This article is available online at http://www.jlr.org Triglycerides (TGs) are the chief route of transport of dietary fat within chylomicrons and VLDLs, as well as the main form of fuel storage in adipose tissue. TGs are synthesized from one glycerol and three FA molecules, which are attached via ester bonds to the hydroxyl groups of the glycerol backbone. Two major diacylglycerol acyltransferase (DGAT) isozymes, DGAT1 and DGAT2, have been identifi ed. Although both enzymes convert diacylglycerol to TG, they do not share similarity in either their nucleotide or amino acid sequences and have most probably arisen by convergent evolution ( 1, 2 ). Although there are some differences in their tissue distributions, both DGAT1 and DGAT2 are highly expressed in organs that synthesize large amounts of TG, such as the liver, adipose tissue, and small intestine ( 3 ).Studies with genetically altered mice, as well as in vivo suppression of DGAT expression, indicate that both DGAT1 and DGAT2 play important roles in TG synthesis. DGAT1 knockout mice (DGAT1 Ϫ / Ϫ ) have reduced tissue TG levels and exhibit increased sensitivity to insulin and leptin ( 4 ). In addition, they are resistant to high-fat dietinduced obesity as a result of an increase in their metabolic rates ( 4 ). In contrast, knockout mice lacking DGAT2 (DGAT2 Ϫ / Ϫ ) are lipopenic and die soon after birth as a result of profound reductions in substrates for energy metabolism and impaired skin permeability ( 5 ). Hepatic suppression of DGAT2 with antisense oligonucleotides (ASOs) reduced hepatic TG content in rodents ( 6, 7 ), and reversed diet-induced hepatic steatosis and insulin resistance Abstract Diacylglycerol acyltransferase (DGAT) catalyzes the fi nal step in triglyceride (TG) synthesis. There are two isoforms, DGAT1 and DGAT2, with distinct protein sequences and potentially different physiological functions. To date, the ability to determine clear functional differences between DGAT1 and DGAT2, especially with respect to hepatic TG synthesis, has been elusive. To dissect the roles of these two key enzymes, we pretreated HepG2 hepatoma cells with

Anandamide amidohydrolase (AAH) catalyzes the hydrolysis of arachidonylethanolamide (anandamide), an endogenous cannabinoid receptor ligand. To delineate the structural requirements of AAH substrates, rat brain microsomal AAH hydrolysis of a series of anandamide congeners was studied using two reverse-phase high-performance liquid chromatography (RP-HPLC) assays developed in our laboratory. Arachidonamide (1) was found to be the best substrate with an apparent Km of 2.34 mM and a Vmax of 2.89 nmol/min/mg of protein. Although anandamide (2) has a similar Km value, its Vmax is approximately one-half that of arachidonamide. N, N-Bis(2-hydroxyethyl)arachidonamide (3) was not hydrolyzed, suggesting specificity for unsubstituted or mono-N-substituted arachidonamides. Analogues with a methyl group at the 1'-position of the ethanolamido headgroup were also found to have greater resistance to enzymatic turnover and therefore increased metabolic stability. The enzyme exhibited high stereoselectivity as the rate of hydrolysis of (R)-alpha-methanandamide (2.4%) (anandamide = 100%) was about 10-fold lower than that of its (S)-enantiomer (23%). In contrast, (R)-beta-methanandamide was 6-times more susceptible (121%) than the (S)-beta-enantiomer (21%). Interestingly, an inverse correlation was shown between AAH stereoselectivity and the brain cannabinoid receptor affinity as the enantiomers with high receptor affinity displayed low susceptibility to hydrolysis by AAH. Metabolic stability is also imparted to analogues with a short hydrocarbon headgroup as well as to those possessing 2-monomethyl or 2,2-dimethyl substituents. 2-Arachidonylglycerol and racemic 1-arachidonylglycerol were shown to be excellent AAH substrates. To identify AAH inhibitors, hydrolysis of anandamide was also studied in the presence of a select group of cannabimimetics. Of these, (-)-Delta8-THC and SR141716A, a biarylpyrazole CB1 antagonist, were found to inhibit enzymatic activity. These newly defined enzyme recognition parameters should provide a foundation for the rational development of stable, therapeutically useful anandamide analogues with high receptor affinity.

