Fenofibrate and human liver. Lack of proliferation of peroxisomes

Efficacy of Pemafibrate Versus Fenofibrate Administration on Serum Lipid Levels in Patients with Dyslipidemia: Network Meta-Analysis and Systematic Review

BACKGROUND

Pemafibrate is a novel fibrate class drug that is a highly potent and selective agonist of peroxisome proliferator-activated receptor α (PPARα). We performed the first ever network meta-analysis containing the largest ever group of patients to test the efficacy of pemafibrate in improving lipid levels compared with fenofibrate and placebo in patients with dyslipidemia.

METHODS

Potentially relevant clinical trials were identified in Medline, PubMed, Embase, clinicaltrials.gov, and Cochrane Controlled Trials registry. Nine randomized controlled trials met the inclusion criteria out of 40 potentially available articles. The primary effect outcome was a change in the levels of triglycerides (TG), high-density lipoproteins (HDL), or low-density lipoproteins (LDL) before and after the treatment.

RESULTS

A total of 12,359 subjects were included. The mean patient age was 54.73 (years), the mean ratio for female patients was 18.75%, and the mean examination period was 14.22 weeks. The dose for pemafibrate included in our study was 0.1, 0.2, or 0.4 mg twice daily, whereas the dose for fenofibrate was 100 mg/day. Data showed a significant reduction in TG and a mild increase in HDL levels across the pemafibrate group at different doses and fenofibrate 100 mg group (with greatest effect observed with pemafibrate 0.1 mg twice daily). A mild increase in LDL was also observed in all groups, but the increase in LDL in the 0.1 mg twice daily dose group was statistically insignificant.

CONCLUSION

Pemafibrate 0.1 mg twice daily dose led to highest reduction in TG levels and the highest increase in HDL levels compared with other doses of pemafibrate, fenofibrate, and placebo.

The Insulin-Sensitizer Pioglitazone Remodels Adipose Tissue Phospholipids in Humans

The insulin-sensitizer pioglitazone exerts its cardiometabolic benefits in type 2 diabetes (T2D) through a redistribution of body fat, from ectopic and visceral areas to subcutaneous adipose depots. Whereas excessive weight gain and lipid storage in obesity promotes insulin resistance and chronic inflammation, the expansion of subcutaneous adipose by pioglitazone is associated with a reversal of these immunometabolic deficits. The precise events driving this beneficial remodeling of adipose tissue with pioglitazone remain unclear, and whether insulin-sensitizers alter the lipidomic composition of human adipose has not previously been investigated. Using shotgun lipidomics, we explored the molecular lipid responses in subcutaneous adipose tissue following 6months of pioglitazone treatment (45mg/day) in obese humans with T2D. Despite an expected increase in body weight following pioglitazone treatment, no robust effects were observed on the composition of storage lipids (i.e., triglycerides) or the content of lipotoxic lipid species (e.g., ceramides and diacylglycerides) in adipose tissue. Instead, pioglitazone caused a selective remodeling of the glycerophospholipid pool, characterized by a decrease in lipids enriched for arachidonic acid, such as plasmanylethanolamines and phosphatidylinositols. This contributed to a greater overall saturation and shortened chain length of fatty acyl groups within cell membrane lipids, changes that are consistent with the purported induction of adipogenesis by pioglitazone. The mechanism through which pioglitazone lowered adipose tissue arachidonic acid, a major modulator of inflammatory pathways, did not involve alterations in phospholipase gene expression but was associated with a reduction in its precursor linoleic acid, an effect that was also observed in skeletal muscle samples from the same subjects. These findings offer important insights into the biological mechanisms through which pioglitazone protects the immunometabolic health of adipocytes in the face of increased lipid storage.

The PPARα-dependent rodent liver tumor response is not relevant to humans: addressing misconceptions

A number of industrial chemicals and therapeutic agents cause liver tumors in rats and mice by activating the nuclear receptor peroxisome proliferator-activated receptor α (PPARα). The molecular and cellular events by which PPARα activators induce rodent hepatocarcinogenesis have been extensively studied elucidating a number of consistent mechanistic changes linked to the increased incidence of liver neoplasms. The weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis is summarized here. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators. The key events (KE) identified in the MOA are PPARα activation (KE1), alteration in cell growth pathways (KE2), perturbation of hepatocyte growth and survival (KE3), and selective clonal expansion of preneoplastic foci cells (KE4), which leads to the apical event-increases in hepatocellular adenomas and carcinomas (KE5). In addition, a number of concurrent molecular and cellular events have been classified as modulating factors, because they potentially alter the ability of PPARα activators to increase rodent liver cancer while not being key events themselves. These modulating factors include increases in oxidative stress and activation of NF-kB. PPARα activators are unlikely to induce liver tumors in humans due to biological differences in the response of KEs downstream of PPARα activation. This conclusion is based on minimal or no effects observed on cell growth pathways and hepatocellular proliferation in human primary hepatocytes and absence of alteration in growth pathways, hepatocyte proliferation, and tumors in the livers of species (hamsters, guinea pigs and cynomolgus monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Despite this overwhelming body of evidence and almost universal acceptance of the PPARα MOA and lack of human relevance, several reviews have selectively focused on specific studies that, as discussed, contradict the consensus opinion and suggest uncertainty. In the present review, we systematically address these most germane suggested weaknesses of the PPARα MOA.

