Epidermal keratinocyte expression of inducible nitric oxide synthase in skin lesions of psoriasis vulgaris

NOS2-derived low levels of NO drive psoriasis pathogenesis

Psoriasis is an IL-23/Th17-mediated skin disorder with a strong genetic predisposition. The impact of its susceptibility gene nitric oxide synthase 2 (NOS2) remains unknown. Here, we demonstrate strong NOS2 mRNA expression in psoriatic epidermis, an effect that is IL-17 dependent. However, its complete translation to protein is prevented by the IL-17-induced miR-31 implying marginally upregulated NO levels in psoriatic skin. We demonstrate that lower levels of NO, as opposed to higher levels, increase keratinocyte proliferation and mediate IL-17 downstream effects. We hypothesized that the psoriatic phenotype may be alleviated by either eliminating or increasing cellular NO levels. In fact, using the imiquimod psoriasis mouse model, we found a profound impact on the psoriatic inflammation in both IMQ-treated NOS2 KO mice and wild-type mice treated with IMQ and the NO-releasing berdazimer gel. In conclusion, we demonstrate that IL-17 induces NOS2 and fine-tunes its translation towards a window of proinflammatory and hyperproliferative effects and identify NO donor therapy as a new treatment modality for psoriasis.

Anti-Inflammatory Effect of Fermented Cabbage Extract Containing Nitric Oxide Metabolites with Silica

The aim of this study was to evaluate the anti-inflammatory effect of fermented cabbage extract (FC) containing nitric oxide metabolites with silica (FCS) on 1-fluoro-2,4-dinitrofluorobenzene (DNFB)-induced atopic dermatitis (AD) in BALB/c mice. Atopic dermatitis-like allergic contact dermatitis was induced by DNFB challenge in the ear after DNFB sensitization on the dorsal skin of mice. FCS alleviated the severity of atopic dermatitis-like skin lesions. In addition, epidermis thickness of the ear and penetration of inflammatory cells in atopic dermatitis-like skin lesions were decreased after topical application of FCS. The serum levels of TNF-α and IL-4 were measured in atopic dermatitis mice using ELISA kits, which were observed to be significantly decreased after topical application of FCS. This study demonstrates that the FCS can be used as a potential therapeutic for the treatment and prevention of AD.

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.

Development of a psoriatic-like skin inflammation rat model using imiquimod as an inducing agent

OBJECTIVE:

The present investigation was undertaken to develop a psoriatic-like skin inflammation rat model using imiquimod (IMQ) as an inducing agent.

MATERIALS AND METHODS:

The hairs of the back dorsal portion of the Wistar rats were removed and 80, 100, and 120 mg of IMQ cream (5% w/w) for 10 consecutive days was applied to different groups of rats. Further, psoriasis area severity index was used for calculating the psoriatic score, which included scoring of erythema, scaling, and thickening. Various biochemical parameters, pro-inflammatory cytokines, vascular endothelial growth factor (VEGF), and histopathological examination were also performed.

RESULTS:

The results demonstrated signs of erythema, scaling, and thickening on group applied with 120 mg and 100 mg of IMQ along with ear thickening. Biochemical evaluation revealed a significant increase in the granulation tissue weight followed by significant decrease in the levels of collagen and hexosamine. The antioxidant parameters superoxide dismutase and catalase were found to decline, while nitric oxide and lipid peroxidation were significantly elevated in skin lesions, also supported by increased pro-inflammatory cytokines expression, i.e., interleukin (IL)-1 β, IL-6, IL-17, tumor necrosis factor-α, and VEGF. Histopathological studies revealed a disturbed natural structure along with increased epidermal proliferation, abnormal differentiation with increased number of keratinocytes in the psoriatic skin tissue.

CONCLUSION:

From the overall study, we have successfully developed a psoriatic-like skin inflammation rat model for the first time on Wistar strain using IMQ as an inducing agent.

Psoriasis and Respiratory Comorbidities: The Added Value of Fraction of Exhaled Nitric Oxide as a New Method to Detect, Evaluate, and Monitor Psoriatic Systemic Involvement and Therapeutic Efficacy

Psoriasis is a chronic inflammatory systemic disease characterized by a wide range of comorbidities. Respiratory comorbidities are currently poorly characterized and with discordant results. The systemic state of inflammation caused by psoriasis acts de novo on respiratory tissues and amplifies preexisting inflammation from asthma or chronic obstructive pulmonary disease. Because the lungs act as a gas exchanger between the internal and external environment, the impact of chronic psoriasis inflammation may be easily assessed through the analysis of exhaled breath. The fraction of exhaled nitric oxide test (FeNO) is a potential noninvasive solution that can provide quantitative and qualitative indices of respiratory airway inflammation. FeNO is routinely used to screen and manage asthmatic patients. Recent pilot studies contain encouraging data that underscore its possible use with systemic inflammatory nonpulmonary diseases, such as psoriasis. FeNO may therefore be a useful tool to evaluate underestimated airway inflammation and at the same time globally evaluate the impact of systemically antipsoriatic therapies.

Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis

Psoriasis is characterized by keratinocyte hyperproliferation, erythema, as well as a form of pruritus, involving cutaneous discomfort. There is evidence from both clinical and murine models of psoriasis that chemical or surgical depletion of small-diameter sensory nerves/nociceptors benefits the condition, but the mechanisms are unclear. Hence, we aimed to understand the involvement of sensory nerve mediators with a murine model of psoriasis and associated spontaneous behaviors, indicative of cutaneous discomfort. We have established an Aldara model of psoriasis in mice and chemically depleted the small-diameter nociceptors in a selective manner. The spontaneous behaviors, in addition to the erythema and skin pathology, were markedly improved. Attenuated inflammation was associated with reduced dermal macrophage influx and production of reactive oxygen/nitrogen species (peroxynitrite and protein nitrosylation). Subsequently, this directly influenced observed behavioral responses. However, the blockade of common sensory neurogenic mechanisms for transient receptor potential (TRP)V1, TRPA1, and neuropeptides (substance P and calcitonin gene-related peptide) using genetic and pharmacological approaches inhibited the behaviors but not the inflammation. Thus, a critical role of the established sensory TRP-neuropeptide pathway in influencing cutaneous discomfort is revealed, indicating the therapeutic potential of agents that block that pathway. The ongoing inflammation is mediated by a distinct sensory pathway involving macrophage activation.-Kodji, X., Arkless, K. L., Kee, Z., Cleary, S. J., Aubdool, A. A., Evans, E., Caton, P., Pitchford, S. C., Brain, S. D. Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis.

miR-203a controls keratinocyte proliferation and differentiation via targeting the stemness-associated factor ΔNp63 and establishing a regulatory circuit with SNAI2

Keratinocyte differentiation plays a pivotal role in the function of epidermal barrier and can be triggered by extracellular calcium in vitro and in vivo, but the precise mechanism still need to be further investigated. On the other hand, it is known that microRNAs control multiple biological events including cellular proliferation and differentiation. The present study demonstrated that miR-203a expression was upregulated in calcium-induced HaCaT Cells in a dose-dependent manner, whereas the stemness-associated factors SNAI2 and ΔNp63 were downregulated. Furthermore, SNAI2 and ΔNp63 were identified as the targets of miR-203a by computational prediction and luciferase reporter assays. The protein levels of SNAI2 and ΔNp63 were suppressed by ectopic expression of miR-203a. Functionally, silencing of miR-203a or overexpression of SNAI2 and ΔNp63 attenuated cell cycle arrest induced by calcium without any changes in cellular apoptosis. Additionally, ectopic expression of SNAI2 inhibited miR-203a in calcium-induced HaCaT cells, by binding to the promoter region of miR-203a. In conclusion, our findings demonstrate that miR-203a plays an essential role in keratinocyte proliferation and differentiation caused by extracellular calcium by targeting the SNAI2 and ΔNp63 genes. Furthermore, SNAI2 was found to suppress the transcription of miR-203a. Our data highlights a coherent cross-talk between two transcription factors (SNAI2 and ΔNp63) and miR-203a in keratinocyte differentiation and epidermal development.

