No abstract

The pulmonary surfactant phospholipid, palmitoyloleoylphosphatidylglycerol (POPG), inhibits TLR2 and TLR4 signaling from the cell surface of macrophages. In this study we sought to develop structural analogs of POPG that vary in polar head group length, hydroxylation and alkyl branching, as novel compounds for suppressing the TLR inflammatory responses. These analogs were synthesized using a transphosphatidylation reaction. Analogs of POPG with C3 and C4 alkyl head group length (POP‐PROPANOL and POP‐BUTANOL) are less effective than POPG as TLR2 and TLR4 antagonists. However, adding a hydroxyl group at the alkyl chain 2, 3 or 4‐position (POP‐PROPANEDIOLS or POP‐BUTANEDIOLS) restored their inhibitory effects against TLR2 and TLR4 agonists. Interestingly, analogs with C1 and C2 alkyl head group length (POP‐METHANOL and POP‐ETHANOL) were effective as LPS antagonists. POP‐DIMETHYLPROPANEDIOL contains 2 methyl groups at the head group alkyl 2 position; and this analog is effective for inhibition of an LPS stimulus. However, it is a weak inhibitor of MALP‐2 induced AA release. Addition of amino group at the alkyl 2 position (POP‐SERINOL) completely abolished the potency of analogs. Collectively, these findings identify new compounds for antagonizing TLR2 and TLR4 activation and define structural properties for discriminating between the two receptor systems. NIH‐HL094629, COLORADO C2D2.

RATIONALE Structural analogs of the bioactive lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol, were synthesized with a xylitol polar headgroup and both diacyl and diether radyl groups. Mass spectral characterization of xylitol phospholipids (PX) was carried out using collisional activation and high resolution mass measurements of positive molecular ion species and compared with the phosphatidylglycerol (PG) analogs. METHODS Xylitol phospholipids were synthesized using a transphosphatidylation reaction catalyzed by phospholipase D and purified by HPLC. Compounds were subjected to electrospray ionization and CID was performed using a tandem quadrupole mass spectrometer to generate positive and negative molecular ions. Diether phospholipids were additionally analyzed by high resolution mass spectrometry as protonated and sodiated molecular species in positive ion mode. RESULTS Ester linked xylitol phospholipid analogs behaved similar to PG after collisional activation of [M-H]−. The product ions formed by CID of the diether PG and PX negative ions only revealed information about the headgroup with no information about the aliphatic chains. In contrast, CID of protonated and sodiated diether phospholipid positive ions, revealed reactions corresponding to cleavage of the ether chain, likely occurring by charge driven reaction mechanisms. CONCLUSIONS Novel xylitol phospholipid analogs with diacyl and diether radyl substituents of the glycerol backbone were characterized by tandem mass spectrometry. These unique diether phospholipid analogs enabled exploration of ether cleavage reactions of the positive molecular ion species induced by collision induced decomposition.