Amidinoquinoxaline N-oxides: synthesis and activity against anaerobic bacteria.

We present herein an in-depth study on the activity of amidinoquinoxaline N-oxides 1 against Gram-positive and Gram-negative anaerobic bacteria. Based on 5-phenyl-2,3-dihydropyrimidoquinoxaline N-oxide 1a, the selected structural variations included in our study comprise the substituents α- to the N-oxide function, the benzofused ring, substitution and quaternization of the amidine moiety, and the amidine ring size. Compounds 1 showed good to excellent antianaerobic activity, evaluated as the corresponding CIM50 and CIM90 values, and an antimicrobial spectrum similar to metronidazole. Six out of 13 compounds 1 had CIM90 values significantly lower than the reference drug. Among them, imidazoline derivatives 1i-l were the most active structures. Such compounds were synthesized by base-promoted ring closure of the corresponding amidines. The N-oxides under study showed no significant cytotoxicity against RAW 264.7 cells, with high selectivity indexes. Their calculated ADME properties indicate that the compounds are potentially good oral drug candidates. The antianaerobic activity correlated satisfactorily with the electron affinity of the compounds, suggesting that they may undergo bioreductive activation before exerting their antibacterial activity.

C5a complement levels in clinical remission AQP4-IgG-positive NMO patients.

BACKGROUND: Neuromyelitis Optica Spectrum Disorders (NMOSD) is an antibody-mediated disorder of the Central Nervous System where a leading role of the complement system has been demonstrated. OBJECTIVE: To measure the levels of complement factors C3, C4 and C5a in serum and plasma of clinical remission patients with AQP4-IgG + NMOSD. METHODS: Twelve patients with NMOSD AQP4 + according to 2015 criteria from a General Hospital in Buenos Aires, Argentina, were included in the study, and 19 age- and sex-matched healthy volunteers as a control group (HC). AQP4 antibodies were measured in serum by CBA analysis. Fresh blood samples were centrifuged to obtain serum and plasma. C3, C4, and AQP4 antibodies were measured in the serum, whereas C5a was measured in the plasma, which was obtained using Futhan (BD FUT-175®, BD Biosciences, San Jose, CA, USA). RESULTS: The complement factors, C3, C4, and C5a were measured in all samples. The mean concentration of C3 was 130.7 mg/dl (SD 16.1 mg/dl), and the mean concentration of C4 was 21.6 mg/dl (SD 4.8 mg/dl); both values were within the normal reference range (C3: 84-193 mg/dl; C4: 20-40 mg/dl) and were not significantly different (p > 0.05) from the mean levels in healthy controls (C3: 116.9 mg/dl; C4: 21.9 mg/dl). When analyzing the mean plasma level of C5a, we found a statistically significant difference (p = 0.0444) between the mean concentration of C5a in NMOSD patients (43.1 ng/ml; SD 48.7 ng/ml) and the HC group (17.7 ng/ml; SD 16.7 ng/ ml). CONCLUSIONS: In conclusion, the present study demonstrates that plasma C5a may be interesting to investigate as a potential biomarker of disease activity in NMOSD, in a larger and prospective cohort.

Lipoteichoic Acid from Lacticaseibacillus rhamnosus GG Modulates Dendritic Cells and T Cells in the Gut.

Lipoteichoic acid (LTA) from Gram-positive bacteria exerts different immune effects depending on the bacterial source from which it is isolated. Lacticaseibacillus rhamnosus GG LTA (LGG-LTA) oral administration reduces UVB-induced immunosuppression and skin tumor development in mice. In the present work, we evaluate the immunomodulatory effect exerted by LGG-LTA in dendritic cells (DC) and T cells, both in vitro and in the gut-associated lymphoid tissue (GALT). During cell culture, LTA-stimulated BMDC increased CD86 and MHC-II expression and secreted low levels of pro and anti-inflammatory cytokines. Moreover, LTA-treated BMDC increased T cell priming capacity, promoting the secretion of IL-17A. On the other hand, in orally LTA-treated mice, a decrease in mature DC (lamina propria and Peyer's patches) was observed. Concomitantly, an increase in IL-12p35 and IFN-γ transcription was presented (lamina propria and Peyer's Patches). Finally, an increase in the number of CD103+ DC was observed in Peyer's patches. Together, our data demonstrate that LGG-LTA activates DC and T cells. Moreover, we show that a Th1-biased immune response is triggered in vivo after oral LTA administration. These effects justify the oral LTA activity previously observed.