NO Exchange for a Water Molecule Favorably Changes Iontophoretic Release of Ruthenium Complexes to the Skin

Ruthenium (Ru) complexes have been studied as promising anticancer agents. Ru nitrosyl complex (Ru-NO) is one which acts as a pro-drug for the release of nitric oxide (NO). The Ru-aqueous complex formed by the exchange of NO for a water molecule after NO release could also possess therapeutic effects. This study evaluates the influence of iontophoresis on enhancing the skin penetration of Ru-NO and Ru-aqueous and assesses its applicability as a tool in treating diverse skin diseases. Passive and iontophoretic (0.5 mA·cm⁻²) skin permeation of the complexes were performed for 4 h. The amount of Ru and NO in the stratum corneum (SC), viable epidermis (VE), and receptor solution was quantified while the influence of iontophoresis and irradiation on NO release from Ru-NO complex was also evaluated. Iontophoresis increased the amount of Ru-NO and Ru-aqueous recovered from the receptor solution by 15 and 400 times, respectively, as compared to passive permeation. Iontophoresis produced a higher accumulation of Ru-aqueous in the skin layers as compared to Ru-NO. At least 50% of Ru-NO penetrated the SC was stable after 4 h. The presence of Ru-NO in this skin layer suggests that further controlled release of NO can be achieved by photo-stimulation after iontophoresis.

Effect of Nitroglycerin Ointment on Psoriatic Plaques

Background:

Nitric oxide is thought to play a major role in a number of inflammatory diseases. Psoriasis is a common inflammatory disease of the skin.

Objective:

To determine the effect of nitric oxide on psoriasis, nitroglycerin that is converted into nitric oxide in human skin was applied to psoriatic plaques.

Methods:

Nine individuals with chronic plaque-type psoriasis were treated with nitroglycerin ointment for 6 weeks.

Results:

The plaque of one individual improved with the application of nitroglycerin. By contrast, one individual's nitroglycerin-treated plaque improved dramatically about 6 weeks after cessation of treatment. On the other hand, the plaques of five individuals worsened with nitroglycerin treatment. Moreover, in one individual, the nitroglycerin-treated plaque increased in size, whereas the placebo-treated plaque improved slightly.

Conclusion:

Nitroglycerin ointment and, by extension, nitric oxide, may affect both the initiation and resolution of psoriasis.

Picea mariana polyphenolic extract inhibits phlogogenic mediators produced by TNF-α-activated psoriatic keratinocytes: Impact on NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Picea mariana ((Miller) Britton, Sterns, and Poggenburg; Pinaceae) bark has been traditionally used by North American natives for treating topical inflammations. It has been also suggested to improve various inflammatory skin disorders like Psoriasis vulgaris. Extracts from this bark storage protein contain polyphenolic compounds which have well-known antiinflammatory activities. Based on the capacity of polyphenolic compounds to modulate functions of normal human keratinocytes, this study was set up to decipher the mechanisms of action of a chemically characterized polyphenolic extract from Picea mariana bark (BS-EAcf) on lesional keratinocytes of skin with psoriasis vulgaris, a disease driven by the immune system in which TNF-α plays a significant role.

MATERIALS AND METHODS

BS-EAcf corresponds to the ethyl acetate soluble fraction from the hot water extract of Picea mariana bark. BS-EAcf effects were evaluated in normal human (NHK) and psoriatic (PK) keratinocytes stimulated by TNF-α. Cell viability was assessed by lactate deshydrogenase release and propidium iodide (PI) staining. The mechanisms of action of BS-EAcf in keratinocytes were investigated by flow cytometry, ELISAs, RT-PCR and western blot analyses.

RESULTS

PK exhibited a higher response to TNF-α than NHK regarding the ICAM-1 expression and the production of NO, IL-6, IL-8, fractalkine and PGE2, whereas BS-EAcf significantly inhibited this TNF-α-induced increase at concentrations without causing keratinocyte toxicity. Additionally, this extract significantly inhibited the TNF-α-induced release of elafin and VEGF by PK and NHK. Since TNF-α activation of most of these factors is dependent on the NF-κB pathway, this latter was studied in TNF-α-activated PK. BS-EAcf inhibited the TNF-α-induced phosphorylation and degradation of total IκBα as well as phosphorylation of NF-κB p65.

CONCLUSIONS

The ethyl acetate fraction from Picea mariana bark extract showed inhibitory effects of cytokines, chemokines, adhesion molecules, nitric oxide and prostaglandins produced by keratinocytes under TNF-α activation through down-regulating the NF-κB pathway. This study demontrated that this extract could be a potential antiinflammatory agent capable of improving psoriatic skin.

Impact of methotrexate on oxidative stress and apoptosis markers in psoriatic patients

Methotrexate (MTX), a cytotoxic chemotherapeutic agent, is considered an effective drug in the treatment of psoriasis. The aim of this study was to find out whether the effect of MTX treatment in psoriasis is due to oxidative stress-induced apoptosis. Psoriasis vulgaris patients (58 in number) were recruited for this study. Healthy volunteers (45 in number) served as control. Samples of psoriatic patients were collected and analyzed for total reactive oxygen species (ROS), malondialdehyde (MDA) levels, nitrite, nitrate levels and the activities of antioxidants like superoxide dismutase (SOD), catalase (CAT) and total antioxidant status (TAS) and also the protein expression of caspase-3, before (Day 0) and after (at the end of 6 and 12 weeks) MTX treatment. Our results show a significant increase in tissue ROS and plasma MDA after MTX treatment when compared with before MTX treatment in psoriasis patients (p < 0.001). The levels of serum nitrite and nitrate were decreased significantly after MTX treatment (p < 0.001). The activities of plasma SOD, TAS and serum CAT levels were decreased, but not significantly after 12 weeks of treatment. The expression of caspase-3 was increased after MTX treatment. In conclusion, MTX induce apoptosis through oxidative stress by reducing NO and increasing caspase-3 levels. MTX-induced apoptosis may account for the beneficial effect of MTX treatment in psoriasis patients, which is characterized by acanthosis.

