Acetate Incorporation Research Articles

Biosynthesis of two dihydropyrrole-polyketides from a marine-derived Penicillium citrinum

Feeding experiments with 13C-labeled precursors were performed in order to establish the biosynthesis of two N-acylated dihydropyrroles, (8E)-1-(2,3-dihydro-1H-pyrrol-1-yl)-2-methyldec8-ene-1,3-dione (1) and 1-(2,3-dihydro-1H-pyrrol-1-yl)-2-methyldecane-1,3-dione (2), isolated from the cultures of a marine-derived Penicillium citrinum. The biosynthesis of both, 1 and 2, involves the incorporation of acetate, methionine and ornithine.

Wickerols A and B: novel anti-influenza virus diterpenes produced by Trichoderma atroviride FKI-3849

Wickerols A and B were produced by a fungus, Trichoderma atroviride FKI-3849. Wickerol A showed potent anti-influenza virus activity against strain A/PR/8/34 (H1N1), whereas wickerol B exhibited weaker impact. The anti-influenza virus spectrum between wickerols A and B was different. The cyclization mechanism of the wickerol carbon-skeleton was investigated by incorporation of 13C-labeled acetate. A pathway through the verticillyl cation was predicted.

Transcriptional regulation of lipid synthesis in bovine mammary epithelial cells by sterol regulatory element binding protein-1

The objective of this study was to investigate the transcriptional regulation of lipid synthesis by sterol regulatory element binding protein-1 (SREBP-1) in bovine mammary epithelial cells. In the current study, bovine mammary epithelial (MAC-T) cells cultured in insulin- and prolactin-containing medium were treated with a transfection reagent as control, a nontargeting small interfering (si)RNA sequence (100nM) as a negative control, or an SREBP-1–specific siRNA (100nM) for 48h. The mRNA expression of SREBP-1 was decreased more than 90% by siRNA. Precursor and mature forms of SREBP-1 protein were undetectable in cells treated with SREBP-1 siRNA. Fatty acid synthesis and fatty acid uptake, measured using isotope incorporation, were reduced significantly in cells treated with SREBP-1 siRNA compared with controls. Transcript abundance of acyl-CoA synthetase short-chain family member 2, acetyl-CoA carboxylase, fatty acid synthetase, and isocitrate dehydrogenase 1 (key enzymes of de novo lipogenesis) was decreased by 40 to 65% with SREBP-1 siRNA, in agreement with acetate incorporation data. The mRNA levels of fatty acid binding protein 3 and stearyl-CoA desaturase 1 (proteins responsible for intracellular fatty acid trafficking and long-chain fatty acid modification) were decreased 76 and 60%, respectively, by SREBP-1 siRNA treatment compared with controls. The mRNA expression of mitochondrial glycerol-3-phosphate acyltransferase and lipin 1 (involved in triglyceride synthesis) was significantly decreased in cells treated with SREBP-1 siRNA compared with control cells. However, the expression of milk fat globule membrane proteins measured did not differ among treatments. In conclusion, SREBP-1 plays an important role in integrated regulation of lipid synthesis in bovine mammary epithelial cells through regulation of key enzymes.

Lipid droplet formation on opposing sides of the endoplasmic reticulum

In animal cells, the primary repositories of esterified fatty acids and alcohols (neutral lipids) are lipid droplets that form on the lumenal and/or cytoplasmic side of the endoplasmic reticulum (ER) membrane. A monolayer of amphipathic lipids, intermeshed with key proteins, serves to solubilize neutral lipids as they are synthesized and desorbed. In specialized cells, mobilization of the lipid cargo for delivery to other tissues occurs by secretion of lipoproteins into the plasma compartment. Serum lipoprotein assembly requires an obligate structural protein anchor (apolipoprotein B) and a dedicated chaperone, microsomal triglyceride transfer protein. By contrast, lipid droplets that form on the cytoplasmic face of the ER lack an obligate protein scaffold or any required chaperone/lipid transfer protein. Mobilization of neutral lipids from the cytosol requires regulated hydrolysis followed by transfer of the products to different organelles or export from cells. Several proteins play a key role in controlling droplet number, stability, and catabolism; however, it is our premise that their formation initiates spontaneously, solely as a consequence of neutral lipid synthesis. This default pathway directs droplets into the cytoplasm where they accumulate in many lipid disorders.

