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Ethylene glycol monomethyl ether (EGME) is a widely used industrial solvent known to cause adverse effects to human and other mammals. Organs with high metabolism and rapid cell division, such as testes, are especially sensitive to its actions. In order to gain mechanistic understanding of EGME-induced toxicity, an untargeted metabolomic analysis was performed in rats. Male rats were administrated with EGME at 30 and 100 mg/kg/day. At days 1, 4, and 14, serum, urine, liver, and testes were collected for analysis. Testicular injury was observed at day 14 of the 100 mg/kg/day group only. Nearly 1900 metabolites across the four matrices were profiled using liquid chromatography-mass spectrometry/mass spectrometry and gas chromatography-mass spectrometry. Statistical analysis indicated that the most significant metabolic perturbations initiated from the early time points by EGME were the inhibition of choline oxidation, branched-chain amino acid catabolism, and fatty acid β-oxidation pathways, leading to the accumulation of sarcosine, dimethylglycine, and various carnitine- and glycine-conjugated metabolites. Pathway mapping of these altered metabolites revealed that all the disrupted steps were catalyzed by enzymes in the primary flavoprotein dehydrogenase family, suggesting that inhibition of flavoprotein dehydrogenase–catalyzed reactions may represent the mode of action for EGME-induced toxicity. Similar urinary and serum metabolite signatures are known to be the hallmarks of multiple acyl-coenzyme A dehydrogenase deficiency in humans, a genetic disorder because of defects in primary flavoprotein dehydrogenase reactions. We postulate that disruption of key biochemical pathways utilizing flavoprotein dehydrogenases in conjugation with downstream metabolic perturbations collectively result in the EGME-induced tissue damage.

Optimization of the amino acid residue of a series of anthranilimide-based glycogen phosphorylase inhibitors is described leading to the identification of serine and threonine ether analogs. t-Butylthreonine analog 20 displayed potent in vitro inhibition of GPa, low potential for P450 inhibition, and excellent pharmacokinetic properties.

Optimization of the amino acid residue within a series of anthranilimide-based glycogen phosphorylase inhibitors is described. These studies culminated in the identification of anthranilimides 16 and 22 which displayed potent in vitro inhibition of GPa in addition to reduced inhibition of CYP2C9 and excellent pharmacokinetic properties.

A series of amino acid anthranilamide derivatives identified from a high-throughput screening campaign as novel, potent, and glucose-sensitive inhibitors of human liver glycogen phosphorylase a are described. A solid-phase synthesis using Wang resin was also developed which provided efficient access to a variety of analogues, and resulted in the identification of key structure-activity relationships, and the discovery of a potent exemplar (IC(50)=80 nM). The SAR scope, synthetic strategy, and in vitro results for this series are presented herein.

Aims/hypothesis. Although retinoid X receptor (RXR) and peroxisome proliferator activated receptor-γ (PPARγ) agonists have antidiabetic effects in hyperinsulinaemic animals, little information exists on their effects after pancreatic beta-cell failure. Thus, we examined if RXR and PPARγ agonists alter distinct metabolic pathways in animals suffering from impaired insulin secretion. Methods. Adverse side effects and antidiabetic responses were measured in db/db mice treated from 14–16 weeks of age with the RXR agonist, LG100268, and/or the PPARγ agonists, BRL49 653 or GW1929. Results. In animals treated with LG100 268 or BRL49653, serum glucose, glycohaemoglobin and the cardiovascular risk factor, fibrinogen, decreased to the same extent. Both of these agonists were equally effective at increasing insulin accumulation in beta cells, although neither agent had an effect on serum insulin concentrations. In contrast, the RXR agonist was less effective than the PPARγ agonists at lowering serum triglycerides and non-esterified fatty acids and increasing interscapular brown fat and body weight. Further, LG100 268 increased serum alkaline phosphatase and liver mass, hepatic fat accumulation, lauric acid hydroxylase activity, catalase-immunostaining and peroxisomal number more than the PPARγ agonists. Moreover, co-treatment with the RXR and PPARγ agonists reduced glucose, triglycerides, non-esterified fatty acids and cholesterol more than either agent alone. Conclusion/interpretation. These data suggest 1) RXR and PPARγ agonists decrease islet degeneration, cardiovascular risk and cachexia during later stages of diabetes, 2) RXR agonists are less effective than PPARγ agonists at decreasing serum lipids and causing weight gain and 3) RXR agonists have a more pronounced effect on liver metabolism (e. g. peroxisome accumulation and hepatomegaly) than PPARγ agonists. [Diabetologia (1999) 42: 545–554]

