Discovery of PEGylated 6-Benzhydryl-4-amino-quinazolines as Peripherally Restricted CB1R Inverse Agonists.

The 6-benzhydryl-4-amino-quinolin-2-ones are peripherally restricted CB1 receptor inverse agonists (CB1RIAs) that have been reported to attenuate obesity and improve insulin sensitivity in the diet-induced obese (DIO) mouse model. However, chronic dosing of select compounds from the series showed time-dependent brain accumulation despite a low brain/plasma exposure ratio. To address this issue, a PEGylation approach was employed to identify a novel series of homodimeric 6-benzhydryl-4-amino-quinazoline-PEG conjugates with an extended half-life. The lead compound 18 engaged peripheral CB1Rs in a gastrointestinal (GI) tract motility study and demonstrated a high level of peripheral restriction in a chronic DIO mouse pharmacokinetic study.

Inter-laboratory reproducibility of an untargeted metabolomics GC-MS assay for analysis of human plasma.

There is a long-standing concern for the lack of reproducibility of the untargeted metabolomic approaches used in pharmaceutical research. Two types of human plasma samples were split into two batches and analyzed in two individual labs for untargeted GC-MS metabolomic profiling. The two labs used the same silylation sample preparation protocols but different instrumentation, data processing software, and database. There were 55 metabolites annotated reproducibly, independent of the labs. The median coefficient variations (CV%) of absolute spectra ion intensities in both labs were less than 30%. However, the comparison of normalized ion intensity among biological groups, were inconsistent across labs. Predicted power based on annotated metabolites was evaluated post various normalization, data transformation and scaling. For the first time our study reveals the numerical details about the variations in metabolomic annotation and relative quantification using plain inter-laboratory GC-MS untargeted metabolomic approaches. Especially we compare several commonly used post-acquisition strategies and found normalization could not strengthen the annotation accuracy or relative quantification precision of untargeted approach, instead it will impact future experimental design. Standardization of untargeted metabolomics protocols, including sample preparation, instrumentation, data processing, etc., is critical for comparison of untargeted data across labs.

Intestinal serine protease inhibition increases FGF21 and improves metabolism in obese mice.

Trypsin is the major serine protease responsible for intestinal protein digestion. An inhibitor, camostat (CS), reduced weight gain, hyperglycemia, and dyslipidemia in obese rats; however, the mechanisms for these are largely unknown. We reasoned that CS creates an apparent dietary protein restriction, which is known to increase hepatic fibroblast growth factor 21 (FGF21). Therefore, metabolic responses to CS and a gut-restricted CS metabolite, FOY-251, were measured in mice. Food intake, body weight, blood glucose, branched-chain amino acids (LC/MS), hormone levels (ELISA), liver pathology (histology), and transcriptional changes (qRT-PCR) were measured in ob/ob, lean and diet-induced obese (DIO) C57BL/6 mice. In ob/ob mice, CS in chow (9-69 mg/kg) or FOY-251 (46 mg/kg) reduced food intake and body weight gain to a similar extent as pair-fed mice. CS decreased blood glucose, liver weight, and lipidosis and increased FGF21 gene transcription and plasma levels. In lean mice, CS increased liver FGF21 mRNA and plasma levels. Relative to pair feeding, FOY-251 also increased plasma FGF21 and induced liver FGF21 and integrated stress response (ISR) transcription. In DIO mice, FOY-251 (100 mg/kg po) did not alter peak glucose levels but reduced the AUC of the glucose excursion in response to an oral glucose challenge. FOY-251 increased plasma FGF21 levels. In addition to previously reported satiety-dependent (cholecystokinin-mediated) actions, intestinal trypsin inhibition engages non-satiety-related pathways in both leptin-deficient and DIO mice. This novel mechanism improves metabolism by a liver-integrated stress response and increased FGF21 expression levels in mice. NEW & NOTEWORTHY Trypsin inhibitors, including plant-based consumer products, have long been associated with metabolic improvements. Studies in the 1980s and 1990s suggested this was due to satiety hormones and caloric wasting by loss of protein and fatty acids in feces. This work suggests an entirely new mechanism based on the lower amounts of digested protein available in the gut. This apparent protein reduction may cause beneficial metabolic adaptation by the intestinal-liver axis to perceived nutrient stress.