Fungal and bacterial growth following the application of slurry and anaerobic digestate of livestock manure to temperate pasture soils

How land-application of digestate sourced from anaerobic digestion (AD) of animal waste influences the functioning of a mixed pasture agroecosystem is not well characterised, particularly with regard to the response of the actively growing microbial community. We studied the impact of the liquid AD digestate on the decomposer community in two different soils, seeded with two different common grassland crops; a mixture of either grass or grass/clover in a greenhouse experiment. We studied bacterial (leucine incorporation into bacteria) and fungal (acetate incorporation into ergosterol) growth responses to AD cattle slurry digestate, undigested cattle slurry, mineral fertiliser (NPK and N) added at a rate equivalent to 150 kg N ha−1, and a no-fertiliser control treatment. Differences in fungal and bacterial growth were evident between the soil and sward types. However, the fertilisers consistently stimulated a higher bacterial growth than the no-fertiliser control, and liquid digestate resulted in a level of bacterial growth higher or equal to that of mineral fertiliser, whilst undigested slurry resulted in lower bacterial growth. These fertiliser effects on bacterial growth mirrored the effects on plant growth. In contrast, the fungal community responded only marginally to fertiliser treatments. We conclude that the application of digestate stimulates the bacterial decomposer community in a similar way to that of mineral fertilisers. Our results suggest that mineral fertiliser can be exchanged for liquid digestate with limited impact on the actively growing soil microbial community that, in turn, regulate important soil processes including nutrient cycling in agricultural soils.

Macrophage-specific transgenic expression of cholesteryl ester hydrolase attenuates hepatic lipid accumulation and also improves glucose tolerance in ob/ob mice

Cellular cholesterol homeostasis is increasingly being recognized as an important determinant of the inflammatory status of macrophages, and a decrease in cellular cholesterol levels polarizes macrophages toward an anti-inflammatory or M2 phenotype. Cholesteryl ester hydrolase (CEH) catalyzes the hydrolysis of stored intracellular cholesteryl esters (CE) and thereby enhances free cholesterol efflux and reduces cellular CE content. We have reported earlier reduced atherosclerosis as well as lesion necrosis and improved insulin sensitivity (due to decreased adipose tissue inflammation) in macrophage-specific CEH transgenic (CEHTg) mice in the LDLR(-/-) background. In the present study, we examined the effects of reduced intracellular accumulation of CE in CEHTg macrophages in an established diabetic mouse model, namely the leptin-deficient ob/ob mouse. Macrophage-specific transgenic expression of CEH improved glucose tolerance in ob/ob-CEHTg mice significantly compared with ob/ob nontransgenic littermates, but with no apparent change in macrophage infiltration into the adipose tissue. However, there was a significant decrease in hepatic lipid accumulation in ob/ob-CEHTg mice. Consistently, decreased [(14)C]acetate incorporation into total lipids and triglycerides was noted in precision-cut liver slices from ob/ob-CEHTg mice. In the primary hepatocyte-macrophage coculture system, macrophages from CEHTg mice significantly reduced the incorporation of [(14)C]acetate into triglycerides in hepatocytes, indicating a direct effect of macrophages on hepatocyte triglyceride biosynthesis. Kupffer cells isolated from ob/ob-CEHTg mice were polarized toward an anti-inflammatory M2 (Ly6C(lo)) phenotype. Taken together, these studies demonstrate that transgenic overexpression of CEH in macrophages polarizes hepatic macrophages (Kupffer cells) to an anti-inflammatory M2 phenotype that attenuates hepatic lipid synthesis and accumulation.

Chalcomoracin and Moracin C, New Inhibitors of <i>Staphylococcus aureus</i> Enoyl-Acyl Carrier Protein Reductase from <i>Morus alba</i>

Bacterial enoyl-acyl carrier protein (ACP) reductase has been confirmed as a novel target for antibacterial drug development. In the screening of inhibitors of Staphylococcus aureus enoyl-ACP reductase (FabI), we found that a methanol extract of leaves of Morus alba L. potently inhibited S. aureus FabI as well as growth of S. aureus. The active principles were identified as chalcomoracin and moracin C by MS and NMR analysis. Chalcomoracin and moracin C inhibited S. aureus FabI with IC(50) of 5.5 and 83.8 µM, respectively. They also prevented the growth of S. aureus with minimum inhibitory concentration (MIC) of 4 and 32 µg/mL, respectively. Consistent with their inhibition against FabI and bacterial growth, they prevented (14)C]acetate incorporation into fatty acid in S. aureus while didn't affect protein synthesis. In this study, we reported that chalcomoracin and moracin C, potent antibacterial compounds from Morus alba, inhibited FabI and fatty acid synthesis.