Purpose. Although the effects of thermogenic agents in cell culture can be measured by direct microcalorimetry, only a few samples can be analyzed over several hours. In this report, we describe a robust non-invasive technique to measure real-time thermogenesis of cells cultured in microtiter plates using infrared thermography. Methods. Yeast were transformed with uncoupling protein-2 (UCP2) or exposed to carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP) or rotenone. Adipocytes were exposed to rotenone, FCCP, cycloheximide, troglitazone, or CL316243. Thermogenesis was measured using infrared thermography. Results. Thermogenesis increased after exposing yeast to the mitochondrial uncoupler, FCCP, or transforming the cells with UCP2. Further, thermogenesis in adipocytes was stimulated by CL316243, a β3-adrenoceptor agonist being developed to treat obesity. The protein synthesis inhibitor, cycloheximide, did not inhibit CL316243-mediated thermogenesis. In contrast, the mitochondrial proton transport inhibitor, rotenone, inhibited thermogenesis in yeast and adipocytes. Similarly, the antidiabetic agent, troglitazone, suppressed thermogenesis in adipocytes. Although increased UCP synthesis resulted in increased thermogenesis in yeast, UCP expression did not correlate with thermogenesis in adipocytes. Conclusions. The results, taken together with the high resolution (0.002°C) and robustness (384-well format) of the approach, indicate infrared-imaging is a rapid and effective method for measuring thermogenesis in vitro.

Troglitazone and metformin are antidiabetic agents that belong to the thiazolidinedione and biguanide classes of drugs, respectively. To evaluate how these drugs influence fuel utilization, we compared their effects on several pathways regulating carbohydrate and lipid metabolism in vitro. Both drugs stimulated glucose transport and utilization in C3H10T1/2 cells, a cell line capable of differentiating into adipocytes when treated with thiazolidinediones. However, we observed that these drugs had a number of different in vitro effects. Unlike metformin, troglitazone stimulated beta3-adrenergic receptor-mediated lipolysis, lipogenesis, and transcriptional activity of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Further, by using a mitochondrial-specific fluorescent dye, we found troglitazone to be more effective than metformin at increasing mitochondrial mass. In contrast to troglitazone, metformin was more effective at increasing mitochondrial fatty acid beta-oxidation, peroxisomal fatty acid beta-oxidation, and anaerobic respiration (i.e. lactate production). Additionally, metformin stimulated and troglitazone inhibited both aerobic respiration and basal lipolysis. Insulin enhanced the effects of troglitazone, but not those of metformin, on these cells. Taken together, the data show that troglitazone and metformin affect two distinct metabolic pathways: one that is anabolic (i.e. troglitazone) and the other that is catabolic (i.e. metformin). Further, these observations suggest that the metabolic activity of mitochondria may be lower in cells treated with troglitazone than with metformin.

Key binding interactions of the anthranilimide based glycogen phosphorylase a (GPa) inhibitor 2 from X-ray crystallography studies are described. This series of compounds bind to the AMP site of GP. Using the binding information the core and the phenyl urea moieties were optimized. This work culminated in the identification of compounds with single nanomolar potency as well as in vivo efficacy in a diabetic model.

Publisher Summary This chapter examines the in vitro and in vivo approaches to studying antiretroviral therapy-induced metabolic complications. HIV protease inhibitors (PIs), as a component of highly active antiretroviral therapy, are effective antiretroviral agents in the treatment of HIV/AIDS. These agents inhibit the HIV-1 aspartyl protease, an enzyme essential for virion maturation and release and have played a major role in reducing the morbidity and mortality associated previously with HIV infection. A study using saquinavir (SQV) and indinavir (IDV) showed the PIs inhibit differentiation of human preadipocytes. In this study, SQV had a greater inhibitory effect than IDV, however, neither PI was shown capable of altering expression of a P2, even when potent stimulators of both proliferator activated receptor γ (PPARγ) and retinoid X receptor (RXR) were present in culture. PI mediated effects on adipogenesis were occurring through a PPARγ/RXR-independent mechanism. The different effects of PIs in rodents and in vitro indicate that each PI has unique pharmacological properties, some of which are influenced by environmental or genetic factors.

