An Action Spectrum for the Production of cis-Urocanic Acid in Human Skin In Vivo

Atopic Dermatitis: Disease Background and Risk Factors

Multiple risk factors have been associated with the development of atopic dermatitis (AD). Recent advances in understanding the role of genetics in this disease have been made, with discovery of the filaggrin (FLG) gene as the most notable so far. In addition to FLG gene mutations as a risk factor for AD, a positive family history of atopic or allergic disease in either parent has been shown to confer a greater risk of developing AD. Atopic dermatitis usually presents early in life and is thought to represent the initial step in the "atopic march," which is characterized by the development of other atopic diseases later in life such as asthma, allergic rhinitis, and/or rhinoconjunctivitis, food allergies, and hay fever. Other comorbid diseases that have been associated with AD include increase risk of viral and bacterial skin infections, neuropsychiatric diseases such as attention-deficit hyperactivity disorders (ADHD), and autistic spectrum disorder (ASD). Patients with AD have also been found to have worse sleep quality overall compared to patients without AD. In this chapter, we will discuss the risk factors associated with development of atopic dermatitis as well as the most commonly reported comorbidities in patients with this disease.

Comparing the Impact of NIR, Visible and UV Light on ROS Upregulation via Photoacceptors of Mitochondrial Complexes in Normal, Immune and Cancer Cells

The effect of UV/visible/NIR light (380/450/530/650/808/1064 nm) on ROS generation, mitochondrial activity and viability is experimentally compared in human neuroblastoma cancer cells. The absorption of photons by mitochondrial photoacceptors in Complexes I, III and IV is in detail investigated by sequential blocking with selective pharmaceutical blockers. Complex I absorbs UV/blue light by heme P450, resulting in a very high rate (14 times) of ROS generation leading to cell death. Complex III absorbs green light, by cytochromes b, c1 and c, and possesses less ability for ROS production (seven times), so that only irradiation lower than 10 mW cm^-2 causes an increase in cell viability. Complex IV is well-known as the primary photoacceptor for red/NIR light. Light of 650/808 nm at 10-100 mW cm^-2 generates a physiological ROS level about 20% of a basal concentration, which enhance mitochondrial activity and cell survival, while 1064 nm light does not show any distinguished effects. Further, ROS generation induced by low-intensity red/NIR light is compared in neurons, immune and cancer cells. Red light seems to more rapidly stimulate ROS production, mitochondrial activity and cell survival than 808 nm. At the same time, different cell lines demonstrate slightly various rates of ROS generation, peculiar to their cellular physiology.

Phenolic Extract from Aralia nudicaulis L. Rhizomes Inhibits Cellular Oxidative Stresses

UV-B and IR-A radiation are important inducers of biological changes in skin involving ROS generation. The overloading of antioxidant defense mechanisms by ROS production could lead to photoaging and photocarcinogenesis processes. Various traditional usages are reported for Aralia nudicaulis L. extracts, including treatment of dermatological disorders. Antioxidant and anti-inflammatory properties have already been reported for other Aralia species possibly due to the presence of phenolic compounds. However, the phenolic composition and the potential activity of A. nudicaulis rhizomes extract against oxidative stress and UV/IR damages have not been investigated. The main aims of this study were to prepare a fraction enriched in phenolic compounds (FEPC) from A. nudicaulis rhizomes, to identify its major phenolic compounds and to assess its potential for protective effects against oxidative stress induced by UV-B, IR-A or inflammation. A quantitative LC-MS study of FEPC shows that chlorogenic, caffeic and protocatechuic acids are the main phenolic compounds present, with concentrations of 15.6%, 15.3% and 4.8% of the total composition, respectively. With a validated analytical method, those compounds were quantified over different stages of the growing period. As for biological potential, first this extract demonstrates antioxidant and anti-inflammatory activities. Furthermore, ROS generation induced by IR-A and UV-B were strongly inhibited by A. nudicaulis extract, suggesting that Aralia nudicaulis L. rhizome extract could protect dermal cells against oxidative stress induced by UV-B and IR-A.

Stratum corneum biomarkers after in vivo repeated exposure to sub-erythemal dosages of ultraviolet radiation in unprotected and sunscreen (SPF 50+) protected skin

BACKGROUND

There is a need for non-invasive biomarkers to assess in vivo efficacy of protective measures aiming at reducing ultraviolet radiation (UVR) exposure. Stratum corneum (SC) biomarkers showed to be promising markers for internal UVR dose and immune response.

