Objective—The objective of this study was to determine whether the potent selective cannabinoid receptor-1 antagonist rimonabant has antiatherosclerotic properties. Methods and Results—Rimonabant (50 mg/kg/d in the diet) significantly reduced food intake (from 3.35±.04 to 2.80±0.03 g/d), weight gain (from 14.6±0.7 g to −0.6±0.3 g), serum total cholesterol (from 8.39±0.54 to 5.32±0.18 g/L), and atherosclerotic lesion development in the aorta (from 1.7±0.22 to 0.21±0.037 mm2) and aortic sinus (from 101 000±7800 to 27 000±2900 &mgr;m2) of LDLR−/− mice fed a Western-type diet for 3 months. Rimonabant also reduced plasma levels of the proinflammatory cytokines MCP-1 and IL12 by 85% (P<0.05) and 76% (P<0.05), respectively. Pair-fed animals had reduced weight gain (6.2±0.6 g gain), but developed atherosclerotic lesions which were as large as those of untreated animals, showing that the antiatherosclerotic effect of rimonabant is not related to reduced food intake. Interestingly, rimonabant at a lower dose (30 mg/kg/d in the diet) reduced atherosclerosis development in the aortic sinus (from 121 000±20 000 to 62 000±11 000 &mgr;m2, 49% reduction, P<0.05), without affecting serum total cholesterol (7.8±0.7 g/L versus 8.1±1.3 g/L in the control group). Rimonabant decreased lipopolysaccharide (LPS)- and IL1&bgr;-induced proinflammatory gene expression in mouse peritoneal macrophages in vitro as well as thioglycollate-induced recruitment of macrophages in vivo (10 mg/kg, po bolus). Conclusions—These results show that rimonabant has antiatherosclerotic effects in LDLR−/− mice. These effects are partly unrelated to serum cholesterol modulation and could be related to an antiinflammatory effect.

Cardiac hypertrophy and failure are associated with alterations in cardiac substrate metabolism. It remains to be established, however, whether genomically driven changes in cardiac glucose and fatty acid (FA) metabolism represent a key event of the hypertrophic remodeling process. Accordingly, we investigated metabolic gene expression and substrate metabolism during compensatory hypertrophy, in relation to other cardiac remodeling processes. Thereto, cardiac hypertrophy was induced in rats by supra-renal aortic constriction to various degrees, resulting in increased heart/body weight ratios of 22% (Aob-1), 24% (Aob-2) and 32% (Aob-3) (p < 0.005) after 4 weeks. The unaltered ejection fraction in all groups indicated that the hypertrophy was still compensatory in nature. beta-Myosin Heavy Chain protein and ANF mRNA levels were increased in all groups. Only in Aob-3 rats were SERCA2a mRNA levels markedly reduced. In this group, glycolytic capacity was modestly elevated (+ 25%; p < 0.01). Notwithstanding these phenotypical changes, the expression of genes involved in FA metabolism and FA oxidation rate in cardiac homogenates was completely preserved, irrespective of the degree of hypertrophy. These findings indicate that cardiac FA oxidative capacity is preserved during compensatory hypertrophy, and that a decline in metabolic gene expression does not represent a hallmark of the development of hypertrophy.

Preferential and specific down-regulation of genes involved in fatty acid (FA) uptake and metabolism is considered a hallmark of severe hypertrophic remodeling and progression to cardiac failure. Therefore, we investigated the time course of changes in cardiac metabolic gene expression (1) in mice subjected to regional myocardial infarction (MI) for 4 days, 1 month, or 3 months and (2) in mice overexpressing calcineurin (Cn) which initially develop concentric hypertrophy progressing after the age of 4 weeks to dilated cardiomyopathy and failure. In both models, hypertrophy was characterized by increased expression of beta-myosin heavy chain protein and atrial natriuretic factor mRNA, indicative of marked structural remodeling. Fractional shortening progressively decreased from 31% to 15.1% and 3.7% 1 and 3 months after MI, respectively. One month post-MI, the expression of several metabolic genes, i.e., acyl-CoA synthetase (-50%), muscle-type carnitine palmitoyl transferase 1 (-37%) and citrate synthase (-28%), was significantly reduced in the surviving myocardium. Despite overt signs of cardiac failure 3 months post-MI, the expression of these genes had returned to normal levels. In hearts of both 4- and 6-week-old Cn mice, genes involved in both FA and glucose metabolism and mitochondrial citrate synthase were down-regulated, reflecting an overall decline in metabolic gene expression, rather than a specific and preferential down-regulation of genes involved in FA uptake and metabolism. These findings challenge the concept that specific and sustained down-regulation of genes involved in FA uptake and metabolism represents a hallmark of the development of cardiac hypertrophy and progression to failure.