energy storage, membrane components, and signaling. Extracellular hydrolysis of dietary TG in circulating lipoproteins yields FFAs and sn -2 MG, which are then taken up by cells ( 1,2 ). MGs are also produced intracellularly from membrane phospholipids and the consecutive action of phospholipase C and diacylglycerol lipase, or from the hydrolysis of stored TG by adipose TG lipase (ATGL) and hormone sensitive lipase (HSL) ( 2-5 ). The ultimate fate of intracellular MGs is hydrolysis to FFAs and glycerol or reesterifi cation by acyltransferases into diacylglycerol and TG ( 6, 7 ).MG lipase (MGL) is considered the rate-determining enzyme in MG catabolism. MGL accounts for roughly 85% of MG hydrolysis in the brain, with the remainder being catalyzed by the enzymes ABHD6 and ABHD12 ( 8,9 ). MGL is expressed in many other tissues as well, including brain, liver, skeletal muscle, adipose, and intestine ( 10-13 ). Within cells, MGL localizes to both the cytosolic and membrane fractions and hydrolyzes sn -1 and sn -2 MGs of varying acyl chain lengths and degrees of unsaturation, with almost no activity toward other lipids, such as TG and lyso-phospholipids ( 10,(14)(15)(16)(17)(18).MGL is involved in energy balance through two important functions. Abbreviations: AA, arachidonic acid; AEA, arachidonoyl ethanolamide; 2-AG, 2-arachidonoyl glycerol; AUC, area under the curve; CB, cannabinoid; EC, endocannabinoid; HFD, high-fat diet; HOMA-IR, homeostatic model assessment of insulin resistance; iMGL, mice that overexpress monoacylglycerol lipase specifi cally in the intestinal mucosa; LFD, low-fat diet; MG, monoacylglycerol; MGL, monoacylglycerol lipase; OFTT, oral fat tolerance test; OGTT, oral glucose tolerance test; RER, respiratory exchange ratio .

In Table 2, the IC 50 's of compounds 3 and 4 should be switched: compound 3, >50 a ; compound 4, 13.3 a .

ABSTRACT:Comparative metabolite profiling of geldanamycin and 17-allylamino-17-demethoxygeldanamycin (17AAG) using human liver microsomes in normoxia and hypoxia was conducted to understand their differential metabolic fates. Geldanamycin bearing a 17-methoxy group primarily underwent reductive metabolism, generating the corresponding hydroquinone under both conditions. The formed hydroquinone resists further metabolism and serves as a reservoir. On exposure to oxygen, this hydroquinone slowly reverts to geldanamycin. In the presence of glutathione, geldanamycin was rapidly converted to 19-glutathionyl geldanamycin hydroquinone, suggesting its reactive nature. In contrast, the counterpart (17AAG) preferentially remained as its quinone form, which underwent extensive oxidative metabolism on both the 17-allylamino sidechain and the ansa ring. Only a small amount (<1%) of 19-glutathione conjugate of 17AAG was detected in the incubation of 17AAG with glutathione at 37°C for 60 min. To confirm the differential nature of quinone-hydroquinone conversion between the two compounds, hypoxic incubations with human cytochrome P450 reductase at 37°C and direct injection analysis were performed. Approximately 89% of hydroquinone, 5% of quinone, and 6% of 17-O-demethylgeldanamycin were observed after 1-min incubation of geldanamycin, whereas about 1% of hydroquinone and 99% of quinone were found in the 60-min incubation of 17AAG. The results provide direct evidence for understanding the 17-substituent effects of these benzoquinone ansamycins on their phase I metabolism, reactivity with glutathione, and acute hepatotoxicity.The benzoquinone ansamycins geldanamycin and 17-allylamino-17-demethoxygeldanamycin (17AAG) (Fig. 1) are potent antitumor agents that have undergone preclinical (Supko et al., 1995;Eiseman et al., 1997) and clinical (Banerji et al., 2005;Ramanathan et al., 2005) evaluations for their potential value in fighting cancers. The mechanism regarding the antineoplastic activity of these ansamycins has been extensively studied and showed to proceed through specific binding to the cytoplasmic heat shock protein 90 (HSP90) (Stebbins et al., 1997;Schulte and Neckers, 1998) and its endoplasmic reticulum homolog, glucose-regulated protein 94 (Chavany et al., 1996). Interaction of these ansamycins with the chaperone protein folding machinery results in disruption of heteroprotein complexes and blocking of the refolding and conformational maturation of numerous oncogenic client proteins, i.e., p185 erbB2 (Miller et al., 1994; Schnur et al., 1995a,b) , which are involved in signal transduction in regulation of cell proliferation, apoptosis, and angiogenesis. It is known that the unfolded client proteins are susceptible to degradation via the ubiquitination-proteasome pathway. However, recent findings from electron spin resonance studies of the production of reactive oxygen species (i.e., superoxide anion and hydrogen peroxide) mediated by geldanamycin leading to oxidative stress and cell death argued against the HSP90 inhi...