Potent Sodium/Glucose Cotransporter SGLT1/2 Dual Inhibition Improves Glycemic Control Without Marked Gastrointestinal Adaptation or Colonic Microbiota Changes in Rodents.

The sodium/glucose cotransporters (SGLT1 and SGLT2) transport glucose across the intestinal brush border and kidney tubule. Dual SGLT1/2 inhibition could reduce hyperglycemia more than SGLT2-selective inhibition in patients with type 2 diabetes. However, questions remain about altered gastrointestinal (GI) luminal glucose and tolerability, and this was evaluated in slc5a1-/- mice or with a potent dual inhibitor (compound 8; SGLT1 Ki = 1.5 ± 0.5 nM 100-fold greater potency than phlorizin; SGLT2 Ki = 0.4 ± 0.2 nM). 13C6-glucose uptake was quantified in slc5a1-/- mice and in isolated rat jejunum. Urinary glucose excretion (UGE), blood glucose (Sprague-Dawley rats), glucagon-like peptide 1 (GLP-1), and hemoglobin A1c (HbA1c) levels (Zucker diabetic fatty rats) were measured. Intestinal adaptation and rRNA gene sequencing was analyzed in C57Bl/6 mice. The blood 13C6-glucose area under the curve (AUC) was reduced in the absence of SGLT1 by 75% (245 ± 6 vs. 64 ± 6 mg/dl⋅h in wild-type vs. slc5a1-/- mice) and compound 8 inhibited its transport up to 50% in isolated rat jejunum. Compound 8 reduced glucose excursion more than SGLT2-selective inhibition (e.g., AUC = 129 ± 3 vs. 249 ± 5 mg/dl⋅h for 1 mg/kg compound 8 vs. dapagliflozin) with similar UGE but a lower renal glucose excretion threshold. In Zucker diabetic fatty rats, compound 8 decreased HbA1c and increased total GLP-1 without changes in jejunum SGLT1 expression, mucosal weight, or villus length. Overall, compound 8 (1 mg/kg for 6 days) did not increase cecal glucose concentrations or bacterial diversity in C57BL/6 mice. In conclusion, potent dual SGLT1/2 inhibition lowers blood glucose by reducing intestinal glucose absorption and the renal glucose threshold but minimally impacts the intestinal mucosa or luminal microbiota in chow-fed rodents.

An In Vivo Rat α-D-glucose Stable Isotope Homeostasis Drug Discovery Screen: A Targeted Metabolomics Approach.

We have developed a targeted metabolomics screen which consists of using two isotopically labeled glucose compounds to conduct a dual oral glucose tolerance test in rats. This dual isotopic oral glucose tolerance test (DIS-OGTT) can be used to select drug candidates that have "on"- target or have "off"-target effects on oral glucose absorption, hepatic glucose production or glucose disposal. The DIS-OGTT assay utilized intravenously administered [6-13C1-6, 6'-2H2]-glucose and orally administered [U-13C6] glucose to monitor glucose homeostasis. In the experiment, a constant intravenous dose of [6-13C1-6, 6'-2H2] glucose was converted in vivo to a series of [M+1] glucose isotopomers and unlabeled [M] glucose via gluconeogenesis while the orally administered [U-13C6] glucose was converted to a series of [M+3] and [M+2] glucose isotopomers via gluconeogenesis. The detection platform of the assay was based on a negative mode electrospray ionization liquid chromatography tandem mass spectrometry method where the deprotonated glucose anion and its various isotopomers were quantitated in rat plasma using multiple reaction monitoring techniques. The in vivo rat DIS-OGTT assay was a sensitive method for understanding drug candidates underlying postprandial effects on glucose absorption, hepatic glucose production, and insulin controlled glucose disposal. Since glucose derivatization was not required for this assay, a higher sample throughput DIS-OGTT was achieved.

Novel LC/MS/MS and High-Throughput Mass Spectrometric Assays for Monoacylglycerol Acyltransferase Inhibitors.