Role of cellular oxidative stress and cytochrome c in the pathogenesis of psoriasis

Oxidative-free radicals and apoptosis have linked to chronic skin diseases. Higher levels of oxidative radicals and the release of mitochondrial cytochrome c may have a role in the pathogenesis of psoriasis. We investigated the possible role of cellular oxidative stress and release of cytochrome c of mitochondria in the pathogenesis of psoriasis. Disease severity was assessed by psoriasis area severity index score (PASI) of 55 psoriasis patients, they grouped as mild (11), moderate (20) and severe (24), also 20 healthy individuals used as controls. All groups were subjected for serum malondialdehyde (MDA), nitric oxide (NO·), superoxide dismutase (SOD), catalase (CAT), total antioxidant status (TAS) and serum cytochrome c concentrations. We found that, (1) Severity wise increase in MDA and NO·, and decrease in SOD, CAT and TAS levels in all patients with different degrees of psoriasis; (2) PASI showed positive correlation with the increase in MDA and NO·, and negatively with decreased SOD, CAT and TAS levels; (3) significant increase in cytochrome c level was observed among psoriasis patients which showed negative correlation to MDA and NO· levels in mild and positively with moderate and severe groups. The release of mitochondrial cytochrome c indicates the induction of apoptosis mediated via oxidative stress which ultimately plays role in the pathogenesis of psoriasis.

Influence of endothelial nitric oxide synthase polymorphisms in psoriasis risk

Nitric oxide (NO) is a potent regulator of keratinocyte growth and differentiation that has been implicated in the pathogenesis of psoriasis (Ps). The NOS3 -786 T/C (SNP id rs2070744; http://www.ensembl.org ), intron 4 variable number tandem repeat (VNTR), and Glu298Asp (SNP id rs1799983) polymorphisms, have been associated with differences in NO plasma concentrations and with the risk of hypertension (HT) and ischemic cardiac disease. The aim of this study was to determine whether the above-mentioned NOS3 variants contributed to the risk of Ps, and were associated with the risk for HT and CAD in these patients. A total of 368 patients with chronic plaque Ps and 400 healthy controls were genotyped for the NOS3 -786 T/C, intron 4 VNTR, and Glu298Asp polymorphisms. Carriers of the -786 C allele were significantly more frequent among the patients (p < 0.001). Carriers of the 4-repeats allele (45 + 44 genotypes) were also more frequent a (p < 0.001). No significant difference was found for the Glu298Asp polymorphism. None of the NOS3 variants was associated with Ht and CAD in our population. In conclusion, NOS3 gene polymorphism would be risk factors for developing Ps.

Biochemistry of nitric oxide

Nitric oxide (NO) a free radical having both cytoprotective as well as tumor promoting agent is formed from l-arginine by converting it to l-citrulline via nitric oxide synthase enzymes. The reaction product of nitric oxide with superoxide generates potent oxidizing agent, peroxynitrite which is the main mediator of tissue and cellular injury. Peroxynitrite is reactive towards many biomolecules which includes amino acids, nucleic acid bases; metal containing compounds, etc. NO metabolites may play a key role in mediating many of the genotoxic/carcinogenic effects as DNA damage, protein or lipid modification, etc. The basic reactions of nitric oxide can be divided as direct effect of the radical where it alone plays a role in either damaging or protecting the cell milieu and an indirect effect in which the byproducts of nitric oxide formed by convergence of two independent radical generating pathways play the role in biological reactions which mainly involve oxidative and nitrosative stress. Nitric oxide is also capable of directly interacting with mitochondria through inhibition of respiration or by permeability transition. Reaction of nitric oxide with metal ions include its direct interaction with the metals or with oxo complexes thereby reducing them to lower valent state. Excessive production of nitric oxide can be studied by inhibiting the synthetic pathway of nitric oxide using both selective or specific nitric oxide synthase inhibitor or non-selective nitric oxide synthase inhibitor with respect to isoforms of nitric oxide.

Suppression of COX-2, IL-1β and TNF-α expression and leukocyte infiltration in inflamed skin by bioactive compounds from Rosmarinus officinalis L

In the present study, we evaluated the effects of extracts and purified compounds from fresh leaves of Rosmarinus officinalis L. Pretreatment with the major anti-inflammatory compounds, carnosic acid (CA) and carnosol (CS), inhibited phorbol 12-myristate 13-acetate (PMA)-induced ear inflammation in mice with an EC(50) of 10.20 μg/cm(2) and 10.70 μg/cm(2), respectively. To further understand the anti-inflammatory mechanism of these compounds, we analyzed the in vivo expression of several inflammation-associated genes in mouse skin by reverse transcriptase-polymerase chain reaction (RT-PCR). Our data showed that CA and CS reduced the expression of IL-1β and TNF-α but had less effect on fibronectin and ICAM-1 expression. Interestingly, both compounds selectively inhibited COX-2 but not COX-1. Histopathological analysis of hematoxylin and eosin (H&E)-stained tissue revealed a marked reduction in leukocyte infiltration and epidermal ulceration of PMA-treated ears when ears were pretreated with ethanolic extracts or pure CA. In vitro, we showed that ethanolic extract, carnosic acid and carnosol significantly inhibited the overproduction of nitric oxide (NO) in a dose-dependent manner in the RAW 264.7 murine macrophage cell line. For the first time in vivo, we showed that CA and CS differentially regulate the expression of inflammation-associated genes, thus demonstrating the pharmacological basis for the anti-inflammatory properties reported for CA and CS.

Role of oxidative stress in various stages of psoriasis

Psoriasis is a chronic inflammatory, proliferative skin disease characterized by pathological skin lesions due to various exogenous and endogenous factors. It is associated with a number of biochemical and immunological disturbances. Recently, it has been suggested that increased reactive oxygen species (ROS) production and compromised function of antioxidant system may be involved in the pathogenesis of this disease. In the present study, 90 psoriasis patients were selected. Disease severity was assessed by psoriasis area severity index score and grouped as mild, moderate and severe (each group consists of 30 subjects) and compared with 30 healthy controls. Serum levels of malondialdehyde, nitric oxide end products and the activities of antioxidant enzymes such as erythrocyte-superoxide dismutase, catalase and total antioxidant status were investigated in these groups/subjects. As compared to controls, we found severitywise significantly increased serum malondialdehyde, nitric oxide end products with decrease in erythrocyte-superoxide dismutase activity, catalase activity and total antioxidant status in patients with psoriasis suggesting worsening of the disease. It seems to be linked with the enhancement of Reactive Oxygen Species production and decreased antioxidant potential in psoriasis.

Arginase is overactive in psoriatic skin

BACKGROUND

Psoriatic keratinocytes are poorly differentiated and hyperproliferative. Low concentrations of nitric oxide (NO) induce keratinocyte proliferation, while high concentrations induce differentiation. The NO-producing enzyme inducible NO synthase is overexpressed in psoriatic skin, but so is arginase. The overexpressed arginase competes for arginine, the common substrate for both enzymes, and may reduce NO production.

OBJECTIVES

To determine whether arginase activity is elevated in psoriatic skin and whether exogenous NO will improve psoriatic plaques.

METHODS

Tape strips were taken from healthy skin of eight control subjects and nonlesional skin of eight patients with psoriasis and L-arginine, L-citrulline and L-ornithine concentrations measured by high-performance liquid chromatography. In a second study, four psoriatic patients with a pair of similar symmetrical plaques were treated with an NO donor and vehicle control. Plaques were scored for size, erythema, induration and scaling at the start and after 6 weeks of treatment.

