Enzyme-independent nitric oxide formation during UVA challenge of human skin: characterization, molecular sources, and mechanisms

Impact of ultraviolet radiation on cardiovascular and metabolic disorders: The role of nitric oxide and vitamin D

BACKGROUND/PURPOSE

Ultraviolet (UV) radiation has both harmful and beneficial effects on human skin and health. It causes skin damage, aging, and cancer; however, it is also a primary source of vitamin D. Additionally, UV radiation can impact energy metabolism and has protective effects on several cardiovascular and metabolic disorders in mice and humans. However, the mechanisms of UV protection against these diseases have not been clearly identified.

METHODS

This review summarizes the systemic effects of UV radiation on hypertension and several metabolic diseases such as obesity, diabetes, and nonalcoholic fatty liver disease (NAFLD) in mice, and we also consider the mechanisms of action of the related regulators nitric oxide (NO) and vitamin D.

RESULTS

UV exposure can lower blood pressure and prevent the development of cardiovascular diseases and metabolic disorders, such as metabolic syndrome, obesity, and type 2 diabetes, primarily through mechanisms that depend on UV-induced NO. UV radiation may also effectively delay the onset of type 1 diabetes through mechanisms that rely on UV-induced vitamin D. UV-induced NO and vitamin D play roles in preventing and slowing the progression of NAFLD.

CONCLUSION

UV exposure is a promising nonpharmacological intervention for cardiovascular and metabolic disorders. NO and vitamin D may play a crucial role in mediating these effects. However, further investigations are required to elucidate the exact mechanisms and determine the optimal dosage and exposure duration of UV radiation.

UV radiation and air pollution as drivers of major autoimmune conditions

Autoimmune diseases comprise a very heterogeneous group of disorders characterized by disruptive immune responses against self-antigens, chronic morbidity and increased mortality. The incidence and prevalence of major autoimmune conditions are particularly high in the western world, at northern latitudes, and in industrialized countries. This study will mainly focus on five major autoimmune conditions, namely type 1 diabetes, multiple sclerosis, inflammatory bowel diseases, rheumatoid arthritis, and autoimmune thyroid disorders. Epidemiological and experimental evidence suggests a protective role of sunlight exposure on the etiology of major autoimmune conditions mediated by the endogenous production of vitamin D and nitric oxide. A historical perspective shows how the rise of anthropogenic air pollutants is temporally associated with dramatic increases in incidence of these conditions. The scattering caused by ambient particulate matter and the presence of tropospheric ozone can reduce the endogenous production of vitamin D and nitric oxide, which are implicated in maintaining the immune homeostasis. Air pollutants have direct detrimental effects on the human body and are deemed responsible of an increasingly higher portion of the annual burden of human morbidity and mortality. Air pollution contributes in systemic inflammation, activates oxidative pathways, induces epigenetic alterations, and modulates the function and phenotype of dendritic cells, Tregs, and T-cells. In this review, we provide epidemiological and mechanistic insights regarding the role of UV-mediated effects in immunity and how anthropic-derived air pollution may affect major autoimmune conditions through direct and indirect mechanisms.

Dietary nitrate supplementation increases nitrate and nitrite concentrations in human skin interstitial fluid

Acute dietary nitrate (NO₃^-) supplementation can increase [NO₃^-], but not nitrite ([NO₂^-]), in human skeletal muscle, though its effect on [NO₃^-] and [NO₂^-] in skin remains unknown. In an independent group design, 11 young adults ingested 140 mL of NO₃^--rich beetroot juice (BR; 9.6 mmol NO₃^-), and 6 young adults ingested 140 mL of a NO₃^--depleted placebo (PL). Skin dialysate, acquired through intradermal microdialysis, and venous blood samples were collected at baseline and every hour post-ingestion up to 4 h to assess dialysate and plasma [NO₃^-] and [NO₂^-]. The relative recovery rate of NO₃^- and NO₂^- through the microdialysis probe (73.1% and 62.8%), determined in a separate experiment, was used to estimate skin interstitial [NO₃^-] and [NO₂^-]. Baseline [NO₃^-] was lower, whereas baseline [NO₂^-] was higher in the skin interstitial fluid relative to plasma (both P < 0.001). Acute BR ingestion increased [NO₃^-] and [NO₂^-] in the skin interstitial fluid and plasma (all P < 0.001), with the magnitude being smaller in the skin interstitial fluid (e.g., 183 ± 54 vs. 491 ± 62 μM for Δ[NO₃^-] from baseline and 155 ± 190 vs. 217 ± 204 nM for Δ[NO₂^-] from baseline at 3 h post BR ingestion, both P ≤ 0.037). However, due to the aforementioned baseline differences, skin interstitial fluid [NO₂^-] post BR ingestion was higher, whereas [NO₃^-] was lower relative to plasma (all P < 0.001). These findings extend our understanding of NO₃^- and NO₂^- distribution at rest and indicate that acute BR supplementation increases [NO₃^-] and [NO₂^-] in human skin interstitial fluid.

Sun Exposure and Intima-Media Thickness in the Mexican Teachers' Cohort Study

Objective: To determine whether long-term sun exposure has a protective role in subclinical cardiovascular disease in adult Mexican women. Materials and Methods: We conducted a cross-sectional analysis of a sample of women from the Mexican Teachers' Cohort (MTC) study. Sun exposure was assessed in the MTC 2008 baseline questionnaire, in which women were asked about their sun-related behavior. Vascular neurologists measured carotid intima-media thickness (IMT) using standard techniques. Multivariate linear regression models were used to estimate the difference in mean IMT and 95% confidence intervals (95% CIs), according to categories of sun exposure and multivariate logistic regression models were used to estimate the odds ratio (OR) and 95% CIs for carotid atherosclerosis. Results: The mean age of participants was 49.6 ± 5.5 years, the mean IMT was 0.678 ± 0.097 mm, and the mean accumulated hours of weekly sun exposure were 2.9 ± 1.9. Prevalence of carotid atherosclerosis was 20.9%. Compared with women in the lowest quartile of sun exposure, women in the highest quartile had lower mean IMT, but this was not significant in the multivariable adjusted analysis. (Adjusted mean % difference: -0.8; 95% CI: -2.3 to 0.8). The multivariate adjusted ORs of carotid atherosclerosis were 0.54 (95% CI: 0.24-1.18) for women who were exposed 9 hours. For women who denied regular sunscreen use, those in the higher exposure category (9 hours) had lower mean IMT compared with those in the lower category (multivariable-adjusted mean % difference = -2.67; 95% CI: -6.9 to -1.5). Conclusions: We observed that cumulative sun exposure was inversely associated with IMT and subclinical carotid atherosclerosis. If these findings are further replicated and seen for other cardiovascular outcomes, sun exposure could be an easy, affordable strategy to lower overall cardiovascular risk.

