Platelet-activating factor downregulates the expression of liver X receptor-α and its target genes in human neutrophils.

Liver X receptors (LXRs) are ligand-activated members of the nuclear receptor superfamily that regulate the expression of genes involved in lipid metabolism and inflammation, although their role in inflammation and immunity is less well known. It has been reported that oxysterols/LXRs may act as anti-inflammatory molecules, although opposite actions have also been reported. In this study, we investigated the effect of platelet-activating factor (PAF), a proinflammatory molecule, on LXRα signalling in human neutrophils. We found that PAF exerted an inhibitory effect on mRNA expression of TO901317-induced LXRα, ATP-binding cassette transporter A1, ATP-binding cassette transporter G1, and sterol response element binding protein 1c. This negative action was mediated by the PAF receptor, and was dependent on the release of reactive oxygen species elicited by PAF, as it was enhanced by pro-oxidant treatment and reversed by antioxidants. Current data also support the idea that PAF induces phosphorylation of the LXRα molecule in an extracellular signal-regulated kinase 1/2-mediated fashion. These results suggest that a possible mechanism by which PAF exerts its proinflammatory effect is through the downregulation of LXRα and its related genes, which supports the notion that LXRα ligands exert a modulatory role in the neutrophil-mediated inflammatory response.

Stimulatory effect of allantoin on imidazoline I1 receptors in animal and cell line.

Allantoin is known as the agonist of imidazoline receptor, especially the I2 subtype. Effect of allantoin on imidazoline I1 receptor (I1R) relating to reduction of blood pressure and its merit in steatosis are still obscure. Also, farnesoid X receptor (FXR) plays an important role in lipid homeostasis related to I1R activation. Thus, we administered allantoin into high fat diet (HFD)-fed mice showing hypertriglyceridemia and hypercholesterolemia. Allantoin significantly improved hyperlipidemia in HFD mice after 4 weeks of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I1R activation, attenuated the action of allantoin. In addition, in cultured HepG2 cells, allantoin increased the expression of farnesoid X receptor (FXR). The allantoin-induced FXR expression was blocked by efaroxan. Similar changes were observed in the expressions of FXR-targeted genes. Otherwise, allantoin also lowered systolic blood pressure (SBP) in HFD mice that can be blocked by efaroxan. Taken together, allantoin has an ability to activate I1R for improvement of metabolic disorders.

Inhibition of human organic anion transporter 3 mediated pravastatin transport by gemfibrozil and the metabolites in humans.

Coadministration of gemfibrozil (600 mg, b.i.d., 3 days) with pravastatin (40 mg/day) decreased the renal clearance of pravastatin by approximately 40% in healthy volunteers. To investigate the mechanism of this drug-drug interaction in the renal excretion process, we undertook an uptake study of pravastatin using human organic anion transporters (hOATs)-expressing S2 cells. hOAT3 and hOAT4 transported pravastatin in a saturatable manner with Michaelis--Menten constants of 27.7 microM and 257 microM respectively. On the other hand, hOAT1 and hOAT2 did not transport pravastatin. Gemfibrozil and its glucuronide and carboxylic metabolite forms inhibited the uptake of pravastatin by hOAT3 with IC(50) values of 6.8 microM, 19.7 microM and 5.4 microM, respectively. Considering the plasma concentrations of gemfibrozil and its metabolites in humans, the inhibition of hOAT3-mediated pravastatin transport by gemfibrozil and its metabolites would lead to a decrease in the renal clearance of pravastatin in clinical settings.

Dietary phytosterols reduce probucol-induced atherogenesis in apo E-KO mice.

