(E)-Phenyl- and -heteroaryl-substituted O-benzoyl-(or acyl)oximes as lipoprotein-associated phospholipase A2 inhibitors

Lipoprotein-associated phospholipase A2: The story continues

Inflammation is thought to play an important role in the pathogenesis of vascular diseases. Lipoprotein-associated phospholipase A2 (Lp-PLA2) mediates vascular inflammation through the regulation of lipid metabolism in blood, thus, it has been extensively investigated to identify its role in vascular inflammation-related diseases, mainly atherosclerosis. Although darapladib, the most advanced Lp-PLA2 inhibitor, failed to meet the primary endpoints of two large phase III trials in atherosclerosis patients cotreated with standard medical care, the research on Lp-PLA2 has not been terminated. Novel pathogenic, epidemiologic, genetic, and crystallographic studies regarding Lp-PLA2 have been reported recently, while novel inhibitors were identified through a fragment-based lead discovery strategy. More strikingly, recent clinical and preclinical studies revealed that Lp-PLA2 inhibition showed promising therapeutic effects in diabetic macular edema and Alzheimer's disease. In this review, we not only summarized the knowledge of Lp-PLA2 established in the past decades but also emphasized new findings in recent years. We hope this review could be valuable for helping researchers acquire a much deeper insight into the nature of Lp-PLA2, identify more potent and selective Lp-PLA2 inhibitors, and discover the potential indications of Lp-PLA2 inhibitors.

Beckmann Rearrangement of Ketoxime Catalyzed by N-methyl-imidazolium Hydrosulfate

Beckmann rearrangement of ketoxime catalyzed by acidic ionic liquid-N-methyl-imidazolium hydrosulfate was studied. Rearrangement of benzophenone oxime gave the desirable product with 45% yield at 90 °C. When co-catalyst P₂O₅ was added, the yield could be improved to 91%. The catalyst could be reused three cycles with the same efficiency. Finally, reactions of other ketoximes were also investigated.

pCRP-mCRP Dissociation Mechanisms as Potential Targets for the Development of Small-Molecule Anti-Inflammatory Chemotherapeutics

Circulating C-reactive protein (CRP) is a key acute-phase protein and one of the main clinical biomarkers for inflammation and infection. CRP is an important upstream mediator of inflammation and is associated with the onset of a number of important disease states including cardiovascular disease and neurodegenerative disorders such as Alzheimer’s disease. This pentraxin exerts pro-inflammatory properties via dissociation of the pentamer (pCRP) to a monomeric form (mCRP). This dissociation is induced by binding of pCRP to cell surface phosphocholine residues exposed by the action of phospholipase A₂ (PLA₂). Given the association of CRP with the onset of a range of serious disease states this CRP dissociation process is a tempting drug target for the development of novel small-molecule therapeutics. This review will discuss potential targets for chemotherapeutic intervention elucidated during studies of CRP-mediated inflammation and provide an up-to-date summary of the development of small molecules, not only targeted directly at inhibiting conversion of pCRP to mCRP, but also those developed for activity against PLA₂, given the key role of this enzyme in the activation of CRP.

Structure-Guided Discovery of Novel, Potent, and Orally Bioavailable Inhibitors of Lipoprotein-Associated Phospholipase A2

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a promising therapeutic target for atherosclerosis, Alzheimer's disease, and diabetic macular edema. Here we report the identification of novel sulfonamide scaffold Lp-PLA2 inhibitors derived from a relatively weak fragment. Similarity searching on this fragment followed by molecular docking leads to the discovery of a micromolar inhibitor with a 300-fold potency improvement. Subsequently, by the application of a structure-guided design strategy, a successful hit-to-lead optimization was achieved and a number of Lp-PLA2 inhibitors with single-digit nanomolar potency were obtained. After preliminary evaluation of the properties of drug-likeness in vitro and in vivo, compound 37 stands out from this congeneric series of inhibitors for good inhibitory activity and favorable oral bioavailability in male Sprague-Dawley rats, providing a quality candidate for further development. The present study thus clearly demonstrates the power and advantage of integrally employing fragment screening, crystal structures determination, virtual screening, and medicinal chemistry in an efficient lead discovery project, providing a good example for structure-based drug design.

