Sebum, inflammasomes and the skin: current concepts and future perspective.

Increasing evidence has identified ultraviolet radiation (UVR) as the skins most potent mutagen as over exposure results in sunburn, inflammation and DNA damage, thus contributing to a photo-ageing phenotype and possibly skin carcinogenesis. The lipid-rich sebum secreted onto the surface of the skin plays an important physiological role in protecting the skin against external challenges. When skin is photosensitised by UVR, the lipid constituents of sebum are easily oxidised, generating several lipid photo-oxidative products (e.g. squalene peroxides). These photo-oxidative products have been shown to exert diverse toxicological, biological and immunological effects in the skin and have therefore been implicated in several detrimental skin alterations including premature skin ageing. The involvement of lipid peroxidation products in UVR-induced inflammatory responses has been inadequately studied and highly controversial. Furthermore, it is unclear to what extent these oxidative products contribute to the underlying mechanisms of skin photo-ageing. Therefore, this viewpoint essay will discuss the current knowledge on the effect of UVR exposure on skin surface lipids and how these may mediate UVR-induced inflammatory responses which may be key contributors to photo-damage in skin. This essay will also examine the potential role of inflammasomes (innate immune complexes) in the inflammatory response associated with UVR-induced lipid peroxidation. Limited evidence is available on the interactions between sebaceous lipids, downstream mediators and concomitant immune response in sun-exposed skin and clearer elucidation may lead to novel biomarkers of photo-ageing and the incorporation of new molecules into current skin therapies which better target oxidised lipids and or downstream mediators/pathways.

A dietary supplement improves facial photoaging and skin sebum, hydration and tonicity modulating serum fibronectin, neutrophil elastase 2, hyaluronic acid and carbonylated proteins.

BACKGROUND AND AIMS: Excessive exposure to the sun can cause severe photoaging as early as the second decade of life resulting in a loss of physiological elastic fiber functions. We designed a first study to assess differences in facial skin pH, sebum, elasticity, hydration and tonicity and serum levels of fibronectin, elastin, neutrophil elastase 2, hyaluronic acid and carbonylated proteins between patients affected by facial photoaging and healthy controls. In a second study we tested the hypothesis that a dietary supplement would improve facial photoaging, also promoting changes in the above mentioned skin and serum parameters. METHODS: In the first study we enrolled 30 women [age: 47.5 ± 1.6 years (mean ± standard error of the mean)] affected by moderate facial photoaging (4 cm ≤ Visual Analogue Scale (VAS)<7 cm) and 30 healthy women [age: 45.9 ± 1.6 years (mean ± standard error of the mean)]. In the second study we enrolled a cohort of 30 women [age: 43.6 ± 1.2 years (mean ± standard error of the mean)], affected by moderate (n = 22) and severe (VAS ≥ 7 cm; n = 8) facial photoaging, who were randomized to receive a pharmaceutical formulation (VISCODERM Pearls; IBSA FARMACEUTICI ITALIA Srl, Lodi, Italy) containing Pycnogenol, collagen, coenzyme Q10, low-molecular-weight hyaluronic acid, chondroitin sulfate and glucosamine sulfate (n = 15) or placebo (n = 15). Dietary supplement and placebo were administered 2 times a day for 4 weeks. Facial photoaging was assessed by VAS in the first cohort of patients affected by facial photoaging and healthy controls and, at baseline and 2 weeks after the end of treatment, in the second cohort of patients who underwent treatment with VISCODERM Pearls and placebo. Skin Tester was used to analyze differences in facial skin parameters between patients affected by facial photoaging and healthy controls. Skin Tester was also used to assess the effect of VISCODERM Pearls on facial skin parameters and compared with placebo 2 weeks after the end of treatment. Serum levels of fibronectin, elastin, neutrophil elastase 2, hyaluronic acid and carbonylated proteins were measured by enzyme-linked immunosorbent assay in the first cohort of patients affected by facial photoaging and healthy controls and, at baseline and 2 weeks after the end of treatment, in the second cohort of patients who underwent treatment with VISCODERM Pearls and placebo. RESULTS: VAS photoaging score was higher in patients affected by photoaging, if compared with healthy controls (p < 0.0001). pH and sebum were increased in patients affected by photoaging, if compared with healthy controls (both p < 0.0001), while elasticity, hydration and tonicity were decreased in patients affected by photoaging, if compared with healthy controls (all p < 0.0001). Serum fibronectin and hyaluronic acid concentrations were lower in patients affected by photoaging, if compared with healthy controls (both p < 0.0001). Serum neutrophil elastase 2, elastin and carbonylated protein concentrations were higher in patients affected by photoaging, if compared with healthy controls (p < 0.01, p < 0.01 and p < 0.0001, respectively). Dietary supplement administration resulted in an improvement in VAS photoaging score, if compared with placebo (p < 0.0001), as observed 2 weeks after the end of treatment. Facial sebum, hydration and tonicity were increased in the active treatment group vs. placebo (p < 0.0001, p < 0.0001 and p < 0.05, respectively) 2 weeks after the end of treatment. Serum fibronectin and hyaluronic acid concentrations were increased in the dietary supplement group, if compared with placebo (p < 0.01 and p < 0.001) 2 weeks after the end of treatment, while no statistical difference in serum elastin concentration was observed between the two groups. Serum neutrophil elastase 2 and carbonylated protein concentrations were decreased in the dietary supplement group 2 weeks after the end of treatment, if compared with placebo (p < 0.001 and p < 0.0001). CONCLUSIONS: We found significantly increased serum levels of neutrophil elastase 2, elastin and carbonylated proteins and decreased levels of hyaluronic acid and fibronectin in patients affected by facial photoaging, if compared with healthy controls. These findings coupled with a significant decrease in skin hydration, tonicity and elasticity and increased skin pH and sebum. Treatment with the dietary supplement VISCODERM Pearls significantly improved VAS photoaging score and skin hydration, sebum and tonicity 2 weeks after the end of a 4-week treatment period in patients affected by moderate to severe facial photoaging. These findings coupled with a significant increase in serum fibronectin and hyaluronic acid and a decrease in serum carbonylated proteins and neutrophil elastase 2 in the active treatment group, if compared with placebo. Our findings suggest that VISCODERM Pearls is effective for treatment of facial photoaging but further studies in larger cohorts of patients are required.