We have previously shown strong pro-atherogenic effects of probucol in apolipoprotein E-knockout (apo E-KO) mice. The aims of the present study were to investigate whether (a) dietary phytosterols reduce probucol-induced atherogenesis and (b) beneficial interactions exist between these agents. Male apo E-KO mice fed with an atherogenic diet supplemented with phytosterols or probucol or their combination for 14 weeks. Single therapy with either phytosterols or probucol resulted in a 25% reduction in plasma total cholesterol (TC) concentrations as compared to the control group. The effects of the combination therapy were more profound (60% reduction). While phytosterols reduced atherogenesis by 60%, probucol caused an increase of 150% in atherogenesis. Addition of phytosterols to probucol substantially reduced pro-atherogenic effects of probucol. This was associated with improved high density lipoprotein (HDL) concentrations. The ratio of TC to HDL cholesterol was markedly reduced in the combination therapy group as compared to the probucol-treated group. A strong positive association between the ratio of TC to HDL cholesterol and the extent of atherosclerotic lesions was observed. The coronary arteries of the probucol-treated group showed various stages of atherogenesis from infiltration of monocytes into intima to complete occlusion of the vessel by atheromatous lesions. Such pathological findings were not observed in the combination therapy group. Approximately 40% of the mice in the probucol-treated group and 10% of the animals in the combination therapy group developed skin lesions. Further studies warrant the investigation of the underlying mechanisms of the observed beneficial interactions between dietary phytosterols and probucol.

Inhibition of in-vitro simvastatin metabolism in rat liver microsomes by bergamottin, a component of grapefruit juice.

Grapefruit juice can modify the pharmacokinetic parameters of many drugs, in particular simvastatin, an orally active cholesterol-lowering agent. The exact components in grapefruit juice responsible for drug interactions are not perfectly known. However, it seems that bergamottin, a furocoumarin derivative, is one of the main active components within grapefruit juice. The objective of this paper was to quantify and to characterize in-vitro the inhibitory effect of bergamottin on simvastatin metabolism by using rat and human liver microsomes. In rat liver microsomes, the incubation conditions (+/-NADPH) of bergamottin were found to influence its inhibiting capacity. In co-incubation with simvastatin, the Ki value (the equilibrium dissociation constant for the enzyme-inhibitor complex) was higher (Ki = 174 +/- 36 microM) than in pre-incubation (Ki = 45 +/- 6 microM and 4 +/- 2 microM, without and with NADPH, respectively). It thus seems that the pre-incubation of bergamottin (in particular with NADPH) increases its inhibiting capacity on simvastatin metabolism. Bergamottin metabolism study in rat liver microsomes showed the formation of two metabolites that were CYP-450 dependent. In contrast, in human liver microsomes, the incubation conditions of bergamottin did not influence its inhibiting capacity of simvastatin metabolism (Ki = 34 +/- 5 microM, Ki = 22 +/- 5 microM, Ki = 27 +/- 11 microM in coincubation and pre-incubation without and with NADPH, respectively). In rat and man, bergamottin was found to be a mixed-type inhibitor of simvastatin hepatic metabolism. However, in rat, bergamottin was partially a mechanism-based inhibitor by involvement of either bergamottin alone or one of its metabolites. The results highlight the importance of validating in-vitro models to help verify the suitability of the in-vitro model for predicting the nature and degree of metabolic drug interactions.

Effect of pravastatin on myocardial protection during coronary angioplasty and the role of adenosine.

Pravastatin has been shown, in an experimental model of ischemia reperfusion, to increase adenosine levels, which exert a potent and protective effect on the heart. The purpose of this study was to investigate whether pravastatin can provide cardioprotection by increased production of adenosine in patients undergoing coronary angioplasty, a clinical model of ischemia reperfusion. Thirty-five hyperlipidemic patients who underwent elective angioplasty for a major epicardial coronary artery were randomly allocated to either 3-month pravastatin or placebo before catheterization. In the placebo group, the mean ST-segment shift during the second balloon inflation was similar that observed during the first inflation, whereas in the preconditioned patients, the shift was significantly less, which is consistent with ischemic preconditioning. In the pravastatin-treated patients, the changes of ST-segment shift were similar between the first and second balloon inflations. In contrast, the patients who received aminophylline developed higher ST-segment shifts during the first and second inflations than those in the pravastatin-treated group alone. Measurements of chest pain score and myocardial lactate extraction ratios during inflation mirrored those of the ST-segment shift. The present study demonstrates that administration of pravastatin results in a significant gain in tolerance to ischemia during angioplasty. The effect of pravastatin was abolished by aminophylline, suggesting that the cardioprotective effect of pravastatin may result from activation of adenosine receptors.

