Fibrates

Oleuropein-Induced Acceleration of Cytochrome P450-Catalyzed Drug Metabolism: Central Role for Nuclear Receptor Peroxisome Proliferator-Activated Receptor α

Oleuropein (OLE), the main constituent of Olea europaea, displays pleiotropic beneficial effects in health and disease, which are mainly attributed to its anti-inflammatory and cardioprotective properties. Several food supplements and herbal medicines contain OLE and are available without a prescription. This study investigated the effects of OLE on the main cytochrome P450s (P450s) catalyzing the metabolism of many prescribed drugs. Emphasis was given to the role of peroxisome proliferator-activated receptor α (PPARα), a nuclear transcription factor regulating numerous genes including P450s. 129/Sv wild-type and Ppara-null mice were treated with OLE for 6 weeks. OLE induced Cyp1a1, Cyp1a2, Cyp1b1, Cyp3a14, Cyp3a25, Cyp2c29, Cyp2c44, Cyp2d22, and Cyp2e1 mRNAs in liver of wild-type mice, whereas no similar effects were observed in Ppara-null mice, indicating that the OLE-induced effect on these P450s is mediated by PPARα. Activation of the pathways related to phosphoinositide 3-kinase/protein kinase B (AKT)/forkhead box protein O1, c-Jun N-terminal kinase, AKT/p70, and extracellular signal-regulated kinase participates in P450 induction by OLE. These data indicate that consumption of herbal medicines and food supplements containing OLE could accelerate the metabolism of drug substrates of the above-mentioned P450s, thus reducing their efficacy and the outcome of pharmacotherapy. Therefore, OLE-induced activation of PPARα could modify the effects of drugs due to their increased metabolism and clearance, which should be taken into account when consuming OLE-containing products with certain drugs, in particular those of narrow therapeutic window. SIGNIFICANCE STATEMENT: This study indicated that oleuropein, which belongs to the main constituents of the leaves and olive drupes of Olea europaea, induces the synthesis of the major cytochrome P450s (P450s) metabolizing the majority of prescribed drugs via activation of peroxisome proliferator-activated receptor α. This effect could modify the pharmacokinetic profile of co-administered drug substrates of the P450s, thus altering their therapeutic efficacy and toxicity.

Fenofibrate, a peroxisome proliferator-activated receptor-alpha agonist, blocks steatosis and alters the inflammatory response in a mouse model of inflammation-dioxin interaction

2,3,7,8-Tetrachlorodibenzo-p-dioxin (dioxin; TCDD) is an environmental contaminant that elicits a variety of toxic effects, many of which are mediated through activation of the aryl hydrocarbon receptor (AhR). Interaction between AhR and the peroxisome proliferator-activated receptor-alpha (PPAR-α), which regulates fatty acid metabolism, has been suggested. Furthermore, with recognition of the prevalence of inflammatory conditions, there is current interest in the potential for inflammatory stress to modulate the response to environmental agents. The aim of this work was to assess the interaction of TCDD with hepatic inflammation modulated by fenofibrate, a PPAR-α agonist. Female, C57BL/6 mice were treated orally with vehicle or fenofibrate (250 mg/kg) for 13 days, and then were given vehicle or 30 μg/kg TCDD. Four days later, the animals received an i.p. injection of lipopolysaccharide-galactosamine (LPS-GalN) (0.05x10⁷ EU/kg and 500 mg/kg, respectively) to incite inflammation, or saline as vehicle control. After 4 h, the mice were euthanized, and blood and liver samples were collected for analysis. Livers of animals treated with TCDD with or without LPS-GalN had increased lipid deposition, and this effect was blocked by fenofibrate. In TCDD/LPS-GalN-treated mice, fenofibrate caused an increase in plasma activity of alanine aminotransferase, a marker of hepatocellular injury. TCDD reduced LPS-GalN-induced apoptosis, an effect that was prevented by fenofibrate pretreatment. LPS-GalN induced an increase in the concentration of interleukin-6 in plasma and accumulation of neutrophils in liver. TCDD exposure enhanced the former response and inhibited the latter one. These results suggest that fenofibrate counteracts the changes in lipid metabolism induced by TCDD but increases inflammation and liver injury in this model of inflammation-TCDD interaction.

