Opposite metabolic response to fenofibrate treatment in pregnant and virgin rats

Feasibility and efficacy of pemafibrate for prevention of maternal high-fat intake-induced glucose metabolic dysfunction in offspring

Given the significance of the intrauterine lipid environment in glucose metabolic homeostasis in offspring, the present study was undertaken to investigate the feasibility and efficacy of pemafibrate, a triglyceride-lowering peroxisome proliferator-activated agent, for maternal high-fat diet (HFD) intake-induced glucose metabolic dysfunction in offspring. A mouse model of HFD-induced gestational obesity was employed, and pemafibrate was orally administered from day 10 of gestation until delivery. The influences of maternal pemafibrate treatment on biological processes and toxicity were evaluated in both newborns and 12-week-old offspring. The findings of a dose-dependent decrease of β cell islet mass and of impairment of glucose tolerance and insulin sensitivity in offspring suggest that maternal pemafibrate intervention can prevent maternal HFD-intake-induced diabetes in offspring. Of particular interest in the prevention of future glucose metabolic dysfunction in offspring, low-dose maternal pemafibrate treatment (0.02 mg/kg/day) had sufficient efficacy and appeared to be safe in offspring. Therefore, pemafibrate may be a potential agent for the prevention of maternal high-fat exposure-induced diabetes in offspring. Abbreviations: CD, control diet; DEG, differentially expressed genes; GTT, glucose tolerance test; HFD, high-fat diet; ITT, insulin tolerance test; MC, 0.5w/v% methyl cellulose 400 solution; PPAR, triglyceride-lowering peroxisome proliferator-activated receptor; RNA-seq, RNA sequencing; TC, total cholesterol; TG, triglycerides.

Fenofibrate ameliorates olanzapine's side effects without altering its central effect: emphasis on FGF-21-adiponectin axis

The present work was designed to investigate whether fenofibrate could ameliorate olanzapine deleterious effect on insulin resistance via its effect on fibroblast growth factor-21 (FGF-21)-adiponectin axis without affecting olanzapine antipsychotic effect in postweaning socially isolated reared female rats. Treatment with olanzapine (6 mg/kg, intraperitoneally) or fenofibrate (100 mg/kg, orally) have been started 5 weeks after isolation, then behavioral tests, hippocampal content of neurotransmitters, and brain-derived neurotrophic factor (BDNF) were assessed. Moreover, insulin resistance, lipid profile, FGF-21, adiponectin, inflammatory, and oxidative stress markers of adipose tissue were assessed. Treatment of isolated-reared animals with olanzapine, or fenofibrate significantly ameliorated the behavioral and biochemical changes induced by postweaning social isolation. Co-treatment showed additive effects in improving hippocampal BDNF level. Besides, fenofibrate reduced the elevation in weight gain, adiposity index, insulin resistance, lipid profile, and FGF-21 level induced by olanzapine treatment. Also, fenofibrate increased adiponectin level which was reduced upon olanzapine treatment. Moreover, fenofibrate improved both adipose tissue oxidative stress and inflammatory markers elevation as a result of olanzapine treatment. Fenofibrate could ameliorate olanzapine-induced insulin resistance without affecting its central effect in isolated reared rats via its action on FGF-21-adiponectin axis.

Dose-dependent effects of prenatal exposure of pioglitazone, the PPARγ agonist, on the hippocampus development and learning and memory performance of rat offspring

It is known that pioglitazone, defined as a PPARγ agonist, has neuron-protective properties in nervous system disorders. The aim of this study is to investigate the effects of pioglitazone administration at different doses during prenatal period on the neurons, glial cells and learning-memory levels in the hippocampus of rat offspring. Pregnant rats were divided into three groups; Low-Dose Pioglitazone (LDP), High-Dose Pioglitazone (HDP) and control (C) (n = 3). Pregnant rats in the HDP and LDP groups were given pioglitazone at 30 mg/kg and 5 mg/kg doses, respectively, by gavage once a day during their pregnancy. No procedure was applied to the rats in the control group. Morris water tank test was applied to offspring obtained from postnatal 24th to 28th day. The offspring were sacrificed on the 29th postal day and their brain tissues removed. Stereological, histopathological and immunohistochemical techniques were used to analyze brain tissues. As a result of the analysis, it was observed that there were delays in learning and memory, the number of pyramidal neurons decreased, and the density of cells stained with glial fibrillar acidic protein (GFAP) positive increased in the HDP group compared to the other groups (p < 0.05). No significant difference was found between the LDP and control groups in terms of these parameters (p > 0.05). Our results showed that pioglitazone administered in the prenatal period had an effect on the hippocampus development and learning and memory performance of rats, depending on the dose.

