Alpha- and beta- alkyl-substituted eicosapentaenoic acids: incorporation into phospholipids and effects on prostaglandin H synthase and 5-lipoxygenase

Stable analogs of 13‑hydroxy-9,10-trans-epoxy-(11E)-octadecenoate (13,9-HEL), an oxidized derivative of linoleic acid implicated in the epidermal skin barrier

Hydroxy-epoxy- and trihydroxy derivatives of linoleic acid are proposed to play an essential function in formation of the mammalian skin permeability barrier, which could account for the essential nature of its precursor, linoleic acid. Recent literature suggests that a specific oxidized enone derivative of LA esterified in ceramides facilitates binding to proteins, potentially serving a structural role in formation of the epidermal skin barrier. However, it is still to be established if other linoleic acid derivatives are also required for skin barrier formation, and whether the essential role is performed exclusively by an esterified, structural lipid or as an unesterified, labile signaling lipid, or by some combination of these derivatives. Progress in this domain is limited by lack of availability of hydroxy‑epoxy-and trihydroxy- and octadecenoate derivatives of linoleic acid and related compounds, and challenges in maintaining them in the unesterified lipid pool. Here we describe methods for the total synthesis of hydroxy‑epoxy-octadecenoate derivatives of linoleic acid (HEL¹), and stable analogs that are designed to be resistant to inactivation by: (a) acylation/esterification (thus trapping these lipids in the free acid pool), (b) dehydrogenation, and (c) analogs combining both modifications. We further provide a total synthesis of corresponding hydroxy‑epoxy- derivatives of sebaleic acid (a regioisomer of linoleic acid present in skin), and of small molecule scaffolds containing the allylic and non-allylic epoxide 7-carbon substructures shared by both families of hydroxy‑epoxy-and trihydroxy- octadecenoates. Finally, we demonstrate that 2,2-dimethyl analogs of hydroxy‑epoxy-and trihydroxy- octadecenoates are resistant to esterification with an in vitro assay and thus provide a novel template for stabilizing labile, bioactive lipids as free acids by preventing acylation/esterification.

Dual targeting of hepatic fibrosis and atherogenesis by icosabutate, an engineered eicosapentaenoic acid derivative

BACKGROUND & AIMS

While fibrosis stage predicts liver-associated mortality, cardiovascular disease (CVD) is still the major overall cause of mortality in patients with NASH. Novel NASH drugs should thus ideally reduce both liver fibrosis and CVD. Icosabutate is a semi-synthetic, liver-targeted eicosapentaenoic acid (EPA) derivative in clinical development for NASH. The primary aims of the current studies were to establish both the anti-fibrotic and anti-atherogenic efficacy of icosabutate in conjunction with changes in lipotoxic and atherogenic lipids in liver and plasma respectively.

METHODS

The effects of icosabutate on fibrosis progression and lipotoxicity were investigated in amylin liver NASH (AMLN) diet (high fat, cholesterol and fructose) fed ob/ob mice with biopsy-confirmed steatohepatitis and fibrosis and compared with the activity of obeticholic acid. APOE*3Leiden.CETP mice, a translational model for hyperlipidaemia and atherosclerosis, were used to evaluate the mechanisms underlying the lipid-lowering effect of icosabutate and its effect on atherosclerosis.

RESULTS

In AMLN ob/ob mice, icosabutate significantly reduced hepatic fibrosis and myofibroblast content in association with downregulation of the arachidonic acid cascade and a reduction in both hepatic oxidised phospholipids and apoptosis. In APOE*3Leiden.CETP mice, icosabutate reduced plasma cholesterol and TAG levels via increased hepatic uptake, upregulated hepatic lipid metabolism and downregulated inflammation pathways, and effectively decreased atherosclerosis development.

CONCLUSIONS

Icosabutate, a structurally engineered EPA derivative, effectively attenuates both hepatic fibrosis and atherogenesis and offers an attractive therapeutic approach to both liver- and CV-related morbidity and mortality in NASH patients.