The olive constituent oleuropein, as a PPARα agonist, markedly reduces serum triglycerides

Oleuropein (OLE), a main constituent of olive, exhibits antioxidant and hypolipidemic effects, while it reduces the infarct size in chow- and cholesterol-fed rabbits. Peroxisome proliferator-activated receptor α (PPARα) has essential roles in the control of lipid metabolism and energy homeostasis. This study focused on the mechanisms underlying the hypolipidemic activity of OLE and, specifically, on the role of PPARα activation in the OLE-induced effect. Theoretical approach using Molecular Docking Simulations and luciferase reporter gene assay indicated that OLE is a ligand of PPARα. The effect of OLE (100 mg/kg, p.o., per day, ×6 weeks) on serum triglyceride (TG) and cholesterol levels was also assessed in adult male wild-type and Ppara-null mice. Molecular Docking Simulations, Luciferase reporter gene assay and gene expression analysis indicated that OLE is a PPARα agonist that up-regulates several PPARα target genes in the liver. This effect was associated with a significant reduction of serum TG and cholesterol levels. In contrast, OLE had no effect in Ppara-null mice, indicating a direct involvement of PPARα in the OLE-induced serum TG and cholesterol reduction. Activation of hormone-sensitive lipase in the white adipose tissue (WAT) and the liver of wild-type mice and up-regulation of several hepatic factors involved in TG uptake, transport, metabolism and clearance may also contribute in the OLE-induced TG reduction. In summary, OLE has a beneficial effect on TG homeostasis via PPARα activation. OLE also activates the hormone sensitive lipase in the WAT and liver and up-regulates several hepatic genes with essential roles in TG homeostasis.

The effect of fenofibrate on cardiometabolic risk factors in bromocriptine-treated women with mixed dyslipidemia: A pilot study

BACKGROUND

Elevated prolactin levels are associated with metabolic and hormonal complications. No previous study has investigated the effect of any fibrate on plasma levels of lipids and other cardiometabolic risk factors in patients receiving dopamine agonist therapy.

METHODS

The study included 36 premenopausal women with mixed dyslipidemia and slightly increased prolactin levels, 17 of whom had already been treated with bromocriptine (5.0-7.5mg daily). The included patients received micronized fenofibrate (200mg daily) for 6 months. Plasma lipids, glucose homeostasis markers, as well as plasma levels of prolactin, uric acid, high-sensitivity C-reactive protein (hsCRP), homocysteine and fibrinogen were determined before and after 12 weeks of fenofibrate therapy.

RESULTS

Insulin sensitivity was more expressed while baseline plasma levels of hsCRP and fibrinogen were lower in patients treated with bromocriptine than in women not receiving dopamine agonist therapy. Although fenofibrate improved plasma lipids and insulin sensitivity, as well as reduced plasma levels of the investigated cardiometabolic risk factors in both groups of patients, its action on HDL cholesterol, triglycerides, insulin sensitivity, hsCRP and fibrinogen was stronger in subjects receiving bromocriptine. Moreover, only in bromocriptine-naïve patients, fenofibrate increased plasma homocysteine.

CONCLUSIONS

Our study shows that the effect of fenofibrate on plasma lipids and circulating levels of cardiometabolic risk factors may be potentiated by bromocriptine treatment. They also suggest that hyperprolactinemic women with mixed dyslipidemia and early glucose metabolism abnormalities may receive the greatest benefits from concomitant treatment with a fibrate and bromocriptine.