RESULTS

Ornithine, the end-product of arginase, was at higher concentrations in nonlesional psoriatic than in healthy skin (mean +/- SEM 2.08 +/- 0.98 vs. 1.13 +/- 0.44 microg mg(-1) protein; P = 0.0002). Arginine, its substrate, was at lower concentrations. Topical application of an NO donor improved psoriatic plaques clinically [mean +/- SD reduction in severity from baseline score (100%) to 35% +/- 16% in active NO donor and to 93% +/- 10% in control].

CONCLUSIONS

Arginase is overactive in psoriatic skin, leading to a relative increase in the consumption of arginine. We therefore hypothesize a relative decrease in NO synthase-derived NO production. NO donors may be effective topical treatments for psoriasis.

Topically applied nitric oxide induces T-lymphocyte infiltration in human skin, but minimal inflammation

Nitric oxide (NO) plays an important role in the cutaneous response to UV radiation and in cutaneous inflammation. The presence of inducible NO synthase protein in a number of inflammatory dermatoses, coupled with the induction of an intense cutaneous inflammatory infiltrate following topical application of the NO donor-acidified nitrite (NO2(-)), has set the paradigm of NO being an inflammatory mediator in human skin. Using zeolite NO (Ze-NO), a chemically inert, pure NO donor, we have shown that NO per se produces little inflammation. Biologically, relevant doses of Ze-NO induce a dermal CD4-positive T-cell infiltrate and IFN-gamma secretion. In contrast acidified nitrite, releasing equal quantities of NO (measured by dermal microdialysis and cutaneous erythema), induces an intense epidermal infiltrate of macrophages with a similar dermal infiltrate of CD3-, CD4-, CD8-, and CD68-positive cells and neutrophils. Suction blisters were created in Ze-NO-treated and control skin. IFN-gamma, but not IL-4, was detected in Ze-NO-treated skin (mean control 0.1+/-0.07 pg mg(-1) protein, mean IFN-gamma 0.6+/-0.4 pg mg(-1) protein). We suggest that the potent inflammation induced by acidified NO2(-) is secondary to the release of additional mediators.

Trichloroethylene induce nitric oxide production and nitric oxide synthase mRNA expression in cultured normal human epidermal keratinocytes

Trichloroethylene (TCE), a major chemical hazard during occupational exposure, can cause obvious skin lesions, including irritant reactions and dermatitis. Nitric oxide (NO) synthesized by nitric oxide synthase (NOS) is involved in a broad array of pathogenesis of skin inflammatory and immune responses. To understand the mechanisms of TCE-induced dermatoxicity, we investigated the effects of TCE on NO production and NOS mRNA expression in cultured normal human epidermal keratinocytes (NHEK). Cells were treated with TCE (0 mM, 0.125 mM, 0.25 mM, 0.5 mM, 1.0 mM, 2.0 mM) for 4 h, and then incubated for 12 h, 24 h, 48 h and 72 h. At each given time point, NO production were evaluated indirectly by measuring nitrite plus nitrate concentration in the culture medium using Griess reaction, as well as cell viability determined by MTT test, iNOS and cNOS activities assayed with a NOS activity detecting kit. The expression of iNOS and cNOS mRNA was detected using RT-PCR. TCE decreases cell viability and enhance NO production from NHEK in concentration- and time-dependent manner. Aminoguanidine (AG), an inhibitor of NOS, can prevent NO production and cell viability decrease in NHEK by TCE induced. Change to NO production was accompanied by increased activities of both types of NOS, but the iNOS activity accounted mainly for the TCE-induced NO production. RT-PCR detection showed that NHEK expressed both iNOS and cNOS mRNA by TCE exposure. Whereas a concentration- and time-dependent up-regulation of the mRNA expression was observed for iNOS and cNOS following TCE exposure, changes to iNOS were more marked. These results suggest that TCE caused increase in NO production, attributed to activation of iNOS as well as cNOS, and expression of iNOS and cNOS mRNA. These cellular changes may contribute to the pathological and physiological features of TCE-induced erythema and skin inflammation.

Nitric oxide levels in patients with psoriasis treated with methotrexate

Psoriasis is a chronic, recurrent, inflammatory, and hyperproliferative disease. Recently there have been studies regarding increases in the levels of NO in inflammatory dermatoses including psoriasis. In this study, 22 patients with psoriasis were scored with PASI (psoriasis area and severity index) and the levels of serum nitrite-nitrate were evaluated before and after therapy with methotrexate (Mtx). The results were compared with age- and sex-matched healthy volunteers. The relation of the results with the clinical severity and the cumulative Mtx dose were also evaluated. The serum levels of nitrite-nitrate of the psoriatic patients with active lesions were found to be significantly higher than the levels of the healthy volunteers and the patients after therapy. The elevated nitrite-nitrate serum levels in the inflammatory period may suggest the possible role of this mediator in the etiopathogenesis of psoriasis and the potential future use of No inhibitors in the treatment of psoriasis.

Clozapine induces oxidative stress and proapoptotic gene expression in neutrophils of schizophrenic patients

The present study examined cellular effects of the atypical antipsychotic drug clozapine on blood cells of treated patients with and without clozapine-induced agranulocytosis (CA). Blood from one patient who commenced clozapine treatment was examined at weekly intervals for 128 days. Olanzapine-treated (n = 5) and polymedicated (n = 14) schizophrenic patients, as well as healthy subjects (n = 19) and septic shock patients (n = 8), were studied for comparison. We observed dramatically increased numbers of native neutrophils stained for superoxide anion production (P < or = 0.005, n = 10) and significantly elevated expression levels of the proapoptotic genes p53 (P < or = 0.020), bax alpha (P < or = 0.001), and bik (P < or = 0.002) in all tested non-CA patients (n = 19) and CA patients (n = 4). In non-CA patients, the expression of these genes did not correlate to the percentage of apoptotic neutrophils (2.0% +/- 1.3%), but in CA patients about 37% of the neutrophils show morphologic signs of apoptosis (P < or = 0.001). Under G-CSF therapy of CA, the number of apoptotic neutrophils and the expression of the proapoptotic genes decreased significantly. In conclusion, high production of reactive oxygen species in neutrophils of clozapine-treated patients, together with increased expression of proapoptotic genes, suggests that neutrophils are predisposed to apoptosis in schizophrenic patients under clozapine therapy. The correlation between drug and proapoptotic markers was highest for clozapine and bax alpha as well as superoxide anion radicals. This indicates oxidative mitochondrial stress in neutrophils of clozapine-treated patients which probably contributes to the induction of apoptosis and sudden loss of neutrophils and their precursors in CA patients.