PURPOSE

To establish a dose-response relationship for SC biomarkers and explore their suitability for in vivo assessment of the blocking effect of two sunscreens with a high sun protection factor (SPF) (50+).

METHODS

Twelve volunteers were exposed to a broad-spectrum UVB (280-320 nm), five times a week, during one week. Unprotected back skin was irradiated with 0.24, 0.48, 0.72 and 1.44 standard erythema dose (SED) and sunscreen-protected skin with 3.6 SED. SC samples for determination of the relative amount of cis-urocanic acid (cUCA) and thirteen immunological makers including cytokines and matrix metalloproteinases (MMP) were collected after each irradiation.

RESULTS

cUCA sharply increased after the first irradiation in a dose-dependent fashion. However, it levelled-off after subsequent exposures and reached a plateau for the highest UV-dose after the third irradiation. None of the immunological markers showed dose-dependency. However, MMP-9, IL-1β and CCL27 increased gradually from baseline during repetitive exposures to the highest UV-dose. Assessed from cUCA, both sunscreens blocked >98% of the applied UV-dose.

CONCLUSIONS

cUCA is a sensitive, non-invasive marker of the internal UVR dose enabling in vivo assessment of the blocking effect of high SPF sunscreens in the UVB-region. Immunological SC markers show low sensitivity in detecting immune response at sub-erythemal UVR dosages, suggesting they might be suitable only at higher and/or repetitive UVR exposure.

Analytical tools for urocanic acid determination in human samples: A review

Urocanic acid is a chromophore found in the skin that has been identified as an important immunosuppressant and carcinogenesis mediator through its photoisomerization from trans to cis form induced by ultraviolet radiation. Research on analytical methods that explore urocanic acid isomerization is indispensable to fully understand the deleterious effects mediated by this biomarker. In this context, the current relevant analytical methods for determination of these isomers in human samples are summarized in this review. The methods presented here are applicable to human samples collected by noninvasive methods (or minimally invasive), encompassing an array of analytical techniques, including high-performance capillary electrophoresis, confocal Raman spectroscopy, gas chromatography, high-performance liquid chromatography, and mass spectrometry, among others. Developed high-performance liquid chromatography methods have proven to be advantageous, allowing noninvasive collections for in vivo analysis and the confocal Raman, specially, for real-time analysis. Among all these methods, high-performance liquid chromatography is the most investigated one with mass spectrometry or ultraviolet detector, and the mass spectrometry detector being the most studied in the last years, demonstrating high sensitivity, very low detection limits, and accurate identification, especially for clinical investigations.

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

UV-B-Induced Inflammasome Activation Can Be Prevented by Cis-Urocanic Acid in Human Corneal Epithelial Cells

Purpose

The cornea is continually exposed to highly energetic solar UV-B (280-320 nm). Our aim was to investigate whether UV-B triggers the activation of NLRP3 inflammasomes and the production of IL-1β and/or IL-18 in human corneal epithelial (HCE) cells. Additionally, we studied the capability of cis-urocanic acid (cis-UCA) to prevent inflammasome activation or alleviate inflammation through other signaling pathways.

Methods

HCE-2 cell line and primary HCE cells were primed using lipopolysaccharide or TNF-α. Thereafter, cells were exposed to UV-B before or after the addition of cis-UCA or caspase-1 inhibitor. Caspase-1 activity was measured from cell lysates by an enzymatic assay. IL-1β, IL-18, IL-6, IL-8, and NLRP3 levels were detected using the ELISA method from cell culture media. Additionally, intracellular NLRP3 levels were determined by the Western blot technique, and cytotoxicity was measured by the LDH assay.

Results

UV-B exposure significantly increased caspase-1 activity in TNF-α-primed HCE cells. This result was consistent with the concurrently induced IL-1β secretion. Both caspase-1 activity and release of IL-1β were reduced by cis-UCA. Additionally, UV-B stimulated the caspase-1-independent production of IL-18, an effect also reduced by cis-UCA. Cis-UCA decreased the release of IL-6, IL-8, and LDH in a time-dependent manner when administered to HCE-2 cells after UV-B exposure.