An Optimized Dual Extraction Method for the Simultaneous and Accurate Analysis of Polar Metabolites and Lipids Carried out on Single Biological Samples

The functional understanding of metabolic changes requires both a significant investigation into metabolic pathways, as enabled by global metabolomics and lipidomics approaches, and the comprehensive and accurate exploration of specific key pathways. To answer this pivotal challenge, we propose an optimized approach, which combines an efficient sample preparation, aiming to reduce the variability, with a biphasic extraction method, where both the aqueous and organic phases of the same sample are used for mass spectrometry analyses. We demonstrated that this double extraction protocol allows working with one single sample without decreasing the metabolome and lipidome coverage. It enables the targeted analysis of 40 polar metabolites and 82 lipids, together with the absolute quantification of 32 polar metabolites, providing comprehensive coverage and quantitative measurement of the metabolites involved in central carbon energy pathways. With this method, we evidenced modulations of several lipids, amino acids, and energy metabolites in HepaRG cells exposed to fenofibrate, a model hepatic toxicant, and metabolic modulator. This new protocol is particularly relevant for experiments involving limited amounts of biological material and for functional metabolic explorations and is thus of particular interest for studies aiming to decipher the effects and modes of action of metabolic disrupting compounds.

Fructose during pregnancy affects maternal and fetal leptin signaling

Fructose intake from added sugars correlates with the epidemic rise in obesity, metabolic syndrome and cardiovascular diseases. Fructose intake also causes features of metabolic syndrome in laboratory animals. Therefore, we have investigated whether fructose modifies lipidemia in pregnant rats and produces changes in their fetuses. Thus, fructose administration (10% wt/vol.) in the drinking water of rats throughout gestation leads to maternal hypertriglyceridemia. This change was not observed in glucose-fed rats, although both carbohydrates produced similar changes in liver triglycerides and in the expression of transcription factors and enzymes involved in lipogenesis. After fasting overnight, mothers fed with carbohydrates were found to be hyperleptinemic. However, after a bolus of glucose, leptinemia in fructose-fed mothers showed no response, whereas it increased in parallel in glucose-fed and control mothers. Fetuses from fructose-fed mothers showed hypotriglyceridemia and a higher hepatic triglyceride content than fetuses from control or glucose-fed mothers. A higher expression of genes related to lipogenesis and a lower expression of fatty acid catabolism genes were also found in fetuses from fructose-fed mothers. Moreover, although hyperleptinemic, these fetuses exhibited increased tyrosine phosphorylation of the signal transducer and activator of transcription-3 (STAT-3) protein, without a parallel increase in the serine phosphorylation of STAT-3 nor in the suppressor of cytokine signaling-3 protein levels whose expression is regulated by leptin through STAT-3 activation. Thus, fructose intake during gestation provoked a diminished maternal leptin response to fasting and refeeding and an impairment in the transduction of the leptin signal in the fetuses, which could be responsible for their hepatic steatosis.

Peroxisome proliferator-activated receptorα agonists differentially regulate inhibitor of DNA binding expression in rodents and human cells

Inhibitor of DNA binding (Id2) is a helix-loop-helix (HLH) transcription factor that participates in cell differentiation and proliferation. Id2 has been linked to the development of cardiovascular diseases since thiazolidinediones, antidiabetic agents and peroxisome proliferator-activated receptor (PPAR) gamma agonists, have been reported to diminish Id2 expression in human cells. We hypothesized that PPARα activators may also alter Id2 expression. Fenofibrate diminished hepatic Id2 expression in both late pregnant and unmated rats. In 24 hour fasted rats, Id2 expression was decreased under conditions known to activate PPARα. In order to determine whether the fibrate effects were mediated by PPARα, wild-type mice and PPARα-null mice were treated with Wy-14,643 (WY). WY reduced Id2 expression in wild-type mice without an effect in PPARα-null mice. In contrast, fenofibrate induced Id2 expression after 24 hours of treatment in human hepatocarcinoma cells (HepG2). MK-886, a PPARα antagonist, did not block fenofibrate-induced activation of Id2 expression, suggesting a PPARα-independent effect was involved. These findings confirm that Id2 is a gene responsive to PPARα agonists. Like other genes (apolipoprotein A-I, apolipoprotein A-V), the opposite directional transcriptional effect in rodents and a human cell line further emphasizes that PPARα agonists have different effects in rodents and humans.