Regulation of lipid production by light-emitting diodes in human sebocytes.

Light-emitting diodes (LED) have been used to treat acne vulgaris. However, the efficacy of LED on sebaceous lipid production in vitro has not been examined. This study investigated the efficacy of 415 nm blue light and 630 nm red light on lipid production in human sebocytes. When applied to human primary sebocytes, 415 nm blue light suppressed cell proliferation. Based on a lipogenesis study using Oil Red O, Nile red staining, and thin-layered chromatography, 630 nm red light strongly downregulated lipid production in sebocytes. These results suggest that 415 nm blue light and 630 nm red light influence lipid production in human sebocytes and have beneficial effects on acne by suppressing sebum production.

Evaluation of drug and sunscreen permeation via skin irradiated with UVA and UVB: comparisons of normal skin and chronologically aged skin.

BACKGROUND: Ultraviolet (UV) exposure is the predominant cause of skin aging. A systematic evaluation of drug skin permeation via photoaged skin is lacking. OBJECTIVES: The aim of this work was to investigate whether UVA and UVB affect absorption by the skin of drugs and sunscreens, including tetracycline, quercetin, and oxybenzone. METHODS: The dorsal skin of nude mice was subjected to UVA (24 and 39 J/cm(2)) or UVB (150, 200, and 250 mJ/cm(2)) irradiation. Levels of skin water loss, erythema, and sebum were evaluated, and histological examinations of COX-2 and claudin-1 expressions were carried out. Permeation of the permeants into and through the skin was determined in vitro using a Franz cell. In vivo skin uptake was also evaluated. Senescent skin (24 weeks old) was used for comparison. RESULTS: Wrinkling and scaling were significant signs of skin treated with UVA and UVB, respectively. The level of claudin-1, an indicator of tight junctions (TJs), was reduced by UVA and UVB irradiation. UVA enhanced tetracycline and quercetin skin deposition by 11- and 2-fold, respectively. A similar enhancement was shown for flux profiles. Surprisingly, a lower UVA dose revealed greater enhancement compared to the higher dose. The skin deposition and flux of tetracycline both decreased with UVB exposure. UVB also significantly reduced quercetin flux. The skin absorption behavior of chronologically aged skin approximated that of the UVA group, with photoaged skin showing higher enhancement. UV generally exhibited a negligible effect on modulating oxybenzone permeation. CONCLUSIONS: Skin disruption produced by UV does not necessarily result in enhanced skin absorption. It depends on the UV wavelength, irradiated energy, and physicochemical properties of the permeant. To the best of our knowledge, this is the first report establishing drug permeation profiles for UV-irradiated skin.