Histopathological Changes in Liver and Heart Tissue Associated with Experimental Ultraviolet Radiation A and B Exposure on Wistar Albino Rats

This study aims to evaluate the influences of ultraviolet radiation A and B (UVA + B) exposure on the liver and heart organs of albino rats. Female Wistar Albino rats, whose hair of the dorsal skin was shaved, were exposed to a combined UVA + B radiation for 2 h/day, for 4 weeks in order to be compared with the control group. Histopathological findings in vital organs (liver and heart) were evaluated. Tissues were fixed in 10% buffered formalin (pH = 7.2) and embedded in paraffin. The histopathological findings were examined on the H&E stained sections with light microscopy. The results show that the liver and the heart were injured in the UVA + B group. Liver tissue in the UVA + B group showed minimal vacuolation, enlargement of hepatocytes and bile duct proliferation, and the heart tissue showed hibernomas; uniform large cells resembling brown fat with coarsely granular to multivacuolated cytoplasm that is eosinophilic or pale with a small central nucleus. The number of hibernoma cases was significantly higher in the UVA + B group compared with the control group (P = 0.021). The control group showed normal liver and heart histology with normal adipose tissue in the pericardium. As a result, UVA + B exposure has toxic effects, especially on the liver and the heart of Wistar albino rats. UV radiation may cause such adverse effects in humans. Therefore, protection against the harmful effects of UV radiation is of significant importance for skin and organs.

Photobiomodulation and nitric oxide signaling

Nitric oxide (NO) is a well-known gaseous mediator that maintains vascular homeostasis. Extensive evidence supports that a hallmark of endothelial dysfunction, which leads to cardiovascular diseases, is endothelial NO deficiency. Thus, restoring endothelial NO represents a promising approach to treating cardiovascular complications. Despite many therapeutic agents having been shown to augment NO bioavailability under various pathological conditions, success in resulting clinical trials has remained elusive. There is solid evidence of diverse beneficial effects of the treatment with low-power near-infrared (NIR) light, defined as photobiomodulation (PBM). Although the precise mechanisms of action of PBM are still elusive, recent studies consistently report that PBM improves endothelial dysfunction via increasing bioavailable NO in a dose-dependent manner and open a feasible path to the use of PBM for treating cardiovascular diseases via augmenting NO bioavailability. In particular, the use of NIR light in the NIR-II window (1000-1700 nm) for PBM, which has reduced scattering and minimal tissue absorption with the largest penetration depth, is emerging as a promising therapy. In this review, we update recent findings on PBM and NO.

Pharmacological applications of nitric oxide-releasing biomaterials in human skin

Nitric oxide (NO) is an important endogenous molecule that plays several roles in biological systems. NO is synthesized in human skin by three isoforms of nitric oxide synthase (NOS) and, depending on the produced NO concentration, it can actuate in wound healing, dermal vasodilation, or skin defense against different pathogens, for example. Besides being endogenously produced, NO-based pharmacological formulations have been developed for dermatological applications targeting diverse pathologies such as bacterial infection, wound healing, leishmaniasis, and even esthetic issues such as acne and skin aging. Recent strategies focus mainly on developing smart NO-releasing nanomaterials/biomaterials, as they enable a sustained and targeted NO release, promoting an improved therapeutic effect. This review aims to overview and discuss the main mechanisms of NO in human skin, the recent progress in the field of dermatological formulations containing NO, and their application in several skin diseases, highlighting promising advances and future perspectives in the field.

Enhancement of Nitric Oxide Bioavailability by Modulation of Cutaneous Nitric Oxide Stores

The generation of nitric oxide (NO) in the skin plays a critical role in wound healing and the response to several stimuli, such as UV exposure, heat, infection, and inflammation. Furthermore, in the human body, NO is involved in vascular homeostasis and the regulation of blood pressure. Physiologically, a family of enzymes termed nitric oxide synthases (NOS) generates NO. In addition, there are many methods of non-enzymatic/NOS-independent NO generation, e.g., the reduction of NO derivates (NODs) such as nitrite, nitrate, and nitrosylated proteins under certain conditions. The skin is the largest and heaviest human organ and contains a comparatively high concentration of these NODs; therefore, it represents a promising target for many therapeutic strategies for NO-dependent pathological conditions. In this review, we give an overview of how the cutaneous NOD stores can be targeted and modulated, leading to a further accumulation of NO-related compounds and/or the local and systemic release of bioactive NO, and eventually, NO-related physiological effects with a potential therapeutical use for diseases such as hypertension, disturbed microcirculation, impaired wound healing, and skin infections.

Reduced nitric oxide synthesis in winter: A potential contributing factor to increased cardiovascular risk

BACKGROUND

Nitric oxide is a key signalling molecule that elicits a range of biological functions to maintain vascular homeostasis. A reduced availability of nitric oxide is implicated in the progression of cardiovascular diseases and increases the risk of pathogenic events.

AIMS

To compare the concentration of nitric oxide metabolites in healthy adults between winter and summer months.

DESIGN

An observational study of healthy adults (age 32 ± 9 years) living in central Scotland.

METHODS

Thirty-four healthy adults (13 females) were monitored for 7 days in summer and winter to record sunlight exposure (ultraviolet-A (UV-A) radiation), diet, and physical activity. At the end of each phase, blood pressure was measured, and samples of blood and saliva collected. The samples were analysed to determine the concentrations of plasma and salivary nitrate and nitrite and serum 25-hydroxyvitamin D (25(OH)D).

RESULTS

The participants maintained similar diets in each measurement phase but were exposed to more UV-A radiation (550%) and undertook more moderate-vigorous physical activity (23%) in the summer than in winter. Plasma nitrite (46%) and serum 25(OH)D (59%) were higher and blood pressure was lower in the summer compared to winter months. Plasma nitrite concentration was negatively associated with systolic, diastolic, and mean arterial blood pressure.

CONCLUSIONS

Plasma nitrite, an established marker of nitric oxide synthesis, is higher in healthy adults during the summer than in winter. This may be mediated by a greater exposure to UV-A which stimulates the release of nitric oxide metabolites from skin stores. While it is possible that seasonal variation in nitric oxide availability may contribute to an increased blood pressure in the winter months, the overall impact on cardiovascular health remains to be determined.

Post-exposure persistence of nitric oxide upregulation in skin cells irradiated by UV-A

Evidence suggests that exposure to UV-A radiation can liberate nitric oxide from skin cells eliciting vasodilation in-vivo. However, the duration of nitric oxide release in skin cells after UV exposure is not well studied, with emphasis on UV-B mediated iNOS upregulation. The current study demonstrated persistence of nitric oxide release in a dark reaction after moderate UV-A exposure, peaking around 48 h post exposure; this effect was shown in keratinocytes, fibroblasts and endothelial cells from neonatal donors and keratinocytes from aged donors and confirmed the hypothesis that UV-A exposure appeared to upregulate cNOS alongside iNOS. Release of nitric oxide in the skin cells induced by a moderate exposure to UV-A in sunlight may be especially beneficial for some demographic groups such as the elderly, hypertensive patients or those with impaired nitric oxide function, not only during exposure but many hours and days after that.