Monoacylglycerol acyltransferase enzymes (MGAT1, MGAT2, and MGAT3) convert monoacylglycerol to diacylglycerol (DAG). MGAT1 and MGAT2 are both implicated in obesity-related metabolic diseases. Conventional MGAT enzyme assays use radioactive substrates, wherein the product of the MGAT-catalyzed reaction is usually resolved by time-consuming thin layer chromatography (TLC) analysis. Furthermore, microsomal membrane preparations typically contain endogenous diacylglycerol acyltransferase (DGAT) from the host cells, and these DGAT activities can further acylate DAG to form triglyceride (TG). Our mass spectrometry (liquid chromatography-tandem mass spectrometry, or LC/MS/MS) MGAT2 assay measures human recombinant MGAT2-catalyzed formation of didecanoyl-glycerol from 1-decanoyl-rac-glycerol and decanoyl-CoA, to produce predominantly 1,3-didecanoyl-glycerol. Unlike 1,2-DAG, 1,3-didecanoyl-glycerol is proved to be not susceptible to further acylation to TG. 1,3-Didecanoyl-glycerol product can be readily solubilized and directly subjected to high-throughput mass spectrometry (HTMS) without further extraction in a 384-well format. We also have established the LC/MS/MS MGAT activity assay in the intestinal microsomes from various species. Our assay is proved to be highly sensitive, and thus it allows measurement of endogenous MGAT activity in cell lysates and tissue preparations. The implementation of the HTMS MGAT activity assay has facilitated the robust screening and evaluation of MGAT inhibitors for the treatment of metabolic diseases.

Metabolic tracing of monoacylglycerol acyltransferase-2 activity in vitro and in vivo.

Monoacylglycerol acyltransferase 2 (MGAT2) catalyzes the synthesis of diacylglycerol (DAG) from free fatty acids (FFA) and sn-monoacylglycerol (MG), the two major hydrolysis products of dietary fat. To demonstrate MGAT2-mediated cellular activity of triglyceride (TG) synthesis, we utilized 1-oleoyl-glycerol-d5 as a substrate to trace MGAT2-driven 1-oleoyl-glycerol-d5 incorporation into TG in HEK293 cells stably expressing human MGAT2. The oleoyl-glycerol-d5 incorporated major TG species were then quantified by liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS) in a 96-well format. Conventional MGAT2 target-engagement in vivo assays measure the elevation of total plasma TG by orally dosing a bolus of TG oil. We developed a novel LC/ESI/MS/MS-based fat absorption assay to assess the ability of MGAT2 inhibitors to inhibit fat absorption in CD1 mice by a meal tolerance test consisting of a mixture of liquid Boost plus® and 0.59 g/kg U13C-TG oil. The newly resynthesized plasma heavy TGs containing three 13C in the glycerol backbone and two U13C-acyl-chains, which represented the digested, absorbed and resynthesized TGs, were then quantitated by LC/ESI/MS/MS. With this assay, we identified a potent MGAT2 inhibitor that blocked MGAT2-mediated activity in vitro and in vivo. The use of 1-oleoyl-glycerol-d5 and U13C-TG oil followed by LC/ESI/MS/MS detection of stable-isotopic labeled DAG, TG, or glycerol provides a wide range of applications to study pathophysiological regulation of the monoacylglycerol pathway and MGAT2 activity.

Global deletion of MGL in mice delays lipid absorption and alters energy homeostasis and diet-induced obesity.

Monoacylglycerol lipase (MGL) is a ubiquitously expressed enzyme that catalyzes the hydrolysis of monoacylglycerols (MGs) to yield FFAs and glycerol. MGL contributes to energy homeostasis through the mobilization of fat stores and also via the degradation of the endocannabinoid 2-arachidonoyl glycerol. To further examine the role of MG metabolism in energy homeostasis, MGL(-/-) mice were fed either a 10% (kilocalories) low-fat diet (LFD) or a 45% (kilocalories) high-fat diet (HFD) for 12 weeks. Profound increases of MG species in the MGL(-/-) mice compared with WT control mice were found. Weight gain over the 12 weeks was blunted in both diet groups. MGL(-/-) mice were leaner than WT mice at both baseline and after 12 weeks of LFD feeding. Circulating lipids were decreased in HFD-fed MGL(-/-) mice, as were the levels of several plasma peptides involved in glucose homeostasis and energy balance. Interestingly, MGL(-/-) mice had markedly reduced intestinal TG secretion following an oral fat challenge, suggesting delayed lipid absorption. Overall, the results indicate that global MGL deletion leads to systemic changes that produce a leaner phenotype and an improved serum metabolic profile.

