The relationship between calcium and the metabolism of plasma membrane phospholipids in hemolysis induced by brown spider venom phospholipase‐D toxin

Abstract

Brown spider venom phospholipase-D belongs to a family of toxins characterized as potent bioactive agents. These toxins have been involved in numerous aspects of cell pathophysiology including inflammatory response, platelet aggregation, endothelial cell hyperactivation, renal disorders, and hemolysis. The molecular mechanism by which these toxins cause hemolysis is under investigation; literature data have suggested that enzyme catalysis is necessary for the biological activities triggered by the toxin. However, the way by which phospholipase-D activity is directly related with human hemolysis has not been determined. To evaluate how brown spider venom phospholipase-D activity causes hemolysis, we examined the impact of recombinant phospholipase-D on human red blood cells. Using six different purified recombinant phospholipase-D molecules obtained from a cDNA venom gland library, we demonstrated that there is a correlation of hemolytic effect and phospholipase-D activity. Studying recombinant phospholipase-D, a potent hemolytic and phospholipase-D recombinant toxin (LiRecDT1), we determined that the toxin degrades synthetic sphingomyelin (SM), lysophosphatidylcholine (LPC), and lyso-platelet-activating factor. Additionally, we determined that the toxin degrades phospholipids in a detergent extract of human erythrocytes, as well as phospholipids from ghosts of human red blood cells. The products of the degradation of synthetic SM and LPC following recombinant phospholipase-D treatments caused hemolysis of human erythrocytes. This hemolysis, dependent on products of metabolism of phospholipids, is also dependent on calcium ion concentration because the percentage of hemolysis increased with an increase in the dose of calcium in the medium. Recombinant phospholipase-D treatment of human erythrocytes stimulated an influx of calcium into the cells that was detected by a calcium-sensitive fluorescent probe (Fluo-4). This calcium influx was shown to be channel-mediated rather than leak-promoted because the influx was inhibited by L-type calcium channel inhibitors but not by a T-type calcium channel blocker, sodium channel inhibitor or a specific inhibitor of calcium activated potassium channels. Finally, this inhibition of hemolysis following recombinant phospholipase-D treatment occurred in a concentration-dependent manner in the presence of L-type calcium channel blockers such as nifedipine and verapamil. The data provided herein, suggest that the brown spider venom phospholipase-D-induced hemolysis of human erythrocytes is dependent on the metabolism of membrane phospholipids, such as SM and LPC, generating bioactive products that stimulate a calcium influx into red blood cells mediated by the L-type channel.

Variable Substrate Preference among Phospholipase D Toxins from Sicariid Spiders

“…In the case of ␤1A1 (SMase II) from L. laeta, SMase D activity has been observed but with a 3-fold higher K m value and a reported 2-fold lower reaction rate at saturating substrate concentrations compared with ␣III1 (SMase I) from the same species (26). References for structure and activity data are as follows: IsSMase (74); LiRecDT6 (11); LiRecDT7 (14); SMase I (8,18,27,35,59,64,75); Ll2 (8); LiRecDT4 (9); LgRec1 (76); Lr1/Lb1/Lb2 (8,25); L. arizonica ␣IB2bi (15,30); Lr2 (19,25); P1/P2 (77-79); LiRecDT1 (6,7,12,13,20,60); 3RLG (61); 3RLH (28); LiRecDT2 (7); LiRecDT5 (9); Lb3 (8,25); LiRecDT3 (7,10); and SMase II (26).…”

Whole venom of Loxosceles similis activates caspases-3, -6, -7, and -9 in human primary skin fibroblasts

“…In erythrocytes, phospholipase-D from the brown spider induces the metabolism of membrane phospholipids, such as sphingomyelin and lysophosphatidylcholine, generating bioactive products that stimulate calcium influx into red blood cells, mediated by L-type channels (Chaves-Moreira et al 2011). In human keratinocytes, Paixão-Cavalcante et al (2006) have shown that Loxosceles phospholipase-D induces apoptosis, associated with an increase in the expression of metalloproteinases-2 and -9.…”

Toxin Fused with SUMO Tag: A New Expression Vector Strategy to Obtain Recombinant Venom Toxins with Easy Tag Removal inside the Bacteria

“…As spiders produce a limited amount of venom, this system has been of extreme value to study interesting toxins with antiarrhythmic [8], antimicrobial [9], analgesic [10], insecticidal [11] and haemolytic activities [12]. Snake toxins have also been expressed into E. coli and this approach has allowed the characterization of toxins with anti-thrombotic [13], anticancer [14], anti-inflammatory [15], antimicrobial activities [16] as well as fused toxins for the development of serotherapy against envenomation [17].…”