Paraoxonase genotype modifies the effect of pravastatin on high-density lipoprotein cholesterol.

Paraoxonase (PON) is an enzyme carried by high-density lipoprotein cholesterol (HDL-C). Two gene polymorphisms leading to amino acid substitutions of methionine for leucine at position 55 (M/L55) and arginine for glutamine at position 192 (R/Q192) modulate the activity of the enzyme and possibly also lipid and apolipoprotein concentrations. Our purpose was to examine the effect of the PON genotype on HDL-C and apolipoprotein AI (apo AI) responses to pravastatin treatment. Fifty-one mildly hypercholesterolemic male subjects (mean age 35 +/- 4 years) were enrolled by this prospective, randomized, double-blind study. Lipid concentrations were measured at baseline and after 6 months of pravastatin (n = 25) or placebo (n = 26) therapy. Low active (MM, ML or QQ) and high active (LL or RQ, RR) PON genotype groups were related to lipid and apolipoprotein concentration changes. Pravastatin increased the apo AI concentration 12% (P = 0.017, RANOVA) and tended to increase the HDL-C concentration (P = 0.095, RANOVA) in R allele carriers but not in QQ homozygotes. Significant predictors of the change in apo AI concentration during pravastatin treatment were R/Q192 genotype (P = 0.002), apo AI concentration at baseline (P = 0.002) and M/L55 genotype (P = 0.042). Correspondingly, R/Q192 (P = 0.009) and M/L55 (P = 0.050) genotypes were the statistically significant determinants of HDL-C concentration change. The PON genotype thus modifies the effect of pravastatin on serum HDL-C and apo AI concentrations. This could partly explain the contradictory results obtained from previous studies on the effects of statins on the serum HDL-C concentration.

Alpha1-adrenoreceptor stimulation causes vascular smooth muscle cell hypertrophy: a possible role for isoprenoid intermediates.

We investigated whether contraction-induced agonists such as alpha1-adrenoceptor agonists are important regulators of smooth muscle cell hypertrophy by examining the effects of one potent agonists, phenylephrine, on the hypertrophy. Under the experimental conditions used, we found that phenylephrine was potent in inducing alpha1-adrenoreceptor-dependent hypertrophy of vascular smooth muscle cells as defined by increased incorporation of [14C]leucine in a dose-dependent fashion. Further, we assessed the effect of lovastatin, an 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on hypertrophy of cultured vascular smooth muscle cells as defined by the increased incorporation of [14C]leucine caused by phenylephrine. Lovastatin (5-15 microM) caused a significant dose-dependent reduction in [14C]leucine incorporation which was completely prevented in the presence of exogenous mevalonate (100 microM). Exogenous low density lipoprotein (100 microg/ml) and cholesterol (15 microg/ml) did not prevent lovastatin inhibition of [14C]leucine incorporation. In contrast, the isoprenoid farnesol largely prevented inhibition of [14C]leucine incorporation by the lovastatin. We conclude that mevalonate metabolites are essential for phenylephrine-induced smooth muscle cell hypertrophy, possibly through the production of the isoprenoid farnesol.

2-Substituted-3-pyridinolethers as hypolipidemic and platelet aggregation inhibiting agents.

Some 2-substituted 3-pyridinolethers were synthesized, with one side chain bearing a carboxylic function; among these there are products having structure analogies with the prostaglandins. The results of hypolipidemic and hypocholesterolemic tests on experimental hyperdyslipidemic animals, as well as those on the inhibition of platelets aggregation and on fibrinolytic activity are reported.