Low Vitamin D Serum Levels in a Cohort of Myasthenia Gravis Patients in Argentina.

There are limited and controversial studies that address the role of vitamin D (vitD), a vitamin with immunomodulatory effects, in myasthenia gravis (MG), a neuromuscular autoimmune disease. We aimed to assess 25-hydroxy vitamin D (25(OH)D) levels and to evaluate possible associations with the clinical severity and other biomarkers of the disease. Serum levels of 25(OH)D, anti-acetylcholine receptor antibodies and complement factor C5a were measured in MG patients (n = 66) and healthy volunteers (HV) (n = 25). Participants were evaluated through questionnaires to determine vitD intake and sunlight exposure. Severity scores were registered for MG patients. We found an 89.4% of MG individuals with nonsufficient levels of vitD, in comparison with 68.0% in the group of HV (OR = 3.96; P = 0.024). In addition, there was an inverse correlation between 25(OH)D levels and one of the scores (P = 0.037 r = -0.26, CI95  = -0.49 to -0.0087). However, when we compared 25(OH)D median serum levels between MG patients and HV, no statistically significant differences have been found. This is the first report of vitD status in a cohort of Argentinean MG patients, where we found that patients are more likely to have nonsufficient levels of vitD compared to healthy people and that patients with more severe disease have lower levels of vitD.

Cholesterol in myasthenia gravis.

The cholinergic neuromuscular junction is the paradigm peripheral synapse between a motor neuron nerve ending and a skeletal muscle fiber. In vertebrates, acetylcholine is released from the presynaptic site and binds to the nicotinic acetylcholine receptor at the postsynaptic membrane. A variety of pathologies among which myasthenia gravis stands out can impact on this rapid and efficient signaling mechanism, including autoimmune diseases affecting the nicotinic receptor or other synaptic proteins. Cholesterol is an essential component of biomembranes and is particularly rich at the postsynaptic membrane, where it interacts with and modulates many properties of the nicotinic receptor. The profound changes inflicted by myasthenia gravis on the postsynaptic membrane necessarily involve cholesterol. This review analyzes some aspects of myasthenia gravis pathophysiology and associated postsynaptic membrane dysfunction, including dysregulation of cholesterol metabolism in the myocyte brought about by antibody-receptor interactions. In addition, given the extensive therapeutic use of statins as the typical cholesterol-lowering drugs, we discuss their effects on skeletal muscle and the possible implications for MG patients under chronic treatment with this type of compound.

C3, C5a and anti-acetylcholine receptor antibody as severity biomarkers in myasthenia gravis.

BACKGROUND: Although the pathogenesis of myasthenia gravis (MG) is well known, prognostic markers are not yet available. We assessed the utility of anti-acetylcholine receptor (AChR) antibody (AChR-ab) titer and concentration of C3, C4, and C5a as potential severity biomarkers in MG. METHODS: Levels of C3, C4, C5a, and AChR-ab were measured in 60 AChR-ab-positive patients with MG. Their relationship with clinical severity was analyzed using the activities of daily living (ADL) and MG composite (MGC) scales. RESULTS: AChR-ab titer correlated with severity of MG according to ADL (p = 0.002) and MGC scales (p = 0.001). When patients were classified according to disease duration, a statistically significant correlation between AChR-ab titer and clinical severity was only found in the subgroup of patients with fewer than 5 years from symptoms onset. C5a levels showed a positive correlation with MG severity according to the ADL scale (p = 0.041; τb = 0.18), although C5a levels were not different from the control group. DISCUSSION: AChR-ab titers and C5a levels could potentially be considered markers of severity in patients with MG.

NADPH oxidase and mitochondria are relevant sources of superoxide anion in the oxinflammatory response of macrophages exposed to airborne particulate matter.