Discovery of Potent and Orally Active Lipoprotein-Associated Phospholipase A2 (Lp-PLA2) Inhibitors as a Potential Therapy for Diabetic Macular Edema

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is considered to be a promising therapeutic target for several inflammation-associated diseases. Herein, we describe the discovery of a series of pyrimidone derivatives as Lp-PLA2 inhibitors. Systematic structural modifications led to the identification of several pyrimidone compounds with promising in vitro inhibitory potency and pharmacokinetic properties. Compound 14c, selected for in vivo evaluation, demonstrated decent pharmacokinetic profiles and robust inhibitory potency against Lp-PLA2 in Sprague-Dawley (SD) rats. Furthermore, 14c significantly inhibited retinal thickening in STZ-induced diabetic SD rats as a model of diabetic macular edema (DME) after oral dosing for 4 weeks. Taken together, these results suggested that 14c can serve as a valuable lead in the search for new Lp-PLA2 inhibitors for prevention and/or treatment of DME.

Effects of A379V variant of the Lp-PLA 2 gene on Lp-PLA 2 activity and markers of oxidative stress and endothelial function in Koreans

A379V variant in the lipoprotein-associated phospholipase A2 (Lp-PLA 2) gene is known to be functional, but there are contradicting data concerning the A379V polymorphism, Lp-PLA2 activity and cardiovascular disease risk. We determined the interplay between A379V SNP, Lp-PLA2 activity, and markers of oxidative stress and endothelial function with and without the effect of V279F variant. 3,220 unrelated and healthy Koreans (40-79 years) were genotyped for the Lp-PLA 2 polymorphism (A379V and V279F). Lp-PLA2 activity and markers of oxidative stress and endothelial function were measured. Lp-PLA2 activity was 3.9% higher in A/V subjects (n = 821) and 7.8% in V/V (n = 79) than in those with A/A (n = 2,320). Urinary levels of 8-epi-PGF2α were significantly lower in subjects with the A/V or the V/V genotype than in those with the A/A genotype (A/A; 1,426 ± 14, A/V; 1,371 ± 26, V/V; 1,199 ± 58 pg/mg creatinine, P = 0.003). Subjects with the 379 V/V genotype had lower serum concentrations of sICAM-1 and p-selectin compared to those with the A/A or the A/V genotype. When subjects were further stratified into subgroups based on the combination of A379V and V279F genotypes, there was no significant association between A379V genotypes and Lp-PLA2 activities in the 279 V/V group. However, the associations of the A379V SNP with levels of 8-epi-PGF2α, sICAM-1, and p-selectin remained in the subset analysis based on the V279F genotypes. This study showed a reduction in oxidative stress in subjects carrying 379V allele and the recessive effect of the A379V on the endothelial function. It is likely that the A379V polymorphism has a qualitative effect, probably by disrupting the affinity of Lp-PLA2 for platelet-activating factor substrate, towards a more anti-oxidative or anti-atherogenic form.

The association of specific metabolites of lipid metabolism with markers of oxidative stress, inflammation and arterial stiffness in men with newly diagnosed type 2 diabetes

OBJECTIVE

To determine whether circulating metabolic intermediates are associated with inflammation, oxidative stress and arterial stiffness in men with newly diagnosed type 2 diabetes and investigate the circulating metabolic intermediates that may predict the risk of developing diabetes.

RESEARCH DESIGN AND METHODS

Men with newly diagnosed type 2 diabetes (n = 26) and age- and body mass index-matched nondiabetic men (n = 27) were included. We measured inflammatory and oxidative markers and arterial stiffness by brachial-ankle pulse wave velocity (ba-PWV). Metabolomic profiling was analysed with ultra performance liquid chromatography and quadrupole time-of-flight mass spectrometry.