Peroxisome proliferator-activated receptor alpha activation regulates lipid metabolism in the feto-placental unit from diabetic rats

Maternal diabetes promotes an overaccumulation of lipids in the feto-placental unit and impairs feto-placental development and growth. Here, we investigated the role played by the nuclear receptor peroxisome proliferator-activated receptor (PPAR)alpha in lipid metabolism in fetuses and placentas from control and neonatal streptozotocin-induced diabetic rats. Placentas and fetuses were studied on day 13.5 of gestation. The concentrations of PPARalpha (by Western blot) and its endogenous agonist leukotriene B(4) (LTB(4)) (by enzyme immunoassay) were analysed. Placental explants and fetuses were cultured with LTB(4) or clofibrate, and then lipid metabolism analysed (concentrations and synthesis from (14)C-acetate of triglycerides, phospholipids, cholesterol and cholesteryl esters; release of glycerol and free fatty acids (FFAs)). We found that maternal diabetes led to increases in placental concentrations of triglycerides and cholesteryl esters, and fetal concentrations of phospholipids. PPARalpha agonists downregulated fetal and placental lipid concentrations in control and diabetic rats. The synthesis of lipids was reduced in the diabetic placenta but increased in fetuses from diabetic animals. PPARalpha agonists reduced the synthesis of lipids in control placenta and in the fetuses from control and diabetic rats. Glycerol and FFA release was enhanced in the diabetic placenta and in control placenta cultured with PPARalpha agonists. Maternal diabetes led to reductions in fetal and placental LTB(4) concentrations and to increases in placental PPARalpha concentrations. Overall, these data support a novel role of PPARalpha as a regulator of lipid metabolism in the feto-placental unit, relevant in maternal diabetes where fetal and placental PPARalpha, LTB(4) and lipid concentrations are altered.

Nonclinical Safety Evaluation of Muraglitazar, a Novel PPARα/γ Agonist

The toxicity of muraglitazar, an oxybenzylglycine, nonthiazolidinedione peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist, was evaluated in a comprehensive nonclinical toxicology program that included single-dose oral toxicity studies in mice, rats, and monkeys; repeat-dose toxicity studies in rats, dogs, and monkeys; a battery of in vitro and in vivo genetic toxicity studies; carcinogenicity studies in mice and rats; reproductive and developmental toxicity studies in rats and rabbits; and studies to investigate species-specific findings. Pharmacologically mediated changes, similar to those observed with other PPARgamma agonists, were observed following chronic administration and included subcutaneous edema, hematologic/hematopoietic and serum chemistry alterations, and morphologic findings in the heart and adipose tissue in rats and monkeys. In dogs, a species highly sensitive to PPARgamma agonists, muraglitazar caused pronounced species-specific clinical toxicity and degenerative changes in the brain, spinal cord, and testes at high doses and exposures. Muraglitazar was nongenotoxic in the standard battery of genotoxicity studies. Gallbladder adenomas in male mice and adipocyte neoplasms in male and female rats were seen at suprapharmacologic exposures, whereas urinary bladder tumors occurred in male rats at lower exposures. Subsequent investigative studies established that the urinary bladder carcinogenic effect was mediated by urolithiasis rather than a direct pharmacologic effect on urothelium. Muraglitazar had no effects on reproductive function in male and female rats at high systemic exposures, was not teratogenic in rats or rabbits, and demonstrated no selective developmental toxicity. Overall, there were no nonclinical findings that precluded the safe administration of muraglitazar to humans.

