Superoxide, nitric oxide and peroxynitrite production by macrophages under different physiological oxygen tensions

Macrophages count on two O2-consuming enzymes to form reactive radical species: NAPDH oxidase 2 (Nox2) and nitric oxide synthase 2 (inducible isoform, iNOS) that produce superoxide radical (O2•-) and nitric oxide (•NO), respectively. If formed simultaneously, the diffusion-controlled reaction of O2•- and •NO yields peroxynitrite, a potent cytotoxic oxidant. In human tissues and cells, the oxygen partial pressure (pO2) normally ranges within 2-14 %, with a typical average pO2 value for most tissues ca. 5 %. Given that O2 is a substrate for both Nox2 and iNOS, its tissue and cellular concentration can affect O2•- and •NO production. Also, O2 is a modulator of the macrophage adaptative response and may influence iNOS expression in a hypoxia inducible factor 1-α (HIF1α-)-dependent manner. However, most of the reported experiments in cellula, analyzing the formation and effects of O2•- and •NO during macrophage activation and cytotoxicity towards pathogens, have been performed in cells exposed to atmospheric air supplemented with 5 % CO2; under these conditions, most cells are exposed to supraphysiologic oxygen tensions (ca. 20 % O2) which are far from the physiological pO2. Here, the role of O2 as substrate in the oxidative response of J774A.1 macrophages was explored upon exposure to different pO2 and O2•- and •NO formation rates were measured, obtaining a KM of 26 and 42 μM O2 for Nox2 and iNOS, respectively. Consequently, peroxynitrite formation was influenced by pO2, reaching a maximum at ≥ 10 % O2, but even at levels as low as 2 % O2, a substantial formation rate of this oxidant was detected. Indeed, the cytotoxic capacity of immunostimulated macrophages against the intracellular parasite T. cruzi was significant, even at low pO2 values, confirming the role of peroxynitrite as a potent oxidizing cytotoxin within a wide range of physiological oxygen tensions.

First evaluation of neustonic microplastics in the Macaronesian region, NE Atlantic

Marine microplastic pollution is an issue of great concern nowadays since high concentrations have been detected in the ocean, mainly in the subtropical gyres that accumulate this type of debris. The long-term effects of this pollution on ecosystems and marine biota are still unknown. The aim of this study is to quantify and characterise microplastics and neustonic zooplankton in sub-surface waters of the Macaronesian region, an area that has been little studied to date. Our results show a great variability in the concentration of microplastics with values between 15,283 items/km² in Los Gigantes (Tenerife, Canary Islands) and 1,007,872 items/km² in Las Canteras (Gran Canaria, Canary Islands). The main types of debris found were plastic fragments and fibres. The abundances of neustonic zooplankton were also very variable between the different sampling areas, being the main components copepods and eggs. Regarding the microplastics-zooplankton ratio, values were obtained between 0.002 and 0.22. In Las Canteras, the highest accumulation zone, was found twice as much microplastics as zooplankton for the 1-5 mm fraction in dry weight. These values highlight the potential hazard of microplastics - and its associated chemical contaminants - for marine biota, especially for large filter feeders.

Mechanism of the Reaction of Human Manganese Superoxide Dismutase with Peroxynitrite: Nitration of Critical Tyrosine 34

Human Mn-containing superoxide dismutase (hMnSOD) is a mitochondrial enzyme that metabolizes superoxide radical (O2(•-)). O2(•-) reacts at diffusional rates with nitric oxide to yield a potent nitrating species, peroxynitrite anion (ONOO(-)). MnSOD is nitrated and inactivated in vivo, with active site Tyr34 as the key oxidatively modified residue. We previously reported a k of ∼1.0 × 10(5) M(-1) s(-1) for the reaction of hMnSOD with ONOO(-) by direct stopped-flow spectroscopy and the critical role of Mn in the nitration process. In this study, we further established the mechanism of the reaction of hMnSOD with ONOO(-), including the necessary re-examination of the second-order rate constant by an independent method and the delineation of the microscopic steps that lead to the regio-specific nitration of Tyr34. The redetermination of k was performed by competition kinetics utilizing coumarin boronic acid, which reacts with ONOO(-) at a rate of ∼1 × 10(6) M(-1) s(-1) to yield the fluorescence product, 7-hydroxycoumarin. Time-resolved fluorescence studies in the presence of increasing concentrations of hMnSOD provided a k of ∼1.0 × 10(5) M(-1) s(-1), fully consistent with the direct method. Proteomic analysis indicated that ONOO(-), but not other nitrating agents, mediates the selective modification of active site Tyr34. Hybrid quantum-classical (quantum mechanics/molecular mechanics) simulations supported a series of steps that involve the initial reaction of ONOO(-) with Mn(III) to yield Mn(IV) and intermediates that ultimately culminate in 3-nitroTyr34. The data reported herein provide a kinetic and mechanistic basis for rationalizing how MnSOD constitutes an intramitochondrial target for ONOO(-) and the microscopic events, with atomic level resolution, that lead to selective and efficient nitration of critical Tyr34.

