Clinical application of nitric oxide synthase inhibitor for atopic dermatitis

Regulatory Role of Nitric Oxide in Cutaneous Inflammation

Nitric oxide (NO), a signaling molecule, regulates biological functions in multiple organs/tissues, including the epidermis, where it impacts permeability barrier homeostasis, wound healing, and antimicrobial defense. In addition, NO participates in cutaneous inflammation, where it exhibits pro-inflammatory properties via the cyclooxygenase/prostaglandin pathway, migration of inflammatory cells, and cytokine production. Yet, NO can also inhibit cutaneous inflammation through inhibition of T cell proliferation and leukocyte migration/infiltration, enhancement of T cell apoptosis, as well as through down-regulation of cytokine production. Topical applications of NO-releasing products can alleviate atopic dermatitis in humans and in murine disease models. The underlying mechanisms of these discrepant effects of NO on cutaneous inflammation remain unknown. In this review, we briefly review the regulatory role of NO in cutaneous inflammation and its potential, underlying mechanisms.

Possible Involvement of Nitric Oxide in the Antipruritic Effect of Metformin on Chloroquine-Induced Scratching in Mice

Background: Metformin ameliorates non-histamine-mediated itch. We have recently reported that the nitric oxide (NO) pathway is involved in chloroquine (CQ)-induced scratching behavior. Here we investigated the involvement of the NO pathway in the antipruritic effect of metformin on CQ-induced itch. Methods: Metformin (5–200 mg/kg, given intraperitoneally [i.p.]) was injected 4 h before CQ (400 µg/site, given intradermally [i.d.]) or compound 48/80 (100 µg/site, i.d.). A nonspecific nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 1 and 10 mg/kg, i.p.), or an NO precursor, L-arginine (10 and 100 mg/kg, i.p.) was administered 30 min before injection of CQ. A neural NOS (nNOS) inhibitor, 7-nitroindazole (7-NI; 1 and 10 nmol/site, i.d.) was concurrently administered with CQ. The scratching behavior was recorded for 30 min following the injection of CQ. We studied the changes in skin and spinal nitrite levels after treatments. Results: Our results showed that metformin (100 and 200 mg/kg) significantly reduced the CQ-induced scratching behavior but not the compound 48/80-induced scratching behavior. L-Arginine inhibited the antipruritic effect of metformin, while L-NAME and 7-NI significantly potentiated the inhibitory effects of a subeffective dose of metformin on the CQ-induced scratching behavior. The skin but not the spinal nitrite level was significantly increased after CQ administration. The elevated cutaneous nitrite level was reversed by effective doses of either metformin or 7-NI, but not by the subeffective doses of metformin + 7-NI. Conclusion: Acute injection of metformin significantly inhibits CQ-induced scratching behavior. This effect is mediated through inhibition of the NO pathway, especially by inhibiting the dermal nNOS enzyme.

Arginase I levels are decreased in the plasma of pediatric patients with atopic dermatitis

BACKGROUND

Serum arginase levels have been shown to be elevated in conditions, such as trauma, cancer, chronic wounds, pregnancy, and diabetes. This also has been found to be true in atopic diseases, such as asthma and allergic rhinitis.

OBJECTIVE

To study arginase activity in patients with atopic dermatitis (AD).

METHODS

In this pilot study, arginase activity levels in 15 pediatric patients with AD were compared with those in controls to determine whether arginase levels in AD are altered as in patients with other atopic diseases.

RESULTS

In contrast to the other diseases studied, arginase activity was found to be decreased in granulocytes and in the plasma of patients with AD compared with controls. This finding was coupled with a trend toward higher L-arginine plasma levels.

CONCLUSION

In AD, a different mechanism of arginine metabolism seems to be stimulated, leading to the formation of nitric oxide pathway components causing suppression of the arginase pathway and impairment in skin hydration, collagen synthesis, and wound healing.