4-Bicyclic heteroaryl-piperidine derivatives as potent, orally bioavailable stearoyl-CoA desaturase-1 (SCD1) inhibitors: part 2. Pyridazine-based analogs.

Design, synthesis, and biological evaluation of pyridazine-based, 4-bicyclic heteroaryl-piperidine derivatives as potent stearoyl-CoA desaturase-1 (SCD1) inhibitors are described. In a chronic study of selected analog (3e) in Zucker fa/fa (ZF) rat, dose-dependent decrease of body weight gain and plasma fatty acid desaturation index (DI) in both C16 and C18 are also demonstrated. The results indicate that the plasma fatty acid DI may serve as an indicator for direct target engagement and biomarker for SCD1 inhibition.

The IC(50) concept revisited.

A major strategy used in drug design is the inhibition of enzyme activity. The ability to accurately measure the concentration of the inhibitor which is required to inhibit a given biological or biochemical function by half is extremely important in ranking compounds. Since the concept of the half maximal inhibitory concentration (IC(50)) is used extensively for studying reversible inhibition enzymatic reactions, it is important to clearly understand the experimental design and the mathematical modeling techniques used to generate IC(50) values. The most important part of the experimental design is to measure the rate of production of [P] during the linear phase of the time course of the reaction and to prove that the enzyme-catalyzed reaction is reversible. The most important part of the mathematical modeling is to select the correct model and to have a firm understanding on how to handle outliers in the data. These topics are discussed in greater detail along with a discussion on how much quantitative and mechanistic information can be reasonably deduced from an experiment.

The use of stable isotope-labeled glycerol and oleic acid to differentiate the hepatic functions of DGAT1 and -2.

Diacylglycerol acyltransferase (DGAT) catalyzes the final 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 (13)C(3)-D(5)-glycerol or (13)C(18)-oleic acid, and profiled the major isotope-labeled TG species by liquid chromatography tandem mass spectrometry. Selective DGAT1 and DGAT2 inhibitors demonstrated that (13)C(3)-D(5)-glycerol-incorporated TG synthesis was mediated by DGAT2, not DGAT1. Conversely, (13)C(18)-oleoyl-incorporated TG synthesis was predominantly mediated by DGAT1. To trace hepatic TG synthesis and VLDL triglyceride (VLDL-TG) secretion in vivo, we administered D(5)-glycerol to mice and measured plasma levels of D(5)-glycerol-incorporated TG. Treatment with an antisense oligonucleotide (ASO) to DGAT2 led to a significant reduction in D(5)-glycerol incorporation into VLDL-TG. In contrast, the DGAT2 ASO had no effect on the incorporation of exogenously administered (13)C(18)-oleic acid into VLDL-TG. Thus, our results indicate that DGAT1 and DGAT2 mediate distinct hepatic functions: DGAT2 is primarily responsible for incorporating endogenously synthesized FAs into TG, whereas DGAT1 plays a greater role in esterifying exogenous FAs to glycerol.

High-content assays for evaluating cellular and hepatic diacylglycerol acyltransferase activity.

Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the terminal step in triglyceride (TG) synthesis using diacylglycerol (DAG) and fatty acyl-CoA as substrates. In the liver, the production of VLDL permits the delivery of hydrophobic TG from the liver to peripheral tissues for energy metabolism. We describe here a novel high-content, high-throughput LC/MS/MS-based cellular assay for determining DGAT activity. We treated endogenous DGAT-expressing cells with stable isotope-labeled [¹³C18]oleic acid. The [¹³C18]oleoyl-incorporated TG and DAG lipid species were profiled. The TG synthesis pathway assay was optimized to a one-step extraction, followed by LC/MS/MS quantification. Further, we report a novel LC/MS/MS method for tracing hepatic TG synthesis and VLDL-TG secretion in vivo by administering [¹³C18]oleic acid to rats. The [¹³C18]oleic acid-incorporated VLDL-TG was detected after one-step extraction without conventional separation of TG and recovery by derivatizing [¹³C18]oleic acid for detection. Using potent and selective DGAT1 inhibitors as pharmacological tools, we measured changes in [¹³C18]oleoyl-incorporated TG and DAG and demonstrated that DGAT1 inhibition significantly reduced [¹³C18]oleoyl-incorporated VLDL-TG. This DGAT1-selective assay will enable researchers to discern differences between the roles of DGAT1 and DGAT2 in TG synthesis in vitro and in vivo.