Conclusions

Our findings demonstrate that UV-B activates inflammasomes in HCE cells. Cis-UCA can prevent the secretion of IL-1β and IL-18 and therapeutically reduces the levels of IL-6, IL-8, and LDH in UV-B-stressed HCE cells.

[2+2] Photodimerization of Stilbazoles Promoted by Oxalic Acid in Suspension

In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio- and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions.

The effects of UVB irradiance on vitiligo phototherapy and UVB-induced photocarcinogenesis

Phototherapy is the most commonly used modality for repigmenting vitiligo. Currently, UVB emitting devices, including narrow-band UVB (NBUVB) and excimer laser/light, are considered as the treatment of choice. While emitting wavelengths at close proximity, excimer lights emit higher irradiance (HI; W/m² ) compared to NBUVB. Clinical reports have shown that excimer light is more efficacious in treating vitiligo compared to NBUVB, and we demonstrated that irradiance plays a critical role in promoting melanoblasts differentiation. UVB radiation from the sun is closely associated with photocarcinogenesis of the skin. Sunscreens were used to protect the skin by reducing UVB irradiance (low irradiance (LI) UVB). Sunscreen use was associated with skin cancer reduction in clinical trials. Paradoxically, sunscreen use was associated with increased sunburn episodes in the real-world settings. It was shown that UVB-induced sunburn depends on fluence (J/m² ) but not irradiance of UVB radiation. We investigated the significance of irradiance in the context of UVB-induced carcinogenesis of the skin. For mice receiving equivalent fluence of UVB exposure, the LIUVB-treated mice showed earlier tumor development, larger tumor burden, and more epidermal keratinocytes harboring mutant p53 as compared to their HIUVB-treated counterparts. These results suggested that at equivalent fluence, LIUVB radiation has more photocarcinogenic potential on the skin compared to its HI counterpart. Since development of sunburn with or without sunscreen use indicates that certain threshold of UVB fluence has been received by the skin at LI and HI, respectively, sunburn episodes with sunscreen use (LIUVB) are more damaging to the skin compared to that without sunscreen (HIUVB) application. In summary, since irradiance plays an important role determining the biological effects of UVB radiation on the skin, future related studies should take this critical parameter into consideration.

UVA and UVB Photoprotective Capabilities of Topical Formulations Containing Mycosporine-like Amino Acids (MAAs) through Different Biological Effective Protection Factors (BEPFs)

The safety and stability of synthetic UV-filters and the procedures for evaluating the photoprotective capability of commercial sunscreens are under continuous review. The influence of pH and temperature stressors on the stability of certain Mycosporine-like amino acids (MAAs) isolated at high purity levels was examined. MAAs were highly stable at room temperature during 24 h at pH 4.5–8.5. At 50 °C, MAAs showed instability at pH 10.5 while at 85 °C, progressive disappearances were observed for MAAs through the studied pH range. In alkaline conditions, their degradation was much faster. Mycosporine-serinol and porphyra-334 (+shinorine) were the most stable MAAs under the conditions tested. They were included in four cosmetically stable topical sunscreens, of which the Sun Protection Factor (SPF) and other Biological Effective Protection Factors (BEPFs) were calculated. The formulation containing these MAAs showed similar SPF and UVB-BEPFs values as those of the reference sunscreen, composed of synthetic UV absorbing filters in similar percentages, while UVA-BEPFs values were slightly lower. Current in vitro data strongly suggest that MAAs, as natural and safe UV-absorbing and antioxidant compounds, have high potential for protection against the diverse harmful effects of solar UV radiation. In addition, novel complementary in vitro tests for evaluation of commercial sunscreens efficacy are proposed.

From Early Immunomodulatory Triggers to Immunosuppressive Outcome: Therapeutic Implications of the Complex Interplay Between the Wavebands of Sunlight and the Skin

