Local anesthetics inhibit receptors coupled to phosphoinositide signaling in

Lysophosphatidic acid, a member of the acidic phospholipid autacoid (APA) family of lipid mediators, elicits diverse cellular effects that range from mitogenesis to the prevention of programmed cell death. Sphingosine 1-phosphate and sphingosylphosphorylcholine have also been proposed to be ligands of the APA receptors. However, key observations that provide the foundation of this hypothesis have not been universally reproducible, leading to a controversy in the field. We provide evidence that 1-O-cis-alk-1-enyl-2-lyso-sn-glycero-3-phosphate (alkenyl-GP) is present in some commercial sphingolipid preparations and is responsible for many of their APA-like effects, which were previously attributed to sphingosylphosphorylcholine. Alkenyl-GP was generated by acidic and basic methanolysis from ethanolamine lysoplasmalogen, which was present in the sphingomyelin fraction that is used to manufacture sphingosylphosphorylcholine. We present the structural identification of alkenyl-GP, using 1 H and 13 C NMR, Fourier transform infrared spectrometry, and mass spectrometry. Alkenyl-GP was a potent activator of the mitogen-activated protein kinases ERK1/2 and elicited a mitogenic response in Swiss 3T3 fibroblasts. In contrast, sphingosylphosphorylcholine at a concentration of 10 M was only a weak mitogen and only weakly activated the extracellular signal-regulated protein kinases. Alkenyl-GP has recently been detected as an injury-induced component in the anterior chamber of the eye (Liliom, K., Guan, Z., Tseng, H., Desiderio, D. M., Tigyi, G., and Watsky, M. (1998) Am. J. Physiol. 274, C1065-C1074), indicating that this lipid is a naturally occurring member of the APA mediator family.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Identification of a Novel Growth Factor-like Lipid, 1-O-cis-Alk-1′-enyl-2-lyso-sn-glycero-3-phosphate (Alkenyl-GP) That Is Present in Commercial Sphingolipid Preparations

Liliom¹,

Fischer²,

Virág³

et al. 1998

“…LPA also binds to albumin, but with a K d in the nanomolar range (30), where it is protected from degradation by phospholipases (40). Surprisingly, 41% of the LPC present in blood is the 1-lyso-2-acyl isomer; however, the half-life of sn2-acyl-LPC is only 8 min in plasma due to isomerization that yields the more stable sn1-acyl isomer (21).…”

Section: Figmentioning

confidence: 99%

Multiple Mechanisms Linked to Platelet Activation Result in Lysophosphatidic Acid and Sphingosine 1-Phosphate Generation in Blood

Sano¹,

Baker²,

Virág³

et al. 2002

242

239

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (Sph1P) production was examined in vitro under conditions that simulated blood clotting. Several approaches were utilized to elucidate the metabolic pathways. 1) Platelet phospholipids were labeled using [ 32 P]orthophosphate, and the production of [ 32 P]Sph1P and LPA was examined. Thrombin stimulation of platelets resulted in rapid secretion of Sph1P stored within the platelet. In contrast, LPA was neither stored within nor secreted from platelets. Nonetheless, extracellular levels of LPA gradually increased following stimulation. 2) Stable-isotope dilution mass spectrometry was used to quantify the molecular species of LPA generated from platelets in vitro. Only 10% of the LPA generated following thrombin stimulation was associated with platelets, the remaining 90% was contained within the extracellular medium. The acyl composition of LPA produced by platelets differed depending on the presence or absence of plasma in the incubation. 3) The fate of exogenously added fluorescent phospholipid analogs was determined. Incubation of [(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]dodecanoyl-(NBD)-labeled phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine with the supernatant fractions from thrombin-stimulated platelets yielded no LPA production. However, these lipids were converted to the corresponding lysolipids by released PLA 1 and PLA 2 activities. When incubated with plasma or serum the NBD-labeled lysophospholipids were readily converted to LPA. Inhibitors of lysophospholipase D and the biological activity of LPA were detected in plasma. These results suggest that the bulk of LPA produced through platelet activation results from the sequential cleavage of phospholipids to lysophospholipids by released phospholipases A 1 and A 2 and then to LPA by plasma lysophospholipase D.Lysophosphatidic acid (LPA) 1 and sphingosine 1-phosphate (Sph1P) are phospholipid mediators with pleiotropic growth factor properties that elicit their actions via the activation of G protein-coupled receptors encoded by the endothelial differentiation gene family (1, 2). Several investigators have identified platelets as the source of Sph1P and LPA. However, contradictions exist in the literature concerning the mechanisms by which these mediators are generated. Although some investigators found no Sph1P generation in thrombin-activated platelets (3), others reported as much as 0.5 M Sph1P in human serum (4). Although it is generally agreed that LPA is generated in thrombin-activated platelets (3, 5, 6), the rate of production found at 0.02 nmol/min/10 9 platelet cannot account for the 5-10 M concentration detected in human serum (7). During the first hour of blood clotting the concentration of LPA increases ϳ300 nM; however, its production continues and an additional 5 M is added to serum during the first 24 h, a time course that is hard to reconcile with that of platelet activation and consequently of platelet only origin. Gerrard and Robinson (6) quantified the molecul...