Selective photothermolysis to target sebaceous glands: theoretical estimation of parameters and preliminary results using a free electron laser.

BACKGROUND AND OBJECTIVES: The success of permanent laser hair removal suggests that selective photothermolysis (SP) of sebaceous glands, another part of hair follicles, may also have merit. About 30% of sebum consists of fats with copious CH(2) bond content. SP was studied in vitro, using free electron laser (FEL) pulses at an infrared CH(2) vibrational absorption wavelength band. METHODS: Absorption spectra of natural and artificially prepared sebum were measured from 200 to 3,000 nm, to determine wavelengths potentially able to target sebaceous glands. The Jefferson National Accelerator superconducting FEL was used to measure photothermal excitation of aqueous gels, artificial sebum, pig skin, human scalp, and forehead skin (sebaceous sites). In vitro skin samples were exposed to FEL pulses from 1,620 to 1,720 nm, spot diameter 7-9.5 mm with exposure through a cold 4°C sapphire window in contact with the skin. Exposed and control tissue samples were stained using H&E, and nitroblue tetrazolium chloride staining (NBTC) was used to detect thermal denaturation. RESULTS: Natural and artificial sebum both had absorption peaks near 1,210, 1,728, 1,760, 2,306 and 2,346 nm. Laser-induced heating of artificial sebum was approximately twice that of water at 1,710 and 1,720 nm, and about 1.5× higher in human sebaceous glands than in water. Thermal camera imaging showed transient focal heating near sebaceous hair follicles. Histologically, skin samples exposed to ~1,700 nm, ~100-125 milliseconds pulses showed evidence of selective thermal damage to sebaceous glands. Sebaceous glands were positive for NBTC staining, without evidence of selective loss in samples exposed to the laser. Epidermis was undamaged in all samples. CONCLUSIONS: SP of sebaceous glands appears to be feasible. Potentially, optical pulses at ~1,720 or ~1,210 nm delivered with large beam diameter and appropriate skin cooling in approximately 0.1 seconds may provide an alternative treatment for acne.

Ultraviolet-induced red fluorescence of patients with acne reflects regional casual sebum level and acne lesion distribution: qualitative and quantitative analyses of facial fluorescence.

BACKGROUND: The ultraviolet (UV)-induced red fluorescence of patients with acne has been considered to be caused by Propionibacterium acnes. OBJECTIVES: To study the correlation of the facial red fluorescence with the casual sebum level and the number of acne lesions and to investigate the difference in clinical features, according to both distribution and proportion of fluorescence. METHODS: A total of 878 patients clinically diagnosed with acne vulgaris were included. Inflammatory and noninflammatory acne lesions were counted separately. UV fluorescent photography and casual sebum level measurements were performed. UV-induced fluorescence patterns were classified according to the facial distribution. The proportions of UV-induced red fluorescence were calculated. RESULTS: We identified six different fluorescence distribution patterns in the T-zone (the forehead, nose and chin) and three different patterns in the U-zone (both cheeks). The proportion of fluorescence in the U-zone showed a positive correlation with the casual sebum level and the number of acne lesions. In the T-zone, the fluorescence proportion correlated with the casual sebum level, but not with the number of acne lesions. As the patients' age and the age at onset increased, the distribution of fluorescence changed from the upper part of the T-zone to the lower part, and to the centre of the face in the U-zone. CONCLUSIONS: Our results support the hypothesis that the origin of facial red fluorescence is sebum. In patients with acne, analyses of the pattern and proportion of UV-induced red fluorescence can be useful for evaluating the sebum secretion and selecting efficient treatment modalities.

Effects of a 1,450 nm diode laser on facial sebum excretion.