Role of peroxisome proliferator-activated receptor alpha in the control of cyclooxygenase 2 and vascular endothelial growth factor: involvement in tumor growth

A growing body of evidence indicates that PPAR (peroxisome proliferator-activated receptor) α agonists might have therapeutic usefulness in antitumoral therapy by decreasing abnormal cell growth, and reducing tumoral angiogenesis. Most of the anti-inflammatory and antineoplastic properties of PPAR ligands are due to their inhibitory effects on transcription of a variety of genes involved in inflammation, cell growth and angiogenesis. Cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) are crucial agents in inflammatory and angiogenic processes. They also have been significantly associated to cell proliferation, tumor growth, and metastasis, promoting tumor-associated angiogenesis. Aberrant expression of VEGF and COX-2 has been observed in a variety of tumors, pointing to these proteins as important therapeutic targets in the treatment of pathological angiogenesis and tumor growth. This review summarizes the current understanding of the role of PPARα and its ligands in the regulation of COX-2 and VEGF gene expression in the context of tumor progression.

Pathogenesis of alcoholic liver disease: the role of nuclear receptors

Ethanol consumption causes fatty liver, which can lead to inflammation, fibrosis, cirrhosis and even liver cancer. The molecular mechanisms by which ethanol exerts its damaging effects are extensively studied, but not fully understood. It is now evident that nuclear receptors (NRs), including retinoid x receptor alpha and peroxisome proliferator-activated receptors, play key roles in the regulation of lipid homeostasis and inflammation during the pathogenesis of alcoholic liver disease (ALD). Given their pivotal roles in physiological processes, NRs represent potential therapeutic targets for the treatment and prevention of numerous metabolic and lipid-related diseases including ALD. This review summarizes the factors that contribute to ALD and the molecular mechanisms of ALD with a focus on the role of NRs.

Mechanisms of resistance of hepatocyte retinoid X receptor alpha-null mice to WY-14,643-induced hepatocyte proliferation and cholestasis

Peroxisome proliferators, such as the lipid-lowering fibrates that function as agonists for peroxisome proliferator-activated receptor alpha (PPARalpha), induce liver tumors in rodents and may produce cholestasis in humans. Considerable attention has focused on peroxisome proliferator-induced hepatocellular carcinoma, a phenomenon not noted in man, whereas limited studies examine fibrates and other therapeutic drugs that induce cholestasis, a common finding in humans. Moreover, the mechanisms by which fibrates induce hepatocyte proliferation and cholestasis are still not fully understood. We have examined the role of hepatocyte retinoid X receptor alpha (RXRalpha), an essential partner of PPARalpha, in modulating WY-14,643-induced hepatocyte proliferation and cholestasis. WY-14,643 treatment induced hepatomegaly in wild type (WT) mice that was also accompanied by induction of the expression of cyclins D1, D3, A2, and B1 and Cdc2 as well as inhibition of Wee 1. Such changes were either absent or greatly reduced in hepatocyte RXRalpha-null mice. Furthermore, neither WY-14,643 treatment nor RXRalpha deficiency affected apoptosis, indicating the importance of PPARalpha/RXRalpha in regulating Wee 1-mediated Cdc2/cyclin B1 expression for cells to enter into mitosis. WY-14,643 treatment also induced cholestasis and liver injury, which is evidenced by induction of alanine aminotransferase, alkaline phosphatase, and hepatic bile acid levels in WT mice. Hepatocyte RXRalpha deficiency protected the mice from WY-14,643-induced liver injury. WY-14,643-mediated induction of the small heterodimer partner, Mrp3, and Cyp3a11 levels was greater in hepatocyte RXRalpha-null than in WT mouse livers suggesting enhanced repression of bile acid synthesis and increased efflux of bile acids into blood for renal excretion as well as hydroxylation of bile acids because of hepatocyte RXRalpha deficiency. These data establish a crucial role of hepatocyte RXRalpha in regulating WY-14,643-mediated cell cycle progression as well as bile acid homeostasis.