Possible involvement of 5-lipoxygenase metabolite in itch-associated response of mosquito allergy in mice

This study investigated endogenous mediators involved in mosquito allergy-associated itching in mice. An intradermal injection of an extract of mosquito salivary gland elicited marked scratching in sensitized mice. The 5-lipoxygenase inhibitor zileuton (100 mg/kg), the 5-lipoxygenase activating peptide inhibitor MK-886 (10 mg/kg), and the glucocorticoid betamethasone 17-valerate (3 mg/kg) inhibited the scratching. The scratching was not affected by the cyclooxygenase inhibitors indomethacin and ketoprofen, the TP prostanoid receptor antagonist SQ-29548, the leukotriene B(4) antagonist ONO-4057, the cysteinyl leukotriene antagonist pranlucast, the leukotriene D(4) antagonist MK-571, the platelet-activating factor antagonist CV-3988, the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester, the H(2) histamine-receptor antagonist cimetidine, the H(1) histamine-receptor antagonist terfenadine plus cimetidine, and cypoheptadine that blocks the 5-HT(1/2) serotonin receptors. Zileuton (100 mg/kg) inhibited the increased activity of the cutaneous nerve branch induced by an intradermal injection of the extract, suggesting the peripheral action. Zileuton and MK-886 (10 and 100 microM) did not affect high K(+)-induced increase in intracellular Ca(2+) concentration in cultured dorsal root ganglion neurons. The results suggest that 5-lipoxygenase metabolite(s) other than leukotriene B(4) and cysteinyl leukotrienes are involved in mosquito allergy-associated itching.

FK506 independently upregulates transforming growth factor beta and downregulates inducible nitric oxide synthase in cultured human keratinocytes: possible mechanisms of how tacrolimus ointment interacts with atopic skin

BACKGROUND

Tacrolimus ointment (FK506) has been used in recent years for the treatment of atopic dermatitis (AD), with favourable results. Most of the therapeutic efficacy of FK506 in AD has been attributed to its immunomodulatory effects on different immune cell types, but its effects on keratinocytes (KCs) have rarely been discussed. Studies have shown that low expression of transforming growth factor (TGF)-beta and high expression of nitric oxide synthase (NOS) are implicated in the pathogenesis of AD.

OBJECTIVES

To investigate the direct effects of FK506 on KCs in terms of TGF-beta and inducible NOS (iNOS), and to explore the interactions between TGF-beta and iNOS in the KC system.

METHODS

Cultured human KCs treated with different concentrations of FK506 were used for investigation. The changes in the KC system induced by FK506 were documented in terms of TGF-beta and iNOS using enzyme-linked immunosorbent assay and Western blotting techniques, respectively. The gene expression of both TGF-beta and iNOS was also determined. A certain amount of tumour necrosis factor (TNF)-alpha was introduced to mimic atopic skin in vivo.

RESULTS

Our results showed that the release of TGF-beta was upregulated in FK506-treated KCs, particularly in the presence of TNF-alpha, while the expression of iNOS was downregulated. The gene expression of iNOS was also downregulated, as shown by reverse transcriptase-polymerase chain reaction analysis. However, the addition of TNF-alpha did not further downregulate the expression of iNOS protein, suggesting that FK506 may regulate TGF-beta and iNOS through different pathways.

CONCLUSIONS

Our findings indicate that the direct effects of FK506 on KCs probably contribute to its therapeutic efficacy in the treatment of AD.

Topical vitamin B12-a new therapeutic approach in atopic dermatitis-evaluation of efficacy and tolerability in a randomized placebo-controlled multicentre clinical trial

BACKGROUND

Vitamin B(12) is an effective scavenger of nitric oxide (NO). As the experimental application of a NO synthase inhibitor, N omega-nitro-L-arginine, led to a clear decrease in pruritus and erythema in atopic dermatitis, it would be reasonable to assume a comparable effect of vitamin B(12).

OBJECTIVES

The efficacy and tolerability of a new vitamin B(12) cream as a possible alternative to current therapies was examined.

METHODS

A prospective, randomized and placebo-controlled phase III multicentre trial, involving 49 patients was conducted. For the treatment duration of 8 weeks, each patient applied twice daily (in the morning and evening) the vitamin B(12)-containing active preparation to the affected skin areas of one side of the body and the placebo preparation to the contralateral side according to the randomization scheme.