Use of propranolol-magnesium aluminium silicate intercalated complexes as drug reservoirs in polymeric matrix tablets

The objective of the present study was to investigate the use of propranolol–magnesium aluminium silicate intercalated complexes as drug reservoirs in hydroxypropylmethylcellulose tablets. The matrix tablets containing the complexes were prepared and characterised with respect to propranolol release and were subsequently compared with those loading propranolol or a propranolol–magnesium aluminium silicate physical mixture. Additionally, the effects of varying viscosity grades of hydroxypropyl methylcellulose, compression pressures and calcium acetate incorporation on the drug release characteristics of the complex-loaded tablets were also examined. The results showed that the complex-loaded tablets have higher tablet hardness than those containing propranolol or a physical mixture. The drug release from the complex-loaded tablets followed a zero-order release kinetic, whereas an anomalous transport was found in the propranolol or physical mixture tablets. The drug release rate of the complex tablet significantly decreased with increasing hydroxypropylmethylcellulose viscosity grade. Increase in the compression pressure caused a decrease in the drug release rate of the tablets. Furthermore, the incorporation of calcium ions could accelerate propranolol release, particularly in acidic medium, because calcium ions could be exchanged with propranolol molecules intercalated in the silicate layers of magnesium aluminium silicate. These findings suggest that propranolol-magnesium aluminium silicate intercalated complexes show strong potential for use as drug reservoirs in matrix tablets intended for modifying drug release.

Field‐scale uranium (VI) bioimmobilization monitored by lipid biomarkers and 13C‐acetate incorporation

AbstractAt the Old Rifle uranium mill‐tailing site in eastern Colorado, a test of subsurface amendment with acetate to stimulate the reductive immobilization of uranium was monitored by using lipid biomarker analysis and incorporation of 13C‐labeled acetate into lipid biomarkers. Both sediment and groundwater samples were analyzed. Within 7 days of acetate addition, groundwater microbial biomass increased by a factor of 5, and remained higher than control values in most samples for the 28 days sampled. At 29 days after the beginning of acetate amendment, 4 of 12 sediment samples had microbial biomass greater than the 95 percent confidence interval of controls. The mole percents of the phospholipid fatty acids 16:1ω7c and 16:1ω5c increased over control values upon acetate amendment, and incorporated high levels of 13C from labeled acetate in groundwater and sediment samples. 16:1ω7c is a biomarker for Geobacter, and evidence is provided that 16:1ω5c represents an unidentified iron‐reducing bacterium, probably a member of the Desulfobulbaceae. Biomarkers for organisms other than iron‐reducing bacteria, iso‐ and anteiso‐branched fatty acids and 18:1ω9c, decreased upon acetate amendment, and had their highest stable isotope incorporation at least 4 days after labeled acetate amendment ended, evidence for carbon‐sharing between iron‐reducers and other microorganisms. © 2011 Wiley Periodicals, Inc.

Effect of reduced heifer nutrition duringin uteroand post-weaning development on glucose and acetate kinetics

Energetic efficiency was evaluated in composite bred heifers born from dams receiving 1·8 or 1·2 kg/d winter supplementation for approximately 80 d before parturition. Heifers were then developed post-weaning and randomly assigned to heifer development treatments of either control (100 %; ad libitum; n 8/year) or restricted (80 %; fed 80 % of supplementation fed to controls adjusted to a common body weight: n 8/year) in a 2-year study. A glucose tolerance test (GTT) and acetate irreversible loss test (AILT) were administered to heifers at the termination of a 140 d development period when the heifers were approximately 403 d of age and consumed a silage-based diet, and again at 940 d of age when pregnant with their second calf and grazing dormant forage. No differences were measured (P>0·08) for dam winter nutrition or heifer development treatment for baseline serum metabolites or measures in either the GTT or the AILT. However, changes in baseline serum concentrations (P>0·05) were different between metabolic challenges, which occurred at different stages of development. No difference in acetate disappearance (P = 0·18) and half-life (P = 0·66) was measured between the two metabolic challenges. A trend for glucose half-life to be shorter in heifers born from dams receiving in utero winter treatments that supplied 1·2 kg/d of winter supplementation was observed (P = 0·083). Heifers developed with lower total DM intake during a 140 d development period had similar glucose and acetate incorporation rates as ad libitum-fed heifers when evaluated at two different production stages.