Phototherapy is an efficient treatment for many cutaneous diseases that involve the activation of inflammatory pathways or the overgrowth of cells with aberrant phenotype. In this review, we discuss recent advances in photoimmunology, focusing on the effects of UV-based therapies currently used in dermatology. We describe the molecular responses to the main forms of photo(chemo)therapy such as UVB, UVA-1, and PUVA that include the triggering of apoptotic or immunosuppressive pathways and help to clear diseased skin. The early molecular response to UV involves DNA photoproducts, the isomerization of urocanic acid, the secretion of biophospholipids such as platelet activating factor (PAF), the activation of aryl hydrocarbon receptor and inflammasome, and vitamin D synthesis. The simultaneous and complex interaction of these events regulates the activity of the immune system both locally and systemically, resulting in apoptosis of neoplastic and/or benign cells, reduction of cellular infiltrate, and regulation of cytokines and chemokines. Regulatory T-cells and Langerhans cells, among other skin-resident cellular populations, are deeply affected by UV exposure and are therefore important players in the mechanisms of immunomodulation and the therapeutic value of UV in all its forms. We weigh the contribution of these cells to the therapeutic application of UV and how they may participate in transferring the direct impact of UV on the skin into local and systemic immunomodulation. Moreover, we review the therapeutic mechanisms revealed by clinical and laboratory animal investigations in the most common cutaneous diseases treated with phototherapy such as psoriasis, atopic dermatitis, vitiligo, and cutaneous T-cell lymphoma. Better understanding of phototherapeutic mechanisms in these diseases will help advance treatment in general and make future therapeutic strategies more precise, targeted, personalized, safe, and efficient.

Atopic Dermatitis: Disease Background and Risk Factors

Multiple risk factors have been associated with the development of atopic dermatitis (AD). Recent advances in understanding the role of genetics in this disease have been made, with discovery of the filaggrin (FLG) gene as the most notable so far. In addition to FLG gene mutations as a risk factor for AD, a positive family history of atopic or allergic disease in either parent, has been shown to confer a greater risk of developing AD. Atopic dermatitis usually presents early in life and is thought to represent the initial-step in the "atopic march" which is characterized by the development of other atopic diseases later in life such as asthma, allergic rhinitis and/or rhinoconjunctivitis, food allergies and hay fever. Other comorbid diseases that have been associated with AD include increase risk of viral and bacterial skin infections, neuropsychiatric diseases such as attention-deficit hyperactivity disorders (ADHD) and autistic spectrum disorder (ASD). Patients with AD, have also been found to have worse sleep quality overall compared to patients without AD. In this chapter, we will discuss the risk factors associated with development of atopic dermatitis as well as the most commonly reported comorbidities in patients with this disease.

Ultraviolet radiation, vitamin D and multiple sclerosis

There is compelling epidemiological evidence that the risk of developing multiple sclerosis is increased in association with low levels of sun exposure, possibly because this is associated with low vitamin D status. Recent work highlights both vitamin D and non-vitamin D effects on cellular immunity that suggests that higher levels of sun exposure and/or vitamin D status are beneficial for both MS risk and in ameliorating disease progression. Here we review this recent evidence, focusing on regulatory cells, dendritic cells, and chemokines and cytokines released from the skin following exposure to ultraviolet radiation.

Investigation of Skin Barrier Functions and Allergic Sensitization in Patients with Hyper-IgE Syndrome

PURPOSE

Hyper-IgE syndrome (HIES) is a severe primary immunodeficiency, characterized by increased serum IgE levels as well as recurrent infections and atopic dermatitis (AD)-like skin lesions. AD is a chronic inflammatory skin disease with immunologic alterations (Th2-Th22 polarization) and characteristic skin barrier dysfunctions. Our aim was to investigate physicochemical skin barrier alterations and allergic sensitization in STAT3-HIES patients in order to explore whether skin barrier dysfunction can play a role in the eczematoid skin lesions in these patients.

METHODS

In our experiments STAT3 and FLG mutation analyses were performed in STAT3-HIES (n = 7) and AD (n = 49) patients. Laboratory parameters (LDH and Eos counts), immunologic alterations (Th17 cell counts), allergic sensitization (total and specific IgE levels, skin prick tests, and medical history records), skin barrier changes [transepidermal water loss (TEWL), skin pH], serum and stratum corneum thymic stromal lymphopoietin (TSLP) levels were also examined.

RESULTS

Impaired Th17 cell numbers, but normal physicochemical barrier functions, as well as serum and stratum corneum TSLP levels, were found in STAT3-HIES, while these parameters were significantly altered in AD patients. Allergic sensitization was detected in nearly all AD patients, while no signs of sensitization occurred in STAT3-HIES.

CONCLUSIONS

Our study demonstrated that the skin barrier functions of STAT3-HIES patients are not damaged and they differ significantly from the altered skin barrier functions of AD patients. A well-functioning physicochemical skin barrier may be one of the explanations on the contradiction between the extremely high total IgE levels and the lack of allergic sensitization in these patients. Our study underlines the importance of skin barrier in the development of allergic sensitization.