RESULTS

On the body side treated with the vitamin B(12) cream, the modified Six Area Six Sign Atopic Dermatitis score dropped to a significantly greater extent than on the placebo-treated body side (for the investigational drug 55.34 +/- 5.74 SEM, for placebo 28.87 +/- 4.86 SEM, P < 0.001). At the conclusion of the study, the investigator and patients awarded mostly a 'good' or 'very good' rating to the active drug (58% and 59%, respectively) and a 'moderate' or 'poor' rating to the placebo (89% and 87%, respectively).

CONCLUSIONS

Topical vitamin B(12) is a new therapeutic approach in atopic dermatitis. These results document a significant superiority of vitamin B(12) cream in comparison with placebo with regard to the reduction of the extent and severity of atopic dermatitis. Furthermore, the treatment was very well tolerated and involved only very low safety risks for the patients.

Antipruritic effects of the fruits of Chaenomeles sinensis

A 35% EtOH extract of the fruits of Chaenomeles sinensis, long utilized as a folk medicine for cough, significantly inhibited the pruritogenic agent compound 48/80 (COM)-induced scratching behavior in mice. Antipruritic activity-guided fractionation and purification yielded active quercetin, apigenin, and catechin derivatives, which exhibited significant inhibitory effects on COM-induced scratching behavior. To the best of our knowledge, apigenin (5), apigenin 7-glucronide (6), and apigenin 4'-methoxy-7-glucronide (acacetin 7-glucronide) (7) were isolated from the fruits of C. sinensis for the first time. The active fraction and these compounds also inhibited serotonin-, platelet activating factor-, and prostaglandin E(2)-induced scratching behavior, but did not inhibit histamine-induced scratching behavior or locomotive behavior. This study also showed that the fruits of C. sinensis could be used to treat allergic itching sensation.

Dexamethasone prevents granulocyte-macrophage colony-stimulating factor-induced nuclear factor-kappaB activation, inducible nitric oxide synthase expression and nitric oxide production in a skin dendritic cell line

AIMS

Nitric oxide (NO) has been increasingly implicated in inflammatory skin diseases, namely in allergic contact dermatitis. In this work, we investigated the effect of dexamethasone on NO production induced by the epidermal cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) in a mouse fetal skin dendritic cell line.

METHODS

NO production was assessed by the method of Griess. Expression of the inducible isoform of nitric oxide synthase (iNOS) protein was evaluated by western blot analysis and immunofluorescence microscopy. Western blot analysis was also performed to evaluate cytosolic IkappaB-alpha (IkappaB-alpha) protein levels. The electrophoretic mobility shift assay was used to evaluate the activation or inhibition of nuclear factor kappa B (NF-kappaB).

RESULTS

GM-CSF induced iNOS expression and NO production, and activated the transcription factor NF-kappaB. Dexamethasone inhibited, in a dose-dependent manner, NO production induced by GM-CSF. Addition of dexamethasone to the culture, 30 min before GM-CSF stimulation, significantly inhibited the cellular expression of iNOS. Dexamethasone also inhibited GM-CSF-induced NF-kappaB activation by preventing a significant decrease on the IkappaB-alpha protein levels, thus blocking NF-kappaB migration to the nucleus.

CONCLUSIONS

The corticosteroid dexamethasone inhibits GM-CSF-induced NF-kappaB activation, iNOS protein expression and NO production. These results suggest that dexamethasone is a potent inhibitor of intracellular events that are involved on NO synthesis, in skin dendritic cells.

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.

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.

LPS induction of I kappa B-alpha degradation and iNOS expression in a skin dendritic cell line is prevented by the janus kinase 2 inhibitor, Tyrphostin b42