Exposure to ambient air particulate matter (PM) is associated with increased cardiorespiratory morbidity and mortality. In this context, alveolar macrophages exhibit proinflammatory and oxidative responses as a result of the clearance of particles, thus contributing to lung injury. However, the mechanisms linking these pathways are not completely clarified. Therefore, the oxinflammation phenomenon was studied in RAW 264.7 macrophages exposed to Residual Oil Fly Ash (ROFA), a PM surrogate rich in transition metals. While cell viability was not compromised under the experimental conditions, a proinflammatory phenotype was observed in cells incubated with ROFA 100 µg/mL, characterized by increased levels of TNF-α and NO production, together with PM uptake. This inflammatory response seems to precede alterations in redox metabolism, characterized by augmented levels of H2O2, diminished GSH/GSSG ratio, and increased SOD activity. This scenario resulted in increased oxidative damage to phospholipids. Moreover, alterations in mitochondrial respiration were observed following ROFA incubation, such as diminished coupling efficiency and spare respiratory capacity, together with augmented proton leak. These findings were accompanied by a decrease in mitochondrial membrane potential. Finally, NADPH oxidase (NOX) and mitochondria were identified as the main sources of superoxide anion () in our model. These results indicate that PM exposure induces direct activation of macrophages, leading to inflammation and increased reactive oxygen species production through NOX and mitochondria, which impairs antioxidant defense and may cause mitochondrial dysfunction.

Oral administration of lipoteichoic acid from Lactobacillus rhamnosus GG overcomes UVB-induced immunosuppression and impairs skin tumor growth in mice.

There is increasing evidence of the relevant connection and regulation between the gut and skin immune axis. In fact, oral administration of lipoteichoic acid (LTA) from Lactobacillus rhamnosus GG (LGG) prevents the development of UV-induced skin tumors in chronically exposed mice. Here we aim to evaluate whether this LTA is able to revert UV-induced immunosuppression as a mechanism involved in its anti-tumor effect and whether it has an immunotherapeutic effect against cutaneous squamous cell carcinoma. Using a mouse model of contact hypersensitivity, we demonstrate that LTA overcomes UV-induced skin immunosuppression. This effect was in part achieved by modulating the phenotype of lymph node resident dendritic cells (DC) and the homing of skin migratory DC. Importantly, oral LTA reduced significantly the growth of established skin tumors once UV radiation was discontinued, demonstrating that it has a therapeutic, besides the already demonstrated preventive antitumor effect. The data presented here strongly indicates that oral administration of LTA represents a promising immunotherapeutic approach for different conditions in which the skin immune system is compromised.

Autoimmune Attack of the Neuromuscular Junction in Myasthenia Gravis: Nicotinic Acetylcholine Receptors and Other Targets.

The nicotinic acetylcholine receptor (nAChR) family, the archetype member of the pentameric ligand-gated ion channels, is ubiquitously distributed in the central and peripheral nervous systems, and its members are the targets for both genetic and acquired forms of neurological disorders. In the central nervous system, nAChRs contribute to the pathological mechanisms of neurodegenerative disorders, such as Alzheimer and Parkinson diseases. In the peripheral nerve-muscle synapse, the vertebrate neuromuscular junction, "classical" myasthenia gravis (MG) and other forms of neuromuscular transmission disorders are antibody-mediated autoimmune diseases. In MG, antibodies to the nAChR bind to the postsynaptic receptors and activate the classical complement pathway culminating in the formation of the membrane attack complex, with the subsequent destruction of the postsynaptic apparatus. Divalent nAChR-antibodies also cause internalization and loss of the nAChRs. Loss of receptors by either mechanism results in the muscle weakness and fatigability that typify the clinical manifestations of the disease. Other targets for antibodies, in a minority of patients, include muscle specific kinase (MuSK) and low-density lipoprotein related protein 4 (LRP4). This brief Review analyzes the current status of muscle-type nAChR in relation to the pathogenesis of autoimmune diseases affecting the peripheral cholinergic synapse.

Message in a Bottle: Dialog between Intestine and Skin Modulated by Probiotics.

At the beginning, probiotics were used exclusively for gastrointestinal conditions. However, over the years, evidence has shown that probiotics exert systemic effects. In this review article, we will summarize recent reports that postulate probiotic treatment as an efficient one against skin pathologies, such as cancer, allergy, photoaging and skin infections. The focus will be restricted to oral probiotics that could potentially counteract the ultraviolet irradiation-induced skin alterations. Moreover, the possible underlying mechanisms by which probiotics can impact on the gut and exert their skin effects will be reviewed. Furthermore, how the local and systemic immune system is involved in the intestine-cutaneous crosstalk will be analyzed. In conclusion, this article will be divided into three core ideas: (a) probiotics regulate gut homeostasis; (b) gut and skin homeostasis are connected;

Selective TNF-α targeting with infliximab attenuates impaired oxygen metabolism and contractile function induced by an acute exposure to air particulate matter.