Abstract —Hyperlipidemia may complicate the use of HIV protease inhibitors (PIs) in AIDS therapy. To determine the cause of hyperlipidemia, the effect of PIs on lipid metabolism was examined with HepG2 liver cells and AKR/J mice. In HepG2 cells, the PIs ABT-378, nelfinavir, ritonavir, and saquinavir stimulated triglyceride synthesis; ritonavir increased cholesterol synthesis; and amprenavir and indinavir had no effect. Moreover, nelfinavir increased mRNA expression of diacylglycerol acyltransferase and fatty acid synthase. The retinoid X receptor agonist LG100268, but not the antagonist LG100754, further increased PI-stimulated triglyceride synthesis and mRNA expression of fatty acid synthase in vitro. In fed mice, nelfinavir or ritonavir did not affect serum glucose and cholesterol, whereas triglyceride and fatty acids increased 57% to 108%. In fasted mice, ritonavir increased serum glucose by 29%, cholesterol by 40%, and triglyceride by 99%, whereas nelfinavir had no effect, suggesting these PIs have different effects on metabolism. Consistent with the in vitro results, nelfinavir and ritonavir increased triglyceride 2- to 3-fold in fasted mice injected with Triton WR-1339, an inhibitor of triglyceride clearance. We propose that PI-associated hyperlipidemia is due to increased hepatic triglyceride synthesis and suggest that retinoids or meal restriction influences the effects of select PIs on lipid metabolism.

AIDS therapies employing HIV protease inhibitors (PIs) are associated with changes in fat metabolism. However, the cellular mechanisms affected by PIs are not clear. Thus, the affects of PIs on adipocyte differentiation were examined in vitro using C3H10T1/2 stem cells. In these cells the PIs, nelfinavir, saquinavir, and ritonavir, reduced triglyceride accumulation, lipogenesis, and expression of the adipose markers, aP2 and LPL. Histological analysis revealed nelfinavir, saquinavir and ritonavir treatment decreased oil red O-staining of cytoplasmic fat droplets. Inhibition occurred in the presence of the RXR agonist LGD1069, indicating the inhibitory effects were not due to an absence of RXR ligand. Moreover, these three PIs increased acute lipolysis in adipocytes. In contrast, two HIV PIs, amprenavir and indinavir, had little effect on lipolysis, lipogenesis, or expression of aP2 and LPL. Although, saquinavir, inhibited ligand-binding to PPARgamma with an IC(50) of 12.7+/-3.2 microM, none of the other PIs bound to the nuclear receptors RXRalpha or PPARgamma, (IC(50)s20 microM), suggesting that inhibition of adipogenesis is not due to antagonism of ligand binding to RXRalpha or PPARgamma. Taken together, the results suggest that some, but not all, PIs block adipogenesis and stimulate fat catabolism in vitro and this may contribute to the effects of PIs on metabolism in the clinic.

Human immunodeficiency virus (HIV) protease inhibitors (PI) may alter lipid metabolism in patients with acquired immunodeficiency syndrome (AIDS). However, the influence of dietary fat on the metabolic effects of PI therapy remains unknown. AKR/J mice were fed high or low fat diets and treated with the PI indinavir (IDV), nelfinavir (NFV), saquinavir (SQV) or amprenavir (APV) by subcutaneous delivery for 2 wk. Serum concentrations of glucose, insulin, triglyceride, free fatty acid, glycerol, pancreatic lipase, bilirubin, alkaline phosphatase, blood urea nitrogen and PI, and interscapular and epididymal fat weights were determined. Some metabolic effects of PI were dependent on diet. IDV- and NFV-treated mice had greater serum glucose concentration and body weight; IDV-treated mice had lower serum insulin; NFV-treated mice had greater interscapular fat mass; and SQV treated mice had lower serum triglyceride concentration than control mice fed the low but not the high fat diet. In contrast, NFV- and IDV-treated mice had greater triglyceride concentration and blood urea nitrogen, and SQV treated mice had greater serum cholesterol than control mice fed the high but not the low fat diet. The serum concentration of SQV was lower in mice fed the high fat compared with the low fat diet. Other effects were not dependent on diet. IDV- and NFV-treated mice had greater fatty acids, and IDV-treated mice had greater pancreatic lipase, bilirubin and alkaline phosphatase than control mice fed either diet. APV treatment had little effect on these serum measurements. Thus, changes in dietary fat can influence some but not all of the effects of PI on metabolism. Furthermore, each PI produces different effects in vivo, indicating that various PI affect distinct metabolic pathways.