“…Bioactive LPA was initially found in culture serum (9) and was further detected in other biological fluids such as plasma (10,11), ascitic fluid (12), follicular fluid (13), aqueous humor (14), and the extracellular fluid of adipose tissue (5). Whereas serum LPA mainly originates from aggregating platelets (15,16), the precise cellular origin of LPA in other biological fluids still remains unclear.…”

mentioning

confidence: 99%

Autotaxin Is Released from Adipocytes, Catalyzes Lysophosphatidic Acid Synthesis, and Activates Preadipocyte Proliferation

Ferry

Tellier

Try

et al. 2003

215

201

Our group has recently demonstrated (Gesta, S., Simon, M., Rey, A., Sibrac, D., Girard, A., Lafontan, M., Valet, P., and Saulnier-Blache, J. S. (2002) J. Lipid Res. 43, 904 -910) the presence, in adipocyte conditioned-medium, of a soluble lysophospholipase D-activity (LPLDact) involved in synthesis of the bioactive phospholipid lysophosphatidic acid (LPA). In the present report, LPLDact was purified from 3T3F442A adipocyte-conditioned medium and identified as the type II ecto-nucleotide pyrophosphatase phosphodiesterase, autotaxin (ATX). A unique ATX cDNA was cloned from 3T3F442A adipocytes, and its recombinant expression in COS-7 cells led to extracellular release of LPLDact. ATX mRNA expression was highly up-regulated during adipocyte differentiation of 3T3F442A-preadipocytes. This up-regulation was paralleled by the ability of newly differentiated adipocytes to release LPLDact and LPA. Differentiation-dependent up-regulation of ATX expression was also observed in a primary culture of mouse preadipocytes. Treatment of 3T3F442A-preadipocytes with concentrated conditioned medium from ATX-expressing COS-7 cells led to an increase in cell number as compared with concentrated conditioned medium from ATX non-expressing COS-7 cells. The specific effect of ATX on preadipocyte proliferation was completely suppressed by co-treatment with a LPA-hydrolyzing phospholipase, phospholipase B. Finally, ATX expression was found in mature adipocytes isolated from mouse adipose tissue and was substantially increased in genetically obesediabetic db/db mice when compared with their lean siblings. In conclusion, the present work shows that ATX is responsible for the LPLDact released by adipocytes and exerts a paracrine control on preadipocyte growth via an LPA-dependent mechanism. Up-regulations of ATX expression with adipocyte differentiation and genetic obesity suggest a possible involvement of this released protein in the development of adipose tissue and obesity-associated pathologies.Because of its ability to store extra energy as triacylglycerol (lipogenesis) and to release fatty acids and glycerol (lipolysis), adipose tissue plays a crucial role in energy balance. In obesity, excessive accumulation of triacylglycerol in adipocytes (hypertrophy) results from an alteration in the balance between lipogenic and/or lipolytic activities of the adipocytes.It is now recognized that, beside their involvement in lipid homeostasis, adipocytes also produce and secrete numerous factors. Among them are endocrine peptides (leptin, adiponectin, angiotensinogen, etc.) which may play an important role in the development of morbid complications of obesity such as cardiovascular diseases, hypertension, diabetes, and cancer. Other adipocyte-secreted factors (tumor necrosis factor, fatty acids, eicosanoids, lysophosphatidic acid, etc.) are produced locally and may influence adipose tissue development and/or metabolism by exerting autocrine/paracrine effects on the different cells composing adipose tissue (adipocytes, preadipocytes, and endothelial...