Growth of saprotrophic fungi and bacteria in soil

Bacterial and fungal growth rate measurements are sensitive variables to detect changes in environmental conditions. However, while considerable progress has been made in methods to assess the species composition and biomass of fungi and bacteria, information about growth rates remains surprisingly rudimentary. We review the recent history of approaches to assess bacterial and fungal growth rates, leading up to current methods, especially focusing on leucine/thymidine incorporation to estimate bacterial growth and acetate incorporation into ergosterol to estimate fungal growth. We present the underlying assumptions for these methods, compare estimates of turnover times for fungi and bacteria based on them, and discuss issues, including for example elusive conversion factors. We review what the application of fungal and bacterial growth rate methods has revealed regarding the influence of the environmental factors of temperature, moisture (including drying/rewetting), pH, as well as the influence of substrate additions, the presence of plants and toxins. We highlight experiments exploring the competitive and facilitative interaction between bacteria and fungi enabled using growth rate methods. Finally, we predict that growth methods will be an important complement to molecular approaches to elucidate fungal and bacterial ecology, and we identify methodological concerns and how they should be addressed.

Overweight induced by chronic risperidone exposure is correlated with overexpression of the SREBP-1c and FAS genes in mouse liver

Weight gain and metabolic disturbances, such as dyslipidemia and hyperglycaemia, are common side effects of most antipsychotic drugs, including risperidone. The aim of this study was to investigate the effects of chronic treatment with risperidone on body weight, fat accumulation, liver weight, and hepatic expression of key genes involved in lipid metabolism in female mice. We also addressed the mechanism of risperidone induction of metabolic side effects by exploring its effect on lipid and cholesterol metabolism in primary cultures of rat hepatocytes. Elevenweeks of treatment with long-acting risperidone (12.5mpk/week) resulted in a significant weight gain associated with an increase of liver and adipose tissue weight. These effects were positively correlated with hepatic mRNA induction of two key genes involved in lipogenesis: sterol regulatory element binding protein-1c (SREBP-1c) and fatty acid synthase (FAS). Furthermore, in line with these in vivo results, risperidone elicited significant inductions of SREBP-1 maturation and FAS mRNA expression in primary cultures of rat hepatocytes associated with an increase of free fatty acid, triacylglycerol, and phospholipid synthesis as assessed by acetate incorporation. The current investigations underscore the usefulness of a mouse model to study the weight gain observed with risperidone treatment in humans. This study shows that risperidone induces similar effects in the liver (in vivo) and in hepatocyte cell cultures (in vitro) on the expression of key genes and/or proteins that control lipid metabolism. This suggests that risperidone could alter lipid metabolism in the liver and induce weight gain in a way that is partly independent of its action on the central nervous system.

Biodegradable polyurethane nanocomposites containing dexamethasone for ocular route

The treatment of posterior segment ocular diseases, such as uveitis, by using eye drops and oral drugs is usually not effective due to the body's natural barriers to drug penetration. In this study, ocular implants to treat uveitis were synthesized by incorporating dexamethasone acetate, an important type of corticoid used in the treatment of some uveitis, into a biodegradable polyurethane containi clay nanoparticles. Biodegradable polyurethane nanocomposites having poly(caprolactone) oligomers as soft segments were obtained by delaminating clay particles within a polyurethane aqueous dispersion. The drug was incorporated into the polymer by dispersing it in the waterborne polyurethane followed by a drying step. Nanoparticles derived from clay were demonstrated to be able to tailor the mechanical properties of polyurethanes to achieve values that can match the properties of ocular soft tissues. Infrared spectra (FTIR) showed that the presence of clay particles was able to change the microphase separation process typical of polyurethanes. X-ray diffraction and small angle x-ray scattering (SAXS) results were explored to show that the incorporation of both dexamethasone acetate and nanocomponents derived from clay led to a less defined two-phase polyurethane. The presence of clay nanoparticles increased the rate of drug release measured in vitro. Human retinal pigment epithelial cells (ARPE-19) were cultured in contact with polyurethanes and polyurethane nanocomposites, and the viability of them (evaluated by using MTT assay after 7days) showed that no toxic components were released from polyurethanes containing no drugs during the test.