Nitric oxide function in the skin

Endogenously produced nitric oxide (NO) has a remarkably diverse range of biological functions, including a role in neurotransmission, smooth muscle relaxation, and the response to immunogens. Over the last 10 years, it has become clear that this extraordinary molecular messenger also plays a vital role in the skin, orchestrating normal regulatory processes and underlying some of the pathophysiological ones. We thought it pertinent to review the current literature concerning the possible function of NO in normal skin, its clinical and pathological significance, and the potential for therapeutic advances. The keratinocytes, which make up the bulk of the epidermis, constitutively express the neuronal isoform of NO synthase (NOS1), whereas the fibroblasts in the dermis and other cell types in the skin express the endothelial isoform (NOS3). Under certain conditions, virtually all skin cells appear to be capable of expressing the inducible NOS isoform (NOS2). The expression of NOS2 is also strongly implicated in psoriasis and other inflammatory skin conditions. Constitutive, low level NO production in the skin seems to play a role in the maintenance of barrier function and in determining blood flow rate in the microvasculature. Higher levels of NOS activity, stimulated by ultraviolet (UV) light or skin wounding, initiate other more complex reactions that require the orchestration of various cell types in a variety of spatially and temporally coordinated sets of responses. The NO liberated following UV irradiation plays a significant role in initiating melanogenesis, erythema, and immunosuppression. New evidence suggests that it may also be involved in protecting the keratinocytes against UV-induced apoptosis. The enhanced NOS activity in skin wounding (reviewed recently in this journal [Nitric oxide 7 (2002) 1]) appears to be important in guiding the infiltrating white blood cells and initiating the inflammation. In response to both insults, UV irradiation and skin wounding, the activation of constitutive NOS proceeds and overlaps with the expression of NOS2. Thus, at a macro-level, at least three different rates of NO production can occur in the skin, which seem to play an important part in organizing the skin's unique adaptability and function.

Nitric oxide: a key mediator in cutaneous physiology

Nitric oxide (NO) is a free radical synthesized from l-arginine by a family of NO synthase (NOS) enzymes, all of which are present in the skin, and also by reduction of sweat nitrate. NO synthesis is regulated by NOS activation (eNOS and nNOS) or synthesis (iNOS) and by substrate availability. Elevated arginase concentrations in psoriatic skin suggest that substrate competition may affect NO production. The balance of NO and reactive oxygen species is probably also important in regulating the biological actions of NO. The physiological functions of NO in the skin are being elaborated. NO release is increased following exposure to ultraviolet radiation (UVR); in eNOS null mice, dermal and epidermal apoptosis following UVR exposure is increased. Experiments in which keratinocytes and melanocytes were cocultured show melanogenesis being dependent on keratinocyte-generated NO, and UVR-induced guinea pig pigmentation is delayed following application of a NOS antagonist to the skin. Wound healing is delayed in eNOS and iNOS null mice.

Arginase 1 overexpression in psoriasis: limitation of inducible nitric oxide synthase activity as a molecular mechanism for keratinocyte hyperproliferation

Abnormal proliferation of keratinocytes in the skin appears crucial to the pathogenesis of psoriasis, but the underlying mechanisms remain unknown. Nitric oxide (NO), released from keratinocytes at high concentrations, is considered a key inhibitor of cellular proliferation and inducer of differentiation in vitro. Although high-output NO synthesis is suggested by the expression of inducible NO synthase (iNOS) mRNA and protein in psoriasis lesions, the pronounced hyperproliferation of psoriatic keratinocytes may indicate that iNOS activity is too low to effectively deliver anti-proliferative NO concentrations. Here we show that arginase 1 (ARG1), which substantially participates in the regulation of iNOS activity by competing for the common substrate L-arginine, is highly overexpressed in the hyperproliferative psoriatic epidermis and is co-expressed with iNOS. Expression of L-arginine transporter molecules is found to be normal. Treatment of primary cultured keratinocytes with Th1-cytokines, as present in a psoriatic environment, leads to de novo expression of iNOS but concomitantly a significant down-regulation of ARG1. Persistent ARG1 overexpression in psoriasis lesions, therefore, may represent a disease-associated deviation from normal expression patterns. Furthermore, the culturing of activated keratinocytes in the presence of an ARG inhibitor results in a twofold increase in nitrite accumulation providing evidence for an L-arginine substrate competition in human keratinocytes. High-output NO synthesis is indeed associated with a significant decrease in cellular proliferation as shown by down-regulation of Ki67 expression in cultured keratinocytes but also in short-term organ cultures of normal human skin. In summary, our data demonstrate for the first time a link between a human inflammatory skin disease, limited iNOS activity, and ARG1 overexpression. This link may have substantial implications for the pathophysiology of psoriasis and the development of new treatment strategies.

Nitric oxide enhances substance P-induced itch-associated responses in mice

1 Substance P (SP) elicits itch and itch-associated responses in humans and mice, respectively. In mice, NK(1) tachykinin receptors are involved in SP-induced itch-associated responses, scratching, and mast cells do not play a critical role. The present study was conducted to elucidate the role of nitric oxide (NO) on SP-induced scratching in mice. 2 An intradermal injection of SP (100 nmol site(-1)) elicited scratching in mice, and it was suppressed by an intravenous injection of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), but not by its inactive enantiomer D-NAME. Intradermal injections of L-NAME (100 nmol site(-1)), another NOS inhibitor 7-nitroindazole (10 nmol site(-1)) and the NO scavenger haemoglobin (0.01-10 nmol site(-1)) also inhibited SP-induced scratching. 3 L-NAME (100 nmol site(-1)) did not affect scratching induced by an intradermal injection of 5-hydroxytryptamine (100 nmol site(-1)). 4 Intradermal injections of L-arginine (300 nmol site(-1)) and the NO donor (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3; 100 nmol site(-1)) increased scratching induced by SP. Intradermal injections of L-arginine (1-1000 nmol site(-1)) or NOR3 (1-100 nmol site(-1)) alone were without effects on scratching. 5 Intradermal injections of SP (10-100 nmol site(-1)) increased the intradermal concentration of NO in a dose-dependent manner in mice. An increase in NO levels induced by SP was inhibited by L-NAME and the NK(1) tachykinin receptor antagonist L-668,169, but not by the NK(2) tachykinin receptor antagonist L-659,877. 6 SP (1-10 micro M) elicited NO production in cultured human keratinocytes and the SP-induced NO production was inhibited by L-NAME and L-668,169. 7 We conclude that intradermal SP increases NO in the skin, possibly through the action on NK(1) tachykinin receptors on the epidermal keratinocytes and that NO enhances SP-induced itch-associated responses.

Interleukin-13 receptor in psoriatic keratinocytes: overexpression of the mRNA and underexpression of the protein

Although several cytokines and their receptors have been involved in the development of psoriasis, the etiology is still unknown. In this study we looked for genes possibly involved in the disease by the reverse transcription-polymerase chain reaction differential display technique in lesional and nonlesional skin biopsies from psoriatic patients. We found the mRNA of the alpha1 chain of the interleukin-13 receptor expressed differentially in psoriatic biopsies. By reverse transcription-polymerase chain reaction, we confirmed an overexpression of the alpha1 chain of the IL-13 receptor and alpha chain of the interleukin-4 receptor mRNA in lesional skin psoriatic biopsies, when compared with skin biopsies from healthy subjects (p<0.01). The nonlesional skin obtained from a region close to a lesional zone in psoriatic patients presented also an overexpression of these mRNA in 50% of the samples. Interleukin-13 and interleukin-4 were not detected either as mRNA or as the proteins in any of the biopsies from psoriatic patients or healthy subjects. A monoclonal antibody to the alpha1 chain of the interleukin-13 receptor detected the receptor in the epidermal keratinocytes of psoriatic patients and of healthy subjects; however, the positive antibody reaction was stronger in skin tissue from healthy subjects than in psoriatic lesional skin tissue (p<0.01), although the mRNA was overexpressed. As interleukin-13 is a pleiotropic immunoregulatory cytokine with a variety of effects on different cell types, including monocytes, B lymphocytes, mast cells, and keratinocytes, we suggest, based on our results, that the interleukin-13 receptor possibly plays an important part in the early inflammatory process of psoriasis; however, its function is lost in the psoriatic keratinocytes.

