Characterization of an Agarophyton chilense Oleoresin Containing PPARγ Natural Ligands with Insulin-Sensitizing Effects in a C57Bl/6J Mouse Model of Diet-Induced Obesity and Antioxidant Activity in Caenorhabditis elegans.

The biomedical potential of the edible red seaweed Agarophyton chilense (formerly Gracilaria chilensis) has not been explored. Red seaweeds are enriched in polyunsaturated fatty acids and eicosanoids, which are known natural ligands of the PPARγ nuclear receptor. PPARγ is the molecular target of thiazolidinediones (TZDs), drugs used as insulin sensitizers to treat type 2 diabetes mellitus. Medical use of TZDs is limited due to undesired side effects, a problem that has triggered the search for selective PPARγ modulators (SPPARMs) without the TZD side effects. We produced Agarophyton chilense oleoresin (Gracilex®), which induces PPARγ activation without inducing adipocyte differentiation, similar to SPPARMs. In a diet-induced obesity model of male mice, we showed that treatment with Gracilex® improves insulin sensitivity by normalizing altered glucose and insulin parameters. Gracilex® is enriched in palmitic acid, arachidonic acid, oleic acid, and lipophilic antioxidants such as tocopherols and ß-carotene. Accordingly, Gracilex® possesses antioxidant activity in vitro and increased antioxidant capacity in vivo in Caenorhabditis elegans. These findings support the idea that Gracilex® represents a good source of natural PPARγ ligands and antioxidants with the potential to mitigate metabolic disorders. Thus, its nutraceutical value in humans warrants further investigation.

A PPARs cross-talk concertedly commits C6 glioma cells to oligodendrocytes and induces enzymes involved in myelin synthesis.

Peroxisome proliferator activated receptors (PPARs, alpha, beta/delta, gamma) control lipid homeostasis and differentiation in various tissues and tumor cells. PPARbeta and PPARgamma increase oligodendrocyte maturation in glial mixed populations and spinal cord oligodendrocytes, respectively, and PPARbeta is known to modulate the activity of other PPARs. To assess a possible interaction between PPARs in glial cell differentiation we used the undifferentiated C6 glioma cell line as model. These cells express all three PPARs, but only PPARgamma shows transcriptional activity in agonist-based reporter gene assay. Agonist-activated PPARgamma up-regulates oligodendrocyte markers, down-regulates an astrocyte marker, and increases alkyl-dihydroxyacetone phosphate synthase, enzyme involved in the synthesis of myelin-rich plasmalogens. Similar effects are induced in PPARgamma overexpressing cells, which in addition show PPARbeta up-regulation. PPARbeta or PPARalpha agonists show no effect. Nevertheless, PPARbeta overexpression up-regulates PPARgamma and commits C6 cells to oligodendrocytes; effect that is abrogated by a PPARgamma antagonist or PPARgamma interference RNA. Moreover, PPARbeta overexpression also induces PPARalpha and its target genes, including acyl-CoA oxidase, enzyme involved in very long chain fatty acid recycling, and in the synthesis of myelin components such as docosahexaenoic acid. These results indicate for the first time, that PPARs concertedly cooperate in C6 glioma cell differentiation to oligodendrocytes. Further, they suggest that active PPARbeta might be essential for increasing oligodendrocyte distinctive markers and enzymes required for myelin synthesis in C6 glioma cells through up-regulation of PPARgamma and PPARalpha.

P450 CYP2C epoxygenase and CYP4A omega-hydroxylase mediate ciprofibrate-induced PPARalpha-dependent peroxisomal proliferation.

Peroxisomal proliferators, such as ciprofibrate, are used extensively as effective hypolipidemic drugs. The effects of these compounds on lipid metabolism require ligand binding activation of the peroxisome proliferator-activated receptor (PPAR) alpha subtype of nuclear receptors and involve transcriptional activation of the metabolic pathways involved in lipid oxidative metabolism, transport, and disposition. omega-Hydroxylated-eicosatrienoic acids (HEETs), products of the sequential metabolism of arachidonic acid (AA) by the cytochrome P450 CYP2C epoxygenase and CYP4A omega-hydroxylase gene subfamilies, have been identified as potent and high-affinity ligands of PPARalpha in vitro and as PPARalpha activators in transient transfection assays. Using isolated rat hepatocytes in culture, we demonstrate that specific inhibition of either the CYP2C epoxygenase or the CYP4A omega-hydroxylase abrogates ciprofibrate-induced peroxisomal proliferation, whereas inhibition of other eicosanoid-synthesizing pathways had no effect. Conversely, overexpression of the rat liver CYP2C11 epoxygenase leads to spontaneous peroxisomal proliferation, an effect that is reversed by a CYP inhibitor. Based on these results, we propose that HEETs may serve as endogenous PPARalpha ligands and that the P450 AA monooxygenases participate in ciprofibrate-induced peroxisomal proliferation and the activation of PPARalpha downstream targets.

The hypolipidemic drug metabolites nafenopin-CoA and ciprofibroyl-CoA are competitive P2Y1 receptor antagonists.

Coenzyme A (CoA-SH), endogenous and drug-derived CoA-derivatives were tested as putative antagonists of P2Y receptors expressed in Xenopus laevis oocytes, a method used to determine calcium-activated chloride current, an indicator of the activation of these receptors. CoA-SH antagonized reversibly and in a concentration-dependent manner the ATP-gated currents evoked by the human P2Y(1) but not the P2Y(2) receptor. Palmitoyl-CoA was four-fold more potent than CoA-SH as an antagonist while palmitoyl-carnitine was inactive, highlighting the role of the CoA-SH moiety in the antagonism. The CoA derivatives of nafenopin and ciprofibrate, two clinically relevant hypolipidemic drugs, increased 13 and three-fold the potency of CoA-SH, respectively. The K(B)s of nafenopin-CoA and ciprofibroyl-CoA were 58 and 148 nM, respectively; the slopes of the Schild plots were unitary. Neither 100 microM nafenopin nor ciprofibrate alone altered the P2Y(1) receptor activity. Neither CoA-SH nor ciprofibroyl-CoA antagonized the rat P2X(2) or the P2X(4) nucleotide receptors nor interacted with the 5-HT(2A/C) receptors. The bulky drug CoA-SH derivatives identify a hydrophobic pocket, which may serve as a potential target for novel selective P2Y(1) antagonists.