Inhibiting wild-type and C299S mutant AKR1B10; a homologue of aldose reductase upregulated in cancers

AKR1B10 is an aldose reductase (AR) homologue overexpressed in liver cancer and various forms of that enzyme in carcinomas catalyze the reduction of anticancer drugs, potential cytostatic drug, and dl-glyceraldehyde but do not catalyze the reduction of glucose. Kinetic parameters for wild-type and C299S mutant AKR1B10 indicate that substitution of serine for cysteine at position 299 reduces the affinity of this protein for dl-glyceraldehyde and enhances its catalytic activity. Fibrates suppress peroxisome proliferation and the development of liver cancer in human. Here we report the potency of fibrate-mediated inhibition of the carbonyl reduction catalyzed by wild-type and C299S mutant AKR1B10 and compare it with known AR inhibitors. Wild-type AKR1B10-catalyzed carbonyl reduction follows pure non-competitive inhibition kinetics using zopolrestat, EBPC or sorbinil, whereas fenofibrate, Wy 14,643, ciprofibrate and fenofibric acid follow mixed non-competitive inhibition kinetics. In contrast, catalysis of reaction by the C299S AKR1B10 mutant is not inhibited by sorbinil and EBPC. Despite these differences, the C299S AKR1B10 mutant still manifests kinetics similar to the wild-type protein with other fibrates including zopolrestat, fenofibrate, Wy 14,346, gemfibrozil and ciprofibrate that show mixed non-competitive inhibition kinetics. The reaction of the mutant AKR1B10 is inhibited by fenofibric acid, but manifests pure non-competitive inhibition kinetics that are different from those demonstrated for the wild-type enzyme.

RXR activators molecular signalling: involvement of a PPAR alpha-dependent pathway in the liver and kidney, evidence for an alternative pathway in the heart

(1) In this study we compared the molecular signalling elicited by rexinoids, selective retinoid X receptor (RXR)-activators, in several organs (i.e. liver, kidney, heart) and in hepatocytes of various species. (2) RXR plays the pivotal role of a hetero-dimerization partner for the members of the class II subset of nuclear receptors which regulate the transcription of numerous target genes, following chemical activation. Several of these selective activators are currently used to treat hyperlipidaemia (fibrates), type II diabetes (glitazones), or skin disorders (retinoic acid). Although these therapeutic pathways are not fully elucidated, receptor activation is considered a pre-requisite for efficacy. Therefore RXR, which accepts numerous dimeric partners, is considered a worthwhile pharmacological target. (3) We analysed a number of biochemical and molecular responses to rexinoids which were given orally to mice. Our results showed a prominent involvement of the peroxisome proliferator-activated receptor (PPARalpha) as a majority of the observed hepatic and renal regulations were abolished in PPARalpha-knockout animals. Therefore we documented the species-specificity of these rexinoid actions which were reproduced in rat primary hepatocyte cultures but not in cultures of rabbit or human origin. Conversely, we established that the regulation of the pyruvate dehydrogenase kinase (PDK4) gene in the heart, by rexinoids, is independent of PPARalpha expression. (4) Our results support the obligatory expression of the active, although quiescent, PPARalpha to sustain a subset of relevant regulations attributable to rexinoids in the liver and kidney. Their cardiac molecular signalling unveiled an alternate transduction pathway and therefore opens new prospects in the therapeutic potential of rexinoids.

Fenofibrate. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in dyslipidaemia

Fenofibrate is a lipid-regulating drug which is structurally related to other fibric acid derivatives, such as clofibrate. At the recommended dosage of 200 to 400 mg daily, it produces substantial reductions in plasma triglyceride levels in hypertriglyceridaemic patients and in plasma total cholesterol levels in hypercholesterolaemic patients. High density lipoprotein (HDL)-cholesterol levels are generally increased in patients with low pretreatment values. Fenofibrate appears to be equally effective in diabetic patients with hyperlipoproteinaemia without adversely affecting glycaemic control. The influence of fenofibrate on the plasma lipid profile is sustained during long term (2 to 7 years) treatment. Comparative studies conducted to date have involved only small groups of patients--in overall terms fenofibrate was at least as effective as other fibrates, but larger comparative studies are needed before valid conclusions on its relative efficacy compared with nonfibrate lipid-lowering drugs can be drawn. The influence of fenofibrate on morbidity and mortality from cardiovascular disease has not been studied. Clinical adverse reactions to fenofibrate have mainly consisted of gastrointestinal disturbances, headache and muscle cramps. Transient elevations in transaminase and creatine phosphokinase levels commonly occur. Isolated cases of hepatitis with substantially elevated transaminase levels have been reported. Fenofibrate induces hepatomegaly, peroxisome proliferation and hepatic carcinomas in rodents, but this type of hepatotoxicity has not been observed in humans. The biliary lithogenic index is increased by fenofibrate, but this has not been shown to have increased the incidence of gallstones in treated patients. Thus, fenofibrate offers an effective and well tolerated alternative to clofibrate or other fibric acid derivatives, but its relative efficacy and tolerability compared with other types of lipid-lowering drugs, and its effect on cardiovascular morbidity and mortality, remain to be clarified.