Clofibrate

Clofibrate is an agonist of PPAR, with EC50s of 50 μM, ∼500 μM for murine PPARα and PPARγ, and 55 μM, ∼500 μM for human PPARα and PPARγ, respectively.

In Vitro:Clofibrate is a PPAR agonist, with E50s of 50 μM, ∼500 μM for murine PPARα and PPARγ, and 55 μM, ∼500 μM for human PPARα and PPARγ, respectively[1]. Clofibrate (0.5, 1, 2 mM) increases FABP1 expression in two fatty acid (FA)-treated rat hepatoma cells. Clofibrate lowers ROS levels after early treatment, much more than late treatment in FA-treated cells[2].

In Vivo:Clofibrate (0.5%) up-regulates serum concentrations and hepatic expression of FGF21 in fetuses, with a return to basal levels after Clofibrate administration withdrawal. Clofibrate administration-offspring have significantly higher expression of thermogenic genes (Ucp1, Cidea, Ppara Ppargc1a, Cpt1b) and UCP1 protein levels in response to HFD in inguinal fat, but not in retroperitoneal (combined with perirenal) or epididymal fat[3].

References:
[1]. Willson TM, et al. The PPARs: from orphan receptors to drug discovery. J Med Chem. 2000 Feb 24;43(4):527-50. [2]. Chen Y, et al. Clofibrate Attenuates ROS Production by Lipid Overload in Cultured Rat Hepatoma Cells. J Pharm Pharm Sci. 2017;20(0):239-251. [3]. Chen SH, et al. Prenatal PPARα activation by clofibrate increases subcutaneous fat browning in male C57BL/6J mice fed a high-fat diet during adulthood. PLoS One. 2017 Nov 2;12(11):e0187507.

Lipid-Lowering Pharmaceutical Clofibrate Inhibits Human Sweet Taste.[Pubmed:27742692]

Chem Senses. 2017 Jan;42(1):79-83.

T1R2-T1R3 is a heteromeric receptor that binds sugars, high potency sweeteners, and sweet taste blockers. In rodents, T1R2-T1R3 is largely responsible for transducing sweet taste perception. T1R2-T1R3 is also expressed in non-taste tissues, and a growing body of evidence suggests that it helps regulate glucose and lipid metabolism. It was previously shown that clofibric acid, a blood lipid-lowering drug, binds T1R2-T1R3 and inhibits its activity in vitro The purpose of this study was to determine whether clofibric acid inhibits sweetness perception in humans and is, therefore, a T1R2-T1R3 antagonist in vivo Fourteen participants rated the sweetness intensity of 4 sweeteners (sucrose, sucralose, Na cyclamate, acesulfame K) across a broad range of concentrations. Each sweetener was prepared in solution neat and in mixture with either clofibric acid or lactisole. Clofibric acid inhibited sweetness of every sweetener. Consistent with competitive binding, inhibition by clofibric acid was diminished with increasing sweetener concentration. This study provides in vivo evidence that the lipid-lowering drug clofibric acid inhibits sweetness perception and is, therefore, a T1R carbohydrate receptor inhibitor. Our results are consistent with previous in vitro findings. Given that T1R2-T1R3 may in part regulate glucose and lipid metabolism, future studies should investigate the metabolic effects of T1R inhibition.

Peroxisome proliferator-activated receptor-alpha stimulation by clofibrate favors an antioxidant and vasodilator environment in a stressed left ventricle.[Pubmed:27110876]

Pharmacol Rep. 2016 Aug;68(4):692-702.

BACKGROUND: Arterial high blood pressure is a risk factor for target organ damage; the most susceptible organs are the arteries, brain, kidneys, and heart. The damage mechanisms include oxidative stress and renin-angiotensin system (RAS) overactivity. Therefore, our aim was to study whether Clofibrate-induced peroxisome proliferator-activated receptor-alpha (PPAR-alpha) stimulation is able to prevent alterations in cardiac functioning derived from RAS overstimulation in the left ventricle of rats with hypertension secondary to aortic coarctation and to improve antioxidant defenses. METHODS: Male Wistar rats were assigned to Control (Sham)- or aortic coarctation-surgery and further divided to receive (1 or 21 days) vehicle, Clofibrate (100mg/kg), captopril (20mg/kg), or Clofibrate+captopril. The left ventricle was obtained to measure: angiotensin II and -(1-7), AT1 and AT2 receptors, angiotensin converting enzyme (ACE)-1 and -2, and MAS receptor; the activity and expression of superoxide dismutase, catalase, endothelial nitric oxide synthase, the production of reactive oxygen species (ROS) and peroxidated lipids; as well as ex vivo cardiac functioning. RESULTS: Clofibrate decreased angiotensin II, AT1 receptor and ACE expression, and raised angiotensin-(1-7), AT2 receptor, ACE-2 expression, superoxide dismutase and endothelial nitric oxide synthase participation. These effects promoted lower coronary vascular resistance and improved mechanical work compared to aortic coarctated vehicle-treated rats. CONCLUSIONS: Clofibrate-induced PPAR-alpha stimulation changes the angiotensin II receptor profile, favors the ACE2/angiotensin-(1-7)/AT2 receptor axis decreasing the vasoconstrictor environment, activates the antioxidant defense, and facilitates endothelial nitric oxide synthase activity favoring vasodilation. This may represent a protection for the stressed heart.

Clofibrate inhibits the umami-savory taste of glutamate.[Pubmed:28248971]

PLoS One. 2017 Mar 1;12(3):e0172534.