Absorption of very-long-chain saturated fatty acids in totally hydrogenated fish oil

Partially hydrogenated fish oil (PHFO) contains a high amount of trans fatty acids (TFA). Total hydrogenation results in a minimal amount of TFA, but a high content of very-long-chain saturated fatty acids (VLCSFA). Absorption and metabolism of VLCSFA from totally hydrogenated fish oil (THFO) were studied in rats. Groups of eight rats were fed one of four diets containing 40 g soyabean oil (SBO)/kg (low-fat diet), 150 g SBO/kg (SBO diet), 40 g SBO+110 g PHFO/kg (PHFO diet) or 40 g SBO+110 g THFO/kg (THFO diet) for 4 weeks. A lower absorption coefficient of the fat content was found in the THFO group (61 %) compared with the other groups (PHFO 95 %, SBO 99 %, low fat 98 %; P<0·05), which was mainly due to reduced absorption of VLCSFA. A reduced weight gain was found for the THFO group compared with the other groups, but this was only significant when compared with the SBO group (P<0·05). Faecal fat excretion (dry weight) was markedly increased in the THFO group (47 %), which was 2·4, 4·8 and 8·3 times higher compared with the groups fed PHFO, SBO and low-fat diets (P<0·05), respectively. Serum total cholesterol was reduced for the PHFO and THFO groups (P<0·05), whereas serum triacylglycerol was increased for the PHFO group compared with the other groups (P<0·05). Animals fed THFO diet had an increased content of 20:0 and 22:0 in the serum triacylglycerol fraction (P<0·05), whereas only 20:0 was increased in the serum phospholipid fraction (P<0·05). The low absorption coefficient of THFO must be considered if this fat is to be used for consumption by animals or man.

Sulfur-substituted and alpha-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an alpha-methyl group and/or a sulfur in the beta-position were tested as peroxisome proliferator-activated receptor (PPAR)alpha, -delta(beta), and -gamma ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARalpha, -delta, and -gamma. For PPARalpha, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C14-S acetic acid (tetradecylthioacetic acid = TTA). The derivatives were poor, and nonsignificant, activators of PPARdelta. For PPARgamma, activation increased with increasing chain length up to C16-S acetic acid. A methyl group was introduced in the alpha-position of palmitic acid, TTA, EPA, DHA, cis9,trans11 CLA, and trans10,cis12 CLA. An increased activation of PPARalpha was obtained for the alpha-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARalpha target genes acyl-CoA oxidase and liver FA-binding protein for alpha-methyl TTA, alpha-methyl EPA, and alpha-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the beta-position and increasing carbon chain length from C9-S acetic acid to C14-S acetic acid have increasing effects as activators of PPARalpha and -gamma in transfection assays. Furthermore, alpha-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARalpha activators than the unmethylated compounds.

Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes

Conjugated linoleic acids (CLAs), tetradecylthioacetic acid (TTA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are all shown to differently affect lipid homeostasis. Additionally, previous studies have shown that introducing a methyl group in the molecule potentiates the hypolipidemic effect of EPA. The objective of this study was to determine how cis9,trans11 CLA, trans10,cis12 CLA, TTA, EPA and DHA affect lipid accumulation in 3T3-L1 adipocytes and in cultured primary rat hepatocytes, and to what extent changes in cis/trans configuration or introducing a methyl group in the molecules influence their way of affecting lipid accumulation in these cells. Our results show that trans10,cis12 CLA is highly specific in preventing lipid accumulation in adipocytes, and that small structural changes in the molecule (changing to trans/trans or introducing an alpha-methyl group) totally abolish this effect and up-regulate the expression levels of adipogenic marker genes towards control levels. Furthermore, all the fatty acids increased hepatic lipid accumulation, whereas the lipid content was normalized after adding an alpha-methyl group into the molecules. Taken together, our data demonstrate that the various fatty acids are highly specialized molecules, and that small structural changes markedly alter their way of affecting lipid accumulation in adipocytes and hepatocytes.

The biochemistry of hypo- and hyperlipidemic fatty acid derivatives: metabolism and metabolic effects

A selection of amphipatic hyper- and hypolipidemic fatty acid derivatives (fibrates, thia- and branched chain fatty acids) are reviewed. They are probably all ligands for the peroxisome proliferation activation receptor (PPARalpha) which has a low selectivity for its ligands. These compounds give hyper- or hypolipidemic responses depending on their ability to inhibit or stimulate mitochondrial fatty acid oxidation in the liver. The hypolipidemic response is explained by the following metabolic effects: Lipoprotein lipase is induced in liver where it is normally not expressed. Apolipoprotein CIII is downregulated. These two effects in liver lead to a facilitated (re)uptake of chylomicrons and VLDL, thus creating a direct transport of fatty acids from the gut to the liver. Fatty acid metabolizing enzymes in the liver (CPT-I and II, peroxisomal and mitochondrial beta-oxidation enzymes, enzymes of ketogenesis, and omega-oxidation enzymes) are induced and create an increased capacity for fatty acid oxidation. The increased oxidation of fatty acids "drains" fatty acids from the body, reduces VLDL formation, and ultimately explains the antiadiposity and improved insulin sensitivity observed after administration of peroxisome proliferators.