PPARalpha activation reverses adverse effects induced by high-saturated-fat feeding on pancreatic beta-cell function in late pregnancy

We examined whether the additional demand for insulin secretion imposed by dietary saturated fat-induced insulin resistance during pregnancy is accommodated at late pregnancy, already characterized by insulin resistance. We also assessed whether effects of dietary saturated fat are influenced by PPARalpha activation or substitution of 7% of dietary fatty acids (FAs) with long-chain omega-3 FA, manipulations that improve insulin action in the nonpregnant state. Glucose tolerance at day 19 of pregnancy in the rat was impaired by high-saturated-fat feeding throughout pregnancy. Despite modestly enhanced glucose-stimulated insulin secretion (GSIS) in vivo, islet perifusions revealed an increased glucose threshold and decreased glucose responsiveness of GSIS in the saturated-fat-fed pregnant group. Thus, insulin resistance evoked by dietary saturated fat is partially countered by augmented insulin secretion, but compensation is compromised by impaired islet function. Substitution of 7% of saturated FA with long-chain omega-3 FA suppressed GSIS in vivo but did not modify the effect of saturated-fat feeding to impair GSIS by perifused islets. PPARalpha activation (24 h) rescued impaired islet function that was identified using perifused islets, but GSIS in vivo was suppressed such that glucose tolerance was not improved, suggesting modification of the feedback loop between insulin action and secretion.

Feeding oxidized fat during pregnancy up-regulates expression of PPARalpha-responsive genes in the liver of rat fetuses

Background

Feeding oxidized fats causes activation of peroxisome proliferator-activated receptor α (PPARα) in the liver of rats. However, whether feeding oxidized fat during pregnancy also results in activation of PPARα in fetal liver is unknown. Thus, this study aimed to explore whether feeding oxidized fat during pregnancy causes a PPARα response in fetal liver. Two experiments with pregnant rats which were administered three different diets (control; oxidized fat; clofibrate as positive control) in a controlled feeding regimen during either late pregnancy (first experiment) or whole pregnancy (second experiment) were performed.

Results

In both experiments pregnant rats treated with oxidized fat or clofibrate had higher relative mRNA concentrations of the PPARα-responsive genes acyl-CoA oxidase (ACO), cytochrome P₄₅₀ 4A1 (CYP4A1), L-type carnitin-palmitoyl transferase I (L-CPT I), medium-chain acyl-CoA dehydrogenase (MCAD), and long-chain acyl-CoA dehydrogenase (LCAD) in the liver than control rats (P < 0.05). In addition, in both experiments fetuses of the oxidized fat group and the clofibrate group also had markedly higher relative mRNA concentrations of ACO, CYP4A1, CPT I, MCAD, and LCAD in the liver than those of the control group (P < 0.05), whereas the relative mRNA concentrations of PPARα, SREBP-1c, and FAS did not differ between treatment groups. In the second experiment treatment with oxidized fat also reduced triacylglycerol concentrations in the livers of pregnant rats and fetuses (P < 0.05).

Conclusion

The present study demonstrates for the first time that components of oxidized fat with PPARα activating potential are able to induce a PPARα response in the liver of fetuses. Moreover, the present study shows that feeding oxidized fat during whole pregnancy, but not during late pregnancy, lowers triacylglycerol concentrations in fetal livers.

Peroxisome proliferator-activated receptor-alpha and glucocorticoids interactively regulate insulin secretion during pregnancy

We evaluated the impact of peroxisome proliferator-activated receptor (PPAR)alpha activation and dexamethasone treatment on islet adaptations to the distinct metabolic challenges of fasting and pregnancy, situations where lipid handling is modified to conserve glucose. PPARalpha activation (24 h) in vivo did not affect glucose-stimulated insulin secretion (GSIS) in nonpregnant female rats in the fasted state, although fasting suppressed GSIS. Dexamethasone treatment (5 days) of nonpregnant rats lowered the glucose threshold and augmented GSIS at high glucose; the former effect was selectively opposed by PPARalpha activation. Pregnancy-induced changes in GSIS were opposed by PPARalpha activation at day 19 of pregnancy. Dexamethasone treatment from day 14 to 19 of pregnancy did not modify the GSIS profile of perifused islets from 19-day pregnant rats but rendered the islet GSIS profile refractory to PPARalpha activation. During sustained hyperglycemia in vivo, dexamethasone treatment augmented GSIS in nonpregnant rats but limited further modification of GSIS by pregnancy. We propose that the effect of PPARalpha activation to oppose lowering of the glucose threshold for GSIS by glucocorticoids is important as part of the fasting adaptation, and modulation of the islet GSIS profile by glucocorticoids toward term facilitates the transition of maternal islet function from the metabolic demands of pregnancy to those imposed after parturition.

