Rimonabant, a selective cannabinoid CB1 receptor antagonist, inhibits atherosclerosis in LDL receptor-deficient mice.

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 mm(2)) and aortic sinus (from 101,000+/-7800 to 27,000+/-2900 microm(2)) 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 microm(2), 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 IL1beta-induced proinflammatory gene expression in mouse peritoneal macrophages in vitro as well as thioglycollate-induced recruitment of macrophages in vivo (10 mg/kg, p.o. 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 fatty acid metabolism is preserved in the compensated hypertrophic rat heart.

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.

Metabolic remodelling of the failing heart: the cardiac burn-out syndrome?

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.

Peroxisome proliferator-activated receptor (PPAR) alpha and PPARbeta/delta, but not PPARgamma, modulate the expression of genes involved in cardiac lipid metabolism.

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.

Peroxisome proliferator-activated receptors: lipid binding proteins controling gene expression.

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 (PPARalpha, beta/delta and gamma, 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 corepressors). 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.

Monolayers of IEC-18 cells as an in vitro model for screening the passive transcellular and paracellular transport across the intestinal barrier: comparison of active and passive transport with the human colon carcinoma Caco-2 cell line.

PURPOSE: previous studies have shown that the rat small intestinal cell line IEC-18 provides a size-selective barrier for paracellularly transported hydrophilic macromolecules. In order to determine the utility of IEC-18 cells as an in vitro model to screen the passive paracellular and transcellular components of the intestinal transport of nutrients and drugs, we have now examined the transport of GlySar (H(+)-coupled di/tripeptide carrier), O-methyl-d-glucose (glucose carrier), vincristine and rhodamine 123 (P-glycoprotein), and calcein and DNPSG (MRPs) and the bidirectional transport of paracellularly transported compounds. Transport of these compounds across the filter grown IEC-18 cells was compared with transport across the human colon carcinoma Caco-2 cells. RESULTS: in IEC-18 cells, transepithelial transport of GlySar and methylglucose was as fast as the transport of mannitol, which is transported passively via the paracellular route. Whereas in Caco-2 cells, mannitol transport was much slower than the transport of GlySar and methylglucose. In contrast to Caco-2 cells, no H(+)-coupled transport of GlySar could be measured in IEC-18 cells. P-Glycoprotein-mediated transport was characterised in Caco-2 cells by an enhanced transport of vincristine and rhodamine 123 in the basolateral to apical direction and by the inhibition of this transport by verapamil. In IEC-18 cells, permeability of vincristine and rhodamine 123 was similar in both directions and verapamil had no effect on the transport of these compounds. Both IEC-18 and Caco-2 cells efflux the organic anions calcein and DNPSG to the apical and basolateral compartments, and this efflux could be inhibited by probenecid. CONCLUSIONS: in conclusion, no carrier-mediated transport of GlySar, methylglucose, vincristine and rhodamine 123 could be determined in IEC-18 cells in contrast to Caco-2 cells. However, both IEC-18 and Caco-2 cells showed MRP-mediated eflux system(s) in the apical and basolateral membrane. Monolayers of IEC-18 cells appear to be more suitable than monolayers of Caco-2 cells as an in vitro system to screen the passive component of the intestinal transport in a deconvoluted screening regimen, where passive transport is represented by the IEC-18 monolayer permeability and active transport is represented by monolayers of cells expressing the transport proteins heterologously.