Severe skin inflammation and filaggrin mutation similarly alter the skin barrier in patients with atopic dermatitis

BACKGROUND

Filaggrin (FLG) deficiency is a well-known predisposing factor for the development of atopic dermatitis (AD). Decreased FLG expression can be the result of haploinsufficiency or severe inflammation, which can cause acquired FLG alterations. FLG mutations are related to several clinical and laboratory parameters of AD; however, some recent data seem to contradict these associations.

OBJECTIVES

Our aim was to determine which clinical and biochemical parameters are connected to FLG haploinsufficiency and which ones are also associated with acquired FLG alterations due to severe skin symptoms in patients with AD.

METHODS

We introduced a novel classification of patients with AD, based on FLG mutations and SCORAD (SCORing Atopic Dermatitis). Based on these parameters, we created three groups of patients with AD: mild-to-moderate wild-type (A), severe wild-type (B) and severe mutant (C). In all groups, we assessed laboratory and clinical parameters and performed immunohistochemical analyses.

RESULTS

Groups B and C contained patients with equally severe symptoms based on the SCORAD. The two severe groups did not differ significantly with respect to barrier-specific parameters, whereas group A had significantly better results for the barrier function measurements. However, significant differences were detected between groups B and C with respect to the allergic sensitization-specific parameters.

CONCLUSIONS

These findings suggest that skin barrier function correlates with the severity of skin inflammation and can be equally impaired in patients with FLG mutant- and wild-type AD with severe symptoms. Nevertheless, our results also suggest that patients with FLG mutant-type AD may have a higher risk of allergic sensitization compared with patients with the wild-type.

New advances in protection against solar ultraviolet radiation in textiles for summer clothing

Clothing is considered one of the most important tools for photoprotection against harmful solar ultraviolet radiation (UVR). The standard for sun-protective clothing is based on erythema despite other biological effects of UVR on the skin. We analyzed the potential protection against UVR in fabrics destined for summer clothing based on several action spectra. We examined 50 garments classified by type of fabric composition, structure of the fiber yarn and color. The ultraviolet protection factor was calculated based on fabric ultraviolet transmittance corrected for erythema according to the EU standard E-13758 as well as the UVA transmittance of fabrics. UVR protection was also analyzed in base of different action spectra as for previtamin D3, nonmelanoma skin cancer, photoimmunosuppression and photoaging. Most knitted fabrics used for sports T-shirts offered excellent ratings for ultraviolet protection while normal shirts showed very low ratings, particularly against photoaging. The cover is the most influential variable in fabric photoprotection, having an exponential relationship with the UPF. The relation between cover and UVA protection was linearly negative. Information about ultraviolet protection in textiles used for summer clothing should be included in labeling as some types of fabrics, especially those used for shirts, offer very low UVR protection.

Filaggrin gene mutation c.3321delA is associated with various clinical features of atopic dermatitis in the Chinese Han population

Background

We confirmed that the filaggrin gene mutation c.3321delA is associated with atopic dermatitis in our previous genome wide association study of the Chinese Han population. c.3321delA is the most common filaggrin gene mutation in Chinese atopic dermatitis patients but is not present in European populations.

Objective

To investigate the genetic model for the c.3321delA mutation and to determine the correlation between c.3321delA and atopic dermatitis clinical phenotypes in the Chinese Han population.

Method

The filaggrin gene mutation c.3321delA was sequenced in 1,080 atopic dermatitis patients and 908 controls from the Chinese population. The χ² test, ANOVA,nonparametric tests and logistic regression were used to investigate the relationship between the c.3321delA genotype and atopic dermatitis clinical phenotypes in the Chinese Han population.

Results

Analyses of the genetic model revealed that the additive model best described the c.3321delA mutation (P = 3.09E-11, OR = 3.43, 95%CI = 2.38–4.96). Stratified analyses showed that the c.3321delA allele frequency distribution is significantly associated with concomitant skin xerosis (P = 1.68E-03, OR = 2.13,95%CI = 1.32–3.46), palmar hyperlinearity (P = 3.64E-17, OR = 4.0,95%CI = 2.86–5.70), white dermatographism (P = 4.25E-03, OR = 1.82,95%CI = 1.22–2.71), food intolerance (P = 1.51E-03, OR = 1.76,95%CI = 1.23–2.50) and disease severity ( P = 9.67E-05).