It has been postulated that the failing heart suffers from chronic energy starvation, and that derangements in cardiac energy conversion are accessory to the progressive nature of this disease. The molecular mechanisms driving this 'metabolic remodelling' process and their significance for the development of cardiac failure are still open to discussion. Next to changes in mitochondrial function, the hypertrophied heart is characterized by a marked shift in substrate preference away from fatty acids towards glucose. It has been argued that the decline in fatty acid oxidation is not fully compensated for by a rise in glucose oxidation, thereby imposing an additional burden on overall ATP generating capacity. Several lines of evidence suggest that these metabolic adaptations are brought about, at least in part, by alterations in the rate of transcription of genes encoding for proteins involved in substrate transport and metabolism. Here, the principal metabolic changes are reviewed and the various molecular mechanisms that are likely to play a role are discussed. In addition, the potential significance of these changes for the aetiology of heart failure is evaluated.

Long-chain fatty acids (FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome proliferator-activated receptors (PPARs). Whereas the significance of PPAR in FA-mediated expression has been demonstrated, the role of the PPAR / and PPAR isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPAR (Wy-14,643), PPAR / (L-165041, GW501516), or PPAR (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPAR and PPAR / ligands, but not to PPAR ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPAR and PPAR / , but not by PPAR ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPAR / , the FA-induced expression of genes was mimicked by the PPAR / ligand only, indicating that FA also act as ligands for the PPAR / isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPAR ligands. However, addition of PPAR and PPAR / ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPAR , PPAR / , but not PPAR , plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPAR / in cardiac disease. (Circ Res. 2003;92:518-524.)

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. The three isoforms (PPARalpha, beta/delta and gamma) have been implicated in the regulation of the expression of genes involved in lipid metabolism. Although their prominent role in lipid homeostasis is well established, the way in which the activity of each of the PPAR isoforms is regulated under physiological and pathological conditions is still subject of intensive research. In skeletal as well as cardiac muscle cells it has been demonstrated that the expression of a large panel of proteins involved in the transport and metabolic conversion of fatty acids is under control of PPARs. The pivotal role of the PPARalpha isoform in cardiac fatty acid metabolism has been confirmed in PPARalpha-null mice. The exact role of PPARbeta/delta in the regulation of muscle metabolism is still a matter of debate. Whereas several studies provided evidence to support the notion that PPARalpha and PPARbeta/delta have redundant roles, other studies suggest that PPARalpha activity is counteracted by PPARbeta/delta. Marked effects of bona fide PPARgamma ligands (the anti-diabetic thiazolidinediones) on skeletal and cardiac muscle function and phenotype, have also been reported. However, next to activating PPARgamma, the thiazolidinediones do affect other cellular processes as well. To date it is being realized that the control of the trans-activating capacity of each of the PPAR isoforms is multi-factorial and, in addition to ligand availability, depends on such factors as isoform-specific phosphorylation and selective interaction with various proteins acting either as co-activator or co-repressor.

Abstract— Long-chain fatty acids (FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome proliferator-activated receptors (PPARs). Whereas the significance of PPAR&agr; in FA-mediated expression has been demonstrated, the role of the PPAR&bgr;/&dgr; and PPAR&ggr; isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPAR&agr; (Wy-14,643), PPAR&bgr;/&dgr; (L-165041, GW501516), or PPAR&ggr; (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPAR&agr; and PPAR&bgr;/&dgr; ligands, but not to PPAR&ggr; ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPAR&agr; and PPAR&bgr;/&dgr;, but not by PPAR&ggr; ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPAR&bgr;/&dgr;, the FA-induced expression of genes was mimicked by the PPAR&bgr;/&dgr; ligand only, indicating that FA also act as ligands for the PPAR&bgr;/&dgr; isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPAR&ggr; ligands. However, addition of PPAR&agr; and PPAR&bgr;/&dgr; ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPAR&agr;, PPAR&bgr;/&dgr;, but not PPAR&ggr;, plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPAR&bgr;/&dgr; in cardiac disease.