Englitazone administration to late pregnant rats produces delayed body growth and insulin resistance in their fetuses and neonates

The level of maternal circulating triacylglycerols during late pregnancy has been correlated with the mass of newborns. PPARgamma (peroxisome-proliferator-activated receptor gamma) ligands, such as TZDs (thiazolidinediones), have been shown to reduce triacylglycerolaemia and have also been implicated in the inhibition of tissue growth and the promotion of cell differentiation. Therefore TZDs might control cell proliferation during late fetal development and, by extension, body mass of pups. To investigate the response to EZ (englitazone), a TZD, on perinatal development, 0 or 50 mg of englitazone/kg of body mass was given as an oral dose to pregnant rats daily from day 16 of gestation until either day 20 for the study of their fetuses, or until day 21 of gestation for the study of neonates. EZ decreased maternal triacylglycerol levels at day 20 of gestation and neonatal mass, but not fetal mass. Fetuses and neonates from EZ-treated mothers exhibited high levels of insulin and were found to be hyperglycaemic. The apparent insulin-resistant state in neonates from EZ-treated pregnant rats was corroborated, since they showed higher plasma NEFA [non-esterified ('free') fatty acid] levels, ketonaemia and liver LPL (lipoprotein lipase) activity and lower plasma IGF-I (type 1 insulin-like growth factor) levels, in comparison with those from control mothers. Moreover, at the molecular level, an increase in Akt phosphorylation was found in the liver of neonates from EZ-treated mothers, which confirms that the insulin pathway was negatively affected. Thus the response of fetuses and neonates to maternal antidiabetic drug treatment is the opposite of what would be expected, and can be justified by the scarce amount of adipose tissue impeding a normal response to PPARgamma ligands and by hyperinsulinaemia as being responsible for a major insulin-resistant condition.

Fenofibrate, a peroxisome proliferator-activated receptor alpha agonist, exerts neuroprotective effects in traumatic brain injury

Peroxisome proliferator-activated receptor alpha (PPARalpha) has been demonstrated to reduce inflammation in various inflammatory diseases. As traumatic brain injury (TBI) caused a neuroinflammatory response, we examined the effect of fenofibrate, a PPARalpha agonist, on the post-traumatic consequences caused by lateral fluid percussion of brain in rats. The effects of fenofibrate (50 and 100mg/kg) were evaluated on the consequences of TBI in the early phase (6 and 24h) and the late phase (7 days) after TBI. Neurological deficit, brain lesion, cerebral oedema and ICAM-1 expression were evaluated. Treatment with fenofibrate (given p.o. at 1 and 6h after TBI) decreases the neurological deficit induced by TBI at 24h. Furthermore, fenofibrate reduces brain oedema and ICAM-1 expression at 24h post-TBI. Rats given fenofibrate at 1, 6, 24, 48 and 72h after TBI show neurological recovery associated with a reduction of the brain lesion at 7 days post-TBI. The present data represents the first demonstration that fenofibrate, a PPARalpha agonist, exerts neuroprotective effects in TBI. The activation of receptor PPARalpha could be beneficial by counteracting the deleterious inflammatory response following TBI. This suggests that PPARalpha activation could be a new and promising therapeutic strategy for the treatment of brain trauma.