Conclusion

Our study indicates that the filaggrin gene mutation c.3321delA is associated with clinical phenotypes of atopic dermatitis in the Chinese Han population, which might help us gain a better understanding on the pathogenesis of atopic dermatitis.

Vitamin D and multiple sclerosis: where do we go from here?

This article briefly introduces the basics of multiple sclerosis' (MS) clinical hallmarks and pathophysiology. Vitamin D is presented, including its metabolism and effects on the immune system. The epidemiological observations linking vitamin D to MS range from a half century old findings of latitude gradients and migrational risk patterns to modern, nested, case-control biobank studies. These observations show an association without doubt although causation has yet to be proven. Vitamin D as a treatment for MS is an emerging concept and both current and anticipated data will be covered. Lastly, we discuss future challenges, ideas on how to move from association to causation, and the prospect of primary prevention of this disabling disease.

UVA-1 therapy of localized scleroderma and other diseases accompanied by skin sclerosis

The study results confirm the efficacy of the UVA-1 therapy for patients with localized scleroderma, extragenital lichen sclerosus et atrophicus, sclerodermatous chronic graft-versus-host disease and scleredema adultorum. The therapy has an anti-inflammatory and anti^m^ action, arrests progression and reduces the activity of the disease process, and has a good efficacy and safety profile.

Regulation of virulence in Brucella: an eclectic repertoire of transcription factors defines the complex architecture of the virB promoter

Many intracellular bacterial pathogens use type IV secretion systems to deliver effector molecules and subvert the eukaryotic host cell defenses. The genus Brucella comprises facultative intracellular bacteria that cause brucellosis, a disease affecting a wide range of mammals including humans. The virB operon codes for a type IV secretion system that plays a central role in intracellular survival and replication of Brucella within the host. Expression of the virB genes is under the control of various transcription factors that allow this system to respond to different types of environmental signals, and display binding site structures and arrangements that define the intrinsic complexity of the virB promoter. This review focuses on summarizing the current state of research concerning regulation of the Brucella virB operon, with special emphasis on describing the nature and function of the implicated regulatory elements and examining the involved protein–DNA interactions.

One remarkable molecule: filaggrin

The discovery, in 2006, that loss-of-function mutations in the filaggrin (FLG) gene are the cause of ichthyosis vulgaris-the most common disorder of keratinization-and also a strong genetic risk factor for atopic eczema, marked a significant breakthrough in the understanding of eczema pathogenesis. Subsequent investigations of the role of FLG-null mutations have identified a series of significant associations with atopic disease phenotypes, including atopic asthma, allergic rhinitis, and peanut allergy. However, many questions remain to be answered in relation to the precise mechanisms by which deficiency of an intracellular protein expressed primarily in the differentiating epidermis may contribute to the development of cutaneous and systemic pathology. This review aims to highlight the key milestones in filaggrin research over the past 25 years, to discuss the mechanistic, clinical, and therapeutic implications, and to consider possible future directions for ongoing investigation.

Ultraviolet radiation and immunosuppression

Ultraviolet (UV) radiation is a complete carcinogen. The effects of UV radiation are mediated via direct damage to cellular DNA in the skin and suppression of image surveillance mechanisms. In the context of organ transplantation, addiction of drugs which suppress the immune system add greatly to the carcinogenicity of UV radiation. This review considers the mechanisms of such effects.

Filaggrin haploinsufficiency is highly penetrant and is associated with increased severity of eczema: further delineation of the skin phenotype in a prospective epidemiological study of 792 school children

Background

Null mutations within the filaggrin gene (FLG) cause ichthyosis vulgaris and are associated with atopic eczema. However, the dermatological features of filaggrin haploinsufficiency have not been clearly defined.

Objectives

This study investigated the genotype–phenotype association between detailed skin phenotype and FLG genotype data in a population-based cohort of children.

Methods

Children (n= 792) aged 7–9 years were examined by a dermatologist. Features of ichthyosis vulgaris, atopic eczema and xerosis were recorded and eczema severity graded using the Three Item Severity score. Each child was genotyped for the six most prevalent FLG null mutations (R501X, 2282del4, R2447X, S3247X, 3702delG, 3673delC). Fisher’s exact test was used to compare genotype frequencies in phenotype groups; logistic regression analysis was used to estimate odds ratios and penetrance of the FLG null genotype and a permutation test performed to investigate eczema severity in different genotype groups.