BACKGROUND AND OBJECTIVE: Laser therapy with a 1,450 nm diode laser is a clinically effective treatment for acne vulgaris, although the mechanism of action is unknown. To investigate this, we conducted a small, prospective, controlled clinical trial to assess this laser's effects on the facial sebum excretion rate (SER). MATERIALS AND METHODS: Fourteen healthy volunteers without active acne were enrolled in this study and received three laser treatments on test areas of the nose and forehead. Nine subjects completed the treatment regimen and were available for follow-up. SER was measured with Sebumeter prior to the first treatment, and at 1 week and 1 month after the third treatment. Photographs were taken and subjective assessment of skin oiliness and pore size determined by questionnaires at 1 month follow-up. RESULTS: No significant reduction in SER was observed comparing treated with control on all treatment sites (P>0.05) on the nose. Reduction in the absolute SER was observed for both test and control sites on the forehead, reaching significance on the treatment site (P = 0.04) and marginal significance on the control site (P = 0.08). CONCLUSION: While our study was designed to detect only large changes in SER, we conclude that three 1,450 nm laser treatment sessions did not cause marked changes in SER compared to the control (i.e., >44%). Thus, major destruction of sebaceous glands as a result of this treatment is unlikely. However, reduced sebum production was observed on both treatment and control sides at 1 month. Therefore alternative mechanisms should also be considered to explain the clinical efficacy of this treatment for acne vulgaris.

Ultraviolet a induces generation of squalene monohydroperoxide isomers in human sebum and skin surface lipids in vitro and in vivo.

At the outermost surface of human skin, skin surface lipids are first-line targets of solar ultraviolet radiation. Therefore, we hypothesized that ultraviolet A and ultraviolet B irradiation induce photo-oxidation of skin surface lipids. To test this, sebum samples were collected from facial skin of 17 healthy volunteers, weighed, and immediately irradiated with either ultraviolet B or ultraviolet A. Squalene, the major sebum lipid, as well as photo-oxidation products were identified in sebum lipid extracts by high-performance liquid chromatography analysis. Upon ultraviolet A exposures squalene was depleted in a concentration-dependent manner, whereas an unidentified sebum lipid photo-oxidation product was detected. Using high-performance thin layer chromatography, high-performance liquid chromatography, atmospheric pressure chemical ionization mass spectrometry, and nuclear magnetic resonance, unidentified sebum lipid photo-oxidation product was identified as a mixture of squalene monohydroperoxide isomers. Squalene monohydroperoxide isomers purified from sebum were identical with squalene monohydroperoxide isomers synthesized by preparative photo-oxidation of squalene. Squalene monohydroperoxide isomers were formed even after small suberythematogenic doses of ultraviolet A (5 J per cm2). Whereas physiologic baseline levels of squalene monohydroperoxide isomers in human skin were only slightly above detection limits, squalene monohydroperoxide isomer levels were strongly increased by suberythematogenic doses of ultraviolet A both in vitro and in vivo. High-performance liquid chromatography results could be complemented by a straightforward thin layer chromatography method for rapid screening of lipid peroxide formation in human sebum/skin surface lipids. In conclusion, specific squalene monohydroperoxide isomers were identified as highly ultraviolet A sensitive skin surface lipid breakdown products that may serve as a marker for photo-oxidative stress in vitro and in vivo.

Changes in skin physiology during bath PUVA therapy.

BACKGROUND: Frequent bathing leads to a skin barrier damage with various changes in physiological skin parameters. Conversely, ultraviolet (UV) irradiation may improve the impaired skin barrier by reducing inflammatory reactions. OBJECTIVES: The aim of this study was to investigate the changes of physiological skin parameters during a therapy with 8-methoxypsoralen (8-MOP) bathing and subsequent UVA irradiation. METHODS: Thirty patients with a skin disease without barrier disruption were treated with daily bathing in a 8-MOP solution (0.0005%) and subsequent UVA irradiation. Multiple physiological skin parameters (transepidermal water loss, skin blood flow, skin colour, sebum content, skin hydration) were measured repeatedly on clinically non-affected skin on the back, forearm and forehead. In addition, patch testing with sodium lauryl sulphate (SLS) (0.5%) was performed on the forearm and on the back. RESULTS: We found a moderate but significant disturbance of skin barrier and hydration on the forearm and the back (bathing + irradiation) after increasing dosages of therapy. In addition, SLS testing leads to stronger reactions. CONCLUSIONS: We conclude that on clinically healthy skin the impairment of skin barrier by frequent bathing cannot be completely compensated by subsequent UVA irradiation. When conducting a treatment with 8-MOP bathing and UVA irradiation a concomitant therapy supporting the recovery of skin barrier, e.g. with moisturizer, should be performed.