Nitric oxide transfer from the NO-donor S-nitroso-N-acetylpenicillamine to monomers and dimers of water-soluble iron-porphyrins

The nitrosylation of two water-soluble iron-porphyrins, the anionic Fe(III)-meso-tetrakis(p-sulfonatophenyl)porphyrin (FeTPPS(4)) and the cationic Fe(III)-meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (FeTMPyP), by the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) was studied using optical absorption spectroscopy. The influence of ionic and non-ionic micelles on rates of nitric oxide transfer was investigated. Initially, the effect of the micelles on the pH-dependent equilibrium between monomeric and micro-oxo-dimeric species of the iron-porphyrins was examined. It is not affected in micelle-porphyrin systems with electric charges identical in sign. The non-ionic micelles of polidocanol induce a small negative pK shift. In contrast, the dimerization equilibrium of porphyrins in oppositely charged micellar phases is displaced to lower pH by approximately 2 units. Nitric oxide binding to monomers and micro-oxo-dimers was examined at pH 5.0 and 8.0, respectively. Contrary to nitrosylation by NO gas, SNAP induces reductive nitrosylation. There was no observed NO-Fe(III)porphyrin intermediate. Nitrosylation rates were obtained and compared in aqueous buffer and in micellar systems. Monomers nitrosylate much faster than micro-oxo-dimers. Oppositely charged micelles prevent nitrosylation of the iron-porphyrins or considerably enhance nitrosylation times. Nitrosylation rates are comparable to transnitrosylation rates between several S-nitrosothiols and thiol-containing proteins, suggesting biological relevance for the process.     

Retracing micro-epidemics of Chagas disease using epicenter regression

Vector-borne transmission of Chagas disease has become an urban problem in the city of Arequipa, Peru, yet the debilitating symptoms that can occur in the chronic stage of the disease are rarely seen in hospitals in the city. The lack of obvious clinical disease in Arequipa has led to speculation that the local strain of the etiologic agent, Trypanosoma cruzi, has low chronic pathogenicity. The long asymptomatic period of Chagas disease leads us to an alternative hypothesis for the absence of clinical cases in Arequipa: transmission in the city may be so recent that most infected individuals have yet to progress to late stage disease. Here we describe a new method, epicenter regression, that allows us to infer the spatial and temporal history of disease transmission from a snapshot of a population's infection status. We show that in a community of Arequipa, transmission of T. cruzi by the insect vector Triatoma infestans occurred as a series of focal micro-epidemics, the oldest of which began only around 20 years ago. These micro-epidemics infected nearly 5% of the community before transmission of the parasite was disrupted through insecticide application in 2004. Most extant human infections in our study community arose over a brief period of time immediately prior to vector control. According to our findings, the symptoms of chronic Chagas disease are expected to be absent, even if the strain is pathogenic in the chronic phase of disease, given the long asymptomatic period of the disease and short history of intense transmission. Traducción al espa?ol disponible en Alternative Language Text S1/A Spanish translation of this article is available in Alternative Language Text S1.     

Species Turnover and Vertical Partitioning of Ant Assemblages in the Brazilian Amazon: A Comparison of Forests and Savannas1

We measured beta diversity, or turnover in species composition, of ant assemblages inhabiting patches of forest and savanna (cerrado) near Alter do Chão, in the Brazilian Amazon. In addition, we assessed vertical partitioning of these assemblages by comparing the ground and lower vegetation strata within each habitat. Ants attracted to sardine baits were collected along transects in 39 savanna and 34 forest sites scattered over a 16 km × 16 km landscape. There were about twice as many species in the forest as in the savanna, and within both habitats, we collected more species on the ground than in the vegetation. Similar results were obtained when analyzing data at the level of individual transects, indicating that ant species richness is affected by both habitat and strata. About two‐thirds of the species recorded in the savanna were also found in the forest. Within both habitats, a large proportion of the species found in the least species‐rich stratum (vegetation) were also found in the richer one (ground). However, ordination analysis, using data from individual transects, revealed that different habitats and strata can be clearly discriminated from each other in terms of their ant species composition. Each habitat and stratum had a number of characteristic (indicator) species which, although generally not exclusive to that particular habitat and stratum, predominated there. Our findings indicate that habitat and strata specialization is an important factor governing the organization of ant communities in Amazonia.     

Leishmanial infection: analysis of its first steps. A review

The first steps in leishmaniasis are critical in determining the evolution of the disease. Major advances have recently been done in understanding this crucial moment. Fundamental research in parasite-vector interaction, parasite biology, insect saliva, and vertebrate host response have shed new light and uncovered a most fascinating and complex moment in leishmaniasis. We review here some of these aspects and we try to connect them in a logical framework.     

Reductive nitrosylation of water-soluble iron porphyrins by S-nitroso-N-acetylpenicillamine: rate constants and EPR characterization

Reductive nitrosylation of the water-soluble iron derivatives of the cationic Fe(III)(TMPyP) and anionic Fe(III)(TPPS) porphyrins [where TMPyP=tetra-meso-(4-N-methylpyridiniumyl)porphinate and TPPS=tetra-meso-(4-sulfonatophenyl)porphinate] by the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) was studied using optical absorption spectroscopy and electron paramagnetic resonance. Nitrosylation rates were obtained, the reaction was found to be first order in the SNAP concentration and the stoichiometry of the reaction was one to one. The similarity between the obtained second-order rate constants for both porphyrins, k(TMPyP)=0.84 x 10(3)M(-1)s(-1) and k(TPPS)=0.97 x 10(3)M(-1)s(-1), suggested that the reaction mechanism is approximately independent of the nature of the porphyrin meso-substituents. A mechanism was proposed involving the hydrolysis of SNAP by an out of plane liganded H(2)O yielding the sulfenic acid of N-acetylpenicillamine and the transfer of NO(-) to Fe(III). The EPR (electron paramagnetic resonance) spectra of the SNAP- and gaseous NO-treated porphyrins were obtained and compared. The difference between the spectra of the cationic and anionic porphyrins indicates different local symmetry and Fe-N-O bond angle. SNAP-treatment produced much more resolved hyperfine structures than gaseous NO-treatment.     