Inflammation plays a central role in the onset and progression of cardiovascular diseases associated with the exposure to air pollution particulate matter (PM). The aim of this work was to analyze the cardioprotective effect of selective TNF-α targeting with a blocking anti-TNF-α antibody (infliximab) in an in vivo mice model of acute exposure to residual oil fly ash (ROFA). Female Swiss mice received an intraperitoneal injection of infliximab (10 mg/kg body wt) or saline solution, and were intranasally instilled with a ROFA suspension (1 mg/kg body wt). Control animals were instilled with saline solution and handled in parallel. After 3 h, heart O2 consumption was assessed by high-resolution respirometry in left ventricle tissue cubes and isolated mitochondria, and ventricular contractile reserve and lusitropic reserve were evaluated according to the Langendorff technique. ROFA instillation induced a significant decrease in tissue O2 consumption and active mitochondrial respiration by 32 and 31%, respectively, compared with the control group. While ventricular contractile state and isovolumic relaxation were not altered in ROFA-exposed mice, impaired contractile reserve and lusitropic reserve were observed in this group. Infliximab pretreatment significantly attenuated the decrease in heart O2 consumption and prevented the decrease in ventricular contractile and lusitropic reserve in ROFA-exposed mice. Moreover, infliximab-pretreated ROFA-exposed mice showed conserved left ventricular developed pressure and cardiac O2 consumption in response to a ß-adrenergic stimulus with isoproterenol. These results provides direct evidence linking systemic inflammation and altered cardiac function following an acute exposure to PM and contribute to the understanding of PM-associated cardiovascular morbidity and mortality.

Time-course study of different innate immune mediators produced by UV-irradiated skin: comparative effects of short and daily versus a single harmful UV exposure.

The modulatory effects of solar UV radiation on the immune system have been widely studied. As the skin is the main target of UV radiation, our purpose was to compare the impact on skin innate immunity of two contrasting ways to be exposed to sunlight. Hairless mice were UV irradiated with a single high UV dose simulating a harmful exposure, or with repetitive low UV doses simulating short occasional daily exposures. Skin samples were taken at different times after UV irradiation to evaluate skin histology, inflammatory cell recruitment, epidermal T-cell population and the mitochondrial function of epidermal cells. The transcriptional profiles of pro-inflammatory cytokines, chemokines, antimicrobial peptides and Toll-like receptors were evaluated by RT-PCR and ELISA in tissue homogenates. Finally, a lymphangiography was performed to assess modification in the lymphatic vessel system. A single high UV dose produces a deep inflammatory state characterized by the production of pro-inflammatory cytokines and chemokines that, in turn, induces the recruitment of neutrophils and macrophages into the irradiated area. On the other hand, repetitive low UV doses drive the skin to a photo-induced alert state in which there is no sign of inflammation, but the epithelium undergoes changes in thickness, the lymphatic circulation increases, and the transcription of antimicrobial peptides is induced.

Lipoteichoic acid from Lactobacillus rhamnosus GG as an oral photoprotective agent against UV-induced carcinogenesis.

Probiotics are live micro-organisms that when administered in adequate amounts confer a health benefit on the host. Cell surface molecules of these micro-organisms are being studied in relation to their ability to interact with the host. The cell wall of lactobacilli possesses lipoteichoic acids (LTA) which are molecules with immunomodulatory properties. UV radiation (UVR) has been proposed as the main cause of skin cancer because of its mutagenic and immunosuppressive effects. Photoprotection with some nutrition interventions including probiotics has recently been shown. The aim of the present study was to investigate whether the oral administration of purified LTA from Lactobacillus rhamnosus GG can modulate the immune-suppressive effect of UVR and skin tumour development in female Crl:SKH-1-hrBR mice. For this purpose, two irradiation models were studied: (1) a chronic irradiation scheme consisting of daily irradiations during twenty consecutive days and (2) a long-term irradiation schedule, irradiating the animals three times per week, during 34 weeks for tumour development. The results showed that T-cells in the inguinal lymph node of LTA-treated mice produced higher levels of (1) interferon-γ and (2) a number of total, helper and cytotoxic T-cells compared with non-treated mice. Moreover, a significant delay in tumour appearance was found in LTA-treated mice. An increased IgA⁺ cell number was found in the small intestine together with a higher number of activated dendritic cells in the mesenteric lymph nodes. The latter results might be indicative of a direct effect of LTA in the gut, affecting the cutaneous immune system and restoring homeostasis through the gut-skin axis.

Skin exposure to chronic but not acute UV radiation affects peripheral T-cell function.