Triglyceridemia and peroxisome proliferator- activated receptor-α expression are not connected in fenofibrate-treated pregnant rats

To investigate the response to fenofibrate in pregnant rats, 0 mg, 100 mg or 200 mg of fenofibrate per kilogram body weight oral doses were given twice a day from day 16 of gestation and studied at day 20. Virgin rats were studied in parallel. Whereas in pregnant rats plasma triglycerides significantly increased, in virgin rats, fenofibrate decreased plasma triglycerides which accumulated in liver. Fenofibrate faithfully modulated the hepatic expression of PPARalpha responsive genes. Fenofibrate increased mRNA contents corresponding to both acyl-CoA oxidase, carnitine palmitoyltransferase (CPT), and peroxisome proliferator-activated receptor alpha (PPAR), and lowered mRNA amounts of apolipoproteins B and C-III, both in virgin and pregnant rats. However, genes related to hepatic lipogenesis, such as PPARy and stearoyl-CoA desaturase (SCD), showed an augmented expression by fenofibrate in virgin rats, but not in pregnant animals. We propose that the opposite effects of fenofibrate treatment in virgin and pregnant rats are a consequence of the enhanced capability for VLDL-triglyceride production in the latter, further promoted by the elevated amount of free fatty acids (FFA), which reach the liver in treated pregnant rats and were not sufficiently oxidized and/or stored, and therefore would have to be canalized as triglycerides to the plasma. Thus, the present study shows how fenofibrate, in spite of efficiently exerting its expected molecular effects in the liver (i.e., to induce fatty acid and lipoprotein catabolism, and to reduce TG-rich lipoprotein secretion), was unable to reverse the typical hypertriglyceridaemia of gestation.

Potential role of peroxisome proliferator-activated receptor-alpha in the modulation of glucose-stimulated insulin secretion

In this review, we discuss the influence of peroxisome proliferator-activated receptor (PPAR)-alpha on islet insulin secretion and develop the hypothesis that modulation of PPAR-alpha function may be important for the regulation of compensatory insulin secretion. We have attempted to analyze the role of PPAR-alpha-linked fatty acid metabolism in islet function in health and in insulin-resistant states linked to lifestyle factors, in particular pregnancy and a diet inappropriately high in saturated fat. We have emphasized the potential for both actions of PPAR-alpha on insulin sensitivity that may be relayed systemically to the islet, leading to modulation of the insulin response in accordance with changes in insulin sensitivity, and direct effects of PPAR-alpha action on the islet itself. Finally, we have developed the concept that compensatory insulin secretion may have a function not only in glucoregulation but also in liporegulation. Thus, augmented insulin secretion may reflect a requirement for lipid lowering as well as for increased glucose disposal and is perceived to aim to compensate for impaired suppression of islet lipid delivery by insulin. This introduces the possibility of a continuum between liporegulation with islet compensation and lipodysregulation leading to islet decompensation in the development of type 2 diabetes.

Peroxisome proliferator-activated receptor-alpha activation during pregnancy attenuates glucose-stimulated insulin hypersecretion in vivo by increasing insulin sensitivity, without impairing pregnancy-induced increases in beta-cell glucose sensing and responsiveness

We investigated the effects of acute (24-h) peroxisome proliferator-activated receptor (PPAR)alpha activation by WY14,643 (pirinixic acid) treatment on glucose-stimulated insulin secretion (GSIS) during pregnancy, in the rat, in relation to insulin sensitivity. GSIS after iv glucose challenge (500 mg/kg) was increased at d 15 of pregnancy but was attenuated by WY14,643 treatment in vivo, with decreases in acute insulin response (51%; P < 0.001) and total suprabasal 30-min area under the insulin curve (deltaI) (55%; P < 0.001). GSIS was unaffected by WY14,643 treatment in unmated rats. Islet perifusions were employed to identify persistent effects of PPARalpha activation. GSIS was enhanced, and the glucose threshold was reduced in perifused islets from pregnant rats, but WY14,643 treatment failed to reverse these effects. WY14,643 treatment of 15-d-pregnant rats significantly lowered (by 63%; P < 0.01) the insulin resistance index [total suprabasal 30-min area under insulin curve x suprabasal 30-min area under glucose curve (deltaI x deltaG)]. A strong positive linear relationship (r = 0.92) between acute insulin response and deltaI x deltaG was evident between groups. Our studies show that acute PPARalpha activation reverses the augmented GSIS evoked by pregnancy in vivo, whereas the isolated islets retain pregnancy-induced enhancement of beta-cell glucose sensing and responsiveness. Normalization of maternal GSIS to that found in the nonpregnant state is observed in association with alleviation of maternal insulin resistance.