The Janus kinase (JAK) family of protein tyrosine kinases are activated in response to a wide variety of external stimuli. Here we have investigated whether the janus kinase 2 (JAK2) is involved in the induction of nitric oxide synthase type II (iNOS) expression in a mouse fetal skin dendritic cell line (FSDC). In FSDC the expression of iNOS protein and nitric oxide production, in response to the lipopolysaccharide (LPS) stimulus (5 microg/ml), is inhibited by the specific inhibitor of the JAK2, tyrphostin B42 with an half maximal inhibitory concentration (IC(50)) of 9.65 microM. The antioxidant compound pyrrolidinedithiocarbamate (PDTC) inhibits both the nitrite production with an IC(50) of 16.6 microM and the iNOS protein expression in FSDC. In addition, LPS induces the activation of NF-kappa B, and tyrphostin B42 prevents the degradation of the cytosolic factor I kappa B-alpha and blocks the translocation of the NF-kappa B p65 protein subunit into the nucleus. These results indicate that the JAK family of protein kinases and the transcription factor NF-kappa B are involved in the induction of iNOS protein expression in FSDC stimulated with LPS.

Inhibition of ultraviolet B-induced skin erythema by N-nitro-L-arginine and N-monomethyl-L-arginine

Ultraviolet B (UVB)-irradiated human keratinocytes and human endothelial cells release nitrogen oxides, i.e. nitric oxide (NO). S-nitrosothiols, hydroxylamine (H2NOH) as well as ammonia (NH3) formed from L-arginine. Generation of these compounds was time and concentration-dependent and decreased by both N-monomethyl-L-arginine (L-NMMA) and N-nitro-L-arginine (L-NA). UVB radiation of the cells resulted in a concomitant increase of soluble guanylate cyclase (sGC) activity which was inhibited by L-NMMA and L-NA. S-nitrosothiols formed during the irradiation of the cells directly increased purified sGC activity by a mechanism characteristic of release of NO from a carried molecule. UVB-irradiated cells promptly increased thiobarbituric acid reacting substance (TBARS) (estimated as malondialdehyde. MDA) production which were inhibited by desferrioxamine. In in vivo experiments using guinea pigs subjected to UVB radiation, a Protection Factor (PF) of 2.25 +/- 0.75 was calculated when an emulsified cream formulation containing L-NMMA (1% w/w) and L-NA (1% w/w) was applied to their skin. In human volunteers subjected to UVB radiation, a dose-dependent increase of PF was observed. When an emulsified cream formulation containing L-NMMA (1% w/w) and L-NA (1% w/w) was applied to their skin the PF was 2.15 +/- 0.80: by increasing the concentration of L-NMMA (1% w/w) and L-NA (2% w/w) the PF was 4.25 +/- 1.25. The present results indicate that UVB radiation acts as a potent stimulator of human keratinocytes and endothelial cells to release nitrogen oxides that may diffuse out of the keratinocytes and endothelial cells, activating sGC in neighboring smooth muscle cells. This may be a major part of the integrated response of the skin leading to vasodilation and erythema.

Langerhans cells express inducible nitric oxide synthase and produce nitric oxide

The importance of nitric oxide (NO) in mediating macrophage functions has been demonstrated, but production of this potent gas has not been examined in Langerhans cells (LC). Using murine LC purified from epidermal cell suspensions and the recently established LC-like cell line derived from newborn BALB/c epidermis (XS-52), it was shown with reverse transcriptase (RT)-PCR that inducible nitric oxide synthase (iNOS) message is present in these cells. Murine keratinocytes did not contain iNOS message. iNOS mRNA was increased in a concentration-dependent manner by lipopolysaccharide (LPS) in purified murine LC and XS-52 cells, and immunofluorescence using an antibody to iNOS revealed bright cytoplasmic staining in LPS-treated XS-52 cells. Anti-iNOS antibody brightly stained LC on human neonatal foreskin cryosections. An increase in NO production by LPS-treated XS-52 cells over 16 h, as measured by the determination of nitrite levels in culture supernatants using the Griess Reaction, was observed. Interferon-gamma (IFNgamma) did not affect NO production on its own. In the presence of LPS and IFNgamma, NO production was 3 times more than observed with LPS alone. NO production was inhibited by the NOS inhibitor L-NAME. Western blots with anti-iNOS antibody demonstrated an increase in iNOS expression in LPS-treated XS-52 cells that was suppressed by IL-10. NO produced in LC may affect LC functions such as microbicidal activity, antigen presentation, and cytotoxicity and may affect adjacent keratinocytes and melanocytes.