Role of nitric oxide in regulating epidermal permeability barrier function

Nitric oxide (NO), a free radical molecule synthesized by nitric oxide synthases (NOS), regulates multiple cellular functions in a variety of cell types. These NOS, including endothelial NOS (eNOS), inducible NOS (iNOS) and neural NOS (nNOS), are expressed in keratinocytes. Expression levels of both iNOS and nNOS decrease with ageing, and insufficient NO has been linked to the development of a number of disorders such as diabetes and hypertension, and to the severity of atherosclerosis. Conversely, excessive NO levels can induce cellular oxidative stress, but physiological levels of NO are required to maintain the normal functioning of cells, including keratinocytes. NO also regulates cutaneous functions, including epidermal permeability barrier homeostasis and wound healing, through its stimulation of keratinocyte proliferation, differentiation and lipid metabolism. Topical applications of a diverse group of agents which generate nitric oxide (called NO donors) such as S-nitroso-N-acetyl-D,L-penicillamine (SNAP) can delay permeability barrier recovery in barrier-disrupted skin, but iNOS is still required for epidermal permeability barrier homeostasis. This review summarizes the regulatory role that NO plays in epidermal permeability barrier functions and the underlying mechanisms involved.

Light-induced nitric oxide release in the skin beyond UVA and blue light: Red & near-infrared wavelengths

Nitric oxide (NO) is omnipresent in the body and synthesized by 3 isoenzymes (nNOS, eNOS and iNOS), all detected in human skin. NO can be stored in a pool of compounds readily converted to NO following skin irradiation by UVR and blue light. This non-enzymatic (without NOS involvement) photolytic reaction mobilizes cutaneous stores of NO derivatives to the bloodstream, lowering blood pressure. However, with the likelihood of skin deleterious effects caused by UVR/blue light, safer wavelengths in the red/near-infrared (NIR) spectrum are becoming potential contenders to release cutaneous NO, possibly via NOS temperature-dependent effects. The use of red/NIR light to mobilize NO stores from the body's largest organ (the skin) is auspicious. This review focuses on UVR, blue, red, and NIR spectra and their capacity to release NO in human skin. PubMed and Google Scholar were used as article databases to find relevant publications related to this particular field.

Low Electrical Resistance Properties of Acupoints: Roles of NOergic Signaling Molecules and Neuropeptides in Skin Electrical Conductance

Early studies from several independent laboratories demonstrated that acupoints possess the characteristics of low electrical resistance. New devices are developing to increase the reliability of electrical skin impedance measurements for counteracting the factors including skin dryness, skin thickness, size of the sensing electrode, pressure applied on the electrode, interelectrode distance, room temperature, and humidity. Morphological studies have identified that blood vessels, hair follicles, and nervous components are enhanced in the meridians/acupoints, which represent areas of potentially high neuronal activity. Recent evidence shows that nitric oxide (NO) concentrations are enhanced in skin acupoints/meridians. L-arginine-derived NO synthesis modifies skin norepinephrine (NE) synthesis/release in acupoints/meridians, and NO-NE activations play an important role in mediating the skin conductance responses to electrical stimulation. NOergic signaling molecules interact with gap junction and transient receptor potential vanilloid type-1. Other studies reported that the high conductance at acupoints is a result of the release of the neuropeptides substance P and calcitonin gene-related peptide during neurogenic inflammation in the referred pain area. Pathological body conditions caused considerable changes in skin conductance or impedance at acupoints. Although systematic research with an improved equipment and research design to avoid the influencing factors are requested for a definite answer in this field, the results from anatomical and biochemical studies consistently show that acupoints exist higher levels of nervous components, and NOergic signaling molecules and neuropeptides involved in the skin low resistance at acupoints. The increased interest in the acupoints/meridians has led to an open-minded attitude towards understanding this system, which is fundamental important to establish the valid aspects of scientific basis of Chinese medicine mechanisms and therapies.

Biological Mechanisms of S-Nitrosothiol Formation and Degradation: How Is Specificity of S-Nitrosylation Achieved?

The modification of protein cysteine residues underlies some of the diverse biological functions of nitric oxide (NO) in physiology and disease. The formation of stable nitrosothiols occurs under biologically relevant conditions and time scales. However, the factors that determine the selective nature of this modification remain poorly understood, making it difficult to predict thiol targets and thus construct informatics networks. In this review, the biological chemistry of NO will be considered within the context of nitrosothiol formation and degradation whilst considering how specificity is achieved in this important post-translational modification. Since nitrosothiol formation requires a formal one-electron oxidation, a classification of reaction mechanisms is proposed regarding which species undergoes electron abstraction: NO, thiol or S-NO radical intermediate. Relevant kinetic, thermodynamic and mechanistic considerations will be examined and the impact of sources of NO and the chemical nature of potential reaction targets is also discussed.

Blue laser-induced selective vasorelaxation by the activation of NOSs

Phototherapy has been tried for treating cardiovascular diseases. In particular, ultraviolet and blue visible lights were suggested to be useful due to their nitric oxide (NO)-production ability in the skin. However, the effects of blue light on the arterial contractility are controversial. Here, we hypothesized that appropriate protocol of blue laser can induce selective vasorelaxation by activating vasodilating signaling molecules in arteries. Using organ chamber arterial mechanics, NO assay, Matrigel assay, and microarray, we showed that a 200-Hz, 300-μs, 445-nm pulsed-laser (total energy of 600 mJ; spot size 4 mm) induced selective vasorelaxation, without vasocontraction in rat mesenteric arteries. The laser stimulation increased NO production in the cord blood-endothelial progenitor cells (CB-EPCs). Both the laser-induced vasorelaxation and NO production were inhibited by a non-selective, pan-NO synthase inhibitor, L-NG-Nitro arginine methyl ester. Microarray study in CB-EPCs suggested up-regulation of cryptochrome (CRY)2 as well as NO synthase (NOS)1 and NOSTRIN (NOS trafficking) by the laser. In conclusion, this study suggests that the 445-nm blue puled-laser can induce vasorelaxation possibly via the CRY photoreceptors and NOSs activation. The blue laser-therapy would be useful for treating systemic hypertension as well as improving local blood flow depending on the area of irradiation.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

The emerging potential of cold atmospheric plasma in skin biology

The maintenance of skin integrity is crucial to ensure the physiological barrier against exogenous compounds, microorganisms and dehydration but also to fulfill social and aesthetic purposes. Besides the development of new actives intended to enter a formulation, innovative technologies based on physical principles have been proposed in the last years. Among them, Cold Atmospheric Plasma (CAP) technology, which already showed interesting results in dermatology, is currently being studied for its potential in skin treatments and cares. CAP bio-medical studies gather several different expertise ranging from physics to biology through chemistry and biochemistry, making this topic hard to pin. In this review we provide a broad survey of the interactions between CAP and skin. In the first section, we tried to give some fundamentals on skin structure and physiology, related to its essential functions, together with the main bases on cold plasma and its physicochemical properties. In the following parts we dissected and analyzed each CAP parameter to highlight the already known and the possible effects they can play on skin. This overview aims to get an idea of the potential of cold atmospheric plasma technology in skin biology for the future developments of dermo-cosmetic treatments, for example in aging prevention.

