Alvarez Fj

The South Atlantic Anticyclone as a key player for the representation of the tropical Atlantic climate in coupled climate models

The key role of the South Atlantic Anticyclone (SAA) on the seasonal cycle of the tropical Atlantic is investigated with a regionally coupled atmosphere–ocean model for two different coupled domains. Both domains include the equatorial Atlantic and a large portion of the northern tropical Atlantic, but one extends southward, and the other northwestward. The SAA is simulated as internal model variability in the former, and is prescribed as external forcing in the latter. In the first case, the model shows significant warm biases in sea surface temperature (SST) in the Angola-Benguela front zone. If the SAA is externally prescribed, these biases are substantially reduced. The biases are both of oceanic and atmospheric origin, and are influenced by ocean–atmosphere interactions in coupled runs. The strong SST austral summer biases are associated with a weaker SAA, which weakens the winds over the southeastern tropical Atlantic, deepens the thermocline and prevents the local coastal upwelling of colder water. The biases in the basins interior in this season could be related to the advection and eddy transport of the coastal warm anomalies. In winter, the deeper thermocline and atmospheric fluxes are probably the main biases sources. Biases in incoming solar radiation and thus cloudiness seem to be a secondary effect only observed in austral winter. We conclude that the external prescription of the SAA south of 20°S improves the simulation of the seasonal cycle over the tropical Atlantic, revealing the fundamental role of this anticyclone in shaping the climate over this region.

FLUORESCENCE ANALYSIS OF CARRIER RAT AND HUMAN ERYTHROCYTES LOADED WITH FITC-DEXTRAN

Rat and human erythrocytes are inherently different with respect to slow dialysis encapsulation used in preparing carrier erythrocytes. The incorporation process, commonly measured with radioactive tracers, is always larger in human erythrocytes, mainly because the rat carrier cells are more fragile. When FITC-Dextran (Dx) is used in the encapsulation process, and loaded rat and human RBCs are studied by fluorescence intensity, some additional events are evident. Not all cells of each population appear with a fluorescence signal, and not all show similar fluorescence intensity. Human RBCs show a higher percentage of marked cells and a higher fluorescence intensity than rat RBCs. Two populations, of high and low fluorescence, appear in FITC-Dx loaded rat erythrocytes. The human loaded RBCs show a similar peak distribution together with another peak in the middle scale of fluorescence. Therefore, a heterogeneity in the cell population as a result of the encapsulation process is manifested for both species. The fractionation of RBCs, loaded with either FITC-Dx or 125I-CA, by centrifugation on Ficoll-Paque reveals that the low density cells have much more substance incorporation than the counterpart cell subpopulation in the pellet. Therefore, the cell modifications produced by the encapsulation process are independent of the substance being incorporated. On the other hand, FITC-Dx, but not 125I-CA, shows a certain degree of association to RBCs membranes, especially in humans.

IN VIVO BEHAVIOUR OF RAT BAND 3 CROSS-LINKED CARRIER ERYTHROCYTES

Rat band 3 cross-linked carrier erythrocytes have been prepared. Iodinated carbonic anhydrase has been encapsulated into rat erythrocytes. Then, carrier erythrocytes were labeled with 51chromium. Eventually, these doubly labeled rat RBCs were treated with a band 3 cross-linking reagent, namely bis(sulfosuccinimidyl)suberate (BS3). 51Chromium labeling and 125I CA showed to have cytosolic localization in cross-linked carrier erythrocytes. Estimation of the band 3 cross-linking induced by BS3 on rat carrier erythrocytes has been done rendering values around 25% of band 3 monomer reduction. BS3-cross-linked carrier erythrocytes when injected into rats are mainly targeted to liver as shown by chromium labeling localization. Also, encapsulated CA radioactivity carried by cross-linked carrier rat erythrocytes when injected into rats is localized predominantly in liver as shown by in vivo experiments. Accordingly, cross-linked carrier erythrocytes are highly recognized by peritoneal macrophages as detected by in vitro analyses of macrophage recognition. Thus, our data revealed a targeting of carrier rat erythrocytes induced by cross-linking of band 3 protein by BS3. These results support claims in favor of this animal model as a feasible system to analyze cross-linked carrier erythrocytes survival and targeting as well as the in vivo efficacy of targeting of loaded compounds to liver.

Influence of Chemical Modification on “ In Vivo ” and “ In Vitro ” Mouse Carrier Erythrocyte Survival and Recognition

Several systems have been developed with therapeutical purposes for drug delivery. Among them, red blood cells (RBCs) have been claimed to be a physiological method to convey and deliver active compounds.4,6,8,11 The preparation of erythrocytes as carriers can require encapsulation procedures or/and chemical modification of erythrocyte surface.3,22 In fact, the efficacy of these systems can be dependent of the use of several chemical treatments which can react with cell membrane proteins. Crosslinking reagents can be applied to red blood cell modification. Glutaraldehyde (GA) has been the most extensively used crosslinker.7,21 Also, other crosslinkers can be applied to carrier erythrocytes preparation.12,16 Biotinylation is another alternative method for carrier preparation.15,19 Eventually, chemical modification can promote targeting of carrier erythrocytes to several organs.12,21 We have focused our attention on the action of crosslinking reagents which react with band 3 in mouse erythrocyte membrane. Additionally, biotinylation of mouse erythrocytes has been studied. “In vivo” behaviour of these chemically modified erythrocytes have been studied. These survival results have been compared to recognition by macrophages. Thus, we described conditions for using these chemical treatments for targeting to organs and macrophages.

Dynamical downscaling of historical climate over CORDEX Central America domain with a regionally coupled atmosphere–ocean model

The climate in Mexico and Central America is influenced by the Pacific and the Atlantic oceanic basins and atmospheric conditions over continental North and South America. These factors and important ocean–atmosphere coupled processes make the region’s climate a great challenge for global and regional climate modeling. We explore the benefits that coupled regional climate models may introduce in the representation of the regional climate with a set of coupled and uncoupled simulations forced by reanalysis and global model data. Uncoupled simulations tend to stay close to the large-scale patterns of the driving fields, particularly over the ocean, while over land they are modified by the regional atmospheric model physics and the improved orography representation. The regional coupled model adds to the reanalysis forcing the air–sea interaction, which is also better resolved than in the global model. Simulated fields are modified over the ocean, improving the representation of the key regional structures such as the Intertropical Convergence Zone and the Caribbean Low Level Jet. Higher resolution leads to improvements over land and in regions of intense air–sea interaction, e.g., off the coast of California. The coupled downscaling improves the representation of the Mid Summer Drought and the meridional rainfall distribution in southernmost Central America. Over the regions of humid climate, the coupling corrects the wet bias of the uncoupled runs and alleviates the dry bias of the driving model, yielding a rainfall seasonal cycle similar to that in the reanalysis-driven experiments.

Rat Carrier Erythrocytes Circulate and Arrive to Organs

Different delivery systems are currently used in therapy. They have the advantage of protecting the active substance from rapid clearance and avoiding toxic side effects. Among the many carrier systems proposed12, RBCs have many desirable properties: they are naturally biodegradable and may stay in circulation over prolonged periods of time11,25; RBCs are easily obtainable and large amounts of material can be entrapped in a small volume of cells by hypotonic dialysis; autologous cells elicit little or no immune response7,16,20.