Biologically active phospholipids as potential cardiovascular drugs

LPA receptor signaling: pharmacology, physiology, and pathophysiology

Lysophosphatidic acid (LPA) is a small ubiquitous lipid found in vertebrate and nonvertebrate organisms that mediates diverse biological actions and demonstrates medicinal relevance. LPA's functional roles are driven by extracellular signaling through at least six 7-transmembrane G protein-coupled receptors. These receptors are named LPA1-6 and signal through numerous effector pathways activated by heterotrimeric G proteins, including Gi/o, G12/13, Gq, and Gs LPA receptor-mediated effects have been described in numerous cell types and model systems, both in vitro and in vivo, through gain- and loss-of-function studies. These studies have revealed physiological and pathophysiological influences on virtually every organ system and developmental stage of an organism. These include the nervous, cardiovascular, reproductive, and pulmonary systems. Disturbances in normal LPA signaling may contribute to a range of diseases, including neurodevelopmental and neuropsychiatric disorders, pain, cardiovascular disease, bone disorders, fibrosis, cancer, infertility, and obesity. These studies underscore the potential of LPA receptor subtypes and related signaling mechanisms to provide novel therapeutic targets.

Radioligand competitive binding methodology for the evaluation of platelet-activating factor (PAF) and PAF-receptor antagonism using intact canine platelets

High-affinity, stereoselective, and ligand-selective specific binding of 3H-labeled platelet-activating factor (PAF) to its receptor on the dog platelet is reproducible over wide mass and concentration ranges of [3H]PAF. The [3H]PAF specific binding can be competitively inhibited by low picogram amounts of nonlabeled PAF. These observations have led to the formulation of radioligand competitive binding methodology for the detection and estimation of PAF in a biological lipid sample and the quantitative evaluation of PAF-receptor antagonism. The methodology is predicated upon correlation between the ability of a PAF analog/biological lipid sample/(synthetic) substance to inhibit [3H]PAF specific binding to the washed canine platelet and the known inhibition of [3H]PAF specific binding by standard, nonradioactive PAF. Application of this methodology to lipid extracts of human saliva has uncovered the finding that subjects with upper respiratory infection and chronic allergies have high saliva PAF contents. Pharmacologically active antiallergy agents known to inhibit PAF-induced pathology in animal models of disease were demonstrated, with the methology advanced, to act as PAF-receptor antagonists, and their potencies were quantified. These investigations indicate that the system proposed, in its ease, economy, sensitivity, specificity and capacity, has practical value for detecting and estimating PAF in biological lipid extracts and for evaluating PAF-receptor antagonism.

Specific binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor) to the intact canine platelet

Binding of 3H-labeled 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor; PAF) to the intact, washed canine platelet has been defined and characterized as being specific and receptor-mediated. Under the conditions described, specific binding to 2 X 10(7) canine platelets reached saturation within 10 min at a [3H]PAF concentration of approximately 0.4 nM. Non-specific binding was accountable for, at most, some 30% of the total PAF bound at equilibrium. Above approximately 0.4 nM [3H]PAF, total binding and non-specific binding increased in parallel. Since no involvement of PAF ligand in dog platelet intermediary metabolism during the binding incubation could be demonstrated, non-specific PAF binding may reflect a partitioning of the molecule into a cellular compartment (perhaps the platelet membranes). Equilibrium analysis revealed that the canine platelet has one class of specific binding sites with a Kd of 0.63 +/- 0.02 nM PAF, a Bmax of 222 +/- 10 fmol/10(7) platelets, and, at most, 1.33 +/- 0.06 X 10(3) binding sites/platelet. [3H]PAF specific binding to the canine platelet is ligand-selective and stereo-selective, as demonstrated by the relative abilities of non-labeled PAF and various PAF analogs/metabolites to inhibit [3H]PAF specific binding in a concentration-dependent manner. The extents to which PAF and PAF analogs were able to displace specifically-bound [3H]PAF from the canine platelet correlated well with their physiological (i. e., pro-aggregatory) effects. These data offer the first quantitative description of canine platelet high-affinity PAF binding sites/receptors and link receptor-mediated PAF binding to canine platelet physiology.