Results

Ten children in this cohort had ichthyosis vulgaris, of whom five had mild–moderate eczema. The penetrance of FLG null mutations with respect to flexural eczema was 55·6% in individuals with two mutations, 16·3% in individuals with one mutation and 14·2% in wild-type individuals. Summating skin features known to be associated with FLG null mutations (ichthyosis, keratosis pilaris, palmar hyperlinearity and flexural eczema) showed a penetrance of 100% in children with two FLG mutations, 87·8% in children with one FLG mutation and 46·5% in wild-type individuals (P< 0·0001, Fisher exact test). FLG null mutations were associated with more severe eczema (P= 0·0042) but the mean difference was only 1–2 points in severity score. Three distinct patterns of palmar hyperlinearity were observed and these are reported for the first time.

Conclusions

Filaggrin haploinsufficiency appears to be highly penetrant when all relevant skin features are included in the analysis. FLG null mutations are associated with more severe eczema, but the effect size is small in a population setting.

Absorption spectra of human skin in vivo in the ultraviolet wavelength range measured by optoacoustics

Knowledge of the optical properties of human skin in the ultraviolet range is fundamental for photobiologic research. However, optical properties of human skin in the ultraviolet spectral range have so far mainly been measured ex vivo. We have determined the absorption spectra of human skin in vivo in the wavelength range from 290 to 341 nm in 3 nm steps using laser optoacoustics. In this technique, optical properties are derived from the pressure profile generated by absorbed light energy in the sample. In a study on 20 subjects belonging to phototypes I-IV, we studied the optical properties at the volar and dorsal aspect of the forearm as well as on the thenar. Analysis of the measured absorption spectra shows that comparable skin areas-like different sides of the forearm-have qualitatively similar optical characteristics. Still, the optical properties may vary substantially within the same area, probably due to the skin structure and inhomogeneities. Comparison of the spectra from different skin sites indicates that the spectral characteristics of the stratum corneum and its chromophores play an important role for the optical properties of human skin in vivo in the ultraviolet B range.

Effect of ultraviolet adaptation on the ultraviolet absorption spectra of human skin in vivo

BACKGROUND

The absorption spectrum of human skin provides a basis for the estimation of the possible photobiological impact of ultraviolet (UV) radiation. The optical properties of human skin in the UV spectral range have so far mainly been measured ex vivo due to a lack of an appropriate in vivo technique and the change of optical properties during the course of adaptation to higher UV doses has hardly been addressed.

METHODS

We have determined the absorption spectra of human skin in vivo in the wavelength range from 290 to 341 nm in 3 nm steps using laser optoacoustics. In this technique, optical properties are derived from the pressure profile generated by absorbed light energy in the sample. Spectra from the volar and dorsal aspects of the forearm of 20 subjects were compared, i.e. sites with native and various facultative pigmentation.

RESULTS

UV adaptation shows as an increase in absorption coefficients over the entire measured UV range and especially in short-range UVB. Subject groups with high vs. low UV exposure can be discriminated by analyzing the difference absorption spectra between dorsal and volar aspects of the forearm. No dependence on the subject's phototype was seen in the degree of adaptation.

CONCLUSION

The difference between native and facultative pigmentation may be explained by the absorption properties of the two prime chromophores responsible for adaptation to higher UV exposure: melanin and keratin. Stronger pigmentation, i.e. a higher melanin concentration, is found as an increase of absorption coefficients over the entire UVA-II/UVB range. The thickening of the horny layer and accordingly, a higher influence of keratin on the absorption spectra is prominent especially in the UVB region.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.