Time course of expression of mRNA of inducible nitric oxide synthase and generation of nitric oxide by ultraviolet B in keratinocyte cell lines

BACKGROUND

Nitric oxide (NO), the ubiquitous free radical, has been implicated in the pathogenesis of various inflammatory diseases, including sunburn and ultraviolet (UV) radiation-induced pigmentation, and it also seems to play an important part in host defence against bacterial infection.

OBJECTIVES

The purpose of this study was to determine the time course of production of NO and time course of expression of inducible NO synthase (iNOS) by UVB irradiation and lipopolysaccharide (LPS) stimulation in keratinocyte cell lines. Furthermore, we intended to elucidate the relationship between iNOS and NO in various stimulated conditions.

METHODS

Normal human keratinocytes (NHK), HaCaT cells and PAM212 cells were irradiated with UVB at a dose of 50 mJ cm-2 and 100 mJ cm-2. Separately, the cell lines were stimulated with 20 micro g of LPS. NO was measured by the Griess assay and iNOS mRNA was isolated by reverse transcriptase-polymerase chain reaction at 12, 24, 48 and 72 h after stimulation.

RESULTS

The generation of NO was induced by UVB irradiation and LPS stimulation. NO production was significantly increased at 72 h after irradiation of UVB 100 mJ cm-2 in NHK, and at 48 and 72 h in HaCaT cells. In PAM212 cells, NO production was significantly increased at 12, 24, 48 and 72 h by UVB 100 mJ cm-2 and at 72 h by LPS. Induction of iNOS mRNA peaked at 48 h and then decreased to basal level at 72 h when treated with UVB irradiation. The time course of production of NO was approximately correlated with the timing of induction of iNOS mRNA.

CONCLUSIONS

These results suggest that the expression of iNOS mRNA is upregulated by UVB irradiation, and that NO produced by this inducible enzyme may play a part as a mediator or an immunomodulator in UV-induced skin reactions such as sunburn reaction and photo-induced immune alterations.

Nitric oxide-peroxynitrite-poly(ADP-ribose) polymerase pathway in the skin

In the last decade it has become well established that in the skin, nitric oxide (NO), a diffusable gas, mediates various physiologic functions ranging from the regulation of cutaneous blood flow to melanogenesis. If produced in excess, NO combines with superoxide anion to form peroxynitrite (ONOO-), a cytotoxic oxidant that has been made responsible for tissue injury during shock, inflammation and ischemia-reperfusion. The opposite effects of NO and ONOO- on various cellular processes may explain the 'double-edged sword' nature of NO depending on whether or not cellular conditions favour peroxynitrite formation. Peroxynitrite has been shown to activate the nuclear nick sensor enzyme, poly(ADP-ribose) polymerase (PARP). Overactivation of PARP depletes the cellular stores of NAD+, the substrate of PARP, and the ensuing 'cellular energetic catastrophy' results in necrotic cell death. Whereas the role of NO in numerous skin diseases including wound healing, burn injury, psoriasis, irritant and allergic contact dermatitis, ultraviolet (UV) light-induced sunburn erythema and the control of skin infections has been extensively documented, the intracutaneous role of peroxynitrite and PARP has not been fully explored. We have recently demonstrated peroxynitrite production, DNA breakage and PARP activation in a murine model of contact hypersensitivity, and propose that the peroxynitrite-PARP route represents a common pathway in the pathomechanism of inflammatory skin diseases. Here we briefly review the role of NO in skin pathology and focus on the possible roles played by peroxynitrite and PARP in various skin diseases.

Cell death and proliferation in Nd-YAG laser, electrocautery, and scalpel wounds on mice skin

The purpose of this study is to compare cell death and proliferation in laser, electrocautery and scalpel wounds on the mice epidermis. Wounds were examined by transmission electron microscopy, the detection of free 3'-OH DNA ends and immunohistochemistry of proliferating cell nuclear antigen (PCNA), inducible nitric oxide synthase (iNOS), keratinocyte growth factor (KGF) and keratinocyte growth factor receptor (KGFR). Reepithelization was first observed 5 days after scalpel and laser incisions and 7 days after electrocautery incision. Ultrastructurally, keratinocytes in both electrocautery and laser wounds showed similar post-apoptotic necrotic changes. Interestingly, dividing cells were often observed 3 days after laser incision. Apoptotic index in electrocautery wounds was higher than in laser wounds, although there was no significant difference in the PCNA expression level between them. The expression of iNOS, KGF and KGFR in laser wounds was more intense than in electrocautery wounds. In scalpel wounds, keratinocytes did not show significant changes in morphology or of markers of cell death and proliferation during the observation period. Therefore, the increase in the number of dividing cells and in the expression level of iNOS, KGF and KGFR may induce earlier and thicker reepithelization in laser wounds than in electrocautery and scalpel wounds.

Mathematical modelling of nitric oxide regulation of rete peg formation in psoriasis

Recent experiments have shown that in patients with psoriasis, highly elevated levels of nitric oxide (NO) are released at the surface of psoriatic plaques. Nitric oxide is a central biological regulator of many aspects of physiology, and it is a natural possibility that the high nitric oxide levels in psoriasis play a causal role in the onset of the disease. Here, we use mathematical modelling to investigate this possibility. We begin by discussing a simple model consisting of a single equation for nitric oxide concentration, which enables nitric oxide secretion rates in the basal epidermis to be calculated from the observed NO release rates at the skin surface. Using this key parameter value, we then develop an extended model that tests the hypothesis that nitric oxide regulates the formation of the extended rete pegs seen in psoriatic plaques. This occurs via the peroxynitrite-dependent activation of the collagenase MMP-8, which is produced by neutrophils present at high levels in psoriatic plaques. The plausibility of the hypothesis is demonstrated and specific testable quantitative predictions about the roles of the various cell types and signalling molecules are made.