Role of PPARα and HNF4α in stress-mediated alterations in lipid homeostasis

Stress is a risk factor for several cardiovascular pathologies. PPARα holds a fundamental role in control of lipid homeostasis by directly regulating genes involved in fatty acid transport and oxidation. Importantly, PPARα agonists are effective in raising HDL-cholesterol and lowering triglycerides, properties that reduce the risk for cardiovascular diseases. This study investigated the role of stress and adrenergic receptor (AR)-related pathways in PPARα and HNF4α regulation and signaling in mice following repeated restraint stress or treatment with AR-antagonists administered prior to stress to block AR-linked pathways. Repeated restraint stress up-regulated Pparα and its target genes in the liver, including Acox, Acot1, Acot4, Cyp4a10, Cyp4a14 and Lipin2, an effect that was highly correlated with Hnf4α. In vitro studies using primary hepatocyte cultures treated with epinephrine or AR-agonists confirmed that hepatic AR/cAMP/PKA/CREB- and JNK-linked pathways are involved in PPARα and HNF4α regulation. Notably, restraint stress, independent of PPARα, suppressed plasma triglyceride levels. This stress-induced effect could be attributed in part to hormone sensitive lipase activation in the white adipose tissue, which was not prevented by the increased levels of perilipin. Overall, this study identifies a mechanistic basis for the modification of lipid homeostasis following stress and potentially indicates novel roles for PPARα and HNF4α in stress-induced lipid metabolism.

Preclinical cancer chemoprevention studies using animal model of inflammation-associated colorectal carcinogenesis

Inflammation is involved in all stages of carcinogenesis. Inflammatory bowel disease, such as ulcerative colitis and Crohn’s disease is a longstanding inflammatory disease of intestine with increased risk for colorectal cancer (CRC). Several molecular events involved in chronic inflammatory process are reported to contribute to multi-step carcinogenesis of CRC in the inflamed colon. They include over-production of free radicals, reactive oxygen and nitrogen species, up-regulation of inflammatory enzymes in arachidonic acid biosynthesis pathway, up-regulation of certain cytokines, and intestinal immune system dysfunction. In this article, firstly I briefly introduce our experimental animal models where colorectal neoplasms rapidly develop in the inflamed colorectum. Secondary, data on preclinical cancer chemoprevention studies of inflammation-associated colon carcinogenesis by morin, bezafibrate, and valproic acid, using this novel inflammation-related colorectal carcinogenesis model is described.

Selective CETP Inhibition and PPARα Agonism Increase HDL Cholesterol and Reduce LDL Cholesterol in Human ApoB100/Human CETP Transgenic Mice

Cholesteryl ester transfer protein (CETP) plays a key role in high-density lipoprotein (HDL) cholesterol metabolism, but normal mice are deficient in CETP. In this study, transgenic mice expressing both human apolipoprotein B 100 (ApoB-100) and human CETP (hApoB100/hCETP) were used to characterize the effects of CETP inhibition and peroxisome proliferator—activated receptor α (PPARα) agonism on lipid profiles. Torcetrapib (3, 10, and 30 mg/kg), a CETP inhibitor, fenofibrate (30 mg/kg), a weak PPARα agonist, and GW590735 (3 and 10 mg/kg), a potent and selective PPARα agonist were given orally for 14 days to hApoB100/hCETP mice and lipid profiles were assessed. The average percentages of HDL, low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL) cholesterol fractions in hApoB100/hCETP mice were 34.8%, 61.6%, and 3.6%, respectively, which is similar to those of normolipidemic humans. Both torcetrapib and fenofibrate significantly increased HDL cholesterol and reduced LDL cholesterol, and there was a tendency for torcetrapib to reduce VLDL cholesterol and triglycerides. GW590735 significantly increased HDL cholesterol, decreased LDL and VLDL cholesterol, and significantly reduced triglycerides. Maximal increases in HDL cholesterol were 37%, 53%, and 84% with fenofibrate, torcetrapib, and GW590735, respectively. These results, in mice that exhibit a more human-like lipid profile, demonstrate an improved lipid profile with torcetrapib, fenofibrate, and GW590735, and support the use of selective PPARα agonism for the treatment of lipid disorders. In addition, these data demonstrate the use of hApoB100/hCETP transgenic mice to identify, characterize, and screen compounds that increase HDL cholesterol.