An action spectrum (290-320 nm) for TNFalpha protein in human skin in vivo suggests that basal-layer epidermal DNA is the chromophore

Terrestrial solar UVB radiation ( approximately 295-320 nm) readily induces cyclobutane pyrimidine dimers (CPDs) in human skin DNA that result in characteristic mutations associated with nonmelanoma skin cancer. The proinflammatory cytokine TNFalpha is important in mouse skin chemical carcinogenesis and is thought to also play a role in UVR-induced skin cancer by its immunomodulatory properties. There is some in vitro evidence that CPDs initiate the production of TNFalpha, and we tested this hypothesis by comparing the wavelength dependence (action spectrum) for TNFalpha protein induction in human skin in vivo with our earlier in vivo action spectra for CPD induction in four different epidermal layers of human skin. Normal volunteers (n = 35) were irradiated with physiologically relevant doses of monochromatic UVB (290-320 nm), and TNFalpha concentration was assessed, by high-sensitivity ELISA, in exudates from skin suction blisters raised 8 h after irradiation. An action spectrum, constructed from the slopes of the dose-response curves at the different wavelengths, showed maximal efficacy at 300 nm. An excellent match was observed for TNFalpha and the CPD action spectrum for cells in the lower basal epidermis. These data strongly suggest that UVB-induced photodamage to DNA in the epidermal basal layer is a major trigger for TNFalpha production. The TNFalpha may originate directly from the keratinocytes in this layer or inflammatory cells that are rapidly recruited into the upper dermis (e.g., neutrophils) as a consequence of DNA photodamage to basal-layer keratinocytes.

Suppression of an established immune response by UVA--a critical role for mast cells

Exposing experimental animals or human volunteers to UVA II (320-340 nm) radiation after immunization suppresses immunologic memory and the elicitation of delayed-in-time hypersensitivity reactions. Previous studies indicated that the mechanisms underlying UVA-induced immune suppression are similar to those described for UVB-induced immune suppression, i.e. transferred by T regulatory cells, overcome by repairing DNA damage, neutralizing interleukin (IL)-10 activity, or injecting recombinant IL-12. Here we continued our examination of the mechanisms involved in UVA II-induced suppression. Antibodies to cis-urocanic acid blocked UVA-induced immune suppression. Treating UVA-irradiated mice with histamine receptor antagonists, calcitonin gene-related peptide (CGRP) receptor antagonists or platelet activating factor receptor antagonists blocked immune suppression in UVA-irradiated mice. In light of the fact that cis-urocanic acid and CGRP target mast cells, which can then release platelet activating factor and histamine, we measured UVA-induced immune suppression in mast cell-deficient mice. No immune suppression was noted in UVA-irradiated mast cell-deficient mice. These findings indicate that exposure to UVA II activates many of the same immune regulatory factors activated by UVB to induce immune suppression. Moreover, they indicate that mast cells play a critical role in UVA-induced suppression of secondary immune reactions.

Botanical antioxidants in the prevention of photocarcinogenesis and photoaging

Exposure of the skin to ultraviolet (UV) radiation, particularly its UV-B component (280-320 nm), from the sun results in erythema, edema, hyperplasia, hyperpigmentation, sunburn cells, immunosuppression, photoaging, and skin cancer. Amongst these various adverse effects of UV-B radiation, skin cancer and photoaging are of great concern. More recent changes in lifestyle have led to a significant increase in the amount of UV-B radiation people receive leading to a surge in the incidence of skin cancer and photoaging. As these trends are likely to continue in the foreseeable future, the adverse effect of UV-B has become a major human health concern. Therefore, development of novel strategies to reduce the occurrence of skin cancer and delay the process of photoaging are highly desirable goals. One approach to reduce their occurrence is through photochemoprevention, which we define as the use of agents capable of ameliorating the adverse effects of UV-B on the skin. Photochemoprevention via use of botanical antioxidants, present in the common diet of human have gained considerable attention as photochemopreventive agents for human use. Many such agents have also found a place in skin care products. This review will focus on the effects of selected botanical antioxidants in the prevention of photocarcinogenesis and photoaging.

Acute effects of UVR on human eyes and skin

Solar UVR ( approximately 295-400 nm) has acute clinical effects on the eyes and the skin. The only effect on the eye is inflammation of the cornea (photokeratitis), which is caused by UVB (and non-solar UVC) and resolves without long-term consequences within 48 h. The effects on the skin are more extensive and include sunburn (inflammation), tanning and immunosuppression for which UVB is mainly responsible. Tanning is modestly photoprotective against further acute UVR damage. Skin colour is also transiently changed by UVA-dependent immediate pigment darkening, the function of which is unknown. Skin type determines sensitivity to the acute and chronic effects of UVR on the skin. Some of the photochemical events that initiate acute effects are also related to skin cancer. Solar UVB is also responsible for the synthesis of vitamin D.