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PubMed1991

Characterization of the cytochrome P450 isozyme that metabolizes ochratoxin A, using metabolic inducers, inhibitors and antibodies.

The phenotypic pattern of drug biotransformation is determined by both host and environmental factors. Debrisoquine is a good probe for phenotyping individuals, as its metabolism is not affected by age, gender, smoking habits or alcohol intake. People with Balkan endemic nephropathy or with urinary tract tumours in endemic areas are more frequently extensive metabolizers of debrisoquine than are healthy people. This finding has led to studies of the possible relationship between the metabolism of ochratoxin A and its toxicity and carcinogenicity on experimental models. Ochratoxin A is metabolized mainly in the liver into R- and S-isomers of 4- and 10-hydroxyochratoxin A, and the reaction is catalysed by cytochrome P450 haemoprotein. Animal species that are genetically different in their capacity to metabolize debrisoquine differ similarly in their capacity to metabolize ochratoxin A: female DA rats that are poor metabolizers of debrisoquine also poorly metabolize ochratoxin A, as assayed by urinary excretion of both the parent compound and of 4-hydroxyochratoxin A. Ochratoxin A hydroxylase activity is low in DA rat liver (and kidney) but is inducible by phenobarbital and 3-methylcholanthrene; debrisoquine hydroxylase is not known to be inducible by enzyme inducers. The reaction of ochratoxin A hydroxylase thus resembles those induced by 3-methyl-cholanthrene and catalysed by cytochrome P450IA. Ochratoxin A hydroxylase activity was further characterized in the livers of B6 and D2 mice that had been treated with typical enzyme inducers. Ochratoxin A hydroxylase was weakly inducible by phenobarbital, 3-methyl-cholanthrene and 2,4,7,8-tetrachlorodibenzodioxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

In vivo nuclear magnetic resonance studies of hepatic methoxyflurane metabolism. II. A reevaluation of hepatic metabolic pathways.

Methoxyflurane (2,2-dichloro-1,1-difluoro-ethyl methyl ether) is believed to be metabolized via two convergent metabolic pathways. The relative flux through these two metabolic pathways has been investigated using a combination of in vivo surface coil NMR techniques and in vitro analyses of urinary metabolites. Analysis of the measured concentrations of inorganic fluoride, oxalate, and methoxydifluoroacetate in the urine of methoxyflurane-treated rats for 4 days after anesthesia indicates that the anesthetic is metabolized primarily via dechlorination to yield methoxydifluoroacetate. The methoxydifluoroacetate is largely excreted without further metabolism, although a small percentage of this metabolite is broken down to yield fluoride and oxalate, as determined by urine analysis of rats dosed with synthetic methoxydifluoroacetate. At early times after methoxyflurane exposure, the relative concentrations of methoxyflurane metabolites indicate that a significant fraction of the metabolic flux occurs via a different pathway, presumably demethylation, to yield dichloroacetate as an intermediate. Direct analysis of dichloroacetate in the urine using water-suppressed proton NMR indicates that the level of this metabolite is below the detection threshold of the method. Measurements made on the urine of rats dosed directly with dichloroacetate indicate that this compound is quickly metabolized, and dichloroacetate levels in urine are again found to be below the detection threshold. These results demonstrate the quantitative importance of the dechlorination pathway in the metabolism of methoxyflurane in rats.

Animals↗
PubMed1984

[Metabolic aspects of alcoholic liver damage: 1984/5 update. 1. Epidemiology and alcohol metabolism].