Long-chain fatty acids ( FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome proliferator-activated receptors (PPARs). Whereas the significance of PPARalpha in FA-mediated expression has been demonstrated, the role of the PPARbeta/delta and PPARgamma isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPARalpha (Wy-14,643), PPARbeta/delta (L-165041, GW501516), or PPARgamma (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPARalpha and PPARbeta/delta ligands, but not to PPARgamma ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPARalpha and PPARbeta/delta, but not by PPARgamma ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPARbeta/delta, the FA-induced expression of genes was mimicked by the PPARbeta/delta ligand only, indicating that FA also act as ligands for the PPARbeta/delta isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPARgamma ligands. However, addition of PPARalpha and PPARbeta/delta ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPARalpha, PPARbeta/delta, but not PPARgamma, plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPARbeta/delta in cardiac disease.

In heart failure, thyroid hormone (TH) treatment improves cardiac performance. The long-term effects of TH on cardiac function and metabolism, however, are incompletely known. To investigate the effects of up to 28 days of TH treatment, male Wistar rats received 3,3',5-triiodo-l-thyronine (200 microg/kg sc per day) leading to a 2.5-fold rise in plasma fatty acid (FA) level and progressive cardiac hypertrophy (+47% after 28 days) (P < 0.001). Ejection fraction (echocardiography) was increased (+12%; P < 0.05) between 7 and 14 days and declined thereafter. Neither cardiac FA oxidation, glycolytic capacity (homogenates) per unit muscle mass, nor mRNA levels of proteins involved in FA and glucose uptake and metabolism (Northern blots and microarray) were altered. After 28 days of treatment, mRNA levels of uncoupling proteins (UCP) 2 and 3 and atrial natriuretic factor were increased (P < 0.05). This indicates that TH-induced hypertrophy is associated with an initial increase in cardiac performance, followed by a decline in cardiac function and increased expression of UCPs and atrial natriuretic factor, suggesting that detrimental effects eventually prevail.

Long-chain fatty acids (FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome proliferator-activated receptors (PPARs). Whereas the significance of PPARα in FA-mediated expression has been demonstrated, the role of the PPARβ/δ and PPARγ isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPARα (Wy-14,643), PPARβ/δ (L-165041, GW501516), or PPARγ (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPARα and PPARβ/δ ligands, but not to PPARγ ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPARα and PPARβ/δ, but not by PPARγ ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPARβ/δ, the FA-induced expression of genes was mimicked by the PPARβ/δ ligand only, indicating that FA also act as ligands for the PPARβ/δ isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPARγ ligands. However, addition of PPARα and PPARβ/δ ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPARα, PPARβ/δ, but not PPARγ, plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPARβ/δ in cardiac disease.

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. Since their discovery in the beginning of the nineties the three isoforms (PPARα, β/δ and γ, encoded by different genes) have been implicated in the regulation of almost every single aspect of lipid metabolism and, consequently, in diseases that involve disturbances in lipid metabolism (obesity, diabetes, atherosclerosis, cardiac failure). Although their prominent role in these processes has hardly been disputed, the way in which the activity of these transcription factors is regulated under physiological and pathological conditions awaits further clarification. An unresolved issue has been the nature of the natural ligand of these receptors. Biochemical studies have shown that the PPAR isoforms are rather promiscuous with respect to ligand binding, with a large variety of naturally occurring lipid-like substances acting as low-affinity ligands. More recently this concept has been confirmed by crystallographic studies on the ligand-binding pocket. In addition to ligand availability, the trans-activating capacity likely depends on phosphorylation status of the PPARs and on the recruitment of auxiliary proteins (co-activators and co-repressors). Accordingly, the biological activity of these key-regulators of metabolism is controlled at multiple levels, which enables each tissue to fine tune its metabolic machinery to the demands of the body in a specific fashion.

Abstract—Long-chain fatty acids (FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome,proliferator-activated receptors (PPARs). Whereas the significance of PPAR in FA-mediated expression has been demonstrated, the role of the PPAR/ and PPAR isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPAR (Wy-14,643), PPAR/ (L-165041, GW501516), or PPAR (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPAR and PPAR/ ligands, but not to PPAR ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPAR and PPAR/, but not by PPAR ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPAR/, the FA-induced expression of genes was mimicked by the PPAR/ ligand only, indicating that FA also act as ligands for the PPAR/ isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPAR ligands. However, addition of PPAR and PPAR/ ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPAR, PPAR/, but not PPAR, plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPAR/ in cardiac disease. (Circ Res. 2003;92:518-524.) Key Words: cardiomyocytes,� H9c2 cells � fatty acids � gene expression � uncoupling,protein I