Nitric oxide diffusion to red blood cells limits extracellular, but not intraphagosomal, peroxynitrite formation by macrophages

Macrophage-derived nitric oxide ((•)NO) participates in cytotoxic mechanisms against diverse microorganisms and tumor cells. These effects can be mediated by (•)NO itself or (•)NO-derived species such as peroxynitrite formed by its diffusion-controlled reaction with NADPH oxidase-derived superoxide radical anion (O(2)(•-)). In vivo, the facile extracellular diffusion of (•)NO as well as different competing consumption routes limit its bioavailability for the reaction with O(2)(•-) and, hence, peroxynitrite formation. In this work, we evaluated the extent by which (•)NO diffusion to red blood cells (RBC) can compete with activated macrophages-derived O(2)(•-) and affect peroxynitrite formation yields. Macrophage-dependent peroxynitrite production was determined by boron-based probes that react directly with peroxynitrite, namely, coumarin-7-boronic acid (CBA) and fluorescein-boronate (Fl-B). The influence of (•)NO diffusion to RBC on peroxynitrite formation was experimentally analyzed in co-incubations of (•)NO and O(2)(•-)-forming macrophages with erythrocytes. Additionally, we evaluated the permeation of (•)NO to RBC by measuring the intracellular oxidation of oxyhemoglobin to methemoglobin. Our results indicate that diluted RBC suspensions dose-dependently inhibit peroxynitrite formation, outcompeting the O(2)(•-) reaction. Computer-assisted kinetic studies evaluating peroxynitrite formation by its precursor radicals in the presence of RBC are in accordance with experimental results. Moreover, the presence of erythrocytes in the proximity of (•)NO and O(2)(•-)-forming macrophages prevented intracellular Fl-B oxidation pre-loaded in L1210 cells co-cultured with activated macrophages. On the other hand, Fl-B-coated latex beads incorporated in the macrophage phagocytic vacuole indicated that intraphagosomal probe oxidation by peroxynitrite was not affected by nearby RBC. Our data support that in the proximity of a blood vessel, (•)NO consumption by RBC will limit the extracellular formation (and subsequent cytotoxic effects) of peroxynitrite by activated macrophages, while the intraphagosomal yield of peroxynitrite will remain unaffected.

Rectal sensation, pelvic floor function and symptom severity in Hispanic population with irritable bowel syndrome with constipation

OBJECTIVE

In patients with irritable bowel syndrome with constipation (IBS-C, Rome II) we determined if pelvic floor function correlates with rectal sensitivity and tone, and if the pelvic and rectal measurements correlate with symptoms.

PATIENTS AND METHODS

Sensory thresholds and tone in fasting and postprandial states were evaluated with an electronic barostat in 34 patients and 10 normal controls. The pelvic floor was assessed by defaecography.

RESULTS

Pain threshold to rectal distension was lower in IBS-C patients (P = 0.007). Postprandially, IBS-C patients showed lower values for sensation of gas, perception of urge, and pain threshold compared with controls. In IBS-C the anorectal angle widened less and showed less perineal mobility during defecation; the rectal tone in fasting IBS-C patients correlated with the angle at rest (P = 0.04) and with the perineal descent at rest (P = 0.01). The severity of abdominal discomfort or pain, and abdominal fullness correlated with the anorectal angle. The duration of symptoms and frequency of bowel movements correlated with perineal descent. Straining, mucus expulsion, and the feeling of incomplete evacuation correlated with rectal sensitivity variables.

CONCLUSION

Patients with IBS-C have lowered sensory thresholds for noxious and non-noxious stimuli, increased visceral sensitivity after food, less perineal mobility during defecation, and symptoms that correlate with rectal sensitivity and pelvic floor parameters.

[Teleradiology. The experience in Panamá]

The technological advances have brought today procedures, that were not possible a few years ago. Telemedicine is one of them. Teleradiology in particular is one of the specialty where this application has been more important.

Measuring chronic rheumatic pain in Mexican Americans: cross-cultural adaptation of the McGill Pain Questionnaire

We performed a cross-cultural adaptation of the McGill Pain Questionnaire (MPQ) from English to Spanish for studying Mexican Americans in South Texas. Each of the 78 single-word pain descriptors in the original MPQ was translated into Spanish by a panel of nine bilingual health researchers, preserving the original structure of the questionnaire. The pain-intensity content (PIC) of the words in each language was then rated on a 100 mm visual analog scale by 8 bilingual health care providers and 10 bilingual health-care consumers. The correlation between Spanish and English average PIC ratings was strong (r = 0.85 for providers, r = 0.80 for consumers). The translated Spanish version was compared to the original English in a group of 50 bilingual Mexican-American patients with musculoskeletal pain, who completed the MPQ in both languages. There was no difference in Average Pain Rating Index between the Spanish and English versions (29.8 +/- 14.7 vs 29.1 +/- 15.8, p = 0.55), and agreement between the two language versions was almost perfect (ri = 0.85). Test-retest reliability was measured in two groups of hospitalized patients (25 per group), one composed of monolingual Spanish speakers and the other of monolingual English speakers. Each subject completed the MPQ, the McGill Pain Map, two 10-cm visual analog scales measuring pain now and within the past week, the bodily pain items of the MOS-SF36 survey, and the Modified Health Assessment Questionnaire, on two occasions one day apart. Test-retest reliability of the Spanish and English components of the MPQ was not significantly different and was comparable to that of the other pain and health status instruments. We conclude that the Spanish MPQ is cross-culturally equivalent to the original English and has similar concurrent validity and reliability. This questionnaire is suitable for cross-cultural studies of pain comparing Spanish-speaking Mexican Americans with English-speaking members of the same and other ethnic groups.