Photochemistry of nitric oxide and S-nitrosothiols in human skin

Nitric oxide (NO) is related to a wide range of physiological processes such as vasodilation, macrophages cytotoxicity and wound healing. The human skin contains NO precursors (NOx). Those are mainly composed of nitrite (NO2-), nitrate (NO3-), and S-nitrosothiols (RSNOs) which forms a large NO store. These NOx stores in human skin can mobilize NO to blood stream upon ultraviolet (UV) light exposure. The main purpose of this study was to evaluate the most effective UV light wavelength to generate NO and compare it to each NO precursor in aqueous solution. In addition, the UV light might change the RSNO content on human skin. First, we irradiated pure aqueous solutions of NO2- and NO3- and mixtures of NO2- and glutathione and NO3- and S-nitrosoglutathione (GSNO) to identify the NO release profile from those species alone. In sequence, we evaluated the NO generation profile on human skin slices. Human skin was acquired from redundant plastic surgical samples and the NO and RSNO measurements were performed using a selective NO electrochemical sensor. The data showed that UV light could trigger the NO generation in skin with a peak at 280-285 nm (UVB range). We also observed a significant RSNO formation in irradiated human skin, with a peak at 320 nm (UV region) and at 700 nm (visible region). Pre-treatment of the human skin slice using NO2- and thiol (RSHs) scavengers confirmed the important role of these molecules in RSNO formation. These findings have important implications for clinical trials with potential for new therapies.

Does Incident Solar Ultraviolet Radiation Lower Blood Pressure?

Background Hypertension remains a leading global cause for premature death and disease. Most treatment guidelines emphasize the importance of risk factors, but not all are known, modifiable, or easily avoided. Population blood pressure correlates with latitude and is lower in summer than winter. Seasonal variations in sunlight exposure account for these differences, with temperature believed to be the main contributor. Recent research indicates that UV light enhances nitric oxide availability by mobilizing storage forms in the skin, suggesting incident solar UV radiation may lower blood pressure. We tested this hypothesis by exploring the association between environmental UV exposure and systolic blood pressure (SBP) in a large cohort of chronic hemodialysis patients in whom SBP is determined regularly. Methods and Results We studied 342 457 patients (36% black, 64% white) at 2178 US dialysis centers over 3 years. Incident UV radiation and temperature data for each clinic location were retrieved from the National Oceanic and Atmospheric Administration database. Linear mixed effects models with adjustment for ambient temperature, sex/age, body mass index, serum Na+/K+ and other covariates were fitted to each location and combined estimates of associations calculated using the DerSimonian and Laird procedure. Pre-dialysis SBP varied by season and was ≈4 mm Hg higher in black patients. Temperature, UVA and UVB were all linearly and inversely associated with SBP. This relationship remained statistically significant after correcting for temperature. Conclusions In hemodialysis patients, in addition to environmental temperature, incident solar UV radiation is associated with lower SBP. This raises the possibility that insufficient sunlight is a new risk factor for hypertension, perhaps even in the general population.

Nanomedicine-Enabled Photonic Thermogaseous Cancer Therapy

Local photothermal hyperthermia for tumor ablation and specific stimuliresponsive gas therapy feature the merits of remote operation, noninvasive intervention, and in situ tumor-specific activation in cancer-therapeutic biomedicine. Inspired by synergistic/sequential therapeutic modality, herein a novel therapeutic modality is reported based on the construction of two-dimensional (2D) core/shell-structured Nb2C-MSNs-SNO composite nanosheets for photonic thermogaseous therapy. A phototriggered thermogas-generating nanoreactor is designed via mesoporous silica layer coating on the surface of Nb2C MXene nanosheets, where the mesopores provide the reservoirs for NO donor (S-nitrosothiol (RSNO)), and the core of Nb2C produces heat shock upon second near-infrared biowindow (NIR-II) laser irradiation. The Nb2C-MSNs-SNO-enabled photonic thermogaseous therapy undergoes a sequential process of phototriggered heat production from the core of Nb2C and thermotriggered NO generation, together with photoacoustic-imaging (PAI) guidance and monitoring. The constructed Nb2C-MSNs-SNO nanoreactors exhibit high-NIR-induced photothermal effect, intense NIR-controlled NO release, and desirable PAI performance. Based on these unique theranostic properties of Nb2C-MSNs-SNO nanocomposites, sequential photonic thermogaseous therapy with limited systematic toxicity on efficiently suppressing tumor growth is achieved by PAI-guided NIR-controlled NO release as well as heat generation. Such a thermogaseous approach representes a stimuli-selective strategy for synergistic/sequential cancer treatment.

Blue light (λ=453 nm) nitric oxide dependently induces β-endorphin production of human skin keratinocytes in-vitro and increases systemic β-endorphin levels in humans in-vivo

β-Endorphin exerts a broad spectrum of physiological activity on mood, immune functions, pain management, reward effects, and behavioral stability. β-Endorphin is produced in certain neurons within the central and peripheral nervous system but also in the skin, especially in response to ultraviolet radiation. In the present study we have investigated the impact of visible blue light at λ = 453 nm (BL) on β-endorphin production of primary human skin keratinocytes (hKC) in-vitro as well as on systemic β-endorphin formation of whole-body exposed subjects in-vivo. We found that BL irradiation significantly enhanced both keratinocytic β-endorphin production of hKC cultures as well as systemic β-endorphin concentrations in light exposed healthy subjects. Interestingly, in hKC cultures elevated β-endorphin formation was paralleled by significantly increased levels of non-enzymatically generated nitric oxide (NO), whereas elevated systemic β-endorphin values of BL-exposed subjects were accompanied by enhanced systemic concentration of bioactive NO-derivates. These findings point to a pivotal role of NO in the molecular mechanism of the observed BL-induced effects, and indeed, exogenously applied NO was able to significantly enhance β-endorphin production in hKC cultures. Thus, our finding of BL-induced increases in systemic β-endorphin concentration in-vivo can be plausibly explained by an event sequence comprising 1.) BL-driven non-enzymatic formation of NO in the exposed skin tissue, 2.) systemic distribution of cutaneously produced NO in the form of bioactive nitroso compounds, 3.) a subsequent NO-dependent induction of β-endorphin synthesis in epidermal keratinocytes, and 4.) probably also a NO-dependent modulation of β-endorphin synthesis in specialized neurons within the central and peripheral nervous system.