In western industrialized countries ethanol is an important etiologic factor in the development of cirrhosis of the liver. Metabolic, immunologic and physico-chemical alterations of the hepatocyte due to ethanol are involved in the pathogenesis of alcoholic liver disease. However, the mechanisms by which ethanol damages the liver are far from clear. During the last two decades, the effect of ethanol on multiple biochemical pathways of the hepatocyte has been investigated intensively. The present paper is focusing on the metabolic aspects of alcoholic liver disease. In the first part of the review, special emphasis has been led on the metabolites of ethanol oxidation, while in the second part microsomal enzyme induction due to alcohol has been discussed. More than 90% of ethanol metabolism takes place in the liver via cytoplasmic alcoholdehydrogenase (ADH) and via a microsomal ethanol oxidizing system (MEOS). The products of these reactions are reduced nicotinadenine dinucleotide phosphate (NADH), acetaldehyde and acetate. NADH alters the redox state of the liver cell favouring all reductive processes. This shift in metabolic pathways results in hyperlactacidaemia, lactacidosis, ketosis and hyperuricaemia. Disturbances of the carbohydrate metabolism may lead either to hypo- or hyperglycaemia. The altered redox state also influences the metabolic pathways of lipid metabolism leading to lipid accumulation within the hepatocyte which can be morphologically observed as alcoholic fatty liver. In addition, porphyrin and collagen metabolism is also affected by the increased NADH/NAD+ ratio. On the other hand, acetaldehyde damages the microtubular system and the mitochondria. Acetaldehyde may also be responsible for the increased lipidperoxidation after chronic ethanol ingestion.

Acetaldehyde↗
PubMed1993

4-Methylpyrazole inhibits fatty acyl coenzyme synthetase and diminishes catalase-dependent alcohol metabolism: has the contribution of alcohol dehydrogenase to alcohol metabolism been previously overestimated?

Alcohol dehydrogenase (ADH)-deficient deer mice were used as an animal model to investigate the effect of 4-methylpyrazole on alcohol metabolism. After intraperitoneal dosing of these mutant mice with 4-methylpyrazole, rates of ethanol and methanol metabolism in vivo were decreased significantly, by 41% and 35%, respectively. In perfused liver, rates of ethanol metabolism were also decreased up to 61% by 100 microM 4-methylpyrazole. Further, when livers were perfused with methanol, a selective substrate for catalase, rates of methanol metabolism were decreased by 64% by 4-methylpyrazole. It was further determined that 4-methylpyrazole administration caused negligible changes in total hepatic catalase activity and in rates of oxidation of ethanol by isolated microsomes; rather, it acts on catalase-dependent alcohol metabolism by limiting the supply of H2O2. In this study, 4-methylpyrazole inhibited fatty acyl CoA synthetase competitively in liver homogenates. Fatty acyl CoA synthetase is a key enzyme involved in the supply of substrate for peroxisomal oxidation of alcohols via catalase-H2O2. When palmitate was studied, rates of formaldehyde production from methanol were reduced competitively by 4-methylpyrazole; however, when the product palmitoyl CoA was used, the addition of 4-methylpyrazole did not alter activity. 4-Methylpyrazole also inhibited fatty acyl CoA synthetase activity measured directly from CoA disappearance. These data indicate that fatty acyl CoA synthetase is inhibited by 4-methylpyrazole, thus reducing the availability of H2O2 for catalase-dependent alcohol metabolism. Inhibition of methanol metabolism in deer mice expressing ADH indicates that this phenomenon also occurs in species with ADH. Taken together, these data support the hypothesis that the contribution of ADH to alcohol metabolism may have been previously overestimated.

Alcohol Dehydrogenase↗
PubMed1997

In vitro metabolism of simvastatin in humans [SBT]identification of metabolizing enzymes and effect of the drug on hepatic P450s.