Niacin and fibrates in atherogenic dyslipidemia: pharmacotherapy to reduce cardiovascular risk

Although statin therapy represents a cornerstone of cardiovascular disease (CVD) prevention, a major residual CVD risk (60-70% of total relative risk) remains, attributable to both modifiable and non-modifiable risk factors. Among the former, low levels of HDL-C together with elevated triglyceride (TG)-rich lipoproteins and their remnants represent major therapeutic targets. The current pandemic of obesity, metabolic syndrome, and type 2 diabetes is intimately associated with an atherogenic dyslipidemic phenotype featuring low HDL-C combined with elevated TG-rich lipoproteins and small dense LDL. In this context, there is renewed interest in pharmacotherapeutic strategies involving niacin and fibrates in monotherapy and in association with statins. This comprehensive, critical review of available data in dyslipidemic subjects indicates that niacin is more efficacious in raising HDL-C than fibrates, whereas niacin and fibrates reduce TG-rich lipoproteins and LDL comparably. Niacin is distinguished by its unique capacity to effectively lower Lp(a) levels. Several studies have demonstrated anti-atherosclerotic action for both niacin and fibrates. In contrast with statin therapy, the clinical benefit of fibrates appears limited to reduction of nonfatal myocardial infarction, whereas niacin (frequently associated with statins and/or other agents) exerts benefit across a wider range of cardiovascular endpoints in studies involving limited patient numbers. Clearly the future treatment of atherogenic dyslipidemias involving the lipid triad, as exemplified by the occurrence of the mixed dyslipidemic phenotype in metabolic syndrome, type 2 diabetes, renal, and auto-immune diseases, requires integrated pharmacotherapy targeted not only to proatherogenic particles, notably VLDL, IDL, LDL, and Lp(a), but also to atheroprotective HDL.

Clofibrate and dalargin increase luminol-dependent chemiluminescence of mouse blood

The effects of hypolipidemic drug clofibrate and polypeptide dalargin on activity of the neutrophil peroxidase system in mice were studied using the method of luminol-enhanced chemiluminescence. Clofibrate and dalargin increased the chemiluminescence of mouse whole blood. Their combined use several-fold potentiated this effect. It is expected that combined use of hypolipidemics and polypeptides will open a new trend in the search for stimulators of oxygen-dependent nonspecific immunity.

Cytotoxicity of peroxisome proliferator-activated receptor alpha and gamma agonists in renal proximal tubular cell lines

Fibrates and thiazolidinediones are agonists of peroxisome proliferator-activated receptors (PPAR) alpha and gamma, pharmacologically designed to control dyslipidemia and insulin resistance, respectively. Several works have reported the toxicity of some agonists in a number of tissues. In this work we have analyzed the toxicity of two PPARalpha (WY14643 and clofibrate) and two PPARgamma (pioglitazone and ciglitazone) agonists, using three different renal proximal tubular cell lines: Opossum OK, pig LLC-PK1, and murine MCT. Cell death was determined by the activity of intracellular lactate dehydrogenase. WY14643 and ciglitazone increased cell death with LC50 values of 92-124 microM and 8.6-14.8 microM, respectively, depending on the cell line. Clofibrate and pioglitazone were, however, non-cytotoxic even at concentrations of 10 and 100 higher than the corresponding EC50, which suggests that cell death is independent of PPAR activation. Discrimination between apoptosis or necrosis was analyzed by light microscopy and stress fiber morphology, double staining with acridine orange and ethidium bromide, binding of annexin V, caspase-3 activity, and DNA laddering. With these methods, no signs of apoptosis were observed, which suggests a direct necrosis of the compounds on these renal proximal tubular cell lines.

Indanylacetic acid derivatives carrying aryl-pyridyl and aryl-pyrimidinyl tail groups—new classes of PPAR γ/δ and PPAR α/γ/δ agonists

Modulation of PPAR activities represents an attractive approach for the treatment of diabetes with associated cardiovascular complications. The indanylacetic acid structural motif has proven useful in the generation of potent and tunable PPAR ligands. Modification of the substituents on the linker and the heterocycle tail group allowed for the modulation of the selectivity at the different receptor subtypes. Compound 33 was evaluated in vivo, where it displayed the desired reduction of glucose levels and increase in HDL levels in various animal models.