BDNF, endurance activity, and mechanisms underlying the evolution of hominin brains

OBJECTIVES

As a complex, polygenic trait, brain size has likely been influenced by a range of direct and indirect selection pressures for both cognitive and non-cognitive functions and capabilities. It has been hypothesized that hominin brain expansion was, in part, a correlated response to selection acting on aerobic capacity (Raichlen & Polk, 2013). According to this hypothesis, selection for aerobic capacity increased the activity of various signaling molecules, including those involved in brain growth. One key molecule is brain-derived neurotrophic factor (BDNF), a protein that regulates neuronal development, survival, and plasticity in mammals. This review updates, partially tests, and expands Raichlen and Polk's (2013) hypothesis by evaluating evidence for BDNF as a mediator of brain size.

DISCUSSION

We contend that selection for endurance capabilities in a hot climate favored changes to muscle composition, mitochondrial dynamics and increased energy budget through pathways involving regulation of PGC-1α and MEF2 genes, both of which promote BDNF activity. In addition, the evolution of hairlessness and the skin's thermoregulatory response provide other molecular pathways that promote both BDNF activity and neurotransmitter synthesis. We discuss how these pathways contributed to the evolution of brain size and function in human evolution and propose avenues for future research. Our results support Raichlen and Polk's contention that selection for non-cognitive functions has direct mechanistic linkages to the evolution of brain size in hominins.

Diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes in young male mice

Recent observational studies have reported that patients with low circulating levels of vitamin D experience larger infarct volumes and worse functional outcomes after ischemic stroke compared to those with sufficient levels. However, it is unknown whether a causal relationship exists between low vitamin D levels and poor stroke outcome. This study aimed to assess the effect of vitamin D deficiency on acute outcomes post-stroke. Male C57Bl6 mice (six week old) were assigned to either a control or vitamin D deficient diet for four weeks prior to stroke. Stroke was induced by 1 h middle cerebral artery occlusion (MCAO) with reperfusion. At 24 h, we assessed functional outcomes, infarct volume, quantified immune cells in the brain by immunofluorescence and examined susceptibility to lung infection. ELISAs showed that the plasma level of hydroxyvitamin D₃ was 85% lower in mice fed the vitamin D-deficient diet compared with the control group. Despite this, vitamin D deficiency had no impact on functional outcomes or infarct volume after stroke. Further, there were no differences in the numbers of infiltrating immune cells or bacterial load within the lungs. These data suggest that diet-induced vitamin D deficiency has no effect on acute post-stroke outcomes.

Blue light exposure decreases systolic blood pressure, arterial stiffness, and improves endothelial function in humans

AIMS

Previous studies have shown that ultraviolet light can lead to the release of nitric oxide from the skin and decrease blood pressure. In contrast to visible light the local application of ultraviolet light bears a cancerogenic risk. Here, we investigated whether whole body exposure to visible blue light can also decrease blood pressure and increase endothelial function in healthy subjects.

METHODS

In a randomised crossover study, 14 healthy male subjects were exposed on 2 days to monochromatic blue light or blue light with a filter foil (control light) over 30 minutes. We measured blood pressure (primary endpoint), heart rate, forearm vascular resistance, forearm blood flow, endothelial function (flow-mediated dilation), pulse wave velocity and plasma nitric oxide species, nitrite and nitroso compounds (secondary endpoints) during and up to 2 hours after exposure.

RESULTS

Blue light exposure significantly decreased systolic blood pressure and increased heart rate as compared to control. In parallel, blue light significantly increased forearm blood flow, flow-mediated dilation, circulating nitric oxide species and nitroso compounds while it decreased forearm vascular resistance and pulse wave velocity.

CONCLUSION

Whole body irradiation with visible blue light at real world doses improves blood pressure, endothelial function and arterial stiffness by nitric oxide released from photolabile intracutanous nitric oxide metabolites into circulating blood.

Computational Structural Biology of S-nitrosylation of Cancer Targets

Nitric oxide (NO) plays an essential role in redox signaling in normal and pathological cellular conditions. In particular, it is well known to react in vivo with cysteines by the so-called S-nitrosylation reaction. S-nitrosylation is a selective and reversible post-translational modification that exerts a myriad of different effects, such as the modulation of protein conformation, activity, stability, and biological interaction networks. We have appreciated, over the last years, the role of S-nitrosylation in normal and disease conditions. In this context, structural and computational studies can help to dissect the complex and multifaceted role of this redox post-translational modification. In this review article, we summarized the current state-of-the-art on the mechanism of S-nitrosylation, along with the structural and computational studies that have helped to unveil its effects and biological roles. We also discussed the need to move new steps forward especially in the direction of employing computational structural biology to address the molecular and atomistic details of S-nitrosylation. Indeed, this redox modification has been so far an underappreciated redox post-translational modification by the computational biochemistry community. In our review, we primarily focus on S-nitrosylated proteins that are attractive cancer targets due to the emerging relevance of this redox modification in a cancer setting.

The health benefits of UV radiation exposure through vitamin D production or non-vitamin D pathways. Blood pressure and cardiovascular disease

The detrimental effects of ultraviolet radiation are well known. Skin cancer, photo-aging, and induction or exacerbation of photosensitive dermatoses have been the focus of most photobiological research since 1928 when Findlay confirmed the carcinogenicity of ultraviolet radiation using a murine model of skin cancer. The epidemiological, mechanistic and clinical trial data have enabled the classification by the International Agency for Research on Cancer of ultraviolet radiation as a Group 1 ('sufficient evidence') carcinogen for human skin. Public health advice in most developed countries with a pale-skinned population following this has advocated limiting exposure to sunlight through use of clothing, sunblock and behavioural alterations. Despite this plethora of data, one striking omission is evidence that ultraviolet radiation shortens life, and as I will lay out in this chapter, epidemiological and now mechanistic data suggest that UV may have significant benefits on health and in particular cardiovascular health.

The effects of two different doses of ultraviolet-A light exposure on nitric oxide metabolites and cardiorespiratory outcomes

Purpose

The present study investigated different doses of ultraviolet-A (UV-A) light on plasma nitric oxide metabolites and cardiorespiratory variables.

Methods

Ten healthy male participants completed three experimental conditions, 7 days apart. Participants were exposed to no light (CON); 10 J cm² (15 min) of UV-A light (UVA10) and 20 J cm² (30 min) of UV-A light (UVA20) in a randomized order. Plasma nitrite [NO₂⁻] and nitrate [NO₃⁻] concentrations, blood pressure (BP), and heart rate (HR) were recorded before, immediately after exposure and 30 min post-exposure. Whole body oxygen utilization (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2), resting metabolic rate (RMR) and skin temperature were recorded continuously.

Results

None of the measured parameters changed significantly during CON (all P > 0.05). \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR were significantly reduced immediately after UVA10 (P < 0.05) despite no change in plasma [NO₂⁻] (P > 0.05). Immediately after exposure to UVA20, plasma [NO₂⁻] was higher (P = 0.014) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR tended to be lower compared to baseline (P = 0.06). There were no differences in [NO₂⁻] or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 at the 30 min time point in any condition. UV-A exposure did not alter systolic BP, diastolic BP or MAP (all P > 0.05). UV-A light did not alter plasma [NO₃⁻] at any time point (all P > 0.05).