Simvastatin (SV) is a lactone prodrug used for the treatment of hypercholesterolemia. Upon incubation of SV with liver microsomal preparations from human donors, four major metabolic products were formed (3'-hydroxy SV, 6'-exomethylene SV, 3',5'-dihydrodiol SV, and the active hydroxy acid, SVA), together with several minor unidentified metabolites. The 3',5'-dihydrodiol SV, a new metabolite, was inactive as an inhibitor of HMG-CoA reductase. Kinetic studies of SV metabolism in human liver microsomes suggested that the major NADPH-dependent metabolites (3'-hydroxy SV, 6'-exomethylene SV, and 3',5'-dihydrodiol SV) were formed with relatively high intrinsic clearances, consistent with the extensive metabolism of SV observed in vivo. Based on four different in vitro approaches, namely 1) correlation analysis, 2) chemical inhibition, 3) immunoinhibition, and 4) metabolism by recombinant human P450, it is concluded that CYP3A is the major enzyme subfamily responsible for the metabolism of SV by human liver microsomes. Both CYP3A4 and CYP3A5 were capable of catalyzing the formation of 3',5'-dihydrodiol, 3'-hydroxy, and 6'-exomethylene metabolites. However, CYP3A4 exhibited higher affinity (> 3 fold) for SV than CYP3A5. Also, the studies indicated that CYP2D6, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP1A2, and CYP2E1 did not play significant roles in the metabolism of SV in vitro. Over the concentration range of 0-40 microM, SV inhibited the activity of CYP3A, but not the activities of CYP2C8/9, CYP2C19, or CYP2D6 in human liver microsomes. The inhibition of hepatic midazolam 1'-hydroxylase, a CYP3A marker activity, by SV was competitive with a Ki value of approximately 10 microM. SV was > 30-fold less potent than ketoconazole and itraconazole as an inhibitor of CYP3A. Under the same conditions, SVA, the hydrophilic hydroxy acid form of SV, did not inhibit CYP3A, CYP2C8/9, CYP2C19, or CYP2D6 activities. The results suggested that the in vivo inhibitory effects of SV on the metabolism of CYP3A substrates likely would be less than those of ketoconazole and itraconazole at their respective therapeutic concentrations. In addition, metabolic activities mediated by the other P450 enzymes tested are unlikely to be affected by SV.

Anticholesteremic Agents↗
PubMed2001

Brain metabolism and brain disease: is metabolic deficiency the proximate cause of Alzheimer dementia?

The potential of impairments in oxidative/energy metabolism to cause diseases of the brain had been proposed even before the major pathways of oxidative/energy metabolism were described. Deficiencies associated with disease are known in all the pathways of oxidative/energy metabolism and are associated with some of the most common disorders of the nervous system, including Alzheimer's disease (AD) and Parkinson's disease. A common mechanism in these conditions appears to be a downward mitochondrial spiral, involving abnormalities in energy metabolism, calcium metabolism, and free radicals (reactive oxygen and nitrogen species). In AD, the spiral appears to interact with abnormalities in the metabolism of the Alzheimer amyloid precursor protein (APP) and its Abeta fragment. Several lines of evidence indicate that the mitochondrial spiral may be a proximate cause of the clinical disabilities in AD. Decreases in cerebral metabolic rate (CMR) characteristically occur in AD and in other dementias. Inducing decreases in CMR leads to clinical disabilities characteristically associated with AD and with analogous problems in experimental animals. Treatments directed toward normalizing CMR appear to help at least some patients. Further studies of this possibility and of treatments designed to ameliorate the mitochondrial spiral may prove useful for treating AD and perhaps some other dementing disorders.

Alzheimer Disease↗
PubMed1976

Adenine nucleotide metabolism of blood platelets. IX. Time course of secretion and changes in energy metabolism in thrombin-treated platelets.

Changes in the energy metabolism of washed human platelets were compared with the kinetics of secretion induced by thrombin (5 units/ml). A 50% decrease in the level of metabolic ATP (3H-labelled), which was essentially complete in 30s, was matched in rate by adenine nucleotide secretion from storage in dense granules. Incubation of platelets with antimycin before thrombin addition increased the rate of fall in metabolic ATP, but did not affect the rate of adenine nucleotide secretion. beta-N-Acetylglucosaminidase secretion, which was slower than adenine nucleotide secretion in control platelets, was noticeably inhibited by antimycin, confirming previous reports that different regulatory mechanisms exist for dense and alpha-granule secretion. The rates of rephosphorylation of metabolic ADP to ATP via glycolysis and oxidative phosphorylation were estimated by measuring lactate production and O2 consumption in resting and thrombin-stimulated platelets and compared to the level of metabolic ATP (9-10 nmol/mg of platelet protein in the resting state). The rate of ATP production was stimulated at least two fold from 12 nmol to 24 nmol/min/mg within seconds of thrombin addition. This increased rate was maintained over the observed period of 5 min although the level of metabolic ATP had decreased to 4-5 nmol/mg within 30 s; the turnover of the remaining metabolic ATP thus increased four fold over the resting state although the actual stimulation of energy production was only two fold.