Ultraviolet A1 radiation induces nitric oxide synthase-2 expression in human skin endothelial cells in the absence of proinflammatory cytokines

Skin exposure to ultraviolet radiation from sunlight causes erythema and edema formation as well as inflammatory responses. As some of these ultraviolet-induced effects are potentially mediated by nitric oxide synthases, we examined the role of cytokines and ultraviolet A1 radiation (340-400 nm) on the expression of the nitric oxide synthase-2 in endothelia of normal human skin biopsies during short-term organ culture as well as expression and activity of the nitric oxide synthase-2 in in vitro cell cultures of human dermal endothelial cells. Both, cytokine challenge (interleukin-1beta + tumor necrosis factor-alpha + interferon-gamma) but also ultraviolet A1 exposure (50 J per cm2) in the absence of cytokines led to the expression of nitric oxide synthase-2 in human skin organ cultures as shown by immunohistochemistry. Moreover, exposing human dermal endothelial cell cultures to proinflammatory cytokines but also to ultraviolet A1 radiation (6-24 J per cm2) in the absence of cytokines resulted in significant nitric oxide synthase-2 mRNA and protein expression as well as enzyme activity. Ultraviolet A1 irradiation of cytokine activated cells led to further increases in nitric oxide synthase-2 mRNA, protein expression, and enzyme activity. Moreover, a reporter gene assay using a human nitric oxide synthase-2 promoter construct provide evidence that ultraviolet A1, in the absence of cytokines, induces nitric oxide synthase-2 expression and activity, as previously shown for cytokines. Thus, the results presented here demonstrate for the first time that in dermal endothelia of human skin ultraviolet A1 radiation alone represents a proinflammatory stimulus sufficient to initiate nitric oxide synthase-2 expression as well as activity comparable with the respective response seen in the presence of proinflammatory cytokines.

Nitric oxide: a review for veterinary surgeons

Nitric oxide (NO) is an endogenous gas that serves as a biologic messenger in many physiologic processes including neurotransmission, blood-pressure control, the immune system's ability to kill tumor cells, and wound healing. NO is produced after oxidation of L-arginine by a family of nitric oxide synthase (NOS) enzymes. Two of the NOS enzymes are present continuously and are thereby termed constitutive NOS. One of the enzymes, inducible NOS, is not typically expressed in resting cells and is induced by various substances including endotoxin, some cytokines, and microbial products. Thus, NO often has paradoxical activities. When NO is over- or underproduced, it can result in potentiation of disease states with disastrous results. This review discusses the biochemistry of NO, its functions in normal and disease states, and therapy for modulating NO production in disease states.

Characterization of lymphocyte-dependent angiogenesis using a SCID mouse: human skin model of psoriasis

From a clinical perspective, angiogenesis is an important component of acute and chronic psoriatic skin lesions as they are erythematous and display a tendency to bleed after superficial removal of scale. By routine histology, numerous microscopic vascular abnormalities are also present. The structural expansion of capillaries and distinctive activated phenotype of lesional endothelial cells are believed not only to be clinical and pathologic hallmarks of the disease, but to play a central role in the pathogenesis of psoriatic plaques. Despite over 20 years of research by leading angiogenesis experts and numerous studies, many details regarding the cellular and molecular basis for angiogenesis in psoriasis remain unknown. In this review, 10 different sections are presented to update recent progress in this active field of investigative skin biology. Highlights of this review include the phenotypic characterization of endothelial cells in acute and chronic psoriatic plaques, and a review of a novel animal model of psoriasis using human skin engrafted onto severe combined immunodeficient mice followed by injection of activated immunocytes. This new experimental model represents a reproducible and pharmacologically validated method to trigger neovascularization and bona fide psoriatic plaque formation. In addition, the potential contribution of epidermal keratinocytes and dermal macrophages to the angiogenic tissue reaction is presented, and a series of questions are then posed that can be answered using the severe combined immunodeficient mouse model of psoriasis. Finally, a model is proposed integrating all available data into a coherent multistep reaction schema that includes active participation by multiple cell types including natural killer T cells, keratinocytes, macrophages, and microvascular endothelial cells.

Nitric oxide inhibits cornified envelope formation in human keratinocytes by inactivating transglutaminases and activating protein 1

Epidermal keratinocytes undergo terminal differentiation to form the stratum corneum, which consists of many layers of flat dead cells. These cells assemble an insoluble cornified envelope composed of specific proteins deposited on the intracellular surface of the cell membrane. The proteins are crosslinked by the action of transglutaminases, which catalyze the formation of isodipeptide bonds between the epsilon-NH2 side chain of a lysine residue and the gamma-amide side chain of a glutamine residue. Transglutaminases share a conserved, highly reactive cysteine in their active site. In this study, we found that nitric-oxide-releasing compounds inhibited cornified envelope formation in cultured keratinocytes and the in vitro crosslinking of loricrin, a natural substrate of transglutaminases. The NO donors inhibited transglutaminase catalytic activity in a dose-dependent manner, in both purified enzymes and keratinocyte extracts. Titration of thiol groups of transglutaminases indicated that NO regulates their enzymatic activity by chemically modifying a cysteine residue, possibly by S-nitrosylation. NO was also found to inhibit DNA-binding activity of activating protein 1 in keratinocyte nuclear extracts, and to interfere with the transactivation of activating protein 1 responsive genes such as transglutaminase 1, involucrin, and loricrin, whose expression is regulated during epidermal differentiation. In conclusion, we propose that NO may inhibit keratinocyte differentiation, acting both at transcriptional level (inactivation of activating protein 1) and at post-translational level (inhibition of transglutaminase activity).

Interleukin-11 therapy selectively downregulates type I cytokine proinflammatory pathways in psoriasis lesions

Psoriasis is a chronic inflammatory skin disease in which epidermal hyperplasia results from skin infiltration by type I T lymphocytes and release of associated cytokines. A multifunctional cytokine, rhIL-11, modulates macrophage and type I T-lymphocyte function in cell culture and shows anti-inflammatory activity in animal models. We are testing subcutaneous delivery of rhIL-11 to patients with psoriasis in a phase 1 open-label dose-escalation clinical trial. Tissue was obtained from lesional and uninvolved skin before and during treatment with rhIL-11 and was examined by histology/immunohistochemistry and quantitative RT-PCR. Expression of over 35 genes was examined in all patients, and multiple genetic markers of psoriasis were identified. Expression of numerous proinflammatory genes was elevated in psoriatic tissue compared with nonlesional skin. Seven of 12 patients responded well to rhIL-11 treatment. Amelioration of disease by rhIL-11, as shown by reduced keratinocyte proliferation and cutaneous inflammation, was associated with decreased expression of products of disease-related genes, including K16, iNOS, IFN-gamma, IL-8, IL-12, TNF-alpha, IL-1beta, and CD8, and with increased expression of endogenous IL-11. We believe that this is the first study in humans to indicate that type I cytokines can be selectively suppressed by an exogenous immune-modifying therapy. The study highlights the utility of pharmacogenomic monitoring to track patient responsiveness and to elucidate anti-inflammatory mechanisms.

The function of nitric oxide in wound repair: inhibition of inducible nitric oxide-synthase severely impairs wound reepithelialization

Recently, we demonstrated a large induction of inducible nitric oxide synthase (iNOS) during cutaneous wound repair. In this study, we established an in vivo model in mice to investigate the role of NO during the wound healing process. During excisional repair, mice were treated with L-N6-(1-iminoethyl)lysine (L-NIL), a selective inhibitor of iNOS enzymatic activity. Compared with control mice, L-NIL-treated animals were characterized by a severely impaired reepithelialization process, as the hyperproliferative epithelia at the wound edges appeared to be delayed and characterized by an atrophied morphology. Immunohistochemical labeling for detection of proliferating cells (BrdU-, Ki67-staining) revealed a strong reduction in proliferating keratinocyte cell numbers during the process of re-epithelialization after inhibition of iNOS activity during repair. Western blot analysis of total wound lysates from PBS- and L-NIL-treated mice clearly demonstrated a reduction in proliferating cell nuclear antigen, representing a marker for cell proliferation, in lysates isolated from L-NIL-treated mice. The dependency between keratinocyte proliferation and NO availability observed during wound repair in vivo is further supported by the observation that proliferation of the keratinocyte cell line (HaCaT) is stimulated by low concentrations of NO-donors also in vitro. In summary, our data demonstrate that the presence of a functionally active iNOS is a crucial prerequisite for normal wound reepithelialization.