Conclusions

This study demonstrates that a UV-A dose of 20 J cm² is necessary to increase plasma [NO₂⁻] although a smaller dose is capable of reducing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR at rest. Exposure to UV-A did not significantly reduce BP in this cohort of healthy adults. These data suggest that exposure to sunlight has a meaningful acute impact on metabolic function.

Nitric oxide signaling molecules in acupoints: Toward mechanisms of acupuncture

Recent clinical trial studies have demonstrated that the effects of acupuncture on pain improvement are small and no difference between acupoints and non-points. Whether acupuncture needles must be inserted in specific points depends on whether acupoint specificity exists that is still not resolved, and is now urgent. Previous anatomical studies have demonstrated that acupoints exist higher number of nerve fibers/trunks, blood vessels, hair follicles, and sweat glands as well as density of the gap junction. Recent evidence shows that nitric oxide (NO) level is elevated in the acupoints/ meridians and is associated with an enhanced expression of NO synthase endowed with transient receptor potential vanilloid type-1. There is growing evidence from international groups showing that acupuncture induces NO-mediated vasodilatation, which increases local blood flow and allows for a flush of algesic or sensitizing substances, leading to pain relief. Previous studies, using a novel biocapture system, have demonstrated that NOx- (total nitrite and nitrate) and cyclic guanosine monophosphate (cGMP) concentrations are consistently increased over skin acupoints compared to non-meridian control regions (NMCR) in humans. Dermal microdialysis in humans showed that NO-cGMP releases in the subcutaneous tissue of acupoint are higher than those in NMCR and increased by electroacupuncture (EA). Recent studies have demonstrated that low-frequency electrical stimulation and manual acupuncture with low stimulating force and rate produce an elevation of NO release predominantly over acupoints. In contrast, NO levels over the areas of the skin regions are moderately reduced by high-frequency EA stimulation. The results from anatomical and biochemical studies consistently show that acupoints exist higher levels of NO signaling molecules, and stimulus-evoked NO release is also with a higher level at acupoints. Results suggest that NO signaling molecules contribute to the specificity of acupoints, and selecting well-trained acupuncturetists for using correct acupoints and appropriate parameters should improve acupuncture clinical trial studies.

Ultraviolet Radiation-Induced Production of Nitric Oxide:A multi-cell and multi-donor analysis

Increasing evidence regarding positive effects of exposure to sunlight has led to suggestions that current advice may be overly weighted in favour of avoidance. UV-A has been reported to lower blood pressure, possibly through nitric oxide (NO) production in skin. Here, we set out to investigate effects of UV-A and solar-simulated radiation on the potential source of dermal NO, the effective doses and wavelengths, the responsiveness of different human skin cells, the magnitude of inter-individual differences and the potential influence of age. We utilised isogenic keratinocytes, microvascular endothelial cells, melanocytes and fibroblasts isolated from 36 human skins ranging from neonates to 86 years old. We show that keratinocytes and microvascular endothelial cells show greatest NO release following biologically relevant doses of UV-A. This was consistent across multiple neonatal donors and the effect is maintained in adult keratinocytes. Our observations are consistent with a bi-phasic mechanism by which UV-A can trigger vasodilatory effects. Analyses of NO-production spectra adds further evidence that nitrites in skin cells are the source of UV-mediated NO release. These potentially positive effects of ultraviolet radiation lend support for objective assessment of environmental influence on human health and the idea of “healthy sun exposure”.

Chitosan nanoparticles for nitric oxide delivery in human skin

The use of nanoparticle-based transdermal delivery systems is a promising approach to efficiently carry and deliver therapeutic agents for dermal and systemic administration. Nitric oxide (NO) is a key molecule that plays important roles in human skin such as the control of skin homeostasis, skin defense, control of dermal blood flow, and wound healing. In addition, human skin contains stores of NO derivatives that can be mobilized and release free NO upon UV irradiation with beneficial cardiovascular effects, for instance the control of blood pressure. In this work, the NO donor precursor glutathione (GSH) was encapsulated (encapsulation efficiency of 99.60%) into ultra-small chitosan nanoparticles (CS NPs) (hydrodynamic size of 30.65 ± 11.90 nm). GSH-CS NPs have a core-shell structure, as revealed by atomic force microscopy and X-ray photoelectron spectroscopy, in which GSH is protected in the nanoparticle core. Nitrosation of GSH by nitrous acid led to the formation of the NO donor S-nitrosogluthathione (GSNO) into CS NPs. The GSNO release from the CS NPs followed a Fickian diffusion described by the Higuchi mathematical model. Topical application of GSNO-CS NPs in intact human skin significantly increased the levels of NO and its derivatives in the epidermis, as assayed by confocal microscopy, and this effect was further enhanced by skin irradiation with UV light. Therefore, NO-releasing CS NPs are suitable materials for transdermal NO delivery to local and/or systemic therapies.

Ultra-short laser-accelerated proton pulses have similar DNA-damaging effectiveness but produce less immediate nitroxidative stress than conventional proton beams

Ultra-short proton pulses originating from laser-plasma accelerators can provide instantaneous dose rates at least 10(7)-fold in excess of conventional, continuous proton beams. The impact of such extremely high proton dose rates on A549 human lung cancer cells was compared with conventionally accelerated protons and 90 keV X-rays. Between 0.2 and 2 Gy, the yield of DNA double strand breaks (foci of phosphorylated histone H2AX) was not significantly different between the two proton sources or proton irradiation and X-rays. Protein nitroxidation after 1 h judged by 3-nitrotyrosine generation was 2.5 and 5-fold higher in response to conventionally accelerated protons compared to laser-driven protons and X-rays, respectively. This difference was significant (p < 0.01) between 0.25 and 1 Gy. In conclusion, ultra-short proton pulses originating from laser-plasma accelerators have a similar DNA damaging potential as conventional proton beams, while inducing less immediate nitroxidative stress, which probably entails a distinct therapeutic potential.

Therapeutic effects of inorganic nitrate and nitrite in cardiovascular and metabolic diseases

Nitric oxide (NO) is generated endogenously by NO synthases to regulate a number of physiological processes including cardiovascular and metabolic functions. A decrease in the production and bioavailability of NO is a hallmark of many major chronic diseases including hypertension, ischaemia-reperfusion injury, atherosclerosis and diabetes. This NO deficiency is mainly caused by dysfunctional NO synthases and increased scavenging of NO by the formation of reactive oxygen species. Inorganic nitrate and nitrite are emerging as substrates for in vivo NO synthase-independent formation of NO bioactivity. These anions are oxidation products of endogenous NO generation and are also present in the diet, with green leafy vegetables having a high nitrate content. The effects of nitrate and nitrite are diverse and include vasodilatation, improved endothelial function, enhanced mitochondrial efficiency and reduced generation of reactive oxygen species. Administration of nitrate or nitrite in animal models of cardiovascular disease shows promising results, and clinical trials are currently ongoing to investigate the therapeutic potential of nitrate and nitrite in hypertension, pulmonary hypertension, peripheral artery disease and myocardial infarction. In addition, the nutritional aspects of the nitrate-nitrite-NO pathway are interesting as diets suggested to protect against cardiovascular disease, such as the Mediterranean diet, are especially high in nitrate. Here, we discuss the potential therapeutic opportunities for nitrate and nitrite in prevention and treatment of cardiovascular and metabolic diseases.