Adenosine Diphosphate↗
PubMed2004

Reduced action of insulin glargine on protein and lipid metabolism: possible relationship to cellular hormone metabolism.

Insulin analogues are used in the treatment of diabetes to mimic physiological insulin secretion. Glargine is used to provide basal insulin levels. Previous work has shown no differences in glucose uptake when glargine was compared to native insulin. The action of insulin on protein and lipid metabolism is studied infrequently, but these important actions should be considered with insulin analogues. In HepG2 cells, protein degradation was inhibited significantly less by glargine (15% over 3 hours) than by insulin (approximately 20% over 3 hours) (P < .05). Lipid metabolism was investigated in 3T3-L1 cells. In these cells glucose oxidation to CO2 was effected equally, but glargine was less potent than insulin at inhibiting epinephrine-stimulated lipolysis (EC50 = 1.4 v 0.35 nmol/L, P < .001) and at stimulating lipogenesis (EC50 = 1.27 v 8.06 nmol/L, P < .01). Since the action of insulin on protein and lipid metabolism has been suggested to be due to the metabolism of the hormone, we compared the cellular handling of 125I[A14]-glargine to 125I[A14]-insulin in HepG2 cells. While binding of glargine to the insulin receptor was identical to insulin, degradation of glargine was reduced compared to insulin (16.3% +/- 0.3% v 21.6% +/- 0.4% degraded/h, P < .01). Less degraded glargine than insulin was released from cells previously loaded with radiolabeled material (50.1% +/- 2.4% v 58.3% +/- 1.4%/2 h, P < .02). The amount of intact glargine released was concomitantly increased compared to insulin (44.8% +/- 2.6% v 35.8% +/- 1.4%/2 h, P < .02). These data provide further evidence for a relationship between insulin metabolism and insulin action on protein and lipid metabolism; however, the clinical relevance of these differences is hard to realize, since for the most part glargine, used as a basal insulin, is administered in addition to other shorter-acting insulin or analogues, and their effects will mask or reduce glargine effects on lipolysis and protein degradation. However, these studies do show that properties of insulin other than glucose metabolism and mitogenesis must be considered when studying insulin analogues.

Cell Membrane↗
PubMed2000

Metabolic mass, metabolic rate, caloric restriction, and aging in male Fischer 344 rats.

Previous investigators have found the metabolic rate to be the same in calorically-restricted and ad-libitum fed rodents, and hence concluded that the Rate of Living Theory does not help explain the longer lifespan of the calorically-restricted (CR) animal. However, these previous instigators may not have used reliable estimates of metabolic mass in their calculations of metabolic rate. Hence the present study investigated the reliability of ten different estimates of metabolic mass (MM) in 21-month-old male Fischer 344 rats fed three different diets to yield a wide range of body compositions. Two criteria were used to rank each estimate of metabolic mass: strong correlation with daily caloric intake (DCI); and zero Y-intercept on the regression curve of DCI versus the MM. The combined weight of the heart, liver, kidneys and brain (OW) was found to be the best estimate of MM. Statistical analysis of the differences in metabolic rate in the three groups of rats showed that the significance of these differences depended on the estimate of MM used. OW yielded different results than did fat-free mass (FFM), body weight (BW), BW(0.75), and BW(0.67). Therefore, because previous investigators used FFM, BW, BW(0.75), or BW(0.67), rather than a more reliable estimate such as OW, their finding that metabolic rate was not different in the CR and ad-lib groups, and their conclusion that the Rate of Living Theory does not help explain the longer lifespan of the CR animal, are called into question.

Aging↗
PubMed1998

A new method for evaluation and dietary therapy of congenital: deficiencies of amino acid metabolic enzymes. Linear system analysis and optimization of feedback inputs for the metabolic pathways of lysine, methionine and isoleucine.