RESULTS

Diabetic men showed higher circulating levels of glucose, triglyceride, oxidized low-density lipoprotein (LDL), high-sensitivity C-reactive protein, interleukin (IL)-6, tumour necrosis factor-alpha (TNF-α), homeostasis model assessment-insulin resistance, urinary 8-epi-prostaglandin F(2α) (8-epi-PGF(2α)) and ba-PWV than nondiabetic men. In plasma, 19 metabolites including three amino acids, eight acylcarnitines, six lysophosphatidylcholines (lysoPCs), and two lysophosphatidylethanolamines (lysoPEs; C18:2 and C22:6) significantly increased in diabetes men, whereas serine and lysoPE (C18:1) decreased. Decanoyl carnitine, lysoPCs (C14:0, C16:1, C18:1 and C22:6) and lysoPE (C18:1) with variable importance in the projection values >1·0 were major plasma metabolites that distinguished nondiabetic and diabetic men. Decanoyl carnitine positively correlated with oxidized LDL, 8-epi-PGF(2α), IL-6, TNF-α and ba-PWV. ba-PWV correlated positively with lysoPCs C14:0 and C16:1, and negatively with lysoPE C18:1. 8-epi-PGF(2α) correlated positively with lipoprotein-associated phospholipase A(2), ba-PWV and lysoPCs (C14:0 and C16:1). The receiver operating characteristic curve estimation suggested that decanoyl carnitine and lysoPC (C14:0) are the best metabolites for predicting the risk of developing diabetes.

CONCLUSIONS

Circulating lipid-related intermediate metabolites can be closely associated with inflammation, oxidative stress and arterial stiffness in early diabetes.

The Val279Phe variant of the lipoprotein-associated phospholipase A2 gene is associated with catalytic activities and cardiovascular disease in Korean men

CONTEXT AND OBJECTIVE

It is unclear whether lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) exerts a pro- or antiatherogenic effect on cardiovascular disease (CVD). We investigated the association between Lp-PLA(2) variant (V279F and A379V) and CVD in Korean men.

DESIGN

CVD patients (n = 532) and healthy controls (n = 670) were genotyped for the Lp-PLA(2) polymorphism (V279F and A379V).

MAIN OUTCOME MEASURES

We calculated odds ratio (OR) on CVD risk and measured anthropometries, lipid profiles, low-density lipoprotein (LDL) particle size, oxidized LDL, lipid peroxides, and Lp-PLA(2) activity.

RESULTS

The presence of the 279F allele was associated with a lower risk of CVD [OR 0.646 (95% confidence interval 0.490-0.850), P = 0.002], and the association still remained after adjustments for age, body mass index, waist circumference, waist to hip ratio, cigarette smoking, and alcohol consumption [OR 0.683 (95% confidence interval 0.512-0.911), P = 0.009]. Lp-PLA(2) activity was lower in CVD patients taking a lipid-lowering drug (31%), those not taking a lipid-lowering drug (26%), and control subjects (23%) with the V/F genotype, compared with those with the V/V genotype. Subjects with the F/F genotype in controls and two CVD patients groups showed no appreciable enzymatic activity. Control subjects with the V/F genotype had larger LDL particle size than those with the V/V genotype. In addition, control subjects carrying the F allele showed lower malondialdehyde concentrations. On the other hand, we found no significant relationship between A379V genotype and CVD risk.

CONCLUSIONS

The association of the F279 loss of function variant with the reduced risk of CVD supports the concept that Lp-PLA(2) plays a proatherogenic and causative role in CVD.

Potent inhibitors of lipoprotein-associated phospholipase A(2): benzaldehyde O-heterocycle-4-carbonyloxime

A series of multi-substituted oximes were prepared and their potencies for inhibiting lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) activity were evaluated in vitro. Among them, compounds 3a, 3b, and 3m were identified to display a micromolar potency for inhibiting Lp-PLA(2) in whole human plasma and isolated human LDL. Based on these results, structure-activity relationship was studied on modification of three parts of R(1), R(2), and R(3) to identify a potent pharmacophore for Lp-PLA(2). In an attempt to introduce various functional groups at R(2) and R(3), we discovered that replacement of less lipophilic groups led to an increase of inhibitory activity. Among the tested oxime derivatives, cyano- and morpholino-substituted analogue 4f at R(2) and R(3) had the highest potency with an IC(50) value of 0.05 microM in whole human plasma.

Lp-PLA2 inhibitory activities of fatty acid glycerols isolated from Saururus chinensis roots

(R)-Glycerol-monolinoleate 4 and (R)-glycerol-monostearate 5 were isolated from the ethyl acetate extracts of Saururus chinensis roots and (R)- or (S)-fatty acid glycerols 4 and 5 were synthesized for confirming their structures and evaluating their inhibitory activities against Lp-PLA(2). The (R)-4 and (S)-4 exhibited Lp-PLA(2) inhibitory activities with IC(50) values of 45.0 and 52.0 microM, respectively.