl)-3-(2,4-dimethoxy-3-methylphenyl) propane (DP), which was found to inhibit the free radical 1-1-diphenyl-2-picryl-hydrazyl (DPPH) with an EC(50) value of 78 mum. DP was also found to inhibit Ultraviolet (UV)C-induced lipid oxidation with an EC(50) of about 30 mum. We next investigated the effects of this antioxidant on skin hyperpigmentation. The reduction of discoloration by different topical treatments has been assessed in human volunteers using an in vivo assay for the rate of fading of UVB-induced tan. Two pharmaceutical formulas containing 4% hydroquinone (HQ) were used as positive controls, and we tested the ability of DP, a plant-derived amphoteric antioxidant, to increase performance of non-HQ cosmetic formulations. We found that the cosmetic formula containing DP produced an increase in the rate of fading compared to the two pharmaceutical treatments containing HQ.

Sunscreens: the impervious path from theory to practice.

The preparation of commercial products able to protect the skin against damage from solar radiation requires safe and photo-stable stable UV-absorbing molecules with high extinction coefficients, prepared with solvents of the appropriate polarities and polarizabilities in formulas which allow the uniform spreading of the UV-absorbing substances. The products should also maintain the ingredients on the top of the skin and provide efficient scavenging activities against singlet oxygen and other directly or indirectly generated reactive oxygen species. Because of the high doses of UV used to test high SPF, simple and reproducible methods are needed to estimate the protection afforded by the product before risking the induction of severe burns to the volunteers, as can occur when the value of the product's SPF is smaller than the expected one. This paper describes several aspects of the preparation of commercial sunscreens. It also points out several of the hidden hypotheses which, when not tested, might lead to the overestimation of the protection factor of a product.

Gender-linked differences in human skin.

BACKGROUND: The physiology of body organs can be affected by gender. Skin and skin appendages are influenced by sex hormones. OBJECTIVE: This review work has been undertaken to point out the most conspicuous physiological differences observed between men's and women's skin. METHODS: The literature has been searched and relevant results have been gathered. RESULTS: Men's and women's skins differ in hormone metabolism, hair growth, sweat rate, sebum production, surface pH, fat accumulation, serum leptins, etc. Examples of differences in the proneness to cutaneous diseases and skin cancer are quoted. CONCLUSION: The knowledge of gender-linked cutaneous differences might help in preparing male-specific products for more appropriate dermatological treatments or cosmetic interventions.

Calculation of apparent age by linear combination of facial skin parameters: a predictive tool to evaluate the efficacy of cosmetic treatments and to assess the predisposition to accelerated aging.

The estimated apparent age (EAA) was estimated by a panel of trained experts, for the individuals in a cohort. Twelve independent clinical, biophysical and biochemical parameters measured on facial skin, have been identified by multiple regression analysis, which influence the EAA of a person of chronological age (CA) (under eye lines, clinically assessed crow's feet, age spots, clinically evaluated firmness, forehead lines, pores, lip lines, instrumentally evaluated firmness, instrumentally evaluated crow feet, skin texture, in vivo fluorescence related to proliferation and glycation). An algorithm has been devised to obtain the calculated age score (CAS) in a cohort of 452 female volunteers, as CAS(n) = ∑RCiPi(n) (i = 1-13, n = 1-452 and P13 = 1) where the coefficients Ci are obtained by minimizing the difference EAA - CAS, and Pi(n) are the experimental values of the i-th parameter for the n-th volunteer. The determination of CAS before and after a specific cosmetic or pharmacological anti-aging treatment can be used to objectively assess the efficacy of the treatment. The comparison of EAA(n) and of CAS(n) with CA(n) allows one to predict the susceptibility of an individual's face to undergo aging. It has been observed that the biophysical and biochemical parameters play a relevant role in the assessment of the predisposition of skin to undergo accelerated aging.

Advancement in skin aging: the future cosmeceuticals.

Aging is a multifactorial process defined as the accumulation of damage. The aging of the skin is characterized by specific clinical end points, the cause of which is not always thoroughly understood. The skin is exposed to environmental aggressions and the reactive oxygen species produced during cellular metabolism. Damage to the cellular and extracellular components of the skin can be avoided or removed by the appropriate topical application of active ingredients. Sunscreens are essential to avoid damage from the most important damaging environmental agent: solar radiation. Liposomes containing deoxyribonucleic acid repair enzymes and accelerate the endogenous removal of pyrimidine dimers after exposure to ultraviolet radiation. Specific antioxidants reduce the rate of formation of secondary ultraviolet-induced damages, particularly those induced by singlet oxygen. Anti-inflammatory agents, immunostimulants, and enhancers of molecular and cellular detoxification could enter the panoply of new cosmeceuticals to avoid age spots, dark circles, wrinkles, and other clinical aspects of skin aging.

Morphological changes associated with aging: age spots and the microinflammatory model of skin aging.

Affymetrix gene-expression analysis was performed on mRNAs from involved and noninvolved skin biopsies from three volunteers with Lentigo senilis. Of the 42,000 transcripts scanned, 17 were downregulated (<1.4 times below the control level) and 23 were upregulated (>1.9 times above the control level). A serine peptidase gene was downregulated in keeping with the suggestion that age spots are associated with impaired melanin degradation. Three genes involved in the keratinization and synthesis and the organization of fibers in the basement membrane were downregulated, two metalloproteinase genes were upregulated, as were six genes associated with the inflammatory response, in keeping with the postulate that the visible aspects of aged skin are causally linked with a microinflammatory response. The regulation of five genes associated with the Wnt family was altered. Antiapoptotic genes were downregulated, and six genes associated with transmembrane transport were upregulated.

A mechanistic model for the aging of human skin.

The microinflammatory model of skin aging is described. This model accounts for the loss of elasticity, resiliene and flexibility of the dermis, as well as for the appearance of wrinkles and for the thinning of the epidermis which are associated with aging. The lack of appropriate apparatuses for the correct measurements of skin hydration does not allow one to test this model for its predictive capability of the appearance of dry skin with age. The micro-inflammatory model of skin aging fails to predict the appearance of age spots on the surface of the skin.