We intended to elucidate an integrated mathematical model of amino acid metabolism and we propose a system for optimization treatment of disturbed metabolic states caused by congenital enzyme deficiencies. Our analysis focused on the metabolic pathway starting at asparaginic acid proceeding to isoleucine, methionine and lysine. The rate of change in the concentration of the biochemical species was expressed as 21 linear rate equations. We obtained the rate constants and the magnitude of feedback from reported experimental data. Linear systems analysis revealed that the metabolic system under study was stable but uncontrollable. These properties were insensitive to changes in the magnitude of feedback. To show the effect of optimizing the feedback so that it minimizes the square of the concentration of the species and the control input, we analyzed the impulse response of the species, transient response and the singular value of the system for four cases; (1) at the physiological state without optimizing the feedback, (2) at the physiological state attained after optimizing the feedback, (3) at the pathophysiological state attained with enzyme deficiency states for lysine and methionine metabolism without optimizing the feedback, and (4) at the pathophysiological state attained after optimizing the feedback for enzyme deficiencies. In the enzyme deficient model, the impulse response oscillated and lasted longer than that in the physiological state. These changes appeared even in the species on other branched pathways. The singular value was elevated in the enzyme deficient state. By optimizing the feedback, all the impulse responses in the enzyme deficient state recovered to nearly those in the normal physiological state. Similarly, the transient response and the singular value in the enzyme deficient state recovered to nearly the normal physiological values. We elucidated the numerical value of the feedback gain for this optimization. The present analysis is useful for the evaluation of the integrated properties of amino acid metabolism and the optimization technique is potentially of use for determining a treatment course for congenital metabolic enzyme deficiencies.

Amino Acid Metabolism, Inborn Errors↗
PubMed2000

Alterations of protein metabolism by metabolic acidosis in children with chronic renal failure.

BACKGROUND: Several reports suggest that metabolic acidosis may induce significant alterations in protein metabolism and that its outbreak may even result in growth retardation in children with chronic renal failure (CRF). However, the effects of metabolic acidosis on protein metabolism kinetics have never been investigated in these settings. METHODS: Postabsorptive leucine metabolism, a marker of whole-body protein metabolism, was measured by using a primed, continuous intravenous infusion of L-[1-13C]leucine in 10 CRF children who were one to four years old. RESULTS: Interindividual values of whole-body protein turnover exhibited a very large range, which was mainly accounted for by acidotic status (plasma HCO3-) and body composition [fat-free mass (FFM)]. After correction for differences in FFM, plasma HCO3- was highly correlated with protein breakdown (R2 = 0.65, P < 0.001), so that CRF children were divided in two groups according to their acid-base status: Group A had a mean plasma HCO3- level of 15.8 +/- 1.5 mmol. L-1 (mean +/- SD, N = 5), whereas group B had near-normal values (HCO3-, 22.6 +/- 3.0 mmol. L-1, N = 5). The leucine rate of appearance from protein breakdown was markedly higher in group A than in group B (4.15 +/- 1.43 vs. 2.46 +/- 0.47 micromol. kg-1. min-1, respectively, P < 0.05), and the net leucine balance tended to be more negative in group A (-0.73 +/- 0.34 vs. -0.44 +/- 0.26 micromol. kg-1. min-1, respectively). CONCLUSIONS: Metabolic acidosis in children with CRF results in an excessive catabolic state, suggesting that acidosis-related protein wasting could contribute to growth retardation.

Acidosis↗
PubMed2002

Glucocorticoid metabolism and the Metabolic Syndrome: associations in an elderly cohort.