Effect of EVA copolymer on properties of different polyethylenes in silane crosslinking process

The effect of molecular structure of polyethylene (PE) [low density PE (LDPE), linear LDPE and high density PE] and silane/peroxide concentration on the grafting level and gel content in silane crosslinking process has been studied. The effect of incorporation of ethylene vinyl acetate (EVA) copolymer on the rate of crosslinking and thermal properties of PEs has been reported. The order of gel content was LDPE>linear LDPE>high density PE. With the incorporation of EVA, the rate of crosslinking increased. The degree of crystallinity did not change with crosslinking significantly. However, the shape of melting and crystallisation peaks changed, and two regions due to gel and sol parts were formed. In EVA/PE blends, two melting points were observed for both crosslinked and uncrosslinked samples. The SEM images showed the droplet matrix morphology with the EVA as the dispersed phase, especially for EVA/LDPE blend. The EVA/PE blends failed in hot set test, while the origin of PEs passed the hot set test successfully.

Effect of formulation design and freeze-drying on properties of fluconazole multilamellar liposomes

Fluconazole-entrapped multilamellar liposomes were prepared using the thin-film hydration method. The effects of cholesterol molar ratio, charge-inducing agents, and α-tocopherol acetate on encapsulation efficiency values and in vitro drug release of multilamellar liposomes were studied. Freeze-dried liposomal products were prepared with or without cryoprotectants. Results showed that incorporation of stearylamine resulted in an increased entrapment of fluconazole, whereas incorporation of dicetyl phosphate decreased the drug entrapment efficiency. The incorporation of α-tocopherol acetate into fluconazole multilamellar liposomes resulted in the increase of entrapment efficiency of fluconazole liposomes. In vitro release studies revealed that incorporation of cholesterol into multilamellar liposomal formulations decreased drug permeability from formulations. Positively charged fluconazole multilamellar liposomes gave rise to a slow release rate compared to neutral liposomes whereas negatively charged fluconazole liposomes showed a rapid release rate. Physical stability studies showed that lyophilized cake of liposomes without cryoprotectants was compact and difficult to reconstitute compared to fluffy easily reconstituted cakes upon using cryoprotectants. Fluconazole retained in freeze-dried liposomes without cryoprotectants was 63.452% compared to 91.877% using three grams of trehalose as a cryoprotectant per gram lipid in positively charged multilamellar liposomes. Physical stability studies showed superior potentials of the lyophilized product after reconstitution in comparison with those of a solution product.

Low-temperature storage of cucumbers induces changes in the organic acid content and in citrate synthase activity

To elucidate the cause of reported pyruvate accumulation in chilled stored cucumbers ( Cucumis sativus L.) cv. ‘Toppugurin’, we have examined differences in the extent of incorporation of acetate-1,2- 14C into the tricarboxylic acid (TCA) cycle and the specific activity of the enzyme citrate synthase between healthy and chilling-injured cucumber tissues stored in the dark for 0, 3, 6 and 12 d at 1 °C or 20 °C. Radioactive tracing, gas chromatography, and enzyme analysis suggest that the incorporation of acetate into citrate, the distribution of organic acids in the tricarboxylic acid cycle, and the specific activity of citrate synthase in the cold-storage (chilling-injured) cucumber tissues differed from those in the healthy tissues. The observed decrease in citrate synthase activity may be the cause of the observed increase in pyruvate accumulation in the chilling-injured cucumber fruit tissue compared to tissues stored at 20 °C. The results also suggest that the increased formation of pyruvate and reduced activity of citrate synthase during cold storage observed in the present study could serve as indicators (biomarkers) of stress-induced changes in chilled cucumbers. Possible mechanisms of the described effects are discussed.