Influence of age, gender, and race on nitric oxide release over acupuncture points-meridians

This study examined the influence of age, gender and race on nitric oxide (NO) release over acupuncture points, meridian without acupoint, and non-meridian regions of the Pericardium (PC) and Bladder (BL) meridian as well as aging on LU meridian in 61 healthy subjects. Biocapture tubes were attached to the skin surface, and total nitrite and nitrate was biocaptured and quantified using chemiluminescence. In elder ages compared to adults, NO levels over the ventral forearm were significantly decreased over LU on radial regions but not altered over PC on medial regions. Conversely, NO content was elevated over BL regions only in overweight/obesity of elder ages. NO levels over PC regions were marginally elevated in overweight/obese males compared to females but did not alter between races. These results suggest a selective reduction of NO release over LU meridian with aging, which is consistent with a progressive decline in lung function and increase in chronic respiratory disease in elder ages. Increased NO levels along the BL meridian in older obese subjects may reflect a modified NO level along somatic-bladder pathway for counteracting bladder dysfunctions with aging. Both of them support somatic-organ connections in the meridian system associated with potential pathophysiological changes with aging.

Damage to skin extracellular matrix induced by UV exposure

SIGNIFICANCE

Chronic exposure to environmental ultraviolet radiation (UVR) plays a key role in both photocarcinogenesis and induction of accelerated skin aging. Although the spatiotemporal consequences of UVR exposure for the composition and architecture of the dermal extracellular matrix (ECM) are well characterized, the pathogenesis of photoaging remains poorly defined. Given the compelling evidence for the role of reactive oxygen species (ROS) as mediators of photoaging, UVR-exposed human skin may be an accessible model system in which to characterize the role of oxidative damage in both internal and external tissues.

RECENT ADVANCES

Although the cell-mediated degradation of dermal components via UVR-induced expression of ECM proteases has long been identified as an integral part of the photoaging pathway, the relative importance and identity of cellular and extracellular photosensitizers (direct hit and bystanders models, respectively) in initiating this enzymatic activity is unclear. Recently, both age-related protein glycation and relative amino-acid composition have been identified as potential risk factors for photo-ionization and/or photo-sensitization. Here, we propose a selective multi-hit model of photoaging.

CRITICAL ISSUES

Bioinformatic analyses can be employed to identify candidate UVR targets/photosensitizers, but the action of UVR on protein structure and/or ROS production should be verified experimentally. Crucially, in the case of biochemically active ECM components such as fibronectin and fibrillin, the downstream effects of photo-degradation on tissue homeostasis remain to be confirmed.

FUTURE DIRECTIONS

Both topical antioxidants and inhibitors of detrimental cell signaling may be effective in abrogating the effects of specific UVR-mediated protein degradation in the dermis.

Ultraviolet radiation, aging and the skin: prevention of damage by topical cAMP manipulation

Being the largest and most visible organ of the body and heavily influenced by environmental factors, skin is ideal to study the long-term effects of aging. Throughout our lifetime, we accumulate damage generated by UV radiation. UV causes inflammation, immune changes, physical changes, impaired wound healing and DNA damage that promotes cellular senescence and carcinogenesis. Melanoma is the deadliest form of skin cancer and among the malignancies of highest increasing incidence over the last several decades. Melanoma incidence is directly related to age, with highest rates in individuals over the age of 55 years, making it a clear age-related disease. In this review, we will focus on UV-induced carcinogenesis and photo aging along with natural protective mechanisms that reduce amount of “realized” solar radiation dose and UV-induced injury. We will focus on the theoretical use of forskolin, a plant-derived pharmacologically active compound to protect the skin against UV injury and prevent aging symptoms by up-regulating melanin production. We will discuss its use as a topically-applied root-derived formulation of the Plectranthus barbatus (Coleus forskolii) plant that grows naturally in Asia and that has long been used in various Aryuvedic teas and therapeutic preparations.

UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase

The incidence of hypertension and cardiovascular disease (CVD) correlates with latitude and rises in winter. The molecular basis for this remains obscure. As nitric oxide (NO) metabolites are abundant in human skin, we hypothesized that exposure to UVA may mobilize NO bioactivity into the circulation to exert beneficial cardiovascular effects independently of vitamin D. In 24 healthy volunteers, irradiation of the skin with two standard erythemal doses of UVA lowered blood pressure (BP), with concomitant decreases in circulating nitrate and rises in nitrite concentrations. Unexpectedly, acute dietary intervention aimed at modulating systemic nitrate availability had no effect on UV-induced hemodynamic changes, indicating that cardiovascular effects were not mediated via direct utilization of circulating nitrate. UVA irradiation of the forearm caused increased blood flow independently of NO synthase (NOS) activity, suggesting involvement of pre-formed cutaneous NO stores. Confocal fluorescence microscopy studies of human skin pre-labeled with the NO-imaging probe diaminofluorescein 2 diacetate revealed that UVA-induced NO release occurs in a NOS-independent, dose-dependent manner, with the majority of the light-sensitive NO pool in the upper epidermis. Collectively, our data provide mechanistic insights into an important function of the skin in modulating systemic NO bioavailability, which may account for the latitudinal and seasonal variations of BP and CVD.

Mechanism and biological relevance of blue-light (420-453 nm)-induced nonenzymatic nitric oxide generation from photolabile nitric oxide derivates in human skin in vitro and in vivo

Human skin contains photolabile nitric oxide (NO) derivates such as nitrite and S-nitrosothiols, which upon UVA radiation decompose under high-output NO formation and exert NO-specific biological responses such as increased local blood flow or reduced blood pressure. To avoid the injurious effects of UVA radiation, we here investigated the mechanism and biological relevance of blue-light (420-453 nm)-induced nonenzymatic NO generation from photolabile nitric oxide derivates in human skin in vitro and in vivo. As quantified by chemiluminescence detection (CLD), at physiological pH blue light at 420 or 453 nm induced a significant NO formation from S-nitrosoalbumin and also from aqueous nitrite solutions by a to-date not entirely identified Cu(1+)-dependent mechanism. As detected by electron paramagnetic resonance spectrometry in vitro with human skin specimens, blue light irradiation significantly increased the intradermal levels of free NO. As detected by CLD in vivo in healthy volunteers, irradiation of human skin with blue light induced a significant emanation of NO from the irradiated skin area as well as a significant translocation of NO from the skin surface into the underlying tissue. In parallel, blue light irradiation caused a rapid and significant rise in local cutaneous blood flow as detected noninvasively by using micro-light-guide spectrophotometry. Irradiation of human skin with moderate doses of blue light caused a significant increase in enzyme-independent cutaneous NO formation as well as NO-dependent local biological responses, i.e., increased blood flow. The effects were attributed to blue-light-induced release of NO from cutaneous photolabile NO derivates. Thus, in contrast to UVA, blue-light-induced NO generation might be therapeutically used in the treatment of systemic and local hemodynamic disorders that are based on impaired physiological NO production or bioavailability.