OBJECTIVE: The phenotype of the Metabolic Syndrome (hypertension, insulin resistance and hyperlipidaemia) bears similarities to Cushing's Syndrome, in which the cause of these features is elevated cortisol production. We have investigated relationships between glucocorticoid production and features of the Metabolic Syndrome in a cohort of elderly subjects. DESIGN: A cross-sectional analysis was carried out of a subset of a birthweight cohort from Sheffield. METHODS: 92 men and 40 women (aged 69-75 y) representative of the original cohort were investigated. Features of the Metabolic Syndrome (blood pressure, BMI, waist hip ratio, fasting glucose, insulin and triglycerides) were recorded and urinary glucocorticoid metabolites were measured by gas chromatography mass spectrometry. RESULTS: Total glucocorticoid metabolites were correlated with the overall phenotype of the Metabolic Syndrome (P = 0.002), whereas specific pathways of metabolism (activity of 11 beta-hydroxysteroid dehydrogenases and A-ring reductases) did not show significant associations. Specifically total glucocorticoid production increased with increasing systolic blood pressure (r = 0.21, P = 0.013), fasting glucose (r = 0.19, P = 0.02) and insulin (r = 0.23, P = 0.025). Glucocorticoid production was greater with increasing abdominal girth (r = 0.19, P = 0.033), but there was no association with enhanced metabolism via a specific pathway. Within this cohort, birthweight was not associated with total glucocorticoid metabolites. However, decreasing birthweight (P = 0.022), increasing obesity (P = 0.026) and increasing total glucocorticoid production (P = 0.009) were all independent predictors of fasting glucose. CONCLUSIONS: These data support the concept that cortisol production is enhanced in the Metabolic Syndrome, although they did not confirm the recent evidence that increased cortisol secretion is predicted by low birthweight.

Aged↗
PubMed2003

[Significance of triglycerides for other metabolic parameters in the familial metabolic syndrome].

BACKGROUND: The relationship between the various degrees of glucose tolerance and metabolic parameters have already been examined in various studies. Whether and to what extent the triglycerides (TG) affect other metabolic parameters in the different degrees of glucose tolerance is not certain. We therefore studied the importance of the triglycerides within a defined glycemic state in patients with an elevated familial risk for metabolic diseases. METHODS: We examined 866 patients (380 men, 486 women, mean age 44,4 years) in the "Familial Metabolic Syndrome Study" (FAMES). The patients were assigned to various degrees of glucose tolerance, according to the result of an oral glucose tolerance test. All degrees were divided into subgroups in respect of the triglyceride level (TG < 1,7 or TG >/= 1,7 mmol/l). In these subgroups we measured various metabolic parameters like fasting glucose, insulin resistance, insulin and proinsulin levels, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), uric acid, HbA (1c), and free fatty acids (FFA). RESULTS: In patients with normal glucose tolerance the hypertriglyceridemia is already associated with other components of the metabolic syndrome like elevated HbA (1c), free fatty acids, proinsulin and insulin levels, worsened insulin sensitivity, elevated uric acid and LDL-C levels as well as a lowered HDL-C level. The patients with diabetes and hypertriglyceridemia also showed higher levels of FFA, proinsulin and insulin, a lower HDL-C level and a more prominent insulin resistance. CONCLUSION: Hypertriglyceridemia is an indicator for insulin resistance and elevated levels of other components of the metabolic syndrome within the various degrees of glucose tolerance.

Adult↗
PubMed2004

Effects of a combination of recombinant human growth hormone with metformin on glucose metabolism and body composition in patients with metabolic syndrome.