Cox-2 inhibitory effects of naturally occurring and modified fatty acids

In the search for new cyclooxygenase-2 (COX-2) selective inhibitors, the inhibitory effects of naturally occurring fatty acids and some of their structural derivatives on COX-2-catalyzed prostaglandin biosynthesis were investigated. Among these fatty acids, linoleic acid (LA), alpha-linolenic acid (alpha-LNA), myristic acid, and palmitic acid were isolated from a CH(2)Cl(2) extract of the plant Plantago major by bioassay-guided fractionation. Inhibitory effects of other natural, structurally related fatty acids were also investigated: stearic acid, oleic acid, pentadecanoic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Further, the inhibitory effects of these compounds on COX-2- and COX-1-catalyzed prostaglandin biosynthesis was compared with the inhibition of some synthesized analogues of EPA and DHA with ether or thioether functions. The most potent COX-2-catalyzed prostaglandin biosynthesis inhibitor was all-(Z)-5-thia-8,11,14,17-eicosatetraenoic acid (2), followed by EPA, DHA, alpha-LNA, LA, (7E,11Z,14Z,17Z)-5-thiaeicosa-7,11,14,17-tetraenoic acid, all-(Z)-3-thia-6,9,12,15-octadecatetraenoic acid, and (5E,9Z,12Z,15Z,18Z)-3-oxaheneicosa-5,9,12,15,18-pentaenoic acid, with IC(50) values ranging from 3.9 to180 microM. The modified compound 2 and alpha-LNA were most selective toward COX-2, with COX-2/COX-1 ratios of 0.2 and 0.1, respectively. This study shows that several of the natural fatty acids as well as all of the semisynthetic thioether-containing fatty acids inhibited COX-2-catalyzed prostaglandin biosynthesis, where alpha-LNA and compound 2 showed selectivity toward COX-2.

Methylated eicosapentaenoic acid and tetradecylthioacetic acid: effects on fatty acid metabolism

We introduced methyl or ethyl groups to the 2- or 3-position of the eicosapentaenoic acid (EPA) molecule to investigate whether the branching of EPA could influence its hypolipidemic effect in rats. The most effective branching involved two methyl groups in the 2-position and one methyl group in the 3-position. These EPA derivatives increased hepatic mitochondrial and peroxisomal beta-oxidation and decreased plasma lipids concomitant with suppressed acetyl-coenzyme A (CoA) carboxylase (EC 6.4.1.2) and fatty acid synthase (EC 2.3.1.85) activities. This was followed by elevated activities of camitine O-palmitoyltransferase (EC 2.3.1.21) and possibly 2,4-dienoyl-CoA reductase (EC 1.3.1.34), as well as induced mRNA levels of these enzymes and fatty acyl-CoA oxidase. The fatty acid composition in liver changed, with an increased 18:1 n-9 content, whereas the expression of delta9-desaturase remained unchanged. We investigated the flux of fatty acids in cultured hepatocytes, and found that oxidation of [1-14C]-labeled palmitic acid increased but the secretion of palmitic acid-labeled triglycerides decreased after addition of 2-methyl-EPA. The fatty acyl-CoA oxidase (EC 1.3.3.6) activity in these cells remained unchanged. A significant negative correlation was obtained between palmitic acid oxidation and palmitic acid-labeled synthesized triglycerides. To investigate whether the hypolipidemic effect occurred independently of induced peroxisomal beta-oxidation, we fed rats 2-methyl-tetradecylthioacetic acid. This compound increased the peroxisomal but not the mitochondrial beta-oxidation, and the plasma lipid levels were unchanged. In conclusion, EPA methylated in the 2- or 3-position renders it more potent as a hypolipidemic agent. Furthermore, this study supports the hypothesis that the mitochondrion is the primary site for the hypolipidemic effect.

Effect of gemfibrozil on serum levels of prostacyclin and precursor fatty acids in hyperlipidemic patients with Type 2 diabetes

Lipid-lowering fibrate drugs are known to affect the synthesis of fatty acids, which may alter the prostacyclin synthesis in diabetic patients. Therefore, the serum levels of precursor fatty acids and 6-keto-prostaglandin F1alpha (6-keto PGF1alpha) were determined in ten hyperlipidemic patients with Type 2 diabetes before and after administration of gemfibrozil (900 mg/day) for 3 months, in comparison with the results in seven non-diabetic hyperlipidemic patients. Gemfibrozil significantly reduced the serum concentration of dihomo-7-linolenic acid, total cholesterol and triglycerides, but did not affect the serum levels of arachidonic acid and 6-keto PGF1alpha in diabetic and non-diabetic patients. Thus, gemfibrozil did not affect the synthesis of prostacyclin in spite of the reduction of precursor fatty acids in diabetic and non-diabetic patients.