Ultraviolet (UV) radiation (UVR) produces deleterious effects that may finally lead to carcinogenesis. These adverse effects include tissue inflammation, free radical formation with consequent oxidation of proteins and lipids, DNA damage, and immune function suppression. The aim of this study was to evaluate the effects of UVR at the local and systemic levels following acute (4 consecutive days with 0.5 minimal erythema dose [MED]) or chronic (20 consecutive days with 0.25 MED) exposure. Locally, histological alterations and epidermal T-cell populations were studied. Systemically, inguinal lymph-node and spleen T cells were analyzed with respect to proliferative response and cytokine production against a nonspecific mitogen. Lymph-node T-cell populations were also characterized. Our results indicated that while both acute and chronic UVR produced epidermal hyperplasia and a decrease in epidermal T-cell density, acute UVR increased T-cell proliferative response, while chronic UVR produced the opposite effect, shifting the cytokine production toward a Th2/Treg profile. Therefore, even though acute irradiation produced a direct effect on skin, it did not correlate with a marked modification of overall T-cell response, which is in contrast to marked effects in chronically irradiated animals. These findings may contribute to understanding the clinical relevance of occupational UVR exposure, typically related to outdoor activities, which is associated with nonmelanoma skin carcinogenesis.

Anti-ribonucleoproteins autoantibodies in patients with systemic autoimmune diseases. Relation with cutaneous photosensitivity.

A common feature between patients with a certain group of systemic autoimmune pathologies (SAPs) with rheumatic component, such as lupus erythematosus (LE) in all its forms, is the presence of cutaneous photosensitivity (CP) as well as the existence of autoantibodies (Aabs). These Aabs have also high incidence in other SAPs that do not present CP, like primary Sjögren's syndrome and rheumatoid arthritis. Cutaneous photosensitivity is a condition that consists of an exacerbated skin reaction to solar radiations; its incidence can reach 90% in systemic LE. The mechanisms involved in the development of CP have been extensively studied focusing on different approaches; however, the exact mechanism has not been fully elucidated yet. There are many theories that relate specifically the presence of circulating anti-Ro/SS-A Aabs with the CP phenomenon, though there are several studies which are in disagreement. In this study, we evaluated the Aabs profile (anti-Ro/SS-A 52 kDa, anti-Ro/SS-A 60 kDa, anti-La/SS-B, anti-Sm and ANAs) as well as their titer or reactivity, in a local cohort of 169 patients with SAPs. We related those Aabs profiles and titers with the presence or absence of CP, and we found that there was no significant association between the presence of anti-Ro/SS-A Aabs and the occurrence of CP. On the other hand, a statistically significant positive association was found between CP and high reactivity anti-Sm Aabs, though this fact could be biased by the incidence of both events in SLE patients. To sum up, in the particular population studied, there is no direct relationship between anti-Ro/SS-A Aabs and CP, which is in agreement with some authors and in disagreement with many others, contributing to the endless discussion of this issue.

Alterations in skin immune response throughout chronic UVB irradiation-skin cancer development and prevention by naproxen.

Skin exposure to UVB radiation has been reported to produce both a significant inflammatory response and marked immunosuppression. This work was aimed to evaluate whether the response of murine skin to an acute UVB dose was modified by pre-exposure to chronic UVB irradiation and by topical treatment with naproxen, a nonsteroidal anti-inflammatory drug. Moreover, the effect of naproxen on the incidence of UV-induced skin tumors was studied. Prostaglandin E(2) (PGE(2)) and tumor necrosis factor alpha (TNF-alpha) levels were increased 96 h post-UVB in acutely irradiated animals and both mediators were modified by topical naproxen application-PGE(2) was decreased while TNF-alpha was increased. Such inflammatory response was suppressed when mice were chronically irradiated. Naproxen application on chronically irradiated mice reduced the incidence of tumor lesions. Taken together, our data suggest that chronic UVB irradiation generates an immunosuppressive state that prevents skin cells from responding normally to an acute irradiation challenge, thus impairing the protective effect of TNF-alpha against skin tumor development. Furthermore, reduction in the incidence of tumor lesions by naproxen may be due to its ability to increase TNF-alpha levels as well as to decrease PGE(2).

Time-course evaluation and treatment of skin inflammatory immune response after ultraviolet B irradiation.