1α,25-Dihydroxyvitamin D3 reduces several types of UV-induced DNA damage and contributes to photoprotection

Vitamin D production requires UVB. In turn, we have shown that vitamin D compounds reduce UV-induced damage, including inflammation, sunburn, thymine dimers, the most frequent type of cyclobutane pyrimidine dimer, immunosuppression, and photocarcinogenesis. Our previous studies have shown most of the photoprotective effects by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) occurred through the nongenomic pathway because similar protection was seen with an analog, 1α,25-dihydroxylumistrol3 (JN), which has little ability to alter gene expression and also because a nongenomic antagonist of 1,25(OH)2D3 abolished protection. In the current study, we tested whether this photoprotective effect would extend to other types of DNA damage, and whether this could be demonstrated in human ex vivo skin, as this model would be suited to pre-clinical testing of topical formulations for photoprotection. In particular, using skin explants, we examined a time course for thymine dimers (TDs), the most abundant DNA photolesion, as well as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is a mutagenic DNA base lesion arising from UV-induced oxidative stress, and 8-nitroguanosine (8-NG). Nitric oxide products, known markers for chronic inflammation and carcinogenesis, are also induced by UV. This study showed that 1,25(OH)2D3 significantly reduced TD and 8-NG as early as 30min post UV, and 8-oxodG at 3h post UV, confirming the photoprotective effect of 1,25(OH)2D3 against DNA photoproducts in human skin explants. At least in part, the mechanism of photoprotection by 1,25(OH)2D3 is likely to be through the reduction of reactive nitrogen species and the subsequent reduction in oxidative and nitrosative damage. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Effects of ultraviolet radiation, visible light, and infrared radiation on erythema and pigmentation: a review

The effects of ultraviolet radiation, visible light, and infrared radiation on cutaneous erythema, immediate pigment darkening, persistent pigment darkening, and delayed tanning are affected by a variety of factors. Some of these factors include the depth of cutaneous penetration of the specific wavelength, the individual skin type, and the absorption spectra of the different chromophores in the skin. UVB is an effective spectrum to induce erythema, which is followed by delayed tanning. UVA induces immediate pigment darkening, persistent pigment darkening, and delayed tanning. At high doses, UVA (primarily UVA2) can also induce erythema in individuals with skin types I-II. Visible light has been shown to induce erythema and a tanning response in dark skin, but not in fair skinned individuals. Infrared radiation produces erythema, which is probably a thermal effect. In this article we reviewed the available literature on the effects of ultraviolet radiation, visible light, and infrared radiation on the skin in regards to erythema and pigmentation. Much remains to be learned on the cutaneous effects of visible light and infrared radiation.

1α,25 dihydroxyvitamin D3 enhances cellular defences against UV-induced oxidative and other forms of DNA damage in skin

DNA damage induced by ultraviolet radiation is the key initiator for skin carcinogenesis since mutations may arise from the photoproducts and it also contributes to photoimmune suppression. The active vitamin D hormone, 1α,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) reduces thymine dimers, the major photoproduct found in human skin after UV exposure, and suppresses the accumulation of nitric oxide derivatives that lead to more toxic reactive nitrogen species (RNS). We examined whether other forms of DNA damage are reduced by 1,25(OH)(2)D(3), and hypothesized that photoprotection by 1,25(OH)(2)D(3) is, in part, due to the suppression of various forms of promutagenic DNA damage, including thymine dimers, through a reduction of genotoxic RNS. Different forms of UV-induced DNA damage were investigated in irradiated skin cells treated with or without 1,25(OH)(2)D(3), or inhibitors of metabolism and inducible nitric oxide synthase. Keratinocytes were also treated with nitric oxide donors in the absence of UV light. DNA damage was assessed by comet assay incorporating site specific DNA repair endonucleases, and by immunohistochemistry using antibodies to thymine dimers or 8-oxo-7,8-dihydro-2'-deoxyguanosine, and quantified by image analysis. Strand breaks in T4 endonuclease V, endonuclease IV and human 8-oxoguanine DNA glycosylase digests increased more than 2-fold in UV irradiated human keratinocytes, and were reduced by 1,25(OH)(2)D(3) treatment after UV exposure, and also by low temperature, sodium azide and an inhibitor of inducible nitric oxide synthase. Conversely, nitric oxide donors induced all three types of DNA damage in the absence of UV. We present data to show that 1,25(OH)(2)D(3) protects skin cells from at least three forms of UV-induced DNA damage, and provide further evidence to support the proposal that a reduction in RNS by 1,25(OH)(2)D(3) is a likely mechanism for its photoprotective effect against oxidative and nitrative DNA damage, as well as cyclobutane pyrimidine dimers.

Vitamin D and death by sunshine

Exposure to sunlight is the major cause of skin cancer. Ultraviolet radiation (UV) from the sun causes damage to DNA by direct absorption and can cause skin cell death. UV also causes production of reactive oxygen species that may interact with DNA to indirectly cause oxidative DNA damage. UV increases accumulation of p53 in skin cells, which upregulates repair genes but promotes death of irreparably damaged cells. A benefit of sunlight is vitamin D, which is formed following exposure of 7-dehydrocholesterol in skin cells to UV. The relatively inert vitamin D is metabolized to various biologically active compounds, including 1,25-dihydroxyvitamin D3. Therapeutic use of vitamin D compounds has proven beneficial in several cancer types, but more recently these compounds have been shown to prevent UV-induced cell death and DNA damage in human skin cells. Here, we discuss the effects of vitamin D compounds in skin cells that have been exposed to UV. Specifically, we examine the various signaling pathways involved in the vitamin D-induced protection of skin cells from UV.

Application of Electrode Methods in Studies of Nitric Oxide Metabolism and Diffusion Kinetics

Nitric oxide (NO) has many important physiological roles in the body. Since NO electrodes can directly measure NO concentration in the nM range and in real time, NO electrode methods have been generally used in laboratories for measuring NO concentration in vivo and in vitro. This review focuses on the application of electrode methods in studies of NO diffusion and metabolic kinetics. We have described the physical and chemical properties that need to be considered in the preparation of NO stock solution, discussed the effect of several interfering factors on the measured curves of NO concentration that need to be eliminated in the experimental setup for NO measurements, and provided an overview of the application of NO electrode methods in measuring NO diffusion and metabolic kinetics in solution and in biological systems. This overview covers NO metabolism by oxygen (O₂), superoxide, heme proteins, cells and tissues. Important conclusions and physiological implication of these studies are discussed.