Up-regulation of interleukin-1beta-stimulated interleukin-8 in human keratinocytes by nitric oxide

Nitric oxide (NO) is able to regulate the expression of a number of inflammatory mediators. In this study, the effect of NO on the expression of the chemokine interleukin-8 (IL-8) by primary human keratinocytes and the lines KB and HaCaT was examined. Incubation with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) for 24 hr increased IL-8 protein only in HaCaT cells, partly due to the presence of constitutive interleukin-1 (IL-1). However, in combination with IL-1beta, SNAP enhanced both IL-8 mRNA and protein in all three cell types. Transfection of cells with an IL-8 promoter reporter gene construct showed that the effect of NO was at least partly due to transcriptional activation. Despite small variations in the response to NO by the three cell types, these results demonstrate that NO can up-regulate IL-1beta-stimulated IL-8 expression in human keratinocytes. This study provides a regulatory mechanism which may be important in the context of skin inflammation, and supports the role of NO as an inflammatory mediator in the skin.

Aberrant timing in epidermal expression of inducible nitric oxide synthase after UV irradiation in cutaneous lupus erythematosus

Photosensitivity is a main criterion for the diagnosis of systemic lupus erythematosus (LE), and ultraviolet (UV) irradiation plays a key role in the pathogenesis of cutaneous LE. Patients with a tentative diagnosis of LE are routinely tested for skin lesion development after experimental UV irradiation, providing an ideal opportunity to evaluate early, preclinical events involved in the pathogenesis of LE. Several reports have shown expression of the cytokine-inducible nitric oxide synthase (iNOS) in autoimmune diseases. Therefore, we investigated the role of iNOS expression at mRNA and protein level in the pathogenesis of LE lesions. Skin biopsies from patients with different subtypes of LE were examined, and iNOS expression was found in six of 18 biopsies from cutaneous LE patients and two of three biopsies from systemic LE patients. In biopsies taken 4-20 d after UV irradiation, epidermal iNOS expression was seen in all patients (n = 10) after UVB and in four of 10 patients provoked by UVA. In healthy controls (n = 8) epidermal iNOS expression was detected 24 h after UV irradiation, persisting for another day before subsiding on day 3. In LE patients (n = 8) the exact reverse situation was seen: an iNOS-specific signal was undetectable in keratinocytes for 2 d after UV irradiation, but became positive on day 3 and persisted for up to 25 d in the evolving skin lesions. Our findings demonstrate a time-restricted, UV-induced iNOS expression in human skin; moreover, the results indicate that both the kinetics of iNOS induction as well as the time span of local iNOS expression may be critical to the development of cutaneous LE lesions.

Occurrence of hepoxilins and trioxilins in psoriatic lesions

We recently found that normal human epidermis produces relatively high amounts of hepoxilins and trioxilins in vitro. Therefore, the aim of this study was to demonstrate the presence of these compounds in psoriatic lesions. Extracts from scales of patients with chronic stable plaque psoriasis were analyzed by a combination of high performance liquid chromatography and gas chromatography-mass spectrometry techniques. We found that the levels of hepoxilin B3 were more than 16-fold higher in psoriatic scales than in normal epidermis (3.2+/-2.3 and < 0.2 ng per mg, respectively), whereas hepoxilin A3 was not detected in any sample. Trioxilins were semiquantitated and referred to 12-hydroxyeicosatetraenoic acid, ratios of trioxilins A3 and B3 12-hydroxyeicosatetraenoic acid in psoriatic lesions were 0.65+/-0.23 and 0.32+/-0.28, respectively, and they were not detected in normal epidermis. The presence of a great amount of trioxilin A3 strongly suggests that hepoxilin A3 was present in psoriatic lesions and it was totally degraded to trioxilin A3 during the analysis procedure. Our results demonstrate that hepoxilins and trioxilins are produced by human skin in vivo and that the levels of these compounds are increased in psoriasis. The reported biologic activities of hepoxilins indicate that they could amplify and maintain the inflammatory response. Our results reinforce the idea that these compounds could play a role as mediators in the inflammatory response in skin, particularly in psoriasis.

Nitric oxide in human skin: current status and future prospects

The gaseous free radical nitric oxide is an important biologic mediator with physiologic and pathophysiologic roles in nearly every organ system. Because of its unique biologic activity, unusual chemical structure, and unprecedented mechanisms of action, nitric oxide, arguably more than any other natural product, has opened new avenues to investigate cellular processes. Nitric oxide is generated in biologic tissues by specific nitric oxide synthases that metabolize arginine and molecular oxygen to citrulline and nitric oxide. Besides its function as a diffusible messenger in the vasculature and in neurons, nitric oxide also plays a key role in innate immunity and inflammation. Recent progress has allowed the identification of the nitric oxide pathway in several cell types that reside in the skin, including keratinocytes, melanocytes, Langerhans cells, fibroblasts, and endothelial cells. Convincing evidence suggests that nitric oxide synthesis in these cells can be modulated by calcium-mobilizing agonists as well as diverse inflammatory and immune stimuli, and thereby contributes to the pathogenesis of several human skin diseases. Characterization of these intrinsic and extrinsic regulatory stimuli of nitric oxide synthesis has afforded substantial insights into the role of nitric oxide in inflammatory, hyperproliferative, and autoimmune skin diseases, as well as skin cancer, and may ultimately form the basis for future therapeutic intervention. The demonstrable and potential roles of nitric oxide in skin disease pathogenesis and treatment are the subjects of this review.

Topical glucocorticoids and the skin--mechanisms of action: an update

The topical glucocorticoids (GCs) represent the treatment of choice for many types of inflammatory dermatoses. Despite the extensive use of this class of drugs as first line therapy the mechanism of their action is uncertain. It is clear that the multiplicity of actions of the topical GCs is an important facet of their scope in the treatment of dermal disorders. The aim of this update is to review past and current theories regarding how these agents might work. Current understanding of the molecular mechanisms of GC action has advanced significantly over the past decade with the realisation that multiple systems are responsible for transduction of GC effects at a molecular level. The two primary modes of action are via interaction directly with DNA or indirectly through modulation of specific transcription factors: the endpoint in both cases being modulation of specific protein synthesis. Both of these mechanisms will be discussed. In particular this review will concentrate on the possibility that a GC-inducible protein, termed lipocortin 1, may have a significant role to play in the anti-inflammatory actions of these drugs. Additionally it has become apparent that several inflammatory enzymes induced in inflammation are sites of inhibitory action of the GCs, and the possibility that this occurs in the skin will be discussed paying particular attention to the inducible phospholipase A2, nitric oxide synthase and cyclooxygenase systems.