Snakebites in “Invisible Populations”: A cross-sectional survey in riverine populations in the remote western Brazilian Amazon

In the Brazilian Amazon, long distances, low healthcare coverage, common use of ineffective or deleterious self-care practices, and resistance to seeking medical assistance have an impact on access to antivenom treatment. This study aimed to estimate snakebite underreporting, and analyze barriers that prevent victims from obtaining healthcare in communities located in 15 municipalities on the banks of the Solimões, Juruá and Purus Rivers, in the remote Western Brazilian Amazon. Information on the participants’ demographics, previous snakebites, access to healthcare, time taken to reach medical assistance, use of self-care practices, and the reason for not accessing healthcare were collected through semi-structured interviews. In the case of deaths, information was collected by interviewing parents, relatives or acquaintances. A total of 172 participants who reported having suffered snakebites during their lifetime were interviewed. A total of 73 different treatment procedures was reported by 65.1% of the participants. Participants living in different river basins share few self-care procedures that use traditional medicine, and 91 (52.9%) participants reported that they had access to healthcare. Living in communities along the Juruá River [OR = 12.6 (95% CI = 3.2–49.7; p<0.001)] and the use of traditional medicine [OR = 11.6 (95% CI = 3.4–39.8; p<0.001)] were variables that were independently associated to the lack of access to healthcare. The main reasons for not accessing healthcare were the pprioritization of traditional treatments (70.4%), and the failure to recognize the situation as being potentially severe (50.6%). Four deaths from complications arising from the snakebite were reported, and three of these were from communities on the banks of the Juruá River. Only one of these received medical assistance. We found an unexpectedly high underreporting of snakebite cases and associated deaths. Snakebite victims utilized three main different healing systems: 1) self-care using miscellaneous techniques; 2) official medical healthcare generally combined with traditional practices; and 3) self-care using traditional practices combined with Western medicines. To mitigate snakebite burden in the Brazilian Amazon, an innovative intervention that would optimize timely delivery of care, including antivenom distribution among existing community healthcare centers, is needed.     

Double-stranded RNA bending by AU-tract sequences

Sequence-dependent structural deformations of the DNA double helix (dsDNA) have been extensively studied, where adenine tracts (A-tracts) provide a striking example for global bending in the molecule. However, in contrast to dsDNA, sequence-dependent structural features of dsRNA have received little attention. In this work, we demonstrate that the nucleotide sequence can induce a bend in a canonical Watson-Crick base-paired dsRNA helix. Using all-atom molecular dynamics simulations, we identified a sequence motif consisting of alternating adenines and uracils, or AU-tracts, that strongly bend the RNA double-helix. This finding was experimentally validated using atomic force microscopy imaging of dsRNA molecules designed to display macroscopic curvature via repetitions of phased AU-tract motifs. At the atomic level, this novel phenomenon originates from a localized compression of the dsRNA major groove and a large propeller twist at the position of the AU-tract. Moreover, the magnitude of the bending can be modulated by changing the length of the AU-tract. Altogether, our results demonstrate the possibility of modifying the dsRNA curvature by means of its nucleotide sequence, which may be exploited in the emerging field of RNA nanotechnology and might also constitute a natural mechanism for proteins to achieve recognition of specific dsRNA sequences.     

Effect of duodenal infusion of trans10,cis12-CLA on milk performance and milk fatty acid profile in dairy goats fed high or low concentrate diet in combination with rolled canola seed

The effect of t10,c12-C18:2 on milk production, and fatty acid (FA) profile of milk fat was studied in 8 goats infused duodenally with t10,c12-C18:2 (2 g.10 h-1) during 3 days, followed by a 2-day infusion of skim milk (SM). The goats were assigned to 4 diets in a factorial arrangement constituted by low (L = 45%) or high (H = 65% of the diet DM) percentage of concentrate without (CS0) or with (CS20) rolled canola seed (20% of the concentrate DM). Milk samples were collected before (basal), and during the t10,c12-C18:2 and SM infusions. The t10,c12-C18:2 in milk fat increased from undetectable basal values to an average of 0.39% of total FA in the 3rd day of t10,c12-C18:2 infusion. DMI, milk yield, and the contents and yield of milk fat, protein, and lactose were similar between basal and the t10,c12-C18:2 infusion. The concentration of saturated FA with 4 to 16C did not change during the t10,c12-C18:2 infusion, whereas C18:0 increased, particularly in the milk fat of the CS20 group. The t10,c12-C18:2 infusion increased the t10- and t11-C18:1 (except a reduction in t11-C18:1 for the H-CS20 group), and it decreased the c9,t11-C18:2 in milk fat, particularly for the H-CS20 group. The t10,c12-C18:2 infusion reduced the c9,t11-C18:2/t11-C18:1 ratio, particularly for the CS0 group. The results indicate that mammary lipogenesis in dairy goats was not decreased by t10,c12-C18:2, however, the desaturation of long chain FA appeared to be equally affected as in dairy cows. This reduction in the desaturase index of milk fat could have been a direct effect of t10,c12-C18:2, or mediated via an increase in t10-C18:1.