Abdominal obesity and insulin resistance are central findings in metabolic syndrome. Since treatment with recombinant human growth hormone (rhGH) can reduce body fat mass in patients with organic GH deficiency, rhGH therapy may also have favourable effects on patients with metabolic syndrome. However, due to the highly increased risk for type 2 diabetes in these patients, strategies are needed to reduce the antagonistic effect of rhGH against insulin. We conducted a 18-month randomised, double-blind, placebo-controlled study to assess the effect of rhGH in combination with metformin (Met) in patients with metabolic syndrome. 25 obese men (55 +/- 6 years, BMI 33.4 +/- 2.9 kg/m (2)) with mildly elevated fasting plasma glucose (FPG) levels at screening (6.1-8.0 mmol/l) were included. All patients received metformin (850 mg twice daily) either alone or in combination with rhGH (daily dose 9.5 microg/kg body weight). An oGTT was performed at baseline, after 6 weeks, and after 3, 6, 12, and 18 months of therapy. Glucose disposal rate (GDR) was measured by euglycemic hyperinsulinemic clamp at 0 and 18 months and body composition was measured by DEXA every 6 months. In the Met + GH group, IGF-I increased from 146 +/- 56 microg/l to 373 +/- 111 microg/l (mean +/- SD) after 3 months and remained stable after that. BMI did not change significantly in either group during the study. Total body fat decreased by -4.3 +/- 5.4 kg in the Met + GH group and by -2.7 +/- 2.9 kg in the Met + Placebo group (differences between the two groups: p = n. s.). Waist circumference decreased in both groups (Met + GH: 118 +/- 8 cm at baseline, 112 +/- 10 cm after 18 months; Met + Placebo: 114 +/- 7 cm vs. 109 +/- 8 cm; differences between the two groups: p = 0.096). In the Met + GH group, FPG increased significantly after 6 months (5.9 +/- 0.7 vs. 6.7 +/- 0.4 mmol/l; p = 0.005), but subsequently decreased to baseline levels (18 months: 5.8 +/- 0.2 mmol/l). FPG remained stable in the Met + Placebo group until 12 months had elapsed, and then slightly decreased (baseline: 6.2 +/- 0.3, 18 months: 5.5 +/- 0.6 mmol/l, p = 0.02). No significant changes were seen in either group regarding glucose and insulin AUC during oGTT or HbA (1c) levels. GDR at 18 months increased by 20 +/- 39% in Met + GH-group and decreased by -11 +/- 25% in the Met + Placebo group (differences between the two groups: p = 0.07). In conclusion, treatment of patients with metabolic syndrome and elevated FPG levels did not cause sustained negative effects on glucose metabolism or insulin sensitivity if given in combination with metformin. However, since our data did not show significant differences between the two treatment groups with respect to body composition or lipid metabolism, future studies including larger numbers of patients will have to clarify whether the positive effects of rhGH on cardiovascular risk factors that have been shown in patients with GH deficiency are also present in patients with metabolic syndrome, and are additive to the effects of metformin.

Aged↗
PubMed2004

Prediction of differences in in vivo oral clearance of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl] ethylamine monohydrochloride (NE-100) between extensive and poor metabolizers from in vitro metabolic data in human liver microsomes lacking CYP2D6 activity and recombinant CYPs.

1. It has previously been reported that N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) was predominantly metabolized by cytochrome P450 (CYP) 2D6 in human liver microsomes (HLM). In the present study, the contribution of CYP forms involved in the formation of the major metabolites of NE-100 in human liver lacking CYP2D6 activity (PM-HLM) has been predicted by use of in vitro kinetic data on recombinant CYPs microsomes (rCYPs). 2. In PM-HLM, NE-100 is predicted to be metabolized to N-despropyl-NE-100 (NE-098), p-hydroxy-NE-100 (NE-152) and m-hydroxyl-NE-100 (NE-163), but not to O-demethy-NE-100 (NE-125), which is a major metabolite in pooled human liver microsomes (EM-HLM). The relative activity factor approach assumed that NE-098 formation is predominantly catalysed by CYP3A4 and CYP2C9 and the NE-152+163mix (a mixture of two hydroxylated metabolites, NE-152 and NE-163) formation is only catalysed by CYP3A4. 3. The predicted contribution rates of CYP3A4 and CYP2C9 for NE-098 formation were 58.1 and 34.6%, respectively, in PM-HLM. These predicted results were strongly supported by kinetic and inhibition studies using PM-HLM. The intrinsic clearance of NE-100 predicted from rCYPs (the predicted CLint-HLM-total) corresponded to those observed from EM- and PM-HLM (the observed CLint-HLM). 4. The in vivo oral clearance (CLoral) of NE-100 in extensive metabolizers and poor metabolizers of CYP2D6 was predicted to be 50times higher in extensive metabolizers than poor metabolizers using in vitro-in vivo scaling method based on the dispersion model. These data suggest that polymorphism of CYP2D6 might greatly affect NE-100 metabolism in vivo.

Administration, Oral↗
PubMed2003

MetaFluxNet: the management of metabolic reaction information and quantitative metabolic flux analysis.

