Endotoxemia alters nucleotide hydrolysis in platelets of rats

Platelets play a critical role in homeostasis and blood clotting at sites of vascular injury, and also in various ways in innate immunity and inflammation. Platelets are one of the first cells to accumulate at an injured site, and local release of their secretome at some point initiate an inflammatory cascade that attracts leukocytes, activates target cells, stimulates vessel growth and repair. The level of exogenous ATP in the body may be increased in various inflammatory and shock conditions, primarily as a consequence of nucleotide release from platelets, endothelium and blood vessel cells. An increase of ATP release has been described during inflammation and this compound presents proinflammatory properties. ADP is a nucleotide known to induce changes in platelets shape and aggregation, to promote the exposure of fibrinogen-binding sites and to inhibit the stimulation of adenylate cyclase. Adenosine, the final product of the nucleotide hydrolysis, is a vasodilator and an inhibitor of platelet aggregation. There is a group of ecto-enzymes responsible for extracellular nucleotide hydrolysis named ectonucleotidases, which includes the NTPDase (nucleoside triphosphate diphosphohydrolase) family, the NPP (nucleoside pyrophosphatase/phosphodiesterase) family and an ecto-5'-nucleotidase. Therefore, we have aimed to investigate the effect of lipopolysaccharide endotoxin from Escherichia coli on ectonucleotidases in platelets from adult rats in order to better understand the role of extracellular adenine nucleotides and nucleosides in the maintenance of blood homeostasis in inflammatory processes. LPS administered in vitro was not able to alter the ATP, ADP, AMP and -Nph-5'-TMP hydrolysis of platelets from untreated rats in all concentrations tested (25-100 g/ml). There was a significant decrease in ATP, ADP, AMP and -Nph-5'-TMP hydrolysis in rat platelets after 48 hours of LPS exposure (2 mg/Kg, i.p.). ATP and ADP hydrolysis has been reduced about 28% whereas it has been observed a significant 30% and 26% decrease on AMP and -Nph-5'-TMP hydrolysis. Platelet aggregation and platelet number have shown a significant decrease in LPS-treated rats (40% and 55%, respectively) when compared to control group. These results suggest that changes observed in platelet count and, consequently, in nucleotidase activities from circulatory system could alter extracellular nucleotide and nucleoside levels, which might modulate the inflammatory process.