In humans, umami taste can increase the palatability of foods rich in the amino acids glutamate and aspartate and the 5'-ribonucleotides IMP and GMP. Umami taste is transduced, in part, by T1R1-T1R3, a heteromeric G-protein coupled receptor. Umami perception is inhibited by sodium lactisole, which binds to the T1R3 subunit in vitro. Lactisole is structurally similar to the fibrate drugs. Clofibric acid, a lipid lowering drug, also binds the T1R3 subunit in vitro. The purpose of this study was to determine whether clofibric acid inhibits the umami taste of glutamate in human subjects. Ten participants rated the umami taste intensity elicited by 20 mM monosodium glutamate (MSG) mixed with varying concentrations of clofibric acid (0 to 16 mM). In addition, fourteen participants rated the effect of 1.4 mM clofibric acid on umami enhancement by 5' ribonucleotides. Participants were instructed to rate perceived intensity using a general Labeled Magnitude Scale (gLMS). Each participant was tested in triplicate. Clofibric acid inhibited umami taste intensity from 20 mM MSG in a dose dependent manner. Whereas MSG neat elicited "moderate" umami taste intensity, the addition of 16 mM clofibric acid elicited only "weak" umami intensity on average, and in some subjects no umami taste was elicited. We further show that 1.4 mM clofibric acid suppressed umami enhancement from GMP, but not from IMP. This study provides in vivo evidence that clofibric acid inhibits glutamate taste perception, presumably via T1R1-T1R3 inhibition, and lends further evidence that the T1R1-T1R3 receptor is the principal umami receptor in humans. T1R receptors are expressed extra-orally throughout the alimentary tract and in regulatory organs and are known to influence glucose and lipid metabolism. Whether clofibric acid as a lipid-lowering drug affects human metabolism, in part, through T1R inhibition warrants further examination.

Clofibrate Demonstrates Efficacy in In Vitro Treatment of Lymphoma and Multiple Myeloma.[Pubmed:27354598]

Anticancer Res. 2016 Jul;36(7):3395-400.

BACKGROUND/AIM: Multiple myeloma (MM), a hematological malignancy of monoclonal B-lymphocytes, remains largely incurable and novel treatments are urgently required. Aberrant activation of wingless-related integration site (WNT)/beta-catenin signaling has been demonstrated in both lymphoma and MM, rendering its signaling molecules attractive for the development of new targeted-therapies. Clofibrate has proven anticarcinogenic effects attributed to peroxisome proliferator-activated receptor alpha (PPARalpha) agonism, also affecting WNT-associated signaling molecules. MATERIALS AND METHODS: The antitumor apoptotic effect of Clofibrate at doses ranging from 0.1-600 muM was investigated on four human and one murine myeloma cell lines, as well as in two human lymphoma cell lines, using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide assay. RESULTS: Clofibrate significantly reduced cell viability in all tested myeloma and lymphoma cell lines in a dose-dependent manner, while healthy cells were hardly affected. CONCLUSION: Given the known safety profile and induction of apoptosis at low effective doses, our data warrant further investigation of Clofibrate as a novel therapy agent in MM.

Peroxisome proliferator-activated receptors in the cardiovascular system.[Pubmed:10696077]

Br J Pharmacol. 2000 Mar;129(5):823-34.

Peroxisome proliferator-activated receptor (PPAR)s are a family of three nuclear hormone receptors, PPARalpha, -delta, and -gamma, which are members of the steriod receptor superfamily. The first member of the family (PPARalpha) was originally discovered as the mediator by which a number of xenobiotic drugs cause peroxisome proliferation in the liver. Defined functions for all these receptors, until recently, mainly concerned their ability to regulate energy balance, with PPARalpha being involved in beta-oxidation pathways, and PPARgamma in the differentiation of adipocytes. Little is known about the functions of PPARdelta, though it is the most ubiquitously expressed. Since their discovery, PPARs have been shown to be expressed in monocytes/macrophages, the heart, vascular smooth muscle cells, endothelial cells, and in atherosclerotic lesions. Furthermore, PPARs can be activated by a vast number of compounds including synthetic drugs, of the Clofibrate, and anti-diabetic thiazoldinedione classes, polyunsaturated fatty acids, and a number of eicosanoids, including prostaglandins, lipoxygenase products, and oxidized low density lipoprotein. This review will aim to introduce the field of PPAR nuclear hormone receptors, and discuss the discovery and actions of PPARs in the cardiovascular system, as well as the source of potential ligands.

Mechanism of action of fibrates.[Pubmed:8497455]

Postgrad Med J. 1993;69 Suppl 1:S34-41.

Fibrates are effective in hypertriglyceridaemia and hypercholesterolaemia. They affect both triglyceride-rich and cholesterol-rich particles and have at least four separate modes of action. These include limitation of substrate availability for triglyceride synthesis in the liver; promotion of the action of lipoprotein lipase; modulation of low density lipoprotein (LDL) receptor/ligand interaction and stimulation of reverse cholesterol transport. Studies of LDL metabolism suggest the existence of two separate catabolic pathways involving the LDL receptor and scavenger mechanism(s). The former route is anti-atherogenic; the latter pro-atherogenic. At low triglyceride levels, the fractional clearance of LDL by the receptor is high. The action of fibrates is to promote the secretion of LDL which is cleared by a receptor-mediated mechanism. Catabolism of this fraction increases from 40% of the plasma pool per day in untreated to 60% per day in treated subjects. By activating lipoprotein lipase, fibrates also reduce the amount of small dense LDL, the fraction which is most likely to generate peroxidation products. Hence, fibrates stimulate LDL receptor-dependent clearance mechanisms and reduce the amount of LDL available for oxidation.

Clofibrate is an agonist of PPAR, with EC50s of 50 μM, ∼500 μM for murine PPARα and PPARγ, and 55 μM, ∼500 μM for human PPARα and PPARγ, respectively.

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