Skin exposure to high doses of ultraviolet B (UVB) radiation generates a severe inflammatory skin response. In the present study we aim to investigate, using in vitro and in vivo models, the time-course of the inflammatory skin immune response after an acute exposure to UVB irradiation, as well as its modulation by a topical non-steroidal anti-inflammatory drug (NSAID) treatment, naproxen. PGE2 production and TNF-alpha levels increase in a post-irradiation time-dependent manner both in vivo and in vitro. This production pattern is also reflected in the iNOS expression levels in vivo and in the IL-6 levels in vitro. Changes observed in these mediators are correlated with histological alterations and dermal infiltration after the acute UVB irradiation. Naproxen treatment notably reduces PGE2 production and iNOS expression, reflecting the COX-NOS crosstalk already reported, although it causes an important increment in TNF-alpha synthesis in the epidermis of irradiated mice. Taken together, our data indicates that the epidermis is severely damaged by UVB radiation but then it is able to fully recover, and that the immune response is modulated by the NSAID treatment, since it is able to reduce the levels of some mediators as well as it can increase others.

Mitochondrial dysfunction and cellular stress progression after ultraviolet B irradiation in human keratinocytes.

BACKGROUND: Ultraviolet (UV) radiation is the major environmental harmful factor that affects human skin. UVB radiation is known to be a potent inducer of reactive oxygen species (ROS) production and has also been associated with the generation of nitric oxide (NO), all of which have been implicated in various skin disorders. It is well known that mitochondria can also be affected by UVB, leading to alterations in their membrane structure and permeabilization with cytochrome c release, which consequently affects the cell function. However, the loss of keratinocyte mitochondrial function generated by UVB, as well as its kinetics, has not been characterized completely. METHODS: We evaluated the effect of UVB irradiation on HaCat cells' mitochondrial function, assessed by membrane potential loss and superoxide anion (O(2)(*-)) production, correlating with apoptosis, p53 expression, ROS levels and NO production, 0, 6, 12, 24 and 48 h post-irradiation. RESULTS: HaCat cells progressed toward apoptotic cell death as the time post-irradiation increased, with the highest levels found 48 h after irradiation. Increased levels of ROS were observed 6 h after irradiation while high O(2)(*-) levels and mitochondrial membrane depolarization were detected 12 h post-UVB. Nevertheless, NO production was not significantly increased at any of the evaluated times. CONCLUSIONS: The kinetics of mitochondrial dysfunction after UVB irradiation in human keratinocytes progressed in a time post-irradiation-dependent manner, and they are closely related to cell death. However, there are certain levels of apoptosis, although low, in the absence of mitochondrial alterations. In addition, our data suggest that ROS play a greater role in keratinocyte UVB damage than reactive nitrogen species.

Skin damage and mitochondrial dysfunction after acute ultraviolet B irradiation: relationship with nitric oxide production.

BACKGROUND: Ultraviolet (UV) radiation is the main environmental carcinogen. It is able to induce injury in the keratinocytes, which triggers mechanisms in order to protect the skin against molecular alterations that may lead to the development of skin cancer. UVB is capable of producing genotoxic damage, directly or indirectly through reactive oxygen species, inducing DNA alterations and mutations. UVB radiation has also been associated with the generation of nitric oxide (NO), which is able to induce many physiological and physiopathological processes. The aim of the current study was to investigate the effect of UVB irradiation in hairless mice skin. METHODS: We evaluated the effect of an acute dose (200 mJ/cm(2)) of UVB irradiation correlating with histological alterations, nitric oxide synthase expression and activity, mitochondrial respiratory function, superoxide anion production and lipid peroxidation, 0, 6, 17 and 24 h post-irradiation treatment. RESULTS: Morphological analysis showed disruption of the epidermal stratum corneum and basale after UVB irradiation. The results indicated that skin UVB irradiation was associated with an increased cytosolic inducible nitric oxide synthase (iNOS) expression, inversely related to lipid peroxidation processes. An increase in mitochondrial superoxide anion (O(2) (*-)) and NO production 17 h post-irradiation was correlated with a mitochondrial dysfunction, all of them integrating the skin response to acute UVB irradiation. CONCLUSIONS: UVB irradiation of the skin produces morphological alterations as a consequence of the induction of molecular mechanisms associated with mitochondrial respiratory dysfunction and O(2) (*-) production, probably mediated by the increased mitochondrial NO production. On the other hand lipid peroxidation decrease inversely correlates with cytosolic iNOS expression, suggesting a protective role for the inflammatory response.