Biotransformation of geldanamycin and 17-allylamino-17-demethoxygeldanamycin by human liver microsomes: reductive versus oxidative metabolism and implications.

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 degrees 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 degrees 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.

Evaluation of the effect of oxygen exposure on human liver microsomal metabolism of mitomycin C in the presence of glutathione using liquid chromatography-quadrupole time of flight mass spectrometry.

This article describes a metabolite profiling method for evaluating the effect of oxygen exposure on human liver microsomal metabolism of mitomycin C (MC) in the presence of glutathione (GSH) and NADPH under hypoxic (100% helium), limitedly and fully aerobic, and hyperoxic (100% oxygen) conditions. MC and its metabolite(s) were characterized and the relative percentages of these components were estimated at different incubation times using liquid chromatography and quadrupole time-of-flight mass spectrometry. The MC metabolite profiles were confirmed using purified human cytochrome P450 reductase, acidic activation, and UV-Vis detection at 550 nm. In hypoxia, MC was exclusively metabolized into 2,7-diaminomitosene-10-glutathione-S-conjugate (2,7-DAM-10-SG) within 30 min, whereas approximately 5% of this conjugate, 16% of 2,7-diaminomitosene (2,7-DAM), and 77% of MC were observed under a fully aerobic condition at 90 min. Under limitedly aerobic conditions, the relative percentages of the two metabolites in incubations varied greatly depending on the volume ratio of air to liquid. In hyperoxia, 2% of 2,7-DAM-10-SG, 9% of 2,7-DAM, and 86% of MC were obtained at 90 min. The results indicate that oxygen strongly inhibits the in vitro metabolism of MC. These data suggest that GSH may serve a dual function in facilitating the formation of a leucoaziridinomitosene followed by electron rearrangement giving intermediate metabolite 2,7-DAM, and then trapping this intermediate giving rise to 2,7-DAM-10-SG. These findings provide direct evidence for understanding the fate of oxygen-sensitive metabolic deactivation of MC by GSH.

Liquid chromatographic and tandem mass spectrometric assay for evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors: application of biomarkers in drug discovery.

A simple and selective assay for the evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors was developed through the simultaneous determination of endogenous 5-hydroxy tryptamine, 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophane, and 2-phenethylamine (PEA) in rat brain using liquid chromatography-tandem mass spectrometry (LC/MS/MS). These analytes were separated on a Zorbax SB-C18 column using a gradient elution with acetonitrile and 0.2% formic acid and detected on an electrospray ionization mass spectrometer in positive-ion multiple-reaction-monitoring mode. The susceptibility and variability of these analytes as potential biomarkers in response to MAO inhibition in vivo were evaluated after application to three MAO inhibitors, tranylcypromine, clorgyline, and pargyline. A dramatic increase (about 40-fold) in PEA brain level and a decrease in 5-HIAA by more than 90% were observed after administration of 15 mg/kg of the nonselective MAO inhibitor tranylcypromine. As expected, the brain level of PEA escalated to about 6-fold, while the 5-HIAA level remained unchanged following a dose of the MAO B inhibitor pargyline at 2mg/kg. In contrast, the brain level of 5-HIAA reduced by approximately 53%, but the PEA level was unaffected following the same dose of the MAO A inhibitor clorgyline. The results indicated that 5-HIAA and PEA were susceptible and effective biomarkers in the rat brain in response to MAO A and B inhibition, respectively. The LC/MS/MS method is useful not only for the determination of inhibitory potency but also for the differentiation of the selectivity of a MAO inhibitor against rat brain MAO A and B in vivo.