Efeitos renais e vasculares do extrato bruto da anêmona marinha Bunodosoma caissarum e sua fração fosfolipase A2 : estudo dos mediadores envolvidos

Abstract

Sea anemones contain a variety of biological active compounds including some potent toxins. For this reason, many investigators have focused their studies in these proteins, isolated from sea anemones, such as Bunodosoma caissarum. The aim of this work was to study the mechanism of functional alterations produced by the crude extract and the PLA2 fraction of B. caissarum in the isolated rat kidney and arteriolar mesenteric bed. Isolated kidneys from Wistar rats, weighing 250-300g, were perfused with Krebs-Henseileit solution containing 6% of bovine serum albumin for 120 min. B. caissarum crude extract (BcE) and PLA2 were added to the system 30 min after the beginning of each experiment (internal control) and Tezosentan (TZN) and Indomethacin (IND) were administered in the initial period of each experiment (T=0min). The mesenteric bed, kept warmed at 37°C, was perfused with Krebs solution at a constant flow, (4mL/min) but with a variable perfusion pressure, measured for 80 min. mRNA expression of TNF-α, IL-1β, rennin and adenosine receptors (A1, A2a, A2b and A3) was evaluated by PCR using 18S mRNA as reference gene. The data were analyzed by Student’s t-test (p<0.05). BcE altered kidney function increasing perfusion pressure (PP), renal vascular resistance (RVR), urinary flow (UF), glomerular filtration rate (GFR) and sodium, potassium and chloride excretion, especially with the intermediary concentração. Tezosentan inhibited these effects only partially. However, indomethacin presented a blockage more expressive that TZN. The PLA2 of B. caissarum showed a higher increase of PP at 60 minutes (Control= 104,17±3,72; PLA2(0,1) = 130,9±5,6*; PLA2(0,3) = 165,1±12,6*; PLA2(1,0) = 142,3±9,6*, *p<0,5) and increased RVR, UF, GFR, sodium, potassium and chloride excretion and urinary osmolarity, with descrease of Na+, K+ and Cl- distal transports.. The blockage of IND was more expressive on the smallest PLA2 concentração and TZN showed a modest effect, blocking more efficiently the intermediary concentração. Neither BcE, nor PLA2 altered the basal perfusion pressure of the isolated arteriolar mesenteric bed. PLA2 increased the gene expression of TNF-α (Control = 1,00 ± 0,00 vs. PLA2 = 1,116 ± 0,033*, com p<0,0001)and upnregulated the expression of adenosine receptors A2a (Control = 1,0 ± 0,01 vs. PLA2 = 1,238 ± 0,043*, com p<0,0001). These results suggest that BcE and PLA2 exert significative actions in the isolated perfusion kidney, without vascular effects in the arteriolar mesenteric bed. COX-2 and endothelin appear to be important mediators of the effects of BcE and PLA2. In addition, adenosine is also involved in the mechanism of action of B. caissarum.