Crack reduction in a large bulk Y–Ba–Cu–O superconductor through liquid binder addition

We have studied the effects of the incorporation of polyvinyl acetate (PVA) aqueous solution on the formability of the precursor Y–Ba–Cu–O samples with the aim of improving the mechanical properties of large bulk RE–Ba–Cu–O superconductors that are susceptible to cracking. We found that the green compacts of YBa2Cu3Oy and Y2BaCuO5 powders added with PVA liquid binder exhibited good mechanical properties and could be mechanically machined without defects. We could successfully drill 17 holes of 1mm diameter into the green compact. The drilled samples were subjected to melt-processing and oxygen annealing, and further characterized with microstructural observations and magnetization measurements. The results showed that liquid binder addition was very effective in reducing cracks for large melt-processed Y–Ba–Cu–O superconductors.

Determination of betaine metabolites and dimethylsulfoniopropionate in coral tissues using liquid chromatography–time-of-flight mass spectrometry and stable isotope-labeled internal standards

A convenient procedure for determination of seven betaine analogs and dimethylsulfoniopropionate (DMSP) in extracts of coral tissues using LC–MS stable isotope dilution is described. Extraction procedures were optimized for selective extraction of polar metabolites from coral tissues. The LC–MS protocol employed a pentafluorophenylpropyl (PFPP) column for HPLC separation, with chromatographic resolution of isobaric and isomeric zwitterionic metabolites optimized by adjusting the acidity of the mobile phase. A ternary gradient was used to exploit the unusual retention characteristics of cationic metabolites on the PFPP column, with incorporation of ammonium acetate in a later gradient stage promoting elution of more hydrophobic betaines which are retained at high organic content in the absence of ammonium acetate. We demonstrate that the new LC–MS based method provides accurate measurements from nanomolar to high micromolar concentrations, and can be applied for profiling of betaine metabolites and DMSP in corals or other aquatic organisms.

ACSVL3 depletion in U87 glioma cells affects both fatty acid and cholesterol homeostasis

Human malignant gliomas overexpress ACSVL3, a member of the very long‐chain fatty acyl‐CoA synthetase family. Depletion of ACSVL3 in cultured human U87 glioma cells by RNA interference decreased both their malignant growth properties in vitro and their ability to produce tumors in mice. To understand how ACSVL3 knockdown (KD) in U87 cells promotes these beneficial effects, we investigated fatty acid and cholesterol homeostasis. Incorporation of [14C]C16:0 into several lipids, including phosphatidylinositol, phosphatidylethanolamine, and non‐hydroxy ceramide, was reduced in KD U87 cells. Although the mass of triacylglycerol (TAG) in U87 cells was barely detectable, [14C]C16:0 incorporation into TAG was robust, and was decreased in KD glioma cells. Surprisingly, the mass of free cholesterol was reduced by ~40% in ACSVL3 KD cells. This was due, in part, to decreased de novo cholesterol synthesis, as measured by [14C]acetate incorporation. Acetate incorporation into free fatty acids was also reduced, indicating that ACSVL3 depletion also affects de novo fatty acid synthesis. We hypothesize that ACSVL3 depletion affects fatty acid and cholesterol homeostasis via a common mechanism. Studies to elucidate this mechanism are in progress. Supported by NIH grant NS062043 and a grant from the National Brain Tumor Society.

Antipsychotic drug action on SREBPs-related lipogenesis and cholesterogenesis in primary rat hepatocytes

The use of some of antipsychotic drugs (APDs) in humans has been hampered by the induction of metabolic disorders such as weight gain, dyslipidemia, and diabetes. In primary rat hepatocytes, we investigated the actions of several APDs on lipid and cholesterol metabolism using [(14)C]acetate incorporation, quantitative reverse transcription-polymerase chain reaction, and western blotting. Clozapine and olanzapine, known to have significant metabolic side effects in man, strongly increased de novo lipid and cholesterol synthesis in rat hepatocytes. Haloperidol, which has less impact in metabolic disorders, enhanced lipogenesis without altering cholesterol production. By contrast, quetiapine, which exhibits few metabolic side effects in man, did not affect lipid and cholesterol synthesis. Interestingly, aripiprazole, which has not yet been reported to induce metabolic disorders in humans, strongly decreases cholesterol synthesis. Furthermore, these inductions of lipid and cholesterol synthesis observed with clozapine and olanzapine were also associated with up-regulation of the transcription factors sterol regulatory element-binding protein (SREBP)-1 and/or SREBP-2 and their associated target genes. Part of the APD-induced metabolic disorders in humans may be due to direct effects on liver metabolism. Our model may also be of interest to assess the action of future drugs on metabolic parameters.