The Lysophosphatidic Acid Type 2 Receptor Is Required for Protection Against Radiation-Induced Intestinal Injury

Background & Aims: We recently identified lysophosphatidic acid (LPA) as a potent antiapoptotic agent for the intestinal epithelium. The objective of the present study was to evaluate the effect of octadecenyl thiophosphate (OTP), a novel rationally designed, metabolically stabilized LPA mimic, on radiation-induced apoptosis of intestinal epithelial cells in vitro and in vivo. Methods: The receptors and signaling pathways activated by OTP were examined in IEC-6 and RH7777 cell lines and wild-type and LPA1 and LPA2 knockout mice exposed to different apoptotic stimuli. Results: OTP was more efficacious than LPA in reducing gamma irradiation-, camptothecin-, or tumor necrosis factor α/cycloheximide-induced apoptosis and caspase-3-8, and caspase-9 activity in the IEC-6 cell line. In RH7777 cells lacking LPA receptors, OTP selectively protected LPA2 but not LPA1 and LPA3 transfectants. In C57BL/6 and LPA1 knockout mice exposed to 15 Gy gamma irradiation, orally applied OTP reduced the number of apoptotic bodies and activated caspase-3-positive cells but was ineffective in LPA2 knockout mice. OTP, with higher efficacy than LPA, enhanced intestinal crypt survival in C57BL/6 mice but was without any effect in LPA2 knockout mice. Intraperitoneally administered OTP reduced death caused by lethal dose (LD)100/30 radiation by 50%. Conclusions: Our data indicate that OTP is a highly effective antiapoptotic agent that engages similar prosurvival pathways to LPA through the LPA2 receptor subtype. © 2007 AGA Institute

Fatty alcohol phosphates are subtype-selective agonists and antagonists of lysophosphatidic acid receptors

A more complete understanding of the physiological and pathological role of lysophosphatidic acid (LPA) requires receptor subtype-specific agonists and antagonists. Here, we report the synthesis and pharmacological characterization of fatty alcohol phosphates (FAP) containing saturated hydrocarbon chains from 4 to 22 carbons in length. Selection of FAP as the lead structure was based on computational modeling as a minimal structure that satisfies the two-point pharmacophore developed earlier for the interaction of LPA with its receptors. Decyl and dodecyl FAPs (FAP-10 and FAP-12) were specific agonists of LPA2 (EC50 = 3.7 ± 0.2 μM and 700 ± 22 nM, respectively), yet selective antagonists of LPA3 (Ki = 90 nM for FAP-12) and FAP-12 was a weak antagonist of LPA1. Neither LPA1 nor LPA3 receptors were activated by FAPs; in contrast, LPA2 was activated by FAPs with carbon chains between 10 and 14. Computational modeling was used to evaluate the interaction between individual FAPs (8 to 18) with LPA2 by docking each compound in the LPA binding site. FAP-12 displayed the lowest docked energy, consistent with its lower observed EC50. The inhibitory effect of FAP showed a strong hydrocarbon chain length dependence with C12 being optimum in the Xenopus laevis oocytes and in LPA3-expressing RH7777 cells. FAP-12 did not activate or interfere with several other G-protein-coupled receptors, including S1P-induced responses through S1P1.2,3.5 receptors. These data suggest that FAPs are ligands of LPA receptors and that FAP-10 and FAP-12 are the first receptor subtype-specific agonists for LPA2

Synthesis and pharmacological evaluation of second-generation phosphatidic acid derivatives as lysophosphatidic acid receptor ligands

Short-chain phosphatidic acid derivatives, dioctanoyl glycerol pyrophosphate (DGPP 8:0, 1) and phosphatidic acid 8:0 (PA 8:0, 2), were previously identified as subtype-selective LPA1 and LPA3 receptor antagonists. Recently, we reported that the replacement of the phosphate headgroup by thiophosphate in a series of fatty alcohol phosphates (FAP) improves agonist as well as antagonist activities at LPA GPCR. Here, we report the synthesis of stereoisomers of PA 8:0 analogs and their biological evaluation at LPA GPCR, PPARγ, and ATX. The results indicate that LPA receptors stereoselectively interact with glycerol backbone modified ligands. We observed entirely stereospecific responses by dioctyl PA 8:0 compounds, in which (R)-isomers were found to be agonists and (S)-isomers were antagonists of LPA GPCR. From this series, we identified compound 13b as the most potent LPA3 receptor subtype-selective agonist (EC50 = 3 nM), and 8b as a potent and selective LPA3 receptor antagonist (Ki = 5 nM) and inhibitor of ATX (IC50 = 600 nM). Serinediamide phosphate 19b was identified as an LPA3 receptor specific antagonist with no effect on LPA1, LPA2, and PPARγ. © 2005 Elsevier Ltd. All rights reserved