SUMMARY: MetaFluxNet is a program package for managing information on the metabolic reaction network and for quantitatively analyzing metabolic fluxes in an interactive and customized way. It allows users to interpret and examine metabolic behavior in response to genetic and/or environmental modifications. As a result, quantitative in silico simulations of metabolic pathways can be carried out to understand the metabolic status and to design the metabolic engineering strategies. The main features of the program include a well-developed model construction environment, user-friendly interface for metabolic flux analysis (MFA), comparative MFA of strains having different genotypes under various environmental conditions, and automated pathway layout creation. AVAILABILITY: http://mbel.kaist.ac.kr/ SUPPLEMENTARY INFORMATION: A manual for MetaFluxNet is available as PDF file.

Database Management Systems↗
PubMed2006

Observing local and global properties of metabolic pathways: 'load points' and 'choke points' in the metabolic networks.

MOTIVATION: The local and global aspects of metabolic network analyses allow us to identify enzymes or reactions that are crucial for the survival of the organism(s), therefore directing us towards the discovery of potential drug targets. RESULTS: We demonstrate a new method ('load points') to rank the enzymes/metabolites in the metabolic network and propose a model to determine and rank the biochemical lethality in metabolic networks (enzymes/metabolites) through 'choke points'. Based on an extended form of the graph theory model of metabolic networks, metabolite structural information was used to calculate the k-shortest paths between metabolites (the presence of more than one competing path between substrate and product). On the basis of these paths and connectivity information, load points were calculated and used to empirically rank the importance of metabolites/enzymes in the metabolic network. The load point analysis emphasizes the role that the biochemical structure of a metabolite, rather than its connectivity (hubs), plays in the conversion pathway. In order to identify potential drug targets (based on the biochemical lethality of metabolic networks), the concept of choke points and load points was used to find enzymes (edges) which uniquely consume or produce a particular metabolite (nodes). A non-pathogenic bacterial strain Bacillus subtilis 168 (lactic acid producing bacteria) and a related pathogenic bacterial strain Bacillus anthracis Sterne (avirulent but toxigenic strain, producing the toxin Anthrax) were selected as model organisms. The choke point strategy was implemented on the pathogen bacterial network of B.anthracis Sterne. Potential drug targets are proposed based on the analysis of the top 10 choke points in the bacterial network. A comparative study between the reported top 10 bacterial choke points and the human metabolic network was performed. Further biological inferences were made on results obtained by performing a homology search against the human genome. AVAILABILITY: The load and choke point modules are introduced in the Pathway Hunter Tool (PHT), the basic version of which is available on http://www.pht.uni-koeln.de.

Bacillus↗
PubMed2005

Comparative genomics of two closely related unicellular thermo-acidophilic red algae, Galdieria sulphuraria and Cyanidioschyzon merolae, reveals the molecular basis of the metabolic flexibility of Galdieria sulphuraria and significant differences in carbohydrate metabolism of both algae.

Unicellular algae serve as models for the study and discovery of metabolic pathways, for the functional dissection of cell biological processes such as organellar division and cell motility, and for the identification of novel genes and gene functions. The recent completion of several algal genome sequences and expressed sequence tag collections and the establishment of nuclear and organellar transformation methods has opened the way for functional genomics approaches using algal model systems. The thermo-acidophilic unicellular red alga Galdieria sulphuraria represents a particularly interesting species for a genomics approach owing to its extraordinary metabolic versatility such as heterotrophic and mixotrophic growth on more than 50 different carbon sources and its adaptation to hot acidic environments. However, the ab initio prediction of genes required for unknown metabolic pathways from genome sequences is not trivial. A compelling strategy for gene identification is the comparison of similarly sized genomes of related organisms with different physiologies. Using this approach, candidate genes were identified that are critical to the metabolic versatility of Galdieria. Expressed sequence tags and high-throughput genomic sequence reads covering >70% of the G. sulphuraria genome were compared to the genome of the unicellular, obligate photoautotrophic red alga Cyanidioschyzon merolae. More than 30% of the Galdieria sequences did not relate to any of the Cyanidioschyzon genes. A closer inspection of these sequences revealed a large number of membrane transporters and enzymes of carbohydrate metabolism that are unique to Galdieria. Based on these data, it is proposed that genes involved in the uptake of reduced carbon compounds and enzymes involved in their metabolism are crucial to the metabolic flexibility of G. sulphuraria.

Algal Proteins↗